Azeotropic Distillation

What is Azeotropic Distillation?

Azeotropic Distillation can be defined as the process of separating the components of an azeotropic mixture by distillation. An azeotropic mixture is a mixture containing two or more liquids that cannot be separated by simple distillation because the vapours formed from the boiling of azeotropic mixtures contain almost the same proportions of liquids as the liquid itself. Therefore, azeotropic distillation is a specialized type of distillation which involves the use of specific techniques to break the azeotropes.

The most common method of breaking an azeotrope involves the addition of a material separation agent that has the ability to change the molecular interactions between the components of the azeotrope. The addition of such a material separation agent tends to alter the activity of the activity coefficient of the components of the azeotropic mixture, thereby changing the relative volatility of the azeotropic mixture as a whole.

How can a Mixture of Ethanol and Water be Separated by Azeotropic Distillation?

Water and ethanol are known to form an azeotropic mixture. This mixture can be separated via the process of azeotropic distillation. In order to achieve this, material separation agents such as benzene, hexane, cyclohexane, pentane, diethyl ether, and acetone are commonly used. Historically, benzene was the most commonly used entrainer for this purpose. However, the discovery of the carcinogenic nature of benzene is believed to have caused a decline in the use of benzene in the azeotropic distillation of mixtures of water and ethanol. In modern practices, the ethanol-water azeotrope is usually broken with the help of toluene. Other suitable options for the dehydration of a mixture of water and ethanol include cyclohexane, isooctane, and even heptane.

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Frequently Asked Questions on Azeotropic Distillation

What is the primary difference between extractive distillation and azeotropic distillation?

The primary difference between extractive distillation and azeotropic distillation is in the process followed while separating the mixture. When it comes to extractive distillation, a specific separation solvent must be used in every mixture which should not tend to form an azeotrope. In this manner, extractive distillation can be considered a relatively easier method when compared to azeotropic distillation.

Why can’t Azeotropic Mixtures be Separated by Simple Distillation?

An azeotrope or an azeotropic mixture (sometimes referred to as a constant boiling point mixture) is a mixture containing two or more liquids whose proportions cannot be changed or altered via the process of simple distillation. The reason why azeotropes cannot be separated by simple distillation is because when azeotropes are boiled, the vapours have the same proportions of the constituents as the unboiled mixtures.

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