CCSG’S Carbon is a form of carbon that can be activated by a carefully controlled oxidation process to develop a porous carbon structure. The imperfect structure results in a high degree of porosity and over a broad range of pore sizes, from visible cracks and crevices to gaps and voids of molecular dimensions. The specified structure of carbon gives it a very large surface area which allows the carbon to adsorb a wide range of compounds. Carbon has the highest volume of adsorbing porosity of any material available to mankind.

To put this into perspective, 5gms of Carbon would have the surface area of a football field

Carbon can be made from many substances containing high carbon content such as coconut shells, coal and wood. The raw material has a very large influence on the characteristics and performance of Carbon and plays a major part in determining it’s ability to adsorb certain molecular species.

Forms of Carbon:

Three main forms of Carbon are

Granular Carbon – Irregular shaped particles with sizes ranging from 0.2 to 5 mm.

Powder Carbon – Carbon with a size predominantly less than 0.21mm (70 US mesh)

Pelleted Carbon – Extruded and cylindrical shaped with diameters from 0.8 to 5 mm.

Structure of Carbon :

The major portion of the surface area is derived from the small diameter micropore and the medium diameter mesopore regions. Micropores have been found to be the most effective in trapping small molecules in gas and liquid phase applications.

The mesopore region is most suitable for adsorbing large molecular species such as colour molecules. Carbon s produced from coconut shells exhibit a predominance of micropores, while coal based carbons have a wider range of mesopores. The development of an extensive macropore structure is found when either peat or wood is used as the raw material.

This reaction being endothermic, temperature is maintained by partial burning of the CO and H2 formed:-

2CO + O2 -> 2CO2 +393,790 kJ/(kg mol)
2H2 + O2 -> 2H2O +396,650 kJ/(kg mol)

The air is added proportionally so as to burn the gases without burning the carbon.

Adsorptive Characteristics :

The effectiveness of Carbon is usually specified by the amount of a certain test chemicals it can absorb per unit weight of Carbon used.

CTC Activity: For Carbon used for filtering air and gases, the test chemical used is usually Carbon Tetrachloride, commonly designated as CTC and is specified as CTC Activity (%). In some areas, this test is being substituted by a similar test which uses n-butane, known as the Butane Number Test. To obtain the Butane Number from Carbon Tetrachloride Number, divide the Carbon Tetrachloride Numbe2.55.

Iodine No. : For Carbon used in filtering water and liquids, the test chemical used is usually Iodine mixed with water and is specified as Iodine no. (mg/gm) of carbon.

Surface Area : Measurement of the extent of the pore surface developed within the matrix of the Carbon . The BET N 2 method, using nitrogen measures the area by determining the amount of liquid nitrogen needed to evenly cover the entire surface in these holes. This is used in Carbon research and is not a practical method to be used as a quality control tool.

The Iodine Number and the CTC Activity, both of which measure the adsorption capacity, are generally used to monitor quality during production and use.

Physical Characteristics :

Hardness: The harder the Carbon, the less it will crumble into fine particles during handling and use. This value gives an idea of the abrasion-resistance of the Carbon and is measured by means of a ball pan. Coconut shell based Carbon has the unique property of the highest hardness (over 99%) which increases the durability and reduces loss in application, handling and regeneration.

Apparent Density: Is the weight of one liter of Carbon (g/ltr). Density depends on the raw material being used and the degree of activation. The density does not affect the effectiveness of the Carbon measured in adsorption per unit weight, but will have an effect on adsorption per unit volume.

Ash Content: This is the inorganic, inert, amorphous and unusable part present in the Carbon. This ash comes initially from the basic material. Lower the ash content, the better the Carbon. The practical limit for the level of ash content allowed in the Carbon varies within 2 to 5%.

Moisture: This is the amount of water physical bound on the Carbon under normal condition. The practical limit for the level of moisture content allowed in the Carbon varies within 3 to 6%.

Particle Size Distribution: Carbons are available in a wide range of granular and powdered grades. The particle size distribution of a grade is defined using test sieves. Different particle size of Carbon offer different flow resistance to the air or water it is filtering. Depending upon the situation, system designers will specify different particle sizes of the carbon to be used. Typically, for filtering air or gases, the larger granule sizes are used; for filtering water or fluids, the smaller granule sizes are used.