Most modern air purifiers use a pre-filter, a mechanical filter, such as a HEPA filter, and an activated carbon filter. Carbon may seem like a strange filter media for air purification, but it is actually quite important. Activate carbon, or activated charcoal, can absorb airborne chemicals, gases and odors, and it has an extremely large surface area, which allows it to trap a great amount of substances relative to its overall size.
Activated carbon, also known as activated charcoal can made from many substances containing a high carbon content such as coal, coconut shells and wood. The choice of raw material does matter and can have an effect on performance and efficiency. Some raw materials are better suited to certain chemicals and gases.
For air filters, the carbon is often mixed or impregnated with other materials in order to make it more effective at attracting and adsorbing specific airborne chemicals, such as ammonia, formaldehyde, benzene, fragrances and volatile organic compounds (VOCs).
Steam-activation is primarily used for coconut charcoal and coal. In the production of steam-activated charcoal, first the coconut shell or coal is heated to create a char. This char is then "activated" in a furnace at high temperatures of 1,700° to 1,800°F with steam in the absence of oxygen. In the steam-activation process, all volatile compounds are removed, and at the same time layer after layer of carbon atoms are peeled off, enlarging the existing internal pores, and leaving behind a carbon skeleton. The carbon plus steam reaction results in producing hydrogen gas and carbon monoxide . As the carbon monoxide gases off it takes carbon atoms with it. Typically 3 pounds of raw charcoal will produce 1 pound of activated charcoal. A reasonably good activated charcoal with a surface area of 1,000 m2/g would have 125 acres of surface area per pound.
This gives the carbon amazing adsorptive qualities and durability. Note that there is a distinction between absorption and adsorption. Absorption is the process of a fluid being absorbed by a solid or another liquid. Adsorption is the process by which atoms, ions or molecules bind to the surface of another substance. In an air purification scenario, chemicals, gases and odors adsorb to the activated carbon where they remain inert until the media is disposed.
Many air purifiers claim to have odor-removing filters, but effectiveness depends entirely on the type and quality of media. Some air purifiers only use a woven carbon cloth, which can be suitable in some scenarios but will underperform in a demanding one. An environment with high levels of odors, chemicals or VOCs requires actual activated carbon, which can be effective for 2 to 5 years based on how high the pollutant levels are.
The best air purifiers are those that have both a HEPA and an activated carbon component and are made by top manufacturers. Specialized units which have a high carbon content are well suited to environments with high gas and chemical levels or for people who are suffering from multiple chemical sensitivities (MCS).
Clean Air Plus is a veteran and family owned small business. We represent the leading manufacturers in HEPA filtration including Austin Air, IQAir, Amaircare, Oransi and Airpura. Shop online or call one of our friendly experts at 888.247.1147. We'll be happy to help.