Method for synthesizing high-purity silica crystal by successive online replenishment

Abstract

The application discloses a synthesis method of high-purity silica crystal with successive online replenishment, and belongs to the technical field of material synthesis. The synthesis method of the application uses water glass as raw material, adds a promoter, and adopts an online successive replenishment hydrothermal crystallization synthesis process. The process is simple, the reaction condition is relatively mild, and the process is easy to control. No new impurities are introduced, and the slow directional growth of the crystal is facilitated. In addition, the high-purity silica crystal obtained by the application has the same crystal lattice as natural quartz, is a quartz crystal type, does not need to be crushed, and can effectively solve the problems of non-crystal synthesis, easy carbon residue, high bubble body coating, high hydroxyl and the like caused by raw materials such as organosilicon alkoxide, and can alleviate the shortage of natural quartz ore to a certain extent, and can be applied to industrial scale production.

Description

Technical Field

[0001] This invention belongs to the field of materials synthesis technology, specifically relating to a method for synthesizing high-purity silica crystals through sequential online replenishment. Background Technology

[0002] Quartz is the most common crystalline silicon in nature. Due to its unique high-temperature thermal stability, excellent optical properties, and superior mechanical and chemical properties, it is widely used in high-tech fields such as electronics, semiconductors, solar energy, lasers, and aerospace. In recent years, with the rapid development of semiconductor technology and photovoltaic materials, the advantages of high-purity quartz sand have been recognized, making it a strategic resource that is scarce globally and in short supply in my country. Global quartz deposits are distributed in countries such as the United States, Norway, India, and Australia, with few operating mines, a very high concentration of deposits, and relatively limited reserves. my country's quartz deposits are mainly vein ores, with scattered and individual ore reserves being relatively small and of relatively poor quality.

[0003] With the continuous depletion of natural crystal resources, research on high-purity synthetic quartz has gradually gained attention. Limited by the natural environment, synthetic quartz is, in the long term, the only technological path that is not subject to human control. Existing synthesis methods mainly include gas-phase synthesis, chemical precipitation, sol-gel methods, and silicon tetrachloride hydrolysis. Because of these synthesis routes, the synthesized quartz sand is primarily amorphous, resulting in drawbacks compared to natural quartz in terms of service life, hardness, and temperature resistance. In particular, the use of TEOS and TMOS organosilicon alkali hydrolysis methods, during high-temperature melting, leads to residual carbon in the synthetic quartz powder, which easily generates CO2 and CO gases, causing defects such as bubble encapsulation and a high number of hydroxyl groups in quartz products. These defects have always been a technological bottleneck, limiting widespread application. Therefore, researching and developing a medium-high temperature, relatively low-pressure hydrothermal synthesis method for high-purity silicon crystals has great potential and significance. Summary of the Invention

[0004] In view of the shortcomings of existing technologies and equipment problems, this invention discloses a sequential online replenishment system and method for synthesizing high-purity silica crystals.

[0005] To achieve the above objectives, the present invention provides an online sequential replenishment process method. Using water glass as raw material, a precursor is formed in a mixer from a high-purity amorphous silica solution and an accelerator. Silicon crystals are then synthesized hydrothermally at medium-high temperature and relatively low pressure. The process involves multiple replenishments, controlling the growth direction and size of the silicon crystals. The process is simple, highly safe, easy to operate, convenient to control, and environmentally friendly.

[0006] Specifically, a sequential online replenishment system for synthesizing high-purity silica crystals includes a hydrothermal reactor, a replenishment system, and a constant pressure system. The hydrothermal reactor is equipped with a feed pipe and an exhaust pipe, and also includes a replenishment system and a constant pressure system.

[0007] The supply system includes a storage tank A, a storage tank B, a mixer, and a channel. Storage tank A and storage tank B are connected to the mixer via metering pump I and metering pump II, respectively. The mixer is connected to the feed pipe via a cable.

