Known since antiquity as a powerful purification agent, activated carbon is used today in a vast array of applications at the home, municipal, and industrial levels. Activated carbon can be made from any organic material with a high natural concentration of carbon, so the specific chemical structure and properties will vary according to which raw material is selected. Here is what you should know.
Q. What is the Chemical Structure of Activated Carbon?
A. Known since antiquity as a powerful purification agent, activated carbon is used today in a vast array of applications at the home, municipal, and industrial levels. Activated carbon can be made from any organic material with a high natural concentration of carbon, so the specific chemical structure and properties will vary according to which raw material is selected. Here is what you should know.
Calcined Structure
Although the raw materials in their natural state have no inherent graphite plate structure, they settle into this structure during the beginning of the production process—slow heating in a minimal-oxygen environment to a temperature exceeding 1450 F. Through calcination, the carbon molecules are rearranged into their most stable calcined structure, which is a graphite plate. However, the specific arrangements of the angles, spacing, and gaps within the structure varies with the type of raw material.
Activation, Maximum Apparent Density, and Porosity
The calcined structure is of limited use due to its limited porosity and density. The calcined material, known as char, must be activated through physical and/or chemical processing, removing carbon atoms in an orderly fashion. Different activation processes create different variations of the base calcined structure. There is an inverse relationship between activated carbon’s apparent density and its porosity. The more carbon atoms are removed, the higher the porosity, but the lower the maximum apparent density.
Properties
Each variation of each base calcined structure has its own unique, predictable properties. This allows users to select the form of activated carbon that best suits a specific application. These properties include:
Pore Size: Activated carbon removes unwanted compounds through the process of adsorption, in which the targeted material bonds with carbon atoms along the activated carbon’s surface. The activation process creates an extensive submicroscopic porous network, vastly increasing the number of available bonding sites. However, different applications call for different pore sizes. “Microporous” activated carbon has pores that are less than 2 nm. “Mesoporous” activated carbon has a pore size of 2 to 5 nm, while “macroporous” activated carbon has a pore size of more than 5 nm.
Iodine, molasses, methylene blue, and tannin numbers: The iodine number (generally 500 to 1200 mg/g) measures the adsorption capability for small molecules. The molasses number (typically 95 to 600 mg/g) shows the capability to adsorb large molecules. The methylene blue number (often 11 to 28 g/100g) indicates the adsorption capability for medium-sized molecules. Since most contaminants contain a variety of molecule sizes, the tannin number (normally 200 to 362 ppm) demonstrates the capability of the activated carbon to adsorb mixtures.
Carbon tetrachloride activity (CTC): Typically 45 to 70% by weight, this represents the activated carbon’s porosity for air/vapor applications.
Dechlorination: This is the depth an activated carbon bed must be to remove half the chlorine from a liquid stream (known as the half-value). The lower the half-value, the better the performance.
Activated carbon is also graded on its physical characteristics. It is available in three different types (powdered, granular, and extruded), each with its own physical attributes that make it ideally suited for specific types of applications.
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If you need activated carbon, along with expert guidance on exactly which product to choose and how to use it effectively, please contact Puragen Activated Carbons today to learn how we can help.