Cross-Linkable Polyimide Membranes for Improved Plasticization Resistance and Permselectivity in Sour Gas Separations

A series of cross-linkable membrane materials based on the 6FDA-DAM:DABA (3:2) polyimide backbone were synthesized for improved sour gas separation performance, in terms of both membrane stability and permselectivity. Short-chain poly(ethylene glycol) (PEG) molecules were used as cross-linking agents in an esterification-based cross-linking reaction. Pure and mixed gas permeation and pure gas sorption experiments were performed on dense films of these materials. Compared to unmodified 6FDA-DAM:DABA (3:2), higher sour gas permselectivity and membrane stability were achieved under aggressive feed conditions. H 2 S-induced plasticization was not evident until pure H 2 S feed pressures greater than approximately 6–8 bar. Pure CO 2 -induced plasticization only occurred at feed pressures greater than about 25 bar. Under mixed gas feed conditions with 20% H 2 S, 20% CO 2, and 60% CH 4 at 35 °C, attractive selectivities above 22 and 27 for H 2 S/CH 4 and CO 2 /CH 4, respectively, were observed for a feed pressure of 62 bar with both triethylene glycol and tetraethylene glycol cross-linking agents.