1. Chemical activation method Chemical activation method is a method in which chemicals are added to raw materials, then heated in an inert gas medium, and carbonized and activated at the same time. Plant-based raw materials such as sawdust are usually used. The drug activation method has three major disadvantages: ① It is very corrosive to the equipment; ② It pollutes the environment; ③ There are chemical activators remaining in the activated carbon, which limits its application. 1.1. Zinc chloride method The zinc chloride method manufacturing process is to add a concentrated zinc chloride solution with a weight of 0.5 to 4 times that of the raw material and a specific gravity of about 1.8 and mix it, let the zinc chloride soak, and then add it to the raw material. The rotary furnace is heated to 600-700°C in isolation from air. Due to the dehydration of zinc chloride, the hydrogen and oxygen in the raw material are mainly released in the form of water vapor, forming carbon with a developed porous structure. 1.2 Phosphoric acid method. In principle, phosphoric acid activation is to mix finely crushed raw materials with phosphoric acid solution, and then the mixture is dried and heated to 400~600°C in a converter. The well-known process is at a higher temperature (1100°C). ℃) carried out. 1.3 Chemical activation method using alkali as activator Recently, chemical activation method using alkaline activator such as potassium hydroxide has attracted attention. Coal char and potassium hydroxide were mixed and subjected to low-temperature and high-temperature secondary heat treatment in an argon gas flow to obtain activated carbon with a specific surface area of ??2918 square meters/g. Use primary carbonized walnut shells or petroleum coke, add 1 to 5 times potassium hydroxide, mix thoroughly, vent the system with nitrogen protection, perform low-temperature dehydration and high-temperature activation to produce high specific surface area activated carbon. The American Standard Oil Company applied for five patents for preparing activated carbon from petroleum coke in the four years from 1971 to 1974. The key points are: using nitric acid to oxidize petroleum coke into petroleum coke acid, and then using excess hydrogen under different process conditions. Activated by potassium oxide, activated carbon with a specific surface area of ??1 000-2 600 m /g is produced. This activation method has low yield, complicated process, and difficult material handling, so it has not been applied in industry. Therefore, the company disclosed a patent in 1978 for using 3 times the amount of potassium hydroxide to activate petroleum coke at 850°C. Japan's Kansal Coke and Chemicals Company directly activated petroleum coke with 3 times the amount of potassium hydroxide under reduced pressure conditions at 800°C to produce activated carbon with a specific surface >3000 square meters/g. 1.2 Gas Activation Method The gas activation method is a method in which the raw materials are carbonized and then activated with water vapor, carbon dioxide, air, flue gas, etc. at 600 to 1200°C. Its main processes are carbonization and activation. Carbonization is to heat the raw materials and remove the volatile components in advance to make carbonized materials suitable for the next step of activation. The carbonization process is divided into three reaction stages: a decomposition reaction below 400°C, an oxygen bond cleavage reaction between 400 and 700°C, and a deoxygenation reaction between 700 and 1000°C. The raw materials, whether they are chain molecular substances or aromatic molecular substances, undergo The above three reaction stages obtain carbonized products that condense benzene ring planar molecules to form a three-dimensional network structure. The adsorption capacity of carbonized materials is low. This is due to the fact that the carbon contains some hydrocarbons, the pore volume is small, and the pores are blocked. The activation stage usually consists of exposing the carbon to an oxidizing gas medium at approximately 900°C for treatment. In the first stage of activation, the adsorbate is removed and the blocked pores are opened; further activation expands the original pores and pathways; subsequently, micropores are formed due to the selective oxidation of the highly reactive parts of the carbonaceous structure. organize.
