Page 92 - Distillation theory

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66 Trajectories of Distillation in Infinite Columns Under Infinite Reflux

2
a)

1 4

13
3

b) c)
1 2 3 4 13 1 2 3 4 13
11 1 1 1 11 1 1 1
2 1 1 2 1 1
3 1 1 1 1 3 1 1 1 1
4 1 4 1
13 1 1 1 13 1 1 1
1 → 13 → 2 → 4 3 → 13 → 2 → 4
Figure 3.18. (a) A acetone(1)-benzene(2)-chloroform(3)-toluene
(4) concentration tetrahedron, and (b) a structural matrix of this
mixture and connection chains 1 → 13 → 2 → 4 and 3 → 13 →
2 → 4. Separatrix surface is shaded.

An example of determination if the feed composition belongs to this or that
product simplex, which was formerly depicted in Fig. 3.14a, is shown in Fig. 3.19.
Besides the direct and the indirect splits that were shown in Fig. 3.14a, we have
three other possible splits: an intermediate split and two splits with one distributed
component. In Fig. 3.19, lines of material balance are shown for all possible splits
of the feed composition under consideration at R =∞ and N =∞.
As an example, let’s examine the industrial polyazeotropic mixture, which is
a by-product of wood pyrolysis (Petlyuk, Kievskii, & Serafimov, 1979). Approxi-
mate composition of this mixture and components boiling temperatures are given
in Table 3.1. Boiling temperatures and compositions of azeotropes are given
in Table 3.2. The structural matrix shown at Fig. 3.20 was synthesized for this
mixture.
It follows from the structural matrix that concentration simplex contains three
distillation regions Reg (1 ⇒ 6, 1 ⇒ 8, and 1 ⇒ 9), with common unstable
∞
node corresponding to the point of acetaldehyde−1. The points corresponding
to ethanol−6, water−8, and diethylketone−9 are stable nodes.
The product simplex Reg simp the feed point belongs to is 1 → 234 → 23 →
38 → 568 → 58 → 78 → 89 → 8 (distillation region is 1 ⇒ 8) (at Fig. 3.20 this
bonds chain is marked). Here are feasible splits in one column without distributed
pseudocomponents: