CO2 and CH4 conversion in a rotating DC glow to arc plasma with big discharge gap

Abstract

In this work, we investigated large-volume, non-thermal discharges in CO₂/CH₄ mixtures with the aim of enabling energy-efficient plasma-based conversion. Building on the fundamental U–I characteristics of gas discharges, we showed how discharge extension and thermal management strongly affect the transition between glow and arc regimes. Using our Big Discharge-gap Glow-to-Arc (BDGTA) reactor, stable rotating discharges were realized at electrode gaps up to 40 mm. Depending on scale, plasma operation was achieved with average currents of 0.24–0.4 A and discharge voltages ranging from 1.5 kV (15 mm) to 4 kV (40 mm), corresponding to power levels between 400 and 1700 W. Optical diagnostics via high-speed camera confirmed the glow-like nature and the dynamics of the elongated discharges. Performance analysis revealed maximum energy efficiencies of 68 % (60 % CO₂, 40 % CH₄) and 60 % for 50/50 mixtures, with conversions up to 68 %. Carbon deposition in methane-rich mixtures was identified as a key challenge but can be mitigated through process adjustments like CO₂ recycling. Replacing ballast resistors with power-electronics plasma control minimized energy losses and ensured regime stability. Overall, the BDGTA reactor demonstrates that efficient, large-volume CO₂/CH₄ plasma conversion is feasible at atmospheric pressure, offering a pathway for sustainable electrification of chemical processes.