[0008] The constant pressure system includes a heat exchanger and a booster pump. The exhaust pipe is connected in sequence to the first branch pipe, the heat exchanger, the second branch pipe, the booster pump, the third pipeline and the feed pipe through the first main pipe. It is connected to the gas exhaust pipe through the pressure relief pipe. The first main pipe is connected to the gas exhaust pipe and the booster pump is connected to the gas supply pipe.

[0009] The first main pipe is equipped with a shut-off valve, a regulating valve, and a check valve; the first branch pipe and the gas exhaust pipe are equipped with shut-off valves; the second branch pipe is equipped with a check valve; the third branch pipe is equipped with a shut-off valve and a check valve; and the pressure relief pipe is equipped with a relief valve.

[0010] Furthermore, the hydrothermal reactor is equipped with a motorized stirrer, a screw seal, and an electrical controller.

[0011] The hydrothermal reactor is equipped with a feed pipe and an exhaust pipe. The feed pipe is inserted into the inner liner of the reactor at a depth of 50-100mm from the bottom. The insertion depth of the exhaust pipe is consistent with the plane of the screw seal at the opening of the inner liner of the reactor.

[0012] The mixer adopts a Y-shaped structure with an included angle of 120°~180°. The outer periphery of the mixer and the channel is sealed by a clamping plate. The outer periphery is a jacketed structure, through which heat exchange medium is introduced to maintain a constant temperature.

[0013] The pipelines connecting metering pump I and metering pump II to the mixer are equipped with buffers, and the pipelines connecting the channel to the feed pipe are equipped with shut-off valves, heating modules and check valves.

[0014] This invention provides a method for synthesizing crystalline silicon dioxide using the aforementioned system, comprising the following steps:

[0015] In stage 1, the prepared silica solution and accelerator are loaded into storage tank A and storage tank B respectively, and metering pump I and metering pump II respectively are fed into the mixer according to the ratio. The constant pressure system provides gas source pressure to guide the material in the mixer. After being heated by the heating module, it is put into the hydrothermal reactor to complete the initial replenishment and raise the temperature to the target crystallization temperature T for crystallization time t.

[0016] Phase 2: Reduce the temperature inside the hydrothermal reactor to 4~100 ℃; complete the secondary replenishment according to the steps of Phase 1; and raise the temperature again to the target crystallization temperature T for crystallization time t.

[0017] Phase 3: Repeat the steps of Phase 2 n times;

[0018] Stage 4: Stop heating, filter, wash with water, and dry to obtain crystalline silicon dioxide;

[0019] Where n is a natural ordinal number.

[0020] Specifically, n is an integer greater than 1.

[0021] More specifically, n is an integer greater than 2.

[0022] Specifically, the amorphous silica solution used is prepared using self-made silica.

[0023] Specifically, the silica is produced from high-purity water glass (content 5.5~25.5wt%), with 0.02~0.5wt% dispersant PEG (Mn4000) added. A variable-temperature growth method is used (maximum temperature 80~100 ℃, minimum temperature 4~60 ℃) to control particle size. Subsequently, it is treated with a strong acid resin (Na: < 0.05 ppm, pH 1.2~5.2) for further purification. After filtration, washing, and calcination (500±50 ℃, 2~6 h), silica ions of different particle sizes are generated, with the particle size adjustable within the range of 0.2~3 μm.

[0024] The channel is a circular structure with a coiled shape, and has a total length of 3.5~7.5 m and a diameter of 0.5~1.5 mm.

[0025] Furthermore, the constant pressure system comprises the supply system, the hydrothermal reactor, and the gas generation system. The gas generation system collects gas from the hydrothermal reactor itself or from an external source to reach a specified threshold, which is adaptively controlled by a regulating valve. Simultaneously, the hydrothermal reactor has an unloading valve to control the maximum safe pressure threshold. The collected steam pressure is controlled by an angle shut-off valve, a regulating valve, a check valve, an unloading valve, a shut-off valve, and a shut-off valve. After being cooled and dehydrated by a heat exchanger, the steam is sent to an adaptive booster pump via a check valve. Simultaneously, an external gas supply path provides timely replenishment. The constant pressure gas source, through the shut-off valve and check valve, guides the material from the supply system through the heating module, into the hydrothermal reactor via the feed pipe, thus serving a replenishment function.

