How to purify indoor air by activated carbon

1. Adsorption principle

Activated carbon air purification belongs to the field of adsorption. Adsorption is caused by the force between the adsorbent molecule and the adsorbent. According to the different forces, it can be divided into physical adsorption and chemical adsorption.Physical adsorption mainly depends on the van der Waals force between molecules. Physical adsorption simply relies on the attraction between molecules to adsorb the adsorbent surface.Physical adsorption is reversible. By reducing the partial pressure of the adsorbent in the gas phase and increasing the adsorption temperature, the adsorbent will quickly desorption without changing its chemical composition.Chemisorption depends on the chemical bonding force between the solid surface and the adsorbed gas molecules.It is the result of chemical action. Its force is much greater than the van der Waals force of physical adsorption. This is usually an irreversible process. High selectivity for chemosorption. This is an adsorption. This reagent only adsorbs specific substances.

After adsorption, the adsorbent changes and its original characteristics change. Adsorbents on the surface of the adsorbent are a reversible process that can only temporarily block pollution and cannot eliminate pollution. In addition, the chemosorption rate increases with the increase of temperature. It is worth noting that physical adsorption of the same substance may occur at lower temperatures, while chemical adsorption may occur at higher temperatures, or both adsorption methods may occur at the same time.

The physical adsorption process can be divided into the following steps:

• Polluted gases pass through the adsorption boundary layer. The molecules of the pollutant gas may be adsorbed or taken away from the activated carbon surface, depending on the difference in the concentration of the components in the carrier gas and in the boundary layer.This value determines the adsorption intensity. When contaminated air passes through activated carbon, the concentration of some harmful gases varies greatly and is therefore adsorbed. However, the inherent components in the air pass normally because the concentration difference is basically zero and some particles (such as smoke) are too large. They stay directly in the macropores and mesopores. When the concentration difference of harmful gases is zero, the activated carbon fails and needs to be reactivated.

• The adsorbed molecules diffuse into the micropores.

• The molecules firmly bind to the adsorbent surface.

• The chemical adsorption of activated carbon mainly relies on the reaction of chemical components on the material with pollutants to form solid components or harmless gases. Activated carbon can also undergo some chemical treatment, such as adding some catalysts, which can help decompose harmful gases such as formaldehyde and VOCs.

• During use, the adsorption capacity will continue to weaken. When it weakens to a certain extent, the filter is scrapped. The pore size of activated carbon used to purify the air must be slightly larger than the pore size of toxic and harmful gas molecules to have the ability to adsorb toxic and harmful gases. Key factors affecting the service life of air purification activated carbon: the total amount of harmful substances in the environment and the desorption frequency.

• Since the mass of harmful gas adsorbed by activated carbon can be close to or even reach its own mass, the mass of harmful gases in the air in ordinary household space is much lower than the amount of activated carbon used.

• Therefore, activated carbon can be used for a long time as long as it is regularly exposed to sunlight. Of course, dust blocks the micropores of activated carbon also reduces its adsorption capacity.

2. Adsorption performance

• Adsorption capacity: The maximum amount of pollutants that can be adsorbed per unit of activated carbon is called the adsorption capacity. The adsorption capacity of different materials will be different; the adsorption capacity of the same material will also be different; when the temperature and background concentration change, the adsorption capacity will also change.

•  Dwell time: The time when air stays in the activated carbon layer is called the dwell time. The longer the residence time, the more thorough the adsorption is. To maintain sufficient residence time, the carbon layer must be thick enough and the filtering wind speed must be as low as possible.

• Service life: The new activated carbon has high adsorption efficiency, but the efficiency continues to decline during use. When the harmful gases downstream of the filter approach the allowable concentration limit, the filter will be scrapped. The service time before scrapping is the service life, also known as the effective protection time.

• Selectivity: Generally speaking, gases that are easily adsorbed in physical adsorption include: gases with large molecular weight, gases with high boiling points and volatile organic gases. If activated carbon is chemically impregnated, it can also remove gases that are often difficult to handle or enhance adsorption capacity to certain types of gases.
  

Guangyuan Carbon has launched several activated carbon products: specially used for air purifier equipment. The effect is significant and the price is good. Welcome to contact us.

· Fujian Guangyuan Carbon Products Co.,Ltd.