Thermodynamics for fluid mixtures near to and far from the vapor–liquid critical point

To describe thermodynamic properties of fluid mixtures near to and far from the vapor–liquid critical point, we need a method where a classical equation-of-state is augmented with a correction based on renormalization group (RG) theory. The advantage of the method described here is that, subject to well-defined assumptions, it can be applied not only to binary mixtures but to mixtures containing any number of components. While our method is based on White’s recursion procedure, our extension to mixtures is based on the isomorphism assumption and on an approximation suggested by Kiselev. To illustrate, calculations are presented for the critical loci of some alkane mixtures containing one discrete component and one pseudo-component whose composition is characterized by a continuous distribution of molecular weight. While critical loci calculated with the RG correction are similar to those calculated by the classical equation-of-state alone, inclusion of the RG correction provides better agreement with experiment.