Azeotropes are a mixture of liquids where the proportion of the liquids (eg: 4:1, 1:1, 1:4 ) cannot be altered by simple distillation. Azeotropic distillation is a process to break azeotropes where another volatile component called the solvent is added to form a new lower boiling azeotrope that is heterogeneous. We will first understand azeotropes more in detail to understand the logic behind azeotropic distillation.
What is azeotropic mixture?
The azeotropic mixture is a mixture of two or more liquids whose proportions cannot be changed by simple distillation. This happens because when azeotropes are boiled, the vapor has the same proportions of constituents as the un-boiled mixtures as their composition is unchanged by distillation. Azeotropes are also called a constant boiling point mixture.
What is azeotropic distillation?
Generally, in chemistry, azeotropic distillation is any method used to break an azeotrope in distillation. It can simply be referred to as the process to separate the components of an azeotropic mixture. In chemical engineering, azeotropic distillation usually refers to the specific technique of adding another component to generate a new, lower boiling azeotrope that is heterogeneous.
An azeotropic mixture consists of two or more liquids that cannot be separated through simple distillation since the vapors that are formed via boiling the azeotropic mixtures consist of the same proportion of the liquids as the mixture itself. Generally, in an azeotropic distillation, a separating agent is added which alters the relative volatility of the whole azeotropic mixture.
How is azeotropic distillation performed?
The azeotropicAzeotropic distillation is mostly used in laboratories and industries. It is performed similar to conventional fractional distillation but with the addition of an azeotropic agent.
- The process is accomplished by adding to the liquid phase a volatile third component(azeotrpoic agent) which changes the volatility of one of the two components more than the other so that the components are separated by distillation. The azeotropic agent is generally added in excess amount.
- Then the mixture(azeotropic mixture plus azeotropic agent) is distilled in the same manner as a conventional fractional distillation. The components are seperated by heating to a specific temperature that will vaporize one or more components. The coponents will generally vary in boiling point temperatures.
- The composition of distillate product then changes as the newly formed azeotropes will be seperated from one of the components.
- Then the distillation should proceed until all other components have been removed as a distillate product.
Examples of azeotropic distillation
The most common example of an azeotropic mixture is ethanol and water. It can be separated by azeotropic agents like benzene, pentane, diethyl ether, etc.
What is the difference between classical distillation and azeotropic distillation?
In chemistry, classical distillation is the process of separating the components or substances from a liquid mixture by using selective boiling and condensation. But in the case of azeotropic mixtures, classical distillation will not work. Hence we add a material that alters the relative volatility of the mixture. This is called azeotropic distillation.
Research
You can read this article by G.D Guido et al. on the separation of water and 2-propanol by azeotropic distillation by using isooctane as an entrainer. An entertainer is a compound that forms an azeotrope with one of the components.
