Method for recovering by-product boric acid and application thereof

Abstract

In order to solve the problem of recovery of a byproduct boric acid in the phenylboronic acid production process, boric acid solids are converted into a fluoboric acid solution, a potassium fluoborate product is prepared through desilicication purification, potassium fluoborate precipitation and impurity removal, and various indexes of potassium fluoborate meet the quality requirements of industrial first-grade products GB / T 22667-2008. According to the technical scheme, boron resources can be effectively recycled, and environmental pollution is reduced; the product raw material cost in the potassium fluoborate industry is reduced; the economic benefit and the environmental benefit are remarkable.

Description

Technical Field

[0001] The present invention belongs to the field of recycling of by - product resources, and particularly relates to a method for recovering by - product boric acid and its application. Background Art

[0002] Potassium fluoborate, also known as potassium boron fluoride, is a white powder or crystal and has a wide range of uses, which mainly include the following aspects: (1) Raw material for preparing aluminum - titanium - boron alloy; (2) Filler in heavy grinding wheels with resin as abrasive binder; (3) Flux for hot welding and copper welding; (4) Raw material for preparing boron trifluoride and other fluoborates.

[0003] The preparation method of potassium fluoborate usually involves first preparing fluoboric acid from hydrofluoric acid and boric acid, and then reacting it with potassium carbonate or potassium hydroxide to prepare potassium fluoborate precipitate. In order to save the preparation cost, production enterprises use borax instead of boric acid, potassium chloride instead of potassium carbonate, and by - product hydrofluoric acid of refrigerant instead of anhydrous acid. However, when using borax as the raw material, it is extremely easy to cause the content of impurities such as sodium, calcium, and magnesium in potassium fluoborate to exceed the standard, which affects the quality of potassium fluoborate and further affects the quality of downstream products using potassium fluoborate as the raw material. Therefore, on the premise of controlling the preparation cost, how to improve the quality of potassium fluoborate products has become a pain point for potassium fluoborate enterprises.

[0004] Phenylboronic acid has high reactivity. As a raw material or intermediate, it has been widely used in the synthesis and separation of various new catalysts and biomolecular materials, such as the synthesis of glycoproteins, drug sustained release, biomass separation, and sugar sensors. During the preparation of phenylboronic acid, by - product boric acid is produced. The by - product boric acid contains organic impurities and cannot be directly sold as a product, resulting in waste of resources. The treatment of by - product boric acid is difficult, and if it is discarded as solid waste, it will cause environmental pollution.

[0005] The invention patent of CN 103402917 A discloses a method for recovering boric acid, which uses an acid to adjust the pH of the boric acid treatment solution to below 4, and separates and purifies boric acid through concentration, boric acid crystallization, and secondary recrystallization. However, due to the small change in the solubility of boric acid with temperature, the secondary recrystallization has high energy consumption, high cost, and low economic benefits. Summary of the Invention

[0006] In order to solve the above - mentioned technical problems, the first aspect of the present invention provides a method for recovering by - product boric acid, including the following steps: Step S1, preparation of fluoboric acid: Dissolve by - product boric acid in water to form a boric acid solution, drop the obtained boric acid solution into fluosilicic acid, and stir for reaction; filter the obtained slurry to obtain a fluoboric acid filtrate; Step S2, desilication of fluoboric acid filtrate: Add sodium fluoride to the fluoboric acid filtrate, stir and react; Filter the obtained slurry to obtain the desilicated fluoboric acid filtrate. Step S3, preparation of potassium fluoborate: Add hydrofluoric acid to the desilicated fluoboric acid filtrate, stir and react; Then add potassium chloride solution to the reacted solution to produce potassium fluoborate precipitate. Step S4, washing and drying of potassium fluoborate: Wash the potassium fluoborate precipitate with water and filter, and place the obtained filter cake in an oven to dry to obtain the potassium fluoborate product.

[0007] The main content of the obtained potassium fluoborate product reaches over 98%, the silicon content is less than 0.2%, and all other indicators can meet the quality requirements of Grade-1 Industrial Products in GB / T 22667-2008.

[0008] The process flow chart of the technical solution of the present invention is shown in Figure 1 .

