Direct Air Capture Using Electrochemically Regenerated Anion Exchange Resins

Abstract

Direct air capture (DAC) aims to remove CO 2 directly from the atmosphere. In this study, we have demonstrated proof-of-concept of a DAC process combining CO 2 adsorption in a packed bed of amine-functionalized anion exchange resins (AERs) with a pH swing regeneration using an electrochemical cell (EC). The resin bed was regenerated using the alkaline solution produced in the cathodic compartment of the EC, while high purity CO 2 (>95%) was desorbed in the acidifying compartment. After regenerating the AERs, some alkaline solution remained on the surface of the resins and provided additional CO 2 capture capacity during adsorption. The highest CO 2 capture capacity measured was 1.76 mmol·g –1 dry resins. Moreover, as the whole process was operated at room temperature, the resins did not show any apparent degradation after 150 cycles of adsorption–desorption. Furthermore, when the relative humidity of the air source increased from 33 to 84%, the water loss of the process decreased by 63%, while CO 2 capture capacity fell 22%. Finally, although the pressure drop of the adsorption column (5 ± 1 kPa) and the energy consumption of the EC (537 ± 33 kJ·mol –1 at 20 mA·cm –2 ) are high, we have discussed the potential improvements toward a successful upscaling.

Measurement of Physicochemical Properties and CO2, N2, Ar, O2, and H2O Unary Adsorption Isotherms of Purolite A110 and Lewatit VP OC 1065 for Application in Direct Air Capture

“…In addition to gathering the data to fully evaluate the potential of adsorbents at scale, expanding the group of easily accessible commercial materials for DAC to cover the wide range of climate conditions will help accelerate the deployment of adsorption-based DAC technologies. In the field of polymeric resins, Shu et al investigated a commercial resin (AmberLite HPR4800 OH) using pH swing regeneration in an electrochemical cell, which had a CO 2 adsorption capacity of 1.76 mmol g –1 under humid conditions at 0.04 kPa CO 2 and 298 K. The particle and bed densities of the adsorbent are available from the manufacturer, but other properties needed for process modeling (see Table ) were not reported in this study. Elfving et al studied an undisclosed resin supplied by Oy Hydrocell Ltd. under various process cycles, regeneration conditions, and dry versus humid conditions. , The adsorbent consists of a polystyrene matrix functionalized with primary amines, like Lewatit, with a dry CO 2 adsorption capacity of 0.8 mmol g –1 at 0.04 kPa CO 2 and 298 K. Single-component CO 2 and H 2 O isotherms at multiple temperatures, as well as CO 2 –H 2 O coadsorption isotherms, have been measured.…”

Carbon Capture Beyond Amines: CO2Sorption at Nucleophilic Oxygen Sites in Materials

“…Electro‐swing processes have also been used in combination with other processes, such as a pH swing, to capture CO 2 directly from air (Figure 12). Kuntke and co‐workers proposed a novel DAC process which combines CO 2 adsorption with amine‐functionalized anion exchange resins (AERs) and CO 2 desorption with an electrochemical cell (Figure 12a) [192] . Within the electrochemical cell, a cation exchange membrane (CEM) separates the adjacent cathode and acidifying compartments, and a membrane electrode assembly (MEA) separates the adjacent acidifying and anode compartments (Figure 12b).…”

“…Kuntke and co-workers proposed a novel DAC process which combines CO 2 adsorption with aminefunctionalized anion exchange resins (AERs) and CO 2 desorption with an electrochemical cell (Figure 12a). [192] Within the electrochemical cell, a cation exchange membrane (CEM) separates the adjacent cathode and acidifying compartments, and a membrane electrode assembly (MEA) separates the adjacent acidifying and anode compartments (Figure 12b). During sorption, air flows into the AERs containing OH À sites, which react with CO 2 to generate HCO 3 À in the resin (Section 3.2).…”

“…While electro-swing CO 2 capture processes benefit from lower regeneration costs compared to traditional temperatureand pressure-swing processes, they suffer from several nonnegligible drawbacks, including: oxidative degradation of the electrogenerated nucleophiles; [180,193] dissolution of electroactive polymers into the electrolyte, which reduces cycling performance; [184,191] slow sorption kinetics; and moderate CO 2 capacities. [191,192] Further development in this area will help answer fundamental questions about the relationships between nucleophile structure, oxygen stability, and CO 2 capture performance, guiding the design of more well-defined materials for electro-swing CO 2 capture under realistic conditions. [193]…”

“…(b) Schematic of the experimental setup highlighting the different compartments within the electrochemical cell. Reproduced with permission from ref[192]. Copyright 2022 American Chemical Society.…”