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 298 K 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 (τiM and τMi) and the ethanol/water vapor–liquid equilibrium data (τ12 and τ21) 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.