Counter-diffusion-based in situ synthesis of ZIF-67 membranes for propylene/propane separation

The zeolitic imidazolate framework ZIF-67, which is a cobalt-substituted ZIF-8 framework (Zn2+ + 2-methylimidazole), can selectively isolate propylene from propylene/propane mixtures via molecular sieving. However, very limited preparation reports exist on propylene-selective ZIF-67 polycrystalline membranes in contrast to their ZIF-8 counterparts. Herein, we report the successful synthesis of highly selective ZIF-67 membranes for propylene through a counter-diffusion-based in situ method. The repetition of the in situ synthesis was essential to yield well-intergrown ZIF-67 membranes with a propylene/propane separation factor of ca. 108 and a propylene permeance of ca. 65.6 × 10−10 mol m−2 s−1 Pa−1.