Preparation method of high-yield electronic-grade phosphoric acid

Abstract

The present application relates to a kind of preparation methods of high yield electronic grade phosphoric acid.The concentration of phosphoric acid is 85%-90%, the initial solution temperature is 30-40 ℃, the solution is stirred and dissolved until there is no undissolved solid particles in the solution, a certain amount of stock solution is punched into the crystallization kettle for cooling, the solution in the kettle is cooled to 20-30 ℃, the crystal seed of 1-10% of the total acid solution mass is introduced, and the stage cooling is carried out, the crystallization time is 2-10 h, the jacket temperature of the crystallization kettle is increased to 25-30 ℃ for 0-2 h before discharging to strip the crystal layer, and the specified concentration can be adjusted according to the requirements of different products after centrifugal washing.The present application can handle a wide range of concentration and purity of raw material acid, solve the problem of low yield and high impurity in existing phosphoric acid production process, and the process uses less equipment, has high applicability, low energy consumption, and is easy to industrialize.

Description

Technical Field

[0001] This invention belongs to the field of phosphoric acid production technology, specifically relating to a method for preparing high-yield electronic-grade phosphoric acid. Background Technology

[0002] Electronic-grade phosphoric acid, as an ultra-clean, high-purity reagent, is one of the most widely used wet electronic chemicals in the electronics industry. Its main applications include cleaning wafer substrates before coating with adhesive, cleaning during silicon wafer fabrication, and etching in photolithography processes (etching of insulating films, semiconductor films, conductor films, and organic materials). Therefore, the purity and quality achievable with electronic-grade phosphoric acid directly impact the overall performance of electronic products.

[0003] In traditional methods for preparing electronic-grade phosphoric acid, multi-stage recrystallization is the preferred technique. To improve yield, the final crystallization temperature is often kept as low as possible. However, the release of heat during crystallization leads to an increasing temperature difference between the inside and outside of the reactor, inevitably causing scaling and crystal layer formation on the reactor wall. Simultaneously, the formation of the crystal layer affects heat conduction between the inside and outside of the reactor, further reducing the driving force for crystal growth within the solution and resulting in a thicker crystal layer. At the end of crystallization, the thick crystals adhering to the reactor wall significantly reduce the product yield (<30% in traditional processes). Removing the crystal layer is difficult, and the mother liquor trapped within it is also challenging to remove. While programmed temperature control can effectively slow down crystal layer formation during crystallization, it is difficult to implement industrially. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a method for preparing high-yield electronic-grade phosphoric acid. This process solves the problems of low product yield and high impurity content in existing phosphoric acid production processes. Furthermore, this process requires less equipment, has high applicability, and low energy consumption, making it easy to promote industrialization.

[0005] To achieve the objectives of this invention, the following technical solution is adopted: A method for preparing high-yield electronic-grade phosphoric acid includes the following steps: S1. Prepare an 85%-90% phosphoric acid solution, and control the temperature of the phosphoric acid solution between 30-40℃; S2. Introducing seed crystals: Cool the phosphoric acid solution obtained in S1 by passing a 20-30℃ coolant through it. After the solution temperature drops to the same level as the coolant, add the seed crystals. S3. Cooling and crystallization: After adding seed crystals and cooling at a constant temperature for 1-4 hours, adjust the temperature of the coolant to gradually reduce the temperature. Once the crystal size grows to 2-10 mm, adjust the temperature of the coolant to rapidly reduce the temperature until the solution temperature reaches the end point of cooling and crystallization. S4. Crystal layer peeling: After the solution temperature reaches the cooling crystallization endpoint, the cooling liquid is heated to 25-30℃ and kept at that temperature for 0-4 hours; S5. Separation and washing: After the crystal layer is peeled off from the vessel wall, centrifugation is performed to separate the mother liquor, and the mother liquor is washed with deionized water to obtain electronic-grade phosphoric acid.

