Experimental Analysis of a Sabatier Reactor for Renewable Natural Gas Generation from Biogas: Ignition, Parameter Sensitivity Analysis, and Stability

Biogas is a product of anaerobic fermentation, which is rich in CO2. The upgrade of biogas to renewable natural gas (RNG) is commercially achieved by separating carbon dioxide (CO2) and impurities to improve its quality. As an alternative, the CO2 contained in biogas can be directly converted into CH4 via the thermocatalytic Sabatier reaction without separation, using H2 generated by water electrolysis (utilizing renewable or surplus, low-carbon-footprint electricity). One of the major elements of this technology is the configuration of the Sabatier reactor. For industrial applications, it is beneficial to eliminate the energy-intensive CO2 separation step, converting biogas to RNG directly. In this study, we report the experimental lab-scale proof of concept of the autothermal Sabatier reactor for direct biogas upgrade. We demonstrate a completely autothermal operation of the air-cooled, stainless steel reactor using a commercial Ni catalyst with a synthetic biogas feed. The effects of feed temperature, space velocity, and reactor cooling were investigated using three prototypes with different sizes and configurations. The maximum CO2 conversion of 91% with 100% selectivity to CH4 generation was achieved in a 10″-length reactor, over 100 h of continuous, stable operation, without any external reactor heating or feed preheating.