The Role of CH4 in Plasma-Assisted CO2 and CH4 Conversion in a Rotating Gliding Arc Plasma: Insights Revealed by Experiments and Modeling

Abstract

We investigated the combined conversion of CO₂ and CH₄, so-called dry reforming of methane (DRM), in a rotating gliding arc (RGA) reactor by experiments and modeling for different CO₂/CH₄ mixing ratios. We obtained the best results at the lowest flow rate (4 L/min) and the lowest amount of CH₄ in the feed gas mixture (25%), reaching a conversion of 22% and 39% for CO₂ and CH₄, respectively, an energy efficiency of 62% and energy cost of 3.25 eV/molecule. A lower energy cost of 2.65 eV/molecule was obtained at 8 L/min. By means of a 3D computational fluid dynamics model, we show that the addition of CH₄ reduces the gas temperature inside the plasma, resulting in slower chemical kinetics, explaining why the least amount of CH₄ (i.e., 25/75 CH₄/CO₂) yields the highest CO₂ and CH₄ conversion. Additionally, the 25/75 CH₄/CO₂ mixture also displays the highest energy efficiency, due to the high conversion, as well as due the high CO concentration produced in this gas mixture, which is the most beneficial product in terms of energy efficiency. Finally, by means of a quasi-1D chemical kinetics model, we demonstrate that the addition of CH₄ suppresses the CO recombination reactions back into CO₂, after the plasma, as H-based radicals from CH₄ quickly react with O radicals that would otherwise recombine with CO.