Polyimide-based membrane materials for CO2 removal from flue gases

This work reports the gas separation properties of polyimides (PIs) with different chemical structures, designed for the removal of carbon dioxide from flue gases. To study the effect of a backbone structure on gas permeability and selectivity, three different methods of chemical modification of the poly (hydroxyimide) (PIOH) were applied. The introduction of bulky pendant groups in a PI chain was accomplished by Mitsunobu reaction; conversion of PIOH to polybenzoxazole rigid structure (PITR) was performed by thermal cyclization in an inert atmosphere, whereas incorporation of CO2-philic polyoxyethylene (PEO) segments into main chain was carried out at the polycondensation stage by using a mixture of aromatic and PEO-based diamines. The modified polymers were characterized by nuclear magnetic resonance (1H NMR) and fourier transform infrared (FTIR) spectroscopies, and thermo gravimetric analysis (TGA), differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD) techniques. It was found that the performed modifications resulted in membrane materials with significantly improved gas permeability and either maintained or even improved CO2/N-2 selectivity.