A device and method for the synthesis of silicon tetrafluoride

Abstract

The application discloses a device and method for synthesizing silicon tetrafluoride, which comprises a reactor, a separator and a cold trap connected in sequence. The reactor comprises a closed vertical tank body, the bottom of the tank body is provided with an air inlet pipe, the air inlet pipe is connected with a raw gas pipe for feeding nitrogen trifluoride into the tank body, the top of the tank body is provided with an air outlet pipe, and a mixing spray pipe for upward spraying is arranged in the silicon powder layer at the bottom of the tank body, the mixing spray pipe and the top of the tank body are connected through a circulating pipe, and a circulating fan is arranged on the circulating pipe. After nitrogen trifluoride gas is fed into the reactor, the gas at the top of the reactor is sprayed upward from the mixing spray pipe through the air return hole and the circulating pipe in sequence, the silicon powder in the silicon powder layer in the reactor is blown upward and diffused in the reactor, so that the contact area and contact time of the silicon powder and the nitrogen trifluoride gas are increased, the reaction is more sufficient, the content of the output silicon tetrafluoride gas is higher, and the production efficiency of the silicon tetrafluoride is improved.

Description

Technical Field

[0001] This invention belongs to the technical field of fluoride preparation, specifically relating to an apparatus and method for synthesizing silicon tetrafluoride. Background Technology

[0002] Silicon tetrafluoride is a widely used organosilicon compound. Its applications include the production of high-purity quartz glass, solar cells, photocopier drums, fluorosilicic acid, aluminum fluoride, methyl silicate, ammonium trifluoride, hardeners for cement and marble, and photosensitizers. In the electronics and semiconductor industries, silicon tetrafluoride is an important raw material, primarily used as an etchant for compounds such as tantalum silicide and silicon nitride, a p-type dopant, and a silicon source for chemical vapor deposition. It can also be used to prepare electronic-grade silanes or polycrystalline silicon.

[0003] Currently, the main methods for synthesizing silicon tetrafluoride (SiFDR) are: the fluorite sulfuric acid method, the fluorosilicate thermal decomposition method, and the silicon powder hydrogen fluoride method. In the fluorite sulfuric acid method, fluorite and quartz sand contain many impurities, leading to a complex composition and low purity in the SiFDR. The fluorosilicate thermal decomposition method involves high pyrolysis temperatures and high energy consumption, generating significant amounts of solid waste, which does not meet environmental protection requirements. The silicon powder hydrogen fluoride method uses highly corrosive hydrogen fluoride, requiring sophisticated equipment.

[0004] There is also a method to synthesize silicon tetrafluoride by reacting nitrogen trifluoride gas through a silicon powder layer. However, the time it takes for nitrogen trifluoride to pass through the silicon powder layer is short, and the reaction time between nitrogen trifluoride and silicon powder is short. As a result, only a small portion of nitrogen trifluoride reacts with the silicon powder, which leads to low silicon tetrafluoride production efficiency. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a process and apparatus for synthesizing silicon tetrafluoride, which solves the problem of low production efficiency when using nitrogen trifluoride gas to synthesize silicon tetrafluoride through a silicon powder layer.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0007] A silicon tetrafluoride synthesis apparatus includes a reactor, a separator, and a cold trap connected in sequence. The reactor includes a closed, vertical tank with an inlet pipe at the bottom connected to a gas pipe for introducing nitrogen trifluoride into the tank. An outlet pipe is located at the top of the tank. A mixing nozzle is installed in the silicon powder layer at the bottom of the tank, and the mixing nozzle is connected to the top of the tank via a circulation pipe with a circulating fan installed on the circulation pipe.

[0008] Furthermore, the mixing nozzle includes a vertical inner tube with the nozzle pointing upwards and an outer tube sleeved outside the inner tube. The inner tube is connected to the circulation pipe, and the outer tube is fixedly connected to the inner tube. The inner tube or the outer tube is fixedly connected to the tank body. The opening at the top of the outer tube extends above the silicon powder layer. There is a gap between the outer tube and the inner tube, and this gap is connected to the silicon powder layer.

