The delivery of high-quality natural gas to consumers requires that the acid gas impurities CO2 and H2S be removed from raw gas in order meet pipeline specifications and to prevent corrosion in transportation lines. Traditionally, amine processes have been used for these separations; however, polymeric membranes have proven an effective, economical alternative under certain conditions. The glassy polyimide 6FDA-DAM:DABA (3:2) and its cross-linkable counterpart, propane-diol monoesterified cross-linkable polyimide (PDMC), have been shown to have promising CO2/CH4 separation capabilities, with PDMC having a mixed gas selectivity of -45 and CO2 permeability above 130 Barrer for 200 psi 20:80 CO2:CH4 feed. These values actually place this polymer above Robeson's processable polymer upper limit for CO2/CH4 gas separations.
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