Modification of polyimide membranes for gas separation

Abstract

Polyimides have become of interest in recent years as membrane materials for gas separation processes, due to their good separation performance and applicability in harsh environments, such as high temperature or strong acidic conditions. However, the development of new polyimides seems to be approaching a limit demonstrated by the trade-off curve for gas permeability and selectivity. The aim of this study was to investigate two different modification methods for polyimide membranes to improve their separation performance and operation durability. In the first method, polyimide membranes were surface cross-linked by PAMAM, a star-like chemical with multi functional groups. The properties of modified membranes were found to be related to modification time, the generation of PAMAM, and post-treatment temperature. In the second modification method, polyimide membranes were put into a vacuum oven and pyrolyzed at high temperatures. The relationship between chemical structures of polyimides and derived carbon membranes was investigated. The results of this study suggest that cross-linking modification and carbonization are two effective methods for improving the gas separation performance of polyimide membranes.