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What do you need about activated carbons?
What is activated carbon?
Activated carbon is considered as crude form of graphite. But unlike graphite structure it has random imperfect structure with macro and micro pores. The graphite structure gives the Activated Carbon it's very large surface area. 3 gram of Activated Carbon can have a surface area of a football field. Activated Carbon has the strongest physical adsorption forces. The surface area of Activated Carbon varies from 500 m2/g to 2000 m2/g.
How is activated carbon manufactured?
Activated Carbon can be manufactured from many materials containing high carbon content such as coconut shell, wood, coal, bituminous, coir, lignite, peat, petroleum pitch etc. Carbonaceous materials can be activated using two methods, steam activation and chemical activation
a) Steam Activation In this process the material is activated with steam at very high temperature. The chemical reaction between the carbon and the steam take place at the internal surface of the carbon. Steam activation enlarges the pore structure and thus increases the internal surface area. It is the most widely used process to activate carbonaceous materials. It is considered as the best pollution free method of activation.
b) Chemical Activation This type of activation is only useful for the carbonization of wood, sawdust or peat. In chemical activation the raw material is mixed with an activating agent such as phosphoric acid that swells the material and open up the cellulose structure. It is then carbonized and dried in a rotary kiln at low temperature. It dehydrates the raw material resulting in the amortization of the carbon, thereby creating high porous structure.
At ACPL we follow steam activation method since it is the most environmental friendly method of activation process.
What is activated carbon adsorption?
Adsorption is the process where the molecules of the substance attract on the surface of the activated carbon. Activated Carbon is characterized with high micro and macro porosity, which enables the carbon to adsorb the adsorbates into its internal surface. There are two types of adsorption.
Physical adsorption
Physical adsorption is happening when the substances to be adsorbed are held on the internal surface of Activated Carbon due to Vander Waals force of attraction between the molecules. The force of attraction diminishes with increase in distance between pore wall and the substance molecules.
Chemisorption
Strong forces of attraction between the molecules of the adsorbate and the chemical complexes that impregnated on the pore walls of Activated Carbon.
Properties of Activated Carbon
Iodine Number: the amount (milligrams) of Iodine adsorbed by one gram of carbon at equilibrium with a 0.02N Iodine concentration filtrate. Iodine Number is often reported in mg/g (typical range 500–1,200 mg/g). It is best understood as an indicator of total pore volume. Iodine Number is the standard measure for liquid phase applications.
Surface area:
Surface area of Activated Carbon varies from 500 m2/g to somewhat 2000 m2/g. That means just 3 gram of Activated Carbon can have the surface area of a football field. The surface area of carbonaceous materials can be increased by activation process.
Total Pore Volume (TPV):
TPV refers to the total space of the pores in an Activated Carbon. The effectiveness of Activated Carbon is increased with increase of total pore volume. It is expressed in milliliters per gram (ml/g)
Pore volume distribution:
The significance of Activated Carbon is its unique distribution of pore sizes. For decolorisation applications high distribution of mesopore is required.
Abrasion/Hardness Number:
Relative measure of the ability of granular or pelletized activated carbon to resist attrition during handling and use.
Apparent Density: usually measured in g/ cm3 (g/ml) or pounds per cubic foot. Apparent Density is used to determine the weight of a fixed volume of activated carbon. The solid or skeletal density (e.g., if all pore spaces were removed) of activated carbons typically ranges between 2.0 and 2.1 g/cm3 (125-130 lbs/ft3). However, a large part of an activated carbon sample consists of void space within and between particles, and the actual operating (apparent) density is therefore lower, typically 0.4 to 0.5 g/cm3 (25-31 lbs/ ft3). Higher apparent density provides greater volume activity and normally indicates better-quality activated carbon when comparing the same source material. It can also indicate different starting materials (such as bituminous coal vs. lignite coal vs. wood).
Removal Mechanisms
Activated carbon performs a variety of functions depending on the application:
• Adsorption: the removal of impurities from liquids, vapors or gases; the most common application for activated carbon
• Reduction: e.g. removal of chlorine and chloramines from water based on chemical reduction reactions
• Catalysis: catalyze a number of chemical conversions, or be a carrier of catalytic agents (e.g. precious metals)
• Carrier of biomass: support material in biological filters
In most applications, activated carbon removes impurities from liquids, vapors or gases by adsorption.
Activated carbon removes chlorine from water by chemically reacting with chlorine via an oxidation-reduction reaction, rather than via adsorption.
