Preparation method of low-cost high-purity potassium fluoborate based on ammonium fluoride

Abstract

The invention discloses a low-cost high-purity potassium fluoborate preparation method based on ammonium fluoride, and belongs to the field of inorganic salt chemical industry, the method comprises the following steps: S1, reacting by-product ammonium fluoride with the purity of more than or equal to 99% with boric acid to synthesize an ammonium fluoborate solution; s2, at 60-80 DEG C, precisely dropwise adding a potassium chloride solution into the ammonium fluoborate solution at a rate of 1-2 mL / (min.L), and carrying out a replacement reaction; s3, performing crystallization and purification by adopting a two-stage gradient cooling program from fast to slow; s4, a low-temperature saturated potassium fluoborate solution and absolute ethyl alcohol are sequentially adopted for targeted washing, and impurities such as chloride ions are effectively removed; and S5, performing vacuum drying to obtain a product. According to the method, the phosphorus fertilizer industrial byproduct ammonium fluoride is originally adopted to replace expensive hydrogen fluoride or fluoboric acid, so that the raw material cost is reduced by 90% or above; meanwhile, impurity inclusion is effectively inhibited, the problem of impurity introduction caused by byproduct raw materials is solved, and the electronic-grade high-purity potassium fluoborate with the main content larger than or equal to 99.95% and the chloride ion smaller than or equal to 10 ppm can be stably prepared.

Description

Technical Field

[0001] This invention belongs to the field of inorganic salt chemistry, and specifically relates to a low-cost, high-purity potassium fluoroborate preparation method based on ammonium fluoride. Background Technology

[0002] High-purity potassium fluoroborate (HBF4), as an important inorganic fluoride, has indispensable applications in many high-tech fields due to its excellent chemical stability and electrochemical properties. These applications include its use as a flux in aluminum and magnesium smelting, a supporting electrolyte in electrochemical analysis, and, in recent years, as a key dopant and etchant raw material in the photovoltaic and semiconductor industries. The purity requirements for HBF4 are becoming increasingly stringent, especially for sodium fluoroborate. + ), chlorine (Cl) - The content of metal and ionic impurities must reach the ppm level (electronic grade standard).

[0003] Currently, the traditional industrial processes for preparing potassium fluoroborate mainly include the following:

[0004] 1. Fluoroboric acid method: This method uses high-purity fluoroboric acid (HBF4) as raw material and reacts it with high-purity potassium hydroxide (KOH) or potassium carbonate (K2CO3) to prepare the product. The process is simple, but the core raw material, fluoroboric acid, is extremely expensive and highly corrosive, resulting in high production costs and huge equipment investment.

[0005] 2. Hydrogen fluoride-boric acid method: Highly toxic and volatile hydrogen fluoride (HF) is passed into a mixed solution of boric acid (H3BO3) and potassium salt (such as KCl) for reaction. This method has relatively low raw material costs, but hydrogen fluoride is a strictly controlled hazardous chemical in China, and its storage, transportation, and use pose significant safety and environmental risks, requiring highly skilled operators and sophisticated equipment.

[0006] 3. Fluoride-boric acid method: This method involves reacting potassium fluoride (KF) or potassium hydrogen fluoride (KHF2) with boric acid. While relatively safe, high-purity potassium fluoride or potassium hydrogen fluoride remains expensive, making the cost advantage less significant.

[0007] The methods described above generally share a common problem: obtaining a high-purity final product often relies on high-purity starting materials, leading to high costs. If industrial-grade raw materials are used, the presence of chloride ions (Cl...) in them... - Impurities such as fluoroborate are easily trapped inside potassium fluoroborate crystals during the crystallization process, and conventional washing methods are difficult to remove them effectively, resulting in product purity that cannot meet the requirements of electronic-grade applications.

[0008] Therefore, developing a green, economical, and safe preparation method that can significantly reduce raw material costs, effectively control impurities, and stably produce electronic-grade high-purity potassium fluoroborate has become a pressing technical challenge in this field. Summary of the Invention

[0009] To address the above deficiencies, this invention provides a low-cost, high-purity potassium fluoroborate preparation method based on ammonium fluoride, comprising the following steps:

[0010] S1. Synthesis of ammonium fluoroborate: Ammonium fluoride and boric acid are added to water at a molar ratio of (4.2-4.5):1, and the mixture is stirred at 60-80℃ for 1-4 hours to obtain an ammonium fluoroborate solution.

