Method for synthesizing silica sol by using loop reactor and method for synthesizing silicon dioxide

Abstract

The invention discloses a method for synthesizing silica sol by adopting a loop reactor and a method for synthesizing silicon dioxide. The vacuum suction feeding mode of the Venturi jet mixer in the loop reactor is adopted, and the system has the advantages that no return gas exists, the blockage and corrosion phenomena caused by return gas of the raw material silicon tetrachloride and the by-product hydrogen chloride are avoided, and the system can stably run for a long time. Compared with the problem of product agglomeration caused by violent reaction, mass transfer and untimely mixing of silicon tetrachloride liquid-phase hydrolysis in a traditional tank reactor, high-speed water flow shears sucked gaseous silicon tetrachloride into fine bubbles and forms turbulent flow, the gas-liquid mixing effect is enhanced, the water amount at the two-phase mixing position is always excessive, and the reaction time is shortened. The problem that the concentration of local silicic acid is too high to cause polycondensation to generate agglomerates is avoided, and homogeneous silica sol can be obtained. The yield of silicon dioxide is greater than 93% and is far greater than the yield in a traditional tank reactor.

Description

Technical Field

[0001] This invention belongs to the field of inorganic non-metallic material synthesis technology, specifically relating to a method for synthesizing silica sol using a loop reactor and a method for synthesizing silicon dioxide. Background Technology

[0002] Silicon tetrachloride is a byproduct of polysilicon production and is highly corrosive and polluting to water, soil, air, and equipment. With the continuous expansion of polysilicon production capacity, the large quantities of silicon tetrachloride are placing severe environmental and safety pressures on the polysilicon industry. Utilizing silicon tetrachloride for high-value-added purposes is not only an economic issue for enterprises to reduce costs and increase efficiency, but also a core issue related to the development of the entire photovoltaic and semiconductor industry chain.

[0003] The liquid-phase hydrolysis method of silicon tetrachloride involves the hydrolysis of silicon tetrachloride in a liquid environment (water) to form silicic acid and hydrogen chloride, which yields silica sol. After further drying, silica can be obtained. Both high-purity silica sol and silica have broad application prospects.

[0004] For example, invention application CN102583397A discloses a method for preparing silicon dioxide and hydrogen chloride by hydrolyzing silicon tetrachloride, a byproduct of polycrystalline silicon. Additives and surfactants are added to a closed reaction vessel containing a 5%-30% (w / w) hydrochloric acid aqueous solution. Then, silicon tetrachloride is added to the closed reaction vessel, with the silicon tetrachloride flow rate controlled at 0.4-0.9 mg / L. 3 The hydrolysis reaction is carried out at a controlled temperature of 20-50℃ per hour to generate silica sol and hydrogen chloride gas. The hydrogen chloride gas is dried and then recycled. The silica sol is allowed to stand and age to form silica precipitate. The silica precipitate is filtered and washed to remove residual additives. The washed silica precipitate is dried to obtain precipitated silica.

[0005] Chinese patent application CN102515104A discloses a method for preparing hydrogen chloride and silicon dioxide by hydrolysis of silicon tetrachloride in an organic solvent. The method involves adding water to a mixed solution prepared from silicon tetrachloride, an organic solvent, and a surfactant, using an organic solvent as the medium, to carry out a hydrolysis reaction that produces hydrogen chloride gas and silicon dioxide. The organic solvent is one or a mixture of two aromatic halogenated compounds containing 6-8 carbon atoms. The surfactant is either sodium dodecylbenzenesulfonate or alkylphenol polyoxyethylene ether.

[0006] However, the liquid-phase hydrolysis reaction of silicon tetrachloride is vigorous and highly exothermic. Silicon tetrachloride has a low boiling point (57.6℃), leading to significant volatilization during feeding and reaction. This volatilization also results in the deposition of large amounts of white solids on the inner wall of the upper gas phase space in traditional batch reactors, easily causing equipment and pipeline blockage. The limited mass transfer and mixing capacity in traditional batch reactors, coupled with excessively high local silicic acid concentrations, causes rapid condensation to form amorphous silica, which easily leads to agglomeration. The hydrolysis byproduct, hydrogen chloride, is highly corrosive, easily corroding equipment and introducing impurities. Therefore, it is difficult to scale up the liquid-phase hydrolysis reaction of silicon tetrachloride using traditional batch reactors. Summary of the Invention

[0007] This invention addresses the aforementioned technical problems by providing a method for synthesizing silica sol and silica using a loop reactor. By utilizing the unique structure of the Wenchuli ejector in the loop reactor and the resulting negative pressure, it achieves non-return gas feeding and enhanced mixing. This solves the problems of solid deposition on the inner wall, uneven mass transfer and mixing, and agglomeration in the liquid-phase hydrolysis reaction of silicon tetrachloride in traditional batch reactors, resulting in a homogeneous high-purity silica sol.

