Adsorption is a concept which is used in the field of physical with reference to process and the result of adsorbing . This verb refers to the attraction and retention that performs a body in its surface of ions, atoms or molecules that belong to a different body.
Through adsorption, a 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.
Adsorption can be carried out in different ways, according to the link 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 the one that takes place due to forces or Van der Waals interactions , 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 at a particular point of the surface , and for this reason you have total freedom to move in the interface;
* chemical adsorption : it takes place when in the active centers of the adsorbent strong bonds are formed by the adsorbate;
* adsorption by exchange : as it happens in the vicinity of an electrode with load This type of adsorption occurs when, because of the electrostatic attraction at the charged points of the surface, the ions of a substance are concentrated therein.
As a 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 are retained on the surface of the body.
The principles of adsorption apply in very different fields. In the world of industry , one of its most popular uses is to use 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, generates 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 bed molecule adsorbs that of water. On the other hand, its regeneration implies releasing the compressed air to the outside and letting a stream of pre-dried 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 treatment; elimination of odors, colors or flavors in certain products such as sugar syrup and oils, to meet industry standards; wastewater treatment, which entails different biological, chemical and physical actions to get rid of the contaminants that result from human use; air drying; moisture removal in fuels.
Adsorption is also applied to obtain nitrogen , and for this, compressed air is passed through the adsorbent bed.