Page 238 - Distillation theory

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212 Distillation Trajectories in Infinite Complex Columns and Complexes

the boundary element of the concentration simplex there is a heteroazeotrope–
unstable node x Haz = N , and top product point y D is close to it (the example
−
is Fig. 6.16d); and (3) at the boundary element of concentration simplex there
is a heteroazeotrope–saddle x Haz = S, the bottom product point x B is located at
this boundary element in the bottom product region Reg B (the example is Fig.
6.16e,f).
Heteroextractive distillation can be effectively used if at the boundary element
of concentration simplex there is a heteroazeotrope–unstable node x Haz = N −
(the example is Fig. 6.17b) or saddle x Haz = S (the example is Fig. 6.17a), and at
the same boundary element there is the intermediate section trajectory tear-off
t
region Reg .
e
In all the above-mentioned cases of application of heteroazeotropic or het-
eroextractive distillation, the second product point of distillation column (of the
second product, obtained at that column end, where there is no decanter) should
belong to the possible product region at the corresponding boundary element
of concentration simplex (of bottom product Reg B at Fig. 6.16a ÷ d and at Fig.
6.17a,b or of top product Reg D at Fig. 6.16e,f).

6.10. Conclusion

The theory of trajectory tear-off from boundary elements of concentration sim-
plex and the theory of joining of section trajectory bundles find possible product
composition regions Reg D and Reg B and to calculate the minimum reflux mode
not only for simple columns, but also for complex columns and complexes.
For intermediate sections of columns with side products, with side sections,
and of Petlyuk columns location of the stationary points of separatrix trajectory
min,R
bundles (regions Reg ) is the same as for simple columns, product composi-
sep,int
tions of which coincide with pseudoproduct compositions of these intermediate
sections (possible product regions Reg D and Reg B of simple columns and possible
pseudoproduct regions Reg D and Reg B of intermediate sections coincide). This
extends the use of methods of minimum reflux mode calculation worked out for
the simple columns to the previously mentioned complex columns and complexes.
The location of intermediate sections trajectories of columns with two feeds, in-
cluding those at extractive, heteroazeotropic, and heteroextractive distillation, has
fundamental distinctions from that of section trajectories of the simple columns.
At sharp extractive or heteroextractive distillation, pseudoproduct point x of
D,e
the intermediate section should be located at the continuation of the boundary
element, to which components of top product and of entrainer belong. If this con-
dition is valid, the whole trajectory bundle of the intermediate section including
t
trajectory tear-off point x from the mentioned boundary element is located in
e
the region Reg R where the top product components are more volatile and the
w,e
entrainer components are less volatile than the rest of components. The trajectory
t
+
tear-off point of the intermediate section is the stable node (x = N ). The con-
e
ditions of intermediate section trajectory tear-off in different points of trajectory
t
tear-off region Reg allow to determine limit modes of extractive distillation for
e
each mixture – the mode of minimum flow rate of the entrainer E min , and for the