Applied Science, Faculty of
Chemical and Biological Engineering, Department of
DSpace
UBCV
Kim, Young Yoon
Master of Applied Science - MASc
University of British Columbia
Biomass gasification converts the carbon and hydrogen in biomass feedstock into useful syngas. While there are notable commercial biomass gasification projects around the world, one of the major roadblocks in further technological advancement is the formation of the byproduct, biomass tar. Tar is a mixture of heavy condensable hydrocarbons that drops out from the gas as viscous liquid at lower temperatures. It easily condenses on cooler surfaces and plugs downstream equipment. It can also form aerosols and further polymerize into more complex structures. Catalytic tar reduction can reduce the tar in syngas by decomposing it into additional syngas, thereby improving the overall efficiency of the gasification process. Bauxite residue, an industrial waste rich in iron content, was investigated as an alternative catalyst for reducing biomass tars in the syngas generated from the Bioenergy Research Demonstration Facility at the University of British Columbia. An experimental unit was designed and commissioned to evaluate the catalytic activity of the bauxite residue. The bauxite residue catalyst was prepared and tested as untreated and as pretreated with calcination and pre-reduction processes. The pretreated bauxite residue was highly effective in reducing the biomass tars in comparison to the untreated catalyst. However, the spent-catalyst analysis revealed that the iron species oxidized back in the syngas environment over the duration of the experiment, demonstrating that a reducing environment is critical to maintain the catalytic activity of the bauxite residue.
THE EFFECTIVENESS OF BAUXITE RESIDUE IN REDUCING BIOMASS GASIFICATION TARS by Young Yoon Kim B.A.Sc., The University of British Columbia, 2014 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 2019 © Young Yoon Kim, 2019 ii The following individuals certify that they have read, and recommend to the Faculty of Graduate and Postdoctoral Studies for acceptance, a thesis/dissertation entitled: The effectiveness of bauxite residue in reducing biomass gasification tars submitted by Young Yoon Kim in partial fulfillment of the requirements for the degree of Master of Applied Science in Chemical and Biological Engineering Examining Committee: Naoko Ellis, Chemical and Biological Engineering Co-supervisor Xiaotao Bi, Chemical and Biological Engineering Co-supervisor Paul Watkinson, Chemical and Biological Engineering Supervisory Committee Member Robert Legros, Chemical Engineering, Polytechnique Montréal Supervisory Committee Member iii Abstract Biomass gasification converts the carbon and hydrogen in biomass feedstock into useful syngas. While there are notable commercial biomass gasification projects around the world, one of the major roadblocks in further technological advancement is the formation of the byproduct, biomass tar. Tar is a mixture of heavy condensable hydrocarbons that drops out from the gas as viscous liquid at lower temperatures. It easily condenses on cooler surfaces and plugs downstream equipment. It can also form aerosols and further polymerize into more complex structures. Catalytic tar reduction can reduce the tar in syngas by decomposing it into additional syngas, thereby improving the overall efficiency of the gasification process. Bauxite residue, an industrial waste rich in iron content, was investigated as an alternative catalyst for reducing biomass tars in the syngas generated from the Bioenergy Research Demonstration Facility at the University of British Columbia. An experimental unit was designed and commissioned to evaluate the catalytic activity of the bauxite residue. The bauxite residue catalyst was prepared and tested as untreated and as pretreated with calcination and pre-reduction processes. The pretreated bauxite residue was highly effective in reducing the biomass tars in comparison to the untreated catalyst. However, the spent-catalyst analysis revealed that the iron species oxidized back in the syngas environment over the duration of the experiment, demonstrating that a reducing environment is critical to maintain the catalytic activity of the bauxite residue. iv Lay Summary Biomass is one of the renewable energy sources that will play a key role in the global energy transition. Biomass gasification can convert waste wood into synthesis gas, or syngas that can be used to generate heat and electricity. However, the biomass syngas contains many contaminants that need to be removed prior to applications. One of the major contaminants is the biomass tar. Tar can cause severe blockage in downstream equipment and cause operational problems. Among the various syngas clean-up methods, catalytic tar reduction is deemed advantageous over others as it uses less energy, does not generate waste-water, and can improve the overall efficiency of the gasification process. In this research project, bauxite residue, a waste from mining industry, was investigated as an alternative catalyst material for tar removal from the syngas produced from the biomass gasification system at the Bioenergy Research Demonstration Facility at the University of British Columbia. v Preface The work presented in this thesis was completed by the author, Young Yoon Kim under the supervision of Professors Naoko Ellis and Xiaotao Bi in the Department of Chemical and Biological Engineering at the University of British Columbia. The experimental unit used in the experiment was designed by the author and modified and built by Doug Yuen, Tobias Donaldson and Serge Milaire at the Department of Chemical and Biological Engineering Workshop. The experimental unit was commissioned and further modified by the author. The pretreated bauxite residue catalyst preparation method presented in Chapter 3 was developed by Dr. Zhiqiang Wu and Bill Cheng of the Tar Cracking Research Group at the Department of Chemical and Biological Engineering. GC-MS results presented in Chapter 4 was completed at the KIST-UBC on-site Biorefinery Laboratory. Catalyst characterization work presented in Chapter 4 was completed at the Electron Microbeam/X-ray Diffraction Facility in the Department of Earth, Ocean and Atmospheric Sciences. Parts of the work presented in the thesis was presented at the 68th Canadian Chemical Engineering Conference on October 31, 2018 in Toronto. Young Yoon Kim prepared the first and the final drafts of the thesis, which was edited by Professors Naoko Ellis and Xiaotao Bi. vi Table of Contents Abstract ......................................................................................................................................... iii Lay Summary ............................................................................................................................... iv Preface .............................................................................................................................................v Table of Contents ......................................................................................................................... vi List of Tables ................................................................................................................................ ix List of Figures ................................................................................................................................. x List of Abbreviations .................................................................................................................. xii Acknowledgements .................................................................................................................... xiii Chapter 1: Introduction ................................................................................................................1 1.1 Climate Change and Energy Transition ............................................................................. 1 1.2 Bioenergy ........................................................................................................................... 2 1.3 Biomass Gasification and Biomass Tar ............................................................................. 4 1.4 Bauxite Residue ................................................................................................................. 6 1.5 UBC Bioenergy Research Demonstration Facility ............................................................ 7 1.6 Objectives .......................................................................................................................... 9 1.7 NSERC CREATE SusSyn ............................................................................................... 10 Chapter 2: Literature Review .....................................................................................................12 2.1 Biomass Gasification ....................................................................................................... 12 2.2 Biomass Tars .................................................................................................................... 14 2.2.1 Definition and Characteristics ................................................................................... 14 2.2.2 Parameters Influencing the Tar Formation ............................................................... 16 2.2.3 Tar Removal Methods ............................................................................................... 23 vii 2.3 Tar Decomposition ........................................................................................................... 25 2.3.1 Tar Decomposition Reactions ................................................................................... 25 2.3.2 Tar Reduction Catalysts ............................................................................................ 26 2.3.3 Catalyst Deactivation ................................................................................................ 30 Chapter 3: Materials and Methods ............................................................................................33 3.1 Bauxite Residue Catalyst ................................................................................................. 33 3.2 Commercial Nickel Catalyst ............................................................................................ 34 3.3 Bioenergy Research Demonstration Facility ................................................................... 35 3.3.1 Biomass Feedstock .................................................................................................... 35 3.3.2 Gasifier ...................................................................................................................... 37 3.3.3 Syngas Characteristics .............................................................................................. 37 3.4 European Tar Sampling Protocol ..................................................................................... 38 3.5 Design and Construction of the Tar Cracking Experimental Unit ................................... 39 3.5.1 Design Considerations .............................................................................................. 40 3.5.2 Detailed Process Description .................................................................................... 42 3.6 Experimental Conditions and Procedure ......................................................................... 48 3.7 Data Analysis ................................................................................................................... 49 3.7.1 GC-FID ..................................................................................................................... 49 3.7.2 GC-MS ...................................................................................................................... 49 3.7.3 XRD .......................................................................................................................... 49 Chapter 4: Results and Discussions ...........................................................................................51 4.1 Experimental Unit Troubleshooting ................................................................................ 51 4.2 Considerations in Working at an Operating Plant ........................................................... 54 viii 4.3 Basis of Tar Removal ....................................................................................................... 55 4.4 BRDF Tars ....................................................................................................................... 56 4.5 Catalyst-blank tests .......................................................................................................... 59 4.6 Nickel Catalyst ................................................................................................................. 63 4.7 Bauxite Residue ............................................................................................................... 64 4.8 Catalyst Deactivation Characteristics .............................................................................. 68 Chapter 5: Conclusion and Recommendations .........................................................................70 Bibliography .................................................................................................................................74 Appendices ....................................................................................................................................84 Appendix A Supplemental Information for the Experimental Unit Design ............................. 84 A.1 Schematics and Photographs of the Experimental Unit .............................................. 84 Appendix B Supplemental Data ................................................................................................ 92 B.1 GC-MS Results ........................................................................................................... 92 B.2 GC-FID Results ........................................................................................................... 95 B.3 XRD Results .............................................................................................................. 104 ix List of Tables Table 2.1 Parameters impacting the syngas quality in biomass gasification ................................ 14 Table 2.2 Tar classification based on molecular weight ............................................................... 15 Table 2.3 Tar classification based on temperature dependence .................................................... 15 Table 2.4 Terminology and definitions for different types of gasifying agents ........................... 21 Table 3.1 Typical composition and parameters of bauxite residue .............................................. 33 Table 3.2 Received biomass feedstock properties at the BRDF ................................................... 36 Table 3.3 Syngas composition at the BRDF ................................................................................. 38 Table 4.1 Components identified in tar samples collected from BRDF gasifier .......................... 57 Table 4.2 BRDF gasifier operating parameters during the sampling period ................................ 59 Table 4.3 Summary of % Tar Reduction results ........................................................................... 67 x List of Figures Figure 1.1 Biomass conversion applications. ................................................................................. 4 Figure 1.2 Tar deposited on the surface of the pipe and fitting at the BRDF ................................. 5 Figure 1.3. Gasifier at the UBC Bioenergy Research Demonstration Facility ............................... 8 Figure 1.4 The Nexterra gasification system at BRDF ................................................................... 8 Figure 2.1 The four main steps during biomass gasification. ....................................................... 12 Figure 2.2 Tar formation at various reaction temperatures ........................................................... 17 Figure 2.3 Chemical structures of cellulose, lignin and hemicellulose. ....................................... 18 Figure 2.4 Schematic of updraft gasifier. ...................................................................................... 22 Figure 2.5 Schematic of downdraft gasifier .................................................................................. 22 Figure 2.6 Primary tar removal method. ....................................................................................... 24 Figure 2.7 Secondary tar removal method. ................................................................................... 25 Figure 3.1 Prepared (a) untreated BR catalyst; and (b) pretreated BR catalyst ............................ 34 Figure 3.2 Fuel receiving and storage area at the BRDF .............................................................. 36 Figure 3.3 BRDF gasifier and oxidizer schematic ........................................................................ 37 Figure 3.4 European Tar Sampling protocol impingement train set-up ....................................... 39 Figure 3.5 Tar Cracking Experimental Unit ................................................................................. 40 Figure 3.6 Plan view of apparatus schematic at the installation location at BRDF ...................... 42 Figure 3.7. BRDF Tar Cracking Experimental Unit process flow diagram ................................. 43 Figure 4.1 Plugged gas sampling tube .......................................................................................... 52 Figure 4.2 Tar maturation sequence .............................................................................................. 58 Figure 4.3 Catalyst blank experiment at 700 °C: (a) before; and (b) after reaction. .................... 60 Figure 4.4 Catalyst blank experiment at 750 °C: (a) before; and (b) after reaction. .................... 60 xi Figure 4.5 PAH formation from phenol precursors ...................................................................... 62 Figure 4.6 Ni-catalyst experiment at 700 °C: (a) before; and (b) after reaction ........................... 63 Figure 4.7 Untreated BR catalyst experiment at 700 °C: (a) before; and (b) after reaction. ........ 65 Figure 4.8 Untreated BR catalyst experiment at 750 °C: (a) before; and (b) after reaction. ........ 66 Figure 4.9 Pretreated BR catalyst experiment at 750 °C: (a) before; and (b) after reaction. ........ 67 xii List of Abbreviations ADES Academic District Energy System BR Bauxite Residue BRDF Bioenergy Research Demonstration Facility CEN European Committee for Standardization (Comité Européen de Normalisation) CHP Combined Heat and Power CREATE Collaborative Research and Training Experience db Dry Basis ER Equivalence Ratio ESP Electrostatic Precipitator FID Flame Ionization Detector GC Gas Chromatography GR Gasifying Ratio HPLC High Performance Liquid Chromatography IPA Isopropyl Alcohol IPCC Intergovernmental Panel on Climate Change KIST Korea Institute of Science and Technology MCWB Moisture Content Wet Basis MS Mass Spectrophotometer NSERC National Sciences and Engineering Research Council of Canada PAH Polycyclic Aromatic Hydrocarbons PEG Polyethylene Glycol SB Steam-to-Biomass Ratio SysSyn Sustainable Synthesis UBC University of British Columbia UN United Nations wb Wet Basis WGS Water-gas Shift XRD X-ray Diffraction xiii Acknowledgements I would like to acknowledge my warmest thanks to my supervisors, Professors Naoko Ellis and Xiaotao Bi for their patience, trust, support, guidance and expertise throughout all stages of the project. I would also like to thank my committee members, Professors Paul Watkinson and Robert Legros for their support and guidance. My deepest appreciation goes out to the brilliant Workshop team of the Department of Chemical and Biological Engineering, Doug Yuen, Tobias Donaldson, Serge Milaire and Graham Liebelt. This project would not have been possible without their help. The appreciation is extended to the departmental staff, especially Ken Wong. The financial support of the CREATE Sustainable Synthesis program funded by the National Sciences and Engineering Research Council of Canada is greatly appreciated. Thanks to Rio Tinto Canada for supplying the bauxite residue for this research project. Many thanks to Jason Rako and the Plant Operators at the Bioenergy Research Demonstration Facility for accommodating the research work and for sharing their knowledge. Nexterra Systems is also thanked for sharing their expertise. Special thanks to the members of the Tar Cracking Research Group, especially Bill Cheng and Dr. Yueqin Song for their help with the catalyst preparation work. Lastly, I would like to thank my family and friends for their unconditional love and support. 