Introduction to Activated Carbon Fiber

 

Activated Carbon Fiber is activated carbon fiber. Viscose-based fiber is pre-oxidized, carbonized, and activated at high temperature to produce nano-scale pores on its surface, increase the specific surface area, and thus change its physical and chemical properties.

 

Definition

Traditional activated carbon is a porous carbon that has been activated and is in powder or granular form, while activated carbon fiber is fibrous and covered with micropores. Its adsorption capacity for organic gases is several to dozens of times higher than that of granular activated carbon in the air, 5 to 6 times higher in aqueous solution, and the adsorption rate is 100 to 1000 times faster! It has only been used for more than 20 years, and only a few countries in the world can produce it. Its products can be in the form of silk, paper, felt, cloth, etc. In industry, its super adsorption capacity is used to recycle organic solvents, purify air, and purify water.

 

ACF (activated carbon fiber) is the third generation of new adsorption material after the widely used powdered activated carbon and granular activated carbon. It is made of fiber as raw material and has the advantages of large specific surface area, moderate pore size, uniform distribution, fast adsorption speed and less impurities. It is widely used in water purification, air purification, aviation, military, nuclear industry, food and other industries;

 

 

 

Structure

The fiber diameter of activated carbon fiber is 5~20μm, the average specific surface area is about 1000~1500m2/g, the average pore size is 1.0~4.0nm, and the micropores are evenly distributed on the fiber surface. Compared with activated carbon, the micropores of activated carbon fiber are small and uniform, the structure is simple, the adsorption rate of small molecular substances is fast, the adsorption speed is high, and it is easy to desorb.

 

The contact area with the adsorbate is large, and it can be uniformly contacted and adsorbed, so that the adsorption material can be fully utilized. It has high efficiency and has various fine surfaces such as fiber, felt, cloth and paper. The pores are directly opened on the fiber surface. The diffusion path of the adsorbate to the adsorption site is short, and its own surface area is two orders of magnitude higher than the internal surface area.

 

Interception Function Comparison Table:

Powdered activated carbon (Pac) <Granular activated carbon (GAC) <Activated carbon rod (CTO) <PP <Activated carbon fiber (ACF)

 

 

Structural Description:

 

Microporous structure: The micropore radius is below 2nm, and its pore size distribution is narrow. The special pores are monodispersed. Its structure is composed of micropores of different sizes, and the diffusion of mesopores and small pores presents a polydispersed distribution. The difference in each pore structure is large, and the main reason is the difference in raw materials.

 

There are no macropores in activated carbon fibers, only a small number of transitional pores. Micropores are distributed on the fiber surface, and the adsorption rate is fast. The space of the activated carbon fiber bundle acts as a macropore, which has a good adsorption effect on gas and liquid substances. Its external specific surface area is large, and the adsorption and desorption speed is fast, which is 10~100 times that of granular activated carbon.

 

As the specific surface area increases, the average pore size of the pores increases accordingly, and the pore volume increases. After adsorption occurs in the pores, the pores are filled. Its specific surface area increases and the adsorption capacity is large, which is 10 times that of granular activated carbon. It can adsorb and treat low-concentration waste gas or highly active substances. Activated carbon fiber has a small volume density, small filtration resistance, can adsorb liquid substances with high viscosity, and has low power loss.

 

Uses:

Activated carbon fiber felt is used for the recovery of organic solvents. For the recovery of organic solvents from the gas phase, such as benzene, ketones, esters, and petroleum waste gases, they can be adsorbed and recovered from the gas phase. Using activated carbon fiber as a solvent recovery material has a fast adsorption and desorption speed, a large processing volume, and a high quality of recovered solvents.

 

The recovery rate can reach more than 90%. With the continuous strengthening of human environmental awareness, the performance requirements for environmentally friendly materials such as activated carbon that are closely related to the living environment, especially air and water purification, are getting higher and higher. Granular or powdered activated carbon can already meet the use requirements well.

 

Traditional activated carbon is a granular or powdered carbon material. Since the industrial production was realized in the early 20th century, it has been widely used in the separation and purification of water and other liquids, deodorization, purification, etc.

 

Granular or powdered structure, its adsorption speed is slow, the separation efficiency is not high, especially its physical form has many inconveniences in application, which limits the scope of application.

 

Activated carbon fiber has a small pore size and narrow distribution, fast adsorption speed, large adsorption capacity, and easy regeneration.

 

Compared with powdered (5nm~30nm) activated carbon, activated carbon fiber produces less micro dust during use and can be made into products in various forms such as yarn, thread, fabric, felt, etc., which is more flexible and convenient to use.

 

Activated carbon fiber is considered to be one of the best environmentally friendly materials in the 21st century. It has been successfully applied in gas and liquid purification, harmful gas and liquid adsorption treatment, solvent recovery, functional electrode materials, etc.

 

Purification of Drinking Water:

 

With the development of industry and the dense urban population, water pollution is becoming more and more serious, and the amount of domestic wastewater treatment in urban areas has become larger and larger.

