The Separation of binary liquid mixtures by pervaporation

ABSTRACT Pervaporation as a membrane process is today considered a basic unit operation with significant potential for the separation of liquid mixtures which are difficult or not possible to separate by conventional methods. In the pervaporation process, the feed mixture is maintained in contact with one side of a membrane, and the permeate is continuously removed from the other side in vapor form by a vacuum pump. In this study, separation of ethyl acetate-water binary system was attempted. As membranes, polymeric films (polyvinylalcohol and polydimethylsiloxane), which will have high flux and selectivity values, were prepared. Tartaric acid was selected as the cross-linking agent for PVA and a commercial cross-linking agent was used for PDMS. Oxalic acid as the cross- linking agent for PVA was eliminated after preliminary tests and evaluation. Based on the preliminary experiments the concentration of the TAc was selected as 20% by weight. Experimental setup consisted of feed tank, water bath, feed pump, vacuum pump, membrane cell (stainless steel) and dewar containers. Pervaporation experiments were conducted continuously in a system which has three traps that were used to collect the permeate condensed by liquid nitrogen held in dewars. Sorption experiments were carried out at 30, 40 and 50 °C in pure water and pure ethyl acetate using PVA and PDMS membranes prepared, and in ethylacetate-water mixtures containing different percentages of water using PVA membranes prepared. Pervaporation experiments conducted using only PVA membranes for the pure components and their binary mixtures at 30, 40, 50 and 63°C showed that the PVA membrane (50 and 100 urn thick) prepared is exteremely effective for the selective permeation of water. The equilibrium curve was determined by conducting vapor-liquid equilibrium calculations using the Wilson Equation for the liquid phase nonideality. A mathematical model found in literature for the permeate sorption and diffusion throughout the membrane which uses free volume theory of Fujita and Flory-Huggins thermodynamics, based on the principle of solution-diffusion, was applied to the pure component permeation. Keywords: Pervaporation, membrane, sorption, polyvinylalcohol, polydimethylsiloxane, tartaric acid, ethyl acetate, water, Flory-Huggins thermodynamics XI