A process for the co-production of silicon tetrafluoride and magnesium fluoride

Abstract

This invention proposes a method for the co-production of silicon tetrafluoride and magnesium fluoride, belonging to the technical field of preparing high-purity fluorides by pyrolysis of fluorosilicates. The method includes: placing magnesium fluorosilicate hexahydrate in a reactor, and under a non-oxidizing atmosphere, first dehydrating it at 60℃~70℃ until the moisture content of the discharged gas is below 50ppm, then pyrolyzing it at 150℃~180℃ for 1.5h~3h to generate silicon tetrafluoride gas and magnesium fluoride solid. The silicon tetrafluoride is collected, adsorbed, and purified by distillation to obtain a 5N~5.5N electronic grade product; the magnesium fluoride is crushed and classified to obtain a coating product with a D50 of 2μm~10μm and a purity of 4N. This invention, through a segmented temperature control strategy, first thoroughly dehydrates and then pyrolyzes at low temperature, effectively suppressing side reactions. The process is simple, with no waste emissions. It can be synthesized fresh from fluorosilicic acid and magnesium hydroxide, or refined from industrially produced magnesium fluorosilicate by recrystallization, resulting in high added value and easy industrialization.

Description

Technical Field

[0001] This invention belongs to the technical field of preparing high-purity fluorides by pyrolysis of fluorosilicates, and specifically relates to a method for the co-production of silicon tetrafluoride and magnesium fluoride. Background Technology

[0002] Electronic-grade silicon tetrafluoride is a key high-purity electronic specialty gas in the fields of integrated circuits, optical fibers, semiconductors and solar cells. It is widely used as an etchant, a P-type dopant, and a silicon source for epitaxial deposition and diffusion. It is also an important raw material for the preparation of electronic-grade silanes and polycrystalline silicon. It belongs to the high-end electronic chemicals that the country strongly encourages to develop.

[0003] Currently, the mainstream methods for preparing silicon tetrafluoride include the phosphate fertilizer by-product recovery method, the sulfuric acid method, the fluorosilicic acid-sulfuric acid method, the fluorosilicate pyrolysis method, the hydrofluoric acid-silica reaction method, and the silicon-hydrogen fluoride direct synthesis method, all of which have obvious drawbacks: 1. Phosphate fertilizer by-product recovery method: This method requires a phosphate fertilizer production line and the gas contains impurities such as HF and H2O, making purification difficult. 2. Sulfuric acid process: Equipment is severely corroded, gypsum is produced as a byproduct, and SiF4 contains impurities such as HF and SO3; 3. Fluorosilicic acid-sulfuric acid method: long process, high energy consumption, requires multi-stage distillation purification; 4. Hydrofluoric acid-silica reaction method: Anhydrous hydrofluoric acid is expensive, highly corrosive, and requires demanding equipment. 5. Direct synthesis of silicon-hydrogen fluoride: high reaction temperature, slow rate, hydrogen gas as a byproduct, and difficult to industrialize.

[0004] Fluorosilicate pyrolysis has advantages such as high product purity, less waste, and less corrosion. However, existing processes generally suffer from problems such as insufficient raw material refining, high pyrolysis temperature, difficulty in consistently achieving 5N product purity, and low quality of co-produced magnesium fluoride (high levels of magnesium hydroxide and silicon dioxide). These issues prevent the simultaneous large-scale co-production of electronic-grade silicon tetrafluoride and coating-grade magnesium fluoride. Summary of the Invention

[0005] In view of the above situation, the main objective of this invention is to propose a method for the co-production of silicon tetrafluoride and magnesium fluoride to solve the above-mentioned technical problems.

[0006] This invention proposes a method for the co-production of silicon tetrafluoride and magnesium fluoride, the method comprising the following steps: Magnesium fluorosilicate hexahydrate is provided; Magnesium fluorosilicate hexahydrate is placed in a reactor and dehydrated at 60℃~70℃ under a non-oxidizing atmosphere until the moisture content in the gas discharged from the reactor is less than 50ppm. Then, the reactor temperature is raised to 150℃~180℃ for pyrolysis for 1.5h to 3h, generating silicon tetrafluoride gas and magnesium fluoride solid products.