[0011] S2, Double decomposition reaction: Preheat the ammonium fluoroborate solution obtained in step S1 to 60-80℃, and add a potassium chloride solution with a concentration of 20-22wt% dropwise at a rate of ≤5mL / (min·L) under strong stirring, wherein the molar ratio of potassium chloride to ammonium fluoroborate is (1.05-1.15):1;

[0012] After the addition is complete, keep it at 60-80℃ for 30-60 minutes to mature;

[0013] S3. Crystallization and purification: Cool the reaction solution from step S2 to 10-15℃ at a rate of 0.5-1℃ / min, and continue stirring at this temperature for 4 to 6 hours. S4. Separation and Washing: Filter at 10-15℃, and wash the filter cake successively with saturated potassium fluoroborate solution at 0-5℃ and anhydrous ethanol until Cl- appears in the filtrate. - The concentration is 5-10 ppm;

[0014] S5. Drying: The washed filter cake is vacuum dried at 60-80℃ to obtain high-purity potassium fluoroborate.

[0015] Further, the ammonium fluoride mentioned in step S1 is a product of the reaction between fluorosilicic acid and ammonia, with a purity ≥99%, and Na... + Content ≤0.1wt%.

[0016] Furthermore, the dropping rate of the potassium chloride solution in step S2 is 1-2 mL / (min·L).

[0017] Furthermore, the cooling process in step S3 is divided into two stages:

[0018] First stage: Cooling from 80℃ to 40℃ at a rate of 0.8℃ / min;

[0019] Second stage: Reduce from 40℃ to 15℃ at a rate of 0.6℃ / min.

[0020] Furthermore, the saturated potassium fluoroborate solution in step S4 is prepared by mixing high-purity potassium fluoroborate and ultrapure water at 0-5°C, and its amount is 20-30% of the filter cake mass.

[0021] Furthermore, step S4 also includes a final washing with anhydrous ethanol, the amount of which is 10-15% of the filter cake mass.

[0022] Furthermore, the vacuum drying conditions in step S5 are a vacuum degree between 0.08 and 0.1 MPa and a drying time of 15 hours.

[0023] Furthermore, steps S1-S5 are carried out entirely in a plastic-lined reactor, and the equipment is made of polypropylene or polytetrafluoroethylene.

[0024] Compared with the prior art, the present invention has the following advantages:

[0025] 1. Significant cost advantage: Using ammonium fluoride, a cheap byproduct of the phosphate fertilizer or fluorosilicic acid industry, as the core fluorine source, replacing expensive fluoroboric acid or dangerous hydrogen fluoride, reduces raw material costs by more than 90%, opening up a new path for the low-cost production of high-purity potassium fluoroborate.

[0026] 2. High product purity and controllable quality: Addressing the issue of impurities introduced by by-product raw materials, this invention employs a combined process of "precision dropping + gradient crystallization + targeted washing." Precision dropping controls the nucleation rate, gradient crystallization promotes perfect crystal growth, and targeted washing with saturated KBF4 solution and anhydrous ethanol efficiently removes Cl... - Key impurities such as Cl are eliminated, and the final product purity can consistently reach over 99.95%. - The content is ≤10ppm, meeting the stringent electronic grade standards.

[0027] 3. The process is environmentally friendly and suitable for industrialization: It uses fluorosilicic acid, a byproduct of the phosphate fertilizer industry, as raw material, avoiding the direct use of hydrofluoric acid and reducing the direct involvement of highly toxic gaseous substances; the reaction conditions are mild, the entire process is carried out in a closed, corrosion-resistant equipment, and the exhaust gas can be effectively collected and treated, reducing secondary pollution, and has good prospects for industrial application. Detailed Implementation

[0028] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. 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 of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0029] Example 1

[0030] This embodiment provides a low-cost, high-purity potassium fluoroborate preparation method based on ammonium fluoride, including the following steps:

[0031] S1. Synthesis of Ammonium Fluoroborate: In a 1000L polytetrafluoroethylene (PTFE)-lined reactor, add 450L of pure water, start stirring, and then sequentially add 112.5kg of boric acid (H3BO3, MW=61.83, 1.82kmol) and 300kg of by-product ammonium fluoride (NH4F, MW=37.04, purity 99.2%, Na... + The content is 0.08wt%, which is equivalent to 8.06kmol of pure NH4F. The molar ratio of NH4F to H3BO3 is 4.43:1. The mixture is heated to 75°C and stirred at this temperature for 2 hours to obtain a clear ammonium fluoroborate (NH4BF4) solution.

