Improvements in the CO2 permeation selectivities of amino acid ionic liquid-based facilitated transport membranes by controlling their gas absorption properties

Abstract A series of amino acid ionic liquids (AAILs) composed of different cations of different sizes, including trihexyl(tetradecyl)phosphonium glycinate, tetrabutylphosphonium glycinate and triethyl(pentyl)phosphonium glycinate have been synthesized for the carrier of CO 2 facilitated transport membrane. Their physical properties, including their viscosity, density, molar volume and N 2 absorption amount were investigated. The amount of N 2 absorption decreased as the size of the cation of the AAIL decreased. Facilitated transport membranes containing these AAILs were prepared, and their CO 2 and N 2 permeabilities were measured. The N 2 permeabilities were systematically investigated both experimentally and theoretically with the aim of improving the selectivity of the CO 2 permeation of the AAIL-based facilitated transport membrane. As expected, the CO 2 permselectivity was improved using triethyl(pentyl)phosphonium glycinate, which contained the smallest cation of the AAILs investigated in this study. We have proposed a methodology for improving the CO 2 selectivity of AAIL-based facilitated transport membranes based on reducing their N 2 permeabilities.