1 Chapter 1: Introduction 1.1 Climate Change and Energy Transition One of the most well-known definitions of sustainable development is the “development that meets the needs of the present without compromising the ability of future generations to meet their own needs” from the report Our Common Future by the United Nations’ Brundtland Commission [1]. Regarding climate change, Brundtland mentioned the serious probability of climate change and the needs of corrective action. The report described that at the time, although there was not a way to prove if climate change will occur, waiting to observe significant changes may be too late for any effective countermeasures. Just three decades later, we realize that we already live in the future that Brundtland described. Climate change is now labeled as an “existential threat” to humanity that needs to be dealt with urgency [2]. Activities related to the changing climate are observed throughout the world, in the form of increasing extreme weather events, including tornados, floods, droughts, and heat waves. These abnormalities are observed locally as well, with the worst wildfire on record in British Columbia in 2018 [3]. In October of 2018, the UN Intergovernmental Panel on Climate Change (IPCC) released a Special Report, the Global Warming of 1.5°C. The report marked that by 2017, earth has reached approximately 1°C of global warming above pre-industrial levels and that the warming effects not only resulted in the aforementioned weather activities but also in sea level rise and biodiversity loss. The report further provided an alarming assessment of the projected impacts of the likely continued warming. 2 Climate change and its mitigation is now a topic that is discussed at all levels of governments, institutions, industries, and communities. It is important to realize that not one solution or approach will enable us to mitigate the potentially irreversible consequences of the climate change. The energy transition is one of the many strategies that has the potential to reduce the severity of the warming. Yet, a successful energy transition will allow the world to reduce the greenhouse gas emissions dramatically. Energy transition can mean a variety of activities that can reduce the greenhouse gas emissions. For example, the Government of Canada sees the energy transition in four main pathways: (i) wasting less energy, (ii) switching to clean power, (iii) using more renewable fuels, and (iv) producing cleaner oil and gas [4]. Clearly, collective efforts are required to achieve the transition. 1.2 Bioenergy A key contribution to the energy transition is bioenergy. While whether bioenergy is a “clean” source of energy or not is often debated, it is a form of renewable energy. Renewable energy refers to the energy that is derived from renewable resources that are replenished at the same or faster rate than at which they are consumed [5]. Although the rate of replenishment of bioenergy is slower than other renewable sources such as the solar, wind or hydro, it is replenished in the timeframe of human species as opposed to fossil fuels. The main benefit of bioenergy is the wide range of feedstocks, including waste resources. For instance, forest residues, agricultural residues, wood waste from industrial activities and municipal solid waste can all be utilized to generate bioenergy. Moreover, biomass feedstocks are less location specific and relatively easy 3 to store and transport in comparison to gas and liquid fuels [6]. In addition, countries that are rich in forest and agricultural resources such as Canada can have tremendous benefits from utilizing bioenergy. In fact, bioenergy is the second most significant type of renewable energy in Canada [5]. It should be noted that bioenergy is not emissions free. Nonetheless, it can be considered carbon neutral as the carbon emissions from utilization are captured by photosynthesis during the growth of biomass [7]. Biomass can be converted to various forms of energy, including heat, solid, liquid, and gaseous fuels. The four main conversion methods are: direct combustion, physical conversion, biochemical conversion and thermochemical conversion (Figure 1.1). The main benefit of the thermochemical conversion over the biochemical conversion is the diverse range of feedstock it can utilize. For instance, biochemical conversion is highly selective on the type of feedstock as the fermentation processes require biomass that are rich in starch or sugar [7]. In addition, the rate of conversion for the thermochemical methods is much faster than that of biochemical methods [7]. 4 Figure 1.1 Biomass conversion applications. Reprinted with permission from [7]. Copyright (2016) Elsevier. 1.3 Biomass Gasification and Biomass Tar Gasification is one of the well-established thermochemical conversion technologies. The history of gasification goes back to as far as 1791, although the earlier studies and applications were mainly for coal or fossil fuel residues [8]. Biomass gasification emerged upon uncertainties in oil security and climate concerns in the 2000s [9]. Biomass gasification converts the carbon and hydrogen in biomass feedstock to synthesis gas (or syngas) in the presence of the gasifying agent (air, oxygen, steam or their mixtures) [10]. In comparison to combustion where the products are limited to heat, CO2 and H2O, gasification results in additional CO and H2. Syngas can be utilized to generate heat through direct combustion and electricity using fuel cells, gas turbines, or engines. It can also be used as feedstocks for high-value chemical synthesis [7]. Combined with its ability to accept a wide range of biomass, the potential for the biomass gasification technology is tremendous. 5 While there are notable commercial biomass gasification projects around the world, one of the major roadblocks in further technological advancement is the formation of the byproduct, biomass tar. Tar is a mixture of heavy condensable hydrocarbons that drops out from the gas as a viscous liquid at lower temperatures. It easily condenses on cooler surfaces and plugs downstream equipment. It can also form aerosols and further polymerize into more complex structures [11]. Furthermore, tar can cause rapid catalyst deactivation in downstream catalytic processes such as methanol and Fischer-Tropsch liquid production [12]. Even just for the simple heat generation applications (e.g., syngas combustion for heat), tar residuals in piping and gas monitoring equipment result in frequent maintenance (Figure 1.2). Figure 1.2 Tar deposited on the surface of the pipe and fitting at the BRDF The tar tolerance level for syngas utilization varies with its end-use. For instance, tar concentration of < 10–100 mg/Nm3 is required for internal combustion engines [8]. With typical tar concentration of 0.1–6 g/Nm3 for downdraft gasifiers and 10–100 g/Nm3 for updraft gasifiers, 6 investigating effective means of removing tar is inevitable for advanced syngas utilization [13]. Tar removal methods are categorized as a primary or secondary method, depending on the location of removal [14]. The primary method refers to limiting tar formation or converting tar in the gasification stage (in-situ); whereas, the secondary method (ex-situ) refers to treatment options occurring downstream of the gasifier [15]. The secondary method is further classified as physical removal, thermal cracking, and catalytic conversion. Typical physical tar removal involves wet scrubbing or filtration. However, such processes generate additional liquid or solid waste which results in an additional cost for waste treatment and disposal, as well as a loss of chemical energy in tar [8], [15]. In addition, these processes require significant intermediate heating and cooling steps, decreasing the overall plant efficiency [16]. On the other hand, thermal cracking can decompose tar into additional CO and H2, therefore it may improve the overall efficiency of the gasification plant. However, the thermal conversion process is highly energy intensive as it requires reaction temperatures > 1000 °C and long residence time [15]. With a catalyst, the required reaction temperature can be lowered and the residence time can be shortened. Nevertheless, the viability of catalytic tar removal depends on inexpensiveness, resistance to deactivation and regenerability of the catalyst. 1.4 Bauxite Residue The alternative catalyst investigated for this project is bauxite residue (BR). BR is an alkaline solid waste that is generated as a byproduct from bauxite processing for aluminum production. 7 For example, the production of 1 tonne of alumina generates about 1.5 tonnes of BR [17]. With an annual production of 200 million tonnes, the global inventory of BR reached approximately 4.6 billion tonnes in 2018 [18]. BR has favourable characteristics such as high surface area (20-30 m2/g) and resistance to sintering and poisoning, making it an attractive alternative catalyst [19]. The composition of BR varies with the type and grade of bauxite ore and how it is processed. The major constituent is iron oxide (Fe2O3), which gives BR the brick-red colour and the alternative name, “red mud” [19]. With high iron content, BR has been studied as an attractive alternative iron-based catalyst in various applications [19]. 1.5 UBC Bioenergy Research Demonstration Facility The University of British Columbia’s Bioenergy Research Demonstration Facility (BRDF) located within the Vancouver campus houses a 6 MW thermal energy biomass gasification system (Figure 1.3). As part of the Academic District Energy System (ADES), the gasifier has been in operation since 2012. Established as part of the University’s Campus as a Living Laboratory initiative, the BRDF Project was a first of its kind project in North America [20]. The facility converts waste biomass to generate thermal energy for heating campus buildings. Since commissioning, the gasification system at BRDF has been providing a quarter of the campus heating needs, equivalent to an estimated reduction of 14% of the campus greenhouse gas emissions compared to 2007 emission levels [20]. In addition to providing a successful demonstration of the technology and achieving 8 greenhouse gas emissions reductions, BRDF also yielded successful academics and industry research collaborations. Figure 1.3. Gasifier at the UBC Bioenergy Research Demonstration Facility The gasification system, was designed originally by a Vancouver based company Nexterra Systems to perform in two modes of operation, the Thermal mode and the Demonstration (co-generation) mode as shown in Figure 1.4 [21]. Figure 1.4 The Nexterra gasification system at BRDF [21] 9 In the Thermal mode, biomass is converted to syngas, which in turn, is oxidized completely in a close-by oxidizer to generate heat. The flue gas from the oxidizer is then processed in a boiler to produce steam, which is run through heat exchangers to produce hot water. This process yields 6 MW of thermal energy and it is distributed to campus buildings through the UBC Academic District Energy System (ADES) [20]. The Cogeneration mode enabled syngas utilization in a Combined Heat and Power (CHP) engine coupled with a generator to produce 2 MW of electricity and an additional 2.4 MW of thermal energy through heat recovery [20]. In this process, the syngas from the gasifier was conditioned to a clean syngas prior to running the engine. The conditioning process involved heating the syngas and passing it through the thermal tar cracking unit to reduce tar. The syngas was then cooled back down, then filtered to remove any remaining impurities (i.e., particulates) that would foul the engine. This method was demonstrated for 450 hours of operation prior to a failure in one of the heat exchangers. Unfortunately, the university decided not to repair the unit after an economic evaluation and the Cogeneration mode, along with the biomass dryer, was phased out. The engine is currently utilizing a mix of renewable natural gas, commonly known as biogas (generated through anaerobic digestion and landfill gas capture) and natural gas to produce 5% of the campus electrical energy [22], [23]. 1.6 Objectives The Tar Cracking Group at the Department of Chemical and Biological Engineering at UBC has been researching for a cost-effective, alternative catalyst for catalytic tar reduction. Through bench-top experiments involving naphthalene as a model tar compound under simulated syngas 10 environments, the group has successfully demonstrated the potential for bauxite residue as an iron-based catalyst for catalytic tar reduction [24]. The research objective of this project is to investigate the viability of bauxite residue as an alternative catalyst for reducing real tar from the real syngas produced from the gasification system at the Bioenergy Research Demonstration Facility at the University of British Columbia. The aim of the study is to: i. identify the characteristics of tar produced at BRDF; ii. to investigate the effectiveness of bauxite residue in cracking biomass tar; and iii. to identify the suitable operating window for tar conversion that demonstrates good tar conversion performance and experience minimal catalyst deactivation. The following tasks were completed to achieve the research objective: i. Designed and constructed a bench-scale experimental unit that can sample product gas and tar from gasification systems and evaluate catalysts for catalytic tar cracking; ii. Determined tar reduction for a range of reaction temperatures; iii. Analyzed tar characteristics from the updraft gasifier at BRDF; and iv. Analyzed the state of iron in the bauxite residue catalyst after tar cracking reactions. 1.7 NSERC CREATE SusSyn The NSERC CREATE Sustainable Synthesis (SusSyn) program is a graduate student training program designed in collaboration with the Canadian industrial partners and the researchers at 11 UBC (2013-2019). Funded by Natural Sciences and Engineering Research Council (NSERC), the program aims to bridge student researchers to companies in clean chemical synthesis and sustainable technology industries. Participants of the CREATE SusSyn program focus on research projects that address challenges in waste management, energy efficiency and alternative energy development. In addition, program participants complete a minimum of a four-month internship with an industrial partner and gain a better understanding of the industrial research applications. Pursuing the research at the BRDF, where waste wood is actively utilized to generate energy for the University’s district energy system was one of the key project components that aligned with the objectives of the SusSyn program. In addition, bauxite residue was chosen to be studied as an alternative catalyst material as opposed to other catalyst options to further support the idea of waste management through adding value to waste materials. Through the collaborations with BRDF Operations and Nexterra Systems, the industrial implications of the problematic biomass tar and the significance of the research topic was realized. 12 Chapter 2: Literature Review 2.1 Biomass Gasification Biomass gasification involves four sequential stages, with no definitive boundary between each stage: (1) Preheating and drying of solids, (2) Pyrolysis, (3) Oxidation and (4) Gasification [25], [26]. In the first stage, the moisture in biomass is evaporated as the moisture content may vary from 30-60% and can even be >90% in some types of biomass [25]. During the pyrolysis stage at 125-500 °C, biomass (cellulose, hemicellulose, and lignin) is decomposed to char, volatiles (condensable hydrocarbons or tar) and non-condensable gases. In the oxidation process with increased temperature, some gases, steam and char are converted to CO, CO2, and H2O by a gasifying agent. Finally, in the gasification stage, char is further converted to syngas, mainly CO and H2, and CH4. [25]. Figure 2.1 The four main steps during biomass gasification. Reprinted with permission from ref. [7]. Copyright (2016) Elsevier. Gasification is a complex process involving numerous reactants and products going through multiple reactions. Some of the main reactions involved in gasification are listed below [7]. C + CO2 ↔ 2CO (Boudouard) R2.1 13 C + H2O ↔ CO + H2 (Steam Gasification) R2.2 C + 2H2 ↔ CH4 (Hydrogasification) R2.3 C + 0.5O2 → CO R2.4 C + O2 → CO2 R2.5 CO + 0.5O2 → CO2 R2.6 CH4 + 2O2 ↔ CO2 + 2H2O R2.7 H2 + 0.5O2 → H2O R2.8 CO + H2O ↔ CO2 + H2 (Water Gas Shift) R2.9 2CO + 2H2 → CH4 + CO2 R2.10 CO + 3H2 ↔ CH4 + H2O R2.11 CO2 + 4H2 → CH4 + 2H2O R2.12 CH4 + H2O ↔ CO + 3H2 R2.13 CH4 + 0.5O2 → CO + 2H2 R2.14 Depending on the end-use, the quality of the syngas can be described by the syngas calorific heating value and the H2/CO ratio. In addition, as the process also yields many byproducts such as the particulates, NOx, SO2, fly ash, HCl, H2S and NH3, “cleaner” syngas is desired to reduce the downstream processing costs. The syngas quality depends on many different factors including feedstock properties, gasifier design, gasifying agent and operating parameters as summarized in Table 2.1. Many of these parameters also influence the formation of biomass tar. 14 Table 2.1 Parameters impacting the syngas quality in biomass gasification [10] Feedstock Properties Gasifier Design Gasifying Agent Operating Parameters - Lignocellulosic composition - Moisture Content - Particle size - Ash content - Volatile compounds - Fixed: updraft, downdraft, cross-flow - Fluidized: circulating, bubbling - Entrained flow - Air - Steam - Oxygen - Pressure - Temperature - Equivalence ratio, Steam-to-biomass ratio, Gasifying ratio - Residence time 2.2 Biomass Tars 2.2.1 Definition and Characteristics As introduced in Chapter 1, the formation of tar is one of the biggest challenges in biomass gasification as it causes operational problems in downstream processing equipment. Tar is formed through a series of steps during the biomass gasification process. As the temperature of biomass is raised to around 400 °C, biomass is pyrolyzed and the primary tars are formed. With the increase in temperature, the primary tars transform to phenolic compounds and eventually to aromatic hydrocarbons at temperatures >700 °C [27]. Due to its complexity, different definitions and tar classifications have been developed. One of the commonly used definitions of biomass tars is “all organic compounds with a molecular weight higher than that of benzene” [11]. Another widely used definition of tar is “a complex mixture of condensable hydrocarbons, including 1 to 5-ring aromatic compounds with other oxygen-containing hydrocarbons and complex polycyclic aromatic hydrocarbons (PAH)” [7]. Researchers have also established classifications to address the great variety of the compounds in 15 the mixture. The tar classification based on molecular weights of compounds and formation temperatures is shown in Table 2.2. Another classification developed through molecular beam mass spectrometry study is shown in Table 2.3. Table 2.2 Tar classification based on molecular weight [28] Class Class name Property Compounds 1 GC-undetectable Very heavy tars that cannot be detected by GC Determined by subtracting GC-detectable tar fraction from total gravimetric tar 2 Heterocyclic aromatics Tars containing hetero atoms; highly water-soluble compounds Pyridine, phenol, cresols, quinoline, isoquinoline, dibenzophenol 3 Light aromatic (1-ring) Light hydrocarbons with 1-ring Toluene, ethylbenzene, xylenes, styrene 4 Light PAH compounds (2-3 rings) 2 to 3-ring compounds; condense at low temperature even at very low concentration Indene, naphthalene, methylnaphthalene, biphenyl, acenaphthalene, fluorene, phenanthrene, anthracene 5 Heavy PAH compounds (4-7 rings) > 3-ring compounds; these components condense at high temperatures at low concentrations Fluoranthene, pyrene, chrysene, perylene, coronene Table 2.3 Tar classification based on temperature dependence [8] Class Description Primary Cellulose-derived products such as levoglucosan, hydroxy- acetaldehyde, and furfurals; analogous hemicellulose-derived products; and lignin-derived methoxyphenols; Secondary Phenolics and olefins Alkyl tertiary Methyl derivatives of aromatics, such as methyl acenaphthylene, methylnaphthalene, toluene, and indene Condensed tertiary PAH without substituents, such as benzene, naphthalene, acenaphthylene, anthracene/phenanthrene, pyrene 16 2.2.2 Parameters Influencing the Tar Formation As with syngas, the tar composition and the yield are influenced by many parameters, including the gasifier temperature, the feedstock composition and condition, the gasifying agent and the gasifier design. Effect of gasifier temperature The most obvious variable influencing tar composition is the reaction temperature as the formation of the different tar compounds is dependent on reaction temperatures as shown in Figure 2.2. Reaction temperature also influences the overall tar yield due to the endothermic nature of cracking and reducing reactions. Many studies agree that tar yield decreases with increasing gasification temperature. For example, Lv et al. studied pine sawdust gasification at temperatures 650 – 850 °C in an updraft gasifier and reported decreasing total tar yield (g tar/kg biomass) with increasing temperature [29]. Dabai et al. also reported a similar trend for birch, pine sawdust, and beechwood downdraft gasification for 700 – 1000 °C [30]. The authors observed a significant decrease in total tar recovery with increasing gasification temperature and concluded that high temperatures increase destruction and reforming of tar, thus results in a decrease in overall tar yield [30]. 