(417c) Direct Air Capture By Aqueous Amine Solvent and Electrochemical Reduction to Carbon Monoxide

The accumulation of greenhouse gases in atmosphere since 1800s has resulted in atmospheric CO₂ levels above 420 ppm. Global actions on transition to renewable energy and carbon capture from stationary carbon sources are deemed insufficient to prevent global climate change. Direct air capture (DAC) directly alleviates atmospheric CO₂ levels and should be the final solution to the global climate change. The most mature DAC technologies are temperature vacuum swing adsorption (TVSA) developed by Climeworks¹ and calcium looping developed by Carbon Engineering.² Both technologies generate pure CO₂ for the purpose of sequestration. On the other hand, carbon utilization to produce chemicals is in the limelight as it allows potential economic benefits in addition to the reduction of CO₂ emission. Combination of DAC and utilization (DACU) provide an alternative option as net-zero economics; however, high energy cost and economic burden still limits further commercialization and deployment of DACU process.

Herein, we propose a noble DACU process that combines amine scrubbing and electrochemical CO₂ reduction to CO. The main strategy is reactive carbon capture (RCC) which uses rich solvent as catholyte to generate CO.^3,4 CO₂ regeneration in TVSA/calcium looping and CO₂ recovery in the CO₂ utilization section can be avoided by RCC (Fig. 1a). When mixed with green hydrogen, syngas with an H₂:CO ratio of 2:1 can be supplied to produce methanol, ethylene, and other products. First, we tested amine scrubbing of air by aqueous amine solvent in a pilot column to examine performance of structed packing as a direct air contactor (Fig. 1b). Then, we tested the electrochemical CO₂ reduction of CO₂-rich solvent in a membrane electrode assembly using Ag-Ag/C cathode (Fig. 1c). Based on the experimental results and assumptions, techno-economic assessment and life cycle assessment is conducted. Other DACU routes are also evaluated to access the competitiveness of our process. The results show that DACU by RCC outperforms other routes in terms of energy consumption, cost, and indirect greenhouse gas emissions.

Figure 1. Direct air capture and utilization (DACU) by reactive carbon capture (RCC). (a) Comparison between RCC and other DACU routes to generate syngas. (b) Pilot test results of CO₂ capture using aqueous amine solvent. (c) Test results of electrochemical CO₂ reduction.

References

[1] Deutz and Bardow, Life-cycle assessment of an industrial direct air capture process based on temperature–vacuum swing adsorption, Nature Energy 6, 203-213, 2021.

[2] Keith et al., A process for capturing CO2 from the atmosphere, Joule 2, 1573-1594, 2018.

[3] Langie et al., Toward economical application of carbon capture and utilization technology with near-zero carbon emission, Nature Commun. 13:7482, 2022.

[4] Song et al., Integrated carbon capture and CO production from bicarbonates through bipolar membrane electrolysis, Energy Environ. Sci. 17, 3570, 2024.