Preparation method of disodium hydrogen phosphate

Abstract

The invention relates to the technical field of preparation of disodium hydrogen phosphate, and discloses a preparation method of disodium hydrogen phosphate, which comprises the following steps: S1, dissolving phosphorous acid and sodium hydroxide in distilled water in an inert gas atmosphere according to a molar ratio of phosphorous acid to sodium hydroxide of 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 to 25-35 DEG C, and filtering to obtain a disodium hydrogen phosphate solid; s3, adding a disodium hydrogen phosphate seed crystal into the filtrate obtained in the step S2, cooling to 15-25 DEG C while stirring, and filtering when crystals are not increased any more to obtain disodium hydrogen phosphate; the adding amount of the disodium hydrogen phosphate seed crystal is 0.5-3% of the weight part of the phosphorous acid added in the S1; the method has the advantage of improving the purity and production efficiency of disodium hydrogen phosphate.

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, soluble in water, insoluble in alcohol, ammonia, etc. It is quite stable at room temperature. When heated to 120 degrees Celsius, it loses five crystal waters and becomes anhydrous. When it is above 200 degrees Celsius, it becomes sodium pyrophosphate, which has strong reducing properties and can precipitate metals from a variety of metal salt aqueous solutions. It is easy to deliquesce. Disodium hydrogen phosphite is often used as a reducing agent, which can reduce 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 help synthesize complex organic matter; it can also be used as a reducing agent in electroplating solution to plate metals on the surface of objects, and it can also be used to treat electroplating waste liquid to remove metal ions.

[0003] Disodium hydrogen phosphite is prepared by neutralization reaction of phosphorous acid and sodium hydroxide, and then concentrated, cooled and crystallized, and solid-liquid separation is prepared. In order to reduce the by-product sodium dihydrogen phosphite, excessive sodium hydroxide is usually added to ensure that the phosphorous acid reacts completely. The excess of sodium hydroxide can affect the purity of disodium hydrogen phosphite, and in the cooling and crystallization stage, the crystallization time is long, which makes the production efficiency not high. Relying on the prior art, glass beads with surface load crystals are added as crystal seeds to accelerate product precipitation, but the added glass beads are difficult to remove, which causes new impurities instead. 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 scheme: A method for preparing disodium hydrogen phosphite comprises the following steps: S1. Under an inert gas atmosphere, dissolve phosphorous acid and sodium hydroxide in distilled water, wherein the molar ratio of phosphorous acid to sodium hydroxide is 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, and washing and drying the precipitate to obtain disodium hydrogen phosphite solid; S3. Add disodium hydrogen phosphite seed crystals to the filtrate obtained in S2, cool it to 15-25° C. while stirring, 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.

[0006] By adopting the above technical scheme, the solution after the reaction is divided into two steps of cooling and crystallization treatment, and after the second step of cooling, disodium hydrogen phosphite seeds are added to the supersaturated solution of disodium hydrogen phosphite, so that the crystallization of disodium hydrogen phosphite can be accelerated, thereby improving the purity and yield of disodium hydrogen phosphite, and in the preparation process, the addition of seeds shortens the crystallization time by 60%, greatly improving the production efficiency; and using disodium hydrogen phosphite with a small particle size as seeds, no new impurities are introduced, and there is no need to remove the seeds through post-treatment, so the purity of the product can be improved.

[0007] Preferably, the added amount of the disodium hydrogen phosphite seed crystals is 1% of the weight of the phosphorous acid added in S1.

[0008] By adopting the above technical scheme, 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; when the amount of seed crystals added is too little, the crystallization time is long and the efficiency is affected; the inventors have found through experiments that the addition amount of disodium hydrogen phosphite seed crystals specified in the present application at 1% can maintain a faster crystallization speed and the purity can be guaranteed.

[0009] Preferably, the average particle size of the disodium hydrogen phosphite seed crystals is in the range of 1-50 μm.

[0010] By adopting the above technical solution, the particle size of the disodium hydrogen phosphate seed crystals can affect the crystallization 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.

