Background and overview[1-2]
Sodium dihydrogen phosphate (NaH2PO4·2H2O) is also called monosodium phosphate and monobasic sodium phosphate. It is colorless crystal or white crystalline powder; odorless and easily soluble in water. Its aqueous solution is acidic and almost insoluble in ethanol. It loses crystal water when heated and can be decomposed into acidic sodium pyrophosphate (Na3H 2P2O7). It is often used in the fermentation industry to adjust pH. In food processing, it is often used in conjunction with disodium hydrogen phosphate as a food quality improver. Such as improving the thermal stability of dairy products, making pH regulators and binding agents for fish products, etc.
ADI: 0～70mg/kg (based on total phosphorus). Sodium dihydrogen phosphate is mainly produced by neutralizing phosphoric acid with caustic soda (or soda ash). If sodium chloride can be used to replace caustic soda or soda ash to produce this product, the production cost can be greatly reduced. However, under normal conditions, the metathesis reaction between sodium chloride and phosphoric acid has a standard free energy of formation greater than zero, so the reaction cannot proceed spontaneously. Therefore, it is more feasible to consider removing HCl from the system.
In recent years, the use of organic solvent extraction technology has become more and more widespread and mature, and it is increasingly used in phosphate production. There are studies on using this technology to produce sodium dihydrogen phosphate, and a water-soluble It is an extractant with low toxicity, good extraction selectivity for hydrochloric acid, and high extraction efficiency. It moves H + and Cl – in phosphoric acid and sodium chloride solutions out of the water phase, while Na + and H2 PO – 4 remain in the water phase. , and then through the crystallization process to obtain the product NaH2PO4·2H2O.
Purpose[4-6]
Sodium dihydrogen phosphate has a wide range of uses. It can be used as a raw material for manufacturing sodium hexametaphosphate and sodium pyrophosphate; it can also be used for tanning and boiler water treatment; as a quality improver and baking powder, it is used in the food industry and fermentation. It is used as a buffering agent and raw material for baking powder in industry; it is also used as a feed additive, detergent and dyeing auxiliary; it can also be used as a buffering agent in the food industry and fermentation industry, as a raw material for baking powder, and as a paste for bread and sauce. It can be used as ingredients and aging agent, powdered sour agent, as a quality improver for evaporated milk; it can also be used as a stabilizer and binder for cheese and other dairy products, meat and fish products, a buffer for baking powder, and mixed salt for pickling, etc. Examples of its application are as follows:
1) It is used to cultivate low-concentration aquatic plants enriched in micro-polluted water bodies, and belongs to the field of sewage treatment. Cultivate a batch of water lilies in a pollution-free pond. Remove the outer leaves of Alba japonica until 3 to 4 leaves remain. Sterilize them and move them into a 5L glass jar filled with deionized water at room temperature. Use a 40W fluorescent lamp. Light; add sodium dihydrogen phosphate, agar, glucose, sodium chloride and magnesium sulfate to the deionized water in the glass jar; when the water lilies grow new leaves, pull out the new leaves and move them into another 5L In a glass jar filled with deionized water, at room temperature, illuminate it with a 40w fluorescent lamp; after a certain period of illumination, move it to the previous glass jar and add a certain amount of sodium dihydrogen phosphate, agar, glucose, sodium chloride and Magnesium sulfate, after 30 days of cultivation, the phosphorus enrichment and concentration factor of water lilies can be obtained. The sewage purification ability of the present invention can be used to control eutrophication of water bodies.
2) For preparing a halloysite-loaded silver phosphate photocatalyst, the specific steps are as follows: add halloysite to a nitric acid solution to obtain acid-treated halloysite, add 4~8g of acid-treated halloysite Place the stone in a vacuum filter bottle, mix it with the silver nitrate ethanol solution under vacuum, let the silver nitrate fully enter the halloysite tube, continue stirring for 2 to 3 hours, separate the solid and liquid, and dry it under vacuum at 70 to 80°C; Add the dried product to 50 mL of sodium dihydrogen phosphate solution with a concentration of 0.5~1.5 mol/L, stir for 4~5 hours, separate the solid and liquid, wash, and dry at 100~105°C to obtain a halloysite-loaded phosphoric acid. Silver photocatalyst. The advantages of the present invention are: emptying the air and water vapor in the halloysite pipe to allow silver nitrate to enter the pipe; removing the aluminum oxide on the inner wall of the halloysite to increase light transmittance and pore size; and obtaining The silver phosphate particles are present inside the halloysite tube to avoid agglomeration and falling off.
