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UBC Theses and Dissertations

Hydrogen generation in a multi-channel membrane reactor 2012

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Hydrogen Generation in a Multi-Channel Membrane Reactor by Alexandre Vigneault BSA Chemical Engineering, Université de Sherbrooke, 2001 MSc Chemical Engineering, Université de Sherbrooke, 2004 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF Doctor of Philosophy in THE FACULTY OF GRADUATE STUDIES (Chemical & Biological Engineering) The University of British Columbia (Vancouver) October 2012 © Alexandre Vigneault, 2012 Abstract A novel Multi-Channel Membrane Reactor (MCMR) has been developed for the decentralized production of hydrogen via Steam Methane Reforming (SMR). The concept alternates steam reforming gas channels to produce the hydrogen and Methane Catalytic Combustion (MCC) gas channels to provide the heat of reac- tion. A palladium-silver (Pd/Ag) membrane inside each reforming gas channel shifts the reaction equilibrium, and produces pure hydrogen in a single vessel. A steady-state, non iso-thermal and two-dimensional modeling of the concept was first developed. Sensitivity analyses from the simulations indicated the im- portance of fast kinetics and thick catalyst coating layers (>80 µm) to avoid lim- itations from the catalyst. An innovative hot substrate air-spray coating method was developed, and thick layer of catalysts (>240 µm) with good adherence under sonication were obtained. A lab-made Ru MgO−La2O3/ γ-Al2O3 catalyst, with carrier and promoters pre-aged by steam, and coated on pre-oxidized Fecralloy, was found to be suitable for the reforming channel. On the combustion side, com- mercial Pd γ-Al2O3 catalysts were successfully coated on stainless steel support. Kinetics parameters were estimated for both reforming and combustion catalysts. A proof-of-concept MCMR was designed and built. Results showed that a methane conversion of 87% was achievable with a pure hydrogen output (99.995%). The reforming experimental results were adequately predicted for a wide range of operating conditions. On the combustion side, the experimental conversions were below the model expectations, likely because of flow distribution and catalyst sta- bility issues. It is shown that the MCMR concept has the potential to give hydrogen yield per reactor volume, and per mass of catalyst, about one order of magnitude higher than for alternate membrane reactor technologies. ii Table of Contents Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ii Table of Contents . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii List of Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . x List of Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xiv Acronyms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xix List of Symbols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xxi List of Greek Letters . . . . . . . . . . . . . . . . . . . . . . . . . . . xxiv List of Subscripts . . . . . . . . . . . . . . . . . . . . . . . . . . . . xxvi Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . xxviii 1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1.1 The Case for Hydrogen . . . . . . . . . . . . . . . . . . . . . 1 1.1.1 Climate Change and Greenhouse Gas Emissions . . . 1 1.1.2 Life Cycle Impact Assessment . . . . . . . . . . . . . 2 1.1.3 Global Hydrogen Production and Consumption . . . . 3 1.1.4 Hydrogen for Transportation . . . . . . . . . . . . . . 4 1.2 Hydrogen Production Pathway . . . . . . . . . . . . . . . . . 6 1.2.1 Feed Sources . . . . . . . . . . . . . . . . . . . . . . 6 1.2.2 Reaction Pathways from Methane to Hydrogen . . . . 6 iii 1.3 Process and Hydrogen Purification . . . . . . . . . . . . . . . 8 1.3.1 Pressure Swing Adsorption . . . . . . . . . . . . . . . 9 1.3.2 Preferential Oxidation . . . . . . . . . . . . . . . . . 10 1.3.3 Membranes . . . . . . . . . . . . . . . . . . . . . . . 10 1.4 Reformer Configuration . . . . . . . . . . . . . . . . . . . . . 12 1.4.1 Current Large-Scale Reactor Design . . . . . . . . . . 12 1.4.2 Neo-conventional Reactor . . . . . . . . . . . . . . . 12 1.4.3 Multi-channel Reactor . . . . . . . . . . . . . . . . . 13 1.5 Novel Membrane Reactors . . . . . . . . . . . . . . . . . . . 16 1.5.1 Packed Bed and Coated Tubular Membrane Reactors . 17 1.5.2 Fluidized Bed Membrane Reactor . . . . . . . . . . . 18 1.5.3 Multi-Channel Membrane Reactor (MCMR) . . . . . 20 1.6 General Objectives and Strategy . . . . . . . . . . . . . . . . 20 2 Steady State Model Development . . . . . . . . . . . . . . . . . . 23 2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 2.2 Concept Description . . . . . . . . . . . . . . . . . . . . . . 26 2.3 Main Assumptions of 2-D model . . . . . . . . . . . . . . . . 26 2.4 Physical Properties . . . . . . . . . . . . . . . . . . . . . . . 28 2.4.1 Diffusivity . . . . . . . . . . . . . . . . . . . . . . . 28 2.4.2 Heat Capacity . . . . . . . . . . . . . . . . . . . . . . 30 2.4.3 Thermal Conductivity . . . . . . . . . . . . . . . . . 30 2.4.4 Viscosity . . . . . . . . . . . . . . . . . . . . . . . . 31 2.5 Concentration and Partial Pressure . . . . . . . . . . . . . . . 32 2.6 Velocity Profiles . . . . . . . . . . . . . . . . . . . . . . . . . 32 2.7 Kinetics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 2.7.1 Reforming . . . . . . . . . . . . . . . . . . . . . . . 34 2.7.2 Combustion . . . . . . . . . . . . . . . . . . . . . . . 39 2.8 Component Material Balance Equations . . . . . . . . . . . . 40 2.8.1 Gas Phase . . . . . . . . . . . . . . . . . . . . . . . . 42 2.8.2 Catalyst Layer . . . . . . . . . . . . . . . . . . . . . 45 2.9 Energy Balances . . . . . . . . . . . . . . . . . . . . . . . . 46 2.9.1 Gas Phase . . . . . . . . . . . . . . . . . . . . . . . . 49 iv 2.9.2 Catalyst Layer . . . . . . . . . . . . . . . . . . . . . 51 2.9.3 Separator Wall . . . . . . . . . . . . . . . . . . . . . 52 2.10 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . 53 3 Steady State 2-D Model Simulations Results . . . . . . . . . . . 54 3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 3.2 Model Equations and Base Case Parameters . . . . . . . . . . 55 3.3 Metrics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 3.3.1 Hydrogen Production . . . . . . . . . . . . . . . . . . 57 3.3.2 Other Performance Indicators . . . . . . . . . . . . . 59 3.3.3 Dimensionless Numbers . . . . . . . . . . . . . . . . 60 3.3.4 Sensitivity Analysis Parameters . . . . . . . . . . . . 62 3.3.5 Performance Improvement Parameters . . . . . . . . . 62 3.4 Solving the Model . . . . . . . . . . . . . . . . . . . . . . . . 63 3.5 Results and Discussion . . . . . . . . . . . . . . . . . . . . . 64 3.5.1 Isothermal and Non-Isothermal Base Case Simulations 64 3.5.2 Isothermal Parametric Sensitivity Analysis . . . . . . 71 3.5.3 Performance Improvement . . . . . . . . . . . . . . . 76 3.6 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . 81 4 Catalyst Coating: Initial Method Development . . . . . . . . . . 83 4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . 83 4.1.1 Gas Phase Techniques . . . . . . . . . . . . . . . . . 83 4.1.2 Liquid Phase Techniques . . . . . . . . . . . . . . . . 85 4.1.3 Surface Pretreatment . . . . . . . . . . . . . . . . . . 87 4.1.4 Coating Strategy . . . . . . . . . . . . . . . . . . . . 87 4.2 Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88 4.2.1 Metal Substrate . . . . . . . . . . . . . . . . . . . . . 88 4.2.2 Modified Sol . . . . . . . . . . . . . . . . . . . . . . 88 4.3 Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92 4.3.1 Sand-Blasting . . . . . . . . . . . . . . . . . . . . . . 92 4.3.2 Substrate Cleaning . . . . . . . . . . . . . . . . . . . 94 4.3.3 Modified Sol Parameters . . . . . . . . . . . . . . . . 94 v 4.3.4 Coating Techniques . . . . . . . . . . . . . . . . . . . 96 4.3.5 Impregnation . . . . . . . . . . . . . . . . . . . . . . 97 4.3.6 Analytical Instruments . . . . . . . . . . . . . . . . . 97 4.3.7 Metrics . . . . . . . . . . . . . . . . . . . . . . . . . 98 4.4 Results and Discussion . . . . . . . . . . . . . . . . . . . . . 99 4.4.1 Metal Surface Preparation . . . . . . . . . . . . . . . 99 4.4.2 Brush Coating, Dip Coating and Cold Substrate Air Spray Coating (Cold Spray) . . . . . . . . . . . . . . . . . . 102 4.4.3 Hot Substrate Air Spray Coating (Hot Spray) . . . . . 102 4.4.4 Thickness Verification . . . . . . . . . . . . . . . . . 110 4.4.5 Impregnation . . . . . . . . . . . . . . . . . . . . . . 114 4.5 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . 117 5 Catalyst Coating: Final Method Development . . . . . . . . . . . 119 5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . 119 5.2 Material and Method . . . . . . . . . . . . . . . . . . . . . . 120 5.2.1 Metal Substrate . . . . . . . . . . . . . . . . . . . . . 120 5.2.2 Final Coating Method . . . . . . . . . . . . . . . . . 120 5.2.3 Analytical Equipment . . . . . . . . . . . . . . . . . 123 5.2.4 Metrics . . . . . . . . . . . . . . . . . . . . . . . . . 124 5.3 Results and Discussion . . . . . . . . . . . . . . . . . . . . . 125 5.3.1 Carbon Deposition during Steaming . . . . . . . . . . 125 5.3.2 Surface Cracks . . . . . . . . . . . . . . . . . . . . . 125 5.3.3 Rust . . . . . . . . . . . . . . . . . . . . . . . . . . . 133 5.3.4 Successful Coating Samples . . . . . . . . . . . . . . 134 5.4 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . 139 6 Reforming Catalyst Activity and Stability . . . . . . . . . . . . . 141 6.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . 141 6.2 Material and Method . . . . . . . . . . . . . . . . . . . . . . 143 6.2.1 Catalyst Preparation . . . . . . . . . . . . . . . . . . 143 6.2.2 Micro-Reactor Configuration . . . . . . . . . . . . . . 143 6.2.3 Experimental Set-up . . . . . . . . . . . . . . . . . . 144 vi 6.2.4 Packed Bed Model . . . . . . . . . . . . . . . . . . . 147 6.2.5 Estimation of Kinetics Parameter . . . . . . . . . . . 147 6.2.6 Estimation of Porosity . . . . . . . . . . . . . . . . . 148 6.2.7 Analytical Equipment . . . . . . . . . . . . . . . . . 149 6.2.8 Metrics . . . . . . . . . . . . . . . . . . . . . . . . . 151 6.3 Results and Discussion . . . . . . . . . . . . . . . . . . . . . 152 6.3.1 Preliminary Stability Test . . . . . . . . . . . . . . . 152 6.3.2 Lab-made Ru Catalyst . . . . . . . . . . . . . . . . . 152 6.3.3 Rust Effect . . . . . . . . . . . . . . . . . . . . . . . 157 6.3.4 Start-up Procedure for Membrane . . . . . . . . . . . 159 6.3.5 Deactivation Mechanisms . . . . . . . . . . . . . . . 163 6.3.6 Catalyst Layer Modeling . . . . . . . . . . . . . . . . 166 6.3.7 Estimation of Jackobsen Pre-exponential Kinetic Parame- ter . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166 6.4 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . 168 7 Methane Catalytic Combustion . . . . . . . . . . . . . . . . . . . 170 7.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . 170 7.2 Material and Method . . . . . . . . . . . . . . . . . . . . . . 172 7.2.1 Catalyst Preparation . . . . . . . . . . . . . . . . . . 172 7.2.2 Experimental Set-up . . . . . . . . . . . . . . . . . . 172 7.2.3 Estimation of Kinetic Parameters . . . . . . . . . . . 174 7.2.4 Analytical Equipment . . . . . . . . . . . . . . . . . 175 7.2.5 Metrics . . . . . . . . . . . . . . . . . . . . . . . . . 175 7.3 Results and Discussion . . . . . . . . . . . . . . . . . . . . . 176 7.3.1 Preliminary Stability Test . . . . . . . . . . . . . . . 176 7.3.2 Stability of Pd 1%/ γ-Al2O3 (Alfa) . . . . . . . . . . . 176 7.3.3 Stability of Pd 5%/ γ-Al2O3 (Alfa) and Lab-made Pd-based Catalysts . . . . . . . . . . . . . . . . . . . . . . . . 179 7.3.4 Deactivation . . . . . . . . . . . . . . . . . . . . . . 183 7.3.5 Estimation of Kinetic Parameters . . . . . . . . . . . 185 7.3.6 Conclusions . . . . . . . . . . . . . . . . . . . . . . . 190 vii 8 Development of the Multi-Channel Membrane Reactor . . . . . 191 8.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . 191 8.2 Material and Method . . . . . . . . . . . . . . . . . . . . . . 192 8.2.1 Reactor Design . . . . . . . . . . . . . . . . . . . . . 192 8.2.2 Process Design . . . . . . . . . . . . . . . . . . . . . 196 8.2.3 Catalyst Preparation . . . . . . . . . . . . . . . . . . 197 8.2.4 Reactor Assembly . . . . . . . . . . . . . . . . . . . 201 8.2.5 Start-up Procedure . . . . . . . . . . . . . . . . . . . 204 8.2.6 Operation . . . . . . . . . . . . . . . . . . . . . . . . 205 8.2.7 Analytical Equipment . . . . . . . . . . . . . . . . . 206 8.2.8 Modeling Parameters and Metrics . . . . . . . . . . . 207 8.3 Results and Discussion . . . . . . . . . . . . . . . . . . . . . 212 8.3.1 Preliminary Results . . . . . . . . . . . . . . . . . . . 212 8.3.2 Multi-Channel Reactor without Membrane . . . . . . 214 8.3.3 Multi-Channel Reactor with Membranes . . . . . . . . 215 8.4 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . 227 9 Overall Conclusions and Recommendations . . . . . . . . . . . . 229 9.1 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . 229 9.2 Recommendations . . . . . . . . . . . . . . . . . . . . . . . . 231 9.2.1 General Recommendations . . . . . . . . . . . . . . . 232 9.2.2 Specific Recommendations . . . . . . . . . . . . . . . 232 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 235 A Supplementary Coating Results . . . . . . . . . . . . . . . . . . 253 A.1 Brush Coating Results . . . . . . . . . . . . . . . . . . . . . 253 A.2 Multi-layer Brush Coating . . . . . . . . . . . . . . . . . . . 254 A.3 Dip Coating . . . . . . . . . . . . . . . . . . . . . . . . . . . 254 A.4 Cold Substrate Air Spray Coating (Cold Spray) . . . . . . . . 258 A.5 Hot Spray Coating Including Metal Precursors . . . . . . . . . 259 A.6 Hot Spray Coating of of Commercial Catalyst: Supplementary Re- sults . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 259 A.7 Thickness vs Mass Data . . . . . . . . . . . . . . . . . . . . . 265 viii B Stability of Reforming Catalysts: Supplementary Results . . . . 268 B.1 Preliminary Stability Test . . . . . . . . . . . . . . . . . . . . 268 B.2 RK-212 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 268 B.3 Early Lab-made Ni catalyst . . . . . . . . . . . . . . . . . . . 270 B.4 Commercial Ru 5%/ γ-Al2O3 Catalyst . . . . . . . . . . . . . 272 C MCMR Supplementary Results . . . . . . . . . . . . . . . . . . . 276 C.1 Lessons Learned During Reactor Commissioning . . . . . . . 276 C.2 Preliminary Results . . . . . . . . . . . . . . . . . . . . . . . 277 C.2.1 Combustion Preliminary Results . . . . . . . . . . . . 281 C.2.2 Reforming Preliminary Results . . . . . . . . . . . . 284 D Micro-Reactor Supplementary Information . . . . . . . . . . . . 292 D.1 Micro-Reactor PI&D . . . . . . . . . . . . . . . . . . . . . . 292 D.2 Micro-Reactor Electrical and Control Diagram . . . . . . . . 297 E Multi-Channel Reactor Supplementary Information . . . . . . . 302 E.1 MCMR PI&D . . . . . . . . . . . . . . . . . . . . . . . . . . 302 E.2 MCMR Electrical Diagram . . . . . . . . . . . . . . . . . . . 308 E.3 MCMR Process Part Mechanical Drawings . . . . . . . . . . 325 E.4 MCMR Mechanical Drawings . . . . . . . . . . . . . . . . . 327 F MATLAB Program . . . . . . . . . . . . . . . . . . . . . . . . . 339 ix List of Tables Table 1.1 U.S. Department of Energy Targets and Progress for Hydrogen in the Transportation Sector . . . . . . . . . . . . . . . . . 5 Table 1.2 Hydrogen Fuel Quality Specifications (partial list) . . . . . 9 Table 1.3 MCR Steam Reforming (A) and Catalytic Combustion (B) - Fabrication Details . . . . . . . . . . . . . . . . . . . . . . 14 Table 1.4 MCR Steam Reforming and Catalytic Combustion - Performance Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Table 2.1 Empirical Values to Determine k and µ . . . . . . . . . . . 32 Table 2.2 Sievert’s Law Parameters . . . . . . . . . . . . . . . . . . 33 Table 2.3 Constants in Xu and Froment (1989) Kinetics . . . . . . . 36 Table 2.4 Constants in Jakobsen et al. (2010) Kinetics . . . . . . . . 37 Table 2.5 Constants in Wei and Iglesia (2004) Kinetics . . . . . . . . 38 Table 2.6 Combustion Kinetic Parameters . . . . . . . . . . . . . . . 41 Table 3.1 Base Case Parameters for Simulations, Part I . . . . . . . . 56 Table 3.2 Base Case Parameters for Simulations, Part II . . . . . . . 57 Table 3.3 Hydrogen Flow Unit Conversion . . . . . . . . . . . . . . 58 Table 3.4 Isothermal and Non-Isothermal Base Case Results . . . . . 65 Table 3.5 Base Case Simulation Dimensionless Numbers . . . . . . . 70 Table 3.6 Parameter Changes for Figure 3.7A from Base Case Values of Tables 3.1 & 3.2 . . . . . . . . . . . . . . . . . . . . . . . 79 Table 3.7 Parameter Changes for Figure 3.7B from Base Case Values of Tables 3.1 &3.2 . . . . . . . . . . . . . . . . . . . . . . . 79 x Table 3.8 Non-Isothermal Base & Best Case Results and Comparison with Experimental Literature . . . . . . . . . . . . . . . . . . . 80 Table 4.1 Boehmites Tested and their Properties . . . . . . . . . . . 89 Table 4.2 Carriers Tested and their Properties . . . . . . . . . . . . . 90 Table 4.3 Metal Precursors Tested . . . . . . . . . . . . . . . . . . . 91 Table 4.4 Commercial Catalysts Tested . . . . . . . . . . . . . . . . 91 Table 4.5 Impregnation Solutions for Figure 4.13 . . . . . . . . . . . 115 Table 5.1 Modified Sol Parameters . . . . . . . . . . . . . . . . . . . 122 Table 5.2 Metal Precursors; Supplier was Alfa Aesar in all cases . . . 123 Table 5.3 Compositions of Impregnation Solutions . . . . . . . . . . 123 Table 5.4 Average Crack Density for Ru- and Pd-based Lab-made Cata- lysts Coatings . . . . . . . . . . . . . . . . . . . . . . . . 132 Table 5.5 Crack Density Results for Pd Commercial Catalyst Coatings 133 Table 6.1 Impregnation Solutions and Desired Metal Contents for Re- forming Catalysts . . . . . . . . . . . . . . . . . . . . . . 143 Table 6.2 Co-Sorption Parameters . . . . . . . . . . . . . . . . . . . 150 Table 6.3 Stability Conditions for Lab-made Ru-based Catalyst: Influ- ence of Steam . . . . . . . . . . . . . . . . . . . . . . . . 153 Table 6.4 Curve Fitting Related to Figure 6.3 and Eq. (6.14) for Stability of Lab-Made Ru-based Catalyst. . . . . . . . . . . . . . . 155 Table 6.5 Surface Area, Pore Volume, Average Pore Diameter, and Metal Dispersion of Lab-made Ru 6%/ γ-Al2O3 Catalyst (carrier not pre-aged by steam) . . . . . . . . . . . . . . . . . . . . . . 155 Table 6.6 Stability Conditions for Lab-made Ru-based Catalyst: Influ- ence of Rust on SS 304 Support . . . . . . . . . . . . . . . 157 Table 6.7 Curve Fitting Related to Figure 6.5 and Eq. (6.14) for Stability of Lab-Made Ru-based Catalyst. . . . . . . . . . . . . . . 158 Table 6.8 Membrane Start-up Steps with H2−H2O mixture . . . . . . 159 Table 6.9 Membrane Start-up Steps with H2−N2 mixture . . . . . . . 160 Table 6.10 Stability Conditions of Lab-made Ru-based Catalyst: Influence of Membrane Start-up Procedure . . . . . . . . . . . . . . 160 xi Table 6.11 Curve Fitting Related to Figure 6.6 and Eq. (6.14) for Stability of Lab-Made Ru-based Catalyst. . . . . . . . . . . . . . . 162 Table 6.12 Details of Ru-based Catalysts on XRD Spectra of Figure 6.7 162 Table 6.13 Surface Area, Pore Volume, Average Pore Size, and Metal Dis- persion of Lab-made Ru Catalysts and Supports . . . . . . 165 Table 7.1 Impregnation Solutions and Desired Metal Contents for Com- bustion Catalysts . . . . . . . . . . . . . . . . . . . . . . . 173 Table 7.2 Curve Fitting Related to Figure 7.2 and Eq. (6.14) for Stability of Pd 1% (Alfa) Catalyst . . . . . . . . . . . . . . . . . . . 178 Table 7.3 Stability Conditions for Pd 5%/ γ-Al2O3 (Alfa) and Lab-made Pd-based Catalysts for Figure 7.3. . . . . . . . . . . . . . . 179 Table 7.4 Curve Fitting Related to Figure 7.3 and Eq. (6.14) for Stability of Pd 5% (Alfa) and Pd-based Lab-made Catalysts . . . . . 181 Table 7.5 Surface Area, Pore Volume, Average Pore Size, and Metal Dis- persion of Pd/ γ-Al2O3 Catalysts . . . . . . . . . . . . . . 182 Table 7.6 Estimated Kinetic Parameters for Pd 1% (Alfa) Catalyst: Ex- perimental Conditions for Figure 7.7 . . . . . . . . . . . . 187 Table 7.7 Estimated Kinetic Parameters for Pd 1% (Alfa) Catalyst: Linear Regression Results for Figure 7.7 . . . . . . . . . . . . . . 187 Table 7.8 Estimated Kinetic Parameters for Experimental Conditions in Figure 7.8 . . . . . . . . . . . . . . . . . . . . . . . . . . 189 Table 7.9 Estimated Kinetic Pre-exponential Factor, A4, from Figure 7.8 189 Table 8.1 Impregnation Solutions and Desired Metal Contents for Cata- lysts used in MCMR . . . . . . . . . . . . . . . . . . . . . 200 Table 8.2 Catalyst Description for MCMR Experiment no.1, without Mem- brane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 200 Table 8.3 Catalyst Description for MCMR Experiment no.2, with Mem- brane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 201 Table 8.4 Catalyst Description for MCMR Experiment 3, with Membrane 202 Table 8.5 Membrane Start-up Procedure . . . . . . . . . . . . . . . . 205 Table 8.6 Experimental Operating Conditions . . . . . . . . . . . . . 206 xii Table 8.7 Parameters for Simulations Predictions, Part I . . . . . . . 209 Table 8.8 Parameters for Simulations Predictions, Part II . . . . . . . 210 Table 8.9 Summary of Preliminary Results for Reforming Channel . 213 Table 8.10 Membrane Effectiveness Calculations . . . . . . . . . . . . 217 Table 8.11 MCMR Experimental Results Compared with Early Simula- tions and Other Membrane Reactors. . . . . . . . . . . . . 226 Table 8.12 Improvement Potential for the Reforming Channel . . . . . 227 Table B.1 Surface Area, Pore Volume, Average Pore Size, and Metal Dis- persion of Commercial Reforming Catalysts . . . . . . . . 270 Table B.2 Stability of RK-212: Operating Conditions for Figure B.1 Part A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 270 Table B.3 Stability Conditions of Ru 5% (Alfa): Modified Sol Parameters and Reduction/Start-up Conditions for Figure B.4 . . . . . 274 Table B.4 Curve Fitting Related to Figure B.4, and Eq. (6.14) for Stability of Ru 5% (Alfa) . . . . . . . . . . . . . . . . . . . . . . . 274 Table C.1 Catalyst Description for MCMR Preliminary Experiments, Part I . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 281 Table C.2 Catalyst Description for MCMR Preliminary Experiments, Part II . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 282 Table C.3 Catalyst Description for MCMR Preliminary Experiments, Part III . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 283 Table C.4 Simulation Parameters for Preliminary Results . . . . . . . 284 xiii List of Figures Figure 1.1 Hydrogen Production Pathways . . . . . . . . . . . . . . 7 Figure 1.2 Thesis Strategy . . . . . . . . . . . . . . . . . . . . . . . 22 Figure 2.1 Schematic of 2-D Model . . . . . . . . . . . . . . . . . . 27 Figure 2.2 Schematics to Evaluate Average Velocity and to Develop En- ergy Balance . . . . . . . . . . . . . . . . . . . . . . . . 34 Figure 2.3 Schematic of Discretization . . . . . . . . . . . . . . . . 43 Figure 3.1 Non-Isothermal Base Case Results - Conversion, Average Tem- perature, Heat Flux and Molar Ratio . . . . . . . . . . . 67 Figure 3.2 Non-Isothermal Base Case Results - Velocity and Temperature Profiles . . . . . . . . . . . . . . . . . . . . . . . . . . . 68 Figure 3.3 Non-Isothermal Base Case Results - Molar Fraction and Cata- lyst Effectiveness Profiles . . . . . . . . . . . . . . . . . 69 Figure 3.4 Sensitivity Analysis - Operating Parameters . . . . . . . . 73 Figure 3.5 Sensitivity Analysis - Catalyst Parameters . . . . . . . . . 75 Figure 3.6 Sensitivity Analysis - Design Parameters & Diffusivity . . 77 Figure 3.7 Performance Improvement . . . . . . . . . . . . . . . . . 78 Figure 4.1 Initial Catalyst Coating Method . . . . . . . . . . . . . . 93 Figure 4.2 Sand-Blasting Images . . . . . . . . . . . . . . . . . . . 101 Figure 4.3 Surface Cleaning Issue . . . . . . . . . . . . . . . . . . . 102 Figure 4.4 SEM Images of Brush Coating and Various Hot Spray Coat- ings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103 Figure 4.5 Hot Spray Coating of γ-Al2O3 Modified Sol . . . . . . . . 106 Figure 4.6 SEM Images of γ-Al2O3 Coatings of Various Thicknesses 107 xiv Figure 4.7 SEM Tilted View Images of Hot Spray Coatings . . . . . 108 Figure 4.8 Hot Spray Coating of α-Al2O3, MgAl2O4 and CeO2−ZrO2 Modified Sol . . . . . . . . . . . . . . . . . . . . . . . . 109 Figure 4.9 Hot Spray Coating of Commercial Pd/γ-Al2O3 Catalysts . 111 Figure 4.10 Temperature Cycles of Hot Spray Coatings with γ-Al2O3 Mod- ified Sol . . . . . . . . . . . . . . . . . . . . . . . . . . . 112 Figure 4.11 SEM Images of Tilted and Side View of Hot Spray Coating of Commercial Ru 5%/ γ-Al2O3 . . . . . . . . . . . . . . . 113 Figure 4.12 Wet Impregnation Issues . . . . . . . . . . . . . . . . . . 116 Figure 4.13 Wet Impregnation on γ-Al2O3 Support Made by Hot Spray Coating . . . . . . . . . . . . . . . . . . . . . . . . . . . 117 Figure 5.1 Final Method for Coating Commercial and Lab-made Cata- lysts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121 Figure 5.2 Carbon Deposition during Steaming . . . . . . . . . . . . 126 Figure 5.3 Delamination and Cracking Issues after Steaming and Impreg- nation with RuNO(NO3)3 on γ-Al2O3 . . . . . . . . . . . 127 Figure 5.4 Comparison of Sonication Test and Crack Test . . . . . . 128 Figure 5.5 TGA Analyses of Boehmite, Pd 5%/ γ-Al2O3 with Boehmite, and RuNO(NO3)3−La2O3/ γ-Al2O3 . . . . . . . . . . . . 129 Figure 5.6 Cracks versus Cluster Formation during Hot Spraying of γ- Al2O3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130 Figure 5.7 Presence of White Lines on Coating . . . . . . . . . . . . 131 Figure 5.8 Rust on Catalyst with SS 304 as Metal Support . . . . . . 135 Figure 5.9 Ru-based Catalyst on SS 304 Support at Various Stages of Coating and Catalyst Life . . . . . . . . . . . . . . . . . 136 Figure 5.10 Commercial Pd-based/ γ-Al2O3 Catalysts on SS 304 Support at Various Stages of Coating and Catalyst Life . . . . . . . 137 Figure 5.11 Ru- and Pd-based/ γ-Al2O3 Catalysts on Fecralloy and SS 310 at Various Stages of Coating and Catalyst Life . . . . . . . 138 Figure 5.12 Commercial Pd 5%/ γ-Al2O3 Catalysts on Fecralloy and SS 310 before and after MCMR run . . . . . . . . . . . . . . 139 xv Figure 6.1 Micro-Reactor Set-up . . . . . . . . . . . . . . . . . . . 145 Figure 6.2 Micro-Reactor Process Flow Diagram . . . . . . . . . . . 146 Figure 6.3 Stability for Lab-made Ru-based Catalyst: Influence of Steam 154 Figure 6.4 FESEM Images of Ru 6%/ γ-Al2O3 . . . . . . . . . . . . 156 Figure 6.5 Stability for Lab-made Ru−La2O3/ γ-Al2O3 Catalyst: Influ- ence of Rust on Support . . . . . . . . . . . . . . . . . . 158 Figure 6.6 Stability of Lab-made Ru-based Catalyst: Influence of Mem- brane Start-up Procedure . . . . . . . . . . . . . . . . . . 161 Figure 6.7 XRD diagram of Lab-made Ru-based Catalyst, Fresh and Spent (after MCMR Exp.) . . . . . . . . . . . . . . . . . . . . . 163 Figure 6.8 Porosity vs Pore Volume for Catalyst with Alumina Support 166 Figure 6.9 Catalyst Layer and Pores Model . . . . . . . . . . . . . . 167 Figure 6.10 Pre-exponential Factor A1 - Estimation for Jackobsen Kinet- ics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 168 Figure 7.1 Preliminary Stability Test of Pd 1%/ γ-Al2O3 (Alfa) with 15% Boehmite . . . . . . . . . . . . . . . . . . . . . . . . . . 177 Figure 7.2 Stability of Pd 1%/ γ-Al2O3 (Alfa) . . . . . . . . . . . . . 178 Figure 7.3 Stability of Pd 5%/ γ-Al2O3 (Alfa) and Lab-made Pd-based Catalyst . . . . . . . . . . . . . . . . . . . . . . . . . . . 180 Figure 7.4 XRD Diagram of Commercial Pd 1%/ γ-Al2O3 (Alfa) with 15% boehmite, Fresh and Spent (after MCMR Exp.) . . . 183 Figure 7.5 XRD Diagram of Commercial Pd 5%/ γ-Al2O3 (Alfa) with 15% Boehmite, Fresh and Spent (after MCMR Exp.) . . . 184 Figure 7.6 XRD Diagram of Lab-made Pd-based Catalyst, Fresh and Spent (after MCMR Exp.) . . . . . . . . . . . . . . . . . . . . . 184 Figure 7.7 Estimated Kinetic Parameters for Pd 1% (Alfa) Catalyst: A. Activation Energy E4; B. Reaction Order for Methane α . 186 Figure 7.8 Estimated Kinetic Pre-exponential Factor, A4 . . . . . . . 188 Figure 8.1 Expanded View of MCMR Prototype . . . . . . . . . . . 193 Figure 8.2 Top View of Temperature and Gas Sampling Locations for both Channels . . . . . . . . . . . . . . . . . . . . . . . . 194 xvi Figure 8.3 MCMR Process Flow Diagram . . . . . . . . . . . . . . . 195 Figure 8.4 Reactor and Process Images I . . . . . . . . . . . . . . . 198 Figure 8.5 Reactor and Process Images II . . . . . . . . . . . . . . . 199 Figure 8.6 Pd/Ag Membrane Installed on Bottom Flange after Experi- ment no.3 . . . . . . . . . . . . . . . . . . . . . . . . . . 203 Figure 8.7 Schematic of MCMR Prototype for Simulations . . . . . . 208 Figure 8.8 Conversion and Temperature Profiles for MCMR Run no.1a without Membrane . . . . . . . . . . . . . . . . . . . . . 215 Figure 8.9 Methane Conversion vs. Methane Flow Rate at Position no.1 for MCMR Exp. no.1, without Membrane . . . . . . . . . 216 Figure 8.10 Process Response on H2 Production to an Increase in CH4 Flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 218 Figure 8.11 Process Response on Temperatures to the Start of Reforming and Combustion Methane Flows . . . . . . . . . . . . . . 219 Figure 8.12 Conversion and Temperature Profiles for MCMR Exp. no.3a with Membrane . . . . . . . . . . . . . . . . . . . . . . . 220 Figure 8.13 Sensitivity on Conversion Profiles for MCMR Run no.3a . 222 Figure 8.14 Conversion and Temperature Profiles for MCMR Exp. no.3b with Membrane . . . . . . . . . . . . . . . . . . . . . . . 223 Figure 8.15 Parametric Study on Effect of S/C Ratio, Reforming Channel Pressure, and CH4 Flow Rate, on H2 Extracted to CH4 Feed Ratio . . . . . . . . . . . . . . . . . . . . . . . . . . . . 225 Figure A.1 Brush Coating of γ-Al2O3, α-Al2O3 and RK-212 Modified Sol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 255 Figure A.2 Multi-Layer Brush Coating of γ-Al2O3 and α-Al2O3 Modified Sol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 256 Figure A.3 Dip Coating of γ-Al2O3 and α-Al2O3 Modified Sol Including Metal Precursors . . . . . . . . . . . . . . . . . . . . . . 257 Figure A.4 Scanned Images of Brush, Cold Spray and Dip Coating Sam- ples, before and after Sonication . . . . . . . . . . . . . . 258 Figure A.5 Hot Spray Coating of γ-Al2O3 Modified Sol Including Metal Precursors . . . . . . . . . . . . . . . . . . . . . . . . . . 260 xvii Figure A.6 Hot Spray Coating Optical Images with Different Solvents for Modified Sol . . . . . . . . . . . . . . . . . . . . . . . . 261 Figure A.7 Hot Spray Coating of α-Al2O3, MgAl2O4 and CeO2−ZrO2 Modified Sol Including Metal Precursors . . . . . . . . . 262 Figure A.8 Hot Spray Coating of Commercial RK-212 Catalyst . . . . 264 Figure A.9 Hot Spray Coating of Commercial Ru 5%/ γ-Al2O3 Catalyst 266 Figure A.10 Coating Thickness vs Mass of Catalyst . . . . . . . . . . 267 Figure B.1 Stability of RK-212: Effect of Operating Conditions and Cat- alyst Loading . . . . . . . . . . . . . . . . . . . . . . . . 269 Figure B.2 Stability of RK-212: Comparing Crushed with Coated Cata- lyst . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 271 Figure B.3 TPR diagrams of Ni-based Catalysts . . . . . . . . . . . . 272 Figure B.4 Stability of Commercial Ru 5%/ γ-Al2O3 (Alfa) . . . . . . 273 Figure C.1 Issues Encountered with MCMR, Part I . . . . . . . . . . 278 Figure C.2 Issues Encountered with MCMR, Part II . . . . . . . . . . 279 Figure C.3 Issues Encountered with MCMR, Part III . . . . . . . . . 280 Figure C.4 Combustion Methane Conversion versus Time on Stream, for MCMR Exp. no.0.3 . . . . . . . . . . . . . . . . . . . . . 285 Figure C.5 Combustion Methane Conversion versus Time on Stream, for MCMR Exp. no.0.4 and 0.5 . . . . . . . . . . . . . . . . 286 Figure C.6 Combustion Methane Conversion versus Time on Stream, for MCMR Exp. no.0.6 and 0.7 . . . . . . . . . . . . . . . . 287 Figure C.7 Reforming Methane Conversion versus Time on Stream, for MCMR Exp. no.0.4 . . . . . . . . . . . . . . . . . . . . . 288 Figure C.8 Reforming Methane Conversion versus Time on Stream, for MCMR Exp. no.0.5 . . . . . . . . . . . . . . . . . . . . . 289 Figure C.9 Conversion and Temperature Profiles for MCMR Exp. no.0.4 and 0.5 . . . . . . . . . . . . . . . . . . . . . . . . . . . 290 Figure C.10 Conversion and Temperature Profiles for MCMR Exp. no.0.7 291 xviii Acronyms ATR Autothermal Reforming BET Brunauer, Emmet and Teller BJH Barrett, Joyner and Halenda CFD Computational Fluid Dynamics CVD Chemical Vapour Deposition EDX Energy-Dispersive X-ray Spectroscopy EPD Electrophoretic Deposition FBMR Fluidized Bed Membrane Reactor FBR Fluidized Bed Reactor FESEM Field Emissions Scanning Electron Microscopy FID Flame Ionization Detector GC Gas Chromatograph GHG Greenhouse Gas H/C Hydrogen-to-Carbon IPCC Intergovernmental Panel on Climate Change xix LCA Life Cycle Assessment LHV Low Heating Value MCC Methane Catalytic Combustion MCMR Multi-Channel Membrane Reactor MCR Multi-Channel Reactor MRT Membrane Reactor Technologies P&ID Process & Instrumentation Diagram PBMR Packed Bed Membrane Reactor PBR Packed Bed Reactor PEMFC Proton Exchange Membrane Fuel Cell PSA Pressure Swing Adsorption S/C Steam-to-Carbon SEM Scanning Electron Microscopy SMR Steam Methane Reforming SS Stainless Steel TCD Thermal Conductivity Detector TGA Thermo Gravimetric Analysis TPR Temperature Programmed Reduction WGS Water Gas Shift WHSV Weight Hourly Space Velocity XPS X-Ray Diffraction XRD X-Ray Diffraction xx List of Symbols Ai Pre-exponential factor for sorption equilibrium constant K j [various units] A j Pre-exponential factor for rate coefficent k j [various units] c Concentration [mol/m3] c1i Concentration of component i after transformation (see Eq. (2.55)) [mol/m3] c2i Concentration gradient of component i after transformation (see Eq. (2.56)) [mol/m4] ci Concentration of component i [mol/m3] Cpi Molar heat capacity for component i [J/(mol K)] Ĉp Specific heat [J/(kg K)] Dh Hydraulic diameter [m] Di,eff Effective diffusion coefficient [m2/s] Di j Binary diffusion coefficient [m2/s] Di,K Knudsen diffusion coefficient [m2/s] Di,mix Mixture diffusion coefficient [m2/s] Dp,ave Average powder (particle) diameter [µm ] E j Activation energy [kJ/mol] xxi FH2,m Molar flow rate of of H2 extracted by membrane, see 3.7 [mol/s] FH2,prod Molar flow rate of H2 produced, see 3.8 [mol/s] Fi Molar flow rate of component i [mol/s] Hflux Heat Flux (See Eq. (3.16)) [kW/m2] Hk Half-height of channel [m] JH2,m Hydrogen molar flux through membrane [mol/(m 2 s)] ~Ji Component i diffusion flux [mol/(m2 s)] k Thermal conductivity [W/(m K)] Ki Sorption equilibrium constant for component i [kJ/mol] k j Kinetic rate of reaction j coefficient [various units] L Channel length [m] Mwi Molecular weight of species i [kg/mol] P Pressure [bar] PeL Mass Peclet number [-] Pi Partial Pressure [bar] ~q Conduction heat flux [W/ m2] Re Reynolds number [-] Rg Universal gas constant: 8.314 [J /(mol K)]; 8.314*10−5 [(bar m3)/(mol K)] Ri Production rate of component i [mol /(m3 s)] r j Rate of reaction j per volume of reactor [mol /(m3 s)] xxii r ′ j Rate of reaction j per mass of catalyst [kmol /(kg h)] Rpore Average catalyst pore radius [m] t Time on stream [h] T Temperature [K] T1 Temperature after transformation (see (2.57)) [K] T2 Temperature gradient after transformation (see (2.58)) [K/m] Thcat,k Catalyst Layer Thickness [m] Thm PdAg Membrane Thickness [m] Ths Separator Wall Thickness [m] u Dependent parameters ci and T , see (2.59) [various units] vz Axial gas velocity [m/s] Wcat Catalyst mass [g] Wk Channel width [m] x Transverse coordinate [m] XCH4 Methane conversion [mol/mol] xi Mass fraction [kg/kg] YH2 Hydrogen production intensity [various units] yi Molar fraction [mol/mol] z Axial coordinate [m] xxiii List of Greek Letters α Exponent in Eq. 2.11 or reaction order for CH4 in Eq. (2.50) [-] β Exponent in Eq. 2.16 or reaction order for O2 in Eq. (2.50) [-] δk Coefficient in Eq. (2.114) [-] ∆H298Krx,j Enthalpy of reaction j at 298 K, 1 bar [kJ/mol] ∆Hsorp Sorption enthalpy [kJ/mol] ∆T Transverse temperature difference (see (2.114))[K] ∆z Discretization step size in axial direction [m] ε Catalyst porosity [-] ηcat Catalyst effectiveness factor [-] ηm Membrane effectiveness: Ratio between real flux and theoretical flux for mem- brane [-] ηreact Reactor efficiency [-] µ Gas viscosity [Pa s] Φi j Coefficient in Eq. (2.10) [-] ρ Catalyst density [kg/m3] xxiv σi j Stoichiometric coefficient of component i for reaction j [-] σM Stoichiometric molar ratio between the reduced metal and the metal precursor, see Eq. (4.4) [-] τ Catalyst tortuosity [-] υ Pore volume [cm3/g] xxv List of Subscripts M Metal sf Surface of micro-reactor ave Average b Discretization grid position in axial direction bed Catalyst bed of a fixed reactor c Combustion gas channel or combustion carr Carrier cat Catalyst layer i Chemical component in Inlet j Reaction numbers, or second chemical component k Either combustion or reforming m Membrane m.area Membrane area m.sup. Membrane support mix Mixture of gas species xxvi o Feed conditions out Outlet r Reforming gas channel or reforming s Separator wall ske Skeleton vol.react. Internal reactor volume xxvii Acknowledgments This thesis was made possible with the contributions of many people. A first special thanks for my supervisors. Prof. John Grace has been extremely supportive throughout those years, by providing valuable advices, and critical fi- nancial and human support. I had the chance to work with Prof. Said Elnashaie, who can combine revolution and reactor modeling as no one else. A very appreciative thank you to the thesis committee, Professors Sue Baldwin, Walter Merida, and Jim Lim, who had to go through this long thesis in a short period of time. This research was also made possible with the contribution of Prof. Tom Troczynski, allowing us to use his ceramic laboratory space, numerous equipments, and giving valuable insights. Special thanks also to Prof. Kevin Smith for his direction and knowledge with the amazing world of catalysis. Thanks to the MRT folks, with Ali Gulamhusein, Anwu Li, and Tony Boyd for all their advice. Several students participated in this project. I would like to acknowledge the contribution of JiYeon Shin, Zaid Ahmad, Helia Yazdanpanah, Bahman Ghiasi, Kit Wong, Philipp Stoesser, Kristian Dubrawski, Dora Ip, and Nick Chow. To my fellow colleagues for their help, moral support, and good conversations, Rakib Ab- dur, Andres Macheta Botero, Siamak Elyasi, Laura Tremblay Boyer, Dylan Gunn, and Ali Shafiei, thank you! A special smile to my family for their on-going moral and financial support, and yes this should be my last degree in school, at least for a while. To all my friends, met through sports, activism, research, beer, and social dancing throughout those years, thank you! I would also like to thank the company Sasol Alumina, providing at no cost various alumina powders and beads. This project was also made possible by the financial support of NSERC, FQRNT, and the Canada Fund for Innovation. xxviii I would like to dedicate this thesis to all of us who believe that applying science with ethics can achieve wonderful things, et à Louis-Philippe, Émile et Julien, car c’est un peu pour vous que je fais tout ce travail! xxix Chapter 1 Introduction Mieux vaut 1% de pas grand chose, que 100% de rien du tout. — My mom (2011) 1.1 The Case for Hydrogen 1.1.1 Climate Change and Greenhouse Gas Emissions In their 4th assessment, the Intergovernmental Panel on Climate Change (IPCC) reported that, to avoid climate change with devastating consequences, we need to limit global temperature rise by 2.0 - 2.4oC above the pre-industrial level. In order to achieve this target, world Greenhouse Gas (GHG) emissions need to be reduced by 50-85% from the 2000 level by 2050 (Intergovernmental Panel on Cli- mate Change, 2007). The reduction target corresponded to a CO2 concentration in the atmosphere of 350-400 ppm, which was already at 379 ppm in 2005 (Inter- governmental Panel on Climate Change, 2007). Trends are not encouraging, since global CO2 concentration, measured in Mauna Loa, Hawaii, reached 392 ppm in 2011 (Earth System Research Laboratory, 2012). In 2004, 13.1% of the world emissions, or 6.4 GT CO2 equivalent (CO2e), were coming from the transportation sector. In Canada, 24% of GHG emissions, corresponding to 166 MT CO2e, were emitted in 2010 by this sector, a 3.6% increase from 2005 (Environment Canada, 2012). 1 1.1.2 Life Cycle Impact Assessment One option to reduce GHG emissions in the transportation sector is to use hydrogen and fuel cell technology. Hydrogen is often mistaken as a zero emission fuel, with claims referring to its combustion only producing water. Hydrogen, like electricity, is an energy carrier, and not a primary energy source. Therefore, it is important to examine hydrogen with Life Cycle Assessment (LCA) in order to understand its environmental impact. Since hydrogen can be produced from a wide variety of feedstocks and energy sources (see Figure 1.1), then combined with fuel cell technology, LCA predictions have varied considerably in the literature (Colella et al., 2005; Granovskii et al., 2006; Schäfer et al., 2006; Dincer, 2007; Ally and Pryor, 2007). Colella et al. (2005) showed that even with conservative assumptions (i.e. Pro- ton Exchange Membrane Fuel Cell (PEMFC) efficiency of 46%, 10% H2 lost by leakage), switching from internal combustion engines to hydrogen fuel cell ve- hicles could reduce GHG emissions by of 14 - 23%, depending on whether the hydrogen is produced from steam reforming of natural gas or electrolysis based on wind turbines. However, for hydrogen from coal without carbon sequestration, the same LCA study showed almost no reduction of GHG. In similar studies (Gra- novskii et al., 2006; Dincer, 2007), assuming a higher efficiency by PEMFC engine (∼ 50-60%), it was found that GHG emissions could be reduced by 25-40% if H2 was extracted from natural gas, and by up to 80-85% if H2 was obtained from wind energy. Most emissions from vehicles are related to the fuel consumption, rather than to vehicle manufacturing and disposal: ∼73% according to (MacLean and Lave, 2003), and nearly 90% according to (Schäfer et al., 2006). Schäfer et al. (2006) also noted that in the future, the share of fuel consumption should diminish as vehicles become more energy efficient. Schäfer et al. (2006) predicted the global warming impact for a wide range of vehicles for 2020. With likely improvement in internal combustion engine vehicles and gasoline-electric hybrid vehicles, unless hydrogen would be produced from renewable sources, they found little energy or GHG emission savings by switching to hydrogen fuel cell vehicles. Ally and Pryor (2007) studied hydrogen fuel cell 2 buses from a demonstration project in Perth, Australia. With available technology, conventional diesel buses were more energy efficient than fuel cell buses, and no GHG reduction benefit was found. However, with expected improvements in future fuel cell buses, the authors believed that at least a 50% reduction in GHG emissions was achievable. In addition to global warming reductions, hydrogen in fuel cells could help im- prove air quality in urban area, where particulate matter, NOx, and volatile organic compounds are concerns. Wang et al. (2008) studied different PEMFC vehicles and hydrogen delivery scenario for Sacramento, CA. Centralized H2 production with pipeline distribution was the best scenario to reduce air pollution. Compared with advanced new gasoline vehicles, centralized H2 production would result in 273 times less CO, 88 times less VOC, 8 times less PM10, and 3.5 times lower NOx concentrations. From our review of LCA studies, hydrogen in fuel cell vehicles has the po- tential to reduce global GHG emissions as well as other air pollutants. However, as the IPCC pointed out, no single technology could solve the entire problem (In- tergovernmental Panel on Climate Change, 2007). Curbing GHG emissions will need a wide range of technological solutions, as well as much smarter land usage, political leadership, pollution pricing, education, and mentality changes. 1.1.3 Global Hydrogen Production and Consumption In 2007 the world produced between 53 to 65 million tonnes of hydrogen. Most was consumed at refineries, surpassing ammonia production (International En- ergy Agency, 2007; Naqvi, 2007). Refineries were once viewed as net producers of hydrogen, but they are now major consumers. H2 production plants are of- ten needed to implement environmental regulations (Ferreira-Aparicio and Benito, 2005; SRI Consulting, 2010). Among other usages for hydrogen are the synthe- sis of methanol, resins and plastics, food processing, electronics, and annealing of steels. Only 5% of the H2 production is sold outside the production plant and distributed as liquid or gas in tanks or by pipelines. Its use for energy purposes constitutes only a small fraction of total production (Ferreira-Aparicio and Benito, 2005). 3 Nearly 96% of hydrogen production is derived from fossil fuels, 49% from natural gas, 29% from liquid hydrocarbons, 18% from coal, while electrolysis and other by-product sources of hydrogen account for ∼4% (SRI Consulting, 2010). Hydrogen from Steam Methane Reforming (SMR) currently sets its reference price. A study by the National Academy of Engineering (2004) shows that large-scale production of hydrogen (1,200,000 kg/day) using current SMR technology is still the most economical option to produce hydrogen (National Academy of Engi- neering, 2004). They estimated the production cost from large scale SMR to be US$1.03/ kg H2 in 2004. 1.1.4 Hydrogen for Transportation Hydrogen is used in the production of various chemicals. Advocates of a “hydro- gen economy” see hydrogen playing a new role as an energy carrier, becoming the main fuel not only for transportation, but as well for stationary power production, building heating, and mobile device power. Transportation Economics In 2002, world hydrogen production was equivalent to less than 10% of the world oil production (Ferreira-Aparicio and Benito, 2005), indicating the scale of invest- ment needed for a transition to hydrogen. Table 1.1 lists various targets from the U.S. Department of Energy (DOE), together with progress achieved according to the California Fuel Cell Partnership, and technical data from Honda Motor Corp. (California Fuel Cell Partnership, 2012; American Motor Honda Co., 2012). Electricity needed for gas and liquid storage represents, respectively, 12% and 35% of the H2 energy content (International Energy Agency, 2007). The US Na- tional Research Council estimated that it would cost US$0.9 and $1.0 million to build a distributed plant producing 500 kg/day from SMR and electrolysis respec- tively (National Research Council, 2008). The lack of refueling infrastructure is a major obstacle to hydrogen fuel cell market penetration. There is a small, but growing number of, demonstration fueling stations around the world. In May 2012, there were ∼238 operating hydrogen refueling stations worldwide, 82 in the U.S. (8 accessible to public), and 14 in 4 Table 1.1: Targets and Progress for Hydrogen in the Transportation Sector (Data collected from California Fuel Cell Partnership (2012); American Motor Honda Co. (2012); Inter- national Energy Agency (2007)). Category Target Progress Fuel Cell Efficiency 60% FCX Clarity claims 60% Fuel Cell Durability 5000 operating hours > 2500 operating h Vehicle Range 480 km FCX Clarity claims 385 km Refueling Rate ∼ 1 kg/ mina ∼ 0.8 kg/min Fuel Cell Cost US$30/ kW by 2015 US$49/ kW in 2011b,c Vehicle Tank Cost - US$3,000 - 4,000 Cost of Delivery Hydrogen US$1/ kgd $3/kgb Hydrogen Cost at the Station US$3/ kgd (2015) to be revised to US$6/ kg (2020) From NG: US$7.7-10.3/ kg; From electrolysis: US$10.0-12.9/ kg aFCX Clarity storage tank capacity: 4 kg at 35 MPA bBased on projections to high-volume manufacturing or delivery cFCX Clarity has a 100 kW fuel cell stack dData were originally written in gge (USGAL gasoline equivalent), and 1 kg H2 has about the same energy content as 1 USGAL (3.79 L) of gasoline Canada (Fuelcells.org, 2012a,b). By comparison, there was ∼12,710 retail gas stations in Canada in 2010 (CNW, 2010). Decentralized production of hydrogen was proposed to break the bottleneck (Ogden, 2001; Ferreira-Aparicio and Benito, 2005). IHS Chemical (2003) esti- mated that with technology commercialized in 2003, the minimum competitive ca- pacity for distributed vs. large centralized plant was ∼10,600 - 12,700 kg H2/day. 10,000 kg/day could supply∼2000 hydrogen fuel cell vehicles a day. Hence, there is still room for technological advancement at smaller scale (<500 kg H2/day), the main market goal for the technology considered in this thesis. 5 1.2 Hydrogen Production Pathway 1.2.1 Feed Sources Hydrogen, present in organic compounds and several inorganic compounds (e.g. water, ammonia, NaOH, H2SO4), can be produced as the main product or as a by- product of various chemical and biological reaction pathways (see Figure 1.1). The focus of this review is on technologies that have potential to be commercialized in a near to mid-term range, in order to supply fueling stations in a decentralized way. The main focus is on methane reforming technologies, since natural gas is most likely to stay the benchmark fuel for economic reasons, but also for thermody- namic efficiency and environmental considerations. Methane, the main component of natural gas, has the highest Hydrogen-to-Carbon (H/C) molar ratio of all hydro- carbons, therefore potentially making less CO2 emissions per mole of hydrogen produced. With inevitable energy losses, it makes little sense thermodynamically to use electricity alone to produce hydrogen, which will be reconverted into electricity in a fuel cell. However, for small scale production, typically up to 100 kg/day, water electrolysis has been commercialized. It has the advantage of being a well-known technology generating high purity, hydrocarbon-free hydrogen. Commercial al- kaline water electrolyzers produce hydrogen with efficiency ranging from 55% - 75%, while 70% - 80% of the cost of production is attributable to electricity (Inter- national Energy Agency, 2007). 1.2.2 Reaction Pathways from Methane to Hydrogen Various chemical reaction pathways to produce hydrogen from methane are listed below. Dry Reforming: CH4+CO2⇔ 2H2+2CO ∆H298Krx =+247 [kJ/mol] (1.1) 6 Feed	
  Source	
   Inorganic	
   Water	
   Ammonia	
   Hydrogen	
  Sulfide	
   Organic	
   Renewable	
   Biomass	
   Biogas,	
  Sugar,	
  Alcohol,	
   Ether	
   Fossil	
   Natural	
  gas,	
  oil,	
  Coal	
   Alcohol,	
  Ether	
   Reac1on	
  Process	
   Electricity	
   Fossil	
   Nuclear	
   Renewable	
   	
  	
  Wind,	
  Solar,	
  Hydro,	
  	
   	
  	
  Geothermal,	
  Biomass	
   	
   Heat	
   CombusAon	
   Geothermal	
   Solar	
   Nuclear	
   	
   Energy	
  Source	
   Biological	
   	
   Chemical	
   Catalysis	
   Reforming	
   ParAal	
  OxidaAon	
   By-­‐product	
  	
  chemical	
  process	
   CatalyAc	
  Cracking	
   CatalyAc	
  DecomposiAon	
   DehydrogenaAon	
   Thermal	
   Thermo-­‐chemical	
  loop	
   Pyrolysis	
   GasificaAon	
   DecomposiAon	
   Electro-­‐chemical	
   Photo-­‐electro-­‐chemical	
   Plasma	
  reforming	
   Electrochemical	
  reforming	
   Electrolysis	
