Typical Properties of Granular Activated Carbon

Typical Properties of Granular Activated Carbon

	Bituminous	Sub-bituminous	Lignite	Nut Shell
Iodine Number	1,000-1,100	800-900	600	1,000
Molasses Number	235	230	300	0
Abrasion Number	80-90	75	60	97
Bulk Density as packed LB/CF	26-28	25-26	23	29-30
Volume Activity	26,000	25,000	13,800	0

Iodine and molasses numbers measure pore size distribution. Iodine number is a relative measure of pores at sizes of 10 to 2 Angstroms. It is reported in milligrams of elemental iodine adsorbed per gram of GAC and determines the area available on the GAC to adsorb low molecular weight organics.

Molasses number measures the degree a GAC removes color from a stock solution. It measures pores greater than 28 Angstroms. These are the pores responsible for removing larger molecular weight organics such as tannins.

Abrasion numbers represent the relative degree of particle size reduction after tumbling with a harder material. No reduction is rated 100, complete pulverization is zero.

Get Benefit from Coal activated carbon

As the name indicates, coal activated carbon is derived from carbonaceous raw materials like coal, and the end product has micro-porous, non-graphite carbon form. Activated carbon can be manufactured from coconut shell, which seems to be high in quality when compared to other resources. Regular home filters contain materials that use active carbon for filtering and removing impurities in an effective manner.

Activated carbon features great adsorptive ability and reflects a wide array of dissolved chlorine and organics. You can custom-make activated carbon to fit your particular requirements.

Activated carbon

Any organic material with high contents of coal, peat and coconut shells can be used to make this type of carbon. This kind of carbon is also called activated charcoal, a content that makes the end product highly porous. It features big surface area exposed for adsorption and chemical reactions. With high level micro-porosity, one gram of active carbon has a surface area of around 2.17 tennis courts. The surface area is determined by nitrogen gas adsorption.

Advanced chemical treatments can increase the adsorbing elements of the material, however proper activation of relevant applications is accessible from high surface areas only. Thermal decomposition done in a heat furnace can transform the carbon based material into activated carbon. Controlled heat and environment is employed to operate the heat furnace.

The end point residue generally has a big surface area per unit volume to facilitate adsorption as it has large network of submicroscopic pores. The walls of the pores offer needed adsorption to the surface molecules.

Uses of activated carbon

It is mainly used to remove odors and chemicals that color the water.
It can remove strong smelling natural gases like hydrogen sulphide from water contents.
It is capable to remove little volumes of iron, mercury and chelated copper.
Chlorine from water is absorbed and removed while leaving an aspect called ammonia.
It can decrease or remove volatile organic chemicals, pesticides, radon, herbicides, benzene and many other compounds and solvents.

During the activation process, a lot of pores, made of molecular dimensions are developed within the structure. The structure can contain a large internal surface that enormously attracts molecules of its surrounding gases and liquids. The whole power of this force is equal to the molecular system of the atmospheric medium. Moreover, this content is a technique that can remove various factors from a given mixture.

These are employed as de-coloring and cleansing agents in a lot of processes because they are capable to absorb 10% to 90% impurities from different Aquarius solutions. Activated carbon works in purification process that involves getting the organic compounds attracted to the activated carbon as the water pass through the filter, and two contents get reaction in form of being chemically bounded to each other.

Pollutants don’t get into the sink or glass as the pores of the filter does not allow big molecules to pass through. Get more information about the forms, process and reason behind activated carbon and its ideas.

Activated Carbon For Filters and Water Treatment

Because of activated charcoal’s incredible adsorption ability, it is an ideal choice for air and water filters. When used appropriately, charcoal filters will effectively clean the air and water by electrostatically binding pollutants to its vast surface area.

Many people use activated charcoal filters in outdoor ponds and aquariums to keep the water clean and the marine life healthy.

Many of us strive to live in a chemical-free world, but doing so is not always easy. Many of the contaminants that we come into contact with on a daily basis actually come from our homes–a place that is supposed to be a safe haven for ourselves and our families. The more we can do to eliminate these chemicals from our lives, the healthier we will all be.

Carbon filtering is a method of filtering that uses a bed of activated carbon to remove contaminants and impurities, using chemical absorption.

Each particle/granule of carbon provides a large surface area/pore structure, allowing contaminants the maximum possible exposure to the active sites within the filter media. One pound (450 g) of activated carbon contains a surface area of approximately 100 acres (40 Hectares).

Activated carbon works via a process called adsorption, whereby pollutant molecules in the fluid to be treated are trapped inside the pore structure of the carbon substrate. Carbon filtering is commonly used forwater purification, in air purifiers and industrial gas processing, for example the removal of siloxanes and hydrogen sulfide from biogas. It is also used in a number of other applications, including respirator masks, the purification of sugarcane and in the recovery of precious metals, especially gold. It is also used in cigarette filters.

Active charcoal carbon filters are most effective at removing chlorine, sediment, volatile organic compounds (VOCs), taste and odor from water. They are not effective at removing minerals, salts, and dissolved inorganic compounds.

