Prediction of azeotropic behavior using equations of state

A shortcut method is developed to determine if an equation of state (EOS) is capable of predicting azeotropes in binary systems and if the azeotrope meets the critical gas–liquid equilibrium line. The method suggested allows an a priori prediction of subcritical azeotropes and an exact prediction of the azeotropic point (if any) at critical conditions. In addition, the approach developed in this work avoids computation of critical lines and simplifies phase equilibrium calculations for mixtures. The technique may be applied to every EOS (and/or mixing rule model), provided that the PVT relation exhibits the van der Waals loop in subcritical ranges. Examples are presented using cubic EOS.