Reversible CO ₂ capture in halogen‐free deep eutectic solvents: Performance and mechanism

Abstract

This work constructs a halogen‐free reversible deep eutectic solvent (DES) system to achieve efficient and recyclable CO ₂ absorption. The CO ₂ capture performance of binary DESs derived from tertiary alkanolamines—specifically triethanolamine and methyldiethanolamine (MDEA)—and alkyl‐substituted imidazoles, including 4‐methylimidazole (4MIM), 2‐ethyl‐4‐methylimidazole (2E4MIM), and 2,4‐dimethylimidazole (2,4‐DMIM) was systematically examined. 2E4MIM:MDEA (1:2) showed the best CO ₂ absorption among the tested DESs. The absorption mechanism was jointly explored via spectral characterization and quantum chemical calculations. Two plausible proton transfer reaction pathways were identified. Furthermore, cyclic tests show good reversibility for 2E4MIM‐based DESs. Upon the addition of water, 2E4MIM and 2,4‐DMIM‐based DESs undergo a solid‐state transition driven by bicarbonate formation following CO ₂ absorption. In contrast, the 4MIM:MDEA (1:2) system remains liquid, with its CO ₂ absorption capacity increasing from 0.101 to 0.183 g‐CO ₂ /g‐DES as the water content rises from 0 to 20 wt%. This work offers mechanistic insights and viable strategies to advance non‐corrosive, reversible CO ₂ capture technologies for industrial deployment.