How do the key steps in the production process of activated carbon affect its adsorption performance?

The adsorption performance of activated carbon is mainly determined by its pore structure, specific surface area, and surface chemical properties. These characteristics are influenced by multiple key steps in the production process of activated carbon:

1. Raw material selection:

-Different raw materials have different fiber structures and chemical compositions, which can affect the pore structure and surface area of activated carbon. For example, coconut shell charcoal usually has high hardness and microporous structure, suitable for adsorbing small molecules, while wood charcoal may have larger pores, suitable for adsorbing large molecules.

2. Carbonization:

-The carbonization temperature and time determine the basic structure and initial pores of the carbonized material. This process removes volatile substances and forms a preliminary pore structure. Insufficient carbonization may result in insufficient pore formation during the activation stage, while excessive carbonization may lead to material embrittlement.

3. Activation:

-Activation is the most critical step in determining the final adsorption performance of activated carbon. The selection of activation temperature, time, and activators (such as water vapor, carbon dioxide, or chemical agents) can all affect the size and distribution of pores.

-Physical activation: Typically, micropores and mesopores are formed through the interaction of high temperature and gases such as water vapor or carbon dioxide. High temperature and appropriate activation time can help increase the specific surface area, but excessive temperature or prolonged time may lead to the collapse of pore structure.

-Chemical activation: The use of chemical reagents such as zinc chloride or phosphoric acid can be carried out at lower temperatures, typically resulting in larger pores and higher specific surface area. The conditions of chemical activation, such as reagent concentration and treatment time, will significantly affect the pore structure.

4. Cooling and washing:

-Rapid cooling helps maintain the stability of the pore structure. The thoroughness of the washing process determines the impact of residual chemicals on the surface chemical properties of activated carbon, which in turn affects its adsorption performance.

5. Drying and molding:

-The drying process needs to be carefully controlled to avoid damage to the pore structure. The pressure and method used during the molding process (such as pressing into particles or columns) can affect the mechanical strength and flowability of activated carbon, but may also affect the availability of surface area.

6. Screening and packaging:

-Screening ensures consistency in particle size, thereby affecting the fluid dynamics characteristics during the adsorption process. Uniform particle size helps to reduce the pressure drop when the fluid passes through the activated carbon bed and improve adsorption efficiency.

By precisely controlling these steps, activated carbon with specific adsorption properties can be produced to meet the needs of different applications.