Definition - What does Adsorption mean?

Adsorption is the process of adhesion of atoms, ions or molecules from a gas, liquid or dissolved solid to a surface of adsorbent. This process creates a film of the adsorbate on the surface of the adsorbent. The most common industrial adsorbents are activated carbon, silica gel and alumina.

Adsorption process should not be confused with the process of absorption as both are different. In absorption, a substance diffuses into a liquid or solid to form a solution whereas in adsorption, the atoms of adsorbate are attracted towards adsorbent. Adsorption is a surface-based process, while absorption involves the whole volume of the material.

Petropedia explains Adsorption

Adsorption enables solid substances to attract molecules of gases or solutions they come in contact with to their surfaces. Solids that are used to adsorb gases or dissolved substances are called adsorbents; the adsorbed molecules are usually referred to collectively as adsorbate. For example, charcoal is an excellent adsorbent used in gas masks to remove poisons or impurities from a stream of air.

Similarly, when liquid hydrocarbons need to be removed from natural gas stream, activated charcoal or silica gel is used which adsorbs the liquid hydrocarbon molecules and settles down at the bottom of the chamber. These heavier liquid hydrocarbon molecules can be later removed and treated with stream so as to recover the hydrocarbons.

Adsorption is present in almost all systems, whether it is physical, chemical or biological, and is widely used in industrial and commercial applications. For example:

  • Carbon as adsorption filter makes drinking water taste better.
  • Activated alumina removes harmful chemicals like fluoride and arsenic from liquids.
  • Synthetic resins can clean up highly hazardous spills.
  • Adsorption of molecules onto polymer surfaces is used in various applications, such as in the development of non-stick coatings and in various biomedical devices.
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