Equation-of-state methods for the modelling of phase equilibria

Abstract

The equation-of-state methods available for the representation of phase equilibria in multicomponent systems are reviewed. Various types of empirical and semi-empirical equations of state are evaluated with respect to their capability of representing pure component properties in the saturation region. Then, the performance of equations of state is examined for mixtures with special emphasis on systems containing polar and associating components. Various methods are discussed for extending equations of state to mixtures, viz. the classical quadratic and related mixing rules, mixing rules used in conjunction with the corresponding states theory, those derived from excess Gibbs energy models, density dependent mixing rules, improved conformal solution models and methods treating explicitly association and polarity. Attention is focussed on their capability of correlating and predicting multicomponent vapor—liquid and liquid—liquid equilibria over a wide range of pressure, temperature and molecular variety.