Carbon Air Filters: What They Are,
How they Work and the Difference in Carbon Filters

Carbon filtering is a method of filtering that uses a piece of activated carbon to remove contaminants and impurities, utilizing chemical adsorption. When a material adsorbs something, it attaches to it by chemical attraction. The huge surface area of activated charcoal gives it countless bonding sites. When certain chemicals pass next to the carbon surface, they attach to the surface and are trapped.

Each piece of carbon is designed to provide a large section of surface area, in order to allow contaminants the most possible exposure to the filter media. One pound (454g) of activated carbon contains a surface area of approximately 100 acres (1 km/kg). This carbon is generally activated with a positive charge and is designed to attract negatively charged water contaminants. Carbon filtering is commonly used for water purification, but is also used in air purifiers.

There are two predominant types of carbon filters used in the filtration industry: powdered block filters and granular activated filters. In general, carbon block filters are more effective at removing a larger number of contaminants, based upon the increased surface area of carbon.

Activated Carbon

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 or chemical reactions. The word activated in the name is sometimes substituted by active. Due to its high degree of microporosity, just one gram of activated carbon has a surface area in excess of 500 m (or about 2 tennis courts), as determined typically by nitrogen gas adsorption. Sufficient activation for useful applications may come solely from the high surface area, though further chemical treatment often enhances the adsorbing properties of the material. Activated carbon is usually derived from charcoal. Properties of activated carbon include:

  • Has a capacity for virtually any vapor contaminant; it will adsorb some of almost any vapor.
  • Has a large capacity for organic molecules, especially solvents.
  • Will adsorb and retain a wide variety of chemicals at the same time.
  • Has an extremely large capacity to catalytically destroy ozone, a major component of smog.
  • Works well under a wide range of temperature and humidity conditions.
  • Adsorbs odors and chemicals preferentially to moisture. It is not a desiccant and will release moisture to adsorb chemicals.
  • Can be used as a carrier of one material to attract and hold or react with another material.
  • Is inert and safe to handle and use.

Activated carbon can be enhanced and impregnated and/or custom blended to be a more specialized adsorbant. For instance, Airpura Air Cleaners offers a super impregnated carbon blend where the problems are formaldehyde or ammonia based.

The Amount of Carbon Matters

Activated carbon adsorbs to it's surface. When there is no more surface left to adsorb to the carbon, it is depleted of its capability to be effective. Large amounts of carbon will last longer then small amounts because it has larger amounts of surface area for adsorption. Also, depending on amounts of pollutants being adsorbed, a small amount of carbon can be depleted within weeks making it useless.Airpura Air Cleaners offer either a 18 or 26 pound carbon bed.

The Thickness of Carbon Matters

The more contact time carbon has with a pollutant, the better chances of it adsorbing it. The thicker the carbon filter the better the adsorption. If the pollutant has to go through a long maze of activated carbon, it's chances are better of being adsorbed. That means that thin carbon filters that are used in inexpensive air purifiers are not very effective at removing chemicals, fumes and odors from the air.

Coconut Shell Activated Carbon

Coconut shell carbon's superior level of hardness makes them cleaner than most other carbons and gives them longer life expectancy. This, combined with their high activity level, makes them well suited for use in any kind of carbon filter or system. Aside from general air purification and deodorization, our coconut shell carbons are also very effective in solvent recovery applications.

Acid Washed Granular Coconut Shell Activated Carbon, like its name, comes from the coconut shell that has been undergone steam activation process to create its activated carbon form. During activation, it creates millions of pores at the surface of the carbon thus increasing the total surface area. Activated carbon pores can be divided into three general sizes:

  • Micro-pores (diameter in the range of less than 2 nm)
  • Meso-pores (diameter in the range of 2 - 25 nm)
  • Macro-pores (diameter in the range of above 25 nm)

Coconut shell carbon has mainly micro-pores to meso-pores, and due to its unique distribution of pores diameter, coconut shell activated carbon are very popular in the gas phase purification and potable water purification industries. Airpura Air Cleaners use Coconut Shell Carbon.

Anthracite Carbon

Anthracite is a hard, compact variety of mineral coal that has a high lustre. It has the highest carbon count and contains the fewest impurities of all coals, despite its lower calorific content. Anthracite is the highest of the metamorphic rank, in which the carbon content is between 92% and 98%. The term is applied to those varieties of coal which do not give off tarry or other hydrocarbon vapors when heated below their point of ignition. Anthracite ignites with difficulty and burns with a short, blue, and smokeless flame. Anthracite carbon is best for exhaust fumes, burning wood or petrochemicals. Airpura offers Anthracit Carbon as an option.

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