Structure and performance characterization of PDMS/PES-based pervaporation membranes for ethanol/water separation

Composite membranes, with a supporting layer of polyethersulfone (PES) and different active layers based on poly(dimethylsiloxane) (PDMS), were prepared to perform pervaporative separation of ethanol from water. Two approaches were adopted to enhance the ethanol selectivity of PDMS by: (1) evaluation of the effects of PDMS viscosity of two different grades and (2) the incorporation of new hydrophobic silica in the active layer. First, the structural morphology of support and active layers of the composite membranes was characterized. AFM images were evidence of the nodular structure of the membrane surfaces. Mean pore size and pore size distribution of PES layer, mean nodular size of PDMS layer, and their surface roughness and water contact angle were determined. The relationship between these structural properties and the pervaporation performance of composite membranes has then investigated. The effects of operating parameters, feed concentration and temperature on the membrane performance indicated that increasing the feed temperature improved PDMS/PES membranes pervaporative efficiency. Based on the results obtained, it was found that PDMS viscosity influenced the pervaporation performance; low-viscosity PDMS had a greater separation factor and greater permeation fluxes than high-viscosity PDMS. Moreover, silica-filled membranes improved the separation factor and enhanced the ethanol flux relatively.