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The Pennsylvania State University The Pennsylvania State University The Graduate School Department of Chemical Engineering A SOLID CATALYST METHOD FOR BIODIESEL PRODUCTION A Dissertation in Chemical Engineering by Dheeban Chakravarthi Kannan Submitted in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy August 2009 The dissertation of Dheeban Chakravarthi Kannan was reviewed and approved* by the following: Jack V. Matson Professor of Environmental Engineering Dissertation Adviser Themis Matsoukas Associate Professor of Chemical Engineering Chair of Committee Joseph M. Perez Senior Research Scientist, Department of Chemical Engineering Wallis A. Lloyd Adjunct Professor of Chemical Engineering Brian A. Dempsey Professor of Environmental Engineering Thomas P. Hettmansperger Professor of Statistics Andrew Zydney Professor of Chemical Engineering Head of the Department of Chemical Engineering *Signatures are on file in the Graduate School ABSTRACT Biodiesel has considerable production potential as a renewable source of energy. The conventional processes use soluble alkali catalysts that contaminate the biodiesel and glycerol products, and present separation problems. An efficient and clean process is crucial for large scale commercial production. Solid catalysts have the potential to eliminate these problems. A method has been developed to produce biodiesel using a solid catalyst. The reaction is carried out at high temperature and pressure conditions (260 °C, 70 atm). The high temperature is not a problem since the solid catalyst is part of a continuous process in which heat energy can be recovered. The reaction time is short (15 minutes) compared to that of the conventional processes (~ 100 minutes). Promising catalysts were identified from batch tests; and MnO was found to be the most effective catalyst from the lab-scale packed-bed reactor tests. The reaction conditions allow for this mild solid base which can have a long life. The conventional process conditions (60~70 °C, 70 atm) need specially prepared strong bases that lose their activity quickly. The kinetics of the MnO-catalyzed reaction has been studied. External mass transfer limited effects have been identified. MnO was not the strongest of the bases tested, but it was the most effective. The reasons have been evaluated. MnO has a long catalyst life (more than 500 hours). Also, the amphoteric nature of MnO aids in the conversion of free fatty acids. This means used vegetable oil can be converted to biodiesel efficiently. MnO can sustain high water content in the feedstock without iii diminishing efficiency. The method has been found to be favourable in terms of low pressure drop. Lastly, the MnO solid catalyst process has been compared with other processes and was found to be favourable in terms of reaction rate, catalyst life, pressure, temperature, side reactions and maintenance. iv TABLE OF CONTENTS ACKNOWLEDGEMENTS……………………………………………………………... ix Chapter 1 Introduction…………………………............................................................... 1 Hypothesis………………………………………………………………………….. 3 Chapter 2 Background…………………………...………………………….................... 5 Vegetable oil composition…………………………...…………………………...... 5 Problems of direct vegetable oil usage in diesel engines………………………….. 6 Methods of modifying vegetable oil for diesel engines…………………………..... 7 Fuel consumption statistics…………………………...…………………………..... 7 Oil yields…………………………...…………………………...………………….. 9 Biodiesel energy balance…………………………...…………………………....... 10 The scope for biodiesel production………………………….................................. 10 Biodiesel and diesel – Performance, handling and usage comparisons…………... 12 Conventional Process…………………………...…………………………............ 14 Drawbacks of the conventional process.…………………………....……… 18 Solid catalysts…………………………...…………………………....................... 20 Solid bases…………………………...…………………………................... 20 Solid acids…………………………...………………………….................... 22 Solid catalysts for biodiesel reaction…………………………...................... 24 Chapter 3 Approach to Method Development…………………………......................... 31 Chapter 4 Initial Tests and Catalyst-Screening…………………………........................ 36 Batch reactor set-up and experimental procedure…………………………............ 36 Product analysis…………………………...………………………….................... 37 Solid base salts…………………………...…………………………...................... 37 Metal oxide bases…………………………...………………………….................. 38 Free fatty acid conversion…………………………...…………………………..... 43 Activity sustenance of the catalysts…………………………...………………….. 43 v Effect of molar ratio…………………………...………………………….............. 44 Effect of cosolvent…………………………...…………………………................ 44 Ultrasonic cavitation without catalyst…………………………............................. 