[0008] The high-purity silica sol synthesized by the present invention can be further dried to obtain high-purity silica with a large specific surface area and uniform pore size.

[0009] This invention first provides a method for synthesizing silica sol using a loop reactor, the loop reactor comprising: The reactor has a water inlet pipe at the top and a discharge pipe at the bottom, the discharge pipe having a liquid outlet. A Venturi injector, comprising an injection inlet, an injection outlet, and an ejector port, wherein the injection inlet and ejector port are located outside the reaction vessel, and the injection outlet extends into the reaction vessel; A circulation pipe is connected at one end to the bottom of the reactor or to the discharge pipe, and at the other end to the injection inlet. A circulation pump is installed on the circulation pipe. A vaporization tank is connected to the injection port via a vaporization pipe; The method includes the following steps: adding water to the reaction vessel through the water inlet pipe, driving the water flow into the injection inlet by the circulation pump, heating the gasification tank to vaporize the silicon tetrachloride stored in the gasification tank, and drawing the vaporized silicon tetrachloride into the reaction vessel from the injection port and reacting with the water flow. The process is repeated until the reaction is completed, and the silica sol product is collected from the liquid outlet of the discharge pipe.

[0010] Furthermore, the other end of the water supply pipe is connected to a water storage tank, and the water supply pipe is equipped with a horizontal flow pump that drives water from the water storage tank into the reaction vessel.

[0011] Furthermore, the vaporization tank is also equipped with a heating element, which may be a heating jacket.

[0012] Furthermore, when heating the vaporization tank to vaporize the silicon tetrachloride stored inside, the heating temperature is 45~65°C.

[0013] Furthermore, the water added to the reactor is ultrapure water with a resistivity of 18.2 MΩ·cm; The silicon tetrachloride is electronic grade silicon tetrachloride with a total metal impurity content of less than 1 ppm.

[0014] To avoid excessively high silica sol concentration leading to gelation and excessively low concentration leading to excessively high drying costs, the molar ratio of water to silicon tetrachloride is preferably 80~120:1.

[0015] To ensure the corrosion resistance of the container and avoid the introduction of metallic impurities, preferably, the reactor is made of one of the following materials: quartz, PVDF, steel-lined polytetrafluoroethylene, and steel-lined PVDF. The vaporization tank is made of one of the following materials: quartz, PVDF, steel-lined polytetrafluoroethylene, and steel-lined PVDF. The Venturi injector is made of PVDF.

[0016] The present invention also provides a method for synthesizing silicon dioxide, wherein silicon dioxide is obtained by drying silica sol, wherein the silica sol is prepared by the method of synthesizing silica sol using a loop reactor.

[0017] Preferably, the drying temperature is 100~140℃.

[0018] Compared with the prior art, the present invention has the following beneficial effects: (1) Compared with the problem of solid deposition on the inner wall of the upper gas phase space due to the volatilization of raw materials in the traditional batch reactor caused by the liquid phase hydrolysis of silicon tetrachloride, the present invention uses the vacuum suction feeding method of the Wenchuli jet mixer in the loop reactor. The advantage is that there is no back gas, which avoids the blockage and corrosion caused by the back gas of raw material silicon tetrachloride and by-product hydrogen chloride, so that the system can operate stably for a long time.

[0019] (2) Compared with the problem of product agglomeration caused by the violent reaction and untimely mass transfer and mixing in the traditional batch reactor due to the liquid phase hydrolysis of silicon tetrachloride, the high-speed water flow in this invention shears the gaseous silicon tetrachloride into fine bubbles and forms turbulence, which enhances the gas-liquid mixing effect. The water volume is always excessive at the two-phase mixing point, avoiding the problem of agglomeration caused by excessive local silica concentration, and a homogeneous silica sol can be obtained.

[0020] (3) The device involved has a simple and reliable structure. The silicon tetrachloride conveying and feeding part has no mechanical moving parts, supports automated continuous conveying, significantly reduces maintenance requirements, and has the feasibility of large-scale scaling.

