EXCLUSION AND TORTUOSITY EFFECTS FOR ALCOHOL WATER SEPARATION BY ZEOLITE-FILLED PDMS MEMBRANES

A resistance model has been developed to describe the increased pervaporation flux and selectivity for the separation of ethanol/water mixtures with silicalite-filled silicone rubber (SR) membranes as compared to unfilled SR membranes. The model interprets the increased component flux for ethanol in terms of an increasing ethanol permeability of the membrane. Membrane permeability is given as a function of rubber and silicalite permeabilities and of the silicalite content of the membrane. It is shown that silicalite permeability varies with the type of alcohol and the alcohol concentration in the feed mixture. In the series methanol, ethanol, propanol, and butanol, the alcohol permeability of silicalite varies with the length of the alcohol molecule, the lowest permeability being found for butanol. In the presence of propanol and butanol, the silicalite particles are impermeable to water and obstruct water transport through the membrane.