MECHANISM OF SULFUR POISONING BY H2S AND SO2 OF NICKEL AND COBALT BASED CATALYSTS FOR DRY REFORMING OF METHANE A Thesis Submitted to the College of Graduate Studies and Research in Partial Fulfillment of the Requirements for the Degree of Master of Science in the Department of Chemical and Biological Engineering University of Saskatchewan Saskatoon By Francisco Javier Pacheco Gómez © Copyright Francisco Javier Pacheco Gómez, March 2016. All rights reserved. PERMISSION TO USE In presenting this thesis in partial fulfillment of the requirements for a Postgraduate degree from the University of Saskatchewan, I agree that the Libraries of this University may make it freely available for inspection. I further agree that permission for copying of this thesis/dissertation in any manner, in whole or in part, for scholarly purposes may be granted by Professor Hui Wang who supervised my thesis work. It is understood that any copying or publication or use of this thesis or parts for financial gain shall not be allowed without my written permission. It is also understood that due recognition shall be given to me and to the University of Saskatchewan in any scholarly use which may be made of any material in my thesis. DISCLAIMER The University of Saskatchewan was exclusively created to meet the thesis and/or exhibition requirements for the degree of Master of Science at the University of Saskatchewan. Reference in this thesis to any specific commercial products, process, or service by trade name, trademark, manufacturer, or otherwise, does not constitute or imply its endorsement, recommendation, or favouring by the University of Saskatchewan. The views and opinions of the author expressed herein do not state or reflect those of the University of Saskatchewan, and shall not be used for advertising or product endorsement purposes. Requests for permission to copy or to make other uses of materials in this thesis in whole or part should be addressed to: i Department Head Department of Chemical and Biological Engineering University of Saskatchewan College of Engineering 57 Campus Drive Saskatoon, SK S7N 5A9 Canada Or Dean College of Graduate Studies and Research University of Saskatchewan 107 Administration Place Saskatoon, Saskatchewan S7N 5A2 Canada ii ABSTRACT Nickel catalysts employed in the production of syngas throughout CO2 reforming of CH4 can be poisoned and deactivated by the presence of H2S or SO2 found in the feedstock. It is necessary to understand the poisoning mechanism to develop more resistant catalysts. The effect of sulfur poisoning by H2S and SO2 on the mechanism of carbon dioxide reforming of methane was studied for Ni/AlMgOx, Ni-Co/AlMgOx and Co/AlMgOx catalysts prepared by coprecipitation and impregnation methods. The method employed for mechanism study was Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS). DRIFTS made possible to observe that the mechanism of carbon dioxide reforming of methane reaction involved: 1) methane adsorption and possibly dissociation into C, CHx and H2; 2) carbon dioxide adsorption and dissociation into CO; 3) formation of carbonates that could occur after CO2 attaches to an oxygen atom or after CO binds to two oxygen atoms present in the catalyst surface. It was found a relation ship between the concentration of carbonates and adsorbed CO. The presence of H2S in reacting gasses caused a decrease in the intensity of the methane and CO2 absorption bands on the nickel (Ni)-monometallic catalysts, suggesting that H2S blocks the - nickel active sites. Also, H2S caused a decrease in the OH species, suggesting that NiS was formed. The band at 2077 cm-1, attributed to linear carbonyl, was replaced by two bands located -1 at 2071 and 2051 cm , which are assigned to carbonyl sulfide produced by the reaction H2S + CO2 ⇌ COS + H2O on the catalyst surface. When SO2 interacted with the catalysts, a band at -1 about 1358 cm was observed, which is assigned to sulfate species. SO2 also caused a decline in the concentration of carbonates and adsorbed CO. This study allowed a better understanding of the poisoning mechanism by H2S and SO2. iii ACKNOWLEDGEMENTS I want to thank all the people and organizations that made the completion of this thesis possible. Firstly, I want to deeply thank my supervisor Dr. Hui Wang for accepting my application to the Master of Science in Chemical Engineering program at the University of Saskatchewan. I appreciate his guidance throughout this journey and also his financial support. I recognize the valuable suggestions received from the members of the advisory committee, Dr. Lifeng Zhang and Dr. Yongfeng Hu. Additionally, I thank Dr. Stephen Foley for accepting to be the external examiner for my thesis defense. I appreciate the scholarship provided by CONACYT throughout the official length of my