CN112299422B - Method for preparing fumed silica and silicon tetrachloride by using fluosilicate - Google Patents
Method for preparing fumed silica and silicon tetrachloride by using fluosilicate Download PDFInfo
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- C01B33/00—Silicon; Compounds thereof
- C01B33/113—Silicon oxides; Hydrates thereof
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Abstract
The invention relates to a method for preparing fumed silica and silicon tetrachloride by utilizing fluosilicate. The method for preparing the fumed silica comprises the following steps: 1) carrying out thermal decomposition on fluorosilicate to prepare silicon tetrafluoride gas; 2) mixing silicon tetrafluoride gas and boron trichloride gas, and introducing the mixture into a priming solution for reaction to obtain silicon tetrachloride; the priming solution is silicon tetrachloride; 3) preparing fumed silica by using the silicon tetrachloride obtained in the step 2) as a raw material. The preparation method of the favorable-gas-phase white carbon black provided by the invention mainly utilizes the reaction of the mixed gas consisting of the silicon tetrafluoride gas and the boron trichloride gas in the priming solution to convert the highly corrosive and dangerous silicon tetrafluoride into silicon tetrachloride, thereby eliminating the potential safety hazard of the silicon tetrafluoride directly participating in the high-temperature hydrolysis reaction to prepare the white carbon black and ensuring that the process route of preparing the gaseous-phase white carbon black by taking the fluosilicate as the upstream raw material is more beneficial to the industrialized implementation.
Description
Technical Field
The invention belongs to the field of preparation of fumed silica, and particularly relates to a method for preparing fumed silica and silicon tetrachloride by using fluosilicate.
Background
The fumed silica is a novel non-toxic, tasteless and amorphous nanoscale inorganic fine chemical product, and has the characteristics of small particle size, large specific surface area, high surface activity and the like. The fumed silica is widely applied to the fields of adhesives, rubber, coatings, medicines, papermaking, printing ink and the like due to the excellent stability, reinforcing property, thickening property and thixotropy of the fumed silica, and has good market prospect.
At present, the gas-phase silicon dioxide is obtained by hydrolyzing the halide of silane at high temperature in oxyhydrogen combustion flame to obtain amorphous silicon dioxide, and the raw materials of the silane halide mainly comprise silicon tetrachloride, trichlorosilane, monomethyl trichlorosilane, dimethyl dichlorosilane and the like. Although the process effectively utilizes industrial byproducts, the process produces a large amount of dilute hydrochloric acid as a byproduct, thereby causing great environmental protection pressure.
The Chinese patent application with publication number CN1208016A discloses a method for producing fumed silica, which comprises the steps of carrying out hydrolysis reaction on silicon tetrachloride, hydrogen and air as raw materials at the temperature of 1000-1100 ℃ to obtain a reactant, and carrying out post-treatment such as aggregation, separation and deacidification on the reactant to obtain the fumed silica product. The industrial cost of the silicon tetrachloride is high, and the production of the fumed silica by directly taking the silicon tetrachloride as the raw material is not beneficial to improving the economic benefit of enterprises.
The Chinese patent with publication number CN103420383B discloses a method for preparing white carbon black and anhydrous hydrofluoric acid by taking fluosilicate which is a phosphate fertilizer byproduct as a raw material, which comprises the steps of pyrolyzing the fluosilicate which is the phosphate fertilizer byproduct at the temperature of 200 ℃ and 400 ℃ to prepare silicon tetrafluoride, mixing the silicon tetrafluoride with air and hydrogen in a hydrolysis reactor after dedusting and washing, carrying out high-temperature hydrolysis reaction, and preparing the anhydrous hydrogen fluoride and the white carbon black by aggregation, separation, dedusting, condensation and rectification. The method has the advantages that the raw materials are easy to obtain and the cost is low, but the toxicity, the corrosivity and the risk degree in the reaction process are high due to the fact that silicon tetrafluoride is used as reaction gas, the free fluorine needs to be reduced by quantitatively adding hydrogen along with the high-temperature decomposition of HF in the later stage of the reaction so as to reduce the damage to a system, and the existing method for producing the fumed silica by taking the fluosilicate as the raw material is not suitable for large-scale industrial production due to the fact that the harsh working condition is controlled and serious corrosion hidden dangers exist at any time.