3) Preparing sodium dihydrogen phosphate to co-produce a special compound fertilizer for cowpeas. The method includes the following three steps: preparing an intermediate by reaction, preparing sodium dihydrogen phosphate, and preparing a special compound fertilizer for cowpeas. The use of this method to prepare sodium dihydrogen phosphate not only has the advantages of low energy consumption, simple preparation process lines, and low equipment requirements, but also does not eliminate three wastes in the entire preparation process, effectively avoiding environmental pollution, and by preparing dihydrogen phosphate The mother liquor produced during the sodium process is controlled and adjusted in terms of temperature and nutrient addition to prepare a special compound fertilizer suitable for the growth of cowpeas. The use of this compound fertilizer can also increase the yield of cowpeas, improve the economic value, and avoid soil pollution by fertilizer residues. Raw materials are fully utilized and costs are reduced.
Preparation method[7-8]
Method 1: Dissolve the raw material sodium chloride in purified phosphoric acid, and filter to remove insoluble impurities; stir and extract the filtered raw material liquid with the extraction agent; let it stand after the reaction is completed, and separate the aqueous phase and organic phase; water The phase is concentrated and crystallized to obtain the product sodium dihydrogen phosphate dihydrate; after crystallization and separation,A part of the mother liquor will be used for the next batching, and a part of it will be heated and concentrated together with the extracted aqueous phase in a vacuum for crystallization; the organic phase will be back-extracted with an appropriate amount of ammonia solution, and the organic phase obtained by phase separation can be recycled after being washed and processed again. The aqueous phase obtained by extraction and back-extraction is cooled and crystallized to obtain the by-product nitrogen and phosphorus compound fertilizer.
Method 2: The method of preparing sodium dihydrogen phosphate using wet phosphoric acid includes the following steps:
(1) Impurity removal of wet phosphoric acid: Use centrifugation or press filtration to remove solid impurities contained in wet phosphoric acid to obtain phosphoric acid for later use;
(2) Synthesis reaction of intermediate: Put the phosphoric acid obtained in step (1) into the intermediate synthesis tank, adjust the phosphoric acid concentration, heat to 40℃-90℃, add carbonamide and phosphoric acid under stirring conditions Carry out the synthesis reaction. The amount of carbonamide added is determined according to the molar ratio of carbonamide to phosphoric acid: (0.9-1.05): 1. The reaction time is 40min-120min;
(3) Cooling crystallization to obtain the intermediate: After the synthesis reaction is completed, put the obtained intermediate slurry into a cooling crystallization tank and cool it to a temperature of ≤40°C, centrifuge, and retain the filter cake, which is the intermediate. Put it into the intermediate storage bin for later use;
(4) Preparation of sodium dihydrogen phosphate: Send the intermediate into the synthesis tank, add a measured amount of sodium hydroxide for mixing reaction, the molar ratio of the intermediate to sodium hydroxide is (1-1.2): 1 , control the addition rate of sodium hydroxide to adjust the temperature in the synthesis tank within the range of 40°C-90°C, stir the reaction for 20min-100min; after the reaction is completed, cool the sodium dihydrogen phosphate slurry to a temperature ≤ 40°C, and cool and crystallize , after the crystals are separated, put them into a centrifuge for centrifugation. The filtrate is a slurry containing carbon amide. The carbon amide is recovered and returned to the intermediate synthesis tank in step (2) for the production of intermediates. The filter cake is dihydrogen phosphate. Sodium products, dried and packaged.
Main reference materials
[1] Health Dictionary
Research on the extraction method of sodium dihydrogen phosphate from [hydroxybutyl acrylate 2]
[4] GB 34456-2017 “Feed Additive Sodium Dihydrogen Phosphate” National Standard
[5] Practical Fine Chemical Dictionary
[6] CN201410303089.9 A method for cultivating aquatic plants enriched in low-concentration phosphorus in slightly polluted water bodies
[7] CN201410479097.9 A method of preparing special compound fertilizer for cowpea co-production with sodium dihydrogen phosphate
[8] Research on the preparation of sodium dihydrogen phosphate by extraction method
[9] CN201410035054.1 A method of preparing sodium dihydrogen phosphate using wet phosphoric acid
