Activated carbon,
also called activated charcoal, activated coal, or carbo activatus, is a form of carbon processed to be riddled with small, low-volume pores that increase the surface area available for adsorption or chemical reactions.
Activated is sometimes substituted with active. Due to its high degree of microporosity, just one gram of activated carbon has a surface area in excess of 500 m2, as determined by adsorptionisotherms of carbon dioxide gas at room or 0.0 °C temperature.
An activation level sufficient for useful application may be attained solely from high surface area; however, further chemical treatment often enhances adsorption properties. Activated carbon is usually derived from charcoal.
Production Activated carbon is carbon produced from carbonaceous source materials such as nutshells, peat,wood, coir, lignite, coal, and petroleum pitch. It can be produced by one of the following processes: Physical reactivation:
The precursor is developed into activated carbons using gases. This is generally done by using one or a combination of the following processes: Carbonization: Material with carbon content is pyrolyzed at temperatures in the range 600–900 °C, in absence of oxygen (usually in inert atmosphere with gases like argon ornitrogen) Activation/Oxidation: Raw material or carbonized material is exposed to oxidizing atmospheres (carbon dioxide, oxygen, or steam) at temperatures above 250 °C, usually in the temperature range of 600–1200 °C. Chemical activation: Prior to carbonization, the raw material is impregnated with certain chemicals.
The chemical is typically an acid, strong base, or a salt [2] (phosphoric acid,potassium hydroxide, sodium hydroxide, calcium chloride, and zinc chloride 25%). Then, the raw material is carbonized at lower temperatures (450–900 °C). It is believed that the carbonization / activation step proceeds simultaneously with the chemical activation. Chemical activation is preferred over physical activation owing to the lower temperatures and shorter time needed for activating material. Activated carbon is made from coconut shell mainly.
It consists of 2 types;
fine powder and pills or flakes. The fine powder is good at diffusing in water, so it is used in solution or liquid related industries. For example, it is used to bleach and absorb odor in sugar industry, to produce cooking oil in food industry, and to purify water.
The pill or flake type is used in gas-purifying industries / products; such as, air purifier, poisonous gas preventor, and cigarette butt, etc. The growth of activated carbon market depends on the growth of industries that use it, which vary greatly from air purifier industry, drinking water and tap water industry, metal-plated industry, and food industry. In addition, activated carbon can be used in household. Its major household usage is found in products that absorb odors; such as a refrigerator's stuffy smell, wardrobe's and closet’s smells, etc.
Hence, it can be seen that activated carbon market is broad and has a potential for consistent demand in the country. Besides, it can be exported to use in the industries that need high quality activated carbon; such as, in particular kinds of air purifiers. However, the import figures are still higher than the export. Important production materials include coconut shells, palm shells, oil, husks, and sawdust, all of which have to be burnt into ashes for activated carbon making. Also, chemicals such as zinc chloride and phosphoric acid are used. Classification Activated carbons are complex products which are difficult to classify on the basis of their behaviour, surface characteristics and preparation methods. However, some broad classification is made for general purpose based on their physical characteristics. Powdered activated carbon (PAC)
A micrograph of activated charcoal under bright fieldillumination on a light microscope. Notice the fractal-like shape of the particles hinting at their enormous surface area. Each particle in this image, despite being only around 0.1 mm wide, has a surface area of several square metres.[citation needed]The entire image covers a region of approximately 1.1 by 0.7 mm, and the full resolution version is at a scale of 6.236 pixels/μm. Traditionally, active carbons are made in particulate form as powders or fine granules less than 1.0 mm in size with an average diameter between .15 and .25 mm.
Thus they present a large surface to volume ratio with a small diffusion distance. PAC is made up of crushed or ground carbon particles, 95–100% of which will pass through a designated mesh sieve. Granular activated carbon is defined as the activated carbon retained on a 50-mesh sieve (0.297 mm) and PAC material as finer material, whileASTM classifies particle sizes corresponding to an 80-mesh sieve (0.177 mm) and smaller as PAC. PAC is not commonly used in a dedicated vessel, due to the high head loss that would occur. PAC is generally added directly to other process units, such as raw water intakes, rapid mix basins, clarifiers, and gravity filters.
Granular activated carbon (GAC) Granular activated carbon has a relatively larger particle size compared to powdered activated carbon and consequently, presents a smaller external surface. Diffusion of the adsorbate is thus an important factor.
These carbons are therefore preferred for all absorption of gases and vapors as their rate of diffusion are faster. Granulated carbons are used for water treatment, deodorization and separation of components of flow system. GAC can be either in the granular form or extruded. GAC is designated by sizes such as 8×20, 20×40, or 8×30 for liquid phase applications and 4×6, 4×8 or 4×10 for vapor phase applications. A 20×40 carbon is made of particles that will pass through a U.S. Standard Mesh Size No. 20 sieve (0.84 mm) (generally specified as 85% passing) but be retained on a U.S. Standard Mesh Size No. 40 sieve (0.42 mm) (generally specified as 95% retained). AWWA (1992) B604 uses the 50-mesh sieve (0.297 mm) as the minimum GAC size. The most popular aqueous phase carbons are the 12×40 and 8×30