Electrochemical CO 2 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 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. ■ INTRODUCTION Energy-efficient capture of CO 2 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 CO 2 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 CO 2 . 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 CO 2 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 electrochem- ical methods, 23,24 and biochemical methods. 25-28 Each present technological challenge prevents them from achieving the CO 2 capture targets proposed by the U.S. Department of Energy (DOE), i.e., 90% capture, while maintaining <35% impact on the cost of electricity (COE). 29 Energy use reduces power output, derating the plant, and is the primary contributor to COE. Amine-based absorption, the most efficient method to date, is unable to achieve the energy target. 9,10,19 The primary driver of energy intensiveness is regeneration of the solvent that requires parasitic energy inputs in the form of temperature (steam) and/or pressure swing (vacuum) for stripping the absorbed CO 2 . The CO 2 emission rate for a typical coal-fired power plant is ∼0.83 kg/KWh, which translates to an emission of 1 kg of CO 2 per 1.2 KWh of power generated from pulverized coal. 30 Therefore, to achieve the DOE goal of <35% COE, energy consumption must be <0.42 KWh/kg of CO 2 . However, an economic analysis on the latest amine-based capture technology revealed 85% COE, which corresponds to ∼1.0 KWh/kg of energy consumption. 19 Therefore, novel methods with reduced energy consumption are required. Methods must be designed that work efficiently at partial pressures observed in flue gas (∼0.15 atm). 30 We designed an electrochemical method that captures CO 2 from flue gas and subsequently releases the captured, purified CO 2 in a single device based on a pH-driven equilibrium shift between gaseous CO 2 and bicarbonate ion. 31 The method functions by in-situ electrochemical pH control using a system Received: August 2, 2013 Revised: October 1, 2013 Accepted: October 7, 2013 Article pubs.acs.org/IECR © XXXX American Chemical Society A dx.doi.org/10.1021/ie402538d | Ind. Eng. Chem. Res. XXXX, XXX, XXX-XXX