MOLECULAR FORMULA: C
MOLECULAR WEIGHT: 12.011
Activated carbon is a form of carbon commonly used to filter contaminants from water and air, among many other uses.
Activated carbon is processed (activated) to have small, low-volume pores that increase the surface area available for adsorption (which is not the same as absorption) or chemical reactions.
Activation is analogous to making popcorn from dried corn kernels: popcorn is light, fluffy, and has a surface area that is much larger than the kernels.
Activated is sometimes replaced by active.
Due to Activated carbon^s high degree of microporosity, one gram of activated carbon has a surface area in excess of 3,000 m2 (32,000 sq ft) as determined by gas adsorption.
Activated carbon has a specific surface area in the range of 2.0–5.0 m2/g.
An activation level sufficient for useful application may be obtained solely from high surface area.
Further chemical treatment often enhances adsorption properties.
Activated carbon is usually derived from waste products such as coconut husks; waste from paper mills has been studied as a source.
These bulk sources are converted into charcoal before being 'activated'.
When derived from coal, Activated carbon is referred to as activated coal.
Activated carbon is derived from coke.
Activated carbon retains pesticides, fats, oils, detergents, disinfection by-products, toxins, color producing compounds, compounds produced by the decomposition of algae, vegetables or animal metabolism.
Activated carbon is considered a “universal antidote”, and is applied in emergency rooms and hospitals.
Activated carbons are a very versatile group of adsorbents, with capability for selectively adsorbing thousands of organic, and certain in- organic, materials.
From medicinal uses of powdered carbons in ancient Egypt, through charred interiors of whiskey barrels, carbon has been activated and used as an adsorbent for centuries.
Activated carbon was first widely used in WWI military gas masks and, in the years between World Wars, commercially in solvent recovery systems.
Activated carbons achieved their first prominent applications following WWI’, in sugar de-colorization and in purification of antibiotics.
Today, there are hundreds of applications if diverse uses under the general heading of environmental control are counted separately, ongoing applications number in the thousands
Activated carbon is an adsorbent derived from carbonaceous raw material, in which thermal or chemical means have been used to remove most of the volatile non-carbon constituents and a portion of the original carbon content, yielding a structure with high surface area.
The resulting carbon structure may be a relatively regular network of carbon atoms derived from the cellular arrangement of the raw material, or it may be an irregular mass of crystallite platelets, but in either event the structure will be laced with openings to appear, under electron micrographic magnification, as a sponge like structure.
The carbon surface is characteristically non-polar, that is, Activated carbon is essentially electrically neutral.
This non-polarity gives the activated carbon surface high affinity for comparatively non-polar adsorbates, including most organics.
As an adsorbent, activated carbon is this respect contrasts with polar desiccating adsorbents such as silica gel and activated alumina.
Activated carbon will show limited affinity for water via capillary condensation, but not the surface attraction for water of a desiccant.
Activated carbon can be produced from various carbonaceous raw materials, each of which will impart typical qualities to the finished pro-duct.
Commercial grades are normally prepared from coconut and other nut shells, bituminous and lignite coals, petroleum coke, and sawdust, bark and Other wood products.
In general, nut shells and petroleum cokes will produce very hard carbons with a pore structure characterized by. above, coals a type structure in comparatively hard carbons, and wood structure in carbons lacking great crush and abrasion resistance.
Activated carbon should be emphasized that specific production techniques may yield carbons that depart from the norm of a given raw material.
The solid, or skeletal, density of most activated carbons will range between 2.0-2.1 g/cc, or about 125-130 lbs/cubic foot.
However, this would describe a material with essentially no surface area and no adsorptive capacity.
For Activated carbon, a much more practical density is the apparent density, or mass of a given volume of adsorbent particles.
This density will be significantly lower than the solid density, due to the presence of pores within particles, and void space between particles.
Since Activated carbons are used in adsorbers of fixed volume, apparent density values can be used to calculate volume activity, which may help determine the work capacity of an adsorber with alternative carbon loadings.
For example, assume that Activated carbon adsorbs iodine to produce a standardized Iodine Number of 1100 mg/g., and has an A.D. of 0.4 g/cc Carbon B has an Iodine Number of 950 mg/g and an A.D. of 0.5 g/cc.