[0007] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) This invention involves a stepwise process of dehydration and pyrolysis. First, the moisture in magnesium fluorosilicate hexahydrate is removed to below 50 ppm at 60℃~70℃, and then pyrolysis is carried out at 150℃~180℃. This segmented temperature control helps reduce side reactions caused by the presence of moisture during pyrolysis, such as the formation of magnesium hydroxide and silicon dioxide, thereby facilitating the acquisition of silicon tetrafluoride and magnesium fluoride products with higher purity. Example data shows that the purity of the obtained silicon tetrafluoride can reach 5N~5.5N, and the purity of magnesium fluoride can reach 4N.

[0008] (2) This invention employs a combination of recrystallization purification and gas distillation purification. By recrystallizing and purifying the raw material magnesium fluorosilicate and distilling and purifying the silicon tetrafluoride gas generated by pyrolysis, the purity of the product is further improved. At the same time, this method can produce two products in one process: electronic-grade silicon tetrafluoride and magnesium fluoride for coating, thereby improving the comprehensive utilization rate of raw materials.

[0009] (3) The pyrolysis temperature used in this invention is relatively low (150℃~180℃), which is lower than the pyrolysis temperature of 200℃ or above in some reported processes. This helps to reduce process energy consumption and reduces the temperature resistance requirements of the equipment, thus slowing down the aging rate of the equipment in a highly corrosive atmosphere.

[0010] (4) This invention has a wide range of adaptability to raw material sources. It can use freshly synthesized magnesium hexahydrate fluorosilicate from the neutralization reaction of fluorosilicic acid and magnesium hydroxide, or it can use industrial-grade magnesium fluorosilicate that has been purified by recrystallization as raw material. Examples show that both routes can yield target products of comparable quality. Among them, the industrial raw material purification route can provide an optional solution for the product upgrading of existing magnesium fluorosilicate production enterprises.

[0011] (5) In the process of the present invention, the crystallization mother liquor can be recycled for batching, and the carrier gas in the pyrolysis tail gas can also be reused after being recovered and treated, which reduces the amount of waste liquid and waste gas emissions, and the process as a whole has good environmental friendliness.

[0012] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by means of embodiments of the invention. Attached Figure Description

[0013] Figure 1 This is a process flow diagram of the co-production method of silicon tetrafluoride and magnesium fluoride proposed in this invention. Detailed Implementation

[0014] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0015] These and other aspects of the embodiments of the present invention will become clear from the following description and accompanying drawings. In these descriptions and drawings, some specific embodiments of the present invention are specifically disclosed to illustrate some ways of implementing the principles of the embodiments of the present invention; however, it should be understood that the scope of the embodiments of the present invention is not limited thereto.

[0016] Example 1 Please see Figure 1 This embodiment provides a method for the co-production of silicon tetrafluoride and magnesium fluoride, the method comprising the following steps: (1) A 30wt% fluorosilicic acid solution was diluted with pure water at a mass ratio of 2.3:1, and a theoretical amount of magnesium hydroxide powder with a purity of 99wt% and a particle size of 200 mesh was added. In a reaction vessel, the two reacted under a stirring speed of 120 rpm for 30 minutes to produce a magnesium fluorosilicate solution. This stirring speed ensured a complete reaction and avoided weighing fluctuations and excessive fluorosilicic acid gas entering the tail gas system due to violent stirring. After the reaction was completed, a 600-mesh plate filter press was used to separate the solid and liquid phases of the reaction solution to remove unreacted trace solid impurities, resulting in a clear and transparent magnesium fluorosilicate mother liquor.

[0017] The mother liquor first enters the synthesis mother liquor tank, where it is preheated by circulating secondary steam generated in the concentration vessel. It then enters the concentration vessel for distillation and concentration under reduced pressure, followed by crystallization in the crystallization vessel. During this process, three concentration and crystallization operations are performed using a mid-process feeding method to maximize the single-pass yield. Finally, centrifugation is used to obtain high-purity wet magnesium fluorosilicate hexahydrate.