[0009] The reaction principle of the technical solution of the present invention is as follows: Preparation of fluoboric acid: 2H2SiF6 + 3H3BO3 → 3HBF4 + 2SiO2↓ + 5H2O Desilication of fluoboric acid filtrate: 2NaF + H2SiF6 → Na2SiF6↓ + 2HF Preparation of potassium fluoborate: HBF4 + KCl → KBF4↓ + HCl As a preferred solution, the mass fraction of boric acid solution in the preparation process of fluoboric acid is 8% - 15%.

[0010] As a preferred solution, the molar ratio of fluorine to boron in the preparation process of fluoboric acid is 3.8 - 4.2.

[0011] As a preferred solution, the dropping time of boric acid solution in the preparation process of fluoboric acid is 30 min - 60 min.

[0012] As a preferred solution, the reaction temperature in the preparation process of fluoboric acid is 70°C - 90°C.

[0013] As a preferred solution, the addition amount of sodium fluoride in the desilication process of fluoboric acid filtrate is 3% - 6% of the mass of the fluoboric acid filtrate.

[0014] As a preferred solution, the reaction temperature in the desilication process of fluoboric acid filtrate is 30°C - 50°C.

[0015] As a preferred solution, the addition amount of hydrofluoric acid in the preparation process of potassium fluoborate is 2% - 4% of the mass of the desilicated fluoboric acid filtrate.

[0016] As a preferred solution, the mass ratio of potassium chloride to the desilicated fluoboric acid filtrate in the preparation process of potassium fluoborate is (1.1 - 1.4):1.

[0017] In the second aspect of the present invention, the method for recycling the by-product boric acid is applied to the preparation of potassium fluoborate.

[0018] In the third aspect of the present invention, a potassium fluoborate is provided, which is prepared by the method for recycling the by-product boric acid described above.

[0019] By the above technical solutions, the present invention has the following technical effects: (1) Aiming at the problem of recycling the by-product boric acid in the production process of phenylboronic acid, the present invention converts solid boric acid into fluoboric acid solution, removes impurities through desilication purification and potassium fluoborate precipitation, and obtains a potassium fluoborate product. All indexes of potassium fluoborate meet the quality requirements of first-class industrial products in GB / T 22667-2008, which can effectively recycle boron resources and reduce environmental pollution.

[0020] (2) Compared with the method for preparing potassium fluoborate using hydrofluoric acid as raw material, the technical solution of the present invention can reduce the raw material cost of products in the potassium fluoborate industry and has high economic benefits.

[0021] (3) When preparing potassium fluoborate using fluosilicic acid as raw material, the obtained fluoboric acid contains two structures of trifluoroboric acid and tetrafluoroboric acid, resulting in low purity of potassium fluoborate, high content of impurity silicon dioxide, and low product quality. Compared with the method for preparing potassium fluoborate using fluosilicic acid as raw material, the technical solution of the present invention can improve the purity of potassium fluoborate. Description of the Drawings

[0022] Figure 1 It is a process flow chart for recycling the by-product boric acid. Detailed Embodiments

[0023] The present invention will be further described below in conjunction with embodiments. Unless otherwise specified, the % in the present invention are all mass fractions.

[0024] The by-product boric acid in the embodiments of the present invention all comes from the by-products in the preparation process of phenylboronic acid.

[0025] Embodiment 1 The preparation method of potassium fluoborate includes the following steps: Step S1, preparation of fluoboric acid: Dissolve the by-product boric acid with water to prepare an 8% boric acid solution by mass fraction; then weigh fluosilicic acid according to the molar ratio of fluorine to boron of 3.8:1; drop the obtained boric acid solution into fluosilicic acid, the dropping time is 30 min, after the feeding is completed, stir and react, the reaction time is 30 min, and the reaction temperature is 70 °C; finally, filter the obtained slurry to obtain a fluoboric acid filtrate; Step S2, desilication of fluoboric acid filtrate: Add sodium fluoride to the fluoboric acid filtrate, and the addition amount of sodium fluoride is 3% of the mass of the fluoboric acid filtrate; stir and react for 30 min, the reaction temperature is 30 °C, and the remaining fluosilicic acid in the filtrate is removed; filter the obtained slurry to obtain the desilicated fluoboric acid filtrate. Step S3, preparation of potassium fluoborate: Add hydrofluoric acid to the desilicated fluoboric acid filtrate, and stir and react for 30 min; the addition amount of hydrofluoric acid is 2% of the mass of the desilicated boric acid filtrate; the mass fraction of the hydrofluoric acid is 40%; then add potassium chloride solution to the reacted solution, the mass fraction of the potassium chloride solution is 20%, and the mass ratio of the addition amount of potassium chloride to the mass of the desilicated fluoboric acid filtrate is 1.1:1, stir and react for 30 min to produce potassium fluoborate precipitate. Step S4, washing and drying of potassium fluoborate: Wash and filter the potassium fluoborate precipitate with 200 g of water, and place the obtained filter cake in an oven at 105 °C and dry for 2 h to obtain the potassium fluoborate product.

