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Partial oxidation of pyrolysis oil by model compounds Zhu, LingXiu 2016

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Partial Oxidation of Pyrolysis Oil by Model Compounds  by  Lingxiu Zhu B.Sc., University of Alberta, 2013  A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF  MASTER of APPLIED SCIENCE in The Faculty of Graduate and Postdoctoral Studies (Chemical and Biological Engineering) The University of British Columbia (Vancouver) December 2016 ©Lingxiu Zhu,2016ii   Abstract  The challenges of upgrading pyrolysis oil to transportation fuel limit the economic viability of biomass pyrolysis. Therefore, this dissertation investigated partial oxidation of pyrolysis oil to produce value-added chemicals. Two model compounds, acetic acid (AcOH) and acetaldehyde (AcH) were selected for gas phase oxidation trials. Thermal oxidation of AcOH emphasized AcOH’s refractory nature as the maximum conversion of AcOH was less than 6% at 350 oC at 1 atm with GHSV of 2000 h-1. AcH was more reactive; conversion of AcH was approximately 40% under identical conditions.  Thermal oxidation of both compounds produced only carbon dioxide (CO2).  Although the true reaction mechanism of AcH thermal oxidation could not be determined, the activation energy was calculated to be between 47.1±0.55 kJ/mol and 55.2±0.6 kJ/mol.   Catalytic partial oxidation (CPO) of AcOH and AcH was examined using vanadium pentoxide supported by titanium oxide (V2O5/TiO2). Conversion of CPO of AcOH was slightly higher than thermal oxidation but produced only CO2. CPO of AcH generated AcOH, a desirable product, as well as formic acid (FA), carbon monoxide (CO) and CO2, suggesting that multiple reactions occurred. However, the selectivity to AcOH was relatively low (43% at 175 oC, GHSV=20000 h-1, 2.4V/TiO2). The selectivity of AcH to AcOH was improved by adjusting temperature, adopting higher vanadium (V) loading catalysts, and increasing oxygen (O2) concentration. At 200 oC, GHSV=20000 h-1, and using 6.9V/TiO2, the selectivity to AcOH increased to 70%. Constant selectivity of all products with respect to residence time indicates the reactions are likely parallel. The rate constant for AcH CPO was calculated assuming an overall 1st order reaction. The linearized Arrhenius law yielded an activation energy of 43.9 kJ/mol for the overall iii  AcH CPO reaction. Simultaneous CPO of AcH and AcOH was also examined. The conversion of AcH in the mixture was similar to the conversion of CPO of AcH alone. This study demonstrated the feasibility of producing AcOH via CPO of AcH. The viability of partial oxidation of pyrolysis oil must be confirmed using model compounds with more complex functional groups and pyrolysis oil.                 iv  Preface  All experimental work including gas and liquid products analysis, oxidation experiments, catalyst properties characterizations and thesis preparation were completed in the Department of Chemical and Biological Engineering at the University of British Columbia.  The literature review, model compound selection, flow reactor system design and construction, catalyst preparation, experimental operations, gas and liquid products analysis, data collection and analysis, as well as thesis formulation, were done by Lingxiu Zhu under the direct supervision of Dr. Trajano. The BET (Brunauer–Emmett–Teller) test was performed by a PhD student, Haiyan Wang, and post-doctoral fellow Dr. Rahman Gholami Shahrestani. Dr. Rahman Gholami Shahrestani also prepared the first batch of 6.9V/TiO2 catalyst. The XRD (X-ray diffraction) was done at the OES Center of UBC.            v  Table of Contents  Abstract .......................................................................................................................................... ii Preface ........................................................................................................................................... iv Table of Contents .......................................................................................................................... v List of Tables ................................................................................................................................. ix List of Figures ............................................................................................................................... xi Nomenclature ............................................................................................................................. xvi List of Acronyms and Abbreviations ........................................................................................ xix Acknowledgements .................................................................................................................... xxi Dedication .................................................................................................................................. xxii Chapter 1. Introduction ................................................................................................................ 1 1.1 Background ...................................................................................................................... 1 1.2 Motivation ........................................................................................................................ 6 1.3 Model compounds selection ............................................................................................ 7 1.4 Thesis objective ................................................................................................................ 8 1.5 Literature review ............................................................................................................ 9 1.5.1 CPO of pyrolysis oil to syngas............................................................................. 9 1.5.2 Partial oxidation of acetic acid.......................................................................... 10 1.5.3 Partial oxidation of acetaldehyde ..................................................................... 13 1.5.4 Catalyst selection ................................................................................................ 15 1.5.5 The effect of metal loading on vanadium oxide catalyst ................................ 19 vi  1.6 Conclusions .................................................................................................................... 20 Chapter 2. Experimental ............................................................................................................ 22 2.1 Experiment .................................................................................................................... 22 2.2 Experimental procedure ............................................................................................... 24 2.3 Compositional analysis ................................................................................................. 30 2.3.1. Gas phase analysis............................................................................................. 30 2.3.2. Liquid phase analysis ........................................................................................ 31 2.4 Carbon balance and experimental repeatability ........................................................ 35 2.5 Catalyst preparation ..................................................................................................... 35 2.6 Catalyst characterization ............................................................................................. 36 2.6.1 ICP-MS ............................................................................................................... 37 2.6.2 BET...................................................................................................................... 37 2.6.3 XRD ..................................................................................................................... 37 2.6.4 XPS ...................................................................................................................... 38 2.7 Study of internal mass transfer effect ......................................................................... 38 Chapter 3. Thermal oxidation of acetic acid and acetaldehyde .............................................. 40 3.1 Thermal oxidation of acetic acid ................................................................................. 40 3.2 Thermal oxidation of AcH............................................................................................ 44 3.3 AcH thermal oxidation: rate constant and activation energy ................................... 48 Chapter 4. Catalytic partial oxidation of acetic acid and acetaldehyde ................................ 56 4.1 Catalytic oxidation of acetic acid ................................................................................. 57 4.2 Catalytic partial oxidation of acetaldehyde ................................................................ 60 vii  4.2.1 Effect of temperature and catalyst metal loading ........................................... 60 4.2.2 Effect of O2 concentration ................................................................................. 65 4.2.3 Effect of residence time ..................................................................................... 69 4.3 CPO of AcH: rate constant and Ea .............................................................................. 73 4.4. Catalytic partial oxidation of mixtures of acetic acid and acetaldehyde ................ 75 Chapter 5. Conclusions and recommendations ........................................................................ 79 5.1 Conclusions .................................................................................................................... 79 5.2 Recommendations. ........................................................................................................ 82 References .................................................................................................................................... 83  Appendix A: Calibration curves and chromatography elution times .................................... 88 A.1 Mass flow controller calibration ................................................................................. 88 A.2 Gas chromatography calibration and gas products elution time ............................ 90 A.3 HPLC calibration and liquid elution time ................................................................. 92 Appendix B: Catalyst characterization ..................................................................................... 94 B.1: BET............................................................................................................................... 94 B.2 XRD ............................................................................................................................... 97 B.3 ICP-MS .......................................................................................................................... 98 B.4 XPS ................................................................................................................................ 99 Appendix C: Sample calculations and equation derivation .................................................. 101 C.1 Conversion, selectivity, and yield.............................................................................. 101 C.2 Catalyst preparation .................................................................................................. 102 C.3 Internal mass transfer ............................................................................................... 103 viii  C.4 Equation derivation ................................................................................................... 104 Appendix D: Supplementary experiments.............................................................................. 106 D.1 Thermal oxidation of AcH ......................................................................................... 106 D.2 CPO of AcOH ............................................................................................................. 107 Appendix E: Experimental error analysis .............................................................................. 108                 ix  List of Tables  Table 1- 1 Pyrolysis oils composition, abundant molecules and their potential high and low content7 ........................................................................................................................... 3 Table 1- 2 Comparison of properties of wood pyrolysis bio-oil and heavy fuel oil.8 ..................... 5 Table 1- 3 Partial oxidation of representative organic species and potential products ................. 18 Table 1- 4 Industrial catalytic processes using vanadium oxides ................................................. 19  Table 2- 1 Experimental conditions for thermal oxidation ........................................................... 27 Table 2- 2 Experimental conditions for catalytic partial oxidation ............................................... 28 Table 2- 3 Experimental conditions for CPO of mixtures of AcH and AcOH .............................. 29 Table 2- 4 Analytical method for GC-14B .................................................................................... 30 Table 2- 5 Chromatographic conditions for Waters e2695 HPLC ................................................ 34  Table 3-1 AcH rate constant assuming 1st order dependence on oxygen concentration  (-rB=kBCB) ..................................................................................................................... 51 Table 3-2 AcH rate constant assuming 2nd order overall reaction rate (-rB=kBCBCA) .................. 53 Table 3-3 Comparison of Ea in AcH oxidation and AcOH oxidation ........................................... 55 x   Table 4- 1 Comparison of fresh catalysts properties and TiO2 ..................................................... 57 Table 4- 2 CPO of AcH overall rate constant and Ea, 6.9V/TiO2 ................................................. 74  Table A- 1 Elution time of AcH, CO and CO2 .............................................................................. 91 Table A- 2 HPLC elution time for AcH, AcOH, and FA .............................................................. 93  Table C- 1 Parameters used to calculate conversion, selectivity, and yield of CPO of AcOH at T=250 oC, O2/AcH=1, 6.9V/TiO2, RT=0.18s .......................................................... 102 Table C- 2 Parameter value used to calculate internal effectiveness factor ................................ 103  Table D- 1 AcH thermal oxidation at T=120 oC ......................................................................... 106     xi  List of Figures  Figure 1- 1 Biomass pyrolysis cycle ............................................................................................... 2 Figure 1- 2 Envisioned partial oxidation process of pyrolysis oil .................................................. 6 Figure 1- 3 Proposed mechanism for AcOH oxidation to VA ....................................................... 11 Figure 1-4 Catalytic performance of V2O5/TiO2 as a function of temperature: conversions of formic acid (1), acetic acid (2) and propionic acid (3). Feed compositions: 2.5 vol% HCOOH (or 1 vol% AcOH, or 0.4 vol% C2H5COOH), 20 vol% O2 and He balance, GHSV = 3600 h-1.28 ................................................................................................... 