studies. It allowed me to focus on my studies without financial concerns. I feel grateful for the help received from Kelly Bader to complete my application. She was the first staff member from the University of Saskatchewan I had communication with. Her help and kindness were very valuable to complete the application to the program. I also acknowledge Wahab Alabi, Mohsen Shakouri and Armin Moniri for helping me to answer questions and showing me their knowledge in the laboratory. My gratitude also goes to Richard Blondin for providing technical support for devices and instruments and to RLee Prokopishyn for helping to fix devices whenever it was needed. iv DEDICATION I dedicate this thesis to my parents for supporting me financially and for encouraging me to study and take important decisions in life. Also, I dedicate this thesis to myself for having the strength to begin, continue and finish this journey in spite of hard and sometimes discouraging challenges. v TABLE OF CONTENTS PERMISSION TO USE................................................................................................................i ABSTRACT………………….....................................................................................................iii ACKNOWLEDGMENTS..........................................................................................................iv DEDICATION..............................................................................................................................v TABLE OF CONTENTS............................................................................................................vi LIST OF TABLES.......................................................................................................................x LIST OF FIGURES.....................................................................................................................xi NOMENCLATURE AND ABBREVIATIONS......................................................................xv CHAPTER 1. INTRODUCTION..............................................................................................1 1.1 OVERVIEW........................................................................................................................1 1.2 PREVIOUS RESEARCH MADE BY DR. HUI WANG’S GROUP.......................…...3 1.3 MOTIVATION TO CARRY OUT THIS THESIS..........................................................5 1.4 ORGANIZATION OF THE THESIS...............................................................................6 CHAPTER 2. LITERATURE REVIEW.................................................................................8 2.1 REFORMING OF METHANE..........................................................................................8 vi 2.2 COMMERCIAL PROCESSES FOR THE PRODUCTION OF SYNGAS...........…..11 2.2.1 CALCOR process………………………………………………………..………..11 2.2.2 SPARG process………………………………………………………………...…12 2.3 DRY REFORMING OF METHANE………………………………………….….……13 2.3.1 Environmental aspects for dry reforming of methane…………………............13 2.3.2 Obtainment of reactants for dry reforming of methane……………..………...14 2.3.3 Thermodynamic analysis…………....................................................…………...16 2.3.4 Mechanisms reported for dry reforming of methane……………………..........18 2.3.5 Catalysts used for dry reforming of methane……………….......................……22 2.3.5.1 Nickel-based catalysts.......................................................................……22 2.3.5.2 Cobalt-based catalysts……........….................……………………….….24 2.3.6 Catalyst deactivation………………………...…………………………..……….25 2.3.6.1 H2S poisoning………………………………………………....…………27 2.3.6.2 SO2 poisoning………………………………….…………….…..………29 2.3.7 Regeneration of catalysts after sulfur poisoning………………………..............31 2.4 KNOWLEDGE GAPS, HYPOTHESES AND RESEARCH OBJECTIVES..............32 2.4.1 Knowledge gaps.......................................................................................................32 2.4.2 Research objectives.................................................................................................32 2.4.3 Hypotheses……..……….........................................................................................32 CHAPTER 3. EXPERIMENTAL SET-UP AND PROCEDURE.......................................33 3.1 SAFETY PRECAUTIONS……………………………………………….……………..33 vii 3.2 CATALYST PREPARATION METHODS....................………...........................……34 3.2.1 Coprecipitation method....................................................................................…..34 3.2.2 Impregnation method.............................................................................................35 3.3 CATALYST CHARACTERIZATION...........................................................................36