Distillation

Contents of this session

• Introduction to distillation

• Theory of distillation

• Applications of distillation

• Typical distillation set up

• Types of distillation

• Simple and steam distillation

Learning objectives

At the end of this PDF Notes student will be able to:

• Define distillation and various terms associated with distillation

• Explain the theories of distillation with equations

• State the pharmaceutical applications of distillation

• Compare distillation with other unit operations

• Draw the diagram of a typical distillation unit

• Enlist the various types of distillation methods

• Describe operation of simple and steam distillation

• List the applications of simple and steam distillation

Summary

• Distillation is an unit operation used for the complete separation of a liquid mixture by vaporization and subsequent condensation

• Vapour-liquid equilibrium relationship data is required to solve any distillation problem

• Distillation depends on the relative volatilities of the components present in the mixture

• Henry’s law states that the amount of a given gas dissolved in a given type and volume of liquid is directly proportional to the partial pressure of that gas in equilibrium with that liquid

• Raoult’s law expresses a quantitative relationship between the concentration and vapour pressure

• Ideal solutions are the one which obeys and real solutions shows varying degree of deviations from Raoult’s law

• Distillation is used for the separation of volatile oils, purification of organic solvents, recovery of solvents and purification of drugs obtained from chemical process and natural sources

• Basic parts of a typical distillation set up are still, condenser and receiver with a boiler

• Various distillation methods include simple, steam, flash, azeotropic and molecular

• Simple distillation or differential is based on the differences in volatilities and vapour pressures of the components in the mixture

• Simple distillation is conducted at its boiling point where liquid boils when its vapour pressure equals atmospheric pressure and used for the preparation of distilled water and water for injection

• Steam distillation, simplest form of differential distillation is used for separating substances which are immiscible with water with the aid of steam and used for the separation of high boiling substance from non-volatile impurities. Camphor can be distilled by this method

• Flash distillation utilizes difference in pressure zone for sudden vaporization of entire liquid mixture and carried out as a continuous process and does not involve rectification

• An azeotrope is a mixture of two or more liquids whose composition cannot be changed by simple distillation. As their composition is unchanged by distillation, azeotropes are also called constant boiling mixtures

• Extractive distillation is carried out in the presence of a miscible, high boiling, relatively non-volatile component, and the solvent.

• Molecular distillation or evaporation distillation or short path distillation is based on the principle of the simple distillation with some modifications and utilizes the concept of mean free path

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