Membrane electrolysis-assisted CO2 and H2S extraction as innovative pretreatment method for biological biogas upgrading

Turning raw biogas into biomethane as energy carrier requires the selective removal of CO2 in a biogas upgrading process or a total conversion of CO2 to CH4 which is generally energy intensive. During membrane electrolysis, electrical energy can be used to simultaneously remove CO2 (and H2S) and produce H-2 as side product. Biogas is thus scrubbed with catholyte and the captured HCO3- and HS-migrate towards the anode. Simultaneously, cathodic H-2 mixes with residual biogas in a ratio that can be fine-tuned. We obtained in one step an ideal 4:1 H-2:CO2 ratio in the reactor off gas. Subsequently the gas could be further upgraded via chemoautotrophic microbial conversion of CO2 to CH4. Biomethanation delivered biomethane with 98.9 +/- 0.9% purity. The electrochemically-assisted scrubbing and stripping of CO2 and H2S resulted in high CO2 removal efficiencies (up to 100%), without addition of chemicals. The system was flexible depending on temporarily available power. Electrochemical biogas upgrading (EBU) can be envisaged as a scalable and decentralized storage of excess or off-peak renewable power, making better use of the power input used to drive a biological CO2 conversion