System and method for removing high and low boilers in polysilicon production

Abstract

This invention provides a system and method for removing high and low boiling points in polysilicon production. The system includes a first distillation column comprising a top rectifying section, a bottom stripping section, and a separation section between the rectifying and stripping sections, all of which are sequentially interconnected. The separation section includes a pre-fractionation section and a main fractionation section arranged side-by-side but not interconnected. The main fractionation section includes, from top to bottom, a first main fractionation section and a second main fractionation section that are interconnected. The pre-fractionation section has a low-boiling material inlet, the stripping section has a bottom outlet, and the first main fractionation section has a first outlet. The outlet of the disproportionation fixed-bed reactor is connected to the low-boiling material inlet. The second distillation column has a high-boiling material inlet and a top outlet, and the bottom outlet of the stripping section is connected to the high-boiling material inlet. The first outlet and the top outlet of the second distillation column are respectively connected to an adsorption column.

Description

Technical Field

[0001] This invention relates to a system and method for removing high and low boiling points in polysilicon production, belonging to the field of chemical separation technology. Background Technology

[0002] With the continuous development of the photovoltaic industry, competition in the polysilicon market is becoming increasingly fierce, which has suddenly increased the survival pressure faced by polysilicon manufacturers. Therefore, polysilicon manufacturers can only be competitive in the market by continuously improving product quality.

[0003] The modified Siemens process is one of the main processes for producing polycrystalline silicon. In this process, impurities in polycrystalline silicon mainly include metallic impurities (such as Fe, Ca, Al, Ti, Cu, etc.) and non-metallic impurities (such as B, P, C, N, etc.). While metallic impurities can generally be removed by distillation, non-metallic impurities (B, P, C, etc.) exist in complex forms and have chemical properties similar to chlorosilanes, making them difficult to remove by ordinary distillation. Currently, P and B in trichlorosilane production are mainly removed through extraction, complexation, adsorption, and partial hydrolysis. Carbon impurities in polycrystalline silicon primarily originate from methylchlorosilane in trichlorosilane. Since the boiling point of methyldichlorosilane (41.9℃) is very close to that of trichlorosilane (31.8℃), it is difficult to remove them through conventional distillation.

[0004] Therefore, it is necessary to provide a system that can efficiently remove high and low boiling points in polysilicon production in order to improve the quality of polysilicon. Summary of the Invention

[0005] This invention provides a system for removing high and low boiling points in polysilicon production. This system can efficiently remove high-boiling and low-boiling substances during the polysilicon production process, thereby improving the quality of polysilicon production.

[0006] This invention provides a method for removing high and low boiling points in polysilicon production. Using the system described above, this method can efficiently remove high-boiling and low-boiling substances during the polysilicon production process, thereby improving the quality of polysilicon production.

[0007] This invention provides a system for removing high and low boiling points in polysilicon production, comprising a first distillation column, a second distillation column, and an adsorption column;

[0008] The first distillation column includes a top rectifying section, a bottom stripping section, and a separation section located between the rectifying section and the stripping section. The rectifying section, the separation section, and the stripping section are sequentially interconnected. The separation section includes a pre-fractionation section and a main fractionation section arranged side by side and not interconnected. The main fractionation section includes a first main fractionation section and a second main fractionation section that are interconnected from top to bottom. The pre-fractionation section has a low-boiling material inlet, the stripping section has a bottom outlet, and the first main fractionation section has a first outlet.

[0009] The rectification section has 30-50 trays, the stripping section has 10-30 trays, the pre-fractionation section has 40-70 trays, and the main fractionation section has 40-70 trays.

[0010] The second distillation column has a high-boiling material inlet and a top outlet, and the bottom outlet of the stripping section is connected to the high-boiling material inlet.

[0011] The first discharge port and the top discharge port of the second distillation column are respectively connected to the adsorption column;

[0012] Low-boiling-point materials include silicon tetrachloride, trichlorosilane, and dichlorosilane;

[0013] High-boiling-point materials include trichlorosilane, silicon tetrachloride, and methyldichlorosilane.

