1 Functional activated carbon activated carbons Activated carbon is an important functional material for national economic development and national defense construction. Activated carbon can be used for gas phase adsorption, liquid phase adsorption, electronic materials, medical treatment and many other aspects, and can be used as a catalyst and catalyst carrier. In recent years, with the rapid development of environmental protection, new energy and other industries, the market demand for functional activated carbon has surged. 2 Activated carbon modification Industrial development has increased the requirements for the adsorption capacity and catalytic activity of activated carbon. Conventional activated carbon can no longer meet the special requirements of various fields, and super activated carbon has emerged as the times require. Super activated carbon has a huge specific surface area and excellent adsorption performance, so it is widely used in fuel gas adsorption and storage, gas separation, catalyst carrier, electrode material of super capacitor and so on. In many applications, special activated carbon has also appeared, such as nickel-coated activated carbon suitable for removing alkyl sulfides in gas or exhaust gas, and special activated carbon for citric acid. Although the advantages of super activated carbon are obvious, the application of shortcomings is insufficiently studied, especially in the process of preparation and use, there are still some shortcomings that need to be further studied and improved. Activated carbon modification is to adjust its adsorption performance, adsorption capacity, catalytic activity and other properties to meet specific working conditions and application conditions. The modification of the adsorption performance of activated carbon is currently mainly focused on two aspects. One is to develop activated carbon with special properties, such as activated carbon fiber and wood activated carbon. The other is to modify the activated carbon to adjust the pore structure of activated carbon to improve the specific adsorption properties. Absorption capacity or desorption capacity. Activated carbon fiber (ACF) is the third-generation activated carbon product. It can be made into products of any shape, which can be decolorized and deodorized. It is suitable for solvent recovery devices, water purifiers, ozone filters, anti-virus masks, medical bandages, cigarette filters, Precious metal recovery equipment, etc. ACF is mainly used to treat micro-polluted raw water and low-concentration wastewater. One of the main reasons limiting its wide application is the high price.
Until the 21st century, the application fields of activated carbons have been further expanded. Activated carbon is also involved in many high-tech fields such as environmental protection, energy and catalysts, gas storage, chemical separation, and biological organisms. Among them, the treatment and purification of industrial waste gas by activated carbon, including the removal of formaldehyde gas, is mainly dependent on its gas phase adsorption application, and activated carbon is dependent on it for pharmaceutical and chemical wastewater, precious metal recovery, and the most basic water treatment. The application of liquid phase adsorption is precisely because of the unique characteristics of activated carbon, so it is always indispensable when treating waste gas and wastewater. Nowadays, the development of activated carbon is becoming more and more diversified, and when dealing with different pollution, scientists have also developed different types of activated carbon to deal with. Targeted development of activated carbon with special adsorption properties has also become a top priority. It is hoped that one day activated carbon can better improve the environment and return the environment to its origin.
Activated carbon is a kind of black porous solid carbon, which is produced by pulverizing and shaping coal or carbonizing and activating uniform coal particles. The main component is carbon, and contains a small amount of oxygen, hydrogen, sulfur, nitrogen, chlorine and other elements. The specific surface area of ordinary activated carbon is between 500 and 1700 m2/g. It has strong adsorption performance and is an industrial adsorbent with a wide range of uses. Activated carbon is a traditional and modern man-made material, also known as carbon molecular sieve. Classification: According to the different sources of raw materials, manufacturing methods, appearance and shape, and application occasions, there are many types of environmentally friendly activated carbon. Up to now, there are no measurable statistical materials, and there are about thousands of varieties. According to the source of raw materials: 1. Wooden activated carbon; 2. Animal bones, blood charcoal; 3. Mineral raw material activated carbon; 4. Other raw material activated carbon; 5. Regenerated activated carbon. According to the manufacturing method: 1. Chemical activated carbon (chemical carbon); 2. Physical activated carbon; 3. Chemical-physical or physical-chemical activated carbon. According to appearance shape: 1. Powdered activated carbon; 2. Granular activated carbon; 3. Unshaped granular activated carbon; 4. Cylindrical activated carbon; 5. Spherical activated carbon; 6. Activated carbon of other shapes. According to the aperture: Macropore radius>20 000nm; transition pore radius 150-20000nm; micropore radius<150nm The surface area of activated carbon is mainly provided by micropores. Classified by material: Coconut shell activated carbon; nut shell activated carbon (including apricot shell activated carbon, fruit core shell activated carbon, walnut shell activated carbon); wooden activated carbon; coal-based activated carbon.
Activated alumina has a large specific surface area, a variety of pore structures and pore size distributions, and rich surface properties. Therefore, it has a wide range of uses in adsorbents, catalysts and catalyst carriers. Alumina for adsorbent and catalyst carrier is a fine chemical and also a special chemical. Different uses have different requirements for physical structure, which is the reason for its strong specificity and many varieties and grades. According to statistics, the amount of alumina used as catalysts and carriers is more than the total amount of catalysts using molecular sieve, silica gel, activated carbon, diatomaceous earth and silica alumina gel. This shows the pivotal position of alumina in catalysts and carriers. Among them, η-Al2O3 and γ-Al2O3 are the most important catalysts and supports. They are both spinel structures containing defects. The difference between the two is: the tetrahedral crystal structure is different (γ>η), and the hexagonal layer stack The row regularity is different (γ>η) and the Al—O bond distance is different (η>γ, the difference is 0.05～0.1nm).
The ability of molecular sieve to separate air depends on the diffusion speed of various gases in the air in the pores of Carbon Molecular Sieves, or the adsorption force, or both. Carbon Molecular Sieves PSA air separation nitrogen production is based on this performance. Carbon Molecular Sieves are used to produce nitrogen. The N2 concentration and gas production volume can be adjusted according to the user's needs. When the gas production time and operating pressure are determined, the gas production volume will be lowered, and the N2 concentration will increase, otherwise, the N2 concentration will decrease. Users can adjust according to actual needs.
Carbon molecular sieve PSA nitrogen generator production relies on van der Waals force to separate oxygen and nitrogen. Therefore, the larger the specific surface area of the molecular sieve, the more uniform the pore size distribution, and the greater the number of micropores or submicropores, the greater the adsorption capacity; , If the pore size can be as small as possible, the van der Waals force field overlaps, and it has a better separation effect on low-concentration substances. Carbon molecular sieve is a non-quantitative compound, and its important properties are based on its microporous structure. Its ability to separate air depends on the different diffusion speeds of various gases in the air in the pores of the carbon molecular sieve, or different adsorption forces, or both effects work at the same time. Under equilibrium conditions, the adsorption capacity of carbon molecular sieve for oxygen and nitrogen is quite close, but the diffusion rate of oxygen molecules through the narrow gaps of the carbon molecular sieve microporous system is much faster than that of nitrogen molecules. Carbon molecular sieve air separation nitrogen production is based on this Performance, before the time to reach equilibrium conditions, the nitrogen is separated from the air through the PSA process.