PDMS mixed matrix membranes containing hollow silicalite sphere for ethanol / water separation by pervaporation

Separation of ethanol/water mixtures through classical separation methods, like distillation, are very energy consuming. Pervaporation is an alternative membrane separation process with much lower energy demand, but still lacking high performance membranes with sufficient flux-selectivity properties. In this study, polydimethylsiloxane (PDMS) based mixed matrix membranes (MMMs) were developed and their pervaporation performance investigated. The fillers consist of hollow spheres (HS) covered with a shell of silicalite-1 crystals. These HS were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), nitrogen physisorption and X-ray diffraction (XRD). The spheres were approximately 1 μm in size with a shell thickness of 30 nm. Nitrogen physisorption revealed the micro- and mesoporous nature of the spherical shells, with a BET surface area of over 800 m2/g. The hollow silicalite spheres were then uniformly distributed in the PDMS membrane to increase the membrane permeability since the hollow core of the HS allows very fast flow of the permeating compound. Furthermore, the zeolitic shell improves the ethanol selectivity through its specific pore structure and hydrophobicity, while additional crosslinking of the HS with the PDMS matrix further increases the selectivity of the polymer matrix, thus reaching a separation factor and flux value of 16 and 3.8×10−6 g.m/m2.s respectively for a 6% aqueous ethanol solution at 40 °C.