UTSA-280 metal–organic framework incorporated 6FDA-polyimide mixed-matrix membranes for ethylene/ethane separation

Mixed-matrix membranes (MMMs), judiciously combining processability of polymer and remarkable separation performance of nanofillers, have been extensive pursuits for molecular separation process. Permeability matching between filler and polymer is one of the necessary requisites to desirable mixed-matrix effect. Considering the superior molecular sieving effect of UTSA-280 metal-organic frameworks on C₂H₄ and C₂H₆, here, we report two types of UTSA-280/6FDA-polyimide MMMs toward C₂H₄/C₂H₆ separation. The molecular sieving effect of UTSA-280 endowed 6FDA-DAM:DABA(3:2) membrane with simultaneous improvements in C₂H₄ permeability and C₂H₄/C₂H₆ selectivity. Optimally, when the filler reached 21.80 wt%, C₂H₄ permeability and C₂H₄/C₂H₆ selectivity was increased to 6.49 Barrer (by 15%) and 4.94 (by 32%), respectively. On the contrary, UTSA-280/6FDA-DAM MMMs showed undesirable mixed-matrix effect that C₂H₄ permeability decreased meanwhile C₂H₄/C₂H₆ selectivity nearly kept at polymeric pristine membrane level. It was found that permeability matching between two phases was responsible to these opposite mixed-matrix effects. More specifically, UTSA-280 had a relatively low gas permeability so that it required a less permeable polymeric matrix like 6FDA-DAM:DABA(3:2) to exert its molecular sieving effect. Furthermore, the optimal-matching 6FDA-matrix in permeability with UTSA-280 fillers was predicted by theoretical model. This work not only reports improving C₂H₄/C₂H₆ separation performance via mixed-matrix formulation, but also emphasizes the importance of permeability matching between polymer and filler to realize the mixed-matrix effect.