Multiplying the A.D. by the weight basis activity value, carbon A has a volume iodine capacity of 440 mg/cc while carbon B has a value of 475 mg/cc.
Therefore, carbon B, which has lower activity, might actually do more work and therefore have a longer service life than carbon A of an equal volume.
If the price of carbon B permitted filling a given adsorber with the greater weight required, it could thus be the most economical of these adsorbents on a net cost basis.
Activated carbons quality and uniformity will fundamentally relate to characteristics involving: adsorption capacity and a physical description of the product.
The activated carbon industry, often in cooperation with A.S.T.M. and other standards organizations, has developed a series of tests that measure these characteristics.
As would be expected, such tests can be used both as production controls and, as published specifications, assurance for prospective buyers.
Not all granular activated carbons manufacturers and distributors publish adsorption specifications.
Among those that adhere to specifications, the same precise group of tests may not be used.
However, some correlation of values is usually possible as, for example, between the vapor phase carbon tetrachloride test used in the U.S. and the benzene and acetone tests more common in Europe and the Far East.
Among physical tests, the methods to determine moisture, apparent density and particle size or distribution are relatively standard among manufacturers.
Hardness or abrasion values may require some interpretation or correlation, as above.
Activated carbon is a crude form of graphite, the substance used for pencil leads.
Activated carbon differs from graphite by having a random, imperfect structure which is highly porous over a broad range of pore sizes from visible cracks and crevices to molecular dimensions.
The graphite structure gives the Activated carbon its very large surface area which allows the carbon to adsorb a wide range of compounds.
Activated carbon has the strongest physical adsorption forces, or the highest volume of adsorbing porosity, of any material known to mankind.
Activated carbon (activated charcoal) can have a surface of greater than 1000m²/g.
This means 3g of activated carbon can have the surface area of a football field.
Activated carbon is used to purify liquids and gases in a variety of applications, including municipal drinking water, food and beverage processing, odor removal, industrial pollution control.
Activated carbon is produced from carbonaceous source materials, such as coconuts, nutshells, coal, peat and wood.
The primary raw material used for activated carbon is any organic material with a high carbon content.
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. Activated carbon is produced specifically so as to achieve a very big internal surface (between 500 - 1500 m2/g).
This big internal surface makes active carbon ideal for adsorption.
Activated carbon is a very useful adsorbent.
Due to their high surface area, pore structure (micro, meso and macro), and high degree of surface reactivity, activated carbon can be used to purify, dechlorinate, deodorize and decolorize both liquid and vapor applications.
Moreover, activated carbons are economical adsorbents for many industries such as water purification, food grade products, cosmetology, automotive applications, industrial gas purification, petroleum and precious metal recovery mainly for gold.
The base materials for activated carbons are coconut shell, coal or wood.
Activated carbon is created by altering the surface structure of activated carbon.
Activated carbon is modified by gas processing at high temperatures to change the electronic structure and create the highest level of catalytic activity on carbon for reducing chloramine and H2S in water.
This added catalytic functionality is much greater than that found in traditional activated carbons.
Activated carbon is an economical solution to treat H2S levels as high as 20 to 30 ppm.
Activated carbon converts adsorbed H2S into sulfuric acid and sulfurous acid which are water soluble, so carbon systems can be regenerated with water washing to restore H2S capacity for less frequent physical change-outs.
Activated carbon is a porous solid able to coordinate to itself various types of molecules.
This interaction can be of merely physical nature (attraction between non-bonded atoms or Van der Waals forces) or physical- chemical origin and its strength can vary depending upon the type of molecule and the type of activated carbon.
Activated carbons are usually produced by steam activation process, during which carbon or starting materials containing carbon atoms are partially gasified by reacting with steam or other oxidizing gases.
Raw materials such as charcoal, bituminous coal, lignite, coconut charcoal, peat coke or hard wood are used.
In addition, chemical activation can also be used to activate raw materials containing cellulose.
Saw dust for example is treated with chemicals that have a dehydrating effect at high temperature.
Both processes result in porous carbon which consists in an extremely porous structure with highly developed internal surface that can range from 500 up to 1500 square meters per gram of carbon.