[0009] Furthermore, the bottom of the outer tube is sealed, and the side wall of the outer tube is provided with a material passage hole for communicating the gap with the silicon powder layer. The top of the outer tube is a funnel-shaped diffusion tube with a larger diameter at the top and a smaller diameter at the bottom.

[0010] Furthermore, the tank body is fitted with an outer tank that is fixedly connected to it. Between the tank body and the outer tank is a closed oil chamber. The bottom of the oil chamber is provided with a heating pipe, which is fixedly installed on the outer tank. The top of the outer tank is provided with an exhaust pipe, and a screw plug with a hole is screwed onto the exhaust pipe. Near the top of the outer tank is an oil filling pipe, and a plug is screwed onto the oil filling pipe.

[0011] Furthermore, the top of the tank is fitted with a hollow return air ring, the circulation pipe is connected to the inside of the return air ring, and the tank is provided with a return air hole at the location of the return air ring that is connected to the inside of the return air ring.

[0012] Furthermore, a distribution plate is fixedly installed at the bottom of the tank, the silicon powder layer is located on the distribution plate, and the air inlet pipe is located below the distribution plate.

[0013] Furthermore, a silicon powder feed pipe is connected to the outer side of the top of the tank, a silicon powder feed hopper is connected to the silicon powder feed pipe, and a silicon powder feed valve is provided between the silicon powder feed hopper and the tank.

[0014] Furthermore, the separator is wrapped with a coil for collecting heat from the separator, and a heat exchanger is provided between the coil and the original gas pipe.

[0015] A method for synthesizing silicon tetrafluoride includes the following steps:

[0016] S1, Place silicon powder in the reactor, preheat the reactor, replace it with inert gas, and then heat the reactor;

[0017] S2, nitrogen trifluoride is introduced from the bottom of the bed reactor to cause a reaction;

[0018] S3, the reaction product is taken out from the top of the reactor and passed through a separator for product separation;

[0019] S4. The separated product is passed into a bag filter to remove impurities and obtain silicon tetrafluoride gas.

[0020] S5, silicon tetrafluoride gas is introduced into the cold trap, condensed and collected, and then the inert gas is vented.

[0021] Further, in step S1, silicon powder is placed in a reactor and preheated to 200°C; after the reactor is purged with an inert gas, the oxygen content is less than 10 ppm, and the heating temperature is 250~400°C. The inert gas used for purging is nitrogen, helium, or argon with a purity of 99.999%. The purging rate during inert gas purging is 1L / h~10L / h, and the time is 2~8h. In step S2, nitrogen trifluoride has a purity of 99.5%, the flow rate of nitrogen trifluoride is 1L / min~10L / min, and the molar ratio of nitrogen trifluoride to silicon powder is 4:3. In step S5, the cold trap temperature is controlled at -100°C~-130°C.

[0022] The positive effects of this invention are:

[0023] 1. This invention comprises a reactor, a cyclone separator, a bag filter, and a cold trap. The reactor is equipped with a return air vent, a circulation pipe, a circulation fan, and a mixing nozzle. When nitrogen trifluoride gas is introduced into the reactor, the gas at the top of the reactor passes through the return air vent and the circulation pipe in sequence and is then sprayed upwards from the mixing nozzle. This blows the silicon powder in the silicon powder layer inside the reactor upwards, allowing it to diffuse within the reactor. This increases the contact area and contact time between the silicon powder and the nitrogen trifluoride gas, making the reaction more complete and resulting in a higher content of silicon tetrafluoride gas in the produced product, thus improving the production efficiency of silicon tetrafluoride.

[0024] 2. The mixing nozzle includes an inner tube and an outer tube with a trumpet-shaped top, which is fitted over the inner tube. The outer tube has a material passage hole. When nitrogen trifluoride gas is sprayed upward through the inner tube, the silicon powder in the silicon powder layer is drawn into the outer tube along with the silicon powder in the silicon powder layer. Then, it is sprayed upward through the trumpet-shaped diffuser at the top of the outer tube with the airflow, making the diffusion more uniform, increasing the spray speed, increasing the spray height, and further increasing the reaction time with nitrogen trifluoride gas.

