AN ABSTRACT OF THE DISSERTATION OF Nicholas J. AuYeung for the degree of Doctor of Philosophy in Chemical Engineering presented on October 14, 2011. Title: Hydrogen Production via a Sulfur-Sulfur Thermochemical Water-Splitting Cycle Abstract approved: ____________________________________________________ Alexandre F.T. Yokochi Thermochemical water splitting cycles have been conceptualized and researched for over half a century, yet to this day none are commercially viable. The heavily studied Sulfur-Iodine cycle has been stalled in the early development stage due to a difficult HI- H2O separation step and material compatibility issues. In an effort to avoid the azeotropic HI-H2O mixture, an imidazolium-based ionic liquid was used as a reaction medium instead of water. Ionic liquids were selected based on their high solubility for SO2, I2, and tunable miscibility with water. The initial low temperature step of the Sulfur-Iodine cycle was successfully carried out in ionic liquid reaction medium. Kinetics of the reaction were investigated by I2 colorimetry. The reaction also evolved H2S gas, which led to the conceptual idea of a new Sulfur-Sulfur thermochemical cycle, shown below: 4I2(l)+4SO2(l)+8H2O(l) ↔4H2SO4(l) + 8HI(l) 8HI(l) +H2SO4(l) ↔H2S(g)+4H2O(l) +4I2(l) 3H2SO4(g)↔3H2O(g)+3SO2(g)+1½O2(g) H2S(g)+2H2O(g)↔SO2(g)+3H2(g) The critical step in the Sulfur-Sulfur cycle is the steam reformation of H2S. This highly endothermic step is shown to successfully occur at temperatures in excess of 800˚C in the presence of a molybdenum catalyst. A parametric study varying the H2O:H2S ratio, temperature, and residence time in a simple tubular quartz reactor was carried out and Arrhenius parameters were estimated. All reactive steps of the Sulfur-Sulfur cycle have been either demonstrated previously or demonstrated in this work. A theoretical heat-to-hydrogen thermal efficiency is estimated to be 55% at a hot temperature of 1100 K and 59% at 2000 K. As a highly efficient, all-fluid based thermochemical cycle, the Sulfur-Sulfur cycle has great potential for feasible process implementation for the transformation of high quality heat to chemical energy. © Copyright by Nicholas J. AuYeung October 14, 2011 All Rights Reserved Hydrogen Production via a Sulfur-Sulfur Thermochemical Water-Splitting Cycle by Nicholas J. AuYeung A DISSERTATION Submitted to Oregon State University in partial fulfillment of the requirements for the degree of Doctor of Philosophy Presented October 14, 2011 Commencement June 2012 Doctor of Philosophy Dissertation of Nicholas AuYeung presented on October 14, 2011 APPROVED: ________________________________________ Major Professor, representing Chemical Engineering ________________________________________ Head of the School of Chemical, Biological, and Environmental Engineering ________________________________________ Dean of the Graduate School I understand that my dissertation will become part of the permanent collection of Oregon State University libraries. My signature below authorizes release of my dissertation to any reader upon request. ________________________________________________________________________ Nicholas J. AuYeung, Author ACKNOWLEDGEMENTS I first would like to acknowledge the financial support for the project. Early work was funded by the California Energy Commission. This material is based upon work supported by the National Science Foundation under Grant No. 0748280. I would like to thank my advisor, Alex Yokochi, who has invested so much time, effort, and patience into my experience as a graduate student. His philosophy is to motivate through inspiration and because of him I will always set my goals high. Always approachable, his enthusiasm and optimism is always contagious and has made graduate school a wonderful experience for me. I am also grateful that he allowed me to pursue interests outside of school and live a balanced life. My graduate committee has been very helpful throughout my studies. In addition to having them serve on my committee, I have also had the honor being a student in classes taught by my committee Professors Chih-hung Chang, Richard Peterson, and Michael Lerner. Special thanks go to committee member Roger Ely for convincing me to attend Oregon State and welcoming me to his research meetings early on. His research group would spearhead the OSU Hydrogen Club, which has been a major outlet for me in the past few years. I also would like to acknowledge my labmates in the Yokochi lab-Alex Bistrika, Kevin Caple, Matt Delaney, Nathan Coussens, Malachi Bunn, Victoria Johnson, and Anees Sardari who have always been supportive sounding boards for many ideas and issues that have come up throughout my studies here. Thanks also go to Andy Brickman for his countless pieces