Granular
Activated Carbon

Granular Activated Carbon (GAC) features larger particles than powdered forms, resulting in a smaller external surface area where adsorbate diffusion is key. Consequently, GAC is favored for gas and vapor absorption due to its enhanced diffusion rate. Applications include water treatment, deodorization, and component separation in flow systems. GAC is available in granular or extruded forms.

Granular activated carbon (GAC) is made from a variety of carbonaceous raw materials, chosen for their high carbon content and suitability for creating a porous structure. The most common starting materials include:  

• Coconut shells: These are a popular choice, especially for water purification, as they produce a GAC with a high proportion of micropores, ideal for adsorbing small organic molecules and disinfection byproducts. The resulting GAC also tends to have high hardness and abrasion resistance.  
• Coal: Different types of coal, such as bituminous, anthracite, and lignite, are used. Coal-based GAC often has a broader pore size distribution, including mesopores and macropores, making it effective for removing a wider range of contaminants, including larger organic molecules and chlorine. It’s frequently used in industrial and municipal water treatment.  
• Wood: Wood-based GAC can be derived from hardwoods or softwoods. It generally exhibits a higher volume of macropores and mesopores compared to coconut shell carbon, making it particularly effective for decolorization and the removal of larger organic compounds.  
• Other carbon-rich materials: Less common but still viable sources include nutshells, fruit pits, and even some petroleum-based residues. The specific raw material chosen significantly influences the final properties of the GAC, such as its pore size distribution, surface area, and hardness.

The production process involves two primary stages:  

1. Carbonization: The raw organic material is heated in an oxygen-deficient environment at temperatures typically ranging from 600 to 900°C. This process pyrolyzes the material, driving off volatile compounds (like water, oxygen, and hydrogen) and leaving behind a carbon-rich char. The char has a rudimentary pore structure.
2. Activation: The char’s porosity and surface area are significantly enhanced during activation. This can be achieved through:
   • Physical Activation (Thermal Activation): The char is exposed to oxidizing gases like steam or carbon dioxide at high temperatures (800-1100°C). These gases selectively react with the carbon structure, creating and widening pores, dramatically increasing the internal surface area.  
   • Chemical Activation: The raw material or char is impregnated with a chemical activating agent, such as phosphoric acid (H3​PO4​), potassium hydroxide (KOH), or zinc chloride (ZnCl2​). The mixture is then heated to lower temperatures (400-700°C). The chemical agent aids in developing the porous structure. After activation, the chemical agent is washed out.  

Following activation, the resulting activated carbon material is often crushed and screened to produce granules of a specific size range, known as the mesh size. This granular form offers advantages in handling, reduces dust formation compared to powdered activated carbon, and is suitable for packed bed filtration systems used in various liquid and gas phase applications. The choice of raw material and the specific activation process dictate the final characteristics and performance of the granular activated carbon.