   Figure 1.1: Hydrogen Production Pathways Methane Decomposition: CH4→ 2H2+C(s) ∆H298Krx =+75 [kJ/mol] (1.2) Partial Oxidation: CH4+0.5O2→ 2H2+CO ∆H298Krx =−36 [kJ/mol] (1.3) 7 Steam Methane Reforming: CH4+H2O⇔ 3H2+CO ∆H298Krx =+206 [kJ/mol] (1.4) CO+H2O⇔ H2+CO2 ∆H298Krx =−41 [kJ/mol] (1.5) CH4+2H2O⇔ 4H2+CO2 ∆H298Krx =+164 [kJ/mol] (1.6) Autothermal Methane Reforming: With Autothermal Reforming (ATR), air or oxygen is added to the methane-water mixture. The following combustion reaction occur, in addition to the SMR reactions. CH4+2O2→ 2H2O+CO2 ∆H298Krx =−803 [kJ/mol] (1.7) CO+0.5O2→ CO2 ∆H298Krx =−283 [kJ/mol] (1.8) H2+0.5O2→ H2O ∆H298Krx =−242 [kJ/mol] (1.9) If the product of interest is H2 rather than syngas, partial oxidation and dry reforming are unlikely to be the best options. By simple mole balances, a mini- mum of 69% of the methane combustion energy is lost with dry reforming. Dry reforming also requires a stream of CO2, which may not be available. Methane de- composition could become a viable option with a strong market for solid carbon or a high price on GHG emissions. ATR can be the most efficient mode of operation since it requires the lowest total energy consumption by avoiding all heat transfer limitations (Grace et al., 2005). ATR using air dilutes the hydrogen concentration in the product stream, increasing purification cost downstream. An alternative to air would be to add an O2 production unit to avoid N2 dilution, but at the cost of increasing complexity. Long term stability of bi-functional catalysts for ATR can also be problematic (Grace et al., 2005). As discussed above, SMR is currently the most economical way of producing hydrogen at large scale. A major challenge at small scale is how to transfer heat as efficiently as possible. 1.3 Process and Hydrogen Purification The conventional process to produce pure hydrogen via large-scale SMR features 5 steps (Farrauto and Bartholomew, 1997; Ferreira-Aparicio and Benito, 2005): 8 Table 1.2: Hydrogen Fuel Quality Specifications (partial list). For complete list, see (SAE International, 2011) Constituent Limits (ppma) Water 5 Total hydrocarbonsb 2 Oxygen 5 Helium 300 Nitrogen, Argon 100 Carbon dioxide 2 Carbon monoxide 0.2 Total Sulfur 0.004 Particulate Concentration 1 mg/kg Hydrogen Content >99.97% aMole basis bCH4 basis (1) Desulfurization, to avoid poisoning of the reforming catalyst; (2) Optional pre-reforming to transform higher molecular weight hydrocarbons to methane, hence avoiding carbon formation during reforming; (3) Steam reforming; (4) High- temperature Water Gas Shift (WGS), optionally followed by low-temperature WGS, reducing the amount of CO to 1-3%; and (5) Pressure Swing Adsorption (PSA) to obtain pure hydrogen. To be used as a fuel for PEMFC, hydrogen must meet stringent quality re- quirements, see Table 1.2. Few technologies exist to purify the hydrogen product stream, among them: PSA, preferential oxidation, and H2 selective membranes. 1.3.1 Pressure Swing Adsorption Most modern production plants use PSA for hydrogen purification. The standard process requires at least two adsorption vessels to ensure continuous operation. They are usually filled with beads of activated carbon, zeolite, molecular sieves or activated alumina (Waldron and Sircar, 2000). New systems use structured ab- sorbents to avoid undesirable fluidization, and hence increase flow rates and reduce size and cost of the unit (Babicki and Hall, 2003). Standard operation consists of 9 a minimum of 4 steps: (1) adsorption of feed impurities at high pressure and col- lection of pure hydrogen; (2) depressurization with desorption of impurities (3) low-pressure countercurrent purge with hydrogen; and (4) pressurization with hy- drogen (Waldron and Sircar, 2000). Hydrogen purity can reach 99.9999% at recov- ery rates from 70-90%, depending on the feed purity and off-gas pressure (Mishra and Prasad, 2011). Commercial units can handle as little as 10 Nm3/h (21 kg/day) to large-scale production of 400,000 Nm3/h (845,000 kg/day) (Xebec Absorption, 2012; Linde Group, 2012). 1.3.2 Preferential Oxidation Preferential oxidation uses the concept of the proven catalytic converter technol- ogy from the automobile industry. The product gas from the water gas shift con- verter is mixed with air in a fixed bed or monolith reactor, to limit pressure drop. Catalyst is usually a noble metals (Pt, Rh, Pd), gold or CuO−CeO2 (Farrauto and Bartholomew, 1997; Mishra and Prasad, 2011). Mishra and Prasad (2011) reported that CO levels <10 ppm can be achieved with such technology. However, the addi- tion of air dilutes the hydrogen stream, and leads to more excess feed at the anode of the fuel cell to avoid mass transfer limitation. Preferential oxidation is probably limited to small and medium scale stationary power production, not requiring high hydrogen purity, or mobile or on-board systems constrained by system volume and weight (Ferreira-Aparicio and Benito, 2005). 1.3.3 Membranes Membranes have the potential to be installed directly inside reformers. In-situ sep- aration can favorably shift the limiting thermodynamic equilibrium. Adhikari and Fernando (2006) reviewed several high-temperature membranes suitable for SMR: microporous ceramic, dense metallic, and dense ceramic membranes. Although microporous ceramic membranes have relatively high hydrogen flux, their selec- tivity is limited, as the separation relies principally on the difference in molecular weights of the gas compounds. As the CO concentration is generally limited to less than 1 ppm in PEM fuel cells, further purification is needed. Dense metallic hydro- gen membranes have the advantage of high selectivity, but lower permeability and 10 lower maximum operating temperature (∼ 575oC for Pd/Ag membrane) than mi- croporous membranes. Dense ceramic membranes operate at high temperature and high selectivity, but lack the flux of the dense metallic and microporous ceramic membranes. The presence of pinholes in dense membranes is a major challenge. The permeation mechanism for dense Pd-based membrane involves seven steps in series: (1) transport of hydrogen molecules to the surface of the metallic mem- brane; (2) reversible chemisorption of H2 on the metal surface; (3) reversible dis- solution of atomic hydrogen into the bulk metal; (4) diffusion of atomic hydrogen through the metal lattice; (5) reassociation of atomic hydrogen on the permeate- side; (6) desorption of adsorbed molecular hydrogen from the metal surface; and (7) gas transport away from the permeate-side surface. Diffusion of atomic hydro- gen (step 4) is generally rate controlling. To resist the necessary pressure gradient acting as the driving force for hydrogen diffusion, a support for the membrane is generally required (Boyd, 2007). Membrane Reactor Technologies (MRT), a UBC spin-off company, developed a 25 µm thick planar Pd/Ag 25wt% hydrogen permselective membrane. The Pd/Ag foil is supported by a porous stainless steel sheet, separated by a ceramic layer to avoid interdiffusion between the Pd and stainless steel, lowering permeability. The major limitation with the Pd/Ag membrane is its maximum operating tem- perature of ∼575oC. At this temperature, the kinetics of the reforming reactions are relatively slow and the equilibrium conversion of methane is relatively low, compared with conventional reactor temperatures. Nonetheless, MRT membranes were successful in several research projects (e.g. Boyd (2007); Mahecha-Botero et al. (2009); Rakib et al. (2011)). This thesis also used this technology. Research on dense Pd-based membranes seeks different alloys, better supports, and thinner membranes to enhance the H2 flux and reduce cost. Ryi et al. (2006b) built a 4 µm thick Pd−Cu−Ni ternary alloy membrane on a 2 mm porous nickel support. They tested the membrane up to 500oC with pressure difference across the membrane up to 3.6 bar, and no defect was detected. Su et al. (2005) made 2-6 µm Pd membranes on porous stainless steel, separated by a SiO2 layer. Per- meation measurements were made at 500oC, with a 0.5 bar pressure difference. Ryi et al. (2011) produced non-alloy, 6.8 µm thick, pinhole-free Ru/Pd composite membranes by electroless plating. 11 Instead of porous supports, dense silicon oxide wafers, perforated by etching, have been proposed as membrane support (Wilhite et al., 2004; Keurentjes et al., 2004; Gielens et al., 2007; Deshpande et al., 2010). Wilhite et al. (2004) made 200 nm thick Pd and Pd/Ag membranes, and operated them up to 425oC. Keurentjes et al. (2004) produced Pd/Ag membrane 0.5 and 1.1 µm thick. Pd/Ag was sputtered onto the wafer using titanium as an adhesion layer. No pinholes were detected at temperatures up to 450oC, and the pressure difference across the membrane was near 1 bar. It is not clear if those thin membranes could sustain SMR operating conditions, with more elevated temperatures and pressures. 1.4 Reformer Configuration 1.4.1 Current Large-Scale Reactor Design Large scale conventional SMR units consist of a stack of long catalyst-filled tubes (12 m), operated at ∼15-25 bar, and ∼850oC (Ogden, 2001). Heat is supplied by burning natural gas or other fossil fuels in a furnace chamber surrounding the catalyst tubes. Heat transfer is limited by the permissible flux through the metal tubing, requiring expensive alloy steels. Inside the catalyst pellets, mass transfer resistance is also important, with low effectiveness factors (<95%) (Adris et al., 1996). To overcome mass and heat transfer limitations, new reactor configurations, novel catalysts, alternative reaction pathways, new heat transfer media, and sep- aration methods are often proposed (Ogden, 2001; Ferreira-Aparicio and Benito, 2005). 1.4.2 Neo-conventional Reactor Neo-conventional reactors typically use fixed bed reformers without radiant burn- ers. These are hard to scale down efficiently. Heat is usually transfered by convec- tion via pre-burned fuel gas, and the reformer tubes are U-shaped, instead of con- ventional straight pipes. Haldor Topsøe developed a medium-scale H2 production plant, to produce 10,600 to 63,000 kg H2/day (Haldor Topsøe, 2009). UTC power commercialized a stationary heat & power unit, PureCell Model 400, that produces 12 400 kW of electricity and 450 kW of heat, with 90% overall fuel efficiency. This means that their reformer produces the equivalent of ∼1300 kg H2/day. The unit recycles all the water generated, and no water is supplied. Their current reformer design uses fixed beds, and they are also testing plate reactor technologies (Kanuri, 2011; UTC Power, 2012). 1.4.3 Multi-channel Reactor Multi-Channel Reactors (MCRs), also known as plate, wall, micro-channel or micro-structured reactors, have been often proposed to generate hydrogen more efficiently (e.g. (Park et al., 2005; Ryi et al., 2006a; Tonkovich et al., 2007; Seris et al., 2008; O’Connell et al., 2011; Hwang et al., 2011)). The basic idea is to imitate the compact design of a plate heat exchanger: Cold channels, where en- dothermic reforming reactions are taking place are juxtaposed with hot channels, where exothermic catalytic combustion is occurring. Typical channel widths range from a few hundred microns to 3-5 mm (Tonkovich et al., 2004). Catalyst is typically coated on the channel walls, but can also be coated on metallic foam (Tonkovich et al., 2004), meshes (Ryi et al., 2006a) or in powder or pellet form (Hwang et al., 2011). MCR increases the surface area for heat exchange and enhances the hydrogen production intensity per volume of reactor. With a thin layer (<100 µm) of coated catalyst, the catalyst effectiveness is also enhanced. Scale-up is achieved by repeating the channel pattern, so that the reaction physics and hydrodynamics stay the same (Tonkovich et al., 2005). MCRs also respond quickly to dynamic changes in feed conditions (Sohn et al., 2007). Challenges include flow distribution among channels, catalyst deactivation, hot spots, fabrication and sealing (Tonkovich et al., 2005; O’Connell et al., 2011). Tables 1.3 and 1.4 present physical details and performance data for several MCR units used for hydrogen production via reforming of various feedstocks. In Table 1.4, reforming methane conversions from Hwang et al. (2011) exceed equi- librium values. The authors explained that this was due to their Ni sintered catalyst pellet having a membrane effect. Their design forced all gases to go through the Ni pellet. Hydrogen diffusing faster than other components shifted the equilibrium methane conversion. 13 Table 1.3: MCR Steam Reforming (A) and Catalytic Combustion (B) - Fabrication Details Reference Feed A - Catalyst Feed B - Catalyst Coating Method - Film Thickness Channel Dim (Width x Height x Length) - Material - Fabrication - Sealing Venkatara- man et al. (2003) CH4 - Rh−Cr2O3−Y2O3/ Al2O3 CH4 - Pt−Cr2O3– Y2O3/ Al2O3 Wash Coating - 10 µm 8 cm x 5 cm x 4 mm - Fecralloy - 1 mm deep corrugated plate - bolted and Fiberfrax paper gasket Park et al. (2005) MeOH - Cu−ZnO/ Al2O3 MeOH - Pt/ Al2O3 Al2O3 under layer and wash coating -N/A 300 x 200 µm x 34a mm - SSb - Wet etching - Brazing Ryi et al. (2006a) CH4 - Rh–Mg/ Al2O3 H2 - Pt−Zr/ FeCrAlY mesh Wash coating - N/Ac 300 x 30 µm x 20 mm - N/A- Etching - N/A Sohn et al. (2007) MeOH - Cu−Zn/ Al2O3 H2 (start-up), MeOH - Pt/ Al2O3 Wash coating -50 µm 450 x 150 µm x 100 mm - SS - Wet etching - Clamping Tonkovich et al. (2007) CH4 - 10 wt% Rh–MgO/ Al2O3 on FeCrAlY Felt H2 - Pd Wash coating - N/A Ref. 10.7 mm x 0.28 mm x 11.4 mm, Comb. 2.54 mm cylindrical - Inconel - N/A- N/A Seris et al. (2008) Nat. Gas - Noble metal (Engelhard) H2/ Pd-based Coated ceramic monolith - N/A N/A-N/A-N/A-N/A Hwang et al. (2011) CH4 - Ni sintered powder H2 (start), H2+CH4/ Pt coated mesh Pellet diffusion bonded - 1.2 mm N/A- N/A- N/A- Diffusion bonding aEstimated bref. = reforming, comb. = combustion, SS = stainless steel, nat. gas = natural gas cN/A: not enough data to estimate or report 14 Table 1.4: MCR Steam Reforming and Catalytic Combustion - Performance Data Reference Reactor Size (w/out insulation) - Total H2 Output Ref.a Feed Conversion - Purity H2 (dry basis) H2 Output/ mass cat. H2 Output/ react. vol. Efficiency Reformerg- External Heating kg/ (day kgcat) kg/ (day m3) Venkatara- man et al. (2003) 48-80b,c,d ml - 0.09-0.25b kg H2/day 90-95% @ ∼600-700oC- 74-78% N/Ah 700- 5200d 45b% - Bunsen burner for start-up Park et al. (2005) 72e ml - 0.04 kg H2/day >99% conv. @ 230-260oC- 73% N/A 590e N/A- No external heating Ryi et al. (2006a) 50f ml - 0.09 kg H2/day 94% conv. @ 700oC- N/A N/A 1780f N/A- No external heating Sohn et al. (2007) 33b,f mL - 0.21 kg H2/day 90% conv. - 70% @ 300oC 355 6408f 57% - No external heating Tonkovich et al. (2007) N/A- 0.06b kg H2/day 88% conv. @ 840oC, 12 bar - N/A 5000 N/A N/A-N/A Seris et al. (2008) 16e L - 10.6 kg H2/day 80% conv. @ 750oC, 2 bar - N/A N/A 650e N/A- N/A Hwang et al. (2011) 80e mL - 0.04 kg H2/day 95% conv. @ 610oC- N/A N/A 470e N/A- No external heating acat. = catalyst, conv. = conversion, ref. = reforming, react. vol. = reactor volume bEstimated c(Venkataraman et al., 2003) has three different reactor configurations, see paper for details dReactor size includes some heat exchangers eReactor size includes heat exchangers fReactor size excludes heat exchangers gEfficiency Reformer: Low Heating Value (LHV) H2* H2 Flow / (LHV * Ref. Feed + LHV * Comb. Flow) hN/A: not enough data to estimate or report 15 The MCR concept allows innovative heat integration to optimize heat transfer and overall efficiency. Heat exchangers to pre-heat reforming feed and cool the products can be integrated directly to the reformer (Ryi et al., 2006a). Some reformers have been developed for mobile device applications (Ryi et al., 2006a; Sohn et al., 2007), where fast start-up is critical. Ryi et al. (2006a) demon- strated that with a Pt-Zr coated-mesh igniter, they were able to reach their desired methanol reforming temperature in less than 1 min. Simsek et al. (2011) compared two catalytic micro-channel configurations for syngas production (CO-H2).They found that wall-coated micro-channel geometry led to higher methane conversions and syngas production rates than with packed catalyst in the same channel configuration. The Institut fur Mikrotechnik Mainz (IMM), Germany performed extensive ex- perimental work on MCR technologies, including both 250 W liquefied petroleum gas and 100 W methanol fuel processors (O’Connell et al., 2011). Ztek Corporation undertook development of a small-scale reformer based on plate reactor technol- ogy (Ferreira-Aparicio and Benito, 2005). They commercialized units that likely use plate reactor technology, producing from 12 to 83 kg H2/day at 99.99% purity. 85% efficiency from the fuel heat value is claimed (Ztek Corporation, 2005). This likely does not include parasitic losses. 1.5 Novel Membrane Reactors Combining H2 selective membranes with reforming reactors allows the thermody- namic equilibrium to be shifted, leading to high feed conversion, while generat- ing pure hydrogen in a single vessel. Given the equilibrium shift and maximum temperature limitations of membranes, lower temperatures are used, reducing heat losses at small to mid production scale, and permitting less expensive stainless alloys to be employed (Grace et al., 2005). The benefit of membrane addition in process intensification has to be weighed against slower kinetics, and the hydrogen being produced at low pressure, therefore needing to be compressed for most applications (Grace et al., 2005). 16 1.5.1 Packed Bed and Coated Tubular Membrane Reactors Several Packed Bed Membrane Reactors (PBMRs) for the production of H2 via reforming reactions have been investigated with various fuels: e.g. methane (Bar- bieri et al., 1997; Kikuchi, 2000; Tsuru et al., 2004; Kusakabe et al., 2006; Tong and Matsumura, 2006; Damle et al., 2008); ethanol (Yu et al., 2009; Papadias et al., 2010; Basile et al., 2008; Iulianelli et al., 2010; Tosti et al., 2010); methanol (Basile et al., 2005; Zhang et al., 2006); and liquid hydrocarbons (Chen et al., 2007a; Damle, 2009). Methanol reforming has the advantage of lower temperatures than other fuels. For instance, Zhang et al. (2006), performed experiments with a carbon membrane reactor, from 200 to 250oC, obtaining conversion as high as 99.87% at 250oC. REB Research sells methanol membrane reformers, ranging from 0.19 kg/day (US$13,500) to 9.6 kg/day (US$140,000) (REB Research, 2012). The ATR pathway has been investigated (Lin et al., 2008; Simakov and Shein- tuch, 2009; Chang et al., 2010). Besides providing heat for reforming reactions, Lin et al. (2008) added oxygen to avoid unwanted reactions and carbon formation during ethanol reforming. Chang et al. (2010) developed a Pd/Ag membrane reac- tor for autothermal reforming of methane. With a molar ratio of 0.4 O2/CH4, the reactions did not need external power. O2 was fed directly instead of air to avoid diluting the H2 with N2. Dry reforming conditions have also been investigated (Galuszka et al., 1998; Coronel et al., 2011). Coronel et al. (2011) successfully tested a dry reforming membrane reactor, using 50 µm commercial Pd/Ag membrane with Rh/ La2O3−SiO2 catalysts. However, Galuszka et al. (1998) had their membrane destroyed by the formation of carbon filament. Cheng et al. (2009) also experienced membrane fail- ure from carbon build-up, this time due to the partial oxidation of methane. A typical PBMR configuration is a tubular fixed bed, with a tubular membrane inserted in the middle. Barbieri et al. (2008) located the membrane tube about half way through the entrance of the reactor. Their goal was to avoid back permeation of hydrogen at the entrance of the reactor. They claimed that they were able to reduce the size of their reactor with this configuration. De Falco et al. (2011) alternated reforming packed bed reactors with Pd membrane modules. This configuration 17 allows the packed beds to operate at higher temperature and provides faster kinetics and more favorable thermodynamic equilibrium. However, the process became more complex and did not lead to process intensification. Membranes are generally not 100% selective to H2, with small amounts of CO in the permeate. Mori et al. (2008) proposed the addition of a CO methanator on the permeate side to reduce the CO content to less than 10 ppm. However, the CH4 content was high, from 83 to 1877 ppm (dry basis), which did not meet hydrogen purity requirement for hydrocarbons (see Table 1.2). Park et al. (2008), for the reforming of di-methyl-ether, added a water gas shift catalyst on the permeate side, leading to <20 ppm CO in the H2 product stream. Some authors have used different membrane separation strategies. Zou et al. (2007) separated CO2 instead of H2 in a water gas shift membrane reactor, filled with a Cu/ ZnO−Al2O3 catalyst. They obtained a H2 stream with a CO concentra- tion <10 ppm. Harale et al. (2010) produced a hybrid adsorbent membrane reactor by adding a CO2 adsorbent. This reactor operated as a PSA unit, providing both H2 and CO2 as pure streams. A composite membrane reactor, with catalyst directly deposited on the mem- brane, has been also proposed (Nomura et al., 2006; Tsuru et al., 2006, 2008). Tsuru et al. (2006) impregnated a Ni catalyst on a γ- α-Al2O3 tubular support, with one surface of the tube coated with microporous silica to create a catalytic membrane. 1.5.2 Fluidized Bed Membrane Reactor Advantages and challenges of Fluidized Bed Reactor (FBR) and Fluidized Bed Membrane Reactor (FBMR) have been summarized by Grace et al. (2005) and Deshmukh et al. (2007). FBR improves heat transfer and reduces pressure drops relative to Packed Bed Reactor (PBR). Catalyst particles are much smaller than fixed bed catalyst pellets, increasing effectiveness factors from as low as ∼0.01 to nearly 1. Fluidization also provides the possibility of replacing deactivated cat- alyst continuously or periodically, without shutting down the reactor. Attrition and entrainment of the catalyst are typical disadvantages associated with FBR. For FBMR, clever mechanical design and fluidization experience are needed to fit a 18 large number of membrane surfaces, and their associated piping, while avoiding excessive congestion. Catalyst particles can also form a film on the membrane, reducing the H2 flux (Rakib et al., 2011). The concept of FBMR for SMR was first proposed by Elnashaie and Adris (1989). Since then, several reactor concepts have been investigated experimentally (Adris et al., 1994; Boyd et al., 2005; Patil et al., 2007; Mahecha-Botero et al., 2011b; Rakib et al., 2011). Patil et al. (2007), using a tubular membrane consisting of a metal tube with 4-5 µm of Pd deposited on each side, obtained methane con- versions from 69% at 550oC to 97% at 650oC. 650oC is a challenging temperature for Pd membranes, which generally operate in the range of 500-575oC to preserve the membrane integrity. Mahecha-Botero et al. (2011b) investigated a reactor with six planar MRT membranes for steam reforming of natural gas. The permeate yield of hydrogen over the methane fed reached ∼2.3, considerably less than the max- imum molar ratio of 4 (excluding steam generation). However, hydrogen purity was high, exceeding 99.99% for all tests, with a relatively long cumulative experi- mentation time of 395 h. Rakib et al. (2011) built a FBMR for the steam reforming of methane, propane and heptane in the temperature range of 450 to 500oC. For SMR, the permeate molar yield of hydrogen over that of methane reached values as high as 3. Autothermal conditions have also been investigated (Mahecha-Botero et al., 2008; Chen et al., 2007b). In those cases, air was split between the entrance and the exit of the reactor. The combustion reaction at the top of the reactor can provide the heat of reaction by normal catalyst recirculation in the bubbling bed. To avoid hydrogen dilution by nitrogen, some have proposed simultaneous O2 and H2 selec- tive membranes (Chen et al., 2003; Rakib and Alhumaizi, 2005; Patil et al., 2007), but proof-of-concept is needed. Chen and Elnashaie (2004) proposed a circulating fluidized bed, operating at low Steam-to-Carbon (S/C) ratio, enabling extensive coking on the catalyst. The coke is then oxidized in a regenerator, providing the necessary heat for the reforming reactions. This configurations, inspired from the refinery catalyst crackers, also needs experimental proof. Mahecha-Botero et al. (2011a) investigated a FBMR assisted by CO2 sorption. The carbonation of CO2 is exothermic providing a portion of the heat needed for the reforming reactions, as well as enhancing the hydrogen flux through the mem- 19 branes because of higher H2 partial pressure on the retentate side. Work is needed to improve the stability of the CaO sorbent, and technical challenges have to be solved to achieve a continuous process including regeneration of the calcium ox- ide. 1.5.3 Multi-Channel Membrane Reactor (MCMR) The concept of Multi-Channel Membrane Reactor (MCMR) was first applied to dehydrogenation. Franz et al. (2000) demonstrated a micro-reactor with a Pd 0.2 µm thick membrane, fabricated using e-beam deposition over a silicon wafer. The concept of MCMR applied to SMR was proposed by Goto et al. (2003), but proof of concept has been quite limited. Karnik et al. (2003) proposed a micro-reactor with Pd membrane for water gas shift. They built a unit, but only tested the flux through their membrane, which was unable to support a pressure differential greater than 1 bar. Wilhite et al. (2006) built a micro reactor with a 0.2 µm thick Pd/Ag mem- brane, supported on perforated silicon wafers, for partial oxidation of methanol. The LaNi0.95Co0.05O3/ Al2O3 catalyst was coated directly onto the membrane sur- face. Overall methanol conversion remained low, ranging from 44 to 63%. Varady et al. (2007) proposed Pd membrane micro-reactors to produce hydrogen from steam reforming and partial oxidation of methanol. They developed an innova- tive valve-less feeding system that used an ultrasonic atomizer. No clear data on methanol conversion and hydrogen purity were reported. No published experimen- tal work has been found on the use of MCMR for SMR, and this thesis addresses this deficiency. 1.6 General Objectives and Strategy This thesis is aimed at coupling two promising technologies for the decentralized production of hydrogen (i.e. <500 kg/day) for fuel cell usage: multi-channel reac- tor and permselective membrane. Several steps are involved: • Steady-state, iso- and non iso-thermal two-dimensional reactor modeling of the MCMR; • Coating of commercial and lab-made catalysts on a metal substrate using modified sol techniques; 20 • Stability, activity testing, and kinetic parameter estimations of reforming and combustion catalysts produced by the coating technique; • Design, fabrication, commissioning, and model verification of a two-channel prototype of the MCMR, i.e. a single reforming channel, one combustion channel and a single-side planar Pd/Ag membrane. Figure 1.2 shows the general strategy employed to build a MCMR prototype. The strategy was not linear and required many iteration loops to achieve a suc- cessful prototype. For instance, lab-made catalysts were developed because some commercial catalysts tested deactivated in an unacceptable manner. The thesis con- cludes with a brief discussion of what has been accomplished and what should be the next steps to obtain a commercially viable technology. 21 II: Coating - Ref. and Comb. Catalyst Can thickness reach 80 µm? Is bonding strength acceptable? III: Stability & Activity Test in Micro Reactor Is catalyst stable and active? Concept Development MCMR with coated catalysts I: Model Development Is high conversion feasible? Is high production intensity feasible? yes Model verification no Model verification IV: Test in Multi-Channel Reactor Is catalyst stable and active? Is coating bonding holding? Concept Evaluation - Is long term stability feasible? - Is high energy efficiency possible? - Economic Analysis? yes yes no no Model verification noyes Figure 1.2: Thesis Strategy 22 Chapter 2 Steady State Model Development 2.1 Introduction To produce hydrogen via Steam Methane Reforming (SMR), Goto et al. (2003) proposed to combine a Pd membrane (0.2 µm thick) with a Multi-Channel Reactor (MCR). Heat was provided by the catalytic combustion of the reforming exhaust gas in a countercurrent configuration. In their 1-D model, to avoid back permeation of hydrogen, the membrane did not start directly at the beginning of the channel. Their model included several assumptions, it assumed plug flow even though the MCR usually operates in the laminar regime; their model was isothermal, which is very unlikely for a countercurrent configuration; and they operated at a temperature of 887◦C, which is much higher than the safe operating range of 500-650◦C for Pd-based membranes. Alfadhel and Kothare (2005) also developed a single micro- channel 1-D model coupled with a Pd membrane to produce hydrogen based on the Water Gas Shift (WGS) reaction. While the modeling of Multi-Channel Membrane Reactor (MCMR) for hydro- gen production is limited in the literature, there have been many attempts to model the MCR, as summarized below. Simulations have been reported with countercurrent configuration. Plate heat exchangers often operate in this mode to provide optimal heat transfer (Kolios et al., 2002). Frauhammer et al. (1999) proposed such a configuration in a 1-D model. Simulations predicted large hot spots (>1200oC) near the entrance of the 23 combustion channel. To limit the formation of hot spots, Kolios et al. (2002) pro- posed a folded plate reactor concept to distribute the combustion fuel along the reactor length. Zanfir and Gavriilidis (2004) compared co-current and countercur- rent configurations. They showed that countercurrent operation led to temperature variations, both in the transverse and axial directions (>300◦C in each case). On the other hand, co-current operation reduced temperature variations in both the transverse (<25oC) and axial directions (<125oC). Due to those large temperature variations, Kolios et al. (2004) suggested that countercurrent operation was prob- ably impractical “for coupling high-temperature steam reforming with in situ heat generation”. However, they suggested that pre-heating of the feed and cooling of the products could still be accomplished with countercurrent flows. Using first order exothermic and endothermic reactions, Zanfir and Gavriilidis (2002) performed 2-D simulations in a co-current configuration. They showed that the inlet temperature, activation energy and pre-exponential factor strongly af- fected the endothermic conversion. Based on the same concept, Zanfir and Gavri- ilidis (2003) simulated SMR and Methane Catalytic Combustion (MCC) reactions. Their results suggested an effectiveness factor of the coated reforming catalyst one order of magnitude higher than for conventional catalyst pellets. However, axial temperature variations remained large (>200oC). Baratti et al. (2003) mentioned that it would possible to minimize temperature gradients by adjusting the catalyst thickness along the reactor. Kolios et al. (2002) pointed out the importance of optimizing the heat fluxes be- tween the channels. Shigarov et al. (2009) made similar comments, suggesting that increasing catalyst activity (or loading) was not always the best solution. Strong combustion activity could lead to hot spot formation, whereas strong reforming activity could lead to the reformer extinction. Encouraged by the growing power of Computational Fluid Dynamics (CFD), 2- D and 3-D modeling of MCR has been reported. Yuan et al. (2007) simulated a 3-D reforming channel with a porous catalyst layer, receiving heat from a combustion channel, assumed to be at constant heat flux. Zhai et al. (2010) conducted a 2- D CFD simulation of SMR with MCR. Only three computational domains were solved and the catalytic reactions were taken as surface reactions. One interesting observation was that reducing channel height could improve conversion, but only 24 to a certain limit, below which there was no further benefit. Vaccaro et al. (2010) used the Comsol MultiphysicsTM platform to solve 2-D and 3-D models for one SMR channel coupled with one MCC channel. The two channels included catalyst and gas phase computational domains. The 3-D model results did not differ significantly from their 2-D model; co-current flow predicted higher conversion than countercurrent flow; and catalyst layer thicknesses >50 µm did not enhance reactor performance significantly. Karakaya and Avci (2011) used the same platform and also suggested that their 2-D model was an appropri- ate approximation of a 3-D model. They modeled hydrogen production by steam reforming of iso-octane, coupled with MCC in a MCR. They found that increasing the wall thickness, which improved the heat distribution along the reactor length, helped obtaining better hydrogen yield. Based on co-current and cross-flow configurations, Arzamendi et al. (2009) modeled 4 to 20 channels coupling SMR and MCC. The catalyst layer seemed to be taken as a catalytic surface reaction in the gas phase, ignoring the reduction of catalyst effectiveness due to diffusion into the catalyst layer. Computational time was nevertheless costly, with one simulation requiring from 24 to 72 h. CFD simulations can be particularly useful to study issues related to the inlet flow distribution in MCR. Laminar flow can lead to uneven feed distribution among the channels. A review by Rebrov et al. (2011) was written on the topic. At the early stage of our proof-of-concept development, our preoccupations were not the flow distribution or dynamic response of such system yet, but rather the feasibility of coupling Pd membranes with both SMR and MCC channels for realistic operating and design parameters. To drive the hydrogen through the mem- brane, the reforming channel must operate at higher pressure (e.g. 10-15 bar) than assumed in most of the simulations cited above. Temperature is also a challenge. All of these simulations operated above 800◦C to favour high methane thermody- namic conversion and faster kinetics. However, with Pd membranes, depending on the suppliers/makers, maximum operating temperature ranges from 575◦C (Mem- brane Reactor Technologies (MRT)) to 650◦C (Patil et al., 2007). To limit hot spots, we chose a co-current configuration. This work sought to find whether the temperature and pressure challenges can, at least in theory, be overcome, with a high level of methane conversion and hydrogen output. Furthermore, in order to 25 design an experimental reactor, estimates are needed of the key design parameters (such as catalyst layer thickness, reactor length, channel height), which can only come from a suitable model. This chapter adopts the steady-state, non-isothermal, 2-D, and co-current model developed by Zanfir and Gavriilidis (2003) as a starting point. The velocity profile is assumed to be that of fully developed laminar flow, and the average velocity is determined by solving the continuity equation. This assumption avoids having to solve momentum balance equations and saves computation time. Our model adds a perm-selective Pd/Ag membrane above the reforming gas channel. It also solves both temperature and concentration profiles in the catalyst layers. 2.2 Concept Description The concept of a single module of MCMR is illustrated in Figure 2.1. There are two channels, each including a gas phase and a catalyst layer. An impermeable separator wall separates the SMR channel and the MCC channel. The reforming heat of reaction is provided by the heat released by combustion. A Pd/Ag mem- brane (subscript m), located above the reforming channel, separates the hydrogen and shifts the reaction equilibrium. The flow is co-current to minimize temperature variations. The catalyst is coated for two purposes: first, to enhance the heat trans- fer, relying on conduction only through the separator wall; second, to minimize the pressure drops, facilitating hydrogen extraction by the membrane. The model was made flexible, so it could be either in mode “concept” or “pro- totype”. In the “concept” mode, only half of the combustion channel was solved, since the other half would belong to the next set of coupled combustion and re- forming channels. We opted for a two-point boundary ordinary differential equation solver “bvp4c" included in the MATLABTM software, coupled with a backward finite difference discretization method, to solve the model. 2.3 Main Assumptions of 2-D model Several assumptions were necessary to develop the model. The major ones were as follows: 26 H2O Pd/Ag Membrane Reforming Gas Channel (25 µm) (1 mm) (40µm) H2 Reforming Catalyst CH4 H2 z A B x Hr Thcat,r Thm CH4 Air Separator Wall Combustion Gas Channel L (300 mm) Combustion Catalyst (40 µm) (1 mm) (100 mm) x (full height combustion channel for prototype only) C D E z Thcat,c Hc Ths Figure 2.1: Schematic of 2-D Model, including base case dimensions, not to scale. (Subscripts: Pd/Ag membrane m; SMR channel r; catalyst layer cat; separator wall s; MCC channel c.) General • Ideal gas behaviour; • Pressure drop is negligible; • Fick’s law of diffusion applies; • Fourier’s law of heat conduction applies; • Viscous dissipation is negligible; • No change of phase for reactants and products: carbon formation is negligi- ble; • Heat transfer by radiation is neglected; • Potential and kinetic energy variations are neglected; • Spatial derivatives of physical properties are neglected; • No heat losses to the surroundings (adiabatic). 27 Gas channels • No homogeneous reaction; • Velocity in transverse x direction is neglected; • Velocity profile in the axial direction z is that of fully-developed laminar flow; • In the axial direction, molar flux by diffusion and heat transfer by conduction are neglected. Catalyst layers • No convection flux in both the transverse and axial directions; • Conduction in the axial direction is negligible; • Molar flux by diffusion in the axial direction is negligible. Separator wall • Conduction in the axial direction is negligible; • Thermal conductivity is constant. Several of those assumptions are verified in Chapter 3, Section 3.5.1. 2.4 Physical Properties 2.4.1 Diffusivity Since we assumed Fick’s law of diffusion, which is normally applied in dilute bi- nary mixtures, we needed to make further assumptions for the diffusion coefficients Di,mix in a gas mixture (subscripts: chemical component i; gas mixture mix). Two options were considered: Option A: Zanfir and Gavriilidis (2003) assumed in their model Di mix =Di j (2.1) 28 Water (steam) and air became component j for the reforming and combustion chan- nels respectively. Option B: From Sherwood et al. (1975) Di mix = 1− yi ∑ j, j 6=i (y j/Di j) (2.2) To evaluate the binary diffusion coefficient Di j, we used the Fuller et al., (1969) equation in (Poling et al., 2000): Di j = 0.00143T 1.75 PM1/2i j ( (Σv) 1/3 i +(Σv) 1/3 j )2 (2.3) where Mi j = 2(1/Mwi+1/Mw j) −1 (2.4) P is the total pressure, Σv is the summation of atomic diffusion volume (see Poling et al. (2000)) and Mwi is the molecular weight. In both catalyst layers, the effective diffusivity Di,eff was assumed as a summa- tion of resistances (Davis and Davis, 2003): Di,eff = ε τ ( 1 Di mix + 1 Di,K )−1 (2.5) With the tortuosity τ estimated (Reyes and Jensen, 1986), as a first approximation, as: τ = 1/ε (2.6) The Knudsen diffusivity Di,K is expressed (Bird et al., 2002) as: Di,K = 2Rpore 3 √ 8RgTcat piMwi (2.7) where Rpore is the average pore radius and Rg is the universal gas constant (8.314 29 J/mol K). 2.4.2 Heat Capacity The heat capacity relationship for a single component Cpi as a function of the temperature T , neglecting pressure effect, was determined (Sandler, 1999) as: Cpi = Ai+BiT +CiT 2+DiT 3 (2.8) 2.4.3 Thermal Conductivity For the thermal conductivity in the gas channels, we neglected the effect of pressure and used the following relation (Bird et al., 2002) for kmix of a gas mixture: kmix =∑ i yiki ∑ j y jΦi j (2.9) where the coefficient Φi j is: Φi j = 1√ 8 ( 1+ Mwi Mw j )−1/2( 1+ ( µi µ j )1/2(Mw j Mwi )1/4)2 (2.10) We obtained data to evaluate gas component thermal conductivity ki at a reference temperature of 600 K in Lide (2004). To evaluate ki’s at the simulation tempera- tures, we used the following empirical equation, based on the relation utilized by Zanfir and Gavriilidis (2003): ki = k re f i ( T T re f )α (2.11) Values of kre fi and α are provided in Table 2.1. For the separator wall, we assumed the same constant value as Zanfir and Gavriilidis (2003): ks = 25 [W/(m K)] (2.12) The catalyst layer is a heterogeneous phase, containing gas and solid phases. 30 kcat depends on both phases present, and therefore on the density ρcat of the catalyst coating. For our first set of simulations, we assumed ρcat ≥ 2000 kg/m3, similar to the values used by Zanfir and Gavriilidis (2003). However, measurements with our own catalyst coating later showed much lower densities (∼400 kg/m3). To find the thermal conductivity, Carberry et al. (1987) expressed a relation between void in porous media and the ratio between gas density and skeleton solid density. For our prototype conditions, we evaluated kcat as about twice kmix. Hence kcat was estimated as: kcat = 0.4 [W/(mK)] if ρcat ≥ 2000 kg/m3 (2.13) or kcat = 2kmix if ρcat ≈ 400 kg/m3 (2.14) 2.4.4 Viscosity Although the momentum equations are not solved in this model, the viscosity, µ of the gas mixture was needed to calculate the coefficient Φi j in (2.10) and dimen- sionless numbers such as the Reynolds number. The viscosity of the mixture was estimated (Bird et al., 2002) from: µmix =∑ i yiµi ∑ j y jΦi j (2.15) We used the same method described earlier for ki to determine component vis- cosity µi at the simulation temperature: µi = µre fi ( T T re f )β (2.16) Values of µre fi and β are listed in Table 2.1. 31 Table 2.1: Empirical values to determine k and µ in Eqns. (2.11) and (2.16). T re f is taken as 600 K. H2 CH4 H2O CO CO2 O2 N2 α 0.7273 1.2878 1.5199 0.8414 1.1877 0.8759 0.7609 k600K ∗ 10−2 (W/(m K)) 30.9 8.41 4.71 4.57 4.16 4.81 4.40 β 1.451 1.381 0.857 1.515 1.183 1.395 1.449 µ600K ∗ 10−5 (Pa s) 1.44 1.94 2.14 2.91 2.80 3.51 2.96 2.5 Concentration and Partial Pressure Based on the assumption of ideal gases, we write: c = P/RgT (2.17) Pi = yiP (2.18) where c is the concentration, Pi the partial pressure of component i, and yi the component molar fraction. 2.6 Velocity Profiles Assuming fully developed laminar flow in the gas channel, the velocity profile in the axial direction vz is assumed to follow the two-dimensional relation (Bird et al., 2002): vz = 3 2 vave,z ( 1− ( x Hk )2) (2.19) Here Hk is half the height of either the reforming or combustion gas channel, rep- resented by subscript k. To determine the average (ave) velocity vave,z in the axial direction, fluxes coming into and out of the box indicated by dashed lines in Figure 32 Table 2.2: Sievert’s Law Parameters Am Em mol/(s m bar0.5) J/mol Chen et al. (2003) 2.00278e-4 15700 MRT’s Pd 25wt%-Ag data 3.427e-5 9180 2.2 were integrated: ∫ Hk or 0 −Hk cvzdx|z=0− ∫ Hk or 0 −Hk cvzdx|z+ ∫ z 0 ∫ Thcat,k 0 ∑ i Ridxdz+ ∫ z 0 JH2,mdz= 0 (2.20) Here Thcat,k is the catalyst layer thickness. Ri is the rate of production of component i, defined as: Ri =∑ j σi jr j (2.21) The rate of reaction r j is defined in section 2.7 below. σi j is the stoichiometric co- efficient of component i for reaction j. JH2,m is the molar flux of hydrogen through the membrane, defined based on Sievert’s law: JH2,m =−ηm Am Thm exp (−Em RgTm )(√ PH2,r− √ PH2,m ) (2.22) Here Thm is the membrane thickness, and ηm, the membrane effectiveness, is a cor- rection factor, the ratio between the real flux and the flux predicted by Sievert’s law. This value is normally obtained experimentally (see Chapter 8). We used ηm = 0.5 in our base case simulations (see Chapter 3). Different values of pre-exponential factor Am and activation energy Em for Pd-based membranes have appeared in the literature. This could be due to the variety of metals alloyed with Pd and different modes of fabrication and support. We used two sets of values in our simulations (see Table 2.2). The first set was employed by Chen et al. (2003), while the second set was provided by the supplier of the membranes used in our prototype reactor. Equations (2.19), (2.21), and (2.22) into (2.20) were employed to solve for vave,z. 33 Pd/Ag Membrane Reforming Gas Channel Reforming Catalyst cvz x z cvz JH2 ∑Ri L a Σ(civxHi + ∆civxHi ) ∆z ∆x ΣcivzHi ΣJi,zHi qz b Σ(civzHi + ∆civzHi ) Σ(Ji,zHi + ∆Ji,zHi ) qz + ∆qz ΣcivxHi ΣJi,xHi qx Σ(Ji,xHi + ∆Ji,xHi ) qx + ∆qx Figure 2.2: Schematics to Evaluate Average Velocity and to Develop Energy Balance: A. Integration box to evaluate average velocity; B. Energy balance over a rectangular cross-section ∆z∆x. 2.7 Kinetics 2.7.1 Reforming The reactions of interest in the reforming channel are: 1. CH4+H2O⇔ 3H2+CO ∆H298Krx,1 = 206 [kJ/mol] (2.23) 2. CO+H2O⇔ H2+CO2 ∆H298Krx,2 =−41 [kJ/mol] (2.24) 3. CH4+2H2O⇔ 4H2+CO2 ∆H298Krx,3 = 164 [kJ/mol] (2.25) 34 where ∆H298Krx,j is the enthalpy of reaction j at 298 K and 1 bar. Two different reforming catalysts were used in this project based on Ni and Ru. Those two catalysts have different mechanisms, requiring different kinetic expressions. Nickel-Based Catalyst Kinetics For a Ni-based catalyst, a study by Elnashaie et al. (1990) showed that the general rate equation based on Langmuir-Hinshelwood-Hougen-Watson approach, devel- oped by Xu and Froment (1989) describes most accurately the kinetics for a wide range of conditions. The reforming catalyst used was Ni 15.2 wt%/ MgAl2O4. The rate equations per mass, r ′ j, for the three reactions are: r ′ 1 = k1 P2.5H2 ( PCH4PH2O− P3H2 PCO Ke,1 ) Den2 [ kmol kgcat h ] (2.26) r ′ 2 = k2 PH2 ( PCOPH2O− PH2 PCO2 Ke,2 ) Den2 [ kmol kgcat h ] (2.27) r ′ 3 = k3 P3.5H2 ( PCH4P 2 H2O − P 4 H2 PCO2 Ke,3 ) Den2 [ kmol kgcat h ] (2.28) where Den= 1+KCOPCO+KH2PH2 +KCH4PCH4 +KH2OPH2O/PH2 (2.29) Ke,1 = exp (−26830 T +30.114 ) [ bar2 ] (2.30) Ke,2 = exp ( 4400 T −4.036 ) [ − ] (2.31) Ke,3 = exp (−22430 T +26.078 ) [ bar2 ] (2.32) The sorption equilibrium constant Ki and kinetic rate coefficient k j are ex- 35 Table 2.3: Constants in Xu and Froment (1989) Kinetics A j Units E j (kJ/mol) k1 4.22e15 bar0.5 kmol / kgcat h 240.1 k2 1.955e6 kmol / kgcat h bar 67.13 k3 1.020e15 bar0.5kmol /kgcat h 243.9 Ai Units ∆Hsorp,i (kJ/mol) KCO 8.23e-5 bar−1 -70.95 KCH4 6.65e-4 bar −1 -38.28 KH2O 1.77e5 - 88.68 KH2 6.12e-9 bar −1 -82.9 pressed as: Ki = Ai exp (−∆Hsorp,i ∗1000 RgT ) (2.33) k j = A j exp (−E j ∗1000 RgT ) (2.34) To obtain the rates of reaction per reactor volume, r j, we need to perform the transformation: r j = r ′ j ρcat k 1000 3600 [ mol m3cat s ] (2.35) Values of Ai, A j, ∆Hsorp, and E j are provided in Table 2.3. The pre-exponential factors A j are dependent on the loading, dispersion and stability of the catalyst. They should ideally be measured experimentally. However, as shown in Chapter 6, Ni-based catalyst was not used in our prototype, but only for the first computer simulations. Therefore, we kept the same A j’s as reported by Xu and Froment (1989). Ruthenium-Based Catalyst Jakobsen et al. (2010) proposed a kinetic model for a Ru 1%/ ZrO2 catalyst. Their model is based on methane dissociative adsorption as the rate-limiting step, with 36 Table 2.4: Constants in Jakobsen et al. (2010) Kinetics A j Units E j (kJ/mol) k1 4.39e7 kmol/(kgcat h bar) 108 k2 400 kmol/(kgcat h bar) 0 Ai Units ∆Hsorp,i (kJ/mol) KCO 2.19e-5 1/bar 87 KH2 7.31e-6 1/bar 0.5 71 CO and H2 competing for active sites. These authors studied conditions with tem- peratures ranging from 425 to 575◦C at 1.3 bar. r ′ 1 = k1PCH4 (1−β1)( 1+KCOPCO+KH2P 1/2 H2 )2 [ kmolkgcat h ] (2.36) where β1 = PCOP3H2 PCH4PH2O 1 Ke,1 (2.37) Jakobsen et al. (2010) did not provide a specific expression for the water gas shift reaction, instead assuming that this reaction was fast enough to reach equilib- rium at all conditions. Therefore, r ′ 2 = f (r ′ 1). We tested these assumptions in our model by assuming a large value for the rate coefficient k2 of the water gas shift reaction (see Table 2.4). r ′ 2 = k2PCO (1−β2)( 1+KCOPCO+KH2P 1/2 H2 )2 [ kmolkgcat h ] (2.38) where β2 = PCO2PH2 PCOPH2O 1 Ke,2 (2.39) Wei and Iglesia (2004) studied the forward methane steam reforming reaction using 1.6% and 3.2% Ru on γ-Al2O3 and ZrO2 supports. They performed their rate measurements between 550 and 750oC, with pressure ranging from 1 to 5 bar. 37 Table 2.5: Constants in Wei and Iglesia (2004) Kinetics A j (kmol/(kgcat h bar)) E j (kJ/mol) k1 1.22e7 91 k2 400 0 They proposed a simple rate expression: r ′ 1 = k1PCH4 (1−β1) [ kmol kgcat h ] (2.40) Wei and Iglesia concluded that C-H bond activation was the rate-limiting step, unaffected by the identity or concentration of other co-reactants or products. They did not find any dependence of the reaction rate on H2O, and they did not study the WGS reaction. For this reason, we used the same technique as for the Jakobsen kinetics, to assure that the WGS reaction approaches very closely the chemical equilibrium, assuming a large value for the rate coefficient k2 (see Table 2.5): r ′ 2 = k2PCO (1−β2) [ kmol kgcat h ] (2.41) Wei and Iglesia (2004) reported the pre-exponential factor A1 for a 3.2% Ru/ γ- Al2O3 catalyst at 600 ◦C, 0.25 bar CH4, 0.25 bar H2O, and 44.2% metal dispersion. We adjusted the units to fit our model (as shown in Table 2.5). Berman et al. (2005) also proposed a kinetic models for a 2% Ru/ (α-Al2O3+ 4.8% MnOx) catalyst. Temperatures ranged from 500 to 900oC and pressures from 1 to 7 bar. They found a negative order with respect to steam, contrary to the two previous models (Wei and Iglesia, 2004; Jakobsen et al., 2010). Their results sug- gested that surface hydroxyl group oxidation and carbon surface oxidation could be the rate-limiting steps. Berman et al. did not consider reaction equilibria in their equations, so we slightly modified their model for our needs. They also observed that practically all of the CO was converted to CO2, indicating a very fast water 38 gas-shift reaction. r ′ 3 = k3PCH4 (1−β3)( bCH4PCH4 +bH2OP 1/2 H2O ) [ kmol kgcat h ] (2.42) r ′ 2 = k2PCO (1−β2)( bCH4PCH4 +bH2OP 1/2 H2O ) [ kmol kgcat h ] (2.43) where β3 = PCO2P 4 H2 PCH4PH2O 1 Ke,3 (2.44) bCH4 = 4.42∗10−6 exp(5694.2/T ) (2.45) bH2O = 8.366∗10−6 exp(4531.7/T ) (2.46) k3 = 2.68 [kmol/(kgcat h bar)] (2.47) k2 = 400 [kmol/(kgcat h bar)] (2.48) 2.7.2 Combustion For the combustion catalyst, we assume that only full oxidation of methane is oc- curring. This assumption is usually valid with a stoichiometric excess of air. How- ever, as reported in Chapter 7, small amounts of CO were detected experimentally. Nevertheless, for simplicity, we ignored CO formation in our model. Methane Combustion: CH4+2O2⇒ CO2+2H2O ∆H298Krx,4 =−803 [kJ/mol] (2.49) Pd is often considered to be the most efficient catalyst for catalytic combustion of methane (Lee and Trimm, 1995). Pd was chosen throughout this project, with 39 an empirical kinetic model to describe the reaction: r4 = k4PαCH4P β O2 [ mol m3cat s ] (2.50) where k4 = A4 exp (−E4 ∗1000 RgT ) (ρcat c ∗1000) [ mol m3cat s barα+β ] (2.51) Lee and Trimm (1995) reviewed studies of methane catalytic combustion with Pd, Pt and Rh. The reaction order α for methane ranged from 0.45 to 1.2. β varied more, from -0.5 to 1.0. Activation energies E4 also varied widely from 52 to 199 kJ/mol. We performed simulations with different sets of values, as summarized in Ta- ble 2.6. For the simulations in Chapter 3, we assumed values adopted by Zanfir and Gavriilidis (2003) for the kinetic combustion parameters ( α = 1, E4 = 90 kJ/- mol, A4 is adapted for our work in order to respect the units chosen in Eq. (2.51)). With excess air, Zanfir and Gavriilidis (2003) assumed that the kinetics of methane combustion are independent of oxygen concentration. However, with β = 0, we found in preliminary work that it was difficult for simulations to converge for ex- cess O2 <25% and with thick catalyst layers >100µm. In those cases, simulations generated negative O2 concentrations, with O2 being a larger molecule than CH4, not diffusing as quickly as needed in the catalyst pores. Therefore, we assumed β = 1. We later estimated the kinetic parameters, as reported in Chapter 7, in order to compare model predictions with MCMR experimental results of Chapter 8. To stay below the lower flamability limit of methane, we employed large excess of air >200%, and we neglected the effect of oxygen. Therefore, we assumed β = 0. 2.8 Component Material Balance Equations The general equation of continuity at steady state for a component i in a mixture (adapted from Bird et al. (2002)) is: −(∇• ci~v)− ( ∇• ~Ji ) +Ri = 0 (2.52) 40 Table 2.6: Combustion Kinetic Parameters A4 (kmol/(kgcat s barα+β )) α β E4 (kJ/mol) Reference 5539 1 1 90 Modification of Zanfir and Gavriilidis (2003) 1635 0.78 0 88 This work on Pd 1%/ γ-Al2O3 (Alfa) (See Chapter 7) 4710 0.78 0 88 This work on Pd 5%/ γ-Al2O3 (Alfa or Lab-made) (See Chap- ter 7) This equation contains three terms: a convection flux vector c~vi, a diffusion flux vector ~Ji, and the rate of production Ri. Assuming Fick’s law of diffusion for ~Ji, we obtain: ~Ji =−Di mix∇ci (2.53) Inserting (2.53) and expanding gradient terms while neglecting velocity component in the transverse direction, and neglecting diffusion in the axial direction, Eq. (2.52) becomes: − ( vz ∂ci ∂ z + ci ∂vz ∂ z ) + ( Di mix ( ∂ 2ci ∂x2 ) + ∂Di mix ∂x ∂ci ∂x ) +Ri = 0 (2.54) To use MATLABTM built-in functions, it was necessary to reduce the order of the differential equations to one for both concentration and temperature. To over- come this limitation, we used first order transformations in the transverse direction: ci = c1i (2.55) ∂c1i ∂x = c2i (2.56) T = T1 (2.57) ∂T1 ∂x = T2 (2.58) From this point in our model development, ci is now referred as c1i, and T be- 41 comes T1. We introduced two new variables in equations (2.56) and (2.58): c2i corresponding to concentration gradient of component i; and T2 is the temperature gradient. We use backward difference discretization in the axial direction for any depen- dent parameter u: ∂ub ∂ z = 1 ∆zb−1 (ub−ub−1) (2.59) Subscript b represents the discretization grid position in the axial direction (see Figure 2.3). With discretization in the axial direction and first order transformation, Eq. (2.54) becomes: − ( vz,b 1 ∆zb−1 (c1i,b− c1i,b−1)+ c1i,b 1∆zb−1 (vz,b− vz,b−1) ) + ( Di mix,b dc2i dx + dDi mix,b dx c2i ) +Ri,b = 0 (2.60) Solving for dc2i,b/dx, Eq. (2.60) becomes: dc2i,b dx = 1 Di mix,b {( vz,b 1 ∆zb−1 (c1i,b− c1i,b−1)+ c1i,b 1∆zb−1 (vz,b− vz,b−1) ) − dDi mix,b dx c2i,b−Ri,b } (2.61) 2.8.1 Gas Phase Using equations (2.56) and (2.61),while ignoring the derivative of Di mix,b and as- suming no reaction in the gas phase, we obtain: dc1i,b dx = c2i,b (2.62) dc2i,b dx = 1 Di mix,b ( vz,b 1 ∆zb−1 (c1i,b− c1i,b−1)+ c1i,b 1∆zb−1 (vz,b− vz,b−1) ) (2.63) ∀i,b 6= 1 42 ∆z1 . . .