Background and overview[1][2]
Sodium salt is a major branch of my country’s chemical industry. Industrial grade disodium and trisodium phosphate are one of the important product series of the phosphate industry. Due to their special properties, they are widely used in modern chemicals, medicine, food, Agriculture and animal husbandry, petroleum, papermaking, detergents, ceramics and other fields. Trisodium phosphate is also known as sodium phosphate. Colorless crystals, easily weathered. When heated to 100°C, it loses crystal water and becomes anhydrous. It is soluble in water and almost completely decomposes into disodium hydrogen phosphate and sodium hydroxide in the aqueous solution. The solution shows a strong alkaline reaction. Used as water softener, sugar juice purifier, metal rust inhibitor, boiler cleaner and drug culture agent such as penicillin.
Prepared by adding caustic soda to disodium hydrogen phosphate solution. Due to the wide range of uses of sodium phosphate products and the large market demand, thermal phosphoric acid, that is, yellow phosphorus, is currently mainly used to produce industrial-grade 85% acid plus soda ash and the neutralization method. Dozens of production companies in my country now all use this technology. Produce this product. This technical production process uses yellow phosphorothermal phosphoric acid as the main raw material, which is seriously polluted during the neutralization process and consumes astonishing energy. It is a high-energy-consuming, high-pollution industry, and the production cost is also very high.
Quality indicators[3]
Apply[1][4]
Sodium phosphate is commonly used as water softener and boiler cleaner in textile, printing and dyeing, papermaking, power generation, chemical industry and other industries. It is also used as metal rust remover, sugar juice purifier and coagulant of rubber latex. Phosphate has a very wide range of application fields. As phosphate fertilizer, it is one of its main applications. Other fields include phosphate molecular sieves, electronics, materials, biology, etc. Lomon titanium dioxide R996 trisodium phosphate is a very important phosphate. Industrial grade trisodium phosphate is used as water softener and detergent, metal descaler, boiler anti-scaling agent in chemical, textile, printing and dyeing, papermaking, power generation and other industries. It has the advantages of easy use and low price.
It can precipitate calcium, magnesium, iron and other metal ions in the water into corresponding insoluble phosphates, thereby removing them from the water. Moreover, excess trisodium phosphate can react with the generated boiler scale, causing it to gradually become soft and fall off. It can be used as a metal descaling and cleaning agent because trisodium phosphate can enhance the wetting ability of water in water and has a certain penetration and emulsification effect, so it can effectively remove dirt on metal surfaces. In addition, trisodium phosphate can also be used as an acid-base buffer, a mercerizing enhancer, a coagulant, and a printing and dyeing fixing agent.
Solid anhydrous trisodium phosphate is often used in containment spray systems. Because it is a strong base and weak acid salt, it has strong alkalinity, high solubility in water, stable chemical properties, and can be stored for a long time. It is often used in the containment spray system to replace sodium hydroxide to adjust the spray liquid. The pH value can effectively remove the iodine vapor released from the leaked cooling water into the containment vessel, thus ensuring the safety of personnel themselves. Food-grade trisodium phosphate can improve the coagulation and water-holding capacity of food, because its own alkalinity can increase the pH and ionic strength of food, and can also increase the complex metal ions in food.
Preparation[4][5][6][7]
Method 1: Thermal phosphoric acid method: neutralization reaction of hot phosphoric acid and caustic soda, the neutralized liquid is cooled, crystallized, centrifuged and dried to obtain the product. However, the production process consumes high energy and causes great pollution, and this method is gradually restricted by national policies.
Method 2: Wet phosphoric acid method: use wet phosphoric acid as raw material, neutralize it with soda ash and caustic soda respectively, and use the batch method to cool and crystallize the obtained trisodium phosphate solution. After centrifugation, use air flow to dry it. product. The entire process includes three major processes.
