azeotrooppi

Azeotrooppi, or azeotrope, is a mixture of two or more liquids that boils at a constant composition. At a given pressure the liquid and vapor phases have the same composition at the azeotropic point, so the mixture behaves like a single substance during distillation. This non-ideal behavior arises from interactions between the components that cause deviations from Raoult’s law.

Azeotropes are classified by their boiling behavior. In a minimum-boiling azeotrope, the boiling point is lower than those of the pure components. In a maximum-boiling azeotrope, the boiling point is higher. The distinction reflects how the components preferentially distribute between liquid and vapor and how this distribution changes with composition.

A well-known example is the ethanol–water system at atmospheric pressure, which forms a minimum-boiling azeotrope around 95.6% ethanol (roughly by volume) with a boiling point near 78.2 °C. Because the vapor and liquid have identical compositions at this point, simple distillation cannot produce ethanol far purer than the azeotropic composition.

Breaking azeotropes requires specialized methods. Azeotropic distillation uses a third component (an entrainer) to form a new azeotrope and shift the separation. Other approaches include extractive distillation with solvents that alter relative volatilities, pressure-swing distillation, or membrane and adsorption techniques. In chemical engineering, understanding azeotropes is essential for designing purification processes and for producing high-purity solvents and products.