[0025] 3. The cyclone separator is equipped with a coil, and a heat exchanger is installed between the coil and the raw gas pipe. When the mixed gas containing silicon tetrafluoride produced by the reactor is separated in the cyclone separator, the waste heat is transferred to the cyclone separator. The liquid medium flowing in the coil transfers the heat of the cyclone separator to the nitrogen trifluoride in the raw gas pipe through the heat exchanger, preheating the nitrogen trifluoride entering the reactor, thereby achieving the purpose of energy saving. Attached Figure Description

[0026] Figure 1 These are system schematic diagrams for Embodiment 1 and Embodiment 2;

[0027] Figure 2 This is a schematic diagram of the reactor structure;

[0028] Figure 3 This is a schematic diagram of the structure of a mixing nozzle;

[0029] Figure 4 This is the system schematic diagram of Example 3;

[0030] In the picture:

[0031] 1. Reactor; 2. Cyclone separator; 3. Baghouse dust collector; 4. Cold trap; 5. Exhaust pipe; 6. First solenoid valve; 7. Vacuum pump; 8. Raw gas pipe; 9. Third solenoid valve; 10. Inlet pipe; 11. Second solenoid valve; 12. Purge pipe; 13. Coil; 14. Heating pipe; 15. Oil chamber; 16. Circulating fan; 17. Mixing nozzle; 18. Circulation pipe; 19. Return air ring; 20. 21. Return air vent; 22. Silicon powder feed valve; 23. Silicon powder feed silo; 24. Air outlet pipe; 25. Tank cover; 26. Extraction pipe; 27. Filter screen; 28. Exhaust pipe; 29. ​​Inner tank; 20. Outer tank; 31. Oil injection pipe; 32. Silicon powder layer; 33. Discharge pipe; 34. Distribution plate; 35. Inner pipe; 36. Material passage hole; 37. Outer pipe; 38. Nozzle; 39. Diffuser; 30. Heat exchanger. Detailed Implementation

[0032] Example 1

[0033] like Figure 1 and Figure 2 As shown, a silicon tetrafluoride synthesis apparatus includes a reactor 1, a separator, and a cold trap 4 connected in sequence. The separator includes a cyclone separator 2 and a bag filter 3 arranged in sequence between the reactor 1 and the cold trap 4. The reactor 1 includes a closed, vertical tank, which includes a lower inner tank 28 and a tank cover 24 covering the top of the inner tank 28. The inner tank 28 and the tank cover 24 are connected by a flange.

[0034] An air inlet pipe 10 is located at the bottom center of the inner tank 28. The air inlet pipe 10 is connected to a source gas pipe 8 and a purge pipe 12 via a T-junction. The source gas pipe 8 carries nitrogen trifluoride, and the purge pipe 12 carries an inert gas (such as nitrogen, helium, or argon). A second solenoid valve 11 is installed on the purge pipe 12, and a third solenoid valve 9 is installed on the source gas pipe 8. An air outlet pipe 23 is located at the top center of the tank cover 24. A distribution plate 33 is fixedly installed near the bottom of the inner tank 28, and a silicon powder layer 31 covers the upper part of the distribution plate 33. The distribution plate 33 has micropores to prevent silicon powder from leaking downwards from the silicon powder layer 31 while allowing gas from the air inlet pipe 10 to pass smoothly. Several upward-spraying mixing nozzles 17 are distributed within the silicon powder layer 31. The mixing nozzles 17 are connected to the top of the tank via a circulation pipe 18, which is equipped with a circulating fan 16.

[0035] The top right side of the can lid 24 is provided with an air extraction pipe 25, which is connected to an air extraction connecting pipe 5. The air extraction connecting pipe 5 is provided with a first solenoid valve 6 and a vacuum pump in sequence from near to far.

[0036] The inner tank 28 is fitted with an outer tank 29, the top of which is fixedly connected to the outer tank 29. Between the inner tank 28 and the outer tank 29 is a sealed oil chamber 15, which is filled with heat-conducting oil. The bottom of the oil chamber 15 is equipped with a heating pipe 14, which is electrically heated and fixedly mounted on the outer tank 29. The top right side of the outer tank 29 has an exhaust pipe 27 with a perforated plug screwed onto it to ensure that the air pressure inside the oil chamber 15 is consistent with the external atmospheric pressure. Near the top of the outer tank 29 is an oil filling pipe 30 with a plug screwed onto it.

