Effect of the amide bond diamine structure on the CO _2, H _2S, and CH _4 transport properties of a series of novel 6FDA-based polyamide-imides for natural gas purification

摘要

A series of higher permeability polyamide-imides based on 2,2′-bis(3,4-dicarboxyphenyl) hexafluoropropane dianhydride with comparable plasticization resistance to Torlon were synthesized and formed into dense film membranes. Polymers possessing 2,4-diamino mesitylene (DAM) were stable up to 56 atm of pure CO _2, which is due to enhanced charge transfer complex formation compared to polymers containing 4,4′- (hexafluoroisopropylidene) dianiline (6FpDA) and 2,3,5,6-tetramethyl-1,4- phenylenediamine (TmPDA). The new polymers containing DAM and TmPDA showed ideal CO _2/CH _4 selectivities of near 50 with CO _2 and H _2S permeabilities over an order of magnitude higher than Torlon. CO _2 and CH _4 sorption in the DAM- and TmPDA-based materials was reduced, whereas H _2S sorption was enhanced relative to membranes containing fluorinated 6FpDA. Consequently, DAM- and TmPDA-based membranes showed increased stability toward high pressure CO _2 but lower plasticization resistance toward pure H _2S. These results highlight the differences between CO _2 and H _2S that challenge the rational design of materials targeting simultaneous separation of both contaminants.