Application of Activated Carbon in VOCs Treatment: Adsorption Mechanism, Desorption Regeneration and Safety Management

Activated carbon is produced from carbonaceous materials such as wood chips, fruit shells and lignite through carbonization and activation. It is available in two forms: powder (particle size: 10–50 microns) and granular (particle size: 0.4–2.4 mm). It is generally porous with a large specific surface area, reaching 500–1000 m² per gram. Its key performance parameters are adsorption capacity and adsorption rate. Adsorption capacity refers to the mass of solute that a unit weight of activated carbon can adsorb when saturated, which is related to raw materials, manufacturing processes and regeneration methods. A higher adsorption capacity means less activated carbon is required.

With the continuous advancement of industrialization, volatile organic compounds (VOCs) have become one of the main sources of air pollution. VOCs not only adversely affect the environment but also pose threats to human health. Therefore, controlling and treating VOCs has become a key task in current air pollution prevention and control. As a traditional gas adsorption material, activated carbon is widely used in VOCs treatment due to its high specific surface area, strong adsorption performance and broad application scope. Activated carbon adsorption has become a mainstream solution for industrial VOCs abatement. This paper elaborates on the adsorption and desorption processes of activated carbon in VOCs treatment and analyzes its application safety issues.

 

 

I. Adsorption Principle of Activated Carbon

Activated carbon is a material with a highly porous structure, capable of adsorbing VOCs in the air through physical and chemical adsorption. Its adsorption process mainly depends on the following factors:

• Specific Surface Area: Activated carbon has an extremely large specific surface area, ranging from hundreds to thousands of square meters per gram, thus providing a large number of adsorption sites.
• Pore Structure: Activated carbon has a variety of pore structures including micropores, mesopores and macropores, enabling it to effectively adsorb VOCs molecules of different sizes.
• Surface Chemical Properties: The surface of activated carbon contains numerous oxygen-containing functional groups, which help enhance interactions with VOCs molecules and improve adsorption efficiency.
• In VOCs treatment, activated carbon removes harmful gases from airflow mainly through physical adsorption. When VOCs molecules come into contact with the surface of activated carbon, they are adsorbed into the carbon pores via non-covalent forces such as van der Waals forces and hydrogen bonds, effectively reducing the concentration of VOCs in the air. Granular activated carbon for VOCs treatment is particularly effective for low-to-medium concentration organic exhaust.

 

 

II. Precautions for Activated Carbon Adsorption

In the process flow of activated carbon adsorption, the gas collection hood is used to collect pollutant molecules; the filter device removes dust, moisture, grease and other substances that may block the pores of activated carbon; the activated carbon adsorption box provides a platform for contact between activated carbon and pollutant molecules; the induced draft fan supplies power for the flow of pollutant molecules; and the chimney discharges the treated clean air.

 

1. Sufficient Contact Between Pollutant Molecules and Activated Carbon

To achieve intermolecular forces in pores and chemical reactions with functional groups, pollutant molecules need to be in close contact with activated carbon, which can be realized by the activated carbon adsorption box and induced draft fan. Additionally, the tortuous design of the activated carbon adsorption box ensures that pollutant molecules entering the box must pass through the activated carbon.

Moreover, the power of the induced draft fan is of crucial importance. Insufficient wind power results in inadequate suction and incomplete extraction of pollutants; excessive wind power leads to too high airflow velocity, reducing the residence time of pollutant molecules in the adsorption box and leaving insufficient time for activated carbon to capture pollutants. In general, the gas velocity for fixed-bed adsorption devices is as follows: <0.60 m/s for granular activated carbon, <0.15 m/s for fibrous activated carbon, and <1.20 m/s for honeycomb activated carbon. Optimizing flow velocity is key to maximizing Activated carbon adsorption efficiency.

 

2. Quantity and Quality of Activated Carbon

Activated carbon captures pollutants through its pores and functional groups. Therefore, ensuring sufficient pores and functional groups requires controlling two key aspects: adequate quantity and high quality of activated carbon. High-quality activated carbon is typically jet black, while low-quality carbon is usually grayish or rust-colored. In-service activated carbon that turns white or moldy has basically lost its adsorption performance. For long-term stable operation, enterprises often choose Granular activated carbon for VOCs treatment due to its durability and ease of replacement. Generally, activated carbon needs to be replaced after 500 hours of cumulative operation or 3 months after installation.

 

3. Protection of Activated Carbon Activity by Filter Devices

Filter devices should be tailored to local conditions. For example, a dust collector should be installed if the exhaust gas contains a large amount of dust, and a dry filter device if the exhaust gas has high moisture content.

 

III. Desorption Process of Activated Carbon

During VOCs adsorption, the VOCs adsorbed by activated carbon will gradually reach saturation over time. Therefore, regular desorption treatment is required to improve the utilization efficiency of activated carbon. Desorption refers to the release of adsorbed VOCs from activated carbon through heating, increasing airflow or using solvents.

• Thermal Desorption: Heating activated carbon provides sufficient energy for adsorbed VOCs molecules, enabling their desorption and discharge. Thermal desorption is usually carried out at high temperatures, which helps break the adsorption interaction between VOCs and the surface of activated carbon. 
• Solvent Desorption: In some cases, washing the surface of activated carbon with solvents is also an effective desorption method. Solvents have an affinity for VOCs molecules, promoting their desorption.
• Airflow Desorption: Increasing airflow velocity carries away VOCs molecules to achieve desorption. This method is suitable for light VOCs pollutants.
• Factors such as desorption temperature, airflow velocity and time affect desorption efficiency and should be reasonably adjusted according to actual conditions.

 

 

IV. Safety Considerations in Activated Carbon Application

The wide application of activated carbon in VOCs treatment also brings various safety issues. The following are common safety problems and corresponding countermeasures:

 

1. Fire and Explosion Risks

Some adsorbed VOCs are flammable or explosive. Excessively high VOCs concentration in activated carbon may trigger fire or explosion. Therefore, VOCs concentration must be strictly monitored during use to avoid exceeding safety limits. In addition, ventilation should be strengthened to ensure the safety of the adsorption system.

 

2. Gas Emission During Desorption

VOCs are released back into the environment during desorption, which may cause secondary pollution without effective recovery or treatment measures. Thus, a complete exhaust gas treatment system, such as a catalytic combustion device or thermal oxidation device, must be equipped during desorption to ensure discharged VOCs meet environmental protection standards.

 

3. Regeneration and Service Life of Activated Carbon

The adsorption performance of activated carbon gradually declines with service time, requiring regular regeneration or replacement. Failure to do so may reduce adsorption efficiency and even pose hazards to equipment and personnel. For different types of activated carbon, the replacement and regeneration cycle should be reasonably arranged based on service conditions and VOCs types.

 

4. Health Risks

Prolonged exposure to powdered activated carbon may harm human health, especially the respiratory system. Therefore, staff handling activated carbon should wear appropriate protective equipment such as dust masks and gloves to avoid direct contact.

 

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