CO2 absorption studies in amino acid-anion based ionic liquids

Several amino acid anion (aminate) based ionic liquids (ILs) were synthesized, characterized and tested for CO2 absorption capacity. Butylmethyl imidazolium ([bmim]+) was chosen as the cation for all the ILs studied. Among all the aminate-ILs studied, arginate anion ([ARG]) IL has shown more CO2 absorption capacity followed by lysinate ([LYS]) and histidinate ([HIS]) in terms of mol CO2/mol IL. The high CO2 absorption capacity of [ARG] anion was attributed to the availability of more accessible amine (N) groups. The CO2 molar uptake in aminate-ILs studied is in the order of [ARG] (4N) > [LYS] (2N) > [HIS] (3N) > [MET] (1N) > [LEU] (1N) > [GLY] (1N) > [VAL] (1N) > [ALA] (1N) > [PRO] (1N). The FTIR of the CO2 absorbed aminate-ILs confirms the chemical absorption of CO2 through the formation of carbamate species. The aminate-ILs showed higher CO2 solubility compared to amine functionalized cation ILs and non-functionalized ILs. On mass basis (g CO2/kg IL), aminate-ILs showed 70% more CO2 absorption capacity than primary amine-cation ILs, 150% more than tertiary amine-cation ILs and 600% more than non-functionalized ILs.