Disclosure of Invention
The invention aims to provide a method for preparing fumed silica and silicon tetrachloride by utilizing fluorosilicate, so as to solve the problems that the existing method is easy to cause serious corrosion to equipment and is not beneficial to industrial production.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows:
a method for preparing fumed silica and silicon tetrachloride by utilizing fluorosilicate comprises the following steps:
1) carrying out thermal decomposition on fluorosilicate to prepare silicon tetrafluoride gas;
2) mixing silicon tetrafluoride gas and boron trichloride gas, and introducing the mixture into a priming solution for reaction to obtain silicon tetrachloride; the priming solution is silicon tetrachloride;
3) preparing fumed silica by using the silicon tetrachloride obtained in the step 2) as a raw material.
The method for preparing fumed silica and silicon tetrachloride by utilizing fluorosilicate mainly comprises the steps of reacting a mixed gas composed of silicon tetrafluoride gas and boron trichloride gas in a priming solution, increasing the contact area of materials by adopting a liquid-phase reaction medium, improving the reaction efficiency of the mixed gas, efficiently synthesizing silicon tetrachloride, and then preparing the fumed silica by taking the silicon tetrachloride as a raw material. According to the method, on the basis of taking fluosilicate as a raw material, highly corrosive and highly dangerous silicon tetrafluoride is converted into silicon tetrachloride, so that the potential safety hazard of the silicon tetrafluoride directly participating in high-temperature hydrolysis reaction to prepare the white carbon black is eliminated.
The existing process route for preparing fumed silica by taking silicon tetrafluoride as a raw material has the disadvantages of harsh control on working conditions, serious corrosion to equipment in the reaction process and potential safety hazard, and the novel process route of silicon tetrafluoride → silicon tetrachloride → fumed silica can be established by utilizing the preparation method, has mild reaction conditions, low requirements on production equipment, is easy to control the reaction at a stable and safe level, and is a process route more suitable for industrial production.
In the step 1), fluosilicate is a phosphate fertilizer byproduct, and fluorine is used as the by-productThe silicate is at least one of lithium fluosilicate, sodium fluosilicate, potassium fluosilicate, magnesium fluosilicate, calcium fluosilicate and barium fluosilicate. The chemical reactions involved in this step are: mxSiF6→MFy+SiF4And ℃, (M) is Li, Na, K, Mg, Ca, Ba, and x, y can be determined by the principle of valence equilibrium.
The thermal decomposition can be carried out in a fluidized bed, a high-temperature converter, a high-temperature calciner, a rotary kiln, a double-cone device or other pyrolysis furnaces. The temperature of the thermal decomposition is 200-800 ℃. And obtaining crude silicon tetrafluoride gas after thermal decomposition, and obtaining the silicon tetrafluoride gas after dedusting, washing and drying the crude silicon tetrafluoride gas.
Preferably, the thermal decomposition comprises heating to 120-. Through the constant-temperature impurity removal process, free water and volatile impurities in the raw materials can be removed, and the impurity content in the crude silicon tetrafluoride gas is reduced.
Step 2) is a process for preparing silicon tetrachloride by reacting silicon tetrafluoride and boron trichloride, and the related chemical reaction is as follows: 3SiF4+4BCl3→3SiCl4+4BF3↑。
The silicon tetrafluoride gas and the boron trichloride gas are mixed in advance, so that the contact area of the two gases is increased, and preparation is provided for the subsequent reaction. The gas can be uniformly mixed in a short time, so that the reaction main body can be carried out in the priming solution, and the conversion rate of the reaction is improved. The volume ratio of the silicon tetrafluoride gas to the boron trichloride gas is 3 (4-5). The temperature of the reaction is 20-50 ℃. In order to control the reaction to be carried out smoothly and orderly, preferably, the speed of introducing mixed gas formed by mixing silicon tetrafluoride gas and boron trichloride gas into the priming solution is 0.1-1m3And/min. The reaction is carried out with stirring, and the stirring speed can be controlled generally at 50 to 150 rpm/min. The dosage of the bottom solution is proper to submerge the stirring blade of the reaction kettle, and the volume of the silicon tetrachloride is controlled not to exceed 2/3 of the volume of the reaction kettle in the continuous production process.