∆z2=∆z1* (1+% Incr.) ∆zb=min(∆zb-1* (1+% Incr.); and ∆zmax) ∆znbz. . . x z u1 u2 u3 ub unbz unbz+1 ub = dependent variables: e.g. c1,b c2,b T1,b T2,b vz,b ub+1 Figure 2.3: Schematic of Discretization Boundary Conditions Gas channel - inlet conditions (z = 0 and b = 1) At the entrance of the reactor, the concentrations c1i are assumed to be constants at the feed conditions: c1i,b=1 = c1i,o (2.64) c2i,b=1 = 0 (2.65) where subscript o denotes feed conditions. Gas channel - catalyst interface (x=−Hk) Performing a material balance across the interface, using Fick’s law, and assuming that there are no velocities on either side of the interface, hence only diffusion fluxes, we obtain: Ji,x|x=−Hk = Ji,x|x=Thcat,k (2.66) −Di mix ∂ci∂x |x=−Hk =−Di,eff ∂ci ∂x |x=Thcat,k (2.67) 43 Using first order transformation and solving for c2i,k,b, we obtain: c2i,k,b|x=−Hk = Di,eff,bc2i,cat k,b|x=Thcat,k Di mix,k,b|x=−Hk (2.68) ∀i,b 6= 1 Reforming gas channel - membrane interface (x = Hr) ∀i, except for H2, there is no flux, hence no gradient: c2i,r,b|x=Hr = 0 ∀i,b (2.69) For H2 only, performing a material balance across the membrane interface, using Fick’s law, discretization, first order transformation, and assuming there are no velocities on either side of the interface, we obtain: JH2,x|x=Hr =JH2,x|m (2.70) −DH2 mix,b c2H2,r,b|x=H =JH2,x|m (2.71) Solving for c2H2,r,b, and inserting Sievert’s law (Eq. (2.22), we obtain: c2H2,r,b|x=H = 1 DH2 mix,b ηm Am Thm exp ( −Em RgTm,b )(√ c1H2,r,bRgT1r,b− √ PH2,m ) |x=Hr (2.72) Combustion gas channel - concept mode: half-channel (x= 0) We assume sym- metry and hence no gradient in the transverse direction: c2i,c,b|x=0 = 0 ∀i,b (2.73) 44 Combustion gas channel - prototype mode: flange side (x = Hc) Since there is no flux, and hence no gradient, we obtain a similar boundary condition: c2i,c,b|x=Hc = 0 ∀i,b (2.74) 2.8.2 Catalyst Layer Using equations (2.56) and (2.61), while ignoring the derivative of Di mix,b, assum- ing no axial and transverse velocity occurring in the catalyst layer, and neglecting diffusion in the axial direction, we obtain this simple system of equations: dc1i,cat k,b dx = c2i,cat k,b (2.75) dc2i,cat k,b dx = 1 Di eff,b (−Ri,b) (2.76) ∀i, b 6= 1 Boundary Conditions Catalyst layer - inlet conditions (z = 0 and b = 1) At the entrance of the reactor, we assume no gradient in the catalyst layer in the axial direction, therefore: c1i,cat k,b=1 = c1i,cat k,b=2 (2.77) Catalyst - gas channel interface (x = Thcat,k) By continuity: c1i,k,b|x=−Hk = c1i,cat k|x=Thcat,k b 6= 1 (2.78) Catalyst - separator wall separator interface (x = 0) There is no flux: c2i,cat k,b|x=0 = 0 b 6= 1 (2.79) 45 2.9 Energy Balances The energy strategy for the one-dimensional problem used by Elnashaie and Garhyan (2003) was adapted for our 2-D simulation. Neglecting pressure drop, kinetic en- ergy, viscous dissipation, and radiation heat transfer, an energy balance was per- formed on a small element ∆x∆z at steady state (see Figure 2.2 B): ∑ i civzHi∆x+∑ i Ji,zHi∆x+qz∆x+∑ i civxHi∆z+∑ i Ji,xHi∆z+qx∆z = ∑ i (civzHi+∆(civzHi))∆x+∑ i (Ji,zHi+∆(Ji,zHi))∆x+(qz+∆qz)∆x+ ∑ i (civxHi+∆(civxHi))∆z+∑ i (Ji,xHi+∆(Ji,xHi))∆z+(qx+∆qx)∆z (2.80) Simplifying and dividing by ∆x∆z leads to: ∑ i ∆(civzHi) ∆z + ∑ i ∆(Ji,zHi) ∆z + ∑ i ∆(civxHi) ∆x + ∑ i ∆(Ji,xHi) ∆x + ∆qx ∆z + ∆qz ∆x = 0 (2.81) Taking the limits when ∆x,∆z→ 0, we obtain: ∑ i ∂ (civzHi) ∂ z +∑ i ∂ (Ji,xHi) ∂ z +∑ i ∂ (civxHi) ∂x +∑ i ∂ (Ji,zHi) ∂x + ∂qx ∂ z + ∂qz ∂x = 0 (2.82) Expanding terms and rearranging leads to: ∑ i ( civz ∂Hi ∂ z +Hi ∂civz ∂ z + Ji,x ∂Hi ∂ z +Hi ∂Ji,x ∂ z + civx ∂Hi ∂x +Hi ∂civx ∂x + Ji,z ∂Hi ∂x +Hi ∂Ji,z ∂x ) + ∂qx ∂ z + ∂qz ∂x = 0 (2.83) From the component material balance Eq. (2.52): (∇• ci~v) =− ( ∇• ~Ji ) +Ri (2.84) 46 Expanding the two gradients and multiplying both sides of Eq. (2.84) by Hi gives: Hi ∂civz ∂ z +Hi ∂civx ∂x =−Hi ∂Ji,x∂ z −Hi ∂Ji,z ∂x +HiRi (2.85) Inserting Eq. (2.85) into (2.83) and simplifying leads to: ∑ i ( civz ∂Hi ∂ z + Ji,x ∂Hi ∂ z + civx ∂Hi ∂x + Ji,z ∂Hi ∂x +HiRi ) + ∂qx ∂ z + ∂qz ∂x = 0 (2.86) For an ideal gas with no phase change: ∂Hi ∂ z = ∂Hi ∂T ∂T ∂ z =Cpi ∂T ∂ z (2.87) ∂Hi ∂x = ∂Hi ∂T ∂T ∂x =Cpi ∂T ∂x (2.88) Inserting Equations (2.21), (2.87) and (2.88) into (2.86) leads to: ∑ i ( Cpi (civz+ Ji,z) ∂T ∂ z +Cpi (civx+ Ji,x) ∂T ∂x ) +∑ i ∑ j Hiσi jr j + ∂qx ∂ z + ∂qz ∂x = 0 (2.89) By definition: ∑ i Hiσi j = ∆Hrx, j (2.90) where: ∆Hrx, j = ∆Hre frx, j + ∫ T Tre f ∆Cp j∂T (2.91) ∆Cp j =∑ i σi jCpi (2.92) Inserting Eq. (2.90) into Eq. (2.89) gives: ∑ i ( Cpi (civz+ Ji,z) ∂T ∂ z +Cpi (civx+ Ji,x) ∂T ∂ z ) +∑ j ∆Hrx, jr j+ ∂qx ∂x + ∂qz ∂x = 0 (2.93) 47 In a more general form, Eq. (2.93) becomes: ∇T •∑ i (Cpici~v)+∇T •∑ i ( Cpi~Ji ) +∇•~q+∑ j ∆Hrx, jr j = 0 (2.94) There are four heat transfer/generation terms in Eq. (2.94), representing in or- der: (1) transfer by convection, (2) transfer by diffusion, (3) transfer by conduction, and (4) heat generation due to reactions. Assuming Fourier’s law of conduction, we write~q as: ~q =−kmix∇T (2.95) Expanding the gradient terms, inserting Fick’s law, Eq. (2.53) and Fourier’s law, Eq. (2.95), and with the same assumptions as for the material balance, i.e. neglecting the velocity component in the transverse direction, and neglecting dif- fusion in the axial direction, we obtain: ∂T ∂ z ∑i (Cpicivz)− ∂T∂x ∑i ( CpiDi mix ∂ci ∂x ) + ( − ∂ ∂x ( kmix ∂T ∂x ) − ∂ ∂ z ( kmix ∂T ∂ z )) +∑ j ∆Hrx, jr j = 0 (2.96) With backward difference discretization in the axial direction and first order trans- formation, Eq. (2.96) becomes: 1 ∆zb−1 (T1,b−T1,b−1)∑ i (Cpi,bc1i,bvz,b)−T2,b∑ i (Cpi,bDi mix,bc2i,b) − ( dkmix,b dx T2,b+ kmix,b dT2,b dx + dkmix,b dz 1 ∆zb−1 (T1,b−T1,b−1)+ kmix,b 1∆z2b−1 (T1,b−2T1,b−1+T1,b−2) ) +∑ j ∆Hrx, jr j = 0 (2.97) 48 If Eq. (2.97) is recast to solve for dT2,b/dx, then: dT2,b dx = 1 kmix,b { 1 ∆zb−1 (T1,b−T1,b−1)∑ i (Cpi,bc1i,bvz,b)−T2,b∑ i (Cpi,bDi mix,bc2i,b) − dkmix,b dx T2,b− dkmix,bdz 1 ∆zb−1 (T1,b−T1,b−1)− kmix,b 1∆z2b−1 (T1,b−2T1,b−1+T1,b−2) +∑ j ∆Hrx, jr j } (2.98) 2.9.1 Gas Phase Using equations (2.58) and (2.98), while ignoring the derivative of kmix,b, ignoring the heat transfer by conduction in the axial direction, and assuming no reaction in the gas phase, we obtain: dT1,b dx = T2,b (2.99) dT2,b dx = 1 kmix,b { 1 ∆zb−1 (T1,b−T1,b−1)∑ i (Cpi,bc1i,bvz,b)−T2,b∑ i (Cpi,bDi mix,bc2i,b) } (2.100) ∀i, b 6= 1 Boundary Conditions Gas channel - inlet conditions (z = 0 and b = 1) At the entrance of the reactor, the temperature T1 is assumed constant at the feed condition: T1,b=1 = T1,o (2.101) T2,b=1 = 0 (2.102) Gas channel - catalyst interface (x=−Hk) Performing an energy balance across the interface, using Fick’s and Fourier’s laws, and assuming velocity = 0 on either 49 side of the interface, we obtain:( ∑ i Ji,x,kHi,k− kmix,kT2,k )∣∣∣∣ x=−Hk = ( ∑ i Ji,x,cat kHi,cat k− kcat kT2,cat k )∣∣∣∣ x=Thcat,k (2.103) To respect continuity, the temperatures and diffusion fluxes at this boundary must be equal, and only the temperature gradients change. Since Hi is only a function of T for an ideal gas, we can write: ∑ i Ji,x,kHi,k ∣∣∣∣ x=−Hk =∑ i Ji,x,cat kHi,cat k ∣∣∣∣ x=Thcat,k (2.104) Inserting (2.104) in (2.103), using discretization and solving for T2,k,b, we obtain: T2,k,b|x=−Hk = kcat k,bT2,cat k kmix,b b 6= 1 (2.105) Gas channel - membrane interface (x = Hk) If heat losses are known: ( JH2,x,rHH2,r− kmix,rT2,r )∣∣∣∣ x=Hr = ( JH2,mHH2,m−Qloss )∣∣∣∣ m (2.106) Simplifying and solving for T2,r gives: T2,r,b ∣∣∣∣ x=Hr = Qloss kmix,r|x=Hr b 6= 1 (2.107) If heat losses are negligible, then: T2,r,b ∣∣∣∣ x=Hr = 0 b 6= 1 (2.108) 50 Gas channel - half-channel (x = 0) We assumed symmetry at the boundary, so that: T2,k,b|x=0 = 0 b 6= 1 (2.109) 2.9.2 Catalyst Layer Using equations (2.58) and (2.98), while ignoring the derivative of kmix,b, and as- suming no axial or transverse velocity in the catalyst layer, we obtain: dT1,cat k,b dx =T2,cat k,b (2.110) dT2,cat k,b dx = 1 kcat k,b { −T2,cat k,b∑ i (Cpi,cat k,bDi eff,bc2i,cat k,b) +∑ j ∆Hrx, j,b r j,b } (2.111) b 6= 1 Boundary Conditions Catalyst layer - inlet conditions (z = 0 and b = 1) At the entrance of the reactor, we assume no gradient in the catalyst layer in the axial direction, so that: T1,cat k,b=1 = T1,k,b=2 (2.112) Catalyst - gas channel interface (x = Thcat,k) There is no discontinuity of tem- perature at the interface, hence: T1,cat k|x=Thcat,k = T1,k,b|x=−Hk b 6= 1 (2.113) Catalyst - separator wall interface (x = 0) There is a flux of energy by con- duction. Using the the same development as for with the Gas channel - catalyst 51 interface above, we obtain: T2,cat k,b|x=0 = δk ksT2,s,bkcat k,b b 6= 1 (2.114) δr =−1 (2.115) δc =+1 (2.116) Because of the change in axis orientation (see Figure 2.1), we added the coefficient δk. 2.9.3 Separator Wall Only conduction is occurring in this solid phase. With (2.58) and (2.98), and ne- glecting derivative of ks, we obtain: dT1,s,b dx = T2,s,b (2.117) dT2,s,b dx = 1 ∆z2b−1 (−T1,s,b+2T1,s,b−1−T1,s,b−2) (2.118) b 6= 1 Neglecting heat conduction in the axial direction, (2.118) become: dT2,s,b dx = 0 (2.119) Boundary Conditions Separator wall - inlet conditions (z= 0 and b= 1) At the entrance of the reactor, we assume no gradient in the separator wall in the axial direction, therefore: T1,s,b=1 = T1,s,b=2 (2.120) 52 Reforming catalyst interface (x = 0) There is no discontinuity at the interface: T1,s,b|x=0 = T1,cat r,b|x=0 b 6= 1 (2.121) Combustion catalyst interface(x = Ths) Ths is the thickness of the separator wall, and again, there is no discontinuity at the interface: T1,s,b|x=Ths = T1,cat c,b|x=0 b 6= 1 (2.122) 2.10 Conclusions This chapter develops the energy balance, mass balance, kinetics and physical property equations necessary to solve a 2-D MCMR model for the gas channels, the heterogeneous catalyst layers and the impermeable separator wall. Fully de- veloped laminar flow was assumed to avoid having to solve momentum balance equations and saves computation time. The resulting set of equations, after dis- cretization, can be solved readily using standard software. In the next chapter, we explore the results for a base case, verify the consistency of the model and several assumptions, perform an isothermal parametric sensitivity study, and explore ways to improve heat transfer between the combustion and reforming channels. 53 Chapter 3 Steady State 2-D Model Simulations Results 3.1 Introduction This chapter presents the first set of simulations performed before building the prototype. Many of the base case parameters are taken or adapted from the MCR simulation of Zanfir and Gavriilidis (2003), the major difference being the reform- ing channel, where the pressure is higher to create the necessary driving force for hydrogen to cross the membrane. We first define key indicators to evaluate the reac- tor performance and verify model consistency and some of the assumptions. Base case isothermal and non-isothermal simulation results are presented. Isothermal simulation can be seen as a special case of the non-isothermal simulation, where all the heat generated and the heat consumed are perfectly balanced. Base case simulations had three objectives: (1) to verify the energy and mass consistency of the model; (2) to verify some assumptions underlying the model; and (3) to obtain first insights into the performance of the MCMR concept. Isothermal simulations were quick to perform, taking about 20 min with an Intel ZeonTM processor. We take advantage of this by performing a 15-parameters sensitivity analysis, including operating, design, catalyst and physical property pa- rameters. Isothermal simulations decoupled the combustion and reforming chan- nels, allowing better understanding how each parameter can improve conversion in 54 each channel. In the last section of this chapter, devoted to non-isothermal simulations, we consider options to improve the reactor performance, without creating hot spots. Among the parameter adjustments, we use the technique mentioned by Baratti et al. (2003), of varying the catalyst thickness and kinetic pre-exponential factor along the reactor length. Note that at this stage of the research, we did not try to optimize the reactor, but rather to understand options which could improve performance, and provide of basis for comparison with experimental results in Chapter 8 . Many catalyst parameters, for instance (density, kinetics) need to be measured before one could attempt a practical optimization. 3.2 Model Equations and Base Case Parameters The 2-D model equations are described in Chapter 2, where modeling options and parameters are identified. In this chapter, we adopt the “concept mode” option (only half-height of the combustion channel, see Fig. 2.1) and the adiabatic reac- tor (Qloss = 0 in Eq. (2.107)). Other options, as well as the base case simulation parameters, are identified in Tables 3.1 and 3.2. To calculate the flow of CH4 and air in the combustion channel, we introduce in Table 3.1 two variables, the feed excesses of CH4 and O2. The feed excess of CH4 in the base case corresponds to an extra 1% of the required heat to convert 100% of the CH4 to H2 at standard conditions. The feed of air is determined by the stoichiometric excess of oxygen, expressed as: FCH4,co = −(1+ExcessCH4)FCH4,ro ∆H298Krx,3 ∆H298Krx,4 [mol/s] (3.1) FO2,co = 2 ( 1+ExcessO2 ) FCH4,co [mol/s] (3.2) FN2,co = .79 FO2,co/.21 [mol/s] (3.3) 3.3 Metrics Many metrics are needed to verify the model and evaluate the reactor performance: 55 Table 3.1: Base Case Parameters for Simulations, Part I Parameters (Symbols) Values (Equations) Units Operating Parameters Temperature of Feed (Tko) 600 oC Pressure in Reforming Channel(Pro) 15 bar Pressure on Permeate Side (Pm) 0.7 bar Pressure in Combustion Channel (Pco) 1.1 bar Reforming Feed Methane Flow (FCH4,ro) 1.29 nL/min Reforming Feed Steam to Carbon Ratio 3 mol/mol Reforming Feed H2 Content (yH2,ro) (Pm/Pro) mol/mol Combustion Feed Excess CH4 1% (Eq. (3.1)) mol% Combustion Feed Excess Air/O2 15% (Eq. (3.2)) mol% Catalyst Parameters Pore Radius (Rpore,k) 10 nm Porosity (εcat k) 0.4 Density (ρk) (2355(1− εcat k)/(1−0.4)) kg/m3 Reforming Kinetics Xu and Froment (1989) Combustion Kinetics nth order (See Eq. (2.50)) (α , β ) 1, 1 (A4) 19.9e7 kmol/(kg s barα+β ) (E4) 90 kJ/mol Design Parameters Length (L) 0.3 m Width (Wk) 0.08 m Catalyst Thickness (Thcat,k) 40 µm Separator Wall Thickness (Ths) 0.01 m Gas Channel Half-Height (Hk) 0.001 m Methane conversion: XCH4 XCH4,k = 1− FCH4,k|z FCH4,k|z=0 [mol/mol] (3.4) 56 Table 3.2: Base Case Parameters for Simulations, Part II Parameters (Symbols) Values (Equations) Units Membrane Parameters Membrane Thickness (Thm) 25 µm Membrane Effectiveness (ηm) 0.5 (Am) 2.003e-4 mol/(s m bar0.5) (Em) 15700 J/mol Physical Properties Diffusivity (Eq. (2.1)) Solution Parameters ∆z1 (See Fig. 2.3) 0.0003 m ∆zmax 0.0025 m % Increase of ∆z per step 10% Initial Relaxation Factor Non-Iso. Sim. 0.05 Initial Relaxation Factor Isothermal Sim. 0.3 where FCH4 , or in a general form Fi, the molar flow rate of any component i in the axial direction, is defined as: Fi,k =Wk ∫ Hr or 0 −Hk ci,kvz,kdx|z [mol/s] (3.5) Ratio of products over methane feed: Ratioi/CH4 = Fi,k|z/FCH4,ko [mol/mol] (3.6) For H2, we could take either the total hydrogen produced (Eq. (3.7)) or the hydro- gen extracted by the membrane (Eq. (3.8)). 3.3.1 Hydrogen Production We define several measures of H2 production: 57 Table 3.3: Hydrogen Flow Unit Conversion kg/day mol/s Nm3/h kg/day 1 87.09 2.114 mol/s 1.148E-2 1 2.427E-2 Nm3/ha 0.4731 41.20 1 nL/min 7.886 686.7 16.67 Sft3/min 0.804 70.01 1.699 GJ /day 0.121 10.5 0.256 kW 1.40 122.0 3.0 aNormal (N,n) or Standard (S) conditions are taken at 273.15 K, 1 bar H2 extracted by membrane: FH2,m FH2,m =Wr ∫ z 0 −JH2,mdz [mol/s] (3.7) where JH2,m is defined in Eq. (2.22) Total H2 produced: FH2,prod FH2,prod. = FH2,r|z+FH2,m|z−FH2,r|z=0 [mol/s] (3.8) FH2 is more commonly reported in [kg/day] or [Nm 3/h]. Table 3.3 shows various conversion factors. Specific hydrogen production: The specific H2 production YH2 is defined as the ra- tio between the hydrogen extracted by the membrane (see Eq. (3.7)) and the reactor volume (vol.react.), mass of catalyst, or membrane area (m.area). How to define reactor volume is not obvious for our reactor. For instance, one could include in- sulation materials, pre-heaters, or flanges. In our case, we only include the internal volumes of the two channels, separator wall and membrane support volumes. This facilitates comparison of our results with other reactors, like Packed Bed Mem- 58 brane Reactors (PBMRs) and Fluidized Bed Membrane Reactors (FBMRs). YH2,vol.react. = 87.1FH2,mMwH2 (2Hr +Ths+Hc+Thm.sup./2)LWr [kg H2/day m 3 react.] (3.9) YH2,kgcat = 87.1FH2,mMwH2 (ρcat rThcat,rWr +ρcat cThcat,cWc)L [kg H2/day kgcat ] (3.10) YH2,m.area = 87.1FH2,mMwH2 LWr [kg H2/day m 2 m] (3.11) For doubled-sided MRT membranes: Thm.sup. = 0.00635 [m] (3.12) where the subscript m.sup. denotes the membrane support. The H2 production per square meter of land (footprint) was also considered, but not selected because this measure is likely to be strongly scale dependent. 3.3.2 Other Performance Indicators Catalyst effectiveness, ηcat : ηcat, j = r j|x r j|x=Thcat,k (3.13) ηcat,ave, j = 1 Thcat,kL ∫ L 0 ∫ Thcat,k 0 ηcat, jdxdz (3.14) Reactor energy efficiency, ηreact : Reactor efficiency is defined as the ratio of the heat of combustion of the hydrogen extracted by the membrane to the total heat of combustion of the methane fed to both channels: ηreact. = LHV 298KH2 FH2,m LHV 298KCH4 FCH4,ro+LHV 298K CH4 FCH4,co (3.15) Reaction heat flux, Hflux: Reaction heat fluxes are calculated by integrating the heat produced and consumed, respectively, by the combustion and reforming reac- 59 tions. Ideally, reaction heat fluxes are equal in both channels to avoid hot spots and reactor extinction. H f lux,r = ∫ Thcat,r 0 ( 3 ∑ j=1 ( ∆HTcat rrx, j r j )) dx/1000 [kW/m2] (3.16) H f lux,c = ∫ Thcat,c 0 ( ∆HTcat crx,4 r4 ) dx/1000 [kW/m2] (3.17) Transverse temperature, ∆T : Transverse temperatures provide an indication of the effectiveness of the heat transfer within a computational domain. ∆Tk = Tk|x=Hr or 0−Tk|x=−Hk [K] (3.18) ∆Tcat k = Tcat k|x=Thcat,k −Tcat k|x=0 [K] (3.19) ∆Ts = Ts|x=Ths−Ts|x=0 [K] (3.20) 3.3.3 Dimensionless Numbers Average physical properties: To evaluate dimensionless numbers in the 2-D model, we needed to define average physical properties (e.g. ρave, Cpave) along the axial direction. Physical properties are functions of dependent parameters u (T , P, ci). We need to evaluate first those average dependent parameters (except for P). In the gas channels, we evaluate uave as: uave,k = ∫ Hk or 0 −Hk uvzdx vz,ave,k [m/s] (3.21) In the catalyst layer and separator wall, where there is no axial velocity, we evaluate uave,k based on the arithmetic mean: 60 Reynolds number, Re: Rek = ρmix,ave,kDh,kvave,k/µmix,ave,k (3.22) where: Dh,k = 4(Wk2Hk)/(2Wk +4Hk) [m] (3.23) ρmix,ave,k =∑ i (cave,i,kMwi) [kg/m3] (3.24) Here Dh is the hydraulic diameter, µmix,ave,k is evaluated from Eq. (2.15) at Tave. Mass Peclet number, PeL: PeL,i,k = Lvz,ave,k/Di,mix,ave,k (3.25) where Di,mix,ave,k is evaluated at Tave. Thermal Peclet number, PeL TH: PeL TH = Lvz,ave,kĈpave,kρmix,ave,k/kmix,ave,k (3.26) Ĉpave,k is the average specific heat capacity of the gas mixture: Ĉpave,k =∑ i ( xi,ave,kĈpi,ave,k ) [J/(kg K)] (3.27) xi,ave,k = (yi,ave,kMwi)/Mwave,k [kg/kg] (3.28) Mwave,k =∑ i (yi,ave,kMwi) [kg/mol] (3.29) Ĉpi,ave,k =Cpi,ave,k/Mwi [J/(kg K)] (3.30) where xi represents the mass fraction, kmix,ave,k is evaluated at Tave, yi,ave from Eq. (2.9), and Cpi,ave,k is evaluated at Tave based on Eq. (2.8). 61 3.3.4 Sensitivity Analysis Parameters In order to perform isothermal sensitivity analysis, we need to consider the overall objective of the study. Obtaining a high overall methane conversion is one pos- sible objective. However, as seen in Table 3.4 with the isothermal simulation re- sults, the final methane conversion in the reforming channel was already closed to 95%, giving limited space for improvement. On the other hand, on the combustion side, final conversion was lower, 82%. Base case parameters were mostly taken from Zanfir and Gavriilidis (2003) and with our operating temperature well below theirs, the final methane conversion in the combustion channel was reduced. To be consistent in both channels, instead of looking at the final conversion, the sen- sitivity analysis focuses on the minimum length L to reach a specific conversion: to avoid an excessively long reactor, we chose 90% for the reforming channel and 70% for the combustion channel. Those two values were chosen because they were slightly lower than the isothermal base case simulation results, thereby limiting the computation time. Ordinates for the sensitivity analysis are defined as: % Change in Input Para. = New Input Para.−Base Case Input Para. Base Case Input Para. (3.31) % Change in Min. L for XCH4 = New L|XCH4 −Base Case L|XCH4 Base Case L|XCH4 (3.32) 3.3.5 Performance Improvement Parameters In the last section of this chapter, we perform a series of simulations to improve the non-isothermal base case reactor performance. We monitor two indicators: the average reforming gas temperature (Tave,r) and the reforming methane conversion (XCH4,r). Tave,r is chosen because it is the most critical temperature to maintain the membrane integrity. CH4 conversion in the reforming channel is an easy parameter to understand, and, it is related directly to hydrogen production. It is also depen- dent on (XCH4,c), since low conversion in the combustion channel results in cooler temperatures, with reduced reforming performance. 62 3.4 Solving the Model As mentioned in Chapter 2, we opted for a two-point boundary ordinary differential equation solver “bvp4c", included in the MATLABTM software, coupled with back- ward finite difference discretization to solve the model. “bvp4c" uses orthogonal collocation on finite elements and was applied in the transverse direction. Back- ward finite differences were applied in the axial direction. To obtain values for the backward finite difference method, polynomials were fitted. Each discretization step was solved sequentially, from the entrance to the exit of the reactor. All in- tegrations were performed using the trapezoidal rule. The sequential technique in the axial direction made the model quite robust, and most simulations conditions reported in this paper were obtained without special tuning. The disadvantage of the sequential technique was that second order terms in the axial direction were difficult to incorporate. In Figure 2.1, A, B, C, D & E represent the five computational domains that must be solved for each discretization step. “bvp4c" required that each domain be solved individually. With each domain depending on the others, relaxation factors were used for convergence purposes. For isothermal simulations, separator Wall (C) was not needed, and only the pairs of domains, A & B and D & E, were solved. For simulations with energy balance, B,C & D domains were solved first. A & B and D & E were then solved in a second iteration loop. Complete convergence was difficult to obtain in a reasonable time while solving the second set of domains. To cope with this, we tolerated a certain level of discrepancies at the gas channel - catalyst layers boundaries, usually up to 1 K for temperatures and 0.001 for molar fractions. Table 3.2 shows some of the solving parameters. Discretization step size ∆z should be small enough that it does not influence the final results. The maximum step size was set at 0.0025 m. We verified that this value was sufficient by per- forming a simulation with ∆zmax = 0.0015 m, which did not change the final result significantly (final XCH4 increased by only 0.07%). We set the initial step size, ∆z1, at the reactor entrance at 0.0003 m. The goal with ∆z1 was to obtain an XCH4 after the first discretization step close to 1% in both channels. Non-isothermal simulations took about 4 hours with an Intel ZeonTM proces- 63 sor, CPU 3.0 GHz with 4.0 GB of RAM. Isothermal simulations were much faster, requiring only 5 min for the combustion channel and about 15 min for the reform- ing channel. We were able to run four or five simulations simultaneously on one computer. 3.5 Results and Discussion 3.5.1 Isothermal and Non-Isothermal Base Case Simulations Base case simulations had three different objectives: (1) to verify the energy and mass consistency of the model; (2) to verify some assumptions underlying the model; and (3) to obtain insights into the potential performance of the MCMR concept. Table 3.4 shows base case results for both non-isothermal and isothermal sim- ulations. The isothermal simulation represents a special case of the non-isothermal simulation, where the heats of reaction of both channels are perfectly balanced. The isothermal simulation performed better, with the methane conversion and hy- drogen production indicators all superior to the non-isothermal case. As shown below, the non-isothermal base case suffers from an insufficient supply of heat from the combustion side, causing the reactor to cool. In the last section of this chapter, we consider some ways to improve the heat supply, and, as a result, to enhance the reactor performance. Figure 3.1 shows various output parameters from the non-isothermal base case simulation. In Figure 3.1A, both reforming and combustion temperatures profiles are predicted to initially dip at the inlet of the reactor, then peak at ∼0.05 m and slowly decrease until the reactor outlet. Final temperatures, ∼780 K, are signifi- cantly lower than the inlet gas temperature of 873 K. The upper part of Figure 3.1B shows the integrated reaction heat fluxes. Those heat fluxes explain the tempera- tures variations in Figure 3.1A: (1) initially, the reforming heat flux is significantly higher than the combustion flux, causing the initial temperature to dip; (2) the combustion flux then becomes higher for a short length, until ∼0.05 m, leading to peak temperatures; (3) finally, the reforming flux became slightly higher, causing the reactor to cool slowly until the outlet is reached. The initial temperature dip 64 Table 3.4: Isothermal and Non-Isothermal Base Case Results Metric Units Value Non-Iso Value Iso Final XCH4 r - 74.6% 94.8% a Final XCH4 c - 72.5% 82.2% Final RatioH2,m/CH4 mol/mol 2.54 3.21 Final RatioH2,prod/CH4 mol/mol 3 .01 3.80 F ′ H2,m kg/day 0.42 0.52 YH2vol. react. kg H2 /day m 3 1070 1350 YH2 kgcat kg H2 /day kgcat 91.8 116 YH2m area kg H2 /day m 2 m 17.3 21.8 ηreact - 63.8% N/A ηcatr,ave,1 - 90.1% 86.3% ηcatc,ave,4 - 81.2% 76.2% Average Residence Time of Ref’s s 3.24 3.20 Average Residence Time of Comb’s s 0.162 0.156 aWithout membranes, thermodynamic equilibrium at isothermal base case conditions would limit XCH4 r to 28%. can be observed in previous MCR models based on a counter-current configuration (Kolios et al., 2002; Zanfir and Gavriilidis, 2004). In Figure 3.1A, although the difference between the temperature maxima and minima in the axial direction reaches almost 100 K, average transverse temperature differences between the reforming and combustion channels are <10 K. Moreover, in the lower part of Figure 3.1B, temperature differences within each domain (gas channels, catalyst layers and wall) are usually<10 K, indicating good heat transfer. Catalyst layer ∆T ’s are, as expected, much smaller than the gas channel ones, not surprising given that their thicknesses are 25-50 times smaller. One can observe a counter-intuitive result in Figure 3.1A: towards the exit of the reactor, the reforming gas average temperatures are predicted to exceed the catalyst combustion average temperature. Several observations help to explain this behaviour. First, reaction heat fluxes towards the exit became small and other heat transfer mechanisms, e.g. convection, can dominate. Second, the reforming gas channel height is twice that of the combustion channel, and the total molar 65 flow rate in the reforming channel is also about twice as large. The reforming gas channel has a higher resistance to changes in temperature, leading to larger ∆T ’s in the transverse direction (Figure 3.1B) and more resistance to change in average temperatures in the axial direction (Figure 3.1A). From Figure 3.1C, one can compare Ratioi/CH4 with XCH4 in Figure 3.1A. Our model respects the expected stoichiometric ratios: in the combustion channel, Ra- tioH2O/CH4,c is twice the RatioCO2/CH4,c, and RatioCO2/CH4,c is equivalent to XCH4,c; in the reforming channel RatioH2 prod/CH4,r is about four times XCH4,r, and (Ra- tioCO2/CH4,r + RatioCO/CH4,r) is equivalent to XCH4,r. Figure 3.2 shows 2-D velocity and temperature profiles. Velocities for both combustion and reforming channels follow similar trends, but variations are pre- dicted to be larger on the reforming side. In both channels, the peak temperatures, observed in parts C & D, decrease the gas density while increasing the gas veloc- ities. In the reforming channel, mole generation due to reactions, combined with withdrawal of moles by the membrane, add to the velocity variations. Isotherms in the catalyst layers (parts E & F) show less curvature than in the gas channels (parts C & D), indicating faster heat transfer. Figure 3.3 shows H2 (parts A & B) and CH4 (parts D & E) molar fraction 2-D profiles, as well as catalyst effectiveness, ηcat (parts C & F) in both reforming and combustion channels. In the reforming channel (right side of the figure), with 40 µm thick coating in the base case, the catalyst effectiveness remains high, generally >0.8. H2 molar fraction gradients in the transverse direction are apparent in the gas channel, suggesting that H2 extraction by the membrane or H2 diffusion limits the reactor performance. On the combustion side, the catalyst effectiveness behaves differently, with lower values (∼0.5) at the reactor entrance. Slower O2 diffusion in the catalyst layer, may explain this observation. CH4 iso-molar-fraction lines in the combustion gas channel are relatively straight (part D), indicating low mass transfer resistance. Verification of Assumptions Based on results of the non-isothermal base case simulation, this section considers some of the model assumptions adopted in Chapter 2. 66 010 20 30 10 20 30 40 R e a ct io n  H e a t F lu x (k W /m 2 ) Te m p e ra tu re  ( K ) T c T r T cat,c T cat,r T s - (Heat Flux r) Heat Flux c 0% 10% 20% 30% 40% 50% 60% 70% 80% 760 780 800 820 840 860 880 900 C H 4 C o n v e rs io n  Te m p e ra tu re  ( K ) T ave,c T ave, cat,c T ave, cat,r T ave,r X CH  ,c X CH  ,r4 4 A B ∆ ∆ ∆ ∆ ∆ -20 -10 -10 0 R e a ct io n  H e a t (k W /m ∆∆ ∆∆ Te m p e ra tu re  ( K ) 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 0 0.05 0.1 0.15 0.2 0.25 0.3 R a ti o  H 2 / C H 4 Fe d  (m o l/ m o l) R a ti o  P ro d u ct  /  C H 4 Fe d  (m o l/ m o l) Axial Coordinate (m) H O,c CO ,c CO,r CO ,r H  Prod. H  Extrac. 2 2 2 2 2 C Figure 3.1: Non-Isothermal Base Case Results - A: XCH4& Average Temper- ature Profiles; B: Transverse ∆T & Reaction Heat Fluxes; C: Ratioi/CH4 . (For base case parameters, see Table 1.) 67 Ch an ne l H ei gh t (m ) A: v r  [m/s]   0 0.1 0.2 0.3 −1 −0.5 0 0.5 1 x 10−3 0 0.05 0.1 0.15 B: v c  [m/s]   0 0.1 0.2 0.3 −10 −8 −6 −4 −2 0 x 10−4 0 0.5 1 1.5 2 2.5 Ch an ne l H ei gh t (m ) C: T r  [K]   0 0.1 0.2 0.3 −1 −0.5 0 0.5 1 x 10−3 780 800 820 840 860 880 D: T c  [K]   0 0.1 0.2 0.3 −10 −8 −6 −4 −2 0 x 10−4 780 800 820 840 860 880 Axial Coordinate (m) Ca ta lys t T hi ck ne ss  (m ) E: T cat r [K]   0 0.1 0.2 0.3 0 1 2 3 4 x 10−5 780 800 820 840 860 880 Axial Coordinate (m) F: T cat c [K]   0 0.1 0.2 0.3 0 1 2 3 4 x 10−5 780 800 820 840 860 880 Student Version of MATLAB Figure 3.2: Non-Isothermal Base Case Results - Velocity and Temperature Profiles 68 Ch an ne l H ei gh t (m ) A: yH 2 ,r   0 0.1 0.2 0.3 −1 −0.5 0 0.5 1 x 10−3 0.05 0.1 0.15 D: yCH 4 ,c   0 0.1 0.2 0.3 −10 −8 −6 −4 −2 0 x 10−4 0.03 0.04 0.05 0.06 0.07 0.08 Ca ta lys t T hi ck ne ss  (m ) B: yH 2 ,cat r   0 0.1 0.2 0.3 0 1 2 3 4 x 10−5 0.05 0.1 0.15 E: yCH 4 ,cat c   0 0.1 0.2 0.3 0 1 2 3 4 x 10−5 0.03 0.04 0.05 0.06 0.07 0.08 Axial Coordinate (m) Ca ta lys t T hi ck ne ss  (m ) C: η cat r,1   0 0.1 0.2 0.3 0 1 2 3 4 x 10−5 0.5 0.6 0.7 0.8 0.9 1 Axial Coordinate (m) F: η cat c,4   0 0.1 0.2 0.3 0 1 2 3 4 x 10−5 0.5 0.6 0.7 0.8 0.9 1 Student Version of MATLAB Figure 3.3: Non-Isothermal Base Case Results - Molar Fraction and Catalyst Effectiveness Profiles 69 Table 3.5: Base Case Simulation Dimensionless Numbers Values Non-Iso Values Iso Inleta Outlet Outlet Rer 54 47 39 PeL,H2,r 962 720 587 PeL TH,r 3280 2600 2100 Rec 31 38 33 PeL,CH4,c 4420 4780 4410 PeL TH,c 4600 5150 4760 aInlet dimensionless numbers are the same for both Non-Iso and Isothermal simulations Gas channels: Table 3.5 shows dimensionless numbers for the gas channels. The low Re numbers, all <55, confirm laminar flow in both channels. The entrance length to produce fully-developed laminar flow (0.06 ∗ Re ∗Dh,k) was evaluated <13 mm in both channels, or <4.5% of the total reactor length. PeL,CH4,c values are high (>4000), but PeL,H2,r values are <1000, indicating some axial dispersion of H2 by diffusion, which is not taken into account in the model. However, PeL,H2,r >500, so that adding a diffusion term in the axial direction at this stage of the project was deemed to be unnecessary. In both channels, PeL TH is mostly >1000, indicating, as assumed, that axial heat transfer by conduction is negligible. Spatial derivatives of the physical properties were also assumed to be negligi- ble. Using data from the simulation, we back-calculated the heat convection term and the terms including the thermal conductivity derivative in the axial direction in Eq. (2.98). The derivative term was ∼3 orders of magnitude smaller than the convective heat flux term, supporting this assumption. Catalyst layers: Both mass diffusion and heat conduction in the axial direction were assumed to be negligible. Based on model predictions, we back-calculated concentration and temperature gradients in both the transverse and axial directions. The axial concentration gradient was∼5 orders of magnitude smaller than the cor- responding transverse concentration gradient. Similarly, the axial heat conduction gradient was ∼4 orders of magnitude smaller than the transverse heat conduction 70 gradient, again supporting the assumptions. It was assumed that the derivative of Di,mix was negligible. We compared the following two terms by back calculations in the catalyst layers: Di mix ( d2ci dx2 ) vs d Di mix dx d ci d x The second term, including the spatial derivative of Di,mix, was ∼3.5 orders of magnitude smaller than the first term, again supporting our assumption. Separator wall: For the separator wall, thermal conduction in the axial direction was assumed to be negligible. Back calculations showed that the driving forces for conduction in the axial and transverse directions were of the same order of magni- tude. Our solving strategy, solving each discretization step sequentially starting at the entrance of the reactor, makes it difficult to take into account second order heat transfer terms in the axial direction. Ideally, all reactor equations would be solved simultaneously. Conduction in the axial direction would diffuse the heat, reducing temperature variations. By neglecting axial heat conduction, we might exacerbate hot spots, which we want to avoid to preserve the membrane. Therefore, our sim- ulations are believed to provide conservative estimates regarding the formation of hot spots. 3.5.2 Isothermal Parametric Sensitivity Analysis Predictions from the isothermal parametric sensitivity analysis are presented in Fig- ures 3.4, 3.5 and 3.6. The y-axis is inverted so the upper quadrants show improve- ments in reactor performance (i.e. decreases in minimum reactor length to achieve a desired methane conversion, corresponding to increases in methane conversion and hydrogen production). For simplicity in this section, instead of mentioning the “Minimum length to achieve a specific conversion”, we use the generic terms “per- formance” and “conversion”. We discuss in this section the parameter adjustments that could improve the reactor performance and link these changes with practical considerations. Figure 3.4 shows sensitivity results regarding some operating parameters. Tem- 71 perature was the most sensitive parameter in both channels. One might be tempted to increase the reactor temperature to increase performance. However, as men- tioned in Chapter 2, Pd/Ag membranes have serious temperature limitations. Un- less Pd-based membrane working >600oC can be developed, higher temperature would not be desired. Furthermore, more expensive alloys would likely be required to reactors to operate at those conditions. Higher pressures led to higher perfor- mance in both channels, but to a lesser extent than higher temperatures. By Le Châtelier’s principle and without any membrane, since there is a net production of moles in the SMR reactions, increasing the reforming pressure reduces the conver- sion. However, increased pressure also increases the driving force for the hydrogen permeation, explaining the slight overall increase in performance with increasing pressure. Despite this advantage, higher pressure also brings challenges. First, the membrane may not withstand increases in pressure (MRT membranes have an upper limit of 25 bar). Second, higher pressures require thicker material require- ments for the reactor, leading to higher equipment cost and longer start-up times. As shown in Figure 3.4A, it was also possible to enhance conversion by lowering the pressure on the permeate side, indicating that H2 extraction might be a ma- jor factor limiting the reactor performance. Lowering permeate pressure generally does not increase significantly the cost of the reactor, but would increase parasitic losses, e.g. for compression of product H2. Figure 3.4 also shows linear effect of varying flow rates, while maintaining the same stoichiometric ratios, on the performance in both channels. Increasing flow rates decreased proportionally the conversions. In light of those results, one can confirm that mass transfer resistance was not limiting the reactor performance in the gas channel. The limited influence of the steam-to-carbon ratios in reforming and of the excess air on the combustion side further supports this assumption. De- creasing the flow rates is not an attractive option: although it increases conversion, it reduces the hydrogen yields YH2 . Practical issues would likely set feed parame- ters. Steam-to-carbon ratio >3 is usually required to avoid carbon formation with Ni-based catalysts, and a large excess of air might be required on the combustion side to stay below the methane lower flammability limit. Figure 3.5 shows the influence of parameters related to the catalyst layers. Ac- tivation energies are predicted to have the strongest effect in both channels. The 72 -100% -75% -50% -25% 0% 25% 50% 75% 100% -100% -75% -50% -25% 0% 25% 50% 75% 100% %  C h a n g e  i n  M in . L fo r 9 0 %  C H 4 C o n v. Temperature Total Pressure Total Flow Rate Steam-to-Carbon Ratio Pressure Permeate Side -100% Temperature A. Ref. * -75% -50% -25% 0% 25% 50% 75% 100% -100% -75% -50% -25% 0% 25% 50% 75% 100% %  C h a n g e  i n  M in . L fo r 7 0 %  C H 4 C o n v.  % Change in Input Parameter Total Pressure Total Flow Rate Excess Air B. Comb. * Figure 3.4: Sensitivity Analysis around Base Case Values of Tables 3.1 & 3.2 - Operating Parameters: A. Reforming Channel; B. Combustion Chan- nel (* Some values are off chart.) 73 only way to influence this parameter would be to change the catalyst itself. Pre- exponential factors could improve performance, especially on the combustion side. The prediction that the reforming channel was less influenced by this parameter, again indicates that H2 extraction was a major performance limiting factor, not the catalyst. Pre-exponential values are functions of the metal catalyst loading and may vary considerably. Those results suggested that a careful selection of metal loading in the catalyst would be required to balance the heat consumption and production. Shigarov et al. (2009) made similar observations, and suggested that increasing cat- alyst activity (or loading) is not always the best solution. Strong combustion activ- ity could cause hot spots, whereas strong reforming activity could cause extinction. The importance of pre-exponential factors also suggests that catalyst deactivation is a major challenge. Increasing pore radius showed a moderate influence on the combustion side and a negligible effect on the reforming. These observations are related to the catalyst effectiveness factors showed in Figures 3.3C & D, where the combustion effective- ness factor was lower than the reforming one near the entrance of the reactor. Pore radius, as well as porosity, are functions of the catalyst support and hence cannot be easily altered. Figure 3.6 shows the effect of some other reactor design parameters and the effect of diffusivity on reactor performance. In Figure 3.6A, a thinner membrane improved conversion, confirming once again that membrane extraction of H2 is limiting the performance. However, when designing the prototype, pinhole free planar membranes thinner than 25 µm were not commercially available. In other words, membrane thinner than those used in the base case would be unlikely to produce fuel cell grade hydrogen. Half-channel heights are predicted to have little influence on the combustion reaction. However, the half-height significantly affects the reforming performance. As mentioned above, the reforming channel height was assumed to be twice that of the combustion channel. The molecules then had twice the distance to travel and based on Fick’s law, the diffusion flux is inversely proportional to the square of the distance traveled. Since the H2 must diffuse across the reforming channel to be extracted, the effect of reforming channel height can be rationalized. Hence, reducing the half-channel height is one option to improve performance, subject to machining tolerances and fabrication methods. Figure 3.6 74 -100% -75% -50% -25% 0% 25% 50% 75% 100% -100% -75% -50% -25% 0% 25% 50% 75% 100% %  C h a n g e  in  M in . L fo r 9 0 %  C H 4 C o n v. * Pre-Exponential Factors Activation Energy Pore Radius A. Ref. -100% -50% 0% 50% 100% 150% 200% -100% -75% -50% -25% 0% 25% 50% 75% 100% %  C h a n g e  in  M in . L fo r 7 0 %  C H 4 C o n v. % Change in Input Parameter Porosity * B. Comb. Figure 3.5: Sensitivity Analysis around Base Case Values of Tables 3.1 & 3.2 - Catalyst Parameters: A. Reforming Channel; B. Combustion Channel (* Some values are off chart.) 75 indicated a small benefit of increasing the catalyst thickness layers, up to about twice the size of the base case thickness (from 40 to 80 µm). The results also showed that the diffusivity is unlikely to limit the performance, at least over the range tested. 3.5.3 Performance Improvement Figure 3.7 shows results of a series of non-isothermal simulations. The y-axis dis- plays both average reforming gas temperature (Tave,r) and the reforming methane conversion (XCH4,r). The non-isothermal base case results show that the methane conversion predicted in the combustion channel is less than in the reforming one (see Table 3.4. As a result, not enough heat is transferred to the reforming side. In Figure 3.7A, key combustion channel parameters are modified (see Table 3.6) from their base case values, with the goal of transferring more heat. In Figure 3.7B, as proposed by Baratti et al. (2003), we varied the combustion catalyst layer thickness and the kinetic pre-exponential factor A4 along the reactor length, with the combustion catalyst layer of Figure 2.1 divided into six intervals, each 50 mm long. Table 3.7 presents the parameter changes from the base case scenario. All parameters varied in Figure 3.7A improved the conversion. However, in- creasing the pressure and augmenting A4 both led to a hot spot >900 K near the reactor entrance. In contradiction to the isothermal simulation (see Figure 3.4), reducing all the flow rates by 25% did not increase the conversion proportionally. This could be explained by the reforming reactions and hydrogen extraction bene- fiting most from flow reduction, causing further cooling and slower combustion. A cooler reactor leads to lower final conversions. In Figure 3.7B, methane conversion improved again, this time with the variable catalyst parameters strategy. Increas- ing A4 after two intervals was more effective than increasing the catalyst thickness after two intervals. Combining the two variations was even better, with conversion improving 10% without hot spot formation. The best conversion (>90%), was ob- tained, without hot spots, by combining A4 and thickness variations with increased excess methane flow. Table 3.8 summarizes the performance improvements between our non-isothermal base case simulation and the best case in Figure 3.7, as well as membrane reactor 76 -100% -50% 0% 50% 100% 150% 200% -100% -50% 0% 50% 100% 150% 200% %  C h a n g e  i n  M in . L fo r 9 0 %  C H 4 C o n v.  Diffusivity Membrane Thickness Catalyst Coating Thickness Half Channel Height * -100% A. Ref. -50% 0% 50% 100% 150% 200% -100% -50% 0% 50% 100% 150% 200% %  C h a n g e  i n  M in . L fo r 7 0 %  C H 4 C o n v. % Change in Input Parameter Diffusivity Catalyst Coating Thickness Half Channel Height * * B. Comb. Figure 3.6: Sensitivity Analysis around Base Case Values of Tables 3.1 & 3.2 - Design Parameters & Diffusivity: A. Reforming Channel; B. Combus- tion Channel (* Some values are off chart.) 77 100%960 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 760 800 840 880 920 960 Pc A Ex Th F Base Case A R e fo rm in g  G a s A v e . T  ( K ) R e fo rm in g  C H 4 C o n v e rs io n  ( m o l% ) 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 760 800 840 880 920 0 0.05 0.1 0.15 0.2 0.25 0.3 Axial Coordinate (m) 1 2 3 4 Base Case B R e fo rm in g  G a s A v e . T  ( K ) R e fo rm in g  C H Figure 3.7: Performance Improvement Trials - A. Constant Catalyst Proper- ties along the Reactor Length; B. Variable Catalyst Properties (Th cat,c, A4) along the Reactor Length. 78 Table 3.6: Parameter Changes for Figure 3.7A from Base Case Values of Ta- bles 3.1 & 3.2 La- bel Parameter Changed Value Units A A4 Multiplication Factor 1.5 - Ex Combustion Feed Excess CH4 15 mol% F Inlet Flow Rates (Ref. and Comb.) Multiplication Factor 0.75 - Pc Combustion Pressure (Pc) 1.6 bar Th Combustion Catalyst Thickness (Thcat,c) 60 µm Table 3.7: Parameter Changes for Figure 3.7B from Base Case Values of Ta- bles 3.1 &3.2 La- bel Combustion Catalyst Thickness (Thcat,c) per Interval (µm) A4 Multiplication Factor per Interval Combustion Excess CH4 (mol%) 1 40-40-60-60-60-60 N/Aa N/A 2 N/A 1-1-2-2-2-2 N/A 3 40-40-60-60-60-60 1-1-2-2-2-2 N/A 4 40-40-60-60-60-60 1-1-2-2-2-2 15 aN/A= Same as base case experimental work reported in the literature. Care is needed when comparing, as operating conditions differed widely, some values are rough estimates (denoted by ∼) and, as shown in later chapters, experimental results are generally lower than simulation predictions. However, some general observations are possible: (1) The MCMR has the potential for higher production per reactor volume and per mass of catalyst; (2) the production per membrane area will likely be similar to other mem- brane technologies; and (3) as long as pin-holes are absent, thinner membranes are desirable. The best case ηreact 76.3%, is lower than desirable, despite the improvements, 79 Table 3.8: Non-Isothermal Base & Best Case Results and Comparison with Experimental Lit- erature Base Case Best Case FBMRa FBMRb FBMRc PBMRd Final XCH4 r - 74.6% 91.5% 70% 73% 73% 80% Final XCH4 c - 72.5% 88.0% N/A N/A N/A N/A Final RatioH2,m/CH4 mol/mol 2.54 3.12 2.5 3.0 1.3 N/A Final RatioH2,prod./CH4 mol/mol 3.0 3.68 3 N/A N/A N/A F ′ H2,m kg/day 0.42 0.51 0.4 1.82 2.27 0.03 YH2vol. react. kg H2/day m 3 1070 1311 ∼40 ∼160 ∼200 420 YH2 kgcat kg H2/day kgcat 91.8 90.0 ∼0.2 ∼2.5 ∼3.1 2 YH2m area kg H2/day m 2 m 17.3 21.2 2 6.81 8.50 15 ηreact 63.8% 76.3% N/A N/A 37% N/A a(Rakib et al., 2011) 773 K, 6 bar, 0.5 bar permeate side, Thm: 25 µm, electric heating b(Mahecha-Botero et al., 2008) 823 K, 10 bar, 0.3 bar permeate side, Thm: 25 µm, electric heating c(Mahecha-Botero et al., 2008) 823 K, 10 bar, 0.3 bar permeate side, Thm: 25 µm, auto-thermal d(Tong et al., 2005) 823 K, 3 bar, sweep flow equivalent to 0.3 bar, Thm: 6 µm , electric heating note the efficiency does not include parasitic and heat losses. In Table 3.8, reactor efficiency calculations for auto-thermal conditions showed low efficiency, likely due to reactor heat losses. Even though operating temperature of 823 K is much lower than in conventional reforming, heat losses were still important for the scale studied (∼2 kg H2/day). In order to have acceptable reactor efficiency with SMR, the scale of production may need to be at least one to two orders of magnitude higher. To improve the MCMR efficiency significantly, one avenue would be to recycle the reforming gas exhaust as a combustion fuel. Reforming conversion could be controlled so that the retentate gas would contain enough energy to supply the required heat, after condensing and separating the steam. This strategy could also save membrane surface area, since a conversion of∼88% would leave enough methane and unextracted hydrogen to supply the reforming heat requirement. With the isothermal base case conditions, ηreact could then reach 90% according to our calculations. 80 3.6 Conclusions This Chapter presents isothermal and non-isothermal simulation results from the 2-D, steady-state reactor model developed in Chapter 2. For the base case simula- tions, the non-isothermal case underperformed the isothermal case, due to a lack of heat generated from the combustion reaction. Except for the entrance of the reac- tor, transverse temperature variations within computational domains could be kept below 10 K. Base case key indicators showed mass and energy consistency. Most model assumptions were verified with dimensionless number calculations and back calculations of heat and mass transfer driving forces. Future model improvements would benefit from incorporation of second-order axial heat transfer terms for the separator wall. Isothermal sensitivity analysis was carried out involving 15 parameters varied one at a time around the base case values. This sensitivity analysis indicated a limited number of parameter adjustments practically available to increase the re- actor performance from the base case scenario. Among these, the most promising were: increasing operating pressure in both channels; lowering permeate pressure on the reforming side; increasing pre-exponential factors and coating thickness on the combustion catalyst; and reducing the half-channel height of the reforming channel. The predictions indicate that H2 membrane extraction is the major fac- tor limiting reforming performance, whereas catalyst activity is the major factor limiting performance in the combustion channel. Several combustion channel parameters were varied in an effort to improve the reactor performance. Without rigorous optimization, it was possible to obtain methane conversion (>90%) without the formation of hot spots. Axial temperature variations were reduced from ∼100 K in the base case to ∼10 K in the best case. Performance could be improved significantly by a combination of varying the pre- exponential factor (metal loading) and catalyst thickness along the length of the reactor, while increasing the methane flow rate on the combustion side. Compared with other membrane reactor technologies, MCMR has the potential to have 1 to 2 orders of magnitude higher hydrogen production per reactor volume and per mass of catalyst. Results in this chapter were promising enough to prompt the design and con- 81 struction of an MCMR prototype reactor. The next two chapters focus on catalyst coating, with a specific goal of obtaining a stable coating thickness >80 µm. 82 Chapter 4 Catalyst Coating: Initial Method Development 4.1 Introduction Previous chapters of this thesis developed the concept of the Multi-Channel Mem- brane Reactor (MCMR). This concept requires both reforming and combustion cat- alysts to be coated on a flat metal substrate. Sensitivity simulations on an isother- mal base case, performed in Chapter 3, suggest that the reactor performance could benefit from a relatively thick layer of catalyst, up to ∼80 µm thick. We review in this Introduction various coating techniques described in the literature, with special attention to techniques with the potential to achieve thick coating layers. 4.1.1 Gas Phase Techniques Low Temperature Plasma Production of catalyst by low temperature plasma was reviewed by Liu et al. (2002). Plasma, an ionized gas, can produce a strong and thick carrier or catalyst deposit on metal or ceramic substrate. Powder is heated to near or above its melting point in a plasma torch, and accelerated by a plasma gas stream toward the substrate. The particle diameter is usually between 5 and 60 µm (Liu et al., 2002). Ismagilov 83 et al. (1999) coated γ-Al2O3 and α-Al2O3 particles on a Ti support. SEM images showed coating thickness >100 µm, but surface areas were low, <1 m2/g. One of the advantages of plasma deposition is that no further heat treatment is necessary, saving time and energy. However, operating cost can be high, due to the gas and energy consumption, and operation generally requires highly trained labour. CVD and Variations In conventional Chemical Vapour Deposition (CVD), a substrate is exposed to a volatile precursor, which reacts on the substrate surface, to form a solid prod- uct (Seshan, 2002). CVD generally produces nanometer thick coating only, and requires a relatively expensive and complex deposition chamber, and/or vacuum system (Meille, 2006). Because CVD does not generate enough surface area to achieve sufficient reactor productivity, Meille (2006) discarded the technique as a suitable method for catalyst production. Choy (2003) provided an exhaustive review of CVD techniques and variations, partially based on his own work. Among the techniques reviewed is Aerosol- assisted CVD. This consists of dissolving catalyst chemical precursors into an or- ganic solvent. The precursor solution is atomized and delivered into a heated zone, where the solvent is rapidly evaporated or combusted. The chemical precursors undergo subsequent decomposition and/or chemical reaction near, or on, a heated substrate to deposit the desired film. One variant of the technique is Electrostatic spray-assisted vapor deposition, where the atomized droplets are sprayed across an electric field, enhancing chemical deposition efficiency (>90%). Using this tech- nique, a 250 µm thick Y2O3−ZrO2 film was produced on a Ni-alloy substrate. Choy and Seh (2000) also reported on a technique named Flame-assisted va- por deposition, called Flame spray deposition by Thybo et al. (2004). The tech- nique consists of mixing organo-metallic precursors into water and combustible organic solvent. During deposition, the precursor solution is atomized and pro- pelled by compressed air into an open flame from a Bunsen burner. The precur- sors are then converted into nanometer-sized metal or metal-oxide particles. Choy and Seh (2000) produced 100 µm thick Ni−Al2O3 coatings, whereas Thybo et al. (2004) reported Au/TiO2 coatings up to 150 µm. A disadvantage of the technique 84 is that the flame temperature is hard to control, causing a potential reproducibility problem. 4.1.2 Liquid Phase Techniques EPD Electrophoretic Deposition (EPD) consists of the application of an electric field between electrodes, making charged particles in suspension migrate to the op- positely charged substrate, causing discharge, and formation of a film (Seshan, 2002). The cathode is generally the substrate to be coated, while the anode is ei- ther an aluminum or stainless steel foil (Meille, 2006). Ferrari et al. (2006) coated Al2O3−ZrO2 films with EPD, reaching 50 µm. Ceramic films, close to 300 µm thick, were reported by Besra and Liu (2007). Suspension The suspension technique, also called slurry, consists in mixing a powder (catalyst support or catalyst itself), an organic binder (usually an organic polymer), an acid, and a solvent (Meille, 2006). Films are prepared by either wash, spin, dip, air spray, or brush coating on a substrate. The coated substrate is then dried and calcined to remove the water and organic material, and to develop the final ceramic structure. Particle size is an important factor affecting coating adherence on the substrate. Agrafiotis et al. (1999), using washcoating on cordierite honeycombs, reported that particles in the range of 2 µm led to much more adherent layers than 17 or 52 µm particles. Germani et al. (2007) successfully coated on stainless steel micro channels 10-50 µm thick layers of γ alumina powder (Dp,ave 3 µm ) and Cu−ZnO/Al2O3 commercial catalyst (Dp,ave 28 µm). Methylhydroxyethyl cellu- lose as binder and no acid led to the best catalyst activity and adhesion. Valentini et al. (2001) created 5-80 µm thick films of γ-Al2O3 using dip coating on aluminum slabs and α-Al2O3 tubes. Adherence was not clearly reported for their 80 µm thick coating. (Meille et al., 2005) reported coating layers 1-200 µm thick using a γ-Al2O3 suspension, including a dispersant agent. Adherence was not clearly reported for their thicker coatings (∼200 µm). 85 Sol-Gel Technique A sol is a dispersion of solid particles in a liquid where the particles are small enough to remain suspended indefinitely by Brownian motion. A gel is a sub- stance that contains a continuous solid skeleton enclosing a continuous liquid phase (Brinker and Scherer, 1990). The sol-gel technique consists of mixing an organo- metallic precursor of the material to deposit with a suitable solvent. Additives can be added to control the viscosity and surface tension of the sol-gel. Enough time must be allowed for the sol to age, allowing gelation. The more complex the oligomers formed, the thicker the coating, but the risk of cracks is then higher (Meille, 2006). The sol-gel technique generally produces layers around 10 µm thick. Cini et al. (1991) coated γ-Al2O3 film on a α-Al2O3 tubes. They reported films up to 100 µm thick, however cracks could not be avoided with layers thicker than 10 µm. Modified Sol-Gel Technique The modified sol-gel technique can be seen as a hybrid between the suspension and sol-gel techniques. Calcined ceramics are dispersed in the sol-gel matrix to prevent large strain in conventional sol-gel films, occurring during heat treatment. Commercial catalyst powder can substitute for ceramic, but sol particles can block partially active sites and reduce catalyst activity (Meille, 2006). Sidwell et al. (2003) used this technique to coat a commercial Pd 5 wt%/ γ-Al2O3 onto a cast- alumina disk. Boehmite was used as sol agent with acetone as the solvent. The mixture was sprayed in thin layers, and a flow of nitrogen partially removed the solvent between each layer. The process was continued until the film thickness reached 90 µm. Modified sol-gel techniques are commonly used in micro-channel reactor tech- nologies. For instance, Sohn et al. (2007) obtained a 50 µm alumina coating for their methanol fuel micro-reactor by mixing α-Al2O3 powder, aluminum iso- propoxide, ethanol, water and nitric acid. Peela et al. (2009) obtained good coating adherence properties, measured by sonication, with γ-Al2O3 coating. The modified sol, containing γ-Al2O3 powder, polyvinyl alcohol, and boehmite, was washcoated on a stainless steel micro-channel to obtain coatings ∼65 µm thick. 