[0021] (4) The silica yield is greater than 93%, which is much higher than the yield in a traditional batch reactor. The total content of metal impurities in the prepared silica sol is less than 1 ppm, and the specific surface area of ​​the silica powder obtained after drying reaches 674.2 m². 2 / g, with uniform pore size. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of a loop reactor structure for synthesizing high-purity silica sol using a loop reactor according to the present invention.

[0023] Figure 2 This is a photograph of the silica sol product obtained in Example 1.

[0024] Figure 3 The nitrogen adsorption-desorption curve is shown for the silica powder obtained after further drying of the silica sol obtained in Example 1.

[0025] Figure 4 The image shows the pore size distribution of silica powder obtained after further drying of the silica sol obtained in Example 1.

[0026] Figure 5 This is a scanning electron microscope (SEM) image of silica powder obtained after further drying of the silica sol obtained in Example 1.

[0027] Figure 6 The image shows the X-ray diffraction (XRD) pattern of silica powder obtained after further drying of the silica sol obtained in Example 1. Detailed Implementation

[0028] The structure of the loop reactor used in this invention for synthesizing high-purity silica sol is as follows: Figure 1 As shown, the loop reactor includes a reactor vessel 1, a Venturi ejector 2, a circulation pipe 5, and a gasification tank 7. A water inlet pipe 3 is located at the top of the reactor vessel 1, and a discharge pipe 4 is located at the bottom, with a liquid outlet. The Venturi ejector 2 includes an inlet, an outlet, and an ejector port; the inlet and ejector port are located outside the reactor vessel 1, and the outlet extends into the reactor vessel 1. One end of the circulation pipe 5 is connected to the bottom of the reactor vessel 1 or to the discharge pipe 4. Figure 1 In the structure shown, one end of the circulation pipe 5 is connected to the discharge pipe 4, so that the bottom of the reactor 1 does not need to be directly connected to the two pipes. The other end of the circulation pipe 5 extends to the injection inlet of the Venturi injector 2, and a circulation pump 6 is provided on the circulation pipe to drive the liquid circulation flow.

[0029] The vaporization tank 7 is used to store liquefied silicon tetrachloride. The vaporization tank 7 is connected to the injection port of the Venturi injector 2 via a vaporization pipe 8. The vaporization tank 7 also has a heating element, which can be a heating jacket. The vaporization pipe 8 can also have a heating element, which can also be a heating jacket covering the vaporization tank 8. After the silicon tetrachloride is vaporized by heating, it is injected into the reaction vessel 1 through the vaporization pipe 8 by the Venturi injector 2.

[0030] The other end of the water supply pipe 3 is connected to the water storage tank 9, and the water supply pipe 3 is equipped with a horizontal flow pump 10 that drives water from the water storage tank 9 into the reaction vessel 1.

[0031] When the circulation pipe 5 is connected to the discharge pipe 4, a three-way valve can be installed at the connection point between the discharge pipe 4 and the circulation pipe 5 to control whether the liquid from the discharge pipe 4 flows into the circulation pipe 5 or is discharged from the outlet of the discharge pipe 4. When one end of the circulation pipe 5 is connected to the bottom of the reactor 1, the circulation pipe 5 and the discharge pipe 4 are each connected to the reactor 1, and the discharge pipe 4 is equipped with a valve to control its opening and closing.

[0032] The loop reactor may also include a storage tank 11 for receiving the silica sol product discharged from the outlet.

[0033] The reactor 1 and the vaporization tank 7 can be made of quartz, PVDF, PTFE-lined steel, or PVDF-lined steel, with PVDF being preferred. The Venturi injector 2 and all pipelines (including the water supply pipe 3, discharge pipe 4, circulation pipe 5, and vaporization pipe 8) can be made of PVDF. The circulation pump 6 is a PTFE pump. The horizontal flow pump 10 is made of 316L stainless steel. The storage tank 11 can be made of PVDF.

[0034] During the reaction, a certain amount of ultrapure water is added to the reactor 1 through the water supply pipe 3 under the action of the horizontal flow pump 10. The high-pressure circulating water flow is formed by the circulation pump 6 and enters the injection inlet of the Venturi ejector 2, and returns to the reactor 1 from the injection outlet. The vaporization tank 7 is heated to vaporize the silicon tetrachloride stored in the vaporization tank 7. During the water circulation driven by the circulation pump 6, the vaporized silicon tetrachloride is drawn into the reactor 1 from the ejector port and reacts with the water flow. The circulation continues until the reaction is completed. All the silicon tetrachloride in the vaporization tank 7 is drawn in and reacts. After the reaction is completed, the silica sol product is collected from the liquid outlet of the discharge pipe 4. The high-purity silica sol product is collected in the storage tank 11.

