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.