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 vap or-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-Hel mholtz 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 w eaknesses were overcome by using modified UNIFAC (Dortmund) instead of the original UNIFAC method, in which the required temperature-dependent paramet ers are fitted simultaneously to a large database covering various types of reliable phase equilibrium and excess property data. Furthermore, 10 new m odified UNIFAC (Dortmund) parameter pairs for the new main group "epoxides" and the interactions between aromatics and perfluorinated compounds are gi ven.