(160a) Tuning Hybrid PIM-PI-OH/Z-MOF-Based Mixed-Matrix Membranes for Highly Efficient Propylene/Propane Separation
Energy-efficient separation of propylene (C3H6) from propane (C3H8) is vital to the chemical process industry where C3H6 is used as feedstock for the production of a variety of important chemicals and plastics. A potentially significant marketplace exists for membrane technology in this separation if it can demonstrate the necessary performance. Currently, the required C3H6 purity is achieved by extremely energy-intensive cryogenic distillation. Recently, we reported the use of hydroxyl-functionalized polyimides of intrinsic microporosity (PIM-PIs) for C3H6/C3H8 separation. The best PIM-PI to date (PIM-6FDA-OH) had a mixed-gas C3H6/C3H8 selectivity of 15 combined with a C3H6 permeability of 2.5 Barrer at a feed pressure of 4 bar. One potential route to improving the permeability and selectivity is development of high-performance polymer-nanoparticle hybrid materials, also known as mixed-matrix membranes (MMM). For the first time, we report the fabrication and exceptional pure- and mixed-gas C3H6/C3H8 gas permeation properties of a PIM-PI-based MMM. Using PIM-6FDA-OH as the polymer matrix, we integrated a zeolitic metal-organic framework (ZMOF), ZIF-8, at various loadings ranging from 20% up to even 65% by weight. SEM imaging demonstrated overall good adhesion between the polymer/nanoparticle interfaces, and establishment of percolative nanoparticle networks upon loadings greater than 45%. This nanoparticle clustering phenomena observed in sufficiently loaded membranes facilitates the formation of dual transport conduits necessary to defy conventional permeability/selectivity tradeoffs observed in solution processable polymers due to the existence of both continuous polymer and inorganic phases. The membranes were tested with a 50:50 C3H6/C3H8 feed mixture at pressures up to 7 bar (p/psat ~0.8). Not only did the membranes demonstrate exceptional pure-gas properties (a >35, P(C3H6) >10 Barrer), but the high performance was also strongly preserved in mixed-gas conditions. Exceptional C3H6/C3H8 mixed-gas selectivities ranging from 20 at 30% loading to 30 at 65% loading were achieved. We also observed minimal onset of plasticization, highlighting the strong potential of PIM-6FDA-OH/ZIF-8 mixed-matrix membranes for C3H6/C3H8 separations.