86 4.1.3 Surface Pretreatment Surface pretreatment can be applied to increase the adherence of a catalyst layer, almost independently of the coating technique. Thermal oxidation: Thermal oxidation consists of creating a thin oxide layer (∼1 µm thick) by thermal treatment in air. It is usually applied to a Fecralloy substrate (Fe 72% Cr 22% Al 5.0%) above 840oC (Meille, 2006). Enger et al. (2008) used the thin oxide layer to impregnate RhCl3 in a Multi-Channel Reactor (MCR) for partial oxidation of methane and propane. Chemical treatment: Surface roughness can also be affected with chemical treat- ment. Depending on the nature of the metal support, by immersing the metal sub- strate into a strong acid or base, etching and/or surface oxidation can occur (Meille, 2006; Valentini et al., 2001). Mechanical treatment: Sand-blasting can also be used to create surface rough- ness (Hawthorne et al., 2004), and it is applicable to any metal substrates that can withstand the mechanical stress of the process. However, it is limited to areas within the line of sight. Primer application: Some authors (Valentini et al., 2001; Park et al., 2005; Peela et al., 2009) reported using sol-gel technique to create a thin oxide layer, as a primer for a second thicker layer. For instance, Park et al. (2005) used an alumina primer on stainless steel, before coating a commercial Cu/ZnO/Al2O3 catalyst. 4.1.4 Coating Strategy After reviewing different coating techniques, we selected the modified sol approach for several reasons: (1) It allows the coating of both lab-made and commercial catalysts. (2) The equipment required is relatively inexpensive (e.g. compared to plasma technique) and available at UBC. (3) Solid material and solvent (usually water) are relatively inexpensive and non-toxic. (4) UBC has some expertise in coating alumina with modified sol (Hawthorne et al., 2004). 87 Coating methodology is often under-reported in the multi-channel/ micro reac- tor literature, where authors give minimal details of their procedure or the effects of coating parameters. In this chapter, we show most of the results obtained during our quest to develop a methodology for coating lab-made and commercial reform- ing and combustion catalysts. The next chapter focuses on solving coating issues related to the catalysts selected for the MCMR prototype. 4.2 Materials 4.2.1 Metal Substrate Experiments were generally conducted on austenitic Stainless Steel (SS) 304, no. 4 finish plates. Metal thickness was generally gauge 24 (0.635 mm), but gauges 22 (0.792 mm) and 20 (0.953 mm) were also tested. Fecralloy (Fe 72% Cr 22% Al 5.0% Y 0.1% Zr 0.1%) plates, 1 mm thick (GoodFellow), which allow thermal treatment for surface oxidation, were also tried. Most plates were sheer cut to 39.5 mm x 39.5 mm. 4.2.2 Modified Sol Boehmites Various boehmites (AlOOH) (see Table 4.1) were mixed with water to create a sol. Initially, experiments were conducted with the Soltonerde P2 boehmite, but after the initial stock was exhausted, we could not buy the same product again, since the company had been purchased by Sasol. Sasol Disperal P2 was found to be the closest product available. Sasol Disperal P3 has the characteristic of not having nitrate, but instead acetate, as a dispersion agent. Unless specified otherwise below, Sasol Disperal P2 was used. Carrier Table 4.2 shows properties for the various carriers tested in this chapter. α-Al2O3 is a common support for reforming catalyst. We used two types of α-Al2O3, one from Sasol and the other one from Alcoa. Alcoa sold their alumina division to 88 Table 4.1: Boehmites Tested and their Properties Name (Code Name) Supplier Particle size BET Sur- face Area Al2O3 content Nitrate Content m2/g wt% wt% Soltonerde P2 (Co) Condea < 25 µm: 31% <45 µm: 70% 287 73.1 3.5 Disperal (P0) Sasol < 25 µm: 69% <45 µm: 83% 181 78.1 - Disperal P2 (P2) Sasol < 25 µm: 40% <45 µm: 83% 287 74.4 3.5 Disperal P3 (P3) Sasol < 25 µm: 4.5% <45 µm: 11% 320 67.8 6.9 (Ac- etate) Brenntag Specialties, and alumina A-16 was not always available for testing. γ- Al2O3 has a much higher surface area than α-Al2O3, but undergoes a phase change at ∼850oC in air (Gitzen, 1970), making it less likely to be used in conventional Steam Methane Reforming (SMR). However, since our Pd/Ag membrane must be operated below 600oC, γ-Al2O3 was considered as option. We also investigated alternatives to alumina: magnesium aluminate spinnel (MgAl2O4), known for its thermal and chemical stability (Guo et al., 2004), and ceria oxide (CeO2), which is known to act both as promoter and carrier (Laosiripojana and Assabumrungrat, 2005). Promoter and Catalyst Precursors Table 4.3 lists all promoter and catalyst precursors covered in this chapter. Ni is commonly used as an SMR catalyst (Twigg, 1997). It is relatively inexpensive compared to noble metals. Noble metals (Rh, Ru, Ir) are, however, more active than Ni per unit mass (Berman et al., 2005). They are also more resistant to carbon deposition and sulfur poisoning. Their cost is usually prohibitive in conventional SMR, but since MCMR has the potential to use much less catalyst, as discussed in Chapter 3, noble metals can be considered. In this work, we tested Ru, being significantly less expensive than Rh. Mg, Mn, Ca and K are common promoters for SMR, while using Ni as catalyst. 89 Table 4.2: Carriers Tested and their Properties Name (Code Name) Supplier Den- sitya Dp,avea BJH Pore Volume BET Surface Area g/cm3 µm ml/g m2/g A-16SG α-Al2O3 (A-16) Alcoa, Brenntag Specialties 2.19 0.4 0.05 9.5 Ceralox α-Al2O3 (Ceral) Sasol Alumina 2.2 0.27 0.04 7.8 Baikalox CR125 γ-Al2O3 (CR125) Baikowski 0.15 0.3 0.78 105 Cerium (IV) oxide (CeO2) Alfa Aeser 5 0.007 0.68 Magnesium Aluminate Spinel (MgAl2O4) Atlantic Equipment Engineers 1-5 0.002 0.54 aSupplier Data Promoters are used to increase the pH of the carrier. Acidic sites promote coke formation and polymerization (Twigg, 1997). For Methane Catalytic Combustion (MCC), Pd is known to be the most active catalyst (Lee and Trimm, 1995), and it is also less expensive than Pt, which is also used for MCC. A more affordable alternative CeO2−ZrO2 was also investigated. This has shown some activity for MCC (Bozo et al., 2000). Commercial Catalyst Table 4.4 lists all commercial catalysts tested for coating. RK-212 was received in pellet form and was mechanically crushed and sieved. To obtain particle size “25 µm”, we passed <45 µm powder 3-4 times through a mechanical crusher (Fritsch, Disk Mill PULVERISETTE 13) with a minimum distance between the two crushing disks. Binder In a limited number of experiments, a binder was added to the modified sol. In this work, we used polyethyleneimine, branched (MW = 10,000) from Alfa Aeser. 90 Table 4.3: Metal Precursors Tested Name (Code Name) Supplier Purity Catalyst Precursors Nickel(II) nitrate hexahydrate (Ni Nitr.) Alfa Aesar 98% Ruthenium(III) chloride hydrate (RuCl3) Alfa Aesar 99.9% , Ru 38% min Ruthenium(III) nitrosylnitrate (Ru Nitr.) Alfa Aesar Ru 31.3% min Palladium(II) nitrate hydrate (Pd Nitr.) Alfa Aesar 99.9% Copper(II) nitrate hemi(pentahydrate) (Cu Nitr.) Alfa Aesar 98% Promoter Precursors Calcium nitrate tetrahydrate (Ca Nitr.) Alfa Aesar 99% Magnesium nitrate hexahydrate (Mg Nitr.) Alfa Aesar 98% Potassium nitrate (K Nitr.) Sigma-Aldrich 99%+ Manganese(II) nitrate tetrahydrate (Mn Nitr.) Alfa Aesar 98%+ Zirconium dichloride oxide octahydrate (ZrCl2) Alfa Aesar 99.9% Table 4.4: Commercial Catalysts Tested Names (Code Name) Sup- plier Composition Particle Size BJH Pore Volume BET Surface Area wt% µm ml/g m2/g RK-212 (RK-212) Haldor Topsoe Ni 15%, MgOa 25-30%, K2O 1-2%, CaO 1-4% various sieved size:  25 - <63 0.06 14.3 - 8.3 #11749 Ru 5%/ γ-Al2O3 (Ru 5%) Alfa Aeser Ru ∼5% 1.3 225 #11711 Pd 1%/ γ-Al2O3 (Pd 1%) Alfa Aeser Pd 1 % 0.58 189 #11713 Pd 5%/ γ-Al2O3 (Pd 5%) Alfa Aeser Pd 5 % 0.45 145 aMgO is in the form of MgAl2O4 91 4.3 Method Figure 4.1 shows the various steps and options for all catalyst coatings investigated in this chapter. There were three main stages, with an optional fourth one. First, a metal substrate was sand-blasted to create roughness on the surface, and to give physical support for the catalyst. If Fecralloy was used, calcination could be per- formed to create a layer of aluminum oxide on the surface. The surface had to be cleaned to avoid contamination from dust and grease. The second stage consisted of preparing the modified sol and applying it to the metal substrate. The modified sol was composed of a solvent (usually distilled water), boehmite, a carrier or commercial catalyst, and a small amount of acid to adjust the pH, generally <5-6. Optionally, metal catalyst and promoter precursors were added. The modified sol was ball-milled overnight. The pH usually changed after the ball-milling and was readjusted before coating. We tested four different coating techniques: brushing, dip coating, cold substrate and hot substrate air-spray (also named “cold spray” and “hot spray”) coating. In the third stage, coated plates were first dried at 65oC for 10+ min and then calcined at 650oC overnight. The calcination step transformed boehmite into γ- Al2O3 and the metal precursors into their oxide form. Since our MCMR is expected to operate below 600oC, calcination aims at pre-aging the carrier or catalyst as well. Multi-layer coating could be achieved by repeating stages 2 & 3 as many times as needed. Impregnation of metal catalyst or promoter precursors may be done in an additional (fourth) stage. 4.3.1 Sand-Blasting Sand-blasting was performed inside a specially designed glove box, which includes a compressed air spray gun and a vacuum to extract the dust. The sand used was brown alumina (Manus Abrasives) at various particle sizes: from coarse particles (grit # 4) to finer particles (grit # 80). The air blasting pressure could be varied from 0 to 6.9 barg (100 psig). For most cases, grit # 80 with 3.5 barg (50 psig) blasting pressure, was employed. After the sand-blasting, the plates were manually flattened. 92 1: Substrate Surface Treatment Sand Blasting 2: Modified Sol Coating Drying & Heat Treatment3: Drying & Heat Treatment Metal Substrate Stainless 304, 316, Fecralloy Surface Cleaning (water & soap; NaOH 0.5 M) Brush Cold Spray Hot Spray Modified Sol: • Solvent (e.g. H2O, Methanol) • Boehmite (AlOOH) • Carrier /commercial catalyst • Acid • Optional: Catalyst and /or promoter precursors  (M) Mixing: Ball Milling Dip Option: Fecralloy Calcination Optional: Impregnation 2AlOOH → γAl2O3 + H2O M(HNO3)y→ MO+yNOx+zH2O 4: Optional: Impregnation Step Optional: Multi-layer Coating Impregnation Solutions: • Solvent (e.g. H2O, Ethanol) • Catalyst and /or  promoter precursors (M) Modified Commercial or Lab-made Catalyst Figure 4.1: Initial Catalyst Coating Method 93 4.3.2 Substrate Cleaning Sand-blasting and plate flattening can introduce dust and oily contaminant on the substrate surface. Various methods were tested to remove contaminant, with var- ious cleaning solutions (distilled water, water with detergent, acetone, NaOH so- lution), aided by scouring sponges, gloves, or sonic bath. In this chapter, water with detergent or ∼0.5 M NaOH solution, followed by a distilled water rinse, was generally employed. 4.3.3 Modified Sol Parameters Carrier or commercial catalyst molar concentration (mol/L): This parameter af- fects directly the viscosity of the modified sol. Therefore, the coating thickness obtained with brush or dip coating is a function of this parameter. For commercial catalysts, since the exact content is not always known, the molar concentrations reported below are based on the molecular weight of their carrier. Boehmite content (wt%): Boehmite content plays a role in determining the bond- ing between the carrier or commercial catalyst particles, as well as in the bonding between the particles and metal substrate. We define this parameter as: Boeh. Content= Mass Boehmite Mass Boeh.+Mass Carr. or Comm. Cat. ∗100 [wt%] (4.1) pH: The pH of modified sol was mainly adjusted with nitric acid, before and after ball milling. Some attempts were also made with formic and acetic acid. Unless specified otherwise, pH data reported in figures are taken after the adjustment made after ball milling, using nitric acid. Metal content (wt%): Metal catalyst and promoter precursors can be added di- rectly to the modified sol or later, via impregnation. If added with the sol, their concentrations were adjusted to obtain a specific mass fraction after calcination and/ or reduction. We report in all figures the desired final mass fractions (oxi- dized form for promoters, reduced form for catalysts) rather than precursors metal 94 concentrations. It is assumed that all nitrates, chlorides and hydrates were totally removed after calcination. CeO2/ZrO2 mole ratio: For CeO2-ZrO2 coatings, we used a constant CeO2/ZrO2 mole ratio of 3, based on Bozo et al. (2000). ZrO2 was obtained from ZrCl2, mixed directly into the CeO2 modified sol. Ball Milling The modified sol was ball milled overnight. Alumina balls of different sizes (1/16 to 0.25”(1.58 to 6.35 mm)), represented about half of the modified sol mass, were added to a container used for ball milling, while about a quarter of the container remained empty. Life Time of Modified Sol Modified sol did not age well, and adherence results could differ significantly one week after ball milling. pH tended to increase over time. Cristiani et al. (2005) reported two pathways for acid consumption; surface charging and dissolution: bulk−AlOHsurf+H+→ bulk−AlOH+2 surf (4.2) Al2O3+6H +→ 2Al3++6H2O (4.3) To keep properties constant, it was best to use the modified sol immediately after ball milling. Modified Sol Description in Figure Legends Legend items can be described as follows (Note that some items can be omitted if they have the default value): [Boehmite content, wt%], [Boehmite Code Name (default is P2)], [Carrier Concentration, mol/L], [Carrier code Name], [pH after ball milling and adjustment], [optional items: presence of binder; particle sieved size; acid used (default is nitric acid); solvent (default is distilled water); sonication time, min (default is 15 min)]. To save space, some parameters omitted in the legend are specified in figure captions. 95 4.3.4 Coating Techniques Brush Coating Brush coating was conducted by simply painting the modified sol on the metal substrate using a regular foam brush, available in hardware stores. Thread brushes, and different painting rolls were also tried during screening tests, but results were unsatisfactory, leading to poor coating uniformity. Dip Coating Dip coating consisted of dipping the metal substrate in a beaker filled with modified sol. A lab-made apparatus, consisting in an electric motor with its shaft attached to a string, and a voltage regulator to control the rotational speed, allowed the withdrawal of the dipped sample at constant speed, 0.2 to 8.3 mm/s. Cold Substrate Air-Spray Coating (Cold Spray) Cold spray coating was conducted by spraying the modified sol using an air spray gun (Graco, Delta Spray, model 239-71XEO2A). This spray gun utilizes com- pressed air at ∼1.7 barg (25 psig). The sol was sprayed by quickly sweeping the gun above the substrate. Between each sweep, air was blown over the substrate to evaporate excess water. Hot Substrate Air-Spray Coating (Hot Spray) Hot spray coating consisted of spraying the modified sol with the same technique as for the cold spray, while the metal substrate was heated by a plate heater. The temperature of the heater (>100oC, up to 180oC) was not controlled, but remained above the water boiling point throughout the spraying. Each sweep allowed a very thin layer of catalyst to be coated, while most of the water contained in the modified sol evaporated instantaneously. 96 4.3.5 Impregnation Wet impregnation Wet impregnation consisted in immersing the catalyst plate, containing the metal support, the carrier and previously impregnated metals, into a solution of metal precursor(s). Plates were left in solutions for 2 to 24 h at ambient temperature. Screen tests were also performed at 65oC, but led to excess metal deposition on the carrier surface. Excess liquid was removed by gravity by tilting the plate of a ∼ 80o angle. Drying was performed in stages. First, plates were allowed to air dry for ∼2 h; second, plates were put in a oven at 110-120oC for a time ranging from 4 h to overnight. Dried samples were then calcined at 650oC overnight for 24 h. Impregnation Solutions Parameters The metal M precursors (M Nitr.) concentrations were estimated according to the following equations: [M Nitr.] = xM xcarrυp,carr 1 MwM 1 σM ∗1000∗Corr. [mol/L] (4.4) where xM is the desired metal mass fraction in the catalyst; xcarr is the estimated carrier mass fraction (carr); υcarr is the carrier pore volume; σM is the stoichio- metric molar ratio between the reduced metal and the metal precursor; and Corr. is a correction factor based on Energy-Dispersive X-ray Spectroscopy (EDX) mea- surement or analytical balance of the final metal content. Corr. was usually∼0.75. 4.3.6 Analytical Instruments SEM-EDX Scanning Electron Microscopy (SEM) images were obtained by a Hitachi 2-3000N. Images were taken with an acceleration voltage of 20 kV, at 1.5 x 10−3 Pa. EDX instrument (Advanced Analysis Technologies), used a silicon-lithium X-Ray de- tector, with resolution of 133 eV. The magnification was usually set at 350x while measuring composition with EDX. Samples were Au−Pd sputtered to overcome 97 the electrical insulation of the ceramic material. Surface Area - Pore volume - Pore size A Micromeritic ASAP 2020 analyzer was used with nitrogen to measure the Brunauer, Emmet and Teller (BET) surface area, Barrett, Joyner and Halenda (BJH) desorp- tion average pore size and BJH desorption pore volume. Optical microscope To obtain coating surface images, a Nikon Eclipse MA200 microscope was used, combined with a Nikon DS-Fi1 camera, having a resolution of 2560 x 1920 pixels. 4.3.7 Metrics In this chapter, coating quality was characterized by two variables: the coating adherence and coating thickness. Coating Adherence Coating adherence was determined by the coating resistance to erosion by cavita- tion. We measured the dried mass of the catalyst before and after immersion in a sonic bath (Esma Ultrasonic System E386) during 15 min, and calculated the % mass losses. This technique, also named sonication, was also used by earlier authors (Germani et al., 2007; Stefanescu et al., 2007). In this work, we set the acceptable limit at 20 wt% loss. Each point in plots featuring the “Mass Loss vs Average Thickness” corre- sponds to thickness and adherence measured on one sample. Coating Thickness To measure the coating thickness, a thickness meter was used, Positector 6000- 1 by Defeslko, based on the eddy current principle. The thicknesses reported in this chapter are averages of five measured values on each plate after coating and calcination. Four points are near the corners and one at the center of the plate. The meter is zeroed by taking a reading on a clean and flat plate of the same material. 98 The sand-blasting of the plates induces a “thickness” reading on the meter, which we called “profile noise”. That value was significant, ranging from 20 to ∼100 µm, depending on the roughness achieved by sand-blasting. Is was not obvious what roles the profile noise played on the measured coating thickness, with the effect seeming to depend on the coating technique. We made several conservative estimates to cope with this issue. For all hot spray coating and dip coating samples, we simply subtracted the average profile noise values from the average measured thicknesses. For single layer brush coat- ing, the measured thickness was often smaller than the profile noise. For coatings with similar sol content, and with constant geometric surface area of the plates (length * width), we proceeded as follows. First, we plotted measured thickness versus mass of catalyst. We then performed a linear regression and subtracted the y-axis intercept, ∼20 µm, from the coating thickness reading. With some brush coating samples, we could not find a correlation between the measured thickness and catalyst mass. In those cases, instead of thickness, we plotted the ratio between the mass of catalyst and the geometric surface area of the plates. For multi-layer brush coating, we did the same subtraction as for single layer coating. However, some thickness data were erroneous, with the thickness becom- ing thinner with increasing catalyst mass. We then took the thickness and catalyst mass after coating the final layer, and we estimate proportionally the thickness of previous layers knowing the mass of the catalyst. 4.4 Results and Discussion 4.4.1 Metal Surface Preparation Sand-Blasting The goal of the sand-blasting is to create maximum roughness on the surface of the plate, while keeping it as flat as possible. Larger particle size (lower grit number) and higher blasting pressure result in more surface roughness, but create more stress on, and deformation of the metal plates. By trial and error, we realized that it was not possible to achieve simultaneously the two goals, and all plates had 99 to be manually flattened after blasting. After trial and error, we chose grit # 80, 3.4 barg (50 psig) blasting pressure, and 24 gauge plates. Sand with grit numbers 4 to 56 required higher air pressure, >4.1 barg (60 psig), to flow through the gun, leading to plate deformations that were very difficult to fix manually. Thicker plates (gauges 20 or 22) did not solve the deformation issue, with the plates being much harder to flatten manually. Figure 4.2 shows the metal substrate before and after sand-blasting. From the tilted view (Part C), we estimated the height of the roughness features, as ∼10 µm. The noise profile reading on this plate was ∼80 µm. This confirmed that our subtracting the noise profile from the coating thickness readings was reasonable. For the Fecralloy samples (right-hand side), it can be observed (between Part E and F) that the heat treatment at 1000oC for 10 h reduced the roughness of the alloy surface. In future work, heat treatment could be optimized. For instance, Jia et al. (2007) showed that oxidation at 900oC created on the surface a larger number of alumina whiskers than oxidation at 1000oC. Surface Cleaning Surface cleaning quickly became a significant step in the process. Figure 4.3 shows contamination on the coating, resulting from improper surface cleaning. The clean- ing method evolved slowly during the project. Initially, brushing with tap water with a small amount of soap, followed by a rinse of distilled water was considered sufficient. However, with this method, we regularly had to discard samples because of contamination. We later used a 0.5 M NaOH solution that removed most oily contaminants. However, NaOH solution can affect the anti-corrosion properties of stainless according to electrochemical equilibria diagrams (Pourbaix, 1974). As a final procedure, mostly used in the next chapter, we rinsed the plates with tap water and clean gloves to remove apparent dust, put the plates in a sonic bath with dis- tilled water for 15 min to remove encrusted dust particles, followed by a further 15 min sonic bath with acetone to remove oily contaminants. Plates were then dried at 65oC in a oven before coating. 100 100 µm A B D E 1000 µm 100 µm 50 µm C F 200 µm 200 µm 9 µm 11.5 µm 14 µm Figure 4.2: Sand-Blasting Images. Left side - SEM images of SS 304 plates: A. Before sand-blasting; B. After sand-blasting; C. After sand-blasting, tilted view. Right side - Optical microscope images of Fecralloy: D. Before sand-blasting; E. After sand-blasting; F. After calcination at 1000oC for 10 h, in static air. 101 10 mm Figure 4.3: Surface Cleaning Issue 4.4.2 Brush Coating, Dip Coating and Cold Substrate Air Spray Coating (Cold Spray) Brush coating and dip coating were a limited success, and results are provided in the Appendix A. In summary, brush coating gave good adherence with some modi- fied sol, but insufficient thicknesses. Figure 4.4A displays a SEM image of a brush coating sample. Multi-layers brush coating could eventually solve the thickness requirement, but was overly time-consuming. With dip coating, although some samples showed thickness >80 µm, adherence quality was unsatisfactory. No sat- isfactory results were obtained with cold spray coating. 4.4.3 Hot Substrate Air Spray Coating (Hot Spray) Of all the techniques tested, hot spray coating was the most promising. Figure 4.4, Parts B-F show SEM images of hot spray coatings obtained from various modi- fied sol compositions. One could observe on those images large variations of 3-D surface structures. The following sections present experimental hot spray coating 102 100 µm A (20 µm) D (100 µm)C (56 µm) 300 µm B (20 µm) F (20 µm) 100 µm100 µm 100 µm100 µm E (20 µm) Figure 4.4: SEM Images of Brush Coating and Various Hot Spray Coatings (coating thickness): Brush Coating A. Ni-MgO/ γ-Al2O3; Hot Spray Coating B. γ-Al2O3; C. Ni-MgO/ α-Al2O3; D. Ni-MgO CaO K2O/ γ- Al2O3; E. MgAl2O4; F. RK-212. 103 work conducted over a wide range of conditions. Hot Spray of Carrier Figure 4.5 shows coating results with γ-Al2O3. Many successful coatings achieved thickness>80 µm, almost reaching 240 µm, while a significant number of samples failed the adherence threshold. More samples succeeded in Fig. 4.5B, where γ- Al2O3 concentration was generally lower than the results plotted in Fig. 4.5A. Results were collected over a period of two years, and some conditions might have changed (e.g. operator skills, γ-Al2O3 powder manufacturer lot, hot spray air pressure). Hence, trends must be treated with caution. Nevertheless, we can report some general observations: as seen in part B, lower γ-Al2O3 concentration ∼1 mol/L reduced variability in adherence results; low pH values of 2 were not necessary to make the coating successful; higher value of boehmite content, ≥ 30 wt%, can improve the bonding quality. Some samples in Part A were inserted in the sonic bath for 60 min instead of the regular 15 min time. Three out of four samples were above the threshold quality limit, but samples with the same modified sol content exhibited a significant variations, and their thicknesses were ∼50% smaller. Therefore, it is not possible to identify the effect of sonic bath, but common sense suggests that more time in the sonic bath would result in more mass losses. Figure 4.6 shows how the physical appearance of the γ-Al2O3 coatings change while the thickness of the coatings increase. γ-Al2O3 coatings form clusters that grow in size while the thickness increases. Some thickness measurements were taken before and after the calcination step. The measured thicknesses shrunk on average by 11% and the mass was lower by 3-5%. Similar behaviour was observed with Pd 5%/ γ-Al2O3 coatings (∼10% thickness reduction). Mass and thickness reduction could be the consequence of phase change from boehmite to γ-Al2O3. Thickness standard deviation on the five measurements on each plate was on average 4.4 µm (for 67 plates). The hot spray coating of γ-Al2O3 was the most successful coating pathway covered in this work. For this reason, combined with its valuable high surface area, we selected this coating method to produce our reforming catalyst. In the 104 next chapter, we present work to reduce the variability in coating bonding quality, which has consequences on further impregnation steps. Figure 4.7 shows SEM images from a tilted perspective. Part A shows the com- plex surface structure of a γ-Al2O3 coating, while B.1 and B.2 show the structure of a commercial Pd 5%/ γ-Al2O3. Pd 5% results are discussed in section 4.4.3. Figure 4.8 shows coating results with α-Al2O3, MgAl2O4 and CeO2−ZrO2 as carriers. α-Al2O3 was the only carrier that produced coatings with acceptable bonding quality. However, more tests are needed for coating thickness of∼80 µm. Neither MgAl2O4 nor CeO2−ZrO2 carriers produced coatings with both accept- able thickness and adherence. For α-Al2O3 coating (Part A), observations were similar to those with γ-Al2O3, regarding modified sol parameters: lower carrier concentration, higher boehmite concentration (≥20 wt%) favour adherence, while low pH might not be necessary. Even though results with α-Al2O3 were encouraging, we did not investigate further coatings with α-Al2O3, since results with γ-Al2O3 were considered superior. Particle sizes for MgAl2O4 and CeO2 were most likely too large and might lack surface area for hot spray coating (see Table 4.2). When we tested their physical properties, we found that those powders were not porous, and hence, were not suitable for impregnation. For this reason, we terminated experiments with those two carriers. Hot Spray Including Metal Precursors As shown on Figure 4.1, catalyst and promoter precursors could either be intro- duced directly in the modified sol or by impregnation, after the coating and calci- nation of the carrier. However, in Chapter 6, we show that introducing the metal precursors with the modified sol did not lead to active and stable catalysts. Coating results are presented in Appendix A.5. In brief, most samples failed the adherence quality test. For this poor adherence results, combined with poor activity reason, spray coating, including metal precursors, was not investigated further. 105 lll ll l l l l l l 60 80 100 120 140 160 180 0 20 40 60 80 100 A l l 22−25%, Co, 2.2 mol/L, pH 5 20%, P2, 1.2 mol/L, pH 2 25%, P2, 1.77 mol/L, pH 4.2 25%, P2, 2.3 mol/L, pH 4 25%, P2, 2.3 mol/L, pH 4, 60 min 28%, P2, 1.84 mol/L, pH 4.5 30%, P2, 0.8 mol/L, pH 4 l l l ll l l ll l 0 50 100 150 200 0 20 40 60 80 100 B l l 20%, P2, 1 mol/L, pH 2 20%, P2, 1 mol/L, pH 5 30%, P2, 1 mol/L, pH 2 30%, P2, 1 mol/L, pH 4 40%, P2, 1 mol/L, pH 2 40%, P2, 1 mol/L, pH 5 40%, P2, 1 mol/L, pH 6 (No Acid) Average Coating Thickness (µm) M as s Lo ss  (w t% ) Figure 4.5: Hot Spray Coating of γ-Al2O3 Modified Sol, Mass Loss vs Aver- age Thickness: A. Various sol parameters; B. Constant carrier concen- tration. Line representing the 20% mass loss limit is shown. 106 56 µm 132066-5 A (12 µm) B (56 µm) C.1 (101 µm) D.1 (178 µm) 100 µm 100 µm 30 38 62 C.2 D.2 100 µm 100 µm 300 µm 300 µm 150 150 187 112 Figure 4.6: SEM Images of γ-Al2O3 Coatings of Various Thicknesses (coat- ing thickness). Sol parameters: 25% boeh., 2.3 mol/L, pH 4. 107 100 µm A B.1 (82 µm) 100 µm 100 µm 46 µm B.2 66 µm Figure 4.7: SEM Tilted View Images of Hot Spray Coatings: A. γ-Al2O3; B. Pd 5%/ γ-Al2O3 (coating thickness). 108 ll l 0 20 40 60 80 0 20 40 60 80 100 A: α−Al2O3 l 10%, Co, 5.3 mol/L, A−16,  pH 2 13%, Co, 3.9 mol/L, A−16,  pH 2 5%, P2, 4.2 mol/L, Ceral,  pH 2 10%, P2, 4.2 mol/L, Ceral,  pH 1 10%, P2, 4.2 mol/L, Ceral,  pH 2 20%, P2, 4.2 mol/L, Ceral,  pH 2 30%, P2, 2.7 mol/L, Ceral,  pH 3.8 l l l 20 40 60 80 100 0 20 40 60 80 100 B: MgAl2O4 l 5%, 1.5 mol/L, pH 5 15%, 1.5 mol/L, pH 5 15%, 4.2 mol/L, pH 5 25%, 1.4 mol/L, pH 5 l ll l 0 20 40 60 80 100 0 20 40 60 80 100 C: CeO2−ZrO2 l 10%, 0.4 mol/L, pH 1 25%, 0.4 mol/L, pH 1 25%, 0.8 mol/L, pH 1.3 Average Coating Thickness (µm) M as s Lo ss  (w t% ) Figure 4.8: Hot Spray Coating of α-Al2O3, MgAl2O4 and CeO2−ZrO2 Mod- ified Sol, Mass Loss vs Average Thickness. Line representing the 20% mass loss limit is shown. 109 Hot Spray of Commercial Catalyst Hoping to save time by using ready-to-use catalysts, we also tested various com- mercial catalysts. The reforming catalyst tested were not selected for the MCMR prototype, and the results are presented in the Appendix A.6. In summary, Ru/γ- Al2O3 catalyst showed good results as well. However, Chapter 6 show that nitric acid adversely affects the activity and stability of this catalyst. Coating of RK-212, a Ni-based/ MgAl2O4 catalyst would be possible, but only for sieved particle sizes <25 µm. As mentioned in the introduction, Pd was selected as the combustion catalyst. Figure 4.9 shows results with Pd 1 wt%/ γ-Al2O3 (Part A) and Pd 5 wt%/ γ-Al2O3 (Part B). Results were in general very positive. Both catalysts achieved good results at 15% boehmite, 0.25 mol/L and pH 5. Furthermore, nitric acid did not adversely affect on the catalyst stability and activity, as shown in Chapter 7. Hence, this modified sol composition was selected for the MCMR prototype. Temperature Cycles The MCMR could go through a series of temperature cycles throughout the life of the catalyst. Resistance to temperature cycles was investigated with γ-Al2O3 coating, and results are reported in Figure 4.10. After two and three temperature cycles, all adherence tests were excellent, with <10% mass losses. Those results suggested, for catalysts using γ-Al2O3 as carrier, that temperature cycles would not be a major issue with respect to coating adherence. 4.4.4 Thickness Verification Some attempts were made to confirm the thickness meter measurements with SEM images. Figure 4.11 shows SEM images of two commercial Ru 5%/ γ-Al2O3 coat- ings. Part A shows one edge of the plate, after polishing. The thickness at the edge was smaller than the measured average thickness at 90 µm. One could ex- pect that the edge value would be below the average one. Therefore, the thickness measurement could not be confirmed with this image. Part B is a cross-sectioned view, near the middle of plate. To obtain this im- age, the sample was covered with epoxy, and then cut with a metal saw. The highly 110 ll l l l 20 40 60 80 100 0 20 40 60 80 100 A: Pd 1 wt% l 5%, 0.14 mol/L, pH 5 5%, 0.26 mol/L, pH 5 5%, 0.53 mol/L, pH 5 15%, 0.25 mol/L, pH 5 15%, 0.39 mol/L, pH 4.3 25%, 0.15 mol/L, pH 5 25%, 0.26 mol/L, pH 4.5 l l l l ll l 40 60 80 100 140 0 20 40 60 80 100 B: Pd 5 wt% l 15%, 0.25 mol/L, pH 5 25%, 0.25 mol/L, pH 5.7 Average Coating Thickness (µm) M as s Lo ss  (w t% ) Figure 4.9: Hot Spray Coating of Commercial Pd/γ-Al2O3 Catalysts, Mass Loss vs Average Thickness: A. Pd 1wt%; B. Pd 5 wt%. Line represent- ing the 20% mass loss limit is shown. 111 ll l 95 100 105 110 0 10 20 30 40 l 1 Cycle 2 Cycles 3 Cycles Average Coating Thickness (µm) M as s Lo ss  (w t% ) Figure 4.10: Temperature Cycles of Hot Spray Coatings with γ-Al2O3 Modi- fied Sol, Mass Loss vs Average Thickness. Sol parameters: 40% boeh. P2, 1 mol/L, pH 5 (no acid); Temperature cycle: Ambient to 650oC in ∼2 h, hold at 650oC overnight, cool to ambient in ∼4 h. Line repre- senting the 20% mass loss limit is shown. porous nature of the γ-Al2O3 support made the epoxy unstable under the SEM vac- uum. As seen on the right-hand side, the epoxy covered the catalyst layer. Also, it appears that cutting the catalyst plate damaged the catalyst layer, and chunks of stainless steel can be seen mixed with the catalyst. Nevertheless, coating thick- nesses measured on the image (114 µm) are close to the average thickness obtained with the meter (120 µm) (after profile noise subtraction). 112 50 µm 57 µm A (90 µm) 100 µm 114 µm B (120 µm) Figure 4.11: SEM Images of Tilted and Side View of Hot Spray Coating of Commercial Ru 5%/ γ-Al2O3: A. Tilted view of one coating edge; B. Cross-section view of catalyst coating in epoxy cast. 113 4.4.5 Impregnation Impregnation can be used to insert promoter and catalyst precursors in subsequent step(s) after carrier coating and calcination. In this section we report preliminary results. Impregnation issue Many issues that occurred during impregnation are presented on Figure 4.12. Cracks: Cracks often occurred during the impregnation. Fig. 4.12A shows a case where a serious network of cracks developed during the process. The solvent added significant stress on the coating. Reducing the number of cracks, that can lead to catalyst delamination, is a key subject of the next chapter. Metal precursor solubility: Some metal precursors may not be soluble in the cho- sen solvent. This problem occurred with Pd nitrate that forms PdO in contact with water. In Fig. 4.12B, PdO crystals can be seen on the surface of the γ-Al2O3 coat- ing. Carrier unwanted solubility: In Fig. 4.12C, it can be observed that ethanol sol- vent dissolved the γ-Al2O3 carrier on the edges of the plate. Drying restored the white appearance of the alumina. We were concerned that the pore structure of the γ-Al2O3 coating could be affected by dissolution. Since we did not have this issue with water, we did not study this potential problem further. Metal precursor corrosion on metal support: Figs. 4.12D, E & F are related to the same issue. We believe that chloride anions in RuCl3 were corroding the stainless 304 support, causing delamination of the catalyst. EDX analysis showed chlorine content up to 8% still present in the catalyst after heat treatment, indicating the difficulty of eliminating this element. In Fig. 4.12E, corrosion is clearly visible on the right side of the metal plate. The corrosion could disturb the bonding between the alumina and stainless. Part F shows an optical microscope image of the coating section not lifted in Part D; large cracks are seen. This issue made us switch to 114 RuNO(NO3)3 as Ru precursor. Coating results for it are presented in the next chapter. The delamination due to corrosion gave us some insight about the bonding be- tween the alumina and stainless steel. Mechanical adhesion with the sand-blasting is not sufficient. Hydrogen bonds and weak electrostatic interaction, (Van der Waals forces) could be disturbed by the iron oxidation. Adherence Testing Figure 4.13 shows thicknesses and mass losses with various impregnation solutions on γ-Al2O3 coatings. Table 4.5 presents the impregnation solution concentrations. Samples with “Sol B” coating, containing 40% boehmite generally performed bet- ter than “sol A”, containing only 30% boehmite. Impregnation time did not show a clear winner, but tests with copper indicated that shorter impregnation times better preserve the coating adherence. In the next chapter, we consider causes of coating failures during the impregnation process in greater detail. Table 4.5: Impregnation Solutions for Figure 4.13 Code Name Desired Metal Content Solution Concentration wt% mol/L Ni-Mg Ca K Ni 7.9% MgO 1.5% CaO 1.5% K2O 1.5% Ni Nitr 1.2; Mg Nitr 0.6; Ca Nitr 0.35; K Nitr 0.32. Mg MgO 3% Mg Nitr 1.1 Cu CuO 2% Cu Nitr 0.15 115 100 µm A B D E 10 mm 10 mm 100 µm C F 100 µm Figure 4.12: Impregnation Issues: A. SEM image of Cu Nitrate on brush coated α-Al2O3; B. SEM image of Pd Nitrate on γ-Al2O3; C. Opti- cal image of γ-Al2O3, using ethanol as solvent for impregnation; D. Ru (from RuCl3)/ γ-Al2O3 ∼3 days after calcination; E. Ru (from RuCl3)/ γ-Al2O3 ∼1 week after calcination; F. Optical microscope image of coating section not lifted in D. 116 ll l l l 40 50 60 70 80 90 100 110 0 20 40 60 80 100 l l Sol A, Ni−Mg Ca K, 2 h Sol A, Cu, 2 h Sol B, Ni −Mg Ca K, 2 h Sol B, Mg, 2 h Sol A, Ni−Mg Ca K, 24 h Sol A, Cu, 24 h Sol B, Ni −Mg Ca K, 24 h Average Coating Thickness (µm) M as s Lo ss  (w t% ) Figure 4.13: Wet Impregnation on γ-Al2O3 Support Made by Hot Spray Coating, Mass Loss vs Average Thickness. Modified Sol parameters: Sol A. 25% boeh., 2.3 mol/L, pH 4; Sol B. 40% boeh, 1 mol/L, pH 5 (no acid); See Table 4.5 for impregnation solutions. After impregna- tion, samples were dried at 65oC for 10+ min, and calcined at 650oC for 24h. Line representing the 20% mass loss limit is shown. 4.5 Conclusions The work reported in this chapter sought a method to coat SMR and MCC cata- lysts on metal supports. To be successful, the coatings needed good adherence, measured by sonication, and a coating layer thickness >80 µm. Among the coating techniques tested, hot spray coating was the most promis- 117 ing. With modified sol containing γ-Al2O3, thicknesses up to 240 µm were ob- tained, while adherence results were well below the 20% mass losses limit. The coating thickness had a strong effect on the surface structure, with clusters grow- ing along with the thickness. γ-Al2O3 coating resisted heat cycles well, making it a strong candidate for the MCMR. Hot spray coating with α-Al2O3 gave encouraging results, but more tests are needed with thickness ≥80 µm. Coating with other carriers, CeO2 and MgAl2O4, did not lead to satisfactory results, likely because of the larger particle size and poor surface area. Introducing promoter and catalyst precursors with the modified sol did not give successful coatings. Hot spray coating of commercial catalysts with γ-Al2O3 as carrier were suc- cessful. Pd/ γ-Al2O3 coatings were successful enough to be selected as the com- bustion catalyst for our MCMR prototype. Ru/ γ-Al2O3 catalyst also showed good results as well. Coating of RK-212, a Ni-based/ MgAl2O4 catalyst would be pos- sible, but only for sieved particle sizes <25 µm. Some observations were made also on the modified sol parameters. Water plays an essential role in the bonding process, switching solvent to methanol has an adverse effect. Acid addition is essential to most coating adherence. However, the pH requirement varies according to the carrier or commercial catalyst. pH is varied in modified sol, indicating that the carrier or metals consumed acid. Therefore, the modified sol should be utilized as soon as possible after ball milling. Boehmite content has a strong influence on the adherence. The optimal content is a function of the type of carrier. Impregnation of the promoter and/or catalyst precursors led to many chal- lenges, especially formation of cracks and corrosion of the metal support, leading to delamination. Thickness measurements with eddy current probes were affected by roughness on the metal surface. The measured “noise profile” should be subtracted from the thickness measurements. Finally, proper cleaning is essential to avoid contamination. 118 Chapter 5 Catalyst Coating: Final Method Development 5.1 Introduction In Chapter 4, we obtained thick coating layers (>80 µm) with good adherence un- der sonication using γ-Al2O3 powder and Pd/γ-Al2O3 commercial catalyst. Start- ing with γ-Al2O3 as carrier for the reforming catalyst, promoters and metal catalyst still need to be impregnated. Preliminary testing in Chapter 4 indicated that cracks and delamination often occurred during impregnation. The sonication method to test catalyst adherence in the previous chapter destroyed the samples. As we moved towards the MCMR prototype and considering the time required to produce a fully- functional catalyst (2-3 weeks), a non-destructive method was needed to assess adherence. Most methods to measure adherence are destructive, e.g. the scratch test, pull- off test and tape test (Chalker et al., 1991). This chapter explores a proxy for ad- herence measurement: counting the number of cracks with an optical microscope. This is a simplification of the “Crack density function” method (Berndt and Lin, 1993), which incorporated both the number of cracks and their size. Chapter 4 focused on finding a method to coat a thick catalyst layer with good adherence. With information from catalyst stability testing in a packed bed micro- reactor (Chapter 6) and preliminary testing with the MCMR prototype (Chapter 119 8), it became clear that coating and catalyst activity testing needed be performed simultaneously. This avoided active catalysts that cannot be coated or catalyst coatings that are not active. 5.2 Material and Method 5.2.1 Metal Substrate Experiments were conducted on various steel plates: austenitic SS 304, no. 4 finish, gauge 24 (0.635 mm); SS 310, gauge 24 (0.635 mm); and Fecralloy 0.5 mm thick (from GoodFellow). Some plates were sheer cut to 39.5 mm x 39.5 mm. Plates intended for the MCMR were water jet cut to 50.55 mm x 89.15 mm (1.990” x 3.510”), with rounded corners, radius 9.525 mm (0.375”), see Appendix E.4. 5.2.2 Final Coating Method Figure 5.1 shows the various steps for coating commercial or lab-made catalyst. There were three main stages for commercial catalyst and four additional stages for lab-made catalyst. First, a metal substrate was sand-blasted with brown alu- mina, grit #80, using compressed air at 3.5 barg. For Fecralloy, calcination was performed at 1000oC for 10 h in static air to create an alumina oxide surface layer. The plate was then manually flattened, then cleaned in two steps: first the plate was immersed for 15 min in a sonic bath containing acetone, followed by a second 15 min bath containing deionised water. The second stage consisted of preparing the modified sol and applying it to the metal substrate. The modified sol was comprised of distilled water, boehmite Disperal P2 (Sasol), and Baikalox CR125 γ-Al2O3 powder (Baikowski), or com- mercial catalyst (Pd 1%, Pd 5%/ γ-Al2O3, Alfa Aeser). The properties of boehmite, carrier, and commercial catalysts are listed in Tables 4.1, 4.2 and 4.4. Nitric acid was added to adjust the pH to∼5 before and after overnight ball-milling. Table 5.1 lists the modified sol parameters employed in this chapter. Hot substrate air spray coating (hot spray) was used throughout, with the technique explained in Section 4.3.4. Depending on the carrier or commercial catalyst concentrations, the time re- 120 A: Substrate Surface Treatment Sand Blasting Brown Alumina Grit no. 80 Air Pressure: 3.5 barg (50 psig) B: Modified Sol Coating Calcination 650oC Overnight in Static Air C: Heat Treatment I 2AlOOH → γAl2O3 + H2O Metal Substrate Stainless 304, 310, 24 gauge Fecralloy, 0.5 mm thickness Surface Cleaning Acetone , water in Sonic Bath Hot Spray Air Pressure: 1.7 barg (25 psig) Hot Plate Temperature: 100-180oC Modified Sol: • H2O • Boehmite (AlOOH) Disperal P2 • Commercial Catalyst, or γ-Al2O3 • Nitric Acid, pH ~ 5 Ball Milling (overnight) Modified Commercial Catalyst Option: Fecralloy Calcination Static Air, 1000oC, 10 hr Impregnation 2 min, Ambient Temp. D: Impregnation I Lab-made Catalyst E: Heat  & Steaming Treatment II γAl2O3 Pores Aging M(HNO3)y→ MO+yNOx+zH2O Promoter Solution: • Solvent: H2O • Precursors  (e.g. Lanthanum Nitrate) Drying 2 h Ambient; 110-120oC Overnight & Steaming 575oC, 24 barg,  24 h F: Impregnation II Impregnation 2 min, Ambient Temp. G: Heat Treatment III e.g. RuNO(HNO3)3 → Ru+4NOx+H2O Drying 2 h Ambient; 110-120oC Overnight & Reduction (in situ) 550oC, 1 bar, H2 & N2 Or Calcination Catalyst Solution: • Solvent: H2O • Precursor  (e.g. Ru Nitrosyl Nitrate) Figure 5.1: Final Method for Coating Commercial and Lab-made Catalysts 121 Table 5.1: Modified Sol Parameters Coating Boehmite Contenta Carrier Concentrationb pH wt% mol/L γ-Al2O3 40 0.5-0.75-1 ∼5 Pd 1% 15 0.25 ∼5.5 Pd 5% 15 0.25 ∼5.5 aSee Eq. (4.1) bBased on the molecular weight of γ-Al2O3 quired to coat one plate varied significantly. At 1 mol/L, it took ∼20-30 min per reactor plate to reach 200 µm, whereas at 0.25 mol/L it could require >60 min per plate to reach the same thickness. In the third stage and first heat treatment, coated plates were first dried at 65oC for 10+ min and then calcined at 650oC overnight. This concluded the procedure for commercial catalyst. For lab-made catalyst, a modified incipient wetness impregnation method for promoter precursors was performed as follows: (1) Metal precursor(s) solution was added dropwise to the top of the coated plate, until it was saturated and a liquid layer formed above the coating surface. (2) After 2 min soaking at room temperature and gentle shaking, excess liquid was removed by tilting the plate at an angle of ∼ 80o for ∼5 min. Drying was performed in stages. First, plates were air-dried for ∼2 h; second, plates were held in an oven at 110-120oC overnight. Tables 5.2 and 5.3 list precursors employed and solution concentrations. For the second heat treatment, catalyst plates were inserted into the reforming channel of the MCMR prototype (as described in Chapter 8). Plates were steamed for 24 h at∼24 bar and 575oC. The sample was then impregnated with the catalyst precursor solution, following the same incipient wetness procedure as described above. Final heat treatment for the reduction of the reforming catalyst was generally performed in-situ, i.e. during the MCMR start-up procedure, with a mixture of N2 and H2 gases. The start-up procedure is explained in detail in Chapter 8. Combus- tion Pd-based catalyst was calcined at 600oC in static air for 5.5 h. 122 Table 5.2: Metal Precursors; Supplier was Alfa Aesar in all cases Name (Code Name) Purity Catalyst Precursors Ruthenium(III) nitrosyl nitrate, Ru 31.3% min (RuNO(NO3)3) - Palladium(II) nitrate, solution, Pd 4-5 wt% (Pd(NO3)2 Sol.) - Promoter Precursors Magnesium nitrate hexahydrate (Mg(NO3)2) 98% Manganese(II) nitrate tetrahydrate (Mn(NO3)2) 98%+ Lanthanum(III) nitrate hexahydrate (La(NO3)3) 99.9% Table 5.3: Compositions of Impregnation Solutions Desired Metal Contenta Solution Concentrationb wt% mol/L Promoters La2O3 6% La Nitr. 0.27 La2O3 4% MgO 4% La Nitr. 0.18; Mg Nitr. 0.72 La2O3 4% MgO 2% MnO 2% La Nitr. 0.18; Mg Nitr. 0.36; Mn Nitr. 0.28 Catalyst Ru 6% Ru Nitr. 0.51 Pd 5% Pd Nitr. Sol. (as received) aMeasured Metal Content can vary by ± 2% bSolution concentrations determined with the help of Eq. (4.4) 5.2.3 Analytical Equipment Optical microscope Optical images were taken with a Nikon Eclipse MA200 microscope, combined with a Nikon DS-Fi1 camera, having a resolution of 2560 x 1920 pixels. TGA Thermo Gravimetric Analysis (TGA) was performed with a TGA-50 from Shi- madzu. About 20 mg of powder were deposited in a ceramic crucible. Under a 123 N2 flow of ∼60 ml/min, from ambient conditions, the temperature was raised to 110oC at 20oC/min and held for 30 min. At a rate of 10oC/min, the temperature was then elevated to 800oC and held for 30 min. 5.2.4 Metrics Crack density As a proxy to measure coating adherence without destroying the sample, we define a crack density as follows: the number of cracks are counted at five locations on plates using optical microscope images at a magnification of 10X, corresponding to an area of 1.9 mm2 per location, or 9.5 mm2 in total. Four images were taken near the plate corners, and one at the middle. At each location, the number of cracks was counted up to 10. Beyond 10, cracks tended to intersect with each others to form a network, making counting difficult. The five counts were averaged to obtain a “crack density”. Any sample with one or more “10” reading was automatically given an overall “10” (failed) as a final value, regardless of the actual average. This method is a simplification of the “Crack density function” method (Berndt and Lin, 1993), which incorporates both the number of cracks and their size. The crack density test has the advantage of not destroying the sample. We recognize that it gives information which differs from the sonication test, and therefore may be an imperfect replacement. Coating Thickness To measure the coating thickness, a Positector 6000-1 thickness meter, by Defes- lko, based on the eddy current principle, was employed. The thicknesses reported in this chapter are averages of five measured values on each plate after coating and calcination. Four points were taken near the corners and one at the center of the plate. The meter was zeroed by taking a reading on a clean flat plate of the same material. Sand-blasting of the plates induces a “thickness” reading on the meter, which we call “profile noise”. The average profile noise was simply sub- tracted from the average measured thicknesses. For samples where Fecralloy was the support, the thickness meter could not measure thickness, due to the magnetic 124 property of the alloy. In that case the thicknesses were estimated from the mass of the catalysts, with the same modified sol composition (see Appendix A.7). 5.3 Results and Discussion 5.3.1 Carbon Deposition during Steaming Pre-aging of the carrier by steaming resulted in some carbon deposition challenges. Figure 5.2 shows coated plates after steaming. Carbon is readily visible on Part A.1 and could be removed by calcination at 650oC as shown in Part A.2, although some carbon remained. Part B.1 shows the effect of adding La2O3, which effectively suppresses carbon deposition. The carbon likely originated from the Grafoil™ gasket used in the MCMR prototype. Another potential source could be the silicone used in the early plate assembly procedure. Steaming and reactor assembly procedures were therefore modified to avoid carbon deposition: (1) Continuous N2 flow was applied during start-up and shut down to flush any deposited carbon from the Grafoil gasket; and (2) Silicone was only used on the gasket and outside the reforming channel. 5.3.2 Surface Cracks The impregnation of Ru after steaming was unsuccessful at first. On the first at- tempt, five of ten plates showed severe coating delamination, as shown in Figure 5.3 Part A. Numerous cracks could also be observed through the microscope on the section of the coating that did not delaminate (Part B). Furthermore, some coating plates, that did not delaminate during the impregnation process, lost material dur- ing the MCMR run (Part C). As the coating method was getting longer, with the addition of steaming and impregnation stages, a non-destructive method was needed to measure coating ad- herence, as an alternative to sonication. We then measured crack density, as de- scribed above. 125 50 mm 50 mm A.1 B.1 50 mm 200 µm A.2 B.2 Figure 5.2: Carbon Deposition during Steaming: (A.1) γ-Al2O3 after steam- ing; (A.2) After calcination of plates in (A.1); (B.1) La2O3 5%/ γ-Al2O3 after steaming (top left plate does not have La2O3); (B.2) Optical mi- croscope image of γ-Al2O3 plate after steaming. Crack Density Test Verification Figure 5.4 compares average crack densities with mass losses after sonication for a γ-Al2O3 coating. Crack densities and sonication show consistency. The plate with the maximum crack density value of 10 lost nearly 50% of its mass under sonication, while a low crack density of 2.3 led to a mass loss of only 5% . Source of Crack Formation Several assumptions could be made to explain crack formation. In fact, cracks could occur at every step of the coating process. Early assumptions were that boehmite phase change, or combustion of ni- trate compounds during calcination, could be the origin of the cracks. Figure 5.5 shows TGA plots for boehmite, boehmite with Pd 5%/ γ-Al2O3 powder, and 126 CA B 10 mm10 mm 100 µm Figure 5.3: Delamination and Cracking Issues after Steaming and Impregna- tion with RuNO(NO3)3 on γ-Al2O3: (A) Catalyst delamination during impregnation step; (B) Microscope image after impregnation and dry- ing; (C) Catalyst delamination after two MCMR runs. 127 A B C(5 wt% / 2.3) (14 wt% / 6.3) (47 wt% / 10) Figure 5.4: Comparison of Sonication Test and Crack Test: Images show corresponding plates after coating material removal due to sonication. Numbers give (mass loss wt% / average crack density). RuNO(NO3)3−La2O3 8%/ γ-Al2O3. This plot indicates that boehmite changes phase at ∼400oC and that RuNO(NO3)3 decomposed at ∼250oC. The Pd 5%/ γ- Al2O3 plot has two peaks, the second one corresponding to boehmite phase change. The origin of the first is not clear. The nitric acid in the modified sol might gener- ate compounds that decompose at ∼250oC. As demonstrated below, phase change and nitrate removal were not found to be critical in crack formation, and the heat treatment procedures were therefore not changed. Figure 5.6 gives the first hint on the source of crack formation. Cracks, as in Part A, were less likely to occur when clusters were abundant, as in Part B. Some clusters could be removed by simply rubbing the coating surface with ones fingers (Part C). However, even with this apparent weakness, samples could keep their material throughout the coating process and MCMR runs. Figure 5.7 gives a second hint on the source of cracks. The white lines on Part A are weak spots that may lead to future cracks, as shown in Part B. Those white lines were generally observed after the first calcination step of the γ-Al2O3 coating. These white lines could lead to water infiltration during impregnation, 128 100 200 300 400 500 600 700 800 −0.0025 −0.0020 −0.0015 −0.0010 −0.0005 0.0000 l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l P2 boeh. Pd 5%/γ−Al2O3 with 15% boeh. RuNO(NO3)3 8% La2O3/γ−Al2O3 Temperature (°C) M as s Lo ss es  R at e (m g/s ) Figure 5.5: TGA analyses of boehmite, Pd 5%/ γ-Al2O3 with 15% boehmite, and RuNO(NO3)3−La2O3/ γ-Al2O3. Lines are smoothed. creating stress on the coating that could lead to cracks and delamination. With the experience gained throughout several hot spray coatings, it was real- ized that cluster formation and white line avoidance were linked to water evapo- ration during the coating. Aside from compressed air pressure, no other hot spray coating parameters were quantified or controlled. However, it was observed qual- itatively that to avoid cracks, water must evaporate instantly while spraying the modified sol. With our equipment for spray coating, best practices include: (1) To 129 200 µm A C B Figure 5.6: Cracks versus Cluster Formation during Hot Spraying of γ- Al2O3: (A) Large cracks visible with few clusters; (B) No cracks vis- ible with many clusters; (C) No cracks visible, with clusters manually removed. 