Desorption and pervaporation properties of zeolite-filled Poly(dimethylsiloxane) membranes

The role played by zeolite fillers in PDMS membranes was studied by desorption and pervaporation. The data on the desorption of different solvents from the membranes made of poly(dimethylsiloxane) (PDMS) filled with silica and different zeolites show that the solvent molecules are extracted in two stages. The first stage, which occurs at a low temperature (ca.50 degreesC), would correspond to the extraction of the solvent molecules in the 'bulk-like state' in PDMS, while the last stage, at high temperature, would correspond to the extraction of the solvent molecules in the 'bound state'. There is a clear contribution of the zeolites to the membrane performances in pervaporation, even at a low zeolite content in PDMS (ca. 20 wt. %). The hydrophobic zeolites enhance significantly the organic flux, leading to an improvement of both the flux and the selectivity of PDMS. The ZSM-5 zeolite imparts to PDMS a higher selectivity but lower flux compared with SY-2 zeolite. The silica filler exhibits a crosslinking effect on PDMS, i.e. a slightly higher selectivity and lower flux than the pure PDMS membrane.