12 Figure 1- 5 Conversion of acetaldehyde and yields of main oxidation products as a function of reaction temperature in oxidation of acetaldehyde on a VOx-TiO2 catalyst in the presence of water vapor29 .......................................................................................... 13 Figure 1- 6 Possible reaction pathways to form oxidation products : (a) acetaldehyde ; (b) propionaldehyde ........................................................................................................ 15 Figure 1- 7 Possible molecular configurations for supported vanadium oxides (with S the support cation): (a) isolated vanadium oxide species; (b) dimeric vanadium oxide species; (c) two-dimensional vanadium oxide chains; (d) V2O5 crystals. ................................... 20  Figure 2- 1 Experimental schematic diagram ............................................................................... 23 xii  Figure 2- 2 Reactor system, Shimadzu GC-14B, Waters e2695 HPLC ........................................ 24 Figure 2- 3 AcH calibration curve for GC-14B ............................................................................ 31 Figure 2- 4 HPLC chromatogram chart of the real oxidation mixture. Peaks: 6, formic acid; 7, acetic acid; 8, acetaldehyde (0.01 H2SO4, 0.8 ml/min, 65 oC) .................................. 32 Figure 2- 5 HPLC chromatogram of calibration standard. Peaks: 6, formic acid; 7, acetic acid; 8, acetaldehyde (0.01 H2SO4, 0.8 ml/min, 65 oC) ......................................................... 33 Figure 2- 6 AcOH calibration curve for Waters e2695 HPLC ...................................................... 34  Figure 3-1 Conversion of AcOH as a function of temperature and O2/AcH molar ratio (5 vol%  AcOH, RT=1.8s) ...................................................................................................... 42 Figure 3-2 Yield of and selectivity to CO2 from thermal oxidation of AcOH as a function of temperature and O2/AcOH molar ratio (5 vol% AcOH, RT=1.8s) ........................... 43 Figure 3-3 Conversion of AcH oxidation as a function of temperature and O2/AcH molar ratio  (5.9 vol% AcH, RT=1.8s)........................................................................................... 46 Figure 3-4 Selectivity and yield of AcH oxidation as a function of temperature and O2/AcH molar ratio (5.9 vol% AcH, RT=1.8s) ................................................................................. 47 Figure3-5 AcH activation energy data fitting at 150 to 300 oC, O2/AcH=1, 1st order assumption, R2≈0.99 ..................................................................................................................... 51 Figure3- 6 AcH activation energy data fitting at 150 to 300 oC, O2/AcH=0.5, 1st order assumption, xiii  R2≈0.99 ..................................................................................................................... 52 Figure 3-7 AcH activation energy data fitting at 150 to 300 oC, O2/AcH=1, 2nd order assumption, R2≈0.98 ..................................................................................................................... 54 Figure3- 8 AcH activation energy data fitting at 150 to 300 oC, O2/AcH=0.5, 2nd order assumption, R2≈0.98 ..................................................................................................................... 54  Figure 4-1 Conversion of AcOH as a function of temperature (5 vol% AcOH, 6.9V/TiO2, O2/AcH=1, GHSV≈20000h-1) .................................................................................. 58 Figure 4- 2 Selectivity of AcOH oxidation as a function of temperature (5 vol% AcOH, 6.9V/TiO2, O2/AcH=1, GHSV≈20000h-1) .................................................................................. 59 Figure 4-3 Conversion of CPO of AcH as a function of temperature (5.9 vol% AcH, O2/AcH=1, GHSV≈20000h-1) ...................................................................................................... 61 Figure 4- 4 Selectivity of CPO of AcH as a function of temperature (2.4V/TiO2,O2/AcH=1, GHSV≈20000h-1, 5.9 vol% AcH) ............................................................................ 63 Figure 4- 5 Selectivity of CPO of AcH as a function of temperature (6.9V/TiO2,O2/AcH=1, GHSV≈20000h-1, 5.9 vol% AcH) ............................................................................. 64 Figure 4- 6 Yield of CPO of AcH as a function of temperature (O2/AcH=1, GHSV≈20000h-1, 5.9 vol% AcH) ............................................................................................................... 65 Figure 4-7 Conversion of CPO of AcH as a function of O2 concentration (GHSV≈20000 h-1, xiv  6.9V/TiO2, T=200 oC, 6.9V/TiO2) ............................................................................ 66 Figure 4- 8 Selectivity of CPO of AcH as a function of O2 concentration (GHSV≈20000 h-1, 6.9V/TiO2, T=200 oC, 6.9V/TiO2) ............................................................................ 68 Figure 4- 9 Yield of CPO of AcH as a function of O2 concentration, GHSV≈20000 h-1, 6.9V/TiO2, T=200 oC, 6.9V/TiO2) .............................................................................................. 69 Figure 4-10 Conversion of CPO of AcH as a function of residence time (O2/AcH=6, T=200 oC, 5.9 vol% AcH, 6.9V/TiO2) ............................................................................................ 71 Figure 4- 11 Selectivity of CPO of AcH as a function of residence time (O2/AcH=6, T=200 oC, 5.9 vol% AcH, 6.9V/TiO2) ............................................................................................ 71 Figure 4- 12 Yield of CPO of AcH as a function of residence time (O2/AcH=6, T=200 oC,    5.9 vol% AcH, 6.9V/TiO2) ............................................................................................ 72 Figure 4-13 AcH CPO activation energy data fitting at O2/AcH=1, 150 to 250 oC, 5.9 vol% AcH, 6.9V/TiO2, 1st order assumption, R2≈0.99 ................................................................ 75 Figure 4- 14 Conversion of CPO of mixture as a function of AcH to (AcH+AcOH) mass ratio ( T=200 oC, O2/AcH=6, RT=0.18s, 6.9V/TiO2) ........................................................ 77 Figure 4- 15 Selectivity of CPO of AcH and AcOH mixture at different AcH to (AcH+AcOH) mass ratio (T=200 oC, O2/AcH=6, RT=0.18s, 6.9V/TiO2) ....................................... 77 Figure 4- 16 Yield of CPO of AcH and AcOH mixture at different AcH to (AcH+AcOH) mass ratio (T=200 oC, O2/AcH=6, RT=0.18s, 6.9V/TiO2) ................................................ 78 xv   Figure A- 1 He calibration curve for MFC ................................................................................... 89 Figure A- 2 O2 calibration curve for MFC .................................................................................... 89 Figure A- 3 GC calibration curve for CO, TCD ........................................................................... 90 Figure A- 4 GC calibration curve for CO2, TCD .......................................................................... 91 Figure A- 5 HPLC calibration curve for AcH, RI detector ........................................................... 92 Figure A- 6 HPLC calibration curve for FA, RI detector.............................................................. 93  Figure B- 1 BET summary report for 6.9V/TiO2 .......................................................................... 95 Figure B- 2 Isotherm linear plot for 6.9V/TiO2 ............................................................................ 96 Figure B- 3 Pore size distribution for 6.9V/TiO2 .......................................................................... 97 Figure B- 4 XRD peak diagram for 6.9V/TiO2 ............................................................................. 98 Figure B- 5 ICP-MS report of actual vanadium for a nominal 10 wt.% V loading ...................... 99 Figure B- 6 XPS spectrum for 6.9V/TiO2 catalyst. ..................................................................... 100       xvi  Nomenclature  Roman symbols      A       AcH B       O2 CA       Concentration of AcH, mol/L CB       Concentration of O2, mol/L d       Distance between two planes of atoms, d-spacing DA       Diffusion coefficient for AcH diffuses in air, m2/s De       Effective diffusivity, m2/s Dp       Particle diameter of 6.9V/TiO2 catalyst, m Ea       Activation energy, kJ/mol Eb       Binding energy, eV Ek       kinetic energy of the photoelectron, eV FAO       Initial flow rate of AcH, mol/min FBO       Initial flow rate of O2, mol/min ∆HO      Standard heat of reaction, kJ/mol hν       Energy of X-ray photon, eV hrs       Hours i       Reactants j       Products kA       AcH oxidation reaction rate constant, min-1 or cm3.mol-1.min-1 kB       O2 oxidation reaction rate constant, min-1 or cm3.mol-1.min-1 xvii  kO       Pre-exponential factor, min-1 or cm3.mol-1.min-1 P       Pressure, atm PO       Inlet pressure, atm -rA       Reaction rate of AcH, mol.cm-3.min-1 -rB        Reaction rate of O2, mol.cm-3.min-1 R       Gas constant, 8.314 J.mol-1.K-1 s       Cross-sectional area of single N2 molecule, 16.2 Å2 S       Selectivity SBET      Specific surface area, m2/g t       Total reaction time, min tavg       The average time for a gas bubble traveled for a fixed volume, s T       Reaction temperature, K TNOR      Normal lab temperature, 298K TO       Inlet temperature, K TSTD      Standard temperature, 273K V       Volume of reactor or catalyst bed, cm3 Vfix    A fixed volume for a gas bubble traveled during time tavg, cm3 Vm       Volume of adsorbed gas for monolayer coverage VO       Molar volume of N2 ?̇?        Total volumetric gas flow rate at reaction, cm3/min 𝑉?̇?        Total volumetric gas flow rate at inlet, cm3/min 𝑉𝑆𝑇𝑃̇        Total volumetric gas flow rate at standard condition, sccm ?̇?He,STP,M      Average helium flow rate at standard condition, cm3/min W       Catalyst weight, g X       Conversion XA       Conversion of AcH xviii  XB       Conversion of O2 y       Gas mole fraction Y       Yield     Greek Symbols 𝜀:  fraction change in volume per moles of O2 reacted resulting from the change in total number of moles, dimensionless η        Internal effectiveness factor, dimensionless θ        Angle of reflection in XRD, degree λ        X-ray wavelength, Å ρ𝑏𝑒𝑑       Catalyst bed density, g/cm3 σ𝐶        constriction factor, dimensionless τ̅        tortuosity, dimensionless φ𝑝        pellet porosity ɸ        Thiele modules for the 1st-order reaction, dimensionless    xix  List of Acronyms and Abbreviations   316SS      316 Stainless steel AcH      Acetaldehyde AcOH      Acetic acid BET      Brunauer–Emmett–Teller BJH      Barrett–Joyner–Halenda cc       Cubic centimeter CPO      Catalytic partial oxidation FA       Formic acid FID       Flame ionization detector FM       Flow meter GC       Gas chromatography GHSV      Gas hourly space velocity, h-1 HHV      Higher heating value, MJ/kg HPLC      High performance liquid chromatography ICP-MS      Inductively coupled plasma mass spectroscopy MFC      Mass flow controller    MW      Molecular weight OD       Outer diameter, cm PBR      Packed bed reactor PFR      Plug flow reactor PG       Pressure gauge PRV      Pressure relief valve PT       Pressure transducer xx  RI       Refractory index RT       Residence time, s sccm      Standard cubic centimeter TC       Thermocouple TCD      Thermal conductivity detector TPO      Thermal partial oxidation V       Vanadium VA       Vinyl acetate XPS      X-ray photoelectron spectroscopy XRD      X-ray diffraction xV/TiO2 Vanadium oxide supported by titanium oxide with x wt.% of vanadium in catalyst            xxi  Acknowledgements  From the moment I came to Vancouver pursuing master degree to the finishing point, I would like to express my warmest gratitude to all individuals have made invaluable contributions, both directly and indirectly to my research, specifically:  Dr. Heather L Trajano, my supervisor, for her instructive suggestions and valuable comments on the project research and editing of this thesis. Without her invaluable help and generous encouragement, the present thesis would not have been accomplished.   Dr. Kevin J Smith and Dr. Wenli Duo, my committee members, for providing me with valuable comments and advice during my MASc research.  Haiyan Wang and Shida Liu, my lab mate, for discussion and suggestions for the research questions.  Alex Imbalut, Mina Alyani, and Xu Zhao who assisted me in the lab.  I would also thank FPInnovations for the financial support for the project.       xxii  Dedication      To my beloved parents and  my girlfriend1   Chapter 1. Introduction  1.1 Background  Energy is a fundamental asset to the economy and modern society. Petroleum based fuel brings a barrage of adverse consequences: greenhouse gases, oil prices, and energy security issues. In addition, fossil fuels are non-renewable. For these reasons, governments are taking action to explore alternatives to fossil fuels  Biomass, either as a raw feedstock or in chemically or biologically refined manifestations, has long been utilized as a source of energy.1 The efficiency of traditional application is low due to the distributed nature and low energy intensity of biomass.1,2 As a result, techniques have been developed to reduce these restrictions. One method is pyrolysis, which benefits from years of research and is an industrial realized process.3  Fast pyrolysis is a heating process that thermally decomposes biomass at 400 oC to 500 oC in the absence of oxygen (O2), to generate a charcoal-like char, non-condensable gases and pyrolysis oil.1,4 Figure 1-15 illustrates a typical biomass pyrolysis process : the char and non-condensable gases are recycled back to provide process heat. The condensable gases are condensed to produce a liquid stream called pyrolysis oil or bio-oil. Up to 75 wt.% of original dry biomass can be produced as pyrolysis oil.6 A variety of feedstocks can be used to produce pyrolysis oil, including forest waste, wood, and agriculture waste. Through the pyrolysis process, density and energy intensity is increased. Thus, pyrolysis oil can be transported more efficiently and upgraded at a central facility, thus enabling economies of scale.7,8  2   Figure 1- 1 Biomass pyrolysis cycle  From a chemistry point of view, pyrolysis oil is a highly complex mixture of more than 300 compounds that can be divided between a hydrophobic (oily) and hydrophilic (aqueous) phase. The exact composition of pyrolysis oil depends on a variety factors: feedstock, pyrolysis conditions (temperature, pressure, residence time), storage temperatures, etc.7 However, it is generally accepted that the major components of pyrolysis oil can be classified by organic functional groups. For example, according to Huber et al., pyrolysis oils can be roughly categorized into acids, alcohols, aldehydes, esters, ethers, and aromatic molecules.7 Table 1-1 summarizes the relative amount and the most abundant molecules of each component of pyrolysis oil. From this table, it is apparent that the carboxylic acids and aldehyde groups are the most abundant by weight. 3  Table 1- 1 Pyrolysis oils composition, abundant molecules and their potential high and low content7 Pyrolysis Oil Composition Most abundant molecules Low wt.% High wt.