Pervaporation separation of water-dioxane mixtures through poly(vinyl alcohol)-silicone based hybrid membranes

Abstract

Hybrid membranes were prepared using poly(vinyl alcohol) (PVA) and tetraethylorthosilicate (TEOS) via hydrolysis followed by condensation. The membranes were subjected to swelling study and observed a remarkable decrease in degree of swelling with increasing the TEOS content in membranes and is attributed to the formation of hydrogen and covalent bonds in the membrane matrix. The pervaporation performance of these membranes for the separation of water- dioxane mixtures was investigated in terms of feed concentration and the content of TEOS used as crosslinking agent. The membrane containing 1:1.5 mass ratio of PVA and TEOS gave the highest separation selectivity of 14,992 with a flux of 0.70 x 10-1 kg/m2 h at 30oC for 10 mass % of water in the feed. For all the membranes the observed values of water flux are very close to the values of total flux in the investigated composition range, signifying that the developed membranes are highly water selective. From the temperature dependence of diffusion and permeation values, the Arrhenius apparent activation parameters have been estimated. The resulting activation energy values, obtained for water permeation being lower than those of dioxane permeation values, suggest that the membranes have higher separation efficiency. The activation energy values calculated for total permeation and water permeation are close to each other for all the membranes, signifying that coupled-transport is minimal as due to higher selective nature of membranes. The negative heat of sorption values (H ) for water in all the membranes suggests the Langmuir’s mode of S sorption.