[0014] In the system described above, the first outlet is located at the 30th-50th tray of the main fractionation section.

[0015] The system described above further includes a disproportionation fixed-bed reactor, the outlet of which is connected to the inlet of the low-boiling material.

[0016] The system as described above further includes a first heat exchanger, and the second main fractionation section has a second outlet.

[0017] The second discharge port is connected to the heat source inlet of the first heat exchanger, the discharge port of the disproportionation fixed bed reactor and the low-boiling material are respectively connected to the cold source inlet of the first heat exchanger, the cold source outlet of the first heat exchanger is connected to the feed port of the low-boiling material, and the heat source outlet of the first heat exchanger is connected to the inlet of the disproportionation fixed bed reactor.

[0018] In the system described above, the second outlet is located at the 60th-75th tray of the main fractionation section.

[0019] In the system described above, the first distillation column has a rectification section outlet that communicates with the feed inlet of the disproportionation fixed-bed reactor; the feed inlet of the disproportionation fixed-bed reactor is located at the top of the reactor, and the discharge outlet is located at the bottom. And / or,

[0020] The adsorption column has a top feed inlet, and the first discharge outlet and the top discharge outlet of the second distillation column are respectively connected to the top feed inlet of the adsorption column.

[0021] The system as described above, wherein the system further includes a second heat exchanger;

[0022] The top outlet of the second distillation column is connected to the heat source inlet of the second heat exchanger, the bottom outlet of the first distillation column is connected to the cold source inlet of the second heat exchanger, the heat source outlet of the second heat exchanger is connected to the feed inlet of the adsorption column, and the cold source outlet of the second heat exchanger is connected to the stripping section.

[0023] The system described above, wherein the second distillation column has 100-120 trays; and / or,

[0024] The high-boiling material inlet is located at trays 80-100 of the second distillation column.

[0025] In the system described above, the first distillation column operates at a pressure of 0.15-0.3 MPaG, a top operating temperature of 35-52°C, and a bottom operating temperature of 93-110°C; and / or,

[0026] In the second distillation column, the operating pressure is 0.65-0.95 MPaG, the top operating temperature is 106-122℃, and the bottom operating temperature is 109-124℃; and / or,

[0027] The adsorption column operates at a temperature of 20-60℃ and a pressure of 0.5-1 MPaG; and / or,

[0028] The reflux ratio of the second distillation column is (5-15):1; and / or,

[0029] The feed to the disproportionation fixed-bed reactor comprises silicon tetrachloride and dichlorosilane, wherein the mass ratio of silicon tetrachloride to dichlorosilane is (5-3):1; and / or,

[0030] The operating temperature in the disproportionation fixed-bed reactor is 50-60℃, and the operating pressure is 0.5-1MPaG.

[0031] This invention provides a method for removing high and low boiling points during polysilicon production, wherein the method employs the system described above.

[0032] This invention provides a system for removing high and low boiling points in polysilicon production. The system includes a first distillation column, a second distillation column, and an adsorption column connected to each other. The first distillation column is a baffle column, which allows for the separation of light and heavy components in low-boiling materials within a single column, improving separation efficiency. The second distillation column is mainly used to concentrate high-boiling components. The adsorption column adsorbs impurities from the trichlorosilane obtained after separation in both the first and second distillation columns, thereby obtaining high-purity trichlorosilane. This invention achieves the recovery of high and low boiling points in polysilicon production through a system including a first distillation column, a second distillation column, and an adsorption column. This reduces equipment investment, floor space, and energy consumption, and has broad application prospects. Furthermore, by designing the number of pedals in the first distillation column, this invention can further improve separation efficiency, thus achieving more efficient recovery of high and low boiling points in polysilicon production.

