Supported Absorption of CO2 by Tetrabutylphosphonium Amino Acid Ionic Liquids

A new type of “task specific ionic liquid”, tetrabutylphosphonium amino acid [P(C4)4][AA], was synthesized by the reaction of tetrabutylphosphonium hydroxide [P(C4)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(C4)4][AA] supported on porous silica gel effected fast and reversible CO2 absorption when compared with bubbling CO2 into the bulk of the ionic liquid. No changes in absorption capacity and kinetics were found after four cycles of absorption/desorption. The CO2 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 CO2. The CO2 absorption mechanisms of the ionic liquids with and without water were different. Task‐specific ionic liquids: Phosphonium amino acid ionic liquids supported on porous silica gel absorb CO2 rapidly with 50 mol % capacity (see figure; □ (blue)=[P(C4)4][Gly]‐SiO2, ○ (green)=[P(C4)4][Ala]‐SiO2, and ▴ (red)=[P(C4)4][β‐Ala]‐SiO2). The absorption is reversible. There are no changes in CO2 absorption capacity and kinetics after four cycles of absorption/desorption.