Optimizing alkaline solvent regeneration through bipolar membrane electrodialysis for carbon capture

This work demonstrates and characterizes the use of a bipolar membrane electrodialysis for pH-driven CO₂ capture and solvent regeneration using potassium hydroxide solutions. The impact of potassium concentration, current density and load ratio on the CO₂ desorption efficiency was analyzed and substantiated with an equilibrium model. The system was tested with partially saturated solutions that mimic the expected carbon content of alkaline solvents that have been in contact with flue gas (carbon loading of 0.6 and K⁺ concentration from 0.5 M to 2 M). Among the tested current densities, 1000 A/m² demonstrated the highest CO₂ desorption efficiency but also the highest energy consumption, whereas 250 A/m² exhibited the lowest energy consumption (8.8 GJ/ton CO₂) but lower CO₂ desorption. Efficiency losses were associated with H⁺ transport across the membranes at high load ratios and decrease of the bipolar membranes water dissociation efficiency at low current densities. This work establishes key performance indicators and describes fundamental characteristics of continuous bipolar membrane electrodialysis systems for regeneration of alkaline solvents used in post-combustion CO₂ capture.