Kinetics of the Hydro-Deoxygenation of Stearic Acid Over
Total Page:16
File Type:pdf, Size:1020Kb
KINETICS OF THE HYDRO-DEOXYGENATION OF STEARIC ACID OVER PALLADIUM ON CARBON CATALYST IN FIXED-BED REACTOR FOR THE PRODUCTION OF RENEWABLE DIESEL Thesis Submitted to The School of Engineering of the UNIVERSITY OF DAYTON In Partial Fulfillment of the Requirements for The Degree of Master of Science in Chemical Engineering By Albert Vam Dayton, Ohio August, 2013 KINETICS OF THE HYDRO-DEOXYGENATION OF STEARIC ACID OVER PALLADIUM ON CARBON CATALYST IN FIXED-BED REACTOR FOR THE PRODUCTION OF RENEWABLE DIESEL Name: Vam, Albert APPROVED BY: Kevin J. Myers, D.Sc., P.E. Heinz J. Robota, Ph.D. Advisory Committee Chairman Research Advisor Professor; Graduate Chemical Engineering Ohio Research Scholar in Alternative Fuels Program Coordinator Alternative Fuels Group Leader Department of Chemical and Materials University of Dayton Research Institute Engineering Amy R. Ciric, Ph.D. Committee Member Senior Lecturer Department of Chemical and Materials Engineering John G. Weber, Ph.D. Tony E. Saliba, Ph.D. Associate Dean Dean, School of Engineering School of Engineering & Wilke Distinguished Professor ii ©Copyright by Albert Vam All rights reserved 2013 iii ABSTRACT KINETICS OF THE HYDRO-DEOXYGENATION OF STEARIC ACID OVER PALLADIUM ON CARBON CATALYST IN FIXED-BED REACTOR FOR THE PRODUCTION OF RENEWABLE DIESEL Name: Vam, Albert University of Dayton Advisor: Dr. Heinz J. Robota Biological oils are potential sources of liquid transportation fuels. In the presence of a precious metal catalyst under reducing conditions, the transformation of biological oils to liquid fuels proceeds sequentially. First, any double bond is quickly saturated. The double bond saturation is followed by the hydrogenolysis of the ester linkages which releases the saturated fatty acids from the propane backbone. The fatty acids are then deoxygenated producing n-alkanes. Typically, the n-alkanes are further treated to meet the required physical properties of a particular fuel fraction. Although important, the deoxygenation of the fatty acid had not yet been studied in production-like conditions. For this reason, in this study, a comprehensive investigation of the deoxygenation of a representative fatty acid was carried out by studying stearic acid (S.A.) diluted in a highly isomerized C24 solvent. The deoxygenation of stearic acid was studied in the presence of hydrogen, in a trickle-bed reactor by using a 3 wt % carbon-supported palladium catalyst. iv In order to simplify the study of the kinetics of the S.A. deoxygenation, a uniform S.A. concentration across the catalyst bed was desired. For this reason, the entire study was conducted under differential conditions, by limiting the S.A. conversion to 10 percent. The limited conversion allowed me to assume uniform S.A. concentration across the catalyst bed. The liquid products were identified early on as n-heptadecane, n-octadecane, and stearyl stearate. The rate of formation for each liquid product was examined over wide-ranging sets of temperature, initial S.A. concentration and hydrogen pressure. Kinetic data for the different products were graphically derived and rate expressions were developed and presented. The S.A. deoxygenation reaction network in the presence of hydrogen was found to be rather complex. The observed rate of n-heptadecane production was a combined rate of two reactions, the stearic acid decarboxylation and the octadecanal decarbonylation. Likewise, the observed rate of n-octadecane production was the sum of the rates of octadecanol reduction and stearyl stearate hydrogenolysis. In order to estimate the contribution of each of the rates of S.A. decarboxylation and octadecanal decarbonylation to the total rate of n-heptadecane production, the relative rate of CO/CO2 production was studied over a range of temperature and hydrogen pressure. And, in order to estimate the contribution of the rate of alcohol reduction and the rate of stearyl stearate hydrogenolysis to the total observed rate of n-octadecane production, a complete study of palmityl stearate hydrogenolysis was carried out to estimate the stearyl stearate hydrogenolysis partial contribution to the overall rate of n-octadecane production. v Dedicated to my family vi ACKNOWLEDGMENTS This research was supported, in part, by the U. S. Air Force Cooperative Grant Numbers F33615-03-2-2347 and FA8650-10-2-2934, Mr. Robert W. Morris Jr., Air Force Grant Monitor. The research was also sponsored by the State of Ohio Subrecipient Award No. COEUS # 005909 to the University of Dayton (Dr. Heinz Robota as the Grant Monitor) under the “Center for Intelligent Propulsion and Advanced Life Management,” program with the University of Cincinnati (Prime Award NO. TECH 09-022). The authors gratefully acknowledge this grant