Afterglow quenching in plasma-based dry reforming of methane: a detailed analysis of the post-plasma chemistry via kinetic modelling†

Abstract

We have developed a kinetic model to investigate the post-plasma (afterglow) chemistry of dry reforming of methane (DRM) in warm plasmas with varying CO₂/CH₄ ratios. We used two methods to study the effects of plasma temperature and afterglow quenching on the CO₂ and CH₄ conversion and product selectivity. First, quenching via conductive cooling is shown to be unimportant for mixtures with 30/70 and 50/50 CO₂/CH₄ ratios, while it affects mixtures containing excess CO₂ (70/30) by influencing radical recombination towards CO₂, H₂ and H₂O, as well as the water gas shift reaction, decreasing the CO₂ conversion throughout the afterglow. This is accompanied by shifts in product distribution, from CO and H₂O to CO₂ and H₂, and the magnitude of this effect depends on a combination of plasma temperature and quenching rate. Second and more importantly, quenching via post-plasma mixing of the hot plasma effluent with fresh cold gas yields a significant improvement in conversion according to our model, with 258% and 301% extra conversion for CO₂ and CH₄, respectively. This is accompanied by small changes in product selectivity, which are the result of interrupted reaction pathways at lower gas temperatures in the afterglow. Effectively, the post-plasma mixing can function as a heat recovery system, significantly lowering the energy cost through the additional conversion ensued. With this approach, our model predicts that energy consumption can be lowered by nearly 80% in comparison to DRM under the same plasma conditions without mixing.