A method for controlling the endpoint of alkaline hydrolysis reaction of fluorosilicates

Abstract

This invention belongs to the field of chemical production technology, specifically relating to a method for controlling the endpoint of an alkaline hydrolysis reaction of fluorosilicates. The method includes the following steps: gradually adding a strong alkali solution to the fluorosilicate for alkaline hydrolysis; near the reaction endpoint, adding an alkali metal carbonate to continue the reaction until the endpoint is reached. This method is simple and convenient to operate, allows adjustment of the reaction endpoint to a predetermined value, avoids affecting the quality of silica due to excessive addition of strong alkali, and ensures complete alkaline hydrolysis of fluorosilicates.

Description

Technical Field

[0001] This invention belongs to the field of chemical production technology, specifically relating to a method for controlling the endpoint of alkaline hydrolysis reaction of fluorosilicates. Background Technology

[0002] Silica, scientifically known as light silica, is mainly used as a dispersant in pesticides and fire extinguishers, and as a reinforcing agent in rubber and plastics. The traditional production method of silica is the water glass acid hydrolysis method, but this method produces complex silica polymers and other impurities, which affect the quality of silica.

[0003] Currently, potassium hydroxide is generally used as an alkaline hydrolysant to prepare potassium fluoride and silica. At the end of the reaction, the alkali addition endpoint is controlled according to the pH value. For example, Chinese invention patent CN 101028934A discloses a method for producing potassium fluoride and silica by reacting potassium hydroxide with fluorosilicic acid or potassium fluorosilicate to obtain potassium fluoride and silica. The pH value at the end of the reaction is between 8 and 11.

[0004] However, the above-mentioned methods for controlling the endpoint of alkali addition are prone to two problems. First, excessive potassium fluorosilicate leads to incomplete alkali hydrolysis, with residual potassium fluorosilicate entering the silica, becoming an impurity and wasting raw materials due to insufficient reaction. Second, the strong alkalinity of potassium hydroxide means that even a slight excess can cause the silica to dissolve, turning it into silica gel or even water glass, thus affecting the product quality. Therefore, existing methods for controlling the endpoint of the fluorosilicate alkali hydrolysis reaction have a significant impact on the quality of the by-product silica and the alkali hydrolysis rate of fluorosilicates. Summary of the Invention

[0005] The purpose of this invention is to provide a method for controlling the endpoint of the alkaline hydrolysis reaction of fluorosilicates. This method can adjust the reaction endpoint to a predetermined value, avoid affecting the quality of silica due to excessive strong alkali, and ensure complete alkaline hydrolysis reaction. The method is simple and convenient to operate.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A method for controlling the endpoint of an alkaline hydrolysis reaction of fluorosilicates includes the following steps: gradually adding a strong alkaline solution to perform alkaline hydrolysis of fluorosilicates; when the reaction is nearing its endpoint, adding an alkali metal carbonate to continue the reaction until the endpoint is reached.

[0008] The fluorosilicate alkaline hydrolysis reaction endpoint control method of the present invention uses an alkali metal carbonate instead of a strong alkali to continue the reaction with the fluorosilicate near the reaction endpoint. Since the alkali metal carbonate is weakly alkaline, the pH change of the system is relatively gradual when the alkali metal carbonate is added, which makes it easier to control the reaction endpoint and ensure that the fluorosilicate reaction is complete. Even if the alkali metal carbonate is slightly excessive, it will not dissolve the silica and will not affect the quality of the silica. The fluorosilicate alkaline hydrolysis reaction endpoint control method of the present invention has good control effect and is simple and convenient to operate. It can not only avoid the impact of excessive strong alkali on the quality of silica, but also ensure the complete alkaline hydrolysis reaction and avoid waste of raw materials.

[0009] To facilitate control of the endpoint of the alkaline hydrolysis reaction of fluorosilicates, preferably, the pH of the reaction system is monitored during the alkaline hydrolysis reaction, and the pH of the system near the reaction endpoint is 8.0-8.5, and the pH of the system at the endpoint is 8.5-9; the pH of the system at the endpoint is greater than the pH of the system near the reaction endpoint.