[0006] Furthermore, the total impurity content of the phosphoric acid solution described in S1 is <50 ppm.

[0007] Furthermore, the seed crystals described in S2 are rhomboid plates with a particle size of 0.1~3mm, and the mass ratio of the seed crystals added to the phosphoric acid solution is 1~10:100.

[0008] Furthermore, the cooling process described in S3 involves 2-4 cooling cycles, with each cooling cycle decreasing by 2-5°C, followed by 1-4 hours of constant-temperature cooling.

[0009] Furthermore, the temperature of the coolant used in the rapid cooling stage described in S3 is 0-10℃, at which point the crystals grow rapidly.

[0010] Furthermore, the crystallization endpoint temperature described in S3 is 10-20℃.

[0011] Furthermore, the cooling rate before adding the seed crystals in S2 can be higher, the seed crystal size should be as small and uniform as possible, and the amount of seed crystals added should be set by the solution mass and initial concentration. The purpose is to induce the most intense exothermic stage of crystallization to occur in the early stage of the crystallization process.

[0012] Furthermore, the cooling and isothermal time in stage S3 should be long enough to ensure that the crystal has sufficient growth space and driving force; rapid cooling should be carried out after the crystal grain size has grown to ensure that the crystal packing density in the crystal layer is small, which facilitates the subsequent peeling of the crystal layer.

[0013] Furthermore, the temperature of the coolant in S4 is set slightly lower than the melting point of hemihydrate phosphoric acid to ensure that while the fine crystals dissolve, the large crystal particles do not dissolve and can even grow to a certain extent. The process of crystal layer peeling is also the process of crystal growth.

[0014] This invention provides a method for preparing high-yield electronic-grade phosphoric acid, which has the following beneficial effects: (1) The method adopts the method of controlling the amount of seed crystals introduced, slow cooling in the early stage after adding seed crystals and rapid cooling in the later stage, which effectively reduces the secondary nucleation phenomenon in the cooling crystallization stage; the stage cooling method provides sufficient time and driving force for crystal growth, and large-particle crystals with relatively uniform particle size can be obtained; the rapid cooling method is adopted in the later stage of cooling crystallization, at which time the new crystals continue to grow on the original crystals, shortening the production time and improving the production efficiency.

[0015] (2) The process design for crystal layer stripping in this method can significantly improve product quality and yield. When crystal layers are formed, the larger the crystal particle size in the solution, that is, the smaller the crystal packing density in the crystal layer, the easier it is to strip the crystal layers later; conversely, the smaller the crystal particle size in the solution when crystal layers are formed, the more difficult it is to strip the crystal layers later. Since the solubility of small particles is greater than that of large particles, in the crystal layer stripping stage, it is only necessary to control the temperature of the coolant slightly below the melting point of hemihydrate phosphoric acid to ensure that small crystals dissolve at this temperature while large crystals are not dissolved, thereby improving the yield.

[0016] (3) This method uses centrifugation and washing to separate the product. Since the mother liquor is rich in a large number of impurity ions, if the mother liquor is not completely separated, the actual purity of the crystal will be reduced. In this invention, the centrifugal force of the material is used to completely separate the crystal from the mother liquor attached to its surface. Furthermore, deionized water is used to wash the crystal during the centrifugation process to improve the purity of the crystal.

[0017] (4) The mother liquor and washing liquid separated by centrifugation in this method can be reused. This process can not only reduce production costs but also be environmentally friendly. Attached Figure Description

[0018] Figure 1 This is a flowchart of the process of the present invention.

[0019] Figure 2 This is a schematic diagram of the apparatus used in this invention.

[0020] Figure 3 This is the main view of the crystal layer before peeling in Example 1.

[0021] Figure 4 This is a top view of the crystal layer before peeling in Example 1.

[0022] Figure 5 Front view after crystal layer peeling in Example 1 Figure 6 This is a top view after the crystal layer was peeled off in Example 1.

