What is Activated Carbon and Why it is being used?
Activated Carbon is made from Porous material like Coal, Wood, Coconut, etc. These Pores are activated by steam activation or chemically activated process to generate large surface area on activated carbon surface. Activated carbon is good at removing organic impurities by Adsorption process. Adsorption process is chemical attraction process through which organics are attracted and attached to activated carbon surface. There are few chemicals like Nitrates, Calcium etc. do not attract with this attraction so activated carbon cannot remove them. Activated carbon is very good in removing Odour, Taste, Chlorine and other organic impurities in Liquid and Vapour Phase applications.
Which Type of Activated Carbon (Powder, Granular or Extruded) is suitable for your application?

Selection of activated carbon for your application is very critical and it generally decides how your system will work.

Powder activated carbon is a fine powder generally less than 200 mesh (0.075mm). Because of very fine particle size, it has very high weight to surface area and it gives highest adsorption capacity. But due to powder form, it gives very high head loss in vessels so generally powder activated carbon is being use in Process Streams where it is added directly in the Process.

As Granular activated carbon has bigger particle size compare with powder carbon, Granular activated carbon offers less weight to surface ration compare to powder carbon. Granular activated carbon increases the diffusion and it is best suited for various Liquid phase and Vapour Phase applications. Granular activated carbon comes with various particle sizes like 8x30, 12x40, 30x60, 20x50 etc. for Liquid phase applications and 4x8, 6x10 and other larger particle sizes are used for Vapour phase applications. As particle size decreases it gives more surface area to Adsorb but at the same time, it gives higher pressure drop so selection of mesh size is critical parameter for optimum result between adsorption and pressure drop.

Extruded activated carbon is made from binding powder activated carbon with a suitable binder to create activated carbon of high hardness and linear surface area. It is generally comes with 1mm – 4mm cylindrical shape and generates very less pressure drop so ideal for vapour phase applications.

Which raw material base Activated Carbon (Coal, Wood or Coconut) is suitable for your application?

Organic impurities in Liquid and Vapour has different sizes and selection of material base is largely depends upon size of organics present.

Coconut shell has more amount of micropores and having pore size of 00A to 200A. Micropores are smallest pores and adsorb small molecular size organic compound so it can be use for final stage of TOC removal, Chlorine and odour removal in domestic water applications.

Coal based carbon has more amount of mesopores and has pore size of 20oA to 5000A. Mesopores are medium size pores and can be use for adsorbing medium size organic compounds. This is good for waste water treatment and to treat water having higher level of TOC.

Wood based carbon has more amount of macropores and has pore size of more than 5000A. Macropores are largest pore sizes and use for decolourization in the liquid phase applications and to remove organics with larger particle size.

Critical Properties of Activated Carbon
Iodine Number:

The amount of Micropores on activated carbon surface is measured by iodine number. Iodine number is amount of iodine adsorb by activated carbon surface. It is in the range of 600 to 1200 m2/g.

Methylene Blue Number:

The amount of Mesopores is measured by methylene blue number. It gives indication of amount of adsorption capacity of activated carbon for medium sized organic compounds.

Molasses Number:

The amount of Macropores is measured by Molasses number. It gives measure of amount of decolourization capacity in liquid phase.

Hardness:

As the name suggest, it refers to how much hard activated carbon is. The more the hardness, better it will be resistive against attrition and crushing loss.

Apparent Density:

Apparent Density represents how kilograms of activated carbon come in liter. Generally coconut shell and coal based activated carbon has density of 0.45 – 0.55 Kg/Liter. So 1 Liter of activated carbon weights between 0.45 Kg to 0.55 Kg.

Mesh Size:

Mesh size is amount of activated carbon can be passes through or retain by particular sieve. For example, 8x30 US mesh size activated carbon means all the particles passes through 8 mesh (2.38mm) sieves and retained by 30 mesh (0.6 mm) sieves. So all the particles come between sieve size of 8 mesh and 30 mesh refer as 8x30 mesh carbon.

Ash Content:

Ash Content reduces capacity of activate carbon and sometimes chemicals gets leach out from activated carbon so for domestic water applications Ash content is very important parameter and less Ash content is better.