Method for producing disodium hydrogen phosphate dodecahydrate from industrial monoammonium phosphate mother liquor

Abstract

The invention discloses a method for producing disodium hydrogen phosphate dodecahydrate from industrial monoammonium phosphate mother liquor, which comprises the following steps of: A, reacting the industrial monoammonium phosphate mother liquor and monocalcium phosphate in a primary reactor to obtain reaction slurry; b, the reaction slurry is subjected to filter pressing for solid-liquid separation, ammonium phosphate clear liquid is obtained, and a filter cake is used for producing powdery ammonium phosphate; c, slowly adding solid sodium hydroxide into the ammonium phosphate clear liquid to obtain disodium hydrogen phosphate slurry; and D, carrying out filter pressing on the reaction slurry to obtain a disodium hydrogen phosphate clear solution, and carrying out concentration, water replenishing crystallization, centrifugation and drying to obtain a disodium hydrogen phosphate dodecahydrate finished product and a mother solution. According to the method, the purity of the obtained disodium hydrogen phosphate dodecahydrate is 97% or above, and the defects in the prior art are overcome.

Description

Technical Field

[0001] This invention relates to the field of chemical technology, specifically to a method for producing disodium hydrogen phosphate dodecahydrate from industrial monoammonium phosphate mother liquor. Background Technology

[0002] During the production of industrial monoammonium phosphate (MAP), a large amount of mother liquor is generated. Some companies reuse this mother liquor in their MAP systems, leading to the enrichment of sulfur and fluorine in the mother liquor, which in turn reduces the nutrient content of industrial MAP. The main components of the mother liquor are MAP, ammonium sulfate, and ammonium fluoride. MAP mother liquor is primarily used to produce low-nutrient fertilizer-grade powdered and granular MAP, thus reducing the value of phosphorus.

[0003] Patent application number 201710492674.1 discloses a method and system for producing potassium dihydrogen phosphate from industrial-grade monoammonium phosphate mother liquor. The specific steps are as follows: a) Reacting wet-process phosphoric acid with phosphate rock slurry, followed by sedimentation and separation to obtain desulfurized phosphoric acid. b) Using the desulfurized phosphoric acid obtained in step a to produce industrial ammonium phosphate, collecting the industrial ammonium mother liquor. c) Adding the desulfurized phosphoric acid obtained in step a to the industrial ammonium mother liquor obtained in step b for a neutralization reaction at a temperature of 60-70℃, adjusting the pH to 3.8-4.0, and obtaining a clear liquid after aging, sedimentation, and filtration. The clear liquid is then concentrated, crystallized, and centrifuged to obtain monoammonium phosphate. d) Dissolving the monoammonium phosphate obtained in step c and reacting it with potassium hydroxide solution for a double decomposition reaction at a temperature of 110-115℃, followed by crystallization and centrifugation to obtain potassium dihydrogen phosphate and a primary mother liquor. e) Heating the primary mother liquor at a temperature of 110-115℃, followed by crystallization and centrifugation to obtain potassium dihydrogen phosphate and a secondary mother liquor. f. Dry the potassium dihydrogen phosphate obtained in steps d and e to obtain the product. This method mainly produces potassium dihydrogen phosphate, primarily composed of phosphoric acid, and impurities in the mother liquor can combine with potassium, affecting the product's nutrient content.

[0004] Disodium hydrogen phosphate dodecahydrate is a water-soluble inorganic compound that is weakly alkaline and has a wide range of applications in food, industry, and medicine. Currently, the main method for preparing disodium hydrogen phosphate dodecahydrate is the neutralization method, which utilizes a thermal process to neutralize phosphoric acid with sodium hydroxide or sodium carbonate, followed by crystallization to obtain disodium hydrogen phosphate. However, this method has high raw material costs. Summary of the Invention

[0005] The purpose of this invention is to address the aforementioned problems by providing a method for producing disodium hydrogen phosphate dodecahydrate from industrial monoammonium phosphate mother liquor. This invention uses industrial monoammonium phosphate mother liquor as the main raw material, then adds calcium dihydrogen phosphate for defluorination, followed by the addition of sodium hydroxide to produce disodium hydrogen phosphate. This improves the purity and phosphorus value of the product, significantly reduces preparation costs, and overcomes the shortcomings of existing technologies.