[0018] (2) The above-mentioned wet magnesium fluorosilicate hexahydrate is fed into a rotary flash dryer and rapidly dried at a temperature of 45°C. This temperature window is precisely controlled within the stable range of magnesium fluorosilicate hexahydrate, which can efficiently remove the free water attached to the crystal surface and between particles, while completely avoiding the loss of crystal water and the destruction of crystal structure, thus providing a dry precursor with a complete hexahydrate morphology for subsequent processes.

[0019] (3) The magnesium fluorosilicate hexahydrate crystals obtained in step (2) and free water removed are subjected to anion and cation detection. Those that pass the test are put into the nitrogen positive pressure dry material silo for later use, and those that fail the test are recycled as industrial magnesium fluorosilicate.

[0020] Magnesium fluorosilicate hexahydrate crystals, after free water removal, are transferred from a nitrogen-pressurized dry feeder to a vacuum rotary kiln (reactor) via a closed screw feeder. First, the kiln is evacuated, then the gas inside is replaced twice with high-purity nitrogen (5N) with a purity of not less than 99.999%, establishing a clean, non-oxidizing, inert atmosphere. Subsequently, nitrogen is continuously introduced into the kiln, and the absolute pressure inside the reactor is maintained at a slightly positive pressure of 40 kPa by adjusting the valves. Heating begins, and the furnace temperature is initially raised steadily to 60°C for deep dehydration, monitored in real time by an online moisture analyzer at the exhaust port. When the moisture content in the exhaust gas is consistently below 50 ppm, it indicates that all free water and water of crystallization have been completely removed. This step is a key control point to suppress the formation of byproducts such as magnesium hydroxide and silicon dioxide during subsequent pyrolysis. After achieving this standard, the reactor temperature is further increased to 150°C, and pyrolysis is carried out at this temperature for 3 hours. During this process, magnesium fluorosilicate undergoes a complete decomposition reaction, producing gaseous silicon tetrafluoride and solid magnesium fluoride.

[0021] (4) The silicon tetrafluoride gas generated by pyrolysis is collected and purified sequentially through an adsorption tower and a distillation tower to finally obtain electronic-grade silicon tetrafluoride product with a purity of 5.5N (i.e., volume fraction of 99.9996%). The magnesium fluoride solid product remaining in the reactor is crushed and air-separated to obtain magnesium fluoride product for coating with a particle size D50 of 4μm and a purity of 4N (i.e., mass fraction of 99.99%).

[0022] (5) The initial gas generated by low-temperature drying, dehydration and pyrolysis is discharged into the three-stage absorption device through the negative pressure system of the exhaust fan system. When it accumulates to a certain amount, it is pumped into the industrial sodium fluoride production.

[0023] Example 2 Please refer to it again. Figure 1 This embodiment provides a method for the co-production of silicon tetrafluoride and magnesium fluoride, the method comprising the following steps: (1) A 40wt% fluorosilicic acid solution was mixed with pure water at a mass ratio of 1:1, and magnesium hydroxide powder with a theoretical purity of 99.5wt% and a particle size of 100 mesh was added. The mixture was stirred at 150 rpm for 30 minutes. The reaction solution was filtered using a 600-mesh plate filter press to obtain a clear mother liquor. The mother liquor was concentrated under reduced pressure, crystallized, and centrifuged three times during the process to obtain wet magnesium fluorosilicate hexahydrate. Using higher concentration raw materials can effectively improve the efficiency of single-batch production and the concentration of mother liquor, and reduce the energy consumption of subsequent evaporation.

[0024] (2) The above wet magnesium fluorosilicate hexahydrate is fed into a rotary flash dryer and dried at 50°C to remove the attached free water and obtain a precursor material that maintains a perfect crystal form without hydration damage.

