(333a) Membraneless Electrochemical Amine Regeneration: A Novel Two-Stage Process for Carbon Capture

Electrochemical CO₂ separations are receiving considerable attention as potentially modular, scalable, and economically viable alternatives to conventional technologies. Electrochemically mediated amine regeneration (EMAR) is a well-established technique employing readily available amine electrolytes [1]; however, the integration of membranes introduces substantial capital expenditures and operational challenges [2]. This study presents a novel two-stage electrochemical system for CO₂ capture achieved through a fundamentally redesigned EMAR process configuration. Gas diffusion electrodes (GDEs) function as gas-breathing interfaces serving as both the anode and cathode to facilitate cathodic absorption (simultaneous CO₂ absorption with Cu²⁺ electroplating) and anodic desorption (simultaneous CO₂ removal during copper oxidation). Taking advantage of the two-stage system, CO₂ absorption and removal at the electrode interfaces induce a shift in the equilibrium Nernstian potential—more positive for the cathodic reaction and more negative for the anodic reaction—enabling the system to approach the electrochemical thermodynamic minimum work more closely [3-4]. The mass transfer of redox species occurs via diffusion and migration under electrochemical forces, enabling batch-mode operation, which eliminates the need for electrolyte circulation. Furthermore, this redesign reduces the system's capital and operational expenditures (CapEx and OpEx) while maintaining high desorption efficiency, dropping the need for pumps, membranes, absorbers, and flash tanks.

In this study, two types of GDE assemblies were used: mesh-attached and electrodeposited. Electrodeposited GDEs demonstrated superior performance, achieving CO₂ removal efficiencies exceeding 90%, compared to 35–55% for mesh-attached GDEs. Copper loading for electrodeposited GDEs, was the determining factor; higher loadings resulted in lower carbon removal efficiency due to the copper layer acting as a physical barrier against CO2 transport. Optimal performance was achieved with a copper loading of 1.7 mg/cm² on a Toray 060 gas diffusion layer (GDL), delivering 87% removal efficiency, 176 A/m² current density, and 76 kJ/molCO₂ energy consumption for flue gas (0.15 bar partial pressure, released at 1 bar). The detection of CO₂ via online gas chromatography confirms the effectiveness of the system in selectively desorbing CO₂ without side reactions or the co-transfer of other flue gas components i.e., N₂ through the electrolyte.

Techno-economic analysis of the membraneless EMAR system indicated a levelized cost of carbon capture (LCOCC) of approximately $69.7/tonneCO₂, about 50% lower than the $137/tonneCO₂ for conventional membrane-based systems. Sensitivity analysis suggests that carbon capture costs may be reduced to as low as $50/tonneCO₂ with further improvements in current density and removal efficiency. This two-stage EMAR system represents a significant advancement in electrochemical carbon capture technology, offering a simpler configuration, smaller footprint, and substantially lower costs compared to conventional systems, making it a promising solution for scalable point-source carbon capture.

References:

[1] A. Hassan et al., “Reviving the absorbent chemistry of electrochemically mediated amine regeneration for improved point source carbon capture,” Chemical Engineering Journal, vol. 484, p. 149566, Mar. 2024, doi: 10.1016/j.cej.2024.149566.

[2] M. Wang, R. Shaw, E. Gencer, and T. A. Hatton, “Technoeconomic Analysis of the Electrochemically Mediated Amine Regeneration CO₂ Capture Process,” Ind. Eng. Chem. Res., vol. 59, no. 31, pp. 14085–14095, Aug. 2020, doi: 10.1021/acs.iecr.0c02166.

[3] L. E. Clarke, M. E. Leonard, T. A. Hatton, and F. R. Brushett, “Thermodynamic Modeling of CO₂ Separation Systems with Soluble, Redox-Active Capture Species,” Ind. Eng. Chem. Res., vol. 61, no. 29, pp. 10531–10546, Jul. 2022, doi: 10.1021/acs.iecr.1c04185.

[4] M. Wang, S. Hariharan, R. A. Shaw, and T. A. Hatton, “Energetics of electrochemically mediated amine regeneration process for flue gas CO₂ capture,” International Journal of Greenhouse Gas Control, vol. 82, pp. 48–58, Mar. 2019, doi: 10.1016/j.ijggc.2018.12.028.