[0006] To achieve the above-mentioned objectives, the technical solution adopted by this invention is as follows: A method for producing disodium hydrogen phosphate dodecahydrate from industrial monoammonium phosphate mother liquor includes the following steps: A. React industrial monoammonium phosphate mother liquor and calcium dihydrogen phosphate in a preliminary reactor to obtain a reaction slurry; B. The reaction slurry obtained in step A is filtered to separate the solid and liquid components, resulting in a clear ammonium phosphate solution and a filter cake. The filter cake is used to produce compound fertilizer, such as powdered ammonium phosphate. C. Slowly add solid sodium hydroxide or sodium carbonate to the ammonium phosphate solution obtained in step B to obtain disodium hydrogen phosphate slurry. D. The disodium hydrogen phosphate slurry obtained in step C is filtered to remove impurities, resulting in a clear disodium hydrogen phosphate solution. The clear disodium hydrogen phosphate solution is then concentrated, replenished with water for crystallization, centrifuged, and dried to obtain the finished product of disodium hydrogen phosphate dodecahydrate and the mother liquor.

[0007] In step A, the reaction temperature is controlled at 50-60℃ (specifically, it can be 50℃, 51℃, 52℃, 53℃, 54℃, 55℃, 56℃, 57℃, 58℃, 59℃, 60℃, etc.), and calcium dihydrogen phosphate is added until the pH is 3.5-4 (specifically, it can be 3.5, 3.6, 3.7, 3.8, 3.9, 4.0, etc.). In step B, the filter cake is sent to produce low-nutrient powdered ammonium phosphate and granular ammonium phosphate.

[0008] In step C, the added solid sodium hydroxide is industrial grade. The filtrate is reacted with sodium hydroxide to produce disodium hydrogen phosphate. The chemical reaction equation is as follows: 2NaOH+NH4H2PO4+11H2O=Na2HPO4∙12H2O+NH 3。

[0009] In a preferred embodiment of this application, in step C of a method for producing disodium hydrogen phosphate dodecahydrate from industrial monoammonium phosphate mother liquor, the amount of sodium hydroxide or sodium carbonate added is preferably 4:1 molar ratio of Na to P2O5.

[0010] In step D, the disodium hydrogen phosphate slurry (reaction slurry) is a white precipitate. Impurities are removed by pressure filtration to obtain a clear disodium hydrogen phosphate solution and a filter cake. The filter cake is sent to low-nutrient powdered ammonium phosphate and granular ammonium phosphate. The clear disodium hydrogen phosphate solution is heated and concentrated to a specific gravity of 1.7-1.8. During concentration, ammonia gas is released, which is recycled into the phosphoric acid neutralization system. Some water is added to the concentrated material until the slurry specific gravity reaches 1.4-1.6 (specifically 1.4, 1.5, 1.6, etc.), and the mixture is cooled in a reactor to 25-30℃ (specifically 25℃, 26℃, 27℃, 28℃, 29℃, 30℃, etc.). It then enters the crystallization system, where water is added and the mixture is dried to obtain the finished disodium hydrogen phosphate dodecahydrate.

[0011] In a preferred embodiment of this application, in step D of a method for producing disodium hydrogen phosphate dodecahydrate from industrial monoammonium phosphate mother liquor, the filtrate obtained by centrifugation is returned to the preliminary reactor of step A for recycling.

[0012] This invention also protects disodium hydrogen phosphate dodecahydrate obtained by any of the above methods or combinations of method steps.

[0013] Preferably, the purity of the finished product of disodium hydrogen phosphate dodecahydrate obtained by this method is not less than 97%.

[0014] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are: This invention uses monoammonium phosphate mother liquor as the main raw material and then improves the purity of the product by removing impurities. The purity of the obtained disodium hydrogen phosphate is over 97%, which increases the value of phosphorus and overcomes the shortcomings of the existing technology. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the process flow for producing disodium hydrogen phosphate dodecahydrate from industrial monoammonium phosphate mother liquor according to the present invention. Detailed Implementation

[0016] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0017] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0018] It should be noted that the terminology used herein is for the purpose of describing particular implementations only and is not intended to limit the exemplary implementations according to this application. As used herein, the singular form includes the plural form unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this description, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0019] In this invention, some conventional operating equipment, devices and components have been omitted or only briefly described.

[0020] Unless otherwise specified in the examples, the conditions shall be performed in accordance with the standard conditions or the conditions recommended by the manufacturer.

[0021] In the following examples, the composition of the monoammonium phosphate mother liquor is shown in Table 1 below: Table 1:

[0022] Example 1 A method for producing disodium hydrogen phosphate dodecahydrate from industrial monoammonium phosphate mother liquor includes the following steps: S1. Heat the monoammonium phosphate mother liquor to 60°C, add calcium dihydrogen phosphate to the mother liquor, control the pH to 3.5, stir for 2 hours, filter under pressure to obtain 1000g of filter clear liquid (ammonium phosphate clear liquid) with a P2O5 mass concentration of 28.74%. The mass fraction of fluorine in the filter clear liquid is 0.06%, and the mass fraction of sulfur trioxide is 2.50%. The filter cake is sent to produce low-oxygen powdered ammonium phosphate.

