Chemical filter is the kind of filter which could remove gaseous pollutants in the air. In the ventilation system and air conditioning, chemical filters use activated carbon as the main filter media. Typical applications of Chemical filters are chip plant, the nuclear industry, airports, environmental protection, museums, etc. Why chemical filter could be used widely? The followings may account for it. Chemical filter‘s absorption of harmful gas is instead of removing impurities rigidly as the ordinary filters. This is a kind of advantages of chemical filter.
The second kind of advantages of chemical filter is its large absorption area. There are large invisible pores in the activated carbon materials. As a result, chemical filter has large absorption area. The activated carbon in the size of a grain of rice has the area equivalent to the size of a large living room wall.
The third kind of advantages of chemical Filter is that it could be physical adsorption or chemical adsorption. After the free molecular which is easy to condense contact activated carbon, some are condensed into a liquid in the microspores and stay there due to the capillary principle. Some free molecular whose size is comparable to the micro porous molecular even become one with the active carbon. The absorption which has no such obvious adsorption chemical reaction is known as physical adsorption. Sometimes people want activated carbon to be treated chemically, in order to enhance their ability to remove specific contaminants. At the moment, the activated carbon is still relying on van der Waals forces to seize the gas molecules and then the chemical composition on materials has reaction with pollutants, producing solids or harmful gases. The absorption mentioned is known as chemical absorption.
The forth advantage of chemical filter is its absorption towards harmful gases. The boiling point of the oxygen, carbon dioxide ware the main component of atmospheric nitrogen is low. As a result, activated carbon under normal temperature cannot has the ability to absorb them. Besides, activated carbon is a hydrophobic material, so its capacity to absorb the water vapor is very limited. Though activated carbon adsorption is not the only material which could absorb things, as all porous materials have the ability of absorption, but those substances which are the main absorption of actives carbon are the harmful gases Air conditioning filters is trying to deal with. The process under use weakens the adsorption capacity of the material. When the ability is reduced to a certain extent, the filter scrapped. If only physical adsorption works, harmful gases are allowed to be separated away from the activated carbon by heating or the method of water vapor fumigation, the activated carbon regenerate.
