Friday, April 1, 2011

Activated carbon from Coconut shell

Coconut shell

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. Coconut shell is used for manufacturing activated carbon. Coconut Shell is carbonized by using pit, drum, destructive distillation method etc.

Uses

Shell based activated carbon is extensively used in the process of refining and bleaching of vegetable oils and chemical solutions, water purification, recovery of solvents and other vapours, recovery of gold etc. It is used in gas masks and a wide range of filters for war gases and nuclear fall outs and for the removal of colour and odour of compounds for protection against toxic gases.

Activation process

Coconut shell based activated carbon units adopt steam activation process to produce good quality activated carbon. Activated carbon manufactured from coconut shell is considered superior to those obtained from other sources mainly because of small macropores structure which renders it more effective for the adsorption of gas/vapour. Steam activation and chemical activation are the two commonly used processes for the manufacture of activated carbon. However coconut shell based activated carbon units are adopting the steam activation process to produce good quality activated carbon.

Steam Activation

The process of steam 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 900-1100 degC 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 900degC the reaction becomes too slow and is very uneconomical. Above 1100degC the reaction becomes diffusion controlled and therefore takes place on the outer surface of the charcoal resulting in loss of charcoal.

Properties

pH Value 6.5 - 7.5, Methylene value adsorption mgm / gm 190 – 350, Adsorption capacity at % by mass (min) 45, Moisture (max.) 5%, Ash (max) 5%, Hardness 90.

Reactivation

Activated carbon is extensively used for the process of refining and bleaching, but after utilization, the "spent" carbon, as it is called, can be removed and re-activated for further use. This is done primarily with granular activated carbon because particles will be too small to be effectively re-activated. This process allows for recovery of approximately 70% of the original carbon. This number also allows for any physically lost in the shipment process. The re-activated carbon is then mixed with a portion of new carbon for higher effectiveness and is then used in the process.

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