New Dieterici-type equations of state for fluid phase equilibria

The vapour–liquid critical properties of binary mixtures are calculated using conformal solution theory, the one-fluid model, the van der Waals and Carnahan–Starling–van der Waals equations, and a new Dieterici-type equation of state reported recently [J. Chem. Phys. 115 (2001) 371]. Comparisons with experimental data are reported for the critical properties of n-alkane mixtures ranging from methane to n-octane. A common feature of these comparisons is that the new Dieterici-type equation of state yields good prediction of the pressure–temperature critical locus without the need to use arbitrary adjustable parameters in the combining rules for mixture properties. In particular, the Dieterici-type equation correctly predicts the maximum in the pressure–temperature curve. In contrast, the van der Waals-type equations are inaccurate. Dieterici-type equations of state may have a useful rule in the prediction of fluid phase equilibria by reducing the need for adjustable parameters in the combining rules.