In the step, the gas obtained after the reaction is cooled to separate out silicon tetrachloride, and then the boron trifluoride product is prepared by rectification and purification. The reacted gas mainly comprises boron trifluoride and a small amount of silicon tetrachloride, boron trichloride gas and silicon tetrafluoride gas. The boiling point difference between the silicon tetrachloride and the other three substances is large, the silicon tetrachloride can be separated by a simple cooling separation means, and the cooling separation temperature is preferably 0-40 ℃, and preferably 20-40 ℃. According to the boiling point difference of boron trifluoride, boron trichloride and silicon tetrafluoride, a high-quality boron trifluoride product can be obtained by utilizing a rectification purification technology. The rectification and purification adopt low-temperature rectification at the temperature of between 80 ℃ below zero and 90 ℃ below zero to achieve good separation and purification effects.
The obtained boron trifluoride product can be used for the industries of novel lithium salt preparation, organic reaction catalysts and semiconductors.
In order to further improve the utilization rate of the raw materials, preferably, the silicon tetrachloride obtained by cooling and separating is returned to the bottoming solution, and the boron trichloride and the silicon tetrafluoride obtained by low-temperature rectification are returned to the bottoming solution.
In the continuous production process, the silicon tetrachloride, the silicon tetrafluoride and the boron trichloride obtained by cooling separation and low-temperature rectification are returned to the step 2), and the obtained high-purity boron trifluoride is compressed, filled and sold.
And step 3) is a process for preparing fumed silica by using silicon tetrachloride, and the fumed silica can be prepared by using a high-temperature hydrolysis reaction of the silicon tetrachloride and water vapor or by using a reaction of the silicon tetrachloride, air and hydrogen. The reactions involved in this step are: SiCl4+2H2+O2→SiO2+4HCl↑。
From the comprehensive consideration of the aspects of reaction efficiency, cost and the like, preferably, the preparation of the fumed silica comprises the following steps: after the silicon tetrachloride is gasified, the silicon tetrachloride is mixed with hydrogen and air to carry out gas-phase hydrolysis reaction. The temperature of the gas phase hydrolysis reaction is 1000-1500 ℃, and 1100-1200 ℃ is preferred. The volume ratio of the hydrogen to the air to the silicon tetrachloride is (1-3) to (3-10) to (0.3-1).
And (3) obtaining a gas-solid mixture containing the fumed silica and the hydrogen chloride gas after the gas-phase hydrolysis reaction, and performing aggregation, dust removal and deacidification treatment on the gas-solid mixture to respectively obtain the fumed silica and the hydrogen chloride gas. The above aggregation, dust removal and deacidification treatments can be realized by using the existing industrial equipment. The carbon white is aggregated into larger particles in the aggregation process, then the larger particles are separated by a dust remover (such as a cyclone separator and the like), the gas-phase white carbon black is sent into a deacidification tower for deacidification treatment, and the byproduct hydrogen chloride gas is returned to a synthesis system for recycling after being dedusted and compressed. The deacidification tower utilizes hot air to remove hydrogen chloride attached to the surface of the fumed silica particles, and the temperature of the hot air can be set to 400-600 ℃.
The method for preparing fumed silica and silicon tetrachloride by utilizing fluorosilicate has the beneficial effects that:
(1) the gas-phase white carbon black and high-purity boron trifluoride are prepared by taking fluosilicate which is a byproduct of phosphate fertilizer as a raw material, and the method has the advantages of low price of the raw material, high added value of products, large market capacity, mature process, low production cost, easy industrial implementation and the like.
