Liquid-liquid equilibria prediction using the area method

The area method, based on the tangent plane criterion of Gibbs provides a sufficient condition for determining the global minimum Gibbs energy of a system at fixed temperature and pressure. The dimensionless Gibbs energy of mixing curve is integrated using a two-dimensional search technique to completely define the number and compositions of phases present in equilibrium. This work has set out to verify and expand on the possible uses of the area method, initially utilising a semi-empirical liquid-phase model for liquid-liquid predictions only. Several representative binary and ternary liquid-liquid mixtures have been predicted using the area method, with some of these results presented here. The liquid-phase excess Gibbs energy modified UNIQUAC equation has been used for all of the system tested with the interaction parameters fitted using the Nelder-Mead simplex algorithm. Overall, the method is shown to be robust in its ability to predict phase instability as accurately as the phase model being used allows.