[0010] Preferably, when the reaction is near its endpoint, the amount of strong alkali solution used is 90-95% of the theoretical amount.

[0011] Preferably, the amount of alkali metal carbonate added is 1.5 to 2 times the theoretical amount. The molar ratio of carbonate ions in the alkali metal carbonate to hydroxide ions in the strong alkaline solution is 0.08 to 0.16:3.6, and the strong alkaline solution is the strong alkaline solution actually used in the alkaline hydrolysis reaction of this invention. Preferably, the molar ratio of carbonate ions in the alkali metal carbonate to hydroxide ions in the strong alkaline solution is 0.16:3.6.

[0012] Preferably, the reaction temperature is 75–95°C.

[0013] Preferably, the alkaline hydrolysis involves gradually adding a strong alkaline solution to fluorosilicate and water, wherein the mass ratio of fluorosilicate to water is 1:4 to 5.

[0014] Preferably, the fluorosilicate is potassium fluorosilicate or sodium fluorosilicate.

[0015] Preferably, the strong alkaline solution is a potassium hydroxide solution or a sodium hydroxide solution.

[0016] Preferably, the alkali metal carbonate is potassium carbonate or sodium carbonate.

[0017] Preferably, after the reaction is completed, solid-liquid separation is performed, and the filter cake is washed and dried to obtain silica. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the process of the present invention. Detailed Implementation

[0019] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0020] I. Specific embodiments of the fluorosilicate alkaline hydrolysis reaction endpoint control method of the present invention are as follows:

[0021] Example 1

[0022] The endpoint control method for the alkaline hydrolysis reaction of fluorosilicates in this embodiment includes the following steps:

[0023] Weigh 100g of 90% potassium fluorosilicate, 172g of 48% potassium hydroxide solution (the theoretical amount of potassium hydroxide solution is the amount of potassium hydroxide required for the complete reaction of potassium hydroxide and potassium fluorosilicate; in this embodiment, the theoretical amount of potassium hydroxide solution is 191g, and the amount added in this embodiment is 90% of the theoretical amount required), and 400g of water. Add the potassium hydroxide solution to the potassium fluorosilicate slurry for alkaline hydrolysis reaction at a reaction temperature of 75℃ and a reaction time of 2h. The reaction formula is shown in formula (1):

[0024] K2SiF6+4KOH→6KF+SiO2+2H2O (1);

[0025] During the alkaline hydrolysis reaction, the pH of the reaction system was monitored. When the pH of the system was 8.2, 22.6 g of potassium carbonate solid (theoretically required amount was 11.3 g) was added and reacted with potassium fluorosilicate until the endpoint was reached. The reaction temperature was 75℃ and the reaction time was 0.5 h. The endpoint pH of the system was 8.5-9. The reaction formula is shown in formula (2).

[0026] K2SiF6+2K2CO3→6KF+SiO2+2CO2↑ (2);

[0027] After the reaction is complete, solid-liquid separation is performed, and the filter cake is washed and dried to obtain silica.

[0028] The flowchart of the fluorosilicate alkaline hydrolysis reaction endpoint control method in this embodiment is shown below. Figure 1 As shown.

[0029] Example 2

[0030] Weigh 100g of sodium fluorosilicate with a content of 90%, 153g of sodium hydroxide solution with a content of 45% (the amount added is 90% of the theoretical required amount), and 330g of water. Add the sodium hydroxide solution to the sodium fluorosilicate slurry to carry out alkaline hydrolysis reaction. The reaction temperature is 95℃ and the reaction time is 2h. The reaction formula is shown in formula (3):

[0031] Na2SiF6+4NaOH→6NaF+SiO2+2H2O (3);

[0032] During the alkaline hydrolysis reaction, the pH of the reaction system was monitored. When the pH of the system was 8.2, 30g of sodium carbonate solid (theoretically required amount is 20g) was added and reacted with sodium fluorosilicate until the endpoint was reached. The reaction temperature was 95℃ and the reaction time was 0.5h. The endpoint pH of the system was 8.5~9. The reaction formula is shown in formula (4):

[0033] Na2SiF6+2Na2CO3→6NaF+SiO2+2CO2↑ (4);

[0034] After the reaction is complete, solid-liquid separation is performed, and the filter cake is washed and dried to obtain silica.

