The principle of the air purifier

The principle of the air purifier

Through the investigation of some air purifiers that can remove formaldehyde on the market, it is found that there are mainly seven kinds of air purifiers on the market.
1. Activated carbon adsorption technology
The porous structure of activated carbon gives it an adsorption property. In the selection of the amount of activated carbon and the size of the activated carbon, it is necessary to fully consider the influence of airflow and other factors. Selecting an appropriate amount of filling and a suitable particle size can fully and effectively enhance the adsorption capacity of the air purifier containing the activated carbon filter. In addition, most of the commercially available air purifiers are modified activated carbon. Air Proce’s AI-600 air purifier contains a combination of modified activated carbon and impregnated activated alumina TVOC filter. Activated carbon adsorption technology is relatively mature, but there are still deficiencies. Activated carbon is only adsorbed and does not decompose, and the adsorption saturation state of activated carbon is only temporary. This results in the activated carbon being cleaned or replaced in time if the adsorption of the activated carbon is saturated. This adds to the cost of used invisibly.

2. HEPA high-efficiency filtration technology HEPA (High-Efficiency particulate air filter) in the multi-layer filter in the air purifier shows a more important role. HEPA has an air filtration efficiency of more than 99.97% for 0.3 μm aerosols and is commonly used to remove submicron aerosol particles. In general, HEPA is randomly arranged from fibers having a finite specific surface area of ​​0.5 to 2 μm in diameter. Therefore, the high filtration efficiency of HEPA is usually at the expense of high resistance and low dust holding capacity. Oransi’s EJ120 air purifier uses HEPA high-efficiency filtration technology. The filter screen of the commercially available air purifier is not single, and the modified activated carbon filter is mainly combined with the HEPA filter, such as the Philips AC4076/01, Dyson Pure Cool AM11, and 352 X80 air purifiers. It is a composite filter.

3. Negative ion technology Negative ions can effectively remove a variety of toxic and harmful pollutants in the air, such as solid particles, soot, some VOCs, etc., because the pollutants in the air are basically positively charged, while the negative ions and particles generated by strong electric fields Contaminants and the like combine to form “heavy ions”, and sedimentation or adsorption occurs. Negative ions can also kill bacteria, and the purification effect is good. However, the household air purifier using this technology generates ozone and nitrogen oxides while generating negative ions, causing secondary pollution. The first country to apply negative ion technology to air purification is Germany. In addition to Germany’s advanced technology, Japan is also recognized as the world’s leading technology. In the 1980s, China began to introduce negative ion technology and developed and sold air purifiers using this technology. Air purifiers such as Mitsubishi Heavy Industries SPA-582AC, Leopard Rice Air Purifier 2, Panasonic F-PDF35C and Haier KJ-F200/EA all use negative ion technology combined with various filters to achieve efficient removal of indoor pollutants.

4. HIMOP material filtration technology HIMOP (Hyman), a high-performance composite strong oxidized modified ceramic particle, is a mung bean-sized spherical particle with a honeycomb magnetic pole surface. The material quickly captures harmful pollutants such as formaldehyde, benzene, TVOC, ammonia, and sulfur dioxide, and rapidly destroys its molecular structure and oxidizes it to carbon dioxide and water. The Hemman material is highly specific for formaldehyde and can be brought to national standards (0.1 mg/m3) in one hour. The Hayman air purifier consists of a 5-layer filter composite, one of which is a sieve of Heimer material. Although the removal of formaldehyde and other contaminants is good, the material is expensive and has higher production costs than other technologies.

5. Low-temperature asymmetric plasma air purification technology
Low-temperature asymmetric plasma technology forms an asymmetric plasma electric field through high-voltage, high-frequency pulse discharge, causing a large number of plasmas in the air to collide step by step, resulting in a series of physical and chemical reactions, such as “avalanche effect.” The process of purifying the air with VOCs is described as a collision between high-energy electrons and VOCs, and the generation of free radicals and other active substances to purify VOCs. This technology has the advantages of energy-saving, no washing and washing, and strong purification ability. However, the downside is that the technology is currently widely used in industrial applications, and the technology has not yet been popularized in indoor air purifiers.

6. Photocatalytic Decomposition Technology Photocatalysis was discovered in 1972 by A. Fujishima and his instructor K. Honda. TiO2 semiconductors exhibit similar plant photosynthesis reactions under light conditions. The photocatalytic oxidation of formaldehyde in the production of formic acid intermediates that ultimately produce water and carbon dioxide. The research of photocatalysis technology is mostly in laboratory research, and there are not many types of research on the application of this technology in air purifiers. Air purifiers such as 3M, DESAY L352 and cado AP-C500-BK use this technology to remove indoor formaldehyde. In addition to the air purifier, the interior decoration will also mix TiO2 with concrete or plate the surface of the wall or ornament. This technology is highly efficient in removing formaldehyde and can decompose part of the pollutants. However, the fly in the ointment is that the technology requires ultraviolet light, and excessive ultraviolet light can cause various adverse symptoms in the human body.
7. Cold catalyst technology
The biggest difference between cold catalyst technology and photocatalysis technology is that it does not require light to react. At normal temperature, the cold catalyst degrades while adsorbing formaldehyde, and decomposes formaldehyde and other harmful gases to form carbon dioxide and water. Although the cold catalyst technology has a good adsorption and decomposition effect, as the temperature and pressure change, the harmful gas adsorbed in the cold catalyst may desorb and pollute the air again. The Kirpal air purifier and the Chulux CL-AP2 air purifier apply this technology. Among the above principles of operation, the seven technologies used in air purifiers have their own advantages and disadvantages. Among these technologies, photocatalytic degradation technology has the advantages of economy, environmental protection and complete degradation of organic matter. At the same time, photocatalysts (such as TiO2) have the advantages of low cost, safety, high stability, high photocatalytic activity, etc., which can promote room temperature. Oxidation of major pollutants in indoor air.

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