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

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 CO 2 from a fuel gas comes at a significant energy cost using the conventional CO 2 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 CO 2 removal from gas mixtures offers an energy-efficient strategy for the capture and removal of CO 2 from biogas. After capturing CO 2 in an aqueous absorption column, the resulting bicarbonate solution was fed through the cathode of an AEM-based electrolyser. Although the CO 2 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 CO 2 removal from biogas using the AEM-based alkaline electrolyser ranges between 0.25 and 0.92 kWh/kg CO 2 at optimum conditions (pH = 9). This could potentially reduce the energy input for CO 2 removal by about 50% compared to commercially available biogas upgrading technologies. [ABSTRACT FROM AUTHOR]