Production method of large ten-thousand-ton superfine silicon nitride powder

Abstract

The invention discloses a large ten-thousand-ton superfine silicon nitride powder production method which is characterized by comprising the following steps: S1, carrying out disproportionation reaction on trichlorosilane to generate a mixture containing silane and silicon tetrachloride, and separating and purifying the mixture to respectively obtain high-purity silane and high-purity silicon tetrachloride; s2, enabling the silane obtained in the step S1 to react with ammonia gas in a fluidized bed reactor to obtain a target product silicon nitride, a byproduct hydrogen and excessive ammonia gas, and collecting the silicon nitride, the hydrogen and the ammonia gas; s3, the silicon tetrachloride obtained in the step S1, the hydrogen obtained in the step S2 and silicon powder are subjected to a cold hydrogenation reaction, and trichlorosilane is regenerated; and S4, returning the trichlorosilane generated in the step S3 to the step S1 for recycling. The system is a closed reaction system, silane is prepared, the production cost is reduced, and mass production is facilitated.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of silicon nitride production, in particular to a large-scale ten-thousand-ton ultra-fine silicon nitride powder production method. BACKGROUND

[0002] Silicon nitride ceramic materials are widely used in packaging ceramic substrates, high-temperature-resistant parts of gas engines, corrosion-resistant and wear-resistant parts in the chemical industry, and high-temperature ceramic bearings.

[0003] At present, the preparation methods of silicon nitride mainly include direct nitriding method, carbothermal reduction method and chemical vapor deposition method. Among them, the gas phase method is an important means for preparing high-purity silicon nitride. The existing gas phase method has the following problems when preparing silicon nitride: 1. The reactants silane and ammonia need to be purchased. Since the price of silane is high, the purchase cost of the entire reactant is high; 2. The reaction steps are single, and the entire system cannot circulate the reaction. Non-target products such as hydrogen gas will be directly discharged, resulting in waste and cost increase. SUMMARY

[0004] In view of the deficiencies of the prior art, the present application provides a large-scale ten-thousand-ton ultra-fine silicon nitride powder production method, which is a closed reaction system, self-made silane, and reduces production cost, facilitating mass production.

[0005] To achieve the above-mentioned purpose, the present application provides the following technical scheme:

[0006] A large-scale ten-thousand-ton ultra-fine silicon nitride powder production method, characterized by comprising the following steps:

[0007] S1, making trichlorosilane undergo disproportionation reaction to generate a mixture containing silane and silicon tetrachloride, and separating and purifying the mixture to obtain high-purity silane and high-purity silicon tetrachloride, respectively;

[0008] S2, reacting the silane obtained in step S1 with ammonia in a fluidized bed reactor to obtain target product silicon nitride, byproduct hydrogen and excess ammonia, and collecting silicon nitride, hydrogen and ammonia;

[0009] S3, performing cold hydrogenation reaction on the silicon tetrachloride obtained in step S1, the hydrogen obtained in step S2 and silicon powder to regenerate trichlorosilane;

[0010] S4, returning the trichlorosilane generated in step S3 to step S1 for recycling.

[0011] Preferably, in step S2, silane and ammonia are introduced into the fluidized bed reactor from the bottom, and the ammonia is added in excess.

[0012] Preferably, the reaction products silicon nitride and hydrogen gas and excess ammonia gas in the fluidized bed reactor are discharged from the fluidized bed reactor, pass through a cooling buffer tank and a collector, so that the silicon nitride is collected by the collector, then pass through a condenser to liquefy and separate the ammonia gas, and finally pass through a hydrogen separation membrane to separate the nitrogen gas to obtain hydrogen gas.

[0013] Preferably, the silicon tetrachloride obtained in step S1 enters a silicon tetrachloride storage tank, the silane obtained enters a silane storage tank, and the hydrogen gas obtained in step S2 enters a hydrogen gas storage tank for use.