[0025] (3) Transfer the material obtained in step (2) into a vacuum rotary kiln, evacuate it, and replace it with 5N nitrogen twice to establish a non-oxidizing atmosphere. Continuously purge with nitrogen and maintain the absolute pressure inside the kiln at 50 kPa. First, raise the temperature to 70°C for dehydration. When the moisture content of the exhaust gas is lower than 50 ppm as monitored online, raise the temperature to 180°C and pyrolyze at a constant temperature for 1.5 h. The slightly increased upper limit of the pyrolysis temperature and the appropriate holding time ensure that the precursor obtained from the high-concentration raw material can also achieve complete decomposition and transformation.

[0026] (4) Silicon tetrafluoride gas was collected, adsorbed and purified by distillation to obtain 5.5N electronic grade silicon tetrafluoride; magnesium fluoride solid was crushed and air-separated to obtain magnesium fluoride product for coating with D50 of 6μm and purity of 4N.

[0027] (5) The initial gas generated by low-temperature drying, dehydration and pyrolysis is discharged into the three-stage absorption device through the negative pressure system of the exhaust fan system. When it accumulates to a certain amount, it is pumped into the industrial sodium fluoride production.

[0028] Example 3 Please refer to it again. Figure 1 This embodiment provides a method for the co-production of silicon tetrafluoride and magnesium fluoride, the method comprising the following steps: (1) A 40wt% fluorosilicic acid solution was mixed with the magnesium fluorosilicate centrifuged mother liquor produced in Example 1 at a mass ratio of 1:1. A theoretical amount of magnesium hydroxide powder with a purity of 99wt% and a particle size of 300 mesh was added, and the mixture was reacted at a stirring speed of 110 rpm for 30 minutes. The reaction solution was filtered using a 600-mesh plate filter press to obtain a clear mother liquor. The mother liquor underwent three rounds of vacuum concentration, crystallization, and centrifugation to obtain wet magnesium fluorosilicate hexahydrate. In this example, by returning the crystallized mother liquor to the batching system, a closed-loop circulation of the reaction medium was achieved throughout the entire process. This not only recovered the residual raw materials in the mother liquor but also achieved zero discharge of process wastewater, significantly reducing production costs and eliminating environmental pressure.

[0029] (2) The above wet magnesium fluorosilicate hexahydrate is fed into a rotary flash dryer and dried at 48°C to remove the attached free water.

[0030] (3) Transfer the dried material into a vacuum rotary kiln, evacuate it, and replace it twice with 5N nitrogen. Continuously purge with nitrogen and maintain the absolute pressure inside the kiln at 45 kPa. First, raise the temperature to 65°C for dehydration. When the moisture content of the exhaust gas is below 50 ppm, raise the temperature to 160°C and pyrolyze at a constant temperature for 2 hours. Using a slightly lower pyrolysis temperature and a longer holding time can effectively reduce energy consumption and mitigate potential corrosion of the equipment while ensuring complete decomposition.

[0031] (4) Silicon tetrafluoride gas was collected, adsorbed, and purified by distillation to obtain electronic-grade silicon tetrafluoride with a purity of 5N (i.e., 99.9993%); magnesium fluoride was crushed and classified to obtain magnesium fluoride for coating with a D50 of 3μm and a purity of 4N (i.e., 99.991%). The product indicators were stable, proving that the mother liquor recycling had no adverse effect on the quality of the final product.

[0032] (5) The initial gas generated by low-temperature drying, dehydration and pyrolysis is discharged into the three-stage absorption device through the negative pressure system of the exhaust fan system. When it accumulates to a certain amount, it is pumped into the industrial sodium fluoride production.

