The group contribution method Modified UNIFAC (Dortmund) is a well-known model for the reliable prediction of phase equilibria (VLE, LLE, SLE of eutectic systems, azeotropic data and γ∞) and excess properties (h E). Compared to the original UNIFAC method, Modified UNIFAC (Dortmund) provides a much better description of the temperature dependence of the activity coefficients, and a more reliable presentation of the real behavior of phase equilibria in the dilute region; in addition, it also leads to better results for asymmetric mixtures (i.e., those involving molecules of very different size). Nevertheless, the parameters published previously sometimes give poor results, especially at high (>140 °C) and low (<0 °C) temperatures. To overcome these weaknesses, solid−liquid equilibria (SLE) of eutectic systems and enthalpies of mixing (h E) at high temperatures have been included additionally in the database used for fitting the required group interaction parameters in order to ensure reliable results at low and high temperatures. This paper contains details of 78 new or revised pairs of group interaction parameters for Mod. UNIFAC (Do) covering a large temperature range.

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 property data. Furthermore, 10 new modified UNIFAC (Dortmund) parameter pairs for the new main group "epoxides" and the interactions between aromatics and perfluorinated compounds are given.

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Solid−liquid equilibria of the seven binary systems benzaldehyde + benzene, benzaldehyde + dodecane, benzaldehyde + cyclohexane, cyclohexane + phenol, methylcyclohexane + tetrachloromethane, 2-butanone + water and acrylic acid + propionic acid have been measured by the visual method. Furthermore, the liquid−liquid equilibrium of the system benzaldehyde + dodecane was determined analytically using gas chromatography. The experimental data of the eutectic systems were compared with predicted results using the modified UNIFAC (Dortmund) method and in two cases correlated with the NRTL equation.