Sodium montmorillonite clay loaded novel mixed matrix membranes of poly(vinyl alcohol) for pervaporation dehydration of aqueous mixtures of isopropanol and 1,4-dioxane

Abstract

Poly(vinyl alcohol)-based mixed matrix membranes loaded with 5 and 10 wt.% of sodium montmorillonite (Na +MMT) clay particles, i.e. (PVA/Na +MMT-5 and PVA/Na +MMT-10), were fabricated by solvent casting method. The uncrosslinked membranes were used in pervaporation (PV) dehydration of aqueous solutions of isopropanol and 1,4-dioxane at 30 °C. Membrane morphology was characterized by scanning electron microscopy. Differential scanning calorimetry, thermogravimetric analysis and dynamic mechanical thermal analysis were used to understand thermal properties. Universal testing machine was used to study mechanical strength properties. Separation factor to water has increased from 1116 to 2241 for PVA/Na +MMT-5 and PVA/Na +MMT-10 mixed matrix membranes when tested for 10 wt.% water-containing isopropanol feed, but the corresponding flux values of 0.051 and 0.075 kg/m 2 h were somewhat lower than those observed for pristine PVA membrane. On the other hand, for water + 1,4-dioxane feed mixtures, separation factors were quite lower and ranged from 216 to 369 with the corresponding flux values of 0.076 and 0.093 kg/m 2 h, respectively, for PVA/Na +MMT-5 and PVA/Na +MMT-10 membranes at 10 wt.% water in the feed. Membranes of this study could extract up to 99.20 and 99.60 wt.% water on the permeate side from water–isopropanol mixture, while from water–1,4-dioxane mixture, only 96.0 and 97.62 wt.% of water were removed for 10 wt.% water-containing feed. The membranes were further tested for PV at 40, 50 and 60 °C for 10 wt.% of water-containing feeds of aqueous isopropanol and 1,4-dioxane solutions to confirm their stability at higher temperatures. Plots of ln J p versus 1/ T are linear in the studied range of 30–60 °C for both the feed mixtures, indicating that flux follows an Arrhenius trend. PV results are discussed in terms of water flux, separation factor, permeation separation index, enrichment factor and activation energy of permeation. Sorption and PV experiments were carried out for the thermally crosslinked and glutaraldehyde crosslinked PVA/Na +MMT mixed matrix membranes for 10 wt.% water-containing feed mixtures at 30 °C. A small increase in separation factor with a slight sacrifice in flux was observed without showing any great difference as compared to uncrosslinked mixed matrix membranes. The hydrophilic nature of Na +MMT clay and the formation of PVA/Na +MMT mixed matrix membranes are responsible to offer such increased separation to water over the organic components of the feed mixtures.