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.

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.

Global Activated Carbon Market Trends and Forecasts

Global activated carbon market size was estimated at USD 2.23 billion in 2013.  Global Activated Carbon market was valued at $2.41 billion in 2014 and is expected to reach a value of $4.46 billion by 2020 showing a compound annual growth rate of 10.8%.

Stringent government regulations for mercury removal in power plants are anticipated to remain a key driver for market growth over the next five years. Environment Protection Agency (EPA) issued the Mercury and Air Toxics Standard, which aims at removal of mercury, acid gas and other metal emissions from coal & oil powered plants. Rapid industrialization coupled with increasing government focus on environmental protection is expected to fuel industry growth over the forecast period.

Activated carbon prices witnessed steady growth from 2007 to 2012 and remained relatively high during 2013 and are expected to rise over the next five years.  Increasing concerns regarding drinking water contamination and shift in trend towards healthy lifestyle coupled with increasing government spending is anticipated to drive demand over the next five years.

North America activated carbon market revenue by product, 2012-2020, (USD Million)

North America activated carbon market

In terms of tonnage, the global market was 1.56 million metric tons in 2014. Asia Pacific dominated the global activated carbon market, accounting for over 40% of total volumes in 2014, with china being a leading exporter, accounting for over 35% of total Asian activated carbon exports in 2014.

To assess the market, activated carbon is divided into three major types – powdered activated carbon (PAC), granular activated carbon (GAC) and extruded activated carbon (EAC).   Activated carbons manufactured from coconut shells are mainly in powdered and granular forms, while those from coal are commonly in granular and extruded forms and those manufactured from wood are majorly powdered form. For more information, please check Raw materials of activated carbons.

the market is expected to grow at a five-year CAGR of 11.3%, to reach $3.7 billion, by 2019. Stricter government regulations across regions for air purification and water treatment will drive the market for powdered and granular activated carbon.

marketing

 

 

Powdered activated carbon (PAC) was the largest product segment and accounted for over USD 1.1 billion in 2013. EPA Mercury and Air Toxics Standard along with the cement and industrial boiler mercury control standards accompanying it are together expected to drive the activated carbon market.

Granular form (GAC) is expected to grow at a CAGR of 12.6% from 2014 to 2020 owing to increasing application scope such as absorption of gases and vapors, deodorization and separation of components of flow system. They are widely preferred owing to properties such as hydraulic head, balance of size and surface area.

Other forms include extruded, bead activated, impregnated and polymer coated. They are expected to grow at a CAGR of 7.1% from 2014 to 2020 on account of end-use application such as gas phase, fluidized bed, hemoperfusion and air pollution control.

 

 

 

Some Raw materials of Activated Carbons

A carbonaceous substance can be used as the raw material for activated carbon.

Materials for activated carbon in use worldwide are as follows:

Powdered activated carbon
  • Sawdust
  • Hard wood chips
  • wood charcoal (carbon from sawdust)
  • Grass ash (peat)
Granulated activated carbon
  • Charcoal
  • Coconut shell charcoal
  • Coal (lignite, brown coal, bituminous coal, anthracite coal, etc.)
  • Oil carbon
  • Phenolic resin
Fibrous activated carbon
  • Rayon
  • Acrylonitril
  • Coal tar pitch
  • Petroleum pitch
  • Phenolic resin, etc.

Coconut shell
Coconut shell

Powdered activated carbon Raw Materials

Activated Charcoal As A Deodorizer

Activated carbon adsorbs. The chemical process of absorption is commonly compared to a sponge soaking up water. The water is fully integrated into the sponge, not being limited to the surface area. Differently, adsorption is a process whereby molecules stick to the surface area only. As mentioned above, activated carbon has a large surface area due to being a porous material. The unwanted substance sticks to the surface area of the carbon particles.

One of the common utilizations of this porous carbon is to filter gas. Not as in fuel, but the gaseous substances that are either naturally produced or expelled from various machinery. Take, for example, air filters. Air is technically a gas, and when the air contains impure elements, a purifier in the form of a filter will help remove these impurities. In a slightly different form, the activated charcoal will perform the same function with water—a use common in fish tanks.

beadactivatedcarbon

Yet one of the long-standing functions of activated charcoal is oral ingestion. Companies make pills that contain activated charcoal which dissolve in the stomach, allowing the granular carbon to remove toxins. You can find a ton of claims on the Internet about the magic that taking a dose of activated charcoal performs, many of which aren’t medically confirmed, however, it is common for hospitals to use activated charcoal for this use. It is widely known to be safe to ingest and acts as a poultice.

