An azeotropic mixture is a mixture of two or more liquids that boil at a constant temperature with a vapor composition identical to the liquid composition. This means the proportions of the constituents in the vapor phase remain the same as in the liquid phase during boiling, making it impossible to separate the components by simple distillation. The boiling point of an azeotrope can be either higher or lower than the boiling points of its individual components, and such mixtures are also called constant boiling point mixtures.
Key Characteristics of Azeotropic Mixtures
- The vapor and liquid phases have the same composition at boiling.
- The boiling point is fixed and can be either a minimum or maximum relative to the components.
- The mixture behaves differently from ideal solutions as it does not follow simple Raoult's law separation.
- Because of the constant boiling composition, components cannot be separated by classical fractional distillation.
Types of Azeotropes
- Positive azeotropes (minimum boiling): Have a lower boiling point than any of their components (e.g., ethanol-water at about 95.6% ethanol).
- Negative azeotropes (maximum boiling): Have a higher boiling point than any of their components (e.g., water-acetic acid).
Applications and Challenges
Azeotropic mixtures present challenges in chemical separation processes, often requiring specialized techniques like azeotropic distillation, pressure swing distillation, or adding entrainers to break the azeotrope.
In summary, an azeotropic mixture is a special type of liquid mixture with a fixed boiling point and vapor composition, resisting separation via simple distillation methods.