To cover a wide variety of applications, GALE, starting from raw activated carbons, manufactures more than 40 different activated carbon finished products which are differing in material origin, physical shape (granular, extrudated or powdered), surface area, pore volume distribution, mesh size and other physical properties, in addition to impregnated carbons for special applications.
Activated carbon is a very useful adsorbent material with high porosity and high carbon content.
It has a wide application range due to its pore structure, large surface area and high reactivity.
Activated carbons, which are economical absorbents for many industries, are used to remove odor and color, to purify and dechlorinate liquid and steam applications.
Common uses are water treatment, food grade products, automotive applications, cosmetics, gas purification and industrial processes.
The main and common production materials of activated carbons are coconut shell, charcoal and wood.
Activated carbon is a highly porous substance that attracts and holds organic chemicals inside it.
The great surface area of this internal pore network results in an extremely large surface area that can attract and hold organic chemicals.
Activated carbon is an adsorbent that is effective at attracting pollutants and trapping them within itself.
Activated carbon’s able to achieve this as a result of its pore structure, high surface area, and high surface reactivity.
Activated carbon is a very economical solution for different industries because it’s easy to source and can be formed from a base material that’s either wood, coal, or coconut shells. Each base material may offer a slightly different product, but it will generally function identically in different applications.
Activated carbon has a large number of applications.
Depending on the application, there is a distinctive type of activated carbon that’s put to use.
Therefore, it’s crucial to pick the appropriate grade and size with consideration of the pollutant that you intend to remove or the degree of purity you wish to achieve.
Activated carbon is used by industries for waste water treatment, sewage water treatment, drinking water treatment, etc.
Apart from water and wastewater treatment, it is also used in flue gas treatment.
The molecule of activated carbon is able to catch the dioxins and furans by adsorption.
Activated carbons are manufactured carbonaceous non-hazardous products that have a porous structure and a large internal surface area.
The chemical structure of activated carbon can be defined as a crude form of graphite with a random or amorphous structure.
This amorphous structure is highly porous over a broad range of pore sizes, varying from visible to molecular sized cracks and crevices.
Activated carbon is a highly porous, high surface-area adsorptive material with a largely amorphous structure.
Activated carbon is composed primarily of aromatic configurations of carbon atoms joined by random cross-linkages.
Activated carbon differs from another form of carbon graphite in that activated carbon has sheets or groups of atoms that are stacked unevenly in a disorganized manner.
The degree of order varies based on the starting raw material and thermal history.
Graphitic platelets in steam-activated coal are somewhat ordered, while more amorphous aromatic structures are found in chemically activated wood.
Randomized bonding creates a highly porous structure with numerous cracks, crevices, and voids between the carbon layers.
The molecular size, porosity, and the resulting enormous internal surface area of activated carbon make this material extremely effective for adsorbing a wide range of impurities from both liquids and gases.
Activated carbon sorbents are tailored for specific applications mainly based on pore size and pore volume requirements.
Porosity and other parameters are controlled by raw material selection, activation process conditions, and the post-processing steps.
Activated carbon is a granular material produced mostly by roasting charcoal from coconut shells or coal at 800 to 1000°C to “activate” it.
Impurities are removed by acid washing.
Typically, Activated carbon has pore sizes ranging from 500 to 1000nm and a surface area of about 1000m2/gram.
A much purer form of activated carbon is produced by pyrolysing polymer beads.
Activated carbon, also known as 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.
Activated carbon has high degree of microporosity.
Activated carbon is usually derived from charcoal.
When derived from coal, Activated carbon is referred to as activated coal.
Activated coke is derived from coke.
Therefore activated carbon, activated charcoal, activated coke, active carbon may be said to perform the same function.
Activated carbons are used as an adsorbent by the separation and purification industries.
Activated carbons are composed of a microporous, homogenous structure with high surface area and show radiation stability.
Activated carbon is a carbon material with great specific surface area and decolorization ability. In the 19th century, people apply sugar, wine and water for decolorization, de-flavor and purification.
There is a history of 100 years for bone charcoal to be used for water filtration.
During the First World War, it has begun to produce activated carbon as gas masks.
