Dehydration of glycerine-water mixtures by pervaporation (PV) was studied with Nafion (NA), cellulose triacetate (CA), polyimide, carboxylated polyvinyl chloride (CPVC), and polyethersulfone (PES) membranes. PES membrane yielded the highest selectivity (6580) and CPVC membrane yielded the lowest selectivity (1552) at 5% by weight of water in the feed and 30°C. The NA membrane yielded the highest permeation flux (0.2-1.45 kg/m 2 h) of water over the entire water concentration range. Energy of activation of permeation for water was in the range of 7-15 kJ/mol, being highest for CPVC and lowest for CA. Comparison of PV and vapor liquid equilibrium data showed that the former gave better results, particularly for concentrating glycerine above 90 wt%.Pervaporation (PV) is a membrane-based separation process suitable for separating liquid mixtures comprising azeotropes and close boiling and temperature-sensitive products (1-3). Extensive research has been carried out to separate ethanol-water mixtures by PV. Apart from ethanol-water mixtures, work dealing with various applications was also published to explore the potential of PV (4-6). Because of its high selectivity and low energy requirements, PV is an alternative separation method in the chemicals industry.Glycerine is used in various products as a solvent, humectant, plasticizer, emollient, sweetener, a fermentation nutrient in the production of antibiotics, antifreeze in automobiles, etc. In the fat-splitting process glycerine is a co-product of soap manufacture and the manufacture of fatty acids (7). Removal of water from crude glycerine is an important step in the production of pure glycerine by the fat-splitting process. Presently, water is removed by evaporation/distillation. The high boiling point of glycerine (290°C), along with its relatively low decomposition temperature (190°C), necessitates the use of vacuum to lower the temperature requirements. For instance, at 10 mm Hg absolute the boiling point of glycerine is 166°C. Even this option cannot prevent the degradation and polymerization of glycerine (7). PV, which can achieve dehydration at much lower temperature, is therefore an attractive alternative.In the present work, attempts were made to use PV for dehydrating aqueous glycerine as a convenient and energy-efficient technique. Various polymeric membranes were prepared and tested for pervaporation of glycerine-water mixtures. PV performance was evaluated in terms of selectivity and flux. The effects of functional groups of the polymer comprising membrane, feed concentration, and feed temperature on the flux and selectivity were studied. Here, selectivity is defined as follows:where α = selectivity (dimensionless), X A = concentration in the feed (wt%) with water, and Y B = concentration in the permeate (wt%) with glycerine. Overall performance of the membrane was evaluated in terms of pervaporation separation index (PSI), defined by Huang (8) as given below:where C pwater and C fwater are water concentrations in the permeate and feed, respectively...
