What is the Definition of Adsorption?


Adsorption is a concept that is used in the field of physics with reference to the process and the result of adsorbing. According to Digopaul, this verb refers to the attraction and retention of a body on its surface of ions, atoms or molecules that belong to a different body.

Through adsorption, one body manages to capture the molecules of another and keep them on their own surface. In this way, adsorption differs from absorption, where the molecules penetrate its surface.

The adsorption can be carried out in different ways, according to the bond established by the adsorbate and the adsorbent. Let’s see below the three types of adsorption that are recognized, taking into account the attraction that exists between the two components just mentioned as a parameter to determine the classification:

* physical adsorption: it is that which takes place due to the forces or interactions of Van der Waals, a concept of physicochemistry that refers to the forces of attraction or repulsion that exist between molecules, or between different portions of the same. These forces are different from those that occur by an intramolecular bond or by the electrostatic interaction of neutral molecules with ions, or of several ions with each other.

In the case of physical adsorption, the adsorbed molecule is not fixed to a particular point on the surface, and for this reason it has complete freedom to move at the interface;

* chemical adsorption: occurs when the formation of strong bonds by the adsorbate occurs in the active centers of the adsorbent;

* exchange adsorption: as occurs in the vicinity of a charged electrode, this type of adsorption occurs when, due to electrostatic attraction at charged points on the surface, ions of a substance are concentrated in it.

In summary, it can be said that adsorption causes the formation of a gaseous or liquid layer on the surface of a solid, or a gaseous layer on the surface of a liquid, which is generated when molecules that are in a certain phase they are retained on the surface of the body.

Adsorption applications

The principles of adsorption apply in very different areas. In the industrial world, one of its most popular uses is to harness it to extract moisture from compressed air. For this, the compressed air is passed through a bed of some material that, before the water molecules, manages to generate adsorption (this can be carried out with the active alumina, for example).

To saturate the bed, the air or gas must be subjected to a certain pressure, so that the molecule in the bed adsorbs that of water. On the other hand, its regeneration involves releasing the compressed air to the outside and letting a stream of predried air flow through the bed. In general, adsorption dryers are developed consisting of two columns: one adsorbs while the other is regenerated by the dry air of the first.

Adsorption is also used in the following processes: water purification; elimination of odors, colors or flavors in certain products such as sugar syrup and oils, to meet industry standards; wastewater treatment, which carries out different biological, chemical and physical actions to get rid of pollutants that result from human use; air drying; removal of moisture in fuels.

Adsorption is also applied to obtain nitrogen, and compressed air is allowed to pass through the adsorbent bed.