Another use gaining momentum is using activated carbon as a teeth stain removal device. Your teeth’s health is important, and the way activated charcoal works also helps to bind plaque, making it an effective whitening tool. Put some of it on your toothbrush with liquid water. It will be weird to brush with at first—seeing the black get smeared on your teeth will feel counterproductive. However, it will rinse off your teeth easily enough and you’ll love the results. Just be careful to avoid staining your sink—keep soap handy to quickly clean up any messes which ensue. Many people swear by this method to whiten their teeth, and its use on teeth as a cleaner and whitener goes back for centuries.

One of the things that using active charcoal as a filter does is the loss of odors in gasses. Odors, and any other prone elements of the gas, get trapped in the activated charcoal through a process called adsorption. Through adsorption the particles bind to the surface of the activated charcoal—which is why it is imperative that activated charcoal actually be activated; the greater the available surface, the better the grade it gets for trapping.

It is effective enough that there are underpants available for purchase which make use of activated charcoal for moments of flatulence. Let’s face it—suspension of flatulence detection would do everyone a world of good. If only they could make activated underwear for dogs and cats; the media would have a field day!

 

Where is Activated Carbons Used ?

Activated carbon is the major adsorbent in global adsorbent market occupying more than 65% of the volume market share due to its high adsorption capacity and large surface area. Activated carbon is mainly divided into three types; powdered, granular and extruded. It has become the preferred option for use in potable water purification, waste water treatment, aquariums, swimming pools and sewage water treatment as well as air and gas filtration. These applications are gaining popularity due to increasing pollution levels, health concerns and stringent government regulations.

Apart from this, activated carbon is used for decolorization and deodorization of food and beverages; and purifies vitamins antibiotics and active pharma ingredients in pharmaceutical industry and 1medical applications. Some of the other applications of activated carbon include control gas emissions in automobiles; personal protection in defense sector; gold and precious metal recovery; and as catalyst in removal of mercaptan in oil refineries.

Scarcity of raw material and increasing concerns over supply chain, the activated carbon market is currently facing pricing issues; however, the market for activated carbon is on rise due to its extensive use in liquid phase and gas phase applications.

Activated Charcoal Applications:

  • industrial/pharmaceutical/chemical/military/agricultural/environmental – adsorption of unwanted chemicals
  • neutralize toxic compounds
  • medical
  • food purification
  • metalurgy
  • carrier for chemical catalysts
  • soil enrichment
  • greenhouse gas reduction
  • soundwave/microwave/radiowave capture

activated carbon

Activated Charcoal Uses:

  • Air filters in gas masks, filter masks, air compressors.
  • Food coloring
  • Gas purification
  • Gold purification
  • Medicine: liver and kidney dialysis machines, laser surgery, breast cancer surgery, stomach decontamination from drug/food poisoning, wound dressing…
  • Metal extraction
  • Metal finishing – the purification of electroplating solutions, as in bright nickel-plating solutions.
  • Nuclear Biological Chemical (NBC) suits
  • Nuclear power plants
  • Recycling solvents
  • Rye grass seed industry
  • Sewage treatment
  • Snow avalanche control – helping to melt snow
  • Soil enhancement
  • Sound systems – “cleaning” out bad background noise
  • Toxic soil cleanup from chemical spills or accumulation of chemical spraying
  • Volatile organic compounds capture: from painting, dry cleaning, gasoline dispensing operations, and other processes.
  • Water purification: aquariums, swimming pools, domestic & municipal water systems, recycling precious water on the orbiting space station (cost $10,000/liter)

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.

Impregnatedcarbon

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.

For Impregnated activated carbon buy and sell Market places, please go to https://www.acarbons.com/market-places/browse-ads/16/impregnated-activated-carbon/

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.

beadactivatedcarbon beadactivatedcarbon

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.