What carbon filtration doesn’t do can be seen in the remaining three categories of the EPA contaminant list. Carbon is mentioned as a treatment for only one of the four Microbiological contaminants listed: turbidity.

It is not recommended for coliform removal or for cysts, though ironically, some of the very tight solid carbon block filters now on the market remove bacteria (though manufacturers seldom make this claim) and cysts like giardia and cryptosporidium quite handily. Multipure solid carbon blocks, in fact, were the first filtration device certified by NSF (the most prestigious independent agency that tests and certifies product performance) for removal of cryptosporidium.

Multipure and some other very tight carbon block filters remove cysts simply because of their restricted pore size. Multipure blocks are absolute 1/2 micron filters, making cryptosporidium organisms about ten times too fat to go through the holes. Thus, although other types of very tight filtration might work as well, the very dense carbon block filters now on the market are very effective against certain forms of microbiological contaminants.

Activated Carbon for drinking water Treatment

Potable or drinking water is a commodity with stringent requirements of being safe and pure. Granular Activated Carbons (GACs) and Powder Activated Carbons (PACs) is your ideal solution in making drinking water free from taste and odor forming compounds such as MIB and geosmin, undesired colors, endocrine disrupting compounds and other micropollutants, chlorinated hydrocarbons, Trihalomethanes and other disinfection byproducts, VOCs, pesticides and their byproducts.

You can treat drinking water with the high quality, standard, and specially processed products complying with NSF 61, NSF 42, PROP 65 certifications with low dechlorination half values, superior flow characteristics, consistent particle size distributions to facilitate pressure drop and adsorption kinetics requirements, extensive pore structures with an ideal balance of both adsorption and transport pores, and high mechanical strength resulting in minimal operational and pressure drop issues. These superior features have made granular carbon products the industry choice for Point of Use (POU) and Point of Entry (POE) water filters.

Activated Carbon for Municipality water treatment

In the treatment of municipal water, removal of organics including VOCs, inorganics and toxins inherent in the rivers, lakes, reservoirs and other surface water sources and ground water systems is essential. You can find a tailor made series of products for surface and ground water treatment in municipality water treatment systems to deliver consistent performance in removing these contaminants.

These products are also geared to adsorb hazardous pesticide and herbicide residues, chlorinated hydrocarbons, disinfectant byproducts, inhibitory compounds for biological treatment systems, non-biodegradable organic compounds, and undesired colored and smell compounds. Our carbons are effective in lowering of Biochemical Oxygen Demand (BOD), Chemical Oxygen Demand (COD), Total Organic Content (TOC) and toxicity. In addition, the high purity of the carbon products prevents the release of contaminants that may damage sensitive membrane systems used in other in-process filtration systems. We also offer custom designed products and total purification solutions to best suit your requirement.

What is Impregnated activated carbons and what it is used for ?

Porous carbons containing several types of inorganic impregnate such as iodine, silver, cations such as Al, Mn, Zn, Fe, Li, Ca have also been prepared for specific application in air pollution control especially in museums and galleries.

Impregnated activated carbons are carbonaceous adsorbents which have chemicals finely distributed on their internal surface. The impregnation optimizes the existing properties of the activated carbon giving a synergism between the chemicals and the carbon. This facilitates the cost-effective removal of certain impurities from gas streams which would be impossible otherwise. For environmental protection, various qualities of impregnated activated carbon are available and have been used for many years in the fields of gas purification, civil and military gas protection and catalysis.

Through a suitable impregnation, the adsorption capacity of the activated carbon can be increased considerably, for economic collection of several hard to adsorb gas pollutants such as hydrogen sulphide, mercury or ammonia.

Typical impregnation chemicals are sulphur (for the removal of mercury), potassium iodide (H2S, AsH3, radioactive isotopes), potassium carbonate (HCl, HF, SO2) and silver (for drinking water treatment).

Due to its antimicrobial and antiseptic properties, silver loaded activated carbon is used as an adsorbent for purification of domestic water. Drinking water can be obtained from natural water by treating the natural water with a mixture of activated carbon and Al(OH), a flocculating agent. Impregnated carbons are also used for the adsorption of Hydrogen Sulfide(H₂S) and thiols. Absorption rates for H₂S as high as 50% by weight have been reported.

KOH, or NaOH impregnated activated carbon, FCK series are kinds of pelletized activated carbon for Respirators and Human protection. In the simplest terms, KOH, or NaOH impregnated activated carbon does double duty: First it grabs the contaminants and then it turns them into something harmless. Accordingly it is ideal for respirator applications. Because impregnated carbon attracts and holds contaminants both physically and chemically.

The activated carbon itself can be used as a catalyst, and its selectivity and conversion rate can reach or exceed the performance of the traditional catalysts supporting the precious metal. In addition, the production cost of catalysts is greatly reduced because the precious metal is not required, and the recovery procedure of used catalysts is simplified, so carbon catalysts have been widely used in various industries.