[0033] Example 4 Please refer to it again. Figure 1 This embodiment provides a method for the co-production of silicon tetrafluoride and magnesium fluoride, the method comprising the following steps: (1) The self-made industrial-grade magnesium hexahydrate wet material and pure water were fed into the primary dissolving tank and dissolved fully under stirring. After standing, the foam and suspended matter on the liquid surface were removed. Then the primary solution was transferred to the secondary dissolving tank and heated to dissolve at 65℃~75℃ (70℃ was used in this embodiment) to further dissolve the residual solids and promote the transformation of impurities. The solution after secondary dissolution was sent to the filter tank for precision filtration to remove insoluble particles and residual suspended matter. The resulting clear filtrate was transferred to the crystallization kettle, cooled and recrystallized, and centrifuged to obtain the refined magnesium hexahydrate wet material. This physical purification process utilizes the difference in solubility between impurities and the main body to effectively remove soluble salt impurities and significantly improve the chemical purity of the raw material.

[0034] (2) The refined wet magnesium fluorosilicate hexahydrate is fed into a rotary flash dryer and dried at 45°C to remove the attached free water.

[0035] (3) Transfer the dried material into a vacuum rotary kiln, evacuate it, and replace it with 5N nitrogen twice. Continuously purge with nitrogen and maintain the absolute pressure inside the kiln at 40 kPa. First, raise the temperature to 60°C for dehydration. When the moisture content of the exhaust gas is less than 50 ppm, raise the temperature to 170°C and pyrolyze at a constant temperature for 2.5 h.

[0036] (4) Silicon tetrafluoride gas was collected, adsorbed, and purified by distillation to obtain 5.5N (i.e., 99.9995%) electronic-grade silicon tetrafluoride; magnesium fluoride solid was crushed and air-separated to obtain magnesium fluoride for coating with a D50 of 2.5μm and a purity of 4N (i.e., 99.993%). This embodiment demonstrates that even industrial-grade raw materials, after being processed by the method of this invention, can achieve the same top-level standards as freshly synthesized materials, showing the excellent universality and stability of the technical solution.

[0037] (5) The initial gas generated by low-temperature drying, dehydration and pyrolysis is discharged into the three-stage absorption device through the negative pressure system of the exhaust fan system. When it accumulates to a certain amount, it is pumped into the industrial sodium fluoride production.

[0038] Example 5 Please refer to it again. Figure 1 This embodiment provides a method for the co-production of silicon tetrafluoride and magnesium fluoride, the method comprising the following steps: (1) Using the same method as step (1) in Example 1, wet magnesium fluorosilicate hexahydrate was prepared.

[0039] (2) The above-mentioned wet magnesium hexahydrate fluorosilicate is spread evenly on a steel-lined PFA tray and placed in a vacuum oven. Static drying is carried out under vacuum conditions of 45℃ and -0.09MPa to remove the attached free water, thereby obtaining magnesium hexahydrate fluorosilicate with the free water removed. This method has strong equipment versatility and also achieves the purpose of removing free water at low temperature, proving that the present invention does not have stringent requirements on the form of drying equipment.

[0040] (3) Transfer the dried material obtained in step (2) into a tubular furnace (a simple type of reactor). After evacuating the furnace tube, completely replace the air in the furnace with high-purity argon (99.999% purity) and continuously introduce argon to maintain a slightly positive pressure non-oxidizing atmosphere in the furnace. First, raise the furnace temperature to 65°C for dehydration treatment. When the moisture content detected by the high-precision dew point meter connected to the exhaust port is lower than 50ppm, the dehydration is considered complete. Then, raise the furnace temperature to 150°C and pyrolyze at a constant temperature for 1.5h to generate silicon tetrafluoride gas and magnesium fluoride solid products. This embodiment verifies the core technical idea of ​​"complete dehydration first, then low-temperature pyrolysis", which is also effective for tubular furnaces other than rotary kilns and non-oxidizing atmospheres constructed with argon other than nitrogen, demonstrating its wide technical adaptability.

[0041] (4) The product purification and classification steps are the same as in Example 1, and high-quality electronic-grade silicon tetrafluoride and magnesium fluoride for coating are finally obtained.

[0042] (5) The initial gas generated by low-temperature drying, dehydration and pyrolysis is discharged into the three-stage absorption device through the negative pressure system of the exhaust fan system. When it accumulates to a certain amount, it is pumped into the industrial sodium fluoride production.

