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 uneasy-oxidizing Cγ 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 high H2/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.

Graphical AbstractControlled by thermodynamics, the realized CO conversion and selectivity to CH4 in syngas methanation in a fluidized bed decreased with rising reaction temperature. At temperature lower than 750 K the kinetic rate was low, so did the CO conversion. Meanwhile, the TPO results revealed that the higher methanation temperature caused the higher carbon deposition and the transformation of the reactive Cβ to the hard-oxidizing Cγ. Therefore, the methanation is thus better to be at temperature between 750 K and 823 K for ensuring both activity and stability of the catalyst.Figure optionsDownload as PowerPoint slide