Non-military applications for impregnated carbon include:

A. Manufacturing of personal protection and first responder masks.
B. Individual gas mask filters.
C. Collective protection filters.
D. Sulfur compounds removal, including H2S, Sulfur based alcohol, SO2, dimethyl sulfide, methyl sulfide, mercury vapor, NH3, etc.
E. Automotive cabin air purification systems.
F. Mercury Removal
G. Odor control
H. Precious metal catalyst carriers
I. home water treatment in bacteriostatic water filters
J. removal of war gases from NBC filters and gas masks (pursuant to international standards such as CEN and NIOSH)
K. ammoniac and amines removal from air.

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Bead Activated Carbon

Bead activated carbon (BAC) is made from petroleum pitch and supplied in diameters from approximately 0.35 to 0.80 mm. Similar to EAC, it 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 liquidized bed applications such as water filtration.

Application

Water treatment facilities
→High flowability, low carbon dust, and precise particle distribution make BAC ideally suited for adsorption on fluidized beds.
Production plant exhaust gas and waste water recovery systems
→High flowability and strength allow for use on the gaseous layer inside pipes, or liquid-fluidized beds
Clean room air and chemical filters
→High purity, low carbon dust and high fill capacity have led to use even in fixed beds, and applications requiring separation from foreign matter.
Polysilicon production process
→High purity prevents contamination by impurities during the production process.

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Extruded Activated Carbon

Extruded activated carbon 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. Also sold as CTO filter (Chlorine, Taste, Odor).

Extruded activated carbons (pressed pellets) are mainly made by mixing pulverised anthracite or charcoal with a suitable binder which are extruded at high pressure into a cylindrical shaped form. Sometimes activation catalysts, like potassium hydroxide, are mixed in prior to extrusion to obtain a specific pore structure.

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Granular Activated Carbon

Granular activated carbon (GAC) 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 suitable for absorption of gases and vapors, because they diffuse rapidly. Granulated carbons are used for water treatment, deodorization and separation of components of flow system and is also used in rapid mix basins. GAC can be either in granular or extruded form.

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 sizes because they have a good balance of size, surface area, and head loss characteristics.

GAC is normally placed in a pressure vessel or gravity filtration tank through which raw water passes. The carbon filters mechanically strain out dirt, sediment, algae, bacteria, microscopic worms, cryptosporidium, and asbestos. When the surface area of the carbon granules is clogged with the contaminants due to adsorption, pressure differential increases and the filter bed is back washed.

Optional Granular Activated Carbon filtration system can be a single treatment step or can be combined with other processes to remove free chlorine and dissolved organics from:

Municipal Water
Municipal Wastewater
Surface Water
Ground Water
Industrial Wastewater

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Powdered Activated Carbon

Normally, activated carbons 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).

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. The ASTMclassifies particles passing through an 80-mesh sieve (0.177 mm) and smaller as PAC. It is not common to use PAC in a dedicated vessel, due to the high head loss that would occur. Instead, PAC is generally added directly to other process units, such as raw water intakes, rapid mix basins, clarifiers, and gravity filters.

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What is the difference between Virgin or reactivated or regenerated charcoal?

Virgin activated charcoal is the original product that has never been used. All the activated charcoal sold by BuyActivatedCharcoal.com is virgin activated carbon.

Reactivated charcoal is activated charcoal that has finished its lifespan in a particular application and is then exposed again to the steam-activation process that removes the adsorbed pollutants and restores about 90% of the activity level, so that it can be safely used again. For example, at the municipal level (water treatment facilities) where large volumes of activated carbon are employed and the spent carbon in the majority, if not all, cases is considered non-hazardous, there is a great opportunity to reactivate the carbon and reuse it. The reactivation process burns up about 10% of the original product producing about 20% of the greenhouse gases compared to new carbon production. There is also the benefit of less landfill.

Regenerated carbon usually refers to a process where the spent carbon is washed with either water or a chemical agent to remove a portion of the contaminants adsorbed by the carbon. For regeneration, the GAC is treated in the adsorption vessel. Only about 5 – 50% of the original activity of the activated carbon is restored.

Is There A Difference Between Activated Carbon And Activated Charcoal?

Most people have a misunderstanding that there is a difference between activated carbon and activated charcoal. Both of these terms can and are used interchangeably. As well, active carbon is another similar word used for activated carbon and activated charcoal.

Activated charcoal tends to be the lay term. “Activated carbon” is more commonly used in the manufacturing/technical sectors. Other terms are activated coal. Sometimes “active” is substituted for “activated”.

Activated charcoal, granular activated carbon, granular active carbon – all different terms which just so happen to refer to one specific type of charcoal. Or, more accurately, it is charcoal reheated and oxidized, making the charcoal highly porous. Even though charcoal on its own is known for being a fairly porous substance, when oxidized (or, in some cases, carbonized with other inert gases) the amount of porous spaces increases significantly.

Activated Carbon Adsorption Mechanism

How the adsorbate is absorbed ?

