System and method for preparing high-purity silicon dioxide

Abstract

The invention discloses a system and method for preparing high-purity silicon dioxide, and the system comprises a Venturi injection pump which is used for mixing silicon tetrafluoride gas with water to form jet flow; the swirler is connected with the venturi injection pump, and the swirler is connected with the venturi injection pump; the jet flow enters the swirler and then is subjected to separation treatment, and underflow and upper-layer overflow are formed; and the separation device is connected with the cyclone and is used for separating the silicon dioxide from the underflow and the upper overflow to obtain silicon dioxide particles. The method for preparing the high-purity silicon dioxide has the advantages of being simple in process, high in product purity, environmentally friendly, low in production cost, convenient for industrial production and the like, and has high economic benefits and social benefits.

Description

Technical Field

[0001] This invention belongs to the field of fluorochemical technology, specifically relating to a system and method for preparing high-purity silicon dioxide. Background Technology

[0002] Silicon dioxide, with the chemical formula SiO2, exists in both crystalline and amorphous forms. It has a Mohs hardness of 7. Crystalline silicon dioxide has a melting point of 1723℃ and a boiling point of 2230℃. It is insoluble in water, has a low coefficient of thermal expansion, and is resistant to thermal shock. Pure silicon dioxide has high transparency and good transmittance to ultraviolet-visible-infrared light. It has high resistivity and is an excellent electrical insulator. Except for fluorine gas and hydrofluoric acid, silicon dioxide does not react with halogens, hydrogen halides, or inorganic acids, but it is soluble in hot concentrated alkalis, molten strong alkalis, or sodium carbonate. High-purity silicon dioxide has a wide range of applications. In semiconductor integrated circuits, it is often used as a raw material for silicon wafers. Through processes such as melting and crystal pulling, it is made into single-crystal silicon rods, which are then sliced ​​into substrates for chip manufacturing. In photolithography, it serves as a glass substrate for carrying circuit patterns, requiring extremely high purity and optical uniformity. In the photovoltaic industry, it is used to manufacture single-crystal and polycrystalline silicon wafers for solar cells. In the optical fiber industry, high-purity silica is a core material for manufacturing optical fiber preforms, primarily used to form the core and cladding of the fiber. Methods for manufacturing fumed silica (SiO2) using silicon tetrafluoride (SiF4) mainly include the following: The high-temperature hydrolysis method involves the reaction of silicon tetrafluoride with hydrogen and oxygen under high-temperature conditions to produce fumed silica, hydrogen fluoride gas, and water vapor. This method is typically carried out at temperatures between 1800°C and 2000°C. The silicon tetrafluoride raw material is first subjected to distillation and evaporation, and then mixed with dried and filtered hydrogen and oxygen in a synthesis hydrolysis furnace. The hydrolysis reaction occurs at high temperatures, producing very fine fumed silica particles that form aerosols that are difficult to collect. Therefore, rapid cooling is required to aggregate the particles, which are then collected using a cyclone separator and finally purged with nitrogen-containing air to a suitable pH value. This method has harsh operating conditions and certain safety risks; therefore, in actual production, other alternatives such as trichlorosilane or silicon tetrachloride are often used.

[0003] Spray pyrolysis utilizes a spray drying tower as a hydrolysis reactor, where silicon tetrafluoride gas and water are separately fed into the reactor for hydrolysis. The reaction temperature is controlled between 90℃ and 450℃. The resulting solid silica and gaseous products are separated, and the solid product is collected. This method has the advantages of high silica purity, low impurities, and uniform particle size, meeting national standards. However, its production process places high demands on equipment, and due to issues with equipment industrialization and standardization, large-scale production has not yet been achieved.

[0004] Therefore, existing technologies mainly produce fumed silica through silicon tetrafluoride, which is difficult to operate and requires high-end equipment. To solve the above problems, this invention proposes a system and method for preparing silica based on a liquid-phase precipitation route. Summary of the Invention

[0005] To address the problems of high operational difficulty and demanding equipment requirements in the existing technology of manufacturing fumed silica primarily through silicon tetrafluoride, this invention proposes a system and method for preparing high-purity silica. This invention employs the following technical solution: A system for preparing high-purity silica, comprising: A Venturi jet pump is used to mix silicon tetrafluoride gas with water to form a jet. A hydrocyclone is connected to the Venturi jet pump; the jet enters the hydrocyclone and undergoes separation to form an underflow and an upper overflow. A separation device, connected to the hydrocyclone, is used to separate silica from the underflow and the upper overflow to obtain silica particles.

