SORPTION AND DIFFUSION OF VOCS IN DAY ZEOLITE AND SILICALITE-FILLED PDMS MEMBRANES

The sorption and diffusion properties of ethanol, 1,1,1-trichloroethan e (TCA) and trichloroethylene (TCE) were determined in silicalite-fill ed and dealuminized-Y-zeolite (DAY)-filled poly[dimethylsiloxane] (PDM S) membranes at 25, 100 and 150 degrees C. Zeolite filling results in increased solubility coefficients (S) for polar solvents Like ethanol over pure PDMS. No significant increase in S is observed in case of TC A and TCE which act as good solvents for PDMS. However, at higher temp eratures, the sorption is higher in zeolite-filled membranes even for the good solvents. The VOC diffusivity decreases with increasing degre e of zeolite filling because of higher characteristic diffusion time i n zeolites (for ethanol) and increasing tortuosity of the diffusion pa th (for TCA). Due to the presence of carbon=carbon double bond, TCE ex hibits marginal diffusivity drop in zeolite-filled membranes, The spec ific zeolite-polymer interactions, that is, tendency of zeolite pore b locking by polymer chains or the formation of voids on zeolite-polymer interface are influenced by the zeolite pore size and type of VOC per meating through the composite membrane. The variation in experimentall y observed ethanol permeability due to zeolite tilling could be qualit atively estimated from the sorption-diffusion data.