Activated carbon can be considered as a material of phenomenal surface area made up of millions of pores – rather like a “molecular sponge”. Activated carbon is a microporous inert carbon matrix with a very large internal surface (700 to 1 500 m²/g). The internal surface is ideal for adsorption. Activated carbon is made from materials containing amorphous carbon, such as wood, coal, peat, coconut shells… It is formed via a thermal process, where volatile components are removed from the carbon-laden material (raw material) in the presence of oxygen.

The process by which such a surface concentrates fluid molecules by chemical and/or physical forces is known as ADSORPTION (whereas, ABSORPTION is a process whereby fluid molecules are taken up by a liquid or solid and distributed throughout that liquid or solid).

In the physical adsorption process, molecules are held by the carbon’s surface by weak forces known as Van Der Waals Forces resulting from intermolecular attraction. The carbon and the adsorbate are thus unchanged chemically. However, in the process known as CHEMISORPTION molecules chemically react with the carbon’s surface (or an impregnant on the carbon’s surface) and are held by much stronger forces – chemical bonds.

In general terms, it is necessary to present the molecule to be adsorbed to a pore of comparable size. In this way the attractive forces coupled with opposite wall effect will be at a maximum and should be greater than the energy of the molecule.

For example, a fine pored coconut shell carbon has poor decolorizing properties because color molecules tend to be larger molecular species and are thus denied access to a fine pore structure. In contrast, coconut shell carbons are particularly efficient in adsorbing small molecular species. Krypton and Xenon, for instance, are readily adsorbed by coconut shell carbon but readily desorb from large pored carbons such as wood.

Maximum adsorption capacity is determined by the degree of liquid packing that can occur in the pores. In very high vapor pressures, multi-layer adsorption can lead to capillary condensation even in mesopores (25A).

Activated Carbon Adsorption Capacity

The effectiveness at which activated carbon can remove contaminants from a stream is not based on the quantity of carbon, but, the activated carbon adsorption capacity. The greater the capacity, the more contaminants the activated carbon will be able to adsorb in volume. However, due to natural carbon’s limitations, it is not able to adsorb certain contaminants, as there molecular weight are to low to be treated through this process alone.

Active carbon is most effective against compounds that hold a high molecular weight and low solubility due to activated carbon having a high molecular weight as well. If there is ever an uncertainty if a specific contaminant will be removed in the adsorption process, referral is to be made to the solubility and molecular weight of said containment.

If adsorption capacity is plotted against pressure (for gases) or concentration (for liquids) at constant temperature, the curve so produced is known as an ISOTHERM. Adsorption increases with increased pressure and also with increasing molecular weight, within a series of a chemical family. Thus, methane (CH4) is less easily adsorbed than propane (C3H8).

Efficiency is determined by the type of pollutant, the type of activated carbon which is used and the temperature and humidity of the waste gases. An effective installation can be expected to realise a yield between 95 – 98 % for input concentrations of 500 – 2 000 ppm.

If effective, concentrations can typically be brought from 400 – 2 000 ppm to under 50 ppm.

In foundries, an end concentration of 20 mg/Nm³ VOC has been established

Mercury can be brought down to less than 0.05 mg/Nm³. Dioxins to less than 0.1 ng TEQ/Nm³ and, for odour and H₂S, yields of 80 – 95 % have been established

This is a useful fact to remember when a particular system has a number of components.

Activated carbon adsorption mechanism

After equilibrium, it is generally found that, all else being equal, the higher molecular weight species of a multi-component system are preferentially adsorbed. Such a phenomenon is known as competitive or preferential adsorption – the initially adsorbed low molecular weight species desorbing from the surface and being replaced by higher molecular weight species. Physical adsorption in the vapor phase is affected by certain external parameters such as temperature and pressure.

The adsorption process is more efficient at lower temperatures and higher pressures since molecular species are less mobile under such conditions. Such an effect is also noticed in a system where moisture and an organic species are present. The moisture is readily accepted by the carbon surface but in time desorbs as the preferred organic molecules are selected by the surface.

This usually occurs due to differences in molecular size but can be also attributable to the difference in molecular charge. Generally speaking, carbon surfaces dislike any form of charge – since water is highly charged (ionic) relative to the majority of organic molecules the carbon would prefer the organic to be adsorbed.

Primary amines possess less charge on the nitrogen atom than secondary amines that in turn have less than tertiary amines. Thus, it is found that primary amines are more readily adsorbed than tertiary amines.

High levels of adsorption can be expected if the adsorbate is a reasonably large bulky molecule with no charge, whereas a small molecule with high charge would not be expected to be easily adsorbed.

Molecular shape also influences adsorption but this is usually of minor consideration. In certain situations, regardless of how the operating conditions can be varied, some species will only be physically adsorbed to a low level. (Examples are ammonia, sulfur dioxide, hydrogen sulfide, mercury vapor and methyl iodide). In such instances, the method frequently employed to enhance a carbon’s capability is to impregnate it with a particular compound that is chemically reactive towards the species required to be adsorbed.

