Process method for producing trichlorosilane through cold hydrogenation of silicon tetrachloride

Abstract

The invention discloses a process method for producing trichlorosilane by cold hydrogenation of silicon tetrachloride, which comprises the following steps: feeding silicon tetrachloride and hydrogen into a bubbling slurry bed reactor for catalytic cold hydrogenation reaction, adopting fused salt as a medium and metal chloride as a catalyst in the bubbling slurry bed reactor, and controlling the working temperature at 450-500 DEG C and the reaction pressure at 2.5-4.0 MPaG. The process is simple, meets the large-scale and continuous production requirements of the device, and is low in investment, low in operation cost, safe and reliable; the silicon tetrachloride conversion rate and the technological process are simple, the reactor investment is far smaller than that of an existing cold hydrogenation reactor, and the problems that an existing cold hydrogenation technology is high in equipment investment, low in reaction conversion rate and the like are solved.

Description

Technical Field

[0001] The invention belongs to the technical field of polysilicon, and in particular relates to a process for producing trichlorosilane by cold hydrogenation of silicon tetrachloride. Background Art

[0002] In the field of polysilicon production technology, cold hydrogenation is a very core technology. Its main principle is that in the presence of silicon powder, catalyst, hydrogen, etc., at 2.0-3.0MPaG and 500-600℃, silicon tetrachloride reacts with hydrogen and silicon powder to produce trichlorosilane and a small amount of dichlorosilane. This process realizes the conversion of silicon tetrachloride into trichlorosilane, greatly reducing the production cost of polysilicon.

[0003] The current cold hydrogenation reactor is large in size, the space utilization efficiency of the reactor is low, and because of the high temperature, the equipment material needs to be nickel-based alloy (NO8120 / NO8810, etc.), and the equipment cost is very high.

[0004] In the current cold hydrogenation process, the single-pass conversion rate of industrial equipment is mostly between 19% and 24%. Some newly built equipment has also achieved a certain improvement in conversion rate by using more distribution grids and improving the bottom nozzles. For example, some companies claim that they have reached a conversion rate of 28%. However, there is still a lot of room for improvement in the overall conversion rate (it is estimated that there is still 10% room, and the lower the temperature, the greater the room for improvement). The improvement in conversion rate can greatly reduce the overall energy consumption and investment of cold hydrogenation equipment. In order to improve the conversion rate of silicon tetrachloride, many companies, research institutes and design institutes have done a lot of research and practical work, but most of them focus on the type and number of grid plates inside the reactor, the type and control of the bottom distributor, etc. There has been no relevant research on changing the type of reactor.

[0005] In the current industrial cold hydrogenation reactor, a mixture of silicon tetrachloride and hydrogen enters from the bottom of the reactor and is then sprayed into the silicon powder bed through a gas nozzle. Under the influence of the airflow, the silicon powder bed is partially fluidized. However, due to the large diameter of the reactor and the low empty tower gas velocity (the empty tower gas velocity is lower than the critical fluidization gas velocity), the silicon powder cannot be fluidized well, so the gas may short-circuit, resulting in a low reaction conversion rate. Practitioners can break large bubbles and improve the distribution of silicon powder by adding grid plates in the reactor, but the effect is very limited. If the fluidization gas velocity is increased, due to the high hardness of the silicon powder, it will cause more serious abrasion to the reactor and its internal parts, so the engineering designers dare not do so. Therefore, the cold hydrogenation reaction can only be carried out under such conditions of low gas velocity and insufficient gas-solid contact, which is the current dilemma.

[0006] Regarding the catalyst of cold hydrogenation reaction, existing studies have shown that various chlorides have certain catalytic effects, such as ferric chloride, cuprous chloride, etc. At present, cuprous chloride is mainly added in industry, and the addition amount is 1-3‰. This part of the catalyst will be discharged together with the bottom slag of the reactor. In order to reduce costs, the addition amount is also relatively low. The solid distribution in the reactor is uneven, and the catalyst is also difficult to be evenly distributed, and the role played is very limited.

