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 <F>RC3H6</F> 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 <F>RC3H6=26</F> GPU and <F>αC3H6/C3H8=22</F> for mixed-component (50/50%) at 373 K and 1 atm. The effect of silicone rubber coating was also investigated. [Copyright &y& Elsevier]