How Activated Carbon Is Made: Understanding the Production Process

As one of the most versatile adsorption materials available today, activated carbon removes contaminants from air, water, gases, and industrial process streams. This makes it essential in applications ranging from drinking water treatment to vapor-phase air purification.

But how is this material made? The answer lies in a carefully controlled manufacturing process. While production methods vary depending on the raw material and intended application, the basic process follows several key steps.

In this guide, we’ll take a look at how something as simple as coal or coconut shell transforms into a highly porous adsorbent capable of trapping microscopic contaminants.

Selecting and Preparing the Raw Material

Activated carbon begins with a carbon-rich source material, known as a precursor. Common raw materials include:

  • Coconut shells
  • Bituminous coal
  • Lignite coal
  • Wood
  • Peat

The choice of raw material has a significant impact on the finished product’s characteristics, including pore size distribution, hardness, density, and adsorption performance, and each material offers unique advantages.

For example, coconut shell activated carbon is extremely hard and contains a high concentration of micropores, making it ideal for removing small organic compounds. Coal-based activated carbon provides a balanced pore structure suitable for many industrial applications, while wood-based carbons contain more mesopores, making them effective for adsorbing large molecules.

Once selected, the raw material is cleaned and processed into a consistent size. This might include:

  • Removing dirt and other foreign matter
  • Drying to reduce moisture content
  • Crushing or sizing into uniform particles

Carbonization

Next is the carbonization process. During this stage, the raw material is heated to 400-600°C in an oxygen-limited environment. Because little or no oxygen is present, the material does not burn. Instead, it undergoes pyrolysis, a thermal decomposition process that drives off volatile compounds like water vapor, tars, and gases.

What remains is a carbon-rich material often called char or charcoal. Although carbonization creates the basic carbon structure, the material still has low adsorption capacity because its pore structure has not yet been fully developed.

Activation

Activation is the step that gives activated carbon its name and its exceptional performance. During this step, portions of the carbon are carefully removed, opening and enlarging an intricate network of microscopic pores throughout each particle. This dramatically increases the internal surface area available for adsorption.

There are two primary activation methods: physical and chemical.

Physical Activation

During physical activation, the carbonized material is heated to temperatures of roughly 800-1,000°C while exposed to carefully controlled steam or carbon dioxide. Steam activation is the most widely used manufacturing process, particularly for coconut shell and coal-based activated carbons.

These gases react with the carbon surface, selectively removing carbon atoms and creating the extensive pore network that gives activated carbon its adsorption properties. Manufacturers carefully control temperature, steam flow, and oxygen levels, because even small changes in these variables can significantly affect the finished carbon’s pore structure and performance.

Chemical Activation

During chemical activation, the carbonized material is impregnated with chemicals, such as phosphoric acid or potassium hydroxide, before heating. These chemicals promote pore formation at lower temperatures than steam activation. After this process, the carbon is thoroughly washed to remove any remaining activating chemicals before drying and further processing.

Cooling and Washing

After activation, the carbon is cooled under controlled conditions. Depending on the production method and intended application, it is washed to prevent impurities and other issues like residual ash, soluble minerals, activation byproducts, and any remaining chemical activating agents.

This cleaning step is particularly important for food-grade, pharmaceutical, and drinking water applications where product purity is essential.

Sizing and Quality Testing

Once cleaned, the activated carbon is processed into its final commercial product. Depending on customer requirements, manufacturers may:

Some activated carbons also go through additional finishing processes, such as acid washing or impregnation with specialized chemicals to enhance performance for specific contaminants, such as hydrogen sulfide (H2S).

To ensure consistent performance, activated carbon undergoes extensive quality control testing. Depending on the application, testing may include:

  • Iodine number
  • Butane activity
  • Molasses number
  • Surface area (BET analysis)
  • Moisture content
  • Ash content
  • Particle size distribution
  • Hardness or abrasion resistance

Many of these performance characteristics are measured using standardized testing methods developed by ASTM International. These standards help manufacturers and customers evaluate activated carbon consistently across products and suppliers.

How Coal-Based Activated Carbon Is Produced

Now that we understand the general production process, let’s take a closer look at how coal-based activated carbon is produced, since it requires several additional processing steps to develop its final shape and performance characteristics.

The process typically begins by grinding coal into a fine powder similar to talc. This finely ground coal is then mixed with a binder and compressed into briquettes or other formed shapes. The binder helps hold the material together during processing and allows manufacturers to create a consistent product with controlled particle size and density.

The formed briquettes are then carbonized and activated. During activation, the carbonized material is exposed to steam or carbon dioxide at high temperatures, which creates the network of pores responsible for activated carbon’s adsorption capacity.

After activation, the material is crushed and screened to achieve the desired particle size distribution. The resulting product is available in a range of granular sizes and forms designed for different adsorption needs.

Why the Production Process Matters

Not all activated carbon is created equal. The combination of raw material, activation method, manufacturing conditions, and finishing processes determines the carbon’s:

For example, a carbon designed to remove volatile organic compounds (VOCs) from industrial air streams may have very different characteristics than one intended for municipal drinking water treatment or food processing.

Activated Carbon for Industrial Applications

When choosing the right activated carbon for your application, it helps to understand the manufacturing process behind the product. Every stage of the activated carbon production process plays a role in determining how well the finished product performs.

At General Carbon, we work closely with you to identify the appropriate carbon type, particle size, and performance characteristics for each application. Contact us today to learn more about our activated carbon solutions.