Effect of the Amide Bond Diamine Structure on the CO2, H2S, and CH4 Transport Properties of a Series of Novel 6FDA-Based Polyamide–Imides for Natural Gas Purification

Abstract

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 CO2, 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 CO2/CH4 selectivities of near 50 with CO2 and H2S permeabilities over an order of magnitude higher than Torlon. CO2 and CH4 sorption in the DAM- and TmPDA-based materials was reduced, whereas H2S sorption was enhanced relative to membranes containing fluorinated 6FpDA. Consequently, DAM- and TmPDA-based membranes showed increased stability toward high pressure CO2 but lower plasticization resistance toward pure H2S. These results highlight the difference...