Cross-Linked and Thermally Rearranged Poly (Benzoxazole-Co-Imide) Hollow Fiber Membranes Derived from Phenolphthalein-Based Copolyimide for Co2/Ch4 Separation

Abstract

Hollow fiber membrane precursors were prepared using a copolyimide 6FDA-DAP:DAM (1:2) containing a lactone ring structure as the raw material via dry-jet wet spinning method. To enhance the anti-plasticization ability of the hollow fiber membranes and address the issue of sublayer collapsing during the thermal rearrangement process, sub-Tg cross-linking was first performed at 350 ℃. Subsequently, the cross-linked thermal rearrangement (XTR) hollow fiber membranes were fabricated at temperatures ranging from 425 to 475 ℃. The occurrence of the TR reaction and the formation of the polybenzoxazole structure were confirmed using Thermogravimetric analysis (TGA), Fourier Transform Infrared spectroscopy (FT-IR), and X-ray Photoelectron Spectroscopy (XPS). The effects of different thermal treatment parameters on the gas separation performance and morphology of the XTR hollow fiber membranes were investigated. The results showed that Sub-Tg cross-linking effectively mitigated the collapse of the sub-layer structure. When the thermal treatment temperature was 475 ℃, the XTR hollow fiber membranes fabricated from the optimized membrane precursors exhibited a CO2 permeance of 436.22 GPU with a CO2/CH4 selectivity of 30.63. When used high pressure CO2, CO2/CH4, and CO2/CH4/N2/ethane/benzene mixed gases, no significant signs of plasticization were observed in the XTR hollow fiber membranes.

Keywords: Sub-Tg cross-linking, Thermal rearrangement, Hollow fiber membrane, Natural gas purification, Anti-CO2 plasticization