% Acids Formic, Acetic,   Propanoic 2 27 Misc Oxy Glycolaldehyde, Acetol 3.5 25 Aldehydes Formaldehyde,    Acetaldehyde, Ethanedial 3 18 Sugars Anhydroglucose, Cellobiose, Fructose, Glucose 5 13 Guaiacols Isoeugenol, Eugenol, Methyl guaiacol 2 13 Phenols Phenol, DiOH-benzene, Dimeth-Phenol 3 12 Furans Furfural, HMF 1.5 11 Syringols syringol 1.5 8.5 Ketones Acetone 4 6 Alcohols Methanol, Ethanol, Ethylene Glycol 2 6 Esters Methyl formate, Butyrolactone, Angelicalactone 0.5 3.5    4  Pyrolysis oil can be used for co-firing, co-gasification, in a stand-alone boiler or catalytically converted to synthesis gas.1,9 Currently, the majority of research is focused on upgrading pyrolysis oil to transportation fuels, as an alternative to petroleum fuels. However, the value of pyrolysis oil as a fuel is in part limited by the high oxygen content of the aqueous phase (e.g. acetic acid, ethanol, acetaldehyde, phenol). The oxygen content of bio-oil is typically around 40-50%, resulting in a calorific value of 16-18 MJ/kg.2 Table 1-2 depicts typical properties of a heavy fuel oil and a wood derived pyrolysis oil.8 The higher heating value (HHV) for a typical pyrolysis oil is approximately 45% of heavy fuel oil. These oxygenated hydrocarbons influence the catalytic performances in exhaust gas converters,10 and therefore, pyrolysis oil is a low-quality fuel and cannot be directly used in gasoline or diesel combustion engines. There have been extensive efforts to upgrade bio-oil through hydrodeoxygenation11–13, zeolite cracking14,15 and aqueous phase processing.2,7,16,17 However, these approaches are limited by the need for hydrogen, high-pressure equipment, and significant carbon production which reduces yields and rapidly deactivates catalysts.12 An alternative approach to utilize pyrolysis oil is needed.            5  Table 1- 2 Comparison of properties of wood pyrolysis bio-oil and heavy fuel oil.8  Physical property Pyrolysis oil Heavy fuel oil Moisture content (wt.%) 15-30 0.1 pH 2.5 - Specific gravity 1.2 0.94 Elemental composition (wt%) C 54-58 85 H 5.5-7.0 11 O 35-40 1.0 N 0-0.2 0.3 Ash 0-0.2 0.1 HHV (MJ/kg) 16-19 40 Viscosity (50 oC, cP) 40-100 180 Solids (wt.%) 0.2-1 1 Distillation residual (wt.%) Up to 50 1         6  1.2 Motivation  These challenges associated with upgrading pyrolysis oil to transportation fuels continue to limit the commercial viability and implementation of pyrolysis. An alternative, production of chemicals through partial oxidation of pyrolysis oil, may improve the project economics of pyrolysis. Potential oxidation products, such as carboxylic acids, glyoxal, and gluconic acid are more valuable than the original pyrolysis oil reactants.18 Furthermore, partial oxidation of pyrolysis oil would simplify product composition and increase the concentration of desired species, thus facilitating subsequent separations. Figure 1-2 depicts an envisioned process for partial oxidation of pyrolysis oil. The process will be integrated onto existing biomass pyrolysis cycle to condense the high molecular weight (MW), hydrophobic compounds by a series of selective condensers. The remaining low molecular weight, hydrophilic compounds and water vapor would then enter a partial oxidation reactor to generate value-added chemicals.     Figure 1- 2 Envisioned partial oxidation process of pyrolysis oil 7  1.3 Model compounds selection  As mentioned in section 1.1, pyrolysis-oil can be extremely complex: it contains several hundred different organic compounds with different oxygenated functional groups. Therefore, in this initial project, to examine the viability of partial oxidation of pyrolysis oil, simple, representative model compounds must be used. By studying partial oxidation of model compounds, insight into the partial oxidation of simple molecules and partial oxidation of molecules with similar functional groups is gained. In this thesis, acetic acid (AcOH) and acetaldehyde (AcH) were selected as model compounds because they are typically present in large quantities in pyrolysis oil.1 In addition, AcOH and AcH are both simple C2 molecules with different but common pyrolysis oil functional groups: carboxylic acid group, aldehyde group, respectively. Based on Table 1-1, acids (27%) and aldehydes (18%) group represent the first and third-most abundant organic group in pyrolysis oil. Moreover, the observed mass fraction range of acids and aldehyde groups is fairly large (25% and 15%, respectively), which means that these molecules affect not only the composition of pyrolysis oil most, but will also have significant effect on the performance of pyrolysis oil partial oxidation. As carboxylic acids can be concentrated from partial oxidation of aldehydes, alcohols, ketones, it would be valuable to recover acetic acid from pyrolysis oil. However, it can potentially be oxidized to less valuable products as outlined in the following reactions: CH3COOH+2O2→2CO2+2H2O       CH3COOH+O2→2CO+2H2O  Partial oxidation of acetaldehyde will produce acetic acid: 2CH3CHO+O2→2CH3COOH        8  However, deep oxidation of acetaldehyde will produce CO2 and CO:      2CH3CHO+5O2→4CO2+4H2O      2CH3CHO+3O2→4CO+4H2O      Finally, although miscellaneous oxygenate compounds also account for a high mass fraction of pyrolysis oil, glycolaldehyde and acetol, the most abundant compounds, were not selected as model compounds as they are both multi-functional compounds. Multi-functional compounds will potentially complicate product spectrum, make it difficult to identify the reactivity of one specific functional group in the partial oxidation reaction.   1.4 Thesis objective  The ultimate goal of partial oxidation of pyrolysis oil is to generate value added chemicals via the process in Figure 1-2 in order to improve the economics of pyrolysis. Partial oxidation can be performed with a catalyst, i.e. catalytic partial oxidation (CPO), or without a catalyst, i.e. thermal oxidation. Thermal oxidation is potentially preferable as it will be inexpensive and simple. However, if thermal oxidation fails to produce AcOH, then a suitable oxidation catalyst will be selected and prepared for CPO. The purpose of the study is to demonstrate the viability of using partial oxidation of AcH to generate AcOH at atmospheric pressure and suitable temperature. Partial oxidation of AcOH is also performed to assess reactivity. In this study, conversion, yield and most importantly, the selectivity to AcOH, were measured and calculated in order to determine technical feasibility of AcH partial oxidation. This thesis explores several hypotheses: 1. AcOH can be generated from thermal oxidation of AcH at suitable temperatures, O2 concentration and residence time; 2. AcOH conversion is low due to its refractory nature; 9  3. The selectivity to AcOH of CPO of AcH is affected by reaction temperature, O2 concentration, and metal loading of the catalyst.  1.5 Literature review  There are relatively few reports on the addition of oxygen to upgrade pyrolysis oil into chemicals either thermally or catalytically. The most relevant research attempted the CPO of pyrolysis oil into synthesis gas (syngas).1,9,19 There are also few reports of thermal oxidation of acetic acid or acetaldehyde. Thus this literature review focuses primarily on CPO of acetic acid (AcOH) and acetaldehyde (AcH) as well as the wider literature of oxidation catalysts. The final decision made on catalyst selection in this study not only depended on CPO of AcH, but also depended on CPO of other organic groups which representatively present in pyrolysis oil.  1.5.1 CPO of pyrolysis oil to syngas   Kruger el al. examined CPO of pyrolysis oil autothermally on Pt/α-Al2O3 and Rh/α-Al2O3 catalysts by using C2 feedstocks with representative functional groups (e.g. acetic acid, acetaldehyde, ethanol) at 400-700 oC and C/O ratio range of 1.2-2. They concluded that the higher conversion was achieved with Rh catalysts than Pt catalysts but the Rh catalyst activity was lower for oxygenate reforming.1 The product spectrum depended on catalyst identity. For example, selectivity to syngas products (i.e. CO and H2) was slightly higher on Rh catalyst, while selectivity to combustion (CO2) and intermediate products (e.g. acetaldehyde) was slightly higher on Pt. In general, acids and ethers appeared to be less reactive than alcohols and esters. In subsequent work,9 Kruger et al. further investigated the effect of α-Al2O3, the catalyst support, and O2 on the course of reaction. The conversion and selectivity of major products were 10  compared in the absence and presence of catalyst support and O2. Kruger et al. found that the presence of O2 generally had a greater impact on conversion and selectivity than α-Al2O3. The catalyst support’s primary role was to transfer heat from the walls of the reactor which axial heat transfer was more likely to occur in the auto thermal system. The α-Al2O3 was relatively inert during the oxidation of most sample compounds.  1.5.2 Partial oxidation of acetic acid  Acetic acid oxidation has been widely studied in catalytic wet air oxidation for the removal of organic carbon from waste water or organic waste using a wide range of catalysts (Ce, Ru, Pt, Zr, Pr etc.). 20–26 As AcOH contains two oxygens and has a refractory nature, AcOH is usually the final oxidation product in waste water. Kruger et al. reported a maximum conversion of 30% of AcOH to CO2 and H2O over a Pt catalyst at 400-700 oC.1,9 In the absence of catalyst, the conversion of AcOH decreased to less than 20%. The refractory nature of AcOH is beneficial to this study as AcOH is the desired product. Partial oxidation will be conducted at lower temperatures suggests that the conversion of AcOH will be lower than those reported by Kruger et al.    Kazem at el.27 examined gas phase oxidation of AcOH and ethylene on Pd-Au to produce vinyl acetate (VA). They concluded that reaction follow the Langmuir-Hinshelwood mechanism. Figure 1-3 illustrates the mechanism proposed by the authors.27 The mechanism is broadly classified into 3 steps: 1. The adsorption of C2H4, O2, and AcOH on catalyst surface 2. Reaction between adsorbed species 3. Products desorb from the surface 11   Figure 1- 3 Proposed mechanism for AcOH oxidation to VA  The product, VA, is produced from absorbed AcOH and ethylene species. In the proposed work, ethylene is not available as a reactant and a different catalyst was applied in partial oxidation reactions. Therefore, VA is unlikely to be produced as a product.  Another report of AcOH’s refractory nature was reported by Sobolev and Koltunov as part of their study of C1-C3 carboxylic acids over V2O5/TiO2 and MoVTeNb oxides in an O2 rich environment.28 Figure 1-4 presents the conversion of C1-C3 carboxylic acids over V2O5/TiO2 as a 12  function of temperature at much excess of O2 and relatively low gas hourly space velocity (GHSV). With both catalysts, Sobolev and Koltunov concluded that AcOH was much more stable than FA and propionic acid. At temperatures below 250 oC, it is clear that the conversion of AcOH is much lower than the other reactants. The conversion of AcOH was less than 15% at 200 oC and only around 3% at 150 oC.    Figure 1-4 Catalytic performance of V2O5/TiO2 as a function of temperature: conversions of formic acid (1), acetic acid (2) and propionic acid (3). Feed compositions: 2.5 vol% HCOOH (or 1 vol% AcOH, or 0.4 vol% C2H5COOH), 20 vol% O2 and He balance, GHSV = 3600    h-1.28   13  1.5.3 Partial oxidation of acetaldehyde  One of the most relevant papers to this study is Suprun et al.’s work on the catalytic partial oxidation of acetaldehyde and propionaldehyde over a V2O5/TiO2 catalyst.29 Figure 1-5 depicts AcH conversion and product yield as a function of reaction temperature (120-280 oC) using the catalyst of 6.1 wt.% of vanadium. The highest yield to AcOH (72%) was reached at 200 oC which corresponded to selectivity of 82%, and then rapidly decreased as temperature increased and combustion products formed.    Figure 1- 5 Conversion of acetaldehyde and yields of main oxidation products as a function of reaction temperature in oxidation of acetaldehyde on a VOx-TiO2 catalyst in the presence of water vapor29  14  The proposed reaction pathways are illustrated in Figure 1-6. The authors proposed that AcOH came from partial oxidation of AcH, while the formation of FA resulted from partial oxidation of AcH or partial oxidation of AcOH. Combustion products (CO2, CO) formed from oxidation of AcOH, AcH or FA. By performing further kinetic modelling, the authors proposed that the oxidation of AcH and propionaldehyde followed 2 main routes: 1. Selective oxidation to respective carboxylic acid, 2. Carbon cleavage to lower carboxylic acid.  Route 1 was favored for both aldehydes at temperatures below 200 oC, while the second route was favored at temperatures above 200 oC. The formation of CO2 was concluded differently: in AcH oxidation, CO2 was proposed to be formed mainly by AcH oxidation, while in propionaldehyde oxidation, CO2 was suggested to be formed mainly by the oxidative cleavage of C1-C3 carboxylic acids.  15   Figure 1- 6 Possible reaction pathways to form oxidation products : (a) acetaldehyde ; (b) propionaldehyde  1.5.4 Catalyst selection  A successful catalyst requires many features: high activity, high selectivity towards the desired products, lowest possible selectivity to byproducts, long life time with respect to deactivation, regeneration, thermal stability against sintering, and structural change. In this study, high product selectivity is the primary focus.  Ethanol is a representative species of alcohols in pyrolysis oil. Oxidation of ethanol has been widely researched using V, Pt, Rh, and Pd catalysts.30–34,34–38,38 Potential products include CO2, 16  CO, syngas, AcH and AcOH and vary by operating conditions and catalyst (e.g. type of metal, mixed metal, promotor). Sobolev et al. examined ethanol oxidation with 12 wt.% and 20 wt.% V2O5, and they found that for both catalysts, the selectivity to AcOH peaked at approximately 70% at 200 oC.39 Despite a significant difference in catalyst loading, for both catalysts, the activity and selectivity to reaction products (AcOH, AcH, CO, CO2) were almost identical. The X-ray Diffraction (XRD) pattern indicated crystalline V2O5 formed on the surface. The selectivity of AcOH increased from 125 to 200 oC as the selectivity of acetaldehyde decreased. When the temperature increased further, the selectivity started to decrease as the production of combustion products (CO, CO2) started to increase.  Table 1-3 summarizes catalytic oxidation of compounds representing a cross-section of those found in pyrolysis oil. A number of different catalysts, have been employed, including Pt, V, Pd, and Rh. Consequently, there is a wide range of potential oxidation products (CO, CO2, AcOH, CH4, H2). There are numerous papers which report partial or full oxidation of organic compounds for different purposes and applications. For example, one industrially recognized process to produce AcOH through partial oxidation of acetaldehyde at mild conditions used manganese acetate or cobalt acetate at atmospheric pressure and temperature from 50 to 60 oC. An AcOH yield of 95% was achieved.40 However, the reaction was in liquid phase and the oxidation performance of manganese acetate with other compounds is unclear.    