[0033] This invention provides a method for removing high and low boiling points in polycrystalline silicon production. Using the system described above, this method can efficiently remove high-boiling and low-boiling substances in polycrystalline silicon production, thereby obtaining high-purity trichlorosilane. Attached Figure Description

[0034] To more clearly illustrate the technical solutions in the embodiments of the present invention or related technologies, the accompanying drawings used in the description of the embodiments of the present invention or related technologies are briefly introduced below. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0035] Figure 1 This invention provides a system for removing high and low boiling points during polysilicon production in some embodiments.

[0036] Explanation of reference numerals in the attached figures:

[0037] 2: Second distillation column;

[0038] 3: Adsorption column;

[0039] 4: First heat exchanger;

[0040] 5: Second heat exchanger;

[0041] 6: Disproportionation fixed-bed reactor;

[0042] 7: Third heat exchanger;

[0043] 11: Rectifying section;

[0044] 12: Stripping section;

[0045] 13: Pre-fractionation section;

[0046] 141: First main fractionation section;

[0047] 142: Second main fractionation section. Detailed Implementation

[0048] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0049] Figure 1 This invention provides a system for removing high and low boiling points during polysilicon production in some embodiments, such as... Figure 1 As shown, the first aspect of the present invention provides a system for removing high and low boiling points in polysilicon production, comprising a first distillation column, a second distillation column 2, and an adsorption column 3;

[0050] The first distillation column includes a top rectifying section 11, a bottom stripping section 12, and a separation section located between the rectifying section 11 and the stripping section 12. The rectifying section 11, the separation section, and the stripping section 12 are sequentially interconnected. The separation section includes a pre-fractionation section 13 arranged in parallel and not interconnected with each other, and a main fractionation section. The main fractionation section includes, from top to bottom, a first main fractionation section 141 and a second main fractionation section 142 that are interconnected. The pre-fractionation section 13 has a low-boiling material inlet, the stripping section 12 has a bottom outlet, and the first main fractionation section 141 has a first outlet.

[0051] The number of trays in the rectifying section 11 is 30-50, the number of trays in the stripping section 12 is 10-30, the number of trays in the pre-fractionation section 13 is 40-80, and the number of trays in the main fractionation section is 40-80.

[0052] The second distillation column 2 has a high-boiling material inlet and a top outlet, and the bottom outlet of the stripping section 12 is connected to the high-boiling material inlet.

[0053] The first discharge port and the top discharge port of the second distillation column 2 are respectively connected to the adsorption column 3;

[0054] Low-boiling-point materials include silicon tetrachloride, trichlorosilane, and dichlorosilane;

[0055] High-boiling-point materials include trichlorosilane, silicon tetrachloride, and methyldichlorosilane.

[0056] It is understood that the low-boiling materials of the present invention also include some impurities, and the high-boiling materials also include some impurities.

[0057] The present invention does not impose any particular limitation on the second distillation column 2. The second distillation column 2 can be a distillation column commonly used in the art. For example, the second distillation column 2 is a conventional distillation column.

[0058] It is understood that the adsorption column 3 of the present invention is filled with an adsorbent, which is used to adsorb impurities in crude trichlorosilane. The present invention does not particularly limit the adsorbent, and the adsorbent can be a resin commonly used in the art for adsorbing impurities.

[0059] In a specific implementation, the low-boiling material output from the front-end distillation column enters the pre-fractionation section 13 through the low-boiling material inlet of the first distillation column. In the pre-fractionation section 13, the light components (mainly including dichlorosilane and trichlorosilane) in the low-boiling material rise to the top rectification section 11. The light components are separated in the rectification section 11, causing the trichlorosilane to descend into the main fractionation section, thereby enriching the main fractionation section with crude trichlorosilane and the rectification section 11 with crude dichlorosilane. The crude dichlorosilane in the rectification section 11 can be fed into other processes of polysilicon production. The heavy components (mainly including silicon tetrachloride, trichlorosilane, and a small amount of heavy components) in the low-boiling material descend to the bottom stripping section 12. In the stripping section 12, the trichlorosilane rises to the main fractionation section, thereby enriching the stripping section 12 with crude silicon tetrachloride and a small amount of heavy components and the main fractionation section with crude trichlorosilane.

