Method for producing large-scale ten-thousand-ton ultrafine silicon nitride powder

Abstract

The application discloses a production method of large-scale ten-thousand-ton ultrafine silicon nitride powder, and is characterized by comprising the following steps: S1, making trichlorosilane undergo a disproportionation reaction to generate a mixture containing silane and silicon tetrachloride, and performing separation and purification on the mixture to obtain high-purity silane and high-purity silicon tetrachloride respectively; S2, making the silane obtained in the step S1 react with ammonia gas in a fluidized bed reactor to obtain a target product silicon nitride, by-products hydrogen and excessive ammonia, and collecting the silicon nitride, hydrogen and ammonia; S3, making the silicon tetrachloride obtained in the step S1, the hydrogen obtained in the step S2 and silicon powder undergo a cold hydrogenation reaction to re-generate trichlorosilane; and S4, returning the trichlorosilane generated in the step S3 to the step S1 for recycling. The application is a closed reaction system, self-made silane, and can reduce production cost and facilitate mass production.

Description

Technical Field

[0001] This invention relates to the field of silicon nitride production, and more particularly to a method for producing large-scale, ten-thousand-ton-level ultrafine silicon nitride powder. Background Technology

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

[0003] Currently, the main methods for preparing silicon nitride include direct nitriding, carbothermal reduction, and chemical vapor deposition. Among these, the vapor phase method is an important means of preparing high-purity silicon nitride. However, existing vapor phase methods for preparing silicon nitride have the following problems: 1. The reactants silane and ammonia must be purchased externally. Due to the high price of silane, the overall cost of purchasing the reactants is high; 2. The reaction steps are singular, and the entire system cannot be recycled. Non-target products such as hydrogen are directly discharged, leading to waste and increased costs. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a method for producing large-scale, ten-thousand-ton-level ultrafine silicon nitride powder. This method is a closed reaction system that uses self-made silane, reducing production costs and facilitating mass production.

[0005] To achieve the above objectives, the present invention provides the following technical solution: A method for producing large-scale, ten-thousand-ton-level ultrafine silicon nitride powder, characterized by 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.

[0006] Preferably, in step S2, silane and ammonia are introduced into the fluidized bed reactor from the bottom, wherein ammonia is added in excess.

[0007] Preferably, the reaction products silicon nitride and hydrogen, as well as excess ammonia, in the fluidized bed reactor are discharged from the fluidized bed reactor, pass through a cooling buffer tank and a collector, where silicon nitride is collected by the collector, then passes through a condenser to liquefy and separate ammonia, and finally passes through a hydrogen separation membrane to separate nitrogen and obtain hydrogen.

[0008] Preferably, 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 use.

[0009] Preferably, when it is necessary to prepare silicon nitride with multiple particle size ranges, in step S2, the silane is divided into two streams, namely a first stream of silane and a second stream of silane. The first stream of silane is fed into a free space reactor, where it is pretreated into nanoscale silicon particles before being fed into a fluidized bed reactor for reaction. The second stream of silane is directly fed into the fluidized bed reactor for reaction.

[0010] Preferably, the collector has three stages: a primary collector, a secondary collector, and a tertiary collector, which respectively collect silicon nitride of three different particle size ranges.

[0011] The advantages of this invention are: 1. The closed-loop reaction system can make full use of by-products and can also produce silanes by simply adding ammonia and silicon powder, which significantly reduces production costs. 2. By decomposing silane into nano-silicon through a free reactor and then reacting it in a fluidized bed reactor, silicon nitride particles with a wide range of particle sizes can be prepared to meet different application requirements. Attached Figure Description

[0012] Figure 1 This is a system diagram of the large-scale, ten-thousand-ton-level ultrafine silicon nitride powder production method provided in this embodiment. Detailed Implementation

[0013] Combination Figure 1 The present invention provides a further description of the method for producing large-scale, ten-thousand-ton-level ultrafine silicon nitride powder.

[0014] A method for producing large-scale, ten-thousand-ton-level ultrafine silicon nitride powder, characterized by 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 liquid silicon tetrachloride, respectively. S2. The silane obtained in step S1 is reacted with ammonia in a fluidized bed reactor 2 to obtain the target product silicon nitride, the byproduct hydrogen and excess ammonia. The silicon nitride, ammonia and hydrogen 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.

