Effect of water in ionic liquids on CO2 permeability in amino acid ionic liquid-based facilitated transport membranes

Abstract Amino acid ionic liquid-based facilitated transport membranes with tetrabutylphosphonium amino acid ionic liquids with glycine, alanine, proline and serine as the anion were prepared and their CO 2 permeation properties were evaluated from the physical and physicochemical properties of the amino acid ionic liquids. A tetrabutylphosphonium proline-based facilitated transport membrane showed an excellent CO 2 permeability of 14,000 Barrer, twice that of the others investigated, and a CO 2 /N 2 selectivity of 100 at 373 K under dry conditions. Thermogravimetric measurement showed that the tetrabutylphosphonium proline had a relatively high water-holding ability compared with the other amino acid ionic liquids investigated. The strong water holding ability of tetrabutylphosphonium proline realized the large absorption amount of CO 2 and established a large concentration gradient for the CO 2 -complex across the membrane. The large concentration gradient provided a large driving force for CO 2 -complex transport through the membrane and increased CO 2 permeability.