[0037] After oil is injected, the liquid level of the heat transfer oil in the oil chamber 15 reaches the height of the oil injection pipe 30. When the heating pipe 14 heats the heat transfer oil in the oil chamber, the heat transfer oil expands and its volume increases, and the liquid level rises. The space above the oil injection pipe 30 in the oil chamber 15 provides expansion space for the heat transfer oil after expansion, preventing the outer tank 29 from bursting.

[0038] The inner tank 28 is provided with a discharge pipe 32 on the right side, which is connected to the bottom of the silicon powder layer 31. Both the inner tank 28 and the outer tank 29 are welded through the discharge pipe 32. The outer end of the discharge pipe 32 is provided with a flange, which is connected to a plug by bolts.

[0039] The inner tank 28 is fitted with a C-shaped return air ring 19 welded to its top. The return air ring 19 is located at the top of the oil chamber 15. The upper end of the circulation pipe 18 passes through the outer tank 29 and communicates with the interior of the return air ring 19. The top of the inner tank 28 has return air holes 20 evenly distributed along the circumference of the inner tank 28 at the location of the return air ring 19, which communicate with the interior of the return air ring 19. The bottom of the tank cover 24 is provided with a filter screen 26.

[0040] A silicon powder feed pipe is provided on the outer left side of the top of the can lid 24, and the silicon powder feed pipe passes downward through the filter screen 26. The upper end of the silicon powder feed pipe is connected to a silicon powder feed hopper 22, and a silicon powder feed valve 21 is provided between the silicon powder feed hopper 22 and the can body. The silicon powder feed hopper 22 is internally sealed, and a cap connected to the top of the silicon powder feed hopper 22 by screws is provided thereto.

[0041] After unscrewing the screws and opening the cap, silicon powder can be injected into the silicon powder feed hopper 22. After opening the silicon powder feed valve 21, silicon powder can be injected into the inner tank 28.

[0042] When nitrogen trifluoride gas is introduced into reactor 1, under the action of circulating fan 16, the gas at the top of inner tank 28 passes through return air hole 20, return air ring 19 and circulation pipe 18 in sequence and is then sprayed upward from mixing nozzle 17. The airflow from mixing nozzle 17 blows the silicon powder in silicon powder layer 31 upward and diffuses it in inner tank 28, thereby increasing the contact area and contact time between silicon powder and nitrogen trifluoride gas, making the reaction more complete, thus making the silicon tetrafluoride gas discharged from outlet pipe 23 more pure and improving the production efficiency of silicon tetrafluoride.

[0043] Each mixing nozzle 17 includes a vertical inner tube 34 and an outer tube 36 sleeved around the inner tube 34. The top of the inner tube 34 is an upward-facing nozzle 37. The inner tube 34 is connected to the circulation pipe 18. The outer tube 36 is fixedly connected to the inner tube 34. The inner tube 34 or the outer tube 36 is fixedly connected to the tank body. The opening at the top of the outer tube 36 extends above the silicon powder layer 31. There is a gap between the outer tube 36 and the inner tube 34, which is connected to the silicon powder layer 31.

[0044] The outer tube 36 is cylindrical, with its bottom sealed and welded to the inner tube 34. Near the bottom, the sidewall of the outer tube 36 has material passage holes 35 that connect the gap to the silicon powder layer 31. The top of the outer tube 36 is a funnel-shaped diffuser 38 with a larger diameter at the top and a smaller diameter at the bottom. The top of the inner tube 34 is a nozzle 37 with a smaller diameter at the top and a larger diameter at the bottom.

[0045] The circulating fan 16 sends the gas from the top of the inner tank 28 to the bottom of the inner tube 34 through the circulating pipe 18, and then sprays it upward through the nozzle 37. According to the principle of fluid dynamics, a low-pressure zone lower than the external air pressure of the outer tube 36 is generated at the material passage 35. The silicon powder in the silicon powder layer 31 is drawn into the gap between the outer tube 36 and the inner tube 34 through the material passage 35, and then sprayed upward through the gap with the airflow sprayed from the nozzle 37. Under the action of the diffuser 38, these silicon powders diffuse upward inside the inner tank 28 and fully react with the nitrogen trifluoride inside the inner tank 28.