[0026] The components of the solution obtained in this example and the quality of the potassium fluoborate product are shown in Tables 1 and 2.

[0027] Example 2 The preparation method of potassium fluoborate includes the following steps: Step S1, preparation of fluoboric acid: Dissolve the by-product boric acid in water to prepare a boric acid solution with a mass fraction of 10%; then weigh fluosilicic acid according to the fluorine-boron molar ratio of 3.9:1; add the obtained boric acid solution dropwise to the fluosilicic acid, the dropping time is 40 min, after the feeding is completed, stir and react, the reaction time is 30 min, and the reaction temperature is 80 °C; finally, filter the obtained slurry to obtain the fluoboric acid filtrate. Step S2, desilication of fluoboric acid filtrate: Add sodium fluoride to the fluoboric acid filtrate, and the addition amount of sodium fluoride is 4% of the mass of the fluoboric acid filtrate; stir and react for 30 min, the reaction temperature is 40 °C, and the remaining fluosilicic acid in the filtrate is removed; filter the obtained slurry to obtain the desilicated fluoboric acid filtrate. Step S3, preparation of potassium fluoborate: Add hydrofluoric acid to the desilicated fluoboric acid filtrate, and stir and react for 30 min; the addition amount of hydrofluoric acid is 3% of the mass of the desilicated boric acid filtrate; the mass fraction of the hydrofluoric acid is 40%; then add potassium chloride solution to the reacted solution, the mass fraction of the potassium chloride solution is 20%, and the mass ratio of the addition amount of potassium chloride to the mass of the desilicated fluoboric acid filtrate is 1.2:1, stir and react for 30 min to produce potassium fluoborate precipitate. Step S4, washing and drying of potassium fluoborate: Wash and filter the potassium fluoborate precipitate with 200 g of water, and place the obtained filter cake in an oven at 105 °C and dry for 2 h to obtain the potassium fluoborate product.

[0028] The components of the solution obtained in this example and the quality of the potassium fluoborate product are shown in Tables 1 and 2.

[0029] Example 3 The preparation method of potassium fluoroborate comprises the following steps: Step S1, preparation of fluoboric acid: Dissolve the by-product boric acid with water to prepare a boric acid solution with a mass fraction of 12%; then weigh fluosilicic acid according to the molar ratio of fluorine to boron of 4.0:1; drop the obtained boric acid solution into the fluosilicic acid, the dropping time is 50 min, after the feeding is completed, stir and react, the reaction time is 30 min, and the reaction temperature is 80 °C; finally, filter the obtained slurry to obtain a fluoboric acid filtrate; Step S2, desilication of the fluoboric acid filtrate: Add sodium fluoride to the fluoboric acid filtrate, and the addition amount of sodium fluoride is 5% of the mass of the fluoboric acid filtrate; stir and react for 30 min, the reaction temperature is 40 °C, and the remaining fluosilicic acid in the filtrate is removed; filter the obtained slurry to obtain a desilicated fluoboric acid filtrate; Step S3, preparation of potassium fluoroborate: Add hydrofluoric acid to the desilicated fluoboric acid filtrate, and stir and react for 30 min; the addition amount of hydrofluoric acid is 3% of the mass of the desilicated boric acid filtrate; the mass fraction of the hydrofluoric acid is 40%; then add a potassium chloride solution to the reacted solution, the mass fraction of the potassium chloride solution is 20%, and the mass ratio of the addition amount of potassium chloride to the mass of the desilicated fluoboric acid filtrate is 1.3:1, stir and react for 30 min, and potassium fluoroborate precipitate is produced; Step S4, washing and drying of potassium fluoroborate: Wash and filter the potassium fluoroborate precipitate with 200 g of water, place the obtained filter cake in an oven at 105 °C and dry for 2 h to obtain the potassium fluoroborate product.

