UNIQUAC and UNIQUAC-HB models for the sorption behavior of ethanol/water mixtures in a cross-linked polydimethylsiloxane membrane

Sorption behaviors were investigated for ethanol/water mixtures in polydimethylsiloxane (PDMS) films at 298K in this study. The classic UNIversal QUAsi Chemical (UNIQUAC) model and UNIQUAC-HB theory (the UNIQUAC model accounting for the hydrogen bonding effect) were employed to predict the individual sorption levels from various ethanol/water mixtures. The binary interaction parameters obtained from pure solvent sorption experiments in the PDMS (τ _iM and τ _Mi) and the ethanol/water vapor-liquid equilibrium data (τ ₁₂ and τ ₂₁) were determined and used for the predictions. The UNIQUAC model provided quick solubility predictions because the ethanol-water binary interaction parameters are readily available from the literature and because the model is easily extended to multi-component systems. The UNIQUAC-HB theory requires additional work to estimate the ethanol-water binary parameters because the molecular surface area parameters must be modified to account for the effects of hydrogen bonding prior to modeling the sorption levels in the ternary ethanol/water/PDMS system. The UNIQUAC-HB model is advantageous over the classic UNIQUAC model and the Flory-Huggins equation because the UNIQUAC-HB model is able to predict the synergistic effect of ethanol on the solubility of water. The UNIQUAC-HB equation generates higher R-square coefficient for the sorption selectivity than the other tested models and resulted in sufficiently high R-square coefficients for the partial solvent uptakes. This finding indicates the important role of hydrogen bonding in the sorption of ethanol/water in membranes.