17 Figure 2.2 Tar formation at various reaction temperatures. Reprinted with permission from ref. [27]. Copyright (2017) American Chemical Society. Effect of feedstock composition While one of the major benefits of biomass gasification is its flexibility to utilize different sources, it is an additional complexity when it comes to tar formation. Biomass mainly consists of lignin, cellulose, and hemicellulose and the composition varies for different feedstocks. For instance, woody biomass contain more lignin and cellulose compared to agricultural residues [31]. As shown in Figure 2.3, lignin, cellulose and hemicellulose have different chemical structures. Therefore, they yield different products as they are thermally broken down in the gasification process. 18 Figure 2.3 Chemical structures of cellulose, lignin and hemicellulose. Reprinted with permission from ref. [26]. Copyright (2017) American Chemical Society. Lignin is a complex polymer composed of p- hydroxyphenyl, guaiacyl and syringil units and known to yield phenolic tar compounds such as phenols, guaiacols and catechols [26]. Amongst the three main components, only lignin is considered aromatic in nature, thus considered as a potential precursor for PAH formation [26]. Cellulose on the other hand yields levoglucosan as an intermediate product, which then converts to tar compounds such as furfural, glycolaldehyde, hydroxyacetone, formic acid and acetic acid [26]. Lastly, hemicellulose is the most complex constituent of biomass. It is the least stable polymer and not chemically homogeneous [26]. As it is the least thermally stable, it decomposes faster at lower temperatures than cellulose and lignin. Pyrolysis products of hemicellulose includes acids, phenols, aldehydes, ketones, esters, and a small amount of carbohydrates [26]. 19 Yu et al. studied individual gasification of cellulose, lignin and hemicellulose (Xylan) and observed that lignin gives higher total tar yield than cellulose and hemicellulose. In addition, when the reaction temperature was increased from 800 to 1000 °C, the degree of reduction in tar yield was less for lignin than the other two components, indicating that tars derived from lignin are more thermally stable [31]. Thus, depending on the type of biomass, total tar yield and composition may vary significantly and influence the characteristic (e.g., the dew point) of the tars. Effect of feedstock moisture content Feedstock moisture content is an important parameter in biomass gasification as it is directly related to the syngas heating value as well as the H2 and CO content. What is less intuitive is that the moisture content also influences the tar formation. Several studies report that higher feedstock moisture content results in the reduction of the total tar yield. Narvaez et al. studied the effect of H/C ratio, varied by biomass moisture content, on tar yield for bubbling fluidized bed air gasification of pine sawdust [32]. The authors reported that on increasing the H/C ratio from 1.6 to 2.2, a significant tar reduction from 18 to 2 g/Nm3 was observed [32]. Another study done by Kiel et al. reported a tar concentration decrease from 14 to 8 g/Nm3 for a fuel moisture increase from 10 to 45% [33]. A high steam content in the syngas or steam-to-biomass ratio in the feed increases steam reforming reactions and reduces the tar yield [34]. Effect of gasifying agent Gasifying agent is the source of oxygen for biomass gasification. For example, air, steam, O2, or any combination of the three, such as air-steam mixture or O2 enriched air or steam can be used 20 as gasifying agents. It is well known that the gasifying agent greatly influences the syngas characteristics. For example, steam gasification results in syngas with higher heating value due to higher H2 content compared to air gasification [34]. Needless to say, the gasifying agent also influences the tar formation. Gil et al. studied the variation in tar content for air, pure steam and O2 enriched steam gasification of pine wood chips in a bubbling fluidized bed gasifier and reported that the pure steam gasification resulted in the highest tar yield (g tars/kg biomass), followed by steam-O2 mixture (3:1), then air [34]. Therefore, in the absence of oxygen or limited oxygen, the tar yield is higher. Depending on the type of gasifying agent used, the gasifying agent-to-biomass ratio has different terminologies as shown in Table 2.4. These ratios are important operational parameters and have strong influence on the gasification products. In the aforementioned study involving air gasification by Narvaez et al., it was presented that an increase in equivalence ratio (ER) from 0.25 to 0.45 (increased O2 concentration) resulted in a decrease in H2 and CO concentration [32]. At the same time, the increase in ER resulted in a sharp reduction in total tar content by 50%, which the authors described as a “positive effect” [32]. The decrease can be explained by the increased availability of O2 to react with tars in the pyrolysis zone within the gasifier. Effect of steam-to-biomass (SB) ratio studied by Herguido et al. showed that an increase in SB ratio from 0.5 to 2.5 resulted in the increase in H2 and CO2 contents, sharp decrease in CO and slight decrease in CH4, and consequently sharp decrease in the heating value. Regarding tar, the researchers reported reduction in tar yield with the increased SB, due to elevated tar steam reforming reactions within the gasifier [11]. Similarly, studies reported that the increase in gasifying ratio (GR) results in the decrease in total tar content [11]. 21 Table 2.4 Terminology and definitions for different types of gasifying agents [34] Gasifying agent Air Steam O2 enriched steam Ratio Equivalence ratio (ER) Steam-to-biomass ratio (SB) Gasifying ratio (GR) Definition O2 content of air/O2 required for complete combustion H2O/Biomass (H2O+O2)/Biomass Effect of gasifier design The design of the gasifier influences tar composition and yield as it dictates the interactions between reacting gases and solids, thus the temperature zones. Gasifiers are commonly categorized as fixed-bed, fluidized bed and entrained flow gasifiers [10]. Fixed-bed gasifiers are further categorized into updraft and downdraft gasifiers. In an updraft gasifier (Figure 2.4), feedstock is commonly fed from the top and the gasifying agent is introduced from the bottom. Oxygen burns char at the bottom of the pile and the resulting hot gases travel upwards through the pile biomass. As the gases travels upwards, it cools and pyrolyzes the biomass at temperatures around 300-500 °C and the volatile compounds, or the primary tar compounds are released. The gas further cools down as it travels upwards and exits at temperatures 300-500 °C [10]. Therefore, the resulting gas has a high level of tar content (30-150 g/Nm3) [10]. In a downdraft gasifier (Figure 2.5Error! Reference source not found.), the gasifying agent and the biomass move in the same direction. As in the updraft gasifier, biomass release the primary tars as it is pyrolyzed. The gases including the volatiles pass through the combustion and gasification zone and exit the gasifier at temperatures of 900 to 1000 °C. The 22 higher temperatures enable cracking and reforming reactions, therefore the resulting gas contains less tar (0.1-1 g/Nm3) than in updraft gasifiers [35]. Figure 2.4 Schematic of updraft gasifier. Reprinted from ref. [36]. Figure 2.5 Schematic of downdraft gasifier. Reprinted from ref. [36] 23 Unlike the fixed bed gasifiers, the fluidized bed gasifiers achieve uniform temperature distributions through excellent gas-solid mixing which enhances reaction rate and conversion efficiencies [37]. Biomass rapidly dry and pyrolyze, releasing the primary tars, which come in contact with hot solids and further crack or reduce to permanent gases. As a result, the product gas from fluidized bed gasifiers has a low tar content (1-15 g/Nm3) [35]. In addition, solids that exhibit catalytic activities (e.g., dolomite) can be used as the fluidized bed material to reduce the tar formation. However, the operating temperature of fluidized bed gasifier is limited by the melting temperature of the bed material and which is typically from 800 to 900 °C [35]. 2.2.3 Tar Removal Methods Tar removal methods are categorized as primary or secondary methods, depending on the location of removal [14]. The primary method (Figure 2.6) refers to limiting the tar formation or reducing the tar content in syngas in-situ, often by controlling the parameters outlined in Section 2.2.2. The secondary method (Figure 2.6) refers to reducing tar ex-situ, downstream of the gasifier [15]. Conceptually, an ideal primary method would completely eliminate the need for secondary treatments. However, an ideal gasification system is yet to be implemented commercially [11]. 24 Figure 2.6 Primary tar removal method. Adapted from ref. [11]. The secondary method is further classified into physical removal, thermal conversion, and catalytic conversion methods. The physical removal methods include physical separation using filters, scrubbers and electrostatic precipitators (ESPs). While proven to be effective, these processes generate additional liquid or solid waste which results in additional cost for waste treatment and disposal [8], [15]. In addition, these processes require significant intermediate heating and cooling steps, decreasing the overall efficiency of the gasification process [16]. For example, tars are captured as condensed aerosols on the surface of the filters. However, as opposed to contaminants like dust, tar is more difficult to be removed from the filter as tar is viscous and sticky in its liquid form, requiring filters to be replaced frequently [38]. Water scrubbers, while proven to be effective, generate additional wastewater and result in a wastewater treatment problem [38]. ESPs are useful when tar is in liquid phase, but useless when tar is in gaseous phase [38]. While these technologies are well studied and commercialized, each technology has its weaknesses when it is applied for tar removal. 25 Figure 2.7 Secondary tar removal method. Adapted from Ref. [11]. Unlike the physical methods where the energy in tar is lost through the removal process, thermal decomposition can yield additional light hydrocarbon gases and CO and H2, thereby improving the efficiency of the gasification process. However, thermal decomposition requires temperatures greater than 1000 °C [15]. While the high temperature can be achieved by providing external heat, it is considered a highly energy intensive process. Catalysts can reduce the reaction temperature and residence time required. Nevertheless, the viability of catalytic tar removal depends on the availability of catalysts which are inexpensive and resistant to deactivation. 2.3 Tar Decomposition 2.3.1 Tar Decomposition Reactions Tar decomposition involves numerous reactions due to the complexity of syngas and tar. Tar, represented as !!!! below, can be decomposed through reforming and cracking reactions as shown below [39]. Light hydrocarbons may also decompose through these reactions [40]. 26 CnHm+nH2O ↔ nCO+ n+ m2 H2 (Steam reforming) R2.15 CnHm+nCO2 ↔ 2nCO+ m2 H2 (Dry reforming) R2.16 CnHm ↔ nC+ m2 H2 (Cracking) R2.17 CnHm+4n-m2H2 ↔ nCH4 (Hydro-cracking) R2.18 The reforming and cracking reactions are endothermic and can require reaction temperatures above 1000 °C in the absence of the catalyst [40]. The reactions above occur in parallel and consecutive along with additional reactions including the water gas shift (R2.9) and the Boudouard reaction (R2.1). 2.3.2 Tar Reduction Catalysts Driven by the need to produce syngas without tar and the advantage of catalytic tar decomposition, there has been extensive research on the subject. The universal goal is to develop an ideal catalyst. Sutton, Kelleher and Ross described such catalyst as follows [41]: i. The catalyst must be effective in removing biomass tars; ii. The catalyst should aid Methane reforming reactions if the desired product is syngas; iii. The catalyst should yield a suitable CO/H2 ratio for the intended purpose; iv. The catalyst should be resistant to deactivation; v. The catalyst should be easily regenerated; vi. The catalyst should be strong and resistant to attrition; and vii. The catalyst should be inexpensive. 27 Nickel and other metal-based catalysts, natural minerals such as dolomites and olivine as well as other iron-based catalysts and their combinations have been studied by many researchers in search for the catalyst that meets the criteria. Nickel based catalysts Nickel-based catalysts are widely used commercially in the petrochemical industry for hydrocracking and methane steam reforming. Ni-based catalysts have shown high activities for tar decomposition, demonstrating nearly-complete tar conversion when used as a secondary treatment catalyst [39]. Moreover, the catalyst is capable of reforming methane and other light hydrocarbons, thereby improving the syngas yield [12]. The main drawback of Ni-based catalysts is the cost and the environmental concern related to its toxicity [42]. Moreover, the catalyst is subject to severe deactivation by coke deposition, making catalyst regeneration through coke combustion necessary. In addition, the thermal regeneration can cause aggregation and structural changes in metal particles which can result in reduced activity and short catalyst life [12]. Noble metal catalysts Noble metal catalysts, such as ruthenium (Ru), platinum (Pt), palladium (Pd) and rhodium (Rh) have also demonstrated high activity towards tar reduction. Tomishige et al. [43] studied tar reforming over the noble metal and Ni catalyst supported on CeO2-SiO2 and found Rh catalyst to be most promising with highest tar reforming activity and minimal coke deposition. In terms of tar reforming activity, the metal catalysts ranked Rh > Pt > Ni > Pd > Ru [43]. However, despite 28 the high activity and its resistance to deactivation, Rh and Pt catalysts are not suitable for commercial applications due to their high cost [16]. Natural mineral catalysts Natural minerals such as dolomite and olivine are one of the most investigated materials due to their abundance and inexpensiveness [6]. Dolomite (MgCO3-CaCO3) is a magnesium ore that have demonstrated tar conversion activity when calcinated [39]. Similarly, olivine (Fe2SiO4 or Mg2SiO4) have also been reported to have comparable catalytic performance to calcinated dolomites [14]. Hu et al. tested the calcinated dolomite and olivine for steam reforming and demonstrated the catalysts to be effective in increasing the H2 yield [44]. However, dolomites and olivine require high reaction temperatures and cannot decompose tar completely [45]. Therefore, these natural minerals are often only used as gasification bed material for primary tar reduction to reduce the tar contents in-situ. However, the catalytic activity can be enhanced with the addition of metals [6]. For example, Virginie et al. reported that while olivine itself demonstrated moderate toluene conversion at 39% at 900 °C, iron impregnated olivine (10% iron) achieved 91% conversion at the same reaction temperature [46]. Iron-based catalysts Iron-based catalysts are less expensive than nickel and other metal catalysts, and are non-toxic. Besides the olivine, limonite and iron oxides are some of the other iron-based catalysts that have been investigated as tar reduction catalysts. 29 Limonite (FeOOH) is another naturally occurring iron ore, but with higher iron content than olivine, around 40 wt.% [39]. Limonite is advantageous as it is inexpensive and the spent catalyst can be used for steelmaking [39]. Li et al. studied the catalytic activity of limonite for coal tar decomposition and demonstrated that under H2 environment, limonite is reduced to magnetite (Fe3O4) at temperatures above 400 °C, which is further reduced to metallic iron above 600 °C [47]. The authors reported that under 50 vol.% H2 atmosphere at 750°C, coal tar decomposed at a high conversion rate with only 0.3 wt.% of carbon remaining in tar or other liquid products after reaction [47]. Many researchers agree that the metallic iron is the active phase for tar conversion, particularly for aromatic hydrocarbons due to their ability to break C-C bonds [15]. For instance, Nordgreen et al. demonstrated that metallic iron is effective in breaking down biomass tar, but iron oxides have no such capability [48]. Contradicting researches show that iron oxides are also catalytically active for tar reduction [49]. Azhar Uddin et al. studied the effect of iron oxide-alumina (Fe2O3-Al2O3) catalysts on biomass tar decomposition and observed that iron oxide catalyst can decompose tar and promote the WGS reaction [49]. Virginie et al. tested iron impregnated olivine catalyst (65% iron oxide) and the reduced form of the catalyst on tar reduction and concluded that tar reduction can occur without metallic iron but is enhanced with the presence of metallic iron [42]. Guan et al. reported that in steam reforming of tar involving iron oxide catalysts, no catalytic activity was observed initially but good activities were achieved once the iron oxides were reduced to the metallic forms in the presence of syngas [6]. The catalytic activity of iron oxide catalyst can be enhanced with addition of dopants. 30 Dulger Irdem et al. studied steam reforming of biomass tar using two iron-based catalyst, the iron-ceria (50% Fe2O3/50% CeO2) and the bauxite residue (41% Fe2O3, 21% Al2O3 and 17% SiO2) [50]. The authors reported that the Fe-Ce catalyst enhanced the WGS reaction and significantly increased the H2 production but the BR did not. The researchers estimated the tar conversion from the product gas analysis and reported that at reaction temperature of 600 °C thermal decomposition without catalyst achieved 59% conversion, whereas Fe-Ce catalyst achieved 95% and the BR catalyst achieved 68% conversion [50]. 