Polymer Composite Membrane with Penetrating ZIF‐7 Sheets Displays High Hydrogen Permselectivity

Oriented and penetrating molecular sieving membranes display enhanced separation performance. A polyimide (PI) solution containing highly dispersed ZIF‐7(III) sheets in CHCl3 was deposited on a glass side and subjected to flat‐scraping with a membrane fabricator. In this way we developed a novel oriented and penetrating ZIF‐7@PI mixed matrix membrane (MMM) with 50 wt. % ZIF‐7 loading. Because the height of the ZIF‐7 sheets (5 μm) is higher than the film thickness, every ZIF‐7 sheet penetrates both surfaces of the polyimide film. Since the ZIF‐7 channels are the dominant pathway for gas permeation, the ZIF‐7@PI MMM displays a high molecular sieve performance for the separation of H2 (0.29 nm) from larger gas molecules. At 100 °C and 2 bar, the mixture separation factors of H2/CO2 and H2/CH4 are 91.5 and 128.4, with a high H2 permeance of about 3.0×10−7 mol m−2 s−1 Pa−1, which is promising for hydrogen separation by molecular sieving. The separation performance of the ZIF‐7@polyimide (PI) mixed matrix membrane (MMM) is determined by the embedded ZIF‐7 sheets rather than by the polyimide matrix. Every ZIF‐7 sheet penetrates both surfaces of the PI matrix such that the ZIF‐7 channels provide the dominant pathway for gas permeation. The ZIF‐7@polyimide MMM is effective at separating H2 from larger gas molecules.