[0026] Furthermore, the material in storage tank A is an amorphous silica solution, and the material in storage tank B is an accelerator, including but not limited to one or more solutions such as sodium carbonate, lithium carbonate, sodium hydroxide, and potassium hydroxide.

[0027] Furthermore, the metering pump I has a pumping flow rate of 0.15~0.55 ml / min; the metering pump II has a pumping flow rate of 0.01~0.25 ml / min;

[0028] Furthermore, the constant pressure system uses a carrier gas to carry the material at a flow rate of 0.015~0.05 m / s; the heating module controls the temperature to be 80~120 ℃.

[0029] Furthermore, the mass concentration of the amorphous silica solution is 1.5~12.5%. The mass concentration of the accelerator is 0.015~0.5%.

[0030] Furthermore, the synthesis temperature of the reactor is 220~320 °C, and the crystallization reaction time is 8~168 h. The feed system, during the feed operation, maintains a reactor temperature of 60~100 °C.

[0031] The beneficial effects of this invention are as follows: Using high-purity water glass as raw material and adding an accelerator, an online sequential hydrothermal crystallization synthesis process is employed to guide and control the slow, directional growth of quartz silicon crystals. The process is simple, does not introduce new impurities, has relatively mild reaction conditions, and is safe, stable, and easy to control. Furthermore, the high-purity silica crystals obtained by this invention have the same crystal lattice as natural quartz, are quartz crystals, and have a particle size >10μm. They do not require pulverization and effectively solve the problems of high carbon residue in the synthesis of amorphous quartz using organosilicon alkoxides, resulting in high bubble coverage and high hydroxyl content. To a certain extent, this can alleviate the current shortage of natural quartz ore and can be applied to industrial-scale mass production, exhibiting significant benefits. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the hydrothermal reactor described in the sequential online replenishment method for synthesizing high-purity silica crystals according to the present invention.

[0033] Figure 2 This is a process flow diagram of a sequential online replenishment method for synthesizing high-purity silica crystals according to the present invention.

[0034] Figure 3 These are X-ray diffraction patterns of the crystalline silicon dioxide prepared in the examples. Among them, (a) is the X-ray diffraction pattern of the crystalline silicon in Example 1; and (b) is the X-ray diffraction pattern of the crystalline silicon in Example 3.

[0035] Figure 4 These are scanning electron microscope (SEM) images of the crystalline silicon dioxide prepared in the examples. Among them, (a) is a scanning electron microscope image of the crystalline silicon in Example 1; and (b) is a scanning electron microscope image of the crystalline silicon in Example 3.

[0036] In the diagram, 1. Hydrothermal reactor; 2. Feed pipe; 3. Exhaust pipe; 4. Storage tank A; 5. Storage tank B; 6-1. Metering pump I; 6-2. Metering pump II; 7-1. Buffer I; 7-2. Buffer II; 8. Mixer; 9. Channel; 10. Clamping plate; 11. Heating module; 12. Control valve; 13-1. Check valve I; 13-2. Check valve II; 13-3. Check valve III; 13-4. Check valve IV; 14. Unloading valve; 15. Heat exchanger; 16. Gas path; 17. Booster pump; 18-1. Shut-off valve I; 18-2. Shut-off valve II; 18-3. Shut-off valve III; 18-4. Shut-off valve IV; 18-5. Shut-off valve V; 18-6. Shut-off valve VI; 19. Inner liner; 20. Notch; 21. Motorized agitator; 22. Screw seal. Detailed Implementation

[0037] The following description, in conjunction with the accompanying drawings, describes preferred embodiments in a more accessible manner so that the advantages and features of the present invention can be more readily understood by those skilled in the art, thereby providing a clearer and more explicit definition of the scope of protection of the present invention.

