Rational Design of Mixed Matrix Membranes Modulated by Trisilver Complex for Efficient Propylene/Propane Separation.

The application of membrane-based separation processes for propylene/propane (C 3 H 6 /C 3 H 8 ) is extremely promising and attractive as it is poised to reduce the high operation cost of the established low temperature distillation process, but major challenges remain in achieving high gas selectivity/permeability and long-term membrane stability. Herein, a C 3 H 6 facilitated transport membrane using trisilver pyrazolate (Ag 3 pz 3 ) as a carrier filler is reported, which is uniformly dispersed in a polymer of intrinsic microporosity (PIM-1) matrix at the molecular level (≈15 nm), verified by several analytical techniques, including 3D-reconstructed focused ion beam scanning electron microscropy (FIB-SEM) tomography. The π-acidic Ag 3 pz 3 combines preferentially with π-basic C 3 H 6 , which is confirmed by density functional theory calculations showing that the silver ions in Ag 3 pz 3 form a reversible π complex with C 3 H 6 , endowing the membranes with superior C 3 H 6 affinity. The resulting membranes exhibit superior stability, C 3 H 6 /C 3 H 8 selectivity as high as ≈200 and excellent C 3 H 6 permeability of 306 Barrer, surpassing the upper bound selectivity/permeability performance line of polymeric membranes. This work provides a conceptually new approach of using coordinatively unsaturated 0D complexes as fillers in mixed matrix membranes, which can accomplish olefin/alkane separation with high performance.