[0030] The components of the solution obtained in this example and the quality of the potassium fluoroborate product are shown in Tables 1 and 2.

[0031] Example 4 The preparation method of potassium fluoroborate comprises the following steps: Step S1, preparation of fluoboric acid: Dissolve the by-product boric acid with water to prepare a boric acid solution with a mass fraction of 15%; then weigh fluosilicic acid according to the molar ratio of fluorine to boron of 4.2:1; drop the obtained boric acid solution into the fluosilicic acid, the dropping time is 60 min, after the feeding is completed, stir and react, the reaction time is 30 min, and the reaction temperature is 90 °C; finally, filter the obtained slurry to obtain a fluoboric acid filtrate; Step S2, desilication of the fluoboric acid filtrate: Add sodium fluoride to the fluoboric acid filtrate, and the addition amount of sodium fluoride is 6% of the mass of the fluoboric acid filtrate; stir and react for 30 min, the reaction temperature is 50 °C, and the remaining fluosilicic acid in the filtrate is removed; filter the obtained slurry to obtain a desilicated fluoboric acid filtrate; Step S3, Preparation of Potassium Fluoborate: Hydrofluoric acid is added to the desilicated filtrate of fluoboric acid, and the mixture is stirred and reacted for 30 min. The addition amount of hydrofluoric acid is 4% of the mass of the boric acid desilicated filtrate, and the mass fraction of the hydrofluoric acid is 40%. Then, potassium chloride solution is added to the reacted solution. The mass fraction of the potassium chloride solution is 20%, and the mass ratio of the potassium chloride addition amount to the mass of the fluoboric acid desilicated filtrate is 1.4:1. The mixture is stirred and reacted for 30 min to produce potassium fluoborate precipitate. Step S4, Washing and Drying of Potassium Fluoborate Precipitate: The potassium fluoborate precipitate is washed and filtered with 200 g of water, and the obtained filter cake is placed in an oven at 105 °C and dried for 2 h to obtain the potassium fluoborate product.

[0032] The components of the solution obtained in this example and the quality of the potassium fluoborate product are shown in Tables 1 and 2.

[0033] As can be seen from Table 1, after the slurry in Step S1 is filtered, the mass fraction of silicon in the fluoboric acid filtrate of the example is 0.23% - 0.28%, and the content is relatively low, indicating that the filtration of the slurry in Step S1 can remove silicon dioxide and purify fluoboric acid. The theoretical fluorine-boron molar ratio of fluoboric acid is 4:1, and the fluorine-boron molar ratio in the fluoboric acid filtrate of the example is (3.42 - 3.52):1, which is relatively close to the theoretical fluorine-boron molar ratio, indicating that the purity of fluoboric acid is relatively high.

[0034] After the slurry in Step S2 is filtered, the mass fraction of silicon in the desilicated filtrate of fluoboric acid of the example is 0.11% - 0.18%, and the silicon content is further reduced, indicating that the filtration of the slurry in Step S2 can remove the remaining fluorosilicic acid in the filtrate and further purify fluoboric acid. The theoretical fluorine-boron molar ratio of fluoboric acid is 4:1, and the fluorine-boron molar ratio in the desilicated filtrate of fluoboric acid of the example is (3.75 - 3.91):1, which is closer to the theoretical fluorine-boron molar ratio, indicating that the purity of fluoboric acid is further improved.

[0035] In the process of desilicating the fluoboric acid filtrate of the present invention, the addition amount of sodium fluoride is strictly controlled (the addition amount of sodium fluoride is 3% - 6% of the mass of the fluoboric acid filtrate), so that the residual fluorosilicic acid in fluoboric acid and sodium fluoride are converted into sodium fluorosilicate precipitate and hydrofluoric acid. On the one hand, the residual fluorosilicic acid in the fluoboric acid filtrate is removed, and at the same time, the generated hydrofluoric acid can further increase the proportion of tetrafluoroboric acid in fluoboric acid, improve the main content of potassium fluoborate, and reduce the content of silicon dioxide impurities.