[0032] S2, Double displacement reaction: The above NH4BF4 solution was maintained at 75℃;

[0033] Prepare a 21 wt% potassium chloride (KCl) solution (containing 149.5 kg KCl, MW = 74.55, 2.00 kmol). The molar ratio of KCl to NH4BF4 is 1.10:1. Under vigorous stirring, add the KCl solution dropwise to the reactor using a metering pump at a rate of 1.5 mL / (min·L) (relative to the initial total volume of the reactor). The dropwise addition process takes approximately 4 hours.

[0034] After the addition is complete, continue to heat and mature at 75°C for 45 minutes. At this time, the system is a slurry containing a large amount of white crystals precipitated.

[0035] S3, Crystallization and Purification: Start the cooling process:

[0036] First stage: The reaction solution is cooled from 75°C to 40°C at a rate of 0.8°C / min;

[0037] Second stage: Continue to reduce the temperature from 40℃ to 15℃ at a rate of 0.6℃ / min. After reaching 15℃, continue stirring at this temperature for 5 hours (it is necessary to ensure continuous stirring for no less than 4 to 6 hours) to ensure that crystallization is fully completed.

[0038] S4. Separation and washing: The above slurry is centrifuged and filtered at 15°C, and the resulting wet filter cake weighs about 265 kg.

[0039] The filter cake was first washed twice with 70 kg (approximately 26% of the filter cake mass) of saturated high-purity KBF4 aqueous solution pre-cooled to 2°C. Then, it was washed with 30 kg (approximately 11% of the filter cake mass) of anhydrous ethanol. The filtrate was tested after each wash. The final filtrate contained Cl... - The concentration was determined to be 8 ppm by ion chromatography (the Cl concentration must be guaranteed for each test). - (Concentration within the standard range of 5 to 10 ppm)

[0040] S5. Drying: Transfer the washed wet filter cake to a vacuum drying oven and dry it for 15 hours at 70°C and a vacuum degree of 0.088MPa (the vacuum degree in the drying oven must be between 0.08 and 0.1MPa) to obtain a white crystalline powder product.

[0041] A total of 219.5 kg of high-purity potassium fluoroborate was obtained after weighing, with a yield (based on boric acid) of 95.1%. Samples were sent for testing, and the product quality analysis results are shown in Table 1.

[0042] Table 1: Product quality analysis results obtained according to the steps in Example 1

[0043]

[0044] The results show that the potassium fluoroborate prepared in this embodiment has better performance than the electronic grade standard in all aspects, and the product quality is extremely high.

[0045] Example 2

[0046] In this embodiment, steps S1 and S2 are the same as in Example 1, but in the metathesis reaction (S2), the dropping rate of KCl solution is increased to 4.5 mL / (min·L);

[0047] In addition, in step S3 crystallization purification: a single-rate cooling method was used, and the reaction solution was directly cooled from 75°C to 12°C at a constant rate of 0.9°C / min, and stirred at 12°C for 4 hours.

[0048] The remaining steps S4 and S5 are the same as in Example 1.

[0049] The final yield was 216.8 kg of high-purity potassium fluoroborate, with a yield of 94.0%. The product quality analysis results are shown in Table 2.

[0050] Table 2: Product quality analysis results obtained according to the steps in Example 2

[0051]

[0052] The results show that even with a faster dropping rate and a single cooling rate, the method of this invention can still produce products that meet electronic grade standards, demonstrating that this technical solution has good process tolerance and stability. The iron, sulfate, heavy metals and moisture are controlled by the purity of the raw materials and general process conditions (such as using high-purity byproduct NH4F, PTFE-lined reactor, and vacuum drying), and will not change significantly due to parameter fine-tuning.

[0053] To more intuitively illustrate the necessity of gradient crystallization and targeted washing steps, the following comparative example is added:

[0054] Steps S1 and S2 are the same as in Example 1;

[0055] Step S3 Crystallization: The 75°C reaction slurry is directly pumped into a crystallization vessel with a jacket containing 0°C cooling water. The temperature is rapidly reduced to 15°C within 30 minutes, and then stirred for 1 hour (i.e., the "impact cooling" method used in traditional industrial production to pursue efficiency is adopted).

[0056] Step S4 Separation and Washing: The filtered filter cake is washed with only an equal volume of 0°C pure water until the washing liquid shows no obvious Cl-. - Reaction (qualitative analysis with silver nitrate);

[0057] Step S1 is the same as in Example 1.

