Carbon, Activated

Abstract Activated carbon is a predominantly amorphous solid that has an extraordinarily large internal surface area and pore volume. These unique characteristics are responsible for its adsorptive properties, which are exploited in many different liquid‐ and gas‐phase applications. Through choice of precursor, method of activation, and control of processing conditions, the adsorptive properties of products are tailored for applications as diverse as the purification of potable water and the control of gasoline emissions from motor vehicles. The structure of activated carbon is best described as a twisted network of defective carbon layer planes, cross‐linked by aliphatic bridging groups. X‐ray diffraction patterns of activated carbon reveal that it is nongraphitic, remaining amorphous. This property of activated carbon contributes to its most unique feature, namely, the highly developed and accessible internal pore structure. Activated carbon is generally considered to exhibit a low affinity for water, which is an important property with respect to the adsorption of gases in the presence of moisture. Commercial activated carbon products are produced from organic materials that are rich in carbon, particularly coal, lignite, wood, nut shells, peat, pitches, and cokes. Manufacturing processes fall into two categories, thermal activation and chemical activation. To meet the engineering requirements of specific applications, activated carbons are produced and classified as granular, powdered, or shaped products. Activated carbon is a recyclable material that can be regenerated. Thus the economics, especially the market growth, of activated carbon is affected by industry regeneration capacity. Landfill disposal is becoming more restrictive environmentally and more costly. Thus large consumers of powdered carbon find that regeneration is an attractive alternative. Activated carbon generally presents no particular health hazard as defined by the National Institute for Occupational Safety and Health (NIOSH). However, it is a nuisance and mild irritant with respect to inhalation, skin contact, eye exposure, and ingestion. On the other hand, spent carbon may contain a concentration of toxic compounds. Activated carbons for use in liquid‐phase applications differ from gas‐phase carbons primarily in pore size distribution. Liquid‐phase carbons have significantly more pore volume in the macropore range, which permits liquids to diffuse more rapidly into the mesopores and micropores. Liquid‐phase activated carbon can be applied either as a powder, granular, or shaped form. Granular and shaped carbons are used generally in continuous systems where the liquid to be treated is passed through a fixed bed. Liquid‐phase applications of activated carbon include potable water treatment, industrial and municipal wastewater treatment, sweetener decolorization, groundwater remediation, and miscellaneous uses including chemical processing, mining and the production of food, beverages, cooking oil, and pharmaceuticals. Gas‐phase applications of activated carbon include separation, gas storage, and catalysis. Most of the activated carbon used in gas‐phase applications is granular or shaped. Applications include solvent recovery, automotive/gasoline recovery, industrial off‐gas control, and catalysis, among others. Separation processes comprise the main gas‐phase applications of activated carbon.