Gas Permeability and Permselectivity in Polyimide Films

Abstract

Gas permeability and permselectivity of commercially available polyimides were investigated at 35°C and 100°C and compared with those of other glassy polymers. The polyimide perpared from 3,3′, 4,4′-benzophenonetetracarboxylic dianhydride (BTDA) and two different diamines, 4,4/-methylenedianiline (MDA) and 2,6-diaminotoluene (BTDA-M/ T, commercially available as PI-2080), and the polyimide from 2,3,5-tricarboxycyclopentyl acetic acid dianhydride (TCDA) and 4,4′-oxydianiline (ODA) had excellent permeability and permselectivity for H2/CO and H2/CH4 systems (PH2= 1X 10-9cm3(STP) cm-1 s-1cmHg-1, PH2Pco= 100, PH2/PCH4500 at 35°C). The polyimide prepared from BTDA and 3,3′-diaminobenzophenone (commercially available as LARC-TPI) had lower permeability and much higher permselectivity (PH2=2X 10-10cm3(STP) cm-1 s-1 cmHg-1, PH2/PCO)=350, PH2/PCH4= at 35°C). Three polyimides containing two ether linkages in the diamine moiety had poor permeability and permselectivity as compared with the above-mentioned polyimides. These results were discussed in terms of packing density and local mobility. All polyimides investigated were not attractive as membane materials for CO2/CH4 separation because of low permeability for CO2. In a BTDA-M/T film, 2% residual dimethylacetamide solvent caused about 30% reductions in permselectivities for H2/CO and H2/CH4 without an appreciable increase in PH2 as a result of the plasticization effect. © 1990, The Society of Polymer Science, Japan. All rights reserved.