[Background and Overview][1][2]
Water-soluble ammonium polyphosphate is also called ammonium polyphosphate or polycondensed ammonium phosphate, referred to as APP. The general molecular formula is (NH4)(n+2)PnO(3n+1), where The content of nitrogen and phosphorus elements is high. According to the degree of polymerization, it can be divided into low polymerization, medium polymerization and high polymerization. The lower the degree of polymerization, the higher the water solubility, and conversely, the lower the water solubility. When n>20, it is a poorly water-soluble APP, and when n<20, it is a highly water-soluble APP. Because of its different water solubility, ammonium polyphosphate is also widely used. Water-soluble ammonium polyphosphate, due to its relatively low melting point and sintering point, can melt quickly at lower temperatures, penetrate into the pores of combustibles, isolate the combustibles from the air, and further polymerize and then decompose to form a film. It quickly covers all levels of combustible materials to extinguish the flame, thus achieving the purpose of extinguishing the fire. Therefore, it can be used to make dry powder fire extinguishing agents, which can be used to extinguish fires on paper, fabric, wood and other materials. In addition, due to its stable chemical properties, pH close to neutral, and good solubility; it also contains high nitrogen and phosphorus elements required by plants, and has a strong chelating effect on metal ions. It can also be used to make liquid compound fertilizers and gradually Hydrolyzed, it is well absorbed and utilized by plants and can be used as a slow-soluble, long-acting fertilizer.
Overseas research on water-soluble ammonium polyphosphate began relatively early. In the early 1970s, the American TVA Company ammoniated wet phosphoric acid with a P2O5 mass fraction of 54% in a tubular reactor. The product contained water-soluble ammonium polyphosphate. Molten ammonium polyphosphate. In the late 1970s, Japan, the former Soviet Union and other countries began to mass-produce water-soluble ammonium polyphosphate and apply it in agriculture. In the late 1980s, India’s RCE Company began to develop a granular water-soluble ammonium polyphosphate fertilizer process. In China, research in this area is relatively late. In the 1980s, research on the synthesis process and application of water-soluble ammonium polyphosphate began. There are few manufacturers selling water-soluble ammonium polyphosphate on the market, the price is relatively expensive and the product performance is not very stable. Further research is needed on the purification and refining of water-soluble ammonium polyphosphate.
[Production process][1 ]
At present, the synthesis methods of water-soluble ammonium polyphosphate that are commonly used at home and abroad mainly include ammonia gas polymerization and urea condensation. Among them, the ammonia gas polymerization method includes: phosphoric acid ammonialation method, polyphosphoric acid amination method and ammonium phosphate-phosphorus pentoxide-ammonia gas polymerization method; urea condensation method includes: phosphate urea condensation method, ammonium phosphate urea condensation method and phosphoric acid Urea method.
1. Ammonia polymerization method
1) Phosphoric acid ammoniation method: The phosphoric acid ammonia method uses phosphoric acid as raw material and mixes it with anhydrous ammonia in a certain proportion. After polymerization, it is solidified and cooled to obtain the product. Wet phosphoric acid and anhydrous ammonia are used as raw materials, heated to 300°C in a tubular reactor, and fully contacted for 5 to 60 seconds. The obtained product ammonium polyphosphate has a mass fraction of 60% to 90% and a high solubility. . This reaction uses an elongated tubular reactor to increase the degree of ammoniation. Local cooling of the elongated tubular reactor can produce a non-sticky and brittle solid product, and unreacted ammonia can be recycled. The water-soluble ammonium polyphosphate produced by the phosphoric ammonification method can be used to make dry powder fire extinguishing agents, liquid fertilizers and other preparations, etc., and has the application prospect of realizing low-cost large-scale continuous production. However, due to the high transportation conditions of the product, it is difficult to obtain The product will dissolve a small amount of ammonia and insoluble ammonium polyphosphate, and the polymerization degree of the product is unstable. If you want to further expand the application, you must continue to improve the process in purification and concentration. In addition, China’s wet phosphoric acid technology still has shortcomings. The products produced contain high impurities. The impurities can easily form precipitates during the reaction process or cause scaling on the surface of the container, making it difficult for the reactants to polymerize, which is not conducive to the progress of the reaction. Therefore, there are still difficulties in implementing the method of producing environmentally friendly plasticizer 168 water-soluble ammonium polyphosphate using wet phosphoric acid ammonialation in China.