[0011] Preferably, the average particle size of the disodium hydrogen phosphite seed crystals is 1 μm.

[0012] By adopting the above technical scheme 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.

[0013] As a preferred method: the preparation method of the disodium hydrogen phosphite seed crystal 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. The solution obtained in S1 is cooled to 20°C or below, and allowed to stand until the precipitation stops increasing, and then filtered and dried to obtain disodium hydrogen phosphite seed crystals.

[0014] By adopting the above technical solution and adding polyvinyl pyrrolidone, the particle size of the disodium hydrogen phosphite seed crystals can be adjusted so that the seed crystals can be suitably applied to the preparation process of disodium hydrogen phosphite.

[0015] Preferably, 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.

[0016] By adopting the above technical solution, the control of the cooling rate can effectively adjust the particle size of the seed crystal.

[0017] Preferably, the molecular weight of the polyvinyl pyrrolidone is 3500-32000.

[0018] By adopting the above technical scheme, polyvinyl pyrrolidone is adsorbed on the surface of disodium hydrogen phosphite crystals to prevent the crystals from continuing to grow, thereby controlling the crystal particle size; when the molecular weight of the polyvinyl pyrrolidone used is low, it is not enough to block the crystal growth, and when the molecular weight is high, due to the steric hindrance, the further adsorption of the polyvinyl pyrrolidone molecules is affected, and it is easy to make the crystal particle size larger 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 seeds, and its particle size can affect the crystallization and precipitation of disodium hydrogen phosphite, and the seeds prepared when its molecular weight is within this range are all suitable for the preparation process of the present application.

[0019] Preferably, the molecular weight of the polyvinyl pyrrolidone is 5500.

[0020] 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.

[0021] In summary, the present application includes at least one of the following beneficial technical effects: 1. The reaction solution is divided into two steps of cooling and crystallization treatment. After the second step of cooling, disodium hydrogen phosphite seeds are added to the supersaturated solution of disodium hydrogen phosphite, so that the crystallization of disodium hydrogen phosphite can be accelerated, thereby improving the purity and yield of disodium hydrogen phosphite. In addition, in the preparation process, the addition of seeds shortens the crystallization time by 60%, greatly improving the production efficiency. Moreover, using disodium hydrogen phosphite with a small particle size as seeds does not introduce new impurities, and there is no need to remove the seeds through post-treatment, so the purity of the product can be improved.

[0022] 2. The purity of the disodium hydrogen phosphite prepared by the preparation method of disodium hydrogen phosphite designed by the present application is 99.86% or more, and the highest can reach 99.99%, and the yield is 89.2% or more, and the highest can reach 97.0%; it 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

[0023] The present application is further described in detail below in conjunction with the specific contents.

[0024] raw material The raw materials used in the preparation examples and embodiments of the present application were all purchased from commercial sources, and the raw materials used were all analytically pure, and the ethanol was anhydrous ethanol.

[0025] Preparation Example Preparation Example 1 A disodium hydrogen phosphite seed crystal, the preparation method of which is as follows: 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. S2. The solution obtained in S1 is cooled to 4°C at a rate of 2°C / min, and allowed to stand until the amount of precipitate no longer increases. The precipitate is filtered, washed with ethanol, and then dried to obtain disodium hydrogen phosphite seed crystals with an average particle size of 8 μm.

[0026] Preparation Example 2 A disodium hydrogen phosphite seed crystal, which is different from Preparation Example 1 in that the molecular weight of polyvinyl pyrrolidone is 5500, and the corresponding model is K15, and the remaining steps are the same as Preparation Example 1; the average particle size of the seed crystal is 2 μm.

[0027] Preparation Example 3 A disodium hydrogen phosphite seed crystal, which is different from Preparation Example 1 in that the molecular weight of polyvinyl pyrrolidone is 10100, and the corresponding model is K17. The remaining steps are the same as Preparation Example 1, and the average particle size of the seed crystal is 15 μm.

[0028] Preparation Example 4 A disodium hydrogen phosphite seed crystal, which is different from Preparation Example 1 in that the molecular weight of polyvinyl pyrrolidone is 32000, and the corresponding model is K25, and the remaining steps are the same as Preparation Example 1; the average particle size of the seed crystal is 18 μm.