To the 20th century, 90 years, the activated carbon has also gotten wide application in the sewage treatment, organic solvent concentration recovery, air purification and other fields such as environmental protection and gold extraction.
The carbon material remaining after the carbonization of the organic matter at 600 to 700 °C has the ability to be active or activated.
However, these carbon materials can firmly adsorb some gaseous hydrocarbons and other substances, reducing their activation capacity need to increase the carbonization temperature to above the critical temperature for the formation of activated carbon.
So that these adsorbed gaseous substances are decomposed and separated. Then apply water vapor and carbon dioxide for activation to improve the activation capacity to industrial applications.
Activated carbons are internally porous microcrystalline, non-graphitic forms of carbon.
Activated carbons possess large surface area (～1000 m2/g) and pore volumes which make them useful for applications in energy storage devices, catalysis, and for removal of impurities from gases and liquids.
Activated carbon has been modified with Bis(2-ethylhexyl)phosphate and is well suited for metal ion removal from water.
Activated carbon is used in methane and hydrogen storage, air purification, capacitive deionization, supercapacitive swing adsorption, solvent recovery, decaffeination, gold purification, metal extraction, water purification, medicine, sewage treatment, air filters in respirators, filters in compressed air, teeth whitening, production of hydrogen chloride, edible electronics, and many other applications.
One major industrial application involves use of activated carbon in metal finishing for purification of electroplating solutions.
For example, Activated carbon is the main purification technique for removing organic impurities from bright nickel plating solutions.
A variety of organic chemicals are added to plating solutions for improving their deposit qualities and for enhancing properties like brightness, smoothness, ductility, etc.
Due to passage of direct current and electrolytic reactions of anodic oxidation and cathodic reduction, organic additives generate unwanted breakdown products in solution.
Their excessive build up can adversely affect plating quality and physical properties of deposited metal.
Activated carbon treatment removes such impurities and restores plating performance to the desired level.
Main article: Activated charcoal (medication)
-Activated charcoal for medical use:
Activated carbon is used to treat poisonings and overdoses following oral ingestion.
Tablets or capsules of activated carbon are used in many countries as an over-the-counter drug to treat diarrhea, indigestion, and flatulence.
However, activated charcoal shows no effect on intestinal gas and diarrhea, and is, ordinarily, medically ineffective if poisoning resulted from ingestion of corrosive agents, boric acid, petroleum products, and is particularly ineffective against poisonings of strong acids or bases, cyanide, iron, lithium, arsenic, methanol, ethanol or ethylene glycol. Activated carbon will not prevent these chemicals from being absorbed into the human body.
Incorrect application results in pulmonary aspiration, which can sometimes be fatal if immediate medical treatment is not initiated.
Activated carbon, in 50% w/w combination with celite, is used as stationary phase in low-pressure chromatographic separation of carbohydrates (mono-, di-, tri-saccharides) using ethanol solutions (5–50%) as mobile phase in analytical or preparative protocols.
Activated carbon is useful for extracting the direct oral anticoagulants (DOACs) such as dabigatran, apixaban, rivaroxaban and edoxaban from blood plasma samples.
For this purpose it has been made into "minitablets", each containing 5 mg activated carbon for treating 1ml samples of DOAC.
Since this activated carbon has no effect on blood clotting factors, heparin or most other anticoagulants this allows a plasma sample to be analyzed for abnormalities otherwise affected by the DOACs.
Activated carbon is usually used in water filtration systems.
In this illustration, the activated carbon is in the fourth level (counted from bottom).
Carbon adsorption has numerous applications in removing pollutants from air or water streams both in the field and in industrial processes such as:
-Drinking water filtration
-Volatile organic compounds capture from painting, dry cleaning, gasoline dispensing operations, and other processes
-Volatile organic compounds recovery (solvent recovery systems, SRU) from flexible packaging, converting, coating, and other processes.
During early implementation of the 1974 Safe Drinking Water Act in the US, EPA officials developed a rule that proposed requiring drinking water treatment systems to use granular activated carbon.
Because of its high cost, the so-called GAC rule encountered strong opposition across the country from the water supply industry, including the largest water utilities in California. Hence, the agency set aside the rule.
Activated carbon filtration is an effective water treatment method due to its multi-functional nature.