[0036] In Step S3, by adding potassium chloride, boron is precipitated and separated from the liquid phase in the form of potassium fluoborate, and all impurities are transferred to the liquid phase, realizing the separation of potassium fluoborate from impurities and further purifying potassium fluoborate. The obtained potassium fluoborate product has a relatively high purity and a relatively low impurity content, meeting the GB / T 22667-2008 standard.

[0037] In the process of preparing potassium fluoborate according to the present invention, the addition amount of hydrofluoric acid is strictly controlled (the addition amount of hydrofluoric acid is 2% - 4% of the mass of the desilicated filtrate of fluoboric acid), so as to ensure that all the fluoboric acid has a tetrafluoboric acid structure, improve the main content of potassium fluoborate, and at the same time avoid excessive addition, resulting in an increase in raw material costs.

[0038] When only using fluosilicic acid as the raw material to prepare potassium fluoborate, the obtained fluoboric acid contains two structures: trifluoroboric acid and tetrafluoroboric acid. The residual trifluoroboric acid structure therein will lead to low purity of potassium fluoborate. By supplementing a small amount of hydrofluoric acid, the residual trifluoroboric acid structure in the fluoboric acid can be completely converted into a tetrafluoroboric acid structure, thereby ensuring that the purity of potassium fluoborate meets the quality requirements.

[0039] Table 1 Analysis results of the solution components in Example 1 (% are all mass percentages) Table 2 Analysis results of the product quality in Example (% are all mass percentages) The specific embodiments described above further elaborate on the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not used to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for recovering by-product boric acid, characterized in that, Comprising the following steps: Step S1, Preparation of fluoboric acid: Dissolve the by-product boric acid in water to form a boric acid solution, drop the obtained boric acid solution into fluosilicic acid, and stir for reaction; Filter the obtained slurry to obtain a fluoboric acid filtrate; Step S2, Desilication of the fluoboric acid filtrate: Add sodium fluoride to the fluoboric acid filtrate and stir for reaction; Filter the obtained slurry to obtain a desilicated fluoboric acid filtrate; Step S3, Preparation of potassium fluoborate: Add hydrofluoric acid to the desilicated fluoboric acid filtrate and stir for reaction; Then add a potassium chloride solution to the reaction solution to produce a potassium fluoborate precipitate; Step S4, Washing and drying of potassium fluoborate: Wash the potassium fluoborate precipitate with water and filter, and place the obtained filter cake in an oven for drying to obtain a potassium fluoborate product.

2. The method for recovering by-product boric acid according to claim 1, wherein During the preparation of fluoboric acid in step S1, the mass fraction of the boric acid solution is 8% - 15%.

3. The method for recovering by-product boric acid according to claim 1, characterized in that, During the preparation of fluoboric acid in step S1, the molar ratio of fluorine to boron is 3.8 - 4.

2.

4. The method for recovering by-product boric acid according to claim 1, wherein During the preparation of fluoboric acid in step S1, the reaction temperature is 70°C - 90°C.

5. The method for recovering by-product boric acid according to claim 4, wherein During the desilication of the fluoboric acid filtrate in step S2, the addition amount of sodium fluoride is 3% - 6% of the mass of the fluoboric acid filtrate.

6. The method for recycling by-product boric acid according to claim 4, characterized in that, During the desilication of the fluoboric acid filtrate in step S2, the reaction temperature is 30°C - 50°C.

7. The method for recovering by-product boric acid according to claim 6, characterized in that, During the preparation of potassium fluoborate in step S3, the addition amount of hydrofluoric acid is 2% - 4% of the mass of the desilicated fluoboric acid filtrate.

8. The method for recovering by-product boric acid according to claim 6, characterized in that, During the preparation of potassium fluoborate in step S3, the mass ratio of potassium chloride to the desilicated fluoboric acid filtrate is (1.1 - 1.4):

1.

9. Application of the method for recovering the by-product boric acid according to claim 1 in the preparation of potassium fluoborate.

10. A potassium fluoroborate, characterized in that, The potassium fluoborate is prepared by the method according to claim 1.

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