From Table 1-3, vanadium oxide seems to be a promising catalyst for partial oxidation as it gave relatively high selectivity to AcOH from a number of different organic species. Looking at the historical development of oxidation catalysts, vanadium oxides are one of the oldest industrial oxidation catalysts and proved to be extraordinarily efficient for a large variety of oxidation reactions. Table 1-441 listed some industrial catalytic processes which utilize vanadium oxide. From Table 1-4, it is clear that vanadium oxides have been widely used for many catalytic 17  processes including sulfuric acid production, and phthalic anhydride production. Vanadium oxides have also proved effective and efficient for the production of carboxylic acids from aldehydes, alcohols, and hydrocarbons. For example, formaldehyde can be oxidized readily to formic acid (FA) over V2O5/TiO2.28 Acetic acid can be achieved in high yield by ethanol oxidation over vanadium oxide.28,34 Therefore, in this study, vanadium oxide was selected as a partial oxidation catalyst for the experiment.                      18  Table 1- 3 Partial oxidation of representative organic species and potential products Functional Group Representative specie  Catalyst used Reaction Products Selectivity to AcOH Alcohol ethanol VOx31,34,38,40 AcOH,AcH,CO,CO2 Up to 70% Pt30,35–37 Ethylene, CO, CO2, AcH, diethyl ether, H2, CH4 N/A Pd32,36 H2,CH4,CO,CO2 AcH N/A Rh33,36,37 CH4, C2H4, AcH, CO, CO2, H2 N/A Aldehyde AcH V2O529 CO,CO2,AcOH,FA 82% Pt1,9,43 CH4,CO2,H2,CO,C2H4,C2H6 N/A Pd27 CH4,CO2 N/A Silica gel44 AcOH, FA,CO2 50% manganese acetate45 AcOH, CO2. N/A Rh1 CO2, CO, H2,C2H4,C2H6, CH4 N/A Ketone methyl ethyl ketone VOx46 CO,CO2,AcH,AcOH,FA, diacetyl 70%-75% ester ethyl lactate and ethyl propionate Pt, Rh47 CO, H2 N/A   19  Table 1- 4 Industrial catalytic processes using vanadium oxides   1.5.5 The effect of metal loading on vanadium oxide catalyst  Potential forms of vanadium oxides include V2O5, VO2, V2O3 and VO.41 The vanadium oxide species found on a catalyst support are typically one of three dominant forms: monomeric isolated, monomeric-polymeric, and amorphous and crystal V2O5 phases. Figure 1-741 demonstrates possible configurations for supported vanadium oxides. The form of the vanadium oxides species mainly depends on the vanadium loading, preparation method, and it is generally accepted that the monomeric isolated, and monomeric-polymeric vanadium species are more active and selective than bulk vanadium oxides.48,49 It is found that with increasing vanadium loading, the chance for forming crystal V2O5 phase increases, and therefore, the selectivity decreases. For example, in CPO of methyl ethyl ketone , higher selectivity to AcOH was achieved by using 4-6 wt.% V loading than using higher V loading as more VOx species agglomerated at high V loading (>6%).46 20   Figure 1- 7 Possible molecular configurations for supported vanadium oxides (with S the support cation): (a) isolated vanadium oxide species; (b) dimeric vanadium oxide species; (c) two-dimensional vanadium oxide chains; (d) V2O5 crystals.  1.6 Conclusions  • Pyrolysis oil is a complex mixture containing of hundreds of oxygenated hydrocarbons. The rich oxygen content limits the application of pyrolysis oil as a fuel. Variety of studies have examined the deoxygenation but face numerous challenges and bottlenecks. • As an alternative, partial oxidation of pyrolysis oil could provide economic benefits as the potential products are more valuable than reactants, and may also simplify the subsequent separation process. • There are few papers on the oxidation of pyrolysis oil to generate chemicals. Recent research concluded that pyrolysis oil can be catalytically partially oxidized at relatively high temperatures over noble catalysts to produce synthesis gas. • However, reports of partial oxidation of organic compounds present in pyrolysis oil (e.g. alcohols, acids, aldehydes, ketone, ester) can be found • The oxidation of acetic acid has been studied in the context of wet air oxidation. AcOH is a relatively refractory, and its oxidation products are mostly combustion products. 21  • A more complex product spectrum is obtained from ethanol oxidation. Ethanol is easily oxidized compared to AcOH. Different catalysts yield to different products. Up to 70% selectivity to AcOH was achieved using vanadium oxide at relatively low temperatures, while syngas (CO and H2) was produced when using Pt and Rh at high temperatures. • Selectivity is the primary criteria for selecting an oxidation catalyst for this study; studies summarized in Table 1-3 suggest that vanadium oxide might be a suitable option as it gave relatively high selectivity to AcOH. • AcH partial oxidation on V2O5/TiO2 revealed that a maximum selectivity of AcOH of 82% could be reached. Combustion products were favored when temperature increased. CO2 was mainly formed from direct combustion of AcH • Based on representative organic groups and their abundant species, two mono-functional C2 molecules: AcOH and AcH were selected as model compounds. • Product selectivity when using V/TiO2 catalyst is affected by catalyst preparation method and vanadium loading. The vanadium loading should be in a moderate range so that high selectivity to AcOH can be maintained.          22  Chapter 2. Experimental  2.1 Experiment  A detailed schematic of the experimental apparatus used in this study is presented in Figure 2-1. Two high-pressure cylinders, air, and helium (Praxair, purity >99.99%) were connected to Swagelok 316 stainless steel (316SS) tube. Each gas cylinder was equipped with a pressure regulator to measure the pressure inside the cylinder; the cylinder was considered “empty” when the inner pressure was less than 10% of the initial maximum pressure. A ball valve was installed on each cylinder to open/shut off the flow of each gas. A pressure relief valve (PRV) and check valves were also installed for safety considerations. Two mass flow controllers (MFC) and one mass flow meter (FM) purchased from Omega were used to control the flow rate of each gas and measure the total flow rate after the reactor, respectively. Detailed information for MFCs calibration is shown in Appendix A.1.  A Harvard PHD Ultra Remote model syringe pump equipped with a 50 ml gas-tight glass syringe was used to pump and control the flow rate of the reactant. A ball valve was installed to open/shut off the flow of reactant; a check valve was installed to prevent gas flow to the syringe. The 316SS reactor was 30.48 cm long and had an outer diameter (OD) of 0.9525 cm and thickness 0.1651 cm. The reactor was installed inside a furnace heater (LINDBERG/BLUE M); the maximum operating temperature of the furnace heater was 1200 oC. A K-type thermocouple (TC) was inserted at the center of the reactor to measure the actual reaction temperature. Heating tapes are wrapped around before and after the reactor, K-type TCs were placed to measure the temperature and ensure temperature uniformity in the heating tape zones. A Variac Transformer was connected to the 23  heating tapes and used to adjust the temperature. A ball valve was installed after the reactor to enable rapid shutdown. A custom condenser was located after the reactor to condense and collect any liquid products formed. Liquid products were analyzed by high performance liquid chromatography (HPLC). Gas sampling bags were used to collect gas products formed; gas products were analyzed by gas chromatography (GC). A pressure gauge (PG) and a pressure transducer (PT) were installed to monitor the system pressure. All TCs, PT, and FM were connected to a data acquisition unit (Omega) in order to record data.    Figure 2- 1 Experimental schematic diagram 24    Figure 2- 2 Reactor system, Shimadzu GC-14B, Waters e2695 HPLC  2.2 Experimental procedure  Before each experiment, reactor leak testing was performed. The reactor was pressurized to approximately 40 psi using helium. Swagelok Snoop was applied to all reactor fittings. The reactor was leaking if significant bubbles occurred. If bubbles were not immediately detected, the sealed reactor was left for 12 hours and the pressure was recorded using the PT. If the change in pressure was less than 5%, the reactor was leak-free. After the leak test, a flow check was needed to ensure the accuracy of gas flow. The exhaust gas line was connected to a burette and helium was introduced to the system. A small amount of water was introduced into the burette in order to track the bubble movement. The flow rate of helium was adjusted to required value (e.g. 200 cm3/min) 25  using the MFC. After approximately 30s, the time for a bubble to travel specific volume (e.g. 20 cm3) was recorded. Equation 2-1 was applied to calculate the gas flow rate of helium at standard condition (273K and 1atm). At least 5 replicate flow checks were conducted; the average of the values predicted by Equation 2-1 was compared to the helium MFC calibration curve (See Appendix A.1). This procedure was repeated using oxygen to verify the oxygen flow accuracy.  If the difference was less than 10%, the experiment was conducted; if not, the calibration curve was remade, and the above procedure was repeated until this requirement was met.  ?̇?𝐻𝑒,𝑆𝑇𝑃,𝑀 =𝑉𝑓𝑖𝑥𝑡𝑎𝑣𝑔× 60 ×𝑇𝑆𝑇𝐷𝑇𝑁𝑂𝑅                                         (2-1)  ?̇?𝐻𝑒,𝑆𝑇𝑃,𝑀: Average He flow rate at standard condition, cm3/min 𝑉𝑓𝑖𝑥: The volume for He bubble travels during 𝑡𝑎𝑣𝑔, cm3 𝑡𝑎𝑣𝑔: Average time recorded by the stop watch for He bubble travels volume of 𝑉𝑓𝑖𝑥, s 𝑇𝑆𝑇𝐷: Standard temperature, 273 K 𝑇𝑁𝑂𝑅: Normal temperature in lab, 298 K  After the flow check, the system was flushed with helium for approximately 15 minutes. For thermal oxidation experiments, the furnace was directly heated to the desired reaction temperature at a ramp rate of 7 oC/min. For catalytic oxidation experiments, the reactor was first loaded with 0.2g catalyst (108-180 μm mesh size) and 1g silicon carbide (SiC) with similar size as an inert to ensure isothermal operation through the 3 cm length of the catalyst bed, the furnace temperature was then increased to 110 oC for 1 hour to remove any possible moisture from the catalyst surface, then the furnace was heated to the desired reaction temperature. The Variac Transformer was turned on to adjust the temperature of the heating tapes; the heating tapes reached to desired temperature (approximately 120 oC) in 15 minutes. The condenser jacket was filled with ice to 26  condense liquid products. The desired concentration of aqueous reactant solution was prepared. After the furnace temperature reached the set temperature and stabilized, the syringe pump was started to feed the reactant solution at a desired flow rate. Data acquisition software recorded temperature and pressure. Gaseous products were collected after 3 hours by SUPELCO Supel™-Inert Multi-Layer Foil gas sampling bags; the liquid products were collected and weighed when the experiment ended. When the experiments ended, the He gas continuously flushed the system for additional half an hour. Each experiment lasted approximately 3.5 hours. Table 2-1, Table 2-2, and Table 2-3 summarize the experimental conditions. In this thesis, the mean residence time and gas hourly space velocity (GHSV) was reported at the standard conditions. (i.e. 273 K and 1 atm)                  27  Table 2- 1 Experimental conditions for thermal oxidation Thermal Partial Oxidation AcOH thermal partial oxidation Temperature (oC) O2/AcOH molar ratio Mean Residence time at standard condition (s) 150 1 1.8 200 1 1.8 250 1 1.8 300 1 1.8 350 1 1.8 150 0.5 1.8 200 0.5 1.8 250 0.5 1.8 300 0.5 1.8 350 0.5 1.8 AcH thermal partial oxidation 150 1 1.8 200 1 1.8 250 1 1.8 300 1 1.8 350 1 1.8 150 0.5 1.8 200 0.5 1.8 250 0.5 1.8 300 0.5 1.8 350 0.5 1.8 28  Table 2- 2 Experimental conditions for catalytic partial oxidation Catalytic Partial oxidation AcOH catalytic partial oxidation Temperature (oC) O2/AcOH molar ratio Gas hourly space velocity (h-1) Catalyst 150 1 20000 6.9V/TiO2 175 1 20000 6.9V/TiO2 200 1 20000 6.9V/TiO2 225 1 20000 6.9V/TiO2 250 1 20000 6.9V/TiO2 AcH catalytic partial oxidation              150 1 20000 2.4V/TiO2 175 1 20000 2.4V/TiO2 200 1 20000 2.4V/TiO2 225 1 20000 2.4V/TiO2 250 1 20000 2.4V/TiO2 150 1 20000 6.9V/TiO2 175 1 20000 6.9V/TiO2 200 1 20000 6.9V/TiO2 225 1 20000 6.9V/TiO2 250 1 20000 6.9V/TiO2 200 0.5 20000 6.9V/TiO2 200 2 20000 6.9V/TiO2 200 4 20000 6.9V/TiO2 200 6 20000 6.9V/TiO2 200 8 20000 6.9V/TiO2 29     AcH catalytic partial oxidation Temperature (oC) O2/AcOH molar ratio Gas hourly space velocity (h-1) Catalyst 200 6 20000 6.9V/TiO2 200 6 10000 6.9V/TiO2 200 6 6667 6.9V/TiO2 200 6 5000 6.9V/TiO2 200 6 4000 6.9V/TiO2  Table 2- 3 Experimental conditions for CPO of mixtures of AcH and AcOH Catalytic Partial oxidation AcH and AcOH mixture Temperature (oC) O2/AcH molar ratio Gas hourly space velocity  (h-1) Catalyst  AcH to (AcH+AcOH) mass ratio 200 6 20000 6.9V/TiO2 0.2 200 6 20000 6.9V/TiO2 0.4 200 6 20000 6.9V/TiO2 0.6 200 6 20000 6.9V/TiO2 0.8       30  2.3 Compositional analysis  2.3.1. Gas phase analysis  The composition of the gas phase products was determined by gas chromatography(GC) (Shimadzu GC-14B) with an Agilent Technologies Inc. HP-PLOT U column (19095P-UO4, inner diameter 0.530mm, length 30 m, film 20.00 mm), a flame ionization detector (FID), and a thermal conductivity detector (TCD). Shimadzu C-R8A Chromatopac integrator was used to analyze the chromatograms. Helium (Praxair, >99.99%) was used as a carrier gas. The temperature profile for gas analysis is summarized in Table 2-4. A mixture cylinder (Praxair) containing acetaldehyde (AcH, 14.9%), carbon monoxide (CO,14.3%), carbon dioxide (CO2 ,14.4%) and nitrogen (56.4%) was used for calibration. The mixture gas was diluted to multiple concentration using helium gas and MFCs to create gas calibration curves. A sample calibration curve for AcH is shown in Figure 2-3, and calibration curves for CO and CO2 and their elution time were depicted in Appendix A.2.  Table 2- 4 Analytical method for GC-14B Temperature (oC) Ramp rate (oC/min) Hold time (min) 35  3 120 5 2 170 10 3     31    Figure 2- 3 AcH calibration curve for GC-14B  2.3.2. Liquid phase analysis  The major liquid products present in this study were expected to be AcOH, AcH and formic acid (FA). Therefore, the utilized HPLC method must resolve the above organics separately. No peak should overlap with another, and the analysis time should be reasonably short. Zhang et al. developed a HPLC method which met the above requirements. The method was meant to analyze the products of oxidation of AcH with HNO3 with the following conditions.50  1. Aminex HPX-87H column,  2. Mobile phase consisting of 0.01N H2SO4, flow rate of 0.8 mL/min  3. Temperature of 65 oC  Figure 2-4 and Figure 2-5 present retention profiles for AcOH, AcH, and FA from the original mixture and standard solution, respectively. It is apparent that the three peaks resolved separately 0.0%0.5%1.0%1.5%2.0%2.5%3.0%0 100000 200000 300000 400000 500000 600000Concentration (mol fraction)Area32  and none of them overlap with each other. The analysis time was relatively short, the last eluted component, AcH, took around 13.2 minutes to identify.   Figure 2- 4 HPLC chromatogram chart of the real oxidation mixture. Peaks: 6, formic acid; 7, acetic acid; 8, acetaldehyde (0.01 H2SO4, 0.8 ml/min, 65 oC)    33   Figure 2- 5 HPLC chromatogram of calibration standard. Peaks: 6, formic acid; 7, acetic acid; 8, acetaldehyde (0.01 H2SO4, 0.8 ml/min, 65 oC)  Liquid products were analyzed by HPLC (Waters e2695 Alliance) using an Aminex HPX-87H column and a refractory index (RI) detector. The protocol developed by Zhang et al. was used. However, for safety and to increase the column lifetime, the mobile phase flow rate was reduced to 0.6 mL/min. The chromatographic conditions are summarized in Table 2-5. All chemicals were HPLC grade and purchased from Sigma-Aldrich; all solutions were prepared using deionized water (DW). A sample calibration curve for AcOH is presented in Figure 2-6, and Appendix A.3 presents calibration curves for AcH and formic acid and the elution times.   