Activated carbon has long been used to remove toxic gases and vapors from a stream of gas or liquid. These activated carbons are also useful in cleaning breathing air or exhaust gases by removing various noxious agents, and may be used in gas mask filters, respirators, collective filters and other applications, and often involve the use of special impregnants to remove gases that would not otherwise be removed through the use of unimpregnated, activated car bons. Chromium and/or other agents impregnated on an activated carbon, function as adsorbents effective in removing a variety of toxic materials from a vapor or liquid. In many applications, it is desirable that a single impregnated adsorbent be effective against a range of toxic agents in a gas stream.

Non-impregnated activated carbons are generally effective against Type A toxic agents. Over the years, a number of carbons have been developed so as to be suitable for removing gases of Type A, B, E and K, as well as combinations thereof. Metals and metal oxides of the first-row transition metal series, such as chromium and copper, are often indicated as the impregnating agents. In preparation of the filter media, the carbon is first treated with a metal reagent, and then the freshly impregnated mixture is dried and heat treated to deposit and to decompose the metal compound to its oxide. This impregnated carbon, while useful for Types A, B and/or E, depending on the application, may not be suitable as an air purification agent for other applications and/or for filters requiring a wider range of utility. Applications requiring filters that protect against a mixture of Types B or E and K toxic agents require filter media which protect against acid gases and alkaline species such as ammonia gases. 

ACIPL has developed many active carbons with and without impregnants modification for gas phase applications as enlisted: