Comparative analysis of CO2 absorption in amino acid ionic liquids with Varying N–H group structures

Amino acid ionic liquids (AAILs) are potential green substitutes of aqueous amine solutions for carbon dioxide (CO 2 ) capture. In this study, we prepared three amino acid ionic liquids, constructed from tetrabutylphosphine hydroxide in combination with glycine, histidine, and arginine. We have conducted a comprehensive study on the CO 2 absorption capacity of structures containing single, double, and triple N–H groups. The solubility of CO 2 in [P 4444 ][Gly], [P 4444 ][His] and [P 4444 ][Arg] were measured experimentally over a temperature range of 30–110 °C and up to a pressure of 0.75 MPa. The results indicate that the solubility of carbon dioxide in amino acid ionic liquids decreases with increasing temperature, while it increases with increasing pressure. The optimal CO 2 absorption conditions of three amino acid ionic liquids were determined to be 50 °C, 0.75 MPa. Moreover, CO 2 absorption capacity of three amino acid ionic liquids followed the order: [P 4444 ][Arg] > [P 4444 ][His] > [P 4444 ][Gly]. Studies on the recycling and regeneration of amino acid ionic liquids verified their reusability in the process and confirmed that the reaction between AAILs and CO 2 could be reversed at 140 °C. Finally, the recycle capacity and CO 2 removal efficiency of [P 4444 ][Gly], [P 4444 ][His] and [P 4444 ][Arg] were evaluated.