[0023] The meanings of the markings in the attached diagram are as follows: 1-Liquid mixing tank, 2-Crystallization kettle, 3-Center, 4-Blending tank, 5-Raw material pump, 6-Mother liquor pump. Detailed Implementation

[0024] The embodiments of the present invention will be described in detail below with reference to the examples. The following examples are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention.

[0025] Example 1 S1. Prepare a phosphoric acid solution with a concentration of 89% in a mixing tank at a solution temperature of 35°C. Stir until there are no undissolved solid particles in the solution, then transfer 30 kg of the phosphoric acid stock solution to a crystallization kettle for later use. S2. Water at 26°C is introduced into the jacket of the crystallization vessel to rapidly reduce the solution temperature. When the solution temperature in the vessel drops to 26°C, 10% of the total acid mass of rhomboid plate-shaped seed crystals are added, with a seed crystal particle size range of 1-2 mm.

[0026] S3. After the jacket water is kept at 26℃ for 2 hours, the jacket water temperature is adjusted to 21℃ and kept at 21℃ for 3 hours. The jacket water temperature is then adjusted to 16℃ and kept at 16℃ for 2 hours. After the crystal length and diameter grow to 5-8 mm, the jacket water inlet temperature is adjusted to 0℃. The crystal grows rapidly, the solid content in the solution increases significantly, and the crystal layer on the reactor wall also thickens.

[0027] S4. When there is basically no mother liquor left in the reactor, heat the jacket water to 30°C and keep it at that temperature for 28 minutes.

[0028] S5. After the crystal layer is peeled off from the reactor wall, the slurry in the crystallization reactor is fed into a centrifuge for mother liquor separation. After the mother liquor separation is completed, 100g of deionized water is added for dehydration and washing. The separated mother liquor is recycled back to the mixing tank for reuse, and the phosphate crystals are fed into the mixing tank and mixed with water to form a product of the specified concentration.

[0029] In the picture: Figure 3 This is a front view before the crystal layers are peeled off. The complete crystal layer morphology can be observed from the figure, and the boundaries are relatively clear. Figure 4 This is a top view before the crystal layer is peeled off. As can be observed from the figure, the thickness of the crystal layer is about 1 cm, and the inner side of the crystal layer is a crystalline slurry with a high solid content. Figure 5 This is the front view after the crystal layers have been peeled off. As can be observed from the figure, the solution is quite viscous and there is no obvious boundary line at the top. Figure 6 This is a top view after the crystal layers have been peeled off. As can be seen from the figure, no crystal layers are present, and the contents of the vessel are a crystal slurry with a relatively uniform density distribution.

[0030] The impurity content and yield at each stage are shown in Table 1.

[0031] Table 1 Impurity content and yield at each stage of Example 1

[0032] Example 2 S1. Prepare a phosphate stock solution with a concentration of 86% from the mixing tank. The solution temperature is 32℃. Stir and dissolve the solution until there are no undissolved solid particles in the solution. Then, transfer 30 kg of the phosphate stock solution to the crystallization kettle for later use. S2. Water at 24°C is introduced into the jacket of the crystallization vessel to rapidly reduce the solution temperature. When the solution temperature in the vessel drops to 24°C, 3% of the total acid mass of rhomboid plate-shaped seed crystals with a particle size range of 1-2 mm are added.

[0033] S3. After adding the seed crystal, the jacket water is kept at 24℃ for 2 hours. The jacket water temperature is then adjusted to 22℃ and kept at 2 hours. The jacket water temperature is then adjusted to 18℃ and kept at 2 hours. The crystal length and diameter are observed to grow to 1-7 mm. The jacket water inlet temperature is then adjusted to 0℃. The crystal grows rapidly, the solid content in the solution increases significantly, and the crystal layer on the reactor wall also thickens.

[0034] S4. When there is basically no mother liquor in the reactor, heat the jacket water to 28°C and keep it at that temperature for 54 minutes.