2.3.3 Catalyst Deactivation Understanding catalyst deactivation is a crucial element for catalyst evaluation. Metal catalysts may lose its activity through coke deposition, sintering, poisoning and in some cases through oxidation [12]. Coke deposition One of the major causes of deactivation for many tar reducing catalysts is the carbon deposition on catalyst active sites [47]. For instance, Dassey et al. studied catalytic cracking of biomass tar for alumina, dolomite, olivine and silica catalysts [51]. The authors reported that the tar cracking efficiency of the alumina and silica catalysts remained constant; while, deactivation caused by filamentous carbon deposits were observed for the dolomite and olivine catalysts [51]. Carbon accumulation may decrease with increasing reaction temperature and the deposit can be removed by H2, steam or air at temperatures above 600 °C [52]. Aiello et al. reported that the filamentous carbon deposits resulting from methane cracking reactions over Ni-based catalyst were removed when treated with steam at 650 °C and the catalytic activity was fully recovered [53]. However, 31 the issue with the thermal regeneration is that the high temperatures may lead to a permanent catalyst deactivation by sintering [52]. As the tar compounds (hydrocarbons) are coke precursors, the composition of tar affects the nature of the carbon deposited. Artetxe et al. studied the nature of carbon deposited on Ni/Al2O3 catalyst after steam reforming reactions for various model tar compounds and reported that the amount and the heterogeneity of carbon deposit were greater for oxygenated compounds, (phenol, furfural and anisol), in comparison with aromatic compounds (toluene and naphthalene) [54]. Catalyst sintering As catalytic tar decomposition occurs at elevated temperatures, the ideal catalyst should be resistant to sintering. Metal sintering causes loss of specific surface area, which may lead to loss in catalytic activity. Artetxe et al. reported that the tar reforming reaction temperature of 850 °C resulted in the growth in nickel crystal size for the Ni/Al2O3 catalyst and irreversibly deactivated the catalyst [55]. Catalyst resistance to sintering can be improved by the addition of suitable dopants that can enhance the thermal stability of catalyst. For example, thermal stability of alumina catalysts can be improved in the presence of silica as a dopant [45]. Catalyst poisoning Other than tar, the biomass gasification product gas also contains other contaminants such as H2S and HCl, depending on the type of biomass feedstock used [12]. Both sulfur and HCl can deactivate catalysts. Between H2S and HCl, studies show that H2S poisoning is more detrimental 32 [52]. Deactivation from sulfur poisoning is caused by chemisorption of sulfur onto the catalyst active sites. However, the degree of the loss of catalytic activity is dependent on reaction temperatures due to the exothermic nature of the chemisorption reactions [56]–[58]. Therefore the sulfur poisoning effects are considered reversible and temporary [59]. Iron phase oxidation As discussed in Section 2.3.2, the catalytic activity of iron-based catalyst is related to the oxidation state of the iron. Many researchers agree that the metallic iron (Fe0) is the most active form of iron for tar reduction [42], [52], [60], [61]. However, the oxidation state can actively change during the course of the reaction due to the simultaneous presence of the reducing agents (H2 and CO) and the oxidizing agents (CO2 and H2O) in the gasification product gas. Therefore, iron-based catalysts may lose activity through oxidation in the oxidizing reaction environment. 33 Chapter 3: Materials and Methods 3.1 Bauxite Residue Catalyst The bauxite residue (BR) used for this project was supplied by Rio Tinto Canada (Jonquière, Quebec). The typical composition and properties of the supplied BR are shown in Table 3.1. As the specific composition may vary from one batch to another, about 150 g of BR catalyst was prepared from a single batch of the received BR for all experiments. Table 3.1 Typical composition and parameters of bauxite residue [62] Component Wt. % Al2O3 12-25 Fe2O3 30-40 SiO2 10-20 TiO2 3-8 CaO 1-6 Na2O 5-10 H2O (Chemical) 10 Particle size 10-250 µm Density (dried) 3.0-3.5 g/cc Specific surface area 10-40 m2/g Alkalinity pH 14 The as-received BR in paste form was first dried in an oven at 110 °C for 48 hours. Once dried, it was carefully crushed using mortar and pestle. The resulting particles were then sieved to achieve a uniform particle size distribution (600<dp<710 µm). The particle size was selected to parallel internal study by Dr. Zhiqiang Wu (Visiting Scholar, School of Chemical Engineering and Technology, Xi’an Jiaotong University) in the Tar Cracking Research Group for consistency 34 and as it had demonstrated enhanced catalytic activity in comparison to larger particle sizes while experiencing minimal pressure drop resulting from coke formation. Both untreated and pretreated BR were used in the study. The BR pretreatment process developed by Dr. Zhiqiang Wu involved catalyst calcination followed by a pre-reduction process [24]. Calcination was completed in air at 600 °C for 3 hours [24]. The calcinated BR was then reduced in 13 vol. % H2 in N2 at 800 °C for 8 hours, then cooled down to ambient temperature in N2 [24]. Ideally, BR would have been reduced and tested in the same reactor. However, due to H2 gas safety concerns at the test location, the catalyst was pre-reduced off-site in a separate reactor. The untreated BR and treated BR catalysts are pictured in Figure 3.1. Figure 3.1 Prepared: (a) untreated BR catalyst; and (b) pretreated BR catalyst For the experiments involving the pretreated BR catalyst, the heating and cooling of the reactor containing the catalyst were conducted in inert N2 environment to prevent re-oxidation at the elevated temperatures. 3.2 Commercial Nickel Catalyst A commercial steam reforming nickel-based catalyst was tested to allow direct comparison of the catalytic performance of BR to a more widely studied nickel-based catalyst. The catalyst 35 manufactured by Haldor Topsoe (RK-212) is described by the manufacturer as a pre-reduced nickel-based catalyst on ceramic calcium magnesium aluminite carrier, promoted with potassium oxide and a noble metal. As with BR, the nickel catalyst was crushed using mortar and pestle and sieved to achieve the same uniform particle size distribution (600<dp<710 µm). 3.3 Bioenergy Research Demonstration Facility 3.3.1 Biomass Feedstock The feedstock at the UBC Bioenergy Research Demonstration Facility (BRDF) consists of construction and demolition waste wood, clean wood from pallet manufacturing operations and municipal green wood (i.e., tree trimmings and residuals) from Metro Vancouver area [63]. At Cloverdale Fuels Ltd., a depot located 50 km from the BRDF, the feedstock is manually sorted to eliminate non-woody materials [63]. The woody materials are then chipped and blended to meet the specific fuel requirements for different applications [63]. The prepared feedstock is stored under a shed [64]. BRDF receives two to three truckloads of wood waste daily (12,500 dry tonnes per year) [63]. Upon its arrival at BRDF, a portion of the wood chips may be sampled for moisture, size, ash content and calorific value measurements. Fuel requirements for the UBC gasifier are 6-76 mm in size, 10-55% MCWB and ash content <10% [63]. The fuel pile at the BRDF fuel receiving and storage area is pictured in Figure 3.2. The fuel storage capacity at BRDF is approximately 40 tonnes of fuel, equivalent to approximately three days of operation [63]. Oveisi et al. analyzed the feedstock properties at BRDF [63]. Table 3.2 summarizes his findings based on 871 truckloads of feedstock over a period of two years. The authors reported that the 36 received feedstock is consistently low in ash content but has a relatively large variation in the moisture content. The large variation in the moisture content is due to the fact that the woodchips are stored in an open shed at the depot, therefore the moisture content is largely influenced by regional precipitation [65]. Figure 3.2 Fuel receiving and storage area at the BRDF Table 3.2 Received biomass feedstock properties at the BRDF [65] Moisture, %wb Bulk density, kg/m3 Calorific value, MJ/kg Ash content, %db Fraction of particles > 76 mm, % Fraction of particles < 6.4 mm, % Average 31.0 187 19.4 0.8 9.1 17.6 Standard Deviation 9.6 38 0.5 0.2 2.9 7.1 Coefficient of Variation, % 31 19 3 25 32 40 Minimum 10.0 92 18.1 0.2 0.0 0.9 Maximum 57.4 328 20.9 1.5 18.4 47.6 37 3.3.2 Gasifier The Nexterra Systems gasifier at the BRDF is a fixed bed, updraft air gasifier coupled with an oxidizer as shown in Figure 3.3. The biomass is fed into the gasifier from the bottom along the centreline of the gasifier with a vertical screw feeder. The gasifier bed temperature is maintained at 815-980 °C, achieved through controlling the biomass feed rate and air flow rate [63]. Ash is removed from the gasifier from the bottom into a hopper, while the product gas rises to the top. The product gas, containing tar, exits the gasifier at around 400 °C and is completely burned in the oxidizer to generate heated flue gas. The thermal energy in the flue gas is subsequently transferred to generate steam in the boiler. Figure 3.3 BRDF gasifier and oxidizer schematic. Reprinted with permission from ref. [65]. Copyright (2018) Elsevier. 3.3.3 Syngas Characteristics The syngas composition is not regularly monitored at the BRDF. Oveisi et al. studied the BRDF syngas composition with over 40 sampling events [63]. The authors’ findings are summarized in 38 Table 3.3. Regarding tar, the authors reported the total tar concentration in the range of 24-170 g/Nm3 with an average value of 78 g/Nm3 [63]. Table 3.3 Syngas composition at the BRDF [63] Component % (v/v) CO 22-26 H2 7-8 CO2 6-11 CH4 0.5-4 N2 Balance Moisture 20-35% wb 3.4 European Tar Sampling Protocol Due to the complex nature of biomass tar, variations in sampling methods may yield incomparable results. As an aid to this problem, the European Tar Sampling Protocol was established by the European Committee for Standardization (Comité Européen de Normalisation; CEN). The standard procedure was verified through parallel testing between nine specialized laboratories in Europe and one in the United States [66]. The tar sampling equipment described in the Protocol consists of four parts: gas pre-conditioning, particle collection, tar collection and volume measurement. The gas-preconditioning equipment refers to nozzles, valves, and sampling lines. The particle collection equipment is the heated particulate filter. Tar collection is based on condensation and liquid phase adsorption using solvent-filled impinger bottles. Lastly, the volume measurement equipment includes the pump, gas meter, flow controller, flowmeter, as well as temperature and pressure indicators. 39 The standard set-up for tar collection includes an impingement train, consisting of six gas impinger bottles connected in series as shown in Figure 3.4 [66]. The first bottle acts as a condenser for the moisture in the syngas. Each bottle in the train, except for the last one, is filled with solvent, isopropyl alcohol (IPA). The last bottle is left empty to catch any solvent carry-over. Bottles 2, 3, 5 and 6 (in Figure 3.4) have fine glass frits at the bottom of the tube to improve tar aerosol capture efficiency. The bottles are kept in two separate baths at two different temperatures, the warm bath at 35-40 °C and the cold bath at -20 °C. The technical background document for the Protocol explains that the temperature gradient increases tar aerosol collection efficiency. At 35–40 °C, IPA evaporates and the gas is saturated with the IPA. When the temperature is dropped to -20 °C, the IPA vapour will condense and form more and larger aerosols, resulting in greater mass-transfer rate [66]. Figure 3.4 European Tar Sampling protocol impingement train set-up 3.5 Design and Construction of the Tar Cracking Experimental Unit One of the key objectives of the project was to design and construct a bench-scale experimental unit that can: (i) sample product gas and tar from gasification systems; and (ii) evaluate catalysts for catalytic tar cracking. This section provides a detailed description of design considerations and the details of the experimental unit pictured in Figure 3.5. Warm Bath (35-40 °C) Cold Bath(-20 °C) 1 2 4 3 5 6Syngas and tar inSyngas out40 Figure 3.5 Tar Cracking Experimental Unit 3.5.1 Design Considerations The key design considerations taken into account include safety, apparatus mobility and structural integrity and the flexibility to accommodate different experimental conditions. In addition, the process was designed to lessen the effects in variability in syngas and tar composition due to variations in feedstock and gasifier operational parameters. The gasification product gas, containing H2, CO, CH4 and tars, is both toxic and highly flammable. It is especially dangerous as the syngas has to be sampled at an elevated temperature, around 400 °C. Furthermore, due to the endothermic nature of the tar decomposition reactions, the gas is further heated, way above the auto-ignition temperature of the syngas. Thus, it was critical to ensure a complete seal such that that no air is introduced. As a result, stainless-steel 41 tubing with compression fittings were used. The apparatus was tested for leak before each run prior to introducing the hot product gas. Mobility was an important consideration as the apparatus was to be constructed within the Department of Chemical and Biological Engineering, and then transported to the BRDF. In addition, it was desired to construct a unit that could be used at any gasification facility not just at the UBC plant. For BRDF, the unit had to be reasonably compact and structurally sound as the apparatus inevitably had to be hoisted up to the upper mezzanine about 5 m above the main level. This was because the best location for syngas and tar sampling was determined as the sampling port on the syngas transfer duct at the top of the gasifier. The sampling ports along the wall of the gasifier were not deemed ideal as they were too close to the fuel pile and would yield inconsistent results and high particulate level. In addition, installing an extended sampling line from the sampling port to the main level was not desired as the extended sampling line would have to be heated to prevent tar condensation. The top view schematic of the installation location is shown in Figure 3.6. The flexibility to accommodate different experimental conditions was another crucial design criterion for several reasons. As the experimental unit was to be used to evaluate catalysts for various reaction conditions, it had to be designed to accommodate the changes in controllable parameters such as the reaction temperature, space velocity and reaction time. In addition, efforts were made to minimize the discrepancy in experimental data arising from the BRDF syngas and tar composition variations, further described in the next section. 42 Figure 3.6 Plan view of apparatus schematic at the installation location at BRDF 3.5.2 Detailed Process Description The process flow diagram of the Tar Cracking Experimental Unit is shown in Figure 3.7. This section describes each component of the unit in detail. Detailed schematic and close-up photographs of key components are included in Appendix A.1. 43 Figure 3.7. BRDF Tar Cracking Experimental Unit process flow diagram Syngas flow~750 °F (400 °C) P2Particulate Filter 1T9Particulate Filter 2Tar Sampling Impinger Train 2*V6P1V11T8P4Gas Sampling Console 1 Existing BRDF Syngas Pipe to Oxidizer & Syngas Sampling PortV0R2Warm Bath Cold BathWarm Bath Cold BathTo Air for OxidizerT10N2R1V1V3 V4V5 V6V7V8P3Tar Sampling Impinger Train 1*V9V10Tar ScrubbersPump, Totalizer,Fine & Coarse Flow Control ValvesGas SamplingV6V12P5Gas Sampling Console 2 R3To Air for OxidizerPump, Totalizer,Fine & Coarse Flow Control ValvesGas SamplingHeat-traced Tubing* Both trains are in same cooling baths; separately drawn for simplicity** Thermocouple communication lines omitted for diagram simplicity. T0 to T7 & T12 are external thermocouples for corresponding heat cables. T8, T9 and T10 are internal thermocouples.Reactor/Shell FurnacePTInsulationFlexible Stainless Steel TubingPressure gaugeThermocouple**Needle ValveGate Valve3-way Ball ValveBall ValveLegendNitrogen in Courtyard Gas Storage CageT1T5T4T2 T3T7T11V2T6T0T12(a) (b) (c) (d) (d) (e) (f) (f) (g) (g) (b) Sampling Tube 44 (a) Sampling tube and sampling line The gas sampling port at the syngas transfer duct is a 1-1/2” pipe with a full-port gate valve and a full port ball valve in series. A gas sampling tube (5/8” stainless steel tube; 0.84 m in length) was inserted through the two valves such that the tip of the sampling tube was at the centre of the transfer duct. An isolation valve was placed in between the tube and the experimental unit to allow isolation from the gasification system. The European Tar Sampling Protocol recommends the sampling lines to be heated to temperatures 300–350 °C to keep most of the tar components in the gaseous state. The sampling line was externally heated using electrical heating cables and insulated with 1” ceramic wool insulation to maintain the gas temperature above 300 °C. Ideally, the sampling lines would be heated to 350 °C. However, to avoid thermal degradation of valve seat material, 300 °C was chosen. Nitrogen line was connected to the experimental unit to allow nitrogen purge through the sampling tube and through the experimental unit. (b) Heated particulate filter As the product gas is drawn into the experimental unit prior to any particulate matter removal, the product gas contains particulates at the sampling port. While the effects of the particulates on catalytic tar conversion efficiency may be a future study, it was out of scope for this project. As it was likely that the particulates would negatively impact the reactions by accumulating on the catalyst bed or blocking the pores of the catalyst, it was desired to eliminate them. Stainless steel particulate filter holder, that can house disposable borosilicate glass fibre filters (99.9% efficiency for 1 µm particles), was installed. In addition, to prevent experiment interruptions due to filters clogging up, two filters were installed in parallel for redundancy, such that if a filter clogs up, the second one can be used while the used-up filter element is replaced. Pressures at the 45 inlet and the outlet of the filter were monitored to indicate filter blockages. As with the sampling line, the filter holders were externally heated with heating cables to prevent the tars from condensing on the filters. (c) Reactor A tubular reactor was placed inside an electric furnace that can reach up to 1400 °C in air. The reactor tube is 23 mm in ID and 440 mm in length made of stainless steel (Grade 316). The total heated length inside the furnace is about 270 mm. A mesh screen, held together by two Circlips was placed near the bottom of the reactor to hold the catalyst in place. The extended length of the reactor allows flexibility in testing a wide range of catalyst loadings. A thermocouple was inserted from the top to measure the gas temperature inside reactor. The reactor wall temperature was also measured and used to control the furnace temperature. Reacting gas entered the reactor from the top, passed through the catalyst bed and exited from the bottom. Ideally, the reactor would be made of quartz or any other catalytically inert material as the nickel and iron components in stainless steel may have catalytic effects at elevated temperatures. However, as syngas can auto-ignite at the required reaction temperatures in the presence of oxygen, ensuring a leak-tight seal was critical. For example, a quartz reactor was not chosen as ensuring a tight metal-to-glass seal is difficult, especially at high temperatures as even the high-temperature resistant O-rings can easily thermally degrade at the required reaction temperatures. An option to avoid the catalytic wall effects is to line the metal reactor with an inert material. However, the option was not explored due to time and resource constraints. 