[0043] Example 6 Please refer to it again. Figure 1 This embodiment provides a method for the co-production of silicon tetrafluoride and magnesium fluoride, the method comprising the following steps: (1) The fluorosilicic acid solution used in this embodiment is derived from a by-product acid produced during the production of anhydrous hydrofluoric acid, with an initial mass concentration of approximately 25 wt%. A theoretical amount of magnesium hydroxide powder with a purity of 99 wt% and a particle size of 300 mesh was added to this 25 wt% by-product fluorosilicic acid solution, and the mixture was reacted for 30 minutes at a stirring speed of 150 rpm. Subsequent solid-liquid separation, concentration, crystallization, and centrifugation steps were the same as in Example 1, ultimately yielding wet magnesium fluorosilicate hexahydrate. This embodiment provides a high-value-added utilization path for low-cost, difficult-to-process industrial by-product acids.

[0044] (2) The above wet magnesium fluorosilicate hexahydrate is fed into a rotary flash dryer and dried rapidly at 50°C to remove the attached free water.

[0045] (3) Using the same segmented temperature control process as step (3) in Example 1, thermal decomposition is carried out in a nitrogen atmosphere in a vacuum rotary furnace to generate silicon tetrafluoride gas and magnesium fluoride solid products.

[0046] (4) The pyrolysis gas and solid products were purified and graded in the same manner as in Example 1 to finally obtain 5.5N electronic-grade silicon tetrafluoride and 4N-grade magnesium fluoride for coating. This example fully demonstrates that the raw material sources of the present invention are highly compatible. Whether it is freshly prepared synthetic acid or industrial by-product acid (or acid synthesized from hydrofluoric acid and silicon dioxide), the same high-quality final product can be obtained, providing solid technical support for the integrated circular economy of upstream and downstream.

[0047] (5) The initial gas generated by low-temperature drying, dehydration and pyrolysis is discharged into the three-stage absorption device through the negative pressure system of the exhaust fan system. When it accumulates to a certain amount, it is pumped into the industrial sodium fluoride production.

[0048] Example 7 This embodiment provides a method for the co-production of silicon tetrafluoride and magnesium fluoride, the method comprising the following steps: (1) Hydrofluoric acid and gelled silica were reacted in stoichiometric ratio to synthesize a fluorosilicic acid solution with a mass concentration of approximately 40 wt%. A theoretical amount of magnesium hydroxide powder with a purity of 99 wt% and a particle size of 200 mesh was added to this synthesized fluorosilicic acid solution, and the mixture was reacted at a stirring speed of 130 rpm for 30 minutes. The reaction solution was filtered using a 600-mesh plate filter press to obtain a clear mother liquor. The mother liquor was concentrated under reduced pressure, crystallized, and centrifuged three times during the reaction to obtain wet magnesium fluorosilicate hexahydrate.

[0049] (2) The above wet magnesium fluorosilicate hexahydrate is fed into a rotary flash dryer and dried at 45°C to remove the attached free water.

[0050] (3) Transfer the dried material into a vacuum rotary kiln, evacuate it, and replace it with 5N nitrogen twice to establish a non-oxidizing atmosphere. Continuously purge with nitrogen and maintain the absolute pressure inside the kiln at 45 kPa. First, raise the temperature to 70°C for dehydration. When the moisture content detected online at the exhaust port is below 50 ppm, raise the temperature to 160°C and pyrolyze at a constant temperature for 3 hours to generate silicon tetrafluoride gas and magnesium fluoride solid products.

[0051] (4) Silicon tetrafluoride gas is collected, adsorbed and purified by distillation to obtain 5N grade electronic grade silicon tetrafluoride; magnesium fluoride solid is crushed and air classified to obtain magnesium fluoride product for coating with D50 of 5μm and purity of 4N.

[0052] (5) The initial gas generated by low-temperature drying, dehydration and pyrolysis is discharged into the three-stage absorption device through the negative pressure system of the exhaust fan system. When it accumulates to a certain amount, it is pumped into the industrial sodium fluoride production.

