Structural Regulation of Ether/Amino Acid Ionic Liquid Biphasic Solvents for Highly Efficient CO2 Capture

Biphasic CO2 absorbents reduce regeneration energy by regenerating only the CO2-rich phase, but high viscosity and poorly controlled phase separation still limit their performance. To address these challenges, diethylenetriamine (DETA) was employed as the primary reactive absorbent, and the effects of the structures of glycol ethers and amino acid ionic liquids on the CO2 absorption performance of DEDM–DETA–water–AAIL (DDWA) biphasic solvents were systematically investigated. The results demonstrated that, compared with long-chain ethers, branched ethers, and hydroxyl-containing glycol ethers, the short-chain linear glycol ether (DEDM) more effectively promoted the enrichment of CO2 reaction products in the CO2-rich phase. Among the amino acid anions investigated, the serinate anion ([Ser]−), containing a short hydroxyl-functionalized side chain, outperformed glycinate and lysinate ([Lys]−) anions by enhancing CO2 absorption through the synergistic effects of amino reactive sites and hydrogen-bonding interactions while simultaneously reducing the viscosity of the CO2-rich phase. The optimized DDWA absorbent exhibited a CO2 dynamic uptake of 2.72 mol kg–1, representing a 12% increase over the ionic liquid-free system. In addition, the absorbent showed excellent cyclic stability, with a total regeneration energy consumption of only 1.78 GJ t–1 CO2. Spectroscopic analyses revealed that the absorption products derived from DETA and [Ser] were predominantly enriched in the lower phase, whereas DEDM remained the principal component of the upper phase. This strategy couples alcohol-ether induced phase separation with AAIL regulation, enabling synergistic optimization of absorption, phase separation, and regeneration.