Parameters determining transport mechanisms through unfilled and silicalite filled PDMS-based membranes and dense PI membranes in solvent resistant nanofiltration: Comparison with pervaporation

Solvent parameters and solvent–membrane interaction parameters that determine the permeation of pure solvents through silicalite-filled and unfilled PDMS-based membranes in solvent resistant nanofiltration (SRNF) were investigated and compared to pervaporation (PV) data. Transport mechanisms were investigated for dense PDMS and PI membranes, using a wide range of solvents and pressures. It was found that in SRNF, the affinity of the solvent for the membrane polymer determines the flux primarily, but viscosity could not be neglected. It was shown that the relation between flux and molar volume/solvent viscosity reported in the literature was not followed, so that also other parameters are to be taken into account to describe transport. This was valid for all investigated membranes. In PV, no influence of selected parameters on solvent transport was observed. PDMS membranes showed a good performance in both SRNF and PV. Retentions mostly above 90% were obtained for all dye/solvent mixtures at 20 bar. Incorporation of 15 wt% silicalite fillers reduced swelling significantly and improved retention for measured dye/propanol systems. This was however not seen for isopropanol. In PV, all membranes used showed similar selectivities (∼4), except for the commercial Pervap 1060 membrane (∼2.8), which was related to the higher hydrophilicity of PDMS.