Plasma-Based CH₄ Conversion into Higher Hydrocarbons and H₂: Modeling to Reveal the Reaction Mechanisms of Different...

Plasma is gaining interest for CH₄ conversion into higher hydrocarbons and H₂. However, the performance in terms of conversion and selectivity toward different hydrocarbons is different for different plasma types, and the underlying mechanisms are not yet fully understood. Therefore, we study here these mechanisms in different plasma sources, by means of a chemical kinetics model. The model is first validated by comparing the calculated conversions and hydrocarbon/H₂ selectivities with experimental results in these different plasma types and over a wide range of specific energy input (SEI) values. Our model predicts that vibrational-translational nonequilibrium is negligible in all CH₄ plasmas investigated, and instead, thermal conversion is important. Higher gas temperatures also lead to a more selective production of unsaturated hydrocarbons (mainly C₂H₂) due to neutral dissociation of CH₄ and subsequent dehydrogenation processes, while three-body recombination reactions into saturated hydrocarbons (mainly C₂H₆, but also higher hydrocarbons) are dominant in low temperature plasmas.