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

We have developed a kinetic model to investigate the post-plasma (afterglow) chemistry of dry reforming of methane (DRM) in warm plasmas with varying CO/CH ratios. We used two methods to study the effects of plasma temperature and afterglow quenching on the CO and CH conversion and product selectivity. First, quenching conductive cooling is shown to be unimportant for mixtures with 30/70 and 50/50 CO/CH ratios, while it affects mixtures containing excess CO (70/30) by influencing radical recombination towards CO, H and HO, as well as the water gas shift reaction, decreasing the CO conversion throughout the afterglow. This is accompanied by shifts in product distribution, from CO and HO to CO and H, and the magnitude of this effect depends on a combination of plasma temperature and quenching rate. Second and more importantly, quenching 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 CO and CH, 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.