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What is a chemical filter?

Release time:

2021-11-27

Chemical filters remove molecular contaminants from the air. In the field of ventilation and air conditioning, chemical filters use activated carbon as the main filter material. Typical applications of chemical filters are: chip factories, nuclear industry, airports, environmental protection, museums, automotive air conditioning, etc., and chemical filter materials are also used in some home appliances.

With the development of industry and the expansion of cities, the concentration of harmful gases around us is increasing. With the advancement of technology and the improvement of life, people's requirements for pure air are increasing. Therefore, people's demand for chemical filters is increasing year by year.

Chemical filters selectively adsorb harmful gas molecules instead of mechanically removing impurities like ordinary filters. There are a large number of invisible micropores in activated carbon materials, most of which are between 5 and 500 (1=0.1 nm), and the total internal surface area of micropores in the unit weight material can be as high as 700 m2/g ~ 2300 m2/g, that is, in a rice grain size activated carbon particles, the internal surface area of micropores is equivalent to a large living room wall.

According to the material treatment method, activated carbon adsorption is divided into "physical adsorption" and "chemical adsorption". Traditionally, people refer to adsorption without significant chemical reactions as physical adsorption, which relies primarily on van der Waals forces. After the free molecules with high boiling point (room temperature or higher) in the air contact with activated carbon, some are condensed into liquid in the micropores and stay there due to the capillary principle, and some are filled with micropores equivalent to the molecular size and become one with the material. The boiling points of the main components of nitrogen, oxygen, carbon dioxide, hydrogen, and argon in the atmosphere are very low, and activated carbon cannot control them. Ordinary activated carbon is a hydrophobic material, so the adsorption capacity of water vapor is also limited. In principle, all porous materials are adsorption materials, activated carbon is not the only, but those substances adsorbed by activated carbon are just those harmful gases to be dealt with in the field of air conditioning.

Physical adsorption is difficult to effectively remove all chemical pollutants. In some cases, people chemically treat activated carbon materials to enhance their ability to remove specific pollutants. Chemisorption is the adsorption of materials that chemically react with harmful gases through chemical treatment. Activated carbon by van der Waals force to catch gas molecules, the chemical composition of the material reacts with pollutants to generate solid components or harmless gas. The main method of chemical treatment is to uniformly incorporate specific reagents into the activated carbon, so the chemically treated activated carbon is also called "impregnated carbon".

In addition to adsorption, the porous material itself can be a catalyst that promotes chemical reactions (participates in the reaction but the material itself is not consumed), such as the catalysis of ozone, and can also be used as a carrier for other catalysts. When it comes to adsorption, the harmful gas in the air is called "adsorbate", and activated carbon is "adsorbent". While the adsorbent grabs the adsorbate, some of the adsorbate will escape. During use, the adsorption capacity will continue to weaken, and when it weakens to a certain extent, the filter will be scrapped. If only physical adsorption, heating or steam fumigation can make harmful gases from activated carbon, so that activated carbon regeneration.