Electrochemical CO₂ Capture Using Resin-Wafer Electrodeionization

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 near-neutral pH.

Challenges and Perspectives on Carbon Fixation and Utilization Technologies: An Overview

“…Except for consecutive addition of freshwater in open ponds, appropriate water treatment/separation processes for the culture can also be applied to maintain the salinity of the culture. Several technologies are available for the culture desalting, such as membrane separation (Datta et al, 2013). However, the potential challenge is the precipitation of calcium salts, especially in calcium-laden water, thereby causing loss of alkalinity and other minerals such as iron and phosphorus (Shimamatsu, 2004).…”

“…Moreover, converting CO 2 into a bicarbonate/carbonate aqueous solution is preferred because it can be easily transported in a water pipeline under normal pressure (Chi et al, 2011). Consequently, to address the issue, various innovative processes have been evaluated for efficient use of CO 2 from flue gases in aqueous bicarbonate/carbonate solution, such as a carbonate-bicarbonate buffer (GonzalezLopez et al, 2012), CO 2 hydrate (Nakano et al, 2014) and an electrochemical membrane process (Datta et al, 2013). A comprehensive comparison among these processes is critical to achieve high engineering performance as well as low cost and environmental impacts.…”

Improved organic acid purification through wafer enhanced electrodeionization utilizing ionic liquids

“…Through EDI, ion removal can progress well beyond the limiting current density found in ED and high recovery of ionic products can be obtained [20,22]. Examples of EDI's use in industry are through metal contamination removal from wastewater, fermentation product recovery and contaminant removal, CO 2 capture, and the development of ultrapure water for electronics and pharmaceutical manufacturing [21,[23][24][25]. Unfortunately, EDI is often limited by membrane fouling resulting in complex and costly shielding and anti-fouling measures to ensure proper membrane performance [26,27].…”

“…Water splitting results in a lower overall resistance in the electrodialytic stack and maximum performance of the EDI cell throughout operation. Previous research has been focused on the recovery of organic acids using wafer EDI techniques [23][24][25]28]; however, this technique has yet to be combined with IL assisted ED [30]. ILs are desirable in electrodialytic separations because of the versatility of these solvents.…”

pH Swing Cycle for CO2 Capture Electrochemically Driven through Proton-Coupled Electron Transfer

“…Among the most promising of these is carbon capture and sequestration (CCS), in which CO2 is 45 separated from a point source [4] (e.g. flue gas from a coal or natural gas power plant), compressed, 46 and sequestered away from the atmosphere. A variant on this idea is direct air capture (DAC) [5], 47 in which CO2 is captured directly from ambient air, compressed and sequestered.…”