What is active charcoal

2023-10-27

Active charcoal is a carbon material with a large specific surface area and strong adsorption and decolorization ability. In the 19th century, people used it to decolorize, deodorize and purify sugar, wine and water. Bone char has also been used for water filtration for more than 100 years, and activated charcoal began to be used to make gas masks during World War I. By the 90s of the 20th century, activated carbon was widely used in sewage treatment, concentration and recovery of organic solvents, air purification and other environmental protection, gold extraction and other fields.

Active charcoal has a powdery, granular or pellet-like amorphous structure, with a porous structure, a large surface void area in the pores, and has a good adsorption effect on some gases. It is usually obtained by dry distillation of wood, hard fruit shells (such as coconut shells) or animal bones and treatment with superheated steam at high temperature (800~900 °C). Activated carbon is structurally irregular due to the irregular arrangement of microcrystalline carbon, and there are fine pores between the cross-connections, which will produce carbon structure defects when activated. Its huge internal surface area is filled with small pores of small volumes, and its fascinating qualities are fascinating, elements that have revolutionized materials science and modern industry due to their unique absorption capacity. Due to the high microporosity of activated carbon, 1 gram of activated carbon provides 600 to 1200 square feet of surface area.

Active charcoal is a complex product that is difficult to classify based on its behavior, surface properties, and other basic criteria. However, there are some broad classifications for general purpose based on their size, preparation method, and industrial application: powdered activated carbon (RI, PAC), granular activated carbon (GAC), extruded activated carbon (EAC), beaded activated carbon (BAC), impregnated activated carbon and polymer-coated activated carbon, activated carbon fiber (ACF). According to the source of raw materials, it can be divided into wood activated carbon, animal bones, blood charcoal, mineral raw material activated carbon, activated carbon of other raw materials and recycled activated carbon. According to the activation method, it can be divided into chemical activated carbon (chemical carbon), physical activated carbon, chemical-physical activated carbon, and physical-chemical activated carbon.

Activated carbon is essentially a specially treated carbon that absorbs a variety of gases or vapors. Before activated carbon was invented as a patent in the early 20th century, there were historical records with many references more about the history of charcoal applications. In 1550 BC, there were records of charcoal as a medicinal use in ancient Egypt. The famous Greek physician Hippocrates (460-359 BC) and the ancient Roman scientist Pliny the Elder have documented the use of charcoal to treat epilepsy and anthrax. In fact, in the Ming Dynasty of China, the "Compendium of Materia Medica" compiled by Li Shizhen also mentioned that charcoal was used to treat diseases.

Nowadays, activated charcoal can indeed be used to treat poisoning and drug overdose after oral administration, and its essence is to use the strong adsorption of activated charcoal, which can absorb the excess drug in the stomach.

It was not until the end of the 18th century that activated carbon really appeared on the stage of history. In 1773, the Swedish chemist Scheler recognized the specific adsorption capacity of carbon, i.e., charcoal, and he measured the volume of various gases that carbon from different sources could adsorb. In 1785, Scheler studied charcoal adsorption gases, from vapor to a series of organic chemical activated carbon, and the use of charcoal decolorization in various aqueous solutions was also fruitful, especially for commercial applications in the production of tartaric acid. This appears to be the first time that the adsorption of charcoal on the liquid phase has been systematically considered. At this time, the sugar industry was looking for an effective way to decolorize syrups. However, ordinary wood charcoal has not been particularly effective in this role, probably because the degree of porosity development has not yet reached the level of charcoal used in syrup decolorization.

In 1794, a British sugar factory successfully produced a syrup that used charcoal decolorization, but the recipe for this charcoal was kept secret. In 1805, the first large-scale production of syrup made from sugar beets was carried out in France using charcoal decolorization. From 1805 to 1808, Delessert successfully used charcoal to decolor sugar beet wine. By 1815, most of the sugar industry had switched to granular bone char as a decolorizing agent.

In 1911, the Austrian company Fanto Works sold the first industrially produced activated carbon "Eponit" (trade name), which they manufactured Eponit from wood using von Ostrejko's gasification method and marketed it as a decolorizing agent in the sugar industry. Prior to this, the main user of activated carbon was the sugar industry, where manufacturers produced activated carbon through their own secret or patented processes.

