Activated charcoal is a common product used to filter and purify numerous substances. Although few people realise it, activated charcoal touches everyone’s lives. If you drink water, use soap, brush with toothpaste or drink decaffeinated coffee, your life involves activated charcoal.
Air purification is an important use for activated charcoal as well. The material is highly effective at removing toxins and odours, creating clean, healthy air for homes and offices.
Activated charcoal is highly effective because it can trap particles of the smallest sizes. Many other filters will not trap extremely small particles – think gases, chemicals, and VOCs. What is Activated Charcoal?
Activated charcoal, often referred to as “activated carbon” is an extremely porous form of carbon that is used in the purification of water and air. The material has been specifically processed to give it a porous quality, increasing the surface area of the product.
Activated charcoal is often suited for many uses, including air purification, water treatment, sewage treatment, and smoke removal. It is commonly used to treat drinking water, but it also has a body-cleansing quality that has been linked to life-saving practices. Because it can be used to cleanse bodies, it is a common product in emergency kits and hospitals.
How is Activated Charcoal Made?
Activated charcoal is made from many different raw materials. The most common are wood, nutshells, coconut shells, coal, and peat. Essentially, the raw carbon material is full of other substances, such as organic matter, that fill microscopic holes, or pores, in the carbon. The process starts by removing these substances and leaving behind pure (or nearly pure) charcoal. The microscopic pore sizes that were filled with other substances are now empty, drastically increasing the surface space of the charcoal. The measure of the void in the material is known as porosity.
The carbon needs to be “activated” through oxidation which will enable it to grab and hold toxins and molecules. There are two commonly used processes for activating the carbon (or charcoal) material. Steam activation uses either carbonization or activation/oxidization and can require temperatures over 600 degrees Celsius. Chemical is where the raw material is impregnated with a chemical and then processed at a lower temperature, usually around 450 to 900 degrees Celsius. Because of the lower required temperatures, chemical activation is often the more efficient and effective method for activating charcoal.
The Surface Area: Why it Matters
At its most fundamental level, the surface area in activated charcoal is what matters the most. Activated charcoal is extremely porous, filled with microscopic and sub microscopic pores that create a dense network of holes in the material. With these millions of pores in a small amount of activated carbon, there is a massive surface space for water or air to pass through. This massive surface space grabs onto toxins and holds them in place, giving activated charcoal its fantastic purifying ability. When the activation process is complete, 50 grams of activated charcoal has the physical surface space of roughly 10 football fields. That’s right, thanks to all those microscopic pores, a small amount of activated carbon has a stunning, nearly unbelievable, surface space! Activated charcoal can be so effective that many people claim it not only filters air and water, but can be used to whiten teeth, alleviate bloating, and treat alcohol poisoning, among other health benefits and uses. (To be fair, some of these claims require further research before being accepted by the scientific community.)
Adsorption vs Absorption
While the basic result is similar, absorption and adsorption are two quite different processes. Understanding how the process of adsorption and absorption work will help you understand the effectiveness of activated charcoal.
Absorption: The process, or at least the term, you are probably more familiar with is absorption. During absorption, one substance enters the bulk of another substance. It involved molecules literally entering the volume of a material. During this process, the two materials come together and essentially form a new material.
Adsorption: Adsorption is slightly different. During this process, a substance basically attaches itself to another material, but does not enter the material. Adsorption happens on the surface level and doesn’t create a new substance, but rather to substances hanging on to each other.
Handy analogy: Think of absorption like people riding in a boat, while adsorption is like skiers attached to the boat; the skiers are along for the ride, but they’re not inside.
Coconut Shell Activated Charcoal
Coconut shells are one of the most used raw materials for creating activated charcoal. Activated charcoal made from coconut shells are high in micro pores. In fact, roughly 85 to 90% of the surface area is micro pores. Why does this matter? Because smaller pores often match the size of contaminant molecules in air and drinking water, and therefore make coconut shell activated carbon highly effective at trapping them. There are numerous benefits to using coconut shell activated charcoal as opposed to other materials, and the advantages go beyond the product’s effectiveness. The raw material, coconuts, is a renewable source of charcoal that grows throughout the year and can be harvested up to four times annually. There is no mining required, and unlike wood activated charcoal, you don’t need the entire tree, only the coconuts.