[0060] The crude silicon tetrachloride and a small amount of heavy components in the stripping section 12 are discharged through the bottom outlet of the stripping section 12. They can be directly fed into the second distillation column 2 through the high-boiling material inlet, or they can be mixed with the high-boiling material and fed into the second distillation column 2 through the high-boiling material inlet. In the second distillation column 2, the crude silicon tetrachloride, a small amount of heavy components and high-boiling material are distilled. The crude trichlorosilane will rise and accumulate at the top of the second distillation column 2, while the silicon tetrachloride and some methyldichlorosilane will descend and accumulate at the bottom of the second distillation column 2. They are then discharged from the bottom of the second distillation column 2 to the slurry treatment process or sold externally.

[0061] The crude trichlorosilane from the main fractionation section of the first distillation column is discharged through the first outlet and can directly enter the adsorption column 3. The crude trichlorosilane produced at the top of the second distillation column 2 is discharged through the top outlet of the second distillation column 2 and can directly enter the adsorption column 3. Alternatively, the crude trichlorosilane from the main fractionation section of the first distillation column is discharged through the first outlet, and the crude trichlorosilane produced at the top of the second distillation column 2 is discharged through the top outlet of the second distillation column 2. The crude trichlorosilane produced in the first distillation column and the crude trichlorosilane produced in the second distillation column 2 are mixed and then directly enter the adsorption column 3. In the adsorption column 3, impurities in the crude trichlorosilane are adsorbed, thereby obtaining trichlorosilane with higher purity. This trichlorosilane can be further purified in the distillation unit to prepare high-purity polycrystalline silicon.

[0062] The present invention discloses a system for removing high and low boiling points in polysilicon production, comprising a first distillation column, a second distillation column 2, and an adsorption column 3 connected to each other. The first distillation column is a plate column, equivalent to 1-3 conventional high and low boiling point recovery columns, which can separate light and heavy components in low-boiling materials in one column, improving separation efficiency. The present invention further improves separation efficiency by designing the number of plates in the first distillation column, thereby achieving more efficient recovery of high and low boiling points in polysilicon production. The second distillation column 2 is mainly used to concentrate high-boiling components, and the adsorption column 3 is used to adsorb impurities in the crude trichlorosilane obtained after separation in the first and second distillation columns 2. This system can remove high-boiling and low-boiling components in polysilicon production and recover high-purity trichlorosilane.

[0063] This invention achieves the recovery of high and low boiling points in polysilicon production through a system including a first distillation column, a second distillation column 2, and an adsorption column 3. This can reduce equipment investment, land occupation, and energy consumption, and has broad application prospects.

[0064] In some embodiments of the invention, the first discharge port is located at the 30th-50th tray of the main fractionation section. In some embodiments, the first discharge port is located at the 40th tray of the main fractionation section.

[0065] By selecting the location of the first discharge port, this invention can improve the separation efficiency of the first distillation column, thereby obtaining trichlorosilane with higher purity.

[0066] In some embodiments of the present invention, a disproportionation fixed-bed reactor 6 is also included, wherein the outlet of the disproportionation fixed-bed reactor 6 is connected to the inlet of the low-boiling material.

[0067] In a specific implementation, silicon tetrachloride and dichlorosilane undergo a disproportionation reaction in the disproportionation fixed-bed reactor 6 to obtain trichlorosilane. The unreacted silicon tetrachloride, unreacted dichlorosilane, and the obtained trichlorosilane in the disproportionation fixed-bed reactor 6 are output from the bottom of the disproportionation fixed-bed reactor 6 and enter the pre-splitting section 13 through the low-boiling material inlet of the first distillation column, together with the low-boiling material output from the front-end distillation column.

