Effect of Ionic Liquid Additives on CO2Permeation and CO2/N2Selectivity through Facilitated Transport Membranes

To improve the CO2 permeability of facilitated transport membranes, we investigated the effect of ionic liquid additives into the membrane. In this study, glycine was used as a CO2 carrier and polyvinyl alcohol as a gel matrix to contain the CO2 carrier and additives. To investigate the effect of the water vapor absorbability of the gel membrane on the CO2 permeability, ionic liquids with various degrees of hydrophilicity were examined as additives. When the highly hydrophilic ionic liquids were added to the membrane, a large amount of water was absorbed in the membrane under humid conditions. With the aid of water, glycine dissolved in a fully water stained gel membrane could react with CO2 under humid conditions and elevated temperatures from 110 to 130℃. Because of the high liquidity of the ionic liquid within a wide temperature range, the formed CO2 complex could easily diffuse into the membrane from the feed side to the permeate side. Thus, CO2 permeability and CO2/N2 selectivity were highly improved; e.g.,at 110℃, the CO2 permeance was increased from 3.6×10–6 to 6.4×10–5 mol/(m2skPa) and CO2/N2 selectivity from 17.3 to 192 (–). Moreover, the non–volatility and thermal stability of an ionic liquid enabled improved CO2 permeation for extended periods under elevated temperature conditions. Therefore, the addition of ionic liquid was useful to enhance the gas permeation properties whilst maintaining high stability.