A system for removing boron impurities from trichlorosilane synthesis product liquid

Abstract

This invention discloses a boron impurity removal system for trichlorosilane synthesis product liquid, belonging to the field of polycrystalline silicon cold hydrogenation post-treatment technology. It includes a mixing tank, the inlet of which is connected to a high-boron product liquid from the trichlorosilane synthesis furnace and also to a cold hydrogenation slurry treatment system. The cold hydrogenation slurry treatment system includes a slurry buffer tank connected to the cold hydrogenation slurry discharge and a high-boiling-point removal tower for treating the slurry to obtain hexachlorodisiloxane. The outlet of the mixing tank is connected to a complexing vessel, and the outlet of the complexing vessel is connected to a distillation column for purifying chlorosilane gas. The outlet of the distillation column is sequentially connected to a condensation unit and a low-boron product liquid storage tank. This invention utilizes the slurry discharged from the bottom of the cold hydrogenation washing tower, which, after treatment by the high-boiling-point removal tower and the high-boiling-point cracking unit, yields the high-boiling-point hexachlorodisiloxane, thus removing boron impurities from the trichlorosilane synthesis product liquid. This achieves both the rational utilization of hexachlorodisiloxane and solves the problem of boron impurities in trichlorosilane synthesis.

Description

Technical Field

[0001] This utility model relates to the field of post-processing technology of polycrystalline silicon cold hydrogenation, specifically to a boron impurity removal system for trichlorosilane synthesis product liquid. Background Technology

[0002] To reduce silicon consumption and costs in polysilicon production systems, silicon powder previously sold or discharged from the cold hydrogenation process is typically sent to a trichlorosilane synthesis unit for reaction with hydrogen chloride. This silicon powder contains approximately 70-80% silicon, with high levels of metals and boron / phosphorus impurities. The high-temperature silicon-containing process gas exiting the top of the trichlorosilane synthesis furnace is filtered to remove 99% of the silicon powder before being sent to a wet scrubbing tower for further washing. The saturated process gas exiting the scrubbing tower is cooled by a condenser unit, and the condensed chlorosilanes are stored in a high-boron product liquid storage tank. The non-condensable gases are sent to a tail gas recovery system for recycling. For details, please refer to... Figure 2 As shown, after washing with a wet scrubbing tower, metallic impurities and phosphorus are easily washed off due to their high boiling points and discharged from the system through the slag discharge at the bottom of the scrubbing tower. However, boron, mainly existing as BCl3 with a boiling point of 12.5℃, is difficult to wash off, resulting in a high boron content in the product solution, reaching 10,000-50,000 ppbw or even higher, while the content of metallic impurities and phosphorus is less than 100 ppbw. Since the product solution eventually returns to the larger system, the cumulative effect of this circulation increases the boron content within the system, affecting product quality and consequently impacting resistivity, minority carrier lifetime, and other parameters.

[0003] Hexachlorodisiloxane is obtained when processing the slurry discharged from the bottom of a cold hydrogenation scrubbing tower. Under existing catalyst technology, hexachlorodisiloxane cannot be cracked and is usually discharged as waste to a hydrolysis unit, resulting in the loss of silicon and chlorine. Research has found that the presence of hexachlorodisiloxane in the purification process of chlorosilanes can reduce the boron content in the product. The core reason is that it can undergo complexation or chemical reaction with boron-containing impurities, thereby achieving separation. Therefore, this solution is proposed to achieve the rational utilization of hexachlorodisiloxane and simultaneously solve the problem of boron impurities in the synthesis of trichlorosilane. Utility Model Content