[0035] The present invention will be further described below with reference to the embodiments.

[0036] Example 1 100 kg of ultrapure water (resistivity 18.2 MΩ·cm) is added to the reactor using a horizontal flow pump. The water is then circulated through a high-pressure pump into the Venturi ejector and returned to the reactor from the ejector's outlet. The silicon tetrachloride vaporization tank contains 9.44 kg of liquid silicon tetrachloride with a purity ≥99.9999%, and a water-to-silicon tetrachloride molar ratio of 100:1. The heating jacket temperature is set to 60°C. The silicon tetrachloride vaporizes and is drawn into the Venturi ejector through the side inlet, where it mixes with the high-speed water flow and reacts. The vaporized water is then ejected into the reactor from the Venturi ejector's outlet. The reactor liquid continues this circulation process using a circulating pump until all the silicon tetrachloride in the vaporization tank is drawn in, at which point the reaction ends. The silica sol product is collected from the outlet of the discharge pipe at the bottom of the reactor. A photograph of the sample taken using a quartz beaker is attached. Figure 2 As shown, the silica sol appears as a uniform, translucent substance with no visible flocculent material.

[0037] Example 2 100 kg of ultrapure water (resistivity 18.2 MΩ·cm) is added to the reactor using a horizontal flow pump. The water is then circulated through a high-pressure pump into the Venturi ejector and returned to the reactor from the ejector's outlet. The silicon tetrachloride vaporization tank contains 7.87 kg of liquid silicon tetrachloride with a purity ≥99.9999%, and a water-to-silicon tetrachloride molar ratio of 120:1. The heating jacket is set to 60°C, and the silicon tetrachloride vaporizes. It is drawn into the Venturi ejector through the side inlet, mixes with the high-speed water flow, and reacts. Finally, it is ejected into the reactor from the Venturi ejector's outlet. The reactor liquid continues to circulate using a circulation pump until all the silicon tetrachloride in the vaporization tank is drawn in, at which point the reaction ends. The silica sol product is collected from the outlet of the discharge pipe at the bottom of the reactor.

[0038] Example 3 100 kg of ultrapure water (resistivity 18.2 MΩ·cm) is added to the reactor using a horizontal flow pump. The water is then circulated into the Venturi ejector by a high-pressure pump and returns to the reactor from the ejector's outlet. The silicon tetrachloride vaporization tank contains 11.80 kg of liquid silicon tetrachloride with a purity >99.9999%, and a water-to-silicon tetrachloride molar ratio of 80:1. The heating jacket is set to 60°C, and the silicon tetrachloride vaporizes. It is drawn into the Venturi ejector through the side inlet, mixes with the high-speed water flow, and reacts. Finally, it is ejected into the reactor from the Venturi ejector's outlet. The reactor liquid continues to circulate using a circulation pump until all the silicon tetrachloride in the vaporization tank has been drawn in, at which point the reaction ends. The silica sol product is collected from the outlet of the discharge pipe at the bottom of the reactor.

[0039] Comparative Example 1 100 kg of ultrapure water (resistivity 18.2 MΩ·cm) was added to the reactor using a horizontal flow pump. The water was then circulated into the Venturi ejector by a high-pressure pump and returned to the reactor from the ejector's outlet. The silicon tetrachloride vaporization tank contained 18.88 kg of liquid silicon tetrachloride with a purity >99.9999%, and a water-to-silicon tetrachloride molar ratio of 50:1. The heating jacket was set to 60°C, and the silicon tetrachloride vaporized. It was drawn into the Venturi ejector through the side inlet, mixed with the high-speed water flow, and reacted. Finally, it was ejected into the reactor from the Venturi ejector's outlet, and the reactor liquid continued this circulation process via a pump. In this comparative example, clogging of the Venturi ejector occurred. This was because, towards the end of the reaction, the concentration and acidity of the silica sol in the reactor liquid became too high, resulting in gel formation and clogging of the nozzles inside the Venturi ejector.

[0040] Comparative Example 2 1 kg of ultrapure water (resistivity 18.2 MΩ·cm) was added to a conventional stirred reactor. Under vigorous stirring, silicon tetrachloride was added via a syringe pump at a flow rate of 15 mL / min. The total amount of silicon tetrachloride added was 94.4 g, with a purity >99.9999%, and the molar ratio of water to silicon tetrachloride was 100:1. After the injection was complete, stirring was continued for 15 minutes to terminate the reaction.

