A preparation method of disodium hydrogen phosphite

Abstract

The present application relates to the technical field of preparation of disodium hydrogen phosphite, and discloses a method for preparing disodium hydrogen phosphite, comprising the following steps: S1, dissolving phosphorous acid and sodium hydroxide in distilled water under an inert gas atmosphere, wherein the molar ratio of phosphorous acid to sodium hydroxide is 1:(1.9-2.3), and stirring for reaction; S2, evaporating and concentrating the solution obtained in S1 to 1 / 4-1 / 3 of the original volume, cooling the solution to 25-35°C, and filtering to obtain solid disodium hydrogen phosphite; S3, adding disodium hydrogen phosphite seed crystals to the filtrate obtained in S2, cooling the solution to 15-25°C while stirring, and filtering when the crystals no longer increase to obtain disodium hydrogen phosphite; the amount of disodium hydrogen phosphite seed crystals added is 0.5-3% by weight of the phosphorous acid added in S1; the method has the advantages of improving the purity and production efficiency of disodium hydrogen phosphite.

Description

Technical Field

[0001] The present application relates to the technical field of preparation of disodium hydrogen phosphite, and in particular to a method for preparing disodium hydrogen phosphite. Background Art

[0002] Disodium hydrogen phosphite is a white, orthorhombic crystalline powder that is soluble in water but insoluble in alcohol, ammonia, and other solutions. It is quite stable at room temperature. When heated to 120 degrees Celsius, it loses five liters of water of crystallization and becomes anhydrous. Above 200 degrees Celsius, it transforms into sodium pyrophosphate, a substance with strong reducing properties that can precipitate metals from various aqueous metal salt solutions. It is easily deliquescent. Disodium hydrogen phosphite is commonly used as a reducing agent, capable of reducing metal ions such as silver and copper, and is used to prepare pure metals or alloys. It can also be used as a reducing agent in organic synthesis to aid in the synthesis of complex organic compounds. It can also be used as a reducing agent in electroplating solutions to plate metals onto surfaces. It can also be used to treat electroplating wastewater to remove metal ions.

[0003] Disodium hydrogen phosphite is made by neutralization reaction of phosphorous acid and sodium hydroxide, then concentrated, crystallisation by cooling, solid-liquid separation is made. And in order to reduce the by-product sodium dihydrogen phosphite, usually excessive sodium hydroxide is added to ensure that the phosphorous acid reaction is complete. The excess of sodium hydroxide can affect the purity of disodium hydrogen phosphite, and in the crystallisation by cooling stage, the crystallization time is long, making production efficiency not high. Relying on the prior art, the glass beads of surface-loaded crystals are added as crystal seeds to accelerate product precipitation, but the glass beads added are more difficult to remove, causing new impurities on the contrary. Summary of the Invention

[0004] In order to improve the purity and production efficiency of disodium hydrogen phosphite, the present application provides a method for preparing disodium hydrogen phosphite.

[0005] The present application provides a method for preparing disodium hydrogen phosphite, which adopts the following technical solution:

[0006] A method for preparing disodium hydrogen phosphite comprises the following steps:

[0007] S1. Under an inert gas atmosphere, dissolve phosphorous acid and sodium hydroxide in distilled water, with the molar ratio of phosphorous acid to sodium hydroxide being 1:(1.9-2.3), and stir to react;

[0008] S2, evaporating and concentrating the solution obtained in S1 to 1 / 4-1 / 3 of the original volume, cooling to 25-35°C, filtering to obtain a precipitate and a filtrate, washing and drying the precipitate to obtain disodium hydrogen phosphite solid;

[0009] S3. Add disodium hydrogen phosphite seed crystals to the filtrate obtained in S2, cool it to 15-25° C. while stirring, and filter when the number of crystals stops increasing. Wash and dry the precipitate, and combine it with the disodium hydrogen phosphite obtained in S2 to obtain disodium hydrogen phosphite; the amount of disodium hydrogen phosphite seed crystals added is 0.5-3% by weight of the phosphorous acid added in S1.