[0004] To address the problem of boron impurities accumulating in the product liquid generated from the synthesis of trichlorosilane using silicon powder discharged from the cold hydrogenation process, which is difficult to remove and ultimately affects the quality of the system's products, this invention proposes a boron impurity removal system for the trichlorosilane synthesis product liquid. This system utilizes the slurry discharged from the bottom of the cold hydrogenation washing tower, which, after being processed by a high-boiling-point de-cracking tower and a cracking unit, yields the high-boiling-point compound hexachlorodisiloxane. This compound is then used to remove boron impurities from the product liquid of the trichlorosilane synthesis unit, achieving both the rational utilization of hexachlorodisiloxane and solving the problem of boron impurities in the trichlorosilane synthesis process. To achieve the above-mentioned objectives, the technical solution of this utility model is as follows: A boron impurity removal system for trichlorosilane synthesis product liquid includes a mixing tank. The inlet of the mixing tank is connected to a high-boron product liquid from a trichlorosilane synthesis furnace and also to a cold hydrogenation slurry treatment system. The cold hydrogenation slurry treatment system includes a slurry buffer tank connected to the cold hydrogenation slurry discharge, a high-boiling point removal tower for treating the slurry to obtain hexachlorodisiloxane, and a high-boiling point cracking unit. The outlet of the mixing tank is connected to a complexing vessel for causing hexachlorodisiloxane to undergo a complexation reaction with boron trichloride to form a complex with a boiling point higher than that of chlorosilanes. The outlet of the complexing vessel is connected to a distillation column for purifying chlorosilane gas. The outlet of the distillation column is sequentially connected to a condensation unit and a low-boron product liquid storage tank.

[0005] Preferably, the low-boron product liquid in the storage tank is connected to the distillation process via a transfer pump, and is also connected to the distillation column via pipelines and control valves for use as a spray liquid.

[0006] Preferably, the gas phase outlet of the complexing vessel is connected to the distillation column, and the bottom slag discharge pipeline of the distillation column is connected to the complexing vessel.

[0007] Preferably, the complexing vessel is provided with a steam jacket, and the steam jacket is connected to a condensate collection tank.

[0008] Preferably, a high-boiling buffer tank is connected between the high-boiling de-coal tower and the high-boiling cracking unit, and a hexachlorodisiloxane storage tank is connected to the outlet of the high-boiling cracking unit.

[0009] Preferably, the bottom outlet pipe of the high-boiling point removal tower is also connected to a reboiler, which is connected to the high-boiling point removal tower.

[0010] The working principle of this utility model is as follows: The remaining material from the high-boiling cracking, hexachlorodisiloxane, is added to a complexing reactor. At the same time, the product liquid synthesized from trichlorosilane is added to the complexing reactor. The two materials are gradually complexed in the complexing reactor by steam heating in the jacket. Hexachlorodisiloxane combines with boron trichloride to form a high-boiling-point complex. The heated and vaporized chlorosilane is purified by a distillation column at the top of the complexing reactor and then cooled by a condenser to become a product liquid with low boron content, which is then sent to the distillation unit for use.

[0011] In summary, this utility model has the following advantages: 1. This utility model utilizes the slurry discharged from the bottom of the cold hydrogenation washing tower, and after treatment by the high-boiling point removal tower, obtains the high-boiling compound hexachlorodisiloxane, which removes boron impurities from the product liquid of the trichlorosilane synthesis unit. This not only realizes the rational utilization of hexachlorodisiloxane, but also solves the problem of boron impurities in the trichlorosilane synthesis. 2. The system proposed in this utility model can reduce the boron content in the trichlorosilane synthesis product from 10,000-50,000 ppbw to less than 100 ppbw by introducing silicon powder with high impurity content from cold hydrogenation. This achieves the purpose of reducing the impurity content of the product liquid and improving product quality. Attached Figure Description

[0012] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments, wherein: Figure 1 This is a structural diagram of a boron impurity removal system for a trichlorosilane synthesis product liquid according to this utility model; Figure 2 A system diagram for the cold hydrogenation of discharged silicon powder to participate in the synthesis of high boron product liquid from trichlorosilane.

[0013] In the picture: 100. Cold hydrogenated silicon powder discharge tank; 101. Silicon powder storage tank; 102. Trichlorosilane synthesis furnace; 103. Filtration and washing unit; 104. Condensation device; 105. High boron product liquid storage tank; 106. High boron product liquid pump; 200. Cold hydrogenated slurry discharge tank; 201. Slurry buffer tank; 202. High-boiling point removal tower; 203. Reboiler; 204. High-boiling point buffer tank; 205. High-boiling point cracking unit; 206. Hexachlorodisiloxane storage tank; 300. Mixing tank; 301. Complexation vessel; 302. Distillation column; 303. Condensation unit; 304. Low boron product liquid storage tank; 305. Low boron product liquid pump. Detailed Implementation

[0014] To more clearly illustrate this utility model, the following description, in conjunction with preferred embodiments and accompanying drawings, further clarifies the present invention. Those skilled in the art should understand that the specific description below is illustrative rather than restrictive and should not be construed as limiting the scope of protection of this utility model.

