In this article, I will discuss about Activated Carbon. Activated Carbon also known as Activated Charcoal.
Table of Contents
What Is Activated Carbon?
Activated carbon is a special type of carbon that has a lot of tiny pores. These pores make its surface area very large, allowing it to effectively filter impurities from water and air, among other things. The process of making activated carbon is like turning dried corn kernels into popcorn, where the popcorn becomes light and fluffy with a high surface area.
Because of its abundant tiny pores, just one gram of activated carbon can have a surface area of over 3,000 square meters. This is much larger than regular charcoal, which only has a surface area of 2.0-5.0 square meters per gram. Sometimes, additional chemical treatments are used to make it even better at filtering.
Activated carbon is often made from waste materials like coconut husks or waste from paper mills. These waste sources are converted into charcoal first and then transformed into activated carbon. When it comes from coal, it is known as activated coal, and if it is made from coke, it is called activated coke.
Activated carbon, or activated charcoal, is a powerful and efficient material used to clean water and air by trapping and removing impurities, thanks to its large surface area and tiny pores.
Characteristics Of Activated Carbon
- Activated carbon possesses an extensive surface area, with a gram capable of exceeding 500 square meters, and up to 3,000 square meters being readily achievable. This high surface area allows for effective adsorption of various substances.
- Under an electron microscope, activated carbon reveals intensely convoluted particles with various types of porosity. Micropores provide excellent conditions for adsorption, as they allow adsorbing materials to interact with many surfaces simultaneously.
- Activated carbon exhibits impressive adsorption behavior. It can adsorb substances from its environment, such as nitrogen gas at 77 K under high vacuum, and even liquid water from steam at 100°C (212°F) and low pressure.
- Activated carbon can effectively adsorb numerous air gases, including oxygen, which can be adsorbed at low temperatures and then released when the carbon warms up again.
- Activated carbon binds materials through van der Waals force and London dispersion force, contributing to its adsorption capabilities.
- Activated carbon does not bind well to certain chemicals, including alcohols, diols, strong acids and bases, metals, and various inorganic substances.
- Activated carbon displays a high affinity for adsorbing iodine, and the measurement of its iodine capacity can be used as an indication of its total surface area.
- Activated carbon is not effective in adsorbing carbon monoxide, which is a concern when using it in filters for respirators or gas control systems, as carbon monoxide is toxic and undetectable to human senses.
- Activated carbon can be used as a substrate for the application of certain chemicals to improve its adsorptive capacity for specific inorganic and problematic organic compounds, such as hydrogen sulfide, ammonia, formaldehyde, mercury, and radioactive iodine-131.
- Activated carbon finds extensive use in adsorbing a wide range of common industrial and agricultural gases, making it a valuable material for various purification and filtration processes.
Uses of Activated Carbon
Industrial Applications
Activated carbon finds diverse applications in various industries:
- Metal Finishing: It is used to purify electroplating solutions by removing organic impurities, ensuring high-quality plating.
- Medicine: Activated carbon is utilized to treat poisonings and overdoses following oral ingestion. It is also used in over-the-counter drugs for treating diarrhea and indigestion.
- Analytical Chemistry: It serves as a stationary phase in chromatographic separation of carbohydrates and is used to extract oral anticoagulants from blood plasma samples.
- Environmental Remediation: Activated carbon aids in removing pollutants from air and water streams, including spill cleanup, groundwater remediation, drinking water filtration, and air purification.
- Agricultural: In organic farming, it acts as a pesticide, feed additive, and processing aid. In winemaking, it is used to adsorb color pigments from grape concentrates.
Medical Applications
- Poisoning Treatment: Activated carbon is used to treat poisonings and overdoses caused by oral ingestion of certain substances.
- Medication: It is used in certain over-the-counter drugs for treating diarrhea and indigestion.
- Limitations: Activated carbon is ineffective against certain poisoning cases, including those caused by strong acids or bases, cyanide, iron, lithium, arsenic, methanol, ethanol, or ethylene glycol.
Environmental Uses
- Water Filtration: Activated carbon is commonly used in water filtration systems to remove impurities and improve water quality.
- Air Purification: It captures volatile organic compounds from various industrial processes, such as painting and dry cleaning operations.
- Radon Measurement: Activated carbon is used to measure radon concentration in the air.
Industrial Gas Storage and Purification
- Fuel Storage: Research is being done to test its ability to store natural gas and hydrogen gas, providing an efficient and low-pressure storage method.
- Gas Purification: Activated carbon filters are used to remove oil vapors, odor, and hydrocarbons from compressed air and gas streams.
Chemical and Laboratory Applications
- Chemical Purification: It is commonly used in laboratories to purify solutions of organic molecules by removing unwanted colored organic impurities.
- Mercury Scrubbing: Activated carbon infused with sulfur or iodine is used to trap mercury emissions from various sources, including coal-fired power plants and medical incinerators.
Other Uses
- Food Additive: Activated, food-grade charcoal has been used as a trend in food products to impart a smoky taste and dark coloring. However, caution is advised for people taking medication, as it can render the medication ineffective.
