Activated carbon to remove H2S

Activated carbon has significant application value in removing hydrogen sulfide (H2S). Hydrogen sulfide is a toxic gas with a strong odor that is widely present in waste gases from industries such as petrochemicals, natural gas extraction, sewage treatment, and biogas production. H2S will not only cause odor pollution and corrode equipment, but may also harm human health and even cause poisoning.

 

Activated carbon has significant application value in removing hydrogen sulfide (H2S). Hydrogen sulfide is a toxic gas with a strong odor that is widely present in waste gases from industries such as petrochemicals, natural gas extraction, sewage treatment, and biogas production. H2S will not only cause odor pollution and corrode equipment, but may also harm human health and even cause poisoning. Therefore, controlling and removing H2S is crucial. Activated carbon is widely used in the purification treatment of H2S due to its unique physical adsorption and chemical adsorption properties.

1. Sources and hazards of hydrogen sulfide

Hydrogen sulfide mainly exists in industrial production waste gas, such as petroleum refining, natural gas purification, coal processing and sewage treatment. The presence of H2S not only brings stench, but also causes serious harm to human body and equipment.

2. Basic characteristics of activated carbon

Activated carbon is a material with high specific surface area, rich pore structure and excellent adsorption properties. It has a pore size distribution of micropores, mesopores and macropores, and these pores give activated carbon good adsorption capacity for various gases. Activated carbon can not only perform physical adsorption, but also perform chemical adsorption through surface functional groups. Depending on specific application needs, activated carbon can further improve its adsorption effect on specific pollutants through a variety of modification methods.

3. Adsorption mechanism of hydrogen sulfide removal by activated carbon

The mechanism of H2S removal by activated carbon mainly includes physical adsorption and chemical adsorption.  

physical adsorption

Physical adsorption uses the rich microporous structure of activated carbon to capture H2S molecules. After H2S molecules enter the pores of activated carbon, they combine with the van der Waals force on the surface of activated carbon and are then adsorbed on the pore wall. Physical adsorption mainly occurs in low temperature and low concentration environments. The adsorbed H2S molecules will not change the chemical properties. However, due to the limitation of adsorption amount, it is difficult to effectively remove large amounts of H2S in high concentration environments.

chemical adsorption

Chemical adsorption is a key process for H2S removal, involving the chemical reaction between H2S and activated carbon surface functional groups (such as carboxyl groups, hydroxyl groups, etc.). H₂S molecules undergo a redox reaction on the surface of activated carbon to generate elemental sulfur or sulfide. The effect of chemical adsorption is affected by the chemical properties of the surface of activated carbon, and is suitable for the adsorption of high concentrations of H2S.  

In addition, in order to improve the H2S removal efficiency of activated carbon, modification treatment (such as acid washing, alkali washing or metal loading) is usually used to increase the active functional groups on the surface. This treatment method can further improve the effect of chemical adsorption and extend the service life of activated carbon.

4. Factors affecting H2S removal by activated carbon

Surface area and pore structure of activated carbon

The surface area and pore size distribution of activated carbon directly affect the adsorption capacity of H2S. The high specific surface area and appropriate micropore structure enable H₂S molecules to be quickly adsorbed. Activated carbon with a larger pore size is more conducive to molecules entering the pores, while a pore size that is too small will hinder gas diffusion.

temperature

The adsorption reaction is usually exothermic, so an increase in temperature will reduce the amount of H2S adsorbed on activated carbon. For physical adsorption, low temperature is beneficial to the adsorption of H2S molecules on activated carbon; for chemical adsorption, an increase in temperature is sometimes beneficial to the reaction, but too high a temperature will affect the stability of activated carbon.

humidity

Humidity plays a dual role in the adsorption of H2S by activated carbon. On the one hand, humidity can promote the dissolution of H2S, thereby promoting the chemical reaction with the functional groups on the surface of activated carbon; on the other hand, excessive humidity can cause water vapor to occupy the pores of activated carbon, reducing the adsorption capacity of H Therefore, moderate humidity helps to improve adsorption efficiency, but excessive humidity will affect the adsorption effect.

gas concentration

The initial concentration of H2S affects the adsorption rate and adsorption amount. High concentrations of H2S will accelerate the adsorption saturation of activated carbon, thereby shortening its service life. Low concentration H2S can be adsorbed for a long time, but the adsorption speed is slow. In order to extend the service life of activated carbon, the initial concentration of H2S is usually controlled to maintain it within an appropriate range.

5. Modification method of activated carbon

In order to enhance the ability of activated carbon to remove H2S, its surface chemical activity can be increased through modification. The following are several common modification methods:  

Alkaline modification

Alkaline modification usually uses alkaline solutions such as potassium hydroxide and sodium hydroxide to treat the surface of activated carbon to generate alkaline functional groups. Basic functional groups can enhance the chemical adsorption capacity of H2S, causing H2S to undergo an oxidation reaction on the surface of activated carbon to generate harmless sulfides.

Acidic modification

Acidic modification uses acidic solutions such as sulfuric acid and phosphoric acid to treat activated carbon to generate acidic functional groups. Acidic modification can increase the specific surface area of ​​activated carbon and enhance its chemical reaction activity with H2S. In particular, phosphoric acid-treated activated carbon performs excellently in removing H2S.

Metal loading modification

Metal loading modification loads metals such as copper, zinc, and iron onto the surface of activated carbon to produce metal oxides on the surface. Metal oxides can serve as catalysts to accelerate the oxidation reaction of H2S and convert it into elemental sulfur or sulfide, thus improving the removal efficiency of H2S.

6 Application fields of activated carbon for H2S removal

Activated carbon removal of H2S has wide applications in many fields, including:  

Natural gas treatment: Natural gas often contains a certain amount of H2S, which needs to be removed with activated carbon to prevent corrosion of pipelines and equipment. Biogas purification: Biogas also contains H2S. Removing H2S can improve the cleanliness of the biogas and facilitate subsequent combustion or power generation. Sewage treatment plant: H2S and other odors are often produced during the sewage treatment process