[0038] As attached Figure 1-2 As shown, a sequential online replenishment system for high-purity silica crystal synthesis includes a hydrothermal reactor 1, a replenishment system, and a constant pressure system. The hydrothermal reactor is equipped with a motorized stirrer 21, a screw seal 22, and an electrical controller. The hydrothermal reactor 1 has a feed pipe 2 and an exhaust pipe 3. The replenishment system includes a storage tank A 4, a storage tank B 5, a mixer 8, and a channel 9. Storage tank A 4 and storage tank B 5 are connected to the mixer 8 via metering pump I 6-1 and metering pump II 6-2, respectively. The mixer 8 is connected to the feed pipe 2 via a cable 9. The mixer 8 adopts a Y-shaped structure. The outer periphery of the mixer 8 and the channel 9 is sealed by a clamping plate 10, and the outer periphery is a heat exchange medium.

[0039] Channel 9 is a circular channel arranged in a coiled manner. Buffer I 7-2 is installed on the pipeline connecting metering pump I 6-1 and mixer 8, and buffer II 7-1 is installed on the pipeline connecting metering pump II 6-2 and mixer 8. Shut-off valve I 18-1, heating module 11, and check valve IV 13-4 are installed on the pipeline connecting channel 9 and feed pipe 2.

[0040] The constant pressure system includes a heat exchanger 15 and a booster pump 17. The exhaust pipe 3 is connected in sequence to the first branch pipe, the heat exchanger 15, the second branch pipe, the booster pump 17, the third pipeline and the feed pipe 2 through the first main pipe. It is connected to the gas exhaust pipe through the pressure relief pipe. The first main pipe is connected to the gas exhaust pipe and the booster pump 17 is connected to the gas supply pipe 16.

[0041] The first main pipe is equipped with a shut-off valve II 18-2, a regulating valve 12, and a check valve I 13-1. The first branch pipe and the gas exhaust pipe are equipped with shut-off valve IV 18-4 and shut-off valve III 18-3, respectively. The second branch pipe is equipped with a check valve II 13-2. The third branch pipe is equipped with a shut-off valve VI 18-6 and a check valve III 13-3. The pressure relief pipe is equipped with an unloading valve 14. The gas supply pipe 16 is equipped with a shut-off valve V 18-5.

[0042] The process parameters for the reactor equipment are as follows:

[0043] Inner tank volume: 500 ml; Design pressure: 19.28 MPa; Design temperature: 350 ℃; Rotation speed: 0~1200 r / min;

[0044] The mixer has an included angle of 180°.

[0045] The channel has a circular structure with a coiled shape, a diameter of 0.68 mm, and a total length of 4.5 m. Example 1

[0046] The specific steps are as follows:

[0047] Preparation of silica: A variable-temperature growth method was adopted. 6 wt% water glass was heated to 80℃ and stirred for 1.5 h. The temperature was then lowered to 55℃, and 0.12 wt% dispersant PEG (Mn4000) was added. Stirring continued at 55℃ for 45 min. Ion exchange was then performed using a strongly acidic resin, controlling the Na content to <0.05 ppm and the pH to 2.2. Further purification, filtration, washing, and calcination (500±50℃, 4 h) yielded silica particles with an average particle size of 0.78 μm. The obtained silica particles were then dissolved in deionized water at room temperature to prepare a 7.5 wt% saturated silica solution.

[0048] In stage 1, 200 g of 7.5 wt% silica saturated solution and 50 g of 0.025 wt% accelerator were loaded into storage tank A and storage tank B respectively. The pumping speed of metering pump I was set to 0.15 ml / min and the pumping speed of metering pump II was set to 0.02 ml / min. The constant pressure system provided the gas source pressure to guide the material in the Y-type mixer through the heating module (set temperature 90℃) and into the inner liner of the crystallization reactor to complete the initial replenishment. The shut-off valves I and II on both sides of the reactor were closed, and the temperature of the hydrothermal reactor was controlled at 255 ℃. The crystallization reaction time was 72 h.

