Page 345 - Distillation theory

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8.9 Questions 319

For homogeneous azeotropic mixtures, the system of automatic sequencing also
includes the stage of determination of possible product compositions (presynthe-
sis) and stage of heuristic selection of splits.
Presynthesis includes the following steps:

1. Scanning of phase equilibrium coefficients of all components in points at
all the edges of concentration simplex.
2. Determination of coordinates of ends of segments Reg t(2) , Reg t(2) , Reg t(2)
r s m
of trajectory tear-off of top, bottom, and intermediate section at edges
of concentration simplex C n at separation of initial mixture and of
all its constituents C (k) with number of components k from three to
(n − 1).
(2) (2)
3. Determination of possible composition regions Reg , Reg of top and
D B
bottom products at reversible distillation of all three-component con-
stituents C (3) of initial mixture.
4. Determination of coordinates of ends of segments of possible top and bot-
(2) (2)
tom products Reg , Reg at edges of concentration simplex C n at sep-
D B
aration of initial mixture and of all its constituents C (k) with a number of
components k from three to (n − 1).
5. Determination of coordinates of vertexes of polygons, polyhedrons, or
(m) (m)
hyperpolyhedrons of possible top and bottom products Reg D , Reg B at
faces and hyperfaces of concentration simplex C n at separation of initial
mixture and of all its constituents C (k) with a number of component k from
four to (n – 1).
6. Determination of possible sharp splits in columns with one feeding with-
out distributed components and with one distributed component with re-
cycles or without them and in the columns with two feedings with one- or
two-component top product and one-component or more component au-
toentrainer at separation of initial mixture and of all its constituents with
number of components from two to (n − 1).

For heteroazeotropic mixtures, presynthesis also includes the most interesting
variants of heteroazeotropic and heteroextractive distillation.
For petroleum mixtures, their peculiarities predetermine the choice of the main
distillation complex (column with side strippings) and of main sequence (atmo-
sphericandvacuumcolumns),butdifferentmodificationsarepossiblefordifferent
sets of products and compositions of crude are possible. These modifications may
significantly improve the economy of the equipment.

8.9. Questions

(2)
1. Let the following segments of component order Reg : 12435, 12453, 21453, and
ord
24153 be located in the direction from vertex 1 to vertex 2 at edge 1-2 of the
concentration pentahedron.
a. Can component 1 be top product?
b. Can mixture 1,2 be top product?