What is a minimum boiling azeotrope?

A minimum boiling azeotrope is a liquid mixture that has a lower boiling point than its individual parts. The boiling point of an azeotrope is a constant, because the vapor is identical in composition to the liquid mix itself.

Due to their unique nature, minimum boiling azeotropes cannot be separated by simple distillation. In simple distillation, a mixture is vaporized and the material is condensed in one attempt. Because azeotropes do not have an ideal vapor-liquid curve, they undergo a process called fractional distillation. In fractional distillation, the mixture is vaporized and condensed multiple times until the components are separated into pure parts.

The opposite of the minimum boiling azeotrope is the maximum boiling azeotrope. In a maximum boiling azeotrope, the liquid mixture has a higher boiling point than the individual parts.