Controlling Solid Carbon Formation in Gliding Arc CH4 Plasmas

Non-oxidative coupling of methane (CH4) in plasma reactors offers a promising route for electrified hydrocarbon production but is hindered by solid carbon formation, reducing efficiency and causing reactor fouling. Here, we systematically investigate solid carbon formation in a rotating gliding arc plasma reactor, linking process parameters to CH4 conversion, product selectivity, and solid carbon deposition. We evaluate the effects of gas flow rate, plasma power, additives (H2, O2), and AC vs DC power supply, and extensively characterize the synthesized carbon. Computational fluid dynamics modeling is used to elucidate the underlying flow dynamics and their effect on solid carbon formation. Our results show that CH4 conversion heavily depends on specific energy input, whereas product distribution remains largely unaffected. H2 effectively suppresses solid carbon by shifting selectivity toward unsaturated hydrocarbons. Conversely, O2 forms CO without significantly reducing carbon deposition. The synthesized carbon is predominantly turbostratic carbon and contaminated by electrode erosion. Modeling indicates that solid carbon formation mainly proceeds via the polycyclic aromatic hydrocarbon mechanism, linking carbons into graphene-like sheets. Our work provides mechanistic insight into solid carbon formation in CH4 gliding arc plasmas and emphasizes the importance of suppressing solid carbon formation at the source to enable selective plasma-driven hydrocarbon formation.