 

There is a trend of increasing organic pollutants in wastewater, especially industrial wastewater, and wastewater in chemical, metallurgical, coking, light industry and other industries is the main source of pollution. The toxic and harmful substances contained in it have already posed a threat to the ecological environment.

 

With the acceleration of urbanization, organic pollution, and the continuous increase in the amount of urban domestic sewage, the organic matter discharged in industrial wastewater has not only increased in quantity but also toxic substances, which has caused great harm to the environment. Therefore, it is of vital importance to ensure the supply of high-quality drinking water.

 

Using activated carbon fiber to treat groundwater can achieve good results. Residual chlorine in tap water can also be adsorbed by activated carbon fiber. Trichloroethylene (TCE) in groundwater not only changes the taste of drinking water, but also induces cancer after accumulation in a certain organ of the human body. Therefore, TCE pollution is a very serious problem.

 

The adsorption of TCE in water by activated carbon fiber is 4 times that of granular activated carbon. For the adsorption of E. coli, the number of adsorbed bacteria increases with the increase of specific surface area. The amount of bacterial adsorption is also related to the size of silver particles on the surface of activated carbon fiber. Activated carbon fiber is also very effective for biological adsorption in water.

 

In recent years, the increase in urban population has caused insufficient supply of drinking water. The effective removal rate of trihalomethane wastewater treated with activated carbon in China is only 40%. The detection of groundwater shows that there are many chlorides in the water, which are carcinogenic. Chlorine-containing substances in tap water can be removed by activated carbon fiber. When using activated carbon fiber to remove trichloroethylene in water, the adsorption of activated carbon fiber is 4 times that of granular activated carbon, which can be one order of magnitude larger than activated carbon in actual treatment.

 

The organic substances that can be adsorbed are: hydrocarbons (benzene, toluene, xylene, trimethylbenzene, n-hexane, cyclohexane, etc.), halogenated hydrocarbons (methyl chloride, dichloromethane, trichloromethane, trichloroethylene, trichloroethane, methyl bromide, tetrachloride, etc.), aldehydes and ketones (acetone, cyclohexanone, formaldehyde, acetaldehyde, furfural, etc.), esters (ethyl acetate, butyl acetate, etc.), ethers (methyl ether, ethyl ether, methyl ethyl ether, etc.), alcohols (methanol, ethanol, isopropanol, butanol, etc.), polymerization monomers (vinyl chloride, etc.)

 

For air purification, it can effectively remove various harmful and odorous substances in the air, especially carcinogens and aromatic compounds (such as benzene, aldehydes), which can make the air clean and fresh.

 

For sewage treatment, it is suitable for treating organic wastewater containing phenols, medicines, thiols, etc. that are difficult to decompose.

 

Used for water treatment of food, beverages, and medicine; decolorization and deodorization in the production of sugar and wine industry, purification and sterilization of drinking water, removal of residual chlorine in tap water, etc.

 

Applications in electronics and energy, can produce high-capacity capacitors, livestock battery electrodes, conductive heating materials, etc.

 

In military protection, it can be used for battlefield rescue gloves, dressings, bandages and chemical protection screens, as well as chemical protection clothing for chemical defense forces, and can also be used for military bedding and military medical bedding.

 

At present, activated carbon fiber has been widely used in water purifiers, especially silver-loaded activated carbon fiber, which has the dual functions of adsorption and sterilization. Silver-loaded activated carbon fiber is used to adsorb Escherichia coli. When the silver content increases and the specific surface area increases, its adsorption amount increases, and it is also effective for the adsorption of other microorganisms in water. Among them, the most well-known ones are the Pais Neptun series of water purifiers;

 

Adsorption Capacity

After high-temperature activation of carbon fiber, the fiber surface is covered with micropores (i.e. the position occupied by hydrogen and oxygen atoms before volatilization), and its pore size is one ten-thousandth of a hair. When the inner surface of these micropores is unfolded, the unfolded area of ​​1g of activated carbon fiber felt is as high as 1600㎡, which is because these micropores play the role of adsorbing odors.

 

From physics, we know that the surface of an object has external gravity. The larger the surface, the greater the adsorption force. Activated carbon fiber adsorbs surrounding molecules and firmly adheres to the micropores through the action of this van der Waals force.

 

Activated Carbon Fiber Regeneration Method

After long-term use of activated carbon fiber felt, the micropores will be filled, resulting in a decrease in adsorption capacity. Using a certain method can increase the kinetic energy of the adsorbate, get rid of gravity, and escape from the activated carbon fiber (cannot be completely desorbed). At this time, the adsorption function of the activated carbon fiber can be restored and reused.

 

There are many methods for desorption and regeneration of activated carbon fiber, such as hot steam desorption method, nitrogen desorption method, etc. Hot steam desorption method is commonly used in organic waste gas treatment. Industrial desorption requires special equipment, while general civilian products only need to be dried in the sun or blown with electric air.