Topological analysis of vapor–liquid equilibrium diagrams for distillation process design

Abstract

Residues curve and distillation line maps have become an important tool for conceptual distillation process design. These maps are based solely on thermodynamic information on the vapor–liquid equilibrium and are called vapor–liquid equilibrium (VLE) diagrams here. They give, among other, information on the composition regions, in which products of a distillation process can be found. The entire composition simplex can be divided into distinct distillation regions separated by distillation boundaries, which usually cannot be passed in distillative separations. Up to now, VLE-diagrams are mostly used for the well-studied case of ternary systems, for which analysis and visualization is straightforward. However, in many applications, systems containing more than three components have to be considered and, hence, multicomponent VLE-diagrams are needed. In the present work, two approaches are suggested for automated synthesis of VLE-diagrams, which can be applied to any system of interest without limitations to its complexity. The first method is hierarchical and based on a sequential consideration of all constituent subsystems of the system of interest and combining the results to synthezise the VLE-diagram. The second approach is evolutional, because the multicomponent system is considered as it is, but the structure of the diagram is changed from the simplest state of a zeotropic system to the end state with all azeotropes. Both approaches are in principle combinatorial, but the first one needs consistency criteria to discriminate the proposed diagrams, whereas the second one produces always consistent diagrams.