Enhanced propylene/propane separation by thermal annealing of an intrinsically microporous Hydroxyl-functionalized polyimide membrane

Effective separation of propylene/propane is vital to the chemical industry where C3H6 is used as feedstock for a variety of important chemicals. The purity requirements are currently met with cryogenic distillation, which is an extremely energy-intensive process. Hybrid arrangements incorporating highly selective membranes (α>20) have been proposed to “debottleneck” the process and potentially improve the economics. Selective and permeable membranes can be obtained by the design of polymers of intrinsic microporosity (PIMs). In this work, a 250 °C annealed polyimide (PIM-6FDA-OH) membrane produced among the highest reported pure-gas C3H6/C3H8 selectivity of 30 for a solution-processable polymer to date. The high selectivity resulted from enhanced diffusivity selectivity due to the formation of inter-chain charge-transfer-complexes. Although there were some inevitable losses in selectivity under 50:50 mixed-gas feed conditions due to competitive sorption, relatively high selectivities were preserved due to enhanced plasticization resistance.