Synthesis of grid compliant substitute natural gas from a representative biogas mixture in a hybrid Ni/Ru catalysed reactor

[Display omitted] •A multi-stage reactor is designed and manufactured.•The performance of the reactor is evaluated in the direct methanation of biogas.•The first stages are performed over Ni-based catalyst, the last over Ru-based.•The temperature profile is optimized over the stages.•Grid-compliant methane is produced already at low pressure (2 bar) We demonstrate biogas upgrading towards full CO2 conversion in mild conditions in a three-step reactor system using Ru- and Ni-based catalysts. In each of the three reactor stages, the temperature is carefully controlled, thus optimizing the reaction thermodynamics and kinetics, resulting in a maximized global CO2 conversion. At ambient pressure, 92% conversion can be achieved over a commercial Ru/Al2O3 catalyst at a space velocity of 2 L/h/gcat in every stage. At 2 bar conversion is enhanced to above 99%. It is possible to substitute the Ru-based catalyst in the first stage with a cheaper Ni-based catalyst, shifting the first-stage temperature to higher values forming also CO. CO has a positive effect on the following step since CO is converted to CH4 in the CO methanation reaction. In this way, it is possible to achieve the same final conversion compared to the Ru-operated reactor system using Ni in the first reactor stage.