Experimental and molecular dynamics simulation study on CO₂ capture by amine-based ionic liquids with varied cation structures

Most of the reported amine-based ionic liquids are aprotic （with complex preparation processes） and future straight side chain structures. which They generally suffer from poor low-temperature fluidity and high viscosity, which adversely affect CO₂ adsorption. Molecular dynamic （MD） simulation and absorption experiment were performed to investigate CO₂ capture using protic ionic liquids （PILs） composed of bis（trifluoromethylsulfonyl）imide （TFSA^─） anion paired with three cations n-hexylammonium （HHexam^＋）, 2-ethylhexylammonium （HEtHexam^＋）, and 2-ethylhexylethylenediaminium （HEtHexen^＋）. These three types of PILs can be prepared via a one-step acid-base neutralization reaction, featuring a simple synthesis process. Additionally, HEtHexenTFSA contain chelating amine groups, which further facilitate the absorption of acidic gases such as CO₂. The results demonstrate that introducing ethyl group into the cation side chains and increasing the number of amine groups significantly enhance CO₂ absorption efficiency. Among these PILs, HEtHexenTFSA exhibited the highest CO₂ absorption capacity, it reaching 0.85 mol CO₂ per mol PIL at 25 ℃ and 1 atm, greater than monoamine-type HEtHexamTFSA （0.68） and HHexamTFSA （0.17）. Analysis of radial distribution function, mean squared displacement, and interaction energy confirmed the superior performance of HEtHexenTFSA across different temperatures. This study achieves efficient CO₂ capture through the synergistic regulation of cationic branches and the number of amine groups, which can provide novel absorbents and theoretical support for the efficient and low-energy-consumption treatment of industrial carbon-containing flue gas.