Mixed matrix membranes were prepared by incorporating ZSM-5 zeolite particles into polydimethylsiloxane. A uniform dispersion of the zeolite in the membrane was obtained. The membranes were characterized with scanning electron microscopy, and the effects of zeolite loading on membrane performance were evaluated. It was found that 80wt.% ZSM-5 loading was optimal for selectivity. Further increase in the zeolite loading either improved the selectivity slightly or even lowered the membrane selectivity while the membrane permeability was consistently reduced. The improved separating performance of the filled membranes was attributed to the filler-polymer interactions, and the mass transfer contribution of surface flow through the zeolite pores. The advantage of the improved membrane performance was demonstrated in a simulated continuous operation enriching 2,3-butanediol in a mixture with 1 -butanol from 5 to 99.5 wt.% as a retentate using both the filled and un-filled PDMS membranes. Results showed that the filled PDMS membrane improved the recovery of 2,3-butanediol significantly while achieving the same product purity. Crown Copyright (C) 2009 Published by Elsevier B.V. All rights reserved.