- Skin Care: The adsorbing properties of activated charcoal are popularly used in skincare products like soaps, face masks, and scrubs to cleanse and purify the skin.
Types of Activated Carbon
1. Powdered Activated Carbon
Powdered activated carbon (PAC) is a type of activated carbon that comes in the form of fine powders or tiny granules. These particles are very small, with a diameter between 0.15 and 0.25 millimeters, and they have a large surface area compared to their volume. This makes them excellent for adsorption, where they attract and trap impurities and contaminants. PAC is commonly used in processes like water treatment, air filtration, and removing unwanted substances from different liquids. It is not usually used on its own in a separate vessel because it would cause high resistance to flow. Instead, PAC is added directly to other parts of the treatment process.
2. Granular Activated Carbon
Granular activated carbon (GAC) has larger particles than powdered activated carbon. The larger size means it has a smaller external surface area compared to PAC, but it is still effective for adsorption. GAC is used to remove gases, vapors, and various impurities from air and water. It is commonly used in air filters and water treatment systems. GAC comes in different sizes, such as 8×20, 20×40, and 4×6, depending on the specific application.
3. Extruded Activated Carbon
Extruded activated carbon is made by combining powdered activated carbon with a binder and forming it into cylindrical blocks. These blocks have diameters ranging from 0.8 to 130 millimeters. Extruded activated carbon is ideal for gas-phase applications due to its low pressure drop, high mechanical strength, and minimal dust content. It is often used for filtering gases and removing chlorine, taste, and odor from water. In the market, it is sometimes referred to as CTO (Chlorine, Taste, Odor) filters.
4. Bead Activated Carbon
Bead activated carbon is created from petroleum pitch and comes in the form of small beads, with diameters ranging from approximately 0.35 to 0.80 millimeters. Like extruded activated carbon, bead activated carbon is known for its low pressure drop, high mechanical strength, and low dust content. Due to its spherical shape, it is well-suited for fluidized bed applications, such as water filtration.
5. Impregnated Carbon
Impregnated carbon is porous activated carbon that contains additional inorganic substances like iodine, silver, and various metal cations (aluminium, manganese, zinc, etc.). These impregnates give the carbon specific properties for certain applications, like air pollution control in museums and galleries. Silver-loaded activated carbon, for example, is used to purify domestic water due to its antimicrobial and antiseptic properties. Impregnated carbons are also effective in removing hydrogen sulfide (H2S) and thiols.
6. Polymer Coated Carbon
Polymer coated carbon is a special type of porous carbon that is coated with a biocompatible polymer. This process creates a smooth and permeable coating without blocking the pores. Polymer-coated carbon is used in a technique called hemoperfusion, where large volumes of a patient’s blood are passed over the carbon to remove toxic substances from the blood.
6. Woven Carbon
Woven activated carbon cloth is made by processing technical rayon fiber into activated carbon cloth for carbon filtering. This cloth has a higher adsorption capacity compared to regular activated charcoal. It finds application in various fields, such as supercapacitors, odor absorbers, and CBRN-defense industries.
Activated carbon is a versatile material with different forms that can be used in a wide range of applications, from purifying water and air to removing toxic substances from the blood. Each type has unique properties that make it suitable for specific uses, and they all play a crucial role in keeping our environment and daily lives clean and safe.
Manufacturing Process
Activated carbon is a versatile material produced from various carbonaceous sources such as bamboo, coconut husk, wood, coal, and more. The production process involves two main methods: physical activation and chemical activation.
Physical Activation
In the physical activation process, the carbonaceous source material undergoes carbonization and activation using hot gases. The process includes the following steps:
a. Carbonization: The raw material with carbon content is subjected to pyrolysis at temperatures ranging from 600°C to 900°C. This process occurs in an inert atmosphere with gases like argon or nitrogen to avoid combustion and preserve the carbon.
b. Activation/Oxidation: The carbonized material is exposed to oxidizing atmospheres, such as oxygen or steam, at temperatures above 250°C. This step is usually carried out within the temperature range of 600°C to 1200°C. The activation process involves heating the sample for a specific duration to create a graded, screened, and de-dusted form of activated carbon. For example, the sample may be heated for an hour in the presence of air at 450°C using a muffle furnace.
Chemical Activation
In the chemical activation process, the carbon material is impregnated with certain chemicals, which are typically acids, strong bases, or salts. Common chemicals used include phosphoric acid, potassium hydroxide, sodium hydroxide, potassium carbonate, calcium chloride, and zinc chloride. The chemical activation process generally consists of the following steps:
a. Impregnation: The carbonaceous source material is soaked or treated with the chemical activating agent.
b. Activation: The impregnated material is then subjected to high temperatures, typically ranging from 250°C to 600°C. The heat from the temperature forces the material to open up and develop more microscopic pores, resulting in activated carbon.
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Conclusion
Activated carbon is widely used in various industries for its exceptional adsorption properties. It is employed for water and air purification, gas and vapor phase filtration, odor removal, gold recovery in mining, food and beverage processing, pharmaceuticals, and many other applications that require efficient adsorption and purification capabilities.