Recent Progress in Amino Acid Ionic Liquid-Based Facilitated Transport Membranes for CO2 Separation

Concerns on CO₂ emissions from coal-fired power plants are rapidly increasing because of their major contribution to global warming and climate change. Hence, the development of an economically viable CO₂ capture technology is inevitable. Recently, ionic liquids (ILs) have been proposed as attractive media for CO₂ separation membranes owing to their distinct properties such as high CO₂ absorption capacity, negligible vapor pressure, huge chemical diversity, and high thermal stability. Recently, we proposed a new class of IL-based CO₂ separation membrane containing amino acid ILs (AAILs) as the CO₂ carrier. The AAIL-based CO₂ separation membranes demonstrated remarkably fast and selective CO₂ permeation based on a facilitated transport mechanism. Furthermore, in our research group, gel membranes containing 80 wt% of AAIL was successfully fabricated. Our fabricated AAIL-based gel membrane had quite high mechanical strength which gave not only pressure resistance to the gel membrane containing a large amount of AAIL but also possibility to fabricate a thin membrane with high CO₂ permeance. The tough AAIL-based gel membranes had specific gel network, termed double-network (DN), which was consisted of two asymmetric polymer networks: the first is a rigid, brittle, and tightly cross-linked polyelectrolyte and the second is a soft, ductile, and loosely cross-linked polymer. The thin AAIL-based DN gel membrane with about 1 x 10^-5 m of its thickness marked ca. 500 GPU of CO₂ permeance and ca. 70 of CO₂/N₂ permselectivity for CO₂/N₂ gas mixture with 10 kPa of CO₂ partial pressure at 353 K under humid condition. The CO₂ permeance of the AAIL-based DN gel membrane was almost identical to that of the AAIL-based supported IL membrane owing to the low diffusion resistance of the double-network.