1. What is activated carbon?
Activated carbon, also called activated charcoal, is a form of carbon that has been processed with oxygen to create millions of tiny pores between the carbon atoms. This increases the surface area of the substance from 500 to 1500m2/g, or 300-2,00 square meters per gram. One pound of activated carbon has the surface area equivalent of six football fields.
2. How does activated carbon work?
The increased surface area of activated carbon makes the material suitable for adsorption, a process by which impurities in substances such as fluids, vapors or gas are removed. Impure molecules are held within the carbon¡¯s internal pore structure by electrostatic attraction or chemisorption. The adsorption process helps carbon reduce dangerous matter, activate chemical reactions, and act as a carrier of biomass and chemicals.
3. What is the activated carbon¡¯s raw material?
Activated carbon is usually made from charcoal, but can be produced from wood, peat or even coconut shells.
4. How many grades does activated carbon have?
There are over 150 grades of activated carbon, each with their own uses and applications. Commercially, there are three major product groups:
¡¤Powdered activated carbon; particle size 1-150 ¦Ìm
¡¤Granular activated carbon, particle size 0.5-4 mm
¡¤Extruded activated carbon, partilce size 0.8-4 mm
5. What is adsorption?
In most applications activated carbon removes impurities from fluids, vapors or gas by a process called adsorption. Adsorption is a surface phenomenon that results in the accumulation of molecules within the internal pores of an activated carbon. This occurs in pores slightly larger than the molecules that are being adsorbed, which is why it is very important to match the pore size of the activated carbon with the molecules you are trying to adsorb.
6. How does activated carbon perform its other functions?
Activated carbon performs other functionalities depending on the application:
¡¤Reduction: e.g. removal of chlorine from water is based on chemical reduction reactions
¡¤Catalysis: activated carbon can catalyze a number of chemical conversions, or can be a carrier of catalytic agents (e.g. precious metals)
¡¤Carrier of biomass: support material in biological filters
¡¤Carrier of chemicals: e.g. slow release applications colorant: activated carbon's function in licorice is its color
7. Which is right for your application, powdered or granular activated carbon?
Apart from the activated carbon product to be selected, a key issue to address is the type of technology to apply. Typically, powdered activated carbon is dosed into the process stream (gas or liquid) and, after a certain contact time, separated by filtration or settling. Some of the issues involved: required contact time, dosing system, single or multi-stage dosing, carbon separation, safety measures.
Granular Activated Carbon (GAC) is mostly used in fixed filter beds, or alternatively in (pseudo-) moving filter beds. Some of the issues involved: required contact time (alternatively: hydraulic space velocity), permanent or mobile filter vessels, filling and emptying facilities, safety measures. Further, a crucial consideration regarding GAC refers to possible regeneration, in situ or off site.
Abrasion/Hardness Number: relative measure of the ability of granular or pelletized activated carbon to resist attrition during handling and use.
Absorption: a process in which molecules are taken up by a liquid or solid and distributed throughout the body of the liquid or solid. Activated carbons do not absorb other materials (impurities).
Activated Carbon: a family of carbonaceous materials manufactured by processes that develop an internal pore structure with adsorptive properties.
Adsorption: a process in which molecules or atoms are concentrated on a surface by chemical or electrostatic (physical) forces, or both.
Apparent or Bulk Density: usually measured in g/ml or pounds per cubic foot. Bulk Density is used to determine the weight of a fixed volume of activated carbon.
Chemisorption (chemical adsorption): the binding of an adsorbate to the surface of a solid by forces whose energy levels approximate those of a chemical bond.
Dosage: the quantity of substance applied per unit weight or volume of the fluid (liquid or gas) being treated with carbon.
Effective Size: in millimeters; the size of screen opening which will permit 10% of the carbon sample to pass but will retain the balance (90% by weight); usually determined by interpolation on a cumulative particle size distribution plot on a logarithmic probability graph.
Granular Activated Carbon (GAC): an activated carbon with at least 90% of the particles greater than than 80 mesh in size.
Impregnated Carbons: activated carbons that are post-treated with various chemical compounds designed to enhance the adsorptive or catalytic properties of the carbon in either liquid or gas phase applications.
Iodine Number: mg/l, the amount of iodine adsorbed by one gram of carbon at equilibrium with a 0.02N iodine concentration filtrate.
