Vapour–Liquid Equilibrium of Water/Ethanol/1-Butanol/Salt: Prediction and Experimental Verification

Abstract

Experimental vapour–liquid equilibrium data of water/ethanol/1-butanol saturated with NaCl, KCl and NH4Cl compared well with those predicted by Tan–Wilson and Tan–NRTL models for multicomponent solvent–solute mixture. The Wilson and NRTL solvent–solvent interaction parameters were obtained by the regression of the experimental vapour–liquid equilibrium data of the salt-free solvent mixture. The solute–solvent interaction parameters were calculated from the experimental bubble points of the individual solvent components saturated with the respective salts. Water was significantly salted-into the liquid phase by all the three salts giving a vapour phase rich in organic solvent components and a liquid phase rich in water. Both NaCl and NH4Cl showed little or no preference in salting-out the two organic solvent components while KCl showed preferential salting-out of ethanol. These results are consistent with previous reports that solvent component i would be salted-in or out of the liquid phase relative to solvent component j depending on whether the ratio of the solute-solvent interaction parameter, Asj/Asi (Tan–Wilson model) or exp(Tis – Tjs) (Tan–NRTL model) is less than or greater than 1. These findings show that the two models describe reasonably well the effect of salts on the liquid–phase activity coefficient of the solvent components in a ternary solvent mixture. The criteria and the rapid screening method proposed by Tan on the selection of a suitable non–volatile soluble solute for the elimination of azeotropes and for the salt distillation of close-boiling and azeotropic binary solvent mixtures are therefore equally applicable to ternary solvent mixture.