[0010] By adopting the above technical solution, the reaction solution is divided into two steps of cooling and crystallization treatment. After the second cooling step, disodium hydrogen phosphite seed crystals are added to the supersaturated solution of disodium hydrogen phosphite, thereby accelerating the crystallization of the disodium hydrogen phosphite, thereby improving the purity and yield of the disodium hydrogen phosphite. In addition, during the preparation process, the addition of the seed crystals shortens the crystallization time by 60%, greatly improving production efficiency. Furthermore, using small-particle disodium hydrogen phosphite as the seed crystals does not introduce new impurities, and there is no need to remove the seed crystals through post-processing, thereby improving the purity of the product.

[0011] Preferably, the amount of the disodium hydrogen phosphite seed crystals added is 1% by weight of the phosphorous acid added in S1.

[0012] By adopting the above technical solution, when the amount of seed crystals added is too much, the crystallization precipitation time of disodium hydrogen phosphite is likely to be too fast, resulting in the entrainment of unreacted phosphorous acid and sodium hydroxide, resulting in a decrease in purity; when the amount of seed crystals added is too small, the crystallization time is long, affecting efficiency; the inventors have found through experiments that the addition amount of the specific disodium hydrogen phosphite seed crystals of the present application at 1% can maintain a faster crystallization rate and the purity can be guaranteed.

[0013] Preferably, the average particle size of the disodium hydrogen phosphite seed crystals is in the range of 1-50 μm.

[0014] By adopting the above technical solution, the particle size of the disodium hydrogen phosphate seed crystals can affect the crystallization and precipitation of disodium hydrogen phosphite. When the particle size of the seed crystals is within this range, the yield and purity of the prepared product are both excellent.

[0015] Preferably, the average particle size of the disodium hydrogen phosphite seed crystals is 1 μm.

[0016] By adopting the above technical solution and optimizing the preparation method of disodium hydrogen phosphite seed crystals, disodium hydrogen phosphite seed crystals with an average particle size of 1 μm can be obtained, which can further ensure the purity of the product while obtaining a higher yield.

[0017] Preferably, the preparation method of the disodium hydrogen phosphite seed crystals is as follows:

[0018] S1. Prepare 90-120 parts by weight of a saturated aqueous solution of disodium hydrogen phosphite at a temperature of 55-65° C., then add 1-4 parts by weight of polyvinyl pyrrolidone and stir until dissolved;

[0019] S2. Cool the solution obtained in S1 to 20°C or below, let it stand until the precipitate no longer increases, filter, and dry to obtain disodium hydrogen phosphite seed crystals.

[0020] By adopting the above technical solution and adding polyvinyl pyrrolidone, the particle size of the disodium hydrogen phosphite seed crystals can be adjusted, making them suitable for application in the preparation process of disodium hydrogen phosphite.

[0021] Preferably, in step S2 of the method for preparing disodium hydrogen phosphite seed crystals, the solution obtained in step S1 is cooled at a rate of 2-5°C / min.

[0022] By adopting the above technical solution, the control of the cooling rate can effectively adjust the particle size of the seed crystal.

[0023] Preferably, the molecular weight of the polyvinyl pyrrolidone is 3500-32000.

[0024] By adopting the above technical solution, polyvinyl pyrrolidone is adsorbed on the surface of disodium hydrogen phosphite crystals, preventing their continued growth, thereby controlling their crystal particle size. When the molecular weight of the polyvinyl pyrrolidone used is low, it is insufficient to block their crystal growth. When its molecular weight is high, the further adsorption of the polyvinyl pyrrolidone molecules is affected due to steric hindrance, and the crystal particle size is easily increased due to the large number of vacancies on the crystal surface. Therefore, the molecular weight of polyvinyl pyrrolidone can affect the particle size of disodium hydrogen phosphite seed crystals, and its particle size can affect the crystallization and precipitation of disodium hydrogen phosphite. The seed crystals prepared when its molecular weight is within this range are all suitable for the preparation process of the present application.

[0025] Preferably, the molecular weight of the polyvinyl pyrrolidone is 5500.

[0026] By adopting the above technical solution, when the molecular weight is 5500, the obtained seed crystal particle size is smaller, which can better adapt to the preparation process of disodium hydrogen phosphite of the present application.

