Dry Reforming of Methane in a Gliding Arc Plasmatron: Towards a Better Understanding of the Plasma Chemistry

Abstract

Dry reforming of methane (DRM) in a gliding arc plasmatron is studied for different CH₄ fractions in the mixture. The CO₂ and CH₄ conversions reach their highest values of approximately 18 and 10 %, respectively, at 25 % CH₄ in the gas mixture, corresponding to an overall energy cost of 10 kJ L^-1 (or 2.5 eV per molecule) and an energy efficiency of 66 %. CO and H₂ are the major products, with the formation of smaller fractions of C₂ H_x (x=2, 4, or 6) compounds and H₂ O. A chemical kinetics model is used to investigate the underlying chemical processes. The calculated CO₂ and CH₄ conversion and the energy efficiency are in good agreement with the experimental data. The model calculations reveal that the reaction of CO₂ (mainly at vibrationally excited levels) with H radicals is mainly responsible for the CO₂ conversion, especially at higher CH₄ fractions in the mixture, which explains why the CO₂ conversion increases with increasing CH₄ fraction. The main process responsible for CH₄ conversion is the reaction with OH radicals. The excellent energy efficiency can be explained by the non-equilibrium character of the plasma, in which the electrons mainly activate the gas molecules, and by the important role of the vibrational kinetics of CO₂ . The results demonstrate that a gliding arc plasmatron is very promising for DRM.