DEVELOPMENT OF A MIXED-MATRIX MEMBRANE FOR PERVAPORATION

In the production of pure alcohol, pervaporation is developing into an important technology. In this study, in order to improve the performance of the pervaporation process, a mixed-matrix polymer-zeolite membrane is developed. In the preparation of these membranes, cellulose acetate as base polymer, acetone or DMF as solvent, and 13X or 4A zeolites as fillers were used. To test the performance of homogeneous and mixed-matrix membranes, a laboratory-scale pervaporation setup was constructed. The effect of the following experimental parameters on the selectivity and flux were experimentally studied to determine the optimum values of operating conditions and to understand the separation mechanism in the indicated ranges: feed concentration, 70-90 wt%; feed temperature, 30-70-degrees-C; feed flow rate, 32-76 L/h. It was observed that the addition of zeolite to the membrane matrix improves the flux value twofold with respect to its homogeneous membranes with some loss in their selectivity. For example, for a feed concentration of 74 wt% EtOH at 50-degrees-C and 1 mmHg, the flux value for the unfilled membrane is 0.6 L/m2.h, and for a 30% zeolite-filled membrane, the flux is increased to 1.33. For these cases, the selectivities are 7.76 and 5.0 for the unfilled and filled membranes, respectively. TEM micrographs of the mixed-matrix membranes show a homogeneous distribution of zeolite particles which produce a cave-like porous structure in the matrix. The combined effect of this modified morphology and zeolite selectivity is the possible reason for the observed pervaporation performances of mixed-matrix membranes.