Activated carbon, sometimes called activated charcoal, is a unique adsorbent prized for its extremely porous structure that allows it to effectively capture and hold materials.
Widely used throughout a number of industries to remove undesirable components from liquids or gases, activated carbon can be applied to an unending number of applications that require the removal of contaminants or undesirable materials, from water and air purification, to soil remediation, and even gold recovery.
Provided here is an overview on this incredibly diverse material.
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 carbonย boasts an impressive pore structure that causes it to have a very high surface area on which to capture and hold materials, and canย be produced from a number of carbon-rich organic materials, including:
- Coconut shells
- Wood
- Coal
- Peat
- And moreโฆ
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.ยฒย 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 ร , with some outlying sizes available. PACโs are typically used in liquid-phase adsorption applications and offer reduced processing costs and flexibility in operation.ยณ
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.
Additionally, they offer improved strength (hardness) and can be regenerated and reused.ยณ
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.ยณ
Additional Types
Additional varieties of activated carbon include:
- Bead Activated Carbon
- Impregnated Carbon
- Polymer Coated Carbon
- Activated Carbon Cloths
- Activated Carbon Fibers
Properties of Activated Carbon
When selecting an activated carbon for a particular application, a variety of characteristics should be considered:
Pore Structure
The pore structure of activated carbon varies and is largely a result of the source material and the method of production.ยนย 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.4
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.4
Depending on the application (liquid or gas), these properties may be indicated by a number of factors, including the iodine number, surface area, and Carbon Tetrachloride Activity (CTC).4
Apparent Density
While apparent density will not affect the adsorption per unit weight, it will affect the adsorption per unit volume.4
Moisture
Ideally, the amount of physical moisture contained within the activated carbon should fall within 3-6%.4
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. 4
pH Value
The pH value is often measured to predict potential change when activated carbon is added to liquid.5
Particle Size
Particle size has a direct effect on adsorption kinetics, flow characteristics, and filterability of the activated carbon.ยน
Activated Carbon Production
Activated carbon is produced through two main processes: carbonization and activation.
Carbonization
During carbonization, the raw material is thermally decomposed in an inert environment, at temperatures below 800 ยบC. Through gasification, elements such as oxygen, hydrogen, nitrogen, and sulfur, are removed from the source material.ยฒ
Activation
The carbonized material, or char, must now be activated to fully develop the pore structure. This is done through oxidizing the char at temperatures between 800-900 ยบC in the presence of air, carbon dioxide, or steam.ยฒ
Depending on the source material, the process of producing activated carbon can be carried out using either thermal (physical/steam) activation, or chemical activation. In either case, a rotary kiln can be used to process the material into an activated carbon.
Activated Carbon Reactivation
One of the many advantages to activated carbon is its ability to be reactivated. While not all activated carbons are reactivated, those that are provide cost savings in that they do not require the purchase of fresh carbon for each use.
Regeneration is typically carried out in a rotary kiln and involves the desorption of the components that had previously been adsorbed by the activated carbon. Once desorbed, the once-saturated carbon is again considered active and ready to act as an adsorbent again.
Activated Carbon Applications
The ability to adsorb components from a liquid or gas lends itself to thousands of applications across a multitude of industries, so much so, in fact, that it would likely be easier to list applications in which activated carbon is not used. The primary uses for activated carbon are listed below. Please note that this is not an exhaustive list, but merely highlights.
Water Purification
Activated carbon can be used to pull contaminants from water, effluent or drinking, an invaluable tool in helping to protect the Earthโs most precious resource. Water purification has a number of sub-applications, including the treatment of municipal wastewater, in-home water filters, treatment of water from industrial processing sites, groundwater remediation, and more.
Air Purification
Similarly, activated carbon can be used in the treatment of air. This includes applications in face masks, in-home purification systems, odor reduction/removal, and the removal of harmful pollutants from flue gases at industrial processing sites.
Metals Recovery
Activated carbon is a valuable tool in the recovery of precious metals such as gold and silver.
Food & Beverage
Activated carbon is widely used throughout the food and beverage industry to accomplish a number of objectives. This includes decaffeination, removal of undesirable components such as odor, taste, or color, and more.
Medicinal
Activated carbon can be used to treat a variety of ailments and poisonings.
Conclusion
Activated carbon is an incredibly diverse material that lends itself to thousands of applications through its superior adsorbent capabilities.
FEECO provides custom rotary kilns for both the production and reactivation of activated carbon. Our rotary kilns are built around the exact process specifications and are built with longevity in mind. For more information on our custom activated carbon kilns, contact us today!
- Seidel, Arza, and Mickey Bickford. Kirk-Othmer Encyclopedia of Chemical Technology. John Wiley and Sons, 2004. Wiley Online Library. Web. Sept. 2016.
- Bansal, Roop Chand, and Meenakshi Goyal. Activated Carbon Adsorption. Boca Raton: Taylor & Francis Group, 2005. Google Books. Web. 19 Sept. 2016.
- “Activated Carbon Basics.” Haycarb. Web. 19 Sept. 2016. http://www.haycarb.com/activated-carbon
- Indo German Carbons Limited. Web. 19 Sept. 2016. http://www.igcl.com/php/activated_carbon.php
- Marsh, Harry, and Francisco Rodrรญguez-Reinoso. Activated Carbon. Elsevier, 2006. Google Books. Web. 19 Sept. 2016.