support. I would also like to express my genuine gratitude to my research advisor and professional mentor Dr. Heinz Robota. First for allowing me to be a member of his outstanding team, and second, for his time, expertise, patience, and for the invaluable chemistry and engineering knowledge that he has shared with me. This has been truly by far the best education I have ever received. Special thanks go to Dr. Kevin. Myers, my advisory committee chairman and graduate studies advisor who was one of the reasons I chose to pursue my graduate studies at UD. Thank you for all your support and for being so helpful. Thanks to Dr. Amy Ciric, my thesis committee member for taking the time to be on this committee and for sharing her knowledge in renewable fuels with me, inside and outside the classroom. vii Sincere thanks to Jhoanna Alger for all her help and contribution to this work in the lab, and for reviewing multiple drafts of this thesis. Thanks to Linda Shafer for analyzing my samples. I also thank Dave Gasper to whom I always reached out with issues related to equipment design that were beyond my knowledge. Thanks to Sophia D’Angelo with whom I shared the office space, and all the people of UDRI who made it a pleasant work environment. viii TABLE OF CONTENTS ABSTRACT ....................................................................................................................... iv DEDICATION…………………………………………………………………………. ..ix ACKNOWLEDGMENTS…………………………………………………………….... vii LIST OF ILLUSTRATIONS ........................................................................................... xiv LIST OF TABLES ........................................................................................................... xvi LIST OF SYMBOLS/ABBREVIATIONS .................................................................... xviii CHAPTER 1 INTRODUCTION ...................................................................................... 1 1.1. Biological Oils for Transportation Fuels .............................................................. 1 1.2. Challenges to the Direct Use of Biological Oils as Fuels .................................... 3 1.3. Methods of Upgrading ......................................................................................... 3 1.3.1 Transesterification of Biological Oils ......................................................... 5 1.3.2 Deoxygenation of Biological Oils .............................................................. 6 1.3.3 Studying Fatty Acid Instead of a Triglyceride ............................................ 8 CHAPTER 2 LITERATURE REVIEW ........................................................................... 9 2.1. Catalyst Selection ................................................................................................. 9 ix 2.2. The Impact of Hydrogen .................................................................................... 10 2.2.1 Zero and Low Hydrogen Pressure ............................................................ 10 2.2.2 Reaction under Pure Hydrogen ................................................................. 13 2.3. Effect of the Initial Concentration of the Fatty Acid ......................................... 16 2.4. Effect of Chain Length ....................................................................................... 16 2.5. Summary ............................................................................................................ 16 CHAPTER 3 EXPERIMENTAL APPROACH ............................................................. 18 3.1. Studying the Kinetics of S.A. Deoxygenation in Place of Triglyceride ............ 18 3.2. Reactor Type, Differential Operation, and S.A. Concentration ......................... 19 3.3. Importance of Hydrogen in Biological Oil Upgrading ...................................... 20 3.4. Materials ............................................................................................................. 22 3.4.1 Catalyst Preparation ..................................................................................... 22 3.4.2 Catalyst Activation....................................................................................... 22 3.4.3 Feed Materials .............................................................................................. 23 3.4.4 Fixed-Bed Reactor ....................................................................................... 24 3.4.5 Liquid Analysis ............................................................................................ 27 3.5. Study Framework ............................................................................................... 28 CHAPTER 4 APPARENT KINETICS OF THE S.A. DEOXYGENATION AND LIQUID SPECIES PRODUCTION ................................................................................