Identification and analysis of possible splits for azeotropic mixtures—1. Method for column sections

The identification of possible splits at the finite reflux has been the main challenge for the creation of efficient flowsheets for the separation of azeotropic mixtures. We show in this paper that this problem can be solved by analyzing the mode of infinitely sharp splits, for which trajectories of distillation and pinch lines have special characteristics. The feasibility of sharp splits depends on the relationship of phase equilibrium constants K of components at certain points of the concentration simplex. Pinch branches and bundles of trajectories can arise only when certain relationships of K are satisfied on edges of the concentration simplex. Bundles of trajectories of both sections of column can intersect each other only at complementary relationships of these values at points of components and azeotropes. In this case, there are profiles of concentrations of both sections, which together connect the points of products with each other, i.e., a split is possible. The theory of infinitely sharp split mode determines the mentioned relationships of K. The method of infinitely sharp split mode has been developed on the base of this theory. This method includes the calculation of K at certain points of the concentration simplex. It is not iterative. Therefore, it is very fast, reliable, and can be easily programmed. For the first time, this method covers all n-component azeotropic mixtures, and all types of sharp and half-sharp splits, at which both or one product of column is sharp. This method can find unknown energy-efficient splits for different azeotropic mixtures because it is based on fundamental regularities of distillation. The automatic identification of possible splits is the basis for the synthesis of flowsheets for distillation units and for the conceptual designing of distillation columns. The theory of infinitely sharp split, the method of delimitation of product regions on elements of the concentration simplex for each section of simple columns, and the method of identification of types, characteristics, and terminals of pinch branches are considered in this article.