Hydrogen\nProduction from Methane Thermal Pyrolysis\nin a Microwave Heating-Assisted Fluidized Bed Reactor

Methane (CH<sub>4</sub>) thermal pyrolysis is a promising,\ncarbon\ndioxide (CO<sub>2</sub>)-free method for hydrogen (H<sub>2</sub>)\nproduction, decomposing CH<sub>4</sub> into H<sub>2</sub> and solid\ncarbon. This highly endothermic and energy-intensive process can sustainably\nbe powered by microwave (MW) heating supported by renewable electricity.\nIn this study, we investigated the efficacy of H<sub>2</sub> production\nand simultaneous carbon capture through CH<sub>4</sub> thermal pyrolysis\nin a lab-scale MW heating-assisted fluidized bed reactor (MW-FBR).\nWe identified the effects of the thermal gradient between the solid\nand gas phases in MW-FBR on the process through direct comparison\nwith a conventional heating-assisted fluidized bed reactor (CH-FBR)\nunder identical operating conditions. Solid dielectric particles in\nMW-FBR reach high temperatures, creating favorable conditions for\nCH<sub>4</sub> thermal decomposition. We examined the influences of\ntemperature (900–1065 °C), mean residence time (0.5–1.5\ns), and inlet CH<sub>4</sub> molar fraction (0.2–0.5) on CH<sub>4</sub> conversion and H<sub>2</sub> selectivity. We obtained the\nhighest CH<sub>4</sub> conversion of 23% and H<sub>2</sub> selectivity\nof up to 98% within the applied experimental conditions. Monitoring\npyrolytic carbon byproducts showed that 90% of the produced pyrolytic\ncarbon remained in the bed and captured by the fluidized particles.\nComparative analysis between MW-FBR and CH-FBR at the same experimental\nconditions revealed that MW heating substantially outperformed conventional\nheating due to MW thermal effect, thermal gradient between solid and\ngas phases, and hotspots formation. On average, CH<sub>4</sub> conversion\nincreased by 150%. Carbon capture efficiency improved by 70%. In addition,\nMW heating produced more graphitic carbon.