46 (d) Tar collection impinger trains As per the European Tar Protocol described in Section 3.4, the 6-stage impinger train was implemented to collect tar. To evaluate the catalyst performance, the tar content in the gasification product gas before and after the catalytic reaction has to be compared. However, as the gas flow rate and the tar composition from the main gasifier fluctuate with time, two parallel impinger trains were installed to allow simultaneous collection of the tar in the “untreated” and the “treated” syngas. Although there is a slight time-delay as the gas has to travel more distance to reach the reactor, it was deemed as the best method to minimize the variation. The 500 mL impinger bottles were filled with 100 mL IPA, except for the 6th bottle, and connected using ball-joint clamps. The warm bath was maintained at ambient temperature at the sampling location, around 35 °C. The cold bath was prepared by mixing crushed ice and salt (NaCl) at a 3:1 ratio to achieve -20 °C. The temperature was well maintained throughout the duration of sampling. (e) Bypass tar scrubbers The bypass tar scrubbers were implemented to bypass the tar collection impinger trains. This was to allow isolation and disconnection of the impinger trains without interrupting the experiment. For instance, if it was desired to sample tar at every hour of the experiment, once the tar collection is completed, the gas can be directed to the bypass scrubbers and the impinger trains can be disconnected for sample removal. As the sole purpose of the scrubbers was to prevent any unreacted tar from reaching the pump, the six-bottle impinger set up was not used. The scrubber system consisted of three standard 1L glass bottles in series. The bottles were sealed with high-temperature resistant tapered round plugs with holes for 3/8” SS tube to go in and out of. Instead of having glass frits or any other means of producing smaller gas bubbles, the bottles were half-47 filled with 4 mm diameter glass beads to improve heat and mass transfer. As with the impinger set up, the bottles except the last bottle were filled with IPA. (f) Gas sampling consoles The gas sampling console (Apex Instruments XC-60C) is a device consisting of a miniature diaphragm vacuum pump, rotameter, pressure gauge, dry gas flow meter, thermocouple inputs and displays, as well as flow control valves. The sampling pump was necessary to withdraw the gas from the syngas transfer duct as the pressure inside the syngas transfer duct is maintained at -1.25 mbar. The gas flow meter measured the total volume of gas sampled. The sampling rate was controlled using flow control valves. Two identical consoles were used for sampling the tar from the treated and untreated gas lines. For each sampling run, the volume and time of sampling were monitored to ensure the same volume of the gas passed through both lines. (g) Gas sampling port and exhaust lines Gas sampling ports (three-way valves, with a tapered port V11 and V12) were installed downstream of the pumps to allow syngas sampling. Although the ports were not utilized for this project, it was deemed as an important feature for future experiments. The sampling ports would allow gas sampling in bags or can be used to connect to a gas analyzer to allow for on-line gas monitoring. Finally, the gas leaving the experimental unit was directed to a nearby process fan that delivers air to the oxidizer. The syngas flow rate from the experimental unit was at a fraction of the air flow rate, therefore the syngas was diluted below its Lower Explosive Limit. Thus, the syngas safely re-entered the gasification system and was combusted in the oxidizer. 48 3.6 Experimental Conditions and Procedure The reaction and the tar sampling were conducted for 60 min at approximately 1 nL/min syngas flowrate at the exit of the experimental unit. The overall gas residence time for the heated portion of the reactor (270 mm) is 0.1 s. Space velocity is typically defined as the flow rate of the gas at the reactor inlet divided by the volume of the catalyst. However, as the gas at the reactor inlet must be maintained at 300 °C, the inlet flow rate could not be measured. Thus, for this study, the space velocity is defined as the flow rate of the gas at the reactor outlet at normal conditions divided by the volume of the catalyst. For the catalyst-blank experiments, the reactor was filled with inert silicon carbide (SiC) particles. The SiC bed was 70 mm in height. For catalytic runs, the catalyst was placed on top of the SiC bed. Catalyst volume was kept constant at 0.014 L or 35 mm in bed height for all catalysts tested. The resulting space velocity was approximately 4000 h-1 for the catalytic runs. The gas temperature at the reactor inlet was maintained at 290-300 °C and the reactor exit was maintained at 300 °C. Furnace was set to maintain reaction temperatures of 700 and 750 °C. The first five impinger bottles were each filled with 100 mL of high purity isopropyl alcohol (>99.5%). At the end of the experiment, the samples in the bottles were combined in a glass container and stored in freezer at -20 °C until analysis. The catalyst was cooled down in nitrogen and collected for spent catalyst analysis. 49 3.7 Data Analysis 3.7.1 GC-FID The tar samples collected in IPA were analyzed using GC-FID at the BRDF research laboratory, courtesy of Nexterra Systems. The column used is a fused silica column (5% diphenyl + 95% dimethyl). The injector port temperature and the detector temperature was set at 300°C. The oven was programmed as follows: initial isothermal held at 50 °C for 5 min, followed by heating rate of 8 °C/min up to final temperature of 300 °C and isothermal held for 5 min. 3.7.2 GC-MS Selected tar samples were analyzed using GC-MS at the KIST-UBC on-site Biorefinery Laboratory to qualitatively identify the various tar compounds. The column used is polyethylene glycol (PEG). The injector port temperature was 250 °C and the oven was programmed as 40°C isothermally held for 5 min, followed by heating at 5 °C/min up to 260 °C, and isothermally held for 5 min. 3.7.3 XRD XRD analysis was completed at the Electron Microbeam/X-ray Diffraction Facility in the Department of Earth, Ocean and Atmospheric Sciences to identify the iron phase of the spent catalyst. Due to the possibility of the samples containing metallic Fe phases, the samples were not micronized as per usual to be reduced to the optimum grain-size range for quantitative X-ray analysis (<10 µm). Instead, the samples were crushed dry, by hand, in an agate mortar and back-mounted as-is. Step-scan X-ray powder-diffraction data were collected over a range 3-80°2θ 50 with CoKα radiation on a Bruker D8 Advance Bragg-Brentano diffractometer equipped with an Fe filter foil, 0.6 mm (0.3°) divergence slit, incident- and diffracted-beam Soller slits and a LynxEye-XE detector. The long fine-focus Co X-ray tube was operated at 35 kV and 40 mA, using a take-off angle of 6°. 51 Chapter 4: Results and Discussions 4.1 Experimental Unit Troubleshooting Prior to the experiments, test runs were completed to get familiarized with the apparatus operation and to address any issues. This section discusses the challenges associated with syngas and tar sampling, how the issues were addressed and how it may be mitigated in future applications. While it is well known in the biomass gasification industry that continuous sampling of syngas and tar is very challenging, not a lot of academic researchers encounter the same problem. This is due to the fact that many researches are based on model tar compounds instead of real tar, and also because of the relatively small quantities of tar utilized in academic researches. As described in Chapter 3, a gas sampling tube was installed at the sampling port at the syngas transfer duct. While the first couple sampling runs were completed without any issues with the sampling tube, at the third trial it was found that the flow was getting severely restricted as the sampling progressed. Eventually, the pressure gauges indicated a close-to complete blockage and the sampling had to be halted. Upon removal of the tube, it was observed that the inside of the tube was completely blocked as shown in Figure 4.1. The residue was also observed on the outside surface of the tube. Although the residue was not analyzed, it is likely a mixture of the solid gasification byproducts (ash, char), tar, and even coke resulting from tar reacting with iron and nickel components in the stainless steel tube. Nexterra, the designer of the gasification system at BRDF advised that steam is widely used in to clean sampling tube in industrial applications. However, steam purging was deemed not feasible for this project due to the lack of 52 access to pressurized steam at the BRDF. Alternatively, a clean tube could be re-installed at the start of the trial and removed at the end of the trial. However, as the uninstallation and re-installation of the tube, the heating cables and the insulation added significantly more time and effort for each trial, which was not desired. In addition, it was not ideal to open the main sampling port on a daily basis, as it must be done with extreme caution under proper plant operator supervision. As an aid to the problem, the procedure was updated to use nitrogen to attempt to unplug the lance by carefully building up pressure inside the tube to push out the blockage. However, the nitrogen flush was unsuccessful at times. In such case, the lance was manually unplugged using a smaller tube and hammer to push out the blockage. Again, this procedure had to be performed under extreme caution. Figure 4.1 Plugged gas sampling tube Another issue was observed when the tube was left inside the syngas transfer duct during a gasifier shutdown process. During the shutdown, the temperature in the syngas transfer duct may be >800 °C, at which the metal tubes can soften and bend by gravity. The bent tube had to be 53 removed and replaced. Therefore, it was made sure to include in the procedure to remove the sampling tube before the gasifier shutdowns. If a sampling tube were to be permanently installed, stainless steel tube is not recommended as it can start to “droop” at higher temperatures. Ceramic thermowells and high-purity alumina can withstand temperatures up to 1200 °C, and are therefore recommended for the application given that a leak-tight seal can be achieved [67]. Maintaining a high syngas temperature at 300 °C was another major challenge. The high temperature is required to maintain the gaseous state of most of tar components, as per the European Tar Sampling Protocol. While the tubing was wrapped with heating cables and heated to a temperature around 350 °C, the internal gas temperature was not able to reach 300 °C due to the heat transfer limitations and higher-than anticipated heat loss. Through a trial-and-error process, additional heating cables and insulation were installed and the temperature set point was increased to reach the internal gas temperature of 300 °C. Despite the efforts, minor tar adsorptions in the inside wall of tube fittings were observed. This was likely a result of multiple causes, including the possibility of having cold spots where the tar is able to condense on the surface. Typically when tar is sampled, the sampling lines are kept to a minimum length. For example, the syngas and tar drawn out of the gasifier would be immediately filtered and washed in the impinger trains. However, for the experimental set up used in this project, the syngas had to travel more distance to reach the reactor. While the temperature of the syngas right before the reactor inlet was kept at 300 °C and the entire length of the pipe was heat traced and insulated, it does not guarantee that there were no cold spots 54 along the way. In addition, as tar is a mixture of a variety of compounds, it is possible that some tar compounds with higher dew point deposited on the walls. 4.2 Considerations in Working at an Operating Plant In addition to the technical challenges described in the previous section, there were additional challenges associated with working at an operating plant. This section is included to share the experience to future researchers who may undertake a project at BRDF or in a similar setting. The most critical aspect when performing experiments at an operating plant is safety as the risks and consequences are great. Therefore, BRDF Operations was consulted in the preliminary design stage of the process to identify any plant-specific hazards. For instance, the wood dust levels can get high at the plant, posing a combustible dust hazard. To mitigate the risk, all heating elements were completely covered with flame-resistant ceramic wool insulation material. In addition, experiments were not performed when the dust levels were high. Surface dust levels were kept at a minimum by vacuuming prior to each experiment. In addition, as a visitor at the plant who poses a greater safety risk, all safety critical activities were notified to the Operators. In addition, high-risk activities such as opening and closing the syngas sampling port were aided by the operators. Another key challenge was coordinating the project schedule with the plant operations’ activities. Regrettably, this research project coincided with the construction of the plant’s expansion project, which experienced a delay. Due to the limitations in available workspace, the installation of the experimental unit was consequently delayed significantly, thereby only 55 allowing a short window to commission and perform the experiments. This unforeseen event, in addition to the plant’s operational challenges significantly reduced the number of experiments conducted. While these challenges were also out of the BRDF Operations’ control, it is recommended to assess all risks, including uncontrollable risks associated with operations. 4.3 Basis of Tar Removal In the catalytic tar cracking and reforming research, the measure of tar reduction is commonly reported as the % Tar Conversion, which is defined as the amount of tar reacted per the amount of tar originally present. For example, the amounts or concentrations of tar at the inlet and the outlet of the reactor are measured to determine the conversion. However, when the research involves real tar instead of model tar compounds, it is inevitable for some tar to adsorb along the pipe and fittings as previously described. In these cases, because the tar loss is not only due to reactions, the term conversion is not adequate unless no adsorption can be guaranteed. Therefore, the basis of tar removal effectiveness for this project is reported as % Total Tar Reduction, where the term total tar is used only for GC-detectable tars as GC-undetectable tars were not captured nor measured. For this project, the amount of tar in the untreated syngas line (equivalent to inlet of the reactor) and the amount of tar in the treated syngas line (equivalent to outlet of the reactor) was quantified and used to determine % Total (GC-detectable) Tar Reduction using the following equation: Total Tar Reduction % = mtar in raw syngas- mtar in treated syngasmtar in raw syngas×100% E4.1 56 In the equation above, m denotes the mass of tar. It is common to quantify the tar components as bulk tar. For instance, the European Tar Protocol includes two methods for quantifying the bulk tar: (i) a method for determining the total gravimetric tar, which is determined as the weight of the tar residue obtained by completely evaporating the solvent; and (ii) the method for determining total-GC detectable tar, which is the sum of all tar components identified using gas chromatography, which can be reported as naphthalene. Therefore, E4.1 can be written in terms of GC peak area of tar instead of the mass of tar. The reason for reporting total tar instead of the individual tar components is that it is not possible to physically separate tar into individual components. In addition, while one can quantify the individual components using chromatography, to do so, the GC or HPLC has to be calibrated for each individual component, which is unrealistic with the variety of tar components and analogs in the mixture. As the ultimate objective of this project is to investigate the catalyst for removing all tar components, the % Total Tar Reduction was calculated using the sum of all tar components detected using GC-FID at the inlet and the outlet of the reactor. 4.4 BRDF Tars To get an understanding of the tars produced from the BRDF gasifier, the individual tar components were identified using GC-MS. Table 4.1 lists the identified compounds. Acetic acid and acetol fall within the primary tar category. Secondary and tertiary tars such as phenols, toluene and indene were also identified. The only polycyclic aromatic hydrocarbon (PAH) identified was naphthalene. It was initially thought that the absence of more complex tars was due to the limitations of the tar sampling and the analysis method. For instance, as the temperature of the syngas and tar is only kept at 300 °C, any compounds with higher dew point 57 could drop out inside pipes before reaching the tar collection impingers. In addition, as the maximum oven temperature of the GC-MS was 260 °C, tars with higher dew point would not be identified. While this theory is a possibility, the result aligns with the literature that updraft gasifiers produce mostly primary tars. Table 4.1 Components identified in tar samples collected from BRDF gasifier Category Compound MW (g) Boiling Point (°C) Acids Acetic acid 60.05 117.9 Aldehydes and ketones 2-Cyclopenten-1-one 112.12 136.0 Phenols Phenol 94.11 181.7 3,5-Xylenol 112.16 221.7 p-Cresol 108.13 201.9 m-Cresol 136.19 202.2 2-ethylphenol 112.16 204.9 Guaiacols Guaiacol 124.14 205.0 Creosol 131.16 221.0 4-Ethylguaiacol 152.19 236.5 Furans Furfural 96.08 161.7 Mixed oxygenates Acetol 58.08 145.5 Aromatic compounds Toluene 92.14 110.6 Indene 116.16 181.6 PAHs Naphthalene 128.17 217.9 The tar compounds resulting from updraft gasifiers are similar to the products of pyrolysis [68]. This is because the tars formed in the pyrolysis zone within the updraft gasifier do not come in contact with higher temperature zones. Therefore, it is unlikely that the primary tars form more complex, secondary and tertiary tars. This process of primary tars transforming to more complex tars with increasing temperature is described by many researchers as “tar maturation” [69]–[71]. The tar maturation process proposed by Elliott is shown in Figure 4.2 [71]. Hernández et al., also studied the effect of gasifier operating temperature on the evolution of tar and found that up to 58 750 °C, the most abundant tar species are phenols and benzene, whereas at 1200 °C, xylenes and naphthalene become more significant [70]. So, while higher temperatures increase the thermal cracking and reforming reactions, thereby decreasing the overall tar yield, the primary tars may transform to refractory polycyclic aromatic compounds [70]. Mixed Oxygenates ! Phenolic Ethers ! Alkyl Phenolics ! Hetrocyclic Ethers ! PAH ! Larger PAH 400 °C 500 °C 600 °C 700 °C 800 °C 900 °C Figure 4.2 Tar maturation sequence [71] As an attempt to further understand the tar formation at the BRDF, operational data such as the fuel pile height, fuel moisture content and syngas temperature were obtained from BRDF Operations. However, as these parameters were not kept constant, and sometimes fluctuated drastically from one sampling period to another, no correlation could be identified. While such fluctuation is normal in the viewpoint of industrial applications, for the purpose of this research project no conclusions could be made, especially with the small sample size. Table 4.2 is a list of some of the gasifier operational variables at BRDF during the sampling period for this project. Omitted from the table are the ER and the air flowrate data as per the non-disclosure agreement with the gasification system designer. The system is designed to maintain an ER of 0.11 to 0.22 at a gasifier temperature range of 875 to 1050 °C [63]. Other variables that likely impacted tar production but not reported here include the fuel particle size, fuel ash content and other operational parameters such as the bin speed and the induced draft fan speed [65]. 