Zeotropic multicomponent mixture

To understand the mutual behavior of the components depending on the degree of the mixture s nonideahty caused by the difference in the components molecular properties, it is better to use graphs yi - x, T - xi,T - yi,Ki - xi, and K2 - xi (Fig. 1.2). In Fig. 1.2, the degree of nonideality increases from atoh.a is an ideal mixture, h is a nonideal mixture with an inflection on the curve y - xi (a and b are zeotropic mixtures), c is a mixture with a so-caUed tangential azeotrope (curve yi - xi touches the diagonal in the point xi = 1), d is an azeotropic mixture with minimum temperature, c is a mixture with a so-called inner tangential azeotrope, / is a mixture with two azeotropes, g is a heteroazeotropic mixture, and h is an azeotropic mixture with two liquid phases. Azeotrope is a binary or multicomponent mixture composition for which the values of phase equihbrium coefficients for all components are equal to one ... 

Fractionation of multicomponent zeotropic mixtures (i.e., mixtures without azeotropes) into all constituents can be performed by a sequence of distillation columns. Generally, different sequences of columns are feasible to achieve the same products. However, investment costs and energy demand of the feasible processes may... 

For zeotropic mixtures, the main difficulty of the solution of synthesis task consists of the large number of alternative sequences that have to be calculated and compared with each other in terms of expenditures. This number greatly increases when the number of the products into which the mixture should be separated increases. The best sequence (or several sequences with close values of expenditures) depends on the concentrations of the components in the mixture under separation and on the field of phase equilibrium coefficients of the components in the concentration simplex. To ensure the solubility of the task of synthesis for multicomponent zeotropic mixtures, it is necessary to create a program system that would include as main modules programs of automatic design... 

The theory of trajectory bundles described in Chapters 5 and 6 ensures the possi-bihty of identification of all feasible splits of multicomponent azeotropic mixtures. The software for synthesis of separation units for multicomponent azeotropic mixtures should include, besides the module of identification of feasible splits, a module of preliminary selection of these splits (i.e., choice of the most interesting splits, a module of determination of necessary recycle flow rates, a module of choice of entrainers, and also modules entering into the system of synthesis for zeotropic mixtures). 

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