Why is ordinary activated carbon not suitable for all gases?

Activated carbon is the most common media in chemical filters, but it is not a universal adsorbent.

Its working mechanism is physical adsorption - retaining gas molecules through surface micropores. This process is selective and not all gases can be effectively adsorbed. The molecular size, polarity, boiling point, and concentration level of different gases will all affect the adsorption effect. Therefore, the description 'containing activated carbon' itself cannot explain what gases it can handle. Please refer to the specific gas classification Discussion on why chemical filters should be selected according to target gases .

Ingredients determine media matching

The physical and chemical properties of different gases vary greatly, and their adsorption performance on activated carbon is also different.

Organic vapor. Some organic solvent volatiles, such as toluene, xylene, ethyl acetate, etc., have moderate molecular weight and weak polarity, and activated carbon usually has a certain adsorption capacity for them. For specific selection methods, please refer to Discussion on how to choose air chemical filters for toluene pollution .

Acid gas. Ordinary activated carbon has limited adsorption capacity for acidic gases such as sulfur dioxide, hydrogen chloride, and nitrogen oxides. This type of gas usually requires the use of impregnated activated carbon or specialized chemical adsorption media. For specific differences, please refer to whether chemical filters can remove sulfur dioxide from the air . Discussion of

alkaline gas. For alkaline gases such as ammonia and amines, ordinary activated carbon also has limited effect. Handling such gases requires media for alkaline components. For specific differences, please refer to Discussion of whether chemical filters can remove ammonia from the air .

Formaldehyde and other small molecules. Formaldehyde has small molecules and strong polarity, and its adsorption on the surface of activated carbon is weak and easy to penetrate. Handling formaldehyde often requires specifically treated media. For specific differences, please refer to Discussion of whether chemical filters can remove formaldehyde .

Therefore, containing activated carbon does not mean that it can handle all acid gas, alkali gas or other gases. Whether the medium is suitable depends on the target gas.

Environment can change performance

Even if activated carbon has the ability to adsorb a certain gas, actual environmental conditions will affect performance.

humidity. In a high-humidity environment, water molecules may compete with the target gas for adsorption sites, reducing the effective capacity. The higher the humidity, the more pronounced this competition may be. In some cases, the adsorption capacity of activated carbon for target gases will significantly decrease after absorbing moisture.

temperature. Temperature affects adsorption equilibrium. When the temperature rises, adsorbed molecules may desorb and the adsorption capacity decreases. If the operating temperature is high, the temperature factor should be taken into consideration when selecting.

concentration level. At low concentrations, the adsorption efficiency of activated carbon may decrease. When the inlet concentration is very low, the probability of contact between gas molecules and the surface of activated carbon is reduced, requiring longer contact time or more media volume.

Mixed contamination. When multiple gases exist at the same time, different components may compete for adsorption sites. Certain ingredients may preferentially occupy the surface of activated carbon, causing the adsorption effect of other ingredients to decrease. For specific differences, please refer to Discussion on how chemical filters compare with photocatalytic purification equipment .

When the test conditions are significantly different from those on site, the sample results cannot be directly copied. The data in the report are obtained under specific conditions and need to be compared with actual working conditions.

Keep itemized verification

If the project needs to handle multiple gases, each key pollutant should have a corresponding applicable basis.

Not all objects can be covered with one representation gas. The data of toluene cannot explain the effect on ammonia, and the data of ammonia cannot explain the effect on acid gas. Each gas has different molecular properties and needs to be checked individually.

Multiple gas requirements require description of ingredients and sequence. If acidic gases, alkaline gases and organic matter are present in the gas stream at the same time, a layered configuration or composite filter media may be required. The sequence, interaction, and resistance superposition of different media need to be confirmed.

Product information should clearly indicate who it is applicable to. If you only write 'VOC processing' or 'odor removal' without specific gas names and test conditions, the applicable scope of this data needs to be confirmed. For specific report interpretation, please refer to Discussion of why chemical filter performance reports list specific target gases .

The basis for replacement should also be judged according to the gas. After the activated carbon is saturated with adsorption of a certain gas, the outlet concentration may increase, but the change in pressure difference may not be obvious. Maintenance judgment depends on the outlet trend of the target gas, not just the pressure difference.

Project judgment example

A project requires the processing of mixed gases, including organic solvents and a small amount of ammonia.

The initial plan is to use ordinary activated carbon filters. After operation, it was found that the organic gas concentration decreased, but the ammonia outlet concentration was still high. Testing confirmed that ordinary activated carbon has limited adsorption capacity for ammonia and requires a special medium for alkaline gases.

Adjustment plan: Add a chemical filtration section for ammonia after the original activated carbon section to form a composite configuration. After the resistance, interfaces and maintenance methods of the two-stage filters were rechecked, the system operation returned to normal.

This case illustrates: Ordinary activated carbon has applicable boundaries, and mixed gases need to be checked separately. involving For the configuration of the chemical filter product series , it is recommended that the target gas list and concentration range be provided to the supplier for verification.

Key points for selection and acceptance inspection

About Aili Industrial’s filter material selection support

The applicable boundary of activated carbon needs to be judged based on the target gas, concentration and environmental conditions.

Aili Industrial has independent manufacturing capabilities in filters, motors, fans, control systems and sheet metal processing, and can provide chemical filter product series and supporting air supply equipment. For projects that need to distinguish between activated carbon and special media, the target gas list, concentration range, temperature, humidity, and air volume can be combined to assist in checking the filter material type and configuration method. When the filter is matched with MAU, FFU, EFU and other equipment, the resistance, interface and maintenance methods can be confirmed uniformly.

Related products:Chemical filter product series、MAU box chemical filter、FFU comes with chemical filter . Provide target gas list and system conditions when enquiring, which will help confirm the appropriate filter material solution. The specific selection is subject to the technical documents and test results confirmed by the project.