Calculation of multi-phase equilibria using the equal area rule with application to hydrocarbon/water mixtures

We have used an efficient, new Gibbs minimization method with an equation of state (EOS) model to predict phase equilibria for hydrocarbon/water binary mixtures. The method utilizes the observation by Eubank and Hall (1995) that a plot of the derivative of the Gibbs energy of mixing against composition exhibits phase loops similar to those associated with the Maxwell rule. Equilibrium exists when the positive and negative areas are equal above and below a specific value of the derivative. Hence, we call the method the Equal Area Rule (EAR). The EAR application procedure automatically performs a stability analysis for the system. EAR also presents exciting possibilities when calculating phase equilibria for multi-component mixtures. Shyu et al. (1995) have applied the method to ternary liquid-phase systems using activity coefficient models.