The breaking up of azeotropic mixtures

The breaking up of azeotropic mixtures. The behaviour of constant boiling point mixtures simulates that of a pure compound, because the composition of the liquid phase is identical with that of the vapour phase. The composition, however, depends upon the pressure at which the distillation is conducted and also rarely corresponds to stoichiometric proportions. The methods adopted in practice will of necessity depend upon the nature of the components of the binary azeotropic mixture, and include — 

---

The breaking up of azeotropic mixtures Steam distillation. Distillation of a pair of immiscible liquids Distillation with superheated steam. ... 

Vapor-liquid equilibrium data at atmospheric pressure (690-700 mmHg) for the systems consisting of ethyl alcohol-water saturated with copper(II) chloride, strontium chloride, and nickel(II) chloride are presented. Also provided are the solubilities of each of these salts in the liquid binary mixture at the boiling point. Copper(II) chloride and nickel(II) chloride completely break the azeotrope, while strontium chloride moves the azeotrope up to richer compositions in ethyl alcohol. The equilibrium data are correlated by two separate methods, one based on modified mole fractions, and the other on deviations from Raoult s Law. 

Azeotropic mixtures require special methods for their separation, which usually consist of adding a third component that has the ability to "break" the azeotrope. Perhaps tire most famous case is that of ethanol-water, which has an azeotropic mole fraction in ethanol of 0.8943 at atmospheric pressure (Table 6.8). Here the added component can be benzene and results, on distillation, in the recovery of pure ethanol and a ternary azeotrope containing benzene. That mixture, on condensation, results in two immiscible aqueous and organic layers, which are separated and further processed by distillation. Changing the operating pressure Pj is yet another potentially useful way of breaking an azeotrope. This is taken up in Illustration 6.14. 

---