Intrinsic kinetics of CO methanation over spherical Ni/Al2O3 catalyst with high attrition resistance
Carbon monoxide and hydrogen can be used to synthesize methane with catalyst application and this reaction is used in the field of coal to substitute natural gas,coke oven gas to liquid natural gas,and biomass synthesis gas to optimize the energy structure in China.Compared with fixed bed,the fluidized bed methanation technology adopting spherical catalyst with small diameters shows obvious superiority in activity and heat transfer efficiency due to the fast surface reaction characteristics of highly exothermic CO methanation.Based on the developed spherical Ni/Al2O3 catalyst with high attrition resistance,the intrinsic kinetics of CO methanation were tested in a differential fixed bed reactor under atmospheric pressure to reveal the reaction mechanism and route.The formation rates of CH4 at different ratios of CO/H2 and reaction temperatures were calculated on the premise of eliminating internal and external diffusion and controlling the CO conversion to less than 15％by decreasing the catalyst amount or increasing the gas feed rate.Then data fitting was conducted based on the power kinetic model and hyperbolic kinetic model,respectively.The results based on the power dynamics model showed that with the increase of reaction temperature from 260℃ to 350℃,the activation energy gradually decreased from 145.99 kJ/mol to 123.54 kJ/mol,the reaction order of CO changed from-1.22 to 0.34,and the reaction order of H2 increased from 0.31 to 2.28.To further analyze the methanation mechanisms,the rate-determining steps were assumed based on the hyperbolic dynamics model according to the effect of CO and H2 concentration on the reaction rate at different temperature ranges.As the rate determining step at 260～280 ℃ was assumed to be H2 dissociation,at 280～310 ℃ was the hydrogenation of CO and at 310～350 ℃ was the hydrogenation of carbon intermediate.The R2 of the hyperbolic rate equations obtained were all greater than 0.99,which indicated that the rate determining step of methanation would change with the temperature.
Ni-based catalystmethanationintrinsic kineticsrate determining stepfluidized bedhyperbolic kinetic model
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