Activated Carbon

What is activated carbon?

Activated carbon is a carbon-based material that has been processed to maximize its adsorptive properties, yielding a superior adsorbent material. Activated carbon boasts an impressive pore structure that causes it to have a very high surface area on which to capture and hold materials, and can be produced from a number of carbon-rich organic materials, including:

  • Coconut shells
  • Wood
  • Coal
  • Peat
  • And more…

Types of activated Carbon

Depending on the source material, and the processing methods used to produce activated carbon, the physical and chemical properties of the end product can differ significantly. This creates a matrix of possibilities for variation in commercially produced carbons, with hundreds of varieties available. Because of this, commercially produced activated carbons are highly specialized to achieve the best results for a given application.

Despite such variation, there are three main types of activated carbon produced:

Powdered Activated Carbon (PAC)

Powdered activated carbons generally fall in the particle size range of 5 to 150 Å, with some outlying sizes available. PAC’s are typically used in liquid-phase adsorption applications.

Granular Activated Carbon (GAC)

Granular activated carbons generally range in particle sizes of 0.2 mm to 5 mm and can be used in both gas and liquid phase applications. GACs are popular because they offer clean handling and tend to last longer than PACs.

Extruded Activated Carbon (EAC)

Extruded activated carbons are a cylindrical pellet product ranging in size from 1 mm to 5 mm. Typically used in gas phase reactions, EACs are a heavy-duty activated carbon as a result of the extrusion process.

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Properties of Activated Carbon

When selecting an activated carbon for a particular application, a variety of characteristics are considered:

Pore Structure

The pore structure of activated carbon varies and is largely a result of the source material and the method of production. The pore structure, in combination with attractive forces, is what allows adsorption to occur.

Hardness/Abrasion

Hardness/abrasion is also a key factor in selection. Many applications will require the activated carbon to have a high particle strength and a resistance to attrition (the breakdown of material into fines). Activated carbon produced from coconut shells has the highest hardness of activated carbons.

Adsorptive Properties

The absorptive properties of the activated carbon encompass several characteristics, including adsorptive capacity, the rate of adsorption, and the overall effectiveness of activated carbon.

Depending on the application (liquid or gas), these properties may be indicated by a number of laboratory tests including BET (Brunaurer-Emmert-Teller) surface area testing and Langmuir adsorption Isotherms.

Density

While apparent density will not affect the adsorption per unit weight, it will affect the adsorption per unit volume.

Moisture

Ideally, the amount of physical moisture contained within the activated carbon should fall within 3-6%.

Ash Content

The ash content of activated carbon is a measure of the inert, amorphous, inorganic, and unusable part of the material. The ash content will ideally be as low as possible, as the the quality of the activated carbon increases as ash content decreases.

pH Value

The pH value is often measured to predict potential change when activated carbon is added to liquid.

Particle Size

Particle size has a direct effect on adsorption kinetics, flow characteristics, and filterability of the activated carbon.