Calibration standards were prepared at five different concentration using the mobile phase as the diluent. The solution was well mixed and filtered through a 0.45 mm membrane filter before use. The liquid product sample was prepared by diluting 1.0 mL of liquid product with 100 mL of mobile phase. The liquid product solution was well mixed and filtered through a 0.45 mm membrane filter before use.  34  Table 2- 5 Chromatographic conditions for Waters e2695 HPLC Column Aminex HPX-87H Mobile Phase 0.01 N H2SO4 Flow Rate (ml/min) 0.6 Column Temperature (oC) 65     Figure 2- 6 AcOH calibration curve for Waters e2695 HPLC      01000200030004000500060000 50000 100000 150000 200000 250000 300000Concentration (ppm)Area35  2.4 Carbon balance and experimental repeatability  The largest discrepancy in the experimental carbon balance was approximately 13%. This error may be due to experimental error, for example, a small amount of product liquid was not collected from the condenser or errors from the syringe pump or the limitation of analytical apparatus (HPLC, GC). The largest standard deviation for conversion was about 3.6%, demonstrating that the reactor system performance was repeatable.   2.5 Catalyst preparation  The catalyst used in this thesis was vanadium oxide on a TiO2 support. The metal content was used to report the composition of the catalyst. For example, a 5V/TiO2 had a vanadium(V) content of 5 wt.%.   The TiO2 (VWR, pellet form,0.38 cm3/g from the specification) was crushed manually using mortar and pestle and sieved to obtain a TiO2 powder with particle size range of 108-180 μm.    The catalyst was prepared using incipient wetness impregnation. To prepare a nominal V content of 3.9 wt.% of the catalyst, approximately 0.5964g of vanadium oxalate (C2O5V) was dissolved in 1.767 ml of water, heated to 55 oC and mixed thoroughly for around 15 minutes to obtain a transparent and homogenous solution. The solution was impregnated onto 4.65g of TiO2 support. The impregnated wet catalyst in solid form was left at room temperature for 24hrs and then dried in an oven at 100 oC for 24 hrs. Finally, the catalysts were calcined by dry air at a temperature of 450 oC for 5hrs and cooled to room temperature, and the calcined catalyst was sieved again to obtain a 36  particle size range of 108-180 μm. The purpose of calcination was to remove volatile and undesired species from the precursor (C2O5V) and stabilize the metal oxide phase. The catalyst was calcined in an oxygen-rich atmosphere before use so that vanadium oxides were stabilized. The metal loading of the calcined catalysts was measured by Canadian MicroAnalytical Service Ltd. using inductively coupled plasma mass spectroscopy (ICP-MS).  In order to prepare a catalyst with a nominal V loading of 10%, a two-time successive incipient wetness impregnation was employed due to the solubility limitations of C2O5V. For the first time impregnation, approximately 0.7613g of C2O5V was dissolved in 1.561 ml of water, heated to 55 oC and mixed thoroughly for around 20 minutes to obtain a transparent and homogeneous solution. The solution was impregnated onto 4.1074g of TiO2 support. The impregnated wet catalyst in solid form was left at room temperature for 24hrs and then dried in an oven at 100 oC for 24 hrs. Then, the catalysts were calcined by dry air at a temperature of 450 oC for 5hrs and cooled to room temperature. The second-time impregnation used the exact same amount of C2O5V and water as the first-time impregnation; the transparent and homogeneous solution was then impregnated onto the calcined catalyst. The catalyst was dried and calcined again as previously mentioned.  2.6 Catalyst characterization  Several characterization techniques, ICP-MS, Brunauer–Emmett–Teller (BET), X-ray Diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) were used to identify the properties of the catalyst.   37  2.6.1 ICP-MS  The vanadium content was determined by ICP-MS using a Thermo Scientific X-Series II with a Cetac ASX-520 autosampler. The fresh catalyst was digested by 1 mL concentrated H2SO4 or HNO3 and then diluted to 50 mL with deionized water. The vanadium loadings (i.e. 2.4 wt.% and 6.9 wt.%) reported in this thesis are actual loading measured by ICP-MS. The ICP-MS report for a nominal 10 wt.% of V loading obtained from Canadian Microanalytical Serive Ltd. can be viewed in Appendix B.3.  2.6.2 BET  BET surface area, pore volume, and pore size of V/TiO2 catalysts were determined by N2 adsorption isotherm at 77 K through a Micromeritics ASAP 2020 analyzer. Approximately 0.1g was weighed and transferred into a glass tube and sealed properly and degassed at 200 oC for 4 hrs in vacuum to remove possible moisture on the surface. The N2 adsorption-desorption isotherm was obtained. The surface area was calculated by the BET method by the isotherm. The average pore size and the total volume of N2 adsorbed were determined by Barrett–Joyner–Halenda (BJH) method. The pore volume of the catalyst was determined at a relative pressure P/Po=0.995. More details provided in Appendix B.1  2.6.3 XRD  A Bruker D8 Advance Bragg-Brentano diffractometer equipped with an Fe monochromator foil, 38  0.6 mm (0.3°) divergence slit, incident- and diffracted-beam Soller slits and a LynxEye-XE detector was used to collect continuous-scan X-ray powder-diffraction data over a range 3-80°2 with CoKa radiation. The long fine-focus Co X-ray tube was operated at 35 kV and 40 mA, using a take-off angle of 6°. The spectrum can be seen in Appendix B.2.   2.6.4 XPS  A Leybold MAX200 X-ray photoelectron spectroscopy (XPS) with Al K-alpha X-ray source was used to detect the V oxidation state. The analyzed area was 4x7 mm2, and the pass energy used for survey scan and narrow scan measurement was 192eV and 48eV, respectively. The peak of V 2p3/2 with a binding energy around 517.5 revealed a high oxidation state of V. After comparing with literature, it was confirmed that the oxidation state of V was vanadium pentoxide (V2O5).46,48 Details of XPS spectrum are provided in Appendix B.4.   2.7 Study of internal mass transfer effect  During gaseous catalytic partial oxidation, internal mass transfer could limit the reaction rate. The role of internal mass transfer was assessed using the Thiele modulus (ɸ) and internal effectiveness factor (η). The Thiele modulus is the ratio of reaction rate to diffusion rate and can be used to calculate the internal effectiveness factor. The internal effectiveness factor is the ratio of the actual overall rate of reaction to the rate of reaction that would obtain if all interior surface were exposed to external pellet surface conditions.51 The value of internal effectiveness factor ranges from 0-1 and indicates whether diffusion or the reaction rate is the rate limiting step.  39  The internal effectiveness factor was calculated by Equation 2-1 to 2-3 assuming a 1st order overall reaction. Detailed calculations are provided in Appendix C.3. As ɸ ≈0.26 and η≈1 at T=250 oC, implying that the intraparticle residence was minimal.   𝐷𝑒 =𝐷𝐴𝜑𝑃𝜎𝐶?̅?                                                     (2-1) ɸ2 =𝐷𝑝2𝑘𝐴𝐷𝑒                                                  (2-2) η =3ɸ2(ɸ coth ɸ − 1)                                         (2-3) 𝐷𝑒: effective diffusivity, m2/s 𝐷𝐴: diffusivity of AcH in air, m2/s 𝜑𝑃: pellet porosity, 0.4, dimensionless 𝜎𝐶: constriction factor, 0.8, dimensionless 𝜏̅: tortuosity, 3.0 dimensionless 𝐷𝑝: catalyst particle diameter, m 𝑘𝐴: overall AcH reaction rate at 250 oC, s-1 ɸ: Thiele modules          40  Chapter 3. Thermal oxidation of acetic acid and acetaldehyde  Chapter 3 discusses thermal oxidation of acetic acid (AcOH) and acetaldehyde (AcH). All experiments performed in this chapter were conducted at the same total inlet flow rate. The change in O2 flow rate for different concentrations was compensated for by adjusting the He flow rate accordingly.   3.1 Thermal oxidation of acetic acid  AcOH was vaporized at 120 oC in the presence of He prior to being mixed with O2 and entering the reactor. Therefore, it is necessary to determine that AcOH did not react prior to entering the reactor before examining the thermal oxidation of AcOH. AcOH can decompose to generate CO and H2 as illustrated in reaction 1.8 In order to verify that AcOH did not react with He or decompose during vaporization, AcOH in presence of pure He was supplied to the furnace. The furnace was maintained at 120 oC (the vaporization zone temperature). The conversion of AcOH under these conditions was determined to be 0% indicating that no reaction occurs during preheating.   𝐶𝐻3𝐶𝑂𝑂𝐻 → 2𝐶𝑂 + 2𝐻2                  ∆𝐻𝑜 ≈ 210 kJ/mol             (1)                  AcOH oxidation can produce several products including CO2, CO, formic acid (FA), CH4, and H2. Under the tested experimental conditions, the primary product was CO2 and minor products were neglected since both conversion and selectivity to minor products (<0.5%) was low. 41  Figure 3-1 shows the conversion of AcOH as a function of temperature and O2 concentrations. It is clear that AcOH is refractory, as reported in the literature, as the maximum conversion was less than 6% at 350 oC and O2/AcOH=1. The refractory nature of AcOH is likely due to its high O/C ratio thus adding additional oxygen atoms is quite difficult. The activation energy of AcOH oxidation in supercritical water was reported as 308 kJ/mol; this significant activation energy barrier is the main reason for low conversion.52 At low temperatures (T<250 oC), the conversion was negligible. Low conversion of AcOH assisted in maintaining isothermal conditions inside the reactor as full combustion of AcOH is an exothermic reaction (reaction 2).8 For both O2 concentrations, conversion of AcOH increased with increasing temperature. At constant temperature, increasing O2 concentration slightly increased conversion as the rate of combustion slightly increases with increasing O2.   𝐶𝐻3𝐶𝑂𝑂𝐻 + 2𝑂2 → 2𝐶𝑂2 + 2𝐻2𝑂                 ∆𝐻𝑜 ≈ −840 kJ/mol     (2)  42   Figure 3-1 Conversion of AcOH as a function of temperature and O2/AcH molar ratio (5 vol% AcOH, RT=1.8s)  The selectivity and yield of AcOH oxidation as a function of temperature and O2 concentration are presented in Figure 3-2. At both O2 levels, the selectivity to CO2 exceeded 99.5% indicating that AcOH underwent a complete oxidation; no liquid products were detected by HPLC for the reaction conditions studied. Both O2 concentration and reaction temperature had little impact on product selectivity. Increasing temperature and O2 concentrations increased the yield of CO2. The yield of CO2 under all conditions exhibited the same trends as conversion because the selectivity of 01234567100 150 200 250 300 350 400Conversion (%)Temperature (oC)Oxygen/Acetic Acid=0.5Oxygen/Acetic Acid=143  CO2 approaches 100%.  Figure 3-2 Yield of and selectivity to CO2 from thermal oxidation of AcOH as a function of temperature and O2/AcOH molar ratio. (5 vol% AcOH, RT=1.8s)  9696.59797.59898.59999.5100012345678100 150 200 250 300 350 400Selectivity (%)Yield (%)Temperature (oC)Yield at Oxygen/Acetic Acid=0.5Yield at Oxygen/Acetic Acid=1Selectivity to Carbon dioxide at Oxygen/Acetic Acid=0.5Selectivity to Carbon dioxide at Oxygen/Acetic Acid=144  3.2 Thermal oxidation of AcH  In order to verify that AcH does not react with He or decompose during vaporization, the validation test described in section 3.1 was repeated. No conversion of AcH was detected under vaporization conditions thus all products detected following thermal oxidation are due to reactions within the reactor.     Compared to AcOH, AcH was much more reactive during oxidation as there is only one oxygen atom present in the molecule. A range of products could result from the oxidation of AcH including AcOH, FA, CO, CO2, and H2. However, thermal oxidation of AcH in this study yielded only one major product (CO2). Minor products were neglected as the selectivity of CO2 was approximately equal to 1.   Figure 3-3 presents the conversion of AcH as a function of temperature (150 to 350 oC) and O2 concentrations. As temperature increased, conversion increased significantly at both O2 concentrations due to increasing reaction rate. For example, when temperature increased from 200 to 250 oC at O2/AcH=1, there was a 100% increase in AcH conversion. Thus, the temperature had an enormous impact on AcH conversion. The maximum conversion for O2/AcH=1 and O2/AcH=0.5 was approximately 40% and 20%, respectively. Based on the initial molar ratio of O2 to AcH and the stoichiometric coefficient for AcH combustion (reaction 3), the combustion reaction approached 100% conversion with respect to O2 at 350 oC for both O2 concentrations. At 150 oC for O2/AcH=0.5 and O2/AcH=1, the conversion of AcH was approximately 2% and 4%, respectively, hence 150 oC may be the initiation temperature of the AcH combustion reaction. Although the reaction is exothermic and the conversion is significant compared with AcOH oxidation, the molar flow rate of AcH was kept low (7.88E-4 mol/min). Thus, the isothermal 45  condition of the reaction was maintained.  Due to a much higher conversion compared with AcOH, the activation energy of AcH oxidation is expected to be much lower than that of AcOH oxidation.  The oxygen concentration was also proportional to conversion of AcH. Compared the conversion of AcH at O2/AcH=1 to O2/AcH=0.5, the conversion almost doubled at each temperature which suggests that there was probably only one reaction, combustion, occurring during the oxidation of AcH. 𝐶𝐻3𝐶𝐻𝑂 + 2.5𝑂2 → 2𝐶𝑂2 + 2𝐻2𝑂                 ∆𝐻𝑜 ≈ −857 kJ/mol     (3)   46   Figure 3-3 Conversion of AcH oxidation as a function of temperature and O2/AcH molar ratio (5.9 vol% AcH, RT=1.8s)  Figure 3-4 presents the selectivity and yield of CO2 from AcH oxidation as a function of temperature and O2 concentration. At all conditions, the selectivity to CO2 exceeded 98.5% indicating that AcH underwent complete oxidation and no significant side reactions occurred. Increasing temperature or O2 concentration increased the yield of CO2. The yield at both O2 concentrations exhibited similar trend to conversion because the selectivity to CO2 approached 100%.  01020304050100 150 200 250 300 350 400Conversion (%)Temperature (oC)Oxygen/Acetaldehyde=1Oxygen/Acetaldehyde=0.547    Figure 3-4 Selectivity and yield of AcH oxidation as a function of temperature and O2/AcH molar ratio (5.9 vol% AcH, RT=1.8s)  9696.59797.59898.59999.5100020406080100100 150 200 250 300 350 400Selectivity (%)Yield (%)Temperature (oC)Yield at Oxygen/Acetaldehyde=0.5Yield at Oxygen/Acetaldehyde=1Selectivity to Carbon dioxide at Oxygen/Acetaldehyde=0.5Selectivity to carbon dioxide at Oxygen/Acetaldehyde=148  A final attempt to achieve partial oxidation of AcH to AcOH under thermal oxidation conditions was made by reducing the temperature to 120oC and the O2/AcH ratio to 0.125-0.5. No AcOH was detected in the liquid collected from the condenser. Further information is provided in Appendix D.  3.3 AcH thermal oxidation: rate constant and activation energy  Based on the stoichiometric ratio of O2 to AcH in reaction (3) and experimental conditions in this study, O2 was the limiting reactant for all AcH thermal oxidation experiments. Due to the limited reaction data on thermal oxidation of AcH, the rate equation of AcH oxidation was determined according to two cases: 1. The reaction was an overall 1st order reaction dependent only on oxygen concentration; 2. The reaction was an overall 2nd order reaction dependent on oxygen and AcH concentration  Case 1: 1st order reaction rate  In case 1, the reaction rate was assumed to have 1st order dependence on O2, therefore, the rate constant of AcH (kA) can be calculated from the plug-flow reactor (PFR) mole balance (Equation 3-1), the proposed rate law (Equation 3-2) and stoichiometry relation (Equation 3-3) of the AcH oxidation reaction51:  dX𝐵dV=−𝑟𝐵𝐹𝐵𝑂                                           (3-1) −𝑟𝐵 = 𝑘𝐵𝐶𝐵                                         (3-2) 49  ?