To achieve the separation of an azeotropic mixture by using pressure-swing dis­tillation, the manipulation of the column pressure is required, e. g., by utilizing a second distillation column working under vacuum conditions (Figure 8.2). This type of distillation makes use of the change of the vapor-liquid phase equilibrium at lower pressures than atmospheric (vacuum) leading to the disappearance of the azeotrope. The pressure required to eliminate the azeotrope in an ethanol-water mixtures is less than 6 kPa. But to obtain a high purity product, distillation columns with a large number of plates (above 40) and a high reflux ratio are needed. These conditions imply significant capital costs (large column diameters) and increased energy costs due to the maintenance of vacuum in distillation towers with many plates. This configuration has no fluxes or refluxes connecting the two columns. In general, pressure-swing distillation cannot always be employed; its utilization is limited to mixtures with azeotropes susceptible to be displaced with small changes of pressure, which is not exactly the case in ethanol-water systems.