[0007] The problems of existing cold hydrogenation reactors are summarized as follows:

[0008] (1) The hardness of silicon powder is high and the fluidizing gas velocity cannot be increased, so the silicon powder and catalyst cannot be evenly distributed.

[0009] (2) Due to uneven gas-solid contact, the single-pass conversion rate of silicon tetrachloride is low.

[0010] (3) Due to the low space utilization efficiency of the reactor and the low single-pass conversion rate, the device investment is large and the energy consumption is high.

[0011] Therefore, how to further improve the cold hydrogenation reaction and reduce the investment and energy consumption of the cold hydrogenation device is a technical problem that needs to be solved by those skilled in the art. Summary of the invention

[0012] The purpose of the present invention is to solve the above technical problems and provide a process for producing trichlorosilane by cold hydrogenation of silicon tetrachloride, which has the advantages of simple process, high product yield, small equipment investment, easy repair and maintenance, and low investment and operating costs.

[0013] To achieve the above object, the present invention provides a process for producing trichlorosilane by cold hydrogenation of silicon tetrachloride, wherein silicon tetrachloride and hydrogen are fed into a bubbling slurry bed reactor for catalytic cold hydrogenation reaction, wherein molten salt is used as a medium and metal chloride is used as a catalyst in the bubbling slurry bed reactor, the operating temperature is 450-500°C, and the reaction pressure is 2.5-4.0MPaG.

[0014] Furthermore, the molten salt is KNO3 or NaNO2.

[0015] Furthermore, the metal chloride is cuprous chloride, and the amount of cuprous chloride added is 1-3% of the amount of silicon powder added.

[0016] Furthermore, a feed gas distributor at the bottom and a gas redistributor in the middle are arranged in the bubbling slurry bed reactor, and a self-rotating blade is arranged on the upper part of the gas redistributor.

[0017] Furthermore, the gas redistributor comprises 5 to 10 layers of sieve plate gas redistributor disks, and the opening rate of the sieve plate gas redistributor disks is 60 to 90%.

[0018] Furthermore, a silicon powder feed inlet is arranged at the upper part of the bubbling slurry bed reactor, and the silicon powder feed inlet is below the molten salt liquid layer.

[0019] Furthermore, the self-rotating blade is located at the lower part of the silicon powder feed inlet.

[0020] Furthermore, the silicon tetrachloride and hydrogen are fed into a bubbling slurry bed reactor for catalytic cold hydrogenation reaction, and the reaction product gas produced is discharged from the top of the bubbling slurry bed reactor, and then enters the product gas filter to separate the molten salt droplets from the gas, and the separated molten salt liquid flows back to the gas phase pipeline at the top of the bubbling slurry bed reactor.

[0021] Furthermore, a slag filtration and molten salt recovery system is arranged at the bottom of the bubbling slurry reactor, and the slag filtration and molten salt recovery system comprises a residue filter connected to the bottom outlet of the bubbling slurry reactor, a molten salt tank, a molten salt pump and a waste residue packaging system; the discharged material enters the residue filter, the solid is filtered out in the residue filter, the molten salt liquid enters the molten salt tank, and the molten salt recovered in the molten salt tank is returned to the bubbling slurry bed reactor through the molten salt pump; after the filtration is completed, the molten salt liquid in the residue filter is continuously pressed out to the molten salt tank by high-temperature gas, and then the solid residue in the residue filter is discharged, and the filtered solid residue is packaged by the waste residue packaging system and transported out of the factory.

[0022] Furthermore, a plurality of density meters are arranged on the side wall of the bubbling slurry bed reactor, and a liquid level meter is arranged on the upper part of the bubbling slurry bed reactor.