[0046] Example 2

[0047] Combination Figure 3 As shown, the difference between this embodiment and Embodiment 1 is that:

[0048] The cyclone separator 2 is wrapped with a coil 13 for collecting heat from the separator, and a heat exchanger 39 is provided between the coil 13 and the original gas pipe 8.

[0049] When the mixed gas containing silicon tetrafluoride discharged from the outlet pipe 23 is separated in the cyclone separator 2, the waste heat is transferred to the cyclone separator 2. The liquid medium in the coil 13 circulates between the cyclone separator 2 and the heat exchanger 39 under the drive of the circulating pump. The heat exchanger 39 transfers the heat of the cyclone separator 2 to the nitrogen trifluoride in the original gas pipe 8, preheating the nitrogen trifluoride, thereby achieving the purpose of energy saving.

[0050] Example 3

[0051] The difference between this embodiment and Embodiment 2 is that a method for synthesizing silicon tetrafluoride is disclosed, as follows:

[0052] S1. Open the cap on top of the silicon powder feed hopper 22, open the silicon powder feed valve 21, add silicon powder to reactor 1. The particle size of the silicon powder is 600 mesh, and the height of the silicon powder layer 31 does not exceed the diffuser tube 38. Close the silicon powder feed valve 21 and close the cap. Start the heating tube 14 to preheat reactor 1 to 200℃. Then, use inert gas for purging. The purging process is as follows: close the third solenoid valve 9 and the second solenoid valve 11, close the valve on the outlet pipe 23, open the first solenoid valve 6, start the vacuum pump 7 to evacuate the inside of reactor 1, then close the first solenoid valve 6 and the vacuum pump 7, open the second solenoid valve 11, and introduce 99.999% pure inert gas (nitrogen, helium, or argon) into reactor 1 for purging 20 times. The purging speed during purging is 1L / h to 10L / h, and the time is 2 to 8 hours. After purging, the oxygen content is less than 10ppm. Then, heat reactor 1 to 250 to 400℃.

[0053] S2, 99.5% pure anhydrous nitrogen trifluoride gas is introduced into reactor 1 through the original gas pipe 8 and the inlet pipe 10 at a flow rate of 10 L / min. It reacts with the silicon powder in reactor 1 to generate silicon tetrafluoride gas. The molar ratio of nitrogen trifluoride to silicon powder is 4:3, and the flow rate of nitrogen trifluoride is 1 L / min to 10 L / min.

[0054] S3, the reaction product discharged from the top of reactor 1 is separated from the unreacted silicon powder by cyclone separator 2. The gaseous reaction product is then filtered by bag filter 3 to remove impurities, resulting in gaseous silicon tetrafluoride gas. This gas is then collected in cold trap 4 at a temperature of -130°C. The cold trap is then evacuated to remove the inert gas, yielding crude silicon tetrafluoride. The silicon tetrafluoride content is tested to be 99.5%.

[0055] The above-described embodiments are detailed and specific, illustrating preferred embodiments of the present invention. They are only used to illustrate the technical ideas and features of the present invention, aiming to enable those skilled in the art to understand and implement the invention. However, they are not limited to the present invention, and the patent scope of the present invention should not be limited to these embodiments. Any equivalent changes or modifications made to the spirit disclosed in the present invention, without departing from the structure of the present invention, such as local improvements within the system and alterations or transformations between subsystems, are still within the patent scope of the present invention. Currently, the technical solution of this application has undergone pilot testing, i.e., small-scale experiments before large-scale mass production. After the pilot testing, user surveys were conducted on a small scale, and the survey results showed high user satisfaction. Preparations are now underway for the formal production and industrialization of the product, including intellectual property risk warning surveys.

