Supported Absorption of CO 2 by Tetrabutylphosphonium Amino Acid Ionic Liquids

A new type of “task specific ionic liquid”, tetrabutylphosphonium amino acid [P(C 4 ) 4 ][AA], was synthesized by the reaction of tetrabutylphosphonium hydroxide [P(C 4 ) 4 ][OH] with amino acids, including glycine, L ‐alanine, L ‐β‐alanine, L ‐serine, and L ‐lysine. The liquids produced were characterized by NMR, IR spectroscopies, and elemental analysis, and their thermal decomposition temperature, glass transition temperature, electrical conductivity, density, and viscosity were recorded in detail. The [P(C 4 ) 4 ][AA] supported on porous silica gel effected fast and reversible CO 2 absorption when compared with bubbling CO 2 into the bulk of the ionic liquid. No changes in absorption capacity and kinetics were found after four cycles of absorption/desorption. The CO 2 absorption capacity at equilibrium was 50 mol % of the ionic liquids. In the presence of water (1 wt %), the ionic liquids could absorb equimolar amounts of CO 2 . The CO 2 absorption mechanisms of the ionic liquids with and without water were different.