[0058] The final yield of potassium fluoroborate product was 215.0 kg. The product quality analysis results are shown in Table 3.

[0059] Table 3: Product quality analysis results obtained according to the steps in the comparative example

[0060]

[0061] A comparison of the results of Examples 1 and 2 with Comparative Example 1 shows that the traditional method of shock cooling and ordinary water washing (Comparative Example 1) results in incomplete crystal growth due to the excessively rapid cooling rate, leading to a large number of impurities (especially Cl). - and Na + Impurities are trapped inside the crystal lattice and cannot be removed even by washing, resulting in low main content and serious excess of impurities in the product, far from meeting the electronic grade standard (although the iron, sulfate, heavy metals and water content are different from those in Table 1, they still meet the standard). The gradient cooling crystallization (Example 1) and specific targeted washing method used in this invention can significantly improve the purity of the product and effectively remove impurities, which is the key to realizing the preparation of high-purity products using low-cost raw materials.

[0062] It should be noted that the structure described in this invention can be implemented in many different forms and is not limited to the embodiments described. Any equivalent transformations made by those skilled in the art based on the content of this specification, or direct or indirect applications in other related technical fields, such as the loading and unloading of other items, are included within the protection scope of this invention.

Claims

1. A low-cost, high-purity potassium fluoroborate preparation method based on ammonium fluoride, characterized in that, Includes the following steps: S1. Synthesis of ammonium fluoroborate: Ammonium fluoride and boric acid are added to water at a molar ratio of (4.2-4.5):1, and the mixture is stirred at 60-80℃ for 1-4 hours to obtain an ammonium fluoroborate solution. S2, Double decomposition reaction: Preheat the ammonium fluoroborate solution obtained in step S1 to 60-80℃, and add a potassium chloride solution with a concentration of 20-22wt% dropwise at a rate of ≤5mL / (min·L) under strong stirring, wherein the molar ratio of potassium chloride to ammonium fluoroborate is (1.05-1.15):1; After the addition is complete, keep it at 60-80℃ for 30-60 minutes to mature; S3. Crystallization and purification: Cool the reaction solution from step S2 to 10-15℃ at a rate of 0.5-1℃ / min, and continue stirring at this temperature for 4 to 6 hours. S4. Separation and Washing: Filter at 10-15℃, and wash the filter cake successively with saturated potassium fluoroborate solution at 0-5℃ and anhydrous ethanol until Cl- appears in the filtrate. - The concentration is 5-10 ppm; S5. Drying: The washed filter cake is vacuum dried at 60-80℃ to obtain high-purity potassium fluoroborate.

2. The method for preparing low-cost, high-purity potassium fluoroborate based on ammonium fluoride as described in claim 1, characterized in that: The ammonium fluoride mentioned in step S1 is a product of the reaction between fluorosilicic acid and ammonia, with a purity ≥99%, Na + Content ≤0.1wt%.

3. The method for preparing low-cost, high-purity potassium fluoroborate based on ammonium fluoride as described in claim 1, characterized in that: The potassium chloride solution is added at a rate of 1-2 mL / (min·L) in step S2.

4. The method for preparing low-cost, high-purity potassium fluoroborate based on ammonium fluoride as described in claim 1, characterized in that: The cooling process in step S3 is divided into two stages: First stage: Cooling from 80℃ to 40℃ at a rate of 0.8℃ / min; Second stage: Reduce from 40℃ to 15℃ at a rate of 0.6℃ / min.

5. The method for preparing low-cost, high-purity potassium fluoroborate based on ammonium fluoride as described in claim 1, characterized in that: The saturated potassium fluoroborate solution in step S4 is prepared by mixing high-purity potassium fluoroborate and ultrapure water at 0-5°C, and its amount is 20-30% of the filter cake mass.

6. The method for preparing low-cost, high-purity potassium fluoroborate based on ammonium fluoride as described in claim 1, characterized in that: Step S4 further includes a final washing with anhydrous ethanol, the amount of which is 10-15% of the filter cake mass.

7. The method for preparing low-cost, high-purity potassium fluoroborate based on ammonium fluoride as described in claim 1, characterized in that: The vacuum drying conditions in step S5 are a vacuum degree between 0.08 and 0.1 MPa and a drying time of 15 hours.

8. The method for preparing low-cost, high-purity potassium fluoroborate based on ammonium fluoride as described in claim 1, characterized in that: Steps S1-S5 are carried out entirely in a plastic-lined reactor, and the equipment is made of polypropylene or polytetrafluoroethylene.

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