130 A B 100 µm 200 µm Figure 5.7: Presence of White Lines on γ-Al2O3 Coating after Calcination: (A) Several white lines visible, with arrows pointing at some of them; (B) White line becomes a regular crack. avoid large droplets of modified sol reaching the plate, it is best to avoid pointing the spray gun directly at plates at the start of a sweep. (2) The modified sol mist should be adjusted to reach the plate perpendicularly. (3) The mist flow rate needs to be adjusted to see no changes in colour on the plate; and (4) Plates should be rotated periodically to improve coating uniformity, while pausing to ensure that the plate temperature always exceeds the water boiling point. Crack Density Measurements Table 5.4 presents crack density results for lab-made catalyst coatings at various stages of the coating method and catalyst life in chronological order. As more insight about the source of cracks and how to avoid them was obtained, fewer measurements were required. The first column shows that cracks can appear after the first calcination step. The second column indicates that lowering the carrier concentration of the modi- 131 Table 5.4: Average Crack Density for Ru- and Pd-based Lab-made Catalysts: Unbracketed numbers on a scale of 0-10 give average number of cracks counted on an area of 9.5 mm2. Bracketed numbers are numbers of plates tested. Plates with crack density >2 were generally discarded before they reached the next coating step. Carrier concentration in modified sol is 0.5 mol/L, except where indicated. Catalyst compositions are approximate. Step Ru 5% (0.75 mol/La) Ru 5% Ru 5% - La2O3 6% Ru 5% - La2O3 6% on Fecralloy, Evap. Monit.b Ru 5% - or Pd 5% - La2O3 6% on SS 310, Evap. Monit. Before γ-Al2O3 Calcination 0.06 (8) 0.00 (5) - (-) - (-) - (-) After γ-Al2O3 Calcination 3.38 (38) 0.03 (32) - (-) 0.00 (2) 0.00 (2) After Promoter Impregn. & Drying 1.73 (3) N/A - (-) - (-) - (-) After Steaming 1.18 (16) 0.63 (6) 0.15 (25) 0.00 (3) 0.00 (4) After Catalyst Impregn. & Drying 6 (11) 5.88 (5) 1.20 (13) 0.00 (1) 0.00 (1) After MCMR Run 5.52 (5) - (-) - (-) 0.00 (2) 0.00 (3) aCarrier concentration in modified sol bEvap. Monit.: water evaporation rate during spraying was monitored fied sol eliminated cracks after the first calcination, but did not guarantee adherence after Ru impregnation. In the third column, La2O3 was added as promoter. Results suggested that La2O3 helps maintain coating integrity throughout the steaming and Ru impregnation stages. However, improving operator coating skills, might have also played a role. In the last two columns, the evaporation rate of water during the hot spray coating was monitored, as explained above. We had essentially elim- inated crack formation at this point. The learnings gained from the lab-made catalyst coating to the commercial Pd 132 Table 5.5: Crack Density Results for Pd Commercial Catalyst Coatings: Scale 0-10. Bracketed numbers are numbers of plates tested. Pd 1 wt% on SS 304 Pd 5 wt% on SS 304 Pd 5 wt% on SS 310 and Fecralloy Before Calcination - (-) 0.00 (6) - (-) After Calcination 0.00 (3) 0.03 (6) 0.00 (2) After MCMR Run - (-) 0.00 (4) 0.00 (2) 5% coating were applied, with the powder concentration kept low in the modified sol at 0.25 mol/L, and the water evaporation rate observed carefully. Table 5.5 shows that cracks were then avoided throughout the coating process and MCMR experiments. If the hot spray coating is performed correctly, it is not expected that the support material (SS 304, SS 310 or Fecralloy) will significantly affect coating adherence. 5.3.3 Rust Figure 5.8 shows plates, with various coating composition, all with visible rust stains. We paid attention to this issue after it was suspected that rust was inhibiting the Ru-based catalyst, as shown in Chapter 6. However, there was no evidence that rust affected the Pd-based combustion catalyst. The presence of rust or iron oxide was first observed after an unsuccessful MCMR run with RK-212 (Part A). The iron presence was confirmed with EDX measurement. Rust appeared at different rates. The SMR environment accelerated the ap- pearance of rust. Rust was observed immediately after the MCMR run (Parts A & B.1). The rust occurred at a much slower rate for plates that went no further than steaming (see Figure 5.1). Plates in Part C.1 displayed little or no rust stains immediately after steaming. However, after 8 months, as can be seen on the image, iron oxide had diffused slowly through the coating layer and reached the surface. Combustion catalyst plates (Part D) were also affected by rust, but less so and at a slower rate than the reforming ones. Scratching catalyst off the plates revealed rust stains on the metal support itself (Part B.2 & C.2), confirming that the rust came 133 from the support (SS 304), from outside contamination. γ-Al2O3 coating plates that were not subjected to steaming were not affected by rust, even though they were experienced to 650oC calcination. However, RK- 212 plates encountered rust formation without experiencing steaming or the SMR environment. Therefore, we speculate that the presence of steam might be needed to trigger rust diffusion through γ-Al2O3, whereas only time is needed to see rust if other metal elements are present. To stop the diffusion of iron oxide, two alternative steel alloys, SS 310 and Fecralloy, were tested. Fecralloy was calcined prior to coating as explained above. We did not see any corrosion issues with Fecralloy throughout the coating and utilization process, but a small amount of stains started being visible on SS 310 a few weeks after the steaming step. Therefore, we selected Fecralloy as support for the reforming catlayst. Since Pd-based catalyst was not as strongly affected by rust, SS 310 was used in the combustion channel of the MCMR. 5.3.4 Successful Coating Samples Figure 5.9 shows images of lab-made Ru-based catalyst on SS 304 support. Figure 5.10 presents commercial Pd-based catalyst on SS 304. Some carbon deposition was often observed on the combustion catalyst surface after the MCMR run. This carbon could be removed by calcination at 650oC. The source of the carbon was likely Grafoil gasket decomposition during start-up and shutdown. The procedure was eventually changed to ensure continuous air flow through the channel to flush away any carbon. Figures 5.11 and 5.12 show images of lab-made and commercial catalyst on Fecralloy and SS 310. As discussed in Chapter 4, Figure 4.2, the Fecralloy surface, contains visible linear furrows, likely from the rolling manufacture process. These furrows influence the position of the clusters, as seen in Figure 5.11 Part A. 134 20 mm A B.1 B.2 C.2 20 mm 5 mm C.1 D E 100 µm 20 mm 20 mm 5 mm Figure 5.8: Rust on Catalyst with SS 304 as Metal Support: (A) RK-212 (Ni/ MgAl2O4) spent (∼2 days after run) ; (B.1) Ru 6%/ γ-Al2O3 spent (∼2 days after run); (B.2) Close-up on (B.1) after catalyst partially scratched off; (C.1) La2O3 6%/ γ-Al2O3 (8 months after coating); (C.2) Close-up on (C.1) after catalyst partially scratched off; (D) Pd 1%/ γ-Al2O3 spent (8 months after run); (E) γ-Al2O3 on optical microscope (3 months after steaming). 135 a A  (155 µm) B.1  (153 µm) B.2 B.3  (147 µm) B.4  C (187 µm) Figure 5.9: Ru-based Catalyst on SS 304 Support at Various Stages of Coat- ing and Catalyst Life (coating thickness): (A) γ-Al2O3 before calcina- tion; (B.1) γ-Al2O3 after calcination; (B.2) After La- Mg- Mn- nitrates impregnation & drying; (B.3) After steaming; (B.4) After RuNO(NO3)2 impregnation & drying; (C) After MCMR run. ((A) & (C) images are from different plates than (B’s) but shared the same coating method and modified sol parameters: 0.5 mol/L, 40 wt% boeh., pH 5.) 136 A.1  (199 µm) A.2 B.1  (180µm) B. 2 C  (162 µm) D  (196 µm) E  (166 µm) Figure 5.10: Commercial Pd-based/ γ-Al2O3 Catalysts on SS 304 Support at Various Stages of Coating and Catalyst Life (coating thickness): (A.1) Pd 5% before calcination; (A.2) After calcination; (B.1) & (B.2) Pd 5% After MCMR run; (C) Pd 5% after run and regeneration (calcination at 650oC); (D) Pd 1% after calcination; (E) Pd 1% after MCMR run. 137 A  (198* µm) D.1 (217 µm) B  (202* µm) D.2 500 µm 200 µm C  (202* µm) E (200 µm) Figure 5.11: Ru- and Pd-based/ γ-Al2O3 Catalysts on Fecralloy (left side) and SS 310 (right side) at Various Stages of Coating and Catalyst Life (coating thickness): (A) γ-Al2O3 after calcination; (B) Ru 8% La2O3 3% MnO 2% MgO 2% after Ru impregnation & drying; (C) Pd 5.6% La2O3 6% after MCMR run; (D.1) Ru 7% La2O3 6% after Ru im- pregnation & drying; (D.2) Sample (D.1) After MCMR run; (E) Pd 5.3% La2O3 4% MgO 4% after MCMR run. (* Estimated, see Coating Thickness Section) 138 A.1  (200* µm) B.1  (195 µm) A.2 B.2 Figure 5.12: Commercial Pd 5%/ γ-Al2O3 Catalysts on Fecralloy (left side) and SS 310 (right side) before and after MCMR run (coating thick- ness): Top Row: After Calcination and before MCMR run; Bottom Row: After MCMR run. (* Estimated, see Coating Thickness Section) 5.4 Conclusions This Chapter describes a successful coating method for reforming and combustion catalysts, lab-made or commercial, on various metal supports. A crack density test provided a non-destructive method to evaluate coating adherence, with results consistent with the sonication test. Crack formation and coating delamination dur- ing impregnation were linked to the presence of white lines, precursors to cracks, on the coating surface, and to the absence of clusters. Cracks could be avoided by lowering carrier or commercial catalyst concentration in the modified sol, and 139 by monitoring the rate of water evaporation during hot spray coating. Water must evaporate instantly while spraying the modified sol. La2O3 was an effective pro- moter to avoid carbon deposition during steaming. Rust appeared on most coatings on SS 304 as support. Rust diffusion could be reduced by using SS 310, and ar- rested completely by using Fecralloy as the metal support. 140 Chapter 6 Reforming Catalyst Activity and Stability 6.1 Introduction Steam Methane Reforming (SMR) is traditionally performed with Ni-based cat- alysts (Twigg, 1997). Nickel has the advantage of being relatively inexpensive compared to more active noble metals. However, as shown in Chapter 3, the multi- channel reactor configuration, compared with a packed bed reactor, could lower the catalyst loading by more than one order of magnitude. Hence noble metals were considered as alternative catalysts. Ruthenium and rhodium are the most active reforming catalysts per unit of weight (Nielsen and Hansen, 1993). However, Rh is approximately an order of magnitude more expensive than Ru on the spot market (eBullion Guide, 2012). For this reason, ruthenium was tested as an alternative to nickel. Several catalyst deactivation mechanisms can occur in an SMR environment: 1. Sintering is a loss of catalytic activity due to a loss of active surface area (Fogler, 2004). Steam and pressure accelerate sintering (Twigg, 1997). There are two types of sintering: pore sintering, where the pores of the catalyst sup- port close, and metal sintering, where active metal sites agglomerate. 2. Fouling occurs when carbon material is deposited on the surface of the cat- 141 alyst (Fogler, 2004). Fouling is common with steam reforming on Ni-based catalyst. High Steam-to-Carbon (S/C) molar ratio (>3) are generally used to avoid this issue. Noble metals are more resistant to carbon formation, allowing a lower S/C molar ratio to be used (Nielsen and Hansen, 1993). 3. Poisoning is the process where molecules become irreversibly chemisorbed onto the active sites. Sulfur, naturally present in many petroleum feedstocks is a common catalyst poison (Fogler, 2004). Catalyst stability can be improved by adding promoters to the carrier. Among them, MgO, MnO, and La2O3 are known to suppress carbon formation, active metal particles sintering and oxidation (Berman et al., 2005). Earth alkaline metals (Mg, Ca) neutralize the acidity of the support, helping to suppress cracking and polymerization (Twigg, 1997). Catalyst preparation, removal of the salts from the metal precursors, pre-aging, and catalyst activation need to be performed carefully. Jakobsen et al. (2010) pre- pared a Ru/ ZrO2 catalyst with extensive aging of the catalyst, treated for 336 h at 750oC, 11 bar and a steam-to-H2 molar ratio of 1. Before kinetic experiments in the 425-575oC range, the temperature was raised to 850oC under a hydrogen flow. Li et al. (2009) showed that calcination in air for 4 h at 500oC adversely affected a Ru/ Al2O3 catalyst for the steam reforming of kerosene. This Chapter is the bridge between coating experiments covered in Chapters 4 & 5, and the Multi-Channel Membrane Reactor (MCMR) experiments, presented in Chapter 8. We present in this Chapter activity and stability tests performed on the packed bed micro-reactor, with both fresh catalysts from the coating trials and catalysts spent during the MCMR runs. Full description of these runs and their operating conditions are provided in Chapter 8. These post-run results are included here so that all of the micro-reactor material related to reforming is presented in one place. They also highlight some deactivation mechanisms that only occur in the MCMR. 142 Table 6.1: Impregnation Solutions and Desired Metal Contents for Reforming Catalysts Desired Metal Contenta Solution wt% mol/L Promoters MgO 3% Mg Nitr. 0.54 La2O3 6% La Nitr. 0.27 La2O3 4% MgO 4% La Nitr. 0.18; Mg Nitr. 0.72 La2O3 4% MgO 2% MnO 2% La Nitr. 0.18; Mg Nitr. 0.36; Mn Nitr. 0.28 Catalyst Ru 6% Ru Nitr. 0.51 aMeasured metal content can vary of ± 2% 6.2 Material and Method 6.2.1 Catalyst Preparation Tests on both commercial and lab-made catalysts are reported in this chapter. Coating methodologies and material employed were described in Chapters 4 and 5. Since many coating options were presented in those chapters, we list specific coating parameters in tables and figures below. After coating and heat treatment or MCMR runs, catalyst particles or pieces were scratched off the metal plates, ground with a mortar and pestle to obtain fine powders, then inserted into the micro-reactor following a procedure described below. For lab-made Ru-based catalysts, impregnation solution concentrations are listed in Table 6.1. 6.2.2 Micro-Reactor Configuration Figure 6.1 illustrates the configuration of the micro-reactor. The reactor consisted of 95 mm (3/8") OD SS 316 tube. From 0.002 to 0.25 g of catalyst was diluted with γ-Al2O3 powder (Dp,ave 80 µm, BASF HiQ-7S19cc) for a total weight of 1.0 g. Two layers of glass wool maintained the particles in place, while alumina beads Ø 0.4-0.6 mm (SEPR Ceramic) kept the catalyst bed at an even height. A thermocouple was inserted inside the bed to monitor the temperature, allowing the 143 temperature to be controlled by a PID controller. 6.2.3 Experimental Set-up Figure 6.2 shows a simplified process flow diagram of the micro-reactor unit, in- cluding some key control instruments. A detailed Process & Instrumentation Dia- gram (P&ID) is included in Appendix D.1. The functioning of the unit can be sum- marized as follows: Water is pressurized with N2 and, after being pre-heated to pro- duce steam, it is mixed with CH4 and H2 at the desired ratios. There is also an addi- tional air line for Methane Catalytic Combustion (MCC) studies. All feed streams are controlled with mass flow controllers. Downstream of the micro-reactor, water is removed by a condenser, and gas products are split into two streams, one going to the Gas Chromatograph (GC), the second being vented. The micro-reactor has one thermocouple inside the bed (subscript bed) (see Figure 6.1) and one on the outside surface of the reactor tube (subscript sf ). Two pressure transducers measure the inlet (Pin) and outlet (Pout) pressures. All tem- peratures reported below are reactor temperatures (Tbed), whereas the pressures are averages of Pin and Pout . In case of emergency shutdown, triggered manually or automatically by a flow, temperature or pressure alarm, the system is flushed with N2, while all other feed lines are isolated with solenoid valves. A detailed electrical and control diagram is found in Appendix D.2. Gases used for the SMR experiments were purchased from Praxair: CH4 (99% purity), H2 (99.995+% purity), and N2 (99.995+% purity). Deonized water was utilized to produce the steam. Start-up Catalysts were reduced from 1 h to overnight, at 550-600oC and 0 barg at the reac- tor outlet, with a H2 flow rate of 42 Nml/min. Once the reduction was completed, N2 was used to adjust the pressure at the desired level, and the steam flow was started. ∼15 min later, the methane flow was started. It took ∼1 h to remove all the hydrogen originating from the start-up and reduction procedure. The start-up procedure needed some modifications to simulate MCMR start- 144 Thermocouple SS 316 3/8" OD Tube (Total length 18") Glass Wool Al2O3 & Catalyst Alumina Beads Glass Wool SS 316 3/16" OD Tube (and Air Inlet) Drawing not to scale Dimensions in mm SS 316 ¼” Tube (with mesh soldered at ending) 3 .4 2 0 .3 2 0 .7 6 .2 1 2 7 2 0 .3 1 2 4 Gas inlet (CH4, H2, Steam) Figure 6.1: Micro-Reactor Set-up 145 Methane (From Cylinder) Hydrogen (From Cylinder) Air (From Cylinder) Nitrogen (From Cylinder) Water Tank BPR Steam Pre- heater Micro- Reactor (see Micro Drawing) Condenser To Vent To GC MFC MFC MFC MFC MFC Pin Pout Tbed PI Chilled Water PI Tsf Line Pressure Regulator, Back Pressure Regulator (BPR) Mass Flow Controller PI Pressure Indicator Pin Pout Tbed Tsf Pressure Reactor Inlet Pressure Reactor Outlet Temperature Reactor - Bed Temperature Reactor – Outside Surface Condensed water manual collection Line Heated with Rope Heater S S Normally Opened Solenoid Valve Ceramic Radiant Cylinder Heater S Normally Closed Solenoid Valve S S S Figure 6.2: Micro-Reactor Process Flow Diagram. For detailed PI&D, see Appendix D.1. up conditions. The Pd/Ag membrane requires specific H2 partial pressures when ramping the temperature. In Section 6.3.4 below, trial and error tests where per- formed to activate the catalyst while respecting, insofar as possible, the membrane requirements. Operation The micro-reactor was operated at temperature of 550-600oC, average pressure 6 - 11 bar, methane flow rate 100-105 Nml/min, S/C 2.5-4, and a Hydrogen-to-Carbon (H/C) molar ratio of 0-1.4. Catalyst loading varied from 0.002 g, for Ru lab-made catalyst, to 0.25 g for RK-212. The average pressure drop through the packed bed was small: <0.2 bar for 146 experiments at an average pressure of 11 bar. For most of the lab-made Ru cata- lysts, the Weight Hourly Space Velocity (WHSV), based on the total flow rate, was ∼8000 h−1. The reactor surface (or skin) temperature differed significantly from the reactor temperature. For example, when the methane conversion was 30% at a reactor temperature of 550oC, the surface temperature could be as high as 640oC. If the catalyst was not active, the surface temperature was ∼20-30oC higher than the reactor temperature. 6.2.4 Packed Bed Model Figure B.1 compares micro-reactor results with predictions of a packed bed model using Xu & Froment kinetics (see Chapter 2, Section 2.7). The model is a sim- plified packed bed reactor, neglecting pressure drop, temperature variation, and external and internal mass transfer resistances, leading to: dFi dWcat =−Ri (6.1) where Ri is the rate of production of component i as defined in (2.21), and Wcat is the mass of the catalyst. MATLAB™ software with the ordinary differential equa- tion function “ode15s”was utilized to solve the model. Equation (6.1) is integrated over the mass of the catalyst. Inlet flow rates, reactor temperature, and average pressure are used as inputs and initial parameters to solve the model. The methane conversion as a function of the mass of catalyst was calculated as: XCH4 = 1−FCH4/FCH4,o (6.2) 6.2.5 Estimation of Kinetics Parameter Chapter 2 detailed the Jackobsen’s kinetic model for a Ru 1%/ ZrO2 catalyst. The pre-exponential factor, A1, was estimated by assuming that the micro-reactor acts as a differential reactor, and average properties between the inlet and outlet of the 147 micro-reactor were calculated, leading to: A1 = r ′ 1 ( 1+KCOPCO,ave+KH2P 1/2 H2,ave )2 exp ( −E1∗1000 RgT ) PCH4,ave (1−β1) [ kmol kgcat h ] (6.3) where r ′ 1 = XCH4,out ∗FCH4,in [ kmol kgcat h ] (6.4) Pi,ave = (yi,in ∗Pin+ yi,out ∗Pout)/2 [bar] (6.5) β1 is defined in Eq. (2.37), while K j is defined by Eq. (2.34) and Table 2.4. E1 is found in Table 2.4. Subscripts in and out refer to the inlet and outlet of the micro-reactor. 6.2.6 Estimation of Porosity The porosity, ε , is needed to calculate the effective diffusivity in the catalyst layer of the MCMR model, developed in Chapter 2 (see Eq. (2.5)). ε =Vpore/Vcat (6.6) Dividing (6.6) by Wcat/Wcat leads to: ε = Vpore/Wcat Vcat/Wcat (6.7) We next introduce: Wske =Wcat (6.8) Vcat =Vske+Vpore (6.9) υ =Vpore/Wcat [ cm3/g ] (6.10) 148 where subscript ske refers to the carrier skeleton properties. Inserting Eqs. (6.8), (6.9) & (6.10) into Eq. (6.7), we obtain: ε = υ Vske+Vpore Wcat (6.11) ε = υ 1/ρske+υ (6.12) For alumina, ρske ≈ 3900 kg/m3; for υ measurements, see Section 6.2.7 below. Note that υ units must be adjusted to be used in Eq. (6.12). 6.2.7 Analytical Equipment FESEM Field Emissions Scanning Electron Microscopy (FESEM) images were obtained from a Hitachi S-4700 FESEM. Images were taken with an acceleration voltage ranging from 2.3 to 4.0 kV at 7 x 10−4 Pa. Samples could be Au−Pd sputtered to overcome the electrical insulation of the ceramic material. Gas Chromatograph The gas product composition was analyzed with a Shimadzu GC-14B, equipped with both a Thermal Conductivity Detector (TCD) and a Flame Ionization Detector (FID). The GC includes three packed columns in series: Porapak-N (80/100 mesh, 3 m), Porapak-Q (80/100 mesh, 3 m) and MS-5A (60/80, 2.25 m). Argon is both the carrier gas and the TCD reference gas, at flow rates of∼22 Nml/min. For CO2, CH4 and CO detection, the FID detector was used for sample concentrations below ∼3 vol%. For more concentrated samples, as well as other gases, the TCD detector was used. Oven temperature started at 60oC for ∼10 min, ramped 7.5 oC/min to 105oC, and was kept constant until the program finished. The FID temperature was set at 200oC and the TCD at 160oC. 149 Table 6.2: Co-Sorption Parameters Step Gas Comp Flow Temp. Target Temp. Rate Hold Time (vol%) (ml/min) (oC) (oC/min) (min) Preparation 1 10% H2−Ar 50 120 10 30 2 10% H2−Ar 50 400 20 30 3 He 50 50 - 30 CO - Pulse 4 10% CO−He 1.81 umol/dose 50 - - Metal Dispersion (CO-Sorption) A Micromeritic AutoChem II analyzer measured the metal catalyst dispersion. About 0.1-0.2 g of catalyst was inserted into the sample tube. Gas and temper- ature settings are listed in Table 6.2. We assumed a 1:1 mole ratio between the Ru or Ni sites and the CO absorbed. TPR Temperature Programmed Reduction (TPR) profiles were recorded on a Micromerit- ics AutoChem II analyzer equipped with a TCD. The following protocol was used: About 0.1-0.2 g of catalyst was inserted into the sample tube. For sample prepa- ration, a stream containing 10% O2 in helium flowed at of 50 ml/min, while the temperature was ramped at 20oC/min until 700oC was reached, and then held for 30 min. The sample was next cooled quickly to 40oC. A cold trap (liquid nitrogen and isopropyl alcohol) was installed to prevent reaction byproducts from reach- ing the detector. The TPR recording was started, with the temperature ramped at 20oC/min to the desired final temperature (700-900oC), with a 10% H2 in argon gas flow of 50 ml/min. A stoichiometric ratio of 1.0 between H2 and Ni is assumed in the reducibility calculations. 150 XRD Catalyst X-Ray Diffraction (XRD) spectra were obtained with a D8 Advanced powder X-ray diffractometer. The device uses Cu radiation and a NaI scintilla- tion detector. The scanning speed was 8-9 s/step at a step size of 0.05o/step. Surface Area - Pore volume - Pore size A Micromeritic ASAP 2020 analyzer was used with nitrogen to measure the Brunauer, Emmet and Teller (BET) surface area, Barrett, Joyner and Halenda (BJH) desorp- tion average pore size, and BJH desorption pore volume. 6.2.8 Metrics Methane Conversion The micro-reactor methane conversion was calculated from the reactor outlet dry composition: XCH4 = yCO2 + yCO yCH4 + yCO2 + yCO [mol/mol] (6.13) Deactivation For experiments with the same operating conditions, exponential curve fitting was performed for comparison purposes only. It was not intended as a rigorous deacti- vation model. XCH4 vs time on stream t was fitted by: XCH4 = a∗ e−bt + c (6.14) where (a+c) is proportional to the initial activity of the catalyst. b is related to the deactivation rate, and c is an indication of the residual activity of the catalyst. 151 6.3 Results and Discussion 6.3.1 Preliminary Stability Test The first stability tests were related to early coating attempts, as explained in Chap- ter 4. Crushed RK-212, RK-212 with boehmite, lab-made Ni catalyst, and com- mercial Ru catalyst were tested first. None of those catalysts were active and/or stable enough to be successful in the MCMR. Detailed stability results are pre- sented in Appendix B. In summary, RK-212 was not stable enough for the MCMR. However, experi- ments with this catalyst demonstrated the importance of providing an appropriate amount of catalyst in the micro-reactor to avoid thermodynamic equilibrium from hiding deactivation. Lab-made Ni-based catalysts, prepared with the initial coating method presented in Chapter 4, were not active. TPR analyses suggested that high temperature >700oC is required to reduce this catalyst, making it undesirable. The commercial Ru/γ-Al2O3 catalyst showed superior stability compared to the RK- 212 catalyst. However, application of nitric acid during the coating had strong negative effects on both the initial activity and stability. Since nitric acid is essen- tial to our modified-sol coating technique, this catalyst was not investigated further. However, stability test with commercial Ru catalyst exposed the importance of ac- tivations conditions. Calcination in air and reduction with H2 at elevated pressure (11 bar) both had strong negative effects on initial activity and stability. 6.3.2 Lab-made Ru Catalyst The first lab-made Ru-based catalyst coatings were prepared according to the initial procedure explained in Chapter 4, with the promoters and ruthenium impregnated in two different steps, after hot spray coating and calcination of the γ-Al2O3 sup- port. Learnings from the commercial Ru catalyst experiments were also applied with the lab-made catalysts not calcined, but only reduced in-situ in the micro- reactor. Figure 6.3 presents the first results with lab-made Ru catalyst. In part A, all lab-made catalyst (curves B,C & D) performed better than the commercial one (curve A). Catalyst containing MgO (curves C & D) was stable under the condi- 152 Table 6.3: Stability Conditions for Lab-made Ru-based Catalyst: Influence of Steam. Catalyst Composition and Steam Conditions for Figure 6.3. Modified sol: 40% boeh., 0.75 mol/L, pH 5 (nitric acid); Metal support: SS 304. La- bel Composition (wt%) Ru Precursor Note Steaming Conditions A Ru 5% (Alfa) N/A for comparison N/A Without Steam B Ru 5% RuNO(NO3)2 - N/A C Ru 5% MgO 5% RuNO(NO3)2 - N/A D Ru 5% MgO 3% RuCl3 - N/A With Steam E Ru 5% MgO 3% RuNO(NO3)2 - 21 bar, 11 h, 550 oC (Support and Metal Catalyst) F Ru 5% RuNO(NO3)2 Spent: after MCMR run Run Conditions: 21 bar, S/C: 2.5, H/C: 0, 5 h G Ru 5% RuNO(NO3)2 Catalyst loading 0.01g 23 bar, 11 h (Support only) tions studied. Note that for curve (C), a steep drop in conversion occurred at ∼20 h. This drop coincided with a sudden pressure change, caused by the purging of the water condenser. The pressure change might have displaced the catalyst bed. Catalyst in curves (C) & (D) were made of RuCl3 and RuNO(NO3)2 respectively, showing that the type of Ru precursor did not influence the activity. However, as presented in Chapter 4, the coating was unstable when using RuCl3. RuNO(NO3)2 was therefore selected for further testing. Table 6.4 lists the curve fitting results. Steam Effect The first trials with the MCMR prototype were at ∼20 bar, almost twice than the maximum pressure tested in the micro-reactor, ∼11 bar. Figure 6.3 Part B, shows the decline in conversion with high pressure steam. Catalyst in curve (F) was scratched off a plate after an unsuccessful trial in the MCMR (See Chapter 8). 153 0 10 20 30 40 50 60 20 25 30 35 40 45 50 lll ll lllll ll l l lll l l (A) Ru (Alfa) (B) Ru (C) Ru MgO (D) Ru (RuCl3) MgO A: Without Steam Effect 0 10 20 30 40 50 60 0 10 20 30 40 50 (E) Ru MgO, support & Ru steamed (F) Ru, spent (G) Ru, support steamed, 0.01 g B: With Steam Effect Time on Stream (h) M et ha ne  C on ve rs io n (m ol% ) Figure 6.3: Stability Test for Lab-made Ru-based Catalyst, Influence of Steam: Methane Conversion vs Time on Stream. Reforming Condi- tions: 550oC, 11 bar, S/C: 2.5, H/C: 0, CH4 flow: 100 Nml/min; Cat- alyst loading (except where specified): 0.02 g. Reduction & Start-up: H2 flow: 42 Nml/min, ramped at 5 oC/min, hold for 1 h at 600oC. Data fitted with Eq. (6.14). Table 6.3 shows changes in catalyst preparation. 154 Table 6.4: Curve Fitting Related to Figure 6.3 and Eq. (6.14) for Stability of Lab-Made Ru- based Catalyst. Label a b c a+c R2 A 16.8 0.0272 16.9 33.7 0.994 B 11.3 0.0141 31.6 42.9 0.93 C Stable over conditions studied D Stable over conditions studied E Activity too low F 8.88 0.232 0.26 9.1 0.999 G 6.20 0.0799 38.6 44.8 0.93 Table 6.5: Surface Area, Pore Volume, Average Pore Diameter, and Metal Dispersion of Lab-made Ru 6%/ γ-Al2O3 Catalyst (carrier not pre-aged by steam) Surface Area Pore Volume Ave. Pore Dia. Metal Dispersion m2/g cm3/g nm mol % Fresh 126 0.52 13.5 5.3% Spent 103 0.51 16.5 2.7% Activity was severely affected. Steam was suspected to be a factor in the deactivation, and several analyses were therefore performed to identify the problem. Figure 6.4 shows FESEM im- ages before and after the MCMR run. Part C (fresh) and Part D (spent) have the same magnification; no noticeable structural change can be observed. The issue seemed to be at a scale smaller than detectable on those FESEM images. Macro pore sintering (>50 nm) and extensive carbon fouling could be discounted as pos- sible reasons. Table 6.5 shows the surface area, pore volume, average pore diameters, and CO-sorption data before and after the MCMR run. While the pore volume stayed constant, the average pore size increased, indicating that smaller pores sintered dur- ing the MCMR experiments. The metal dispersion also dropped by 50%, indicating that both metal and pore sintering may have occurred at the same time. In order to resolve the issue, high-pressure (∼20 bar) steam was contacted with 155 A	
   B	
   E	
   F	
   C	
   D	
   Figure 6.4: FESEM Images of Ru 6%/ γ-Al2O3 (carrier not steamed): A,D spent catalyst; B,C,E,F fresh catalyst. Modified sol: 40% boeh., 0.75 mol /L, pH 5. 156 Table 6.6: Stability Conditions for Lab-made Ru-based Catalyst, Influence of Rust on SS 304 Support for Figure 6.5. γ-Al2O3 support with La2O3 steamed 24 h, 23 bar, 590oC. Modi- fied Sol: 40% boeh., 0.75 mol/L, pH 5 (nitric acid). Label Composition (wt%) Note A Ru 8% La2O3 5% No rust, fresh, Fecralloy support a B Ru 6% La2O3 6% Rusty b, fresh, repeat 1 C Ru 6% La2O3 6% Rusty b, fresh, repeat 2 D Ru 5% La2O3 3% Rusty, spent: after MCMR run aData taken from Figure 6.6 for comparison purpose bRust appeared while leaving plate with catalyst support at ambient temperature for 4 months after the steaming step. Ru impregnation was then made on that rusty support. the carrier prior to impregnation with RuNO(NO)3. The catalyst in curve (G) on Figure 6.3B had its carrier pre-aged with steam and showed high activity, but still showed some deactivation. Hence, promoters are likely still needed. In the next sections, La2O3, known to help stabilize γ-Al2O3 (Schaper et al., 1983), and proven to be effective in suppressing carbon formation in Chapter 4, was added. We also added to some catalyst ∼2-4% MgO, which has been shown to be beneficial for stability in Figure 6.3A, and ∼2% MnO, used by Berman et al. (2005). 6.3.3 Rust Effect Our first trial with Ru−La2O3 on hydro-aged γ-Al2O3 in the MCMR was success- ful (see Chapter 8). However, there were issues repeating the experiments with fresh catalyst and also while reusing the catalyst plates that appeared to be active at the end of a previous run. As in Chapter 5, rust appeared on many samples under different conditions with SS 304 as metal support. It was suspected that the rust affected the activity of the Ru catalyst. Figure 6.5 examines the rust issue. Only 0.002 g of catalyst were loaded into the micro-reactor in order to observe faster deactivation. Spent catalyst (curve D), recovered after the MCMR run, was completely inactive. Curve (A) represents rust-free fresh catalyst. Curves (B) & (C) belongs to the same fresh catalyst, where rust was visible on the surface of the plate. The residual activity factors “c”on Table 157 0 10 20 30 40 50 0 5 10 15 20 25 30 Time on Stream (h) M et ha ne  C on ve rs io n (m ol% ) l l l l l ll l l (A) Fresh, rust−free (B) Fresh, rusty, repeat 1 (C) Fresh, rusty, repeat 2 (D) Spent, rusty Figure 6.5: Stability for Lab-made Ru−La2O3/ γ-Al2O3 Catalyst, Influence of Rust on Support: Methane Conversion vs Time on Stream. Start-up conditions: H2 flow: 42 Nml/min, ramped 6.3 oC/min, hold at 600oC for 1 h. Reforming Conditions: 550oC, 11 bar, CH4 flow: 100 Nml/min; S/C: 2.5, H/C: 0; Catalyst loading: 0.002 g. Data fitted with Eq. (6.14). Table 6.6 provides details on the catalysts studied. Table 6.7: Curve Fitting Related to Figure 6.5 and Eq. (6.14) for Stability of Lab-Made Ru- based Catalyst. Label a b c a+c R2 A 19.2 0.0661 10.8 30.0 0.998 B 20.6 0.0795 2.74 23.3 0.999 C 19.7 0.0556 4.92 24.7 0.999 D Activity null 158 Table 6.8: Membrane Start-up Steps with H2−H2O mixture (starting at room temperature) Step Temperature Flow Rates Pave PH2 Ramp (oC/min) Final Value (oC) H2O (g/h) H2( Nml/min) bar bar 1 6.3 400 69 10 6 0.04 2 6.3 450 29 10 6 0.10 3 6.3 500 12 14 6 0.32 4 6.3 550 12 14 6 0.32 5 - 550 0 0 11 0.00 6.7 suggest a loss of activity for “rusty” catalysts. However, more tests would be needed to prove the difference statistically. Rust stains on spent catalyst were larger than those on rusty supports (see Chap- ter 4, Figure 5.8 Parts C.1 vs B.1). The extent of iron oxide coating could explain the difference of activity between fresh & spent rusty catalysts. To the best of our knowledge, there is limited indication that iron oxide could deactivate Ru catalyst, acting as a poison. Arena (1992) suggested that a Ru/Al2O3 catalyst for glucose hydrogenation could have been deactivated by iron build-up on the catalyst, but other compounds like sulfur were also present. As described in Chapter 5, the rust issue was solved by changing the metal support. Fecralloy proved to be effective, whereas SS 310 reduced rust diffusion, but did not stop it completely. With Fecralloy as metal suppport, the MCMR was finally able to produce pure hydrogen, as shown in Chapter 8. 6.3.4 Start-up Procedure for Membrane The regular reduction and start-up procedure consisted of feeding pure hydrogen while ramping the micro-reactor temperature. In order to maintain the integrity of the Pd/Ag membrane, tight control on hydrogen partial pressure was required during the MCMR start-up. We observed in previous sections that the start-up pro- cedure can influence catalyst activity. The micro-reactor was employed to develop a procedure acceptable for both the membrane and for catalyst activity. Tables 6.8 and 6.9 show trial procedures, using steam and nitrogen respectively. The mem- brane start-up procedure is finalized in Chapter 8. 159 Table 6.9: Membrane Start-up Steps with H2−N2 mixture (starting at room temperature) Step Temperature Flow Rates Pave PH2 Ramp (oC/min) Final Value (oC) N2 (Nml/min) H2 (Nml/min) bar bar 1 6.3 400 356 10 1.5 0.04 2 6.3 500 225 10 1.5 0.06 3 6.3 550 180 43 1.5 0.29 4 6.3 550 180 43 11 2.12 5 - 550 0 43 11 0.00 Table 6.10: Stability Conditions of Lab-made Ru-based Catalyst: Influence of Membrane Start-up Procedure for Figure 6.6. Modified Sol: 40% boeh., 0.5 mol/L, pH 5 (nitric acid). γ-Al2O3 carrier and promoters steamed for 24 h, at 23 bar, and 590oC on Fecral- loy (except where specified). La- bel Composition (wt%) Note / Start-up Conditions Regular Reduction & Start-upa A Ru 8% La2O3 5% - B Ru 8% La2O3 5% SS 304 as metal support C Ru 8% La2O3 5% SS 304 as metal support D Ru 7% La2O3 4% MgO 4% Start-up Modified for Membrane E Ru 7% La2O3 4% MgO 4% Steam & N2 mix b F Ru 7% La2O3 4% MgO 4% Heated at 600oC for 1 h with N2, cooled to 350 oC, pressurized to 6 bar, H2−H2O mix start-up (Tab. 6.8) G Ru 7% La2O3 4% MgO 4% Heated at 625oC for 1 h with N2, cooled to 350 oC, follow by H2−N2 mix start-up (Tab. 6.9) H Ru 7% La2O3 4% MgO 4% H2−N2 mix start-up (Tab. 6.9) aRegular Reduction & Start-up: H2 flow: 42 Nml/min, ramped 6.3 oC/min, hold for 1 h at 600oC. bRatio Steam / N2 not measured 160 0 10 20 30 40 50 60 10 15 20 25 30 l l l ll l lll ll l (A) On Fecralloy (B) On SS 304, repeat 1 (C) On SS 304, repeat 2 (D) On Fecralloy, with MgO A: Regular Start−up 0 5 10 15 20 25 30 35 0 10 20 30 40 l l l l l l l l l l (E) H2O−N2 mix (F) Heated at 600°C, H2O−N2 mix (G) Heated at 625°C, H2−N2 mix (H) H2−N2 mix B: Start−up Modified for Membrane Time on Stream (h) M et ha ne  C on ve rs io n (m ol% ) Figure 6.6: Stability of Lab-made Ru-based Catalyst, Influence of Membrane Start-up Procedure: Methane Conversion vs Time on Stream. Reform- ing Conditions: 550oC, 11 bar, CH4 flow: 100 Nml/min; S/C: 2.5, H/C: 0; Catalyst loading: 0.002 g. Data fitted with Eq. (6.14). Table 6.10 shows changes in catalysts and start-up conditions. 161 Table 6.11: Curve Fitting Related to Figure 6.6 and Eq. (6.14) for Stability of Lab-Made Ru- based Catalyst. Label a b c a+c R2 A 19.2 0.0661 10.8 30.0 0.998 B 23.4 0.0335 5.19 28.6 0.996 C 24.6 0.0274 5.56 30.1 0.998 D 13.9 0.0986 14.5 28.4 0.996 E 15.0 0.0594 0.0 15.0 0.996 F 17.8 0.0662 6.59 24.4 0.9998 Ga 18.2 0.0490 10.4 28.6 0.9997 Ha 28.7 0.0819 9.89 38.5 0.998 aFirst two data points skipped, where stronger deactivation than the exponential model fit occurred. Table 6.12: Details of Ru-based Catalysts on XRD Spectra of Figure 6.7. Modified sol: 0.5- 0.75 mol /L, 40% boeh., pH 5; Ru from RuNO(NO3)3. Label Composition (wt%) Steaming Fresh/Spent Note A Ru 5% no fresh calcined B Ru 5% no spent C Ru 7% La2O3 5% yes fresh D Ru 6% La2O3 6% yes spent E Ru 4% La2O3 6% yes spent Figure 6.6 Part A shows stability results with the regular reduction and start- up procedure for a Ru−La2O3 catalyst. All catalysts showed similar initial ac- tivity, while Table 6.11 indicated some variations in the rate of deactivation and residual activity. Variations are more apparent in Figure 6.6 Part B. Start-up with steam (curves E & F) affected the Ru activity, while start-up with H2−N2 mix- tures (curves G & H) gave activity results similar to those in Part A. Even with pre-reduced catalyst (curve F), the activity was affected by steam. Based on these results, a H2−N2 mixture was selected for the MCMR start-up. 162 α α αγα C: Ru La O Fresh D: Ru La2O3 Spent-1 E: Ru La2O3 Spent-2 γγ α: α−Al2O3γ: γ−Al2O3 L i n ( C p s ) 0 100 2-Theta - Scale 35 40 50 Ru RuO RuO Ru A: Ru Fresh B: Ru Spent 2 3 2 heta-Scale L i n  ( C p s ) Figure 6.7: XRD diagram of Lab-made Ru-based Catalyst, Fresh and Spent (after MCMR Exp.). See Table 6.12 for details on the catalysts. 6.3.5 Deactivation Mechanisms This section tries to explain the catalyst deactivation decays presented in this chap- ter, using both fresh catalysts and catalysts spent during the MCMR experiments. Figure 6.7 presents XRD spectra of lab-made Ru-based catalysts. Spectra (A) and (B) are for early lab-made catalysts, with the support not steamed, no promoters, and the RuNO(NO3)3 calcined. The presence of large Ru and RuO peaks indicates poor Ruthenium dispersion. Poor dispersion was already observed in Table 6.5 with a similar catalyst. It was previously noted that during calcination, Ru could be oxidized to RuO4 and vaporise. The large RuO peaks could also indicate that the calcination caused severe metal sintering. Poor dispersion was obtained also by Li et al. (2009), while a calcined Ru 1%/ Al2O3 catalyst had a dispersion of only 2.8%, compared to 55.9% for the same catalyst without calcination. 163 Spectra (C), (D), and (E) represent active catalysts with La2O3 as promoter. No Ru peaks are visible, indicating good dispersion for both fresh and spent cata- lysts. The two spent catalysts show the appearance of α-Al2O3, indicating a phase change that would cause inevitable pore sintering. In air, γ-Al2O3 would only change to α-Al2O3 around 800oC (Gitzen, 1970). The steam itself, during the hydro-aging of the carrier and promoters, did not cause a phase change (spectrum C). However, the SMR environment seems to have promoted the phase change at a much lower temperature than air, since the MCMR operated at a maximum temperature of 575oC in the reforming channel. Table 6.13 summarizes surface area, pore volume, average pore diameter data for the catalyst support and various catalysts. As expected, steaming reduced the surface area, slightly lowered the pore volume and increased the average pore di- ameter. Even though we observed some phase changes on XRD spectra (Figure 6.7), this did not translate into significant drops in pore volume. However, the slight decrease in surface area, and increase in average pore sizes, indicated some pore sintering. The presence of rust did not seem to affect either the pores or the metal dis- persion. The catalyst with a rusty support had a slightly higher dispersion than the rust-free one. Iron oxide might not be a conventional poison, but the presence of iron oxide could, nevertheless, change the electro-negativity of the Ru affecting the absorption/ desorption processes necessary for the SMR reactions. Promoters helped maintain high metal dispersion. The catalysts without pro- moters saw their metal dispersion drop on average from 38 to 6.5%, while cata- lysts with promoters maintained at least half of the dispersion of the fresh samples. There are not enough data to draw conclusions about the optimal promoter concen- trations and compositions. This could be a topic for future work. Porosity Estimation Based on Eq. (6.12), the porosity is plotted vs pore volume in Figure 6.8 for the range of pore volume data reported previously. 164 Table 6.13: Surface Area, Pore Volume, Average Pore Size, and Metal Dispersion of Lab- made Ru Catalysts and Supports Surface Area Pore Volume Ave. Pore Size Metal Dispersion m2/g cm3/g nm mol % Catalyst Support γ-Al2O3 Baikalox CR125 104 0.78 28.6 N/Aa Boehmite Disperal P2 b 260 0.5 - N/A γ-Al2O3 with 40% boeh. after calcination 154 0.55 12.3 N/A La2O3 7%/ γ-Al2O3 after steaming 92 0.52 19.1 N/A La2O3 3% MgO 3%/ γ-Al2O3 after steaming 93 0.49 17.9 N/A La2O3 4% MgO 2% MnO 2%/ γ-Al2O3 after steaming (rusty) 96 0.49 17.7 N/A Lab-made Ru-based Catalyst/ γ-Al2O3 (γ-Al2O3 and promoters steamed) Ru 7% (fresh) 117 0.50 14.7 38% Ru 7% (spent)c 89 0.48 20.0 6.5% Ru 6% La2O3 6% (fresh) 93 0.39 14.9 42% Ru 6% La2O3 6% (rusty support, fresh) 48% Ru 7% La2O3 5% (spent) e 93 0.46 17.5 17% Ru 7% La2O3 4.6% (spent) e 88 0.44 17.8 22% Ru 7.5% La2O3 4% MgO 4% (fresh) 106 0.41 12.7 34% Ru 7% La2O3 4% MgO 4% (spent) f 88 0.40 16.3 27% Ru 7.5% La2O3 4% MgO 4% (spent) f 98 0.43 15.8 N/Ab Ru 7% La2O3 4.6% MgO 2.3% (spent) d 94 0.41 16.0 N/Ab Ru 8% La2O3 3.2% MnO 1.6% MgO 1.6% (spent)e 97 0.42 16.0 22% aN/A: Not applicable, or not measured, due to insufficient sample available or faulty instrument bSupplier data, after activation at 550oC cAfter Exp. no.0.4 (See Section C.2.2) dAfter Exp. no.1 (See Table 8.6) eAfter Exp. no.2 (See Table 8.6) fAfter Exp. no.3 (See Table 8.6) 165 0.30 0.35 0.40 0.45 0.50 0.55 0.60 0.55 0.60 0.65 0.70 Pore Volume (ml/g) Po ro si ty Figure 6.8: Porosity vs Pore Volume for Catalyst with Alumina Support 6.3.6 Catalyst Layer Modeling With the information gained in previous chapters, we can discuss the validity of the catalyst and pore model developed in Chapter 2. Figure 6.9 illustrates the simulation model (Part A) and an improved model (Part B), based on microscope images, γ-Al2O3 particle size data, pore volume and pore diameter measurements. Note that our pore volume measurements only inlude pore diameters between 2 and 150 nm, and a fraction of the inter-particle voids in Part B.2 might be included in the measured pore volumes. 6.3.7 Estimation of Jackobsen Pre-exponential Kinetic Parameter Figure 6.10 shows the estimated Jakobsen kinetic pre-exponential factor based on our experimental data. Our estimation is very similar to published data (Jakobsen et al., 2010), even though their catalyst was different (Ru 1%/ ZrO2). The curves 166 pores Pores Ave. Ø ~17-20 nm Catalyst Layer Thickness A: Model for Simulations B.1: More Realistic Model B.3: Particles ~ 300 nm (before ball milling) Average Measured Thickness ~200 µm void void B.2: Close up on building blocks Ave distance between clusters ~50-200 µm Metal Support Sand Blasted Profile ~ 5 µm Figure 6.9: Catalyst Layer and Pores Model: A. As Simulated; B. Improved Model. Drawings not to scale. seem to settle around a ratio of 1. The challenge with our MCMR experiments is that the catalyst was unstable during the first 24 h, a time of the same order as the time of operation. 167 0 10 20 30 40 0 1 2 3 4 5 Time on Stream (h) R at io  A 1 Es tim at ed  / A 1  Pu bl is he d l l l l l l l l l G H Figure 6.10: Pre-exponential Factor A1 - Estimation for Jackobsen Kinet- ics: Ratio between Estimated Value (Eq. (6.3)) over Published Value (Jakobsen et al., 2010) vs Time on Stream. Data are taken from Figure 6.6 curves (G), & (H) and fitted with Eq. (6.14). 6.4 Conclusions Micro-reactor activity experiments allowed various reforming catalysts to be tested for their suitability in the MCMR prototype, the development of a start-up proce- dure for the MCMR, and the estimation of the pre-exponential kinetic parameter. A lab-made Ru-based catalyst had better activity and stability than a commer- cial Ru catalyst, and was selected for the MCMR. Aging of the support with steam was necessary to avoid total catalyst deactivation. Rust appeared to poison the Ru 168 catalyst. Fecralloy, initially oxidized in air, effectively stopped rust diffusion from the metal support. Steam should be avoided during start-up of the MCMR since it negatively affected the initial activity. A H2−N2 gas mixture was able to activate the catalyst and imitate MCMR start-up conditions. MgO and La2O3 improved the stability of the lab-made Ru catalyst. Insuffi- cient data were collected to reach conclusions on the effectiveness of MnO, as well as the optimal concentrations for the promoters. XRD analyses showed a phase change from γ-Al2O3 to α-Al2O3. Average pore size generally increased during MCMR runs, confirming that pore sintering was a deactivation mechanism. Fitted pre-exponential factors were similar to those reported by Jakobsen et al. (2010). Based on microscope images and catalyst physical properties, an improved pore model was obtained, but model equations to describe it is still needed. 169 Chapter 7 Methane Catalytic Combustion 7.1 Introduction Catalytic combustion allows the production of heat at lower temperature than ho- mogeneous combustion, leading to less generation of nitrogen oxides and fewer constraints on reactor design (Zanfir and Gavriilidis, 2003; Chauhan et al., 2009). Noble metals (Pd, Pt, Rh) and their oxides are often used as catalysts for this appli- cation (Chauhan et al., 2009). Less costly alternatives have also been investigated. For instance, Terribile et al. (1999) studied CeO2−ZrO2 catalysts, some doped with Mn and Cu; Zou et al. (2011) investigated LaMnO3 perovskite; and Thaicharoen- sutcharittham et al. (2009) looked at NiO/CeZrO2. However, for methane com- bustion, palladium is generally seen as the most efficient catalyst (Lee and Trimm, 1995; Chauhan et al., 2009). The general pattern of catalytic combustion of hydrocarbons can be described as follows (Lee and Trimm, 1995): As temperature is increased, oxidation is ini- tiated at a temperature that depends on the hydrocarbon and the catalyst; after the ignition, conversion increases exponentially with temperature until the reaction be- comes mass transfer controlled, also called the “light off” point. Deactivation mechanisms were summarized in Chapter 6. Fouling, pore and metal sintering, and poisoning, can also occur with MCC. With Pd-based catalyst, another deactivation mechanism could be the change in oxidation states. There is controversy in the literature about which of the reduced or oxidized palladium 170 state (Pd or PdO) is more active (Lyubovsky and Pfefferle, 1999). Some authors suggested that Pd is not or less active, and can be a source of deactivation at tem- peratures above 700oC, where metallic Pd particles are formed from PdO (Colussi et al., 2009). Gao et al. (2008) suggested that deactivation could also come from the transition from PdO to PdO2. Hellman et al. (2012) used density functional theory and in-situ surface XRD to identify and characterize atomic sites yielding high methane conversion. Assuming that the rate-limiting step is the breaking of the first C-H bond, they found that PdO sites in the crystal plane (101) and metallic Pd sites in the crystal plane (211) gave the lowest activation energies. Since con- trolling the crystal structure of palladium can be difficult and is rarely reported, the Hellman et al. (2012) findings give some hints about the source of the controversy. Promoters can be added to stabilize the Pd oxidation state and reduce the rate of metal sintering. For instance, Ozawa et al. (2003) added of Nd2O3 and La2O3 to Al2O3, effectively slowing the transformation from PdO to Pd and preventing PdO particle growth. Pd-catalysed combustion kinetics is also subject to controversy since interac- tions with the support, catalyst preparation, gases used for catalyst pre-treatment, partial pressure of oxygen, temperature, oxidation state and crystal structure, can all affect the kinetics (Lee and Trimm, 1995; Lyubovsky and Pfefferle, 1999; Hell- man et al., 2012). Lee and Trimm (1995) reviewed studies of methane catalytic combustion with Pd, Pt and Rh. For palladium, the reaction order for methane ranged from 0.5 to 1; for oxygen, the order from 0 to 0.1. Activation energy also varied widely from 52 to 138 kJ/mol. Water is often recognized as an inhibitor (Ciuparu et al., 2001). Some kinetic models include water and give it a negative order (Groppi et al., 2001). We present in this chapter activity and stability tests performed in the packed bed micro-reactor, with both fresh combustion catalysts from the coating trials and catalysts spent during the MCMR runs. Full description of these runs and their operating conditions are provided in Chapter 8. These post-run results are included here so that all of the micro-reactor material related to combustion is presented in one place. We also estimate kinetic parameters for the Pd-based catalysts used in the MCMR. 171 7.2 Material and Method 7.2.1 Catalyst Preparation Commercial and a limited amount of lab-made oxidation catalysts were tested. Coating methodologies and materials are described in details in Chapters 4 and 5. In brief, for commercial catalyst, Disperal P2 boehmite (Sasol) was mixed in distilled water with the commercial catalyst powder. Boehmite represented 15% of the total solid mass. The concentration of the catalyst powder was 0.25 mol/L (based on molecular weight of alumina). The mixture was ball milled overnight, and the pH was adjusted with nitric acid to ∼5 before and after the ball milling. The modified sol was air-spray coated onto a stainless metal substrate, after being heated to >100oC, and previously sand-blasted. Once the thickness of the coating was judged acceptable, the samples were calcined overnight in static air at 650oC. For lab-made catalyst, Baikalox CR125 γ-Al2O3 (Baikowski) was mixed with the boehmite, which represented 40% of the total solid mass. The concentration of the γ-Al2O3 powder was 0.5 mol/L. After the air-spray coating and calcination, promoters were impregnated using a modified incipient wetness procedure. Plates were flooded with the impregnation solution, and excess solution was removed after 2 min. The mixture was air dried for 2 h, and heated at 110oC overnight in static air. Impregnation solution concentrations are listed in Table 7.1. The support and promoters were steamed and heated under pressure at 25 bar and 575oC for 24 h. Pd was then impregnated following the same procedure as for the promoters. Plates were calcined at 600oC in static air for 5.5 h. After the heat treatment, for “fresh” samples, or after MCMR runs, for “spent” samples, catalysts were scratched off the metal plates, and ground with a mortar and pestle to obtain a fine powder. 1.7 to 2.0 mg of catalyst were diluted in γ- Al2O3 powder (BASF HiQ-7S19cc) to obtain a total of 1 g. The solid mixture was inserted into the micro-reactor, following the procedure described in Chapter 6. 