[0006] It should be noted that the water used in the Venturi jet pump is ultrapure water and / or mother liquor. This mother liquor is a high-purity fluorosilicic acid solution obtained by absorbing silicon tetrafluoride gas into ultrapure water.

[0007] Optionally, a mother liquor circulation device may also be included; The separation device separates silica from the underflow and the upper overflow to obtain silica and mother liquor; The mother liquor circulation device is used to send the mother liquor to the Venturi jet pump; The Venturi jet pump uses a mixture of mother liquor and silicon fluoride gas to form a jet.

[0008] Optionally, the separation device includes a thickening tank and a collecting tank; the thickening tank is connected to the underflow outlet of the hydrocyclone; and the collecting tank is connected to the upper overflow outlet of the hydrocyclone. The thickening tank is used to treat the underflow to obtain silica particles and thickening tank supernatant, and the collection tank is used to treat the upper overflow to obtain silica particles and collection tank supernatant. The supernatant from the thickening tank and the supernatant from the collection tank are used as mother liquor and sent to the Venturi jet pump through a mother liquor circulation device.

[0009] Optionally, a filtration and washing device is also included, which is connected to the separation device and is used to wash and filter the silica particles.

[0010] Optionally, the filtrate obtained from the filtration and washing device is used as the mother liquor.

[0011] Optionally, the filter washing device is connected to a drying device, which is used to dry the silica particles.

[0012] It should be noted that the solution of the present invention is highly corrosive, therefore all equipment in the system has a PFA liner.

[0013] A method for preparing high-purity silica, using the above-described system, includes the following steps: Step 1: A venturi jet pump is used to mix silicon tetrafluoride gas with water to form a jet, which is then injected into the hydrocyclone. Step two, the hydrocyclone processes the material in the jet to form an underflow and an upper overflow; Step 3: Perform solid-liquid separation on the underflow and the upper overflow to obtain silica particles.

[0014] Optionally, the method further includes: washing and filtering the silica particles obtained in step three; Preferably, in step three, the underflow and the upper overflow are subjected to solid-liquid separation to obtain silica particles and mother liquor; and the mother liquor is sent to a Venturi jet pump. The silicon tetrafluoride gas is mixed with the mother liquor using a Venturi jet pump to form a jet that is then injected into the hydrocyclone. Preferably, the filtered filtrate is used as the mother liquor.

[0015] Optionally, the injection pressure of the Chinese jet pump in step one is 0.1~1.0MPa; the temperature of the jet is 25~45℃; The weight ratio of silicon tetrafluoride gas to water is 1~10:100; The solid concentration of the overflow from the upper part of the hydrocyclone is <1%; Preferably, the method further includes: monitoring the content of fluorosilicic acid in the mother liquor, and draining the mother liquor when the content of fluorosilicic acid in the mother liquor exceeds the upper limit value; the upper limit value is 30%~40%.

[0016] Optionally, the method further includes drying the washed and filtered silica particles; Preferably, the drying process includes pre-drying at 110~120℃ and then calcining at 300~700℃.

[0017] Compared with the prior art, the present invention has the following outstanding advantages: In this invention, silicon tetrafluoride is absorbed by ultrapure water using a Venturi jet pump and directly injected into a hydrocyclone to complete the reaction and separation in one step. The resulting heavy component, coarse-grained silicon dioxide, can ultimately yield high-purity silicon dioxide (purity ≥ 99.9999%). The method for preparing high-purity silicon dioxide provided by this invention has advantages such as simple process, high product purity, environmental friendliness, low production cost, and ease of industrial production, resulting in significant economic and social benefits. Attached Figure Description

[0018] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0019] Figure 1 This is a schematic diagram of the system of the present invention. Detailed Implementation

[0020] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention. It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the present invention.

[0021] Furthermore, regarding the numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, are also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0022] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar to or equivalent to those described herein may be used in the implementation or testing of this invention.

