AN ABSTRACT OF THE DISSERTATION OF Peter B. Kreider for the degree of Doctor of Philosophy in Chemical Engineering presented on September 11, 2015. Title: Applications of Nonthermal Microplasmas in Chemical Reaction Engineering Abstract approved: ______________________________________________________ Alexandre F.T. Yokochi Nonthermal plasmas generate high concentrations of excited species that can simultaneously exist at high energy and far from thermodynamic equilibrium, making them useful tools in chemistry and engineering. Microplasmas, roughly defined as plasmas that are generated within sub-millimeter dimensions, provide enhanced stability, improved excited species density, increased nonequilibrium properties, higher electron temperature, and better energy efficiency along with reduced onset voltages compared to traditional nonthermal plasmas, making them promising candidates for novel chemical processing pathways. This work summarizes current knowledge regarding the advantages gained by generating nonthermal microplasmas in constricted spaces, on reduced timescales, and with engineered electrodes. Those insights are then used in the experimental evaluation of DC microplasma reaction systems in methane processing and the oxidation of model refractory sulfur compounds in fuel-like media. The reaction environment generated by nonthermal plasmas is well suited for the activation of non-spontaneous gas phase reactions. Here, a microreactor capable of generating low power atmospheric pressure glow discharges is used in methane processing. The reactor effectively performs oxidative methane coupling to C2 and C3 hydrocarbons with methane conversions up to 50% and selectivity to C2/C3 products greater than 90%, achieving one pass yields that surpass state-of-the-art catalysis. The generation of DC nonthermal plasmas in fuel-like media for the oxidative desulfurization of dibenzothiphene has also been investigated. At discharge gaps around 250 microns, plasmas can be initiated with DC potentials above 6 kV for short periods of time before carbon bridges are formed that short the reactor. These simple DC discharges show little promise for continuous flow desulfurization processes. However, in flat plate reaction systems with silver epoxy electrode surfaces with discharge gaps less than 50 microns, electrically driven reactions can occur at much less than 1,000 volts. These discharges warrant further investigation and characterization in future works, and could be promising systems for the oxidative desulfurization of diesel fuel. Complementary to experimental investigations, COMSOL multiphysics models have been developed to provide insight into the kinetics of gas phase plasmachemical reactions, as well as the electric field of point-to-plane microplasma reactor designs. The kinetic models of the oxidative coupling of methane are preliminary, however, the current simulations produce the same compounds as the experimental system with realistic kinetic parameters. These models provide an excellent platform for more complicated kinetic modeling. Increasing the number of modeled plasmachemical reaction pathways will likely allow the model to converge on experimental data and be used in predictive analysis of the constructed microplasma reactor in the oxidative coupling of methane. © Copyright by Peter B. Kreider September 11, 2015 All Rights Reserved Applications of Nonthermal Microplasmas in Chemical Reaction Engineering by Peter B. Kreider A DISSERTATION Submitted to Oregon State University in partial fulfillment of the requirements for the degree of Doctor of Philosophy Presented September 11, 2015 Commencement June 2016 Doctor of Philosophy dissertation of Peter B. Kreider presented on September 11, 2015 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. Peter B. Kreider, Author ACKNOWLEDGEMENTS Graduate school has been a great experience for me. Many people in my life deserve my gratitude for their support, guidance, and companionship. So first and foremost, thank you to the multitude that will go unnamed here, for all that you did for me and continue to do for those around you. I’d like to acknowledge the ACS Petroleum Research Fund (ACS-PRF #52025-ND9), the National Science Foundation (NSF-CBET 1134249), and the Oregon Nanoscience and Microtechnologies Institute (ONAMI) for financial support throughout this project. Thank you to my adviser, Alex Yokochi. I’m forever grateful for your guidance and support through grad school. You’ve always trusted in me and my abilities, even in the times that you probably shouldn’t have, and that confidence in me has instilled a confidence of my own. Thank you for all of the opportunities you’ve provided, and for the opportunities your support has and will continue to unlock. I’d also like to thank my co-adviser, Chih-Hung Chang. I truly appreciate the time I spent working with you and your lab group. Your patience and understanding allowed me to complete graduate school in the way that best suited me, and for that, I am grateful. To all of the members of the Yokochi and Chang Labs who’ve helped in ways great and small: thank you. To Ki-Joong Kim: Thank you for being such a great friend and mentor. I owe much of my success in graduate school to you. We really do make a great team! No graduate school experience is complete without friends to share, laugh, and commiserate with. These people comprise a collection of graduate school peers and people who I’ve had the good fortune of meeting in Corvallis. Matt Coblyn, Mike Knapp, Justen Dill, Matt Ryder, Kegan Sims, Alex Sims, Carson Dunlap, Malachi Bunn. You have all become true friends. Finally, I’d like to thank my parents, Rea and Sharon, for their unwavering support in all that I do. They always see the best in me and have shown nothing but positive encouragement at all times. I continually strive to meet the example they have set for me, and I feel proud to be their son. To my sister, Natalie: Thank you for always making me feel smarter and more accomplished than I am, and for simply being you. I love you all. TABLE OF CONTENTS Page Introduction ......................................................................................................................... 1 Research Plan ...................................................................................................................... 2 Background Information and Motivation ........................................................................... 5 Microreactors ............................................................................................................................... 5 Methane Partial Oxidation ........................................................................................................... 5 Desulfurization ............................................................................................................................. 8 Literature Review: Nonthermal Plasmas in Reaction Engineering .................................. 10 Methane and Hydrocarbon reactions .......................................................................................... 10 Methane Reactions in Dielectric barrier Discharge ................................................................ 10 Methane Reactions in Corona Discharge ............................................................................... 12 Other Methane Reactions ....................................................................................................... 13 Hydrocarbon and Alcohol Reactions in Plasmacatalytic Systems ......................................... 13 Destruction of VOCs and Hazardous Compounds ..................................................................... 14 Ammonia Synthesis and Nitrogen Fixation ............................................................................... 15 Nanoparticle and Materials Synthesis ........................................................................................ 16 CO2 and H2O Dissociation ......................................................................................................... 17 Liquid Phase Reactions in Nonthermal Plasmas ........................................................................ 18 Nonthermal Microplasmas in Chemical Reaction Engineering: A Review ..................... 19 Abstract ...................................................................................................................................... 19 Introduction ................................................................................................................................ 20 Background ................................................................................................................................ 22 Energy Distributions in Plasma .............................................................................................. 22 Plasmachemistry and Electron Impact Ionization .................................................................. 24 Types of Electrical Discharges ............................................................................................... 29 Microplasmas ............................................................................................................................