7.2.2 Experimental Set-up A simplified process flow diagram of the micro-reactor unit was provided in Figure 6.2, and a detailed P&ID is included in Appendix D.1. The functioning of the unit 172 Table 7.1: Impregnation Solutions and Desired Metal Contents for Combustion Catalysts Desired Metal Contenta Solution wt% mol/L Promoters La2O3 6% La Nitr. 0.27 La2O3 4% MgO 4% La Nitr. 0.18; Mg Nitr. 0.72 Catalyst Pd 5% Pd Nitr. Sol. Pd 4-5% w/w (Alfa Aesar, as received) aMeasured metal content can vary by ± 2% from the desired value for the catalytic combustion experiments can be summarized as follows: Air was pre-heated to 300-380oC with rope heaters, before being mixed with CH4 to the desired composition. All feed streams are controlled with mass flow controllers. Downstream of the micro-reactor, water was removed with a condenser, and gas products were split into two streams, one going to the GC, the other being vented. The micro-reactor has one thermocouple inside the bed and one on the outside surface of the reactor tube. Pressure transducers measure the inlet (Pin) and outlet (Pout) pressures. All temperatures reported in the results section below are reactor temperatures (Tbed), whereas the pressures are averages of Pin and Pout . Gases used for the MCC experiments were purchased from Praxair: CH4 (99% purity), air (extra dry grade), and N2 (99.995+% purity). Start-up and Operation Start-up was difficult for the MCC. Uncontrolled temperature jumps, when reach- ing the light-off point were common, and could trigger automatic shut down of the unit. The start-up was performed as follows to minimize temperature jumps: Air was fed to the reactor at 200 Nml/min, and atmospheric pressure (Pout), while the temperature was increased at 10oC/min from ambient temperature to 400oC. Air flow was then increased to 1000-1900 Nml/min and methane flow was started (30- 37 Nml/min), to obtain the desired inlet composition of 2-3% CH4 in air. The pres- sure was then increased to the desired value (average pressure from 3.8 to 8.4 bar). After the pressure stabilized, the temperature was increased at 2-3oC/min to 510oC. 173 After reaching this temperature, if a higher temperature was needed, the ramping rate was reduced to 1oC/min until the final desired temperature (550-575oC) was reached. The P&ID temperature controller often needed manual adjustment >510oC to stabilize the temperature at the desired set point: unlike the reforming reaction, MCC requires less heating, since the combustion is exothermic. Due the to large excess of air sought, resulting in large air flow, pressure drops through the packed bed were significant: for instance, for an average pressure of 5.7 bar, the pressure drops was 1.3 bar. WHSV varied from 38,000 to 71,000 h−1. The reactor surface (or skin) temperature differed significantly from the re- actor temperature. For example, when methane conversion was 10% at a reactor temperature of 575oC, the surface temperature could reach be as high as 665oC. 7.2.3 Estimation of Kinetic Parameters As in Chapter 6, we estimated kinetic parameters by assuming that the micro- reactor was acting as a differential reactor. Kinetic parameters were evaluated for methane conversions less than 15%, to avoid mass transfer limitations. Initially, catalysts were subject to considerable deactivation, but after 24-48 h, the catalysts were more stable, and kinetics measurements were then performed. Chapter 2 provided an empirical nth order kinetic model to describe the com- bustion reaction (Eqs. (2.50), (2.51)). To stay below the CH4 explosion limit, a large stoichiometric excess of air (240-415%) was provided. The effect of oxy- gen on the kinetics was neglected (β = 0 in Equation (2.50)). Experimentally, we determined the rate of reaction as: r ′′ 4 = XCH4,out ∗FCH4,in [ kmol kgcat s ] (7.1) By varying the temperature, with constant flow rates and pressure, taking the natu- 174 ral logarithm of r ′′ 4 in Eq. (2.50), we obtain: ln(r ′′ 4) = ln ( A4 exp (−E4 ∗1000 RgT ) PαCH4,ave ) (7.2) = (−E4 ∗1000 RgT ) + ( ln(A4)+ ln ( PαCH4 )) (7.3) From the slope of a plot of ln(r ′′ 4) versus (1/T ), we can extract the activation energy E4. By varying the total pressure of the system, while keeping flow rates constant, we can obtain several values of PCH4,ave. Taking the natural logarithm of r ′′ 4, we obtain: ln(r ′′ 4) = αln ( PCH4,ave ) + ln ( A4 exp (−E4 ∗1000 RgT )) (7.4) The slope of ln(r ′′ 4) versus Pave represents the reaction order α . Finally the pre-exponential factor A4 is evaluated with: A4 = r ′′ 4 exp ( −E4∗1000 RgT ) PαCH4,ave [ kmol kgcat s barα ] (7.5) E4 and α were evaluated with experiments on commercial Pd 1%/ γ-Al2O3 (Alfa). A4 was estimated for Pd 1% and 5%/ γ-Al2O3 (Alfa), and for lab-made Pd La2O3−MgO/ γ-Al2O3 catalysts. 7.2.4 Analytical Equipment All instrumentations utilized in this chapter is described in Chapter 6. 7.2.5 Metrics Equations (6.13) and (6.14)), from Chapter 6 were used to evaluate the methane conversion and to fit the stability data with an exponential decay relationship. 175 7.3 Results and Discussion 7.3.1 Preliminary Stability Test To investigate a less costly alternative to Pd, tests with CeO2 powder, and CeO2– ZrO2–Al2O3 from the coating procedure (see Chapter 4) were initially performed. No significant conversion was observed, although previous researchers, e.g. Ter- ribile et al. (1999) reported some success with CeO2. We showed in Chapter 4 that our purchased CeO2 was non-porous, so a lack of active sites could explain the lack of activity. No further work were performed on the CeO2-based catalysts, since tests with Pd-based catalysts were successful, as shown below. 7.3.2 Stability of Pd 1%/ γ-Al2O3 (Alfa) Figure 7.1 shows the stability of Pd 1%/ γ-Al2O3 (Alfa) with 15% boehmite. Two different deactivation mechanisms could be observed. First, there was a similar exponential decay deactivation behaviour as observed with the reforming stability tests presented in the previous chapter. However, with the combustion catalyst, some of the deactivation was reversible, a finding not observed with reforming catalysts. After unplanned shutdowns (denoted by “*” in Fig. 7.1A), causing the reactant flows to stop and N2 to purge the unit, the conversion came closed to its initial level, but quickly deactivated again in a similar exponential decay pattern. Meanwhile, CO concentration (Fig. 7.1B) increased with the decreasing CH4 conversion. CO concentration also increased with increasing temperature and pres- sure. Water is known to inhibit the combustion reaction (Groppi et al., 2001), and it can take a significant time for the surface water concentration and the gas phase water concentration to reach equilibrium (Ciuparu et al., 2001). We speculate that water molecules could not desorb from the Pd sites as quickly as the methane dis- sociated, causing incomplete methane combustion, and CO formation. Figure 7.2 shows the effect of the coating on the activity and stability of Pd 1%/ γ-Al2O3 (Alfa). Curves (A), (B) & (C) are for freshly coated catalysts, whereas curve (D) is the “as received” catalyst from the supplier. The curve fitting results in Table 7.2 show that the initial activity (a+ c) and residual activity (c) for the coated catalysts were lower than for the “as received” catalyst, but the deactivation 176 05 10 15 M et ha ne  C on ve rs io n (m ol% ) ll lllll lll l ll 0.0 0.5 1.0 1.5 CO  C on ce nt ra tio n (m ol% ) A: Conversion and CO Concentration (*) (**) lll lll ll ll l l ll ll ll ll l l l ll ll 0 20 40 60 80 100 120 500 520 540 560 580 600 Te m pe ra tu re  (° C) 4 6 8 10 12 Pr es su re  (b ar a) B: Temperature and Pressure Time on Stream (h) Figure 7.1: Preliminary Stability Test of Pd 1%/ γ-Al2O3 (Alfa) with 15% Boehmite: A. Methane Conversion and CO Concentration vs Time on Stream; (*) 10 min shut down (**) 20 min shut down. B. Temperature and Pressure vs Time on Stream. Catalyst Loading: 0.002 g. Inlet Conditions: CH4 Flow: 37.3 Nml/min, 3% in air. 177 0 10 20 30 40 50 60 70 0 5 10 15 20 25 30 35 Time on Stream (h) M et ha ne  C on ve rs io n (m ol% ) l ll lllll l l l l ll l l lll l (A) 15% boeh., fresh, 5.9 bar (B) 15% boeh., fresh, 5.7 bar (C) 15% boeh., fresh, 7.5 bar (D) no boeh., as received, 5.8 bar Figure 7.2: Stability of Pd 1%/ γ-Al2O3 (Alfa): Methane Conversion vs Time on Stream. Catalyst Loading: 0.0017 g (excluding boehmite). Inlet Condition: CH4 flow 37 Nml/min, 2 mol% in air; 575 oC. Data fit with Eq. (6.14). Catalyst description (boehmite content) and average pres- sure are listed in the legend. Table 7.2: Curve Fitting Related to Figure 7.2 and Eq. (6.14) for Stability of Pd 1% (Alfa) Catalyst Label Description a b c a+c R2 A 15% boeh. (fresh), 5.9 bar 4.99 0.078 6.42 11.4 0.96 B 15% boeh. (fresh), 5.7 bar 5.02 0.218 8.94 14.0 0.82 C 15% boeh. (fresh), 7.5 bar 16.2 0.138 12.1 28.3 0.95 D No boehmite, as received, 5.8 bar 16.3 0.147 21.0 37.3 0.94 178 Table 7.3: Stability Conditions for Pd 5%/ γ-Al2O3 (Alfa) and Lab-made Pd- based Catalysts for Figure 7.3. La- bel Catalyst Fresh / Spent Note A Pd 5% (Alfa) with 15% boeh. Fresh 7.4 bar B Pd 5% (Alfa)with 15% boeh. Spent - C Pd 5% (Alfa) with 15% boeh. Fresh - D Pd 4.5% La2O3 6% Fresh E Pd 5% La2O3 4% MgO 4% Spenta SS 310 support, rust visible. Repeat 1 F Pd 5% La2O3 4% MgO 4% Spent Same as (E), Repeat 2 aMCMR run: 16.5 h on stream at 555-575oC, 3.8 bar, 3-3.5% CH4 in Air. rate (b) did not differ significantly. It might appear that boehmite would cover some of the active sites for the re- action, but CO-sorption analyses, contradicted this assumption, with both samples, as received and coated, exhibited metal dispersion virtually identical at ∼28% (see Table 7.5). Nevertheless, all samples were active after 40 h and relatively stable, making them good candidates for the MCMR. Ahmad (2011), based on data in Figure 7.2, suggested that the deactivation could be fitted with a second-order decay model, commonly used for sintering. 7.3.3 Stability of Pd 5%/ γ-Al2O3 (Alfa) and Lab-made Pd-based Catalysts Figure 7.3 presents results for a commercial (Part A) and lab-made (Part B) Pd 5%/ γ-Al2O3 catalysts. Table 7.4 shows the exponential curve fitting results. All fresh catalysts in this section were found suitable for the MCMR. Curves (A) and (C) are both for fresh catalysts, but (A) is for a higher pressure, 179 0 5 10 15 20 25 30 35 5 10 15 20 25 30 l (A) Fresh, 7.4 bar (B) Spent (C) Freshl l ll l lll A: Commercial Catalysts 0 5 10 15 20 25 30 35 5 10 15 20 25 30 (D) Fresh (E) Spent, Repeat 1 (F) Spent, Repeat 2 B: Lab−made Catalysts Time on Stream (h) M et ha ne  C on ve rs io n (m ol% ) Figure 7.3: Stability Test with Pd 5%/ γ-Al2O3 (Alfa) and Lab-made Pd- based Catalyst, Fresh and Spent Catalysts after MCMR runs: Methane Conversion vs Time on Stream. Catalyst Loading: 0.002 g; Inlet Con- ditions: CH4 flow 30 Nml/min, 3 mol% in air, 510 oC, 3.8 bar (unless otherwise noted in legend). Data fit with Eq. (6.14). Catalysts are de- scribed in the Legends, with more information in Table 7.3. 180 Table 7.4: Curve Fitting Related to Figure 7.3 and Eq. (6.14) for Stability of Pd 5% (Alfa) and Pd-based Lab-made Catalysts Label a b c a+c R2 A 19.0 0.237 9.26 28.2 0.991 B 12.7 0.242 15.2 27.9 0.993 C 13.2 0.101 15.2 28.4 0.990 D 11.2 0.383 13.9 25.1 0.88 E 11.3 0.163 18.7 30.1 0.999 F 13.6 0.0013 0.0 13.6 0.43 7.4 bar instead of 3.8 bar. Initial activities (a+ c) were similar, but deactivation (b) was stronger at higher pressure. Not shown on this graph was the CO con- centration, which went up to ∼1200 ppm at higher pressure, but was close to the detection limit at 3.8 bar, <20 ppm. The activity of the spent catalyst, curve (B), was unexpected. In Table 7.5, the metal dispersion dropped from 14% to 2% from fresh to spent catalyst. Pore volume analyses showed a significant drop in pore volume and surface area, while the pore size remained stable. However, the activity of the spent catalyst (B) was similar to that of the fresh sample for the same operating conditions (C). Catalyst activity might not be very sensitive to metal dispersion. Hellman et al. (2012) suggested that a relatively thick film of PdO favours methane dissociation, also indicating that high metal dispersion might not be essential. For initial and residual activities, fresh lab-made catalyst (curve D) were slightly lower than for the fresh commercial catalyst at the same conditions (curve C). The added promoters (initially intended for reforming catalyst), and pre-aging by steam, did not enhance the catalyst performance compared to the commercial cata- lyst. Catalysts corresponding to curves (E) & (F) had some rust on the support, but this did not seem to affect the activity and stability, unlike the Ru-based catalyst for reforming (Chapter 6). Curve (F) had further unexpected behaviour, being mostly stable during the stability test, and giving poor fitting. We experienced some issue with our GC at that time that might have hidden differences between the samples tested in this section. However, the catalyst deac- 181 Table 7.5: Surface Area, Pore Volume, Average Pore Size, and Metal Dispersion of Pd/ γ- Al2O3 Catalysts. Surface Area Pore Volume Ave. Pore Size Metal Dispersion m2/g cm3/g nm mol% Commercial Catalyst Pd 1% (Alfa) (as received) 189 0.58 9.4 28% Pd 1% (Alfa) with 15% boeh. (fresh) 159 0.46 8.7 27% StandDev (with 3 samples) 15 0.05 0.11 Pd 1%(Alfa) with 15% boeh. (spent)a 133 0.44 10.7 1.3% Pd 5% (Alfa) (as received) 145 0.45 9.3 14% Pd 5% (Alfa) with 15% boeh. (fresh) 139 0.41 9.2 14% Pd 5% (Alfa) with 15% boeh. (spent)b,c 93 0.28 9.9 1.9% Lab-made Catalyst Pd 4.3% La2O3 6% (fresh) 92 0.46 18.3 14% Pd 5.3% La2O3 4% MgO 4% (spent)d 84 0.40 17.8 N/Ae Pd 4.4% La2O3 3.5% MgO 3.5% (spent)d 88 0.43 18.3 N/Ae Pd 5.6% La2O3 6% (spent) d 87 0.46 17.8 N/Ae aAfter Exp. no. 0.3 & 0.4 (See Section C.2.1) bAverage of 2 samples, except for Metal Dispersion, where there was only one sample. cAfter Exp. no.2 (See Table 8.6) dAfter Exp. no.3 (See Table 8.6) eN/A: Not Measured tivation observed in the MCMR in Chapter 8 cannot be explained by a significant decrease in catalyst activity alone. 182 L i n  ( C p s ) 50 60 70 80 90 α α αγ γγ PdO PdOα PdO Legend α: α−Al2O3 γ: γ−Al2O3 Pd: PdO Spent L i n  ( C p s ) 0 10 20 30 40 2-Theta - Scale 25 30 40 50 Fresh - heta-Scale Figure 7.4: XRD Diagram of Commercial Pd 1%/ γ-Al2O3 (Alfa) with 15% Boehmite, Fresh and Spent (after MCMR Exp. no.0.3, see Table C.2). 7.3.4 Deactivation This section tries to explain the catalyst deactivation decays presented in this chap- ter, using both fresh catalysts and catalysts spent during the MCMR experiments. Figure 7.4 presents XRD spectra for Pd 1% (Alfa) fresh and spent catalysts. α- Al2O3 is present in the fresh sample, but peaks did not grow or were even reduced in spent sample. One PdO peak appeared in the spent spectrum, but it was not backed up by two other peaks that should normally have also appeared. In Table 7.5, for Pd 1% samples, surface area dropped for the spent sample, while pore size increased, indicating some pore sintering. Metal dispersion decreased dramatically from 27 to 1.3%, but we cannot conclude at this stage whether metal sintering was significant due to the absence of clear peaks in the XRD spectra. Figure 7.5 presents XRD spectra for Pd 5% (Alfa) fresh and spent catalysts. There is a clear growth in α-Al2O3 peaks, indicating a beginning of phase change, possibly causing pore sintering. PdO peaks remained stable. In Table 7.5, both sur- 183 L i n  ( C p s ) 200 α α αγ γγ PdO PdOα PdO Legend α: α−Al2O3 γ: γ−Al2O3 L i n  ( C p s ) 0 100 2-Theta - Scale 25 30 40 50 Fresh Spent Figure 7.5: XRD Diagram of Commercial Pd 5%/ γ-Al2O3 (Alfa) with 15% Boehmite, Fresh and Spent (after MCMR Exp. no.2, see Chapter 8). L i n  ( C p s ) 70 80 90 100 110 120 130 140 150 α α αγ γγ PdO PdOα PdO Legend α: α−Al2O3 γ: γ−Al2O3 L i n  ( C p s ) 0 10 20 30 40 50 60 2-Theta - Scale 26 30 40 50 Fresh Spent Figure 7.6: XRD Diagram of Lab-made Pd-based Catalyst, Fresh (Pd 4.3% La2O3 6% γ-Al2O3) and Spent (after MCMR Exp. no.3, see Chapter 8, Pd 5.3% La2O3 4% MgO 4% γ-Al2O3). 184 face area and pore volume dropped significantly, confirming pore sintering, likely causing the drop in metal dispersion. Figure 7.6 shows XRD spectra for lab-made Pd 5% La2O3−MgO/ γ-Al2O3. No growth in α-Al2O3 peaks is observed, but rather a growth in PdO peaks, indi- cating metal sintering. In Table 7.5, the surface area, pore volume and average pore size were stable. It can then be concluded that the steam-aged support, with pro- moters, was stable under the MCC conditions. However, promoters might have had an adverse effect of the Pd site stability. More work is clearly needed to improve the stability of the the lab-made Pd-based catalyst. 7.3.5 Estimation of Kinetic Parameters Activation Energy E4 and Reaction Order for Methane α Using Pd 1% (Alfa) catalyst, Figure 7.7 shows data obtained in order to calculate the activation energy E4 and the reaction order for methane, α . Table 7.7 presents the slopes from the linear regressions, as well as the calculated kinetic parameters. The kinetic parameters are in the range of those reported in the literature (Lee and Trimm, 1995). The error in α is large, possibly indicating temperature dependence of the coefficient. The A4 value for Pd 1% (Alfa) was ∼3 times smaller than for Pd 5% (Alfa). However, the experimental scatter for the Pd 5% samples was large. Lab-made catalyst had A4 similar to the commercial Pd 5% catalyst. Pre-exponential Factor, A4 Figure 7.8 presents the data used to estimate the pre-exponential Factor, A4, for the Pd-based catalysts tested in this chapter. Table 7.8 details the experimental con- ditions, and Table 7.9 presents the A4 results. The catalysts and rate of reaction seemed to stabilize after ∼30-40 h, allowing the use of the residual fitting parame- ter c from Eq. (6.14) to estimate A4. 185 0.0011 0.0012 0.0013 0.0014 0.0015 −9 −8 −7 −6 −5 −4 1/T [K−1] l l l l l l l l (A) 15% boeh., 5.9 bar (B) 15% boeh., 5.9 bar (C) 15% boeh., 7.8 bar (D) As received, 5.9 bar A: Activation Energy −2.4 −2.2 −2.0 −1.8 −1.6 −8.0 −7.5 −7.0 −6.5 −6.0 ln(PCH4) [ln(bar a)] l l ll l (A) 585°C (B) 585°C (C) 550°C B: Methane Reaction Order α ln (r 4 ) [l n(k mo l/s  kg )] Figure 7.7: Estimated Kinetic Parameters for Pd 1% (Alfa) Catalyst: A. Acti- vation Energy E4; B. Reaction Order for Methane α . Catalyst Loading: 2.0 mg (except for curve (D) at 1.7 mg). Inlet Condition: CH4 flow: 37 Nml/min, 2 mol% in air; Pressure, temperature and catalyst details are listed in Table 7.6. Linear regression results appear in Table 7.7. 186 Table 7.6: Estimated Kinetic Parameters for Pd 1% (Alfa) Catalyst: Experi- mental Conditions for Figure 7.7 La- bel Catalyst Constant Pressure for Part A Temperature Variation for Part A Pressure Variation for Part B Tempera- ture for Part B bar oC bar oC A Pd 1%, 15% boeh. 5.9 500-600 4.8-8.4 585 B Pd 1%, 15% boeh. 5.9 450-600 4.1-8.0 585 C Pd 1%, 15% boeh. 7.8 450-585 4.5-7.4 550 D Pd 1% (as received) 5.9 400-550 N/A Table 7.7: Estimated Kinetic Parameters for Pd 1% (Alfa) Catalyst: Linear Regression Results for Figure 7.7 Activation Energy E4 Reaction Order for Methane α Label Slope R2 Label Slope R2 A -12320 0.995 A 0.66 0.98 B -10110 0.998 B 0.51 0.98 C -9374 0.995 C 1.16 0.94 Average -10600 Average (α) 0.78a E4 (kJ/mol) 88 a Std. Error (kJ/mol) 14 Std. Error 0.39 D -8274 0.990 E4 (kJ/mol) 69 aAs an alternative, multivariate non-linear regression for all of the data gave a reaction order α of 0.83, and an activation energy of 96 kJ/mol. 187 0 10 20 30 40 1000 1500 2000 2500 3000 3500 l l l lllll l ll l lll llllll l l l l ll A: Pd 1% (Alfa) l (A) 5.7 bar (B) 5.9 bar (C) 7.5 bar 0 10 20 30 40 50 4000 6000 8000 10000 12000 B: Pd 5% Commercial (Alfa) and Lab−made (D) Alfa, 7.4 bar, 37 Nml/min (E) Alfa, 3.8 bar, 30 Nml/min (F) Lab, 3.8 bar, 30 Nml/min Time on Stream (h) Ap pa re nt  A 4 [km ol/ (s kg  ba rα )] Figure 7.8: Estimated Kinetic Factor, A4. Data fitted with Eq. (6.14). Exper- imental conditions are listed in Table 7.8. 188 Table 7.8: Estimated Kinetic Parameters for Experimental Conditions in Figure 7.8 La- bel Catalyst Tempera- ture Ave. Pressure CH4 Flow % CH4 in Air WHSV oC bar Nml/min mol% h−1 A Pd 1% (Alfa), 15% boeh. 575 5.7 37 2.0 71,000 B Pd 1% (Alfa), 15% boeh. 575 5.9 37 2.0 71,000 C Pd 1%(Alfa), 15% boeh. 575 7.5 37 2.0 71,000 D Pd 5% (Alfa), 15% boeh. 510 7.4 37 3.0 47,000 E Pd 5% (Alfa), 15% boeh. 510 3.8 30 3.0 38,000 F Pd 4.5% La2O3 6% 510 3.8 30 3.0 38,000 Table 7.9: Estimated Kinetic Pre-exponential Factor, A4, from Figure 7.8 Label Catalyst A4 R2 kmol/(s kg barα ) A Pd 1% (Alfa), 15% boeh. 1842 0.82 B Pd 1% (Alfa), 15% boeh. 1306 0.93 C Pd 1%(Alfa), 15% boeh. 1757 0.95 Average 1635 Std. Error 326 D Pd 5% (Alfa), 15% boeh. 3153 0.999 E Pd 5% (Alfa), 15% boeh. 6267 0.990 Average 4710 Std. Error 3052 F Pd 4.5% La2O3 6% 5080 0.88 189 7.3.6 Conclusions Micro-reactor experiments allowed combustion catalysts to be tested for their suit- ability in the MCMR prototype, as well as estimation of kinetic parameters. Commercial Pd 1% and 5%/ γ-Al2O3 catalysts (Alfa Aesar) as well as lab- made Pd 5% La2O3−MgO/ γ-Al2O3, were found to be suitable for the MCMR prototype. The activity of the catalysts was generally stable after 24-48 h on stream. In the stability experiments on Pd 1% (Alfa) catalyst, reversible deactivation was observed, and CO concentration increased with increasing temperature, pres- sure and time on stream. Inhibition by water molecules is likely to have been the cause of the reversible deactivation. XRD spectra and pore analyses suggest that pore sintering was the major source of deactivation for the two commercial Pd catalysts, while metal sintering was more important for the lab-made Pd La2O3−MgO catalyst. Further work is needed to improve the stability of the catalysts. For the Pd 1% (Alfa) catalyst, the activation energy E4 was evaluated to be 88 kJ/mol, and the reaction order for methane α was estimated to be 0.78. The pre- exponential factor for commercial Pd 1% catalyst was about three times less than for the commercial and lab-made Pd 5% catalysts. 190 Chapter 8 Development of the Multi-Channel Membrane Reactor 8.1 Introduction In Chapter 1, the importance of developing small-scale hydrogen production tech- nologies (<500 kg/day), to enable the market penetration of hydrogen powered vehicles, was highlighted. Several technologies with potential to achieve this ob- jective economically were reviewed. In Chapter 2, the concept of a Multi-Channel Membrane Reactor (MCMR) was presented, combining a Multi-Channel Reactor (MCR) and perm-selective palladium-silver (Pd/Ag) membrane technologies. The MCMR alternates Steam Methane Reforming (SMR) gas channels to produce hy- drogen with Methane Catalytic Combustion (MCC) gas channels to provide the reforming heat of reaction. Pd/Ag membranes, located in the reforming gas chan- nel, shift the reaction equilibrium, and produce pure hydrogen in a single vessel. The concept was proposed by Goto et al. (2003), but proof-of-concepts are limited. No previous experimental work has been published on MCMR using SMR. This chapter presents the design, commissioning and results of a MCMR proto- type. Results are compared with predictions from the 2-Dimensional (2-D) model 191 developed in Chapters 2 and 3. Reforming and combustion catalysts were coated on metal plates, with the innovative air-spray hot substrate coating method devel- oped in Chapters 4 and 5. The activity and stability of those catalysts were tested in Chapters 6 and 7, with Ru and Pd-based catalysts on γ-Al2O3 support selected for the reforming and combustion channels respectively. 8.2 Material and Method 8.2.1 Reactor Design Figure 8.1 presents an expanded view of the MCMR prototype. The core com- ponent of the design is the separator. In addition to transferring heat from the combustion to the reforming channel, the separator had several functions: (1) To distribute the feed and remove gas products; (2) to hold the catalyst plates with five recesses located on each side; (3) to monitor reforming and combustion tempera- ture profiles on four locations on each side; and (4) to host four sampling tubes on each side to collect and measure gas compositions along the reactor. The reforming frame created a space between the separator and the membrane to provide the reforming channel. Experiments were conducted both without and with membranes. The Pd/Ag 25µm thick membrane, was provided by Membrane Reactor Technologies (MRT) and was fabricated using an electroless plating tech- nique. A dummy membrane with the same dimensions as the Pd/Ag membrane was used to preserve the desired channel height when there was no membrane. In order to avoid hot spots on the combustion side, an optional frame was designed to distribute the air evenly along the reactor, as suggested by Tonkovich et al. (2004). However, a hot spot was never an issue in practice, so the combustion frame was never used as intended. Once assembled, from the extremities of the flanges, the reactor measured 500 mm x 254 mm x 125 mm. Internal channel volumes were ∼50 ml for both chan- nels. Sealing was by GrafoilTM gaskets with Tang 316/316L inserts. All parts were tightened with 18 bolts going through the flanges. Mechanical drawings are provided in Appendix E.4. The MCMR was monitored by 16 thermocouples: 8 located inside each car- 192 Top Flange Cartridge heater hole Combustion feed hole Gaskets (3-4) Separator Recesses for catalyst plates Thermocouples or Sampling Lines Combustion Frame (optional) Bottom Flange Cartridge heater hole Hydrogen Product Lines (2) Membrane (support only shown) Feed Lines (one each side) Product Lines (one each side) Reforming Frame 508 mm (20.0 in) 254 mm (10.0 in) Figure 8.1: Expanded View of MCMR Prototype tridge heater, inserted in the two flanges; and 8 divided equally between the reform- ing and the combustion channels. Figure 8.2 shows where the four temperatures and gas samples were taken along the reactor length for each channels. In this chap- ter, methane conversion or temperature data at positions 1 to 4, refer to the location numbers on this figure. On the combustion channel, Part B, there is a GrafoilTM strip, for mechanical support, that divides the channel into two sub-channels. Aver- age channel temperatures Tave, reported in this chapter, represent the average of all four thermocouples readings. The average temperature on the reforming channel was used as the set point for temperature control, accomplished by a custom-made 193 Reactor Description 50 mm 1 2 3 4 A: Reforming B: Combustion 50 mm 1 2 3 4 Figure 8.2: Top View of Thermocouple and Gas Sampling Locations for both Channels. A: Reforming Channel, B: Combustion Channel. Squares: Thermocouple locations; Circles: Gas sampling tube inlets; Arrows: Feed inlet and products outlet. LabVIEWTM program. Two gauge pressure transducers measured the pressure in both channels, at the first and last sampling points. 194 Reforming Gas Channel Bottom Flange Top Flange PdAg Membrane Combustion Gas Channel Separator (Solid Wall) Methane Hydrogen Air Low P. N2 Methane High P. N2 Water Tank BPR To Vent To GC PI To Vent To GC PI Water Bath Vacuum pump MFCTC FM PI PI G-L MFC S MFC S MFC S MFC S S S PI BPR PI G-L BPR To Vent To GC PIPI TI x16 G-L PI Pressure Indicator Line Heated with Rope Heater S Normally Opened Solenoid Valve S Normally Closed Solenoid Valve TI Temperature Indicator MFCTC Temperature Controler Catalyst Plates Radiant Heater Cartridge Heater with Thermocouple Thermocouple and Sampling Location MFC Normally Closed Bonnet Valve Gas-Liquid Separator with drain Mass Flow Controller BPR Back Pressure Regulator FM Flow Meter PI Rotameter Figure 8.3: MCMR Process Flow Diagram. For detailed PI&D, see Appendix E.1. 195 8.2.2 Process Design Figure 8.3 shows a simplified flow diagram of the MCMR unit, including some key control instruments. A detailed Process & Instrumentation Diagram (P&ID) is included in Appendix E.1. The functioning of the unit can be summarized as fol- lows: For the reforming side, water is pressurized with N2 and, after pre-heating to produce steam, it is mixed with CH4 at the desired ratios. The H2 line is only used for start-up and membrane testing purposes. For the combustion side, an air line is pre-heated with rope heaters, and CH4 is mixed to the desired composition before entering the reactor. All feed streams are controlled with mass flow controllers, except for the H2, where the flow is adjusted when needed with the needle valve of a rotameter, previously calibrated. Downstream of the reactor, products are cooled by a water bath, and condensed water is removed with gas-liquid separators (see drawing in Appendix E.3). Gas products are split into two streams, one going to a Gas Chromatograph (GC), the second being vented. For the hydrogen perme- ate, two options are available, selected according to the desired permeate pressure: vane pump for vacuum, or back-pressure regulator for higher permeate pressure. Vacuum was generated with a 24V rotary vane pump (Clark Instrument, model no. 16987). Pressures in both channels were controlled by back-pressure regulators, located downstream of the gas-liquid separators. In case of emergency shutdown, triggered manually or automatically by a flow, temperature or pressure alarm, the system is flushed with N2, while all other feed lines are isolated with solenoid valves. A detailed electrical and control diagram is found in Appendix E.2. Gases in the experiments were purchased from Praxair: CH4 (99% purity), H2 (99,995+% purity), air (extra dry grade), and N2 (99,995+% purity). Deonized water was utilized to produce the steam. Figures 8.4 and 8.5 display images of the MCMR prototype, reactor skid, and process and control equipment. The sampling of reforming gases was challenging, since water needed to be removed. However, non-insulated 1/16” (1.6 mm) lines (Fig. 8.5B) quickly cooled the gas to be sampled, and no external cooling was needed. Gases for sampling passed through a batch gas-liquid separator that needed to be flushed after each 196 sampling. 1 L tedlar bags, shown on Figure 8.5C, were filled and emptied twice to remove the previous sample gas, before keeping one sample. The bags were filled at a rate of ∼0.5 L/min. It took ∼30 min to sample all 8 sampling locations. 8.2.3 Catalyst Preparation Coating methodologies and material employed are described in detail in Chap- ters 4 and 5. In brief, for commercial catalyst, Disperal P2 boehmite (Sasol) was mixed in distilled water with the commercial catalyst powder. Boehmite repre- sented 15% of the total solid mass. The concentration of the catalyst powder was 0.25 mol/L (based on the molecular weight of alumina). The mixture was ball milled overnight, and the pH was adjusted with nitric acid to ∼5 before and after the ball milling. The modified sol was air-spray coated onto a stainless or Fecralloy metal substrate, while being heated >100oC. The metal substrate was previously sand-blasted and calcined for Fecralloy. About 0.2-0.3 g of catalyst were coated on each metal plate, each measuring 50 mm x 88.5 mm. Once the masses of the catalyst coatings were judged acceptable, the samples were calcined overnight in static air at 650oC. For lab-made catalyst, Baikalox CR125 γ-Al2O3 (Baikowski) was mixed in distilled water with the boehmite, which represented 40% of the total solid mass. The concentration of the γ-Al2O3 powder was 0.5 mol/L. After the air-spray coat- ing and calcination, promoters were impregnated using a modified incipient wet- ness procedure, in which plates were flooded with the impregnation solution, and excess solution was removed after 2 min. The mixture was air dried for 2 h, and heated at 110oC overnight in static air. Impregnation solution concentrations are listed in Table 8.1. Support and promoters were steamed and heated under a pres- sure of 25 bar, and then maintained at 575oC for 24 h. Ru or Pd was then impreg- nated following the same procedure as for the promoters. Pd-based catalyst plates were calcined at 600oC in static air for 5.5 h and Ru-based catalyst plates were reduced in-situ. Catalyst compositions were estimated by weighing the plates after impregnation and heat treatment. Tables 8.2 - 8.4 describe the catalyst samples employed for the MCMR for this chapter. 197 Figure 8.4: Reactor and Process Images I: (A) MCMR prototype on skid, without insulation; (B) MCMR with insulation and aluminum casing, electrical panel and monitor; (C) Front panel for pressure control; (D) Inside the electrical Panel. 198 A B C D Figure 8.5: Reactor and Process Images II: (A) Sampling side of the MCMR; (B) Close-up on the sampling tube coming out of the reactor; (C) Sam- pling panel; (D) Water bath for products cooling and gas-liquid separa- tors 199 Table 8.1: Impregnation Solutions and Desired Metal Contents for Catalysts used in MCMR Desired Metal Contenta Solution wt% mol/L Promoters La2O3 6% La Nitr. 0.27 La2O3 4% MgO 4% La Nitr. 0.18; Mg Nitr. 0.72 La2O3 4% MgO 2% MnO 2% La Nitr. 0.18; Mg Nitr. 0.36; Mn Nitr. 0.28 Catalyst Pd 5% Pd Nitr. Sol. Pd 4-5% w/w (Alfa Aesar, as received) Ru 6% Ru Nitr. 0.51 aMeasured metal content can vary by ± 2% from the desired value Table 8.2: Catalyst Description for MCMR Experiment no.1, without Membrane Catalyst on γ-Al2O3 support Plate Position Mass Catalyst Ave. Coating Thickness Density of Catalyst Layer Metal Support g µm kg/m3 Ru 7.5% La2O3 3.5% MgO 3.5% 1 0.342 236 327 Fecral- loy Ru 5.6% La2O3 5% MgO 2.% 2 0.313 208 340 SS 310 Ru 8% La2O3 4% MnO 2% MgO 2% 3 0.299 217 312 Fecral- loy Ru 8% La2O3 4% MnO 2% MgO 2% 4 0.286 210 308 SS 310 Ru 7% La2O3 6% 5 0.295 207 322 SS 310 Total mass / Ave. Thickness / Ave. Density 1.535 216 322 Pd 5% (Alfa) 1 0.268 232 261 SS 310 Pd 5% (Alfa) 2 0.255 196 294 SS 310 Pd 5% (Alfa) 3 0.205 120 386 SS 304 Pd 5% (Alfa) (reused from run 0.9) 4 0.268 199 304 SS 304 Pd 5% (Alfa) (reused from run 0.9) 5 0.261 180 328 SS 304 Total mass / Ave. Thickness / Ave. Density 1.257 185 315 200 Table 8.3: Catalyst Description for MCMR Experiment no.2, with Membrane Catalyst on γ-Al2O3 support Plate Position Mass Catalyst Ave. Coating Thickness Density of Catalyst Layer Metal Support g µm kg/m3 Ru 8% La2O3 3% MnO 1.5% MgO 1.5% 1 0.306 220 315 Fecral- loy Ru 6% La2O3 3% MgO 3% 2 0.316 211 338 SS 310 Ru 8% La2O3 5% 3 0.279 208 304 Fecral- loy Ru 7% La2O3 4.5% 4 0.282 209 305 Fecral- loy Ru 7% La2O3 6% 5 0.296 217 308 SS 310 Total mass / Ave. Thickness / Ave. Density 1.479 213 314 Pd 5% (Alfa) 1 0.213 111 433 SS 304 Pd 5% (Alfa) 2 0.264 195 306 SS 310 Pd 5% (Alfa) 3 0.290 172 382 SS 304 Pd 5% (Alfa) 4 0.263 194 306 Fecral- loy Pd 5% (Alfa) 5 0.287 205 317 SS 304 Total mass / Ave. Thickness / Ave. Density 1.317 175 349 8.2.4 Reactor Assembly The reforming catalyst plates were located on the lower side of the separator. In order to assemble them in the prototype, the following procedure was developed: the five reforming plates were deposited in the recesses of the separator. One gasket and the reforming frame were placed above the separator and plates (the gaskets were previously calcined at 400oC for 2 h, in an attempt to remove volatile sulfur compounds that could be present). Silicone glue was then applied onto the outside contour of the gasket. A flat heavy piece of metal was put on top of the separator and left overnight. The next day, the reforming frame was removed and fitted with another gasket on the bottom flange, to install the dummy or Pd/Ag membrane, which also sits on a 201 Table 8.4: Catalyst Description for MCMR Experiment 3, with Membrane Catalyst on γ-Al2O3 support Plate Position Mass Catalyst Ave. Coating Thickness Density of Catalyst Layer Metal Support g µm kg/m3 Ru 7.5% La2O3 5% 1 0.309 221 316 Fecral- loy Ru 7.5% La2O3 4% MgO 4% 2 0.294 214 310 Fecral- loy Ru 7% La2O3 4% MgO 4% 3 0.292 214 309 Fecral- loy Ru 6.5% La2O3 4.5% MgO 4.5% 4 0.325 228 321 Fecral- loy Ru 6% La2O3 3.5% MgO 3.5% 5 0.308 221 315 Fecral- loy Total mass / Ave. Thickness / Ave. Density 1.528 220 314 Pd 5.5% La2O3 6% 1 0.263 200 297 Fecral- loy Pd 5.5% La2O3 4% MgO 4% 2 0.262 200 296 SS 310 Pd 4.5% La2O3 4% MgO 2% MnO 2% 3 0.278 207 303 SS 310 Pd 4.5 La2O3 3.5% MgO 3.5% 4 0.26 208 282 SS 310 Pd 5% (Alfa) 5 0.232 160 328 SS 304 Total mass / Ave. Thickness / Ave. Density 1.295 195 301 gasket. To minimize feed by-pass under and along the sides of the membrane, strips of gasket were used to fill gaps as much as possible (See Figure 8.6). Despite these efforts, we estimated that between 13 to 23% of the feed by-passed the reforming channel. Details are provided in Section 8.2.8. The separator, including the reforming plates and gaskets, were next placed on the reforming frame. The combustion plates were added, as well as Grafoil gasket and the Grafoil strip serving as mechanical support. The top flange was lowered carefully on to the top of the assembly. Bolts and nuts were greased with anti- 202 Figure 8.6: Pd/Ag Membrane Installed on Bottom Flange after Experiment no.3. Arrows indicate locations of gasket under the membrane and strips used on sides to fill gaps. They also indicate where feed by-passing is suspected to have occurred. 203 seize (Loctite, Metal Free Heavy Duty, no. 51606) and then tightened at 155 N-m. Feed, products and sampling connections were attached, and pressure tests on both channels were conducted. A layer of 150 to 200 mm of alumina fibre (Thermal Ceramics) was added to surround the reactor, as well as a 3.2 mm (1/8”) thick aluminum casing, to contain the insulation material, and to reduce heat losses by radiation. 8.2.5 Start-up Procedure Without Membrane After assembly, the temperature of the reactor was increased at ∼1.6oC/min from ambient to 350oC, at atmospheric pressure. With N2 cylinders replacing methane, N2 was injected at a rate of 0.26 and 0.13 nL/min into the reforming and combus- tion channels respectively. Those conditions were left overnight to provide time for some anti-seize grease to oxidize and the resulting smoke to dissipate. The next day, the set point of the bottom and top flange heaters were increased to 500 and 555oC respectively. On the combustion side, N2 flow was stopped, and air flow was started at 2.0 L/min. On the reforming side, N2 flow was also stopped, and hydrogen flow was started at ∼0.6 nL/min. Steam and air pre-heaters were started with skin temperature set points at 400-450oC. Water flow was started at 0.18 kg/h. 45 to 60 min later, with the steam flow well established in the reactor, methane flow for reforming was started (0.5-1 nL/min) and the water flow was adjusted to reach the desired Steam-to-Carbon (S/C) molar ratio. Pressure was then increased gradually to 10-15 bar. On the combustion side, air flow was increased to 5.5 - 6.5 nL/min, pressure was adjusted to 1-5 bar, and methane flow was started to obtain a concentration of 2-3.5% in air. With Membrane To preserve the membrane integrity, specific H2 partial pressures are required when ramping the temperature. A hydrogen flow was then added to the procedure de- scribed above. The steps are listed in Table 8.5. 204 Table 8.5: Membrane Start-up Procedure Steps Temp. Set Point for Flanges Heaters (Bottom - Top)a Pressure Flow Rate Note Pr PH2,r Pm N2 H2 oC bar bar bar nL/ min nL/ min 1. Ambient 4 0 1 0.2 0 2. (290 -350) 4 0 1 0.2 0 Left overnight at those conditions 3. Reactor Pressure increased to 6 bar with N2 4. (400 - 400) 6 0.05 1 14.5 0.1 5. (450 - 450) 6 0.10 1 6 0.1 6. (500 - 500) 6 0.3 1 3.8 0.2 7. (500 - 555) 6 0.8 1 1.3 0.2 8. (500 - 555) 6 6 1 0 10 Permeate test 8. Reactor Pressure increased to 11 bar with H2 9. (500 - 555) 11 1 0 0.2 Steam start-up & methane start-up 10. (500 - 555) 11 1 0 0 Normal operating conditions aMembrane sit on the bottom flange, where temperature was kept lower to insure membrane integrity. 8.2.6 Operation Table 8.6 details the operating conditions during the experiments. Residence times and average velocities were respectively ∼3 s and ∼0.09 m/s in the reforming channel, and ∼0.5 s and ∼0.5 m/s in the combustion channel. Only the top flange cartridge heaters were utilized during the operation, to represent conditions where all heat transfer was coming from the combustion channel, as in a multi-channel assembly. Transverse temperature differences were small between the reforming and combustion channels, ∼3-5oC. However, the top flange temperature could be as high as 610oC when the reforming channel was at 550oC. Axial temperature variations were generally less than 15oC in the channel. The heat losses to the surrounding were estimated by leaving the reactor at 550oC overnight, without any 205 Table 8.6: Experimental Operating Conditions Exp. No. Reforming Conditions Per- meate Combustion Conditions Time of Stream Pr S/C FCH4,ro Tr,ave Pm Pc FCH4,co yCH4,co (in air) Tc,ave bar mol/ mol nL/ min oC bar bar nL/ min mol% oC h 1b 11.4 2.8 1.35 552 N/A 2.4 0.22 3.4 555 9.3 1f 8.43 2.7 2.33 549 N/A 2.4 0.22 3.4 555 19.4 2a 15.7 3.4 0.740 552 1.02 3.6 0.22 3.4 555 1.2 2b 15.7 3.8 0.495 552 1.01 3.6 0.22 3.4 555 4.5 2c 15.4 3.4 0.740 561 1.01 3.6 0.22 3.4 565 12.5 2d 15.4 3.4 0.740 570 0.78 3.7 0.28 3.5 575 18.4 3a 16.0 3.8 0.495 552 1.02 3.8 0.22 3.4 555 1.3 3b 13.2 4.0 0.633 570 0.79 3.8 0.20 3.0 575 12.7 gas flowing into the reactor. By measuring the time the cartridge heaters were on during one hour, knowing the total power installed (3kW), the heat losses were estimated to be at ∼530 W. Comparatively, the heat of reaction for endothermic reforming reactions was ∼60 W. Pressure transducers were not able to detect pressure drops in the channels, since the drops were below or of the same order of magnitude as the instrument er- rors. Using Darcy-Weisbach equation for friction head loss in laminar flow regime, the pressure drop in both channels was estimated to be <3 Pa. Differential pressure transducers would be needed to measure accurately such small values. 8.2.7 Analytical Equipment A GC was used to measure product gas compositions as described in Chapter 6. To take images of coating surfaces, a Nikon Eclipse MA200 microscope was used, combined with a Nikon DS-Fi1 camera, with a resolution of 2560 x 1920 pixels. To measure the coating thicknesses, a Positector 6000-1 thickness meter by 206 Defeslko, based on the eddy current principle, was used. Details of this method are provided in Chapter 4. 8.2.8 Modeling Parameters and Metrics To compare the experimental results with predictions from the model presented in Chapter 2, some modifications were made on the catalyst layers and the membrane, as shown in Figure 8.7. Only part of the entire facial surface of the membrane plate could actually permeate hydrogen. The membrane contour is used to seal the mem- brane on the stainless support, and about 61% of the surface is active. In Figure 8.6, one can see a difference in foil polish appearance. The membrane center, with a mirror appearance, permeates hydrogen, whereas the frame does not. Also, in order to insert thermocouples and tubes for sampling, a gap existed between each of the catalyst plates. Therefore, membrane dead zone and no-catalyst zone cor- rections were added to the model. The model also allowed a distinct thickness for each plate. Tables 8.7 & 8.8 list the parameters utilized in the simulations. We did not expect the catalyst layers to affect the laminar flow. Relative to channel imperfections, due to machining, gasket compression, and catalyst plates flatness, the catalyst layer thickness and surface roughness variations were negligi- ble. Methane Conversion, XCH4 Equation (6.13) from Chapter 6 was used to evaluate the methane conversion in both channels. Specific Hydrogen Production, YH2 Various performance indicators were defined in Chapter 3, including the specific hydrogen production indicators defined as the ratio between the mass flow of hy- drogen extracted by the membrane and any of the reactor volume (vol.react.), mass of catalyst (kgcat), or membrane area (m.area). For the reactor volume, we only included the internal volumes of the two channels, separator wall, and half the membrane support. This allowed our results to be compared with a Packed Bed Membrane Reactor (PBMR) and Fluidized Bed Membrane Reactor (FBMR). 207 H2O Pd/Ag Membrane Reforming Gas Channel (25 µm) (0.85-1 mm) (~200 µm) H2 Reforming Catalyst CH4 H2 z A B x (12.8 mm) Hr Thcat,r Thm (11.9 mm) (5.02 mm) CH4 Air Separator Wall Combustion Gas Channel L (278 mm) Combustion    Catalyst (~190 µm) (1 mm) (127 mm) x C D E z Membrane Dead Zones No Catalyst Zones (6.8 mm each) Thcat,c Hc Ths Figure 8.7: Schematic of MCMR Prototype for Simulations, Including Di- mensions, Not to Scale. (Subscripts: Pd/Ag membrane m; SMR channel r; catalyst layer cat; separator wall s; MCC channel c.) Temperature Profile As discussed below, the methane conversion in the combustion channel under- performed the simulation predictions. For the experimental combustion methane flow, and the 2-D model with energy transfer developed in Chapter 2, tempera- tures would have quickly jumped, giving erroneous predictions. It is likely that flow distribution and catalyst deactivation caused the large discrepancies. Hence, the model could not be used to its full extent, and temperature profiles measured experimentally were imposed as input, instead of solving the energy balance. Sec- ond order polynomials were fitted to extrapolate the measured temperatures to the 208 Table 8.7: Parameters for Simulations Predictions, Part I. Physical properties options and so- lution parameters are the same as expressed in Table 3.2 Parameters (Symbols) Values (Equations) Units Operating Parametersa Reforming Feed H2 Content (yH2,ro) 0.001 mol/mol Reforming Feed CO Content (yH2,ro) 0.001 mol/mol Reforming Feed CO2 Content (yH2,ro) 0.001 mol/mol Catalyst Parameters Pore Radius (Rpore,r) 9 nm Pore Radius (Rpore,c) 4.5 (Alfa) - 9 (Lab-made) nm Pore Volume (υr) 0.42 cm3/g Pore Volume (υc) 0.35 (Alfa) - 0.42 (Lab-made) cm3/g Porosity (εcat,k) See Eq. (6.12) Density (ρcat,k) see Tables 8.2- 8.4 kg/m3 Reforming Kineticsb Jakobsen et al. (2010) Combustion Kinetics nth order (See Eq. (2.50)) Reaction orders (α , β ) 0.78, 0 Pre-exponential Factor (A4)b 1635 (Pd 1%) 4710 (Pd 5%) kmol/(kg s barα ) Activation Energy (E4) 88 kJ/mol aOperating parameters vary and are detailed in Table 8.6 bSee Section 8.2.8. channel inlet and outlet, and only the material balance equations were then solved. Estimation of Membrane Effectiveness, ηm From Eq. (2.22), ηm was evaluated by: ηm = FH2,m/Aream Am Thm exp ( −Em RgTr,ave )(√ PH2,r− √ PH2,m ) (8.1) To evaluate the membrane area (Aream), dead-zones (see Figure 8.7) were excluded to obtain an effective membrane surface of 0.020 m2 (the full membrane surface being 0.022 m2). Am, Thm and Em are listed in Table 8.8. The hydrogen perme- 209 Table 8.8: Parameters for Simulations Predictions, Part II. Physical properties options and solution parameters are the same as expressed in Table 3.2 Parameters (Symbols) Values (Equations) Units Design Parameters Length (L) 0.251 - 0.278a m Reforming Width (Wr) 0.081 m Combustion Width (Wc) 0.074 m Catalyst Thickness (Thcat,k) See Tables 8.2 - 8.4 µm Ref. Gas Channel Half-Height (Hr) Without memb. 1.0; with membrane 0.85; mm Comb. Gas Channel Half-Height (Hc) 1.0 m Membrane Parameters Membrane Thickness (Thm) 25 µm Membrane Effectiveness (ηm) 0.56 (See Eq. (8.1) and Section 8.3.3) Pre-exponential Factor (Am) 3.427e-5 mol/(s m bar0.5) Activation Energy (Em) 9180 J/mol Membrane Dead Zone See Figure 8.7 aFor predictions with membrane, 5 plates, each 0.0502 m, and separated with a 6.75 mm gap, give a total length of 0.278 m. ate flow (FH2,m), reforming channel average temperature (Tr,ave), reforming channel hydrogen partial pressure (PH2,r), and hydrogen permeate pressure PH2,m were mea- sured experimentally. Estimation of Feed By-pass Despite repeated attempts to eliminate the problem, the MCMR prototype had a design fault, with a portion of the reforming feed by-passing the channel by going under or beside the dummy and Pd/Ag membranes. It is probable that the by- passing caused the outlet conversion to be less than the measurements inside the reactor with the sampling tubes. By mass balance, the following equation is obtained to estimate the extent of the 210 by-passing: By-pass= XCH4,out −XCH4,expected XCH4,expected [mol/mol] (8.2) XCH4,out is the measured outlet conversion. For experiments with membranes, we assumed that the XCH4,expected should have been a conservatively-extrapolated 5% higher than the conversion measured after the 4th plate (XCH4,4): XCH4,expected = XCH4,4 ∗1.05 [mol/mol] (8.3) The by-pass estimate was used in two places: In some simulation predictions with the membrane, the reforming feed was multiplied by (1-By-pass). Secondly, in the Parametric Study section below, the mole ratio of the hydrogen permeate (FH2,m) over the reforming methane fed FCH4,ro, was corrected as: RatioH2,m/CH4 = FH2,m FCH4,ro(1−By-pass) (8.4) Catalyst Coating Density, ρcat k ρcat k was evaluated by dividing the mass of catalyst, Wcat , by the area of the metal plate times the average thickness of the catalyst layer, Thcat,k,ave: ρcat k = Wcat 0.0885∗0.05058∗Thcat,k,ave [kg/m 3] (8.5) Combustion Kinetics Modification In Chapters 2 and 3, the kinetic model includes a term for the O2 partial pres- sure, in order to avoid negative concentrations while solving the model. In Chapter 7, while evaluating combustion kinetic parameters, the effect of oxygen was ne- glected, since a large excess of oxygen (∼240%) was employed. The literature usually also neglects the effect of oxygen for Pd catalysts (Lee and Trimm, 1995). However, at a high methane conversion >80%, with Pd 5%, our model had diffi- 211 culty to converge. To cope with this issue, a multiplication factor was applied to the pre-exponential factor, A4. Above 80% methane conversion, A4 was multiplied by 0.5, and above 95%, by 0.1. Reforming Kinetics In Chapter 2, three SMR kinetic models for Ru-based catalyst were presented. Pre- liminary simulations with Berman et al. (2005) and Wei and Iglesia (2004) mod- els were judged not satisfactory for the MCMR prototype results. Berman et al. (2005) model largely underestimated the reaction rates and Wei and Iglesia (2004) model largely overestimated them. As shown in Chapter 6, Jakobsen et al. (2010) model could fit adequately our reaction rates in the packed bed micro-reactor. The reforming kinetics equations based on Jakobsen et al. (2010) were then utilized. However, for cases without membrane, when the methane conversion reached ther- modynamic equilibrium, the model became unstable and the kinetic model was switched to the Xu and Froment (1989) model to complete the simulation. 8.3 Results and Discussion 8.3.1 Preliminary Results Table 8.9 summarizes preliminary results obtained with the reforming channel. Only three of nine preliminary experiments were successful in producing hydro- gen. Details are provided in Appendix C, as well as lessons learned during the reactor commissioning. To summarize the reforming preliminary results, the commercial Ni-based RK- 212 was not active in the MCMR, as well as catalysts whose support was not pre- aged by steam. In the preliminary experiments, the metal support was SS 304, and corrosion on the catalyst surface usually appeared a few weeks after the steaming step, or during the MCMR runs. As discussed in Chapter 6, it is suspected that iron oxide poisoned the catalyst, making it inactive. SS 310 and Fecralloy were there- fore adopted for the experiments presented in this chapter. Finally, the methane conversion was improved with the addition of La2O3 (See Section C.2.2). On the combustion side, the commercial oxidation catalyst converted methane, 212 Table 8.9: Summary of Preliminary Results for the Reforming Channel. See Ap- pendix C for more details about the catalysts and experimental conditions. Exp. Num- bera Catalyst Note Catalyst Result Problem 0.1 RK-212 with 20% boeh. - Not measured Water in GC lines 0.2 Plates from Exp. 0.1 reused CH4 conversion ≤3% Catalyst not active 0.3 Ru (6.1wt%)/ γ-Al2O3 γ-Al2O3 support not steamed CH4 conversion <1% Catalyst support not stable 0.4 Ru (6-7%) MgO (5%, plate no.1 only)/ γ-Al2O3 γ-Al2O3 support steamed Exp. partially successful, see Appendix C.2.2 Positive effect of pre-steaming 0.5 Ru 6-10% La2O3 (4%, plate no.2 only)/ γ-Al2O3 Exp. partially successful, see C.2.2 Positive effect of La2O3 0.6 Ru (5-8%) La2O3 (10-14%)b/ γ-Al2O3 Support steamed, catalyst 2 months old CH4 conversion <5% Catalyst poorly active, likely from rust 0.7 Ru 4-8% MnO (2% plate no.2) MgO (2-3% plates no.2 & 3) La2O3 (3-7%) Support steamed Exp. partially successful, see Appendix C.2.2 Positive effect of La2O3 observed 0.8 Same plates as Exp. 0.7 Catalyst ∼3.5 months old CH4 conversion <1% Catalyst not active, likely from rust 0.9 Ru 4-10% La2O3 (3-15%)/ γ-Al2O3 Catalyst ∼3.5 months old CH4 conversion <5.5% Catalyst poorly active, likely from rust aThese runs are separate from those covered in other tables of this chapter. b4th plate did not contain La2O3 213 but to a lower extent than predicted by the model. Results are again presented in Appendix C. In summary, a large channel height (9 mm) had a negative effect on the conversion. Pd 5% performed better than Pd 1%, but none of the commercial catalysts performed according to the model expectations. Some operating condi- tions led to faster deactivation, in particular higher methane concentration (4%), high temperature (565oC), and pressure above 3.2 bar. 8.3.2 Multi-Channel Reactor without Membrane Figure 8.8 presents methane conversion and temperature profiles along the reactor for an experiment without a membrane. On the reforming side, the conversion quickly reached equilibrium, and the model adequately predicted the results. On the combustion side, only the outlet conversion could be measured due to sampling issues caused by back-flow created by a short Grafoil strip for mechanical support (see Section “Lesson Learned” in Appendix C). Nevertheless, is it clear that the combustion conversion under-performed the expected results. One can see with the combustion model prediction (curve E) some singularities. Those are due to the variations in coating thicknesses (See Table 8.2). For the Exp. no.1, the combustion conversion started at 90% and dropped to 40% after 21 h on stream. A large drop in conversion, 19% within 1 h, occurred when methane concentration in the feed was 4.1%, confirming previous observa- tions that higher methane concentrations are associated with faster deactivation. The methane conversion at the outlet of the reactor was a function of the ther- modynamic equilibrium, and not of the kinetics. To test the model predictions without any membrane, the conversion at location no.1 (see Figure 8.2) was plot- ted as a function of the methane flow rates. Figure 8.9 shows the results, and despite some scatter in the experimental data, the trend adequately matches the simulations. 214 0.00 0.05 0.10 0.15 0.20 0.25 0 20 40 60 80 100 M et ha ne  C on ve rs io n (m ol% ) l 500 510 520 530 540 550 560 l (A) Ref. Exp. Conv. (B) Thermo. Equil. Ref. (C) Comb. Exp. Conv. (D) Ref. Model Conv. (E) Comb. Model Conv. (F) Ref. Temp. (G) Comb. Temp. Axial Coordinate (m) M et ha ne  C on ve rs io n (m ol% ) Te m pe ra tu re  (° C) Figure 8.8: Conversion and Temperature Profiles for MCMR Run no.1a with- out Membrane. Operating Conditions: Reforming: CH4 Flow: 1.35 nL/min, S/C: 2.8, Pr: 11.4 bar; Combustion: CH4 Flow: 0.22 nL/min, 3.4% in air, Pc: 2.4 bar. Temperature data are fitted with a second order polynomial. Time on Steam: 9.3 h 8.3.3 Multi-Channel Reactor with Membranes Effectiveness Factor The membrane effectiveness factors were evaluated at the beginning of both Exp. 2 & 3, using Eq. (8.1). Results are presented in Table 8.10. ηm at ∼56% is relatively low. However, the area taken includes zones on the sides of the membrane that do not permeate hydrogen. Taking the H2 permeable area only, ηm would be closer to 215 0.5 1.0 1.5 2.0 2.5 10 15 20 25 30 Methane Flow Rate (nL/min) M et ha ne  C on ve rs io n (m ol% ) Experimental Data Simulation Data Thermo. Equil. Figure 8.9: Methane Conversion versus Methane Flow Rate at Position no.1 for MCMR Exp. no.1, without Membrane. Operating Conditions Re- forming: S/C: 2.7-2.9, Pr: 11.4 bar; Combustion: CH4 Flow: 0.22 nL/min, 3.4-4.1% in air, Pc: 2.4 bar. 80%, which, according to the supplier, MRT, is a reasonable value. Hydrogen Quality The hydrogen permeate was tested for impurities. At the end of Exp. no.3, CO, CO2 and CH4 contents were 4, 21 and 27 ppm respectively, giving a hydrogen purity of 99.995% a. Exp. no.3 reused the same membrane as Exp. no.2, suggesting aDue to being at the lower end of the scale of the analytical instrument, this is a best estimate. We believe that the purity is at level “4 nines”, i.e. 99.99%, but it is impossible to fully quantify the errors in the estimate. 