Highly permeable zeolitic imidazolate framework (ZIF)-71 nano-particles enhanced polyimide membranes for gas separation

• ZIF-71 nano-sized crystals of less than 100 nm have been synthesized in DMF.
• Novel highly permeable MMMs based on ZIF-71 and 6FDA-Durene for gas separation.
• ZIF-71 enhances gas permeation properties of the resultant MMMs.
• A higher loading of ZIF-71 leads to a higher free volume and diffusivity.
• ZIF-71 nano-particles exhibit molecular sieving effect for C3H6/C3H8 separation.

Zeolitic imidazolate framework (ZIF)-71 nano-particles have been demonstrated as potential inorganic fillers for fabricating high-performance membranes for gas separation. The newly synthesized ZIF-71 nano-particles with a particle size of less than 100 nm were compatibly incorporated in 6FDA-Durene polyimide membranes as novel mixed matrix membranes (MMMs). No obvious agglomeration between ZIF-71 nano-particles and the 6FDA-Durene matrix was observed. The effect of ZIF-71 loading on gas separation performance was investigated for H2, O2, N2, CO2, CH4, C2H4, C2H6, C3H6 and C3H8. The incorporation of ZIF-71 nano-particles improves both gas permeation properties and membrane resistance against plasticization. With a 20 wt% ZIF-71 addition, the pure CO2 permeability of the MMM is increased by 3-fold, while the ideal CO2/CH4 selectivity is reduced from 16.4 to 12.8. In addition, the CO2 plasticization pressure is increased from 16 atm to 30 atm. The MMM embedded with 20 wt% ZIF-71 also displays a remarkable enhancement of C3H6 permeability from 57.6 Barrer to 371 Barrer without significantly compromising the ideal C3H6/C3H8 selectivity. The Positron Annihilation Lifetime Spectroscopy (PALS) and gas sorption characteristics further indicate that the permeability improvement is mainly due to the enhanced diffusivity and the molecular sieving effect of ZIF-71 nano-particles for separating C3H6/C3H8.

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