Methanol-ethyl acetate preferential solvation number

A method of prediction of the salt effect of vapor-liquid equilibrium relationships in the methanol-ethyl acetate-calcium chloride system at atmospheric pressure is described. From the determined solubilities it is assumed that methanol forms a preferential solvate of CaCl296CH OH. The preferential solvation number was calculated from the observed values of the salt effect in 14 systems, as a result of which the solvation number showed a linear relationship with respect to the concentration of solvent. With the use of the linear relation the salt effect can be determined from the solvation number of pure solvent and the vapor-liquid equilibrium relations obtained without adding a salt. 

The preferential solvation formed between salt and solvent molecules causes a salt effect on vapor-liquid equilibria. A method of prediction of salt effect based on the preferential solvation number was reported previously for the case in which salt was solved below the saturation level. The idea introduced in this chapter applies for salt solved in saturation. The alcohol-ester-calcium chloride system for which the preferential solvation was thought to be formed was examined. Specifically, calcium chloride dissolves readily in alcohol but only sparingly in ester. Thus, when calcium chloride is solved into alcohol-ester mixed solvent, the calcium chloride will form a preferential solvation with alcohol only. Methanol-methyl acetate, butanolr-butyl acetate, and methanol-ethyl acetate systems were selected for the mixed-solvent systems. 

Figures 4, 5, and 6 indicate caluculated results of the preferential solvation numbers for the three systems. As shown by each figure, preferential solvation numbers are almost constant against compositions of the solvent. On the other hand, the concentration of salt increases linearly against an increase in the concentration of alcohol in the solvent as indicated in Figures 1, 2, and 3. This fact denotes that for an increase of solvent which forms a preferential solvate in a solvent mixture, the salt required to form a certain solvation number with that solvent is dissolved. For essential concentration x1SL in Equations 3 and 4, which are required in calculating solvation numbers, the data observed by the author et al. (I) were used for the methanol-ethyl acetate system ...

Figure 4. Preferential solvation number in the methanol-ethyl acetate system at 1 atm (O), CaCl2 5 wt % (A), CaCl2 10 wt % (V), CaCl2 20 wt % (D)y CaCl2 25 wt % (%), CaCl2 saturated (1).

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