Page 124 - Distillation theory

P1: FCH/FFX P2: FCH/FFX QC: FCH/FFX T1: FCH
0521832772c04 CB644-Petlyuk-v1 June 11, 2004 17:49

98 Trajectories of Thermodynamically Reversible Distillation

Let’s show in the beginning that, for example, for an ideal mixture, for which
K 1 > K 2 > K 3 , in the intermediate section not the heaviest component as for the
top section and not the lightest component as for the bottom section, but the
intermediate component m = 2 can be exhausted.
Let’s take a column, the main feeding of which contains all three components
andadditionalupperfeeding(entrainer, E ≡ F 2 , x E ≡ z F2 )containsonlytheheav-
iest component 3 (x E3 = 1). We call this the column of autoextractive distillation
(Fig. 4.18a).
Let’s accept that the top product point coincides with vertex 1 (x D = 1). Then
it follows from Eq. (4.22) that the pseudoproduct point should lie on the straight
line passing though side 1 (top product)-3 (entrainer).
It follows from Eq. (4.22) that

d =−F 2 z F2,3 =−F 2 (4.25)
3
Two cases are possible:

D < 0 (4.26)
D > 0 (4.27)

2
a)

y
x

' x
D
1 t 3
x
rev
2

b)

x
y

' x
D
1 x rev 3
t
Figure 4.19. Reversible intermediate section trajectories of sharp
auto-extractive distillation of ideal ternary mixture (K 1 > K 2 > K 3 ):
(a) D < E, and (b) D > E. Component 1, overhead product; com-
ponent 3, entrainer; x and y, composition in arbitrary cross-section;
x , composition of pseudoproduct.

D