Activated carbon is a kind of specially treated carbon. Organic raw materials (fruit shells, coal, wood, etc.) are heated under the condition of air isolation to reduce the non-carbon components (this process is called carbonization), and then react with gas and the surface is eroded to produce a micro-pore developed structure (this process is called activation). Since the activation process is a microscopic process, i.e., the surface erosion of a large number of molecular carbons is a punctiform erosion, resulting in an activated carbon surface with numerous tiny pores. Most of the micro-pores on the surface of activated carbon are between 2 and 50 nm in diameter, and even a small amount of activated carbon has a huge surface area of 500~1500 m2 per gram of activated carbon, and almost all applications of activated carbon are based on this feature of activated carbon.
Activated carbon adsorption media is easy to use and easy to handle. If stored properly, it has an indefinite shelf life. If it becomes wet or damaged due to improper storage, it can usually be easily dried out or restored. After it has been saturated with contaminants, it can usually be reactivated to almost its original adsorption capacity with only slight volume loss during reprocessing.
Activated carbon is stable and can be stored in its shipping container or packaging for many years if protected from vapor and liquid contamination. Typical packaging options include large super sacks (1,000-2,000 lbs.), mini super sacks (200-500 lbs.), pouches (20-55 lbs.), Gaylord-type boxes (200-1,000 lbs.) and steel or fiber drums (50-200 lbs.). Activated carbon only deteriorates by doing work; i.e., by acting as a catalyst or by adsorbing vapors, gases and dissolved substances. Because it is relatively pure carbon, it is resistant to most acids, bases, chemicals and corrosive substances. Repeated heating and cooling have little or no effect on its physical structure. In solvent recovery plants, adsorbents have been subjected to as many as 10,000 heating and cooling cycles without significant breakdown of the granules or pellets.
The best grades of granular activated carbon are hard and abrasion resistant, but processing methods that tend to grind the product should be avoided. In vapor treatment systems, high velocity or uneven airflow may cause particle movement and rapid particle wear or breakage, especially if the top of the carbon bed is not held in place by a screen. Fluid flowing upward at high velocities during adsorption should be avoided as it tends to lift the particles and cause channeling. The method of handling activated carbon must be appropriate to the exact characteristics of the product being used. For example, there are different considerations for handling powder versus granular materials. Impregnated carbon usually has a slightly lower ignition point than unimpregnated carbon. There are exceptions to this, but special attention must be paid to the ignition points associated with carbon that has been impregnated or otherwise specially treated.
Activated carbon is non-toxic. Dust exposure is an issue with some activated carbons and normal dust handling procedures should be used, such as goggles and dust masks for personnel handling the carbon and the use of room dust filters to control dust levels.
Activated carbon is combustible, but does not ignite easily. Even hot activated charcoal has difficulty supporting combustion without forced ventilation, and in some cases will extinguish itself. It should not, however, be subjected to air impingement at temperatures above about 400°F. In the case of adsorption of high concentrations of vapor, the heat of adsorption (adsorption is an exothermic reaction) may be sufficient to significantly raise the temperature of the carbon. In such cases, it is best to operate with carbon partially wetted with water, which is usually done in solvent recovery plants, or by adding additional air to reduce the vapor concentration.
Activated carbon has a certain life or capacity to perform its function. When the limit is reached, the adsorbent should be replaced or reactivated.
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