Article pubs.acs.org/IECR
Electrochemical CO2 Capture Using Resin-Wafer Electrodeionization Saurav Datta, Michael P. Henry, YuPo. J. Lin, Anthony T. Fracaro, Cynthia S. Millard, and Seth W. Snyder* Energy Systems, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, Illinois, United States
Rebecca L. Stiles, Jitendra Shah, Jianwei Yuan, Lisa Wesoloski, Robert W. Dorner, and Wayne M. Carlson Air Protection Technologies, Nalco Company, an Ecolab Company, 1601 West Diehl Road, Naperville, Illinois 60563, United States ABSTRACT: Energy-efficient capture of CO2 from power-plant flue gas is one of the grand challenges to reduce greenhouse gas (GHG) emissions. Current CO2-capture technologies are limited by parasitic energy loss, inefficient capture, and unfavorable process economics. We present a novel electrochemical method for CO2 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 CO2 from flue gas in the basic chamber followed by release (recovery) of the captured CO2 (purified) in the acidic chamber of the same device. The approach is based on the sensitivity of the thermodynamic equilibrium of CO2 hydration/dehydration reactions over a narrow pH range. The method enables simultaneous absorption (capture) of CO2 from flue gas and desorption (release) at atmospheric pressure without heating, vacuum, or consumptive chemical usage. In other words, the method concentrates CO2 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 CO2 using an electrochemical method. We describe the method, the role of operating parameters on CO2 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 CO2 capture rates. We also discuss the importance of using an enzyme/catalyst in enhancing the reaction kinetics. CO2 capture was observed to be a strong function of gas and liquid flow rates and applied electrical field. Up to 80% of the CO2 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 CO2 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 CO2 recovery nearneutral pH.
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INTRODUCTION Energy-efficient capture of CO2 from power-plant flue gas is one of the grand challenges to reduce greenhouse gas (GHG) emissions and is crucial for improving the environmental profile of the power generation industry. Coal-fired power plants contribute about 35% of the total CO2 emissions in the United States and even higher in other countries.1 A typical 600 MW coal-fired power plant produces ∼460 ton/h of CO2.2 This represents a major hurdle for deploying fossil-fuel-based energy generation technologies in a carbon-constrained world. Various technologies have been evaluated for postcombustion CO2 capture that includes adsorption,3−5 absorption,6−12 pressure swing adsorption,13,14 membrane separations,2,15−19 cryogenic separations,20 ionic-liquid-based separations,21,22 electrochemical methods,23,24 and biochemical methods.25−28 Each present technological challenge prevents them from achieving the CO2 capture targets proposed by the U.S. Department of Energy (DOE), i.e., 90% capture, while maintaining 98% purity from a simulated flue gas (containing 15% CO2 and 85% N2). Extended performance was observed over hours, suggesting the device could achieve targeted performance. CO2 capture rate was dependent on the gas and liquid flow rates at a constant applied current. Significant improvements in process design and engineering were reported. Due to the impact of gas−liquid interactions, more efficient gas−liquid delivery manifold and distributors were designed. The gas delivery manifold and distributors increased CO2 capture rates by an order of magnitude. A potential pathway for energy-efficient CO2 capture was considered by employing limited pH swing near neutral pH (between pH 8 and 6) utilizing the electrochemical platform. When CA was used near neutral pH, kinetics was enhanced, recovery rate was increased, and energy consumption was reduced. Performance with the enzyme declined with continuous operation, suggesting that more robust catalysts are required. Although the DOEs target of