[0027] In summary, this application includes at least one of the following beneficial technical effects:

[0028] 1. The reaction solution is subjected to two-step cooling and crystallization treatment. After the second cooling step, disodium hydrogen phosphite seed crystals are added to the supersaturated solution of disodium hydrogen phosphite, so that the crystallization of the disodium hydrogen phosphite can be accelerated, thereby improving the purity and yield of the disodium hydrogen phosphite. In addition, during the preparation process, the addition of the seed crystals shortens the crystallization time by 60%, greatly improving the production efficiency. Furthermore, using the disodium hydrogen phosphite with a small particle size as the seed crystals does not introduce new impurities, and there is no need to remove the seed crystals through post-processing, thereby improving the purity of the product.

[0029] 2. The purity of the disodium hydrogen phosphite prepared by the preparation method of disodium hydrogen phosphite designed in this application is 99.86% and above, and the highest can reach 99.99%, and the yield is 89.2% and above, and the highest can reach 97.0%. This shows that the preparation method of disodium hydrogen phosphite of the present application can take into account the purity and yield of disodium hydrogen phosphite at the same time, and through the use of disodium hydrogen phosphite seed crystals, the crystallization time is greatly shortened, and the production efficiency is improved. DETAILED DESCRIPTION

[0030] The following is a further detailed description of this application in conjunction with the specific content.

[0031] raw material

[0032] The raw materials used in the preparation examples and examples of this application were all purchased from commercial sources, and the raw materials used were all analytically pure, and the ethanol used was anhydrous ethanol.

[0033] Preparation Example

[0034] Preparation Example 1

[0035] A disodium hydrogen phosphite seed crystal, the preparation method of which is as follows:

[0036] S1. Prepare 100 g of a saturated aqueous solution of disodium hydrogen phosphite at 60° C., then add 2.5 g of polyvinyl pyrrolidone, and stir until dissolved. The molecular weight of polyvinyl pyrrolidone is 3500, and the corresponding model is K12.

[0037] S2. The solution obtained in S1 was cooled to 4°C at a rate of 2°C / min, allowed to stand until the precipitate no longer increased, filtered, and the precipitate was washed with ethanol and then dried to obtain disodium hydrogen phosphite seed crystals with an average particle size of 8 μm.

[0038] Preparation Example 2

[0039] A disodium hydrogen phosphite seed crystal, which is different from that in Preparation Example 1 in that the molecular weight of the polyvinyl pyrrolidone is 5500, corresponding to the model K15, and the remaining steps are the same as those in Preparation Example 1; the average particle size of the seed crystal is 2 μm.

[0040] Preparation Example 3

[0041] A disodium hydrogen phosphite seed crystal, which is different from that in Preparation Example 1 in that the molecular weight of the polyvinyl pyrrolidone is 10100 and the corresponding model is K17. The remaining steps are the same as those in Preparation Example 1, and the average particle size of the seed crystal is 15 μm.

[0042] Preparation Example 4

[0043] A disodium hydrogen phosphite seed crystal, which is different from that in Preparation Example 1 in that the molecular weight of the polyvinyl pyrrolidone is 32,000 and the corresponding model is K25, and the remaining steps are the same as those in Preparation Example 1; the average particle size of the seed crystal is 18 μm.

[0044] Preparation Example 5

[0045] A disodium hydrogen phosphite seed crystal, which is different from Preparation Example 2 in that the amount of polyvinyl pyrrolidone added is 1 g, and the remaining steps are the same as Preparation Example 2; the average particle size of the seed crystal is 17 μm.

[0046] Preparation Example 6

[0047] A disodium hydrogen phosphite seed crystal, which is different from Preparation Example 2 in that the amount of polyvinyl pyrrolidone added is 4 g, and the remaining steps are the same as Preparation Example 2. The average particle size of the seed crystal is 1 μm.

[0048] Example

[0049] Example 1

[0050] A method for preparing disodium hydrogen phosphite comprises the following steps:

[0051] S1. Under a nitrogen atmosphere, phosphorous acid and sodium hydroxide were dissolved in distilled water. The weight ratio of the total weight of phosphorous acid and sodium hydroxide to water was 1:10, and the molar ratio of phosphorous acid to sodium hydroxide was 1:2.1. The mixture was stirred for 1 hour.