[0068] This invention uses a first distillation column for removing high and low boiling points and a second distillation column 2 to separate the material after the disproportionation reaction, which can reduce the operating load of the front-end distillation column and reduce the column diameter.

[0069] In some embodiments of the present invention, the first distillation column has a distillation section outlet, which is connected to the feed inlet of the disproportionation fixed-bed reactor 6.

[0070] Specifically, the crude dichlorodihydrosilane enriched in the rectification section 11 is output through the rectification section outlet and enters the disproportionation fixed-bed reactor 6 through the disproportionation fixed-bed reactor 6 to continue participating in the disproportionation reaction, thereby saving raw materials.

[0071] Furthermore, the feed inlet of the disproportionation fixed-bed reactor 6 is located at the top of the reactor 6, and the discharge outlet of the reactor 6 is located at the bottom of the reactor 6. That is, crude dichlorosilane enters the disproportionation fixed-bed reactor 6 through the feed inlet at the top, participates in the disproportionation reaction, and the resulting unreacted dichlorosilane, unreacted silicon tetrachloride, and the product trichlorosilane are discharged through the discharge outlet at the bottom of the reactor 6 into the first distillation column.

[0072] Because the resin packed in the disproportionation fixed-bed reactor 6 will break down and clog the discharge cap after prolonged operation, the feeding method of the disproportionation fixed-bed reactor 6 is modified to top-in, bottom-out. The material flows downward, while the resin, which is less dense, flows upward. The interaction of these two forces reduces resin wear, delays clogging, and thus extends the service life of the system.

[0073] In some embodiments of the present invention, the system further includes a first heat exchanger 4, and the second main fractionation section 142 has a second discharge port;

[0074] The second discharge port is connected to the heat source inlet of the first heat exchanger 4. The discharge port of the disproportionation fixed bed reactor 6 and the low-boiling material are respectively connected to the cold source inlet of the first heat exchanger 4. The cold source outlet of the first heat exchanger 4 is connected to the low-boiling material feed inlet. The heat source outlet of the first heat exchanger 4 is connected to the inlet of the disproportionation fixed bed reactor 6.

[0075] The main fractionation section of this invention comprises, from top to bottom, a first main fractionation section 141 and a second main fractionation section 142 that are interconnected. The first main fractionation section 141 is more enriched in trichlorosilane, and the second main fractionation section 142 is more enriched in silicon tetrachloride. Since the material output from the main fractionation section of the first distillation column has a higher temperature, the crude silicon tetrachloride output from the second main fractionation section 142 of the first distillation column can be used to preheat low-boiling materials, thereby saving energy and reducing production costs.

[0076] Specifically, the system also includes a first heat exchanger 4. The crude silicon tetrachloride separated by the first distillation column can be output through the second outlet of the second main fractionation section 142 and enter the first heat exchanger 4 through the heat source inlet. The material output from the disproportionation fixed-bed reactor 6 and the low-boiling material enter the first heat exchanger 4 through the cold source inlet. In the first heat exchanger 4, the crude silicon tetrachloride separated by the first distillation column will exchange heat with the material output from the disproportionation fixed-bed reactor 6 and the low-boiling material to achieve preheating of the material output from the disproportionation fixed-bed reactor 6 and the low-boiling material. The preheated material is output through the cold source outlet of the first heat exchanger 4 and enters the first distillation column through the low-boiling material inlet for distillation treatment. The crude silicon tetrachloride after heat exchange is output to the disproportionation fixed-bed reactor 6 through the heat source outlet of the first heat exchanger 4.

[0077] The present invention does not impose any particular limitation on the first heat exchanger 4, as long as it can achieve heat exchange between crude silicon tetrachloride and low-boiling materials.

[0078] Furthermore, the second outlet is located at trays 60-75 of the main fractionation section. In some embodiments, the second outlet is located at tray 70 of the main fractionation section.