Since carbon possesses such a large surface (a carbon granule the size of a “quarter” has a surface area in the order of ½ square mile!) coating of this essentially spreads out the impregnant over a vast area. This, therefore, greatly increases the chance of reaction since the adsorbate has a tremendous choice of reaction sites. When the adsorbate is removed in this way the effect is known as CHEMISORPTION.

Unlike physical adsorption the components of the system are changed chemically and the changed adsorbate chemically held by the carbon’s surface and desorption in the original form is nonexistent. This principle is applied in many industries, particularly in the catalysis field, where the ability of a catalyst can be greatly increased by spreading it over a carbon surface.

The effect of activated carbon on the adsorbate in water comes from two aspects: on the one hand, physical adsorption, the internal force of the activated carbon is in a balanced state under the force from all directions of the water body, and the external molecules are not balanced, so that the molecules adsorb to the activated carbon On the surface; on the other hand, it is chemical adsorption, because there is a chemical interaction between activated carbon and the adsorbed substance.

The adsorption of activated carbon on pollutants in water is the result of the combined action of the above two kinds of adsorption. There are four steps in the adsorption process of activated carbon on the adsorbate in water: first, due to the convection effect of the water body, the adsorbate diffuses onto the surface of the activated carbon; second, the adsorbate molecules diffuse into the large pores of the activated carbon through the liquid film; Third, the adsorbate molecules reach the micropores due to surface diffusion; fourth, the adsorbent molecules in water are adsorbed on the surface of the activated carbon pores.

Activated carbon adsorption equilibrium is a state of dynamic equilibrium. When the adsorption rate and the desorption rate of activated carbon in the solution are equal, that is, when the amount of activated carbon adsorption per unit time is equal to the amount of desorption, the concentration of the adsorbed substance in the solution and the concentration on the surface of the activated carbon will no longer change. For adsorption equilibrium.

Adsorption capacity and adsorption speed are two important indicators to measure the adsorption process of activated carbon. The adsorption capacity is reflected by the adsorption amount qe, which is mainly affected by the pore size and structure of activated carbon. In addition, temperature and pH value also affect the adsorption capacity of activated carbon.

Adsorption speed refers to the amount of material adsorbed per unit weight of adsorbent per unit time, which is mainly determined by the contact time of water and adsorbent. Because the adsorption reaction is an exothermic reaction, low temperature is usually beneficial to accelerate the adsorption rate.

Activated Carbon Structure

In order to explain the capabilities of activated carbon an appreciation of its structure is most useful. Much of the literature quotes a modified graphite-like structure; the modification resulting from the presence of microcrystallites, formed during the carbonization process, which during activation have their regular bonding disrupted causing free valencies which are very reactive.

In addition, the presence of impurities and process conditions influence the formation of interior vacancies, in the microcrystalline structures. Such theory generally explains pores as the result of faults in crystalline structures.

However, more recent research studies provide a more feasible explanation of the carbon structure. The generally accepted graphite-like structure theory falls down since the hardness of activated carbon is not in keeping with the layered structure of graphite.

Furthermore, the manufacturing conditions are different; in particular the temperature range utilized for activated carbon production is lower than that required for graphitization. Supporters of the graphite-like structure generally only explain the modified microcrystalline structure and ignore photographic and other methods of examining the residual macro structure. High magnification electron scanning microscopy, at 20,000x magnification, has revealed the presence of residual cellular structures.

These were previously unseen and unsuspected, except in the case of wood based activates which have sufficiently open structures visible to the naked eye. Cellular units are built from sugars, the most important being glucose.

Sugars ultimately will build to cellulose (the most important single unit in cellular construction) and cellulose polymers cross-link to form the wall of individual plant cells. Glucose units are wound into very tight helical spirals and under polarized light these exhibit anisotropy – demonstrating the presence of crystalline structures.

Although not as yet proven, it has been postulated that in the areas of maximum strain in cellulose chains it is conceivable that smaller crystalline units could be produced. In addition to cellulose, other materials also exist in cell wall structure.

Hemi-cellulose, which undergoes degradation more easily than cellulose and Lignin (the structure of which is still unproven) also exists and this is the most resistant to oxidation. Most theories attribute the structure of activated carbon to be aromatic in origin, thus, allowing the carbon structure itself to be described as aromatic in order to explain active centers, etc. Structures of the size of cell dimensions obviously do not influence physical adsorption but illustrate that the only material available for oxidation lies within the cell walls themselves.

Final activates consist almost entirely of elemental carbon together with residual ash which, in the case of wood and coconut, originate from minerals within the vessels of living tissues; silica being the only constituent actually incorporated within the cell wall tissue matrix.

The ash content of coal is of different composition and due to intrusion of inorganic materials during coalification. Thus, the overall structure consists of a modified cellular-like configuration with varying ash components depending on the particular raw material. The cellular-like structure theory offers a logical explanation for the differences in apparent density between activates of wood, coal and coconut.

Wood activates have a very open structure with thin wall cells whereas coconut activates show very thick walls with many pits. Furthermore, measurements taken from photomicrographs of coconut show good agreement with mercury penetration data. It is known that the carbonization and activation processes destroy, to varying degrees, intercellular walls and sieve plates between cells.

