Phase equilibria in mixtures of polar and nonpolar compounds: Derived thermodynamic quantities for alcohols and hydrocarbon

Abstract

The properties of vapor mixtures and liquid solutions which determine phase equilibria are of special importance in separation processes. They include the vapor-phase h p e rfections ; the liquid-phase activity coefficients ; and the excess heat, entropy, and free energy of mixing.Correlation of these properties in nonpolar mixtures is relatively simple, but in mixtures of polar and nonpolar compounds the molecular interactions lead to more complex relations. Semiempirical relations reported earlier (3, 4 ) have been used to calculate the vapor imperfections and to correlate the liquid-phase activity coefficients.Temperature variations of the activity coefficients can reflect the true heat and entropy effects in solution if sufficient vapor-liquid equilibria are available for a careful and consistent treatment. This is illustrated with binary mixtures of benzene and the n-aliphatic alcohols, methanol to pentanol. The results are compared with calorimetric data available in the literature.?he consistent set of cross-correlated coefficients provides a basis for calculating both isothermal and isobaric vapor-liquid equilibria at various conditions for the binaries and for certain ternary and multicomponent mixtures without any additional data.Most industrial petroleum and chemical processes involve separations in which the products of interest are separated from the undesirable components. Many of these separation schemes depend directly or indirectly on the phase equilibria in the mixtures. Consequently the properties of vapor mixtures and liquid solutions which determine the phase equilibria are of special importance. These include the vapor-phase imperfections ; the liquidphase activity coefficients; and the excess heat, entropy, and free energy of mixing.Correlation of these properties in nonpolar mixtures is relatively simple, but molecular intcractions in mixtures of polar and nonpolar compounds are more complex and lead to more involved algebraic relations.Even though the excess free energy of mixing does not appear highly sensitive to change in temperature, the heat of mixing depends directly on these changes. Correlations which incorporate temperature variations of the activity coefficients Vol. 5, No. 2 can reflect the true heat and entropy effects in solution if sufficient vaporliquid equilibria are available for a careful and consistent, treatment. This is illustrated with binary mixtures of benzene and the n-aliphatic alcohols, methanol to n-pentanol. These represent some of the more complex cases, as interassociation between unlike molecules as well as dissociation of thc alcohol polymers takes place upon mixing.From the cross-correlated results both isothermal and isobaric equilibria can be predicted a t any prescribed condition in the range of the correlations. This is illustrated for ten alcohol-hydrocarbon binaries and for some ternary and multicomponent mixtures of the components. The more extensive tabulations are available through the American Documentation Institute.* A.1.Ch.E. Journal CORRELAT...

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