ZIF-8 membranes prepared at miscible and immiscible liquid–liquid interfaces

• ZIF-8 membranes for propylene/propane separation were prepared.
• Immiscible and miscible solution pairs were used in the counter diffusion method.
• Defects in ZIF-8 layer were decreased after the reaction in miscible solution pair.

ZIF-8 membranes are currently attracting attention for the separation of propylene/propane based on the molecular sieve effect. We have recently reported the preparation of ZIF-8 membranes using the counter-diffusion method, which is advantageous in reducing defects in the selective layer. In the present study, ZIF-8 membranes were prepared at the interface of miscible and immiscible pairs of solvents such as water/methanol and water/1-octanol, respectively. ZIF-8 membranes prepared from the immiscible pair of water and 1-octanol showed a propylene permeance of 5.2 × 10−9 mol m−2 s−1 Pa−1 and a propylene/propane permselectivity of 7.2 at 25 °C. As for the ZIF-8 membrane prepared by the initial reaction using the immiscible pair of water/1-octanol and the successive reaction using the miscible pair of water/methanol mixture, the average propylene permeance and average propylene/propane permselectivity increased to 1.2 × 10−8 mol m−2 s−1 Pa−1 and 20 at 25 °C, respectively. The successive reactions in water/1-octanol and water/methanol mixtures successfully decreased the defects in the ZIF-8 selective layer, resulting in high propylene permeance and high permselectivity for propylene/propane. The structure and gas permeation properties were also thoroughly characterized.

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