The operation of activated carbon plants is based on the adsorption process, i. e. on the phenomenon of molecular diffusion between components in gaseous phase, defined as adsorbed, and a solid, defined as adsorber. The experimentation showed that gas molecules (VOC) adhere to solid surface and form one or more superposed layers of substance, created by electrostatic attraction forces (Van Der Waals forces) or by adhesion forces arising from capillarity phenomena.

As it is a phenomenon of molecule migration between a gaseous phase and a solid phase, a fundamental feature of the adsorbing material is the activated surface that allows the contact between the components. Particularly, the extremely diffused presence of micro porosity in the activated carbon generates a very large surface development. Just think that 1 kg of activated carbon may include a total surface of two millions of square meters.

From the thermodynamic point of view, the adsorption is always followed by heat development, arising from the molecule settlement on a more energetically stable state. Effectively, we assist to a free energy decrease due to the formation of bonds within the adsorbed and the adsorber as well as an entropy decrease because of a lesser freedom degree of the molecules.