Method for preparing ammonium fluoride and white carbon black by using silicon tetrafluoride

Abstract

The present application relates to a kind of silicon tetrafluoride preparation ammonium fluoride co-production white carbon black method, belong to fluorosilicic comprehensive utilization technical field, comprising the following steps: S1, the mixed gas of silicon tetrafluoride and ammonia is excessively introduced into the ether solution of water, and after reaction and aging, solid-liquid separation is carried out;S2, the solid obtained in S1 is dissolved in water, and solid-liquid separation is carried out again, and the high-quality white carbon black is obtained by washing and drying solid, and the liquid is evaporated and crystallized to obtain ammonium fluoride.The raw material water is dissolved and dispersed in ether solvent, and the silicon dioxide generated in situ after reaction is also dispersed in ether solvent in small particles, so that nanoscale silicon dioxide is obtained, aging makes the particle further stable, reduces agglomeration, and high-quality white carbon black with small particle size and large specific surface area is obtained;Reaction realizes the complete separation of fluorine and silicon, and fluorine element is all transferred to ammonium fluoride, and ammonium fluoride is easy to apply in industry.

Description

Technical Field

[0001] This invention belongs to the field of comprehensive utilization technology of fluorosilicic acid, specifically relating to a method for preparing ammonium fluoride from silicon tetrafluoride and co-producing silica. Background Technology

[0002] In the inorganic fluorine chemical industry, hydrogen fluoride or fluoride salts are commonly used raw materials. Hydrogen fluoride is usually obtained by reacting fluorite and other minerals with acids. However, fluorite resources, especially fluorite, are currently a significant resource, and their mining is strictly controlled. Meanwhile, fluorosilicic acid and silicon tetrafluoride, as byproducts of phosphate fertilizers, contain relatively high levels of fluorine, but their application is difficult or insufficient.

[0003] For example, hydrofluoric acid can be prepared by reacting fluorosilicic acid with concentrated sulfuric acid. This method is simple, low-cost, and has already been industrialized. The chemical reactions involved include:

[0004] H₂SiF₆ + H₂SO₄ (concentrated) → 2HF + SiF₄ + H₂SO₄ (dilute)

[0005] 3SiF4 + 2H2O → 2H2SiF6 + SiO2

[0006] However, as can be seen from the above reaction equation, the separation of fluorine and silicon is incomplete. Only one-third of the fluorine is separated, while the other two-thirds remain in a state of combination with silicon.

[0007] Therefore, how to produce hydrogen fluoride or fluoride salts from silicon tetrafluoride at low cost and high efficiency has always been a challenge in the industry. Patents CN102351150B and CN111960426B provide a method for preparing hydrogen fluoride and co-producing silica by reacting silicon tetrafluoride with water vapor. The two raw materials undergo a hydrolysis reaction at 200-800℃, and the products are separated into hydrogen fluoride and silica by gas-solid separation. The process is simple and efficient, but the rapid separation of hydrogen fluoride and gaseous silica after the reaction is a challenge. If the separation is too slow, hydrogen fluoride may react with silica again to form fluorosilicic acid. Controlling the particle size of silica during the reaction is also a challenge.

[0008] Patent application CN108203096A discloses a method for producing high-purity silica. The method involves reacting high-purity silicon tetrafluoride with high-purity ammonia to generate a silica precipitate. Through solid-liquid separation, washing, and vacuum drying, high-purity silica powder is prepared. However, the resulting silica has a large particle size and a small specific surface area, making it unsuitable for use as silica (generally requiring a specific surface area of ​​190-300 μm²). 2 / g). Patent CN1110450C provides a method for producing activated silica by one-step hydrolysis of silicon tetrafluoride. The method involves directly passing the purified silicon tetrafluoride gas into deionized water containing an appropriate amount of surfactant while stirring rapidly. The hydrolysis temperature is preferably between 45-75℃, and the mass percentage of silica in the final silica-containing slurry is preferably controlled to be between 0.2% and 1.5%. However, this method still has the problem of incomplete separation of fluorine and silicon.

[0009] Patent application CN117023596A describes the addition of an imidazole dispersant during the reaction of fluorosilicic acid and ammonia. After solid-liquid separation and drying, highly dispersible silica is obtained. Patent application CN116022798A describes the addition of a pore-expanding agent during the reaction of fluorosilicic acid solution and ammonia solution. After the reaction is completed, highly dispersible silica is obtained through solid-liquid separation and drying. The pore-expanding agent is a soluble aluminum salt. Summary of the Invention

[0010] This application overcomes the above-mentioned shortcomings and provides a method for preparing ammonium fluoride from silicon tetrafluoride and co-producing silica, achieving the separation of fluorine and silicon, fully utilizing fluorine resources to completely convert them into ammonium fluoride, and simultaneously converting silicon into silica, an important industrial raw material. The objective of this invention is achieved through the following scheme, specifically including the following steps:

[0011] S1, an excess of a mixture of silicon tetrafluoride and ammonia is passed into an ether solution of water, and after reaction and aging, solid and liquid are separated.

