From UNIFAC to Modified UNIFAC (Dortmund)

The group contribution method UNIFAC has become very popular because of its availability via commercial process simulators, its reliably predicted vapor−liquid equilibrium (VLE) results, its simple usage, and, above all, its large range of applicability. Nevertheless, the original UNIFAC shows a few weaknesses. For example, there is no chance to describe simultaneously VLE data and excess enthalpies with the required accuracy. This means that the temperature dependence of the activity coefficient following the Gibbs−Helmholtz equation cannot be described correctly. Furthermore, predictions of the real phase behavior in the dilute region and for asymmetric systems can lead to poor results. The aim of this paper is to show how the mentioned weaknesses were overcome by using modified UNIFAC (Dortmund) instead of the original UNIFAC method, in which the required temperature-dependent parameters are fitted simultaneously to a large database covering various types of reliable phase equilibrium and excess proper...