[0023] In order to solve the problems existing in the background technology, the inventor has made the following improvements:

[0024] (1) Use slurry bed instead of gas-solid semi-fluidized bed. Because the density of molten salt is 1.8-2.0 g / cm 3 The density of silicon powder particles is 2.33g / cm 3 , the difference between the two is small, and the density of gas is only 0.02g / cm 3 , which has a large density difference with silicon powder. Therefore, in the molten salt liquid phase, a small amount of airflow can keep the silicon powder in suspension, while in the gas-solid semi-fluidized bed, the fluidization of silicon powder requires a higher airflow velocity. This not only achieves a uniform distribution of solid silicon powder and catalyst, but also avoids the abrasive effect of high-speed flowing silicon powder on the reactor and internal parts. The more uniform distribution of catalysts and silicon powder creates favorable conditions for improving the volume utilization of the reactor and improving the reaction conversion rate.

[0025] (2) Based on the bubbling slurry bed reactor, in order to enhance gas distribution and avoid bubble accumulation to form large bubbles, multiple sieve plate gas redistribution plates are set in the reactor; the high porosity is to reduce the ineffective accumulation of solids on the plate.

[0026] (3) A slurry bed is used, and the silicon powder is suspended in the molten salt liquid, so there is no need for a cyclone separator for gas-solid separation. The traditional cold hydrogenation reactor requires a built-in cyclone separator, which wastes a lot of reactor volume. The slurry bed has a high effective volume utilization rate, which greatly reduces the reactor volume and reduces the reactor investment.

[0027] (4) The original gas-solid reaction is transferred to the molten salt liquid. The molten salt may hinder the contact between the gas and the solid, but the molten salt of many metal chlorides can play a catalytic role. In addition, the catalyst exists in liquid form, so the contact between the gas and the liquid will be more uniform and sufficient. The hydrogen chloride generated by the catalytic hydrogenation of silicon tetrachloride and silicon powder reacts quickly. Although the molten salt liquid hinders the reaction of the two, it will not become the controlling step of the entire cold hydrogenation process.

[0028] (5) By adopting the present invention, the volume of the cold hydrogenation reactor is expected to be reduced by 50-60%, and the single-pass conversion rate of silicon tetrachloride is expected to be increased to 32-35%.

[0029] The process of the invention is simple, meets the requirements of large-scale and continuous production of the device, and has low investment, low operating cost, safety and reliability; the silicon tetrachloride conversion rate and process flow are simple, and the reactor investment is much smaller than the existing cold hydrogenation reactor, thereby solving the problems of high equipment investment and low reaction conversion rate in the existing cold hydrogenation process. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 The present invention is a process flow chart of the process for producing trichlorosilane by cold hydrogenation of silicon tetrachloride. DETAILED DESCRIPTION

[0031] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0032] like Figure 1 The process method for producing trichlorosilane by cold hydrogenation of silicon tetrachloride (catalytic cold hydrogenation process) is shown, in which silicon tetrachloride and hydrogen are fed into a bubbling slurry bed reactor R01 for catalytic cold hydrogenation reaction. Molten salt is used as a medium in the bubbling slurry bed reactor, so that the suspension state of silicon powder in the molten salt liquid can be achieved under low gas velocity stirring; the catalyst in the bubbling slurry bed reactor is a metal chloride, the operating temperature is 450-500°C, and the reaction pressure is 2.5-4.0MPaG.

[0033] The molten salt uses KNO3 or NaNO2, and the working temperature of the molten salt is 150-600°C, which must meet the requirement of being greater than the melting point of the catalyst; the metal chloride uses cuprous chloride, and the melting point of cuprous chloride is 426°C. It exists in liquid form in the molten salt and will not be lost in large quantities during the slag discharge process. Therefore, the addition ratio can be increased, that is, the addition amount of cuprous chloride is 1-3% of the addition amount of silicon powder, thereby improving the catalytic effect and reducing the reaction temperature.