There are specific types of activated carbon filtration methods and equipment that are indicated – depending upon the contaminants involved.
Activated carbon is also used for the measurement of radon concentration in air.
Activated carbon (charcoal) is an allowed substance used by organic farmers in both livestock production and wine making.
In livestock production Activated carbon is used as a pesticide, animal feed additive, processing aid, nonagricultural ingredient and disinfectant.
In organic winemaking, Activated carbon is allowed for use as a processing agent to adsorb brown color pigments from white grape concentrates.
Activated carbon is sometimes used as biochar.
-Distilled alcoholic beverage purification:
Activated carbon filters (AC filters) can be used to filter vodka and whiskey of organic impurities which can affect color, taste, and odor.
Passing an organically impure vodka through an activated carbon filter at the proper flow rate will result in vodka with an identical alcohol content and significantly increased organic purity, as judged by odor and taste.
Research is being done testing various activated carbons' ability to store natural gas and hydrogen gas.
The porous material acts like a sponge for different types of gases.
The gas is attracted to the carbon material via Van der Waals forces.
Some carbons have been able to achieve bonding energies of 5–10 kJ per mol.
The gas may then be desorbed when subjected to higher temperatures and either combusted to do work or in the case of hydrogen gas extracted for use in a hydrogen fuel cell.
Gas storage in activated carbons is an appealing gas storage method because the gas can be stored in a low pressure, low mass, low volume environment that would be much more feasible than bulky on-board pressure tanks in vehicles.
Filters with activated carbon are usually used in compressed air and gas purification to remove oil vapors, odor, and other hydrocarbons from the air.
The most common designs use a 1-stage or 2 stage filtration principle in which activated carbon is embedded inside the filter media.
Activated carbon filters are used to retain radioactive gases within the air vacuumed from a nuclear boiling water reactor turbine condenser.
The large charcoal beds adsorb these gases and retain them while they rapidly decay to non-radioactive solid species.
The solids are trapped in the charcoal particles, while the filtered air passes through.
Activated carbon is commonly used on the laboratory scale to purify solutions of organic molecules containing unwanted colored organic impurities.
Filtration over activated carbon is used in large scale fine chemical and pharmaceutical processes for the same purpose.
The carbon is either mixed with the solution then filtered off or immobilized in a filter.
Activated carbon, often infused with sulfur or iodine, is widely used to trap mercury emissions from coal-fired power stations, medical incinerators, and from natural gas at the wellhead.
However, despite its effectiveness, activated carbon is expensive to use.
Since Activated carbon is often not recycled, the mercury-laden activated carbon presents a disposal dilemma.
The problem of disposal of mercury-laden activated carbon is not unique to the United States.
In the Netherlands, this mercury is largely recovered and the activated carbon is disposed of by complete burning, forming carbon dioxide (CO2).
Activated, food-grade charcoal became a food trend in 2016, being used as an additive to impart a "slightly smoky" taste and a dark coloring to products including hotdogs, ice cream, pizza bases and bagels.
People taking medication, including birth control pills and antidepressants, are advised to avoid novelty foods or drinks that use activated charcoal coloring, as it can render the medication ineffective.
The adsorbing aspects of activated charcoal have made it a popular additive in many skin care products.
Products such as Activated Charcoal Soaps and Activated Charcoal Face Masks and scrubs combine the use of the charcoal's adsorption ability along with the cleansing ability of soap.
TYPES OF ACTIVATED CARBON:
-Granulated activated carbon
-Pelletized activated carbon
-Powdered activated carbon
-Impregnated activated carbon
-Catalytic activated carbon
-Activated carbon is widely used in sugar, glucose, caramel, oil, fruit juice and wine drinks for decolorization purification, removal of colloidal substances and water treatment.
-Activated carbon is used for PSA separation of air and preparation of nitrogen;
-Activated carbon is mainly used in the Chinese or western original drug in pharmaceutical industry;
-Activated carbon is suitable for the decoloring and deodorization of brewing industry, production of edible oil and food additive with special decoloring capability on caramel and molasses.
-Activated carbon can be used for desulfurization, water purification, air purification, recovery of solvents, absorption and as a catalyst carrier;
-Activated carbon can be used in gas, coke oven gas, natural gas, carbon dioxide and shift gas to remove hydrogen sulfide.