[0014] Preferably, when silicon nitride of multiple particle size ranges is needed to be prepared, the silane is divided into two paths in step S2, into a first path silane and a second path silane, the first path silane is introduced into the free space reactor to be pretreated into nano-sized silicon particles and then introduced into the fluidized bed reactor for reaction, and the second path silane is directly introduced into the fluidized bed reactor for reaction.

[0015] Preferably, the collector has three, respectively a first collector, a second collector and a third collector, and the three collectors respectively collect silicon nitride of three particle size ranges.

[0016] The advantages of the present application are:

[0017] 1. The closed loop reaction system can make full use of by-products, and can also self-produce silane, only needs to add ammonia gas and silicon powder, and significantly reduces production cost.

[0018] 2. The silane is decomposed into nano silicon in the free space reactor and then enters the fluidized bed reactor for reaction, so that silicon nitride particles of multiple particle size ranges can be prepared to meet different use requirements. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 The system diagram of the large-scale ten-thousand-ton ultra-fine silicon nitride powder production method provided in the present embodiment. DETAILED DESCRIPTION

[0020] Combination Figure 1 The large-scale ten-thousand-ton ultra-fine silicon nitride powder production method is further described.

[0021] A large-scale ten-thousand-ton ultra-fine silicon nitride powder production method, characterized by comprising the following steps:

[0022] S1, dismutation reaction of trichlorosilane to generate a mixture containing silane and silicon tetrachloride, separation and purification of the mixture to obtain high-purity silane and high-purity liquid-phase silicon tetrachloride, respectively;

[0023] S2, reacting the silane obtained in step S1 with ammonia gas in the fluidized bed reactor 2 to obtain target product silicon nitride, byproduct hydrogen gas, and excess ammonia gas, and collecting the silicon nitride, ammonia gas, and hydrogen gas;

[0024] S3, performing a cold hydrogenation reaction on the silicon tetrachloride obtained in step S1, the hydrogen gas obtained in step S2, and silicon powder to regenerate trichlorosilane;

[0025] S4, returning the trichlorosilane generated in step S3 to step S1 for recycling.

[0026] Specifically, in step S1, the purity of the obtained silane is 99.9999% or higher, and the silane can be directly used as a raw material for the fluidized bed of particulate silicon; the silicon tetrachloride is collected using a silicon tetrachloride storage tank 13, and the silane is collected using a silane storage tank 15 for recycling; the steps of preparing the silane and the silicon tetrachloride are described in the patent document CN115321540A, which is prior art, and therefore this embodiment will not be described in detail.

[0027] In step S2, the ammonia gas is preheated to 400°C and then introduced into the fluidized bed reactor 2 from the bottom of the fluidized bed reactor 2, passes through the gas distribution plate and the gas flow distribution device at the bottom of the reaction section in the fluidized bed reactor 2, and then enters the middle reaction section after being fully mixed with the silane. The reaction section is heated to a temperature of 650°C by the electric heating rod inserted into the top of the reactor, and the pressure in the fluidized bed reactor 2 is controlled to be 0.4 bar by controlling the flow rate and pressure of the reaction gas. The combination reaction is carried out to generate silicon nitride powder and byproduct hydrogen gas.

[0028] The reaction of silane and ammonia gas generates a large amount of hydrogen gas, which increases the volume and pressure. Therefore, the upper end of the fluidized bed reactor 2 is expanded by 9 to accommodate the increase in gas volume. In this embodiment, in order to make the reaction products in the fluidized bed reactor flow out by the pressure difference, there is still a certain pressure rise inside the fluidized bed reactor 2 after the upper end of the fluidized bed reactor 2 is expanded, forming a pressure difference with the outside.

[0029] During the introduction of silane and ammonia gas, the mass ratio of ammonia gas to silane is 1:3-5, and in the specific implementation of this embodiment, it is 1:4. This allows the silane to be fully decomposed and reacted in the fluidized bed reactor 2, and also facilitates the removal of the products in the fluidized bed reactor 2.

