Comparison of Gas Absorption and Distillation Unit Operations

An Absorption is a technique which commonly used for scrubbing operation, to separate a component present in a gas mixture with the help of a solvent which dissolves a particular selected component. Some of the main characteristics of absorption operation are compared with distillation operation. Distillation is such a unit operation that uses thermal energy to separate component into fraction based on their boiling points:

Comparison of Gas Absorption and Distillation:


  • Gas absorption is an operation which deals with the separation of the constituent present in a gas mixture.
  • A liquid is used for separation of a gas mixture
  • The solvent in liquid form is below its boiling point
  • The principle of solute diffusion governs the absorption operation that is a component from gas phase diffuse into the liquid phase
  • Pure products are not obtained further purification operations are required
  • The heat of solution will dominate the heat effect caused by dissolved gas
  • The high performance of gas absorption column is attained when it operates below dew point temperatures conditions
  • The best equipment for gas absorption is packed bed column
  • The degree of separation depends on the selection of solvent and solubility of a gas in that solvent
  • Example:
  1. Separation of ammonia from air using water
  2. Separation of sulphur dioxide from flue gas using base solutions


  • A liquid mixture can be separated into individual components
  • Thermal energy influence the separation of a liquid mixture
  • The liquid exists at the bubble point
  • Equimolar counter diffusion take place that is mass is transferred between liquid phase and gas phase simultaneously
  • Pure products are produced nearly 99.99%
  • Latent heat of vaporisation and condensation are dominating heat effect of the distillation tower
  • All vapour should be at dew point temperature for continuous operation of the distillation column
  • The high performance of distillation operation is obtained by a plate tower equipment
  • Separation of the component by distillation depends on the volatility of individual component present in the feed liquid mixture. The large the difference of volatility between them the higher the separation can be done
  • Example :
  1. Separation of crude petroleum into fuels as gasoline, diesel etc.
  2. Separation of methanol and water

Diagrammatic representation of Comparison of Gas Absorption and Distillation operations