Adsorption

Adsorption represents the transfer of molecules from gaseous or vapor phase to solid one. This phenomenon takes place on the surface of highly porous solid media. There exist different kind of solid adsorbent, but in odor control systems activated carbon represents the most widespread solution. Application of activated carbons is fit for VOC recovery in highly frequent handling systems (vapor recovery unit), with in-situ regeneration. On the other hand, when the gas flow to be deodorized is restrained, a very common and straightforward solution is the usage of disposable (or ex-situ regenerated) granulated activated carbons. With a correct choice of the solid adsorbent, compatible with the gas flow under control, and a proper design and precise maintenance, adsorption can provide an essentially absolute abatement efficiency. An important parameter for adsorbent selection is the equilibrium capacity, which means essentially the amount of odorant that can be thermodynamically removed by the gas flow per mass unit of adsorbent. This information is rarely available and only generic and expeditious features are available: porosity, dimension, iodine number and CTC index. Anyway, the application of activated carbon for the adsorption of VOC and odorants has been extensively investigated: there are different available references which have estimated the adsorption capacity for different molecules and solid media. A major drawback of adsorption is the need for low surface velocity (∼ 0.5 m/s): this results in a high cross-sectional area. To limit this problem different geometries for carbon beds have been developed.