Macropore: in activated carbon, a pore having a diameter greater than 500 angstroms.
Mesopore: in activated carbon, a pore having a diameter between 20-500 angstroms.
Micropore: in activated carbon, a pore having a diameter less than 20 angstroms.
Molasses DE (Decolorizing Efficiency): a measure of a carbon's ability to remove color from a standard molasses solution. The test carbon performance is compared to a standard at 90% color removal. Hence, 100 RE for a carbon means it adsorbs color from molasses like the standard carbon.
Particle Size: affects the rate of contaminant adsorption or catalytic activity. Particle size also affects PAC filtration performance or filtration rate in water or wastewater treatment.
Phenol Number: the concentration of phenol in excess of 0.01 ppm required in one liter of water, so that after adding one gram of a pulverized activated carbon, stirring four hours, and filtering to remove the carbon, only 0.01 ppm of phenol will be left in the solution.
Powdered Activated Carbon (PAC): an activated carbon with particles predominantly smaller than 80 mesh in size.
Reactivation: the act of restoring adsorptive character to a contaminated activated carbon by a process similar to the original activation process.
Surface Area (B.E.T.): the total surface area of a solid calculated by the B.E.T. (Brunauer, Emmett, Teller) equation, from nitrogen adsorption or desorption data obtained under specified conditions; square meters per gram.
Total Ash Content: a relative indicator of the amount of mineral matter (Ca, Mg, Si, Fe, etc.) in activated carbon.
9. The history if activated carbon
The exact date and time that man began using activated carbon or charcoal is lost to history. However, there is evidence of its usage and importance throughout history, from the ancient world to the modern era.
Around 3750 B.C., the Ancient Egyptians made use of charcoal to smelt ores to create bronze. By 1500 B.C., according to the first documented use of charcoal as written on papyrus, the Egyptians¡¯ use of charcoal had progressed, using the material to absorb unpleasant odors, cure intestinal ailments and even preserve the dead.
In 400 B.C., the Ancient Hindus and Phoenicians had started using charcoal to purify water because of its antiseptic properties. The Phoenicians were noted for charring barrels to hold water on long sea voyages. This practice was adopted by many other seafarers throughout history, including Christopher Columbus, and continued until the 1800s.
By 50 A.D, Hippocrates, one of the most historic figures in the history of medicine started using charcoal for a number of medical purposes, including treating epilepsy, chlorosis and vertigo. By 2 A.D., another important figure in medical history, Claudius Galen produced almost 500 treatises on the use of charcoal in medicine.
Though charcoal was in steady use throughout the centuries, it made a strong resurgence in the late 1700s. More doctors, chemists and other scientific figures began experimenting with the material for both medical and manufacturing processes. In 1773, chemist Carl Wilhelm Scheele quantified the adsorption forces for porous carbon by measuring the volume of gases adsorbed by the material. In 1776, Lowitz performed the first experiments that proved that carbon could be used to decolor solutions, noting the adsorptive properties of charcoal in liquid phase.
One of the biggest discoveries in this period, however, was in 1794, when an English sugar refinery found that carbon could be used as a decoloring agent. This revolutionized the sugar industry, which was looking for a way to produce a whiter, more appealing product. In turn, this development pushed the experimentation of activated carbon further. By 1805 all of Europe was using charcoal to decolor sugar.
Charcoal continued to be a strong force in the 19th century, especially in medicine. It was used for poultices, sloughing ulcers and treating gangrenous sores. After the activated carbon process was developed around 1820, it became noted in medical journals as an antidote for poison and a treatment for intestinal disorders. In 1883, French chemist, Gabriel Bertrand, in an effort to prove charcoal¡¯s worth as a poison treatment, swallowed arsenic mixed with charcoal. Others followed suit and performed the same trick.
In 1862, Frederick Lipscombe helped pave the way for commercial applications of activated carbon by using the material to purify potable water. German physicist, Heinrich Kayser, coined the term "adsorption" to describe charcoal¡¯s ability to uptake gases in 1881.
THE 20TH CENTURY
Activated carbon was first produced on an industrial scale at the beginning of the twentieth century. In 1909 a plant named ¡°Chemische Werke¡± was built to manufacture carbon for commercial use, producing various carbon such as Eponit, Purit and our very own Norit. The Norit Company, a manufacturer in Holland, was started in 1911 and became widely known in the sugar industry for their powdered solutions, widely used in the chemical and food industries for decolorization.