-Activated carbon is mainly used for the deodorization, dechlorination and liquid decolorization in food, beverage, pharmaceutical and high-purity drinking water; as well as widely used in the chemical industry for solvent recovery and gas separation.
-Activated carbon is widely used in the pre-treatment of industrial water and domestic water and the deep purification treatment on chemical, printing and dyeing, electronics, coking, environmental protection and other industrial wastewater.
-Activated carbon is widely used in the recycling of organic solvents including toluene, xylene, ether, ethanol, acetone, gasoline, trichloropropane and carbon tetrachloride.
-For the absorption of gas, liquid hazardous substances, the removal of various organic vapors and filtering out harmful gases and air odor.
-Removal of volatile organic compounds such as Benzene, TCE, and PCE.
-Hydrogen Sulfide (HS) and removal of waste gases
-Impregnated activated carbon used as a bacteria inhibitor in drinking water filters
-Removal of taste and odor causing compounds such as MIB and geosmin
-Recovery of gold
-Removal of chlorine and chloramine
WHAT DOES ACTIVATED CARBON DO?
Activated carbon attracts and holds organic chemicals from vapor and liquid streams cleaning them of unwanted chemicals.
Activated carbon does not have a great capacity for these chemicals, but is very cost effective for treating large volumes of air or water to remove dilute concentrations of contamination.
For a better perspective, when individuals ingest chemicals or are experiencing food poisoning, they are instructed to drink a small amount of activated carbon to soak up and remove the poisons.
HOW IS ACTIVATED CARBON MADE?
There are two different ways to make activated carbon but for this article we will provide you with the more efficient way that will create higher quality and purer activated carbon.
Activated carbon is made by being placed in a tank without oxygen and subjecting it to extremely high temperatures, 600-900 degrees Celsius.
Afterwards, the carbon is exposed to different chemicals, commonly argon and nitrogen, and again placed in a tank and superheated from 600-1200 degrees Celsius.
The second time the carbon is placed in the heat tank, it is exposed to steam and oxygen.
Through this process, a pore structure is created and the usable surface area of the carbon greatly increases.
-Very high surface area characterized by a large proportion of micropores
-High hardness with low dust generation
-Excellent purity, with most products exhibiting no more than 3-5% ash content.
-Renewable and green raw material.
-Hard materials with minimal dust generation.
-Relatively low density
-Renewable source of raw material
The surface area of activated carbon varies between 500-2000 m2/g.
That is, only 3 grams of activated carbon can have a surface area the size of a football field.
The surface area of carbonaceous materials can be expanded by the activation process.
-Total Pore Volume (TPV):
TPV refers to the total volume of the space created by the pores in an activated carbon.
The effectiveness of activated carbon increases as the total pore volume increases and is expressed in ml/g.
-Pore Volume Distribution:
The property of activated carbon is measured by the distribution of the pore size.
Activated carbon with a high dispersion ratio is required in decolorization applications.
STRUCTURE OF ACTIVATED CARBON:
The structure of activated carbon has long been a subject of debate.
WHAT IS ACTIVATED CARBON MADE FROM?
Activated carbon (activated charcoal) can made from many substances containing a high carbon content such as coal, coconut shells and wood.
The raw material has a very large influence on the characteristics and performance of the activated carbon.
Activated carbon is carbon produced from carbonaceous source materials such as bamboo, coconut husk, willow peat, wood, coir, lignite, coal, and petroleum pitch.
Activated carbon can be produced (activated) by one of the following processes:
The source material is developed into activated carbon using hot gases.
Air is then introduced to burn out the gasses, creating a graded, screened and de-dusted form of activated carbon.
This is generally done by using one or more of the following processes:
Material with carbon content is pyrolyzed at temperatures in the range 600–900 °C, usually in an inert atmosphere with gases such as argon or nitrogen
Raw material or carbonized material is exposed to oxidizing atmospheres (oxygen or steam) at temperatures above 250 °C, usually in the temperature range of 600–1200 °C.
The activation is performed by heating the sample for 1 h in a muffle furnace at 450 °C in the presence of air.
The carbon material is impregnated with certain chemicals.