of practical advice; Manfred Dittrich for his willing help in many machining tasks; and Mohammad Azizian, Alan Milligan, and Glenn Watson for their consultation on various analytic issues. I must also thank Skip Rochefort, who gave me excellent advice upon meeting him at an AIChE conference as an undergraduate: ―Well, I hope you’re considering graduate school‖. Both Skip and my influential high school chemistry teacher Stan Bebyn would agree with my worldview that chemists should also be runners. Professors Jim Stuart, Richard Parnas, Michael Cutlip, Ben Wilhite, and Joe Helble were all wonderful mentors at UConn who invested many outside-the-classroom hours into the biodiesel project and gently pushed me into pursuing an advanced degree. Most importantly, I would like to thank my parents, brothers Ben and Nate, and my wonderful partner Aida for all their unwavering love and support. My parents both instilled in me the principles of hard work and never giving up. Through all these years they have always believed in me and have shared my emotional investment in whatever I decided to pursue. They have both made countless sacrifices for me and I will forever be grateful. Without them I would not be here. Table of Contents 1 INTRODUCTION ....................................................................................................... 1 1.1 Background .......................................................................................................... 1 1.2 Literature Review ................................................................................................. 4 2 INVESTIGATION OF THE BUNSEN REACTION IN IONIC LIQUIDS ............. 22 2.1 Screening of commercially available ionic liquids as to their ability to release hydrogen iodide (HI(g)) from the Bunsen reaction. ....................................................... 24 2.2 Investigation of Bunsen Reaction Kinetics ........................................................ 27 2.3 Investigation into the evolution of hydrogen sulfide via the side reaction: ....... 34 2.4 Demonstration of sulfur trioxide/sulfuric acid separation from ionic liquid ..... 36 3 DEMONSTRATION OF STEAM REFORMATION OF H2S ................................. 37 3.1 Preliminary Proof of Concept ............................................................................ 37 3.2 Investigation of Thermal Splitting of Hydrogen Sulfide in a Quartz Reactor ... 43 3.3 Parametric Study of Steam Reformation of Hydrogen Sulfide .......................... 48 4 PROCESS DESIGN OF SULFUR-SULFUR CYCLE ............................................. 68 4.1 Estimation of Overall Thermal Efficiency of the Sulfur-Sulfur Cycle .............. 68 4.2 Process Considerations ....................................................................................... 73 5 CONCLUSION AND FUTURE WORK .................................................................. 76 5.1 Conclusion .......................................................................................................... 76 5.2 Future Work ....................................................................................................... 77 BIBLIOGRAPHY ............................................................................................................. 81 APPENDICES: ................................................................................................................. 90 APPENDIX A: Physical and Chemical Properties of Sulfur-Sulfur Cycle Species ..... 93 APPENDIX B: Kinetics of the Bunsen Reaction.......................................................... 95 APPENDIX C: Preliminary Investigation into Steam Reformation of Hydrogen Sulfide ..................................................................................................................................... 101 APPENDIX D: Steam Reformation of Hydrogen Sulfide .......................................... 103 LIST OF FIGURES FIGURE PAGE Figure 1.1: A thermochemical cycle conceptualized as a heat engine. ............................. 2 Figure 2.1: Structures of some imidazolium ionic liquids ................................................ 25 Figure 2.2: Spectral differences of iodine in dichloromethane with and without ionic liquid [BMIM][OTf].. ................................................................................................ 29 Figure 2.3: Spectral variation of iodine in ionic liquid [BMIM][OTf]with temperature (diluted in dichloromethane). .................................................................................... 30 Figure 2.4: Normalized iodine concentration profile over time for small-scale batch reactions. .................................................................................................................. 32 Figure