59 Table 4.2 BRDF gasifier operating parameters during the sampling period Variable Average Minimum Maximum Fuel pile height (m) 1.8 1.6 2.1 Syngas temperature at transfer duct (°C) 431 374 503 Fuel moisture content (%) 26 25 30 4.5 Catalyst-blank tests Catalyst-blank tests were performed to identify the effects that impact the determination of the % Total Tar Reduction. This includes the aforementioned tar loss in piping, potential thermal cracking effects, as well as the catalytic effects of the reactor wall material. Ideally, the tar yield (g tar/g biomass or equivalent) obtained with and without catalyst would be reported, if the amount of the reactant tar can be kept constant. However, for this project, the reactant tar was not at a constant concentration. Therefore, as an alternative, the % Total Tar Reductions of catalyst-blank tests are reported such that the extent of the effects can be observed. The catalyst-blank tests were conducted with inert SiC material at gas flowrate of 1 nL/min gas flowrate for 60 min. Reaction temperatures of 700 and 750 °C were tested. At 700 °C, the % Total Tar Reduction was determined as 0.1%. However, it was later discovered that the tar samples from this experimental run and the Nickel catalyst run were contaminated with compounds that remained unchanged with the reaction. Because the contaminants were unaffected by the reaction, the actual % Total Tar Reduction is likely higher than 0.1%. The source of the contamination is further explained in Section 4.6. At 750 °C, the % Total Tar Reduction was found to be 9.5%. In addition, at 700 °C there was no visible difference between the fresh and the spent SiC particles, However, coke deposits were observed on the SiC used at 750 °C, indicating that there were some catalytic and possibly thermal cracking effects at 750 °C. 60 An interesting observation was made while analyzing the GC-FID chromatograms. Although the total areas of the peaks before and after the reaction were similar, shifts in individual peaks were observed. For both temperatures, the phenol and naphthalene peaks increased with the reaction, while smaller peaks of unidentified compounds either decreased or disappeared as shown in Figure 4.3 andFigure 4.4. The arrows indicate phenol and naphthalene peaks. Figure 4.3 Catalyst blank experiment at 700 °C: (a) before; and (b) after reaction. Figure 4.4 Catalyst blank experiment at 750 °C: (a) before; and (b) after reaction. 61 This occurrence relates back to the discussion of tar maturation. Morf et al. performed an extensive study of the temperature effects on individual tar compounds [72]. Similar to this study, the gas and tar produced in a pyrolysis unit were thermally treated in a secondary reactor at temperatures from 500 to 1000 °C [72]. The authors reported the primary tar compounds such as acetol, acetic acid guiacol showed decreasing trends with the increase in temperature, with the extent of decrease in the order of guiacol > acetol > acetic acid [72]. For the secondary tar compounds, the researchers reported scattered results for phenol, attributed from difficulty in separating phenol peaks and a decrease in o-cresol with the increase in temperature. Finally for the tertiary tar compound, a dramatic increase in naphthalene for reaction temperature > 750 °C was reported [72]. The tar samples from this experiment could have been quantified using GC-MS to confirm the theory of maturation and to verify the trends for individual compounds. However, it was not completed as it was beyond the scope of this project and due to the limitations in time and resources. One theory on the observed increase in phenol with the secondary thermal reaction is that guiacols and cresols can be thermally converted to phenol. For example, Kawamoto proposed a pathway for guiacol conversion to phenols and cresols at temperatures > 450 °C [73]. Cresols can go through dealkylation reactions to yield phenol. Assafi and Duprez studied the steam and hydro-dealkylation of m-cresol and found the products to be phenol and H2, CO, CO2 and CH4 [74]. 62 The observed increase in naphthalene is explained by the fact that phenols are precursors for PAH formation as demonstrated by many researchers [72]. The PAH formation pathway from phenol, proposed by Font Palma, is shown in Figure 4.5 [26]. The phenolic compounds lose CO radical to form cyclopentadiene, which then loses H to form its radical form, then two of the radical compounds combine to form naphthyl compounds [31]. Vassilatos et al. studied the effect of temperature for thermal cracking of biomass tar and reported that phenols are stable at 700 °C, but decompose and yield naphthalene and indene at 900 °C [75]. Yu et al., reported a similar trend that phenol and toluene convert to thermally stable components such as benzene and naphthalene at elevated temperatures [76]. So, while the thermal effects on total tar yield seemed insignificant, in reality, the simpler primary tars mature into more complex and thermally stable tars at higher temperatures. Figure 4.5 PAH formation from phenol precursors. Reprinted with permission from ref. [26]. Copyright (2003) Elsevier 63 4.6 Nickel Catalyst To allow for direct comparison of the bauxite residue catalyst to a commercially available catalyst, a nickel-oxide based catalyst was tested at 700 °C. A commercial steam reforming nickel catalyst was crushed and sieved to achieve a uniform particle size distribution of 600 – 710 µm. The catalyst was not pretreated prior to use. The gasification product gas containing tar was passed through the catalyst bed at a rate of 1 nL/min 700 °C for an hour. The resulting % Total Tar Reduction was 65%. As opposed to the catalyst-blank tests, significant reduction in phenol (92%) and naphthalene (88%) were observed. However, the GC-FID results indicated many significant unidentified peaks that remained unchanged with the reaction as shown in Figure 4.6. This result was unexpected for two reasons. First, naphthalene is widely known as one of the more difficult tars to be reduced and nickel-based catalysts are known to be effective in reducing tars. The fact that naphthalene disappeared but many others remained unchanged raised suspicions. Figure 4.6 Ni-catalyst experiment at 700 °C: (a) before; and (b) after reaction. 64 The samples were further analyzed using GC-MS to identify the unknown components and it was discovered that the samples contained a variety of forms of decane. Decane is alkane hydrocarbon chain, which is a main component in diesel and used in rubber and paint manufacturing industries. As BRDF sources waste wood, it is possible that waste wood treated with varnishes or paint were mixed into the feedstock. Because the contaminants were unaffected by the reaction, the actual % Total Tar Reduction is likely higher than the determined value. The chromatograms of this experimental run resembled that of the catalyst blank experiment at 700 °C (Figure 4.3), which was conducted a day earlier, therefore likely contaminated as well. It was desired to repeat the two experiments, but was not completed due to the limitations in time and resources. On the other hand, the GC-MS analysis further confirmed the disappearance of phenol and naphthalene beyond the detection limits with the nickel catalyst. In addition, no compounds other than the contaminants were detected after the reaction. 4.7 Bauxite Residue The bauxite residue (BR) catalyst was prepared as described in Section 3.1. For the initial experiments, it was desired to test the effectiveness of the untreated BR. One of the key benefits of the BR is that it is an abundant industrial waste, which can be sourced at a fraction of the cost of other catalysts. Thus, if it can be utilized without any costly treatments or modifications it would be truly beneficial. For instance, a common pretreatment option for iron-based catalysts is pre-reduction with reducing agents such as H2 and CH4, which can be costly. A hypothesis was that the reducing agents contained in the syngas (H2 and CO) may reduce the BR catalyst in-situ and demonstrate good tar reduction performance. 65 The untreated BR catalyst of uniform size distribution (600-710 µm) was tested at 700 and 750 °C at gas flowrate of 1 nL/min for an hour. The resulting % Total Tar Reduction was 45%. The GC-FID chromatograms (Figure 4.7) indicated a decrease in phenol and other unidentified minor components and a significant increase in naphthalene. This trend was similar to the results of the catalyst-blank experiments, except that the phenols decreased after the reaction with BR. As discussed in Section 4.5, phenols are PAH precursors. The trend was further confirmed as no phenols were detected through GC-MS analysis, but naphthalene was still present in the sample. Another observation was that after the reaction with BR, additional compounds, namely P-xylene, styrene, 1-methyl naphthalene and biphenyl were detected, of which the latter two are PAHs. Figure 4.7 Untreated BR catalyst experiment at 700 °C: (a) before; and (b) after reaction. It was desired to test the catalyst at a higher temperature, given the mediocre performance of the BR catalyst. Yet, 750 °C was chosen as the upper end of the test temperature to avoid sintering effects that were previously described by Shiva Madadkhani of the Tar Cracking Research 66 Group [62]. When the untreated BR was tested at 750 °C, 74% Total Tar Reduction was achieved, which was a notable increase from the same reaction at 700 °C. When accounting for the previously discussed thermal effect of the increase in temperature, the effect of the higher temperature was a 20% increase in tar reduction. When comparing the individual compounds, phenols almost completely disappeared with the reaction, along with all minor unidentified peaks (Figure 4.8). However, the concentration of naphthalene increased with the reaction as before, but the degree of the increase was less, possibly due to the naphthalene cracking reactions at the elevated temperature. Figure 4.8 Untreated BR catalyst experiment at 750 °C: (a) before; and (b) after reaction. With the mediocre results of the untreated BR, pre-reduced BR was prepared off-site and tested at BRDF. The same experimental procedure was followed except that the heating and cooling of the catalyst bed was completed under inert condition (in N2) to preserve the state of iron for the experiment and for the spent catalyst analysis. The experiment took place at 750 °C, and the observed % Total Tar Reduction was 84%. As opposed to the untreated BR where naphthalene was detected after the reaction, no naphthalene or phenols were detected in the treated sample 67 (Figure 4.9). Only few unidentified peaks remained with the reaction. It was clear that the pre-reduced BR was significantly more effective than the untreated BR. Figure 4.9 Pretreated BR catalyst experiment at 750 °C: (a) before; and (b) after reaction. The results are summarized in Table 4.3. Due to unforeseen circumstances at the facility, only a limited number of experiments were conducted, in which some data were discarded due to operational challenges experienced during the experiments. The reported values were not replicated and reproducibility cannot be guaranteed. Yet, the reported data provides a clear idea of the discussed trends. Table 4.3 Summary of % Tar Reduction results Catalyst Blank Blank RK-212 BR BR Pretreated BR Reactor temperature (°C) 700 750 700 700 750 750 % Total Tar Reduction 0.1%* 9.5% 65%* 45% 74% 84% % Δ Phenol +84% +30% -92% -81% -97% -100% % Δ Naphthalene +440% +230% -88% +250% +145% -100% *The tar samples from these experimental runs were likely contaminated. As the contaminants were unaffected by the reaction; the actual % Total Tar Reduction would be higher than the value shown. 68 4.8 Catalyst Deactivation Characteristics It was clearly demonstrated that the pre-reduced BR outperformed the untreated BR for reducing biomass gasification tars. However, the reaction was only conducted for an hour, which may not be long enough for a catalyst to exhibit deactivation characteristics. In addition, as the final form of iron species post reaction was unknown, XRD analyses were conducted. Bill Cheng of the Tar Cracking Research Group previously identified the most significant iron species in the as-received BR as Goethite (FeOOH) and Hematite (Fe2O3). The most significant iron species identified in the spent BR after the reaction were hematite (Fe2O3) and is further reduced form Magnetite (Fe3O4). The disappearance of Goethite with the reaction was expected as Goethite consists of 90% hematite and 10% water, which is evaporated at >300 °C as shown in R4.1 [77]. Therefore, when the untreated BR was used, some of the hematite reduced to Fe3O4 in the reaction environment as shown in R4.2 and 4.3. However, the gasification gas environment is unable to further reduce the iron oxides to metallic iron. 2FeOOH → Fe2O3 + H2O R4.1 3Fe2O3 + H2 → 2Fe3O4 + H2O R4.2 3Fe2O3 + CO → 2Fe3O4 + CO2 R4.3 The BR pre-reduction method outlined in Section 3.1 results in transformation of hematite to metallic iron. However, the most significant iron species identified in the spent pre-reduced BR catalyst was Magnetite and almost no metallic iron remained post reaction. That is, when pre-reduced BR was used in the reaction, the metallic iron first oxidized to FeO, and subsequently to Fe3O4 as shown in R4.4 – 4.7. 69 Fe0 + H2O → FeO + H2 R4.4 Fe0 + CO2 → FeO + CO R4.5 3FeO + H2O → Fe3O4 + H2 R4.6 3FeO + CO2 → Fe3O4 + H2 R4.7 Therefore, under the gasification product gas environment at the BRDF, pre-reduced BR catalyst would quickly (in ≤ 1 hr) transform to its oxidized form and eventually lose its catalytic activity. That is, unless a reducing environment can be achieved with increased syngas (H2 and CO) concentration or with any other reducing agents, the BR catalyst will lose its activity. The catalyst still can be regenerated by means of reduction, but may not make sense if the deactivation is significant within hours of the catalyst use. The XRD results are included in Appendix B.1. 70 Chapter 5: Conclusion and Recommendations The main objective of this research project was to investigate the viability of bauxite residue as an alternative catalyst for cracking tar in the syngas produced at the Bioenergy Research Demonstration Facility (BRDF) at the University of British Columbia. To accomplish the task, considerable efforts were put into designing, commissioning and testing the experimental unit. There were many challenges and limitations as the project involved real biomass gasification tar from a commercial-scale gasifier as opposed to model tar compounds in simulated environments. Yet, the research granted additional insights into the actual performance and viability of the BR as an alternative catalyst. The key findings are summarized below: - The tars produced as byproducts from the updraft, fixed-bed air gasifier at the BRDF consist of primary tars such as acetic acid and acetol, phenolic secondary tars, as well as aromatic compounds such as toluene, indene and naphthalene. - Within the gasifier, not all of the primary and secondary tars come in contact with higher temperature zones as the gas rises to the top. Therefore they remain as primary and secondary tars without maturating into more complex tars. - The tar maturation phenomenon was observed in the catalyst-blank tests performed at 700 and 750 °C. At the reaction temperatures, both phenol and naphthalene components became more significant with the thermal treatment, while minor unidentified compounds decreased or completely disappeared from the chromatogram. The findings were in 71 alignment with literature that guiacols and cresols can be thermally converted to phenols and that the phenols are naphthalene precursors. - The % Total Tar Reduction may have contradicting results to the actual performance of a catalyst. At higher reaction temperatures, the primary tars are easily reduced, thereby lowering the total tar yield. However, the aforementioned tar maturation can yield more stable and complex tar components that are more difficult to be removed and cause the same if not worse operational problems in downstream processes. - For the untreated BR catalyst, the increase in reaction temperature from 700 to 750 °C caused a 20% increase in the % Total Tar Reduction, when the thermal and tar loss effects are subtracted. However, naphthalene concentration increased with the reaction, further supporting the above point. - The main iron species in the untreated BR is Hematite (Fe2O3). After 1-hour reaction in the syngas environment, some of the hematite was reduced to Magnetite (Fe3O4). However, the BRDF syngas environment is unable to further reduce the iron oxides to metallic iron. - The pretreatment of BR (Calcination in air at 600 °C for 3 hours followed by reduction in 13 vol. % H2 in N2 at 800 °C for 8 hours) yields metallic iron. The pretreated BR was effective in removing tar and demonstrated the ability for complete reduction of phenol and naphthalene during the 1-hour reaction. The performance of the pretreated BR was similar to or slightly better than the commercial nickel-based catalyst. 72 - The metallic iron species in the pretreated BR quickly (in ≤ 1hr) transformed to Magnetite (Fe3O4) in the syngas environment. That is, unless a reducing environment can be achieved and maintained with increased syngas (H2 and CO) concentration or with the addition of any other reducing agents, the catalytic activity of pretreated BR catalyst will eventually decline. Based on the understanding of the challenges and limitations faced in this project, recommendations for improving the experiments in the future research are summarized below: - If model tar compound is to be used for future studies, it is recommended to continue to use naphthalene as the model tar compound as it was demonstrated to be the most difficult tar compound to reduce. - Quantitative analysis of the key individual tar components is recommended as a future study to allow for an in-depth analysis of the tar maturation phenomenon. For instance, phenols or other tar components can be reacted in the absence of catalyst at elevated temperatures and the product tar compounds can be analyzed. In addition, it is recommended to use the GC-MS as the main tar analysis method, as there are limitations in identifying the tar components only by the retention time. - It is recommended to increase the sampling volume and reaction duration in future studies. The experimental unit was designed to handle large gas volume and reaction duration. However, the functions were not utilized due to the limited time allowed for 73 experiments in this project. Increased tar concentrations can improve the accuracy of tar analysis. - Syngas samples can be collected from the experimental unit. It is recommended to investigate the products of the tar cracking and reducing reactions through analyzing the syngas composition before and after the catalytic reactions. Again, the function was not utilized due to limited time and resources. - If the BR catalyst can be modified to resist the sintering effects, higher reaction temperatures can be tested. 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The sampling tube is essentially a 5/8” tube with two 5/8” compression-to-3/4” MNPT adapters, as shown in the schematic. The first adapter connects the sampling tube to the valve on the sampling port and the second adapter connects to an isolation valve to the flexible tube, which is connected to the experimental unit. From the lessons learned in this project described in Section 4.1, it is recommended to use high-temperature resistant tube instead of stainless steel. For example, ceramic thermowells or high-purity alumina can be used, given that a leak-tight seal can be achieved. In addition, if possible, it is recommended to increase sampling tube diameter to reduce the clogging issue. However, it is important to leave some wiggle room between the port and the inserted tube. Otherwise, tar can quickly build-up and glue the two tubes together, making it impossible to be removed. Figure A.1 Syngas and tar sampling tube used in the project 85 Figure A.2 Gas sampling port located on the syngas transfer duct at BRDF Nitrogen gas cylinder was kept in the gas storage cage outside the facility. The facility’s existing gas piping was used to bring the nitrogen gas into the plant. The experimental unit included a secondary gas regulator, rotameter with needle valve for flow control and a shut-off valve built in to accommodate the nitrogen intake line. The nitrogen gas intake line components are shown in Figure A.3. 