Activated Carbon

Depending Factors

Applications of it

Activated carbon, is a term that generally covers carbon material. It is chiefly derived from charcoal. Activated Charcol shows a very high surface area. One gram of activated carbon has the surface area of 500 m2(approx). It shows a large amount of microporosity. Activated Carbon is made up of miniscule clusters of carbon atoms that are stacked upon each other. The carbon is sourced from a variety of materials, like peanut shells, coal or coconut husks. The carbon is activated by passing oxidizing gases at very high temperatures. This activation process actually produces the pores that result in such a high adsorptive capability.

The adsorption process depends on the following factors:

• Physical properties such as pore size distribution and surface area of the Activated Carbon.
• The chemical nature of the particular carbon source, or the quantity of oxygen and hydrogen associated with it.
• Concentration and Chemical composition of the contaminant

Application of Activated Carbon in PSA processes:
Use of Activated Carbon is very popular in PSA processes of gas separation. A large number of gases are separated using activated carbon as the adsorbent material. We will discuss here the use of activated carbon in Hydrocarbon vapour recovery system. The process works like this. The activated carbon PSA system uses two identical adsorber vessels that is filled with activated charcol specially selected for vapor phase applications. It is necessary that the two adsorption vessels maintain continuous operation. The first adsorber is on-stream that receives the fuel vapours (a mixture of Volatile organic compounds and air) while the second is under regeneration. Slightly above the atmospheric pressure, the activated carbon preferentially adsorbs the impurities like non-methane and non-ethane VOCs from the vapor mixture. It then vents the clean air directly to the atmosphere.

A General set of Parameters for selecting Activated Carbon: Mehtylene blue adrsorption >320mg/gm Surface area > 1500 Sp. mt pH Value 6.0 to 7.0 Ash content < 2% Iron content < 100 ppm Chloride content < 0.04% Moisture < 5% Acid soluble < 1% Water soluble < 0.85% Mesh size 200 mesh

The quantity of activated carbon required for the two adsorber depends on two factors. The factors are:

• Volumetric flows from the vapor source.
• Recycle loading that takes place from the liquefaction process downstream of the vacuum system.

Carbon selected for this process is very important. Not all carbon are suitable for vapour recovery. The retention factor must not be too high or too low then both can create complications.