Activated carbon is used to remove pollutants from air or water streams, both in the field and in industrial processes such as spill cleanup, groundwater remediation, drinking water filtration, air purification, and the capture of volatile organic compounds (VOCs). Activated carbon filters and activate carbon filter media are also used in odor control and reverse osmosis applications. Most activated carbon is made of bituminous coal or lignite, a low-sulfur coal with high moisture content. The material source and mode of activation determine the specific properties of active carbon. Property standards are also important to consider when selecting products from activated carbon suppliers.
Activated carbon is available in various forms. Examples include activated carbon beds and activated carbon blankets. There are two main types of activated carbon beds: fixed and fluidized. Although fixed beds are suitable for some applications, fluidized beds offer excellent gas distribution and lower resistance to gas flow. Activated carbon blankets are used to absorb fumes and odors from products such as new carpeting, cars, furniture, and homes. Activated carbon cloth and activated carbon fabric is characterized by its large adsorption volume, fast adsorption speed, heat resistance, and chemical resistance.
Activated carbon filters such as blocks, canisters, cartridges, and pellets are also available. Activated carbon blocks are blends of mesh-activated carbon, water, and a plastic binder. They are hardened and extruded to form a solid matrix. Although the plastic binder occludes a percentage of the adsorption sites, activated carbon blocks feature a finer mesh size that provides faster adsorption kinetics and a greater adsorption capacity. Activated carbon canisters, cartridges, and pellets are also available. Most activated carbon canisters and activated carbon cartridges are used for air and water filtration. Activated carbon pellets are used in vapor applications. Their particle size and pore structure adsorb impurities from a vapor steam with limited flow resistance.
Specifications for activated carbon include particle size or mesh, surface area, pore volume, moisture range, adsorption characteristics, pH, water solubility, and tamped bulk density. The percentage of ash, iron, and phosphates is also important to consider. For high-purity applications, activated carbon filters should contain very low amounts of iron, typically 100 parts per million (ppm). Activated carbon with extremely high adsorptive capacities is suitable for decolorizing applications, and may carry product specifications for methylene blue adsorption and have a molasses decolorizing number.