ZIF-8/Polybenzimidazole Mixed-Matrix Membranes for Gas Separations

Non-precious metal membranes that operate at high temperatures (≥300 ^oC) and pressures (≥15 atm) are required by 2015 DOE targets for hydrogen separation membranes.  Mixed-matrix membranes (MMMs) comprising thermally and chemically stable zeolitic imidazolate framework (ZIF) materials and thermally stable polymers that display high permselectivity can satisfy this requirement.  MMMs combine the advantages of the ZIF's superior separation performance and the polymer's processability.  In this study, weight loadings up to 45 wt% of ZIF-8 were incorporated in polybenzimidazole (PBI). At 35 ^oC and 3 atm, a 26 wt% ZIF-8/PBI MMM displayed a 2x increase in H₂ permeability. At high temperatures (up to 300 ^oC) and pressures (up to 15 atm), this MMM showed an impressive 7000% increase in H₂ permeability with a H₂/CO₂ selectivity of 14, placing this result above Robeson's upper bound and into the target region for H₂/CO₂ separations.