216 Table 8.10: Membrane Effectiveness Calculations (membrane area estimated at 0.020 m2). PH2,r Pm Tave,r H2 Flux ηm bar bar oC mol/(m2 s) Exp. no.2 9.12 1.09 552 0.40 0.56 6.875 1.07 552 0.31 0.54 8.865 1.09 552 0.39 0.56 Exp. no.3 7.12 1.07 548 0.32 0.56 7.19 1.07 549 0.33 0.56 7.06 2.04 550 0.25 0.57 7.06 2.04 550 0.25 0.57 Average 0.56 that the membrane start-up and cool-down procedure was successful in preserving the membrane integrity. Our GC was not calibrated for low ppm concentrations, and the accuracy of these results is uncertain. More tests with a GC calibrated for <10 ppm impurities and a dedicated sampling line for hydrogen permeate would be needed to confirm compliance with the hydrogen quality requirements for Proton Exchange Membrane Fuel Cells (PEMFCs) (see Table 1.2). Dynamic Behaviour Sohn et al. (2007) reported that MCRs respond promptly to dynamic changes in feed conditions. This observation was confirmed in our system. Figures 8.10 and 8.11 displays screenshots of flow and temperature trends, while methane flows were either being increased or started. On Figure 8.10 the permeate hydrogen in- creased immediately when the methane flow increased. The top row of Figure 8.11 displays channel temperature trends, and the arrows point towards the two thermocouples at the first location. Temperatures dropped and then increased with successive start-up of reforming and combustion flows. The bottom row displays the flange temperature for one thermocouple located inside a cartridge heater. The 217 Add labview screenshot Methane Flow for Reforming Increased Flow  Rate Trends F l o w  R a t e  ( n L / m i n ) 1 2 Product Hydrogen Flow F l o w  R a t e  ( 0 7:40: 30 PM 7:49: 42 PM Figure 8.10: Process Response on H2 Production to an Increase in CH4 Flow: LabVIEWTM screenshot of permeate hydrogen and reforming methane flow rates. temperature trend cycled as the heater was turned on and off. The heater turned off initially when the combustion methane flow started and the temperature dropped. However, heat losses to the surrounding exceeded the heat provided by the com- bustion, and heaters eventually returned to their heating cycles (not displayed on the Figure). 218 Methane Flow for Combustion Started Methane Flow for Reforming Started Temperature (oC) Reactor Channels Trends Temperature (oC) Reactor Channels Trends 10:03:30 PM 2:11:39 M 2:21:39 M10:13:30 PM 570 535 570 535 Temperature (oC) Reactor Flanges Trends 10:03:30PM 2:11:39 M 2:21:39 M10:13:30 PM 630 510 630 510 24 Temperature (oC) Reactor Flanges Trends Figure 8.11: Process Response on Temperatures to the Start of Reforming and Combustion Methane Flows: LabVIEWTM screenshots of channel temperatures (top row) and flange temperatures (bottom row). Methane Conversion and Temperature Profiles Figure 8.12 presents methane conversion and temperature profiles along the reactor for Exp. no.3a with membrane. On the reforming side, the conversion quickly sur- passed the equilibrium value, then peaked at the 4th position, above 80%, to finally drop 7% points at the outlet. Except for the outlet, the model slightly underesti- mates the conversion. Based on Eq. (8.2), it was estimated that the feed by-pass was 13% for this case. The simulations on the next figures below consider the feed by-passing. On the combustion side, the experimental data confirmed that the combustion catalyst performance was less than expected from the model, even though the con- 219 0.00 0.10 0.20 0.30 0 20 40 60 80 100 M et ha ne  C on ve rs io n (m ol% ) l l l l l l Axial Coordinate (m) M et ha ne  C on ve rs io n (m ol% ) 500 520 540 560 580 600 l (A) Ref. Exp. Conv. (B) Thermo. Equil. Ref. (C) Comb. Exp. Conv. (D) Ref. Model Conv. (E) Comb. Model Conv. (F) Ref. Temp. (G) Comb. Temp. Te m pe ra tu re  (° C) Figure 8.12: Conversion and Temperature Profiles for MCMR Exp. no.3a with Membrane. Operating Conditions: Reforming: CH4 Flow: 0.495 nL/min, S/C: 3.8, Pr: 16.0 bar, Pm: 1.02 bar; Combustion: CH4 Flow: 0.22 nL/min, 3.4% in air, Pc: 3.8 bar. Temperature data are fitted with a second order polynomial. Time on Steam: 1.3 h. version almost reached 90%. One can observe kinks in both reforming and com- bustion model conversion curves. These are due to the no-catalyst zones (see Fig- ure 8.7) and the variations in coating thicknesses (see Tables 8.3 & 8.4). In Figure 8.13, several parameters were varied in an effort to explain the dis- crepancies between the experimental data and simulations. On the reforming side (Part A), wrong temperature readings were probably not the reason. However, multiplying the pre-exponential factor, A1 by 2, or multiplying the feed flow rate 220 by (1-By-pass), both predicted well the first four experimental points. In Chapter 6, after a period of quick deactivation, the A1 estimate was similar to that reported by Jakobsen et al. (2010). Since the deactivation rate of the catalyst was uncertain in the MCMR, A1 was kept identical to the Jakobsen et al. (2010) value for further simulations below. The by-pass factor was utilized instead. On the combustion side, Fig. 8.13B reveals that doubling the combustion flow rate could explain the lower-than-expected performances. A smaller pre-exponential factor, or wrong temperature readings could not explain the discrepancy. One could speculate that a flow distribution issue might be the problem for the com- bustion channel. Flow distribution is a common problem in MCR technologies, and Rebrov et al. (2011) reviewed various ways of improving flow distribution. 3-D Computational Fluid Dynamics (CFD) simulations might assist in testing this hypothesis. Figure 8.14 presents methane conversion and temperature profiles along the re- actor for Exp. no.3b with membrane. The learnings from the simulation presented in Figure 8.13 were applied. By multiplying the methane flow rate by (1 - the es- timated by-pass factor), in this case 17%, the simulation predicted accurately the experimental data. However, for the combustion side, even multiplying the flow rate by 2 did not provide a match to the under-performing conversion data. This suggest that flow distribution was not the only problem. Instead, catalyst deactiva- tion likely also played a role. Some dimensionless numbers were evaluated for Experiment no.3b. Reynolds numbers were low in both channels, <40, confirming laminar flow. Mass Peclet numbers for hydrogen (see Eq. (3.25)) at the entrance of the reforming channel and methane in the combustion channel were 631 and 4920 respectively. The Peclet number for hydrogen was <1000, indicating some axial dispersion, neglected in the model. However, as shown in the previous figures, the reforming simulations predicted well the experimental data, and we did not see the benefit of adding second order axial dispersion terms at this stage. 221 020 40 60 80 100 A: Exp. no.3a, Reforming (A) Ref. Exp. Conv. (B) Base Case Sim. (C) Tr + 20°C (D) A1 * 2 (E) Flow * (1 − 13%) (By−pass) l l l l l l 0 20 40 60 80 100 0.00 0.05 0.10 0.15 0.20 0.25 0.30 B: Exp. no.3a, Combustion l (F) Comb. Exp. Conv. (G) Base Case Sim. (H) Tc − 20°C (I) A4 * 0.5 (J) Flow * 2 Axial Coordinate (m) M et ha ne  C on ve rs io n (m ol% ) Figure 8.13: Sensitivity on Conversion Profiles for MCMR Run no.3a with Membrane. Operating conditions were detailed in Figure 8.12. 222 0.00 0.10 0.20 0.30 0 20 40 60 80 100 M et ha ne  C on ve rs io n (m ol% ) l l l l l l Axial Coordinate (m) M et ha ne  C on ve rs io n (m ol% ) 460 480 500 520 540 560 580 l (A) Ref. Exp. Conv. (B) Thermo. Equil. Ref. (C) Comb. Exp. Conv. (D) Ref. Flow * (1 − 17%) (E) Comb. Flow * 2 (F) Ref. Temp. (G) Comb. Temp. Te m pe ra tu re  (° C) Figure 8.14: Conversion and Temperature Profiles for MCMR Exp. no.3b with Membrane. Operating Conditions: Reforming: CH4 Flow: 0.63 nL/min, S/C: 3.98, Pr: 13.2 bar, Pm: 0.79 bar; Combustion: CH4 Flow: 0.20 nL/min, 3.0% in air, Pc: 3.8 bar. Temperature data are fitted with a second order polynomial. Time on Steam: 12.7 h. Parameters Study Figure 8.15 displays several experimental data with simulation predictions, while varying one parameter at a time. For S/C experiments (Part A), experimental and simulation data showed an optimum point, but the experimental optimum occurred at slightly higher S/C than predicted. In Part B, the model predicted well lower pressure experiments, but could not explain why the experimental hydrogen yield reached a peak and began to decrease 223 at higher pressure. The Jakobsen et al. (2010) kinetic model was developed at low pressure (1.3 bar). The Xu and Froment (1989) kinetic model was tried as well, where the data were up to 15 bar, but no peak was observed. It is uncertain at this stage whether the pressure effect results from an inaccurate kinetic model, strong deviation from ideal gas behaviour as assumed in the model, or feed by- pass increasing with increasing pressure. Kinetic experiments in the micro-reactor at higher pressures, and incorporating high pressure correlations for physical prop- erties and equation of states in the model could be investigated in future. In Part C, the methane flow rate effect was well predicted by the model. Our prototype is likely limited by the membrane flux, with the flow increase automati- cally lowering the hydrogen yield. Performance Review Table 8.11 summarizes several performance indicators with data obtained exper- imentally. We also compare the experimental results with predictions made in Chapter 3 and membrane reactor experimental work reported in the literature. In term of methane conversion, the MCMR experimental results underper- formed the best case scenario of Chapter 3 for various reasons: (1) The experi- ments were conducted at lower temperature than the simulation (average temp. of 550-570oC instead of a feed temperature of 600oC), slowing down the kinetics and the membrane flux, and lowering the SMR equilibrium conversion; (2) The proto- type was shorter than the simulation (0.278 m instead of 0.3 m); (3) The vacuum pump on the experimental set-up did not give as high a vacuum as the simulation (0.8 instead of 0.7 bar); and (4) There was a design issue with appreciable feed by-passing. Despite these deficiencies, the hydrogen yields per mass of catalyst were be- tween one and two orders of magnitude higher than estimated for two FBMRs and one PBMR from the literature (Rakib et al., 2011; Mahecha-Botero et al., 2008; Tong et al., 2005). The hydrogen yields per reactor volume was about one order of magnitude higher than estimated (Rakib et al., 2011; Mahecha-Botero et al., 2008) for the FBMRs, confirming the technical potential for MCMR technology. The hydrogen yields per membrane area also performed well, considering that vacuum 224 2 3 4 5 6 7 1.5 2.0 2.5 3.0 3.5 4.0 S/C (mol/mol) A: Steam/Carbon Ratio 5 10 15 20 1.5 2.0 2.5 3.0 3.5 4.0 Pr (bar) l l l l l l B: Retentate Pressure 0.4 0.6 0.8 1.0 1.2 1.5 2.0 2.5 3.0 3.5 4.0 Methane Flow Rate (nL/min) l l l l l C: Methane Flow H 2 Pe rm e a te  to  C H 4 Fe e d Ra tio  (m ol/ mo l) l Exp. Data (corrected) Pm 1 bar Simulation Data Pm 1 bar Exp. Data (corrected) Pm 0.8 bar Simulation Data Pm 0.8 bar Figure 8.15: Parametric Study on Effect of Steam-to-Carbon Molar Ratio, Reforming Channel Pressure, and CH4 Flow Rate, on H2 Extracted to CH4 Feed Ratio. Operating Conditions: A. CH4 Flow: 0.495 nL/min, Pr: 15.8 bar, Tave,r: 552oC; B. CH4 Flow: 0.495 nL/min, S/C: 4.7, Tave,r: 552oC; C. Pr: 13.2 bar, S/C: 3.5-4.4, Tave,r: 570oC. Exp. data of H2 Extracted to CH4 Feed Ratio was corrected using Eq. (8.4), with feed by-pass of 13%. Time on Steam: 1.7-12.4 h. 225 Table 8.11: MCMR Experimental Results Compared with Early Simulations and Other Mem- brane Reactors. Membrane thickness for this work is 25 µm. See Table 8.6 for experi- mental conditions. Exp. No. XCH4 a Ratio H2,prod./CH4 Ratio H2,m/CH4 F ′ H2,m YH2vol.react. b YH2 kgcat YH2m.area mol% mol/mol mol/mol kg/- day kg/ (day m3) kg/ (day kgcat) kg/ (day m2) 1b 22.2 0.77 N/A 0.13c 472 105 N/A 1f 24.1 0.72 N/A 0.21c 766 170 N/A 2a 73.5 2.5 2.1 0.20 736 135 8.6 2b 87.3 2.9 2.4 0.15 562 103 6.6 2c 74.2 2.6 2.1 0.20 732 134 8.6 2d 91.2 2.9 2.5 0.23 861 153 10.1 3a 82.7 3.0 2.7 0.17 629 111 7.4 3b 87.4 2.94 2.90 0.23 860 152 10.1 Best Case Sim.d 91.5 3.68 3.12 0.51 1311 90.0 21.2 FBMRe 70 3.0 2.5 0.4 40 0.2 2 FBMRf 73 N/A 3.0 1.8 165 2.5 6.8 PBMRg 80 N/A N/A 0.03 420 2 15 aConversions in MCMR were taken at position no.4 bFor the MCMR, the internal volumes of the two channels, separator wall, and half the membrane support were included. cNo membrane was present. Value is the hydrogen produced, F ′ H2,prod . Hydrogen purity was ∼43%. dFrom Chapter 3, 600oC, 15 bar, 0.7 bar permeate, Thm: 25 µm, reactor length 0.3 m (refer to chapter for other simulation parameters). e(Rakib et al., 2011) 500oC, 6 bar, 0.5 bar permeate side, Thm: 25 µm, electric heating f(Mahecha-Botero et al., 2008) 550oC, 10 bar, 0.3 bar permeate side, Thm: 25 µm, electrical heating g(Tong et al., 2005) 550oC, 3 bar, sweep flow equivalent to 0.3 bar, Thm: 6 µm , electric heating on the permeate side was less in our case than in the other reported work. Improvement Potential for Reforming Channel Table 8.12 presents options to improve the reforming results. As in Chapter 3, we looked at the effect of parameter changes on the minimum reactor length to 226 Table 8.12: Improvement Potential for the Reforming Channel Parameter Modified Value Unit Min. L to 90% XCH4 (m) % Change Base Case: Exp. No.3b - - 0.277 - Pressure Permeate Pm 0.4 bar 0.204 26 Membrane Thickness Thm 12.5 µm 0.210 24 ηm 80% 0.237 14 Pre-exp. Factor A1 x 1.5 0.254 8 Catalyst Thickness Thcat,r x 1.5 µm 0.263 5 No Membrane Dead Zone 0.275 0.5 reach 90% methane conversion. The top three improvements were related to the membrane, confirming that the permeation flux is currently the major factor lim- iting the conversion. The membrane catalyst effectiveness ηm could be improved by using the impermeable region of the membrane as a surface to seat the gasket. Increasing the vacuum with a better pump is also a realistic option. Decreasing the membrane thickness will depend on research advances in membrane technology and the hydrogen purity required. Catalyst-related parameters in Table 8.12 generated less than 10% improve- ment. Therefore, at the current stage of the development of the technology, there is little incentive to improve the catalyst activity, but research should rather focus on catalyst stability. 8.4 Conclusions A two-channel MCMR prototype was design, built and tested to produce pure hy- drogen in a single vessel. Without any membrane, the reforming methane con- version quickly approached equilibrium and the model predicted the results ade- quately. With a membrane, the model underestimated the conversion. A design issue created by a portion of the feed by-passing the reforming channel accounted for at least part of the discrepancy. With a by-pass factor incorporated in the model, the reforming experimental results, for a wide range of flow, pressure and steam- 227 to-carbon ratio conditions, were adequately predicted. 87% methane conversion was achieved on the reforming side, and the extracted hydrogen-to-methane feed molar ratio reached 2.94. On the combustion side, the experimental data fell below the model expec- tations. Even though methane conversion almost reached 90%, it is suspected that the flow distribution and catalyst deactivation caused significant discrepan- cies. Some operating conditions promoted higher deactivation decay, in particular higher methane concentration (4%), high temperature (565oC), and pressure above 3.2 bar. Research is needed to improve the combustion catalyst performance. The hydrogen permeate was tested for impurities. CO content was estimated at 4 ppm, while hydrogen purity reached 99.995%. The reactor responded promptly to dynamic changes in feed conditions, with the permeate hydrogen increasing immediately when the methane flow increased. Even though the MCMR experimental results under-performed the best case scenario of the simulation performed in Chapter 3, hydrogen yields per mass of catalyst, were between one and two orders of magnitude higher than estimated for two FBMRs and one PBMR from the literature. The hydrogen yields per reactor volume were about one order of magnitude higher than estimated for the FBMRs. Simulations suggested that the prototype was likely limited by the membrane flux. Lowering the permeate pressure, increasing membrane effectiveness and low- ering membrane thickness should be adopted to improve the reactor performance. 228 Chapter 9 Overall Conclusions and Recommendations 9.1 Conclusions A proof-of-concept Multi-Channel Membrane Reactor (MCMR) was designed, built, and operated for the decentralized production of hydrogen via Steam Methane Reforming (SMR). The concept alternates steam reforming gas channels to pro- duce the hydrogen and Methane Catalytic Combustion (MCC) gas channels to provide the heat of reaction. A palladium-silver (Pd/Ag) membrane inside the reforming gas channel shifts the reaction equilibrium and produces pure hydrogen (99.995%) in a single compact vessel. A 2-Dimensional (2-D), steady state model of the MCMR was first created, including all energy balances, mass balances, chemical kinetics and physical prop- erties for a representative geometry including one reforming channel and one MCC channel. Most model assumptions were verified with dimensionless number cal- culations and back calculations of heat and mass transfer driving forces. Future model improvement would benefit from incorporation of second order heat trans- fer terms in the axial direction for the separator wall. Isothermal sensitivity analysis indicated that the H2 membrane extraction is the major factor limiting reforming performance, whereas catalyst activity is the major factor limiting combustion per- formance. Non-isothermal simulation results predicted good heat transfer. Except 229 for the reactor entrance, transverse temperature variations within the computational domains could be kept below 10 K. Without rigorous optimization, it was possible to obtain methane conversion (>90%) without the formation of hot spots. Per- formance could be improved significantly by a combination of varying the pre- exponential factor (metal loading) and catalyst thickness along the length of the reactor, while increasing the methane flow rate to the combustion channel. A method to coat both SMR and MCC catalysts on a metal support was de- veloped. After many trials, the initial goal of producing coating with good adher- ence, measured by sonication, with coating layer thickness >80 µm was achieved. Air-spray hot substrate coating (hot spray) achieved thicknesses up to 240 µm with γ-Al2O3, while adherence tests gave satisfactory results. Hot spray coating of commercial catalysts with γ-Al2O3 as carrier were successful as well. Pd/ γ- Al2O3 coatings were selected as the combustion catalyst for the MCMR prototype. A crack density test was devised as a non-destructive method to evaluate coating adherence, giving results consistent with the sonication test. Crack formation and coating delamination during impregnation were linked to the presence of white lines, precursors to cracks, on the coating surface, and to the absence of clusters. Cracks could be avoided by lowering carrier or commercial catalyst concentration in the modified sol, and by monitoring the rate of water evaporation during hot spray coating. La2O3 was an effective promoter to avoid carbon deposition during steaming. Rust appeared on most coatings where SS 304 was the support, and was suspected to deactivate the reforming catalyst. Rust diffusion was reduced by SS 310, and arrested completely by using Fecralloy as the metal support. Micro-reactor activity experiments allowed various reforming and combustion catalysts to be tested for their suitability in the MCMR prototype. For reforming catalyst, a lab-made Ru ∼5%/ γ-Al2O3 catalyst was selected for the MCMR. Ag- ing of the support with steam was necessary to avoid total catalyst deactivation. The addition of MgO and La2O3 to the alumina improved the stability of the Ru catalyst. For combustion catalyst, commercial Pd 1% and 5%/ γ-Al2O3 catalysts (Alfa Aesar) as well as lab-made Pd 5% La2O3−MgO/ γ-Al2O3, were found to be suitable for the MCMR prototype. Based on X-Ray Diffraction (XRD) and pore analyses, sources of deactivation were investigated. For the reforming Ru-based catalyst, pore sintering was a deactivation mechanism, with a phase change from 230 γ-Al2O3 to α-Al2O3, and average pore size increasing during MCMR operation. For the combustion catalyst, pore sintering was also found to be the major source of deactivation for the two commercial Pd catalysts, while metal sintering was more important for the lab-made Pd La2O3−MgO catalyst. Kinetic parameters were estimated. For reforming Ru-based catalyst, the pre- exponential factor was similar to that reported by Jakobsen et al. (2010). For com- bustion, the Pd 1% (Alfa) catalyst activation energy, E4, was estimated to be 88 kJ/mol, while the reaction order for methane α was 0.78. The pre-exponential factor for commercial Pd 1% catalyst was about three times smaller than for the commercial and lab-made Pd 5% catalysts tested. A MCMR prototype was designed, built and tested. Without a membrane, the reforming methane conversion quickly reached equilibrium and the 2-D model predicted adequately the results. With a Pd/Ag membrane, except for the out- let conversion, the model slightly underestimated the conversion. A design fault allowed a portion of the feed to by-pass the reforming channel. Incorporating a by- pass correction factor in the model, the reforming experimental results, for a wide range of flow, pressure and steam-to-carbon ratio conditions, were generally pre- dicted adequately. 87% methane conversion was achieved on the reforming side, and the extracted hydrogen-to-methane feed molar ratio reached 2.94. CO content was estimated at 4 ppm. On the combustion side, the experimental conversions were consistently less than predicted by the models. Even though some methane conversions reached almost 90%, it is suspected that flow distribution and catalyst deactivation were causing the large discrepancies. Hydrogen yields per mass of catalyst, were between one and two orders of magnitude higher than estimated for two Fluidized Bed Membrane Reactors (FBMRs) and one Packed Bed Membrane Reactor (PBMR) from the literature. The hydrogen yields per reactor volume was about one order of magnitude higher than estimated for the FBMRs, confirming the technical potential for the technology. 9.2 Recommendations The MCMR concept is promising, producing pure hydrogen in two experimental sets, over a total period exceeding 34 hours. However, scale-up, long-term catalyst 231 activity, energy efficiency, membrane longevity, and economical viability have yet to be proven. The next steps should be directed towards a pre-commercial proto- type, designed to recover the heat, minimize emissions, and operate several months without servicing. Recommendations are divided in to general and specific ones, the latter ex- tracted from the main document. 9.2.1 General Recommendations The improvement of the MCMR concept requires a multi-disciplinary approach. Expertise should be sought in: • Mechanical Engineering: To improve flow distribution in channels, expand- ing the number of channels, eliminating feed by-passing, designing a heat exchanger to recover products heat, and facilitating the assembly and disas- sembly; • Catalysis: To improve stability of the catalysts, in order to maintain high activity for at least several months; • Materials Engineering: To develop thinner, robust membranes adapted to the MCMR; • Process Engineering: To recover reforming product gases as a fuel for the combustion channel. 9.2.2 Specific Recommendations Specific recommendations are summarized as follows: • Reactor Modeling – Include 2nd order terms for heat transfer in the transverse direction. A more powerful simulation software than MATLABTM should be con- sidered, e.g. gPROMsTM or ANSYSTM; – Consider adding hydrogen axial dispersion to the model; – Conduct 3-D Computational Fluid Dynamics (CFD) flow simulations on the feed distribution, and investigate options to improve the design; 232 – A catalyst model could be improved to reflect a more realistic pore configuration, as shown in Figure 6.9; – Review physical properties and equations of state for higher pressure >12 bar; – Model flow distribution between multiple plates and channels. • Catalyst Coating – Automate the coating process to improve catalyst coating uniformity; – Heat treatment for Fecralloy could be optimized. For instance, Jia et al. (2007) showed that oxidation at 900oC created a larger number of alu- mina whiskers on the surface than oxidation at 1000oC; – Optimize coating parameters to reduce the number of clusters on the coating surface, while maintaining adherence, optimal layer structure and active area; – Investigate electrostatic-spray-assisted vapour deposition, to reduce the amount of material losses while coating, as suggested by Choy (2003); – Consider alternatives to γ-Al2O3 as carrier, since phase change to α- Al2O3 was observed; – Design and build specific equipment to steam at high pressure (>20 bar) carrier plates and pre-reduce the catalyst plates. • Reforming Catalyst – Select and optimize promoter contents; – The literature shows advantages of bi-metallic catalysts (Jeong et al., 2006; Zhou et al., 2009). For instance Ni combined with Ru, Rh, or Pt could be tried; – Improve experimental procedures to test stability in order to improve the repeatability of the experiments; – Perform kinetic estimations at higher pressures. • MCC – A better understanding of CO formation is needed; 233 – The effect of water should be studied, since the inhibition on the reac- tion rate is likely (Ciuparu et al., 2001); – Find better promoters and/or supports to improve the stability of the oxidation catalysts; – Catalysts, combining Pd with Pt and Rh could be tried. • MCMR Process – Investigate the potential of using the reforming product gas, after water removal, as fuel for the combustion channel. Conversion in the reform- ing could be optimized in such a way that the exhaust gas would con- tain enough energy to supply all the heat required, avoiding excessive methane conversion in the reforming channel, while achieving higher overall methane conversion (including the combustion channel); – Improve ventilation around the unit to eliminate smoke coming from insulating materials and anti-seize oxidation during start-up; – The back pressure regulator on the reforming side was not working properly and pressure was not as stable as it should be. The regulator size may be the issue. 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A novel solid-gas process to synthesize LaMnO3 perovskite with high surface area and excellent activity for methane combustion. Journal of Natural Gas Chemistry, 20(3):294 – 298. Zou, J., Huang, J., and Ho, W. S. W. (2007). CO2-selective water gas shift membrane reactor for fuel cell hydrogen processing. Industrial & Engineering Chemistry Research, 46(8):2272–2279. Ztek Corporation (2005). High performance steam reforming. Accessed on June 12th, 2012, http://www.ztekcorporation.com/hpsr.htm. 252 Appendix A Supplementary Coating Results Many coating experiments were unsuccessful, and several were not included in Chapter 4. This Appendix presents results with catalyst coatings not selected for further investigation. Refer to Chapter 4 for the material and methods descriptions. A.1 Brush Coating Results Using the brush coating technique, Figure A.1 shows adherence and thickness re- sults with γ-Al2O3, α-Al2O3 (Part A) and RK-212 (Part B). On Part A, one can observe the relation between the carrier concentration and the thickness. The thickness is generally proportional to the carrier concentration, but that parameter cannot be increased indefinitely. For CR125 (γ-Al2O3), at the highest carrier concentration, mass losses are above the acceptable limit of 20 wt%. For A-16 (α-Al2O3), increasing carrier concentration after 7 mol/L did not increase the thickness, but mass losses were acceptable. Higher carrier concentration gener- ally led to a more viscous modified sol, and then, a thicker film and thicker coating. However, above a certain concentration, the modified sol became too viscous and coating was difficult. Not shown on the plots, the standard deviation for the five thickness measurements on each plate was usually ∼4-6 µm. Figure 4.4 Part A shows an SEM image of a Ni-MgO/ γ-Al2O3 sample obtained by brush coating. The effect of the metal substrate roughness is still visible on the coating surface. Figure A.4A.1 shows image of a γ-Al2O3 sample. The brush 253 sweep can be clearly seen. On the same figure, plate picture were taken after being subjected to the sonication test. On Figure A.1B, it can be seen that brush coating of the commercial catalyst RK-212 was more challenging than with γ-Al2O3 and α-Al2O3. Very few samples achieved their adherence target. The largest particles performed the worst, but no reproducible sol recipe was found with smaller particle sizes. Brush coating was of limited success. Since good adherence, but insufficient thickness, was obtained with some modified sol, multi-layer brush coating was investigated next. A.2 Multi-layer Brush Coating Figure A.2 shows the average coating thickness progression after addition of coat- ing layers. ∼40 µm for γ-Al2O3 and∼45 µm for α-Al2O3 coatings were obtained after five layers. Not shown on the plot, a sol containing MgAl2O4 was also tried, but after seven layers, the estimated coating thicknesses were still <20 µm. Three γ-Al2O3 plates were put in the sonic bath after the fifth layer. Adherences were all acceptable, with 2.3, 15.7 and 10.3% mass losses. Since it requires about one day of work per layer of coating, and even though we believed that multi-layer coating could eventually achieve coatings of ∼80 µm thickness with acceptable adherence, this technique was overly time consuming, and therefore abandoned. A.3 Dip Coating Figure A.3 shows thickness and adherence results using the dip coating method. Similar to the brush coating method, the coating thickness is generally propor- tional to the carrier concentration. Although some samples showed thickness >80 µm, adherence quality was unsatisfactory. Not shown on the plots, the standard deviation for the five thickness measurements on each plate ranged from 2-11 µm, with an average at ∼6 µm. Figure A.4 Part C.1 shows a sample obtained by dip coating. Part C.2 shows the extensive mass losses after sonication. Since the adherence criteria was not met on Figure A.3 at higher coating thick- nesses, dip coating was rejected for further investigation. 254 ll l ll l 15 20 25 30 0 20 40 60 80 100 Average Coating Thickness (µm) A: γ−Al2O3and α−Al2O3 l l 25%, Co, 1.8 mol/L, CR125, pH 5 25%, Co, 2.3 mol/L, CR125, pH 5 25%, Co, 2.6 mol/L, CR125, pH 5 10%, Co, 5.3 mol/L, A−16, pH 2 10%, Co, 6.9 mol/L, A−16, pH 2 10%, Co, 7.9 mol/L, A−16, pH 2 l l l l l l 0.0000 0.0005 0.0010 0.0015 0 20 40 60 80 100 Weight over Area(g/cm2) B: RK−212 l 10%, Co, 2.6 mol/L, pH 6, < 25 um 15%, Co, 2.3 mol/L, pH *, 25−38 um 15%, Co, 2.3 mol/L, pH *, 38−45 um 10%, Co, 2.6 mol/L, pH *, 45−63 um 20%, P2, 2.1 mol/L, pH 5, bind, 25−38 um M as s Lo ss  (w t% ) Figure A.1: Brush Coating of γ-Al2O3, α-Al2O3 and RK-212 Modified Sol: A: γ-Al2O3 and α-Al2O3, Mass Loss vs Average Thickness; B: RK- 212, Mass Loss vs Weight over Area (pH * = final pH not measured). Line representing the 20% mass loss limit is shown. 255 ll l l l 1 2 3 4 5 6 0 10 20 30 40 50 60 Coating Layer l CR125, Plate 1 CR125, Plate 2 CR125, Plate 3 CR125, Plate 4 A−16, Plate 1 Av e ra ge  C oa tin g Th ick ne ss  (µ m ) Figure A.2: Multi-Layer Brush Coating of γ-Al2O3 and α-Al2O3 Modified Sol, Average Thickness vs Coating Layer. Sol parameters: Ni 15% MgO 5%/ γ-Al2O3, 57% boeh., Co, 0.31 mol/L, CR125, pH not mea- sured; Ni 11% MgO 5%/ α-Al2O3, 21% boeh., Co, 1.55 mol/L, A-16, pH not measured. 256 ll l l l 0 20 40 60 80 100 120 0 20 40 60 dn$Thick.net l l .3 mol/L, Ceral .5 mol/L, Ceral .7 mol/L, Ceral .3 mol/L, CR125 .5 mol/L, CR125 .7 mol/L, CR125 Average Coating Thickness (µm) M as s Lo ss  (w t% ) Figure A.3: Dip Coating of γ-Al2O3 and α-Al2O3 Modified Sol Including Metal Precursors to Obtain Ni 15% MgO 5%/ γ-Al2O3, or α-Al2O3: Mass Loss vs Average Thickness. Withdrawal speed: 3.7 mm/s; α- Al2O3 modified sol: 10% boeh., P2, pH 4; γ-Al2O3 modified sol: 25% boeh., P2, pH 4. Line representing the 20% mass loss limit is shown. 257 A.1 (~10 µm) B.1 (~10 µm) C.1 (~10 µm) 15 mm 15 mm 15 mm First Row: Before Sonic Bath A.2 (15 wt%) B.2 (15 wt%) C.2 (38 wt%) Second Row: After Sonic Bath Figure A.4: Scanned Images of Brush, Cold Spray and Dip Coating Samples, before and after Sonication (top row: thickness, bottom row: mass loss after sonication): A. Brush Coating: γ-Al2O3 (25% boeh., 2.7 mol/L, pH 2); B. Cold Spray: Ni 11%-MgO 5%/ α-Al2O3 (30% boeh., 2.1 mol/L, pH 2); C. Dip Coating: Ni 15%-MgO 5%/ α-Al2O3 (10% boeh., 1.6 mol/L, pH 4). A.4 Cold Substrate Air Spray Coating (Cold Spray) Attempts with cold spray coating were unsuccessful. In order to be used with the air-spray gun, the viscosity of the modified sol must be kept low by adjusting the carrier concentration. For α-Al2O3, concentration had to be ≤ 2 mol/L. However, at low carrier concentration, a very thin coating layer was obtained between each sweep. In order to obtain a 40+ µm thick film, considerable time (>40 min) was needed to spray & air-dry all layers. Furthermore, visual inspection showed poor coating uniformity (see Figure A.4 B.1). Screen testing using ethanol instead of water as solvent for the modified sol was also tried, but uniformity was no better. 258 The coating thickness standard deviation within a plate was as high as 17 µm for a 60 µm coating. For those reasons, cold spray coating was discontinued. A.5 Hot Spray Coating Including Metal Precursors As shown in Chapter 4 (see Figure 4.1), catalyst and promoter precursors could ei- ther be introduced directly in the modified sol or by impregnation, after the coating and calcination of the carrier. In this section, we report results where catalyst and promoter precursors were introduced in the modified sol. Figure A.5 shows hot spray coating results for Ni-based catalyst with γ-Al2O3 as carrier. In Part A, only one set of samples gave acceptable results (30% boeh., P2, 1.08 mol/L, pH 4). In Part B, water was substituted for methanol as the solvent. Optical microscope images with methanol were encouraging, since this eliminated cracks (see Figure A.6). However, the absence of cracks did not result in an im- provement in the adherence, as seen in Figure A.5 Part B. These results indicate the fundamental role played by water on the bonding process. Figure A.7 shows coating results for Ni-based catalysts with α-Al2O3, MgAl2O4 or CeO2−ZrO2 as carriers. Results were not encouraging. Most samples failed the adherence quality test at larger coating thicknesses. For α-Al2O3 tests, Dispersal boehmite (P0) was also tried, but coarse cracks were visible after calcination and no thickness measurements were taken. Appendix B.3 demonstrates that the introduction of metal precursors with the modified sol did not lead to active and stable catalysts. Because of the poor activity, combined with poor adherence results, spray coating, including metal precursors, was not investigated further. A.6 Hot Spray Coating of of Commercial Catalyst: Supplementary Results Figure A.8 shows results with the Ni-based RK-212 catalyst. Part A shows at- tempts to coat this catalyst with sieved particles <45 µm. Results were negative, with most samples not meeting the bonding quality requirement, regardless of the modified sol parameters. Part B shows results with particles size 25 µm, where the results were better. Many samples had acceptable adherence in this case, but 259 ll l 20 40 60 80 120 0 20 40 60 80 100 A l 67%, Co, 0.23 mol/L, pH 1.5 67%, P0, 0.23 mol/L, pH 1.5, * 60%, P2, 0.31 mol/L,  pH 4, * 30%, P2, 1.08 mol/L, pH 4 l l ll 55 60 65 70 75 80 0 20 40 60 80 100 B l l 0.5 mol/L , in water 0.25 mol/L, in water 0.13 mol/L,  in water 0.50 mol/L,  in MeOH 0.25 mol/L,  in MeOH 0.13 mol/L,  in MeOH Average Coating Thickness (µm) M as s Lo ss  (w t% ) Figure A.5: Hot Spray Coating of γ-Al2O3 Modified Sol Including Metal Precursors, Mass Loss vs Average Thickness: A. Ni 15% MgO 5% CaO 0-1.5% K2O 0-1.5%/ γ-Al2O3, various sol parameters, with water as solvent (* Ni-MgO only); B. Ni 15% MgO 4% CaO 2% K2O 2%/ γ-Al2O3, Comparison between water and methanol as solvent for the sol (30% boeh., P2, pH 4). 260 A (77 µm) B (80 µm) 200* µm Figure A.6: Hot Spray Coating Optical Images with Methanol vs Water as Solvent for Modified Sol. Catalyst: Ni 11%-MgO 4% CaO 2% K2O 2%/ γ-Al2O3 (Coating Thickness): A. Water as solvent; B. Methanol as solvent, * approximative dimension. 261 30 40 50 60 70 80 90 0 20 40 60 80 100 A: α−Al2O3 10%, 0.5 mol/L , Ceral, pH 5, * 20%, 1.88 mol/L , Ceral, pH 5 30%, 1.08 mol/L , Ceral, pH 2 20%, 1.5 mol/L , A−16, pH 2.5, * 20 40 60 80 0 20 40 60 80 100 B: MgAl2O4 l l 10 20 30 40 50 60 0 20 40 60 80 100 C: CeO2−ZrO2 l Ni Ni−CaO K2O Average Coating Thickness (µm) M as s Lo ss  (w t% ) Figure A.7: Hot Spray Coating of α-Al2O3, MgAl2O4 and CeO2−ZrO2 Modified Sol Including Metal Precursors, Mass Loss vs Average Thick- ness: A. Ni 12-15% MgO 4-5% CaO 0-2% K2O 0-2%/ α-Al2O3 (* Ni-MgO only) B. Ni 15%/ MgAl2O4 (46% boeh., 0.5 mol/L, pH 1-2); C. Ni 15% CaO 0-2% K2O 0-2%/ CeO2−ZrO2-γ-Al2O3 (25% boeh., 0.4 mol CeO2/L, pH 1). Line representing the 20% mass loss limit is shown. 262 more work would be needed at thicknesses ≥ 80 µm. In Part A, black squares corresponds to coating samples without boehmite. Even though samples with 5% and 10% boehmite did not yield acceptable coating quality, the adherence improvement on the graph is noticeable, indicating the im- portance of boehmite in the bonding process. One can also see that binder did not help the coating process. Some effects of acid addition can be observed in Part B. RK-212 has a strong alkalinity. Without addition of acid, the pH was 11.8. Samples without acid, as well as samples with formic acid at pH of 8.5, were unsuccessful. Many samples with nitric acid (default acid) at pH 8 had acceptable adherence. Since alumina is slightly acidic in water, these results with RK-212 were the first to show ac- ceptable adherence with alkaline pH. Also in Part B, 8 of 10 samples >50 µm had boehmite content ≥20%. High boehmite content is not necessarily desirable, since it dilutes the commercial catalyst and can potentially blocks active sites, as reported by Meille (2006). As shown in Appendix B.2, RK-212 stability and activity were not satisfac- tory for our MCMR application. For this reason, even though there were some encouraging results with particles 25 µm, we did not conduct further tests with RK-212. Ruthenium-based commercial catalyst was next considered as an alternative to RK-212. Figure A.9 shows coating results for a commercial Ru 5% catalyst. In Part A, it can be seen that multiple samples were successfully coated to a thickness >80 µm with acceptable adherence. Results suggested that pH 5 could lead to less variation than pH 6.5. More testing would be needed to find the optimal boehmite content. As mentioned in Appendix B.4, coated Ru 5% catalyst activity and stability were noticeably inferior to fresh catalyst (received from the supplier). The nitric acid was likely to be responsible for the losses in activity and stability. Figure A.9B shows various attempts to replace nitric acid. More clarity was obtained regarding what did not work. First, acid is necessary, results without it being clear failures. Using P3 boehmite, which contains acetate instead of nitrate, did not work either with formic or acetic acid. Some samples were successful with formic acid using P2 boehmite, but reproducibility was poor. We will see in Appendix B.4 that P2 263 ll l l l l l l 10 20 30 40 50 0 20 40 60 80 100 A: < 45 µm l 0%, 4.2 mol/L , pH 4 5%, 4.2 mol/L , pH 4 10%, 4.2 mol/L , pH 4 20%, 2.1 mol/L, pH 4 20%, 2.1 mol/L, pH 5.5,  binder l l l l l l l l l l l 30 40 50 60 70 0 20 40 60 80 100 B: << 25 µm l l 10%, 0.6 mol/L, pH 8 15%, 0.18 mol/L, pH 5 15%, 0.35 mol/L, pH 5 15%, 0.35 mol/L, pH 8 15%, 0.35 mol/L, pH 11.8 (No Acid) 20%, 0.25 mol/L, pH 8 20%, 0.25 mol/L, pH 8.5 (Formic) 20%, 0.6 mol/L, pH 8 25%, 0.53 mol/L, pH 5.3 25%, 2.1 mol/L, pH 5.3 Average Coating Thickness (µm) M as s Lo ss  (w t% ) Figure A.8: Hot Spray Coating of Commercial RK-212 Catalyst, Mass Loss vs Average Thickness: A. Sieved particles size of <45 µm; B. Particle sizes estimated to be 25 µm. Line representing the 20% mass loss limit is shown. 264 boehmite is not necessarily bad for Ru catalyst. More tests would be needed with the combination of P2 boehmite and formic acid. However, as shown in Chapter 6, we finally decided to produce our own Ru-based catalyst, allowing us to pre-steam the carrier and add promoters. Ru-based commercial catalyst coating was therefore not investigated further. A.7 Thickness vs Mass Data For catalyst plates with Fecralloy, the thickness meter was not functional due to the magnetic property of the alloy. To estimate the thickness, linear regression was performed with thickness versus mass of catalyst data. The catalyst plates from MCMR Exp. no.1, 2 & 3, were used to generate the plot. Those coatings had SS 310 as metal support, and were made of the same modified sol as the samples on Fecralloy (see Figure A.10). 265 l l l l 60 80 100 120 140 0 20 40 60 80 100 A l 15%, 0.25 mol/L,  pH 5 15%, 0.25 mol/L,  pH 6.5, * 15%, 0.5 mol/L,  pH 6.5, * 15%, 0.75 mol/L,  pH 6, * 25%, 0.25 mol/L,  pH 5 ll l l 70 80 90 100 0 20 40 60 80 100 B l l P2, pH 8.6 (No Acid) P2, pH 6 (Nitric Acid) P2, pH 8 (Nitric Acid) P2, pH 6 (Formic Acid) P2, pH 8 (Formic Acid) P3, pH 6 (Formic Acid) P3, pH 6 (Acetic Acid) Average Coating Thickness (µm) M as s Lo ss  (w t% ) Figure A.9: Hot Spray Coating of Commercial Ru 5%/ γ-Al2O3 Catalyst, Mass Loss vs Average Thickness: A. Coating with various sol parame- ters (* manual size reduction attempt with pillar and mortar) B. Coating with various acids, sol parameters: 15% boeh., 0.25 mol/L. Line repre- senting the 20% mass loss limit is shown. 266 ll l ll l l l 0.25 0.27 0.29 0.31 190 200 210 220 230 Catalyst Mass (g) Co at in g Th ick ne ss  (µ m ) Thickness = 452.7* Wcat + 81.4   R2 =0.6373 Figure A.10: Coating Thickness vs Mass of Catalyst. Modified sol: 40% boeh., γ-Al2O3 0.5 mol L, pH 5, adjusted with nitric acid. 267 Appendix B Stability of Reforming Catalysts: Supplementary Results Many reforming catalysts tested in the micro-reactor were rejected for various rea- sons, and several of them were not included in Chapter 6. This Appendix presents those results. Refer to Chapter 6 for material and method descriptions. B.1 Preliminary Stability Test The first reforming stability tests were related to early coating attempts, as ex- plained in Chapter 4 and Appendix A. Crushed RK-212, RK-212 with boehmite, lab-made Ni catalyst, and commercial Ru catalyst were tested first. Physical prop- erties of the commercial catalysts are presented in Table B.1. B.2 RK-212 Figure B.1 Part A shows results of stability tests with crushed RK-212 at various operating conditions and catalyst loadings (see Table B.2). None of the conditions studied showed long term stability. Figure B.1 Part B reveals the importance of catalyst loading with respect to deactivation. Low catalyst loading data showed strong deactivation, while high catalyst loading led to negligible deactivation, with stable conversion near the pre- dicted equilibrium value. 268 0 50 100 150 0 10 20 30 40 Time on Stream (h) ll l lll l l l lll llll l ll ll l l (A) (B) (C) (D) A 0.00 0.05 0.10 0.15 0.20 0.25 0.30 0 5 10 15 20 25 Mass of Catalyst (g) l l l l l Xu and Froment Model 1 h 5 h 10 h 20 h B M et ha ne  C on ve rs io n (m ol% ) Figure B.1: Stability of RK-212: Effect of Operating Conditions and Catalyst Loading. (A) Methane Conversion vs Time on Stream. Catalyst: RK- 212 after crushing. Catalyst loadings varied from 0.05 to 0.2 g, as given in Table B.2, where other operating parameters are also tabulated; (B) Methane Conversion vs Mass of Catalyst. Catalyst: RK-212 with 20 wt% boeh. Operating parameters: 550oC, 10.6 bar, S/C: 4, H/C: 0.5, CH4 Flow: 105 Nml/min. 269 Table B.1: Surface Area, Pore Volume, Average Pore Size, and Metal Dispersion of Commercial Reforming Catalysts Surface Area Pore Volume Ave. Pore Dia. Metal Disper- sion m2/g cm3/g nm mol % RK-212 (after crushing, Dp,ave 25 µm) 14.3 0.06 19.1 0.77% RK-212 with 20% boehmite (fresh) 59.4 0.18 10.3 - Ru 5%/ γ-Al2O3 (Alfa) (as received) 225 1.27 19.7 17% Ru 5%/ γ-Al2O3 (Alfa) with 15% boeh. (fresh, average of two samples) 158 0.67 16.4 - Table B.2: Stability of RK-212: Operating Conditions for Figure B.1 Part A. Legend Code Mass Catalyst CH4 flow H2O/CH4 H2/CH4 Temperature Pressure (g) (Nml/min) (mol/mol) (mol/mol) (oC) (bar) A 0.12 100 4 0.5 550 11 B 0.05 100 4 1 550 6 C 0.2 100 3.5 1.35 550 D 0.1 112 3.5 1 550 5 Figure B.2 shows the effects of the coating process on the catalyst activity and stability. It can be seen that the coating method decreased the initial activity and increased the rate of deactivation. Neither catalyst showed signs of residual long- term activity. Our first test with the MCMR prototype was performed with RK-212 (see Chapter 8). After an unsuccessful first trial, the coated RK-212 catalyst was scratched off the plates and tested in the micro-reactor. Conversion was nil. With all these poor results, the RK-212 catalyst was rejected for further testing. B.3 Early Lab-made Ni catalyst One option with the initial coating procedure, explained in Appendix A.5, was to insert metal catalyst and promoter precursors directly into the modified sol. We 270 0 10 20 30 40 50 60 0 5 10 15 20 Time on Stream (h) M et ha ne  C on ve rs io n (m ol% ) (A)  XCH4=18.2*exp(−0.048*T) + 0,  R2=0.9984 ll l l l l ll ll l l (B)  XCH4=10.6*exp(−0.094*T) + 0,  R2=0.9705 (A) (B) Figure B.2: Stability of RK-212: Comparing Crushed with Coated Catalyst: Methane Conversion vs Time on Stream. S/C: 4, H/C: 0.4, CH4 Flow: 100 Nml/min; Catalyst loading: 0.02 g. (A) RK-212 powder after crushing; (B) RK-212 with 20 wt% boeh., pH 8 adjusted with nitric acid, calcined in air at 650oC overnight. tested on the micro-reactor 0.05 g of a NiO 15% MgO 5%/ α-Al2O3 catalyst. Methane conversion was nil. Slightly better results were obtained with 0.2 g of a NiO 15%/ CeO2−ZrO2, with an initial conversion of 3.3% at 600oC, 11 bar. Nevertheless, this catalyst, was under-performing, even relative to RK-212. Figure B.3 helps to explain why lab-made Ni catalysts under-performed com- pared to RK-212. A high temperature ∼750oC would be needed to reduce the lab-made catalyst, instead of ∼440oC for RK-212. Reducing at 750oC could cre- 271 C o n c e n t r a t i o n  c m ³ / m i n 5.0 5.1 5.2 2 2 2 1 C o n c e n t r a t i o n  ( c m 3 / m i n ) RK-212 (78% @ 700oC) Ni-MgO/αAl2O3 (lab made) (43% @ 700oC) (100% @ 900oC) 5.2 5.1 5.0 Final Temperature (°C) 100 200 300 400 500 600 700 800 900 C o n c e n t r a t i o n  c m ³ / m i n 4.7 4.8 4.9 1 1 Temperature (oC) H 2 C o n c e n t r a t i o n  Ni/CeO2-ZrO2-γAl2O3 (lab made) (91% @ 900oC) 4.9 4.8 4.7 Temperature 100         200         300         400         500        600         700         800        900 Figure B.3: TPR diagrams of Ni-based Catalysts (% reduction @ reduction temperature). See Section 6.2.7 for procedure description. ate issues with the MCMR. If the reduction was performed in-situ, a temperature of 750oC would damage the Pd/Ag membrane. With the poor catalyst activity of lab-made Ni catalysts, combined with poor coating results mentioned in Appendix A.5, the catalyst strategy, consisting in inserting metal precursors with the modify sol, was not investigated further. B.4 Commercial Ru 5%/ γ-Al2O3 Catalyst After the poor results obtained with both lab-made and commercial Ni-based cat- alysts, we started investigating Ru-based catalysts. The first attempts were made with a Ru 5%/ γ-Al2O3 from Alfa Aeser. 272 0 2 4 6 8 10 0 5 10 15 20 l l l l l l (A) P2 boeh., Nitric, 11 bar a (B) P3 boeh., Acetic (C) P2 boeh., Nitric (D) P2 boeh., No Acid (E) P2 boeh., No Acid, 1 h A: With Calcination 0 10 20 30 40 50 60 0 10 20 30 40 50 llllll lllll l ll ll l (F) P2 boeh., Nitric, 30 min (G) As Received (H) P2 boeh., Formic (I) P3 boeh., Acetic B: Without Calcination Time on Stream (h) M et ha ne  C on ve rs io n (m ol% ) Figure B.4: Stability of Commercial Ru 5%/ γ-Al2O3 (Alfa): Methane Con- version vs Time on Stream. Reforming Conditions: 550oC, 11 bar, S/C: 2.5, H/C: 0, CH4 Flow: 100 Nml/min; Catalyst loading: 0.02 g; Modi- fied Sol: 15% boeh., 0.25 mol/L. Data fitted with Eq. (6.14). See Table B.3 shows change in modified sol parameters and start-up/ reduction conditions. 273 Table B.3: Stability Conditions of Ru 5% (Alfa): Modified Sol Parameters and Reduction/Start-up Conditions for Figure B.4 Label Boeh. Acid (pH) Calcinationa (Y/N) Start-up Changesb A P2 Nitric (6) Y 11 bar B P3 Acetic (6) Y No change C P2 Nitric (6) Y No change D P2 No Acidc Y No change E P2 No Acidc Y 1 h F P2 Nitric (6) N 30 min G As Received N No change H P2 Formic (6) N 600oC, 1 h I P3 Acetic (6) N 1.5 h aNormal calcination: calcined overnight in static air at 600oC. bNormal start-up/reduction: catalyst reduced overnight at 550oC, 1.01 bar, with 42 Nml/min H2. cpH not measured Table B.4: Curve Fitting Related to Figure B.4, and Eq. (6.14) for Stability of Ru 5% (Alfa) Label a b c a+c R2 A Activity too low B 4.92 0.245 0 4.92 0.97 C 42.4 0.382 0 42.4 0.98 D 13.5 0.282 4.0 17.5 0.97 E 12.7 0.187 3.5 16.2 0.999 F 42.3 0.0737 0 42.3 0.995 G 17.5 0.0410 15.4 32.9 0.996 H 16.8 0.0272 16.9 33.7 0.994 I 18.5 0.0298 19.7 38.2 0.996 274 Figures B.4 A & B show stability and activity results for the Ru 5% (Alfa) cat- alyst. The modified sol and start-up parameters are listed in Table B.3. Exponential curve fitting data are presented in Table B.4. The samples submitted to calcination in air (Figure B.4 Part A) during the coating procedure suffered both from loss of activity and stronger deactivation, compared to samples that were not calcined in air (Part B). The problem could come from formation of Ruthenium tetroxide (RuO4), which has a melting point of 40oC, and could be volatile during calcination. Another explanation could be that calcination sintered the Ru metal sites, as suggested in Section 6.3.5, with lab- made Ru catalyst. Another interesting, but failed experiment, is portrayed by curve (A). Here the catalyst was reduced by mistake overnight at 11 bar instead of 1 bar. The result was a complete loss of activity. Samples using nitric acid, curves (A), (C) and (F), showed stronger deactivation than samples with no acid, acetic acid or formic acid. Curves (H) and (I) gave similar similar results to those “as received” catalyst. We also observe that both boehmites, P2 and P3, did not adversely affect activity, and that overnight reduction was unnecessary, 1 h at 600oC was sufficient. The explanation behind the negative effect of nitric acid on the catalyst activity is unclear. The electrochemical equilibrium diagram (Pourbaix, 1974) indicates that nitric acid could corrode Ru in aqueous solution. The possibility that corrosion might introduce irreversible changes to the Ru oxidation state was tested with X- Ray Diffraction (XPS) surface analyses. The test results were inconclusive, with Ru peaks hidden by carbon peaks. Carbon peaks are inevitable when catalyst has been in contact with dust particles in ambient air. The Ru corrosion could also have provoked sintering of Ru metal sites, but there were not enough samples to perform CO-sorption analysis. However, the commercial Ru-based catalyst was less active and stable than the lab-made Ru-based catalyst (see Chapter 6). For this reason, as well as some difficulty in coating commercial catalyst with acetic or formic acid, no further testing and analysis with Ru 5% (Alfa) were performed. 275 Appendix C MCMR Supplementary Results C.1 Lessons Learned During Reactor Commissioning Many issues occurred during the commissioning of the reactor. Some of the issues are illustrated in Figures C.1, C.2, and C.3. • The reforming product gas-liquid separator had originally a drain trap func- tioning on thermodynamic principle. The trap was found to be unsafe, with a little dirt preventing the trap from sealing, causing a sudden pressure drop on the reforming side. Two bonnet valves in series were installed to replace it. • A computer, with a custom-made LabVIEW program, controlled the temper- atures and set the flow rates. The computer was disconnected from Internet or other networks, because automatic software updates could trigger auto- matic reboot of the computer, causing automatic shut down of the unit. • Heat cycles were an issue for the MCMR. Metal expansion and contraction weaken the seal, and gasket burst had occurred (see Fig. C.1A) on one occa- sion. Temperatures of the reactor should not be lowered in sleeping mode; only feed gases should be shut off. • SS wool used inside steam pre-heaters oxidized (Fig. C.1B) causing rust to be introduced in the MCMR during the pre-aging of the catalyst support C.2A&B). The wool was therefore changed to alumina beads. 276 • Thermocouples installed inside cartridges heaters were not reliable. Electri- cal noise from the heaters prevented continuous reading of the thermocou- ples, which therefore could not be used for temperature control. • Anti-seize must be chosen carefully. Bolts and nuts seized during an early experimental run (Fig. C.1C). The anti-seize was changed to one more suit- able for higher temperatures. Nuts were changed to Stainless Steel (SS) 316, and bolts were kept to SS 304, to reduce the possibility of galling. • Grafoil gaskets without SS insert were not resistant to the operating condi- tions, as shown in Fig. C.1D. • Grafoil gaskets decomposed with heat. Carbon formation was visible on combustion catalyst after runs. A flow of air or nitrogen was applied during start-up, shut down or sleeping mode, to avoid the problem. • To maximize oxidation catalyst exposure to the feed, in some experiments, the Grafoil strips were reduced in length, only covering the middle three plates (see Fig. C.2C). This configuration caused issues with gas sampling, where back-flow from the second half of the channel occurred, creating erro- neous conversion results. The strip should cover all catalyst plates. Another issue occurred when the Grafoil was too long. Figure C.3 presents three images of the catalyst plates after Exp. no.3. A thin layer of carbon was deposited on the first plate, likely from the gasket. The catalyst of the dark region was scratched off and analyzed for carbon content. Even though car- bon was visible, its amount was below the detection limit of the analyzer. • The design provided the option of feeding air from the top flange, while methane was fed through the separator. However, methane decomposition occurred in the feeding area of the separator, causing flow distribution issues. Figures C.2D.1 & D.2 show carbon formation on one side of the plates. C.2 Preliminary Results Preliminary results from the MCMR experiments are detailed here. For informa- tion on material and methods, refer to Chapter 8. Active catalysts used in this section are detailed in Tables C.1 - C.3. Table C.4 lists simulation parameters that differ from Tables 8.7 & 8.8. 