Olefin/paraffin separation performance of carbonized membranes derived from an asymmetric hollow fiber membrane of 6FDA/BPDA–DDBT copolyimide

Carbonized membranes were prepared by pyrolyzing an asymmetric hollow fiber membrane of a copolyimide from equimolar portion of 2,2-bis(3,4-dicarboxyphenyl)hexafluoro-propane dianhydride (6FDA) and 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA) with 3,7-diamino-2,8(6)-dimethyldibenzothiophene sulfone (DDBT) at temperatures of 773–973 K under a nitrogen stream. The carbonized membranes had an asymmetric structure with a skin layer of around 200 nm in thickness and a much denser support layer compared with the precursor hollow fiber. The increase in permeance to propylene RC3H6 by the pyrolysis was up to 10 times. An appropriate holding time during the pyrolysis in a nitrogen stream tended to increase the olefin/paraffin selectivity. The membranes pyrolyzed at 813 K for 1 h displayed the best performance of RC3H6=26 GPU and αC3H6/C3H8=22 for mixed-component (50/50%) at 373 K and 1 atm. The effect of silicone rubber coating was also investigated.