[0030] A cooling buffer tank 3 is connected to the gas outlet end of the fluidized bed reactor 2, and nitrogen gas is injected into the cooling buffer tank 3 to cool the reaction products entering the cooling buffer tank 3 to below 200°C, preferably 50-200°C.

[0031] The reaction products in fluidized bed reactor 2 include nitrogen, hydrogen, trace amounts of undecomposed ammonia, and silicon nitride powder. The silicon nitride powder has a very low density, only 0.1–0.3 g / cm³. 3 Therefore, it can also flow into the cooling buffer tank 3 with the airflow. During the cooling process, occasionally larger silicon nitride powder particles with a particle size in the range of 0.5 to 1 micrometer are generated. Therefore, a collection tank 8 is provided at the bottom of the cooling buffer tank 3. The collection tank 8 can collect a small amount of larger powder particles generated during the cooling process. That is, silicon nitride powder products with a particle size in the range of 0.5 to 1 micrometer are preferentially settled down and collected by the collection tank 8. The remaining products flow upward after cooling and enter the collector for classification and collection to obtain the target product silicon nitride. The remaining gas passes through the condenser 10 to liquefy and collect the ammonia gas. The remaining nitrogen and hydrogen are separated by the hydrogen separation membrane 11. The nitrogen gas is discharged through the tail gas treatment device. Finally, the remaining hydrogen gas is collected in the hydrogen storage tank 12 for use.

[0032] In step S3, silicon tetrachloride in silicon tetrachloride storage tank 13, hydrogen in hydrogen storage tank 12, and silicon powder are combined and reacted in a reactor to generate trichlorosilane. Finally, the trichlorosilane is collected in trichlorosilane storage tank 14. This reaction system method is described in patent document with publication number CN118929669A and is prior art. Therefore, it will not be described in detail in this embodiment.

[0033] In step S4, the trichlorosilane in the trichlorosilane storage tank 14 is sent to step S1 for reaction according to the reaction requirements to prepare silane and silicon tetrachloride.

[0034] In the aforementioned method for producing silicon nitride powder, only ammonia and silicon powder are required as raw materials. In contrast, the traditional gas-phase method for preparing silicon nitride powder requires silane and ammonia. Since silane is expensive, and the method of this application can generate silane itself without the need for external purchase, production costs can be significantly reduced.

[0035] Specifically, the raw materials required for the actual production of 10,000 tons of silicon nitride are shown in the table below:

[0036]

[0037] Since the price of silane is significantly higher than that of silicon powder, with the current market cost of silane being four to five times that of silicon powder, the table above shows that a production capacity of 10,000 tons of silicon nitride can save 70%-80% of the cost.

[0038] When it is necessary to prepare silicon nitride with multiple particle size ranges, namely 0.8–1.5 μm, 0.5–0.8 μm, and less than 0.5 μm, in step S2, the silane obtained in step S1 is divided into two streams: a first stream of silane and a second stream of silane. The first stream of silane is introduced into the free space reactor 1, and hydrogen from the hydrogen storage tank 12 is also introduced into the free space reactor 1 as a carrier gas. After pretreatment into nanoscale silicon particles at 500°C, it is then introduced into the fluidized bed reactor 2 for reaction. The second stream of silane is directly introduced into the fluidized bed reactor 2 for reaction. During this process, ammonia is still maintained in excess in the fluidized bed reactor. In specific operation, the amount of second stream of silane can be reduced, and the reduced amount of second stream of silane can be filled by nanoscale silicon particles, so that the nanoscale silicon particles and the second stream of silane can react fully. Correspondingly, three collectors are set up. Except for the filter cartridge 7 which has a different filtration precision, the three collectors have the same structure. They are the first-stage collector 4, the second-stage collector 5, and the third-stage collector 6, which collect silicon nitride particles with three different particle sizes: 0.8-1.5μm, 0.5-0.8μm, and less than 0.5μm, respectively.

