General Methods of Fractionation

There are several methods by which fractionation can be obtained. The more important among them are (1) successive distillation of condensed distillate, (2) fractional condensation, and (3) rectification. 

Successive Distillation. The first method, successive distillation of the condensed distillate, can be shown best by referring to Fig. 2-1. Starting with a large amount of liquid of the composition X5 which boils at 760 mm. pressure, temperature U, a small amount of vapor of the composition Xi is removed from the apparatus and condensed, giving a liquid of the composition Xi. If this new liquid is again distilled, the first portion of the distillate will have a composition X2. Continuing this process, successive compositions of the distillates can be estimated by following a series of steps which eventually approach the point C, pure carbon disulfide, as a limit. 

Removal of any vapor of the composition Xi from the liquid of the composition xs will change the composition of the liquid in the direction of pure carbon tetrachloride. Therefore, if the distillation of the liquid is continued, the composition will approach pure carbon tetrachloride as a limit, and the last of the liquid to be distilled would have this composition. 

It is therefore possible by a systematic series of distillations to separate any mixture of carbon disulfide and carbon tetrachloride into practically pure carbon disulfide and pure carbon tetrachloride. This systematic fractionation may be shown diagramatically as in Fig. 5-1, in which the original mixture (1) is divided into a distillate (3) and a residue (2). (3) and (2) are then distilled separately and produce dis- 

The procedure outlined in Fig. 5-1 would appear to result in a number of intermediate products and only a small amount of the desired 

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