1.2.1 The carbon-containing raw materials of activated carbon prepared by microwave heating method are preheated at a temperature above 600°C, contacted with water vapor, carbon dioxide, oxygen-containing gas or gas generated by activation, and then directly heated by microwave to complete the activation. However, it is impossible to use microwaves to heat coal, petroleum, wood and other raw materials from which activated carbon can be produced to complete activation temperature using microwaves. For example, if raw materials such as coal, asphalt, and wood are irradiated with microwaves, the water will initially generate heat, and the temperature can reach about 100°C. Then, when the water evaporates, the heat will be very small. It may be impossible or take a long time to heat up to above 100°C. time. 1.2.2 Activated carbon microwave heating steam activation method The microwave heating steam activation method can significantly expand the internal surface area of ??activated carbon. The specific process is: first make the raw material into a certain particle size and specific gravity, add water vapor and stir thoroughly to make it evenly moist. According to the capillary phenomenon, there is free water in the micropores between the fibers of the plant cellulose raw material, thus making the raw material moist. Then, using these free water as electrolyte, using microwave radiation, the free water evaporates rapidly, generates vapor pressure, and is explosively pressed outward from the inside of the raw material. Such a drastic action expands the space between fibers, dries rapidly at the same time, and produces numerous cracks. The porous structure of the raw material becomes more significant, and the internal surface area further expands. Then continuous carbonization and carbonization, while passing steam, the steam continuously flows to the porous and cracked parts of the raw material, suppressing and eliminating the fixation of hydrocarbon until the carbonization is completed, and its porous structure can be well maintained. 1.3 The combined use of drug activation and gas activation. Gas activation and drug activation are sometimes used together. Further steam activation of carbon that has been activated by chemicals can sometimes produce products with special pore distribution and increase the number of pores over a wide range. When activated carbon is used to treat gases containing substances that can clog the pores of the carbon, for example, when granular activated carbon is used to adsorb and remove benzene from city gas, the pores of the activated carbon are blocked by dienes in the city gas and age rapidly. In order to produce activated carbon that can be used in this situation, this combined activation method has been used. The Benzolbon brand activated carbon produced by Legi Company is a representative example of this type of activated carbon. 1.4 Continuous carbonization activation method is an activated carbon production method that uses a relatively simple flow heating furnace to continuously perform carbonization and limited oxidation activation. It saves labor in operation and has good product quality. The characteristics of this method are: the activated carbon raw material with moisture content adjusted to 15% to 30% is continuously fed into the flow heating furnace, and an appropriate amount of air is blown from the bottom of the furnace to carbonize and limit oxidation activation in the furnace. From the front of the furnace to the time of loading into the furnace, only a small amount of fire is fed into the furnace, and an appropriate amount of air is blown from the lower part of the furnace to promote partial combustion of the raw materials in order to heat the raw materials themselves. The temperature in the furnace and the carbonization speed are adjusted by the amount of blown air and the amount of feed. In addition to being used for partial combustion and heating of raw materials, air blast is also used to fluidize particles during the carbonization process and for continuous activation reactions.
1.5 One-step fluidized bed method for manufacturing activated carbon. The one-step fluidized bed method for manufacturing activated carbon is a new coal-to-activated carbon technology developed in recent years. In this method, the raw materials are screened and directly sent to the fluidized bed, where they are carbonized and activated at the initial fluidization speed. The activation temperature and activation gas are evenly distributed, which can effectively activate the reaction raw materials. It can handle both powdery and granular raw materials. The production process is simple and has received great attention. The British National Coal Board uses this method to produce anthracite activated carbon and has been put into commercial operation. However, a single-stage fluidized bed is generally suitable for intermittent operation, and activation is uneven in continuous operation. Misi Tasaki's research shows that increasing the number of fluidized bed sections can enable continuous operation and intermittent operation to receive the same activated products. However, this process causes serious wear when manufacturing molded activated carbon. If fine particles of pulverized coal are mixed and activated with molding raw materials, the wear can be greatly reduced, and powdered and granular activated carbon can be produced at the same time. The process is simpler than adding inert fine particles, and the equipment production capacity is also large. 