PERVAPORATION OF ETHANOL-WATER THROUGH A POLY(VINYL ALCOHOL) CYCLODEXTRIN (PVA CD) MEMBRANE

A poly (vinyl alcohol)/cyclodextrin (PVA/CD) membrane was utilized in the pervaporation of ethanol/water mixtures. The membrane was prepared by casting an aqueous solution of PVA and beta-cyclodextrin oligomer. The CD oligomer was successfully immobilized in the membrane by the crosslinking of PVA with glutaraldehyde for 1 h. The content of CD was up to 33%. The effect of CD on the pervaporation performances of water/ethanol was investigated by measurements of the sorption equilibrium and the calculations of the diffusion coefficient of the permeants in the membrane. The addition of CD increased the water selectivity of the pervaporation of water/ethanol, especially at lower (< 40%) and higher (> 90%) ethanol concentrations in the feed. The water selectivity through the sorption equilibrium, on the contrary, decreased by the addition of CD; this indicated that the effect of CD on the diffusion coefficient was predominant on the pervaporation performance. At lower ethanol concentrations, the addition of CD increased the permeation rate of water because of the large increase in the diffusion coefficient. The permeation rate of ethanol decreased due to the large decrease in the diffusion coefficient. At higher ethanol concentrations, the permeation rate of water slightly decreased; the diffusion coefficient of water increased but the water solubility decreased. The permeation rate of ethanol largely decreased because both the diffusion coefficient and solubility of ethanol decreased.