[0012] S2, the solid obtained from S1 is dissolved in water, and solid-liquid separation is performed again. The solid is washed and dried to obtain high-quality fumed silica, and the liquid is evaporated and crystallized to obtain ammonium fluoride.

[0013] In step S1, the preferred molar ratio of silicon tetrafluoride to ammonia in the mixed gas is 1:4. The percentage of water in the ether solution is 0.1-2 wt%. An excess of the mixed gas is introduced to ensure complete reaction of the water in the ether solution. The chemical reaction formula is as follows:

[0014] SiF4+4NH3+2H2O→4NH4F+SiO2.

[0015] The silica produced by the above reaction is insoluble in ether and precipitates in solid form. Since a small amount of water is dispersed in the ether solvent, the silica generated in situ after the reaction is also dispersed in the ether solvent as small particles, thus obtaining primary nanoscale silica. The ammonium fluoride produced in the reaction is initially dissolved in water, but as the water is consumed and used up, the ammonium fluoride becomes insoluble in ether and also precipitates in solid form.

[0016] In step S1, the reaction pressure is controlled at 0.1-10 MPa. Under high pressure, the reaction rate between gas and liquid is accelerated, thus improving the reaction efficiency.

[0017] The aging process described in step S1 involves maintaining a temperature of 50-70°C for 1-5 hours after stopping the ventilation and restoring normal pressure. This process further stabilizes the silica particles, reduces agglomeration, and yields high-quality silica with small particle size and large specific surface area.

[0018] Furthermore, adjusting the percentage of water in the mixture can change the amount of silica generated per unit volume, thereby obtaining silica particles with different particle sizes and achieving control over the particle size of the silica product.

[0019] In step S1, the ether solvent in the aqueous ether solution is preferably at least one of tetrahydrofuran, 1,4-dioxane, ethylene glycol dimethyl ether, and diethyl ether. The ether solvent does not participate in the reaction, and the water added after solid-liquid separation can be reused in step S1.

[0020] In step S2, ammonium fluoride is soluble in water, while silicon dioxide is insoluble in water; separation is achieved through water dissolution. Furthermore, because ammonium fluoride readily sublimates upon heating, the mixture of ammonium fluoride and silicon dioxide can also be heated to sublimate the ammonium fluoride, thus achieving separation. This method yields ammonium fluoride with high purity.

[0021] The beneficial effects of this invention are as follows:

[0022] (1) Water is uniformly dissolved and dispersed in the ether solvent, and the silica generated by the reaction is also dispersed in the ether solvent as small particles, thereby obtaining nano-sized silica. Aging further stabilizes the particles, reduces agglomeration, and yields high-quality white carbon black with small particle size and large specific surface area.

[0023] (2) Adjusting the percentage of water in the ether solution can control the degree of dispersion of silica, and thus control the particle size;

[0024] (3) The reaction achieves complete separation of fluorine and silicon, and all fluorine is transferred to ammonium fluoride, which is easy to use in industry.

[0025] This invention, based on the preparation of hydrofluoric acid from fluorosilicic acid (a byproduct of phosphate fertilizer) by reacting with concentrated sulfuric acid, fully utilizes the fluorine and silicon elements in silicon tetrafluoride, which is environmentally friendly and has significant economic and social benefits. Detailed Implementation

[0026] The technical solution of the present invention will be further described in detail below with reference to specific embodiments.

[0027] Example 1

[0028] A method for preparing ammonium fluoride and co-producing silica from silicon tetrafluoride:

[0029] S1. Add 1000g of tetrahydrofuran solution containing 0.5wt% water to a closed reaction vessel, and introduce 240g of a mixture of silicon tetrafluoride and ammonia gas in a molar ratio of 1:4. Maintain the pressure at 0.5MPa, stir slowly to fully react, and after depressurization, maintain the temperature at 60℃ for 3h to separate the solid and liquid.

[0030] S2: The solid obtained from S1 is dissolved in water, and solid-liquid separation is performed again. The solid is washed and dried to obtain 8.1g of high-quality silica, with a yield of 97.1%. The liquid is evaporated and crystallized to obtain 19.2g of ammonium fluoride, with a yield of 93.4%.

[0031] Example 2

[0032] A method for preparing ammonium fluoride and co-producing silica from silicon tetrafluoride:

[0033] S1. Add 1000g of ethylene glycol dimethyl ether solution containing 2wt% water to a closed reaction vessel, and introduce 1800g of a mixture of silicon tetrafluoride and ammonia gas in a molar ratio of 1:4. Maintain the pressure at 1.2 MPa, stir slowly to ensure full reaction, and after depressurization, maintain the temperature at 70°C for 1.5h to separate the solid and liquid.

