Date of Award

Spring 1985

Document Type


Degree Name

Doctor of Engineering Science in Chemical Engineering


Chemical Engineering and Chemistry

First Advisor

Dimitrios P. Tassios

Second Advisor

Dana E. Knox

Third Advisor

R. P. T. Tomkins

Fourth Advisor

Theodore Petroulas

Fifth Advisor

Ching-Rong Huang


A group-contribution model for the prediction of salt-effects on the vapor-liquid equilibria of multicomponent electrolytic solutions containing a single electrolyte is presented. Coulombic interactions are represented through a Pitzer term. Solvation effects and short-range interactions are represented through a UNIQUAC-type expression. An ion-size, a solvation and three ion-solvent interaction parameters per salt-solvent binary are required for multicomponent predictions.

All parameters are obtained only through the correlation of binary salt-solvent osmotic coefficient and vapor-pressure depression data at 25°C, in most cases, and binary solvent VLE data. The salt-solvent binary data were correlated with an average percent error in CD of 2.5 and an average percent error in P of 0.35 mm Hg up to a molality of 6 for 1-1 and 2-1 salts. The model is also useful in the prediction of aqueous binary salt data up to a molality of 6 and 200°C and nonaqueous binary salt data up to a molality of 6 and 60°C.

Methods are also presented for the estimation of the ion-solvent interaction parameters needed for multicomponent prediction when the constituent binary data are not available.

25 data sets of isothermal and isobaric salt-alcohol-water and salt-alcohol mixtures were predicted using the binary interaction parameters and gave an average absolute error in the vapor phase composition of 0.019. The model predicts correctly the salting-in of the appropriate component.

Vapor-pressure depression data of Nal, KCH3COO, NaSCN, and NH4SCN in methanol at temperatures of 25 and 40°C were measured in the molality range of 0.1-5.0 m using a static method, where the vapor pressure of the electrolytic solution is compared to that of the pure solvent.

Osmotic coefficients were calculated from the vapor pressure data. This data was used to obtain additional binary interaction parameters which could not be determined from the existing literature data.