Group contribution methods - ideal tools for the synthesis and design of separation processes

Even though the reactor can be considered as the heart of a chemical plant, the greatest part of the costs (investments, operating costs) is in most cases due to the separation step in which the compounds leaving the reactor are separated in such a way that the desired products are obtained with the required purity, side-products are removed and unconverted reactants recycled. Various thermal separation processes can be applied for the separation. The computer supported synthesis and design of separation processes requires a reliable knowledge of the phase equilibrium behavior of the system to be separated. During the last years powerful thermodynamic models have been developed, which allow the calculation of the various phase equilibria (VLE, LLE, SLE, etc.) of multicomponent systems using only binary experimental data. Furthermore with the help of a comprehensive data bank (Dortmund Data Bank) reliable predictive group contribution methods (g(E)-models, equations of state) with a large range of applicability have been developed. In this paper the current status and typical results of the group contribution methods modified UNIFAC and PSRK are presented. At the same time the potential of these group contribution methods for the synthesis and design of separation processes will be highlighted.