During World War I activated carbon was used in gas masks worn by American soldiers to protect them from poison gas. This development led to the production of granular carbon on a large scale.
ACTIVATED CARBON TODAY
Today, the uses of activated carbon continue to grow. It can be found in virtually every hospital, clinic or doctor¡¯s office in the world, used on almost a daily basis. The material is used in a variety of industries, including corn and cane sugar refining, gas adsorption, dry cleaning, pharmaceuticals, fat and oil removal, alcoholic beverage production and much more. The biggest market for activated carbon is in the purification of municipal water supplies. Activated carbon filters are used in water treatment to remove organic compounds that produce carcinogens during the disinfection of water.
10. Proper ties and applications
The quality and use of activated carbon is evaluated on a number of criteria dependent on their intended use. Here are a few of the most common properties important for manufacturers.
Density: The higher the density of a sample of activated carbon, the greater the volume of activity or adsorption possible. This is also an indicator of quality.
Particle Size Distribution: The greater the particle size of an activated carbon, the greater the access to surface area, and the faster the rate of adsorption by the material.
Mesh Size: The physical size or mesh size of the carbon can significantly impact its resistance to flow within a system. The smaller the mesh, the greater the resistance to flow, and the greater the adsorption.
Molasses Number: The molasses number is the measure of the mesopore content of the activated carbon, and the degree of decolorization. A high molasses umber indicates a high adsorption of big molecules.
Ash Level: The ash level is a measure of the purity of a sample of activated carbon. This is important when the carbon is used as a catalyst in an industrial process.
Activated carbon is utilized by a number of industries for its purification properties.
Water Treatment: The biggest application of activated carbon is in the purification of water. It is used in a variety of water treatment industries, from municipal water supply treatment, wastewater treatment, swimming pools, aquariums and even home filtration systems.
Air Purification: Activated carbon is used to control potentially harmful, environmentally damaging or unpleasant odors in a number of environments, including homes, manufacturing facilities and in operating rooms.
Food & Beverage: The Food & Beverage industry uses activation as part of various processes, such as the decolorization of sugar, purify organic compounds, chlorine removal, decaffeination and many other practices.
Industrial: Activated carbon is used as a catalyst for many industrial applications, gas processing, gas storage and delivery, gold recovery, pharmaceutical purification and many other practices.
Medical: Activated carbon can be found in almost every hospital, clinic or doctor¡¯s office in the world. It is used to as a poison treatment, odor control, filtration, respiration masks and wound dressing just to name a few applications.
11. Activated carbon manufacturing process
Activated carbon is manufactured through two different processes.
The Physical or Steam Activation Process is known for yielding higher quality activated carbon. However, due to the amount of heat necessary to produce activated carbon using this method, it is more expensive and requires industry manufacturing.
Physical Activation, or Steam Activation, places a carboneous source material such as wood, coal, petroleum pitch or even coconut shells in a tank without oxygen, and pyrolizes them at a high temperature, usually 600¡ã - 900¡ã C, to create a char. Next, the source material is exposed to different chemicals such as argon and nitrogen. Then, the char is oxidized or ¡°activated¡± at temperatures above 250¡ã C, usually 600¡ã - 1200¡ã C, blasted by steam.
Through this process, all of the volatile compounds are removed, as layer after layer of carbon atoms are pealed off, enlarging the internal pores and leaving behind a carbon skeleton. By decreasing the number of carbon atoms, the internal surface area of the material is increased. After the process is complete, 3 lbs. of source material usually yields 1 lb. of activated carbon.
Chemical Activation is often the preferred method due to its shorter production time and lower temperatures required to produce activated carbon.
During chemical activation, the source material is impregnated with certain chemicals, typically an acid, a strong base or a salt (phosphoric acid, potassium, hydroxide, calcium chloride and zinc chloride). The chemical solution chews away at the internal structure of the Then, the raw material is carbonized at a low temperature, usually 450¡ã ¨C 900¡ã C. It is believe that in this process, the carbonization / activation steps proceed simultaneously.
This process results in a very large surface area, that is about 600 ¨C 1,200 sq. ft. per gram, depending on the source material.