Activated Carbon, also called activated charcoal or activated coal, is a form of carbon that has been processed to make it extremely porous and thus to have a very large surface area available for adsorption (adsorption, not to be confused with absorption, is the adhesion of atoms, ions, biomolecules or molecules of gas, liquid, or dissolved solids to a surface) .
The word activated in the name is sometimes replaced with active. Due to its high degree of micro porosity, just 1 gram of activated carbon has a surface area in excess of 500 m2 (about one tenth the size of a football field), as typically determined by nitrogen gas adsorption. Sufficient activation for useful applications may come solely from the high surface area, though further chemical treatment often enhances the absorbing properties of the material. Activated carbon is usually derived from charcoal, wood or coconut shells.
Activated carbon, as viewed by an electron microscope
Traditionally, active carbons are made in a particular form as powders or fine granules less than 1.0 mm in size with an average diameter between 0.15 and 0.25 mm. In this way they present a large surface to volume ratio with a small diffusion distance. PAC is made up of crushed or ground carbon particles, 95-100% of which will pass through a designated mesh or sieve.
Granular activated carbon has a relatively larger particle size compared to powdered activated carbon and consequently, presents a smaller external surface. These carbons are preferred for all adsorption of gases and vapors as their rate of diffusion is faster. Granulated carbons are used for water treatment and deodorization. GAC can be either in the granular form or extruded. GAC is designated by sizes such as 8×20, 20×40, or 8×30 for liquid phase applications and 4×6, 4×8 or 4×10 for vapor phase applications. The most popular aqueous phase carbons are the 12×40 and 8×30 sizes because they have a good balance of size and surface area characteristics.
Extruded activated carbon combines powdered activated carbon with a binder, which are fused together and extruded into a cylindrical shaped activated carbon block with diameters from 0.8 to 130 mm. These are mainly used for water treatment and gas phase applications because of their low pressure drop, high mechanical strength and low dust content.