There are two main activation techniques used to produce activated carbon:
Steam Activation - Activation is carried out at high temperatures of 800 - 1000°C in the presence of steam. Initially, gasification of the carbonized material with steam occurs; a reaction known as the Water-Gas reaction. This reaction is endothermic so temperature must be maintained by partial burning of the CO and H2 formed.
Air is added to burn the gases without burning the carbon, producing a graded, screened and de-dusted activated carbon. Activated carbons produced by steam activation generally exhibit a 'fine' pore structure, ideal for the adsorption of compounds from both the liquid and vapor phase.
Chemical Activation - The raw material is impregnated with a strong dehydrating agent, typically phosphoric acid (P2O5) or zinc chloride (ZnCl2) mixed into a paste and then heated to temperatures of 500 - 800°C to activate the carbon. Activated carbons produced by chemical activation generally exhibit a very 'open' pore structure, ideal for the adsorption of large molecules.