Page 131 - Distillation theory

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4.10 Questions 105

4.8.2. Four-Component Azeotropic Mixtures

Figure 4.25 shows the boundary of semisharp reversible distillation for the
four-component mixture acetone(1)-benzene(2)-chloroform(3)-toluene(4). This
boundary is a surface passing through point of azeotrope 13 and through the ends
of possible product composition segments at edges 2-3 and 3-4 at separation of
mixtures 1,2,3 and 1,3,4 correspondingly. For the points x best lying on this surface,
B
the trajectory of reversible distillation goes to point of branching x branch , from
rev
which three branches of the trajectory go to bottom section nodes 1, 3, and 13
1
↑ →N rev
3
(x best →x branch →N ).
B rev rev
↓ →N 13
rev
4.9. Conclusion
At sharp reversible distillation, the heaviest component is absent in the top prod-
uct and the lightest one is absent in the bottom product. The product points of
sharp reversible distillation should belong to possible product composition regions
Reg or Reg on boundary elements of concentration simplex. The trajectory of
D B
the section at sharp reversible distillation goes from the product point x D or x B to
the tear-off point x t or x t inside boundary element and then from this point
rev,D rev,B
to the feed point x F inside the concentration simplex. In the points of the section
trajectory, inside the concentration simplex including the tear-off point, the pa-
rameter L/V is equal to the phase equilibrium coefficient K j of the component
absent in the product of the section. In the points of reversible distillation trajec-
tory of extractive section, the phase equilibrium coefficient K j of the component
that is absent in pseudoproduct should be smaller than that of the top product
components K D,i and should be higher than that of the entrainer components
K E,i . In the tear-off points of reversible distillation trajectory from k-component
boundary element into (k + 1)-component boundary element, the equation of
reversible distillation should be valid both for the components i present in the
k-component boundary element and for the component j, which is absent there. It
allows definition of the boundaries of possible product composition region Reg
D
or Reg at sharp reversible distillation.
B
To define the frame of possible product composition regions Reg or Reg
D B
at the edges of concentration simplex, it is enough to determine values of phase
equilibrium coefficients in the points of edges for the components present and for
the component, which is absent in the product.

4.10. Questions

1. Define the main notions: (1) region of reversible distillation of top Reg h , bot-
rev,r
tom Reg l , and intermediate sections Reg m ; (2) regions of trajectory tear-off
rev,s rev,e
Reg t(k) and Reg t(k) and Reg t(k) ; (3) region of possible product points of sharp
rev,r rev,s rev,e
reversible distillation Reg , Reg , and Reg ; and (4) node of trajectory bundle
D B D,E
of reversible distillation N rev .