[0049] Phase 2: After the crystallization reaction is completed, the temperature of the hydrothermal reactor is lowered to 90 °C; the process of Phase 1 above is repeated to complete the secondary replenishment; then, the hydrothermal reactor is heated to the target crystallization temperature of 255 °C for 72 h.

[0050] Phase 3: Repeat the process of Phase 2 once, stop heating, allow to cool naturally to room temperature, open the vessel, wash the extracted powder with ultrapure water until neutral, filter, and dry in a 90 ℃ oven.

[0051] The X-ray diffraction pattern and scanning electron microscope image of the product obtained in Example 1 are shown below. Figure 3 (a) and Figure 4 (a). Example 2

[0052] Preparation of silica: A variable-temperature growth method was adopted. 15 wt% water glass was heated to 80 ℃ and stirred for 1.5 h. The temperature was then lowered to 25 ℃, and 0.12 wt% dispersant PEG (Mn4000) was added. Stirring was continued at 25 ℃ for 2 h. Subsequently, ion exchange was performed using a strong acid resin, controlling the Na content to <0.05 ppm and the pH value to 2.2. After further purification, filtration, washing, and calcination (500±50℃, 4 h), silica particles with an average particle size of 0.78 μm were generated. The obtained silica particles were then added to deionized water at room temperature to prepare a 5.5 wt% silica saturated solution.

[0053] Stage 1: 200 g of 5.5 wt% silica saturated solution and 50 g of 0.055 wt% accelerator were respectively loaded into storage tank A and storage tank B. The pumping speed of metering pump I was set to 0.35 ml / min and the pumping speed of metering pump II was set to 0.15 ml / min. The constant pressure system provided the gas source pressure to guide the material in the Y-type mixer through the heating module, set the temperature to 85℃, and put it into the inner liner of the reactor to complete the initial replenishment. The shut-off valves I and II on both sides of the reactor were closed, and the hydrothermal reactor was controlled at 235℃ for a crystallization reaction time of 72 h.

[0054] In stage 2, when t≥72 h, the temperature of the hydrothermal reactor is reduced to 60 ℃; the process of stage 1 above is repeated to complete the secondary replenishment; then, the hydrothermal reactor is heated again to the target crystallization temperature of 235 ℃, and the crystallization time is 72 h.

[0055] Phase 3: Repeat the process of Phase 2 once, stop heating the hydrothermal reactor, allow it to cool naturally to room temperature, open the reactor, wash the extracted powder with ultrapure water until neutral, filter, and dry in a 90 ℃ oven. Example 3

[0056] Preparation of silica: A variable-temperature growth method was adopted. 12 wt% water glass was heated to 95 ℃ and stirred for 1.5 h. The temperature was then lowered to 4 ℃, and 0.2 wt% dispersant PEG (Mn4000) was added. Stirring was continued at 4 ℃ for 2 h. Subsequently, ion exchange was performed using a strong acid resin, controlling the Na content to <0.05 ppm and the pH value to 2.2. After further purification, filtration, washing, and calcination (500±50℃, 4 h), silica particles with an average particle size of 1.5 μm were generated. The obtained silica particles were added to deionized water at room temperature to prepare a 3.2 wt% silica saturated solution.

[0057] Stage 1: 200 g of 3.2 wt% silica saturated solution and 50 g of 0.025 wt% accelerator were respectively loaded into storage tank A and storage tank B. The pumping speed of metering pump I was set to 0.22 ml / min and the pumping speed of metering pump II was set to 0.15 ml / min. The constant pressure system provided the gas source pressure to guide the material in the Y-type mixer through the heating module, set the temperature to 110 ℃, and put it into the inner liner of the reactor to complete the initial replenishment. The shut-off valves I and II on both sides of the reactor were closed, and the hydrothermal reactor was controlled at 300 ℃ for a crystallization reaction time of 144 h.