2) Polyphosphoric acid amination method: Polyphosphoric acid generally contains 75% to 85% P2O5. Polyphosphoric acid and gaseous ammonia are added in a certain proportion, and the polymerization reaction is carried out under high temperature and high pressure to prepare ammonium polyphosphate products. Polyphosphoric acid and anhydrous ammonia enter the reactor through pipelines respectively, stir to fully mix the polyphosphoric acid and anhydrous ammonia, and carry out polymerization reaction. The product is solidified, cooled, and pulverized to obtain the product. The obtained product has a polymerization degree of less than 10 and can be used to make fire extinguishers. agents and liquid fertilizers. During the reaction process, the composition of the product is affected by temperature, pressure, reaction time and stirring speed. Due to the heat generated by the ammoniation of polyphosphoric acid, a cooling tube needs to be installed inside the reactor for cooling, but the temperature cannot be too low to prevent the product from sticking to the cooling on the tube wall. The partial pressure of ammonia in the reactor increases as the stirring speed increases. The partial pressure of ammonia increases, which is beneficial to the reaction, and the degree of ammoniation also increases accordingly. The process was then optimized again, using polyphosphoric acid as the raw material, and other conditions being the same. The molten product was left to cool, dissolved, filtered, and dried to obtain the finished product. The filtrate by-product can be used as liquid fertilizer.
3) Ammonium phosphate-phosphorus pentoxide-ammonia polymerization method: This method uses ammonium phosphate and phosphorus pentoxide to mix and polymerize in an ammonia atmosphere. The principle is:
In an ammonia environment, ammonium phosphate and phosphorus pentoxide are mixed, and a single reaction is used.By changing the reactor and appropriately changing the reaction temperature, products with different average degrees of polymerization can be obtained. The liquid ammonia is vaporized in the gas tank and passed into a screw extruder with an aspect ratio of 20 to 100 at a pressure of 0.05 to 1.5 MPa and a temperature of 0 to 350°C. Add phosphorus pentoxide and diammonium hydrogen phosphate with a mass ratio of 0.1 to 10 from the side feeding port of the reactor. Polymerize for 0.5 to 60 minutes at 25 to ℃ and a rotation speed of 5 to 600 r/min. The ammonium polyphosphate product is obtained through a gas-solid separator. The ammonium polyphosphate produced by this method contains water-soluble ammonium polyphosphate and some insoluble ammonium polyphosphate. This method has a short process route and is relatively simple to operate. Using phosphorus pentoxide as the condensing agent, there is no large amount of waste gas discharged, and the product quality is better. However, phosphorus pentoxide is highly active and the reaction is difficult to control. In addition,
Due to the presence of ammonia, the reaction vessel is also required to be a closed system and resistant to high temperature and pressure, which consumes a lot of energy and costs. And a stirring device needs to be installed to prevent the production of viscous intermediate products during the reaction, resulting in low product yield. Therefore, the required equipment costs are high and it is not suitable for large-scale production. In the ammonia gas polymerization method, ammonia gas participates in the condensation reaction, which requires the reaction system to be sealed. It has high requirements for reaction conditions and equipment, high energy consumption, and low safety. It requires a large investment for continuous large-scale production and is not suitable for large-scale production. Production of water-soluble ammonium polyphosphate.
2. Urea condensation method
1) Phosphoric acid urea condensation method: phosphoric acid and urea are mixed according to a certain material ratio, heated, foamed, polymerized, cooled and solidified to obtain a white dry finished product. The reaction principle is:
Using chemically pure phosphoric acid and urea with a mass fraction of 85% as raw materials, ammonium polyphosphate is prepared through polymerization reaction. During the reaction process, as the reaction time increases and the reaction temperature increases, the degree of polymerization increases; as the amount ratio of reactants increases, the degree of polymerization increases slowly. When the amount ratio of reactants [n (urea): When n (phosphoric acid)] is greater than 2.2, the degree of polymerization of the product decreases and the product is difficult to solidify, affecting the yield. It was finally determined that under the conditions of a mass ratio of urea and phosphoric acid of 2.0 and a reaction temperature of 130°C, a product with an average degree of polymerization of about 9 was obtained after reacting for 14 to 16 minutes. The melting point of the product was 141°C and the sintering point was 183°C. Can be used to make dry powder fire extinguishing agents.
2) Ammonium phosphate urea condensation method: Mix ammonium phosphate and urea in a certain proportion, polymerize at high temperature, cool and pulverize to obtain ammonium polyphosphate product. The reaction principle is:
When the ratio of ammonium phosphate to urea is higher than 1.2:1, the main product is ammonium pyrophosphate or ammonium tripolyphosphate. To obtain water-soluble ammonium polyphosphate with a polymerization degree greater than 6, the material ratio of ammonium phosphate and urea is (1~1.2):1, and the reaction is carried out under normal pressure or reduced pressure at a temperature of 145~160°C. , which provides a theoretical basis for the production of water-soluble ammonium polyphosphate.
