Steam Distillation – Principle, Advantages, How it Works?

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

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.

Extraction Procedure- In the extraction process, the steam passes through the organic matter that contains the compounds for separation. The steam condenses and forms a mixture of steam and matter.

This mixture gets heated further by passing more steam, which continues to pass through the matter, evaporating the mixture. Due to the reduced vapour pressure, the required organic compounds evaporate as a part of the mixture. Moreover, its extraction takes place from organic matter.

Separation Procedure- The evaporated mixture of steam and the organic compounds passes through a container that has cold water entering inside from one end. After passing the evaporated mixture through the container, it consists of cold water. This mixture passes through hot water from another end. This results in condensation of the mixture.

This collection of the mixture takes place and it settles down for separation. When the settling process occurs, the extracted organic compounds come to the top. Their separation takes place by filtering out the water from below.

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

Solved Question For You

Q. In steam distillation, the liquid boils when the sum of vapour pressure due to organic liquid and due to water becomes
A) Greater than atmospheric pressure
B) Lesser than atmospheric pressure
C) Equals to atmospheric pressure
D) None of the mentioned

Answer: The correct answer is option C. In steam distillation, a mixture of the organic compound and water boils at a temperature when the sum of the vapour pressures of the organic compound and water becomes equal to the atmospheric pressure. The vapour pressure of water at its boiling point is high and the organic compound will vaporize at a temperature, which is below its normal boiling point.

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