[0023] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0024] First, this invention provides a system for preparing high-purity silicon dioxide, comprising: A Venturi jet pump is used to mix silicon tetrafluoride gas with water to form a jet. It is a device that uses positive pressure airflow to generate suction and form a jet. It includes an air inlet, a liquid inlet, and a jet outlet. The air inlet allows silicon tetrafluoride gas to enter, the liquid inlet allows ultrapure water to flow in, and the jet outlet mixes the silicon tetrafluoride gas and water to form a jet that is then injected into a hydrocyclone.

[0025] A hydrocyclone, connected to a Venturi jet pump, separates the jet stream into an underflow and an upper overflow. A hydrocyclone is a common separation and classification device, typically based on centrifugal sedimentation. When the two-phase mixture to be separated enters the hydrocyclone tangentially from its periphery under a certain pressure, it generates intense three-dimensional elliptical, strong rotating shear turbulent motion. Due to the size difference between coarse and fine particles, they experience different magnitudes of centrifugal force, centripetal buoyancy, and fluid drag. Under centrifugal sedimentation, most coarse particles are discharged through the underflow outlet, while most fine particles are discharged through the overflow pipe, thus achieving separation and classification.

[0026] A separation device, connected to the hydrocyclone, is used to separate silica from the underflow and the upper overflow to obtain silica particles.

[0027] Silicon tetrafluoride is absorbed by ultrapure water using a Venturi jet pump and then sprayed into a cyclone reactor to complete the reaction and separation. The resulting heavy component (coarse silicon dioxide) is then filtered, washed, and dried three times to finally obtain high-purity silicon dioxide (purity ≥ 99.9999%).

[0028] The reaction that occurs during this process is: SiF4(g) + H2O(l) = SiO2(s) + H2SiF6(l) + Q.

[0029] Furthermore, the system also has a mother liquor circulation device; The separation device separates silica from the underflow and the upper overflow to obtain silica and mother liquor; The mother liquor circulation device is used to send the mother liquor to the Venturi jet pump; The Venturi jet pump uses a mixture of mother liquor and silicon fluoride gas to form a jet.

[0030] The supernatant from the thickening tank and the supernatant from the collection tank are used as mother liquor and sent to the Venturi jet pump through a mother liquor circulation device.

[0031] The use of ultrapure water can be significantly reduced by using a mother liquor circulation system. The system initially uses ultrapure water for the reaction, gradually switching to mother liquor for absorption as the reaction progresses. When the fluorosilicic acid content in the mother liquor becomes too high, all the mother liquor is drained from the circulation system, the fluorosilicic acid is recovered, and the Venturi jet pump switches back to using only ultrapure water for the next cycle.

[0032] The working process of this invention is as follows: Silicon tetrafluoride is absorbed by ultrapure water or mother liquor at a temperature of 25-45 degrees Celsius using a Venturi jet pump at a pressure of 0.1-1.0 MPa to obtain silicon dioxide and fluorosilicic acid. The ratio of silicon tetrafluoride gas to ultrapure water can be adjusted, controlling the weight ratio to 1-10%. A jet is formed at the outlet of the Venturi jet pump and sprayed into a hydrocyclone to complete the reaction and separation. Most of the generated silicon dioxide separates from the nozzle at the bottom of the hydrocyclone and enters a thickening tank (coarse-particle solid-liquid separation). The supernatant from the thickening tank enters a mother liquor circulation device, while the bottom liquid (coarse-particle silicon dioxide) enters a filtration and washing device. The overflow from the top of the hydrocyclone reactor enters a collection tank, where fine-particle silicon dioxide and mother liquor are separated by precipitation. The supernatant from the collection tank enters the mother liquor system, and the bottom flow from the collection tank merges with the silicon dioxide from the thickening tank and enters the filtration and washing device. The filtration and washing device filters and washes three times with ultrapure water, and finally dries to obtain high-purity silicon dioxide (SiO2 purity ≥ 99.9999%).

[0033] Silicon tetrafluoride (colorless gas) used in the examples: Silicon tetrafluoride: ≥99.9999%; H2: ≤0.0002%; N2: ≤0.0003%; O2+Ar: ≤0.0001%; ​​CO: ≤0.00005%.

[0034] The ultrapure water (colorless and transparent liquid) used in the examples has a resistivity ≥18 MΩ·cm and a total organic carbon content ≤50%. / L; Sodium ions ≤1 / L.

