The Science Behind Activated Carbon: How It Works and Why It’s Effective

Introduction

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”. (“Activated Carbon & Charcoal Frequently Asked Questions | FAQ Page,” n.d.) 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. (Activated Carbon, 2023)

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. (“The Science Behind Activated Carbon Water Filters,” 2020)

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. Chemical processes, commence from raw materials before carbonisation. (“What Is Activated Carbon and What Is It Used For?,” n.d.)

The term “carbonisation” pertains to the process of extracting pure carbon by 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. (Activated Carbon, 2023)

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. (Engber, 2005; “The Science Behind Activated Carbon Water Filters,” 2020)

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. (“An Evaluation of Activated Carbon for Drinking Water Treatment,” 1980; Engber, 2005)

Activated Carbon: Application

Activated carbon’s applications can be seen 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. (Activated Carbon & Carbon Absorption – Everything To Know, n.d.; “Activated Carbon & Charcoal Frequently Asked Questions | FAQ Page,” n.d.)

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. (2023, July 26). Chemviron. https://www.chemviron.eu/products/activated-carbon/
2. 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
3. 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/
4. 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/
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. The Science Behind Activated Carbon Water Filters. (2020, August 13). Clean Tech Water. https://www.cleantechwater.co.in/science-behind-activated-carbon-water-filters/
7. 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