Hydrogen Production from Methane Thermal Pyrolysis in a Microwave Heating-Assisted Fluidized Bed Reactor

Methane (CH4) thermal pyrolysis is a promising, carbon dioxide (CO2)-free method for hydrogen (H2) production, decomposing CH4 into H2 and solid carbon. This highly endothermic and energy-intensive process can sustainably be powered by microwave (MW) heating supported by renewable electricity. In this study, we investigated the efficacy of H2 production and simultaneous carbon capture through CH4 thermal pyrolysis in a lab-scale MW heating-assisted fluidized bed reactor (MW-FBR). We identified the effects of the thermal gradient between the solid and gas phases in MW-FBR on the process through direct comparison with a conventional heating-assisted fluidized bed reactor (CH-FBR) under identical operating conditions. Solid dielectric particles in MW-FBR reach high temperatures, creating favorable conditions for CH4 thermal decomposition. We examined the influences of temperature (900–1065 °C), mean residence time (0.5–1.5 s), and inlet CH4 molar fraction (0.2–0.5) on CH4 conversion and H2 selectivity. We obtained the highest CH4 conversion of 23% and H2 selectivity of up to 98% within the applied experimental conditions. Monitoring pyrolytic carbon byproducts showed that 90% of the produced pyrolytic carbon remained in the bed and captured by the fluidized particles. Comparative analysis between MW-FBR and CH-FBR at the same experimental conditions revealed that MW heating substantially outperformed conventional heating due to MW thermal effect, thermal gradient between solid and gas phases, and hotspots formation. On average, CH4 conversion increased by 150%. Carbon capture efficiency improved by 70%. In addition, MW heating produced more graphitic carbon.