[0029] Preparation Example 5 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.

[0030] Preparation Example 6 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, and the average particle size of the seed crystal is 1 μm. Example

[0031] Example 1 A method for preparing disodium hydrogen phosphite comprises the following steps: 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, and the reaction was stirred for 1 hour; 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; 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 come from Preparation Example 1, and the amount of disodium hydrogen phosphite seed crystals added is 1% of the weight of the phosphorous acid added in S1.

[0032] Example 2 A method for preparing disodium hydrogen phosphite is different 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, and after stirring, subsequent operations are performed when crystals no longer increase, and the remaining steps are the same as those in Example 1.

[0033] Example 3 A method for preparing disodium hydrogen phosphite is different 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, and after stirring, subsequent operations are performed when crystals no longer increase, and the remaining steps are the same as those in Example 1.

[0034] Example 4 A method for preparing disodium hydrogen phosphite is different 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, and after stirring, subsequent operations are performed when crystals no longer increase, and the remaining steps are the same as those in Example 1.

[0035] Example 5 A method for preparing disodium hydrogen phosphite, which is different 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 of Example 3.

[0036] Example 6 A method for preparing disodium hydrogen phosphite, which is different 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 of Example 3.

[0037] Example 7 A method for preparing disodium hydrogen phosphite, which is different 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 of Example 3.

[0038] Example 8 A method for preparing disodium hydrogen phosphite, which is different 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 of Example 3.

[0039] Example 9 A method for preparing disodium hydrogen phosphite, which is different 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 of Example 3.

[0040] Example 10 A method for preparing disodium hydrogen phosphite, which is different from Example 9 in that the amount of disodium hydrogen phosphite seed crystals added is 3% of the weight of phosphorous acid added in S1, and the remaining steps are the same as Example 3.

[0041] Embodiment 11 A method for preparing disodium hydrogen phosphite is different from that in Example 1 in that polyvinyl pyrrolidone is not added to the added disodium hydrogen phosphite seed crystals during preparation, the seed crystal particle size can reach more than 150 μm, and the remaining steps are the same as those in Example 1.

[0042] Example 12 A method for preparing disodium hydrogen phosphite, which is different from Example 1 in that the cooling rate of S2 in the added disodium hydrogen phosphite seed crystals during preparation is 8°C / min, the average particle size of the prepared seed crystals is 23 μm, and the remaining steps are the same as those in Example 1.

[0043] Comparative Example Comparative Example 1 A method for preparing disodium hydrogen phosphite, which is different 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.

[0044] Comparative Example 2 A method for preparing disodium hydrogen phosphite, which is different from Example 1 in that the preparation method is as follows: 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, and the reaction was stirred for 1 hour; S2. The solution obtained in S1 is evaporated and concentrated to 1 / 3 of the original volume, cooled to 20° C., filtered to obtain a precipitate and a filtrate, the precipitate is washed with ethanol, and then dried to obtain disodium hydrogen phosphite.

[0045] Performance testing Detection method / test method 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.

[0046] 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 to the scale with distilled water, and mix it. Transfer 1ml to a 50ml volumetric flask, dilute it to the scale with water, filter it through a 0.22um filter membrane, and inject it. Use Dionex ICS-90A ion chromatograph, the chromatographic column is Dionex IonpacAS22 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 method is isocratic elution; mobile phase flow rate is 1.2ml / min; detector is conductivity detector; injection volume is 10uL. Calculate PO in the sample according to the standard curve 3 3- The content is then converted into the purity of disodium hydrogen phosphite.

[0047] Phosphorus stock solution (p(PO 3 3- )2000ug / ml): Weigh 1.4306g of dried premium grade disodium hydrogen phosphite. Place in a 250ml beaker, add 100ml water and stir to dissolve. Add 2ml nitric acid, transfer to a 500ml volumetric flask, dilute to volume with water, and mix well.