̇? = 𝑉?̇?(1 + 𝜀𝑋𝐵)𝑃𝑃𝑂𝑇𝑂𝑇                                 (3-3) 𝑋𝐵: conversion of O2, dimensionless V: reactor volume, cm3 -rB: O2 reaction rate expression, mol.cm-3.min-1  FBO: initial molar flow rate of O2, mol/min kB: rate constant of O2, assuming 1st order, min-1 CB: concentration of O2, mol/cm3 ?̇?: total volumetric flow rate after reaction, cm3/min 𝑉?̇?: total volumetric flow rate at inlet, cm3/min 𝜀: fraction change in volume per moles of O2 reacted resulting from the change in total number of moles, dimensionless P: reaction pressure, atm T: reaction temperature, K PO: inlet pressure of the system, atm TO: inlet temperature of the system, K  Since the inlet mole fraction (y) of O2 was small, it was reasonable to assume that the total volumetric flow rate was not changed. Combining Equations 3-1 to 3-3 and assuming constant pressure and temperature, yields Equation 3-4 to calculate kB (see Appendix C.4 for derivation), and the rate constant of AcH can be determined from Equation 3-8: 𝑘𝐵 =𝑉𝑂𝑉̇ln (11−𝑋𝐵)                           (3-4) 𝑉?̇? = 𝑉𝑆𝑇𝑃̇𝑇273                                (3-5) 𝑋𝐵 = 2.5𝑋𝐴 (for O2/AcH=1)                   (3-6) 𝑋𝐵 = 5𝑋𝐴 (for O2/AcH=0.5)                   (3-7) 𝑘𝐴 = 0.4𝑘𝐵                                  (3-8) 50  𝑉𝑆𝑇𝑃̇ : total volumetric flow rate normalized at standard conditions, sccm 𝑋𝐴: AcH conversion, dimensionless 𝑘𝐴: AcH rate constant, min-1  Table 3-1 summarizes the rate constant for AcH oxidation as a function of temperature for both O2 concentrations. The rate constant of AcH increased with temperature as expected. The activation energy (Ea) of AcH oxidation was obtained using the linearized Arrhenius law (Equation 3-9) and plotting ln(kA) vs. 1/T (see Figure 3-5 and Figure 3-6). It should be noted that the rate constant at 350 oC was not used to predict Ea as the conversion of O2 reached 100% at this temperature. The curve fit reasonably well as R2 approaches to 1. The differences between the two calculated rate constant for different oxygen concentration is insignificant (<9%) due to the experimental errors.  ln(𝑘𝐴) = ln 𝑘𝑜 −𝐸𝑎𝑅1𝑇                             (3-9) 𝑘𝑜: pre-exponential factor, min-1 R: gas constant, 8.314 J.K-1.mol-1 T: reaction temperature, K          51  Table 3-1 AcH rate constant assuming 1st order dependence on oxygen concentration  (-rB=kBCB) Temperature (oC) AcH rate constant at O2/AcH=1, 𝑘𝐴  (min-1) AcH rate constant at O2/AcH=0.5, 𝑘𝐴 (min-1) Differences (%) 150 2.3 2.1 8.7% 200 7.8 7.3 6.4% 250 21.6 22.9 6.0% 300 83.3 80.1 3.8% Ea (kJ/mol) 47.1 48.2 2.3%    Figure 3-5 AcH activation energy data fitting at 150 to 300 oC, O2/AcH=1, 1st order assumption, R2≈0.99 00.511.522.533.544.550.0015 0.0017 0.0019 0.0021 0.0023 0.0025ln(kA), (min-1)1/T, (1/K)52   Figure3- 6 AcH activation energy data fitting at 150 to 300 oC, O2/AcH=0.5, 1st order assumption, R2≈0.99  Case 2: 2nd order reaction rate  In the second case, a second order overall reaction rate was assumed, and the rate expression was written as Equation 3-10. By adopting the same assumptions used for case 1 (constant T, P, and total volumetric flow rate) and combining Equations 3-1, 3-3, 3-5, and 3-6, the rate constant, kB, can be determined according to Equation 3-11 (for O2/AcH=1). The detailed derivation is shown in Appendix C.4. Rate constant, 𝑘𝐴, is then obtained using Equation 3-8. Table 3-2 summarizes kA as a function of temperature and the activation energy of AcH oxidation assuming a 2nd order overall reaction rate. The activation energy was calculated by fitting Equation 3-9 by ln(𝑘𝐴) vs. 1/T (Figure 3-7 and Figure 3-8). Again, only temperatures from 150 to 300 oC were used to fit the 00.511.522.533.544.550.0015 0.0017 0.0019 0.0021 0.0023 0.0025ln(kA), (min-1)1/T, (1/K)53  Equation as 100% conversion with respect to O2 was achieved at 350oC. The differences between the two calculated rate constant for different oxygen concentration is insignificant (~20%) due to the experimental errors. At each temperature, the value of 𝑘𝐴 was much larger compared the one obtained from 1st order assumption due to the presence of CA in the overall rate expression. Comparing Figure 3-5, Figure 3-6 with Figure 3-7, Figure 3-8, it can be seen that the curve derived using the 1st order assumption fit the data slightly better than the curve obtained using the 2nd order assumption. However, due to insufficient supporting literature and limited data, it is not possible to definitively select one case over the other.    −𝑟𝐵 = 𝑘𝐵𝐶𝐵𝐶𝐴                              (3-10) 𝑘𝐵 =53𝑉𝑂2𝑉𝐹𝐴𝑂[̇ln(0.4) − ln(𝑋𝐵−1𝑋𝐵−2.5)]               (3-11)  𝐹𝐴𝑂: initial flow rate of AcH, mol/min 𝑘𝐵: O2 rate constant, assuming 2nd order, cm3.mol-1.min-1  Table 3-2 AcH rate constant assuming 2nd order overall reaction rate (-rB=kBCBCA) Temperature (oC) AcH rate constant at O2/AcH=1, 𝑘𝐴 (cm3.mol-1.min-1) AcH rate constant at O2/AcH=0.5, 𝑘𝐴 (cm3.mol-1.min-1) Differences (%) 150 1.386E6 1.267E6 8.6% 200 5.465E6 4.960E6 9.2% 250 1.818E7 1.80E7 0.99% 300 9.315E7 7.414E7 20.4% Ea (kJ/mol) 55.2 54.0 2.2% 54    Figure 3-7 AcH activation energy data fitting at 150 to 300 oC, O2/AcH=1, 2nd order assumption, R2≈0.98   Figure3- 8 AcH activation energy data fitting at 150 to 300 oC, O2/AcH=0.5, 2nd order assumption, R2≈0.98 051015200.0015 0.0017 0.0019 0.0021 0.0023 0.0025ln(kA), (cm3.mol-1.min-1)1/T, (1/K)051015200.0015 0.0017 0.0019 0.0021 0.0023 0.0025ln(kA), (cm3.mol-1.min-1)1/T, (1/K)55  The Ea of AcH oxidation from both cases as well as Ea of AcOH oxidation reported in literature are presented in Table 3-3. The Ea of AcH oxidation is significantly smaller than the Ea of AcOH oxidation further demonstrating that AcH is more reactive than AcOH.  Table 3-3 Comparison of Ea in AcH oxidation and AcOH oxidation Ea (AcOH oxidation, kJ/mol)52 Ea (AcH oxidation,1st order assumption, kJ/mol Ea (AcH oxidation, 2nd  order assumption, kJ/mol 308 47.1±0.55 55.2±0.6              56  Chapter 4. Catalytic partial oxidation of acetic acid and acetaldehyde  As discussed in Chapter 3, thermal oxidation of AcOH and AcH resulted in complete combustion to produce CO2 at the tested conditions. Hence, in order to generate acetic acid, a catalyst is needed. A catalyst provides a suitable surface for one or multiple chemical reactions to occur via different routes. On the catalyst surface, the reacting particles collide more easily with each other, and consequently, more of the collisions yield a chemical reaction due to the lowered activation energy facilitated by the catalyst. In this study, vanadium oxide supported by TiO2 was used as the oxidation catalyst; two different metal loadings (2.4V/TiO2 and 6.9V/TiO2) were prepared by incipient wetness impregnation. The temperature range investigated was reduced to 150 to 250 oC as combustion products (CO, CO2) were generally favored at high temperatures.   A BET test (N2 adsorption and desorption, 77K) was performed to evaluate fundamental catalyst properties. The catalysts were preheated and dried prior to the BET test. The surface area, pore volume and pore size of both catalysts as well as the fresh support, TiO2, are compared in Table 4-1. Both catalysts had a relatively high surface area. However, compared with fresh support, the surface area of the catalysts were reduced. The decrease in surface area could be due to the reason that the micropores of the support were blocked by the catalyst particle. The pore volume and pore size did not change appreciably after impregnation implying that the catalyst particles were dispersed uniformly on the support surface. The pore size distribution indicates both catalysts contain primarily mesoporous pores (Appendix B.1).      57  Table 4- 1 Comparison of fresh catalysts properties and TiO2  2.4V/TiO2 6.9V/TiO2 TiO2a  Surface Area (m2/g) 92 107 >150 Pore volume (cc/g) 0.36 0.41 0.38 Pore size (nm) 12 12 14 aProvided by VWR   X-ray diffraction (XRD) analysis was conducted in order to determine the crystalline phases of the catalyst. However, only the support, TiO2 was detected by XRD, indicating that there was no crystalline form of vanadium oxide present in the catalyst. Further details on the XRD analysis are provided in Appendix B.2.    Blank experiments were performed by using only SiC and TiO2, respectively, to exclude any possible catalytic effect by the inert or support at 150 to 250 oC. There was no indication that SiC and TiO2 could act as a catalyst to oxidize AcH to AcOH.  4.1 Catalytic oxidation of acetic acid  AcOH was shown to be difficult to oxidize thermally due to its high activation energy. However, one of the most important functions of catalysts is to lower the activation barrier of reactions thus catalytic oxidation of AcOH may occur to a greater extent than thermal oxidation.  Figure 4-1 and Figure 4-2 present the conversion and selectivity of AcOH oxidation, respectively, 58  at 150 to 250 oC.  Similar to thermal oxidation, conversion of AcOH was low and increased slightly with increasing temperature. A maximum conversion of approximately 5% was achieved at 250 oC. This conversion is lower than what has been previously reported in the literature for the oxidation of AcOH over V/TiO2. For example, a conversion of approximately 12.5% was reported using V/TiO2 at 200 oC28 (GHSV=3600h-1, O2/AcH=20) while only 3.8 % conversion was obtained in this study. This difference is likely due to the short residence time (RT) and low oxygen concentration employed in this study. CO2 was the only major product detected at all temperatures investigated for catalytic partial oxidation. The selectivity to CO2 during catalytic partial oxidation was similar to the selectivity to CO2 during thermal oxidation.    Figure 4-1 Conversion of AcOH as a function of temperature (5 vol% AcOH, 6.9V/TiO2, O2/AcH=1, GHSV≈20000h-1) 0%1%2%3%4%5%6%100 125 150 175 200 225 250 275Conversion/Yield (%)Temperature,  (oC)59    Figure 4- 2 Selectivity of AcOH oxidation as a function of temperature (5 vol% AcOH, 6.9V/TiO2, O2/AcH=1, GHSV≈20000h-1)  Comparison of Figures 3-1 and 4-1 reveals that at 150 to 250 oC, conversion of acetic acid increased with the use of 6.9V/TiO2 catalyst. In addition, in order to achieve equivalent conversion to conversion achieved during catalytic partial oxidation, thermal oxidation must be conducted at a higher temperature. These observations indicate that the activation energy of catalytic oxidation was lower than the thermal oxidation.  0%20%40%60%80%100%100 125 150 175 200 225 250 275Selectivity (%)Temperature, (oC)CO260  4.2 Catalytic partial oxidation of acetaldehyde  4.2.1 Effect of temperature and catalyst metal loading  AcH conversion as a function of temperature and vanadium loading is presented in Figure 4-3. For both catalysts, AcH conversion increased with increasing temperature due to the increase in reaction rate. The maximum conversions for 6.9V/TiO2 and 2.4V/TiO2 were 69% and 62%, respectively. The 6.9V/TiO2 catalyst resulted in greater AcH conversion than 2.4V/TiO2 catalyst due to the increase in the number of active sites with increased metal loading. Comparison of Figures 3-3 and 4-3, reveals that the use of V/TiO2 increased conversion of AcH relative to thermal oxidation at 150 to 250 oC. This parallels the results observed for catalytic partial oxidation of AcOH.   61   Figure 4-3 Conversion of CPO of AcH as a function of temperature (5.9 vol% AcH, O2/AcH=1, GHSV≈20000h-1)  The selectivity of CPO of AcH for both catalysts is presented in Figures 4-4 and 4-5. CPO products (AcOH and FA) and combustion products (CO and CO2) were formed. The product spectrum indicates that at least four reactions occurred during AcH CPO reaction. The 12 possible reactions that could have occurred during oxidation were presented in Figure 1-6 in Chapter 1. The 0%10%20%30%40%50%60%70%80%100 125 150 175 200 225 250 275AcH Conversion (%)Temperature (oC)2.4V/TiO26.9V/TiO262  selectivity to AcOH increased from 36% at 150 oC to 43.3% at 175 oC with 2.4V/TiO2 while the use of 6.9V/TiO2 caused the selectivity to increase from 42.4% at 150 oC to 62% at 200 oC. Further temperature increases caused the selectivity to AcOH to decrease. The FA selectivity followed a similar trend for both catalysts; maximum FA selectivities of 16.5% and 16.7% occurred at 200 oC over 2.4V/TiO2 and 6.9V/TiO2, respectively.  The increasing selectivity of CPO products was due to the decrease in selectivity of CO2 as temperature was increased from 150 oC to 200 oC. CPO of AcH to AcOH was favored at low temperatures. From 200 to 225 oC, the selectivity of CPO products started to drop significantly and the selectivity of CO increased dramatically. The selectivity of CO at temperatures below 200oC was negligible considering the error bars. As temperature was increased from 225oC to 250oC, there was no further decrease in selectivity of CPO products or increase in selectivity of CO2 within the calculated standard deviations over either catalyst. There is a slight increase in selectivity of CO over 6.9V/TiO2 when temperature was increased from 225oC to 250oC.  The plateau in the selectivity of CO2 at temperatures above 200 oC could be due to increased combustion of AcH, AcOH, FA or CO. The 6.9V/TiO2 catalyst resulted in a much higher maximum selectivity to AcOH (62% at 200 oC) than the 2.4V/TiO2 (43% at 175 oC) therefore the 6.9V/TiO2 catalyst was selected for subsequent experiments.       63   Figure 4- 4 Selectivity of CPO of AcH as a function of temperature (2.4V/TiO2,O2/AcH=1, GHSV≈20000h-1, 5.9 vol% AcH)  0%10%20%30%40%50%60%70%100 125 150 175 200 225 250 275Selectivity (%)Temperature (oC)CO2COAcOHFormic Acid64   Figure 4- 5 Selectivity of CPO of AcH as a function of temperature (6.9V/TiO2,O2/AcH=1, GHSV≈20000h-1, 5.9 vol% AcH)  Figure 4-6 shows the yield of AcH CPO products as a function of temperature for both catalysts. The maximum yield of 20% AcOH achieved using 6.9V/TiO2 at 200 oC was due to the high selectivity of the catalyst at 200 oC. For both catalysts, the yield of AcOH and FA increased as temperature increased from 150 to 200 oC and then decreased when temperature was further increased to 225 oC. Within the calculated standard deviations, FA and AcOH yield did not change when temperature increased from 225 to 250 oC. For 2.4 V/TiO2, the decrease in selectivity to AcOH from 175 to 200 oC was offset by increase in conversion. Therefore, the 0%10%20%30%40%50%60%70%100 125 150 175 200 225 250 275Selectivity (%)Temperature (oC)CO2COAcOHFormic Acid65  yield to AcOH was increased from 175 to 200 oC for 2.4V/TiO2.  