[0034] Using composite molten salt as a liquid phase carrier can better achieve the suspension of silicon powder; on the other hand, the catalyst melts in the molten salt and is dispersed more evenly, resulting in a better catalytic effect. 3 The density of silicon powder particles is 2.33g / cm 3 , the difference between the two is small, and the density of gas is only 0.02g / cm 3 , and the density difference with silicon powder is large, so in the molten salt liquid phase, a small amount of airflow can keep silicon powder in suspension, while in the gas-solid semi-fluidized bed, the fluidization of silicon powder requires a higher airflow velocity. In conventional gas-solid phase cold hydrogenation reactors, it is difficult to disperse the gas and solid evenly, and the role of the catalyst cannot be played, while the slurry bed can provide sufficient contact area and catalytic effect for the cold hydrogenation reaction.

[0035] A feed gas distributor c at the bottom and a gas redistributor in the middle are arranged in the bubbling slurry bed reactor R01. A self-rotating blade a is arranged on the upper part of the gas redistributor. The self-rotating blade a rotates under the action of rising bubbles, thereby playing a certain stirring effect on the solid and liquid. The gas redistributor includes 5 to 10 layers of sieve plate gas redistributor disks b, and the opening rate of the sieve plate gas redistributor disks b is 60 to 90%.

[0036] Silicon powder is added from the top of the bubbling slurry bed reactor and distributed in the molten salt liquid under the stirring of the self-rotating blades; the mixed gas of hydrogen and silicon tetrachloride enters from the bottom of the bubbling slurry bed reactor, passes through the built-in gas distributor, is evenly distributed, and then slowly rises; since a multi-layer sieve plate gas redistribution disk is set in the bubbling slurry bed reactor, the rising mixed gas can be distributed multiple times. At the same time, the upward movement of the mixed gas also drives the stirring of the molten salt liquid. Since the difference between the density of the molten salt and the density of the silicon powder particles is much smaller than the difference between the density of the mixed gas and the density of the silicon powder particles, the silicon powder is in a suspended state in the molten salt liquid, thereby achieving full contact between gas and solid. The mixed gas of silicon tetrachloride and hydrogen contacts the silicon powder and catalyst in the molten salt liquid from bottom to top, and a cold hydrogenation reaction occurs to generate some trichlorosilane.

[0037] Again Figure 1As shown, a silicon powder feed port d is provided at the upper part of the bubbling slurry bed reactor, and the silicon powder feed port d is below the molten salt liquid layer to avoid dust generation during feeding; at the same time, a self-rotating blade is located at the lower part of the silicon powder feed port, and the self-rotating blade automatically rotates under the action of the rising airflow to disperse the incoming silicon powder; in addition, in order to avoid the fluctuation of the liquid level of the bubbling slurry bed reactor, the silicon powder is fed continuously by a rotary feed valve. In this embodiment, the silicon powder feeding system Z01 is used for feeding, and the silicon powder feeding system Z01 is a conventional facility, which is only for better illustrating the principle of the present invention.

[0038] The reaction product gas is discharged from the top of the bubbling slurry bed reactor (some molten salt droplets may be mixed in the reaction product gas), and then enters the product gas filter FI01 to separate the molten salt droplets from the gas. The separated molten salt liquid flows back to the gas phase pipeline at the top of the bubbling slurry bed reactor, playing a certain flushing role.

[0039] A slag filtration and molten salt recovery system is set at the bottom of the bubbling slurry reactor, which includes a residue filter FI02 connected to the bottom outlet of the bubbling slurry reactor, a molten salt tank V01, a molten salt pump P01 and a waste slag packaging system Z02. The discharged materials mainly contain silicon powder that is difficult to continue to react and deposited impurity chlorides, such as calcium chloride (melting point 772°C), etc. These solids are discharged together with the molten salt liquid and enter the residue filter FI02. The solids are filtered out in the residue filter FI02, and the molten salt liquid enters the molten salt tank V01. The molten salt recovered in the molten salt tank V01 is returned to the bubbling slurry bed reactor through the molten salt pump P01; after the filtration is completed, the molten salt liquid in the residue filter FI02 is continuously pressed out to the molten salt tank by high-temperature gas, and then the solid slag in the residue filter FI02 is discharged, and the filtered solid slag is packaged by the waste slag packaging system Z02 and transported out of the factory.