[0023] S2. Add 297.3g of solid sodium hydroxide to the filtered liquid, react for 30min, and then filter to obtain 1160.6g of clear liquid and 54.7g of filter cake.

[0024] S3. Concentrate the clear liquid obtained in S2 to a specific gravity of 1.8 to obtain a concentrated liquid; add water to the concentrated liquid to control the specific gravity to 1.46, cool to 25℃, and crystallize.

[0025] Finally, 915.2 kg of disodium hydrogen phosphate dodecahydrate product was obtained. After testing, the purity of the disodium hydrogen phosphate dodecahydrate product was 97.3%, which meets the requirements of HG / T 2965-2000 standard. The industrial disodium hydrogen phosphate standard requirements (HG / T 2965-2000) are shown in Table 2.

[0026] Example 2 A method for preparing disodium hydrogen phosphate dodecahydrate includes the following steps: S1. Heat the monoammonium phosphate mother liquor to 50°C, add calcium dihydrogen phosphate to the mother liquor, control the pH to 4.0, stir for 2 hours, filter under pressure to obtain 1000g of filter liquid with a P2O5 mass concentration of 26.25%, the mass fraction of fluorine in the filter liquid is 0.07%, the mass fraction of sulfur trioxide is 3.13%, and the filter cake is sent to produce low oxygen granular ammonium phosphate.

[0027] S2. Add 296g of solid sodium hydroxide to the filtered liquid, react for 30min, and then filter to obtain 908.2g of clear liquid and 387.8g of filter cake.

[0028] S3. Concentrate the clear liquid to a specific gravity of 1.8 to obtain a concentrated liquid; add water to the concentrated liquid to control the specific gravity to 1.45, cool to 30℃, and crystallize.

[0029] The final product yielded 874.2 kg of disodium hydrogen phosphate dodecahydrate. After testing, the product purity was 97.1%, meeting the requirements of HG / T2965-2000 standard. The industrial disodium hydrogen phosphate standard requirements (HG / T 2965-2000) are shown in Table 2.

[0030] Example 3: A method for producing disodium hydrogen phosphate dodecahydrate from industrial monoammonium phosphate mother liquor includes the following steps: S1. Heat the monoammonium phosphate mother liquor to 60°C, add calcium dihydrogen phosphate to the mother liquor, control the pH to 3.5, stir for 2 hours, filter under pressure to obtain 1000g of filter clear liquid (ammonium phosphate clear liquid) with a P2O5 mass concentration of 28.74%. The mass fraction of fluorine in the filter clear liquid is 0.06%, and the mass fraction of sulfur trioxide is 2.50%. The filter cake is sent to produce low-oxygen powdered ammonium phosphate.

[0031] S2. Add 161.5g of solid sodium carbonate to the filtered liquid and react for 30 minutes. Then add 175.4g of solid sodium hydroxide and filter to obtain 1154.3g of clear liquid and 62.5g of filter cake.

[0032] S3. Concentrate the clear liquid obtained in S2 to a specific gravity of 1.8 to obtain a concentrated solution; add water to the concentrated solution to control the specific gravity to 1.45, cool to 25℃, and crystallize.

[0033] Finally, 909.4 kg of disodium hydrogen phosphate dodecahydrate was obtained. After testing, the purity of the disodium hydrogen phosphate dodecahydrate was 97.4%, which meets the requirements of HG / T 2965-2000 standard. The industrial disodium hydrogen phosphate standard requirements (HG / T 2965-2000) are shown in Table 2.

[0034] Comparative Example 1: The preparation of disodium hydrogen phosphate dodecahydrate was carried out using the same method as in Example 1, except for step S1. The monoammonium phosphate mother liquor was heated to 50°C, and calcium dihydrogen phosphate was added to the mother liquor to control the pH to 4.3. The specific preparation steps are as follows: A method for producing disodium hydrogen phosphate dodecahydrate from industrial monoammonium phosphate mother liquor includes the following steps: S1. Heat the monoammonium phosphate mother liquor to 60°C, add calcium dihydrogen phosphate to the mother liquor, control the pH to 4.3, stir for 2 hours, filter under pressure, and obtain 1000g of filtered clear liquid (ammonium phosphate clear liquid) with a P2O5 mass concentration of 28.74%. The mass fraction of fluorine in the filtered clear liquid is 0.32%, and the mass fraction of sulfur trioxide is 3.45%.