[0041] Test Example 1 The uniformity, yield, and total metal impurity content of the silica sols obtained in the above examples and comparative examples were calculated, and the results are shown in Table 1.

[0042] Table 1 Note: Yield refers to the ratio of the mass of silica powder obtained after drying to the theoretical maximum yield of silica. Total metal impurity content refers to the sum of the contents of each metal impurity in the silica sol as measured by inductively coupled plasma optical emission spectrometry (ICP-OES).

[0043] The ICP-OES determination results of the content of various metal impurities in the silica sol obtained in Example 1 are shown in Table 2.

[0044] Table 2 (Unit: ppm) Test Example 2 The silica sol obtained in Example 1 was dried at 120°C to obtain silica powder, which was then characterized by BET, SEM, and XRD tests. The test and characterization results will be further explained below with reference to the accompanying drawings.

[0045] According to BET testing, the specific surface area of ​​the silica powder was measured to be 674.2 m². 2 / g.

[0046] Figure 3 The nitrogen adsorption-desorption curves obtained from the BET test are from... Figure 3 The nitrogen adsorption-desorption curve shows a saturated adsorption plateau, indicating that the pore size distribution is uniform.

[0047] Figure 4 The image shows the pore size distribution obtained from the BET test. The average pore size of the silica powder is 4.04 nm.

[0048] Figure 5 The image shows a SEM image of the obtained silica powder at a magnification of 50K. Figure 5 It can be seen that the obtained silica has a porous structure with small pore size.

[0049] Figure 6 The XRD pattern of the obtained silica powder is shown below. Figure 6 It can be seen that the obtained silica powder has an amorphous structure.

Claims

1. A method for synthesizing silica sol using a loop reactor, characterized in that, The loop reactor includes: The reactor has a water inlet pipe at the top and a discharge pipe at the bottom, the discharge pipe having a liquid outlet. A Venturi injector, comprising an injection inlet, an injection outlet, and an ejector port, wherein the injection inlet and ejector port are located outside the reaction vessel, and the injection outlet extends into the reaction vessel; A circulation pipe is connected at one end to the bottom of the reactor or to the discharge pipe, and at the other end to the injection inlet. A circulation pump is installed on the circulation pipe. A vaporization tank is connected to the injection port via a vaporization pipe; The method includes the following steps: adding water to the reaction vessel through the water inlet pipe, driving the water flow into the injection inlet by the circulation pump, heating the gasification tank to vaporize the silicon tetrachloride stored in the gasification tank, and drawing the vaporized silicon tetrachloride into the reaction vessel from the injection port and reacting with the water flow. The process is repeated until the reaction is completed, and the silica sol product is collected from the liquid outlet of the discharge pipe.

2. The method for synthesizing silica sol using a loop reactor according to claim 1, characterized in that, The other end of the water supply pipe is connected to a water storage tank, and the water supply pipe is equipped with a horizontal flow pump that drives water from the water storage tank into the reaction vessel.

3. The method for synthesizing silica sol using a loop reactor according to claim 1, characterized in that, The vaporization tank is also equipped with a heating element.

4. The method for synthesizing silica sol using a loop reactor according to claim 1, characterized in that, When the vaporization tank is heated to vaporize the silicon tetrachloride stored inside, the heating temperature is 45~65℃.

5. The method for synthesizing silica sol using a loop reactor according to claim 1, characterized in that, The water added to the reactor was ultrapure water with a resistivity of 18.2 MΩ·cm; The silicon tetrachloride is electronic grade silicon tetrachloride with a total metal impurity content of less than 1 ppm.

6. The method for synthesizing silica sol using a loop reactor according to claim 1, characterized in that, The molar ratio of water to silicon tetrachloride is 80~120:

1.

7. The method for synthesizing silica sol using a loop reactor according to claim 1, characterized in that, The reactor is made of one of the following materials: quartz, PVDF, steel-lined polytetrafluoroethylene, and steel-lined PVDF. The vaporization tank is made of one of the following materials: quartz, PVDF, steel-lined polytetrafluoroethylene, and steel-lined PVDF. The Venturi injector is made of PVDF.

8. A method for synthesizing silicon dioxide, characterized in that, The silica sol is dried to obtain silica, which is prepared by the method of synthesizing silica sol using a loop reactor as described in any one of claims 1 to 7.

9. The method for synthesizing silicon dioxide according to claim 8, characterized in that, The drying temperature is 100~140℃.

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