(551d) Vapor Phase Processing of Zeolitic Imidazolate Framework Membranes

Zeolitic imidazolate framework (ZIF) membranes possess unique properties for the separation of important industrial gas mixtures, such as propylene/propane. High quality ZIF membranes are typically fabricated with solution-based methods involving the use of at least one solvent. These methods are difficult to scale up due to the uncontrolled homogeneous nucleation/growth of ZIFs and the possible dissolution of membrane materials during membrane synthesis. Here, we report a vapor phase membrane fabrication approach that combines atomic layer deposition (ALD) and ligand vapor treatment. In this method, ZnO is deposited on porous ceramic support by ALD and then converted to ZIF-8 by exposure to 2-methylimidazole vapor. The membranes exhibit excellent and stable performance for propylene/propane separation. Under an equimolar propylene/propane mixture feed and ~7 atm feed pressure, the membranes show a combination of high separation factor (>45) and highest propylene flux reported (>10^-2 mol m^-2 s^-1). Without the use of any solvents, the vapor phase processing method has environmental, cost, and scalability advantages.