[0015] BCl3 is a typical Lewis acid, while the oxygen atom in hexachlorodisiloxane possesses a lone pair of electrons, which can act as a Lewis base to donate electron pairs and combine with the empty p orbitals of BCl3 to form a stable complex. This complex differs significantly from chlorosilanes (such as silicon tetrachloride) in terms of boiling point, polarity, and other physical properties, and can be separated by methods such as distillation. Therefore, by forming a stable complex with boron impurities, hexachlorodisiloxane increases the separation difference with the target chlorosilane, thereby reducing the boron impurity content. Based on this principle, this invention discloses... Figure 1 The system shown is a boron impurity removal system for the product liquid of trichlorosilane synthesis. The system uses the slurry discharged from the bottom of the cold hydrogenation washing tower, which is treated by the high-boiling-point de-boiling tower 202 and the high-boiling-point cracking unit 205 to obtain the high-boiling-point compound hexachlorodisiloxane, which is then used to remove boron impurities from the product liquid of the trichlorosilane synthesis unit.

[0016] like Figure 1 As shown, the system includes a mixing tank 300. The inlet of the mixing tank 300 is connected to the high-boron product liquid from the trichlorosilane synthesis furnace 102, and is also connected to the cold hydrogenation slurry treatment system. The cold hydrogenation slurry treatment system includes a slurry buffer tank 201 connected to the cold hydrogenation discharge slurry 200, a deboiling tower 202 for treating the slurry to obtain hexachlorodisiloxane, and a high-boiling cracking unit 205. The outlet of the mixing tank 300 is connected to a complexing vessel 301 for causing hexachlorodisiloxane to undergo a complexation reaction with boron trichloride to form a complex with a boiling point higher than that of chlorosilane. The outlet of the complexing vessel 301 is connected to a distillation column 302 for purifying chlorosilane gas. The outlet of the distillation column 302 is connected in sequence to a condensation unit 303 and a low-boron product liquid storage tank 304.

[0017] Preferably, the low-boron product liquid in the low-boron product liquid storage tank 304 is introduced into the distillation process through the low-boron product liquid pump 304, and is also introduced into the distillation column 302 through pipelines and control valves for use as a spray liquid.

[0018] Preferably, the vapor outlet of the complexing vessel 301 is connected to the distillation column 302, and the bottom slag discharge line of the distillation column 302 is connected to the complexing vessel 301. This arrangement can further remove impurities such as metal chlorides that enter the distillation column along with the chlorosilane.

[0019] Preferably, the complexing vessel 301 is provided with a steam jacket, and the steam jacket is connected to a condensate collection tank.

[0020] In the cold hydrogenation slurry treatment system, a high-boiling-point de-boiling tower 202 and a high-boiling-point cracking unit 205 are connected by a high-boiling-point buffer tank 204. The outlet of the high-boiling-point cracking unit 205 is connected to a hexachlorodisiloxane storage tank 206. The slurry discharged from the bottom of the cold hydrogenation washing tower is first sent to the slurry buffer tank 201, and then from the slurry buffer tank 201 to the high-boiling-point de-boiling tower 202 (the bottom temperature of the high-boiling tower is about 90-150℃, and the top pressure of the tower is 50-150kPa) for processing, to obtain the main high-boiling-point substances hexachlorodisiloxane and hexachlorodisiloxane stored at the bottom of the high-boiling-point de-boiling tower 202. These are then sent to the high-boiling-point buffer tank 204 through slag discharge. In order to reduce the silicon and chlorine consumption of the system, the high-boiling-point substances in the high-boiling-point buffer tank 204 are sent to the high-boiling-point cracking unit 205 for cracking of hexachlorodisiloxane. The hexachlorodisiloxane that cannot be cracked is then separated and sent to the hexachlorodisiloxane storage tank 206.

[0021] Preferably, the bottom outlet pipe of the high-boiling point removal tower 202 is also connected to a reboiler 203, which is connected to the high-boiling point removal tower 202 and serves to provide a heat source.

[0022] The process for the cold hydrogenation of 100g of externally discharged silicon powder to participate in the synthesis of high boron product liquid from trichlorosilane can be found in the instruction manual. Figure 2 The silicon powder discharged from the cold hydrogenation process is sent to the trichlorosilane synthesis furnace 102 to react with hydrogen chloride. The high-temperature silicon powder-containing process gas exiting from the top of the trichlorosilane synthesis furnace 102 is filtered by the filter and washing unit 103 to remove 99% of the silicon powder, and then sent to the wet dust removal and washing tower for further washing. The saturated process gas exiting from the top of the washing tower is cooled by the condenser 104, and the condensed chlorosilane is stored in the high boron product liquid storage tank 105. The non-condensable gas is sent to the tail gas recovery system for recovery. For details, please refer to the following... Figure 2 As shown.