[0040] A plurality of density meters DI are arranged on the side wall of the bubbling slurry bed reactor to monitor the solid content in the liquid phase; a liquid level meter LI is arranged on the upper part of the bubbling slurry bed reactor to monitor the stock of molten salt.

[0041] Compared with the existing gas-solid semi-fluidized bed, the bubbling slurry reactor of the present invention no longer needs to be equipped with a cyclone separator, so the volume of the reactor is greatly reduced; because the silicon powder is well dispersed in the slurry bed, a large amount of silicon powder is no longer required in the reactor, the silicon powder flow rate is also greatly reduced, and the wear degree of the reactor is reduced; the reaction product gas contains almost no solid powder, so it is no longer necessary to perform multi-stage cyclone and filtration on the product gas, and the investment of the device is reduced; because the catalytic effect is strengthened, the reaction temperature can be appropriately reduced, the single-pass conversion rate is improved, and the total energy consumption of the device is reduced; at the same time, the amount of catalyst is increased and the temperature is reduced. The reaction temperature of the traditional gas-solid cold hydrogenation reactor is between 550 and 580°C, and the reaction temperature of the present invention is between 450 and 500°C.

[0042] Example

[0043] The raw materials are silicon powder, silicon tetrachloride and hydrogen. The mixed gas flow rate of hydrogen and silicon tetrachloride is 100t / h, of which hydrogen is 70% mol and silicon tetrachloride is about 30% mol. The mixed gas temperature is 580°C and the pressure is 2.8MpaG. The industrial silicon feed flow rate is 1.92t / h and the purity is >99%wt.

[0044] The mixed gas of hydrogen and silicon tetrachloride enters from the lower part of the bubbling slurry bed reactor, passes through the built-in gas distributor, is evenly distributed, and then slowly moves upward, with a gas flow rate between 0.3 and 0.5 m / s. A multi-layer sieve plate gas redistribution plate is set in the bubbling slurry bed reactor, and the rising gas can be distributed multiple times. At the same time, the upward movement of the gas also drives the stirring of the molten salt liquid, so that the silicon powder in the molten salt liquid is in a suspended state. Hydrogen reacts with silicon tetrachloride under the action of the catalyst to produce silicon trichloride and hydrogen chloride, and hydrogen chloride reacts with silicon powder. The overall reaction is that silicon tetrachloride, silicon and hydrogen react to produce trichlorosilane. A silicon powder feed port is set at the upper part of the bubbling slurry bed reactor, and the silicon powder feed port is below the liquid layer to avoid dust during feeding. A self-rotating paddle is set at the lower part of the feed port. The paddle rotates automatically under the action of the rising airflow to disperse the incoming silicon powder. In order to avoid fluctuations in the reactor liquid level, the silicon powder feed is continuously fed using a rotary feed valve.

[0045] The bubbling slurry bed reactor of the present invention has a diameter of 2000 mm and a barrel height of 14000 mm. Compared with the conventional cold hydrogenation process of the same scale, the conventional reactor has a diameter of 3800 mm and a barrel height of 18000 mm.

[0046] The reaction product gas is drawn out from the top of the reactor and then enters the product gas filter. After filtration, the gas phase goes to the downstream heat exchange equipment. The content of trichlorosilane in the reaction product gas is 11.24% mol, the content of silicon tetrachloride is 20.4% mol, and the rest is mainly hydrogen.

[0047] After the reaction system has been running for a period of time, the content of silicon powder and impurities that are difficult to react gradually increases at the bottom of the reactor. At this time, proper slag discharge is required. The slag discharge control flow rate is ≯5t / h, and the slag discharge time is determined according to the density change of the liquid in the bubbling slurry bed reactor. The slag is discharged into the filtration system, the molten salt is recovered, and the waste slag is discharged. After cooling, it is packaged and shipped out.