Figure 4- 6 Yield of CPO of AcH as a function of temperature (O2/AcH=1, GHSV≈20000h-1, 5.9 vol% AcH)  4.2.2 Effect of O2 concentration  The influence of O2/AcH ratio on CPO of AcH was determined. All experiments in this section were performed at 200oC with the 6.9V/TiO2 catalyst. The total gas volumetric flow rate was kept constant by manipulating He flow rate to compensate for decreased or increased O2 flow 00.050.10.150.20.25100 125 150 175 200 225 250 275YieldTemperature (oC)2.4V/TiO22.4V/TiO26.9V/TiO26.9V/TiO266  rate.   Figure 4-7 presents conversion of AcH during CPO as a function of O2 concentration. Conversion increased with increasing O2 concentration. At O2/AcH=10, the maximum conversion of 63.4% was obtained. Relative to thermal oxidation of AcH at 200oC, increasing the O2/AcH ratio to 10 and utilizing 6.9V/TiO2 catalyst increased the AcH conversion from 11.4% (thermal oxidation, O2/AcH=1) to 63.4%.    Figure 4-7 Conversion of CPO of AcH as a function of O2 concentration (GHSV≈20000 h-1, 6.9V/TiO2, T=200 oC, 6.9V/TiO2) 0%10%20%30%40%50%60%70%0 2 4 6 8 10 12AcH Conversion (%)O2 to AcH molar ratio67  From the literature, the excess oxygen concentration has a positive impact on the selectivity to AcOH due to the lattice oxygen present in the catalyst.29,53–55 Figure 4-8 presents the selectivity of CPO of AcH as a function of O2 concentration. There was a significant increase in selectivity of AcOH as O2/AcH increased from 0.5 to 2 due to a sharp drop in the selectivity of CO. Selectivity of AcOH continued to increase as O2/AcH was increased to 6; maximum observed selectivity of AcOH was 69%. Further increase of O2 concentration resulted in a decrease of selectivity of AcOH, and accompanying increase in CO2 formation. Hence, AcOH was favored to be formed in at moderate values of O2/AcH ratios. Similarly, the selectivity of FA increased as O2/AcH was increased from 0.5 to 6; however, selectivity of FA remained approximately constant (20%) for O2/AcH>6. CO formation, as discussed in section 4.2.1, was favored by higher temperatures and insufficient O2, therefore, increasing oxygen concentrations generally decreased the selectivity of CO. At high O2 concentrations, the selectivity of CO was negligible given the calculated standard deviations. Comparing Figures 4-7 and 4-8 to Figures 4-3 and 4-5 reveals that increasing O2 concentrations increases conversion of AcH and selectivity to AcOH from 32.7% to 53.1% and 62% to 69%, respectively.   68   Figure 4- 8 Selectivity of CPO of AcH as a function of O2 concentration (GHSV≈20000 h-1, 6.9V/TiO2, T=200 oC, 6.9V/TiO2)   Figure 4-9 presents the yield of CPO products as a function of O2 concentration. For both products, the yield increased as O2/AcH increased from 0.5 to 6. The yield of FA remained constant when oxygen concentration further increased while the yield of AcOH decreased due to the decrease in the selectivity of AcOH.   0%10%20%30%40%50%60%70%80%0 2 4 6 8 10 12Selectivity (%)O2 to AcH molar ratioCO2COAcOHFA69   Figure 4- 9  Yield of CPO of AcH as a function of O2 concentration (GHSV≈20000 h-1, 6.9V/TiO2, T=200 oC, 6.9V/TiO2)  4.2.3 Effect of residence time  This section focused on the effect of residence time (RT) on CPO of AcH. Since the highest selectivity to AcOH was at O2/AcH=6 and 200oC with 6.9 V/TiO2, these conditions were maintained for all experiments in this section. The amount of catalyst loaded in the reactor was kept constant and the RT was increased by decreasing the total gas flow rate.  0%5%10%15%20%25%30%35%40%0 2 4 6 8 10 12Yield (%)Oxygen to AcH molar ratioAcOHFA70   Figure 4-10 presents AcH conversion as a function of RT. As expected, AcH conversion increased with increasing RT. Increasing RT from 0.18s to 0.9s increased conversion from 53% to 88%. The increase in AcH conversion with residence time implies that the reaction was not limited by internal mass transfer or reaction equilibrium.   Product selectivity is shown as a function of RT in Figure 4-11. Given the calculated standard deviations, no change in selectivity with RT can be observed. The AcOH and FA selectivities were approximately 70% and 19%, respectively. The insensitivity of product selectivity to RT suggests that the potential reactions occur in parallel. Suprun et al. studied the simultaneous CPO of AcH and propionaldehyde over 6.1V/TiO2. Suprun et al. reported a maximum selectivity to AcOH of 82% at 200 oC, which compares well to the maximum selectivity, 70%, obtained in this study. Despite different experimental conditions on oxygen concentration and GHSV, the higher selectivity of AcOH obtained from literature may also be due to the simultaneous partial oxidation of propionaldehyde.           71   Figure 4-10 Conversion of CPO of AcH as a function of residence time (O2/AcH=6, T=200 oC, 5.9 vol% AcH, 6.9V/TiO2)   Figure 4- 11 Selectivity of CPO of AcH as a function of residence time (O2/AcH=6, T=200 oC, 5.9 vol% AcH, 6.9V/TiO2) 0%10%20%30%40%50%60%70%80%90%100%0 0.2 0.4 0.6 0.8 1AcH Conversion (%)Residence time, (s)0%10%20%30%40%50%60%70%80%90%0 0.2 0.4 0.6 0.8 1Selectivity (%)Residence time (s)CO2COAcOHFA72  Figure 4-12 presents the yield of AcOH and FA at different RT. The yield of FA remained essentially constant (12%) with increasing RT due to low, constant selectivity of FA.  Although selectivity to AcOH was constant with respect to RT, the yield of AcOH increased with RT. This indicates that the increase in conversion of AcH was primarily due to increased production of AcOH. The maximum yield of AcOH was approximately 66% at RT=0.9s.    Figure 4- 12 Yield of CPO of AcH as a function of residence time (O2/AcH=6, T=200 oC, 5.9 vol% AcH, 6.9V/TiO2)     0%10%20%30%40%50%60%70%80%0 0.2 0.4 0.6 0.8 1Yield (%)Residence time (s)AcOHFA73  4.3 CPO of AcH: rate constant and Ea  Given the complexity of potential reactions that could occur in the course of CPO of AcH and the available data, it is not feasible to determine the true reaction mechanism. The rate constant calculated in this section treated CPO of AcH as an overall reaction and therefore, the values of rate constant and Ea derived in this section are an overall rate constant and Ea.  The overall reaction was assumed to be a 1st order reaction which depended only on AcH concentration because it is lattice oxygen (not O2 or disassociated O) that played a key role in catalytic oxidation reaction with for metal oxide type catalysts.53–55 Therefore, combining mole balance of PBR (Equation 4-1), rate law (Equation 4-2) and stoichiometry relation (Equation 4-3) and assuming constant total gas flow rate, pressure, and temperature, Equation 4-4 is obtained for 𝑘𝐴.   dX𝐴dW=−𝑟𝐴𝐹𝐴𝑂                                          (4-1) −𝑟𝐴 = 𝑘𝐴𝐶𝐴                                        (4-2) ?̇? = 𝑉?̇?(1 + 𝜀𝑋𝐴)𝑃𝑃𝑂𝑇𝑂𝑇                                (4-3) 𝑘𝐴 =𝑉𝑂𝑊̇ln (11−𝑋𝐴)                                    (4-4) 𝑋𝐴: conversion of AcH, dimensionless W: catalyst weight, g -rA: CPO of AcH overall reaction rate expression, mol.g catalyst-1.min-1  FAO: initial molar flow rate of AcH, mol/min 𝑘𝐴: overall rate constant of AcH, cm3 g catalyst-1.min-1 CA: concentration of AcH, mol/cm3 74  ?̇?: total volumetric flow rate after reaction, cm3/min 𝑉?̇?: total volumetric flow rate at inlet, cm3/min 𝜀: fraction change in volume per moles of AcH reacted resulting from the change in total number of moles, dimensionless P: reaction pressure, atm T: reaction temperature, K PO: inlet pressure of the system, atm TO: inlet temperature of the system, K  Table 4-3 summarizes the overall rate constant of CPO of AcH using Equation 4-4. The overall 𝑘𝐴 increases with temperature as expected. The overall Ea was calculated using the linearized  Arrhenius law as shown in Figure 4-13; a good fit was obtained with R2≈0.99.  Table 4- 2 CPO of AcH overall rate constant and Ea, 6.9V/TiO2 Temperature (oC) CPO, 𝑘𝐴 (cm3.g catalyst-1.min-1) 150 310 175 625 200 1030 225 2058 250 3384 Ea (kJ/mol) 43.9  75   Figure 4-13 AcH CPO activation energy data fitting at O2/AcH=1, 150 to 250 oC, 5.9 vol% AcH, 6.9V/TiO2, 1st order assumption, R2≈0.99  4.4. Catalytic partial oxidation of mixtures of acetic acid and acetaldehyde  The CPO of mixtures of AcOH and AcH was conducted at the optimal conditions determined for the CPO of AcH: O2/AcH=6, T=200 oC, 6.9V/TiO2, RT=0.18s. According to Table 1-2, the aldehyde and acids group compounds in pyrolysis oil account for 3-18 wt.% and 2-27 wt.% 55.566.577.588.50.0018 0.0019 0.002 0.0021 0.0022 0.0023 0.0024ln (k A), (cm3.g catalyst-1.min-1)1/T, (1/K)76  respectively; this corresponds to a ratio of AcH/(AcH+AcOH) of 40 to 60%. Therefore, in this study experiments were conducted by varying AcH/(AcH+AcOH) from 20 to 80 wt.%. Given the complexity of CPO of AcH, the refractory nature of AcOH, and the insignificant O2 effect on CPO of AcOH, it was assumed that the conversion of AcOH would be equal to 4.5%, the conversion observed at 200 oC and O2/AcOH=6 (Appendix D.2). In addition, it was assumed that the CPO of AcOH only produced CO2 as reported in Appendix D.2. The conversion and selectivity of AcH as a function of AcH/(AcH+AcOH) are presented in Figure 4-14 and Figure 4-15, respectively. From Figure 4-14 it is clear that conversion of AcH is approximately 51% and independent of AcH/(AcH+AcOH) in the range tested. The conversion of pure AcH during CPO at the same conditions was 53% (Figure 4-7); the difference is negligible given the calculated standard deviations. The selectivity of each oxidation product remained constant with respect to AcH/(AcH+AcOH) ratio. Comparison of Figure 4-15 with Figure 4-8 at the same condition reveals that the selectivity of CO and FA are unchanged. However, a slightly increase of 1% in CO2 selectivity was found in the mixture reaction, and consequently, the selectivity to AcOH was found to decrease by 1%. The reason for the slight change in CO2 and AcOH selectivity may due to increased CO2 formation from CPO of AcOH. Overall, the presence of AcOH in solution with AcH solution did not significantly influence the CPO of AcH as AcOH is a relatively refractory compound, and the reverse reaction converting AcOH to AcH is difficult to achieve at the experimental conditions.   77   Figure 4- 14 Conversion of CPO of mixture as a function of AcH to (AcH+AcOH) mass ratio (T=200 oC, O2/AcH=6, RT=0.18s, 6.9V/TiO2)  Figure 4- 15  Selectivity of CPO of AcH and AcOH mixture at different AcH to (AcH+AcOH) mass ratio (T=200 oC, O2/AcH=6, RT=0.18s, 6.9V/TiO2) 30%35%40%45%50%55%0% 20% 40% 60% 80% 100%AcH Conversion (%)AcH/(AcH+AcOH) mass ratio0%10%20%30%40%50%60%70%80%0% 20% 40% 60% 80% 100%Selectivity (%)AcH/(AcH+AcOH) ratioSelectivity of AcOHselectivity of FAselectivity of CO2selectivity of CO78  Figure 4-16 presents the yield of the CPO of the mixture as a function of AcH concentration. The yield of each product remained constant as conversion and selectivity were also constant with respect to concentration. Comparison of Figure 4-16 to Figure 4-9 reveals that the yield to FA and AcOH did not change when AcH was mixed with AcOH.    Figure 4- 16 Yield of CPO of AcH and AcOH mixture at different AcH to (AcH+AcOH) mass ratio (T=200 oC, O2/AcH=6, RT=0.18s, 6.9V/TiO2)    0%5%10%15%20%25%30%35%40%0% 10% 20% 30% 40% 50% 60% 70% 80% 90%YieldAcH/(AcH+AcOH) ratioYield:AcOHYield of FACO yieldCO2 yield79  Chapter 5. Conclusions and recommendations  5.1 Conclusions  The use of pyrolysis oil as a fuel has been limited by its high oxygen content. Significant research has been devoted to reducing the high oxygen content but has encountered substantial challenges, such as high-pressure equipment, catalyst coking, and deactivation. Partial oxidation of pyrolysis oil to value added chemicals may be feasible and may improve the project economics of pyrolysis. There is little research on partial oxidation of pyrolysis oil to value added chemicals. As pyrolysis oil is inherently a complex mixture containing several hundred organic compounds, AcOH and AcH were selected as model compounds. The aim of the study was to determine the feasibility of chemical production through partial oxidation by assessing the oxidation of AcH to AcOH.  A fixed bed reactor was refurbished to perform experiments; the liquid and gas products were analyzed by HPLC and GC, respectively. Incipient wetness impregnation was used to prepare V/TiO2 catalysts using precursor vanadyl oxalate. Results from BET analysis showed that both catalysts had a relatively large surface area, approximately 100 m2/g with primarily mesopores. Comparison of catalyst pore volume with pore volume of the support implied a uniform dispersion of particles onto catalyst surface. However, the XRD analysis only detected the crystalline phase of the support, TiO2. High oxidation state of V, V2O5, was confirmed from further XPS analysis.   Both thermal oxidation and CPO of AcOH and AcH were examined at a range of conditions. For thermal oxidation of AcOH, it was found that the conversion of AcOH increased with increasing 80  temperature and O2 concentrations. Moreover, the conversion of AcOH was low with maximum conversion of 6% achieved at 350 oC and O2/AcOH=1. The low conversion of AcOH is beneficial as AcOH is the desired product. In contrast to the refractory nature of AcOH, AcH was more reactive. Conversions of 40% and 20% were achieved at 350 oC for O2/AcH=1 and O2/AcH=0.5, respectively. However, nearly 100% selectivity to CO2 indicated that both AcOH and AcH undergo complete oxidation even at low O2 concentration. Hence, partial oxidation with a catalyst is necessary to produce AcOH. Rate constant and Ea of AcH thermal oxidation were calculated through two different assumptions. By linearizing Arrhenius law and fitting the data, the 1st order assumption gave a slightly better curve fitting with R2≈0.99 compared to the 2nd order assumption which yielded R2 ≈0.98. The activation energies for 1st order assumption and 2nd order assumption were calculated at 47.1±0.55 and 55.2±0.6 kJ/mol, respectively. Ultimately, it was not possible to produce AcOH from AcH via thermal oxidation; a catalyst was required.  CPO of AcOH and AcH was performed using 0.2g 6.9V/TiO2 catalyst mixed with 1g SiC. Control experiments with only TiO2 and SiC verified their inert nature. The maximum conversion of AcOH by CPO increased to 5% at 250oC in comparison to conversion of AcOH by thermal oxidation of 1.5% at 250oC. CPO conversion of AcOH exhibited the same trends as observed for thermal oxidation.  CPO of AcH was tested using two catalysts, 2.4V/TiO2 and 6.9V/TiO2 at 150 to 250 oC. Generally, conversion of AcH increased with increasing temperature. Both catalysts produced deep oxidation products (CO2 and CO) and partial oxidation products (AcOH and FA). The 6.9V/TiO2 catalyst gave higher conversion compared to the 2.4V/TiO2 catalyst. A maximum of 62% selectivity to AcOH by 6.9V/TiO2 catalyst was observed at 200 oC while only 43% selectivity to AcOH was obtained with the 2.4V/TiO2 catalyst. The difference was due to the reduction in CO2 formation when using the 6.9V/TiO2 catalyst.  81   The effect of O2/AcH ratio on CPO of AcH was tested using the 6.9V/TiO2 catalyst at 200 oC.  Maximum conversion of 63% was obtained at the highest O2/AcH ratio. The highest selectivity to AcOH, 69%, was achieved at O2/AcH=6. It was also shown that CO selectivity was greater at low O2 concentrations and decreased sharply when O2 content increased. CO2 selectivity tended to increase when O2/AcH ratio was high (>6).   