Page 73 - Distillation theory

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3.3 Distillation Trajectories of Finite and Infinite Columns 47

3.3.4. Feasible Splits for Ideal Mixtures

At some boundary values of the parameter D/F, at which it is equal to the con-
centration of the lightest component or to the sum of concentrations of a few light
components in the feeding, we have sharp separation without distributed compo-
nent and at other values of the parameter D/F we have sharp separation with one
distributed component. These are sharp splits without distributed components:
1 : 2,3,4; 1,2 : 3,4; 1,2,3 : 4 (here and further the components of the top product are
shown before the colon and those of the bottom product follow the colon).
In the case of sharp separation of ideal mixture without distributed compo-
nents, the initial mixture is separated into two different groups of components:
the top product components and the bottom product components. The heaviest
component among the top product components is called the light key compo-
nent and the lightest component among bottom product components is called
the heavy key component. The light and the heavy key components neighbour in
volatility.
The following splits in Fig. 3.4 belong to the splits with one distributed compo-
nent: 1,2 : 2,3,4, lines 1 and 5; 1,2,3 : 3,4, lines 2 and 6.
Splits with the number of distributed components bigger than one at R =
∞ and N =∞ are impossible (e.g., for four-component mixture, the split 1,2,3 :
2,3,4 with two distributed components is impossible).
Another important property of the mode of R =∞ and N =∞ consists in
the following: feasible splits do not depend on the form of c-lines inside the con-
centration simplex and on the availability of α-lines. For example, for the ideal
mixture in Fig. 3.5a and for the zeotropic mixture in Fig. 3.5b, the set of feasible
splits is one and the same: 1 : 2,3; 1,2 : 3 and 1,2 : 2,3.
At an arbitrary location of the point x F , any point of edges 1-2 and 3-4 and
any point of faces 1-2-3 and 2-3-4 (Fig. 3.4) can be top x D or bottom x B product
point. Further, we call the set of possible product points in each of the boundary

2
a)

123
1 3
Figure 3.5. C-lines for ternary zeotropic mixtures: (a) ideal mix-
ture, and (b) mixture with α-line. 123, 213, component order
2 regions.
b)

α 12

123
213
1 α 12 3