Transforming polymer hollow fiber membrane modules to mixed-matrix hollow fiber membrane modules for propylene/propane separation

Mixed-matrix membranes (MMMs) have shown promising performances for gas separation, in particular, propylene/propane separation. Their commercial applications require to fabricate MMMs in scalable forms, i.e., asymmetric mixed-matrix hollow fiber membranes (MMHFMs). Up until now, however, there have been few reports on MMHFMs due to the fundamental engineering challenges associated with current fiber spinning processes using filler-suspended dope solutions. Recently, we proposed a scalable MMM fabrication strategy, namely polymer-modification-enabled in-situ metal-organic framework formation (PMMOF). The PMMOF has potential to overcome some of the engineering challenges since it decouples hollow fiber spinning step and MMM formation step. Herein, we report asymmetric 6FDA-DAM (4,4′-(hexafluoroisopropylidene) diphthalic anhydride-2,4,6-trimethyl-1,3-diaminobenzene)/ZIF-8 MMHFM modules by transforming 6FDA-DAM coated hollow fiber membrane (HFM) modules using the PMMOF. The resulting asymmetric MMHFM modules showed a promising propylene/propane separation performance (i.e., propylene permeance of ~2.15 GPU and separation factor of ~23.4) without additional defect healing steps. The membranes showed stable separation performance over a period of up to 25 days and at the total feed pressures of up to 6 bar. Finally, we demonstrated MMHFM modules consisting of up to seven individual fiber strands. To the best of our knowledge, this is the first multi-strand MMHFM modules showing promising propylene/propane separation performances, thereby opening up the possibility of the commercial applications of MMMs.