Effect of Functionalization of Metal Organic Framework (MOF) Material in Polyimides for Gas Separations

The selectivity/permeability tradeoff of polymer membranes in gas separations has motivated research to develop membranes that surpass the upper bound on Robeson’s plot of selectivity and permeability. Mixed-matrix membranes (MMMs) comprising thermally and chemically stable metal-organic framework (MOF) materials and thermally stable polymers present a promising material to achieve this goal. MMMs combine the advantages of the ZIF’s superior separation performance and the polymer’s processability.  In this study, synthesized amino-MIL-53 and MIL-53 nanoparticles are incorporated into a thermally stable polyimide at 20 wt% loadings. The effect of the presence of the amino functional group in the MOF on its gas separation performance was investigated. SEM images of the MMM’s cross-section showed an improved dispersion of the amino-functionalized MOF in the polyimide over the pure MIL-53. This improved dispersion can be attributed to the interaction of the amino functional group of the MIL-53 with the polyimide. The MMMs tested at 35 ^oC and 2.5 atm showed significant permeability increases for all the gases tested, and no change in H₂/CO₂ selectivity. The pure polyimide showed improvements in hydrogen permeability (5 to 133 Barrers) at 300 ^oC and 20 atm.  Testing at high temperatures and pressures of these MMMs are currently underway.