[0053] This embodiment demonstrates that high-quality co-products can also be obtained using the method of the present invention with fluorosilicic acid synthesized from hydrofluoric acid and gelled silica as raw material, and the process has good raw material adaptability.

[0054] Comparative Example 1 (1) The same raw materials and steps as in Example 1 were used, but the 60°C dehydration section was omitted and the temperature was directly raised to 150°C for pyrolysis.

[0055] (2) The gas generated by pyrolysis was tested with an HP5890 (TCD detector); the collected solid material was evenly divided into 4 parts. The particle size was detected by a Winner3003 laser particle size analyzer. The thermal weight loss and thermal peak of the material were determined by an HQT3 comprehensive thermal analyzer. The ion leaching was determined by a Shenghan IC-D100. The content of Mg, Si, F and other solid samples was determined by EDX 6000C tablet pressing. The results were then calculated and judged comprehensively.

[0056] Table 1. Solids not collected after dehydration at 60℃.

[0057] (3) In magnesium fluorosilicate, free water and crystal water are not completely removed. At high temperature, the dehydration and decomposition of MgSiF6.6H2O occur almost simultaneously. A large amount of water vapor is discharged during the cracking and collection process. During the cooling and condensation process, silicon tetrafluoride is basically hydrolyzed, and a large amount of SiO2.xH2O is generated, which causes pipeline blockage and leads to abnormal detection.

[0058] (4) The same raw materials and steps as in Example 1 were used, but the 60°C dehydration section was omitted, and the temperature was directly raised to 150°C for pyrolysis. Because a large amount of water was present in the later stage of pyrolysis, many side reactions occurred, and normal products could not be obtained. This fully demonstrates that a low-temperature dehydration of 60°C to 70°C must be performed before pyrolysis to ensure the purity of the subsequent pyrolysis reaction.

[0059] Comparative Example 2 (1) The same raw materials and steps as in Example 1 were used, but dehydration was carried out at 60°C. After the exhaust moisture content was controlled at 300ppm, the temperature was raised to 150°C and pyrolyzed at a constant temperature for 3h.

[0060] (2) The gases generated by pyrolysis were tested using an HP5890 (TCD detector); the collected solid material was evenly divided into three parts. The first part was determined by an HQT3 comprehensive thermal analyzer to determine the thermal weight loss and thermal peak appearance of the material. The second part was determined by an IC-D100 to determine the ion leaching. The third part was determined by EDX 6000C tablet pressing to determine the content of Mg, Si, F, etc. in the solid sample. The results were then calculated and a comprehensive judgment was made.

[0061] Table 3. Solids collected during normal dehydration (water content controlled at 300 ppm)

[0062] (3) In magnesium fluorosilicate, most of the water of crystallization has been removed. MgSiF6 decomposes at high temperature. A small amount of water vapor is discharged during the cracking and collection process. The temperature is lowered and condensed. A trace amount of silicon tetrafluoride is hydrolyzed.

[0063] (4) The same raw materials and steps as in Example 1 were used, but the moisture control in the low-temperature dehydration stage was changed from less than 50 ppm to 300 ppm. The purity of silicon tetrafluoride and magnesium fluoride could only reach 2N to 3N industrial primary products.

[0064] Comparative Example 3 (1) The same raw materials and steps as in Example 1 were used, but the pyrolysis was carried out at 350°C and constant temperature pyrolysis was performed for 3 hours.

[0065] (2) The gases generated by pyrolysis were tested using an HP5890 (TCD detector); the collected solid material was evenly divided into three parts. The first part was determined by an HQT3 comprehensive thermal analyzer to determine the thermal weight loss and thermal peak appearance of the material. The second part was determined by an IC-D100 to determine the ion leaching. The third part was determined by EDX 6000C tablet pressing to determine the content of Mg, Si, F, etc. in the solid sample. The results were then calculated and a comprehensive judgment was made.