[0035] The flowchart of the fluorosilicate alkaline hydrolysis reaction endpoint control method in this embodiment is shown below. Figure 1 As shown.

[0036] II. Comparative Example

[0037] Comparative Example 1

[0038] The endpoint control method for the alkaline hydrolysis reaction of fluorosilicate in this comparative example differs from that in Example 1 in that the mass of potassium carbonate solid is 11.3 g and the pH of the reaction endpoint system is 8.5–9.

[0039] III. Experimental Examples

[0040] Experimental Example 1

[0041] The residual amount of potassium fluorosilicate in the silica prepared in Examples 1-2 and Comparative Example 1 was determined, and the results are shown in Table 1:

[0042] Table 1. Residual potassium fluorosilicate in silica

[0043] Group Residual potassium fluorosilicate in silica Example 1 0.2％ Example 2 0.2％ Comparative Example 1 1.5％

[0044] The residual potassium fluorosilicate in silica must be below 1% to meet the requirements. In Comparative Example 1, 11.3g of potassium carbonate was the theoretical feed amount, but the result did not meet the requirements. In Example 1, twice the amount was added, which met the requirements, and the addition of potassium carbonate did not affect the quality of silica. Furthermore, as shown in Table 1 above, the residual potassium fluorosilicate in the silica prepared in Examples 1-2 is very low, indicating that the endpoint control method for the alkaline hydrolysis reaction of fluorosilicates of the present invention has good control effect. It not only avoids affecting the quality of silica due to excessive potassium hydroxide, but also ensures the complete alkaline hydrolysis reaction.

Claims

1. A method for controlling the end point of hydrolysis of a fluosilicate salt, characterized by, The method comprises the following steps: alkali dissolution of fluorosilicate by gradually adding strong alkali solution, and adding alkali metal carbonate to continue the reaction to the end point near the end point of the reaction; The pH of the reaction system is monitored during the alkali dissolution reaction, the pH of the system near the end point of the reaction is 8.0-8.5, and the pH of the system at the end point is 8.5-9; the pH of the system at the end point is greater than the pH of the system near the end point of the reaction.

2. The fluosilicate salt alkaline hydrolysis reaction end point control method according to claim 1, characterized by, The molar ratio of carbonate ions in the alkali metal carbonate to hydroxide ions in the strong alkali solution is 0.08-0.16:3.

6.

3. The fluosilicate salt alkaline hydrolysis reaction end point control method according to claim 1, characterized by, The amount of strong alkali solution near the end point of the reaction is 90-95% of the theoretical amount.

4. The fluosilicate salt alkaline hydrolysis reaction end point control method according to claim 1, characterized by, The addition amount of the alkali metal carbonate is 1.5-2 times the theoretical amount.

5. The method for controlling the end point of the hydrolysis reaction of fluosilicate salt according to any one of claims 1 to 4, characterized by, The temperature of the reaction is 75-95℃.

6. The fluosilicate salt alkaline hydrolysis reaction end-point control method according to claim 1, characterized by, The alkali dissolution is gradually adding strong alkali solution to fluorosilicate and water, and the mass ratio of the fluorosilicate to water is 1:4-5.

7. The fluosilicate salt alkaline hydrolysis reaction end-point control method according to claim 6, characterized in that, The fluorosilicate is potassium fluorosilicate or sodium fluorosilicate.

8. The fluosilicate salt alkaline hydrolysis reaction end point control method according to claim 4, characterized by, The strong alkali solution is potassium hydroxide solution or sodium hydroxide solution.

9. The fluorosilicate alkali decomposition reaction end point control method according to claim 4, characterized by, The alkali metal carbonate is potassium carbonate or sodium carbonate.

10. The fluosilicate salt alkaline hydrolysis reaction end-point control method according to claim 1, characterized by, After the reaction is completed, solid-liquid separation is carried out, the filter cake is washed and dried to obtain white carbon black.

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