[0035] S5. After the crystal layer is peeled off from the reactor wall, the slurry in the crystallization reactor is fed into a centrifugal dehydrator for mother liquor separation. After the mother liquor separation is completed, 100g of deionized water is added for dehydration and washing. The separated mother liquor is recycled back to the mixing tank for reuse, and the phosphate crystals are fed into the mixing tank and mixed with water to form a product of the specified concentration.

[0036] The impurity content and yield at each stage are shown in Table 2.

[0037] Table 2 Impurity content and yield at each stage of Example 2

[0038] Example 3 S1. Prepare a phosphate stock solution with a concentration of 85% from the mixing tank. The solution temperature is 31℃. Stir and dissolve the solution until there are no undissolved solid particles in the solution. Then, transfer 30kg of the phosphate stock solution to the crystallization kettle for later use. S2. Water at 25°C is introduced into the jacket of the crystallization vessel to rapidly reduce the solution temperature. When the solution temperature in the vessel drops to 25°C, 8% of the total acid mass of rhomboid plate-shaped seed crystals with a particle size range of 1-2 mm are added.

[0039] S3. After adding the seed crystal, the jacket water is kept at 25℃ for 2.5 hours. The jacket water temperature is then adjusted to 23℃ and kept at 2 hours. The jacket water temperature is then adjusted to 21℃ and kept at 1.5 hours. The crystal length and diameter are observed to grow to 3-6 mm. The jacket water inlet temperature is then adjusted to 0℃. The crystal grows rapidly, the solid content in the solution increases significantly, and the crystal layer on the reactor wall also thickens.

[0040] S4. When there is basically no mother liquor in the kettle, heat the jacket water to 29°C and keep it at that temperature for 40 minutes.

[0041] S5. After the crystal layer is peeled off from the reactor wall, the slurry in the crystallization reactor is fed into a centrifugal dehydrator for mother liquor separation. After the mother liquor separation is completed, 100g of deionized water is added for dehydration and washing. The separated mother liquor is recycled back to the mixing tank for reuse, and the phosphate crystals are fed into the mixing tank and mixed with water to form a product of the specified concentration.

[0042] The impurity content and yield at each stage are shown in Table 3.

[0043] Table 3 Impurity content and yield at each stage of Example 3

[0044] Comparative Example S1. Prepare a phosphate stock solution with a concentration of 85% from the mixing tank. The solution temperature is 30℃. Stir and dissolve the solution until there are no undissolved solid particles in the solution. Then, transfer 30 kg of the phosphate stock solution to the crystallization kettle for later use. S2. Water at 25°C is introduced into the jacket of the crystallization vessel to rapidly reduce the solution temperature. When the solution temperature in the vessel drops to 25°C, 5% of the total acid mass of rhomboid plate-shaped seed crystals with a particle size range of 1-2 mm are added.

[0045] S3. After adding the seed crystals, the jacket water inlet temperature was adjusted to 0℃. The crystals initially showed some growth, with significant secondary nucleation. The solution turbidity increased, and the crystal length ranged from 0.2 to 3 mm. Simultaneously, numerous fine crystals gradually formed along the vessel wall. As the temperature difference between the inside and outside of the vessel increased, the heat transfer efficiency decreased, the crystal layer on the vessel wall thickened, and the crystal growth rate in the solution slowed down further.

[0046] S4. After the jacket water is kept at a constant temperature for 8 hours, when the solution temperature drops to 11℃, the suspension density of the crystals in the solution is low. The jacket water is then heated to 29℃ and kept at a constant temperature for 2 hours and 10 minutes. After the crystal layer peels off the vessel wall, the mother liquor is discharged to separate.

[0047] S5. The slurry in the crystallization vessel is fed into a centrifugal dehydrator for mother liquor separation. After the mother liquor separation is completed, 100g of deionized water is added for dehydration and washing. The yield of the unwashed crystals is 32%, and the yield after washing is only 25%.

[0048] The impurity content and yield at each stage are shown in Table 4.

