Permeation and separation of SO2, H2S and CO2 through thermally rearranged (TR) polymeric membranes

Abstract The permeabilities of sulfur dioxide and hydrogen sulfide are reported here for two copolymer based TR membranes, as a function of feed partial pressure and temperature. The two TR membranes are formed from the precursor co-polyimide 4,4′-(hexafluoroisopropylidene) diphthalic anhydride (6FDA), 3,3′-dihydroxyl-4,4′-diaminobiphenyl (HAB) and 2,4,6-trimethyl-m-phylenediamine (DAM) (6FDA-HAB-DAM), where one of the membranes undergoes crosslinking with 3,5-diaminobenzoic acid (DABA) during TR. It was observed that SO 2 permeability decreased with increasing partial pressure and temperature in both TR membranes. This is indicative that SO 2 permeability is dominated by SO 2 solubility within the TR membranes, and is attributed to the high condensability of SO 2 . Both polymeric membranes displayed selectivity for SO 2 against CO 2 , with separation performance similar to other classes of polymeric membranes. H 2 S permeability was observed to decrease with increasing partial pressure and temperature for the cross-linked TR (XTR) membrane. The non-cross-linked TR membrane displayed constant H 2 S permeability with pressure and permeability increased with increasing temperature. Hence, permeability within the XTR membrane was H 2 S solubility dominated, while in the non-crosslinked TR membrane permeability was H 2 S diffusivity dominated. This was attributed to the difference in free volume and cavity size distribution in the TR membrane as a result of crosslinking. It was observed that both membranes displayed H 2 S/CO 2 selectivity of less than one, indicative that they favor CO 2 over H 2 S.