Preyssler type heteropolyacid-incorporated highly water-selective sodium alginate-based inorganic–organic hybrid membranes for pervaporation dehydration of ethanol

Sodium alginate (NaAlg) hybrid membranes containing 6, 8 and 10 wt.% of Preyssler type heteropolyacid H14[NaP5W30O110] (HPA) were prepared and characterized by FTIR, SEM, TGA, DSC, UTM and contact angle measurements. Hybrid membranes were more hydrophilic than pristine NaAlg membrane and exhibited increased pervaporation separation index (PSI) for selectively separating water from the azeotropic mixture (4 wt.% water + 96 wt.% ethanol) with ethanol. The highest separation factor of 59,976 with a flux of 0.043 kg/m2 h was obtained for the hybrid membrane i.e., NaAlg-6, which was further investigated in greater details to study the effect of feed water composition on its pervaporation (PV) performance. All the membranes were mechanically stable as tested by UTM during the PV operations. Degree of swelling and sorption selectivity values increased with increasing feed water composition giving a decrease in separation factor. Flory–Huggins-type interaction parameter for water and ethanol were computed to offer thermodynamic explanations. Membranes of this study are highly water-selective. Activation energies for total permeation, permeation of water and ethanol were determined at various temperatures. The negative heat of sorption indicates the predominance of Langmuir sorption mode for NaAlg-6 hybrid membrane.