High gas permselectivity in ZIF-302/polyimide self-consistent mixed-matrix membrane

Zeolitic imidazolate framework-302 (ZIF-302) was incorporated within a polyimide (PI) matrix in order to develop a highly selective and permeable mixed-matrix membrane (MMM) for gas separation processes. On the basis of varying fabrication procedures, two different MMMs were formed: a dense MMM (ZIF-302/d-PI) and a spongy, self-consistent MMM (ZIF-302/s-PI). The spongy membrane was shown to have self-consistent and disconnected pores with a reduction in overall membrane density. For ZIF-302/d-PI, a 1.2–1.5-fold increase in the permeability of H₂, O₂, N₂, CO₂, and CH₄ was observed when compared with the pure d-PI membrane. For ZIF-302/s-PI, even better improvements (up to 19-fold higher) in permeance were achieved with negligible effects on selectivity. The gas transport mechanism was then analyzed and showed a considerable enhancement of diffusion coefficients for ZIF-302/s-PI, while ideal gas pair selectivities for CO₂/N₂, H₂/CH₄, and H₂/N₂ were found to be 24.8, 42.3, and 62.6, respectively.