For Bead Activated Carbon Market Places, please check https://www.acarbons.com/market-places/browse-categories/15/bead-activated-carbon/

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.

 

For marketplaces of Extruded Activated Carbon, please go to  https://www.acarbons.com/market-places/browse-categories/4/extruded-activated-carbon/

 

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.

GAC

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

Granular Activated Carbon market places here https://www.acarbons.com/market-places/browse-categories/2/powdered-activated-carbon/

 

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.

coconut-shell-activated-carbon-powder

 

Post Your Powered Activated Carbons here https://www.acarbons.com/market-places/browse-categories/2/powdered-activated-carbon/

How is an activated charcoal selected for a particular application?

  • Applications are divided broadly into two groups: air/vapor filter and water/fluid filter applications. Air and vapor filters tend to use the larger sizes of GAC, while water and fluid applications use smaller GAC or even powdered activated charcoal (PAC).
  • The flow rate of the medium through the charcoal filter will determine the size of the charcoal particle. Sufficient contact time with the charcoal is paramount. The smaller the charcoal particles in the filter bed the faster they will work, but the smaller particles will also restrict the flow rate. The perfect formula will match the particle size to the desire flow rate.
  • The molecular size of the target contaminant is the next deciding factor. There are three basic activated carbon pore structures: micro (smallest – less than 20 Å) meso (intermediary – 20 Å – 50 Å) and macro (largest – greater than 50 Å)
  • The target contaminant is matched to an activated carbon with a particular pore size.
  • Activated charcoal produced from coconut shell is known for its micro pore structure which works well for small air/gas molecules. Wood-based charcoal has a more mid-range pore structure and coal-based has larger macro-pores that accommodate the larger color and protein molecules.

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.

Carbon Filtering

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

Activated Carbon is a non-graphite form of carbon which could be produced from any carbonaceous material such as coal, lignite, wood, paddy husk, coir pith, coconut shell, etc. Activated carbon manufactured from coconut shell is considered superior to those obtained from other sources mainly because of small macrospores structure which renders it more effective for the adsorption of gas/ vapor and for the removal of colour and odour 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 can have a surface of greater than 1000m²/g.

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 for water 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.

Typical particle sizes that can be removed by carbon filters range from 0.5 to 50 micrometres. The particle size will be used as part of the filter description. The efficacy of a carbon filter is also based upon the flow rate regulation. When the water is allowed to flow through the filter at a slower rate, the contaminants are exposed to the filter media for a longer amount of time.

 

There are 2 predominant types of carbon filters used in the filtration industry: powdered block filters and granular activated filters. In general, carbon block filters are more effective at removing a larger number of contaminants, based upon the increased surface area of carbon. Many carbon filters also use secondary media such as silver to prevent bacteria growth within the filter.  Alternatively, the activated carbon itself may be impregnated with silver to provide this bacteriostatic property.

 

Activated Carbon: Mesh Size and Ash Content

Mesh Size

The physical size, or mesh size, of a carbon must be considered in relation to the flow rate in the system it is to be used. Naturally, the smaller the carbon’s mesh size, the greater its resistance to flow. Thus, it is usual to select the smallest mesh size carbon that will satisfy the pressure drop limitations of the system.

Mesh Size
Mesh Size

 

Ash Content

Ash content is less important except where the carbon is used as a catalyst support since certain constituents of the ash may interfere or destroy the action of precious metal catalysts. Ash content also influences the ignition point of the carbon—this may be a major consideration where adsorption of certain solvents is concerned.

Density

The density of carbon is, of course, of great importance to many users in estimating the weight required to fill a vessel.

Activated Carbon Interrelation of Properties

There is a relationship between BET surface area and CTC adsorption and this is taken into account when specifications are formulated.

CTC activity, density and ash content are interrelated and provide a simple means of manufacturing control. As quality, or degree of activation increases, CTC activity and ash content increase and density decreases.

Furthermore, CTC activity being equal, coconut carbons show higher density and lower ash content than coal based carbons. Wood based carbons show much lower density than either coal or coconut carbons but ash contents midway between coal and coconut carbons.

Thus, these properties are not only a means of controlling quality during manufacture but may also assist in determining the raw material and quality of an unknown carbon.