[0015] Specifically, in step S1, the silane obtained has a purity of over 99.9999% and can be directly used as a raw material for granular silicon fluidized beds; silicon tetrachloride is collected using silicon tetrachloride storage tank 13, and silane is collected using silane storage tank 15 for recycling; the steps for preparing silane and silicon tetrachloride are described in patent document with publication number CN115321540A and are prior art, therefore this embodiment will not describe them in detail.

[0016] In step S2, ammonia gas is preheated to 400°C and then introduced into the fluidized bed reactor 2 from the bottom along with silane. After passing through the gas distribution plate and airflow distribution device at the bottom of the reaction section in the fluidized bed reactor 2, the ammonia gas 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°C, the pressure inside the fluidized bed reactor 2 is controlled to 0.4 bar by controlling the flow rate and pressure of the reaction gas, so as to carry out the chemical reaction and generate silicon nitride powder and hydrogen gas as a byproduct.

[0017] The reaction between silane and ammonia produces powder and a large amount of hydrogen, which increases the volume and pressure. Therefore, the upper dimension of the fluidized bed reactor 2 is enlarged by 9 to accommodate the increased gas volume. In this embodiment, in order to allow the reaction products in the fluidized bed reactor to flow out through the pressure difference, the upper end of the fluidized bed reactor 2 is widened. However, there is still a certain pressure rise inside the fluidized bed reactor 2, forming a pressure difference with the outside.

[0018] During the introduction of silane and ammonia, ammonia is in excess, and the mass ratio of the two is 1:3 to 5. In this specific embodiment, it is 1:4, which allows the silane to fully decompose and react in the fluidized bed reactor 2, and also facilitates the removal of the products from the fluidized bed reactor 2.

[0019] A cooling buffer tank 3 is connected to the gas outlet of the fluidized bed reactor 2. Nitrogen gas is injected into the cooling buffer tank 3 to cool the reaction products entering the cooling buffer tank 3, cooling the reaction products to below 200°C, preferably between 50°C and 200°C.

[0020] The reaction products in fluidized bed reactor 2 include nitrogen, hydrogen, trace amounts of undecomposed ammonia, and silicon nitride powder. Silicon nitride powder has a very low density, only 0.1–0.3 g / cm³, so it can also flow with the gas flow into cooling buffer tank 3. During the cooling process, occasionally larger silicon nitride powder particles with a diameter in the range of 0.5–1 micrometer are generated. Therefore, a collection tank 8 is provided at the bottom of cooling buffer tank 3. This collection tank 8 collects the small amount of larger powder particles generated during the cooling process. Specifically, silicon nitride powder products with a diameter in the range of 0.5–1 micrometer preferentially settle down and are collected by collection tank 8. The remaining products, after cooling, flow upwards into a collector for graded collection to obtain the target product, silicon nitride. The remaining gas passes through condenser 10 to liquefy and collect ammonia. The remaining nitrogen and hydrogen are separated by hydrogen separation membrane 11. The nitrogen is discharged through a tail gas treatment device, and the remaining hydrogen is collected in hydrogen storage tank 12 for later use.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] Specifically, when producing 10,000 tons of silicon nitride, the price of silane is significantly higher than that of silicon powder. Currently, the cost of silane on the market is four to five times that of silicon powder, thus saving 70%-80% of the cost.

[0025] 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.

[0026] 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.

[0027] 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; and the height of the expansion section is 2000–5000 mm, specifically 5000 mm in this embodiment. The first stream of silane is introduced into the free-space reactor 1, passes through the gas distribution disk 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, specifically 8000 mm in this embodiment; and the height of the expansion section is 2000–5000 mm. In this embodiment, the 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 the second silane stream 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 inside 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, secondary collector 5 and tertiary collector 6 are tested and the data are obtained in Tables 1, 2 and 3 respectively.

[0028]

[0029] Table 1

[0030] Table 2

[0031] Table 3 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.

[0032] 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 uniformly entering 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 also 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. In this embodiment, the specific diameter is 5000 mm. After ammonia 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 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°C, 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 data in Table 2 and Table 3 above are obtained respectively. There are no silicon nitride particles or very few silicon nitride particles in the primary collector 4.

[0033] 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.

[0034] The inner diameter of the stainless steel fluidized bed reactor 2 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. Ammonia gas is preheated to 400°C and then 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 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 above data table 3. There are no silicon nitride particles or very few silicon nitride particles in the primary collector 4 and the secondary collector 5.

[0035] 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.

Images