Further experiments examined the effect of RT on CPO of AcH at O2/AcH=6. Increasing RT did increase the conversion of AcH. A maximum of 88% conversion was achieved at RT=0.9s. The increase in conversion with RT implied the reactions occurred in the kinetic regime. The selectivity to all reaction products remained nearly constant given the calculated standard deviations indicating the potential reactions might be parallel. By manipulating the metal loading, temperature, O2 concentration and RT, CPO conversion of AcH increased from 8% to 88% and selectivity to AcOH increased from 36% to 70%. Compared with thermal oxidation, the selectivity to AcOH increased from 0% to 70%.    Given the complexity of potential reactions that could occur, only an overall rate constant was calculated using a 1st order assumption which assumed the rate only depended on the concentration of AcH. The concentration of O2 was excluded from the rate expression because in many catalytic oxidation reactions only lattice oxygen participates in the reaction. The curve fitting showed a fairly good fit with R2> 0.99; the overall activation energy was determined to be 43.9 kJ/mol.  The CPO of AcH to AcOH is feasible at the optimal condition investigated in this thesis as the maximum selectivity to AcOH was around 70%. In order to explore the viability of partial oxidation of pyrolysis oil, model compounds with other representative functional groups will 82  need to be studied. 5.2 Recommendations.  The exact reaction mechanism is not clear in this study. Multiple experiments in which O2 concentration and temperature are simultaneously varied are needed in order to assess the rate constant and activation energy of proposed reaction mechanisms.  In addition, different structures of V/TiO2 catalysts may affect the oxidation performance of AcH, and should be considered in the future work. For example, monolayer and. crystallized vanadium oxide catalysts showed different selectivities to AcOH during the oxidation of ethanol.  Finally, as pyrolysis oil is a complex mixture, more model compounds must be tested in order to realize the overall partial oxidation of pyrolysis oil, such as alcohols and ketones, which can also be partial oxidized to produce carboxylic acid. In addition, compounds with two or more functional groups, such as glycolaldehyde and guaiacol, should be considered as well. However, the carbon number of the model compounds should be less than 8 due to the proposed partial condensation in the envisioned process.  Ultimately, real pyrolysis oil should be adopted to perform the partial oxidation experiment.        83  References  1. Kruger, J. S. et al. Effect of functional groups on autothermal partial oxidation of bio-oil . Part 1 : role of catalyst surface and molecular oxygen. Energy & Fuels 25, 3157–3171 (2011). 2. Vispute, T. Pyrolysis Oils: characterization, stability analysis, and catalytic upgrading to Fuels and Chemicals. 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( Accessed October 26, 2016)  88  Appendix A: Calibration curves and chromatography elution times  A.1 Mass flow controller calibration  Two mass flow controllers (MFC, Omega) were used to control the flow rate of O2 and He. Each MFC was calibrated for a broad range of flow rates. To calibrate the He flow rate, the exit gas line was connected to a burette. A small amount of water was introduced into the burette, and the flow rate of He was set using the MFC. After waiting approximately 30s, a stopwatch was used to record the time for a bubble to travel specific volume (e.g. 20 cm3) in the burette. The He flow rate was then determined by dividing the volume traveled by the He bubble to the recorded time. Then Equation 2-1 was applied to calculate the standard gas flow rate of helium. Each measurement was repeated at least five times and an average was taken as the final value. Finally, the standard gas flow rate of helium was plotted against the MFC set flow rate. The He MFC calibration curve is presented in Figure A-1. O2 calibration was done following the same method, and the calibration curve is shown in Figure A-2. ?̇?𝐻𝑒,𝑆𝑇𝑃,𝑀 =?̇?𝑓𝑖𝑥,20𝑡𝑎𝑣𝑔× 60 ×𝑇𝑆𝑇𝐷𝑇𝑁𝑂𝑅                                       (2-1)  89   Figure A- 1 He calibration curve for MFC  Figure A- 2 O2 calibration curve for MFC 0501001502002503003500.00 100.00 200.00 300.00 400.00 500.00MFC set flow rate (cc/min)Measured flow rate at standard condition (cc/min)051015202530354045500.00 10.00 20.00 30.00 40.00 50.00Setup flow rate (cc/min)Measured flow rate (cc/min)90  A.2 Gas chromatography calibration and gas products elution time  The calibration curve for CO and CO2 was obtained by varying concentration and observing response area from GC. Figure A-3 and Figure A-4 depict the calibration curves for CO and CO2, respectively.   Figure A- 3 GC calibration curve for CO, TCD   0.0%0.5%1.0%1.5%2.0%2.5%3.0%0 50000 100000 150000 200000 250000Concentration (mol fraction)Area91   Figure A- 4 GC calibration curve for CO2, TCD  The elution time of each gas for GC is summarized in Table A-1  Table A- 1 Elution time of AcH, CO and CO2 Gas species Elution time (min) Detector AcH 13.1 FID CO 9.2 TCD CO2 23.1 TCD    0.0%0.5%1.0%1.5%2.0%2.5%3.0%0 50000 100000 150000 200000 250000Concentration (mol fraction)Area92  A.3 HPLC calibration and liquid elution time  The calibration curves for AcH and FA were made by preparing calibration standards at varying concentrations and observing the HPLC response. The preparation method was discussed in Chapter 2. Figure A-5 and Figure A-6 present the calibration curves for AcH and FA, respectively.   Figure A- 5 HPLC calibration curve for AcH, RI detector  0200040006000800010000120000 100000 200000 300000 400000 500000Concetration (ppm)Area93   Figure A- 6 HPLC calibration curve for FA, RI detector Table A-2 summarizes the elution times of AcH, AcOH, and FA using the method discussed in Chapter 2.  Table A- 2 HPLC elution time for AcH, AcOH, and FA Liquid species Elution time (min) Detector AcH 18.4 RI AcOH 15.3 RI FA 14.1 RI    0200400600800100012000 10000 20000 30000 40000Concentration (ppm)Area94  Appendix B: Catalyst characterization  B.1: BET  The surface area, pore volume and pore size of mesoporous material were determined by BET analysis with N2 adsorption at 77K. The amount of N2 absorption was measured volumetrically by the BET unit. BET theory assumes the following: 1. Physical adsorption of gas molecules on a solid in layers is infinite; 2. No interactions between adsorption layers; 3. Langmuir theory can be applied to each adsorption layer. The linearized form of the BET is: 𝑃𝑉(𝑃𝑜−𝑃)=1𝐶𝑉𝑚+𝐶−1𝐶𝑉𝑚(𝑃𝑃𝑜)                                       B-1 where P and Po are partial and saturation pressure of N2, respectively. V is the volume of adsorbed gas and Vm is the volume of adsorbed gas for monolayer coverage. In the BET plot, 𝑃𝑉(𝑃𝑜−𝑃) is plotted as a function of 𝑃𝑃𝑜 for 𝑃𝑃𝑜< 0.3 (linear regime of Equation B-1). The slope and the intercept are then used to determine Vm and C by following equation: 𝑉𝑚= 1𝑆𝑙𝑜𝑝𝑒+𝑖𝑛𝑡𝑒𝑟𝑐𝑒𝑝𝑡                                          B-2 C= 1+𝑠𝑙𝑜𝑝𝑒𝑖𝑛𝑡𝑒𝑟𝑐𝑒𝑝𝑡                                              B-3 The specific surface area (SBET) is then obtained by Equation B-4 𝑆𝐵𝐸𝑇 =𝑉𝑚𝑠𝑁𝐴𝑉𝑜𝑎                                               B-4 where s is cross-sectional area of a single molecule of N2 (16.2 Å2),𝑁𝐴 is Avogadro constant, and 𝑉𝑜 is the molar volume of N2. Figure B-1 displays the summary report of BET analysis for 6.9 V/TiO2. Figure B-2 demonstrate the N2 adsorption and desorption isotherm, and Figure B-3 95  shows the pore size distribution of the 6.9V/TiO2 catalyst.  Figure B- 1 BET summary report for 6.9V/TiO2   96   Figure B- 2 Isotherm linear plot for 6.9V/TiO2   97   Figure B- 3 Pore size distribution for 6.9V/TiO2  B.2 XRD  Bulk crystalline phases in catalysts can be identified by X-ray diffraction analysis (XRD) which includes the structure of materials, crystallite size, and degree of crystallinity. Bragg’s law (Equation B-5) describes the distance between two different planes when the material diffracts the X-ray beam.   nλ = 2dsinθ                                               B-5 98  where n is the order of the diffracted beam, λ is the X-ray wavelength; θ is the angle of reflection, and d is the distance between two planes of atoms (d-spacing). The d-spacing can be obtained from knowledge of θ and λ. The peak diagram is then compared with a standard database to identify the material. Figure B-4 shows the peak diagram of XRD analysis, and only TiO2 was observed after comparing with a standard database.   Figure B- 4 XRD peak diagram for 6.9V/TiO2  B.3 ICP-MS  Figure B-5 shows a report for ICP-MS for a nominal V loading of 10%, the result showed a 6.9 wt.% of V loading on the catalyst surface. 99   Figure B- 5 ICP-MS report of actual vanadium for a nominal 10 wt.% V loading  B.4 XPS  X-ray photoelectron spectroscopy is based on photoelectric effect, and it is used to measure the oxidation state of the elements. In this technique, a photon of energy, hν, is absorbed by an atom so that a core electron with a binding energy, Eb, is ejected with a specific amount of kinetic energy of Ek. Then the kinetic energy, Ek, can be calculated as follows: 100  Ek=hν-Eb By measuring Ek and having hν, the binding energy (Eb) can be determined. The electron emitted from each compound has a specific binding energy. Therefore, the value of binding energy was used to determine the oxidation state of the atom. For example, Figure B-6 demonstrates the XPS spectrum of the 6.9V/TiO2 catalyst. A binding energy around 517.5 eV for V 2P3/2 indicated the oxidation state of V is V2O5.    Figure B- 6 XPS spectrum for 6.9V/TiO2 catalyst.  2400026000280003000032000340003600038000512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528Response AreaBinding Energy (eV)V 2P1/2V 2P3/2O(S)101  Appendix C: Sample calculations and equation derivation  C.1 Conversion, selectivity, and yield  The conversion (X), selectivity (S), and yield (Y) of a specific reactant or product can be determined by the following equations for a packed bed reactor:  𝑋𝑖 =𝐹𝑖,𝑖𝑛−𝐹𝑖,𝑜𝑢𝑡𝐹𝑖,𝑖𝑛                                          C-1 𝐹𝑖,𝑜𝑢𝑡 = 𝐹𝑖,𝑜𝑢𝑡,𝑙𝑖𝑞𝑢𝑖𝑑 + 𝐹𝑖,𝑜𝑢𝑡,𝑔𝑎𝑠             C-2 𝑆𝑗 =𝐹𝑗𝐹𝑡𝑜𝑡𝑎𝑙 𝑝𝑟𝑜𝑑𝑢𝑐𝑡𝑠             C-3 𝑌𝑗 = 𝑋𝑖 ∗ 𝑆𝑗                 C-4 𝐹𝑖,𝑜𝑢𝑡,𝑙𝑖𝑞𝑢𝑖𝑑 =𝑁𝑖,𝑙𝑖𝑞𝑢𝑖𝑑𝑡                                     C-5 where i refers to reactant (AcH or AcOH), j relates to products (CO, CO2, AcOH or FA). F is flow rate in mol/min. In and out refer to the inlet and outlet condition and t refers to total experiment time. 𝑁𝑖 is moles of i.         102  Table C- 1 Parameters used to calculate conversion, selectivity, and yield of CPO of AcOH at T=250 oC, O2/AcH=1, 6.9V/TiO2, RT=0.18s Parameter Value 𝐹𝐴𝑐𝑂𝐻,𝑖𝑛 (mol/min) 6.79E-4 𝐹𝐴𝑐𝑂𝐻,𝑜𝑢𝑡,𝑔𝑎𝑠 (cc/min) 0 𝐹𝐴𝑐𝑂𝐻,𝑜𝑢𝑡,𝑙𝑖𝑞𝑢𝑖𝑑 (mol/min) 6.45E-4 t (min) 210 𝑁𝐴𝑐𝑂𝐻 (mol) 0.1355 𝐹𝑡𝑜𝑡𝑎𝑙 𝑝𝑟𝑜𝑑𝑢𝑐𝑡𝑠 (mol/min) 6.51E-4 AcOH conversion (%) Selectivity to CO2 (%) Yield to CO2 (%) 4.96 99 4.91   C.2 Catalyst preparation  A sample calculation for a nominal 10 wt.% V supported by TiO2 is as follows:  Total catalyst weight: 5 g Mass of vanadium = 5g × 10% = 0.5g ; Mass of V2O5= 0.5g ×181.88𝑔𝑚𝑜𝑙 𝑉2𝑂550.9𝑔𝑚𝑜𝑙 𝑉×2= 0.8926g Total mass of precursor needed (C2O5V) =0.5g V ×155𝑔𝑚𝑜𝑙 𝐶2𝑂5𝑉 50.9𝑔𝑚𝑜𝑙 𝑉≈ 1.523𝑔 Mass of TiO2=5 − 0.8926 = 4.1074g Pore volume of TiO2: 0.38 cm3/g Maximum volume of solution to impregnate TiO2=4.1074g ×0.38𝑐𝑚3𝑔≈ 1.561𝑐𝑚3  103  C.3 Internal mass transfer  In order to calculate the internal effectiveness factor, η, at 250 oC for CPO of AcH by Equation 2-1 to 2-3, the rate constant unit at 250oC must be modified to a unit of s-1. To do so, kA is divided by catalyst bed density (ρb) and then the unit conversion factor from minute to second is applied. Table C-3 summarizes the values used to calculate η. The value for 𝜑𝑃, 𝜎𝐶, and 𝜏̅ were obtained from the book of Elements of Reaction Engineering.51 𝐷𝑝 is the average value for the catalyst size (106-180 μm). ρb was obtained by using the weight of catalyst used (0.2g) divided by the catalyst bed volume (≈0.9 cm3). The results showed η≈1. Hence the internal mass transfer was not a rate limiting step for the reaction  Table C- 2 Parameter value used to calculate internal effectiveness factor Parameter Value 𝐷𝐴 at T=250 oC (m2/s)56 3.57E-556 𝜑𝑃 (dimensionless) 51 0.4 𝜎𝐶 (dimensionless) 51 0.8 𝜏̅ (dimensionless) 51 3 𝐷𝑝 (m) 1.42E-4 𝐷𝑒 (m2/s) 3.808E-6 𝑘𝐴 (cm3.g catalyst-1.min-1) at T=250 oC 3384 ρb (g catalyst/cm3) 0.22 𝑘𝐴 (s-1) 12.5 ɸ (dimensionless) 0.26  104  C.4 Equation derivation  Chapter 3 assumed a 1st order and 2nd rate expressions for the thermal oxidation of AcH. For the 1st order assumption at O2/AcH=1, the ultimate Equation 3-4 to calculate rate constant of AcH was derived as follows:  dX𝐵dV=−𝑟𝐵𝐹𝐵𝑂                                           (3-1) −𝑟𝐵 = 𝑘𝐵𝐶𝐵                                         (3-2) ?̇? = 𝑉?̇?(1 + 𝜀𝑋𝐵)𝑃𝑃𝑂𝑇𝑂𝑇                                 (3-3) 𝑘𝐵 =𝑉𝑂𝑉̇ln (11−𝑋𝐵)                                     (3-4) 𝑘𝐴 = 0.4𝑘𝐵                                          (3-8)  Since the inlet concentration of O2 is small (≈5%),𝜀 ≈0. By assuming constant pressure and temperature, Equation 3-3 yielded ?̇? = 𝑉?̇?. Substituting Equation 3-2 into Equation 3-1 yields:  dX𝐵dV=𝑘𝐵𝐶𝐵𝐹𝐵𝑂=𝑘𝐵𝐶𝐵𝑂(1 − X𝐵)𝐹𝐵𝑂  Separating variables and integrating on both sides, the equation becomes: ∫11 − 𝑋𝐵𝑑𝑋𝐵 = ∫𝑘𝐴𝐶𝐴𝑂𝐹𝐴𝑂𝑑𝑉𝑉0𝑋𝐵0 Solving the above equation yields Equation 3-4. The combustion reaction of AcH needs 2.5 moles of O2 as every 1 mole of AcH reacted. (See Chapter 3. Reaction 3) Therefore, 𝑘𝐴 can be calculated by Equation 3-8. 105   Using the 2nd order assumption at O2/AcH=1, Equation 3-2 changes to the following: −𝑟𝐵 = 𝑘𝐵𝐶𝐵𝐶𝐴 = 𝑘𝐵𝐶𝐵𝑂(1 − X𝐵)𝐶𝐴𝑂(1 − 0.4X𝐵) Substituting the above equation into Equation 3-1 yields: dX𝐵dV=𝑘𝐵𝐶𝐵𝑂(1 − X𝐵)𝐶𝐴𝑂(1 − 0.4X𝐵)𝐹𝐵𝑂 Separating variables yields: ∫1(1 − X𝐵)(1 − 0.4X𝐵)𝑑𝑋𝐵 = ∫𝑘𝐵𝐶𝐴𝑂𝐶𝐵𝑂𝐹𝐵𝑂𝑑𝑉𝑉0X𝐵0 Solving the above equation yields: 𝑘𝐵 =53𝑉𝑂2𝑉𝐹𝐴𝑂[̇ln(0.4) − ln(𝑋𝐵 − 1𝑋𝐵 − 2.5)] With V≈9.1 cm3 for reactor volume of thermal oxidation and 𝐹𝐴𝑂 ≈7.88*10-4 mol/min, 𝑘𝐵 can be calculated, and then 𝑘𝐴 can be obtained from Equation 3-8.             106  Appendix D: Supplementary experiments  D.1 Thermal oxidation of AcH  The thermal oxidation of AcH was further tested at T=120 oC using lower ratios of O2/AcH. Table D-1 summarized the additional experiments for AcH thermal oxidation.  The composition of the liquid phase products was tested by HPLC and no AcOH was detected thus demonstrating the necessity of CPO of AcH.  Table D- 1 AcH thermal oxidation at T=120 oC  O2/AcH ratio Mean residence time (s) AcOH detected in liquid product 0.5 1.8 No 0.4 1.8 No 0.3 1.8 No 0.25 1.8 No 0.125 1.8 No 0.125 3.6 No       107  D.2 CPO of AcOH  The CPO of AcOH was also tested at the optimal CPO condition for AcH (O2/AcOH=6, T=200 oC, 6.9V/TiO2).  AcOH conversion was around 4.5% and the selectivity to CO2 was around 99.5%. In comparison, conversion during CPO of AcOH at T=200 oC and O2/AcOH=1 with 6.9V/TiO2 was 3.9%, 0.6% less. Hence, O2 concentration does not significantly influence AcOH conversion and selectivity.                  108  Appendix E: Experimental error analysis  The experimental error may be due to limitations of analytical apparatus, the operation for conducting experiments, and chemical impurities. For this study, all chemicals were of at least HPLC grade. The largest standard deviation for conversion was around ±3.6%, and the biggest difference in carbon balance was around 3.2 % for AcOH oxidation and 13% for AcH oxidation, respectively. The larger error from AcH oxidation was primarily due to its volatile nature which might result in a mass loss of AcH when preparing the solution.   

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