CTC activity, density, hardness, mesh size and raw material information will enable selection of a suitable carbon for most common applications (excepting those utilizing chemisorption as the prime mechanism).

Activated Carbon Hardness

The hardness and resistance to attrition of activated carbons is becoming more and more important.  The loosely applied term of “hardness” is somewhat difficult to measure on activated carbon.

Three forces can mechanically degrade an activated carbon – impact, crushing and attrition. Of these three, the force of attrition, or abrasion, is the most common cause of degradation in actual end use. At the present time, there are two commonly used methods available to evaluate a carbon’s hardness.

The first of these is the Ball-pan Hardness Test.

activate carbon Ball-pan Hardness Test
activate carbon Ball-pan Hardness Test

 

A screened, weighed sample of carbon is placed in a special hardness pan with a number of stainless steel balls and subjected to combined rotating and tapping action for ½ hour. The particle size degradation is measured by determining the weight of carbon retained on a sieve (with an opening closest to one half the opening of the sieve defining the minimum nominal particle size of the original sample). The ball-pan hardness method has been used widely in the past and has a broad history in the activated carbon industry for measuring the property loosely described as “hardness”. In this context, the test is useful in establishing a measurable characteristic, conceding that it does not actually measure in-service resistance to degradation, it can be used to establish comparability of differing batches of the same material. This test actually applies all of the three forces mentioned earlier, in a variable manner determined by the size, shape and density of the particles.

The second method used is the Stirring Bar Abrasion Test.

In this procedure, a sample of carbon is placed in a cylindrical vessel where an inverted T-shaped stirrer is turning rapidly at a controlled rate. The percentage reduction in average particle size, resulting from the Tbar action, is recorded after 1 hour. This method measures attrition of the carbon, as long as the particle size is smaller than a 12 mesh. There is evidence showing that the results of this method are influenced by particle geometry.

Whichever of these tests is performed on carbon it is generally accepted that granular coconut based carbons show the least rate of physical degradation.

This is possible due to two factors.First, granular coconut carbon is produced from pieces of raw coconut shell whereas, most other carbons are produced from reconstituted powders. In consequence, carbons other than coconut based types, can only breakdown to a powder or dust. Coconut carbon essentially chips and breaks into smaller pieces and thus degradation to powder, is a relatively lengthy process. Second, as outlined earlier, the coconut carbon structure is different to other types, producing a material of relatively high density and physical strength.

 

 

Activated Carbon Surface Area

The internal surface area of a carbon is usually determined by the BET method (Brunauer, Emmett and Teller).This method utilizes the low-pressure range of the adsorption isotherm of a molecule of known dimensions (usually nitrogen).

This region of the isotherm is generally attributed to monolayer adsorption.

 

Thus, by assuming the species is adsorbed only one molecule deep on the carbon’s surface, the surface area may be calculated using the equation:

S = XmNA/M

  • S = specific surface in m2/g
  • Xm = sorption value (weight of adsorbed N2 divided by weight of carbon sample)
  • N = Avagadro’s Number, 6.025 E+23
  • A = cross-sectional area of nitrogen molecule in angstroms
  • M = molecular weight of nitrogen

 

Most manufacturers will specify the surface area of their products but as with CTC activity, it does not necessarily provide a measure of their effectiveness, merely demonstrating their degree of activation. It is also impractical to utilize surface area measurement as a means of quality control since this is a very lengthy procedure.

Carbon Tetrachloride Activity

The most widely used method is to measure the carbon’s capacity to adsorb carbon tetrachloride (referred to as CTC) and express this as a w/w %. This is determined by flowing CTC laden air through a sample of carbon of known weight, under standard conditions, until constant weight is achieved.

The apparatus essentially consists of a means to control the supply of air pressure, produce a specified concentration of CTC and control the flow rate of the air/CTC mixture through the sample.

The weight of CTC adsorbed is referred to as the carbon’s % CTC activity. However, this test does not necessarily provide an absolute or relative measure of the effectiveness of the carbon for other adsorbates or under different conditions. CTC activity is now universally accepted as a means of specifying the degree of activation or quality of activated carbon. Commercially available carbons range from 20% to 90% CTC activity.