ANALYSIS OF THE RELATIONSHIP BETWEEN TERNARY MIXTURES AND THEIR BINARY SUBSYSTEMS AS REPRESENTED BY THE UNIQUAC AND NRTL MODELS

The second derivative of the Gibbs free energy of mixing, G11, was cal culated for the binary mixtures water + alcohol and solvent + alcohol (alcohol is methanol or ethanol, solvent is n-amyl acetate, iso-amyl a cetate, hexyl acetate or l-octanol) using, for G, binary UNIQUAC and N RTL equations with interaction parameters obtained by fitting the corr esponding ternary equations to liquid-liquid equilibrium data for the ternary systems water + alcohol + solvent. Apart from the usual result that the binary interaction parameters of the UNIQUAC and NRTL equati ons, and the corresponding thermodynamic descriptions of binaries in t erms of G11, depend heavily on the system from which they have been ob tained (which should be borne in mind when using the binary parameters in calculations for multicomponent systems), the chief conclusion of this work is that the UNIQUAC and NRTL models do not imply any consist ent relationship between the slopes of the ternary tie-lines and the c haracteristics of the G11 of the corresponding homogeneous binary mixt ures.