Activated carbon filter

Recently, there has been increased interest inactivated carbon filters. And as often happens, there is a lot of ambiguity and simplification around this topic. You often hear that “a carbon filter is a panacea for everything,” or, conversely, that “they are absolutely useless.” The reality, as always, is somewhere in the middle. I would like to share some observations based on many years of experience and, perhaps, a series of unsuccessful experiments that helped to better understand how to properly use this technology.

What does activated charcoal actually do?

I would like to immediately dispel a common misconception - this is not just 'black dust'. Activated carbon is a material with a huge surface area created artificially. This large area allows it to adsorb, that is, attract and retain, many different substances. In the context of air filtration, we are talking about various gases, odors, volatile organic compounds (VOCs) and other pollutants.

It is important to understand that adsorption is not absorption. Adsorbed molecules are held on the surface of the carbon structure due to various physical and chemical forces. This means thatactivated carbon filterhas a limited resource and “dries up” over time, losing its effectiveness. This is one of the most often underestimated factors, in my opinion.

For example, we once produced filters to purify the air in a server room. Initially, the result was excellent - unpleasant odors were eliminated and the VOC content was noticeably reduced. But after six months, the filter’s efficiency dropped sharply. A detailed analysis revealed that the adsorbent was completely saturated with pollutants. Simply replacing the filter did not solve the problem - either more aggressive pre-filtration or periodic replacement of the carbon layer was necessary.

Types of Activated Carbon and Their Applications

Not all activated carbon is created equal. There are different types, differing in particle size, porous structure and processing method. Choosing the Right Typeactivated carbonis a key factor in filtration efficiency.

For example, to remove odors in household filters, carbon with a fine structure is often used. And to remove harmful gases in industrial environments, where the concentration of pollutants is higher, coal with larger particles and increased porosity is used. We frequently collaborate with the air conditioning research institute of the China Institute of Building Sciences to develop filters for a variety of environments, from home use to industrial applications. This experience showed that there is no “universal” coal.

Don't underestimate the importance of quality standards. Activated carbon must meet certain specific surface area, porosity and chemical composition requirements. Cheap coal, not produced using the same technology, may not only not provide effective filtration, but, on the contrary, release harmful substances into the air.

Factors influencing efficiencyactivated carbon filter

In addition to the type of activated carbon, other factors that affect filtration efficiency include air flow rate, humidity, temperature, and contaminant concentration. For example, at high humidity, the adsorption properties of coal may decrease. Therefore, in some cases, it is necessary to provide a preliminary stage of air drying.

In our practice, we often encounter the problem of non-compliance with the recommended air flow rate. If the flow is too slow, the contaminants do not have time to contact the adsorbent. If the flow is too fast, the carbon does not have time to effectively adsorb contaminants. Therefore, when designing filtration systems, all these factors must be taken into account.

Another important point is prefiltration. Before air reaches the carbon filter, it must be cleaned of large particles of dust and dirt. Otherwise, the coal quickly becomes clogged, losing its effectiveness. We use combination filters that combine pre-filters and carbon filters to provide maximum protection.

Experience with formaldehyde filters

Of particular interest is the useactivated carbonto remove formaldehyde. This is a very urgent task, given the widespread use of chipboard and other materials containing formaldehyde in the construction and furniture industry. In this case, carbon with a high adsorption capacity for formaldehyde is required. And, of course, a sufficient concentration of this carbon in the filter must be ensured.

We developed filters to clean the air in residential areas from formaldehyde. Several tests were carried out and it seemed that the effectiveness of the filter depended on the surface area of ​​the carbon bed and the air flow rate. The results showed that the optimal air flow rate is 0.5 m3/h per unit area of ​​the coal layer. It is this mode that allows for maximum adsorption of formaldehyde.

It is important to note that formaldehyde adsorption is a fairly slow process. Therefore, to achieve the required degree of purification, a long filter operating time is required. And, of course, regular filter replacement is necessary.

In addition, it should be taken into account that the adsorption of formaldehyde may be accompanied by the release of other substances. Therefore, it is important to use high-quality carbon and control the composition of the air after filtration.