Present status of group-contribution methods for the synthesis and design of chemical processes

The reliable knowledge of the phase equilibrium behavior and the excess properties of the system to be separated is a prerequisite for the synthesis, design and optimization of separation processes. Two different approaches (g(E)-models, equations of state) can be used to predict the behavior of multicomponent systems using binary data alone. When experimental data are missing, group-contribution methods can be successfully applied to predict the phase equilibrium behavior or to supplement the existing data base. While at the beginning the main objective of group-contribution methods was the prediction of vapor-liquid equilibria (VLE) of subcritical compounds in a limited temperature range, an improved model allows not only to predict VLE, bur also solid-liquid equilibria (SLE), liquid-liquid equilibria (LLE), gamma(x) and h(E) in the whole composition and a large temperature range. By using group-contribution methods in g(E)-mixing rules of equations of state the advantages of the phi-phi-approach can be exploited and the range of applicability of the group-contribution concept can be extended to supercritical compounds and for the prediction of other important properties (densities, enthalpies, etc.). In this paper, the present status and typical results of the different group-contribution models will be shown and an outlook on future developments will be given. (C) 1998 Elsevier Science B.V.