High temperature hydrogen separation performances of thermally rearranged polybenzoxazole membranes from polyhydroxyamide

Abstract

Thermally rearranged polybenzoxazole (TR-PBO) membrane prepared from various polyhydroxyamide (PHA) precursors, where the high molecular weight of PHA can be achieved via silylation. The aromatic PHAs can be rearranged by thermal conversion at 350℃ which is lower than the original route usually required for TR-PBO from hydroxylpolyimide (HPI) at higher thermal treatment temperature (~450℃). PHA route to TR-PBO requires dehydratioin instead of decarboxylation for HPI route. Three representative aromatic PHA were synthesized by reacting dihydroxydiamine with three diacid chloride. Structural analysis of monomers and polymers were, carried out by analyzing characteristic band by IR. The Thermogravimetric analysis (TGA) data showed that their H2O is evolved at around 330oC as evidenced by mass spectrometer gravemetric to TGA. H2/CO2 separation performance of TR-PBO was conducted and noticed that they exhibited superior performance at high temperature due to the rigid polymer structure and CO2 diffusion coefficient as temperature increased. The polymer membrane with large group (CF3)2 showed the highest gas permeability but low selectivity, while the meta structure polymer was the highest gas selectivity but the lowest selectivity. These results exhibited that gas permeation properties of the TR-PBO was discussed in detail depended on polymer structure.