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 ([P₄₄₄₄]) 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 [P₄₄₄₄]­[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 [P₄₄₄₄]­[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 [P₄₄₄₄]­[AAs] were slightly reduced in the presence of water vapor, due to much more rapid sorption of H₂O than CO₂.