Spirobisindane-based polyimide as efficient precursor of thermally-rearranged and carbon molecular sieve membranes for enhanced propylene/propane separation

Swaidan, Ramy J.; Ma, Xiaohua; Pinnau, I.

Spirobisindane-based polyimide as efficient precursor of thermally-rearranged and carbon molecular sieve membranes for enhanced propylene/propane separation

2016

Swaidan, Ramy J. | Ma, Xiaohua | Pinnau, I. (Ingo)

High performance thermally-rearranged (TR) and carbon molecular sieve (CMS) membranes made from an intrinsically microporous polymer precursor PIM-6FDA-OH are reported for the separation of propylene from propane. Thermal rearrangement of PIM-6FDA-OH to the corresponding polybenzoxazole (PBO) membrane resulted in a pure-gas C3H6/C3H8 selectivity of 15 and C3H6 permeability of 14 Barrer, positioning it above the polymeric C3H6/C3H8 upper bound. For the first time, the C3H6/C3H8 mixed-gas properties of a TR polymer were investigated and showed a C3H6 permeability of 11 Barrer and C3H6/C3H8 selectivity of ~11, essentially independent of feed pressure up to 5bar. The CMS membrane made by treatment at 600°C showed further improvement in performance as demonstrated with a pure-gas C3H6/C3H8 selectivity of 33 and a C3H6 permeability of 45 Barrer. The mixed-gas C3H6/C3H8 selectivity dropped from 24 to 17 from 2 to 5bar feed pressure due to a decrease in C3H6 permeability most likely caused by competitive sorption without any evidence of plasticization.

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