[0066] Table 5. Solids collected during normal dehydration (water content < 50 ppm)

[0067] (3) The water of crystallization in magnesium fluorosilicate is basically completely removed. MgSiF6 decomposes at high temperature, the pyrolysis temperature is too high and the energy consumption is increased. At the same time, the types of solid impurities increase, but the actual data obtained are basically close to those in Example 1.

[0068] (4) The same raw materials and steps as in Example 1 were used, but the pyrolysis temperature was increased from 150°C to 350°C. The overall power consumption increased, the purity of magnesium fluoride remained basically stable at 3.5N, and the purity of silicon tetrafluoride remained basically stable at 4.5N. There is still room for improvement through subsequent process optimization.

[0069] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A method for the co-production of silicon tetrafluoride and magnesium fluoride, characterized in that, The method includes the following steps: Magnesium fluorosilicate hexahydrate is provided; Magnesium fluorosilicate hexahydrate is placed in a reactor and dehydrated at 60℃~70℃ under a non-oxidizing atmosphere until the moisture content in the gas discharged from the reactor is less than 50ppm. Then, the reactor temperature is raised to 150℃~180℃ for pyrolysis for 1.5h to 3h, generating silicon tetrafluoride gas and magnesium fluoride solid products.

2. The method for co-producing silicon tetrafluoride and magnesium fluoride according to claim 1, characterized in that, The method further includes: collecting, adsorbing and distilling silicon tetrafluoride gas to obtain electronic-grade silicon tetrafluoride with a purity of 5N to 5.5N; The solid magnesium fluoride product was crushed and classified to obtain magnesium fluoride for coating with a D50 of 2μm to 10μm and a purity of not less than 99.99%.

3. The method for co-producing silicon tetrafluoride and magnesium fluoride according to claim 1, characterized in that, The magnesium hexahydrate fluorosilicate provided is magnesium hexahydrate fluorosilicate with attached free water removed.

4. The method for co-producing silicon tetrafluoride and magnesium fluoride according to claim 3, characterized in that, The method for removing attached free water is to dry it at a temperature of 45℃~50℃.

5. The method for co-producing silicon tetrafluoride and magnesium fluoride according to claim 4, characterized in that, The non-oxidizing atmosphere is achieved by continuously introducing nitrogen into the reactor, while maintaining the absolute pressure inside the reactor at 40 kPa to 50 kPa during this process.

6. The method for co-producing silicon tetrafluoride and magnesium fluoride according to claim 4, characterized in that, Before performing the dehydration process, the reactor is evacuated and then purged at least twice with nitrogen gas of a purity of not less than 99.999%.

7. The method for co-producing silicon tetrafluoride and magnesium fluoride according to claim 4, characterized in that, The magnesium fluorosilicate hexahydrate is prepared by the following steps: A fluorosilicic acid solution with a mass concentration of 30wt% to 45wt% is mixed with magnesium hydroxide powder with a purity of not less than 99wt% and reacted. The reaction solution is then separated into solid and liquid to obtain a mother liquor. The mother liquor is then concentrated, crystallized, and separated into solid and liquid again to obtain wet magnesium fluorosilicate hexahydrate. Finally, it is dried to remove free water.

8. The method for co-producing silicon tetrafluoride and magnesium fluoride according to claim 7, characterized in that, The centrifuged mother liquor produced after concentration and crystallization is returned to the reaction system for recycling.

9. The method for co-producing silicon tetrafluoride and magnesium fluoride according to claim 4, characterized in that, The magnesium fluorosilicate hexahydrate is prepared by the following steps: Industrial magnesium fluorosilicate is dissolved in water and filtered. The resulting filtrate is recrystallized and separated into solid and liquid components to obtain wet magnesium fluorosilicate hexahydrate. Finally, it is dried to remove free water.

10. The method for co-producing silicon tetrafluoride and magnesium fluoride according to claim 4, characterized in that, The magnesium hydroxide powder has a particle size of 100-300 mesh; the mixing reaction is carried out at a stirring speed of 110-150 rpm for 30 minutes; the solid-liquid separation of the reaction solution is performed by a 600-mesh plate filter press.

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