[0039] The first silane is pretreated into highly active nanoscale silicon particles in a free-space reactor 1, and then fed into a fluidized bed reactor 2 for reaction. During this process, the nanoscale silicon has more time to grow, and then reacts with nitrogen to form larger silicon nitride particles. In contrast, the silicon particles obtained by the decomposition of the second silane in the fluidized bed reactor 2 do not have enough time to grow before reacting with nitrogen to form silicon nitride, resulting in smaller silicon nitride particles. Therefore, this method can control the growth range of the prepared silicon nitride powder and collect it in a graded manner to obtain silicon nitride powders with three particle size ranges: less than 0.5 μm, 0.5–0.8 μm, and 0.8–1.5 μm, for different applications.

[0040] Specifically, the inner diameter of the free-space reactor 1 is 1000-2000 mm, specifically 2000 mm in this embodiment; the height of the reaction section is 5000-10000 mm, specifically 8000 mm in this embodiment; the height of the expansion section is 2000-5000 mm, specifically 5000 mm in this embodiment. The first silane stream is introduced into the free-space reactor 1, passes through the gas distribution plate and airflow distribution device at the bottom of the reaction section, and enters the middle reaction section evenly. After reacting to generate nano-silicon powder, it enters the middle reaction section of the stainless steel fluidized bed reactor 2 with the airflow. The inner diameter of the fluidized bed reactor 2 is 1000-2000 mm, specifically 2000 mm in this embodiment; the height of the reaction section is 5000-10000 mm. In the specific embodiment, the diameter is 8000 mm, and the height of the expansion section is 2000-5000 mm. In this embodiment, it is 5000 mm. After the ammonia gas is preheated to 400°C, it is introduced into the fluidized bed reactor 2 along with the second silane. After passing through the gas distribution plate and airflow distribution device at the bottom of the reaction section, the ammonia gas and the second silane are fully mixed and then enter the middle reaction section. Under the condition that the heating temperature of the electric heating rod inserted at the top of the reactor reaches 650°C, the pressure in the fluidized bed reactor 2 is controlled at 0.4 bar to carry out the chemical reaction and generate silicon nitride powder. After cooling in the buffer tank 3 and product collection, the powder in the primary collector 4, the secondary collector 5 and the tertiary collector 6 are tested and the data are obtained in Tables 1, 2 and 3 respectively.

[0041]

[0042] Table 1

[0043]

[0044] Table 2

[0045]

[0046] Table 3

[0047] If only silicon nitride with particle sizes in the range of less than 0.5 μm and 0.5 to 0.8 μm is required, the implementation method is as follows.

[0048] The free-space reactor 1 has an inner diameter of 1000–2000 mm, specifically 2000 mm in this embodiment; a reaction section height of 5000–10000 mm, specifically 8000 mm in this embodiment; and an expansion section height of 2000–5000 mm, specifically 5000 mm in this embodiment. A first-stage silane stream is introduced into the free-space reactor 1, passing through a gas distribution plate and airflow distribution device at the bottom of the reaction section, and then uniformly enters the middle reaction section. After reacting to generate nano-silicon powder, it is carried by the airflow into the middle reaction section of the stainless steel fluidized bed reactor 2. The fluidized bed reactor 2 has an inner diameter of 1000–2000 mm, specifically 2000 mm in this embodiment; and a reaction section height of 5000–10000 mm, specifically 8000 mm in this embodiment. The height of the expansion section is 2000-5000mm, specifically 5000mm in this embodiment. After ammonia is preheated to 400℃, it is introduced into the fluidized bed reactor 2 along with the second silane. After passing through the gas distribution plate and airflow distribution device at the bottom of the reaction section, the ammonia and silane are fully mixed and then enter the middle reaction section. Under the condition that the heating temperature of the electric heating rod inserted at the top of the reactor reaches 650℃, the pressure in the fluidized bed reactor 2 is controlled at 0.2 bar to carry out the chemical reaction and generate silicon nitride powder. After cooling in the buffer tank 3 and product collection, the powder in the secondary collector 5 and the tertiary collector 6 are tested and the above data Table 2 and Table 3 are obtained respectively. There are no silicon nitride particles or very few silicon nitride particles in the primary collector 4.

