Fluid Modeling of the Plasma-Assisted Conversion of Greenhouse Gases to Value-Added Chemicals in a Dielectric Barrier Discharge
9 December 2016
UAntwerpen, Campus Drie Eiken, Promotiezaal Q0.02 - Universiteitsplein 1 - 2610 Antwerpen-Wilrijk (route: UAntwerpen, Campus Drie Eiken
Organization / co-organization:
Department of Chemistry
Christophe De Bie
PhD defence Christophe De Bie - Faculty of Science- Department of Chemistry
The aim of this dissertation was to describe in detail the plasma chemistry in an atmospheric pressure cylindrical dielectric barrier discharge (DBD), used as a chemical reactor for gas conversion, by means of a 1D fluid model. More specifically, the goal was to develop a reliable chemistry set for the description of the gas phase chemistry in pure CH4, CH4/O2, CH4/CO2 and CO2/H2 gas discharges. A large number of different plasma species (i.e., electrons, molecules, radicals, ions) are included in our model, as well as a comprehensive set of chemical reactions, into which these species participate.
In this way, calculation results could be obtained for the densities of the different plasma species, the conversions of the inlet gases, the yields and selectivities of the end products and the dominant reaction pathways for each of the gas mixtures studied. This allows us to determine whether or not a specific gas mixture is suitable for the production of a specific end-product of interest. Our calculation results were validated with reported results in literature, and for pure CH4 also with some experiments for the reactor set-up under study.
Higher hydrocarbons (C2Hy and C3Hy) and hydrogen gas are typically found as end products for the conversion of pure CH4. Dry reforming of CH4 in a DBD favors the formation of H2, CH2O, CH3CHO and CH2CO, while the densities of H2O2, CH3OH, C2H5OH, CH3OOH and C2H5OOH are higher for the partial oxidation of CH4 in a DBD. CO is formed at high density in both gas mixtures, i.e., CH4/O2 and CH4/CO2. In the gas mixtures with O2 as co-reactant, also a significant amount of undesired CO2 is formed. The most abundant reaction products for the hydrogenation of CO2 in a DBD are CO, H2O and CH4, and to a lower extent also CH2O, C2H6, O2 and CH3OH. However, the conversion of CO2 was found to be very low (i.e., in the order of 2-7 %) in all CO2/H2 gas mixtures, and much lower than in a CO2/CH4 mixture, where typical conversions in the order of 3-20 % were obtained at similar conditions.