[0058] In stage 2, when t≥144 h, the temperature of the hydrothermal reactor is reduced to 60 ℃; the process of stage 1 above is repeated to complete the secondary replenishment; then, the hydrothermal reactor is heated again to the target crystallization temperature of 300 ℃, and the crystallization time is 144 h.

[0059] Phase 3: Repeat the process of Phase 2 once, stop heating the hydrothermal reactor, allow it to cool naturally to room temperature, open the reactor, wash the extracted powder with ultrapure water until neutral, filter, and dry in a 90 ℃ oven.

[0060] The X-ray diffraction pattern and scanning electron microscope image of the product obtained in Example 3 are shown below. Figure 3 (b) and Figure 4 (b) Example 4

[0061] Preparation of silica: A variable-temperature growth method was adopted. 10 wt% water glass was heated to 80 ℃ and stirred for 1.5 h. The temperature was then lowered to 25 ℃, and 0.05 wt% dispersant PEG (Mn4000) was added. Stirring was continued at 25 ℃ for 45 min. Subsequently, ion exchange was performed using a strongly acidic resin, controlling the Na content to <0.05 ppm and the pH value to 2.2. After further purification, filtration, washing, and calcination (500±50 ℃, 4 h), silica particles with an average particle size of 0.54 μm were generated. The obtained silica particles were then added to deionized water at room temperature to prepare a 4.2 wt% silica saturated solution.

[0062] Stage 1: 200 g of 4.2 wt% silica saturated solution and 50 g of 0.25 wt% accelerator were respectively loaded into storage tank A and storage tank B. The pumping speed of metering pump I was set to 0.2 ml / min and the pumping speed of metering pump II was set to 0.05 ml / min. The constant pressure system provided the gas source pressure to guide the material in the Y-type mixer through the heating module, set the temperature to 95℃, and put it into the inner liner of the reactor to complete the initial replenishment. The shut-off valves I and II on both sides of the reactor were closed, and the temperature of the hydrothermal reactor was controlled at 250℃. The crystallization reaction time was 36 h.

[0063] In stage 2, when t≥36 h, the temperature of the hydrothermal reactor is reduced to 72 ℃; the process of stage 1 above is repeated to complete the secondary replenishment; then, the hydrothermal reactor is heated again to the target crystallization temperature of 250 ℃, and the crystallization time is 36 h.

[0064] In stage 3, when t≥36 h, the temperature of the hydrothermal reactor is reduced to 72 ℃; the process of stage 2 above is repeated to complete the secondary replenishment; then, the hydrothermal reactor is heated again to the target crystallization temperature of 250 ℃, and the crystallization time is 36 h.

[0065] In stage 4, after repeating the process of stage 3 once, stop heating the hydrothermal reactor, allow it to cool naturally to room temperature, open the reactor, wash the extracted powder with ultrapure water until neutral, filter, and dry in a 90 ℃ oven.

[0066] Comparative Example 1

[0067] Using a conventional feeding method, 200 g of a 4.2 wt% saturated silica solution with a particle size of 0.54 μm and 50 g of a 0.25 wt% accelerator were fed in one batch. The crystallization temperature was 250 ℃ and the crystallization time was 144 h. The hydrothermal reactor heating was stopped, and the mixture was allowed to cool naturally to room temperature. The reactor was then opened, and the extracted powder was washed with ultrapure water until neutral. The powder was filtered and dried in a 90 ℃ oven.

[0068] The particle size of silica prepared in Examples 1-4 and Comparative Example 1 was determined using X-ray diffraction. The specific data are shown in Table 1. The sequential online replenishment method of the present invention can significantly improve the crystal size of silica.

[0069] Table 1 Summary of experimental data from examples and comparative examples

[0070]

[0071] Note: Crystal size refers to the maximum field of view of an electron microscope.

