Electrochemical Regeneration of Spent Alkaline Absorbent from Direct Air Capture

Abstract

CO 2 capture from the atmosphere (or direct air capture) is widely recognized as a promising solution to reach negative emissions, and technologies using alkaline solutions as absorbent have already been demonstrated on a full scale. In the conventional temperature swing process, the subsequent regeneration of the alkaline solution is highly energy-demanding. In this study, we experimentally demonstrate simultaneous solvent regeneration and CO 2 desorption in a continuous system using a H 2 -recycling electrochemical cell. A pH gradient is created in the electrochemical cell so that CO 2 is desorbed at a low pH, while an alkaline capture solution (NaOH) is regenerated at high pH. By testing the cell under different working conditions, we experimentally achieved CO 2 desorption with an energy consumption of 374 kJ·mol –1 CO 2 and a CO 2 purity higher than 95%. Moreover, our theoretical calculations show that a minimum energy consumption of 164 kJ·mol –1 CO 2 could be achieved. Overall, the H 2 -recycling electrochemical cell allowed us to accomplish the simultaneous desorption of high-purity CO 2 stream and regeneration of up to 59% of the CO 2 capture capacity of the absorbent. These results are promising toward the upscaling of an energy-effective process for direct air capture.

Low energy carbon capture via electrochemically induced pH swing with electrochemical rebalancing

“…CO 2 separation work with “th” subscript denotes thermal energy inputs, whereas “e” subscript denotes electrical work input. Method Purpose CO 2 separation work inputs (kJ mol CO2 −1 ) Current density (mA cm −2 ) Alkaline solvent 2 , 9 DAC 264–396 th a N/A Solid amine sorbents 2 DAC 150–211 th b N/A Amino acid solvents and solid bis-iminoguanidines 10 DAC 152–422 th c N/A Fuel cell concentrator 17 DAC 350 e d 0.5 Electrochemical alkaline sorbent regeneration 31 DAC 374 e f 0.5 Processing seawater within a BPMED reactor 13 DOC 155 e g 3.3 Titrating seawater with BPMED acid/base 12 DOC 394 e h 100 Traditional amine ab-/desorption 4 Point source capture 132–150 th N/A Amine ad-/desorption with advanced flash stripper 32 Point source capture 92 th i N/A Shell Cansolv 6 Point source capture 103 th N/A Petra Nova 33 Point source capture 89 th j N/A Quinone Direct binding 7 Point source capture 56 e k 0.5 …”

Direct Air Capture Using Electrochemically Regenerated Anion Exchange Resins

“…Moreover, a small amount of CO 2 could leak from the electrochemical system during desorption as already observed in our previous work. 26 Despite the leakage of CO 2 , the resins could be sufficiently regenerated during the desorption steps as a consistent amount of adsorption was observed during consecutive adsorption steps.…”

“…The design and materials of the electrochemical cell have been described in detail in our previous work. 26 The anode is a membrane electrode assembly (MEA) (FuelCellsEtc, TX) that comprises a platinum-coated (0.5 mg Pt·cm –1 ) gas diffusion layer (GDL) (10 cm × 10 cm) and a Nafion N117 cation exchange membrane (CEM) (15 cm × 15 cm). During operation, H 2 gas flows into the anode compartment, where it is oxidized to H + on the surface of the GDL.…”

“…Recently, we developed an electrochemical system that can regenerate spent alkaline absorbents from DAC and desorb high-purity CO 2 gas under atmospheric pressure. 26 The electrochemical system uses a pH swing to regenerate the solution in two adjacent compartments separated by a cation exchange membrane (CEM). At low pH, the CO 2 equilibria displace toward the formation of carbonic acid (H 2 CO 3 *) due to the H + production at the anode.…”

Limits to Paris compatibility of CO2 capture and utilization

“…45 The two main categories of DAC methods are based on (1) amine-functionalized solid sorbents, which require regeneration at low temperatures or via moisturizing, 46 and (2) alkaline hydroxide capture solutions, which require high-temperature solvent regeneration. 47 Less energy-intensive regeneration processes are under development, including electrochemical regeneration 48 and bipolar membrane electrodialysis. 49 Utilization of CO 2 Direct uses of CO 2 CO 2 can be used directly, without conversion, in several sectors.…”