CO₂ methanation in a bench-scale bubbling fluidized bed reactor using Ni-based catalyst and its exothermic heat transfer analysis

CO₂ methanation, as a power-to-gas technology, is considered to be an important method to secure energy supply by utilizing CO₂ and H₂ gases. In this study, a 0.2 kW CH₄ bench-scale fluidized bed reactor was used for CO₂ methanation using approximately 13 kg nickel-based catalyst to investigate the effect of temperature, gas velocity, and H₂/CO₂ ratio on CO₂ conversion, CH₄ purity, and CH₄ selectivity. Response surface methodology (RSM) was employed to design the experimental conditions to statistically evaluate the effect of operating variables. Reduced quadratic model equations for CO₂ conversion and CH₄ purity were derived, which determined the optimal conditions within the experimental conditions. The suggested conditions for the highest CO₂ conversion were 297 °C, 4.66H₂/CO₂, and 4.0 U_g/U_mf (velocity ratio), whereas different conditions were determined for the highest CH₄ purity. Among the operating variables, temperature was the most influential factor, followed by the gas ratio. The highest CO₂ conversion and CH₄ purity were 98% and 81.6%, respectively. Additionally, the heat transfer coefficient (h_o) was found to be 115 W/m²∙°C during a 10-h continuous CO₂ methanation experiment, which is an important design factor for the further scale-up of the process.