Investigating reaction rates in microwave heating-assisted methane pyrolysis

• Estimation of kinetic parameters for CH 4 pyrolysis in a microwave-heated fluidized bed reactor. • Development of a global kinetic model incorporating gas–solid temperature differences. • Comparison with conventional heating shows higher CH 4 conversion and lower activation energy under microwave heating. • Identification of microwave-induced hotspots originating from particle–particle interactions. • Quantification of microscale hotspots by integrating experimental analysis and numerical simulation. Microwave (MW)-assisted methane (CH 4 ) pyrolysis is a novel method for hydrogen (H 2 ) production without direct CO 2 emissions. MW heating benefits from selective volumetric heating and rapid energy transfer. In this work, we investigated the kinetics of CH 4 thermal pyrolysis under MW heating in a fluidized bed reactor (MW-FBR), and we compared it to a conventional heating-assisted fluidized bed reactor (CH-FBR). We conducted experiments across a temperature range of 950–1065 °C and residence times of 0.5–8.0 s at atmospheric pressure. The reaction kinetics were described by a first-order global kinetic model and considered the non-isothermal conditions in MW-FBR between the solid phase and the gas phase. The solid temperature exceeded the gas temperature by ∼200 °C and the bulk temperature by ∼100 °C. MW-FBR showed higher CH 4 conversion and lower apparent activation energy compared to CH-FBR. These observations are attributed to localized microscale hotspots. We estimated an apparent activation energy of 288 kJ/mol for MW-FBR and 310 kJ/mol for CH-FBR. We estimated the thermal contribution of hotspots to the reaction by comparing the activation energies between MW-FBR and CH-FBR. The hotspots effect corresponds to a 5 % higher bed effective temperature than the measured solid temperature. Numerical simulation showed that particle–particle contact causes hotspots due to higher MW power dissipation at contact points compared to isolated particles. Model predictions based on the estimated kinetic parameters indicate that complete CH 4 conversion is achieved at solid temperatures of 1100–1200 °C, corresponding to bulk temperatures of 1000–1075 °C, at mean residence times of 3–10 s.