The end result on wood is a very open, sponge-like macrostructure seriously reducing the probability of adsorbate contact with cell walls. Activation of coconut produces a composition of rod-like cells in very close contact and large surface cavities are formed by destruction of dividing walls but these are shallow and do not extend through the activate’s granule.

The coconut activates thus differ significantly from wood activates in mechanical strength and density. Coconut activates exhibit extensive micropore volume, whereas wood activates have a definite trend to mesopores/macropores and a corresponding change in their basic properties. In the case of coal based carbons, pre-treatment of the raw coal is necessary in order for it to be processed, since raw coal swells during heating to produce coke-like structures. Control of this is achieved by first grinding the raw coal and mixing it with various additives, such as pitch, before it is introduced to the activation furnace.

However, the grinding process destroys the mechanical strength of coal – therefore, ground coal is reconstituted into briquettes prior to processing. Despite such pre-treatment, mercury penetration data for coal activates support the presence of structures similar to those identified in activates of wood and coconut, but to date no detection of residual plant structures has been found in coal activates.

Isotherm determinations reveal extensive micropore structures, although coal activates’ pore spectra are different to those of coconut activates with a tendency toward mesopores at lower activation.

The most reliable carbon structure model suggested to date is similar to that of polyamantane (C66 H59) which allows for a large degree of non-aromaticity, electron transfer and resonance. Progressive activation would tend to increase the number of active sites, and in turn the surface activity, similar to observed reactions with higher activates.

AWWA Standard for Granular Activated Carbon

This standard covers the use of granular and extruded activated carbons as a filter medium and adsorbent in water treatment. It involves the selection, placement, and use of granular activated carbon (GAC) in filter-adsorbers where the GAC must function as both a filter medium and adsorbent, as well as those systems where the primary function is adsorption. Section 1 discusses scope, purpose and application. Sections 2 and 3 list references and definitions.

Section 4 lists requirements, including: physical requirements; performance criteria; and, impurities. Section 5 discusses verification including: sampling; test procedures; and, rejection. Section 6 discusses delivery including: marking; packaging and shipping; and, affidavit of compliance. Section 7 discusses placing of GAC filter material including: preparation; placement of support media; placement of GAC; top surface elevation; and, contamination. Section 8 discusses preparation of filter for service including: backwashing; scraping; disinfection; cleaning; and, safety. Appendices provide a bibliography, and methods for adsorptive capacity testing including tannin and phenol.

The major revisions in this edition of ANSI/AWWA B604-96 include the following: the format has been changed to AWWA standard style; and, parameters required to specify GAC as a filter/adsorber, as well as an adsorbent, have been included.

How Does Activated Carbon Work?

Activated carbon, also called activated charcoal, activated coal, or carbo activatus, is a form of carbon processed to have small, low-volume pores that increase thesurface 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 gas adsorption. An activation level sufficient for useful application may be attained solely from high surface area; however, further chemical treatment often enhances adsorption properties.

Physical adsorption is the primary means by which activated carbon works to remove contaminants from water. Carbon’s highly porous nature provides a large surface area for contaminants (adsorbates) to collect. In simple terms, physical adsorption occurs because all molecules exert attractive forces, especially molecules at the surface of a solid (pore walls of carbon), and these surface molecules seek other molecules to adhere to.

Activated carbon attracts organic chemicals from vapor and liquid streams cleaning them of unwanted chemicals. It 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.

The large internal surface area of carbon has many attractive forces that work to attract other molecules. Thus, contaminants in water are adsorbed (or held) to the surface of carbon by surface attractive forces similar to gravitational forces. Adsorption from solution occurs as a result of differences in adsorbate concentration in the solution and in the carbon pores.

The adsorbate migrates from the solution through the pore channels to reach the area where the strongest attractive forces are. With this understanding of how the adsorption process works, we must then understand why it works, or why water contaminants become adsorbates. Water contaminants adsorb because the attraction of the carbon surface for them is stronger than the attractive forces that keep them dissolved in solution.

Those compounds that are more adsorbable onto activated carbon generally have a lower water solubility, are organic (made up of carbon atoms), have a higher molecular weight and a neutral or non-polar chemical nature. It should be pointed out that for water adsorbates to become physically adsorbed onto activated carbon, they must be both dissolved in water and smaller than the size of the carbon pore openings so that they can pass into the carbon pores and accumulate.

What Is Activated Carbon?

Activated carbon is a highly porous substance that attracts and holds organic chemicals inside it. The media is created by first burning a carbonaceous substance without oxygen which makes a carbon “char”. Next, the “char” is treated chemically or physically to develop an interconnected series of “holes” or pores inside the carbon. The great surface area of this internal pore network results in an extremely large surface area that can attract and hold organic chemicals.

The primary raw material used for activated carbon is any organic material with a high carbon content (coal, wood, peat, coconut shells). Granular activated carbon media is most commonly produced by grinding the raw material, adding a suitable binder to give it hardness, re-compacting and crushing to the correct size.

