Activated carbon is a form of carbon which could be produced from any carbonaceous material such as coal, rice husk, paddy husk, coconut shell, wood etc. Due to their low ash content, high carbon content and natural pore structure, coconut shells are ideal for producing high quality activated carbon. Activated carbon manufactured from coconut shell is considered superior to those obtained from other sources mainly because of small macro-pores structure which renders it more effective for the adsorption of gas/vapor and for the removal of color and odour of compounds and as pre-filters in water purification because of the large internal surface area which makes it as a very good adsorbent for many contaminants in drinking water. The activated carbon is also used
- In food and non-food industries.
- In processing of cooking oil, sugar, and chemical matter purification
- Used in drinking water and waste-water treatment.
- Refining and bleaching of vegetable oils.
- Recovery of solvents and other vapours & gold.
- In gas mask for protection against toxic gases etc
Steam activation is the most widely used process because it is generally used to activate both coconut shell and coal based carbons. Steam activated carbons are produced in a two-stage process. Firstly the raw material, in the form of lumps, pre-sized material is carbonized by heating it in an inert atmosphere such as flue gas, so that de-hydration and devolatilization of the carbon occur. Carbonization reduces the volatile content of the source material to fewer than 20%. A coke is produced which has pores that are either small or too restricted to be used as an adsorbent. The second stage is the activation stage which enlarges the pore structure, increases the internal surface area and makes it more accessible. The carbonized product is activated with steam at a temperature between 900°C and 1100°C. The chemical reaction between the carbon and steam takes place at the internal surface of the carbon, removing carbon from the pore walls and thereby enlarging the pores. The steam activation process allows the pore size to be readily altered and carbons can be produced to suit specific end-sues. Steam Activation produce activated carbon in the form of 1mm to 3mm pieces, which are crushed and screened to remove fines and dust to meet the specifications for granular activated carbons. To produce powdered activated carbons, the carbon pieces are further grinded using a gentle pulverizing action.
ADVANTAGE OF ACTIVATION
The activation process generates a network of minute openings of different diameters on the carbon surface which become the path for water to access the extended internal surface created by activation. Carbon has a natural affinity for organic pollutants which bind to its surface. Once activated, the carbon forms little pores and pockets that increase its surface area. An imbalance of forces then exists on the activated carbon atoms at the pore wall surface. To neutralize this imbalance, molecules are physically adsorbed, i.e., drawn and held physically to the pore wall (Van der Waals forces). In other words, compounds like pesticides, chloroform, and contaminants slide into the holes of this honeycomb-like substance and hold fast through a process called adsorption. The porosity of activated carbons offers a vast surface on which this adsorption can take place. Adsorption occurs in pores slightly larger than the molecules that are being adsorbed, which is why it is very important to match the molecule you are trying to adsorb with the pore size of the activated carbon.