Prediction of salt effect on vapor–liquid equilibria

In this paper, a newly proposed model based on solvation between pure solvent and salt for prediction of salt effect on vapor–liquid equilibria is presented by using only the vapor pressure depression data of pure solvent+salt systems that compose the mixed solvent with salt system. The proposed model predicts thermodynamically the salt effect by solvation number between each pure solvent and salt determined from the vapor pressure depression data with an assumption of the vapor pressure depression caused by the solvation. Three points differ from the originally proposed model by the author [S. Ohe, 1976. Advances in Chemistry Series, No. 155, American Chemical Society.]. First, it is assumed that each solvent component solvates with salt instead of the preferential solvation of the original model. It, however, is superficial phenomenon, since the difference between the solvation numbers is thought to be equivalent to it. Second, it is also assumed that the vapor pressure depression is caused by the solvation. Third, the method predicts the effect from VLE with no salt and vapor pressure depression data of pure solvent with salt. The salt effect on vapor–liquid equilibria was satisfactorily predicted for a methanol+ethanol+water+CaCl2 (16.7 wt.%) system from the solvation numbers determined from vapor pressure depression data of methanol+CaCl2, ethanol+CaCl2, and water+CaCl2 system.