The carbon-based material is converted to activated carbon by thermal decomposition in a furnace using a controlled atmosphere and heat. The resultant product has an incredibly large surface area per unit volume, and a network of submicroscopic pores where adsorption takes place.

The walls of the pores provide the surface layer molecules essential for adsorption. Amazingly, one pound of carbon (a quart container) provides a surface area equivalent to six football fields.

Almost all materials containing a high fixed carbon content can potentially be activated. The most commonly used raw materials are coal (anthracite, bituminous and lignite), coconut shells, wood (both soft and hard), peat and petroleum based residues.

Many other raw materials have been evaluated such as walnut shells, peach pits, babassu nutshell and palm kernels but invariably their commercial limitation lies in raw material supply. This is illustrated by considering that 1,000 tons of untreated shell type raw material will only yield about 100 tons of good quality activated carbon.

Most carbonaceous materials do have a certain degree of porosity and an internal surface area in the range of 10-15 m2/g. During activation, the internal surface becomes more highly developed and extended by controlled oxidation of carbon atoms – usually achieved by the use of steam at high temperature.

After activation, the carbon will have acquired an internal surface area between 700 and 1,200 m2/g, depending on the plant operating conditions.

The internal surface area must be accessible to the passage of a fluid or vapor if a potential for adsorption is to exist. Thus, it is necessary that an activated carbon has not only a highly developed internal surface but accessibility to that surface via a network of pores of differing diameters.

As a generalization, pore diameters are usually categorized as follows:

micropores <40 Angstroms
mesopores 40 – 5,000 Angstroms
macropores >5,000 Angstroms (typically 5000-20000 A)

During the manufacturing process, macropores are first formed by the oxidation of weak points (edge groups) on the external surface area of the raw material. Mesopores are then formed and are, essentially, secondary channels formed in the walls of the macropore structure. Finally, the micropores are formed by attack of the planes within the structure of the raw material.

All activated carbons contain micropores, mesopores, and macropores within their structures but the relative proportions vary considerably according to the raw material.

A coconut shell based carbon will have a predominance of pores in the micropore range and these account for 95% of the available internal surface area. Such a structure has been found ideal for the adsorption of small molecular weight species and applications involving low contaminant concentrations.

In contrast wood and peat based carbons are predominantly meso/macropore structures and are, therefore, usually suitable for the adsorption of large molecular species. Such properties are used to advantage in decolorization processes.

Coal based carbons, depending on the type of coal used, contain pore structures somewhere between coconut shell and wood.

In general, it can be said that macropores are of little value in their surface area, except for the adsorption of unusually large molecules and are, therefore, usually considered as an access point to micropores.

Mesopores do not generally play a large role in adsorption, except in particular carbons where the surface area attributable to such pores is appreciable (usually 400 m2/g or more).

Thus, it is the micropore structure of an activated carbon that is the effective means of adsorption. It is, therefore, important that activated carbon not be classified as a single product but rather a range of products suitable for a variety of specific applications

Adsorption/Adsorbents/Activated Carbon

Since adsorption is a comparatively specialized technology, a capsule definition of terms may be helpful. Adsorption is a surface phenomenon, in which molecules of adsorbate are attracted and held to the surface of an adsorbent until an equilibrium is reached between adsorbed molecules and those still freely distributed in the carrying gas or liquid. While the atoms within the structure of the adsorbent are attracted in all directions relatively equally, the atoms at the surface exhibit an imbalanced attractive force which the adsorbate molecules help to satisfy. Adsorption can then be understood to occur at any surface, such as window glass or a table top. The characteristic which typifies an adsorbent is the presence of a great amount of surface area; normally via the wall area or slots, capillaries or pores permeating its structure, in a very small volume and unit weight.

The type of adsorption which is dependent primarily on surface attraction, in which factors such as system temperature, pressure, or impurity concentration may shift the adsorption equilibrium, is given the further classification of physical adsorption. The electronic forces (Van der Waal’s forces) responsible for adsorption are related to those which cause like molecules to bind together, producing the phenomena of condensation and surface tension. Conceptually, some prefer the analogy of physical adsorption being like iron particles attracted to, and held by, a magnet. Physical adsorption is the most commonly applied type, but an important sub-classification is chemisorption. Chemisorption refers to a chemical reaction between the adsorbate and the adsorbent , or often reaction with a reagent which may be impregnated on the extensive adsorbent surface (see Impregnated Carbons, below). Thus physical adsorption/desorption retains the chemical nature of the adsorbate, while chemisorption alters it.

The surface phenomenon of adsorption may now be contrasted with apsorption, in which one material intermingles with the physical structure of the other; for example, phenol dissolving into fibers of cellulose acetate (absorption) versus being adhered by surface attraction to the outer layer of the fibers (adsorption).

Activated charcoal) 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, it 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. Granular Activated carbon will show limited affinity for water via capillary condensation, but not the surface attraction for water of a desiccant.