[0049] Table 4. Impurity content and yield at each stage of the comparative example

[0050] Unlike the example, the comparative example did not perform staged cooling after introducing the seed crystals, but directly adjusted the cooling water temperature to 0°C. However, in actual operation, after adding the seed crystals, the temperature of the solution inside the reactor will continue to rise due to the exothermic reaction of crystallization. The low temperature of the jacket water leads to an increased temperature difference between the inside and outside of the reactor. This temperature difference makes the stagnant layer of solution on the reactor wall more prone to crystallization and the formation of crystal layers. As the thickness of the crystal layer increases, the heat transfer efficiency between the inside and outside of the reactor decreases, and the crystal layer becomes thicker and thicker. This cycle makes it difficult to lower the solution temperature, takes a long time to cool and crystallize, results in small crystal particles, and a thick crystal layer. At the same time, the ever-increasing temperature difference also causes severe secondary nucleation. Since the crystals entrained in the crystal layer are mostly formed by secondary nucleation, the particle size is basically less than 3mm. The excessively high density of crystals in the crystal layer makes the later crystal layer peeling stage time longer, and the fine crystals will melt away during the process, leading to a decrease in product yield. In addition, due to the small particle size and large specific surface area of ​​the crystal slurry, the quality of the crystals is difficult to improve after centrifugation and washing.

[0051] The present invention and its embodiments have been described above. This description is not restrictive. In short, if a person skilled in the art is inspired by this description and designs a similar structure and embodiment without departing from the spirit of the present invention, such design should fall within the protection scope of the present invention.

Claims

1. A method for preparing high-yield electronic-grade phosphoric acid, characterized in that, Includes the following steps: S1. Prepare a phosphoric acid solution; S2. Introduction of seed crystals: Cooling the phosphoric acid solution obtained in S1 by passing a coolant through it, and adding seed crystals after the solution temperature drops to the same level as the coolant; S3. Cooling and crystallization: After adding seed crystals, keep the temperature constant and then gradually cool down. Once the crystal size grows to 2-10 mm, cool down rapidly until the solution temperature reaches the end point of cooling and crystallization. S4. Crystal layer peeling: After the solution temperature reaches the cooling crystallization endpoint, the temperature is raised and held. S5. Separation and washing: After the crystal layer is peeled off from the vessel wall, centrifugation is performed to separate the mother liquor, and the mother liquor is washed with deionized water to obtain electronic grade phosphoric acid; S3 describes 2-4 cooling cycles, with a single cooling range of 2-5℃, followed by 1-4 hours of constant-temperature cooling after each cooling cycle. The rapid cooling stage described in S3 uses a coolant at 0-10℃ for cooling.

2. The method for preparing high-yield electronic-grade phosphoric acid as described in claim 1, characterized in that, The phosphoric acid solution described in S1 has a total impurity content of <50ppm, a phosphoric acid concentration of 85%-90%, and a temperature of 30-40℃.

3. The method for preparing high-yield electronic-grade phosphoric acid as described in claim 1, characterized in that, The coolant temperature described in S2 is 20-30℃.

4. The method for preparing high-yield electronic-grade phosphoric acid as described in claim 1, characterized in that, The seed crystals described in S2 are rhomboid plates with a particle size of 0.1~3mm, and the mass ratio of the seed crystals added to the phosphoric acid solution is 1~10:

100.

5. The method for preparing high-yield electronic-grade phosphoric acid as described in claim 1, characterized in that, The constant temperature cooling time after adding the seed crystals, as described in S3, is 1-4 hours.

6. The method for preparing high-yield electronic-grade phosphoric acid as described in claim 1, characterized in that, The crystallization endpoint described in S3 is 10-20℃.

7. The method for preparing high-yield electronic-grade phosphoric acid as described in claim 1, characterized in that, The heating and heat preservation method described in S4 is to heat the coolant to 25-30℃ and keep it at that temperature for 0-4 hours.

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