Chemistry and applications of activated carbon

­Charcoal is carbon. Activated charcoal is charcoal that has been treated with oxygen to open up millions of tiny pores between the carbon atoms.

Carbon can be produced from many raw materials i.e. Softwood, Coconut shell, Peat lignite (Both mineral & coal). The raw material is ignited and charcoal is produced.

Ordinary commercial charcoal has very limited ability to adsorb substances in the liquid or gas phase. To give charcoal this property it must first be activated by removing the tarry materials which block the structure of the pure carbon skeleton of the charcoal. When this is done the surface area of the porous carbon skeleton is increased literally millions of times providing equally large numbers of sites where molecules of other substances can be ‘held’ or adsorbed and thus removed from gases or from liquids in which the treated charcoal is placed.

Charcoal processed in this way is called “Activated Charcoal”. Charcoal is not the only type of carbon used for activation but it is an important raw material for activated carbons.

Activated carbons are carbons which have undergone an intricate treatment to increase their adsorption properties.

Charcoal

One gram  of ground carbon has an external surface area of 2 to 4 square meters, whereas when carbon has been activated this one gram of carbon may acquire an internal surface area of more one thousand square meters.

Activated carbons are available in powdered, granular and pelletised form and are used in liquid and gas phase adsorption processes.

The chemical and activated carbon industries prefer lump charcoal. This is partly due to their process requirements. Fine charcoal particles behave more reactively, but airborne losses in processing make fines an undesirable raw material. Fines usually have a higher ash content than lump charcoal and may be more contaminated generally.

Activated carbons with large total surface areas but with a microporous structure may be effective in removing slight odour causing impurities from gases, but ineffective in adsorbing large colour-forming compounds from solutions.

More than seventy types of activated carbons are currently marketed.

 M.B. VALUE OF ACTIVATED CARBON

MB value means Methylene Blue adsorption value.

Charcoal is titrated with Methylene Blue solution and its adsorption capacity is calculated. Charcoal 180 MB implies that 0.1g of activated charcoal adsorb minimum of 12 ml of 0.15% MB solution.

APPLICATION:

Treatment of liquids

Drinking water purification, municipal waste water and industrial waste, water treatment plants, swimming pools and acquaria are examples.

Purification of fats, oils, beverages, water purification in breweries, cleaning of bottles and tanks in wineries, cleaning of tanks for insecticides and pesticides, spraying, cleaning of electroplating baths, dry cleaning. Decolourization of cane and beet sugar solutions, vitamin solutions and pharmaceuticals and high fructose syrup are also important uses

Treatment of Gases and Vapours

Purification of exhaust emissions of re-circulated air purification. Recovery of solvent from printing machines and processes where highly volatile matter is continuously being released. Reduction of toxic and harmful vapour levels and objectionable odours in air. Air purifiers for commercial and domestic kitchens. Gas masks for military and civilian purposes.

Speciality markets

  • Horticulture: Charcoal is used in different grades as a top dressing for the improvement of lawns and bowling greens. These top dressings act as mulch and also provide valuable trace elements and sweeten the soil. Pottery mixtures used in nurseries often contain fine charcoal.
  • Poultry and Animal Feeds: These are sometimes supplemented with charcoal fines to control certain diseases.
  • Pharmaceuticals: Charcoal is used for controlling infections of the digestive tract.
  • Pigments: Vegetable (charcoal) blacks are dead black and of great strength.

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