Activated carbon is used as adsorbent because it has the best physical properties compared to other adsorbents.
Activated carbon has a very large active surface. This surface consists of a large number of different pore sizes.
This means that the active carbon can adsorb various kinds of solvents that may be present in the process air.
It is primarily this feature that makes activated carbon superior as an adsorbent.
Different porosities of coal-based
Microporosity <2 nm wide
Mesoporosity 2-50 nm wide
Macroporosity >50 nm wide
Process air including contaminants diffuses into carbon
The macroporosity represents the three-lane highways that allow easy
and quicktransport of the bulk fluid containing the adsorbate into the
grains of the adsorbent whilst contributing little to actual adsorption
The mesoporosity then acts like the dual lane or feeder roads distributing
that adsorbate to reaction sites or micropores in the adsorbent.
The microporosity then acts like a car park providing a space where the
adsorbate can be “trapped” and removed from the bulk fluid and the micropore volume is the major portion of the adsorption capacity of an adsorbent.