[0052] S2, evaporating and concentrating the solution obtained in S1 to 1 / 3 of the original volume, cooling to 30°C, filtering to obtain a precipitate and a filtrate, washing the precipitate with ethanol, and then drying to obtain disodium hydrogen phosphite solid;

[0053] S3. Add disodium hydrogen phosphite seed crystals to the filtrate obtained in S2, cool it to 20°C while stirring, filter when the crystals no longer increase, wash the precipitate with ethanol, and then dry it, and combine it with the disodium hydrogen phosphite obtained in S2 to obtain disodium hydrogen phosphite; the disodium hydrogen phosphite seed crystals are from Preparation Example 1, and the amount of disodium hydrogen phosphite seed crystals added is 1% by weight of the phosphorous acid added in S1.

[0054] Example 2

[0055] A method for preparing disodium hydrogen phosphite differs from that in Example 1 in that, in step S2, after the solution obtained in S1 is cooled to 30° C., a step of adding 1 volume of ethanol is added. After stirring, subsequent operations are performed until crystals no longer increase. The remaining steps are the same as in Example 1.

[0056] Example 3

[0057] A method for preparing disodium hydrogen phosphite differs from that in Example 1 in that, in step S2, after the solution obtained in S1 is cooled to 30° C., a step of adding 2 times the volume of ethanol is added. After stirring, subsequent operations are performed until crystals no longer increase. The remaining steps are the same as in Example 1.

[0058] Example 4

[0059] A method for preparing disodium hydrogen phosphite differs from that in Example 1 in that, in step S2, after the solution obtained in S1 is cooled to 30° C., a step of adding 3 times the volume of ethanol is added. After stirring, subsequent operations are performed until crystals no longer increase. The remaining steps are the same as in Example 1.

[0060] Example 5

[0061] A method for preparing disodium hydrogen phosphite, which differs from Example 3 in that the disodium hydrogen phosphite seed crystals come from Preparation Example 2, and the remaining steps are the same as those in Example 3.

[0062] Example 6

[0063] A method for preparing disodium hydrogen phosphite, which differs from Example 3 in that the disodium hydrogen phosphite seed crystals come from Preparation Example 3, and the remaining steps are the same as those in Example 3.

[0064] Example 7

[0065] A method for preparing disodium hydrogen phosphite, which differs from Example 3 in that the disodium hydrogen phosphite seed crystals come from Preparation Example 4, and the remaining steps are the same as those in Example 3.

[0066] Example 8

[0067] A method for preparing disodium hydrogen phosphite, which differs from Example 3 in that the disodium hydrogen phosphite seed crystals come from Preparation Example 5, and the remaining steps are the same as those in Example 3.

[0068] Example 9

[0069] A method for preparing disodium hydrogen phosphite, which differs from Example 3 in that the disodium hydrogen phosphite seed crystals come from Preparation Example 6, and the remaining steps are the same as those in Example 3.

[0070] Example 10

[0071] A method for preparing disodium hydrogen phosphite, which differs from Example 9 in that the amount of disodium hydrogen phosphite seed crystals added is 3% by weight of the phosphorous acid added in S1, and the remaining steps are the same as Example 3.

[0072] Example 11

[0073] A method for preparing disodium hydrogen phosphite is different from that in Example 1 in that polyvinyl pyrrolidone is not added during the preparation of the added disodium hydrogen phosphite seed crystals, and the seed crystal particle size can reach more than 150 μm. The remaining steps are the same as those in Example 1.

[0074] Example 12

[0075] A method for preparing disodium hydrogen phosphite, which differs from Example 1 in that the cooling rate of the added disodium hydrogen phosphite seed crystals in S2 is 8°C / min during preparation, the average particle size of the prepared seed crystals is 23 μm, and the remaining steps are the same as in Example 1.

[0076] Comparative Example

[0077] Comparative Example 1

[0078] A method for preparing disodium hydrogen phosphite, which differs from Example 1 in that no disodium hydrogen phosphite seed crystals are added in step S3, and the remaining steps are the same as those in Example 1.

[0079] Comparative Example 2

[0080] A preparation method of disodium hydrogen phosphite, which is different from Example 1, is as follows:

[0081] S1. Under a nitrogen atmosphere, phosphorous acid and sodium hydroxide were dissolved in distilled water. The weight ratio of the total weight of phosphorous acid and sodium hydroxide to water was 1:10, and the molar ratio of phosphorous acid to sodium hydroxide was 1:2.1. The mixture was stirred for 1 hour.