46 Chapter 5 Lab-Scale Packed-Bed Reactor………………………….............................. 47 Experimental set-up……………………………...…………………………......... 47 Experiments…………………………...………………………….......................... 54 Results…………………………...…………………………...…………………... 59 Data validation………..…………...…………………………...………………… 62 Chapter 6 Reaction Kinetics…………………………...…………………………........ 63 External mass transfer…………………………...………………………….......... 63 Internal mass transfer…………………………...…………………………........... 66 Order of reaction and rate constant…………………………................................. 67 Effect of temperature on reaction rate…………………………............................ 74 Surface area and activity…………………………...…………………………...... 82 BET surface area…………………………...…………………………........ 82 Cumulative pore area over pore size range………………………….......... 84 Comparative acidity/basicity scale…………………………........................ 86 Thermogravimetric analysis of temperature-programmed CO2 desorption.. 88 Rate constant vs surface area per unit volume…………………………...... 93 Proposed Reaction Mechanism…………………………....................................... 94 Chapter 7 Studies for Commercialization…………………………............................. 100 Activity sustenance tests…………………………...………………………….... 100 Optimal molar ratio...………………………...…………………………............. 104 Effect of pressure…………………………...…………………………............... 107 Free fatty acid conversion…………………………...………………………….. 112 Effect of water……………………...…………………………........................... 116 Equilibrium conversion…………………………...…………………………..... 120 Process pressure-drop…………………………...…………………………........ 124 High temperature considerations………………………….................................. 129 vi Alcohol side reaction…………………………...…………………………. 129 Vegetable oil side reaction…………………………................................... 135 Chapter 8 Comparison of MnO Catalyst Method with Other Methods……………… 137 Reaction comparison…………………………...………………………….......... 137 Supercritical methanol process…………………………............................ 138 Tateno/Goto method…………………………...…………………………. 138 Mcgyan process…………………………...…………………………........ 143 Two-step supercritical process…………………………............................ 144 Propane cosolvent process…………………………................................... 144 Di Serio catalysts and calcined hydrotalcites…………………………...... 145 Other methods…………………………...…………………………........... 147 Comparison with calcium oxide…………………………………………... 149 Activation energy…………………………...…………………………...... 150 Process design comparison with the conventional process……………………... 150 Chapter 9 Conclusion…………………………...…………………………................. 157 Future work…………………………...…………………………...……………. 160 Abbreviations, Notations and Symbols…………………………................................. 164 References…………………………...………………………….................................. 166 Appendices…………………………...…………………………................................. 181 Appendix A Thin Layer Chromatography...………………………................... 181 Appendix B Gas Chromatography………………………….............................. 182 Appendix C Water and Saponification…………………………....................... 189 Appendix D Titrimetry…………………………...………………………….... 190 Appendix E LHSV and WHSV………………………….................................. 191 Appendix F ZSM-5…………………………...………………………….......... 191 Appendix G Cetane number…………………………...……………………… 192 Appendix H Capital Cost Estimation of 34 Million Gallon per Year Biodiesel …………………………………………………………………… Plant….. 193 vii Appendix I Process Design of a Mobile Biodiesel Production Unit………….. 199 viii ACKNOWLEDGEMENTS My time of doctoral research has been a dream, and I shall cherish that forever. There are many wonderful people who made it what it was. This has been a different project from other doctoral projects in that the basic idea behind the research did not exist in advance, nor were there any pre-allocated funds. I had basically approached my adviser Dr. Jack Matson that I wanted to do a project of environmental significance. We looked at a variety of ideas and settled on the biodiesel project at the end of the first semester, fall 2004. We took the whole spring 2004 semester for literature review. There was not a single experimental data collected in the first two semesters. He had that kind of confidence in me and that kind of interest in environmental issues. I never knew the pressure of finances, and we did not have any outside funding for the research. That is how well he took care of me and the project. The freedom he gave me and the confidence he had in me are what that essentially made up this research. On looking back, that kind of blind confidence in the project to be shared by two people until we identified MnO as a promising catalyst 20 months into the project, feels remarkable. Dr. Matson is a special adviser,
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