Sorption and diffusion of VOCs in DAY zeolite and silicalite-filled PDMS membranes

The sorption and diffusion properties of ethanol, 1,1,1-trichloroethylene (TCA) and trichloroethylene (TCE) were determined in silicalite-filled and dealuminized-Y-zeolite (DAY)-filled poly[dimethylsiloxane] (PDMS) membranes at 25, 100 and 150°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 TCA and TCE which act as good solvents for PDMS. However, at higher temperatures, the sorption is higher in zeolite-filled membranes even for the good solvents. The VOC diffusivity decreases with increasing degree of zeolite filling because of higher characteristic diffusion time in zeolites (for ethanol) and increasing tortuosity of the diffusion path (for TCE). Due to the presence of carbon=carbon double bond, TCE exhibits marginal diffusivity drop in zeolite-filled membranes. The specific zeolite-polymer interactions, that is, tendency of zeolite pore blocking by polymer chains or the formation of voids on zeolite-polymer interface are influenced by the zeolite pore size and type of VOC permeating through the composite membrane. The variation in experimentally observed ethanol permeability due to zeolite filling could be qualitatively estimated from the sorption-diffusion data.