[0035] Example 1 like Figure 1 As shown, the present invention first provides a system for preparing high-purity silica, comprising: A Venturi jet pump is used to mix silicon tetrafluoride gas with ultrapure water and / or mother liquor to form a jet; it includes an air inlet, a liquid inlet, and a jet outlet. The air inlet is used to introduce silicon tetrafluoride gas, the liquid inlet is used to introduce ultrapure water, and the jet outlet mixes the silicon tetrafluoride gas and water to form a jet that is directly injected into the hydrocyclone.

[0036] A hydrocyclone is connected to the Venturi jet pump; the jet enters the hydrocyclone and undergoes separation treatment to form an underflow and an upper overflow; silicon tetrafluoride gas is mixed with water to form a jet that is directly injected into the hydrocyclone to react and separate.

[0037] A separation device, connected to the hydrocyclone, is used to separate silica from the underflow and the upper overflow to obtain silica particles.

[0038] A mother liquor circulation device; the separation device separates silica from the underflow and the upper overflow to obtain silica and mother liquor; the mother liquor circulation device is used to send the mother liquor to a Venturi jet pump; the Venturi jet pump uses a mixture of mother liquor and silicon fluoride gas to form a jet. The mother liquor circulation device can use a mother liquor pump to transport the mother liquor.

[0039] The separation device includes a thickening tank and a collecting tank; the thickening tank is connected to the underflow outlet of the hydrocyclone; the collecting tank is connected to the upper overflow outlet of the hydrocyclone. The thickening tank is used to treat the underflow to obtain silica particles and thickening tank supernatant, and the collection tank is used to treat the upper overflow to obtain silica particles and collection tank supernatant. The supernatant from the thickening tank and the supernatant from the collection tank are used as mother liquor and sent to the Venturi jet pump through a mother liquor circulation device.

[0040] A filtration and washing device, connected to a separation device, is used to wash and filter silica particles. The filtration and washing device uses ultrapure water to wash and filter the silica particles, and the filtrate is recycled as a mother liquor.

[0041] Drying device, used to dry silica particles.

[0042] The Venturi jet pump, hydrocyclone, separation device, mother liquor pump, thickening tank, collection tank, filtration and washing device, and drying device mentioned above are all lined with PFA to avoid reaction corrosion problems.

[0043] Example 2 A method for preparing high-purity silica, using the system of Example 1, includes the following steps: Step 1: Silicon tetrafluoride gas and ultrapure water are mixed using a Venturi jet pump to form a jet, which is then injected into a hydrocyclone. The weight ratio of silicon tetrafluoride gas to water is 2:100. The injection pressure of the Venturi jet pump in Step 1 is 0.2 MPa. The temperature of the jet is 30°C. The system initially uses ultrapure water for the reaction, gradually switching to mother liquor for absorption as the reaction progresses. When the fluorosilicic acid content in the mother liquor becomes too high, all mother liquor is drained from the mother liquor circulation system, the fluorosilicic acid is recovered, and the Venturi jet pump switches back to using only ultrapure water for the next cycle. The fluorosilicic acid content in the mother liquor is monitored; when the content exceeds an upper limit of 30%, the mother liquor is drained to recover the fluorosilicic acid.

[0044] Step two: The hydrocyclone processes the material within the jet, forming an underflow and an upper overflow; the solid concentration in the upper overflow of the hydrocyclone is <1%; Step 3: Solid-liquid separation is performed on the underflow and the upper overflow to obtain silica particles and mother liquor. The supernatant from the thickening tank and the supernatant from the collection tank are sent to the Venturi jet pump as mother liquor through the mother liquor circulation device.

[0045] Step four: Wash and filter the silica particles obtained in step three using ultrapure water; the filtrate is then sent as mother liquor to a Venturi jet pump. Step 5: Dry the washed and filtered silica particles; the drying process involves pre-drying at 110°C and then calcining at 500°C to complete the drying.

[0046] Example 3 In this embodiment, step one involves using a Venturi jet pump to mix silicon tetrafluoride gas with water to form a jet, which is then injected into the hydrocyclone. The weight ratio of silicon tetrafluoride gas to water is 1:100, the injection pressure of the Venturi jet pump in step one is 0.1 MPa, and the temperature of the jet is 25°C. The remaining steps are the same as in Embodiment 1.

