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What is activated carbon?

Carbón activado qué es y para qué sirve?

Keep reading this complete guide, to know how activated carbon works, its main applications, and if you read to the end you will find a complete table with specific article references to each characteristic of activated carbon. The topics we will address are the following:

  1. Índice del contenido

    What is activated carbon?

  2. What is activated carbon used for?

  3. Where can you purchase activated carbon?

  4. How does activated carbon work?

  5. What raw materials can produce activated carbon?

  6. Coconut shell activated carbon

  7. Mineral coal

  8. What is activated carbon’s adsorption capacity?

  9. How does activated carbon work in dechlorination?

  10. What’s the best activated carbon for water treatment purposes?

  11. What’s the best activated carbon for air and gas purification?

  12. Activated carbon related article table

1. What is activated carbon?

Activated carbon or activated charcoal is a porous element that traps compounds, mainly organic, present in a gas or liquid. It does so with such effectiveness that it is the most widely used purifying agent by humans.

Organic compounds are derived from the metabolism of living beings, and their basic structure consists of chains of carbon and hydrogen atoms. Among them are all the derivatives of the vegetable and animal world, including oil and the compounds obtained from it.

The property of a solid to adhere a flowing molecule to its walls is called “adsorption”. The solid is called “adsorbent” and the molecule, “adsorbate.”

After filtration – which is intended to retain solids present in a fluid – there is no single purification process with more applications than activated carbon.

2. What is activated carbon used for?

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.

E.g. in cartridge respirators, air recirculation systems in public spaces, drainage vents and water treatment plants, paint application booths, spaces hat store or apply organic solvents.

Activated carbon is considered a “universal antidote”, and is applied in emergency rooms and hospitals.

Coal retains the proteins that give color to the cane juice; the main objective of this process is to prevent sugar from fermenting and spoiling.

  • Vegetable oil color removal

Removes color from coconut oil, maize glucose and other liquids used in the food industry.

  • Alcoholic distillate deodorization and color removal

Removes color and odor from grape wines and distillates from other sources.

Gold that cannot be separated from minerals by a flotation process, is dissolved in sodium cyanide and adsorbed onto activated carbon.

3. Where can you purchase activated carbon?

You can purchase activated carbon directly from us at: [email protected]

We also sell activated carbon for intoxications and indigestion problems.

4. How does activated carbon work and what are its benefits?

Activated carbon is an adsorption medium, its function is to adsorb organic molecules in its micropores. It is activated using thermal or chemical processes to extend its adsorption capacity.

Here’s a simple graphical explanation on how activated carbon works.

On the other hand, activated carbon is not an absorbent, as explained by the following images

What gives activated carbon the property of adsorbing, mainly organic molecules?

Any carbon particle has the ability to adsorb. That is why some people put carbon in the refrigerator to eliminate odors. The same is true if you put carbon in a container of water: it removes color, taste and odor. Or, in the countryside, people burn tortillas and eat them to relieve digestive problems (such as mild infections, indigestion or flatulence).

Activating a carbon consists of making it porous to increase its adsorption capacity. One gram of carbon has a surface area of about 50 m2. With the activation process, it reaches 600 or 800 m2. That is to say, it increases between 12 and 16 times.

Carbon atoms.

The carbon atoms that form a solid that we call “carbon” are bound together by covalent bonds. Each atom shares an electron with four other carbon atoms (remember that in ionic bounds, the most electronegative atom steals one or more electrons from the other).

The atoms that are not on the surface distribute their four bonds in all directions. But the surface atoms, although they are bound to four other atoms, are forced to do so in less space, and an imbalance of forces remains in them. This imbalance is what leads them to trap a molecule of the fluid that surrounds the carbon.

London Force.

The force with which the surface carbon atom traps the other, is called the “London Force”, which is one of the seven types of “Van de Waals Forces”. It is considered a physicochemical bond, strong enough to retain the adsorbate, but not so strong as to be considered an irreversible chemical bond that forms a new molecular structure. Therefore, the adsorption is reversible and the activated carbon can be reactivated for use again.

As we said, the molecules that carbon adsorbs tend to be covalent; not ionic, as the latter would try to steal or donate electrons to the carbon atoms. The bonds between carbon and hydrogen atoms are covalent, and that is why carbon is a good adsorbent of organic molecules.

Not all organic molecules tend to be covalent. They usually contain oxygen, Sulphur and other high electronegativity atoms, which give an ionic tendency to the part of the molecule that contains them. On the other hand, not all inorganic molecules tend to be ionic; there are also those with a covalent tendency. Such is the case of gold dicyanide, which makes activated carbon an essential part of the extraction process of this precious metal.

From which raw materials can an activated carbon be obtained?

