Study of the role of water in the transport of water and THF through hydrophilic membranes by pervaporation

The influence of water on the water and THF transports through interpenetrating polymer network (IPN) membranes based on poly(vinyl pyrrolidone) (PVP)/poly(vinyl alcohol) (PVA) blends, was investigated with the pervaporation technique. The THF permeability was surprisingly high for such glassy hydrophilic membranes. However, it drastically decreased with the increase of water content, if small amounts of water are added to THF. When the water content was 1 wt.%, the partial flux of THF was lower than 100 g m−2 h−1, and the selectivity of the permeation to water increases with the trace water content. The higher is the PVP content, the larger the influence of the water on membrane performances will be. The combination of the pervaporation results with IR data on membrane-solvent systems allows us to interpret the membrane behaviors on the basis of the preferential interactions of PVP carbonyl groups with water molecules via hydrogen bonds. The formed hydration layer depletes the permeation of THF by excluding THF molecules from the membranes. The study of the dependence of the membrane performances on time showed that the hydration of the membrane in pervaporation is a dynamic sorption–desorption process in the membrane and is related to concentration polarization.