CO2 separation performances of composite membranes of 6FDA-based polyimides with a polar group

2,2-bis(3,4-Dicarboxyphenyl) hexafluoropropane dianhydride (6FDA)–based polyimides with a polar group of hydroxyl or carboxyl such as 6FDA–BAPAF, 6FDA–DAP, and 6FDA–DABA were synthesized by the thermal imidization method. The corresponding composite membranes were then prepared by the dip-coating technique using a poly (ether sulfone) (PES) membrane as a supporting layer. Some alcohols and glycol ethers were used as coating solvents during the membrane preparation. The solubility of the polyimides synthesized in this study in these solvents depended on the nature of polymers and solvents. CO2 permeances for these composite membranes were measured in comparison with those for other gases such as H2, O2, N2, and CH4. The membrane performances were affected considerably by the preparation conditions such as the kinds of diamine moiety, coating solvent, and coating polymer concentration. It was expected that these composite membranes could be applied usefully to the CO2 separation, considering the CO2 permeances in the range of 20–38 gas permeation unit (GPU) and the selectivities for CO2/N2 and CO2/CH4 equal to or even higher than those of other dense or asymmetric membranes of 6FDA-based polyimides reported in the literature.