[0082] S2. Evaporate and concentrate the solution obtained in S1 to 1 / 3 of the original volume, cool to 20° C., filter to obtain a precipitate and a filtrate, wash the precipitate with ethanol, and then dry to obtain disodium hydrogen phosphite.

[0083] Performance testing

[0084] Detection method / test method

[0085] Disodium hydrogen phosphite was prepared according to the preparation methods of Examples 1-12 and Comparative Examples 1-2, respectively, and then tested according to the following test method. The test results are shown in Table 1.

[0086] Purity of disodium hydrogen phosphite: The purity of disodium hydrogen phosphite is determined by ion chromatography. Take 1.0000g of disodium hydrogen phosphite sample, dissolve it in water, transfer it to a 500ml volumetric flask, dilute it with distilled water to the scale, and mix it. Pipette 1ml into a 50ml volumetric flask, dilute it with water to the scale, filter it through a 0.22um filter membrane, and inject it. Use Dionex ICS-90A ion chromatograph, the chromatographic column is Dionex Ionpac AS22 anion separation column (4mm*250mm), with AG (4mm*50mm) guard column, column temperature 30℃; eluent is a mixed solution of 1.4mmol / L sodium bicarbonate and 4.5mmol / L sodium carbonate; elution mode is isocratic elution; mobile phase flow rate is 1.2ml / min; detector is conductivity detector; injection volume is 10uL. Calculate PO3 in the sample according to the standard curve 3- The content is then converted into the purity of disodium hydrogen phosphite.

[0087] Phosphorus stock solution (p(PO3 3- 2000ug / ml): Weigh 1.4306g of oven-dried premium-grade disodium hydrogen phosphite. Place in a 250ml beaker and add 100ml of water, stirring to dissolve. Add 2ml of nitric acid, transfer to a 500ml volumetric flask, dilute to volume with water, and mix thoroughly.

[0088] Phosphorus standard solution (p(PO3 3- )200ug / ml): Pipette 10ml of phosphorus stock solution into a 100ml volumetric flask, dilute to volume with water, and mix thoroughly.

[0089] Preparation of standard curve: Take 1.00, 2.00, 3.00, 5.00, 10.00 and 25.00 ml of phosphorus standard solution and transfer them into 6 50 ml volumetric flasks respectively, dilute to the scale with water and shake well to obtain p(PO3 3- ) are 4, 8, 12, 20, 40, and 100 μg / ml phosphorus standard solutions. Take the above standard solutions and inject them into the ion chromatograph in sequence to draw a standard curve.

[0090] Yield: Yield (%) = ((m 实际质量 -m 晶种添加质量 ) / m 理论质量 )×100%

[0091] Table 1 Test results of Examples 1-12 and Comparative Examples 1-2

[0092] purity(%) Yield (%) Example 1 99.99 90.2 Example 2 99.99 92.3 Example 3 99.99 95.2 Example 4 99.88 95.4 Example 5 99.99 96.5 Example 6 99.99 95.3 Example 7 99.99 95.1 Example 8 99.99 95.0 Example 9 99.99 96.7 Example 10 99.86 97.0 Example 11 99.99 89.7 Example 12 99.99 89.2 Comparative Example 1 99.99 83.8 Comparative Example 2 99.86 85.4

[0093] It can be seen from Examples 1-12 and Comparative Examples 1-2, as well as the test data in Table 1, that the purity of the disodium hydrogen phosphite prepared by the method for preparing disodium hydrogen phosphite designed in the present application is 99.86% or more, and can reach up to 99.99%, and the yield is 89.2% or more, and can reach up to 97.0%; this shows that the method for preparing disodium hydrogen phosphite in the present application can take into account both the purity and yield of disodium hydrogen phosphite, and by using disodium hydrogen phosphite seed crystals, the crystallization time is greatly shortened, and the production efficiency is improved.

[0094] The test data of Example 1 and Comparative Example 1 show that the addition of disodium hydrogen phosphite seed crystals can improve the purity and yield of disodium hydrogen phosphite, and the addition of seed crystals during the preparation process can shorten the crystallization time by 60%, greatly improving production efficiency. The reduced purity in Comparative Example 1 is considered to be due to factors such as excessive crystallization time and oxidation by air during the processing.