86 Figure A.3 Nitrogen intake set-up of the experimental unit Particulate filters The particulate filter was made of disposable borosilicate glass filter elements housed in stainless steel filter holders. Other in-line sintered metal filters were considered but were deemed undesirable as they may demonstrate catalytic effects at elevated temperatures. In addition, disposable filters are beneficial as used filter elements can be easily replaced. As described in Section 3.5.2, two parallel filter lines were implemented. This was to allow alternate usage of the two filtration lines to enable continuous operation without interruptions arising from blockages. Pressure gauges were installed upstream and downstream of the filters to indicate the blockages. The schematic of the filter set-up in the preliminary design stage is shown in Figure A.4. The orientations of the filter lines were modified so as to be able to be mounted onto the experimental unit. The final filter set-up is pictured in Figure A.5. For any future applications, it is strongly 87 recommended to keep the filtration line as short as possible to reduce the tar loss through adsorptions on the inside wall along the lines. Figure A.4 Preliminary design of the parallel filtration lines Figure A.5 Final filtration line set-up, heat traced and partially insulated Reactor The reactor schematic is shown in Figure A.6. A mesh screen was held in place with two Circlips to hold the catalyst bed in place. While the total length of the reactor was 440 mm, the heating 88 elements inside the furnace only extended about 270 mm. A thermocouple measuring the reactor wall temperature was used to control the temperature of the furnace. Another thermocouple was inserted from the top, about 1/3 into the reactor to measure the internal temperature of the reactor. For future applications, it is highly recommended to insert the thermocouple all the way to the catalyst bed to accurately measure the reaction temperatures. Figure A.6 Packed-bed reactor schematic. Tar collection impinger trains The impinger bottles used in the project are pictured in Figure A.7. As described in Section 3.5.2, two sets of impinger trains had to be set up. The twelve bottles were placed inside coolers on the bottom level of the experimental unit. As a solution to the space limitation and to allow easy-access, a pull-out tray was implemented as shown in Figure A.8. The samples collected in 89 the two impinger trains were combined in a separate glass jar (Figure A.9) and kept in the freezer at -20 °C until analysis. Figure A.7 Impinger bottles Figure A.8 Impinger bottles, baths and pull-out tray of the experimental unit 90 Figure A.9 Tar in isopropanol collected from the two impinger trains; before (left) and after (right) reaction. Bypass tar scrubbers The bypass tar scrubber schematic is shown in Figure A.10. The set-up consists of three 1 L borosilicate glass bottles in series. The bottles are connected with the two tubings going through tapered silicon plugs. The holes in the plug were sized slightly smaller than the tubes, and the plug was sized larger than the opening of the glass bottles. The screw cap allowed for an acceptable seal (tested to be able to hold vacuum for >20 min). As the sole purpose of the bypass tar scrubber was to scrub the tars, complete seal was not required. The close-up top-view of the set up is pictured in Figure A.11. While the bottles were filled with glass beads to produce smaller gas bubbles to enhance mass transfer, it is recommended to install a perforated end-cap at the bottom of the tubes. 91 Figure A.10 Scrubber bottle set-up schematic Figure A.11 Top-view of the scrubber bottle set-up 92 Appendix B Supplemental Data B.1 GC-MS Results Table B.1 Tar components before reaction from untreated BR experiment at 700 °C Peak no. Ret. Time Area % Library/ID 1 4.47 2.0309 Toluene $$ Benzene, methyl $$ Methacide $$ Methylbenzene $$ Methylbenzol $$ Tol 2 4.75 0.9733 1-Propanol $$ Propyl alcohol $$ n-Propan-1-ol $$ n-Propanol $$ n-Propyl alcohol 7 12.68 1.7846 2-Propanone, 1-hydroxy- $$ Acetol $$ CH3C(O)CH2OH $$ Hydroxyacetone 10 17.30 3.7636 Acetic acid $$ Ethanoic acid $$ Ethylic acid $$ Glacial acetic acid $$ CH3COOH 11 17.56 1.9059 2-Furancarboxaldehyde (CAS) $$ Furfural $$ 2-Furaldehyde $$ Fural $$ Furole 16 24.43 0.906 Naphthalene (CAS) $$ White tar $$ NAPHTALINE $$ Naphthene $$ Albocarbon 19 26.62 0.7082 2-Cyclopenten-1-one, 2-hydroxy-3-methyl- $$ Corylon $$ Corylone $$ Cycloten 20 27.30 1.1272 Phenol, 2-methoxy- $$ Phenol, o-methoxy- $$ o-Guaiacol $$ o-Hydroxyanisole 21 29.41 1.2748 2-Methoxy-4-methylphenol $$ Phenol, 2-methoxy-4-methyl- (CAS) $$ p-Creosol 22 30.44 2.8565 Phenol (CAS) $$ Izal $$ PhOH $$ Benzenol $$ Oxybenzene $$ Monophenol 23 30.98 0.4872 Phenol, 4-ethyl-2-methoxy- $$ p-Ethylguaiacol $$ 2-Methoxy-4-ethylphenol 24 32.04 2.382 Phenol, 3,5-dimethyl- $$ 3,5-Xylenol $$ 1-Hydroxy-3,5-dimethylbenzene 25 32.19 0.9917 Phenol, 4-methyl- $$ p-Cresol $$ p-Hydroxytoluene $$ p-Kresol $$ p-Methylphenol 26 33.72 0.5221 Phenol, 2-ethyl-5-methyl- $$ m-Cresol, 6-ethyl- $$ 2-Ethyl-5-methylphenol 27 33.88 0.7381 Phenol, 3-ethyl- $$ Phenol, m-ethyl- $$ m-Ethylphenol $$ 3-Ethylphenol 1 4.48 3.3424 Benzene, methyl- (CAS) $$ Toluene $$ Methylbenzene $$ Toluol $$ Methacide 2 4.80 1.4094 1-Propanol (CAS) $$ Propanol $$ n-Propanol $$ n-Propyl alcohol $$ Optal 7 12.29 1.7758 Methane, dimethoxy- (CAS) $$ Dimethoxymethane $$ Formal $$ Methylal 8 12.68 3.4266 2-Propanone, 1-hydroxy- $$ Acetol $$ CH3C(O)CH2OH $$ Hydroxyacetone 10 14.29 0.7835 2-Cyclopenten-1-one $$ Cyclopenten-3-one $$ Cyclopentenone $$ 2-Cyclopentenone 11 17.29 7.1252 Acetic acid $$ Ethanoic acid $$ Ethylic acid $$ Glacial acetic acid $$ CH3COOH 12 17.56 3.6317 2-Furancarboxaldehyde (CAS) $$ Furfural $$ 2-Furaldehyde $$ Fural $$ Furole 13 17.93 0.8723 1H-Indene (CAS) $$ Inden $$ Indene $$ Indonaphthene $$ 1H - indene (CAS) 15 20.49 1.0643 2-Furancarboxaldehyde, 5-methyl- $$ 2-Furaldehyde, 5-methyl- 18 24.43 2.0481 Naphthalene $$ Albocarbon $$ Dezodorator $$ Moth flakes $$ Naphthalin 21 26.62 1.0429 2-Cyclopenten-1-one, 2-hydroxy-3-methyl- $$ Corylon $$ Corylone $$ Cycloten 22 27.30 2.0793 Phenol, 2-methoxy- $$ Phenol, o-methoxy- $$ o-Guaiacol $$ o-Hydroxyanisole 23 29.41 2.3742 Phenol, 2-methoxy-4-methyl- $$ p-Cresol, 2-methoxy- $$ p-Creosol $$ Creosol 24 30.44 5.4658 Phenol (CAS) $$ Izal $$ PhOH $$ Benzenol $$ Oxybenzene $$ Monophenol 25 30.97 1.0872 Benzeneethanol, 2-methoxy- (CAS) $$ Phenethyl alcohol, o-methoxy- (CAS) 26 32.04 4.4859 Phenol, 3,4-dimethyl- $$ 3,4-Xylenol $$ 1-Hydroxy-3,4-dimethylbenzene 27 32.19 1.8473 Phenol, 4-methyl- $$ p-Cresol $$ p-Hydroxytoluene $$ p-Kresol $$ p-Methylphenol 28 33.72 1.1934 Phenol, 2-ethyl-5-methyl- $$ m-Cresol, 6-ethyl- $$ 2-Ethyl-5-methylphenol 29 33.88 1.41 Phenol, 3-ethyl- (CAS) $$ m-Ethylphenol $$ 1-Hydroxy-3-ethylbenzene 93 Table B.2 Tar components before reaction from nickel catalyst experiment at 700 °C Peak no. Ret. Time Area % Library/ID 2 4.82 1.20 1-Propanol (CAS) $$ Propanol $$ n-Propanol $$ n-Propyl alcohol $$ Optal 4 6.50 0.78 Undecane (CAS) $$ n-Undecane $$ Hendecane $$ n-C11H24 $$ UNDECAN 6 9.95 5.14 Dodecane $$ n-Dodecane $$ Adakane 12 $$ Ba 51-090453 $$ CH3(CH2)10CH3 10 11.76 1.84 Tridecane, 7-methyl- $$ 7-Methyltridecane 14 12.69 1.41 2-Propanone, 1-hydroxy- $$ Acetol $$ CH3C(O)CH2OH $$ Hydroxyacetone 15 13.17 4.21 Tridecane $$ n-Tridecane $$ Tridecane, n- 16 14.29 0.57 2-Cyclopenten-1-one $$ Cyclopenten-3-one $$ Cyclopentenone $$ 2-Cyclopentenone 18 16.13 1.24 Tetradecane $$ n-Tetradecane 19 17.30 4.19 Acetic acid (CAS) $$ Ethylic acid $$ Vinegar acid $$ Ethanoic acid $$ CH3COOH 20 17.57 2.47 2-Furancarboxaldehyde (CAS) $$ Furfural $$ 2-Furaldehyde $$ Fural $$ Furole 25 24.43 1.28 Naphthalene $$ Albocarbon $$ Dezodorator $$ Moth flakes $$ Naphthalin 27 26.62 0.63 2-Cyclopenten-1-one, 2-hydroxy-3-methyl- $$ Corylon $$ Corylone $$ Cycloten 28 27.30 2.42 Phenol, 2-methoxy- $$ Phenol, o-methoxy- $$ o-Guaiacol $$ o-Hydroxyanisole 29 29.41 2.87 Phenol, 2-methoxy-4-methyl- $$ p-Cresol, 2-methoxy- $$ p-Creosol $$ Creosol 30 30.45 3.05 Phenol (CAS) $$ Izal $$ PhOH $$ Benzenol $$ Oxybenzene $$ Monophenol 31 30.98 1.03 Phenol, 4-ethyl-2-methoxy- (CAS) $$ p-Ethylguaiacol $$ 4-Ethylguaiacol 33 32.19 1.06 Phenol, 4-methyl- (CAS) $$ p-Cresol $$ p-Toluol $$ 4-Cresol $$ p-Kresol 36 34.25 0.63 2-Methoxy-4-vinylphenol $$ Phenol, 4-ethenyl-2-methoxy- $$ p-Vinylguaiacol 37 37.09 0.84 Phenol, 2-methoxy-4-(1-propenyl)-, (E)- $$ Phenol, 2-methoxy-4-propenyl-, (E)- 39 45.53 2.85 Hexanedioic acid, bis(2-ethylhexyl) ester $$ Adipol 2EH $$ Bisoflex DOA $$ Beha 2 4.82 1.01 1-Propanol (CAS) $$ Propanol $$ n-Propanol $$ n-Propyl alcohol $$ Optal 4 6.49 0.96 Undecane $$ n-Undecane $$ Hendecane $$ n-C11H24 6 9.95 5.33 Dodecane $$ n-Dodecane $$ Adakane 12 $$ Ba 51-090453 $$ CH3(CH2)10CH3 10 11.76 1.88 Octane, 2,6-dimethyl- $$ 2,6-Dimethyloctane 14 12.69 1.64 2-Propanone, 1-hydroxy- $$ Acetol $$ CH3C(O)CH2OH $$ Hydroxyacetone 15 13.17 4.41 Tridecane $$ n-Tridecane $$ Tridecane, n- 18 16.14 1.23 Tetradecane $$ n-Tetradecane 19 17.30 4.29 Acetic acid (CAS) $$ Ethylic acid $$ Vinegar acid $$ Ethanoic acid $$ CH3COOH 20 17.57 2.55 2-Furancarboxaldehyde (CAS) $$ Furfural $$ 2-Furaldehyde $$ Fural $$ Furole 25 24.43 1.32 Naphthalene $$ Albocarbon $$ Dezodorator $$ Moth flakes $$ Naphthalin 28 27.31 2.52 Phenol, 2-methoxy- $$ Phenol, o-methoxy- $$ o-Guaiacol $$ o-Hydroxyanisole 29 29.41 2.85 Phenol, 2-methoxy-4-methyl- $$ p-Cresol, 2-methoxy- $$ p-Creosol $$ Creosol 30 30.45 3.17 Phenol (CAS) $$ Izal $$ PhOH $$ Benzenol $$ Oxybenzene $$ Monophenol 31 30.98 1.06 Phenol, 4-ethyl-2-methoxy- (CAS) $$ p-Ethylguaiacol $$ 4-Ethylguaiacol 32 32.05 2.52 Phenol, 3,4-dimethyl- $$ 3,4-Xylenol $$ 1-Hydroxy-3,4-dimethylbenzene 33 32.19 1.09 Phenol, 3-methyl- $$ m-Cresol $$ m-Cresole $$ m-Cresylic acid $$ m-Kresol 36 34.26 0.68 2-Methoxy-4-vinylphenol $$ Phenol, 4-ethenyl-2-methoxy- $$ p-Vinylguaiacol 37 37.10 0.91 Phenol, 2-methoxy-4-(1-propenyl)-, (E)- (CAS) $$ (E)-Isoeugenol 39 45.54 2.85 Hexanedioic acid, bis(2-ethylhexyl) ester $$ Adipol 2EH $$ Bisoflex DOA $$ Beha 94 Table B.3 Tar components after reaction from untreated BR experiment at 700 °C Peak no. Ret. Time Area % Library/ID 1 4.50 14.14 Toluene $$ Benzene, methyl $$ Methacide $$ Methylbenzene $$ Methylbenzol $$ Tol 2 4.77 3.08 1-Propanol (CAS) $$ Propanol $$ n-Propanol $$ n-Propyl alcohol $$ Optal 4 7.54 1.69 Benzene, 1,4-dimethyl- (CAS) $$ p-Xylene $$ p-Xylol $$ 1,4-Xylene $$ Chromar 7 11.34 5.33 Styrene $$ Benzene, ethenyl- $$ Bulstren K-525-19 $$ Cinnamene $$ Phenethylene 10 24.43 10.57 Naphthalene $$ Albocarbon $$ Dezodorator $$ Moth flakes $$ Naphthalin 11 27.03 2.60 Naphthalene, 1-methyl- $$ .alpha.-Methylnaphthalene $$ 1-Methylnaphthalene 12 27.80 2.08 Naphthalene, 1-methyl- (CAS) $$ 1-Methylnaphthalene $$ 1-METHYL NAPHTHALENE 13 30.02 2.23 1,1'-Biphenyl (CAS) $$ Biphenyl (CAS) $$ Diphenyl $$ Bibenzene $$ 1,1'-Diphenyl 14 34.09 1.44 Biphenylene (CAS) $$ 1,1'-Biphenylene (CAS) $$ Diphenylene $$ BIPHENYL 1 4.50 15.55 Toluene $$ Benzene, methyl $$ Methacide $$ Methylbenzene $$ Methylbenzol $$ Tol 2 4.78 3.43 1-Propanol $$ Propyl alcohol $$ n-Propan-1-ol $$ n-Propanol $$ n-Propyl alcohol 4 7.54 1.81 Benzene, 1,2-dimethyl- (CAS) $$ o-Xylene $$ o-Xylol $$ 3,4-Xylene $$ 1,2-Xylene 7 11.34 5.73 Styrene $$ Benzene, ethenyl- $$ Bulstren K-525-19 $$ Cinnamene $$ Phenethylene 9 14.49 1.98 Benzene, 1,1'-(1-ethenyl-1,3-propanediyl)bis- $$ 3,5-Diphenyl-1-pentene 10 24.43 11.49 Naphthalene $$ Albocarbon $$ Dezodorator $$ Moth flakes $$ Naphthalin 11 27.03 2.77 Naphthalene, 1-methyl- (CAS) $$ 1-Methylnaphthalene $$ 1-METHYL NAPHTHALENE 12 27.80 2.20 Naphthalene, 1-methyl- $$ .alpha.-Methylnaphthalene $$ 1-Methylnaphthalene 13 30.02 2.39 1,1'-Biphenyl (CAS) $$ Biphenyl (CAS) $$ Diphenyl $$ Bibenzene $$ 1,1'-Diphenyl 14 34.09 1.57 Biphenylene (CAS) $$ 1,1'-Biphenylene (CAS) $$ Diphenylene $$ BIPHENYL Table B.4 Tar components after reaction from nickel catalyst experiment at 700 °C Peak no. Ret. Time Area % Library/ID 1 4.71 5.64 1-Propanol (CAS) $$ Propanol $$ n-Propanol $$ n-Propyl alcohol $$ Optal 3 6.61 4.55 Undecane $$ n-Undecane $$ Hendecane $$ n-C11H24 5 9.94 18.30 Dodecane $$ n-Dodecane $$ Adakane 12 $$ Ba 51-090453 $$ CH3(CH2)10CH3 10 11.76 6.80 Tridecane, 7-methyl- $$ 7-Methyltridecane 14 13.17 16.92 Tridecane (CAS) $$ n-Tridecane $$ Tridecane, n- $$ n - tri - decanene 16 16.13 5.12 Tetradecane (CAS) $$ n-Tetradecane $$ Isotetradecane $$ n - tetra - decane 17 45.53 9.86 Hexanedioic acid, bis(2-ethylhexyl) ester $$ Adipol 2EH $$ Bisoflex DOA $$ Beha 1 4.70 6.31 1-Propanol $$ Propyl alcohol $$ n-Propan-1-ol $$ n-Propanol $$ n-Propyl alcohol 3 6.60 5.10 Undecane (CAS) $$ n-Undecane $$ Hendecane $$ n-C11H24 $$ UNDECAN 5 9.94 19.28 Dodecane $$ n-Dodecane $$ Adakane 12 $$ Ba 51-090453 $$ CH3(CH2)10CH3 12 13.16 18.26 Tridecane (CAS) $$ n-Tridecane $$ Tridecane, n- $$ n - tri - decanene 14 16.13 5.43 Tetradecane $$ n-Tetradecane 15 45.53 11.44 Hexanedioic acid, bis(2-ethylhexyl) ester $$ Adipol 2EH $$ Bisoflex DOA $$ Beha 95 B.2 GC-FID Results Table B.5 Tar components before and after reaction from catalyst-blank experiment at 700 °C Tar sample before reaction Tar sample after reaction Component Ret. time Area Area % Component Ret. time Area Area % Methanol 0.066 31165.47 87.8054 Methanol 0.066 31232.39 87.8199 (unknown) 0.366 6.603 0.0186 (unknown) 0.366 15.782 0.0444 Acetone 0 0 0 Acetone 0 0 0 (unknown) 1.883 606.2565 1.7081 (unknown) 1.983 271.603 0.7637 (unknown) 2.15 390.5415 1.1003 (unknown) 2.133 452.4825 1.2723 (unknown) 2.433 706.766 1.9912 (unknown) 2.4 1258.314 3.5382 (unknown) 3.166 188.574 0.5313 (unknown) 4.183 62.527 0.1758 (unknown) 3.583 177.551 0.5002 Phenol 4.766 7.726 0.0217 (unknown) 4.183 45.493 0.1282 Phenol 5.166 192.687 0.5418 (unknown) 4.45 7.0455 0.0198 (unknown) 5.766 1.872 0.0053 (unknown) 4.75 9.7935 0.0276 (unknown) 5.95 4.897 0.0138 Phenol 5.116 104.459 0.2943 (unknown) 6.25 22.238 0.0625 (unknown) 6 13.1085 0.0369 (unknown) 6.633 81.584 0.2294 (unknown) 6.283 54.154 0.1526 (unknown) 7.05 8.7725 0.0247 (unknown) 6.666 27.312 0.0769 (unknown) 7.216 4.026 0.0113 (unknown) 7.2 39.454 0.1112 (unknown) 7.4 10.152 0.0285 (unknown) 7.566 70.242 0.1979 (unknown) 7.55 24.739 0.0696 (unknown) 8.05 48.44 0.1365 (unknown) 7.966 7.706 0.0217 (unknown) 8.283 69.029 0.1945 (unknown) 8.233 68.704 0.1932 (unknown) 8.7 35.895 0.1011 (unknown) 8.633 36.515 0.1027 (unknown) 9.166 65.219 0.1837 (unknown) 9.1 64.75 0.1821 (unknown) 9.466 134.8485 0.3799 (unknown) 9.4 156.1705 0.4391 (unknown) 9.833 27.117 0.0764 (unknown) 9.783 22.457 0.0631 (unknown) 10.316 76.435 0.2153 (unknown) 10.1 42.9925 0.1209 Naphthalene 10.6 31.003 0.0873 Naphthalene 10.5 168.46 0.4737 (unknown) 10.783 32.275 0.0909 (unknown) 11.05 35.818 0.1007 (unknown) 11.133 103.79 0.2924 (unknown) 11.216 8.138 0.0229 (unknown) 11.616 20.39 0.0574 (unknown) 11.633 11.73 0.0330 (unknown) 11.916 8.928 0.0252 (unknown) 11.783 10.796 0.0304 (unknown) 12.4 301.362 0.8491 (unknown) 12.233 305.168 0.8581 (unknown) 12.883 113.839 0.3207 (unknown) 12.7 106.95 0.3007 (unknown) 13.333 8.308 0.0234 (unknown) 13.183 12.722 0.0358 (unknown) 13.65 22.63 0.0638 (unknown) 13.516 21.3865 0.0601 (unknown) 14.233 27.53 0.0776 (unknown) 14.016 33.64 0.0946 (unknown) 14.55 123.05 0.3467 (unknown) 14.366 127.971 0.3598 (unknown) 15.3 292.067 0.8229 (unknown) 15.033 312.742 0.8794 Acenaphthylene 15.766 38.472 0.1084 Acenaphthylene 15.433 3.654 0.0103 Acenaphthene 0 0 0 Acenaphthylene 15.666 11.9425 0.0336 (unknown) 16.666 3.4785 0.0098 Acenaphthene 16.3 5.668 0.0159 (unknown) 16.866 7.2375 0.0204 Acenaphthene 16.483 3.782 0.0106 (unknown) 17.166 24.7 0.0696 (unknown) 16.816 41.8745 0.1177 (unknown) 17.683 91.825 0.2587 (unknown) 17.25 78.125 0.2197 Fluorene 0 0 0 (unknown) 17.866 1.721 0.0048 (unknown) 18.883 5.276 0.0149 Fluorene 0 0 0 (unknown) 19.1 6.253 0.0176 (unknown) 18.5 4.813 0.0135 (unknown) 19.533 8.625 0.0243 (unknown) 19.1 5.561 0.0156 (unknown) 20.183 4.564 0.0129 (unknown) 19.366 1.4585 0.0041 Phenanthrene 0 0 0 (unknown) 19.683 6.4135 0.0180 96 Tar sample before reaction Tar sample after reaction Component Ret. time Area Area % Component Ret. time Area Area % (unknown) 20.733 1.5005 0.0042 Phenanthrene 0 0 0 Anthracene 0 0 0 Anthracene 20.966 1.56 0.0044 (unknown) 21.05 5.434 0.0153 (unknown) 21.35 1.317 0.0037 (unknown) 21.266 1.55 0.0044 (unknown) 22.416 1.134 0.0032 (unknown) 21.85 3.526 0.0099 (unknown) 22.583 1.861 0.0052 (unknown) 23.05 2.5655 0.0072 (unknown) 23.333 21.0055 0.0591 (unknown) 23.333 1.054 0.003 (unknown) 24.133 3.785 0.0106 (unknown) 23.6 9.153 0.0258 Fluoranthene 0 0 0.0000 Fluoranthene 0 0 0 (unknown) 24.95 11.752 0.0330 O-terphenyl 0 0 0 O-terphenyl 0 0 0 Pyrene 25.216 9.708 0.0274 Pyrene 0 0 0 (unknown) 26.366 3.433 0.0097 (unknown) 26.1 6.601 0.0186 (unknown) 28.733 4.354 0.0123 (unknown) 28.583 1.5075 0.0042 Chrysene 29.533 2.1875 0.0062 Chrysene 29.283 2.815 0.0079 (unknown) 32.25 81.4875 0.2296 (unknown) 30.666 1.531 0.0043 (unknown) 33.566 1.466 0.0041 (unknown) 31.883 83.047 0.2335 (unknown) 34.1 6.277 0.0177 (unknown) 33.866 10.469 0.0294 (unknown) 35.75 1.404 0.004 (unknown) 34.716 1.543 0.0043 Benzo(a)pyrene 36.633 10.9225 0.0308 (unknown) 35.15 4.042 0.0114 (unknown) 38.133 2.3475 0.0066 Benzo(a)pyrene 36.1 8.297 0.0233 Benzo(a)pyrene 36.533 1.877 0.0053 (unknown) 37.733 28.387 0.0798 Total area % of tar components 12.1946 Total area % of tar components 12.1770 % Total tar reduction 0.14% Table B.6 Tar components before and after reaction from catalyst-blank experiment at 750 °C Tar sample before reaction Tar sample after reaction Component Retention Area Area % Component Retention Area Area % (unknown) 0.05 1.106 0.0033 Methanol 0.083 34279.075 94.9464 Methanol 0 0 0 (unknown) 0.366 4.198 0.0116 (unknown) 0.35 3.734 0.011 Acetone 0 0 0 Isopropanol 0.566 32101.693 94.414 (unknown) 2.133 374.62 1.0376 (unknown) 2.116 339.5305 0.9986 (unknown) 2.416 709.278 1.9646 (unknown) 2.383 492.365 1.4481 (unknown) 4.166 3.2935 0.0091 (unknown) 3.083 124.541 0.3663 (unknown) 4.733 6.648 0.0184 (unknown) 3.5 87.2165 0.2565 Phenol 5.05 181.434 0.5025 (unknown) 4.066 13.976 0.0411 (unknown) 6.6 113.9055 0.3155 (unknown) 4.3 1.875 0.0055 (unknown) 7.55 16.7535 0.0464 (unknown) 4.616 22.269 0.0655 (unknown) 8.25 18.613 0.0516 Phenol 4.916 131.586 0.387 (unknown) 8.516 10.195 0.0282 Phenol 5.45 1.412 0.0042 (unknown) 9 1.145 0.0032 (unknown) 5.833 12.908 0.038 (unknown) 9.883 14.871 0.0412 (unknown) 6.133 31.759 0.0934 Naphthalene 10.516 165.938 0.4596 (unknown) 6.516 23.54 0.0692 (unknown) 11.366 1.028 0.0028 (unknown) 7.083 8.213 0.0242 (unknown) 11.716 3.712 0.0103 (unknown) 7.4 54.086 0.1591 (unknown) 13.483 23.583 0.0653 (unknown) 7.916 11.207 0.033 (unknown) 13.8 17.423 0.0483 (unknown) 8.1 72.315 0.2127 (unknown) 14.583 1.3425 0.0037 (unknown) 8.433 4.949 0.0146 Acenaphthylene 15.516 3.861 0.0107 97 Tar sample before reaction Tar sample after reaction Component Retention Area Area % Component Retention Area Area % (unknown) 8.6 5.213 0.0153 (unknown) 16.1 1.0405 0.0029 (unknown) 8.866 2.708 0.008 Acenaphthene 16.3 1.216 0.0034 (unknown) 9.083 3.261 0.0096 (unknown) 16.616 24.939 0.0691 (unknown) 9.7 17.197 0.0506 (unknown) 17.733 1.946 0.0054 (unknown) 9.9 5.189 0.0153 Fluorene 18.083 2.739 0.0076 (unknown) 10.133 35.035 0.103 (unknown) 19.166 2.291 0.0063 Naphthalene 10.45 47.1365 0.1386 (unknown) 19.466 2.263 0.0063 (unknown) 10.8 7.969 0.0234 (unknown) 20.283 1.0305 0.0029 (unknown) 10.966 16.285 0.0479 Phenanthrene 20.666 1.952 0.0054 (unknown) 11.416 9.987 0.0294 Anthracene 0 0 0 (unknown) 12.033 22.084 0.065 (unknown) 22.133 15.467 0.0428 (unknown) 12.433 4.587 0.0135 (unknown) 22.883 12.389 0.0343 (unknown) 12.666 13.641 0.0401 (unknown) 23.916 2.117 0.0059 (unknown) 12.833 1.385 0.0041 Fluoranthene 24.65 8.954 0.0248 (unknown) 13.416 25.116 0.0739 Pyrene 0 0 0 (unknown) 13.766 12.397 0.0365 (unknown) 25.9 3.237 0.009 (unknown) 14.4 47.642 