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 1000mē/g.
There are two types of processing process.
We manufacture Steam Activated carbon which is commonly used across the world
Process of Steam Activation
The process of activation is carried out in two stages. First the coconut shell is converted into shell charcoal by carbonization process which is usually carried out in mud-pits, brick kilns and metallic portable kilns. The coconut shell charcoal is activated by reaction with steam at a temperature of 900oC - 1100oC under controlled atmosphere in a rotary kiln. The reaction between steam and charcoal takes place at the internal surface area, creating more sites for adsorption. The temperature factor, in the process of activation is very important. Below 900oC the reaction becomes too slow and is very uneconomical. Above 1100oC the reaction becomes diffusion controlled and therefore takes place on the outer surface of the charcoal resulting in loss of charcoal.
Properties of Activated Carbon
There is wide variety of activated carbon with exhibits different characteristics depending upon the raw material and activation technique used in their production. Understanding both Absorptive and Physical characteristics of the material is very important in the selecting an activated carbon.
Surface area (BET N2) :- measurement, using nitrogen (N2), of the extent of the pore surface developed within the matrix of the activated carbon. Used as a primary indicator of the activity level, based on the principle that the greater the surface area, the higher the number of adsorptive sites available.
Pore size distribution :-determination of the pore size distribution of an activated carbon is an extremely useful way of understanding the performance characteristics of the material. The International Union of Pure and Applied Chemistry (IUPAC) define the pore size distribution as:
Micropores r < 1nm
The macrospores are used as the entrance to the activated carbon, the mesopores for transportation and the microspores for adsorption.
Mesopores r 1-25nm
Macropores r > 25nm
Iodine number :-measurement of the porosity of an activated carbon by adsorption of iodine from solution.
Carbon tetrachloride activity :- measurement of the porosity of an activated carbon is being tested by the adsorption of saturated carbon tetrachloride vapour.
Particle size distribution.
Hardness - an important factor in system design, filter life and product handling. There are large differences in the hardness of activated carbons, depending on the raw material and activity level.
Bulk Density - should be carefully considered when filling fixed volumes as it can have considerable commercial implications
The backwashed and drained density will show a lower value due to the water film between the particles of activated carbon. .
Particle size distribution- the finer the particle size of an activated carbon, the better the access to the surface area and the faster the rate of adsorption kinetics. In vapour phase systems this needs to be considered against pressure drop, which will affect energy cost.
Careful consideration of particle size distribution can provide significant operating benefits.