Activity Level

Activity level is often expressed as total surface area per unit weight, usually in square meters per gram. This total exposed surface will typically be in the range of 600-1200 m2/g. Toward the higher end of this range, one might better visualize one pound, about a quart in volume, of granular activated carbon with a total surface area of 125 acres.

To be useful in adsorption, surface area must be present in openings large enough to admit the adsorbate molecule(s). To provide some guidance on this topic, and for quality control purposes, the carbon industry has developed additional standardized vapor and liquid adsorption tests, using adsorbates of varying molecular size and chemical nature such as iodine, phenol, methylene blue, carbon tetrachloride, benzene and the color in standard black strap molasses. However activity level is measured, it is most meaningful when considered with additional characteristics described in the following sections.

Pore Structure

While openings into the carbon structure may be of various shapes, the term “pore,” implying a cylindrical opening, is widely used. A description of the minute distances between walls of these pores, normally expressed as a function of the total surface area or total pore volume presented by pores of various “diameters,” is the pore structure curve. The following sketches show some sample pore structure curves and what approximate pore shapes are described by the curves. Please note that the average pore shape depicted is derived from a summation of pores of various sizes and shapes. Thus no pore within the activated carbon is likely to have precisely the average shape, but the granular activated carbon overall will often perform as if all its surface area were in pores of that shape.

The smallest diameter pores make up the micropore structure, and are the highest adsorption energy sites. Microporosity is helpful in adsorbing lower molecular weight, lower boiling point organic vapors, as well as in removing trace organics in water to non-detectable levels. Larger pore openings make up the macroporosity, which is useful in adsorbing very large molecules and aggregates of molecules, such as “color bodies” in raw sugar solutions. Another important function of the macropore structure is in assisting diffusion of fluids to adsorption sites in the interior of the carbon particle.

Given the above, pore structure. (1) would be effective in adsorbing high volatility solvents, for certain types of odor control, and in removing trace organics from water; the latter with the liability of marginal diffusion characteristics. Pore structures along the lines of. (2) offer a good balance of selectivity for molecules of various sizes, ability to reduce vaporous and liquid contamination to ultra low levels, and good diffusion characteristics. Structure (3) would allow excellent diffusion and can accommodate very large molecular sizes, but has little micro- pore structure and would have very poor retentivity for most organics.

Activated carbon properties

Activated carbon is a non-hazardous carbon-bearing product with a porous structure and a very large internal surface area. The chemical structure of activated carbon can be defined as a crude form of graphite, with a random amorphous structure that is highly porous over a range of pore sizes, from visible cavities and gaps to those of molecular dimensions.

Treatment with activated carbon is based primarily on the phenomenon known as adsorption, in which molecules of a liquid or gas adhere to an external or internal surface of a solid substance. Activated carbon has a very large internal surface area (up to 1,500 m²/g) which makes it highly suitable for adsorption. Activated carbon can be impregnated with certain chemicals in order thus to enhance its properties for certain applications.

Applications:

Water and liquid applications for:

municipal drinking water treatment (taste, odour and micro pollutant removal e.g. pesticides, …),
domestic water treatment (in-line and cartridge filters),
process water (de-chlorination and de-ozonation),
ground water remediation,
waste water treatment – tertiary treatment (trace organics and COD removal, deodourisation and decolourisation, powdered as bio-flock improvement in an aerobic or anaerobic biological waste water treatment plant, as an additive for physical- chemical treatments),
raw material purification (purification of oils and fats, alcoholic and softdrinks, dyestuffs, …, decolourisation of sugar and glucose, food, chemicals, pharmaceuticals) and
catalytic processes.

Air and gas applications for:

air purification and environmental protection (removal of solvents and hydrocarbons, deodourisation, air conditioning, cooker hoods, flue gases, in powdered form the removal of dioxins, mercury and other trace elements from flue gases),
cleaning process gases (removal of contaminants from hydrogen, natural gas, carbon dioxide, landfill gas, solvent recovery, …),
respiration protection (gas masks, removal of harmful of toxic compounds),
tank venting,
ground water remediation,
molecular sieves.

Is There A Difference Between Activated Carbon And Activated Charcoal?

What Does Activated Carbon Do?

Activated carbon attracts and holds organic chemicals from vapor and liquid streams cleaning them of unwanted chemicals. It 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.

What Will Activated Carbon Remove?

Organic chemicals are attracted to carbon the best. Very few inorganic chemicals will be removed by carbon. The molecular weight, polarity, solubility in water, temperature of the fluid stream and concentration in the stream are all factors that affect the capacity of the carbon for the material to be removed. VOCs such as Benzene, Toluene, Xylene, oils and some chlorinated compounds are common target chemicals removed through use of carbon. Other large uses for activated carbon are the removal of odors and color contamination.

What Is Activated Carbon Made From?

Granular 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.(1) above, coals a (2) type structure in comparatively hard carbons, and wood (3) structure in carbons lacking great crush and abrasion resistance. It should be emphasized that specific production techniques may yield carbons that depart from the norm of a given raw material.Here at General Carbon, we carry activated carbon made from bituminous coal, lignite coal, coconut shell and wood.