Catalyst-Free Methane Pyrolysis in a 2.45 GHz Microwave Atmospheric-Pressure Plasma: Effects of Microwave Power and Methane Flow Rate

This study experimentally investigates a 2.45 GHz microwave atmospheric pressure plasma-driven catalyst-free methane pyrolysis (without additional gases) for hydrogen production. A plasma source, recently patented by us, operated without a dielectric tube, is utilized to process methane flow rates up to 60 NL/min at absorbed microwave power of up to 3.5 kW. The work evaluates the effects of the microwave power and gas flow rate on the parameters of methane conversion. Results show that increasing microwave power enhances hydrogen concentration (up to 38%), methane conversion (up to ~30%), and hydrogen production rate (up to 102 g/h). Increasing the methane flow rate reduces methane conversion rates (due to the combined effect of the decreased specific energy input and residence time) but improves hydrogen production rate and energy yield of hydrogen production (due to higher throughput). Consequently, the effect of the inlet methane flow rate highlights the central trade-off of the process: higher flow rates reduce single-pass methane conversion but enhance overall hydrogen productivity and energy yield. These findings demonstrate that microwave plasma enables efficient, catalyst-free methane decomposition and highlight the importance of optimizing energy input and residence time for improved performance.