SIMPLE DISTILLATION - Pharmaceutical Engineering B. Pharm Third Semester PDF Notes


Simple distillation is a process of converting a single constituent from a liquid (or mixture) into its vapour, transferring the vapour to another place and recovering the liquid by condensing the vapour, usually by allowing it to come in contact with a cold surface.

• This process is known differential distillation, as distillation is based on the differences in volatilities and vapour pressures of the components in the mixture.

Principle: Liquid boils when its vapour pressure is equal to atmospheric pressure. Simple distillation is conducted at its boiling point. The higher the relative volatility of a liquid, the better is the separation by simple distillation. Heat is supplied to the liquid so that it boils. The resulting vapour is transferred to a different place and condensed.

Assembling of apparatus

The construction of a simple distillation apparatus is shown in Figure. It consists of a distillation flask with a side arm sloping downwards.

Condenser is fitted into the side arm by means of a cork.

The condenser is usually water condenser, i.e., jacketed for circulation of water. The condenser is connected to a receiver flask using an adapter with ground glass joints.

On a laboratory scale, the whole apparatus is made of glass.

Simple Distillation Process

• When a mixture AB of a specific composition is heated, the total vapor pressure (composed of the contributions of PA and PB) will rise until it is equal to the external vapor pressure.

• The mixture will begin to boil.

• Assume a two component mixture with a composition of 30%A:70%B (point W). The boiling point of this mixture is found by drawing a vertical line from W to where it intersects the lower curve (point X).

• A horizontal line drawn from X to where it intersects the vertical axis (the temperature) gives the boiling point of composition W.

• From the point (X) where this horizontal line intersects the upper curve (vapor) drop a vertical line to intersect the lower axis (the composition).

• Point Z gives the composition of the vapor which is in equilibrium with a liquid of composition W at its boiling point.


The liquid to be distilled is filled into the flask to one-half to two-third of its volume.

Bumping is avoided by adding small pieces of porcelain before distillation.

A thermometer is inserted into the cork and fixed to the flask.

The thermometer bulb must be just below the level of the side arm.

Water is circulated through the jacket of the condenser.

The contents are heated gradually. The liquid begins to boil after some time.

The vapour begins to rise up and passes down the side arm into the condenser.

The temperature rises rapidly and reaches a constant value.

The temperature of the distillate is noted down, which is equal to the boiling point of the liquid.

The vapour is condensed and collected into the receiver.

The flame is adjusted so that the distillate is collected at the rate of one to two drops per second.

Distillation should be continued until a small volume of liquid remains in the flask.


(I) Simple distillation is used for the preparation of distilled water and water for injection

(2) Volatile and aromatic waters are prepared

(3) Organic solvents are purified

(4) A few official compounds are prepared by distillation

Examples are spirit of nitrous ether and aromatic spirit of ammonia

(5) Non-volatile solids are separated from volatile liquids


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