CO2 absorption in amino acid-based ionic liquids: Experimental and theoretical studies

Abstract

In this study, eight amino acid-based ionic liquids (AAILs) with 1-butyl-4-methyl pyridinium cation ([B4MPyr][AA]s) were synthesized and characterized. The CO2 absorption capacity of AAILs was studied using quartz crystal microbalance (QCM) at pressures up to 6 bars and at temperature 298.15 K. Based on the “deactivated model”, the reaction equilibrium constant and Henry's law constant were calculated to evaluate the efficiency of AAILs for CO2 absorption. The results indicate that CO2 absorption capacities are in the order of [Arg] > [Lys] > [His] > [Tyr] > [Gly] > [Val] > [Ala] > [Pro]. The accessibility of more available amine groups in AAIL with arginate anion is the main factor for the high CO2 absorption capacity. Also, the chemical absorption of CO2 through carbamate formation was corroborated by spectroscopy of FT-IR. Beside, the density functional theory (DFT) method was also employed to confirm the adsorption energy of CO2 onto AAILs with various anions.