Weakly pressure-dependent molecular sieving of propylene/propane mixtures through mixed matrix membrane with ZIF-8 direct-through channels

Metal organic frameworks (MOFs) hold great potential as one of the most promising membrane materials for propylene/propane separation which is a challenging process in petrochemical industries. However, the dramatic performance decline of MOF-based membranes arising from either increased feed pressure or blended polymer limits their application. Here, we demonstrate mixed matrix membranes (MMMs) with ZIF-8 direct-through channels (DTC) can delicately solve the above two critical problems. The 6FDA-DAM polymer network surrounding ZIF-8 was speculated to restrain the linker or seal the defects between ZIF-8 crystals. Accordingly, DTC-MMMs exhibit weakly pressure-dependent separation performance. At a feed pressure of 6 bar, the separation factor decrease of DTC-MMMs is only 9.1% in comparison with 35.7, 54.1, and 52.3% from conventional mixed matrix membranes (cMMMs), 6FDA-DAM and ZIF-8, respectively. Meanwhile, the DTC-MMMs exhibit a high propylene permeability of 582 Barrer and propylene/propane separation factor of 42.8, which is respectively 8.6 and 2.1 times higher than those from the state-of-the-art cMMMs and retains nearly 70% of the ZIF-8 crystal's separation performance according to Maxwell modeling. Considering the high-pressure stability, superior separation performance, and solution-processability, we anticipate that the DTC-MMMs could pave a new avenue to the design of next-generation MMMs for diverse molecular separations.