Cross-linked PI membranes with simultaneously improved CO2 permeability and plasticization resistance via tunning polymer precursor orientation degree

Abstract

Polyimides (PIs) have gained recognition as highly desirable membrane materials for efficient CO2/CH4 separation. However, the practical utilization of these materials has been impeded by the issue of the substantial susceptibility to plasticization when exposed to high-feed-pressure conditions. Although thermal cross-linking has been widely employed to enhance plasticization resistance in PI membranes, cross-linking will normally sacrifice CO2 permeability. Thus, the advancement of PI membranes that exhibit both remarkable CO2 permeability and exceptional plasticization resistance is highly desired. The current work designed a series of cross-linkable PIs with different polymer chain orientation degrees. Different from conventional PIs, by properly controlling the polymer chain orientation, the CO2 permeability can be enhanced by 2.3 times without compromising the membrane plasticization resistance. Various techniques, including FTIR, WAXD, TGA, and DMA, were employed to thoroughly characterize the obtained membranes. These characterizations verified that optimizing the polymer chain orientation constitutes an efficacious strategy to enhance the resistance of PI membranes against plasticization, while simultaneously preserving their CO2 permeability. Additionally, the thermally cross-linked membranes exhibited good long-term stability during an 1100-h test.