Claims

1. An apparatus for synthesizing silicon tetrafluoride, characterized in that: The reactor (1), separator, and cold trap (4) are connected in sequence. The reactor (1) includes a closed vertical tank with an inlet pipe (10) at the bottom and a raw gas pipe (8) for introducing nitrogen trifluoride into the tank. The tank has an outlet pipe (23) at the top and a mixing nozzle (17) for upward injection in the silica powder layer (31) at the bottom of the tank. The mixing nozzle (17) and the top of the tank are connected by a circulation pipe (18) and a circulation fan (16) is provided on the circulation pipe (18). The mixing nozzle (17) includes a vertical inner tube (34) with the nozzle (37) pointing upwards and an outer tube (36) sleeved outside the inner tube (34). The inner tube (34) is connected to the circulation pipe (18). The outer tube (36) is fixedly connected to the inner tube (34). The inner tube (34) or the outer tube (36) is fixedly connected to the tank. The opening at the top of the outer tube (36) is higher than the silicon powder layer (31). There is a gap between the outer tube (36) and the inner tube (34), and this gap is connected to the silicon powder layer (31). The bottom of the outer tube (36) is sealed, and the side wall of the outer tube (36) is provided with a material passage hole (35) for communicating the gap with the silicon powder layer (31). The top of the outer tube (36) is a funnel-shaped diffuser tube (38) with a larger diameter at the top and a smaller diameter at the bottom.

2. The apparatus for synthesizing silicon tetrafluoride according to claim 1, characterized in that: The tank body is fitted with an outer tank (29) which is fixedly connected to it. Between the tank body and the outer tank (29) is a closed oil chamber (15). The bottom of the oil chamber (15) is provided with a heating pipe (14). The heating pipe (14) is fixedly installed on the outer tank (29). The top of the outer tank (29) is provided with an exhaust pipe (27). A screw plug with a hole is screwed onto the exhaust pipe (27). The outer tank (29) is provided with an oil injection pipe (30) near the top. A plug is screwed onto the oil injection pipe (30).

3. The apparatus for synthesizing silicon tetrafluoride according to claim 1, characterized in that: The top of the tank is fitted with a hollow return air ring (19), the circulation pipe (18) is connected to the inside of the return air ring (19), and the tank is provided with a return air hole (20) at the location of the return air ring (19) that is connected to the inside of the return air ring (19).

4. The apparatus for synthesizing silicon tetrafluoride according to claim 1, characterized in that: A distribution plate (33) is fixedly installed at the bottom of the tank, the silicon powder layer (31) is located on the distribution plate (33), and the air inlet pipe (10) is located below the distribution plate (33).

5. The apparatus for synthesizing silicon tetrafluoride according to claim 1, characterized in that: A silicon powder feed pipe is connected to the outer side of the top of the tank, and a silicon powder feed hopper (22) is connected to the silicon powder feed pipe. A silicon powder feed valve (21) is provided between the silicon powder feed hopper (22) and the tank.

6. The apparatus for synthesizing silicon tetrafluoride according to claim 1, characterized in that: The separator is wrapped with a coil (13) for collecting heat from the separator, and a heat exchanger (39) is provided between the coil (13) and the original gas pipe (8).

7. A method for synthesizing silicon tetrafluoride, characterized in that: The apparatus for synthesizing silicon tetrafluoride according to any one of claims 1 to 6 includes the following steps: S1, place silicon powder in reactor (1), preheat reactor (1), replace with inert gas, and then heat reactor (1). S2, nitrogen trifluoride is introduced from the bottom of the bed reactor (1) and a reaction occurs; S3, the reaction product is taken out from the top of the reactor (1) and separated by a separator; S4, the separated product is passed into a bag filter (3) to remove impurities and obtain silicon tetrafluoride gas; S5, silicon tetrafluoride gas is introduced into the cold trap (4), condensed and collected, and then the inert gas is vented.

8. The method for synthesizing silicon tetrafluoride according to claim 7, characterized in that: In step S1, silicon powder is placed in reactor (1) and preheated to 200°C. After reactor (1) is replaced with inert gas, the oxygen content is less than 10 ppm. The heating temperature is 250~400°C. The inert gas used for replacement is nitrogen, helium or argon with a purity of 99.999%. The purging speed during inert gas replacement is 1L / h~10L / h and the time is 2~8h. In step S2, nitrogen trifluoride has a purity of 99.5% and a flow rate of 1L / min~10L / min. The molar ratio of nitrogen trifluoride to silicon powder is 4:

3. In step S5, the temperature of cold trap (4) is controlled at -100°C~-130°C.

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