Page 110 - Distillation theory

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0521832772c04 CB644-Petlyuk-v1 June 11, 2004 17:49

84 Trajectories of Thermodynamically Reversible Distillation

be the heaviest (for the top section) and the lightest (for the bottom section) along
this trajectory].
Therefore, one or several trajectory bundles, filling up that region inside the
concentration simplex, where one and the same component is the heaviest (for
the top section) or the lightest (for the bottom section), will correspond to all
the product points located at one and the same (n − 1) component edge, face, or
hyperface of concentration simplex. We call this region the region of reversible
j=h j=l
distillation Reg (n−1) or Reg (n−1) (Petlyuk, 1978). It is the unification of several
rev,r rev,s
i i ijk
regions of equal order of components Reg ord , and it is separated from other
regions of reversible distillation by the corresponding α-lines, surfaces, or hyper-
surfaces.
As one can see in Fig. 4.2, the trajectory of each section at sharp reversible
distillation consists of two parts: the part, located inside the (n − 1) component
boundary element C n−1 of concentration simplex, lying between the product point
t
x D or x B and the tear-off point of the trajectory from this boundary element x ,
rev
and the part located inside concentration simplex C n , lying between the tear-off
point of the trajectory and the feed point x F . Only the second part should be
located inside a region of reversible distillation Reg h or Reg l , and product
rev,r rev,s
point x D or x B can lie outside this region.
Unlike trajectories of distillation at infinite reflux, which may come off the
boundary elements of the concentration simplex in the saddle points S only, re-
t
versible distillation trajectories come off in ordinary points x .
rev
Let’s illustrate the location of trajectory bundles of reversible distillation by
the example of three-component acetone(1)-benzene(2)-chloroform(3) mixture
with one binary saddle azeotrope with a maximum boiling temperature (Fig. 4.7)

2

a) α
23
α 13

Figure 4.7. Sharp reversible section trajectories of ace-
1 α 3 tone(1)-benzene(2)-chloroform(3) mixture: (a) rectifying
23 13
section, (b) bottom section. Double line, possible overhead
product Reg rev,D ; thick solid line, possible bottom product
2
Reg rev,B ; dotted lines with arrows, reversible section tra-
jectories; dotted lines without arrows, lines of stationarity.
b) α 23

α
13

1 α 23 13 3