Activated carbon (also known as activated charcoal) is recognised for its porosity. It has the ability to attract and retain organic compounds within its structure. The process begins with the burning of carbon-rich substances, resulting in carbon “char”. ¹ Subsequently, it undergoes chemical or physical treatment to create a network of pores within the carbon. In terms of physical adsorption forces or adsorptive porosity, activated carbon is known to be the most porous substance ever created. Additionally, it has a surface area greater than 1000m²/g. This means that 3g of activated carbon can possess the surface area of a football field. ²

Activated carbon is utilised in numerous fields such as healthcare, air purification, and even water purification. Renowned for its exceptional adsorption capabilities, this post aims to uncover the underlying science of activated carbon, delving into its activation process, versatile uses, and its effectiveness across different domains. ³

How is activated carbon formed?

Thermal or chemical processes are employed to activate carbon. Thermal processes induce partial oxidation of the coal. This generates pores while avoiding gasification and excessive loss of coal. This occurs at temperatures between 600 and 1100 °C. Regarding chemical processes, they commence from raw materials before carbonisation. ⁴

The term “carbonisation” pertains to the process of extracting pure carbon through heating a carbonaceous source, such as coal, peat, or other organic carbonaceous substances. This heating technique is termed pyrolysis. The material is carbonised at a low temperature (around 550 °C) and subsequently washed to eliminate reagent residues and other by-products.

Once oxidation is complete, activated carbon can then be tailored for various uses. For instance, granular activated carbon (GAC), powdered activated carbon (PAC), and extruded activated carbon (EAC).

• GAC consists of irregularly shaped particles ranging from 0.2 to 5 mm. This versatile type is found in both liquid and gas phases. It features a sand-like structure with larger grains compared to powdered activated carbon (PAC).
• PAC is carbon that has been ground to a size smaller than 0.18 mm. This is primarily employed in liquid-phase applications and for flue gas treatment.
• EAC is extruded and adopts a cylindrical shape with diameters spanning from 0.8 to 5 mm. Due to their excellent mechanical strength, minimal dust content, and low-pressure loss, these are predominantly used for gas-phase applications. ²

How Does it Work?

Activated carbon is commonly used in water filtration systems. It aids in reducing unwanted odours, enhancing water clarity, and removing chlorine. However, it is ineffective at getting rid of viruses, fluoride, some metals, or some hazardous chemicals. In addition, alcohol is only marginally adsorbable by activated carbon, making it ineffective as a removal agent.

Chlorine, tannins, phenol, chloramine, hydrogen sulphide, and other volatile chemicals that cause smells, as well as some medications and small amounts of metals including iron, mercury, and chelated copper, are all filtered by activated carbon.

However, it leaves behind nitrates, nitrites, ammonia, fluoride, sodium, substantial levels of heavy metals like iron or copper, substantial concentrations of hydrocarbons like petroleum distillates, and other microorganisms including bacteria, viruses, and protozoa.

The phenomenon linked to the adsorption of activated carbons is connected to van der Waals forces that take place between molecules. This interaction is the weakest of all intermolecular forces that hold molecules together. The force that takes place here is short-ranged and is sensitive between the carbon surface and the adsorbate molecule. Activated carbon is also additive, thus making it have the strongest physical adsorption forces. ^3,5

Activated Carbon’s effectiveness

Several factors influence the effectiveness of activated carbon’s adsorption:

1. Pore Size and Distribution: Pore size impacts the types of molecules absorbed; smaller pores capture gases, while larger ones tackle larger molecules and particles.
2. Contact Time: Longer contact time enhances thorough adsorption, but particle considerations must be balanced.
3. Temperature and pH: Higher temperatures boost adsorption, but extreme temperatures may alter absorbate molecules. pH affects the surface charge of both carbon and absorbate, influencing overall attraction. ^5,6

Activated Carbon: Application

Activated carbon’s applications can be see widely seen in:

1. Water Filtration: Granular activated carbon (GAC) is a tried-and-true method for removing specific pollutants from water. This is due to its exceptional adsorption abilities, which enable it to effectively remove organic pollutants, chlorine, and disagreeable odours from drinking water, considerably boosting water quality.
2. Air Quality Enhancement Employed in activated carbon filters, it eliminates volatile organic compounds (VOCs), noxious gases, and smoke particles from indoor air. This holds particular importance in environments where air quality is crucial, such as hospitals and laboratories.
3. Medical Applications: For drug overdoses and poisonings, activated carbon is a life-saving treatment. It functions as a sponge, attracting toxins to its surface and inhibiting their absorption by the body by utilising finely powdered charcoal mixed with liquids or via feeding tubes. This technique is extremely effective when dealing with toxins that comprise carbon, oxygen, hydrogen, or nitrogen. ^1,7

Embracing Sustainability

The growing demand for eco-friendly solutions aligns with the use of activated carbon. It serves as an environmentally friendly choice in various applications, owing to its capacity to eliminate pollutants without introducing unwanted by-products.

Conclusion

The unmatched adsorption properties of activated carbon, based on its porous structure and attractive forces, have strengthened its position in industries ranging from water treatment to air filtration and beyond. Its adsorption mechanisms, along with its numerous applications and benefits in terms of sustainability, secure its place in contemporary society. Understanding the science of activated carbon reveals its amazing potential, changing it from a chemical into a scientific wonder that has the power to significantly alter the course of human history.