[0095] It can be seen from the test data of Examples 1-4 that since disodium hydrogen phosphite is insoluble in ethanol, adding ethanol to S2 can accelerate its precipitation and improve its yield. However, when too much ethanol is added, its precipitation is too fast, and it is easy to carry unreacted sodium hydroxide, phosphorous acid, etc. out, resulting in reduced purity. Therefore, the optimal addition amount of ethanol is 2 times the volume of the solution.

[0096] It can be seen from the test data of Example 3 and Example 5-7 that the molecular weight of polyvinyl pyrrolidone can affect the particle diameter of disodium hydrogen phosphite crystal seeds, and its particle diameter can affect the crystallization of disodium hydrogen phosphite. It can be seen from the test data that when its seed particle diameter is 2 μm, the yield is maximum. In conjunction with Example 8-9, the addition of polyvinyl pyrrolidone is also a factor affecting the seed particle diameter. When its addition increases, it helps to further reduce the particle diameter of the seed. When its addition is 4g, it is a better addition. In conjunction with Example 11-12, the addition of polyvinyl pyrrolidone and the control of temperature can effectively control the particle diameter of the seed, improve the yield and production efficiency of disodium hydrogen phosphite.

[0097] It can be seen from the test data of Example 3 and Example 10 that when the amount of seed crystals added is too much, the crystallization time of disodium hydrogen phosphite is likely to be too fast, resulting in the entrainment of unreacted phosphorous acid and sodium hydroxide, resulting in a decrease in purity.

[0098] It can be seen from the test data of Example 1 and Comparative Example 2 that by dividing the crystallization step of disodium hydrogen phosphite into two steps, first cooling to 30° C., filtering, and then crystallizing the supersaturated solution by adding seed crystals, the precipitation amount of disodium hydrogen phosphite can be increased, the precipitation time can be reduced, and the production efficiency can be improved.

[0099] This specific embodiment is merely an explanation of the present invention and is not intended to limit the present invention. After reading this specification, those skilled in the art may make non-creative modifications to this embodiment as needed. However, as long as such modifications are within the scope of the claims of the present invention, they are protected by patent law.

Claims

1. A method for preparing disodium hydrogen phosphite, characterized in that: It includes the following steps: S1. Under an inert gas atmosphere, dissolve phosphorous acid and sodium hydroxide in distilled water in a molar ratio of phosphorous acid to sodium hydroxide of 1:(1.9-2.3), and stir to react; S2, evaporating and concentrating the solution obtained in S1 to 1 / 4-1 / 3 of the original volume, cooling to 25-35°C, filtering to obtain a precipitate and a filtrate, washing and drying the precipitate to obtain disodium hydrogen phosphite solid; S3, adding disodium hydrogen phosphite seed crystals to the filtrate obtained in S2, cooling it to 15-25°C while stirring, and filtering when the number of crystals no longer increases. The precipitate is washed, dried, and combined with the disodium hydrogen phosphite obtained in S2 to obtain disodium hydrogen phosphite; the amount of disodium hydrogen phosphite seed crystals added is 0.5-3% by weight of the phosphorous acid added in S1; The average particle size of the disodium hydrogen phosphite seed crystals is 1 μm; The preparation method of the disodium hydrogen phosphite seed crystals is as follows: S1. Prepare 90-120 parts by weight of a saturated aqueous solution of disodium hydrogen phosphite at a temperature of 55-65° C., then add 1-4 parts by weight of polyvinyl pyrrolidone and stir until dissolved; S2. Cool the solution obtained in S1 to 20°C or below, let it stand until the precipitate no longer increases, filter, and dry to obtain disodium hydrogen phosphite seed crystals; The molecular weight of the polyvinyl pyrrolidone is 5500.

2. The method for preparing disodium hydrogen phosphite according to claim 1, wherein: The amount of the disodium hydrogen phosphite seed crystals added is 1% by weight of the phosphorous acid added in S1.

3. The method for preparing disodium hydrogen phosphite according to claim 1, wherein: In S2 of the method for preparing disodium hydrogen phosphite seed crystals, the solution obtained in S1 is cooled at a rate of 2-5°C / min.