A History of Activated Charcoal
While few people are aware of the impact activated charcoal has had on mankind’s history, it is arguably one of the most important innovations we have ever discovered. It is believed that the use of charcoal as a cleaning and purifying agent has been known for millennia. Some even believe humans were using charcoal for cleaning for over 3,500 years.
Throughout history, charcoal was used to reduce odours in the air and to purify water. It was used in hospitals to reduce smells, and ancient sailors learned to use activated charcoal on the inside of their water barrels to keep drinking water safe for a longer period.
While regular charcoal was used for centuries, activated charcoal has only been around for less than 200 years.
There is a story of a French professor who was so confident in activated charcoal's purifying capabilities that he drank a vial of poison along with a dose of powdered activated charcoal. As the legend holds, the professor walked away to the astonishment of his peers. Activated charcoal is now a common cure for stomach disorders and can even be used as an antidote for poison.
Activated charcoal saw significant industrial production starting in the early 20th century. Around 1910, plants began mass producing activated charcoal for the decolorization and purification of foods, including sugar.
In World War I, activated charcoal was used extensively in gas masks, saving countless lives from gas poisoning. Activated charcoal is now found in nearly every hospital and clinic. It is used in food refinement, dry cleaning, pharmaceuticals, and more.
Important Properties of Activated Charcoal
There are many different properties and characteristics of activated carbon and understanding these factors will help you understand how the material is measured and analysed.
Iodine Number: Iodine adsorption is used to measure the effectiveness of activated charcoal. During this test, activated carbon is added to a liquid holding a specific amount of iodine. The carbon is mixed thoroughly until it has dissolved into the solution. After a few minutes, the solution is filtered into another container, removing the charcoal particles and allowing the liquid to pass through. The iodine number is a gauge of the amount of iodine removed from the liquid. Essentially, the higher the number, the more iodine was removed.
Pore Diameter: The diameter of the pores on and inside activated charcoal will make a significant difference in how the materials performs. Pore diameter can determine the specific use of a charcoal, as activated charcoal with more micropores (smaller pores) can be effective for removing low concentrations of organic matter found in water. Activated charcoal with both small and large pores are very versatile and can be used to remove both chlorine and a wide variety of organic matter at the same time.
Surface Area: The surface area is another important property that is often cited on activated charcoal. Depending on the raw material, the activation process, and other factors, the surface area will vary, giving the charcoal more or less adsorption potential. Surface area for activated carbon is often measured using a BET nitrogen adsorption test.
Density: Density will affect the volume activity. Generally, a higher density will indicate a higher-quality activated charcoal. There are numerous ways to define density, including real density, which is the density excluding the voids of the material, as well as particle density, which is the measured density of the charcoal particles alone. There is also wetted density, apparent density, bed or bulk density, and tamped density. All of these density measurements provide specific data on activated charcoal performance.
Ash Content: Ash content is an important measurement for activated charcoal and can drastically change the effectiveness and specific use for the product. Ash in the activated charcoal reduces the speed and reliability of reactivation and metal oxides can be released from charcoal with high ash content, resulting in discoloration when used to purify water. Carbon with high ash content is not good for fish tanks, as they can lead to heavy metal poisoning in the aquatic life, including fish and coral species. The type of ash can vary as well. For example, activated charcoal made from coconut shells often has a higher concentration of alkali earth metals, while carbon made from coal is often loaded with heavy metals.
Mesh: The size of granular activated charcoal (activated charcoal that is in the form or a powder or fine grains) is measured using a Mesh system. It is measured by shaking a sample of the granulated carbon through a series of fine sieves. Imagine sieves like a window screen only much finer, with far smaller holes between the wires. Using a system that measures how much of the carbon passes through the screens, the activated carbon can be measured for general size.
Molasses Number: The molasses number for activated charcoal is a measurement of the charcoal’s effectiveness for removing large molecules. This is done by allowing the activated charcoal to adsorb a molasses solution. The higher the molasses number, the better the activated charcoal is at removing these large molecules.
Source: This text has been reproduced with kind permission of Oransi. Further details of activated carbon usage in air purifiers can be found on their website.
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