Activated carbon, also known by the terms “activated charcoal” or “activated coal” is a form of the element carbon that passed through some process to obtain a by-product that has the characteristic of being porous or heavily permeable in order to allow heavy adsorption or other chemical reactions. Most people simply know this as “active carbon” instead of activated carbon. This type of carbon filter has an extremely large surface area for the chemical reactions. To illustrate its high degree of microporosity, one gram of active carbon possesses a surface area in excess of 500 m2 (square meter), as determined by nitrogen gas adsorption. Adsorption is the accumulation of substance on surface, or the process by which a layer of atoms or molecules of a substance, usually a gas, is formed on the surface of a solid or liquid (definition by Microsoft Encarta Reference Library). High surface area provides sufficient activation for common useful applications. However, some methods such as chemical treatment may be done to further enhance the ability of the material for absorption. Charcoal is usually the major source where activated carbon is derived.
Production of Activated Carbon
The production of activated carbon is derived from materials like peat, wood, nutshells, lignite, coir, and petroleum pitch. The following processes may be employed to produce activated carbon:
Physical reactivation process. The precurson, a chemical compound that leads to another, usually more stable, product in a series of connected reactions, is processed using gases to develop activated carbon which is done through either or combination of the following processes:
Carbonization: A process called pyrolysis or the heating of a substance to decompose it at temperatures from 600 – 900 degrees centigrade is done in certain materials with carbon content, in conditions where air is absent or usually in inert atmosphere like nitrogen and other inert gases.
Activation/Oxidation:
Chemical activation. The raw materials necessary for the production of activated carbon are introduced with certain chemicals prior to carbonization. These chemicals are usually acid, strong base, or salt (acid such as phosphoric acid, strong bases such as sodium hydroxide and potassium hydroxide, and salt such as zinc chloride). Afterwards, at temperature ranging from 450 degrees to 900 degrees Centigrade, the raw material undergoes carbonization, a simultaneous process which it undergoes along with the chemical activation. This method could sometimes be troublesome because the end product may contain residues of zinc traces which are not desired. Notwithstanding the disadvantages, chemical activation is still employed over physical activation due to the relatively lower temperature range required and the short period of time required for activation of the raw material.
Activated carbon water filter
The main application of activated carbon is in water filtration process. Such process uses either granular activated carbon (GAC) or powdered block carbon. Both are regarded as effective in filtration but, however, the latter is generally employed due to its higher efficiency in removing the contaminants in water. The efficiency of activated carbon filters is affected by two factors, namely: (1) the amount of the carbon present in the unit, and; (2) the length of time the contaminants are in contact with the activated carbon. By principle, the more activated carbon present, the better or efficient the filtration method. Also, the longer the period of time that activated carbon is in contact with the water, the more contaminants are absorbed. Another factor affective the efficiency of activated carbon is particle size. Activated carbons may filter particles ranging from 50 microns (the unit of measurement of the particle size) to 0.5 microns. The lower the particle size filtered, the better the filtration.
How does activated carbon remove contaminants from water? There are two principal methods or ways. One is adsorption or the accumulation of substance on surface or the process by which a layer of atoms or molecules of a substance, usually a gas, is formed on the surface of a solid or liquid. The other method is catalytic reduction or the process which involves the attraction of negatively-charged contaminant ions to the activated carbon which is positively charged. Adsorption removes organic compounds while catalytic reduction removes residual disinfectants like chlorine and chloramines.
These contaminants that are filtered by activated carbon are volatile organic compounds (commonly referred as VOC), chlorine, benzene, pesticides and herbicides, trihalomethane (THM) compounds, solvents, radon, and various other man-made chemicals present in tap water.
However, activated carbon are not effective in filtering inorganic contaminants dissolved in water such as minerals or salts, asbestos, antimony, arsenic, and many other contaminants. In order to remove the said contaminants, a process called reverse osmosis or a distiller is required in water filter systems.
How does the Activated Carbon Air Filter Work?
The activated carbon which is positively charged attracts impurities or contaminants which are negatively charged. Said process is earlier defined as adsorption. To illustrate the said process, the gas molecules of the impurities or contaminants are trapped in the activated carbon's surface area which has numerous tiny pores or holes. The filtered impurities are directly proportional to the amount of the carbon present and its thickness. The reason for a large surface area of carbon filter is to attract and clean large amount of air which comes into contact with it. A relatively small amount of activated carbon is sufficient in filtering or cleaning the air of the entire house.
Compared with air fresheners which are sprayed or mounted near windows or other areas in the house, activated carbon air filters are far better and efficient in cleaning the air. Unlike air fresheners which only creates an impression of clean air by its sweet scents but actually does not eliminate the impurities present in the air like carbon filters can as the latter works by capturing the gas molecules which are the cause of foul odors. Most manufactured air filters employ activated carbon as secondary filters. The different types of filters which employs activated carbon are the following:
Activated Carbon Pleated Panel Filters: Gets rid of particulate pollutants, gases and odors.
High Efficiency Gas Adsorption (HEGA) Filters: Efficient in removing a wide range of vapors and odors.
Carbon Loaded Rigid-Box Filters: These filters are capable of removing odors effectively even with a small concentration of active carbon.
High Mass Zero Dust (HMZD) Panels: Highly suitable for certain areas requiring high quality of clean air such as airports, museums, water-treatment facilities, semi conductor manufacturing units, industrial plants, etc.
Carbon V-Bank Filters: Aside from having the quality as disposable, these filters offer high contamination removal as well. For filtration, numerous media may be used such as cloth, pads, etc. but the media used is dependent on the type of impurities desired to be eliminated
Military Carbon Cloth Media: This media is used to trap allergy pollutants.