In theory, any carbon particle could be activated. However, if the carbon is very ordered (as is the case with diamond or graphite), it is difficult to remove some carbon atoms to generate pores.

One way of classifying carbons, is based on the degree of “coking” or ordering of their carbon atoms. The less ordered, the less hard the carbon is and the more easily it can be activated.

Coconut shell and wood charcoal.

The most commonly used raw materials to make activated carbon are: soft woods (such as pine), mineral carbons “coal” (lignite, bituminous and anthracite) and vegetable shells or bones (coconut shells, olive or peach pits, walnut shells).

Activated carbons made from soft woods, form large diameter pores and are particularly suitable for discoloring liquids.

Mineral coals.

Those made from coal, tend to form a wide range of pores; they are usually more suitable for applications where the compounds to be retained are of different molecular sizes.

Those that come from hard shells or bones, form small pores, and are applied in the treatment of gases or in the purification of water coming from wells.

Carbón de concha de coco

What is the physical form of an activated carbon?

Carbon can be produced in the form of powder, granules or cylindrical pellets.

Dust is only applied in the purification of liquids; the coal is dosed in a tank with agitation and then separated from the liquid by means of a suitable filter to retain small particles (such as the filter press).

In the case of granular coal, it is produced in different particle ranges, which are specified based on the particle size or mesh number. A 4 mesh, for example, is one that has four holes in every linear inch. They are applied both in the purification of liquids and gases.

Pellets are normally applied in gas treatment, as they cylindrical shape produces a lower pressure drop.

If a granular carbon or pellet is desired, if the raw material is not hard enough, it can be re-agglomerated with a binding agent that imparts hardness to it to prevent it from breaking when the fluid passes through.

How is carbon activated?

Carbon can be activated by thermal or chemical processes. Thermal processes consist of provoking a partial oxidation of the carbon, to achieve that the pores are formed, but avoiding that it gets gasified and loses more carbon than necessary. This occurs at temperatures between 600 and 1100 °C (1112 °F and 2012 °F), and in a controlled atmosphere (achieved by injecting an appropriate amount of water vapor or nitrogen).

The chemical processes start from the raw material before it is carbonized. The reagents are dehydrating agents (such as phosphoric acid) that break the bonds that bind the cellulose chains together. After this stage, the material is carbonized at a relatively low temperature (about 550 °C or 1022 °F) and then washed to remove reagent residues and other by-products.

Furnaces in which a carbon is thermally activated or in which a carbon previously treated with a chemical is carbonized, can be either rotary or vertical (staged).

What is the adsorption capacity of activated carbon?

The capacity of an activated carbon to retain a given substance is not only given by its surface area, but also by the proportion of pores that are the right size, i.e. a suitable carbon has a diameter of between one and five times the molecule to be adsorbed.

If this condition is .

How does activated charcoal work in dechlorination?

Dechlorination is a complicated mechanism that can follow different reaction paths in which activated carbon can intervene as a reactive or a catalyst.
Free chlorine can be added to water in the form of chlorine gas, sodium hypochlorite solution, or calcium hypochlorite tables (granules).

In any of these cases the chlorine is dissolved in the form of hypochlorous acid (HOCl), a weak acid that tends to partially dissociate.

The distribution between hypochlorous acid and hypochlorite ion depends on the pH and concentration of these species. Both molecular forms are defined as free chlorine.

Both are strong oxidants that when added to water react almost immediately with organic and inorganic impurities, and exert a biocidal effect on microorganisms.

The chlorine that reacts and the one that intervenes in this stage of disinfection, stops being free and remains combined and stops being free. Once this stage is finished, it is necessary to eliminate the residual free chlorine, by means of granular activated carbon.

When the carbon is exposed to free chlorine, reactions take place in which the HOCl or OCl is reduced to chloride ion. This reduction is the result of different possible reactions paths.

In two of the most common, the GAC acts according to the following reactions:

Where C* represents activated carbon. C*O and C*O2 are surface oxides, which gradually occupy spaces that, when blocked, no longer participate in the reaction. Some of these oxides are released into solution as CO and CO2. This leaves spaces available again which therefore increase the capacity of the granular activated carbon for this reaction.

As for Cl, it also accumulated on the surface of the coal during the first moments of operation. As HOCl or OCl continues to reach the surface of the carbon, the reaction slows down a little, and then Cl begins to be released. This slowdown is due to the poisoning of the carbon by surface oxides. This poisoning continues gradually, while the capacity for both adsorption and dechlorination of activated carbon decreases.

In the above reactions you can intervene instead of HOCl, with the difference that no H+ is produced. It can be seen that the activated carbon reacts and therefore disappears. If there were no accumulation of surface oxides, the reaction would continue until the complete disappearance of the carbon.

What type of carbon is best suited for bleaching?