[0048] Phosphorus standard solution (p(PO 3 3- )200ug / ml): Pipette 10ml of phosphorus stock solution into a 100ml volumetric flask, dilute to volume with water and mix well.

[0049] Preparation of standard curve: Pipette 1.00, 2.00, 3.00, 5.00, 10.00, and 25.00 ml of phosphorus standard solution into 6 50 ml volumetric flasks respectively, dilute to the mark with water, and shake well to obtain p(PO 3 3-) are 4, 8, 12, 20, 40, 100ug / ml series phosphorus standard solutions. Take the above standard solutions, inject them into the ion chromatograph in sequence, and draw a standard curve.

[0050] Yield: Yield (%) = ((m 实际质量 -m 晶种添加质量 ) / m 理论质量 )×100% Table 1 Test results of Examples 1-12 and Comparative Examples 1-2 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 Embodiment 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 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 by 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 of 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.

[0051] It can be seen from the test data of Example 1 and Comparative Example 1 that the purity and yield of disodium hydrogen phosphite can be improved by adding disodium hydrogen phosphite seed crystals, and in the preparation process, adding seed crystals can shorten the crystallization time by 60%, greatly improving the production efficiency. It is considered that the purity of Comparative Example 1 is reduced because of factors such as too long crystallization time and oxidation by air during the treatment process.

[0052] It can be seen from the test data of Examples 1-4 that since disodium hydrogen phosphite is insoluble in ethanol, by adding ethanol in S2, its precipitation can be accelerated and its yield can be improved. However, when too much ethanol is added, it precipitates too quickly, and unreacted sodium hydroxide, phosphorous acid, etc. are easily entrained and precipitated, resulting in a decrease in its purity. Therefore, the addition amount of ethanol is twice the volume of the solution, which is a better addition amount.

[0053] 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 size of disodium hydrogen phosphite crystal seeds, and its particle size can affect the crystallization of disodium hydrogen phosphite. It can be seen from the test data that when its seed particle size is 2 μm, the yield is maximum. In conjunction with Example 8-9, the addition amount of polyvinyl pyrrolidone is also a factor affecting the seed particle size. When its addition amount is increased, it helps to further reduce the particle size of the seed. When its addition amount is 4g, it is a better addition amount. In conjunction with Example 11-12, the addition of polyvinyl pyrrolidone and the control of temperature can effectively control the particle size of the seed, and improve the yield and production efficiency of disodium hydrogen phosphite.

[0054] 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.

[0055] 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.

[0056] This specific embodiment is merely an explanation of the present invention and is not a limitation of the present invention. After reading this specification, those skilled in the art may make non-creative modifications to the present embodiment as needed. However, as long as they are within the scope of the claims of the present invention, they are protected by the 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, wherein the molar ratio of phosphorous acid to sodium hydroxide is 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, and washing and drying the precipitate to obtain disodium hydrogen phosphite solid; S3. Add disodium hydrogen phosphite seed crystals to the filtrate obtained in S2, cool it to 15-25° C. while stirring, 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.

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

3. A method for preparing disodium hydrogen phosphite according to claim 1, characterized in that: The average particle size of the disodium hydrogen phosphite seed crystals is in the range of 1-50 μm.

4. A method for preparing disodium hydrogen phosphite according to claim 3, characterized in that: The average particle size of the disodium hydrogen phosphite seed crystals is 1 μm.

5. A method for preparing disodium hydrogen phosphite according to claim 1, characterized in that: The preparation method of the disodium hydrogen phosphite seed crystal 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. The solution obtained in S1 is cooled to 20°C or below, and allowed to stand until the precipitation stops increasing, and then filtered and dried to obtain disodium hydrogen phosphite seed crystals.

6. A method for preparing disodium hydrogen phosphite according to claim 5, characterized in that: 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.

7. The method for preparing disodium hydrogen phosphite according to claim 5, characterized in that: The molecular weight of the polyvinyl pyrrolidone is 3500-32000.

8. The method for preparing disodium hydrogen phosphite according to claim 5, characterized in that: The molecular weight of the polyvinyl pyrrolidone is 5500.