Electrochemical CO₂ Capture Using Resin-Wafer Electrodeionization

Energy-efficient capture of CO 2 from power-plant flue gas is one of the grand challenges to reduce greenhouse gas (GHG) emissions. Current CO 2 -capture technologies are limited by parasitic energy loss, inefficient capture, and unfavorable process economics. We present a novel electrochemical method for CO 2 capture from coal-fired power-plant flue gas. The method utilizes in-situ electrochemical pH control with a resin wafer electrodeionization (RW-EDI) device that continuously shifts the pH of the process fluid between basic and acidic in sequential chambers (pH swing). This pH swing enables capture of CO 2 from flue gas in the basic chamber followed by release (recovery) of the captured CO 2 (purified) in the acidic chamber of the same device. The approach is based on the sensitivity of the thermodynamic equilibrium of CO 2 hydration/dehydration reactions over a narrow pH range. The method enables simultaneous absorption (capture) of CO 2 from flue gas and desorption (release) at atmospheric pressure without heating, vacuum, or consumptive chemical usage. In other words, the method concentrates CO 2 from ∼15% in flue gas to >98% in the recovery stream. To the best of our knowledge, this is the first experimental study focusing on simultaneous capture and release (recovery) of CO 2 using an electrochemical method. We describe the method, the role of operating parameters on CO 2 recovery, and advancements in process design and engineering for improved efficiency. We report on a method to enhance gas/liquid mixing inside the RW-EDI, which significantly increased CO 2 capture rates. We also discuss the importance of using an enzyme/catalyst in enhancing the reaction kinetics. CO 2 capture was observed to be a strong function of gas and liquid flow rates and applied electrical field. Up to 80% of the CO 2 was captured from a simulated flue gas stream with >98% purity. The results indicate that a narrow pH swing from 8 to 6 (near-neutral pH) could offer a viable pathway for energy-efficient CO 2 capture if the reaction kinetics are enhanced. Carbonic anhydrase enzyme enhances the reaction kinetics at near-neutral pH; however, the enzyme lost activity due to the instability at the operating conditions. This observation highlighted the necessity of robust enzymes/catalysts to enhance kinetics of CO 2 recovery near-neutral pH.