References

1. Activated Carbon & Charcoal Frequently Asked Questions | FAQ Page. (n.d.). General Carbon Corporation. Retrieved August 16, 2023, from https://generalcarbon.com/facts-about-activated-carbon/activated-carbon-faq/
2. Activated Carbon. (2023, July 26). Chemviron. https://www.chemviron.eu/products/activated-carbon/
3. The Science Behind Activated Carbon Water Filters. (2020, August 13). Clean Tech Water. https://www.cleantechwater.co.in/science-behind-activated-carbon-water-filters/
4. What is activated carbon and what is it used for? And What is it for? -% Carbotecnia%. (n.d.). Carbotecnia. Retrieved August 16, 2023, from https://www.carbotecnia.info/learning-center/activated-carbon-theory/what-is-activated-carbon/?lang=en
5. Engber, D. (2005, November 29). How Does Activated Carbon Work? Slate. https://slate.com/news-and-politics/2005/11/how-does-activated-carbon-work.html
6. An Evaluation of Activated Carbon for Drinking Water Treatment. (1980). In Drinking Water and Health: Volume 2. National Academies Press (US). https://www.ncbi.nlm.nih.gov/books/NBK234593/
7. Activated Carbon & Carbon Absorption—Everything To Know. (n.d.). Oransi. Retrieved August 14, 2023, from https://oransi.com/blogs/how-it-works/activated-carbon-activated-carbon-adsorption

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PAC works by using the adsorption process to remove contaminants from water. Adsorption is the process by which contaminants are attracted to and stick to the surface of the activated carbon. As water passes through the PAC, the contaminants are trapped and removed, leaving behind clean, purified water.

One of the advantages of using PAC is that it has a large surface area, which makes it effective at removing a wide range of contaminants from water. It is also easy to use and can be easily added to water treatment systems.

However, PAC does have some limitations. It can be difficult to remove from water, as it tends to clump and settle to the bottom of treatment tanks. It is also more expensive than other types of water treatment media, such as granular activated carbon.

In general, PAC is a useful water treatment media that is effective at removing a wide range of contaminants from water. It is commonly used in a variety of water treatment applications, including municipal water treatment plants, industrial water treatment systems, and point-of-use water filtration systems.

Kajah Activated Carbon offers the PAC of -200 grade. Please get in touch for more details.

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Activated coconut shell charcoal has a number of applications due to its ability to remove impurities and toxins from liquids, gases, and other substances. Some common applications of activated coconut shell charcoal include:

1. Water filtration: Activated coconut shell charcoal is often used in water filtration systems to remove impurities and contaminants from drinking water. The pores of coconut-based activated charcoal are the most suitable to trap contaminants from drinking water.
2. Air purification: Activated coconut shell charcoal can be used to purify air by removing impurities and odors. It is often used in air purifiers and air filters.
3. Medical treatment: Activated coconut shell charcoal is sometimes used in medical settings to treat poisonings and drug overdoses. It can absorb toxins and help to remove them from the body. It is also used in manufacturing pharmaceuticals to isolate active ingredients.
4. Food and beverage processing: Activated coconut shell charcoal is often used in the food and beverage industry to remove impurities and color and improve the quality of products.
5. Industrial processes: Activated coconut shell charcoal is used in a variety of industrial processes, including the production of chemicals, refining of oil, and the purification of gases.
6. Personal care products: Activated coconut shell charcoal is sometimes used in personal care products, such as toothpaste and face masks, due to its ability to remove impurities and toxins from the skin.
7. Waste treatment: Activated coconut shell charcoal is used in waste treatment facilities to remove impurities and contaminants from water and other materials.

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Process

Charcoal is converted to activated charcoal by treating it in a rotary kiln in a process known as Steam Activation. The kiln usually has a length of up to 60 ft and attains a temperature of 800 – 1100°C.

After initial screening, the charcoal is inserted into the rotary kiln where it passes through several chambers.  This activation process causes the charcoal to become more porous, increasing its surface area drastically. The output is activated charcoal which has strong adsorption properties due to its large surface area. 

The material is then destoned and dedusted to remove stones and excess dust.

Following this, the material is inserted into the Gyro screener for particle separation. Here it is sorted into different grades based on mesh sizes.

Finally, the materials are processed in the packing area, and packed according to the customer’s specifications.

Activated Charcoal Grades

The common activated charcoal grades are as follows:

• 4X8
• 4X10
• 8X16
• 8X30
• 12X30
• 12X40
• 30X60

These numbers represent standard US mesh sizes. For instance, “4X8” implies that the granular size of the material is smaller than 4 mesh, and larger than 8 mesh. 

Other Important Properties

Apart from particle size, these are the main properties considered when grading activated charcoal.

1. Iodine number: The iodine number is a measure of the iodine adsorption capacity of the activated carbon. It is determined by the mass of iodine adsorbed by 1 gram of carbon.
2. Methylene blue value: The methylene blue value is a measure of the activated carbon’s ability to adsorb a specific dye, methylene blue. It is determined by the mass of methylene blue adsorbed by 100 gram of carbon.
3. Molasses number: The molasses number is a measure of the activated carbon’s ability to remove molasses. It is determined by the amount of molasses adsorped from a solution per 100 gram of carbon.
4. Particle size: The particle size of activated carbon can be graded based on the size of the particles. This can be determined using a sieve analysis.
5. Pore size distribution: The pore size distribution of activated carbon can be determined using a variety of techniques. This helps to identify the size and distribution of the pores within the carbon.

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