[0049] If only silicon nitride particles smaller than 0.5 μm are to be prepared, the first silane stream is shut off, the free space reactor 1 does not need to be started, and the fluidized bed reactor 2 can be used directly, as shown in the following implementation method.

[0050] The stainless steel fluidized bed reactor 2 has an inner diameter of 1000-2000 mm, specifically 2000 mm in this embodiment, a reaction section height of 5000-10000 mm, specifically 8000 mm in this embodiment, and an expansion section height of 2000-5000 mm, specifically 5000 mm in this embodiment. Ammonia gas is preheated to 400°C and then introduced into the fluidized bed reactor 2 along with the second silane stream. After passing through the gas distribution plate and airflow distribution device at the bottom of the reaction section, the ammonia gas and silane are fully mixed and then enter the middle reaction section. The temperature of the reaction section reaches 650°C under the heating of the electric heating rod inserted at the top of the reactor. The pressure inside the fluidized bed reactor 2 is controlled at 0.2 bar to carry out the chemical reaction and generate silicon nitride powder. After cooling in the buffer tank 3 and product collection, the powder in the tertiary collector 6 is tested to obtain the data in Table 3 above. There are no silicon nitride particles or very few silicon nitride particles in the primary collector 4 and the secondary collector 5.

[0051] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A method for producing large-scale, ten-thousand-ton-level ultrafine silicon nitride powder, characterized by: Includes the following steps: S1. Trichlorosilane undergoes a disproportionation reaction to generate a mixture containing silane and silicon tetrachloride. The mixture is then separated and purified to obtain high-purity silane and high-purity silicon tetrachloride, respectively. S2. The silane obtained in step S1 is reacted with ammonia in a fluidized bed reactor to obtain the target product silicon nitride, the byproduct hydrogen, and excess ammonia. The silicon nitride, hydrogen, and ammonia are collected. S3. The silicon tetrachloride obtained in step S1, the hydrogen gas obtained in step S2, and the silicon powder are subjected to a cold hydrogenation reaction to regenerate trichlorosilane. S4. The trichlorosilane generated in step S3 is returned to step S1 for recycling.

2. The method for producing large-scale, ten-thousand-ton-level ultrafine silicon nitride powder according to claim 1, characterized in that: In step S2, silane and ammonia are introduced into the fluidized bed reactor from the bottom, with an excess of ammonia.

3. The method for producing large-scale, ten-thousand-ton-level ultrafine silicon nitride powder according to claim 2, characterized in that: The reaction products silicon nitride and hydrogen, as well as excess ammonia, are discharged from the fluidized bed reactor. After passing through a cooling buffer tank and a collector, the silicon nitride is collected. Then, the ammonia is liquefied and separated in a condenser. Finally, the nitrogen is separated through a hydrogen separation membrane to obtain hydrogen.

4. The method for producing large-scale, ten-thousand-ton-level ultrafine silicon nitride powder according to claim 3, characterized in that: The silicon tetrachloride obtained in step S1 is placed in a silicon tetrachloride storage tank, the silane obtained is placed in a silane storage tank, and the hydrogen obtained in step S2 is placed in a hydrogen storage tank for future use.

5. The method for producing large-scale, ten-thousand-ton-level ultrafine silicon nitride powder according to claim 1, characterized in that: When it is necessary to prepare silicon nitride with multiple particle size ranges, in step S2, the silane is divided into two streams, namely the first stream silane and the second stream silane. The first stream silane is fed into the free space reactor, where it is pretreated into nanoscale silicon particles before being fed into the fluidized bed reactor for reaction. The second stream silane is directly fed into the fluidized bed reactor for reaction.

6. The method for producing large-scale, ten-thousand-ton-level ultrafine silicon nitride powder according to claim 5, characterized in that: The collector has three stages: a primary collector, a secondary collector, and a tertiary collector, which respectively collect silicon nitride particles in three different size ranges.

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