277 A B C D Figure C.1: Issues Encountered with MCMR, Part I: (A) Gasket burst due to heat cycle; (B) SS wool oxidized in steam pre-heater; (C) Galling of bolts with nuts, resulting in stripping of bolt threads while removing nuts; (D) Wrong gasket used: Grafoil without SS foil insert. 278 20 mm A B 50 mm C D.1 200 µm 200 µm D.2 Figure C.2: Issues encountered with MCMR, Part II: (A) Rust deposition on γ-Al2O3 plates from rusty wool inside steam pre-heater; (B) Optical mi- croscope image of (A); (C) Grafoil strip skipping first and last plates, causing issues with gas sampling; (D) Flow distribution issue, with feed not reaching the combustion channel properly, causing carbon forma- tion. 279 25 mm 50 mm A B C Figure C.3: Issues Encountered with MCMR, Part III: (A) Combustion plates after Exp. no.3. (B) Flow distribution issue causing carbon formation. (C) Optical microscope image of (B). 280 Table C.1: Catalyst Description for MCMR Preliminary Experiments, Part I. Metal support is SS 304. No membrane was used. Experiments Numbering is consistent with Table 8.9. Catalyst on γ-Al2O3 support Plate Position Mass Catalyst Ave. Coating Thickness Density Catalyst Layer g µm kg/m3 Experiment no.0.3 Pd 1% (Alfa) 1 0.22 166 300 Pd 1% (Alfa) 2 0.23 164 319 Pd 1% (Alfa) 3 0.24 170 321 Pd 1% (Alfa) 4 0.38 157 546 Pd 1% (Alfa) 5 0.32 148 489 Total mass / Ave. Thickness / Ave. Density 1.39 161 395 Experiment no.0.4 Ru 6% MgO 5% 1 0.237 87 617 Ru 6% 2 0.324 147 499 Ru 6% 3 0.289 121 541 Ru 7% 4 0.326 147 500 Ru 7% 5 0.276 130 480 Total mass / Ave. Thickness / Ave. Density 1.452 126 527 Pd 1% (Alfa) 1 0.293 160 413 Pd 5% (Alfa) 2 0.172 85 458 Pd 5% (Alfa) 3 0.224 122 415 Pd 5% (Alfa) 4 0.236 152 350 Pd 5% (Alfa) 5 0.204 126 367 Total mass / Ave. Thickness / Ave. Density 1.129 129 401 C.2.1 Combustion Preliminary Results First attempts with the MCMR prototype failed to produce hydrogen in the re- forming channel. We instead collected data with only the combustion channel performing. Figure C.4 shows the influence of the channel height. In the first part of the graph, the reactor included the combustion frame, which created a 9 mm channel height. Outlet values were lower than intermediate sampling values, since gas sam- 281 Table C.2: Catalyst Description for MCMR Preliminary Experiments, Part II. Metal support is SS 304. No membrane was used. Experiments Numbering is consistent with Table 8.9. Catalyst on γ-Al2O3 support Plate Position Mass Catalyst Ave. Coating Thickness Density Catalyst Layer g µm kg/m3 Experiment no.0.5 Ru 10% 1 0.266 149 403 Ru 8% La2O3 4% 2 0.272 133 462 Ru 8% 3 0.27 123 496 Ru 7% 4 0.354 148 541 Ru 6% 5 0.317 136 525 Total mass / Ave. Thickness / Ave. Density 1.479 138 485 Pd 1% (Alfa) (all plates reused from Exp. no.0.4) 1 0.293 160 413 Pd 5% (Alfa) 2 0.172 85 458 Pd 5% (Alfa) 3 0.224 122 415 Pd 5% (Alfa) 4 0.236 152 350 Pd 5% (Alfa) 5 0.204 126 367 Total mass / Ave. Thickness / Ave. Density 1.129 129 401 ples were taken near the bottom of the channel, where the conversions were higher. After removing the combustion frame, the intermediate points became lower than at the outlet. Experimental data were under-performing the model predictions. In Figure C.5, the palladium content in the last four plates was increased from 1% to 5%. Initially, the conversion was higher than in Figure C.4. Since we ob- served performance improvement going from 9 mm to 2 mm with the channel height, a thinner gasket was tried to give a 1 mm channel height. The conversion deteriorated, but this was due to the carbon in the feed line that disturbed the flow distribution. After experiencing this issue, the methane feed was pre-mixed with air to avoid thermal decomposition. The same catalyst was used a third time, but suffered permanent deactivation. Experimental data again fell below model pre- dictions in this Figure. Figure C.6 shows several operating conditions where a rapid loss of activity 282 Table C.3: Catalyst Description for MCMR Preliminary Experiments, Part III. Metal support is SS 304. No membrane was used. Experiments Numbering is consistent with Table 8.9. Catalyst on γ-Al2O3 support Plate Position Mass Catalyst Ave. Coating Thickness Density Catalyst Layer g µm kg/m3 Experiment no.0.6 Ru 8% La2O3 4% (reused) 1 0.272 133 463 Ru 8% La2O3 10% 2 0.342 149 518 Ru 6% La2O3 12% 3 0.286 120 537 Ru 9% 4 0.255 144 400 Ru 5% La2O3 14% 5 0.204 89 519 Total mass / Ave. Thickness / Ave. Density 1.359 127 487 Pd 1% (Alfa) 1 0.256 166 349 Pd 5% (Alfa) (light) 2 0.262 162 366 Pd 5% (Alfa) (dark) 3 0.268 199 304 Pd 5% (Alfa) (light) 4 0.284 173 371 Pd 5% (Alfa) (dark) 5 0.261 180 328 Total mass / Ave. Thickness / Ave. Density 1.331 176 344 Experiment no.0.7 Ru 5% La2O3 7% 1 0.326 195 377 Ru 4.2% MgO 3% La2O3 3% 2 0.421 226 421 Ru 8% MnO 2% MgO 2% La2O3 4% 3 0.262 147 403 Ru 5% La2O3 7% 4 0.344 194 401 Ru 8% La2O3 7% 5 0.318 187 384 Total mass / Ave. Thickness / Ave. Density 1.671 190 397 Pd 5% (Alfa) (dark) (all plate reused from Exp. 0.6, but in different order) 1 0.256 199 290 Pd 5% (Alfa) (light) 2 0.262 162 366 Pd 5% (Alfa) (dark) 3 0.268 180 337 Pd 5% (Alfa) (light) 4 0.284 173 371 Pd 1% (Alfa) 5 0.261 166 355 283 Table C.4: Simulation Parameters for Preliminary Results Parameters (Symbols) Values (Equations) Units Catalyst Parameters Pore Volume (υr) 0.49 (γ-Al2O3 only); 0.42 (with La2O3) cm3/g Density (ρcat,k) see Tables C.1 - C.3 kg/m3 Reforming Kinetics Xu and Froment (1989) Design Parameters Length (L) 0.251 m Reforming Width (Wr) 0.081 m Combustion Width (Wc) 0.074 m Catalyst Thickness (Thcat,k) See Tables C.1 - C.3 µm Separator Wall Thickness (Ths) 0.0127 m Reforming Gas Channel Half-Height (Hr) 2; mm Combustion Gas Channel Half-Height (Hc) 0.5 - 1 - 4.5 mm was observed. The amount of data is insufficient to conclude the exact conditions that affect the stability. However experiments involving higher methane concen- tration (4%), temperature at 565oC and pressure above 3.2 bar were more likely to generate higher deactivation decay. The negative effect of higher pressure was also observed in Chapter 7. C.2.2 Reforming Preliminary Results Figure C.7 shows the first experiments that produced hydrogen. Outlet conversion was less than the equilibrium conversion, but intermediate points were above or at equilibrium. The outlet suffered from feed by-passing, as explained in Chapter 8, and the catalyst slowly deactivated. Figure C.8 presents the second experiments that produced hydrogen. Two changes were made from the first experiments: (1) the second plate contained La2O3, and (2) it was attempted to correct the feed by-pass by filling gap below and beside the dummy membrane with Grafoil. The by-pass appeared to be only corrected at lower flow rate (0.52 nL/min). The conversion at the second position was high, suggesting a positive effect of La2O3. The reforming catalyst slowly 284 0 5 10 15 20 0 20 40 60 80 100 Time on Stream (h) M et ha ne  C on ve rs io n (m ol% ) l l l l l l l l l l l l l l l ll l l Position 1 Position 2 Position 3 Position 4 (A) Outlet Model (A) (B) Outlet Model (B) Channel Height: 9 mm Channel Height: 2 mm (*) (**) Figure C.4: Combustion Methane Conversion versus Time on Stream, for MCMR Exp. no.0.3. Operating Conditions: (A) CH4 Flow: 0.10 nL/min, 3.5% in air, Pc: 6.0 bar. Tave,c: 550oC. (B) CH4 Flow: 0.10 nL/min, 3.0% in air, Pc: 6.0 bar, Tave,c: 550oC. deactivated again. Figure C.9, Parts A & B present methane conversion and temperature profiles along the reactor length (axial coordinate) for experiments no.0.4 and 0.5. The conversions at the first location are well below model predictions, but approached equilibrium at the second location. On the combustion side, as mentioned above, the experimental data under-performed the model predictions. There was little dif- ference between the temperatures on the reforming and combustion sides, because both top and bottom flange heaters were on. 285 0 5 10 15 20 25 30 35 0 20 40 60 80 100 Time on Stream (h) M et ha ne  C on ve rs io n (m ol% ) l l l l Position 1 Position 2 Position 3 Position 4 Exp. Outlet Model Outlet Channel Height: 2 mm 1 mm(*) 2 mm Figure C.5: Combustion Methane Conversion versus Time on Stream, for MCMR Exp. no.0.4 and 0.5. Operating Conditions: (A) CH4 Flow: 0.20 nL/min, 3.0% in air, Pc: 3.6 bar. Tave,c: 550oC. Figure C.10 displays methane conversion and temperature profiles along the reactor length for Exp. no.0.7. For the first time, all reforming plates had La2O3 as promoter, and the effect was visible with the conversion at the first point, matching for the first time the model predictions. The bottom flange heaters were shut down, and transversal temperature difference emerged: ∼3oC difference between the combustion and reforming channel at locations 2 and 3. The conversion dropped at the outlet, showing the difficulty to stop by-passing at higher flow rates. 286 0 10 20 30 40 50 0 20 40 60 80 100 Time on Stream (h) M et ha ne  C on ve rs io n (m ol% ) ll l l lll l (A) 3.0%, 3.5 bar, 550°C (B) 3.6%, 2.5 bar, 550°C (C) 3.6%, 2.5 bar, 560°C (D) 3.6%, 4.0 bar, 560°C (E) 3.0%, 2.3 bar, 550°C (F) 3.4%, 2.3 bar, 565°C (G) 4.1%, 4.0 bar, 565°C (H) 4.1%, 3.2 bar, 565°C (I) 3.4%, 3.2 bar, 565°C Day 1 Day 2 Day 3 Day 4 Figure C.6: Combustion Methane Conversion versus Time on Stream, for MCMR Exp. no.0.6 and 0.7. CH4 Flow: 0.20 nL/min, other operation conditions are detailed in Legend. Channel height: 1mm. 287 0 2 4 6 8 10 12 0 10 20 30 40 Time on Stream (h) R ef o rm in g M et ha ne  C on ve rs io n (m ol% ) l l l l l l l l l ll l Position 1 Position 2 Position 3 Position 4 (A) Outlet Thermo. Equil. (B) Ref. 0.31 nL/min (C) Ref. 0.53 nL/min (D) Comb. 0.2 nL/min, 3.6 bar Pressure: 6 bar a 11 bar a 0 20 40 60 80 100 Co m bu st io n M et ha ne  C on ve rs io n (m ol% ) Figure C.7: Reforming Methane Conversion versus Time on Stream, for MCMR Exp. no.0.4. Reforming Operating Conditions: S/C: 4.4 Tave,r: 550oC. Other operating conditions are detailed on Figure. Channel Height: 4 mm. 288 0 2 4 6 8 10 12 0 5 10 15 20 25 30 Time on Stream (h) R ef o rm in g M et ha ne  C on ve rs io n (m ol% ) l l l l l l l l Position 1 Position 2 Position 3 Position 4 (A) Outlet Thermo. Equil. (B) R: 0.52 nL/min, 11.2 bar (C) R:. 1.0 nL/min, 11.2 bar (D) R: 1.0 nL/min, 16.6 bar (E) C: 0.2 nL/min, 3.6 bar (*) 0 10 20 30 40 50 Co m bu st io n M et ha ne  C on ve rs io n (m ol% ) Figure C.8: Reforming Methane Conversion versus Time on Stream, for MCMR Exp. no.0.5. Reforming Operating Conditions: S/C: 4.7 (B) - 2.5 (C&D). Tave,r: 550oC. Other operating conditions are detailed on Figure. Channel Height: 4 mm. (*) By-pass corrected. The first set of data on the left side are from Exp. no.0.4. In legend, R = reforming, C = combustion. 289 020 40 60 80 100 l l l l l l 510 520 530 540 550 560 570A: Exp. no. 0.4 0 20 40 60 80 100 l l l l l l 510 520 530 540 550 560B: Exp. no. 0.5 l (A) Ref. Exp. Conv. (B) Thermo. Equil. Ref. (C) Comb. Exp. Conv. (D) Ref. Model Conv. (E) Comb. Model Conv. (F) Ref. Temp. (G) Comb. Temp. 0.00 0.05 0.10 0.15 0.20 0.25 Axial Coordinate (m) M et ha ne  C on ve rs io n (m ol% ) Te m pe ra tu re  (° C) Figure C.9: Conversion and Temperature Profiles for MCMR Exp. no.0.4 and 0.5. Operating Conditions: (A. Exp. no.0.4) Reforming: CH4 Flow: 0.53 nL/min, S/C: 4.4, Pr: 11.0 bar; Combustion: CH4 Flow: 0.20 nL/min, 3.0%, Pc: 2.5 bar. Time on Steam: 10.6 h. (B. Exp. no.0.5) Reforming: CH4 Flow: 0.53 nL/min, S/C: 4.7, Pr: 11.2 bar; Combus- tion: CH4 Flow: 0.20 nL/min, 3.0% in air, Pc: 3.6 bar. Time on Steam: (ref.) 4.9 h, (comb.) 24.1 h. Temperature data are fitted with a second order polynomial. 290 0.00 0.05 0.10 0.15 0.20 0.25 0 20 40 60 80 100 M et ha ne  C on ve rs io n (m ol% ) l l l l l l 500 510 520 530 540 550 560 l (A) Ref. Exp. Conv. (B) Thermo. Equil. Ref. (C) Comb. Exp. Conv. (D) Ref. Model Conv. (E) Comb. Model Conv. (F) Ref. Temp. (G) Comb. Temp. Axial Coordinate (m) M et ha ne  C on ve rs io n (m ol% ) Te m pe ra tu re  (° C) Figure C.10: Conversion and Temperature Profiles for MCMR Exp. no.0.7. Operating Conditions: Reforming: CH4 Flow: 1.01 nL/min, S/C: 2.5, Pr: 16.4 bar; Combustion: CH4 Flow: 0.20 nL/min, 3.0%, Pc: 2.0 bar. Time on Steam: (ref.) 10 h, (comb.) 30 h. Temperature data are fitted with a second order polynomial. 291 Appendix D Micro-Reactor Supplementary Information D.1 Micro-Reactor PI&D 292 CG-CH4-002 As built Date Created: 2008-03-16 CONFIDENTIAL M. A. Rakib and A. Vigneault Catalyst Evaluation Unit Feeding System Part I (Micro-Reactor at Clean Energy Research Center, UBC) SIZE FSCM NO DWG NO REV 001 2.2 SCALE N/A SHEET 1 OF 4 V-001 CG-H2-001 2200 psig 150 psig SV-HC-031 S FC PRV-001 001 MFC SV-H2-001 S NC 0-500 SCCM H2 HH LL FI-H2-001 V-004 H2 001-0.125"-0.028" Set @ 190 psig V-011 150 psig 2200 psig 013 PI 003 PI V-031 V-003 001 PI 002 PI 011 PI 012 PI CG-AIR-004 V-041 150 psig 2200 psig 041 PI 042 PI Page 3 V-021 V-022 021 PI 022 PI V-042 V-002 V-013 E-DS-001 Desulfurizer 021 TT CG-C3-003 110 psig 95 psig 041 MFC SV-AIR-041 S FC 0-5000 SCCM AIR HH LL FI-AIR-041 V-044 043 PI V-043 PRV-041 Set @ 190 psig V-012 011 MFCHH LL V-023 021 MFCHH LL CH4-001-0.125"-0.028" Air-001-0.125"-0.028" Page 3 V-042 Page 4 To Vent Page 4 To Vent HH L 0-160 SCCM ME 022 TT 023 PI VENT-001-0.250"-0.035" HC-001-0.125"-0.028" HC-002-0.125"-0.028" VENT-002-0.250"-0.035" FI-CH4-011 C3-001-0.125"-0.028" FI-C3-021 V-024 0-500 SCCM C3 REV. DESCRIPTION DATE BY 2.2 Flow rates and pressure updates 09-02-20 AV 293 As Built Date Created: 2008-03-16 CONFIDENTIAL M. A. Rakib and A. Vigneault Catalyst Evaluation Unit Feeding System Part II (Micro-Reactor at Clean Energy Research Center, UBC) SIZE FSCM NO DWG NO REV 001 1.4 SCALE N/A SHEET 2 OF 4 C7-001-0.125"-0.028" SV-N2-051 S FO V-054 V-051 CG-N2-005 150 psig2200 psig V-055FI-N2-051 WTR-001-0.125"-0.028" V-084E-081 1L E-082 0.8L 053 PI V-081 V-072 FI-WTR-81 V-083 FI-WTR-82 Page 3 Page 3 V-052 V-071 051 PI 052 PI 071 PI SV-WTR-081 FC S 081 MFC HH L 0-100 g/h H2O V-074V-073 PSV-051 NG-373-XXX"-SPE E-061 Heptane Tank N2-003-0.125"-0.028" N2-002-0.125"-0.028" V-061 Vent Vent V-065SV-C7-061 FC S 061 MFC HH L V-062 To Vent NG-375-XXX"-SPE I-295 PI V-064 Set @ 190 psig 0-150 g/h C7 Filter E-083 V-063 Water Tanks V-053 Vent N2-001-0.125"-0.028" N 2 - 0 0 4 - 0 . 1 2 5 " - 0 . 0 2 8 " RF-001-0.125"-0.028" N 2 - 0 0 1 V - 0 . 2 5 0 " - 0 . 0 3 5 " REV. DESCRIPTION DATE BY 1.3  Vent and change outlet on C7 line 09-02-20 AV        1.4 Rotameter for water disconnected 11-01-01 AV Page 3 Page 4 VENT-003-0.125"-0.028" For Calibration 294 Cooling Water E-COND-101 V-111 091 To Vent PT As Built Date Created: 2008-03-16 CONFIDENTIAL M. A. Rakib and A. Vigneault Catalyst Evaluation Unit MicroReactor (Micro-Reactor at Clean Energy Research Center, UBC) SIZE FSCM NO DWG NO REV 001 1.3 SCALE N/A SHEET 3 OF 4 Page 2 Page 1 Page 1 091 TT Page 1 H2 + CH4 Water / Water & Heptane N2 Air 092 TT HH L 092 PT 093 TT 094 TT V-102 Page 4 V-121 E-GC-112 Gas Chromatograph To Vent Page 4 E-BM-121 Bubble Meter E-PH-091 Ceramic Radiant Cylinder Heater E-MR-092 Ceramic Radiant Cylinder Heater V-389 V-101 CERC CW CW-001-0.250-???-Brass CW-002-0.250-???-PVC CW-003-0.250-???-PVC Condensed water manual collection FEED-001-0.375-0.0??? REAC-001-0.375-0.??? PREHR-001-0.50-0.??? PRT-001-0.250-0.035 PRT-002-0.125-0.028 PRT-004-0.250-0.???-PVC PRT-005-0.0625-0.??? PRT-006-0.375-0.???-PVC AIR-003-0.1875"-0.???" E-TRAP-111 Moisture Trap 095 TT 101 PI 101 TT V-112 Manual Sampling HH L HH L HH L HH HH L HH L HH HH Page 2 Heptane REV. DESCRIPTION DATE BY 1.2 Rope heater added on Air line 09-02-20 AV         1.3 V-131 changed for Bonnet Valve 11-01-01 AV 600 W 400oC 600 W 500-700oC 25-100oC 092 TT HH L V-131 E-PH-091b&c Rope Heater x 2 380oC 295 Page 1 Page 1 Page 2 As built Date Created: 2008-03-16 CONFIDENTIAL M. A. Rakib and A. Vigneault Catalyst Evaluation Unit Vent (Micro-Reactor at Clean Energy Research Center, UBC) SIZE FSCM NO DWG NO REV 001 1.2 SCALE N/A SHEET 4 OF 4 From PRV-001 From PRV-041 From MicroReactor Page 2 From GC To CERC Ventilation System VENT VENT-005-0.500"-0.???"-PVC VENT-004-0.500"-0.???"-PVC Page 3 From Heptane Vent REV. DESCRIPTION DATE BY 1.2 Add heptane vent  line 09-02-20 AV 296 D.2 Micro-Reactor Electrical and Control Diagram 297 As built Created: 2008-03-30 CONFIDENTIAL M. A. Rakib and A. Vigneault ing. jr. Electrical Connections Multi Channel Reactor: LEGEND SIZE FSCM NO DWG NO REV 002 2.2 SCALE N/A SHEET 1 OF 4 AC / DC Ethernet Thermocouple Wires Connectors Outlet AC + Terminal Blocks Emergency Push Button Ground Overload Switch AC Power Source Wire denomination: E-Device code name- number wire line: specs (amperage used) Ethernet DC - / commun Terminal Block Solid State Relay 002 FCV Flow control valve/ Mass Flow Meter 051 PT Pressure Transducer Instrument Heater E-TT004-002 Quick Connect for Thermocouple Manual Switch (Salzer) Temperature Indicator & Controller Ethernet AC, DC current lines E-112 Pump Fuse SSR-CCT1A ABB01-CCT1A Coil in contactor Switch in Contactor DC + Terminal Block Light 002 TIC AC - Terminal Blocks REV. DESCRIPTION DATE BY 2.2 Name updates 2009-02-20 AV 298 As Built Date created: 2008-03-30 CONFIDENTIAL M. A. Rakib and A. Vigneault Catalyst Evaluation Unit Electrical Diagram: AC Supply (Micro-Reactor at Clean Energy Research Center, UBC) SIZE FSCM NO DWG NO REV N/A Micro-Electrical-001 1.2 SCALE N/A SHEET 2 OF 4 CCT-1A (120 VAC, 20A max) W a l l  O u t l e t Power Bar N 125VAC, 15A 12V, 15A 125VAC, 13A EC1  Heaters Instrument & Control Emergency Shut Down Box, part 1 Mass Flow Controllers Box To Control Box Instrument & Control Overload switch @ 15A JTEC489B15 Overload switch @ 15A To Solenoid Valves Extra power outlet SSR-CCT1A SSR-CCT1B L 120V SSR-E-001 With Heat Sink SAR6-25-1D ESD Buttom D7M-MT44PX01 DC Output Card (52) 0V DC (53) L1a L1b 45 46 48 42 47 43 44 RED REV. DESCRIPTION DATE BY 1.2 Change names, reconnected red light 2009-02-20 AV 299  AC Supply 003 TIC 004 TIC 002 TIC 001 TIC N Control Pannel Part 1 As Built Date Created: 2008-03-30 CONFIDENTIAL M. A. Rakib and A. Vigneault Catalyst Evaluation Unit Electrical Diagram: Instruments (Micro-Reactor at Clean Energy Research Center, UBC) SIZE FSCM NO DWG NO REV N/A Micro-Electrical-001 2.1 SCALE N/A SHEET 3 OF 4 Water Heater Reactor Heater, need ramping function Feed Rope Heater Propane Rope Heater Note about grounding: - Proper ground should be installed, connected to one of the ground line wire - All Solenoid valves must be grounded AC Supply SV-HC- 001 S SV-N2-002 S SV-WTR- 003 S SV-Air-004 S  Methane/Propane Normally closed Asco 8262G19 High Pressure Nitrogen Normally Opened Asco 8262G260 High Pressure Water Normally closed Asco 8262G19 Air Normally closed Asco 8262G19 SV-H2-005 S Hydrogen Normally Closed Asco 8262G19 SSR-E-02 125V 1A, load 2-32VDC control  (120VAC, 0.05A)  (120VAC, 0.1A) (120VAC, 0.05A) (120VAC, 0.05A)  (120VAC, 0.05A) Emergency Shut Down, part II 24VDC power supply, 1A SV-C7-006 S Heptane Normally Closed Asco 8262G19 (120VAC, 0.05A) 0V DC (51) Overload switch @ 6A Overload switch @ 6A DC Output Card (50) 41 Fuse 0.25A 5L1I 6 23 33 Fuse 0.8A 24 40 REV. DESCRIPTION DATE BY 2.0 Renamed as built, add fuse before power supply 2009-02-20 AV 300 AC Supply @10A, 125V @10A, 125V 26 28 @2A, 125V @2A, 125V 30 32 N SSR-H01 Load 25A, Control 2-32VDC, SAS3-25-1D Thermopad SSR-H02 Load 25A, Control 2-32VDC, SAS3-25-1D Thermopad SSR-H03 Load 10A, Control 2-32VDC, SAS3-10-1D Thermopad SSR-H04 Load 10A, Control 2-32VDC, TSAS3-10-1D hermopad Control Pannel Part II Preliminary Last update: 2008-06-16 CONFIDENTIAL M. A. Rakib and A. Vigneault Catalyst Evaluation Unit Electrical Diagram: Heaters (Micro-Reactor at Clean Energy Research Center, UBC) SIZE FSCM NO DWG NO REV N/A Micro-Electrical-001 2 SCALE N/A SHEET 4 OF 4 Water Feed Heater 5A, 25Ω Reactor Heater 5A, 25Ω Feed Rope Heater 1A Propane Rope Heater 1A 25 27 29 31 REV. DESCRIPTION DATE BY 2.0 Renamed as built, change fuses to breakers 20080616 AV JTECUL 1B10 JTECUL 1B10 JTECUL 1B02 JTECUL 1B02 0V DC (3) 0V DC (3) 0V DC (6) 0V DC (6) L1H From output T control (19) From output T control (20) From output T control (21) From output T control (22) GREEN 301 Appendix E Multi-Channel Reactor Supplementary Information E.1 MCMR PI&D 302 N2H-001-0.125"-0.028" H2-001-0.125"-0.028" N2H-004-0.250"-0.035" N2H-005A-0.250"-0.035" CH4R-003-0.250"-0.035" FR-001-0.250"-0.035" H2-003 - 0.250"-0.035" CH4R-001-0.125"-0.028" WTR-006-0.250"-0.035" Methane Cylinder V-013 (1 psi) SV-002 S FO E-001 28 L?? V-014 (1 psi) 002 PI V-017 N2H-006B-0.250"-0.035" V-015 V-016 N2H-006A-0.250"-0.035" 002 FCV H-01 WTR-007-0.250"-0.035" H C H-02 002 TT 001 TIC 004 TT 002 TIC I HH LL Reforming Feed N2H-005B-0.250"-0.035" Sheet no. 3 V-004 (1psi) As Built Drawing created: 2007-11-14 CONFIDENTIAL Alexandre Vigneault Multi Channel Reactor: Reforming Feed SIZE FSCM NO DWG NO REV N/A 001 2.1 SCALE N/A SHEET 1 OF 5 S FC SV-003 001 FCV V-001 V-005 I-008V-006 H2 Start-up V-009 (1psi) V-10 High Pressure Nitrogen Cylinder V-11 V-002 130 bar (a) 5-25 bar(a) 5-35 bar (a) 130 bar (a) 5-25 bar (a) 5-27 bar (a) Steam Heater 200-300oC Radiant Heater: 1300 W 0.5 – 4.5 - 30 ml/min liquid water Reforming Feed: 300-500oC Radiant heater 1300W E-002 WTR-001-0.250"-PVC E-003 V-003 To vent SV-001 S FC 0.5-2-10 SLM 0.1-0.4-1.3 SLM 130 bar (a) Set @ 30 bar(a) Set @ 29 bar(a) V-019 Vent V-007 015 PI HH LL HH LL 001 LS V-022 (1psi) 003 TT 001 TT 001 PTHH L V-018 V-021 WTR-005-0.250"-PVC CH4R-002V-0.250"-0.035" F-022 CH4R-002-0.250"-Brass N2H-003-0.250"-0.035" H2-002-0.250"-Brass N2H-002-0.250"-Brass 002 LS H L WTR-003-0.250"-0.035" WTR-002-0.250"-PVC WTR-004-0.250"-0.035" V-020 I HH LL 01B TT I HH LL Steam Rope Heater H-01c 200-300oC 125 W REV. DESCRIPTION DATE BY       2.1 Steam rope heater added 2010-03-24 AV V-012 01B TIC 303 CH4C-003-0.250"-0.035" CH4C-001-0.125"-0.028" N2L-001-0.125"-0.028" AIR-001B-0.125"-0.028" AIR-001B-0.125"-0.028" AIR-004-0.250"-0.035" N2L-004A-0.250"-0.035" AIR-003-0.250"-0.035" As Built Drawing created: 2007-11-14 CONFIDENTIAL Alexandre Vigneault Multi Channel Reactor P&ID: Combustion Feed SIZE FSCM NO DWG NO REV N/A 001 2.1 SCALE N/A SHEET 2 OF 5 HC FC V-35 (0.3psi) 32 TT 31 TICI HH V-39 (0.3 psi) V-30 Air Cylinders V-31 1-5 bar (a) V-32 V-33 H-31: Air Heater 300-500oC Rope heater 650 W V-34 130 bar Set @ 9 bar(a) S SV-031 2.1 - 7.4 - 51 SLM AIR-003V-0.250"-0.035" 31 TT SV-033 S32 FCV FC Combustion CH4 Sheet no. 3 V-44 (0.3psi) 1-5 bar (a) V-41 V-42 V-43 To vent 0.1-0.4-3.5 SLM 130 bar (a) Set @ 5 bar(a) Methane Cylinder Sheet no.4 N2 Purge for H2 HH LL Low Pressure Nitrogen Cylinder 5-8 bar (a) 31 PTHH LL SV-032 S NO V-38 N2L-003B-0.250"-0.035" V-40 (0.3 psi) 130 bar (a) N2L-004B-0.250"-0.035" Vent N2LL-005-0.250"-0.035" V-36 V-37 1-5 bar (a) N2L-003A-0.250"-0.035" CH4C-004-0.250"-0.035" Sheet no.3 Combustion Air CH4C-003V-0.250"-0.035" AIR-002-0.250"-Brass 31 FCVHH LL N2L-002-0.250"-Brass CH4C-002-0.250"-Brass" REV. DESCRIPTION DATE BY       2.1 Rope heater, modified controls for TIC 31 2010-03-24 AV AIR-003B-1.00" 33 TT V-204 V-205 S NO 1-5 bar (a)       2.1 Add separated purge line for H2 products 2010-03-24 AV 304 Reforming End Plate (Bottom plate) Combustion End Plate (Top plate) Cooling bath RSP-007-0.125"-0.028" CSP-007-0.125"-0.028" H2-002-0.250"-0.035" PdAg Membrane Reforming Gas Channel Combustion Gas Channel Solid Wall: (Middle Plate) Sheet no. 2 Combustion CH4 Sheet no. 1 Reforming Feed 58 TT 52 TIC To vent V-51 V-54V-52 V-53 V-58 V-59 V-61 V-62 As Built File created: 2008-06-04 CONFIDENTIAL Alexandre Vigneault Multi-Channel Reactor: Reactor SIZE FSCM NO DWG NO REV N/A 001 2.2 SCALE N/A SHEET 3 OF 5 52 TT To Vent CH4C-004-0.250"-0.035" Sheet no. 4 Sheet no. 4 57 TT 64 TT 63 TT 69 TT 68 TT 67 TT V-55 V-56 V-82 (0.3psi) V-81 (0.3psi) SP-001-0.125"-0.028" Combustion Products Reforming Products HC RP-001-0.250"-0.035" 51 TIC I S h e e t  n o .  4 Hydrogen Product V-63 52 PT 55 PT 53 PT 54 PT Relief Valve disconnected (leaking and not necessary) Sheet no. 5 2000W 51 A-CO 12 samples lines: Reforming: RSP-001-0.0625"-0.02"- to RSP-004-0.0625"- 0.02" Combustion: CSP-001-0.0625"-0.02" to CSP-004-0.0625"-0.02" Hydrogen lines: Outside H2-001A-0.5"-xxx"; H2-001B-0.5"-xxx" Inside: H2-001C-0.25"-00.035", H2-001D-0.5"-0.035" Outside and Inside line are sealed with Buffalo?? Pressure transducer lines: Reforming: RSP-001P-0.125"-0.35"; RSP-006P-0.125"- 0.035" Combustion: CSP-001P-0.125"-0.035"; CSP-006P-0.125"-0.035" Note: all tubes coming out of the reactor are 3/ 16" OD, unless specified otherwise 2000W 56 TT 55 TT 62 TT 61 TT 66 TT 74 TT 73 TT 72 TT 71 TT AIR-004-0.250"-0.035" V-60 Catalyst Plates Thermocouple positions CP-001-0.250"-0.035" I HH (Top flange Thermocouples) 51 TT 51 PT Sheet no. 2 H C Combustion Air HC CH4C-004V-0.250"-0.035" V-57 81 TT 82 TT AIR-005-0.375"-x.xx" E-51: Multi-Channel Membrane Reactor Cartridge Heaters (500W each)  with embedded thermocouple V-84 SP-.1875ID-PVC SP-004-0.125"-0.028" V-84 Gas-Liquid Separator 50 ml, 68.9 bar V-85 To Sampling bag REV. DESCRIPTION DATE BY       2.1 Sampling line modifications 2010-03-24 AV       2.2 Sampling line modifications 2011-01-01 AV H-52A TT-58 H-52B TT-64 Computer side H-52C TT-69 Cylinders Side H-52D TT-74 Not installed Not installed FR-002-0.250"-0.035" Steam & Methane Rope Heater H-02c 300-500oC, 125 W 050 TT H-51C TT-66 Cylinders side H-51A TT-55 Computer side H-51D TT-71 Cylinders Side H-51C TT-61 Computer Side CO detector Located on micro-reactor unit I HH LL (Combustion Thermocouples) HH LL (Reforming Thermocouples) HH  (Bottom Flange Thermocouples) I 050 TIC I HH V-215 SP-002B-0.25"-PVC SP-002A-0.125"-0.028" SP-003-0.125"-0.028" Drain NG-246-XXX"-SPE 305 GC-005-0.125"-0.028" RP-005-0.250"-PVC V-111 (0.3 psi) GC-008-0.125"-0.028"GC-007-0.125"-0.028" GC-004-0.125"-0.028" H2-004B-0.250"- 0.035" RP-002-0.250"-0.035" RP-003-0.250"-0.035" CP-003-0.250"-0.035"CP-002-0.250"-0.035" V-093 093 PI V-095 092 TT Sheet no. 3 Sheet no. 3 V-091 As Built Drawing created: 2007-11-15 CONFIDENTIAL Alexandre Vigneault Multi-Channel Reactor: Products SIZE FSCM NO DWG NO REV N/A 001 2.1 SCALE N/A SHEET 4 OF 5 To Vent To Vent V-103 103 PI V-105 101 TT V-101 To Vent To Vent V-096 (0.3 psi) Combustion Products Reforming Products 112 PTV-112 V-115 To GC E-112 W 117 FT To Vent V-116 (0.3 psi) I-121 111 TT I Sheet no. 3 H2-002-0.250"-0.035" H2-006-0.250"-0.035" H2-004A-0.250"-0.035" To Vent V-113 V-115 Hydrogen Product E-111: Buffer Tank DC Motor Controller E-113 V-114 1.5 – 9.3 SLM 0.5 – 0.7 bar(a) Set @ 5 bar(a) Set @ 30 bar(a) Set @ 2-5 bar(a) 2.2– 7.8- 56 SLM 1.5 – 10 - 47 SLM < 60oC < 60oC 1.1 – 2 bar(a) up stream 5 – 26 bar(a) up stream V-106  (0.3 psi) 1– 2 bar(a) up stream V-116 V-117 GC-009-0.0625"-0.02" HH HH CP-002V-0.250"-0.035" RP-002V-0.250"-0.035" H2-003V-0.250"-0.035" N2L-003C-0.250"-0.035" V-113 (0.3 psi) N2 Purge for H2 E-091 E-101 116 PI HH H2-005-0.250"- 0.035" Sheet no.2 CP-003V-0.250"-0.035" RP-003V-0.250"-0.035" H2-006V-0.250"-0.035" E-121: Gas demoisturizer 091 TT E- 91: Cooling bath E- 91 V-092 < 60oC H2-003-0.250"-0.035" CP-004-0.250"-0.035" RP-004-0.250"-0.035" CP-005-0.250"-PVC GC-006-0.125"-0.028" 113 PIC V-102B HH LL REV. DESCRIPTION DATE BY       2.1 Outlet valves changed for bonnet type 2010-03-25 AV      2.2 Drain trap removed (not working) 2011-01-01 AV V-094 V-104 V-102A Air Cooled only 306 As Built Drawing created: 2007-11-15 CONFIDENTIAL Alexandre Vigneault Multi-Channel Reactor: Venting SIZE FSCM NO DWG NO REV N/A 001 2.1 SCALE N/A SHEET 5 OF 5 CH4R-002V-0.250"-0.035" CH4C-003V-0.250"-0.035" Sheet no. 1 Sheet no. 2 CERC General High Head Ventilation System VENT-001B-0.375"-PVC Sheet no. 4 RP-002V-0.250"-0.035" Sheet no. 4 VENT-002-0.375"-PVC Sheet no. 4 H2-003V-0.250"-0.035" VENT-001A-0.250"-0.035" CP-002V-0.250"-0.035" Sheet no. 4 CP-003V-0.250"-0.035" VENT-003-0.375"-PVC Sheet no. 4 H2-006V-0.250"-0.035" VENT-003-0.375"-Brass Sheet no. 4 RP-003V-0.250"-0.035" VENT-004-0.375"-PVC Sheet no. 4 H2-005V-0.250"-0.035" V-133 (0.3 psi) V-131 (0.3 psi) V-132 (0.3 psi) CERC H2 High Head Ventilation System Sheet no. 3 CH4C-004V-0.250"-0.035" Sheet no. 3 SP-004-0.125"-0.028" V-134 (0.3 psi) REV. DESCRIPTION DATE BY       2.1 SP-004 line added 2010-03-25 AV 307 E.2 MCMR Electrical Diagram 308 Preliminary Last update: 2008-05-05 CONFIDENTIAL Alexandre Vigneault Electrical Connections Multi Channel Reactor: LEGEND SIZE FSCM NO DWG NO REV 002 3 SCALE N/A SHEET 1 OF 16 AC / DC Ethernet Thermocouple Wires Connectors Wall Outlet AC Connector/junctions Emergency Push Button Ground Overload Switch AC Power Source Wire denomination: E-Device code name- number wire line: specs (amperage used) Ethernet DC - / common SSR: Solid State Relay MR: Mechanical Relay Connector Block Terminal Block 002 FCV Flow control valve/ Mass Flow Meter 051 PT Pressure Transducer Instrument Heater E-TT004-002 Quick Connect for Thermocouple Manual Switch 56 TT Thermocouple Ethernet AC, DC current lines E-112 Pump Fuse SSR-CCT1A ABB01-CCT1A Coil in contactor Switch in Contactor DC + Light Fan @20A REV. DESCRIPTION DATE BY 309 As Built CONFIDENTIAL Alexandre Vigneault Electrical Connections Multi Channel Reactor: AC Supply SIZE FSCM NO DWG NO REV 002 3.4 SCALE N/A SHEET 2 OF 16 CCT-3 (120 VAC, 20A max) CCT-6 (120 VAC, 20A max) CCT-2/4 (208 VAC, 20A max) CCT-1 (120 VAC, 20A max) Feed HeatersE-CCT1A-001: 120V, 15A(11A), 25 ft  Feed Heaters To H01 To H31 Feed Heaters To H02 E-CCT3A-001: 120V, 15A(11A), 25 ft E-CCT6A-001: 120V, 15A (7.5A), 25 ft E-CCT6B-001: 120V, 15A, 30 ft E-CCT2/4-001 (L1): 208V, 20A(14.5A), 25 ft EMC1-B EMC1-D EMC1-E EMC2-A E l e c t r i c a l  P a n e l E l e c t r i c a l  P a n e l E-003 Water Tank Pump (with 5ft of AC wire) E-E003-002: (120AC, 2.4A) 120VAC N AC/DC Converter See DC Supply Sheet 120V AC N Reactor (L2) To H51 & H52 Solenoid UPS 120VAC N Power Bar EMC1-A EMC1-C Fan for electric box SSR-FAN-001 Electrical Pannel Control Electrical Pannel, part 1 EMC1 -coil EMC2- coil @20A @20A @20A @20A Emergency Stop REV. DESCRIPTION DATE BY 3.4 Remove CCT-1b, 3b, replace fuse by breakers, fix L1,  L2 2009-05-05 AV 50 51 52 53 54 55 red CB1 @15A CB2 @15A CB3 @15A CB4 @15A, slow CB5 @1A CB6 @10A 56 E-CCT2/4-001 (L2) EMC2-A CB7 @20A 70 74 78 82 71 72 75 76 79 80 83 63 85 86 87 89 90 92 91 93 95 94 96 Reactor (L1) L1 L2 310 As Built CONFIDENTIAL Alexandre Vigneault Electrical Connections Multi Channel Reactor: DC Supply SIZE FSCM NO DWG NO REV 002 3.5 SCALE N/A SHEET 3 OF 16 V+ 24VDC (3A) AC/DC Converter Note on Power Supply P-24VDC-001 22.5-28.5VDC, 7.5A max Normal: 24VDC, 5A Power supply mounted on rail UTA 107 Leave 5cm below and above for sufficient convection, Unused terminal should be closed, Stripped 7mm for wire ends Use wire: AWG 24-14, 75oC Brand: Quint Power  E-FCV001-4-001: 0V PowerE-FCV002-7-001: +Us (24VDC, 320mA) E-FCV001-7-001: +Us (24VDC, 320mA)  E-FCV002-4-001: 0V Power  E-FCV003-4-001: 0V PowerE-FCV032-7-001: +Us (24VDC, 320mA)  E-FCV004-4-001: 0V PowerE-FCV031-7-001: +Us (24VDC, 320mA) 0V DC Common 001 FCV 032 FCV 031 FCV 002 FCV cFP-1808-01 F1 @3A, 32V E-cFP-02, 24VDC (0.62A) cFP-1808-02 F2 @3A, 32V E-cFP-02, 24VDC (0.39A) CFP-AI100-01 CFP-AI100-02 CFP-AI100-03 CFP-AO210-01 CFP-DO401-01 F3 @2A, 32V, slow E-LS002-002 E-LS002-001: 10-30VDC E-LS001-002E-LS001-001: 10-30VDC High Level Switch Omega LVK-50 Normally closed?? (dry) 002 LS 001 LS CFP-AI100-01 CFP-AI100-01 117 FT E-FT117-1-001: +Us (24VDC, ?mA) E-112: H2 Vacuum pump DC Motor Controller E-113 Pololu TReX Jr Dual Motor Controller E-H2VP-001 (1.3A) F5 @1A, 32V F6 @1A, 32V Low  Level Switch F4 @2A, 32V Electrical Control Pannel, part II REV. DESCRIPTION DATE BY 3.4 Revome disconnect switch before CFP’s 20080604 AV 3.5 Add names, connectors 2009-05-07 AV 100 101 120 122 123 124 105 103 103 104 311 As built CONFIDENTIAL Alexandre Vigneault Electrical Connections Multi Channel Reactor: H01 & H31 SIZE FSCM NO DWG NO REV 001 3.3 SCALE N/A SHEET 4 OF 16 H-01-A 650W, 5.42A H-01-B 650W 5.42A E-H01A-001: 10A E-H01B-001: 10A E-H01A-002: 10A E-H01B-002: 10A E-H01-001: 120V, 15A I 001 TIC AC Supply H-31 650W, 5.42A E-H31-002: 120V,10A E-H31-001: 120V, 15A E-H31-003: 120V, 15A I 031 TIC AC Supply Steam Heaters (for Reforming) Air Heater (for Combustion) 120VAC N SSR2 SSR3 SSR4 SSR5 H-02-A 650W, 5.42A H-02-B 650W 5.42A E-H02A-001: 120V,10A E-H02B-001: 120V, 10A E-H02-001: 120V, 15A I 002 TIC AC Supply SSR6 SSR7 Methane & Steam Heaters (Reforming Feed) 120VAC N Electrical Control Pannel, Part III All green lights are located on the electrical control pannel Junction Box REV. DESCRIPTION DATE BY 3.2 Renaming relays, change all MR of SSR 20080604 AV 3.3 Remove junctions boxes, name connectors 2009-05-09 AV 72 73 57 58 59 76 77 80 81 312 As Built CONFIDENTIAL Alexandre Vigneault Electrical Connections Multi Channel Reactor: Reactor Heaters SIZE FSCM NO DWG NO REV 001 4.3 SCALE N/A SHEET 5 OF 16 H-51A 375W, 1.8A H-51B 375W, 1.8A E-H51A-001: 240V,5A? E-H51B-001: 240V,5A E-H51-001: 240V, 20A (15A) E-H51-001: 240V, 15A (7.4A) I 051 TIC H-51C 375W, 1.8A H-51D 375W, 1.8A E-H51C-001: 240V,5A E-H51D-001: 240V,5A Top Flange Heaters (Combustion Side) H-52A 375W, 1.8A H-52B 375W, 1.8A E-H52B-001: 240V,5A E-H52-001: 240V, 15A (7.4A) 052 TIC H-52C 375W, 1.8A H-52D 375W, 1.8A E-H52C-001: 240V,5A E-H52D-001: 240V,5A Bottom Flange Heaters (Reforming Side) Bottom Flange Heaters location B A C D Air Inlet Side Top Flange Heaters location C D A B Air Inlet Side Cartridge Heaters and Thermocouple Location SSR10 SSR8 SSR9 AC Supply L1  208V L2  208V L2  208V N Junction Box Electrical Control Pannel, part IV Junction Box REV. DESCRIPTION DATE BY 4.2 Renaming relays, change MR to SSR 2008-06-04 AV         4.3 Add 2 contactors, in order to control the lights 2009-05-13 AV 97 60 61 TT 69 TT 58 TT 74 TT 64 TT 66 TT 71 TT 55 TT 61 H51C-Coil H51C-Coil H51C-S1 H52C-S1 H52C-S2 H51C-S2 L1 E-H52A-001: 240V,5A L2 208V Electrical Control Pannel, part V Should it be connected to 97 instead?? green green 313 As Built CONFIDENTIAL Alexandre Vigneault  Electrical Connections Multi Channel Reactor: Solenoid Valves SIZE FSCM NO DWG NO REV 002 3.1 SCALE N/A SHEET 6 OF 16 SV-001 S SV-002 S SV-003 S SV-031 S High Pressure Methane Normally closed Asco 8262G80 High Pressure Nitrogen Normally Opened Asco 8262G260 High Pressure Water Normally closed Asco 8262G80 Air Normally closed Asco 8262G20 SV-032 S Low Pressure Nitrogen Normally Opened Asco 8262G261 SV-033 S Low Pressure Methane Normally Closed Asco 8262G20 AC Supply E-SV-001: Load (120VAC, 0.40A) 120 VAC N E-SV001-001: AC IN (120VAC, 0.05A) SSR0 E-SV002-001: AC IN (120VAC, 0.1A) E-SV003-001: AC IN (120VAC, 0.05A) E-SV031-001: AC IN (120VAC, 0.05A) E-SV032-001: AC IN (120VAC, 0.1A) E-SV033-001: AC IN (120VAC, 0.05A) Electrical Control Pannel, part V REV. DESCRIPTION DATE BY        3.1 Add Pilot Light 2009-05-13    AV 62 85 green 314 As Built CONFIDENTIAL Alexandre Vigneault Electrical Connections Multi Channel Reactor: Grounding SIZE FSCM NO DWG NO REV 002 3 SCALE N/A SHEET 7 OF 16 Reactor Top Flange Reactor Bottom Flange Heat Shield cFP-1808-01 cFP-1808-02 AC/DC Converter Grounding block Electrical Control Pannel, Part VI REV. DESCRIPTION DATE BY          3 Rewiring as Built 2009-05-13 AV Front Pannel Back Pannel Grounding block on Control Pannel Panel X CCT-1 CCT-3 CCT-6 CCT-2/4 315 CFP-TC120-01 As Built CONFIDENTIAL Alexandre Vigneault Electrical Connections Multi Channel Reactor: Thermocouple Input SIZE FSCM NO DWG NO REV 002 2.1 SCALE N/A SHEET 8 OF 16 E-cFPTC-01-00 E-cFPTC-01-01 E-cFPTC-01-02 E-cFPTC-01-03 E-cFPTC-01-04 E-cFPTC-01-05 E-cFPTC-01-06 E-cFPTC-01-07 E-cFPTC-02-00 E-cFPTC-02-01 E-cFPTC-02-02 E-cFPTC-02-03 E-cFPTC-02-04 E-cFPTC-02-05 E-cFPTC-02-06 E-cFPTC-02-07 CFP-TC120-02 CFP-TC120-03 E-cFPTC-03-00E-TT051-002 E-TT052-002 E-cFPTC-03-01 E-TT0XX-002 E-cFPTC-03-02 E-TT081-002 E-cFPTC-03-03 E-TT082-002 E-cFPTC-03-04 E-TT0XX-002 E-cFPTC-03-05 E-TT0XX-002 E-cFPTC-03-06 E-TT0Box-002 E-cFPTC-03-07 E-cFPTC-04-00E-TT056-002 E-TT062-002 E-cFPTC-04-01 E-TT067-002 E-cFPTC-04-02 E-TT072-002 E-cFPTC-04-03 E-TT057-002 E-cFPTC-04-04 E-TT063-002 E-cFPTC-04-05 E-TT068-002 E-cFPTC-04-06 E-TT073-002 E-cFPTC-04-07 All thermocouples are type K For the sake of simplicity, one of two wires are shown for thermocouple wires Each thermocouple comes with a 80" wire E-cFPTC-05-00 E-cFPTC-05-01 E-cFPTC-05-02 E-cFPTC-05-03 E-TT0XX-002 E-cFPTC-05-04 E-TT0XX-002 E-cFPTC-05-05 E-TT0XX-002 E-cFPTC-05-06 E-TT0XX-002 E-cFPTC-05-07 CFP-TC120-04 CFP-TC120-05 51 TT 52 TT XX TT 81 TT 82 TT XX TT XX TT box TT 56 TT 62 TT 67 TT 72 TT 57 TT 68 TT 63 TT 73 TT 091 TT 092 TT 101 TT 111 TT XX TT XX TT XX TT XX TT E-TT056-001E-TT051-001 E-TT052-001 E-TT0XX-0XX E-TT081-001 E-TT082-001 E-TT062-001 E-TT067-001 E-TT072-001 E-TT057-001 E-TT063-001 E-TT068-001 E-TT073-001 001 TT 002 TT 003 TT 004 TT 031 TT XXX TT 032 TT XXX TT 055 TT 061 TT 066 TT 071 TT 058 TT 069 TT 064 TT 074 TT + - + - - - - + + + REV. DESCRIPTION DATE BY        2.1 Removed TT 000, add quick connect connectors 2009-05-13 AV 316 As Built CONFIDENTIAL Alexandre Vigneault Electrical Connections Multi Channel Reactor: Analog I/O SIZE FSCM NO DWG NO REV 002 2.1 SCALE N/A SHEET 9 OF 16 CFP-AI100-03 (Interface 1 Bank 8) E-cFPAI-01-07 E-FCV002-2-001: (0-5VDC)E-cFPAI-01-06 E-FCV003-2-001: (0-5VDC)E-cFPAI-01-05 E-FCV004-2-001: (0-5VDC)E-cFPAI-01-04 E-FT117-3-001: (0-5VDC) E-cFPAI-01-03 E-cFPAI-01-02 E-LS002-001: (0-30VDC?) E-cFPAI-01-01 E-LS001-001: (0-30VDC?) E-cFPAI-01-00 E-cFPAI-02-00 Low Pressure N2: E-PT001-G-001: (0-5V) High Pressure N2: E-PT031-C?-001: (4-20mA) E-cFPAI-02-01 Air Inlet: E-PT051-R-001: (0-5V) E-cFPAI-02-02 Reforming In: E-PT052-2-001: (4-20mA) E-cFPAI-02-03 Combustion In: E-PT053-2-001: (4-20mA) E-cFPAI-02-04 Reforming Out: E-PT054-2-001: (4-20mA) E-cFPAI-02-05 Combustion Out: E-PT055-2-001: (4-20mA) E-cFPAI-02-06 H2 Permeate: E-PT112-2-001: (0-5V) E-cFPAI-02-07 CFP-AI100-02 (Interface 1 Bank 6) 1 3 18 20 22 24 26 28 30 32 5 7 9 11 13 15 1 4 5 8 10 11 13 15 E-PT001-R-001: +V E-PT031-C?-001:  +V E-PT051-R-001: +V E-PT052-3-001: +V E-PT053-3-001: +V E-PT054-3-001: +V E-PT055-3-001: +V E-PT112-3-001: +V 001 LS 002 LS 001 FCV 002 FCV 031 FCV 032 FCV CH4 Reforming Flow Water Flow Air Combustion CH4 Combustion DC DC V in / I in V in / I inV sup 031 PT 053 PT 001 PT 051 PT 052 PT 054 PT 055 PT 112 PT 18 20 22 24 26 28 30 32 Notes: - See Pressure Sheet for more info on pressure transducers connections- - 16-26 AWG copper wires, 6mm of insulation stripped at the end Common Common 17 19 21 23 25 27 29 31 117 FT H2 Flow REV. DESCRIPTION DATE BY       2.1 Fix PT 001- 031 positions 2009-05-12 AV 317 E-cFPAI-02-00 E-cFPAI-02-01 E-cFPAI-02-02 E-cFPAI-02-03 E-cFPAI-02-04 E-cFPAI-02-05 E-cFPAI-02-06 E-cFPAI-02-07 18 20 22 24 26 28 30 32 1 3 6 7 9 11 13 15 E-cFPAO-01-00  E-FCV001-003: (0-5VDC) E-FCV002-003: (0-5VDC)E-cFPAO-01-01 E-FCV031-003: (0-5VDC)E-cFPAO-01-02 E-FCV032-003: (0-5VDC) E-cFPAO-01-03 E-cFPAO-01-04 E-E113-AI-001 (2.5-5V) E-cFPAO-01-05 E-cFPAO-01-06 E-cFPAO-01-07 CFP-AO210-01 (Interface 2 Bank 3) 18 20 22 24 26 28 30 32 1 3 5 7 9 11 13 15 Preliminary Last update: 2009-05-13 CONFIDENTIAL Alexandre Vigneault Electrical Connections Multi Channel Reactor: Analog I/O SIZE FSCM NO DWG NO REV 002 2.1 SCALE N/A SHEET 10 OF 16 001 FCV 002 FCV 031 FCV 032 FCV DC Motor Controller E-113 CFP-AI100-02 (Interface 1 Bank 7) Gas alarm?? Gas alarm?? V in / I in V in / I in V sup 17 19 21 23 25 27 29 31 001 GAE-GA001-001 (0-5V??) 001 GAE-CO001-001 (4-20mAmp) Common Common REV. DESCRIPTION DATE BY 318 SSR0 SSR3 Temp Control SSR2 Safety Stop As Built CONFIDENTIAL Alexandre Vigneault Electrical Connections Multi Channel Reactor: Digital Output SIZE FSCM NO DWG NO REV 002 4.3 SCALE N/A SHEET 11 OF 16 cFP-DO401-01 (Interface 2, Bank 2) E-cFPDO-01-00 E-I-TIC001-001 E-cFPDO-01-01 E-cFPDO-01-02 E-cFPDO-01-03 E-cFPDO-01-04 E-cFPDO-01-05 E-cFPDO-01-06 E-cFPDO-01-07 E-cFPDO-01-08 E-cFPDO-01-09 E-cFPDO-01-10 E-cFPDO-01-11 E-cFPDO-01-12 E-cFPDO-01-13 E-cFPDO-01-14 E-cFPDO-01-15 E-TIC001-001 E-TIC031-001 E-I-TIC031-001 E-TIC002-001 E-I-TIC002-001 E-I-TIC051-001 E-TIC051-001 1 18 2 20 3 4 5 6 7 8 9 10 11 12 13 14 15 16 22 24 26 28 30 32 I 001 TIC SSR5 Temp Control SSR4 Safety Stop I 031 TIC SSR7 Temp Control SSR6 Safety Stop I 002 TIC SSR8 Temp Control SSR10 Safety Stop I 051 TIC S SV-001 E-SV001-001 E-TIC052-001 SSR9 Temp Control052 TIC REV. DESCRIPTION DATE BY 4.2 Rewiring COM side, name editing, adding one SSR TIC 052 20080604 AV Common        4.3 Swtich SSR2 (ch no. 0 broken), rename SSR’s 2009-05-12 AV SSR1 Temp Controlbox TIC 319 Preliminary Last update: 2009-05-13 CONFIDENTIAL Alexandre Vigneault Electrical Connections Multi Channel Reactor: Relays SIZE FSCM NO DWG NO REV 002 3 SCALE N/A SHEET 12 OF 16 cFP-RLY421-01 E-cFPRLY-01-NO-00 E-cFPRLY-01-NO-01 E-cFPRLY-01-NO-02 E-cFPRLY-01-NO-03 E-cFPRLY-01-NO-04 E-cFPRLY-01-NO-05 E-cFPRLY-01-NO-06 E-cFPRLY-01-NO-07 2 4 6 10 12 14 16 1 3 5 7 9 11 13 15 8 E-cFPRLY-01-IC-00 E-cFPRLY-01-IC-01 E-cFPRLY-01-IC-02 E-cFPRLY-01-IC-03 E-cFPRLY-01-IC-04 E-cFPRLY-01-IC-05 E-cFPRLY-01-IC-06 E-cFPRLY-01-IC-07 NO + IC - 320 Preliminary Last update: 2008-02-25 CONFIDENTIAL Alexandre Vigneault Electrical Connections Multi Channel Reactor Annexe: Compact Field Point, Main Slot Boards & Ethernet network SIZE FSCM NO DWG NO REV 002 2 SCALE N/A SHEET 13 OF 16 Ground no. 1 from Backpane 14 AWG with rig lug Ground no. 2 from Backpane 14 AWG with rig lug cFP-1808-01 (8 Slots Board / Ethernet  Connection) C F P - T C 1 2 0 - 0 1 C F P - T C 1 2 0 - 0 2 C F P - T C 1 2 0 - 0 3 C F P - T C 1 2 0 - 0 4 C F P - T C 1 2 0 - 0 5 C F P - A I 1 0 0 - 0 1 C F P - A I 1 0 0 - 0 2 C F P - A I 1 0 0 - 0 3 E-cFP-01, 24VDC, 1.5Amax, V+ E-cFP-01, 24VDC, 1.5Amax, V- E-cFP1808-01:Ethernet Back up V- Back up V+ Ground no. 1 from Backpane 14 AWG with rig lug Ground no. 2 from Backpane 14 AWG with rig lug cFP-1808-02 (8 Slots Board / Ethernet  Connection) c F P - R L Y 4 2 1 - 0 1 c F P - D O 4 0 1 - 0 1 c F P - A O 2 1 0 - 0 1 E m p t y E m p t y E m p t y E m p t y E m p t y E-cFP-02, 24VDC, 1.5Amax, V+ E-cFP-02, 24VDC, 1.5Amax, V- Back up V- Back up V+ E-cFP1808-01:Ethernet Ethernet: UBC Internet (30 ft) E-Computer-001: (25ft) UBC Internet Ethernet Switch 321 As Built Last update: 2009-05-13 CONFIDENTIAL Alexandre Vigneault Electrical Connections Multi Channel Reactor Annexe: Mass Flow Controllers Wiring 1&2 SIZE FSCM NO DWG NO REV 002 1.1 SCALE N/A SHEET 14 OF 16 001 FCV  E-FCV001-001: 9 PIN Cable White: E-FCV001-2-001: Ana Out (0-5VDC) Blue:  E-FCV001-3-001: Ana In (setpoint) (0-5VDC) CFP Analog Shield E-FCV001-9-001 Brown: E-FCV001-8-001: 0V Sense Red: E-FCV001-7-001: +Us (24VDC, 320mA) 002 FCV  E-FCV002-001: 8 PIN Cable E-FCV002-GRD-001: Ground/ Shield (Connect with cable) Water Flow Controller High Pressure Methane Controller (Same as FCV 31 & 32) 1 2 3 4 5 6 7 8 8 DIN Diagram for FCV-002 Power Supply CFP Analog Power Supply 2 1 4 3 6 5 8 7 9 To AI 001 From AO 01 From 24V To 0V To 0V 2 blue Connector on Pannel 4 3 1 5 Black: E-FCV001-4-001: 0V Power purple white Red Black White: E-FCV001-2-001: Ana Out (0-5VDC) Blue:  E-FCV001-3-001: Ana In (setpoint) (0-5VDC) CFP Analog Brown: E-FCV001-8-001: 0V Sense Red: E-FCV001-7-001: +Us (24VDC, 320mA) Power Supply CFP Analog Power Supply 2 1 4 3 6 5 8 7 To 0V To 0V 2 blue Connector on Pannel 4 3 1 5 Black: E-FCV001-4-001: 0V Power purple white Red Black 322 Grey: +Vdc White: gnd Pink output Green gnd valve?? Yellow setpoint As Built Last update: 2009-05-13 CONFIDENTIAL Alexandre Vigneault  Electrical Connections Multi Channel Reactor Annexe: H2 Flow Meter & H2 Pressure Controller SIZE FSCM NO DWG NO REV 002 2.1 SCALE N/A SHEET 15 OF 16 117 FT  E-FT117-001: 5 PIN Cable, 9ft Pink E-FT117-4-001: Ana Out (0-5VDC) White: E-FT117-2-001: 0V Power Gray: E-FT117-1-001: +Us (24VDC, ?mA) H2 Mass Flow Meter MW Instrument D-6210-HAB-22-SV- 24-0-S-A 2 1 4 3 5 Control Motor for H2 pump 1 Connector on Pannel 2 3 Red Black White 104 24V 0V CFP Analog 1 To AI-003 323 001 PT As Built Last update: 2008-02-25 CONFIDENTIAL Alexandre Vigneault  Electrical Connections Multi Channel Reactor Annexe: Pressure Transducers SIZE FSCM NO DWG NO REV 002 2 SCALE N/A SHEET 16 OF 16 053 PT 031 PT 051 PT 052 PT 054 PT 055 PT 112 PT E-PT001-001: Cable E-PT001-R-001: Excitation Voltage (10-30VDC, <3.0mA) E-PT001-G-001: Analog Output (0-5VDC) E-PT001-W-001:  Commun E-PT031-001: Cable, 16" E-PT031-C?-001: +V E-PT031-C?-001: -V (4-20mA) Low Pressure Ni OMEGA PX603 High Pressure Ni OMEGA PX182  (0-500psig, 34.5barg) Don’t have manuel Reactor: Reforming side inlet E13-5-1-H25R (0-500psig, 34.5barg) Plug DIN 43650 - C Plug DIN 43650 - C Plug DIN 43650 - C Hydrogen Product PX209-100A5V (0-100psia,  6.9bara) Reactor: Reforming side inlet E13-5-1-H25R  (0-500psig, 34.5barg) Reactor: Combustion side inlet E13-5-1-H20R (0-100psig,  6.9barg) Air Inlet OMEGA PX603 E-PT051-R-001:  Exitation Voltage (10-30VDC, <3.0mA) E-PT051-G-001:  Analog Output (0-5VDC) E-PT051-W-001: Commun E-PT051-001: Cable Plug DIN 43650 - C Reactor: Combustion side Outlet E13-5-1-H20R (0-100psig, 6.9barg) 3 1 2 E-PT112-1-001: (Red) Excitation Volt. (7-35VDC, 15mA) E-PT112-3-001: (White) Analog Output (1-5VDC) E-PT112-2-001: (Black) Commun 3 1 4 2 PIN 3 1 2 PIN 3 1 2 PIN 3 1 2 PIN E-PT052-2-001: V- (4-20mA) E-PT052-3-001: V+ E-PT053-3-001: V+ E-PT053-2-001: V- (4-20mA) E-PT054-3-001: V+ E-PT054-2-001: V- (4-20mA) E-PT055-3-001: V+ E-PT055-2-001: V- (4-20mA) E-PT112-001: Cable 3ft 324 E.3 MCMR Process Part Mechanical Drawings 325 Preliminary Alexandre Vigneault ing. Jr. Confidential Department of Chemical and Biological Engineering University of British Columbia Gas water separator SIZE FSCM NO DWG NO REV GasWaterSeparator_20070801 1 SCALE No scale August 1st 2007 SHEET Pr1 OF 1 Pipe Material: Seamless SS Tolerance: xx" Dimensions in inches Gas outlet 1/4" compression swagelok fittings, welded on cap Gas Inlet 1/4" compression swagelok fittings, bored through, welded on tube Pipe, Schedule 40S, 2" ID Cap Mesh Water outlet compression fittings, ¼’’ welded on cap Mesh support?? R e f :  7 "  ;  C o m b :  1 0 " 4 Tube ¼’’, for support?? 326 E.4 MCMR Mechanical Drawings 327 21 4 " 1.50 1 4 " min " 6 . 0 0 1 0 . 0 0 20.00 2 4.500 " 3 4.53125 1 4.500 2 81 4 4 5 1  b o l t s f o r  1  1 / 4 "  " 1 6 42 1 " 42 1 " 4 1 2 1 " " 4 "8 3 1 " 6 . 0 0 ( 1 8 )  2 1 6 . 5 0  ( 6 . 0 0  m i n ) 3 "3 " 1 1 8 8 ( 4 )  3 8 "  t a p p e d DO NOT SCALE DRAWING 03top flange 1 SHEET 1 OF 2 UNLESS OTHERWISE SPECIFIED: REVDWG.  NO. A SIZE TITLE: NAME DATE COMMENTS: Q.A. MFG APPR. ENG APPR. CHECKED DRAWN SS 304 FINISH MATERIAL 2 TOLERANCING PER: INTERPRET GEOMETRIC 3      BEND 45 TWO PLACE DECIMAL PROHIBITED. THREE PLACE DECIMAL APPLICATION USED ONNEXT ASSY PROPRIETARY AND CONFIDENTIAL DIMENSIONS ARE IN INCHES TOLERANCES: FRACTIONAL ANGULAR: MACH THE INFORMATION CONTAINED IN THIS DRAWING IS THE SOLE PROPERTY OF <INSERT COMPANY NAME HERE>.  ANY REPRODUCTION IN PART OR AS A WHOLE WITHOUT THE WRITTEN PERMISSION OF <INSERT COMPANY NAME HERE> IS July 18, 2007  2 . 0 0 3 " 8 0 . 5 0 0 (4) 3 8 "  328 "16 5 " " 5 16 5 8 5 16 " "16 5 5 8 " 03 DO NOT SCALE DRAWING top flange SHEET 2 OF 2 UNLESS OTHERWISE SPECIFIED: REVDWG.  NO. A SIZE TITLE: NAME DATE COMMENTS: Q.A. MFG APPR. ENG APPR. CHECKED DRAWN SS 304 FINISH MATERIAL INTERPRET GEOMETRIC TOLERANCING PER: DIMENSIONS ARE IN INCHES TOLERANCES: 0.020 FRACTIONAL ANGULAR: MACH      BEND TWO PLACE DECIMAL THREE PLACE DECIMAL APPLICATION USED ONNEXT ASSY PROPRIETARY AND CONFIDENTIAL THE INFORMATION CONTAINED IN THIS DRAWING IS THE SOLE PROPERTY OF <INSERT COMPANY NAME HERE>.  ANY REPRODUCTION IN PART OR AS A WHOLE WITHOUT THE WRITTEN PERMISSION OF <INSERT COMPANY NAME HERE> IS PROHIBITED. 5 4 3 2 1 July 18, 2007 26.54° 1 . 7 5 "  m i n 10.00 2 "  n o m 1 1 2 " 0.032(6) 0 . 3 8 6 1 1 8 " 329 both faces have identical recess 1 4 8 5 8 " " 2 (8)  R 1 1 " 5 8 " 3 1  (gasket) 13.00 5  (rib) "4 " 1 13 1 4 " (4 ) R 3 8 " 4 3 4 " 5 1 INTERPRET GEOMETRIC TWO PLACE DECIMAL DO NOT SCALE DRAWING 02 2 THREE PLACE DECIMAL      BEND PROPRIETARY AND CONFIDENTIAL FINISH APPLICATION NEXT ASSY USED ON TOLERANCING PER: SHEET 1 OF 1 UNLESS OTHERWISE SPECIFIED: 4 SCALE: 1:2 3 REVDWG.  NO.SIZE NAME DATE COMMENTS: Q.A. MFG APPR. ENG APPR. CHECKED MATERIAL DRAWN PROHIBITED. DIMENSIONS ARE IN INCHES TOLERANCES: FRACTIONAL ANGULAR: MACH THE INFORMATION CONTAINED IN THIS DRAWING IS THE SOLE PROPERTY OF <INSERT COMPANY NAME HERE>.  ANY REPRODUCTION IN PART OR AS A WHOLE WITHOUT THE WRITTEN PERMISSION OF <INSERT COMPANY NAME HERE> IS July 12, 2007 Combustion Frame TITLE: SS 304  gasket finish (graphite gasket) 4 3 " 0 . 1 4 5 0 . 0 4 5 14 815 5 " 0 . 2 3 5 - 0 . 0 0 5 + 0 . 0 1 0 0 . 0 4 5 - 0 . 0 0 2 + 0 . 0 0 5 330 4 2 DATE 01 THREE PLACE DECIMAL TWO PLACE DECIMAL NEXT ASSY PROHIBITED. TOLERANCING PER: USED ON MATERIAL INTERPRET GEOMETRIC DO NOT SCALE DRAWING gasket 5 SHEET 1 OF 1 UNLESS OTHERWISE SPECIFIED: SCALE 1:2 REVDWG.  NO. 3 A SIZE TITLE: NAME      BEND COMMENTS: Q.A. MFG APPR. ENG APPR. APPLICATION CHECKED 1 DRAWN PROPRIETARY AND CONFIDENTIAL FINISH DIMENSIONS ARE IN INCHES TOLERANCES: FRACTIONAL  0.005 ANGULAR: MACH THE INFORMATION CONTAINED IN THIS DRAWING IS THE SOLE PROPERTY OF <INSERT COMPANY NAME HERE>.  ANY REPRODUCTION IN PART OR AS A WHOLE WITHOUT THE WRITTEN PERMISSION OF <INSERT COMPANY NAME HERE> IS July 12, 2007 Graphoil GRAPH-LOCK 3125 SS 11 4 1 6 " 1 1 0 .2 5 "16 R 14 3 1 6 3 " 16 "13 3 R0 .3 75 1 1 6 " 331 11 . 7 7 3.52 5.63 0. 02 0 2 . 3 1 3 R0.38 1 1 . 1 3 1 5 . 6 3 0 . 2 5 0 2 . 0 0 DO NOT SCALE DRAWING UNLESS OTHERWISE SPECIFIED: SHEET 1 OF 1 <INSERT COMPANY NAME HERE> IS SCALE: 1:5 REVDWG.  NO. A SIZE TITLE: July, 30, 2007NAME DATE COMMENTS: Q.A. MFG APPR. ENG APPR. CHECKED DRAWN SS 304 FINISH MATERIAL 1 TOLERANCING PER: INTERPRET GEOMETRIC 23      BEND 45 TWO PLACE DECIMAL PROHIBITED. APPLICATION USED ONNEXT ASSY PROPRIETARY AND CONFIDENTIAL THREE PLACE DECIMAL DIMENSIONS ARE IN INCHES TOLERANCES: FRACTIONAL ANGULAR: MACH THE INFORMATION CONTAINED IN THIS DRAWING IS THE SOLE PROPERTY OF <INSERT COMPANY NAME HERE>.  ANY REPRODUCTION IN PART OR AS A WHOLE WITHOUT THE WRITTEN PERMISSION OF Separator Preliminary 332 R0.2500 R0.3500 5 . 6 2 5 0 15.6250 0 . 7 5 0 0 3 . 2 5 0 0 13.2500 0 . 0 6 0 0 0 . 0 6 0 0 0 . 3 5 0 0 0 . 2 3 0 0 Reformer Frame 1 DO NOT SCALE DRAWING - SHEET 1 OF 2 UNLESS OTHERWISE SPECIFIED: SCALE: 1:2 1 REVDWG.  NO. A SIZE TITLE: UBC - CHBE NAME DATE COMMENTS: Q.A. MFG APPR. ENG APPR. CHECKED DRAWN Miror polish recess SS 304 FINISH MATERIAL INTERPRET GEOMETRIC TOLERANCING PER: DIMENSIONS ARE IN INCHES TOLERANCES: +0.050 FRACTIONAL ANGULAR: MACH   BEND TWO PLACE DECIMAL THREE PLACE DECIMAL APPLICATION USED ONNEXT ASSY PROPRIETARY AND CONFIDENTIAL THE INFORMATION CONTAINED IN THIS DRAWING IS THE SOLE PROPERTY OF <INSERT COMPANY NAME HERE>.  ANY REPRODUCTION IN PART OR AS A WHOLE WITHOUT THE WRITTEN PERMISSION OF <INSERT COMPANY NAME HERE> IS PROHIBITED. 5 4 3 2 1 333 Reforming Frame Iso view DO NOT SCALE DRAWING SHEET 2 OF 2 UNLESS OTHERWISE SPECIFIED: SCALE: 1: 2 REVDWG.  NO. A SIZE TITLE: UBC: CHBENAME DATE COMMENTS: Q.A. MFG APPR. ENG APPR. CHECKED DRAWN ERROR!:Finish ERROR!:Material FINISH MATERIAL INTERPRET GEOMETRIC TOLERANCING PER: DIMENSIONS ARE IN INCHES TOLERANCES: FRACTIONAL<MOD-PM> ANGULAR: MACH<MOD-PM>     BEND <MOD-PM> TWO PLACE DECIMAL    <MOD-PM> THREE PLACE DECIMAL  <MOD-PM> APPLICATION USED ONNEXT ASSY PROPRIETARY AND CONFIDENTIAL THE INFORMATION CONTAINED IN THIS DRAWING IS THE SOLE PROPERTY OF <INSERT COMPANY NAME HERE>.  ANY REPRODUCTION IN PART OR AS A WHOLE WITHOUT THE WRITTEN PERMISSION OF <INSERT COMPANY NAME HERE> IS PROHIBITED. 5 4 3 2 1 334 R3 0 .4 0 8.00 " 3 1 8 " 1 " 48 3 "4 1 1 9 " "11 R 8 4 2 1 10 1 8 " " 1 4 0 . 0 5 0 2 DO NOT SCALE DRAWING 01 3 APPLICATIONPROHIBITED. TWO PLACE DECIMAL NEXT ASSY USED ON THREE PLACE DECIMAL PROPRIETARY AND CONFIDENTIAL      BEND SHEET 1 OF 1 July 12, 2007 UNLESS OTHERWISE SPECIFIED: REVDWG.  NO. A SIZE 1 TITLE: NAME DATE COMMENTS: Q.A. MFG APPR. ENG APPR. CHECKED 5 4 DRAWN FINISH MATERIAL TOLERANCING PER: INTERPRET GEOMETRIC DIMENSIONS ARE IN INCHES TOLERANCES: FRACTIONAL ANGULAR: MACH THE INFORMATION CONTAINED IN THIS DRAWING IS THE SOLE PROPERTY OF <INSERT COMPANY NAME HERE>.  ANY REPRODUCTION IN PART OR AS A WHOLE WITHOUT THE WRITTEN PERMISSION OF <INSERT COMPANY NAME HERE> IS membrane 335 4.00 4.00 02 DO NOT SCALE DRAWING bottom flange SHEET 1 OF 2 UNLESS OTHERWISE SPECIFIED: REVDWG.  NO. A SIZE TITLE: NAME DATE COMMENTS: Q.A. MFG APPR. ENG APPR. CHECKED DRAWN FINISH MATERIAL INTERPRET GEOMETRIC TOLERANCING PER: DIMENSIONS ARE IN INCHES TOLERANCES: FRACTIONAL ANGULAR: MACH      BEND TWO PLACE DECIMAL THREE PLACE DECIMAL APPLICATION USED ONNEXT ASSY PROPRIETARY AND CONFIDENTIAL THE INFORMATION CONTAINED IN THIS DRAWING IS THE SOLE PROPERTY OF <INSERT COMPANY NAME HERE>.  ANY REPRODUCTION IN PART OR AS A WHOLE WITHOUT THE WRITTEN PERMISSION OF <INSERT COMPANY NAME HERE> IS PROHIBITED. 5 4 3 2 1 July 18, 2007 Preliminary 5 . 0 0 20.00 1 0 . 0 0 1 1 5.00 "8 16 THRU ALL 5  "1 " 8 3 th ru "42 1 "42 1 "42 1 "42 1 "42 1 "42 1 " 4 2 1 " 4 " 8 3 7 7 2 x 3 1 2 " 8 " ,  t a p p e d 6 . 0 0 6 . 0 0 11.125 18 x ( 4 )  3 8 8.875 5 . 0 0 336    with 3/8" counterbore, 1/4" deep " 3 8 " 2 x "8 3 2 . 0 0 7 8  ( n o m ) " 87 4 . 0 0 3  tubing"8(2) (2) 5 16 " 1 4 "  d e e p  3 / 8 "  c o u n t e r b o r e 02 DO NOT SCALE DRAWING bottom flange SHEET 2 OF 2 UNLESS OTHERWISE SPECIFIED: REVDWG.  NO. A SIZE TITLE: NAME DATE COMMENTS: Q.A. MFG APPR. ENG APPR. CHECKED DRAWN SS 304 FINISH MATERIAL INTERPRET GEOMETRIC TOLERANCING PER: DIMENSIONS ARE IN INCHES TOLERANCES: FRACTIONAL ANGULAR: MACH      BEND TWO PLACE DECIMAL THREE PLACE DECIMAL APPLICATION USED ONNEXT ASSY PROPRIETARY AND CONFIDENTIAL THE INFORMATION CONTAINED IN THIS DRAWING IS THE SOLE PROPERTY OF <INSERT COMPANY NAME HERE>.  ANY REPRODUCTION IN PART OR AS A WHOLE WITHOUT THE WRITTEN PERMISSION OF <INSERT COMPANY NAME HERE> IS PROHIBITED. 5 4 3 2 1 July 18, 2007 Preliminary 337 3.510 1 . 9 9 0 R0.375 Note: Make as many coupons as you can from two sheets of metals (material provided): First one is 1ft x 3ft, material is SS 310, 24 gauge Second is 19.68 in x 7.87 in x (200mm x 500mm) Fecralloy (Fe-Cr-Al alloy), 0.5 mm thick Tolerance is - 0.010" (we can't go higher than specified dimensions) Please remove the tabs after the water jet cutting, plates need to stay flat. A bent corner will make the coupons useless. Metal Coupons DO NOT SCALE DRAWING UNLESS OTHERWISE SPECIFIED: SCALE: 1:1 REVDWG.  NO. A SIZE TITLE: UBC- CHBENAME DATE COMMENTS: Q.A. MFG APPR. ENG APPR. CHECKED DRAWN no finish stainless FINISH MATERIAL INTERPRET GEOMETRIC TOLERANCING PER: - 0.01 DIMENSIONS ARE IN INCHES TOLERANCES: FRACTIONAL: -.010 ANGULAR: -0.010 APPLICATION USED ONNEXT ASSY PROPRIETARY AND CONFIDENTIAL THE INFORMATION CONTAINED IN THIS DRAWING IS THE SOLE PROPERTY OF <INSERT COMPANY NAME HERE>.  ANY REPRODUCTION IN PART OR AS A WHOLE WITHOUT THE WRITTEN PERMISSION OF <INSERT COMPANY NAME HERE> IS PROHIBITED. 5 4 3 2 1 1.1 338 Appendix F MATLAB Program The MATLAB program can be downloaded here: https://www.dropbox.com/s/zhjxfr9o45zwqcf/ VigneaultSimulationFiles.zip 339

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