Simple energy-efficient electrochemically-driven CO2 scrubbing for biogas upgrading

Abstract

The conversion of biogas to biomethane represents an attractive solution to replace fossil gas with a renewable gas. However, removal of such a large percentage of CO2 from a fuel gas comes at a significant energy cost using the conventional CO2 capture technologies and hence has led to an opportunity to develop an alternative technique for large-scale carbon capture. Results of the current study suggest that employing an anion exchange membrane (AEM)-based alkaline water electrolyser for CO2 removal from gas mixtures offers an energy-efficient strategy for the capture and removal of CO2 from biogas. After capturing CO2 in an aqueous absorption column, the resulting bicarbonate solution was fed through the cathode of an AEM-based electrolyser. Although the CO2 absorption rate increased from about 300 to 900 mol m−3 h−1 when the pH was elevated from 9 to 13, the system's energy requirement was lowest at pH = 9. The economic assessment shows that the electrochemical work requirement for CO2 removal from biogas using the AEM-based alkaline electrolyser ranges between 0.25 and 0.92 kWh/kg CO2 at optimum conditions (pH = 9). This could potentially reduce the energy input for CO2 removal by about 50% compared to commercially available biogas upgrading technologies.