Fig. 4. Binary T-x phase diagram at a fixed pressure for heterogeneous azeotrope; adapted from the reference: S. Widagdo and W.D. Seider [29].

Note that forming homogeneous azeotrope doesn't mean that the separation method is homogeneous azeotropic distillation, and forming heterogeneous azeotrope also doesn't mean that the separation method is heterogeneous azeotropic distillation, while depending on physical property of the entraîner used. Homogeneous and heterogeneous azeotropic distillation correspond to the real state of the mixture, consisting of the components to be separated and the entraîner, in the liquid phase on a tray or a section of packing in a distillation column.

In addition, either for homogeneous or for heterogeneous azeotropic distillation, the entraîner must be vaporized into the column top and thus much energy is consumed compared with extractive distillation. For this reason, the cases of azeotropic distillation are used less than those of extractive distillation.

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