In-situ linker doping as an effective means to tune zeolitic-imidazolate framework-8 (ZIF-8) fillers in mixed-matrix membranes for propylene/propane separation

Zeolitic-imidazole framework-8 (ZIF-8) has been extensively studied as a molecular sieving filler in mixed-matrix membranes (MMMs) for propylene/propane (C3) separation. The C3 separation performance of ZIF-8-containing MMMs has yet to meet the commercial viability criteria. Recently, doping or mixing linkers in ZIF-8 framework has been found effective in tuning the molecular sieving properties of ZIF-8. Herein, we attempted to tune the molecular sieving properties of ZIF-8 fillers in MMMs by doping with 2-ethylimidazole (eIm) linkers in order to improve their C3 separation performance. MMMs were prepared by in-situ forming eIm-doped ZIF-8 fillers in polyimide using our recently reported polymer-modification-enabled in-situ MOF formation (PMMOF) process. As eIm linkers were doped into ZIF-8 filler crystals, the propylene/propane separation factor of the resulting MMMs was dramatically enhanced. Lastly, doped-linker ZIF-8 based mixed-matrix hollow fiber membranes were successfully prepared, demonstrating potential of their scalable practical applications.