An azeotrope is a mixture of two or more liquids that displays the same level of concentration in the liquid and vapor phase. Simple distillation cannot alter their proportions. These mixtures can either have a lower boiling point or a higher boiling point of the components.
An azeotrope is a mixture that, at a given pressure (the azeotropic pressure), boils at a constant temperature (the azeotropic temperature), and has the same composition (azeotropic composition) in the equilibrium vapour and liquid phases.
They are termed as constant boiling mixtures as their composition remains unchanged by distillation. That is the constitution stay in the same proportion even when the azeotrope is boiled. When distillation cannot alter a fraction of a liquid, it results in azeotropes.
An azeotropic compound is a mixture of two substances which distil at the same temperature. An azeotrope is a mixture of compounds with the same composition in the vapour as in the liquid. In other words, an azeotrope is a liquid mixture that has a constant boiling point and whose vapour has the same composition as the liquid. Several compounds, such as toluene, benzene, and cyclohexane, form suitable azeotropes with water.
Azeotropic distillation as an early and important special distillation process is commonly used in laboratories and industry. Azeotropic distillation is accomplished by adding to the liquid phase a volatile third component which changes the volatility of one of the two components more than the other so that the components are separated by distillation.
- An azeotropic distillation performed in a laboratory is normally done in batches in a conventional fractional distillation column. In such a case, an excess of the usually required amount of the azeotropic agent is added with the charge to the still.
- The mixture is then distilled in the same manner as a conventional fractional distillation. If the mixture of binary compound and azeotrope is a minimum boiling point type then the distillate product should contain only one of the original components and the azeotropic agent.
- The composition of the distillate product then changes as the distillation proceeds since the separation taking place is between the different azeotropes.
- Then the distillation should proceed until all other components have been removed as a distillate product leaving the bottom product as the remaining component and the azeotropic agent.
Types of Azeotropes
1. Heterogeneous and Homogeneous Azeotropes
If azeotropes are found in constitutions of mixtures and if they are not completely miscible then they are termed as heterogeneous azeotropes. Homogeneous Azeotropes are azeotropes in which the constitutions of a mixture are miscible completely. Hetero Azeotropic distillation comprises two liquid phases.
2. Maximum boiling Azeotropes
The liquid solution which shows negative deviation from the ideal solution boil at a constant temperature which is higher than that of the pure component is called maximum boiling azeotropes
Water boils at a hundred degree Celsius and hydrochloric acid boil at around eight four degree Celsius, whereas azeotropes boil at around hundred and ten degree Celsius indicating that it has a higher boiling point than their constituents.
3. Minimum boiling Azeotropes
The liquid solution which shows a positive deviation from the ideal solution boil at a constant temperature which is less than that of pure components is called minimum boiling azeotropes.
Water boils at a hundred degrees Celsius, and ethanol boils at around seventy-eight-degree Celsius, whereas azeotropes boil at around seventy-eight-degree Celsius indicating that it has a lower boiling point than their constituents.
4. Binary Azeotropes
Binary Azeotropes are azeotropes consisting of two constitutions as mentioned above illustration. Ternary Azeotropes are azeotropes consisting of more than three constitutions.