The chemical is typically an acid, strong base, or a salt (phosphoric acid 25%, potassium hydroxide 5%, sodium hydroxide 5%, calcium chloride 25%, and zinc chloride 25%).
Activated carbon is then subjected to high temperatures (250–600 °C).
Activated carbon is believed that the temperature activates the carbon at this stage by forcing the material to open up and have more microscopic pores.
Chemical activation is preferred to physical activation owing to the lower temperatures, better quality consistency, and shorter time needed for activating the material.
Activated carbons are complex products which are difficult to classify on the basis of their behaviour, surface characteristics and other fundamental criteria.
However, some broad classification is made for general purposes based on their size, preparation methods, and industrial applications.
-Powdered activated carbon:
Normally, activated carbons (R 1) are made in particulate form as powders or fine granules less than 1.0 mm in size with an average diameter between 0.15 and 0.25 mm.
Thus they present a large surface to volume ratio with a small diffusion distance.
Activated carbon (R 1) is defined as the activated carbon particles retained on a 50-mesh sieve (0.297 mm).
Powdered activated carbon (PAC) material is finer material. PAC is made up of crushed or ground carbon particles, 95–100% of which will pass through a designated mesh sieve.
-Granular activated carbon:
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.
Activated carbons are suitable for adsorption of gases and vapors, because gaseous substances diffuse rapidly.
Activated carbons are used for air filtration and water treatment, as well as for general deodorization and separation of components in flow systems and in rapid mix basins.
Activated carbon can be obtained in either granular or extruded form.
Activated carbon 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.
-Extruded activated carbon (EAC):
Extruded activated carbon (EAC) combines powdered activated carbon with a binder, which are fused together and extruded into a cylindrical shaped activated carbon block with diameters from 0.8 to 130 mm.
These are mainly used for gas phase applications because of their low pressure drop, high mechanical strength and low dust content.
-Bead activated carbon (BAC):
Bead activated carbon (BAC) is made from petroleum pitch and supplied in diameters from approximately 0.35 to 0.80 mm.
Similar to EAC, Activated carbon is also noted for its low pressure drop, high mechanical strength and low dust content, but with a smaller grain size.
Its spherical shape makes it preferred for fluidized bed applications such as water filtration.
-Polymer coated carbon:
This is a process by which a porous carbon can be coated with a biocompatible polymer to give a smooth and permeable coat without blocking the pores.
The resulting carbon is useful for hemoperfusion.
Hemoperfusion is a treatment technique in which large volumes of the patient's blood are passed over an adsorbent substance in order to remove toxic substances from the blood.
Activated carbon appears as black porous odorless material with grain shape varying from the cylindrical, coarse particles to fine powder particles.
The particle diameter is generally 1~6mm, the length of about 0.7 to 4 times the diameter, or exhibiting irregular particles with a particle size of 6 to 120 mesh.
Activated carbon is odorless, tasteless and is insoluble in water and organic solvents.
The packing density is about 0.3-0.6g/ml, the micropore volume is about 0.6-0.8ml/g, and the specific surface area is about 500-1500m2/g.
Activated carbon has a strong absorption force on the organic polymer material so having a high removal capacity on the trace elements, pigments, odor substances in the liquid phase.
The most suitable pH value is 4.0~4.8, the optimum temperature is 60~70 ℃.
A gram of activated carbon can have a surface area in excess of 500 m2 (5,400 sq ft), with 3,000 m2 (32,000 sq ft) being readily achievable.
Carbon aerogels, while more expensive, have even higher surface areas, and are used in special applications.
Under an electron microscope, the high surface-area structures of activated carbon are revealed.
Individual particles are intensely convoluted and display various kinds of porosity; there may be many areas where flat surfaces of graphite-like material run parallel to each other, separated by only a few nanometers or so.
These micropores provide superb conditions for adsorption to occur, since adsorbing material can interact with many surfaces simultaneously.
Tests of adsorption behaviour are usually done with nitrogen gas at 77 K under high vacuum, but in everyday terms activated carbon is perfectly capable of producing the equivalent, by adsorption from its environment, liquid water from steam at 100 °C (212 °F) and a pressure of 1/10,000 of an atmosphere.
