Four-component mixtures reversible distillation trajectories

Let s examine the analysis of structure of reversible distillation trajectory bundles at the concrete example of four-component mixture acetone(l)-benzene(2)-chloroform(3)-toluene(4). At the beginning, the segments of the components order Regff at the edges of the concentration tetrahedron are defined by means of scanning and calculation of the values Ki (Fig. 4.13a). The corresponding regions of components order Reg in the tetrahedron are shown in Fig. 4.13b and in its faces - in Fig. 4.14. The whole face 1-2-3, where the component 4 that is absent... 

Figure 4.23. Reversible intermediate section trajectories for extractive distillation of four-component mixtures (a) mixture 1,2 is overhead product, and component 4 is en-trainer (b) component 1 is overhead product, and mixture 3,4 is entrainer. Short segments with arrows, liquid-vapor tie-lines in arbitrary cross-sections.

Figure 5.25 shows the evolution of top section trajectory bundle at separation of four-component ideal mixture, when the product is ternary mixture 1,23 (i.e., at indirect split) K >K2>Kj,> K, xdi -I-xd2+xd3 = 1). At small values of the parameter L/V, the stable node Ai+ that at the increase of the parameter L/F moves away from the product point along reversible distillation trajectory appears at face 1-2-3 (Fig. 5.25a). After this node reaches reversible distillation trajectory tear-off point from face 1-2-3 inside concentration tetrahedron, it turns into the saddle...

Locations of reversible distillation trajectories depends on position of pseudoproduct point (i.e., on compositions and on flow rates of feeds and of separation products, as is seen from Eq. [6.3]). Difference from the top and bottom sections appears, when the pseudoproduct point of the intermediate section is located outside the concentration simplex (i.e., if concentrations of some components x j)i obtained from Eq. [6.3], are smaller than zero or bigger than one), which in particular takes place, if concentration of admixture components in separation products are small components (i.e., at sharp separation in the whole column). The location of reversible distillation trajectories of the intermediate sections at x j i < 0 or x, > 1 differs in principle from location of ones for top and bottom sections, as is seen from Fig. 6.3 for ideal three-component mixture (Ki > K2 > K3) and from Fig. 6.4 for ideal four-component mixture (Ki > K2 > K3 > K4). 

Figure 6.4. Reversible distillation trajectories of ideal four-component mixtures (Ki > K2 > K3 > K4) for intermediate section of two-feed column (a) <0 (b) 4 < 0. Solid...

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