Performance characteristics of fluidized bed syngas methanation over Ni-Mg/Al2O3 catalyst

The performance characteristics of isothermal fluidized bed syngas methanation for substitute natural gas are investigated over a self-made Ni-Mg/Al₂O₃ catalyst. Via atmospheric methanation in a laboratory fluidized bed reactor it was clarified that the CO conversion varied in 5% when changing the space velocity in 40-120 L·g^-1·h^-1 but the conversion increased obviously by raising the superficial gas velocity from 4 to 12.4 cm·s^-1. The temperature at 823 K is suitable for syngas methanation while obvious deposition of uneasyoxidizing C_γ occurs on the catalyst at temperatures around 873 K. From a kinetic aspect, the lowest reaction temperature is suggested to be 750 K when the space velocity is 60 L·g^-1·h^-1. Raising the H₂/CO ratio of the syngas increased proportionally the CO conversion and CH₄ selectivity, showing that at enough highH₂/CO ratios the active sites on the catalyst are sufficient for CO adsorption and in turn the reaction with H₂ for forming CH₄. Introducing CO₂ into the syngas feed suppresses the water gas shift and Boudouard reactions and thus increased H₂ consumption. The ratio of CO₂/CO in syngas should be better below 0.52 because varying the ratio from 0.52 to 0.92 resulted in negligible increases in the H₂ conversion and CH₄ selectivity but decreased the CH₄ yield. Introducing steam into the feed gas affected little the CO conversion but decreased the selectivity to CH₄. The tested Ni-Mg/Al₂O₃ catalyst manifested good stability in structure and activity even in syngas containing water vapor.