0.1401 (unknown) 26.483 1.028 0.0028 (unknown) 15.183 4.476 0.0132 (unknown) 26.983 1.307 0.0036 Acenaphthylene 15.6 16.104 0.0474 (unknown) 28.25 3.9005 0.0108 (unknown) 16.033 1.413 0.0042 Chrysene 29.366 1.033 0.0029 (unknown) 16.266 4.5725 0.0134 (unknown) 30.766 4.005 0.0111 Acenaphthene 0 0 0 (unknown) 31.85 28.024 0.0776 (unknown) 16.6 9.7965 0.0288 (unknown) 33.783 4.638 0.0128 (unknown) 17.25 9.0605 0.0266 Benzo(a)pyrene 36.566 19.2135 0.0532 Fluorene 18.15 4.204 0.0124 (unknown) 37.85 7.973 0.0221 (unknown) 18.45 15.955 0.0469 (unknown) 19.066 1.157 0.0034 (unknown) 19.366 3.6385 0.0107 (unknown) 20.033 1.2855 0.0038 Phenanthrene 20.533 2.557 0.0075 Anthracene 0 0 0 (unknown) 21.116 7.309 0.0215 (unknown) 21.983 7.533 0.0222 (unknown) 22.766 21.2665 0.0625 (unknown) 24.516 8.538 0.0251 Fluoranthene 0 0 0 Pyrene 0 0 0 (unknown) 25.8 4.125 0.0121 (unknown) 26.933 2.291 0.0067 Chrysene 29.216 1.265 0.0037 (unknown) 31 3.816 0.0112 (unknown) 31.866 34.9565 0.1028 (unknown) 33.866 2.592 0.0076 Benzo(a)pyrene 36.616 10.992 0.0323 (unknown) 38.05 3.733 0.011 (unknown) 38.2 1.2315 0.0036 Total area % of tar components 5.586 Total area % of tar components 5.0536 % Total tar reduction 9.5% 98 Table B.7 Tar components before and after reaction from nickel catalyst experiment at 700 °C Tar sample before reaction Tar sample after reaction Component Ret. time Area Area % Component Ret. time Area Area % (unknown) 0.066 1.111 0.0031 Methanol 0 0 0 Methanol 0 0 0 Isopropanol 0.333 32170.354 95.6702 Isopropanol 0.366 31883.424 87.6915 Acetone 0 0 0 Acetone 0 0 0 Phenol 5.016 8.9885 0.0267 (unknown) 1.916 708.207 1.9478 (unknown) 5.466 8.336 0.0248 (unknown) 2.183 444.478 1.2225 (unknown) 5.8 1.75 0.0052 (unknown) 2.466 468.81 1.2894 (unknown) 5.983 4.858 0.0144 (unknown) 2.85 233.896 0.6433 (unknown) 6.283 16.308 0.0485 (unknown) 3.2 167.168 0.4598 (unknown) 6.7 7.6505 0.0228 (unknown) 3.7 174.9785 0.4813 (unknown) 7.083 9.143 0.0272 (unknown) 4.216 36.3455 0.1 (unknown) 7.25 2.775 0.0083 (unknown) 4.766 6.403 0.0176 (unknown) 7.416 24.593 0.0731 Phenol 5.15 123.098 0.3386 (unknown) 8 8.231 0.0245 (unknown) 5.833 1.146 0.0032 (unknown) 8.216 26.96 0.0802 (unknown) 6 23.0695 0.0634 (unknown) 8.65 23.3585 0.0695 (unknown) 6.283 43.938 0.1208 (unknown) 9.116 50.276 0.1495 (unknown) 6.683 34.171 0.094 (unknown) 9.4 121.289 0.3607 (unknown) 7.183 27.589 0.0759 (unknown) 9.783 6.597 0.0196 (unknown) 7.566 64.395 0.1771 (unknown) 10.116 41.637 0.1238 (unknown) 8.033 84.44 0.2322 Naphthalene 10.366 6.4055 0.019 (unknown) 8.25 75.042 0.2064 Naphthalene 10.5 3.406 0.0101 (unknown) 8.7 31.3845 0.0863 Naphthalene 10.7 37.492 0.1115 (unknown) 9.15 53.28 0.1465 (unknown) 11.05 47.153 0.1402 (unknown) 9.433 107.5345 0.2958 (unknown) 11.35 1.131 0.0034 (unknown) 9.816 16.227 0.0446 (unknown) 11.6 8.4445 0.0251 (unknown) 10.25 61.389 0.1688 (unknown) 11.75 8.918 0.0265 Naphthalene 10.55 30.319 0.0834 (unknown) 12.183 230.043 0.6841 Naphthalene 10.733 26.207 0.0721 (unknown) 12.616 47.488 0.1412 (unknown) 11.033 140.964 0.3877 (unknown) 12.85 7.431 0.0221 (unknown) 11.533 17.6195 0.0485 (unknown) 13.066 10.63 0.0316 (unknown) 11.816 7.516 0.0207 (unknown) 13.3 3.378 0.01 (unknown) 12.25 261.2005 0.7184 (unknown) 13.6 4.683 0.0139 (unknown) 12.7 87.353 0.2403 (unknown) 13.85 16.571 0.0493 (unknown) 13.15 4.341 0.0119 (unknown) 14.15 99.22 0.2951 (unknown) 13.4 36.06 0.0992 (unknown) 14.766 229.0415 0.6811 (unknown) 13.933 31.437 0.0865 (unknown) 15.166 7.8045 0.0232 (unknown) 14.2 111.645 0.3071 (unknown) 15.4 13.842 0.0412 (unknown) 14.8 227.192 0.6249 Acenaphthylene 0 0 0 (unknown) 15.2 17.833 0.049 (unknown) 15.983 4.979 0.0148 Acenaphthylene 15.45 18.204 0.0501 (unknown) 16.15 2.1825 0.0065 (unknown) 15.833 1.115 0.0031 Acenaphthene 16.433 19.46 0.0579 (unknown) 16.016 2.341 0.0064 (unknown) 16.883 58.621 0.1743 (unknown) 16.216 5.764 0.0159 (unknown) 17.533 2.107 0.0063 Acenaphthene 16.45 20.1465 0.0554 Fluorene 18.05 7.382 0.022 (unknown) 16.866 85.161 0.2342 (unknown) 18.716 3.9345 0.0117 (unknown) 17.5 3.951 0.0109 (unknown) 19.3 5.482 0.0163 Fluorene 18.066 16.811 0.0462 (unknown) 20.45 2.663 0.0079 Fluorene 18.383 41.86 0.1151 Phenanthrene 0 0 0 (unknown) 18.683 5.4595 0.015 Anthracene 0 0 0 (unknown) 19.266 4.6635 0.0128 (unknown) 22.033 7.724 0.023 (unknown) 19.966 4.39 0.0121 (unknown) 22.7 24.2795 0.0722 99 Tar sample before reaction Tar sample after reaction Component Ret. time Area Area % Component Ret. time Area Area % (unknown) 20.433 19.778 0.0544 (unknown) 23.516 2.28 0.0068 Phenanthrene 0 0 0 (unknown) 24.266 8.5475 0.0254 Anthracene 0 0 0 Fluoranthene 0 0 0 (unknown) 21.066 16.529 0.0455 O-terphenyl 0 0 0 (unknown) 21.6 3.439 0.0095 (unknown) 25.083 6.3625 0.0189 (unknown) 22.266 13.3025 0.0366 Pyrene 0 0 0 (unknown) 22.583 5.459 0.015 (unknown) 25.583 2.2235 0.0066 (unknown) 22.8 6.7905 0.0187 (unknown) 26.3 2.982 0.0089 (unknown) 24.466 11.001 0.0303 (unknown) 27.533 1.214 0.0036 Fluoranthene 0 0 0 (unknown) 27.9 6.101 0.0181 O-terphenyl 0 0 0 (unknown) 28.466 4.8915 0.0145 Pyrene 25.233 3.681 0.0101 Chrysene 29.65 2.135 0.0063 (unknown) 25.666 3.72 0.0102 (unknown) 30.066 1.46 0.0043 (unknown) 26.533 1.2925 0.0036 (unknown) 30.916 33.9775 0.101 (unknown) 27.116 1.5185 0.0042 (unknown) 31.333 1.913 0.0057 (unknown) 28.033 13.069 0.0359 (unknown) 32.566 14.619 0.0435 (unknown) 28.483 1.614 0.0044 (unknown) 33.883 8.701 0.0259 Chrysene 29.383 1.88 0.0052 (unknown) 34.933 7.8515 0.0233 (unknown) 31.1 68.061 0.1872 (unknown) 35.1 1.6735 0.005 (unknown) 31.6 1.156 0.0032 Benzo(a)pyrene 36.2 48.2015 0.1433 (unknown) 32.783 14.476 0.0398 (unknown) 37.616 3.3285 0.0099 (unknown) 33.733 2.1545 0.0059 (unknown) 38.366 5.9655 0.0177 (unknown) 34.216 5.08 0.014 (unknown) 39.1 1.304 0.0039 (unknown) 35.483 26.186 0.072 (unknown) 40.933 5.557 0.0165 Benzo(a)pyrene 36.6 48.692 0.1339 (unknown) 37.916 5.75 0.0158 (unknown) 39 1.276 0.0035 (unknown) 40.916 1.6265 0.0045 Total area % of tar components 12.3085 Total area % of tar components 4.3298 % Total tar reduction 64.8% 100 Table B.8 Tar components before and after reaction from untreated BR catalyst experiment at 700 °C Tar sample before reaction Tar sample after reaction Component Ret. time Area Area % Component Ret. time Area Area % Methanol 0.066 28965.621 88.2636 Methanol 0.083 31912.6035 93.5763 (unknown) 0.366 15.222 0.0464 (unknown) 0.366 2.596 0.0076 Acetone 0 0 0 Acetone 0 0 0 (unknown) 1.9 1165.7835 3.5524 (unknown) 2.183 411.988 1.2081 (unknown) 2.45 510.328 1.5551 (unknown) 2.466 1225.813 3.5944 (unknown) 2.833 262.626 0.8003 Phenol 4.833 9.35 0.0274 (unknown) 3.183 220.263 0.6712 Phenol 5.283 27.407 0.0804 (unknown) 3.65 215.6815 0.6572 (unknown) 6.3 2.603 0.0076 (unknown) 4.2 43.3765 0.1322 (unknown) 6.716 6.962 0.0204 Phenol 4.766 14.2685 0.0435 (unknown) 7.066 1.814 0.0053 Phenol 5.15 140.475 0.4281 (unknown) 7.45 3.267 0.0096 (unknown) 5.983 25.2605 0.077 (unknown) 8.266 3.641 0.0107 (unknown) 6.283 43.3155 0.132 (unknown) 8.683 3.185 0.0093 (unknown) 6.666 31.399 0.0957 (unknown) 9.15 6.3395 0.0186 (unknown) 7.183 15.1565 0.0462 (unknown) 9.45 14.7185 0.0432 (unknown) 7.383 6.571 0.02 (unknown) 10.15 8.748 0.0257 (unknown) 7.566 58.7525 0.179 Naphthalene 10.533 154.672 0.4535 (unknown) 8.05 50.9605 0.1553 (unknown) 11.083 5.801 0.017 (unknown) 8.266 86.87 0.2647 (unknown) 11.55 1.177 0.0035 (unknown) 8.716 22.2355 0.0678 (unknown) 11.816 1.1275 0.0033 (unknown) 8.983 4.6875 0.0143 (unknown) 12.25 28.412 0.0833 (unknown) 9.166 8.523 0.026 (unknown) 12.716 10.151 0.0298 (unknown) 9.45 19.959 0.0608 (unknown) 13.183 1.4105 0.0041 (unknown) 9.8 19.992 0.0609 (unknown) 13.55 18.4595 0.0541 (unknown) 10 8.793 0.0268 (unknown) 13.9 20.498 0.0601 Naphthalene 10.25 47.7515 0.1455 (unknown) 14.35 12.043 0.0353 Naphthalene 10.55 42.3675 0.1291 (unknown) 15.033 29.8785 0.0876 Naphthalene 10.866 9.737 0.0297 Acenaphthylene 15.733 14.065 0.0412 (unknown) 11.05 59.986 0.1828 Acenaphthene 0 0 0 (unknown) 11.25 2.4875 0.0076 (unknown) 16.616 1.644 0.0048 (unknown) 11.483 18.991 0.0579 (unknown) 16.933 15.361 0.045 (unknown) 12.216 122.4295 0.3731 (unknown) 17.416 6.07 0.0178 (unknown) 12.683 35.9325 0.1095 Fluorene 0 0 0 (unknown) 13.45 28.714 0.0875 (unknown) 18.566 14.2765 0.0419 (unknown) 13.883 17.615 0.0537 (unknown) 20.316 5.476 0.0161 (unknown) 14.316 26.437 0.0806 Phenanthrene 0 0 0 (unknown) 14.766 4.4045 0.0134 Anthracene 0 0 0 (unknown) 15.166 50.086 0.1526 (unknown) 21.65 2.849 0.0084 Acenaphthylene 15.666 26.771 0.0816 (unknown) 23.066 12.029 0.0353 Acenaphthene 0 0 0 (unknown) 23.683 22.8085 0.0669 (unknown) 17.15 12.245 0.0373 Fluoranthene 0 0 0 (unknown) 17.483 3.3645 0.0103 O-terphenyl 0 0 0 Fluorene 18.283 37.1545 0.1132 Pyrene 25.216 10.863 0.0319 (unknown) 19 7.825 0.0238 (unknown) 26.35 2.2175 0.0065 (unknown) 19.6 2.06 0.0063 (unknown) 27.233 4.158 0.0122 (unknown) 19.966 24.9075 0.0759 (unknown) 28.7 9.549 0.028 Phenanthrene 20.616 7.392 0.0225 Chrysene 29.4 3.761 0.011 Anthracene 0 0 0 (unknown) 31.35 1.319 0.0039 (unknown) 21.533 1.254 0.0038 (unknown) 31.866 1.6125 0.0047 (unknown) 22.566 5.173 0.0158 (unknown) 33.916 7.8715 0.0231 (unknown) 22.733 8.512 0.0259 (unknown) 35.633 2.957 0.0087 101 Tar sample before reaction Tar sample after reaction Component Ret. time Area Area % Component Ret. time Area Area % (unknown) 23.833 7.7615 0.0237 Benzo(a)pyrene 36.35 8.287 0.0243 (unknown) 24.35 2.875 0.0088 Benzo(a)pyrene 36.733 2.5195 0.0074 Fluoranthene 24.616 3.73 0.0114 (unknown) 38.116 27.9015 0.0818 O-terphenyl 24.983 14.4985 0.0442 (unknown) 39.283 1.041 0.0031 Pyrene 0 0 0 (unknown) 25.716 1.0115 0.0031 (unknown) 26.55 12.4295 0.0379 (unknown) 27.483 9.099 0.0277 (unknown) 28.116 2.726 0.0083 (unknown) 29.166 9.054 0.0276 Chrysene 29.783 2.656 0.0081 (unknown) 30.75 2.531 0.0077 (unknown) 31.85 48.515 0.1478 (unknown) 33.333 9.788 0.0298 (unknown) 34.633 5.919 0.018 Benzo(a)pyrene 0 0 0 (unknown) 36.983 114.971 0.3503 (unknown) 38.716 3.649 0.0111 (unknown) 40.083 6.229 0.019 Total area % of tar components 11.7364 Total area % of tar components 6.4237 % Total tar reduction 45.3% Table B.9 Tar components before and after reaction from untreated BR catalyst experiment at 750 °C Tar sample before reaction Tar sample after reaction Component Ret. Time Area Area % Component Ret. Time Area Area % Methanol 0 0 0 (unknown) 0.05 1.215 0.0036 Isopropanol 0.333 33255.537 94.6646 Methanol 0 0 0 (unknown) 2.383 627.973 1.7876 Isopropanol 0.35 33045.839 98.6091 (unknown) 3.1 127.324 0.3624 Acetone 0 0 0 (unknown) 3.7 115.761 0.3295 Phenol 5.316 3.986 0.0119 (unknown) 4.133 12.851 0.0366 Naphthalene 10.55 100.531 0.3 (unknown) 4.35 1.372 0.0039 (unknown) 13.7 4.086 0.0122 (unknown) 4.683 16.3265 0.0465 (unknown) 14.033 4.894 0.0146 Phenol 5.083 133.505 0.38 (unknown) 15.216 1.157 0.0035 Phenol 5.533 2.1645 0.0062 Acenaphthylene 0 0 0 (unknown) 5.916 15.6295 0.0445 (unknown) 16.05 5.127 0.0153 (unknown) 6.2 30.5725 0.087 Acenaphthene 0 0 0 (unknown) 6.583 23.662 0.0674 (unknown) 17.35 3.8745 0.0116 (unknown) 7.133 8.695 0.0248 Fluorene 0 0 0 (unknown) 7.3 6.431 0.0183 (unknown) 19.1 21.1175 0.063 (unknown) 7.483 56.8585 0.1619 Phenanthrene 0 0 0 (unknown) 7.966 46.725 0.133 Anthracene 20.916 13.291 0.0397 (unknown) 8.2 66.869 0.1903 (unknown) 21.966 1.421 0.0042 (unknown) 8.5 3.979 0.0113 (unknown) 22.35 5.47 0.0163 (unknown) 8.683 5.256 0.015 (unknown) 23.583 1.551 0.0046 (unknown) 8.933 4.015 0.0114 (unknown) 23.983 7.53 0.0225 (unknown) 9.15 3.882 0.0111 Fluoranthene 24.666 40.242 0.1201 (unknown) 9.766 39.589 0.1127 O-terphenyl 0 0 0 (unknown) 10.25 34.066 0.097 Pyrene 25.166 1.535 0.0046 102 Naphthalene 10.533 42.932 0.1222 (unknown) 26.266 23.735 0.0708 (unknown) 11.05 80.9345 0.2304 (unknown) 27.216 7.442 0.0222 (unknown) 11.516 11.07 0.0315 (unknown) 28.216 5.295 0.0158 (unknown) 12.25 12.4675 0.0355 Chrysene 29.6 9.023 0.0269 (unknown) 12.433 3.169 0.009 (unknown) 30.35 5.207 0.0155 (unknown) 12.833 20.606 0.0587 (unknown) 31.933 1.6175 0.0048 (unknown) 13.65 36.844 0.1049 (unknown) 32.983 65.773 0.1963 (unknown) 14.05 17.4535 0.0497 Benzo(a)pyrene 0 0 0 (unknown) 14.583 4.079 0.0116 (unknown) 37.5 59.337 0.1771 (unknown) 15.016 5.153 0.0147 (unknown) 38.483 25.263 0.0754 Acenaphthylene 15.333 1.2055 0.0034 (unknown) 39.066 2.7695 0.0083 (unknown) 15.933 4.619 0.0131 (unknown) 40.333 43.6445 0.1302 Acenaphthene 16.483 4.2105 0.012 1.3909 (unknown) 17.316 18.235 0.0519 Fluorene 0 0 0 (unknown) 18.416 10.275 0.0292 (unknown) 18.883 2.828 0.0081 (unknown) 19.5 6.667 0.019 (unknown) 19.833 17.988 0.0512 (unknown) 20.216 5.2215 0.0149 Phenanthrene 0 0 0 Anthracene 0 0 0 (unknown) 21.216 1.9165 0.0055 (unknown) 21.55 1.2495 0.0036 (unknown) 21.816 1.619 0.0046 (unknown) 22.8 5.371 0.0153 (unknown) 23.6 2.688 0.0077 (unknown) 24.033 2.575 0.0073 (unknown) 24.3 2.218 0.0063 Fluoranthene 24.65 11.369 0.0324 O-terphenyl 0 0 0 (unknown) 25.083 2.425 0.0069 Pyrene 0 0 0 (unknown) 26.25 9.035 0.0257 (unknown) 27.516 1.38 0.0039 (unknown) 29.1 1.1295 0.0032 Chrysene 29.966 3.663 0.0104 (unknown) 33.45 81.141 0.231 Benzo(a)pyrene 0 0 0 (unknown) 37.55 42.348 0.1205 (unknown) 39.25 14.723 0.0419 Total area % of tar components 5.3354 Total area % of tar components 1.3909 % Total tar reduction 73.9% 103 Table B.10 Tar components before and after reaction from pretreated BR catalyst experiment at 750 °C Tar sample before reaction Tar sample after reaction Component Ret. time Area Area % Component Ret. time Area Area % (unknown) 0.066 1.189 0.0038 Methanol 0.083 30164.166 98.9205 Methanol 0 0 0 (unknown) 0.366 7.5855 0.0249 (unknown) 0.35 11.7585 0.0372 Acetone 0 0 0 Isopropanol 0.566 29431.714 93.2361 Phenol 0 0 0 (unknown) 2.083 354.3665 1.1226 (unknown) 9.1 1.367 0.0045 (unknown) 2.366 351.7585 1.1143 (unknown) 9.7 1.0275 0.0034 (unknown) 2.733 156.3885 0.4954 Naphthalene 0 0 0 (unknown) 3.066 121.889 0.3861 (unknown) 11.5 2.169 0.0071 (unknown) 3.55 96.827 0.3067 (unknown) 14.233 17.892 0.0587 (unknown) 4.05 9.8925 0.0313 Acenaphthylene 0 0 0 (unknown) 4.266 1.4915 0.0047 (unknown) 15.966 3.334 0.0109 (unknown) 4.583 16.153 0.0512 Acenaphthene 0 0 0 Phenol 4.9 114.247 0.3619 (unknown) 17.833 25.925 0.085 Phenol 5.433 2.09 0.0066 Fluorene 0 0 0 (unknown) 5.8 22.194 0.0703 (unknown) 19.583 13.985 0.0459 (unknown) 6.116 33.279 0.1054 (unknown) 20.466 2.116 0.0069 (unknown) 6.516 14.81 0.0469 Phenanthrene 0 0 0 (unknown) 7.016 21.8965 0.0694 (unknown) 20.75 6.089 0.02 (unknown) 7.4 52.4865 0.1663 Anthracene 0 0 0 (unknown) 7.883 43.405 0.1375 (unknown) 21.8 1.9985 0.0066 (unknown) 8.1 73.433 0.2326 (unknown) 22.283 9.146 0.03 (unknown) 8.433 2.998 0.0095 (unknown) 22.966 34.93 0.1145 (unknown) 8.583 4.514 0.0143 (unknown) 23.283 2.113 0.0069 (unknown) 8.833 5.51 0.0175 (unknown) 23.666 1.31 0.0043 (unknown) 9.05 2.806 0.0089 Fluoranthene 24.7 22.7605 0.0746 (unknown) 9.666 11.839 0.0375 Pyrene 0 0 0 (unknown) 9.866 10.018 0.0317 (unknown) 25.9 9.248 0.0303 (unknown) 10.116 40.151 0.1272 (unknown) 27.016 6.155 0.0202 Naphthalene 10.433 23.0005 0.0729 (unknown) 28.466 9.768 0.032 (unknown) 10.933 94.531 0.2995 Chrysene 29.45 4.856 0.0159 (unknown) 11.4 10.864 0.0344 (unknown) 30.883 3.114 0.0102 (unknown) 11.983 48.195 0.1527 (unknown) 31.95 85.419 0.2801 (unknown) 12.416 7.058 0.0224 (unknown) 33.716 9.877 0.0324 (unknown) 12.666 14.8075 0.0469 Benzo(a)pyrene 36.066 13.8185 0.0453 (unknown) 12.833 1.44 0.0046 Benzo(a)pyrene 36.5 3.044 0.01 (unknown) 13.35 34.1745 0.1083 (unknown) 37.8 28.057 0.092 (unknown) 13.75 6.729 0.0213 (unknown) 41.166 2.075 0.0068 (unknown) 14.133 6.8915 0.0218 (unknown) 14.366 50.408 0.1597 (unknown) 15.183 8.5185 0.027 Acenaphthylene 15.6 21.777 0.069 (unknown) 16.233 9.315 0.0295 Acenaphthene 0 0 0 (unknown) 16.566 12.2885 0.0389 (unknown) 17.066 10.361 0.0328 (unknown) 17.3 2.9515 0.0093 (unknown) 17.516 2.123 0.0067 Fluorene 17.983 1.463 0.0046 Fluorene 18.183 2.404 0.0076 (unknown) 18.5 36.734 0.1164 104 Tar sample before reaction Tar sample after reaction Component Ret. time Area Area % Component Ret. time Area Area % (unknown) 19.15 1.996 0.0063 (unknown) 19.55 1.489 0.0047 (unknown) 19.916 6.843 0.0217 Phenanthrene 0 0 0 (unknown) 20.75 8.02 0.0254 Anthracene 0 0 0 (unknown) 21.316 11.898 0.0377 (unknown) 21.866 1.219 0.0039 (unknown) 22.55 7.493 0.0237 (unknown) 22.85 4.769 0.0151 (unknown) 23.1 6.7175 0.0213 (unknown) 23.833 1.45 0.0046 Fluoranthene 24.783 7.406 0.0235 Pyrene 0 0 0 (unknown) 25.95 2.904 0.0092 (unknown) 26.5 3.3095 0.0105 (unknown) 28.333 2.519 0.008 Chrysene 29.416 2.5055 0.0079 (unknown) 30.133 2.374 0.0075 (unknown) 30.733 1.074 0.0034 (unknown) 31.866 42.185 0.1336 Benzo(a)pyrene 0 0 0 (unknown) 36.8 32.124 0.1018 (unknown) 38.083 3.434 0.0109 Total area % of tar components 6.7639 Total area % of tar components 1.0795 % Total tar reduction 84.0% B.3 XRD Results The X-ray diffractograms were analyzed using the International Centre for Diffraction Database PDF-4 using Search-Match software by Bruker. X-ray powder-diffraction data of the sample were refined with Rietveld program Topas 4.2 (Bruker AXS). The results of quantitative phase analysis by Rietveld refinements are given in Table B.1. The values represent the relative amounts of crystalline phases normalized to 100%. The Rietveld refinement plots are shown in Figures B.1 – 2. The X-ray pattern of the untreated BR (Figure B.1) shows the presence of amorphous/nanoscale material (broad calculated peaks at ~36º, ~42° and ~52°2θ) estimated to be 105 about 15+wt%. Both samples show a small, unidentified peak at 55.2°2θ. Due to the unanalyzed amorphous content, missing peaks and poor fit of some phases, the results for these samples should be considered semi-quantitative. Table B.11 Results of quantitative phase analysis Mineral Ideal Formula Spent untreated bauxite residue, wt.% Spent pretreated bauxite residue, wt.% Baddeleyite ZrO2 0.5 0.2 Carnegieite NaAlSiO4 9.2 9.1 Cohenite Fe3C - 0.6 Freudenbergite Na2(Ti,Fe)8O16 1.8 1.9 Gehlenite Ca2Al(AlSiO7) 1.3 2.0 Hercynite Fe2+Al2O4 - 16.3 Ilmenite Fe2+TiO3 3.3 2.1 Iron-alpha α-Fe - 0.6 Maghemite Fe2O3 43.1 - Magnetite Fe3O4 12.3 34.4 Nepheline (Na,K)AlSiO4 5.4 6.4 Perovskite CaTiO3 3.6 4.2 Quartz SiO2 0.2 - Rutile TiO2 0.4 - Sodalite Na8Cl2Al6Si6O24 3.1 - Sodium Aluminum Silicate Al1.15Na1.15Si0.85O4 14.1 14.9 Ulvöspinel, ferrian Fe2+2TiO4 1.7 7.3 Total 100.0** 100.0 *results are semi-quantitative due to unanalyzed amorphous/nanoscale material and some missing peaks. **15+% of amorphous/nanoscale material not accounted for. 106 Figure B.1 Rietveld refinement plot of spent untreated bauxite residue sample. (blue line - observed intensity at each step; red line - calculated pattern; solid grey line below - difference between observed and calculated intensities; vertical bars - positions of all Bragg reflections; vertical blue lines - positions of peak phases). Coloured lines are individual diffraction patterns of all phases. 1YK_BauxiteResidue BR.raw2Th Degrees8075706560555045403530252015105Sqrt(Counts)10050036.07551 42.4664 52.28419 Ilmenite 3.27 %Nepheline 97294 5.40 %Gehlenite 1.25 %Perovskite 3.62 %Sodalite basic 3.12 %Freudenbergite 1.81 %Maghemite C 43.06 %Magnetite 12.31 %Ulvoespinel, ferrian 1.69 %Quartz low ? 0.25 %Baddeleyite ZrO2 ? 0.47 %Carnegieite low 9.21 %Al1.15 Na1.15 O4 Si0.85 14.15 %Rutile 0.39 % 107 Figure B.2 Rietveld refinement plot spent pretreated bauxite residue sample. (blue line - observed intensity at each step; red line - calculated pattern; solid grey line below - difference between observed and calculated intensities; vertical bars - positions of all Bragg reflections; vertical blue lines - positions of peak phases). Coloured lines are individual diffraction patterns of all phases 2YK_ReducedBauxiteResidue RBR.raw2Th Degrees8075706560555045403530252015105Sqrt(Counts)100500Magnetite 34.45 %Cohenite Fe3C 99016 ? 0.63 %Ulvoespinel, ferrian 7.27 %Iron-alpha ? 0.57 %Freudenbergite 1.88 %Carnegieite low 9.09 %Al1.15 Na1.15 O4 Si0.85 14.92 %Nepheline 97294 6.36 %Perovskite 4.17 %Hercynite 16.31 %Gehlenite 1.98 %Ilmenite 2.15 %Baddeleyite ZrO2 ? 0.22 %
Thesis/Dissertation
eng
Chemical and Biological Engineering
Vancouver : University of British Columbia Library
Attribution-NonCommercial-NoDerivatives 4.0 International
Graduate
The effectiveness of bauxite residue in reducing biomass gasification tars
Text