Simultaneous correlation of vapor―liquid equilibrium and excess enthalpies for binary mixtures of n-hexane and n-octane with hexane isomers

Abstract Vapor-liquid equilibrium (VLE) data for binary mixtures of n -hexane and n -octane with hexane isomers are accurately predicted from excess enthalpy ( h E ) data using the prediction method of Hanks, Gupta and Christensen in conjunction with several well-known models for the excess Gibbs energy. The accuracies of the correlation of data for these nearly ideal mixtures are of similar magnitude to those obtained for the typical non-ideal mixtures previously studied using this method. When the usual approach to correlate h E and VLE data is attempted, the higher relative errors associated with the evaluation of the small excess Gibbs energies characteristic of the almost ideal systems lead to large errors in the values of the excess enthalpies which are also small. This seems to be a consequence of the error magnification associated with the differentiation process required to obtain h E data from VLE data.