(2) The invention avoids the technical difficulties of harsh working condition control, serious equipment corrosion, low conversion rate, poor product quality, high risk and the like in the process of preparing the fumed silica by hydrolyzing the silicon tetrafluoride at high temperature, and is more beneficial to the rapid implementation and popularization of industrialization.
(3) And a liquid phase reaction medium is adopted, so that the contact area of materials is increased, and the reaction conversion rate is improved to more than 90%.
(4) Opens up a new process for producing the fumed silica, does not discharge three wastes, realizes closed cycle of the process, and belongs to the category of clean production.
Drawings
Fig. 1 is a process flow diagram of a method for preparing fumed silica and silicon tetrachloride by using fluorosilicate in embodiment 1 of the present invention.
Detailed Description
The following examples are provided to further illustrate the practice of the invention.
First, a specific embodiment of the method for preparing fumed silica and silicon tetrachloride by using fluorosilicate according to the present invention
Example 1
The method for preparing fumed silica and silicon tetrachloride by using fluorosilicate according to the embodiment has a process flow as shown in fig. 1, and comprises the following steps:
1) preparing silicon tetrachloride: and (3) placing the calcium fluosilicate byproduct of the phosphate fertilizer in a pyrolysis furnace, heating to 200 ℃ firstly, removing impurities at a constant temperature for 0.5h, then continuously heating to 400 ℃, carrying out thermal decomposition to obtain mixed gas, removing calcium fluoride from the mixed gas through dust removal, and washing with concentrated sulfuric acid to remove water and impurities to obtain silicon tetrafluoride gas.
Adding silicon tetrachloride into the reaction kettle as a bottoming solution, wherein the liquid level of the bottoming solution at least submerges the stirring blade, starting stirring, and keeping the rotating speed at 150 rpm/min; uniformly mixing silicon tetrafluoride gas and boron trifluoride gas in a volume ratio of 3:4 in a premixer, and then mixing at 0.5m3The speed of/min is introduced below the liquid level of the bottom solution in the reaction kettle through a bottom inserting pipe, the reaction temperature is controlled to be 50 ℃, and silicon tetrachloride and boron trifluoride are continuously synthesized.
Silicon tetrachloride is discharged from a discharge outlet at the bottom of the reaction kettle. And (3) introducing gas discharged from the top of the reaction kettle into a cooling tower and a rectifying tower, controlling the temperature of the cooling tower to be 20 ℃ and the temperature of the rectifying tower to be 80 ℃ below zero, and removing impurities and purifying to obtain the high-purity boron trifluoride.
2) Hydrolysis of silicon tetrachloride: gasifying silicon tetrachloride, uniformly mixing the gasified silicon tetrachloride with air and hydrogen according to the volume ratio of 0.3:5:1, feeding the mixture into a hydrolysis reactor, controlling the reaction temperature to be 1100 ℃, and carrying out high-temperature gas-phase hydrolysis reaction on the silicon tetrachloride gas to obtain a gas-solid mixture containing the gas-phase white carbon black and the hydrogen chloride gas.
And (3) gathering the gas-solid mixture discharged from the outlet of the hydrolysis reactor into larger particles by a collector, separating by a cyclone separator, feeding the fumed silica into a deacidification tower, and blowing hydrogen chloride attached to the silica particles by hot air at 400 ℃ to obtain the fumed silica product. And dedusting and compressing the byproduct hydrogen chloride gas to obtain a hydrogen chloride product.
Example 2
The method for preparing fumed silica and silicon tetrachloride by using fluorosilicate in the embodiment adopts the following steps:
1) preparing silicon tetrachloride: and (3) placing the sodium fluosilicate byproduct of the phosphate fertilizer into a pyrolysis furnace, heating to 150 ℃ firstly, removing impurities at constant temperature for 1.5h, then continuously heating to 650 ℃, carrying out thermal decomposition to obtain mixed gas, removing sodium fluoride from the mixed gas through dust removal, and washing with concentrated sulfuric acid to remove water and impurities to obtain silicon tetrafluoride gas.
