Activated carbon: what is it and how to characterize its extraordinary properties?
Activated carbon, active carbon or activated charcoal is a form of carbon processed to have small, low-volume pores that increase the surface area available for adsorption or chemical reactions. Adsorption is a process where a solid is used for removing a soluble substance from the water. In this process active carbon is the solid.
Due to its high degree of microporosity, one gram of activated carbon can reach a surface area of 3,000 m2 as determined by gas adsorption. Activated carbon is produced specifically so as to achieve a very big internal surface from 500 m2/g and higher, making it ideal for adsorption.
Activated carbon is used to purify liquids and gases in a variety of applications, including water treatment (drinking, domestic or waste water treatment), raw material purification such as purification of oils and fats, alcoholic and softdrinks, dyestuffs, decolourisation of sugar and glucose, or other food, chemicals or pharmaceuticals. Activated carbon is used for odor removal, industrial pollution control, air purification and environmental protection, as well as for catalytic processes.
Activated carbon is produced from any organic material with a high carbon content, such as coconuts, nutshells, coal, peat and wood, each of which will impart typical qualities to the finished product.
Active carbon comes in several variations: Powder Activated Carbon (PAC), Granular Activated Carbon (GAC) or Extruded Activated Carbon. The basic difference between granular activated carbon and powdered activated carbon is in the cost of manufacture. For a given starting material and activation process, the only difference between PAC and GAC is particle size. Granular Activated Carbon (GAC) is milled and sieved to achieve particles in the range of 0.2 to 5 mm. Typically the drinking water industry uses an 8 x 30 mesh (effective size of 0.80-1.0 mm), or a 12 x 40 mesh (effective size of 0.5 - 0.7 mm). GAC is used in both liquid and gas phase applications. Powdered activated carbon is also milled and sieved and has a smaller particle size than the GAC. The PAC particles are 10 to 100 times smaller, usually with a median diameter of 15 to 30 microns. PACs are generally used in liquid phase applications and for flue gas treatment, the smaller particle size allowing faster adsorption kinetics. Pelletised / Extruded Activated Carbon are mainly used for gas phase applications because of their low pressure drop, high mechanical strength and low dust content.
In Alfatestlab we are used to analyse activated carbon using orthogonal techniques to provide:
- BET surface area
- Particle size and shape
- Powder flow properties
- High resolution SEM images
- EDX elemental analysis
Biochemistry and Biophysics Reports, Volume 17, March 2019, Pages 71-80
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