Zeolite-filled PDMS membranes .2. Pervaporation of halogenated hydrocarbons

In order to study in more detail the influence of the filler on pervaporation performance, silicalite, ZSM-5, and zeolite Y were incorporated in poly(dimethylsiloxane) (PDMS) and tested in pervaporation experiments with binary mixtures of chlorinated hydrocarbons (Cl-HC's) in water. The results were compared with unfilled PDMS as a reference. The highest selectivities were obtained with the silicalite-filled membranes. However, these membranes showed a decrease in permeability for voluminous components due to molecular sieving effects. In this respect, the results with zeolite Y were rather disappointing, as its larger pore size was counteracted by its high polarity, whereas ZSM-5-filled membranes showed intermediate selectivities. Therefore, mesoporous silicas were synthesized, silylated to assure their apolarity, and incorporated in PDMS. The resulting membranes showed both improved organic fluxes and selectivities in comparison with all other membranes, even for voluminous organics, proving the absence of molecular sieving effects.