[0047] Example 4 In this embodiment, step one involves using a Venturi jet pump to mix silicon tetrafluoride gas with water to form a jet, which is then injected into the hydrocyclone. The weight ratio of silicon tetrafluoride gas to water is 10:100, the injection pressure of the Venturi jet pump in step one is 1 MPa, and the temperature of the jet is 40°C. The remaining steps are the same as in Embodiment 1.

[0048] The parameters of the silicon dioxide obtained in the examples are shown in Table 1: Table 1: Product Quality Analysis Indicators

[0049] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A system for producing high purity silicon dioxide, characterized by, include: A Venturi jet pump is used to mix silicon tetrafluoride gas with water to form a jet. A hydrocyclone is connected to the Venturi jet pump; the jet enters the hydrocyclone and undergoes separation to form an underflow and an upper overflow. A separation device, connected to the hydrocyclone, is used to separate silica from the underflow and the upper overflow to obtain silica particles.

2. The system for preparing high purity silicon dioxide according to claim 1, wherein It also includes a mother liquor circulation device; The separation device separates silica from the underflow and the upper overflow to obtain silica and mother liquor; The mother liquor circulation device is used to send the mother liquor to the Venturi jet pump; The Venturi jet pump uses a mixture of mother liquor and silicon tetrafluoride gas to form a jet.

3. The system for preparing high purity silicon dioxide according to claim 1, wherein The separation device includes a thickening tank and a collecting tank; the thickening tank is connected to the underflow outlet of the hydrocyclone; the collecting tank is connected to the upper overflow outlet of the hydrocyclone. The thickening tank is used to treat the underflow to obtain silica particles and thickening tank supernatant, and the collection tank is used to treat the upper overflow to obtain silica particles and collection tank supernatant. The supernatant from the thickening tank and the supernatant from the collection tank are used as mother liquor and sent to the Venturi jet pump through a mother liquor circulation device.

4. The system for preparing high purity silicon dioxide according to claim 1, wherein It also includes a filtration and washing device, which is connected to the separation device and is used to wash and filter the silica particles.

5. The system for preparing high purity silicon dioxide according to claim 4, wherein The filtrate obtained from the filtration and washing device is used as the mother liquor.

6. The system for preparing high-purity silica according to claim 4, characterized in that, The filtration and washing device is connected to a drying device, which is used to dry the silica particles.

7. A method for preparing high-purity silicon dioxide, characterized in that, The system according to any one of claims 1 to 6 comprises the following steps: Step 1: A venturi jet pump is used to mix silicon tetrafluoride gas with water to form a jet, which is then injected into the hydrocyclone. Step two, the hydrocyclone processes the material in the jet to form an underflow and an upper overflow; Step 3: Perform solid-liquid separation on the underflow and the upper overflow to obtain silica particles.

8. The method of producing high purity silicon dioxide according to claim 7, characterized by, The method further includes washing and filtering the silica particles obtained in step three; Preferably, in step three, the underflow and the upper overflow are subjected to solid-liquid separation to obtain silica particles and mother liquor; and the mother liquor is sent to a Venturi jet pump. The silicon tetrafluoride gas is mixed with the mother liquor using a Venturi jet pump to form a jet that is then injected into the hydrocyclone. Preferably, the filtered filtrate is used as the mother liquor.

9. The method of claim 8, wherein the high purity silicon dioxide is prepared by the steps of: The injection pressure of the Chinese jet pump in step one is 0.1~1.0MPa; the temperature of the jet is 25~45℃; ​ The weight ratio of silicon tetrafluoride gas to water is 1~10:100; The solid concentration of the overflow from the upper part of the hydrocyclone is <1%; Preferably, the method further includes: monitoring the content of fluorosilicic acid in the mother liquor, and draining the mother liquor when the content of fluorosilicic acid in the mother liquor exceeds the upper limit; The upper limit is 30% to 40%.

10. The method of claim 8, wherein the high purity silica is prepared by the steps of: The method further includes drying the washed and filtered silica particles; ​ Preferably, the drying process includes pre-drying at 110~120℃ and then calcining at 300~700℃.

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