ZIF-7/PDMS mixed matrix membranes for pervaporation recovery of butanol from aqueous solution

In this contribution, zeolitic imidazolate framework (ZIF-7)/polydimethylsiloxane (PDMS) mixed matrix membranes (MMMs) with uniformly dispersed ZIF-7 were fabricated. The homogeneous dispersion of ZIF-7 nanoparticles in PDMS matrix and better interface compatibility were characterized by SEM and EDS. PV performance reveals that the MMMs display increased total flux and the highest separation factor occurs at 20 wt% ZIF-7 loading, which were 1689 g m−2 h−1 and 66 respectively as compared to 1080 g m−2 h−1 and 51 for pure PDMS membrane when separating 1 wt% butanol aqueous solution at 60 °C. The total flux reaches 3496 g m−2 h−1 with 80 wt% butanol in permeate for the enrichment of 5 wt% butanol solution at 60 °C. The enhanced flux may result from enlarged free volume in the polymer matrix caused by the incorporation of ZIF-7 nanoparticles. Moreover, the super-hydrophobic ZIF-7 pore channels and butanol preferential permeation may contribute to the improvement of separation factor. The result also shows that there is a 21.1% reduction of energy barrier for penetrant transportation for 20 wt% ZIF-7 filled PDMS membrane as compared to pristine PDMS membrane. A long period of pervaporation experiment was also carried out to investigate the structure stability of the ZIF-7/PDMS membrane, and the MMM remains intact during the 240 h continuous operation, which is the key to industrial application for membrane-based separation process. All above indicated that ZIF-7 is a good filler to fabricate butanol permselective pervaporation membranes for butanol separation and enrichment.