[0072] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A sequential online replenishment system for synthesizing high-purity silica crystals, comprising a hydrothermal reactor (1), wherein the hydrothermal reactor (1) is provided with a feed pipe (2) and an exhaust pipe (3), characterized in that, It also includes a supply system and a constant pressure system; The supply system includes a storage tank (4), a storage tank (5), a mixer (8), and a channel (9). The storage tank (4) and the storage tank (5) are connected to the mixer (8) through metering pump I (6-1) and metering pump II (6-2), respectively. The mixer (8) is connected to the feed pipe (2) through the channel (9). The constant pressure system includes a heat exchanger (15) and a booster pump (17). The exhaust pipe (3) is connected in sequence to the first branch pipe, the heat exchanger (15), the second branch pipe, the booster pump (17), the third pipeline and the feed pipe (2) through the first main pipe. It is connected to the gas exhaust pipe through the pressure relief pipe. The first main pipe is connected to the gas exhaust pipe and the booster pump (17) is connected to the gas replenishment pipe. The first main pipe is equipped with a shut-off valve, a regulating valve and a check valve; the first branch pipe and the gas exhaust pipe are equipped with shut-off valves; the second branch pipe is equipped with a check valve; the third branch pipe is equipped with a shut-off valve and a check valve; and the pressure relief pipe is equipped with a pressure relief valve. The mixer (8) adopts a Y-shaped structure with an included angle of 120°~180°. The outer periphery of the mixer (8) and the channel (9) is sealed by a clamping plate (10). The outer periphery is a jacketed structure, through which the heat exchange medium is introduced. The channel (9) is a circular channel with a diameter of 0.5~1.5mm and a length of 3.5~7.5m arranged in a coiled manner.

2. The synthesis system according to claim 1, characterized in that, A buffer is provided on the pipeline connecting metering pump I (6-1), metering pump II (6-2) and mixer (8), and a shut-off valve, heating module and check valve are provided on the pipeline connecting channel (9) and feed pipe (2).

3. A method for synthesizing crystalline silicon dioxide using the system described in claim 1, characterized in that, Includes the following steps: In stage 1, the prepared silica solution and accelerator are loaded into storage tank A (4) and storage tank B (5) respectively. They are then fed into mixer (8) by metering pump I (6-1) and metering pump II (6-2) according to the ratio. The constant pressure system provides gas source pressure to guide the material in mixer (8). After being heated by the heating module, the material is put into the hydrothermal reactor to complete the initial supply and raise the temperature to the target crystallization temperature T for crystallization time t. In stage 2, the temperature inside the hydrothermal reactor (1) is reduced to 4~100℃; the secondary supply is completed according to the steps of stage 1; the temperature is raised again to the target crystallization temperature T, and the crystallization time is t. Phase 3: Repeat the steps of Phase 2 n times; Stage 4: Stop heating, filter, wash with water, and dry to obtain crystalline silicon dioxide; Where n is a natural ordinal number.

4. The method according to claim 3, characterized in that, The metering pump I (6-1) has a pumping flow rate of 0.15~0.55 ml / min; the metering pump II (6-2) has a pumping flow rate of 0.01~0.25 ml / min.

5. The method according to claim 3, characterized in that, The constant pressure system has a material flow rate of 0.015~0.05m / s carried by the carrier gas; the heating temperature of the heating module (11) is 80~120℃.

6. The method according to claim 3, characterized in that, The silica solution has a mass concentration of 1.5-12.5%, and the accelerator has a mass concentration of 0.015-0.5%.

7. The method according to claim 3, characterized in that, The temperature of the raw material before entering the feed pipe is 60~100℃; the crystallization temperature T is 220~320℃, and the crystallization time t is 8~168h.

8. The method according to claim 3, characterized in that, The accelerator is selected from at least one of sodium carbonate, lithium carbonate, sodium hydroxide, and potassium hydroxide solution.

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