Activated Carbon and its Mechanism
Activated carbon is the generic term used to describe a family of carbonaceous adsorbents in a highly crystalline form with extensively developed internal pore structure. Many substance of base material are used to make activated carbon. The most common of these are wood, coal, lignite and coconut shell. For drinking water purposes, coconut shell is the ideal base material as it is hard compared to wood. Coconut shell-based carbon is predominately microporous and is well suited for organic chemical adsorption, including volatile organic chemicals while having higher chlorine reduction capabilities. Coconut shell carbon is known to make good tasting “sweet water”.
Filtrex products are 100% Coconut Shell Carbon.
Activation Process: The process of activation and good process controls are vital in the manufacturing of good quality activated carbon that gives consistently high level of porosity. The process of activation includes first carbonization of the shell, which is achieved by slow heating in the absence of oxygen to form carbonaceous mass full of tiny pores. This carbonized base material is then activated at high temperature (1100 degree C) in the presence of steam with regulating oxygen and carbon dioxide levels. Activation temperature and the amount of activation (time) are important to create internal pore network and to impart certain surface chemistries (functional group) inside each particle of the carbon. In essence, the total activation process gives carbon the unique adsorption characteristics for the removal of pollutants. This total control enables us to produce consistently high quality of activated carbon.
How Activated Carbon Works
Activated Carbon is extremely porous with a very large surface area. The reason that activated carbon is such an effective adsorbent material is due to its large number of cavernous pores. This provides a large surface area relative to the size of the actual carbon particle and its visible exterior surface. An approximate ratio is 1 gram = 100 meter square of surface area. The intermolecular attractions in the smallest pores result in adsorption forces. The molecules of the contaminants in the water are adsorbed on to the surface of the Activated carbon by either physical or chemical attraction. The two main reasons that chemicals adsorb onto Activated Carbon are:
- A “dislike” of water.
- Attraction to the Activated carbon.
Activated carbon adsorption proceeds through three basic steps:
- Substances adsorb to the exterior of the carbon surface,
- Substances move into the carbon pores
- Substances adsorb to the interior walls of the carbon. Many organic compounds such as chlorinated and non-chlorinated solvents, triholmethanes, pesticides and VOC are adsorbed into the inner pores. Activated carbon is also effective in removal of chlorine and moderately effective for removal of some heavy metals.
Important Properties of Activated Carbon
Iodine Number, surface area, pore size and particle size distributions are the key parameters for effective adsorption of activated carbon. Premium Carbons have a minimum iodine number of 1100, ash content of less than 3% and bulk density of 0.45g/ml.
Activated Carbon Properties and ASTM
Adsorption Properties The effectiveness of activated carbon is usually specified by the amount of a certain test chemicals it can adsorb per weight of activated carbon used. Activated carbon when used for filtering air and gases, the test chemical used is usually Carbon Tetrachloride, commonly designated as CTC and when used in filtering water and liquids, the chemical used is usually Iodine or methylene blue mixed with water.