[0034] S2: The solid obtained from S1 is dissolved in water, and solid-liquid separation is performed again. The solid is washed and dried to obtain 32.4 g of high-quality silica, with a yield of 97.1%. The liquid is evaporated and crystallized to obtain 78.6 g of ammonium fluoride, with a yield of 95.6%.

[0035] Example 3

[0036] A method for preparing ammonium fluoride and co-producing silica from silicon tetrafluoride:

[0037] S1. Add 1000g of ether solution containing 1wt% water to a closed reaction vessel, and introduce 300g of a mixture of silicon tetrafluoride and ammonia gas in a molar ratio of 1:4. Maintain the pressure at 0.2MPa, stir slowly to fully react, and after depressurization, maintain the temperature at 50℃ for 5h to separate the solid and liquid.

[0038] S2: The solid obtained from S1 is dissolved in water, and solid-liquid separation is performed again. The solid is washed and dried to obtain 15.5g of high-quality silica, with a yield of 92.9%. The liquid is evaporated and crystallized to obtain 37.7g of ammonium fluoride, with a yield of 91.7%.

[0039] The silicon tetrafluoride used is obtained by reacting fluorosilicic acid, a byproduct of the phosphate fertilizer industry, with concentrated sulfuric acid.

[0040] Comparative Example 1

[0041] A method for preparing ammonium fluoride and co-producing silica from silicon tetrafluoride involves increasing the water content of the ether solution:

[0042] S1. Add 1000g of tetrahydrofuran solution containing 3wt% water to a closed reaction vessel, and introduce 1200g of a mixture of silicon tetrafluoride and ammonia gas in a molar ratio of 1:4. Maintain the pressure at 0.5 MPa, stir slowly to fully react, and after depressurization, maintain the temperature at 60°C for 3 hours to separate the solid and liquid.

[0043] S2: The solid obtained from S1 was dissolved in water, and solid-liquid separation was performed again. The solid was washed and dried to obtain 48.5 g of silicon dioxide, with a yield of 96.9%. The liquid was evaporated and crystallized to obtain 114.3 g of ammonium fluoride, with a yield of 92.7%.

[0044] Comparative Example 2

[0045] A method for preparing ammonium fluoride and co-producing silica from silicon tetrafluoride involves the direct reaction of ammonia water with silicon tetrafluoride gas.

[0046] S1. Add 1000g of 25wt% ammonia solution to a closed reactor, introduce 50g of silicon tetrafluoride gas, stir slowly to fully react, and maintain at 60℃ for 3h to separate solid and liquid.

[0047] S2, the solid obtained from S1 is washed and dried to obtain 26g of silicon dioxide, and the liquid is evaporated and crystallized to obtain 64g of ammonium fluoride.

[0048] The particle size and specific surface area of ​​the silica or silicon dioxide obtained in the above examples and comparative examples are shown in the table below:

[0049] Example 1 0.5 3.4 230 Example 2 2 6.2 191 Example 3 1 4.4 214 Comparative Example 1 3 8.7 128 Comparative Example 2 / 29.9 36

[0050] The data in the table shows that the particle size and specific surface area of ​​the silica produced vary depending on the percentage of water in the ether solution. In contrast, the silica produced by the direct reaction of silicon tetrafluoride with ammonia has a large particle size and a small specific surface area, and therefore cannot be used as silica.

Claims

1. A method for preparing ammonium fluoride and co-producing silica from silicon tetrafluoride, characterized in that... Includes the following steps: S1, an excess of a mixture of silicon tetrafluoride and ammonia is passed into an ether solution of water, and after reaction and aging, solid-liquid separation is performed; the percentage of water in the ether solution of water is 0.1-2 wt%. S2, the solid obtained from S1 is dissolved in water, and solid-liquid separation is performed again. The solid is washed and dried to obtain high-quality fumed silica, and the liquid is evaporated and crystallized to obtain ammonium fluoride.

2. The method according to claim 1, characterized in that, In step S1, the molar ratio of silicon tetrafluoride to ammonia in the mixed gas is 1:

4.

3. The method according to claim 1, characterized in that, The reaction pressure in step S1 is controlled at 0.1-10 MPa.

4. The method according to claim 1, characterized in that, In step S1, aging involves maintaining a temperature of 50-70°C for 1-5 hours after stopping ventilation and restoring normal pressure.

5. The method according to claim 1, characterized in that, The ether solvent in the aqueous ether solution of step S1 is at least one of tetrahydrofuran, 1,4-dioxane, ethylene glycol dimethyl ether, and diethyl ether.

6. The method according to claim 1, characterized in that, The silicon tetrafluoride is obtained by reacting fluorosilicic acid with concentrated sulfuric acid.

7. The method according to claim 6, characterized in that, The fluorosilicic acid is a byproduct of the phosphate fertilizer industry.