Supported liquid membranes incorporating amino acid ionic liquids remarkably facilitate CO(2) permeation under dry and low humid conditions.

No abstract

Task-specific ionic liquid (IL)-based facilitated transport membranes were prepared with tetrabutylphosphonium amine-functionalized glycinate or 2-cyanopyrrolide ILs. CO 2 permeabilities and viscosity and CO 2 absorbance of ILs were evaluated. Viscosities of glycinate-or methylglycinate-containing ILs drastically increased with CO 2 absorption, probably from hydrogen bonding between their CO 2 complexes. The temperature dependence of the CO 2 permeability of the IL-based membranes was opposite to that of the viscosity of the corresponding ILs. The CO 2 permeability at low temperature under dry conditions was improved by using tetrabutylphosphonium 2-cyanopyrrolide, which barely forms hydrogen bonds among its CO 2 complexes. However, above 363 K, the tetrabutylphosphonium 2-cyanopyrrolide-based membrane had a lower CO 2 permeability than the tetrabutylphosphonium glycinate-based membrane because tetrabutylphosphonium 2-cyanopyrrolide absorbed less CO 2 . The major factors controlling CO 2 permeability of task-specific IL-based facilitated transport membranes appear to be the viscosity of the CO 2 complex (which is the most important factor) and the amount of CO 2 absorbed.

Novel ion-gel films containing an amino acid ionic liquid were fabricated by free radical polymerization of vinyl monomers. These high strength materials demonstrated superior CO2 permeability and separation performance.

Amino acid ionic liquids (AAILs) composed of different sizes and numbers of amino groups, including tetrabutylammonium glycinate, tetramethylammonium glycinate, and 1,1,1-trimethylhydrazinium glycinate, were synthesized as CO 2 carriers for facilitated transport membranes. The physical properties of the fabricated AAILs, such as density, viscosity, and N 2 and CO 2 absorption capacities, were measured, and the fractional free volume was calculated using molecular dynamics (MD) simulations. The results showed that the molar and fractional free volumes decreased with decreasing AAIL size, which caused increased CO 2 absorption and decreased N 2 absorption. In addition, the CO 2 absorption increased with higher numbers of amino groups in the AAILs. The gas permeation properties of facilitated transport membranes containing the synthesized AAILs were investigated. The small AAILs with two amino groups showed better CO 2 permeability and N 2 barrier properties under humid conditions. We propose that ionic liquids optimized as CO 2 carriers for facilitated transport membranes under humid conditions should have high amino-group density, which could be realized by decreasing the molecular size and introducing more amino groups in the molecule.