High-temperature hydrogen/propane separations in asymmetric carbon molecular sieve hollow fiber membranes

Catalytic propane dehydrogenation membrane reactors require membranes with highly attractive high-temperature H2/C3H8 separation performance. In this work, we show that polyimide-derived asymmetric carbon molecular sieve (CMS) hollow fiber membranes with thin (∼5 μm) separation layers can provide outstanding high-temperature (up to 600 °C) H2/C3H8 separation factors 2–100 folds higher than microporous oxide membranes. The effects of CMS membrane pyrolysis condition, permeation temperature, and feed composition on high-temperature H2/C3H8 separation performance were systematically investigated. CMS hollow fiber membranes pyrolyzed at 675 °C showed stable H2 permeance of 430 GPU and H2/C3H8 separation factor of 511 at 600 °C using a 50%/50% H2/C3H8 feed mixture under a continuous permeation test of ∼130 h. It was found that CMS membrane pore structure and separation performance may be modulated by hydrogenation and coke deposition by the H2/C3H8 mixture under high-temperature permeation. A trade-off between these two potential reactions is achieved by controlling H2/C3H8 compositions, leading to stable CMS under high-temperature conditions. The results suggest that asymmetric CMS hollow fiber membranes are potentially attractive for catalytic propane dehydrogenation membrane reactors under controlled high-temperature reaction conditions.