Physically, activated carbon binds materials by van der Waals force or London dispersion force.
Activated carbon does not bind well to certain chemicals, including alcohols, diols, strong acids and bases, metals and most inorganics, such as lithium, sodium, iron, lead, arsenic, fluorine, and boric acid.
Activated carbon adsorbs iodine very well.
The iodine capacity, mg/g, may be used as an indication of total surface area.
Carbon monoxide is not well adsorbed by activated carbon.
This should be of particular concern to those using the material in filters for respirators, fume hoods or other gas control systems as the gas is undetectable to the human senses, toxic to metabolism and neurotoxic.
Substantial lists of the common industrial and agricultural gases adsorbed by activated carbon can be found online.
Activated carbon can be used as a substrate for the application of various chemicals to improve the adsorptive capacity for some inorganic (and problematic organic) compounds such as hydrogen sulfide (H2S), ammonia (NH3), formaldehyde (HCOH), mercury (Hg) and radioactive iodine-131(131I).
This property is known as chemisorption.
Many carbons preferentially adsorb small molecules.
Iodine number is the most fundamental parameter used to characterize activated carbon performance.
Activated carbon is a measure of activity level (higher number indicates higher degree of activation) often reported in mg/g (typical range 500–1200 mg/g).
Activated carbon is a measure of the micropore content of the activated carbon (0 to 20 Å, or up to 2 nm) by adsorption of iodine from solution.
Activated carbon is equivalent to surface area of carbon between 900 and 1100 m2/g.
Activated carbon is the standard measure for liquid-phase applications.
Iodine number is defined as the milligrams of iodine adsorbed by one gram of carbon when the iodine concentration in the residual filtrate is at a concentration of 0.02 normal (i.e. 0.02N).
Basically, iodine number is a measure of the iodine adsorbed in the pores and, as such, is an indication of the pore volume available in the activated carbon of interest.
Typically, water-treatment carbons have iodine numbers ranging from 600 to 1100. Frequently, this parameter is used to determine the degree of exhaustion of a carbon in use.
However, this practice should be viewed with caution, as chemical interactions with the adsorbate may affect the iodine uptake, giving false results.
Thus, the use of iodine number as a measure of the degree of exhaustion of a carbon bed can only be recommended if it has been shown to be free of chemical interactions with adsorbates and if an experimental correlation between iodine number and the degree of exhaustion has been determined for the particular application.
Activated carbon is a measure of the activated carbon's resistance to attrition.
Activated carbon is an important indicator of activated carbon to maintain its physical integrity and withstand frictional forces.
There are large differences in the hardness of activated carbons, depending on the raw material and activity levels.
MODIFICATION OF PROPERTIES AND REACTIVITY:
Acid-base, oxidation-reduction and specific adsorption characteristics are strongly dependent on the composition of the surface functional groups.
The surface of conventional activated carbon is reactive, capable of oxidation by atmospheric oxygen and oxygen plasma steam, and also carbon dioxide and ozone.
Oxidation in the liquid phase is caused by a wide range of reagents (HNO3, H2O2, KMnO4).
Through the formation of a large number of basic and acidic groups on the surface of oxidized carbon to sorption and other properties can differ significantly from the unmodified forms.
Activated carbon can be nitrogenated by natural products or polymers or processing of carbon with nitrogenating reagents.
Activated carbon can interact with chlorine, bromine and fluorine.
Surface of activated carbon, like other carbon materials can be fluoralkylated by treatment with (per)fluoropolyether peroxide in a liquid phase, or with wide range of fluoroorganic substances by CVD-method.
Such materials combine high hydrophobicity and chemical stability with electrical and thermal conductivity and can be used as electrode material for super capacitors.
Sulfonic acid functional groups can be attached to activated carbon to give "starbons" which can be used to selectively catalyse the esterification of fatty acids.
Formation of such activated carbons from halogenated precursors gives a more effective catalyst which is thought to be a result of remaining halogens improving stability.
Activated carbon is reported about synthesis of activated carbon with chemically grafted superacid sites –CF2SO3H.
Some of the chemical properties of activated carbon have been attributed to presence of the surface active carbon double bond.
The Polyani adsorption theory is a popular method for analyzing adsorption of various organic substances to their surface.