Distillation: Types & Principles | chemca

chemca.in

Home Articles Quizzes About

Organic Chemistry

Distillation and Its Types

Purification of liquids based on differences in boiling points.

By chemca Team • Updated Jan 2026

Distillation is a method used to separate volatile liquids from non-volatile impurities or to separate a mixture of volatile liquids having different boiling points. The process involves heating a liquid to create vapor and then cooling the vapor back into a liquid.

1. Simple Distillation

Principle

Used for separating liquids with a large difference in boiling points (typically > 25 K or 25°C), or separating liquids from non-volatile solids.

Examples:

• Separation of Acetone (B.P. 329 K) and Water (B.P. 373 K).
• Separation of Ether (B.P. 308 K) and Toluene (B.P. 384 K).

2. Fractional Distillation

Principle

Used when the difference in boiling points of the two liquids is small (typically < 25 K). A Fractionating Column is fitted between the distillation flask and the condenser.

The column provides obstacles (glass beads or plates) for the rising vapor, causing repeated condensation and vaporization. The more volatile component moves up faster.

Examples:

• Separation of Crude Oil into petrol, diesel, kerosene.
• Separation of Acetone (329 K) and Methanol (338 K).

3. Distillation under Reduced Pressure (Vacuum)

Principle

Used for liquids that have very high boiling points or decompose at or below their boiling points. By reducing the pressure on the liquid surface using a vacuum pump, the liquid boils at a much lower temperature.

B.P. $\propto$ External Pressure

Examples:

• Purification of Glycerol (decomposes at 563 K, distilled at 453 K under 12 mmHg pressure).
• Concentration of sugarcane juice in sugar industry.

4. Steam Distillation

Principle

Used for substances that are:

• Immiscible with water.
• Steam volatile (volatile in steam).
• Possess a high vapor pressure at 100°C.

The mixture boils when the sum of vapor pressures equals atmospheric pressure ($P_{atm}$):

$$ P_{Total} = P_{Water} + P_{Organic Liquid} = P_{atm} $$

Since $P_{Water} < P_{atm}$, the liquid boils at a temperature lower than 100°C (and much lower than its normal B.P.).

Examples:

• Purification of Aniline from aniline-water mixture.
• Separation of Essential Oils (e.g., Lemon grass oil, Eucalyptus oil).
• Separation of o-Nitrophenol (Steam volatile) from p-Nitrophenol (Not steam volatile).

Knowledge Check

Test your understanding of Distillation Types

© 2026 chemca.in. All rights reserved.

Optimized for learning Organic Chemistry.

Quiz Revision Notes Downloads Class Notes Video Lectures