Page 119 - Distillation theory

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

4.5 Trajectories Bundles of Reversible Distillation for Multicomponent Mixtures 93

x i new
1
) 2 (
x
i
) 4 (
x
i Figure 4.12. Iteration of component concentration at
x ) 3 ( old
i calculation reversible section trajectories. x and
i
x i ) 1 ( x new , initial and calculated concentration of compo-
i
(1)
(3)
(4)
(2)
nent; x , x , x , x , successive iteration concen-
i i i i
tration of component i.
old
x
0 1 i
x i ) 2 ( x ( )4 i x i ) 3 ( x i ) 1 (
of components. An easier way to get the general picture of the location of trajec-
tory bundles is to scan the whole area of the concentration triangle, defining at
each point the values K i and – with the help of Eq. (4.6) ÷ (4.13) – values x D and
x B (Petlyuk & Serafimov, 1983).
4.4.2. Scanning the Sides of the Concentration Triangle
It was shown (Petlyuk, 1986) that the diagram of reversible distillation of any
three-component mixture can be forecasted by scanning only the sides of the
concentration triangle, defining at each point the values of phase equilibrium
coefficients of all the components and using Eqs. (4.19) and (4.20). The latter
way defines trajectory tear-off segments Reg t(2) or Reg t(2) and possible product
rev,r rev,s
(2) (2)
segments Reg or Reg . The node points N rev of the trajectory bundles are
D B
determined hypothetically on the basis of the data on the location of azeotropes
points and α-points.
The diagrams of reversible distillation were constructed for some types of three-
component azeotropic mixtures. It is interesting that some types of mixtures with
one binary azeotrope and with two distillation regions [types 3 and 5 according
to classification (Gurikov, 1958)] permit sharp separation into component and
binary zeotropic mixture at some feed compositions. The mixture acetone(1)-
benzene(2)-chloroform(3) is an example of such mixture.

4.5. Trajectories Bundles of Reversible Distillation for
Multicomponent Mixtures

Let’s examine the analysis of structure of reversible distillation trajectory bun-
dles at the concrete example of four-component mixture acetone(1)-benzene(2)-
chloroform(3)-toluene(4). At the beginning, the segments of the components or-
ijk
der Reg at the edges of the concentration tetrahedron are defined by means of
ord
scanning and calculation of the values K i (Fig. 4.13a). The corresponding regions
ijk
of components order Reg in the tetrahedron are shown in Fig. 4.13b and in its
ord
faces – in Fig. 4.14. The whole face 1-2-3, where the component 4 that is absent