This is one of the most commonly used methods, especially for controlling emissions from small sources. It can be physical adsorption or chemisorptions. The later is rarely used for the VOC emission control because, it involves a less-reversible chemical bonding of the adsorbate (pollutant) and the adsorbing solid ( packing) and is relatively expensive. Physical adsorption uses the Van der Waals force, giving the advantage of reversibility and regeneration due to the weaker bonding of the gas and adsorbent material. The adsorbed material can be either recovered or incinerated. Regeneration is usually accomplished by heating or extraction/displacement.
Activated carbon is a commonly used adsorbent because of its high surface area and material hardness. It has between 800 and 1200 m2/g of surface area. In general, activated carbon and other adsorbents such as hollow aluminum spheres coated with a catalyst can be employed in a fixed, moving or fluidized bed system.
Fluidized bed systems, though more expensive to build and operate, yield high contacting with low pressure loss and regeneration can be accomplished within the system. The fixed beds are less expensive and provide longer packing life, but provide less contacting per unit length and require a larger pressure loss; because they are regenerated individually.
Moving beds have properties between fixed and fluidized beds. The useful life of activated carbon can be determined using break through curves.
Regeneration can be achieved by contact with a hot, inert gas, contact with a low pressure gas stream and pressure reduction over the bed.
Steam desorption is the most commonly used process for regeneration.