On NuAire's (Class II, Type A2) Biological Safety Cabinets, the optional Lay-in charcoal Filter Module may be used inline with our exhaust transitions when venting to the outside, or alone when units are vented into the room. The optional lay-in charcoal filter can be added on top of the exhaust HEPA filter on our Class II, type B1 or B2 Biological Safety Cabinets, with a special exhaust filter housing.
Charcoal will not remove hydrogen, carbon monoxide, mercury, etc., but, in general, it is very effective for removing aromatics - non polar, high molecular weight compounds.
The selection of the carbon used in charcoal filters is dependent upon the specific application. It is usually based on the type of contaminant filtration, pressure drop allowable, flashpoint temperature of contaminants that will be absorbed, relative humidity affecting absorption, and contaminant-removal efficiency desired.
Although charcoal is used extensively for contamination control, it also has some shortcomings -- it can explode or ignite if high concentrations of ozone are present in a highly contaminated bed -- and it will not remove gases such as NO, CO, CH4, etc.
For many toxic chemical removal applications, the charcoal must be impregnated to remove specific contaminants such as H2S, NH3, Hg, etc. By impregnating specific reactive chemicals over the surface area of carbon, various pollutants that might be difficult to handle can readily be removed from the stream. Sulfur and/or KI-impregnated charcoals are used to capture mercury. Metal oxide-type impregnated carbon improves the capacity for H2S. Many types of impregnates can be employed with charcoal. It should be realized, however, that as the capacity of the carbon for the difficult contaminants is increased, its ability to handle other pollutant is decreased. Unimpregnated charcoal does not have much absorptive activity with reactive gases, such as ammonia, chlorine or formaldehyde. [Potassium Permanganate odoroxidant (activated alumina and potassium permanganate) is reactive with ammonia, formaldehyde and many others.] Generally, activated charcoal has high capacity for less volatile materials. Also, the higher the boiling point of a given contaminant, the weight absorbed will generally increase accordingly.