Adding silicon tetrachloride into the reaction kettle as a bottoming solution, wherein the liquid level of the bottoming solution at least submerges the stirring blade, starting stirring, and keeping the rotating speed at 100 rpm/min; uniformly mixing silicon tetrafluoride gas and hydrogen chloride gas in a volume ratio of 3:4.5 in a premixer, and then mixing at a volume of 0.8m3And introducing the solution into the reaction kettle from a bottom inserting pipe at a speed of/min below the liquid level of the bottom solution, controlling the reaction temperature to be 35 ℃, and continuously synthesizing the silicon tetrachloride and the boron trifluoride at normal pressure.
Silicon tetrachloride is discharged from a discharge outlet at the bottom of the reaction kettle. And (3) introducing gas discharged from the top of the reaction kettle into a cooling tower and a rectifying tower, controlling the temperature of the cooling tower to be 30 ℃ and the temperature of the rectifying tower to be-85 ℃, and removing impurities and purifying to obtain the high-purity boron trifluoride.
2) Hydrolysis of silicon tetrachloride: gasifying silicon tetrachloride, uniformly mixing the gasified silicon tetrachloride with air and hydrogen according to the volume ratio of 0.6:8:2, feeding the mixture into a hydrolysis reactor, controlling the reaction temperature to be 1200 ℃, and carrying out high-temperature gas-phase hydrolysis reaction on the silicon tetrachloride gas to obtain a gas-solid mixture containing the gas-phase white carbon black and the hydrogen chloride gas.
And (3) gathering the gas-solid mixture discharged from the outlet of the hydrolysis reactor into larger particles by a collector, separating by a cyclone separator, feeding the fumed silica into a deacidification tower, and blowing hydrogen chloride attached to the silica particles by hot air at 500 ℃ to obtain the fumed silica product. And dedusting and compressing the byproduct hydrogen chloride gas to obtain a hydrogen chloride product.
Example 3
The method for preparing fumed silica and silicon tetrachloride by using fluorosilicate in the embodiment adopts the following steps:
1) preparing silicon tetrachloride: and (3) placing the potassium fluosilicate byproduct of the phosphate fertilizer into a pyrolysis furnace, heating to 120 ℃ firstly, removing impurities at constant temperature for 2 hours, then continuously heating to 700 ℃, carrying out thermal decomposition to obtain mixed gas, removing potassium fluoride from the mixed gas through dust removal, and washing with concentrated sulfuric acid to remove water and impurities to obtain silicon tetrafluoride gas.
Adding silicon tetrachloride into a reaction kettle as a bottoming solution, and dissolving the bottoming solutionThe liquid level of the liquid at least submerges the stirring paddle, then stirring is started, and the rotating speed is kept at 50 rpm/min; uniformly mixing silicon tetrafluoride gas and hydrogen chloride gas in a volume ratio of 3:5 in a premixer, heating to 35 ℃, and then mixing at a pressure of 1.0m3The speed of/min is introduced below the liquid level of the bottom solution in the reaction kettle through a bottom inserting pipe, the reaction temperature is controlled to be 20 ℃, and silicon tetrachloride and boron trifluoride are continuously synthesized under normal pressure.
Silicon tetrachloride is discharged from a discharge outlet at the bottom of the reaction kettle. And (3) introducing gas discharged from the top of the reaction kettle into a cooling tower and a rectifying tower, controlling the temperature of the cooling tower to be 40 ℃ and the temperature of the rectifying tower to be-90 ℃, and removing impurities and purifying to obtain the high-purity boron trifluoride.
2) Hydrolysis of silicon tetrachloride: gasifying silicon tetrachloride, uniformly mixing the gasified silicon tetrachloride with air and hydrogen according to the volume ratio of 1:10:3, feeding the mixture into a hydrolysis reactor, controlling the reaction temperature to be 1300 ℃, and performing high-temperature gas-phase hydrolysis reaction on the silicon tetrachloride gas to obtain a gas-solid mixture containing the fumed silica and the hydrogen chloride gas.