[0035] The fluoride impurities in the filter liquid are too high, making it unsuitable for subsequent production.

[0036] Comparative Example 2: The preparation of disodium hydrogen phosphate dodecahydrate was carried out using the same method as in Example 1, except for step S3, in which the supernatant was concentrated to a specific gravity of 1.65 to obtain a concentrated solution. The specific preparation steps are as follows: S1. Heat the monoammonium phosphate mother liquor to 50°C, add calcium dihydrogen phosphate to the mother liquor, control the pH to 4.0, stir for 2 hours, filter under pressure to obtain 1000g of filter liquid with a P2O5 mass concentration of 26.25%, the mass fraction of fluorine in the filter liquid is 0.07%, the mass fraction of sulfur trioxide is 3.13%, and the filter cake is sent to produce low oxygen granular ammonium phosphate.

[0037] S2. Add 296g of solid sodium hydroxide to the filtered liquid, react for 30min, and then filter to obtain 908.2g of clear liquid and 387.8g of filter cake.

[0038] S3. Concentrate the clear liquid to a specific gravity of 1.65 to obtain a concentrated liquid; add water to the concentrated liquid to control the specific gravity to 1.45, cool to 30℃, and crystallize.

[0039] Due to insufficient concentration, some ammonia gas remained in the concentrate, resulting in partial production of monoammonium phosphate and insufficient nutrients in the final product.

[0040] Table 2 Standard requirements for industrial disodium hydrogen phosphate (HG / T 2965-2000)

[0041] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for producing disodium hydrogen phosphate dodecahydrate from industrial monoammonium phosphate mother liquor, characterized in that, Includes the following steps: A. React industrial monoammonium phosphate mother liquor and calcium dihydrogen phosphate in a preliminary reactor to obtain a reaction slurry; B. The reaction slurry obtained in step A is filtered to separate the solid and liquid components, resulting in clear ammonium phosphate solution and filter cake; the filter cake is used to produce powdered ammonium phosphate. C. Slowly add solid sodium hydroxide or sodium carbonate to the ammonium phosphate solution obtained in step B to obtain disodium hydrogen phosphate slurry. D. The disodium hydrogen phosphate slurry obtained in step C is filtered to remove impurities, and then the disodium hydrogen phosphate clear liquid is concentrated, replenished with water for crystallization, centrifuged and dried to obtain the finished product of disodium hydrogen phosphate dodecahydrate and the mother liquor.

2. The method for producing disodium hydrogen phosphate dodecahydrate from industrial monoammonium phosphate mother liquor as described in claim 1, characterized in that, In step A, slowly add calcium dihydrogen phosphate and control the pH to 3.5-4.

3. The method for producing disodium hydrogen phosphate dodecahydrate from industrial monoammonium phosphate mother liquor as described in claim 1, characterized in that, In step A, the reaction time is 1-2 hours and the reaction temperature is 50-60℃.

4. The method for producing disodium hydrogen phosphate dodecahydrate from industrial monoammonium phosphate mother liquor as described in claim 1, characterized in that, In step C, the amount of sodium hydroxide or sodium carbonate added is based on a molar ratio of Na to P2O5 of 4:

1.

5. The method for producing disodium hydrogen phosphate dodecahydrate from industrial monoammonium phosphate mother liquor as described in claim 1, characterized in that, In step D, the specific gravity of the concentrated disodium hydrogen phosphate solution is 1.7-1.

8.

6. The method for producing disodium hydrogen phosphate dodecahydrate from industrial monoammonium phosphate mother liquor as described in claim 1, characterized in that, In step D, the ammonia-containing vapor generated during the concentration process enters the phosphoric acid neutralization system.

7. The method for producing disodium hydrogen phosphate dodecahydrate from industrial monoammonium phosphate mother liquor as described in claim 1, characterized in that, In step D, the finished product, disodium hydrogen phosphate dodecahydrate, has a purity of not less than 97%.

8. The method for producing disodium hydrogen phosphate dodecahydrate from industrial monoammonium phosphate mother liquor as described in claim 1, characterized in that, The solid sodium hydroxide is of industrial grade.

9. The method for producing disodium hydrogen phosphate dodecahydrate from industrial monoammonium phosphate mother liquor as described in claim 1, characterized in that, In step D, the filtrate obtained from centrifugation is returned to the initial reactor from step A for recycling.

10. A method for producing disodium hydrogen phosphate dodecahydrate from industrial monoammonium phosphate mother liquor, characterized in that, The sodium hydrogen phosphate dodecahydrate described herein is prepared by any of the methods described in claims 1-9.

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