Recent Developments in Gas Separations by Facilitated Transport Membranes with High Selectivity

Recent developments in the facilitated transport membranes (FTMs) for gas separations with high selectivity are described focusing on CO2/N2, 02/N2 and olefin/paraffin separations. There are two types of FTM, i.e., mobile carrier membrane and fixed carrier membrane. For both types of membrane, the rate and equilibrium of the reaction between the carrier and the penetrant gas have decisive effects on the membrane performance. With respect to fixed carrier membranes for O2/N2 separation, a composite membrane with a very thin active layer of Co (II) -porphyrin complex of about 80nm thickness on a porous support exhibits promising O2 permeance and selectivity. Very efficient solid polymer electrolyte membranes containing silver salts have been developed for olefin/paraffin separations, and the threshold carrier concentration behavior has been elucidated from the coordination behavior of silver ion in the membrane. Finally, a novel type of “facilitated transport membrane” accompanied by permeation of a carrier solution, which overcomes the drawback of liquid membranes such as instability and low permeability, is shown to be very effective for CO2/N2 and C2H4/C2H6 separations.