1.6 Rapid carbonization activation method Researchers believe that the rapid pyrolysis process can be used to produce cheap activated carbon. This activated carbon has good adsorption performance and does not need to be regenerated after use. It can be directly used as a gasification raw material. Existing experimental research results show that rapid pyrolysis can significantly increase the specific surface area of ??activated carbon. The introduction of high-temperature water vapor medium during the rapid pyrolysis process has a significant impact on the surface structure of activated carbon. Qiu Jieshan et al. used a dropped bed radiant furnace and potassium carbonate as a catalyst to explore the possibility of catalytic rapid carbonization of Huangxian lignite in water vapor medium to produce activated carbon. The results show that the void structure index and adsorption performance index of the activated carbon obtained in the experiment have reached or are close to the level of some commercially available activated carbon. 1.7 Lignite semi-coke briquette activation process Currently, the lignite semi-coke briquette activation process is more commonly used in lignite-based activated carbon production. This process first converts lignite into coal, then crushes the semi-coke to less than 0.1mm, adds asphalt binder to form briquettes, and then adds the briquettes into an activation furnace for activation. After screening or grinding, granular or powdery forms can be obtained. Activated carbon. Australia and Europe both use this process. 1.8 Other production methods Zhang Shuangquan and others discussed a new process for preparing coal-based activated carbon using an oxidative composite catalyst based on nitrate, and used this catalyst to unify catalysis and oxidation. The results show that barium nitrate has poor activity and is not suitable for use as a catalyst; potassium compounds are good catalysts for making activated carbon; co-catalyst phosphorus plays an important role in the development of the void structure of activated carbon; ash in the raw material hinders the effectiveness of the catalyst ; The experimental composite catalyst can increase the activation reaction speed by more than l times, obtain higher adsorption performance at the same combustion loss rate, or increase the activation yield at the same combustion loss rate, thereby reducing the production cost of activated carbon. Robert from Australia mixed 70-75 ml of 20% potassium hydroxide solution and 20 g of dry raw coal or pickled coal into a gel paste, and used a compression molding machine to press a coal section with a diameter of 6 mm. After drying, the diameter became 3 mm and hard. Then, it is distilled under nitrogen protection at 900°C for 16 hours, and the carbonized carbon is leached with dilute acid to recover the potassium salt to obtain the product. The surface area of ??raw coal activated carbon is l 340 m /g, and that of pickled coal activated carbon is l 500 m /g. A similar process has been developed in the United States, but the amount of potassium hydroxide is larger, and the surface area of ??the powdered activated carbon produced is as high as 3,000 square meters/g. However, in the United States, the raw material lignite and sub-bituminous coal are treated with dilute acid (such as phosphoric acid). The main purpose of the treatment is not to leach minerals, but to cross-link some components in the coal, and then directly briquette and activate it to make activated carbon. The output and activity are greatly improved. improve. 2 Development Trend of Activated Carbon Preparation 2.1 In terms of activated carbon raw materials, traditional activated carbon preparation mostly uses wood, charcoal, sawdust, coconut shells, fruit cores, etc. as raw materials. With the increasing awareness of social environmental protection, especially in the Yangtze River and Songhua River in 1998, The catastrophic floods in the Jiang and Nen river basins have made people realize the huge negative impact of ecological deterioration on national survival and sustainable development. The country quickly banned logging of natural forests. As a result, the sources of wood and charcoal have shrunk, that is, the raw materials for preparing activated carbon have been greatly restricted, and prices have also shown an upward trend. Under this situation, using practical new processes to replace biomass raw materials with mineral raw materials to prepare activated carbon has great prospects. and meaning. 2.2 Activated carbon preparation method Due to the wide range of activated carbon raw materials, the same material also differs due to different geographical environments and natural conditions. Sometimes the ingredients are very different. If the same preparation method is used, the quality of activated carbon and the maximum effect of the material Utilization is greatly limited. Therefore, in the future, the preparation of activated carbon will develop towards diversification, novelty and pertinence based on traditional preparation. With the new application fields of activated carbon
With the emergence and demand for new products with better performance, developing energy-saving and efficient new processes and new equipment, improving product quality, and reducing production costs have become important tasks for the activated carbon industry.