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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 CO<sub>2</sub>/CH<sub>4</sub>ratios. We used two methods to study the effects of plasma temperature and afterglow quenching on the CO<sub>2</sub>and CH<sub>4</sub>conversion and product selectivity. First, quenching<italic>via</italic>conductive cooling is shown to be unimportant for mixtures with 30/70 and 50/50 CO<sub>2</sub>/CH<sub>4</sub>ratios, while it affects mixtures containing excess CO<sub>2</sub>(70/30) by influencing radical recombination towards CO<sub>2</sub>, H<sub>2</sub>and H<sub>2</sub>O, as well as the water gas shift reaction, decreasing the CO<sub>2</sub>conversion throughout the afterglow. This is accompanied by shifts in product distribution, from CO and H<sub>2</sub>O to CO<sub>2</sub>and H<sub>2</sub>, and the magnitude of this effect depends on a combination of plasma temperature and quenching rate. Second and more importantly, quenching<italic>via</italic>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<sub>2</sub>and CH<sub>4</sub>, 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. |
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