[Application][3]
1. Use as fertilizer
Ammonium polyphosphate contains two elements, nitrogen and phosphorus, needed for crop growth. Its N mass fraction is 14.6% ~ 22.8%, and its P2O5 mass fraction is 57.7% ~ 73.2%. It is a high-concentration nitrogen- and phosphorus-containing fertilizer. . Due to its good water solubility and easy absorption and utilization of nutrients by crops, low-polymer ammonium polyphosphate is often made into agricultural solid fertilizers and liquid fertilizers and used as high-concentration fertilizers. Ammonium polyphosphate cannot be directly absorbed by plants. Instead, it is slowly hydrolyzed into orthophosphate in the soil before it can be absorbed by plants. The hydrolysis rate increases with the increase of temperature and time. Common ammonium polyphosphate fertilizers abroad are liquid concentrate fertilizers, such as brands CL-10-34-0, CL-8-24-0, etc. In the ammonium polyphosphate production process, the molten product is cooled and filtered by adding water before solidification. The filtrate with a low degree of polymerization can be used as a liquid fertilizer. It has high nitrogen and phosphorus content, nearly neutral pH, low salting-out temperature, and is resistant to some metal ions. It has the characteristics of chelating 3m and other characteristics, and can be used as a base fertilizer to add some trace elements to improve fertilizer efficiency. Research has found that when ammonium polyphosphate liquid fertilizer is applied to the soil surface, the available phosphorus migrates to the deeper layers of the soil after a period of time, with the maximum depth reaching 15cm. By comparing the wheat fertilizer efficiency tests of heavy calcium (TSP), diammonium phosphate (DAP), nitric acid phosphate (NP), solid ammonium polyphosphate and liquid ammonium polyphosphate, it was shown that the yield of wheat using solid ammonium polyphosphate was higher than that of diphosphate. Ammonium and nitrate phosphate fertilizers. R. Holloway et al. [15] found in a grain fertilizer efficiency test that liquid ammonium polyphosphate was superior to other granular solid fertilizers. In the first year, the former increased grain yield by 14% compared to the latter. In the second year, the residual fertilizer efficiency increased grain yield compared with the latter. 15%.
2. Used as fire extinguishing agent and flame retardant
The decomposition temperature of ammonium polyphosphate is greater than 250°C and has high thermal stability, so it is often used as a fire extinguishing agent and flame retardant. It can be formulated into solution or dry powder fire extinguishing agent, and can also be used in intumescent fire retardant coatings, intumescent flame retardant systems, etc. In the 1960s and 1970s, countries such as the United States and Canada used liquid concentrated fertilizers to fight forest fires. Chemonics Industrial Company formulates forest fire extinguishing agents Fir-Trol-931, Fir-Trol-934 and Fir-Trol-936 based on liquid concentrated fertilizer. Liquid concentrated fertilizer has a low freezing point, strong adhesion to plants, wood and buildings, good surface coverage on the ground, low dosage, and is environmentally friendly. Ammonium polyphosphate with a degree of polymerization greater than 50 is used as a dry powder fire extinguishing agent, and its fire extinguishing efficiency and coverage capabilities are superior to general dry powder fire extinguishing agents. However, ammonium polyphosphate has not been promoted as a fire extinguishing agent because of its high cost. In addition, ammonium polyphosphate also has certain applications in cellulose matrix materials, copolymers, and ion conductivity.
[References]
[1] Xu Baoming, Xu Sisi, Tang Qiang, et al. Progress in the synthesis process of water-soluble ammonium polyphosphate [J]. Inorganic Salt Industry, 2017, 49(4): 5-8.
[2] Lan Guozhi, Gu Lili, Ming Dazeng, et al. Latest research progress in water-soluble ammonium polyphosphate synthesis technology [J]. Chemical Science and Technology, 2016 (2): 64-66.
[3] Jiao Liqiang, Tang Jianwei, Hua Quanxian, et al. Research and development, production and application of ammonium polyphosphate [J]. Inorganic Salt Industry, 2009, 41(4): 4-7.
As a dry powder fire extinguishing agent, ammonium phosphate has better fire extinguishing efficiency and coverage than general dry powder fire extinguishing agents. However, ammonium polyphosphate has not been promoted as a fire extinguishing agent because of its high cost. In addition, ammonium polyphosphate also has certain applications in cellulose matrix materials, copolymers, and ion conductivity.
[References]
[1] Xu Baoming, Xu Sisi, Tang Qiang, et al. Progress in the synthesis process of water-soluble ammonium polyphosphate [J]. Inorganic Salt Industry, 2017, 49(4): 5-8.
[2] Lan Guozhi, Gu Lili, Ming Dazeng, et al. Latest research progress in water-soluble ammonium polyphosphate synthesis technology [J]. Chemical Science and Technology, 2016 (2): 64-66.
[3] Jiao Liqiang, Tang Jianwei, Hua Quanxian, et al. Research and development, production and application of ammonium polyphosphate [J]. Inorganic Salt Industry, 2009, 41(4): 4-7.