In the First World War, activated carbon ushered in its highlight moment. German chemists led by Haber[9] developed poison gas for use in the battlefield, and on April 22, 1915, Germany attacked the combined forces of France, Canada and Algeria with chlorine gas at the Second Battle of Ypres. After that, the two armies used each other and developed new types of poisonous gas, mainly mustard gas, phosgene and chlorine. Under the leadership of Chaney in the United States, a research team studied various precursors for the production of sorbents for gas mask canisters, and by activating wood chips with zinc chloride, developed granular activated carbon with sufficient adsorption capacity and low resistance to the flow of air through the respirator filter. Soon, granular activated carbon was produced on a large scale as an adsorbent for the manufacture of gas mask filter canisters for military use.

After World War I, the development of large-scale activated carbon production during the war promoted the commercial production and application of activated carbon after the war. Great progress has been made in manufacturing new raw materials for activated carbon in Europe, and activated carbon produced by adding coconut, almond shell and zinc chloride has high mechanical and adsorption capacity for gases and vapors.

Since the middle of the 20th century, activated carbon materials began to move towards "high adsorption, large specific surface area (>2500㎡/g), multi-form (powder, spherical, granular, etc.), high strength, low cost", widely used in air purification, solvent and precious metal refining and recovery, food preservation, pharmaceutical refining, blood purification, gas masks, anti-radioactive substances and other fields, and achieved satisfactory results, while achieving large-scale industrial production.

Today, the largest market for activated carbon is in the municipal water purification industry. Among the EPA's indicators of organic pollution of drinking water, activated carbon is the most effective technology for 51 of the 64 indicators. Therefore, water treatment is the most widely used market for activated carbon and will be the fastest growing field of activated carbon application in the 21st century. In water filtration systems for polyvinyl chloride (PVC) pipes, activated carbon is the core component. The system consists of pebbles, palm, palm fiber, alum, activated carbon (AC), gravel, chlorine (Cl2), smooth sand and gravel, each component is separated with a sponge filter to hold it in a fixed place.

Here is another introduction to the unknown application of activated carbon.

1. Treatment of cancer

In the United States, activated charcoal has been used in the surgery and interventional treatment of malignant tumors such as breast, gastric, esophageal and rectal cancer. Activated carbon is used to adsorb different anti-cancer drugs, selectively allow high concentrations of anticancer agents to be distributed for a long time in the presence of cancer cells, and in other healthy parts, do not allow anticancer agents to be distributed as much as possible. Because the drug is absorbed in activated carbon, it is conducive to attaching to the surface of cancer tissue to exert its effect, so it has fewer side effects on the human body than the aqueous solution of the drug. Activated carbon has excellent adsorption performance and has a specific tendency to the lymphatic system, so it can stain lymph nodes black, thereby guiding the removal of lymph nodes.

2. Air separation and enrichment of oxygen

One of the main problems in the chemical industry is how to efficiently separate oxygen from the air, and the study of oxygen separation with activated carbon specific adsorption has been reported for a long time, such as the directional regulation of the pore size of activated carbon by chemical vapor deposition method, and the preparation of activated carbon with molecular sieve performance and uniform pore size distribution, the separation and enrichment of oxygen in the air has been applied in foreign commercialization.

3. Energy storage materials

By using activated carbon as the anode material, lithium-ion batteries replace the metal lithium anode that still has problems in the charging reaction, which retains the advantages of high energy density and high voltage of primary lithium batteries, and greatly improves the cycle service life and safety performance, forming a secondary lithium battery with excellent performance. By regulating the pore size distribution of activated carbon with high specific surface area, improving the surface adsorption performance of lithium ions, so as to obtain high energy density, and greatly improve the charge and discharge rate, it is expected to develop lithium-ion batteries with higher energy density.

4. Catalyst carrier

Metals or metal oxides as catalysts are due to having an active center Only then is there catalytic activity, and crystallization defects are the main reason for the existence of activation centers. Graphitized carbon and amorphous carbon are components of the activated carbon crystal form, which exhibit similar functions to crystallization defects because of their unsaturated bonds. Activated carbon is widely used as a catalyst because of the existence of crystallization defects, especially in redox reactions such as flue gas desulfurization, phosgene oxidation, synthesis of cyanide chloride, ozone decomposition and depolarization of oxygen in batteries. At the same time, because of its large internal surface area, activated carbon is also an ideal catalyst carrier, especially in the field of photocatalyst loading, and supporting photocatalysts through activated carbon and using it for the degradation of organic waste gas will be an important direction for future development.

The outside looks like a few gray activated carbon, but the inside is unique. This fascinating material is like "activated carbon with strong adsorption", attracting a group of scientists to cultivate deeply in this black soil, through continuous modification and adjustment, to make more valuable activated carbon products to better serve human society.