[0023] The working principle of this utility model is as follows: The hexachlorodisiloxane that cannot be hydrolyzed during the original slurry treatment process is collected and then mixed with the high-boron product liquid synthesized from trichlorosilane at a ratio of 1:1 to 1:100 before being sent to complexing reactor 301. The temperature of complexing reactor 301 is controlled at 80-150℃. In complexing reactor 301, boron trichloride and hexachlorodisiloxane undergo further complexation or chemical reaction to form high-boiling-point substances. Complexing reactor 301 is heated by steam, and the gas phase is connected to distillation column 302. The bottom slag discharge line of distillation column 302 is connected to the complexing reactor. The reactor 301 is connected to the distillation column 302 for purification. Boron trichloride, due to forming a high-boiling-point substance with hexachlorodisiloxane, remains in the complexation reactor 301. Through intermittent slag discharge, it is discharged from the system, thereby achieving the separation of boron trichloride and chlorosilane in the trichlorosilane synthesis product liquid. The pressure of the distillation column 302 is controlled at 100-500 kPa. The low-impurity chlorosilane gas exiting from the top of the distillation column 302 is condensed by the condensation unit 303 and collected in the low-boron product liquid tank, and finally sent to the distillation process.

[0024] By using the impurity removal system of this invention, the boron content in the trichlorosilane synthesis product can be reduced from 10,000-50,000 ppbw to less than 100 ppbw, thereby reducing the impurity content of the product liquid and improving product quality.

[0025] The above description is merely a preferred embodiment of the present utility model and is not intended to limit the present utility model in any way. Any simple modifications or equivalent changes made to the above embodiments based on the technical essence of the present utility model shall fall within the protection scope of the present utility model.

Claims

1. A boron impurity removal system for trichlorosilane synthesis product liquid, characterized in that, The system includes a mixing tank (300), whose inlet is connected to a high-boron product liquid from a trichlorosilane synthesis furnace (102) and a cold hydrogenation slurry treatment system. The cold hydrogenation slurry treatment system includes a slurry buffer tank (201) connected to a cold hydrogenation discharge slurry (200), a deboiling tower (202) for treating the slurry to obtain residual hexachlorodisiloxane, and a high-boiling cracking unit (205). The outlet of the mixing tank (300) is connected to a complexing vessel (301) for causing hexachlorodisiloxane to undergo a complexation reaction with boron trichloride to form a complex with a boiling point higher than that of chlorosilane. The outlet of the complexing vessel (301) is connected to a distillation column (302) for purifying chlorosilane gas. The outlet of the distillation column (302) is connected in sequence to a condensation unit (303) and a low-boron product liquid storage tank (304).

2. The boron impurity removal system for trichlorosilane synthesis product liquid as described in claim 1, characterized in that, The low-boron product liquid in the low-boron product liquid storage tank (304) is connected to the distillation process via a transfer pump, and is also connected to the distillation column (302) via pipelines and control valves for use as a spray liquid.

3. The boron impurity removal system for trichlorosilane synthesis product liquid as described in claim 1, characterized in that, The gas phase outlet of the complexing vessel (301) is connected to the distillation column (302), and the bottom slag discharge pipeline of the distillation column (302) is connected to the complexing vessel (301).

4. The boron impurity removal system for trichlorosilane synthesis product liquid as described in claim 1, characterized in that, The complexing vessel (301) is provided with a steam jacket, and the steam jacket is connected to a condensate collection tank.

5. The boron impurity removal system for trichlorosilane synthesis product liquid as described in claim 1, characterized in that, A high-boiling buffer tank (204) is connected between the high-boiling deboiling tower (202) and the high-boiling cracking unit (205), and a hexachlorodisiloxane storage tank (206) is connected to the outlet of the high-boiling cracking unit (205).

6. The boron impurity removal system for trichlorosilane synthesis product liquid as described in claim 1, characterized in that, The bottom outlet pipe of the high-boiling point removal tower (202) is also connected to a reboiler (203), which is connected to the high-boiling point removal tower (202).

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