Roles of Cation and Anion of Amino Acid Anion-Functionalized Ionic Liquids Immobilized into a Porous Support for CO2 Capture

The impact of cation and anion of amino acid (AA) anion-functionalized ionic liquids (ILs) immobilized into a porous support on the CO2 capture performance was investigated in dry or humidified gas flow conditions. 1-Ethyl-3-methylimidazolium ([EMIM]) cation and tetrabutylphosphonium ([P-4444]) cation were used as a cations for synthesizing AAILs and compared, since they have different molecular structures and hydrophilicities from each other, affecting gas sorption behaviors. The experimental results showed that supported [P-4444][AAs] had higher CO2 capture capacities than the corresponding supported [EMIM][AAs] in units of mol/mol-AAIL under dry gas inlet, exhibiting the effect of cation on the CO2 adsorption performance. Under humidified gas flow, supported [P-4444][AAs] adsorbed much lower amounts of water vapor than supported [EMIM][AAs]. On the other hand, CO2 capture capacities of both supported [EMIM][AAs] and [P-4444][AAs] were slightly reduced in the presence of water vapor, due to much more rapid sorption of H2O than CO2.