The colors that appear in liquids are usually relatively large molecules. Therefore, they are adsorbed in large pores, which makes the carbon more suitable for retaining them the ones with the highest macroporosity.

Wood charcoals, particularly those from not very hard woods (such as pine) that are chemically activated, are the most macro-porous and, are therefore, the most suitable for discoloring.

The problem with these carbons is that they are not very hard and not very resistant to abrasion, which means that they have to be applied in powder form. When bleaching carbon is required to be granular, the best alternative is usually lignite carbon. This is the carbon with the highest macroporosity.

What type of activated carbon is the most suitable for purifying water?

The contaminants typically present in well water are usually of low molecular weight and, for these cases, the most suitable carbon is one with high microporosity.

The carbons that best meet this condition are, firstly, coconut shell carbons and, subsequently, bituminous minerals.

Why does the pH of the water vary when a virgin carbon is installed?

When a carbon is chemically activated, it is impractical and unnecessary for the manufacturer to remove all the chemical used from the final product. Therefore, if the chemical was an acid, it will lower the pH of the first few liters of water that come in contact with the carbon. The opposite will occur if the chemical used was an alkali.

In the case of thermally activated carbon (without the presence of chemicals other than water vapors and combustion gases), the pH of the first liters of water treated with it increases.

This is because all vegetables have significant amounts of sodium, potassium, calcium and other cation that, in the carbonization process, remain in the carbon in the form of oxides. These oxides are converted into hydroxides when they come into contact with water, dissolve in the water and increase its pH.

When the pH of the first liters of water that come into contact with a carbon does not change, it can be a pH-adjusted carbon or an ultra-pure carbon (free of soluble).

What type of activated carbon is best suited to purify air and gases?

All contaminants in the gaseous state have molecular diameters less than 2 nm. This means that they are preferably adsorbed in micropores. Coconut shell carbons have the highest microporosity and are therefore the most commonly used in air and gas purification.

There is modified structure activated carbons, special activated carbons, which are used when a standard activated carbon cannot retain other non-organic compounds.

 

 

In Carbotecnia we are manufacturers and specialists of activated carbon. You can check the different types of activated carbon that we have here.

Are you interested in knowing more about activated carbon?

We have many resources available:

Description

Related Posts:

Activation

Activation types:The first is thermal activation
The second chemical activation

Capacity

The capacity of an activated carbon depends on several factors. The main ones are listed below.Activated carbon related factors:
– Average pore diameter
– pore size distribution
– Superficial area
– Surface chemistry
– Activated carbon particle size distributionFactors related to adsorbate that requires retention
– Ionic or covalent character
– Presence of acidic or alkaline groups
– Mass and molecular size

Medical use – Poisoning

How does activated charcoal work in the treatment of poisonings?Reasons why activated carbon adsorbs molecules, mainly organic. There are many different forms of pure carbon in nature. Some examples are diamond, graphite, carbon black, mineral coals, or simple charcoal used to grill meat. The difference between each of them is in the structure of their carbon atoms.

Reactivation

Profitability in the GAC reactivation process depends on the mechanical strength of your granules. The lower it is, the higher the percentage of material loss due to breakage.Types of activated carbon reactivation
1. Thermal reactivation.
2. Reactivation with steam
3. Reactivation with hot gases
4. Reactivation with acid.
5. Reactivation by modifying the pH in aqueous solution
6. Biological reactivation

Coal sanitization

Why should coal be sanitized?
Due to the fact that GAC adsorbs organic compounds, it becomes a favorable substrate for bacterial growth. The rough and cracked surface of the charcoal makes it easy for bacteria to stick. When chlorinated water comes into contact with the top of the bed, the charcoal reacts with the free chlorine and its disinfecting effect disappears. Since this reaction is rapid, no free chlorine reaches the middle and lower part of the carbon bed.

Features

It is porous carbon. Activating carbon is simply creating more pores in the carbon to increase its surface area and thus its natural adsorption capacity. Every publication that defines or explains what this material consists of, mentions it with this simplicity.

Types of mineral coal

Types of mineral coals:
1. Anthracite
2. Bituminous
3. Sub-bituminous.
4. Lignite or Lignitic.

Iodine number

The iodine number as a variable to evaluate the operational capacity of granular (or pelleted) activated carbons.

Charcoal impregnated with silver

In order to inhibit bacterial growth, the surface of the carbon is impregnated with metallic silver. The resulting carbon is called bacteriostatic.

Dechlorination

One of its main applications is water dechlorination.This compound does not come from natural sources of supply, such as wells, rivers or lakes. Nor is it a pollutant, but rather a chemical that is added to water, mainly as a disinfectant, and sometimes to control odor and taste, control biological growth, or remove ammonia.

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