Question

Explain 'Steam distillation'.
Chapter : Organic chemistry - Some basic principles and techniques.​

Answer 1

Answer :

★ Method : Steam distillation

★ Principle :

• This method is used to separate substances which are steam volatile, immiscible with water, possess a vapour pressure of 10-15 mm Hg and contain non-volatile impurities.

★ Applications :

• Aniline is separated from aniline-water mixture.
• Essential oils, turpentine oil, o-nitrophenol, bromobenzene, etc. can be purified$.$

Other methods of purification of organic compounds :

• Crystallisation
• Sublimation
• Distillation
• Fraction distillation
• Differential extraction
• Chromatography

Answer 2

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# Introduction to Steam Distillation

=> Steam distillation is a separation process which purifies isolate temperature-sensitive materials, such as natural aromatic compounds. In steam distillation, dry steam is passed through the plant material. These vapours undergo condensation and collection in receivers.

We use steam distillation for extraction of essential oil. Steam distillation implements low-pressure steam, this replaces the volatile compounds from the intact plant material. Furthermore, steam distillation allows us to control the temperature and amount of steam that we apply to the plant material.

# Steam Distillation: The Process

=> Steam distillation is the process by which we can extract oil from plant matter. In the apparatus, there is a chamber with holes in the bottom for steam to come through with either fresh or dried herbs.

It consists of a lid that keeps the oil from diffusing into the air when the steam is applied to it. We can collect the water and oil droplets which had undergone condensation. Then the separation of water and oil takes place by passing through a filter.

# Principle of Steam Distillation

=> When a mixture of two immiscible liquids (e.g., water and organics) is heated and agitated, the surface of each liquid exerts its own vapour pressure as though the other component of the mixture was absent. Here an individual constituent on its own extracts vapour pressure independently. Vapour pressure of the system increases consequently.

The two immiscible liquids start to boil when the vapour pressure of these liquids outplace the atmospheric pressure. Many organic compounds are insoluble in water. At an absolute temperature, we can purify that is below the point where these compounds decompose.

# How Steam Distillation Works

=> Most of the complex organic compounds do not dissolve in water, instead, they form a mixture, which separates if allowed to settle as the water settles down and the organic compounds float on top.

The principle behind the steam distillation process is that when the heating of a mixture of two or more immiscible liquids takes place, the vapour pressure exerted by the system increases.

This is because it now becomes the sum of the vapour pressures of all of the components of the mixture combined together. This allows for evaporation of elements with high boiling points at much lower temperatures merely by allowing them to form a mixture with water.

# Advantages of Steam Distillation

=> Advantages of steam distillation are:

• The method generates organic solvent-free products,
• There is no need for subsequent separation steps,
• Possesses large capacity for processing at the industrial scale,
• The equipment is inexpensive,
• Requires less fuel for the steam boiler for extraction of oils.