Sodium alginate–magnesium aluminum silicate mixed matrix membranes for pervaporation separation of water–isopropanol mixtures

Abstract

Sodium alginate (NaAlg) is a well-known carbohydrate polymer occurring in natural sources. In this study, mixed matrix membranes of NaAlg filled with sub-micron size magnesium aluminum silicate (MAS) particles have been prepared by incorporating different amounts (5, 10 and 15 wt.%) of MAS into NaAlg by solution casting and crosslinked with glutaraldehyde. The membranes prepared have been tested for pervaporation (PV) separation of water–isopropanol mixtures at 30 °C. Membranes were characterized by Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) to confirm the chemical interactions and homogeneity of the mixed matrix membranes. PV separation characteristics of the crosslinked NaAlg–MAS membranes have been studied by varying the feed water compositions and temperature. It was found that NaAlg membrane filled with 15 wt.% MAS gave the highest selectivity of 17,991 when tested for 10 wt.% of water containing feed mixture. Comparatively, a lower selectivity of 653 was observed for plain crosslinked NaAlg membrane for 10 wt.% water containing feed mixture; selectivity was further decreased with increasing water concentration of the feed mixture up to 50 wt.%. Water flux for the plain NaAlg membrane increased from 0.062 to 0.177 kg/m 2 h for the feed compositions ranging from 10 to 50 wt.% water; however at these compositions, flux values of NaAlg filled with 15 wt.% of MAS increased from 0.056 to 0.174 kg/m 2 h, suggesting no significant improvement. The observed water flux is lower for the mixed matrix membranes, but higher for the plain NaAlg membrane; nevertheless, selectivity is higher for NaAlg–MAS mixed matrix membranes than observed for the plain NaAlg membrane. Similar trends have been observed at 40 and 50 °C for the feed water compositions of 10–30 wt.%. The PV performance has been studied in terms of flux ( J), selectivity ( α), pervaporation separation index (PSI) and enrichment factor ( β). Permeation flux followed the Arrhenius trend over the investigated temperature range.