The first step is neutralization, that is, the reaction between wet phosphoric acid and soda ash to generate disodium hydrogen phosphate. In this process, attention should be paid to controlling the amount of soda ash added so that the pH value at the end of the reaction reaches 8.4-8.6, thereby ensuring that the product is Do not exceed the amount of disodium hydrogen phosphate and soda ash, because the excess soda ash is difficult to remove in subsequent steps; the second step is neutralization, that is, the reaction between disodium hydrogen phosphate and sodium hydroxide to generate trisodium phosphate. Pay attention to controlling the amount of sodium hydroxide. Add the amount so that the end point of the reaction reaches a pH value between 11.5-12.5; the third step is cooling crystallization. Before cooling crystallization, in order to reduce the energy consumption of the crystallization process in industry, evaporation and concentration are required to concentrate it to a relative density of 1.24- 1.26, and then carry out cooling crystallization, crystal filtration, and low-temperature drying to obtain the product.
Trisodium phosphate dodecahydrate and trisodium phosphate anhydrous can be obtained by controlling different drying conditions. There are studies using wet phosphoric acid as the raw material and complex R (simply expressed as M4R) as the iron remover. The two react under certain conditions to generate an insoluble iron-containing complex precipitate, which is filtered and the filtrate is used After neutralization with alkali, filter again. The filtrate is concentrated and crystallized to obtain the product. The iron-containing complex is treated with caustic soda and regenerated into the complex Na4R, which can be recycled as an iron remover. The main chemical reactions are as follows:
The test process flow is shown in the figure:
Method 3: Preparation of a sodium phosphate saltThe method uses sodium pyrophosphate as raw material, mixes it with wet phosphoric acid and undergoes a hydrolysis reaction to obtain: sodium orthophosphate, then adds purified wet phosphoric acid, and adjusts the pH value to obtain disodium phosphate and/or trisodium phosphate, and then undergoes a polymerization reaction. Sodium tripolyphosphate is obtained. Including the following steps:
1) Preparation of sodium orthophosphate: Thoroughly mix crude sodium pyrophosphate, water and wet phosphoric acid, add impurity removing agent and decolorizing agent, carry out hydrolysis reaction at a temperature of 130-140°C, and let it stand after the reaction , when hydrolysis is complete, sodium pyrophosphate reacts completely to form sodium orthophosphate;
2) Preparation of disodium phosphate and trisodium phosphate: Step 1) The obtained sodium orthophosphate salt solution is filtered to remove impurities, and purified wet phosphoric acid is added for further hydrolysis. When the pH is adjusted to 7.5, the complete reaction generates diphosphate Sodium, when the pH is adjusted to 13, will react completely to form trisodium phosphate. Just adjust the pH as needed, and then cool it to less than 18°C to obtain the corresponding Na2PO4·12H2O and/or Na3PO4·12H2O crystals;
Method 4: A method for producing sodium phosphate salt from glyphosate by-product disodium hydrogen phosphate. This method for producing phosphoric acid detergent sodium salt from glyphosate by-product disodium hydrogen phosphate includes the following preparation steps: (1) heating disodium hydrogen phosphate until it melts; (2) adding sodium hydrogen phosphate to the molten disodium hydrogen phosphate Add an oxidant to form a mixture. The mass ratio of disodium hydrogen phosphate to the oxidant is 1:0.005?0.03; (3) Add activated carbon to the mixture. The mass ratio of the mixture to activated carbon is 1000:1?3. Filter to obtain a sodium phosphate solution; (4) Adjust the pH value of the sodium phosphate solution to 3.5 to 13.5. This method can effectively remove organic matter in the by-product disodium hydrogen phosphate and convert disodium hydrogen phosphate into sodium phosphate salt.
Main reference materials
[1] Encyclopedia of Chinese Adult Education·Chemistry·Chemical Engineering
[2] CN201510177885.7 . Preparation method of sodium phosphate salt
[3] Chemical additives
[4] Research on the crystallization process of trisodium phosphate
[5]CN201510177885.7. A preparation method of sodium phosphate
[6] CN201710587631.1. A method for producing sodium phosphate from glyphosate by-product disodium hydrogen phosphate
[7] Liao Kunsheng, Xian Lihua, Luo Biao. Research on a new process for producing trisodium phosphate from wet phosphoric acid [J]. Phosphate Industry, 2002 (4): 19-23.
