The bath is then heated to temperatures of 450-900 degrees Celsius (much less than the heat needed for gas activation) and left for a specific amount of time. A bath of acid, base, or other chemicals is prepared, and the material is submerged in this solution. First, carbonization and chemical activation occur simultaneously in chemical treatment. The process of chemical treatment is slightly different from the gas activation of carbon. Then, an oxygenated gas is pumped into the environment and heated between 9 degrees Celsius, causing the oxygen to bond to the carbon's surface. For physical gas treatment, the carbonization/pyrolysis process must take place in an inert environment at 600-900 degrees Celsius. After being oxidized, the active carbon gains its good adsorption characteristics and is ready to collect contaminants in liquid/gaseous applications. This environment exposes it to oxygen for oxidization purposes. The activating of carbon can be done directly through heating carbon in a chamber while gas is pumped in. This can occur in one of two ways: gas or chemical treatment. Once the porous form of carbon is produced, it needs to undergo oxidization so it can be adsorbent, or “activated”. This is very similar to “coking,” a method of producing coke from charcoal, a type of carbon-based fuel. What remains is usually 20-30 percent of the beginning weight and consists of mostly carbon with a small percentage of inorganic ash. Carbon-rich material is placed in a small (relative to the amount of material) furnace and cooked at extreme temperatures topping 2000 degrees Celsius. Very dense carbonaceous material is used in the beginning, because the result needs to be extra-porous for activated carbon purposes. This heating process, called pyrolysis, comes from an ancient technique for making charcoal. CarbonizationĬarbonization is the process of taking a carbon-rich piece of material and converting it to pure carbon through heating. The sections below will briefly detail these processes. Once the material is carbonized, the material needs to be oxidized or treated with oxygen either by exposure to CO 2 or steam or by an acid-base chemical treatment. A carbonaceous source such as wood, coal, peat, or any organic carbonaceous material is carbonized, which means the pure carbon is extracted by a heating method known as pyrolysis. The production process of activated carbon, or the activation of carbon, exists in two forms. This means activated carbon is constantly produced to meet the demands of its uses and is kept in large supply to ensure no delay exists in the replacement process. Activated carbon is therefore highly valued in filtering, deodorization, medical, and chemical applications, as most contaminants easily bind to it and remain trapped in the carbon microstructure via many small distance-dependent atomic attractions (known as London dispersion forces).īecause carbon is produced through a relatively inexpensive and simple series of activation processes, it is widely available for applications however, activated carbon must be constantly changed as it becomes clogged with contaminants, water, and becomes a breeding ground for dangerous microorganisms after a certain contact time. These small, low-volume pores allow for increased adsorption capacity (the process of chemical surface bonding, not to be confused with absorption) and allow more reactions between the carbon and other media. Due to this structure, a pound of activated carbon, for instance, can have as much as 100 acres of surface area packed into it. Microscopes show a surface honeycombed with holes and crenelated with ridges which join to a similar structure deeper within the carbon. The pore structure of activated carbon can be seen with an electron microscope and is primarily responsible for its usefulness. There are a variety of similar substances that fall under the general classification of activated carbon such as activated coal and activated coke, but they all share the properties of vast surface area per mass, exceptional microporosity, and a composition of almost exclusively elemental carbon. It is typically made from wood, but also can be made using bamboo, coconut husk, peat, woods, coir, lignite, coal, pitch, and other dense carbon sources. Activated carbon (also known as active carbon or activated charcoal), is an artificial carbonaceous (carbon-rich) material.
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