Page 82 - Distillation theory

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56 Trajectories of Distillation in Infinite Columns Under Infinite Reflux

2
a) 80.1°C

77.3°C

78.6°C 61.7°C Figure 3.13. An example of bonds ambiguity at the
1 3
78.8°C same azeotropes and components boiling tempera-
tures for methyl-ethyl ketone(1)-benzene(2)-chloro-
2 form(3) mixture. Arrows, directions of residium
b) 80.1°C
curves.

77.3°C

78.6°C 61.7°C
1 3
78.8°C

necessary, in particular, at the examination of sequences with recycles when feed
composition depends on the recycle flow rate.
To build a structural matrix, it is necessary to obtain information about com-
positions and boiling temperatures of all the pure components and azeotropes.
It is possible to get this information in various reference books on azeotropy
(Gmehling et al., 1994a, 1994b) and/or by calculation using the known models
of phase equilibrium. In Fidkowski, Malone, & Doherty (1993), there is a gen-
eral algorithm based on the method of homotopy that allows all azeotropes of
n-component mixture to be found simultaneously.
In the majority of cases, the information about azeotropes’ and components’
boiling temperatures is sufficient for the unique determination of connections
between them, but sometimes it is not sufficient. The example of such ambi-
guity is shown in Fig. 3.13 for the mixture methyl-ethyl ketone(1)-benzene(2)-
chloroform(3), the boiling temperatures for which are the following:
◦
◦
◦
◦
◦
T 1 = 79.6 C, T 2 = 80.2 C, T 3 = 61.2 C, T 12 = 78.1 C, T 13 = 79.9 C.
The special algorithms of structural matrix synthesis were developed. In
Petlyuk, Kievskii, & Serafimov (1975a, 1975b) and Petlyuk et al. (1977), the algo-
rithm is based only on the information about azeotropes’ and components’ boiling
temperatures. This algorithm includes the organized sorting out of the stationary
points pairs and the checking of the possibility of connection between them. First,
the binary constituents of n-component mixtures are examined, then the three-
component constituents, four-component constituents, etc.
This algorithm was tested on a number of industrial polyazeotropic mix-
tures: fractions of oxidate of naphtha (14 components, 23 binary and 6 ternary