And (3) gathering the gas-solid mixture discharged from the outlet of the hydrolysis reactor into larger particles by a collector, separating by a cyclone separator, feeding the fumed silica into a deacidification tower, and blowing hydrogen chloride attached to the silica particles by hot air at 600 ℃ to obtain the fumed silica product. And dedusting and compressing the byproduct hydrogen chloride gas to obtain a hydrogen chloride product.
Second, test example
The test examples were conducted to examine the performance indexes of fumed silica and high-purity boron trifluoride obtained in each example, and the results are shown in tables 1 and 2.
TABLE 1 detection results of fumed silica obtained in examples
TABLE 2 examination results of boron trifluoride products obtained in examples
| Item | GB/T14603-2009 | Example 1 | Example 2 | Example 3 |
| Purity of boron trifluoride/10-2 | 99.995 | 99.995 | 99.996 | 99.995 |
| Nitrogen content/10-6 | 20 | 16 | 12 | 13 |
| Oxygen + argon content/10-6 | 10 | 8 | 6 | 7 |
| Carbon dioxide content// 10-6 | 5 | 3 | 3 | 3 |
| Carbon tetrafluoride content// 10-6 | 5 | 2 | 1 | 2 |
| Silicon tetrafluoride content// 10-6 | 10 | 9 | 8 | 9 |
| Total impurity content// 10-6 | 50 | 42 | 35 | 40 |
As can be seen from the test results in Table 1, the method of the embodiment realizes the preparation of fumed silica and boron trifluoride by using fluorosilicate, which is a byproduct of phosphate fertilizer, through a milder reaction process, reduces the corrosion to production equipment and the risk degree, and is more beneficial to the rapid implementation and popularization of industrialization. The obtained fumed silica and boron trifluoride have high quality and high added value of products, no three wastes are discharged in the whole production process, and the green and efficient utilization of phosphate fertilizer byproducts is realized.
Claims (8)
1. A method for preparing fumed silica and silicon tetrachloride by utilizing fluorosilicate is characterized by comprising the following steps:
1) carrying out thermal decomposition on fluorosilicate to prepare silicon tetrafluoride gas;
2) mixing silicon tetrafluoride gas and boron trichloride gas, and introducing the mixture into a priming solution for reaction to obtain silicon tetrachloride;
the priming solution is silicon tetrachloride;
3) preparing fumed silica by using the silicon tetrachloride obtained in the step 2) as a raw material;
in the step 2), cooling and separating silicon tetrachloride from the gas obtained after the reaction, and rectifying and purifying to obtain a boron trifluoride product; and returning the silicon tetrachloride obtained by cooling and separating to the bottoming solution, and returning the rectified boron trichloride and silicon tetrafluoride to the bottoming solution.
2. The method for preparing fumed silica and silicon tetrachloride according to claim 1, wherein the thermal decomposition step 1) comprises heating to 120-.
3. The method for preparing fumed silica and silicon tetrachloride by using fluorosilicate according to claim 1, wherein in step 2), the volume ratio of the silicon tetrafluoride gas to the boron trichloride gas is 3 (4-5).
4. The method for preparing fumed silica and silicon tetrachloride according to claim 1, wherein the rate of introducing the mixed gas formed by mixing the silicon tetrafluoride gas and the boron trichloride gas into the priming solution in step 2) is 0.1-1m3/min。
5. The method for preparing fumed silica and silicon tetrachloride by using fluorosilicate according to any one of claims 1 to 4, wherein the temperature of the reaction in step 2) is 20 to 50 ℃.
6. The method for preparing fumed silica and silicon tetrachloride by using fluorosilicate according to claim 1, wherein in step 3), the preparation of fumed silica comprises the following steps: after the silicon tetrachloride is gasified, the silicon tetrachloride is mixed with hydrogen and air to carry out gas-phase hydrolysis reaction.
7. The method for preparing fumed silica and silicon tetrachloride according to claim 6, wherein the volume ratio of hydrogen, air and silicon tetrachloride in step 3) is (1-3): (3-10): (0.3-1).
8. The method for preparing fumed silica and silicon tetrachloride by using fluorosilicate according to claim 6 or 7, wherein the temperature of the vapor phase hydrolysis reaction is 1000-1500 ℃.
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