8.1. Breaking Azeotropes with Other Separators

Azeotropic systems normally limit the separation that can be achieved. For an azeotropic system such as ethanol and water (shown in Figures 2-2 and 4-13), it isn’t possible to get past the azeotropic concentration of 0.8943 mole frac ethanol with ordinary distillation. Some other separation method is required to break the azeotrope. The other method could employ adsorption (Chapter 18), membranes (Chapter 17), extraction (Chapter 13), and so forth. It could also involve adding a third component to the distillation to give the azeotropic and extractive distillation systems discussed later in this chapter.

Two ways of using an additional separation method to break the azeotrope are shown in Figure 8-1. The simplest, but least likely to be used, is the completely uncoupled system shown in Figure 8-1A. The distillate, which is near the azeotropic concentration, is sent to another separation device, which produces both the desired products. If the other separator can completely separate the products, why use distillation at all? If the separation is not complete, what would be done with the waste stream?