[0048] The process method of the invention has high silicon tetrachloride conversion rate, simple process flow, low investment, small footprint, low operating energy consumption, and reactor investment is much smaller than that of the existing cold hydrogenation reactor, thereby solving the problems of high equipment investment, low reaction conversion rate, etc. in the existing cold hydrogenation process.

[0049] Comparison between Example and Comparative Example

[0050]

Claims

1. A process for producing trichlorosilane by cold hydrogenation of silicon tetrachloride, characterized in that: Silicon tetrachloride and hydrogen are sent into a bubbling slurry bed reactor for catalytic cold hydrogenation reaction. The bubbling slurry bed reactor uses molten salt as a medium and metal chloride as a catalyst. The operating temperature is 450-500°C and the reaction pressure is 2.5-4.0MPaG.

2. The process for producing trichlorosilane by cold hydrogenation of silicon tetrachloride according to claim 1, characterized in that: The molten salt is KNO3 or NaNO2.

3. The process for producing trichlorosilane by cold hydrogenation of silicon tetrachloride according to claim 1, characterized in that: The metal chloride is cuprous chloride, and the amount of cuprous chloride added is 1-3% of the amount of silicon powder added.

4. The process for producing trichlorosilane by cold hydrogenation of silicon tetrachloride according to claim 1, characterized in that: The bubbling slurry bed reactor is provided with a feed gas distributor at the bottom and a gas redistributor in the middle, and a self-rotating blade is provided on the upper part of the gas redistributor.

5. The process for producing trichlorosilane by cold hydrogenation of silicon tetrachloride according to claim 4, characterized in that: The gas redistributor comprises 5 to 10 layers of sieve plate gas redistributor disks, and the opening rate of the sieve plate gas redistributor disks is 60 to 90%.

6. The process for producing trichlorosilane by cold hydrogenation of silicon tetrachloride according to claim 1, characterized in that: A silicon powder feed port is arranged at the upper part of the bubbling slurry bed reactor, and the silicon powder feed port d is below the molten salt liquid layer.

7. The process for producing trichlorosilane by cold hydrogenation of silicon tetrachloride according to claim 6, characterized in that: The self-rotating blade is located at the lower part of the silicon powder feed inlet.

8. The process for producing trichlorosilane by cold hydrogenation of silicon tetrachloride according to claim 1, characterized in that: The silicon tetrachloride and hydrogen are fed into a bubbling slurry bed reactor for catalytic cold hydrogenation reaction, and the reaction product gas produced is discharged from the top of the bubbling slurry bed reactor, and then enters the product gas filter to separate the molten salt droplets from the gas, and the separated molten salt liquid flows back to the gas phase pipeline at the top of the bubbling slurry bed reactor.

9. The process for producing trichlorosilane by cold hydrogenation of silicon tetrachloride according to claim 1, characterized in that: A slag filtration and molten salt recovery system is arranged at the bottom of the bubbling slurry reactor, and the slag filtration and molten salt recovery system comprises a residue filter connected to the bottom outlet of the bubbling slurry reactor, a molten salt tank, a molten salt pump and a waste residue packaging system; the discharged material enters the residue filter, the solid is filtered out in the residue filter, the molten salt liquid enters the molten salt tank, and the molten salt recovered in the molten salt tank is returned to the bubbling slurry bed reactor through the molten salt pump; after the filtration is completed, the molten salt liquid in the residue filter is continuously pressed out to the molten salt tank by high-temperature gas, and then the solid residue in the residue filter is discharged, and the filtered solid residue is packaged by the waste residue packaging system and transported out of the factory.

10. The process for producing trichlorosilane by cold hydrogenation of silicon tetrachloride according to claim 1, characterized in that: A plurality of density meters are arranged on the side wall of the bubbling slurry bed reactor, and a liquid level meter is arranged on the upper part of the bubbling slurry bed reactor.

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