[0079] By selecting the location of the second discharge port, this invention can further improve the separation efficiency of the first distillation column, thereby obtaining trichlorosilane with higher purity.

[0080] In some embodiments of the present invention, the system further includes a second heat exchanger 5;

[0081] The top outlet of the second distillation column 2 is connected to the heat source inlet of the second heat exchanger 5, the bottom outlet of the first distillation column is connected to the cold source inlet of the second heat exchanger 5, the heat source outlet of the second heat exchanger 5 is connected to the feed inlet of the adsorption column 3, and the cold source outlet of the second heat exchanger 5 is connected to the stripping section 12.

[0082] It is understood that in this invention, the crude trichlorosilane separated by the second distillation column 2 has a high temperature, while the bottom of the first distillation column requires a heat source to provide heat for the first distillation column. Therefore, the heat of the crude trichlorosilane separated by the second distillation column 2 can be used to provide heat for the bottom of the first distillation column, and the temperature of the crude trichlorosilane obtained by the second distillation column 2 can be reduced, so that the temperature of the crude trichlorosilane obtained by the second distillation column 2 is better matched with the temperature in the subsequent adsorption column 3, thereby improving the adsorption efficiency.

[0083] Specifically, the crude trichlorosilane produced in the second distillation column 2 is discharged through the top outlet of the second distillation column 2 and enters the second heat exchanger 5 through the heat source inlet. The heavy components (including crude silicon tetrachloride and a small amount of heavy impurities) produced at the bottom of the first distillation column are discharged through the bottom outlet of the first distillation column and enter the second heat exchanger 5 through the cold source inlet. In the second heat exchanger 5, the material output from the first distillation column and the crude trichlorosilane produced in the second distillation column 2 undergo heat exchange treatment. The heavy components (including crude silicon tetrachloride and a small amount of heavy impurities) that have absorbed some heat are discharged through the cold source outlet of the second heat exchanger 5 to provide heat to the bottom of the first distillation column. The crude trichlorosilane, which has been cooled down, is discharged through the heat source outlet of the second heat exchanger 5 and enters the adsorption column 3 for adsorption treatment or enters the second distillation column 2 for further treatment.

[0084] The present invention does not impose any particular limitation on the second heat exchanger 5, as long as it can achieve heat exchange between the heavy components produced by the first distillation column and the crude trichlorosilane.

[0085] In some embodiments, a third heat exchanger 7 is also included, through which the crude trichlorosilane is cooled before entering the adsorption column 3. Further, the third heat exchanger 7 cools the crude trichlorosilane to 20-40°C before it enters the adsorption column 3; the low temperature facilitates the adsorption process and improves the adsorption efficiency.

[0086] In this invention, the first heat exchanger 4, the second heat exchanger 5, and the third heat exchanger 7 may have the same model or different models.

[0087] In some embodiments of the present invention, the second distillation column 2 has 100-120 trays; and / or,

[0088] The feed inlet for high-boiling materials is located at trays 80-100 of the second distillation column 2.

[0089] The system for removing high and low boiling points in polysilicon production according to the present invention can be used to treat any high and low boiling points generated during polysilicon production, enabling the recycling of raw materials. It is particularly suitable for treating high-boiling materials with a methyldichlorosilane content of 1-100 ppm.

[0090] It is understood that the operating temperature and pressure of the first distillation column, the second distillation column 2, and the adsorption column 3 have a crucial impact on the processing efficiency, processing load, and processing results. Therefore, the present invention can further select the operating temperature and pressure of the first distillation column, the second distillation column 2, and the adsorption column 3 to improve the processing efficiency, processing load, and processing effect of the system.

[0091] Exemplarily, in some embodiments of the present invention, the operating pressure in the first distillation column is 0.15-0.3 MPaG, the operating temperature at the top of the column is 35-52°C, and the operating temperature at the bottom of the column is 93-110°C; and / or,

[0092] In the second distillation column 2, the operating pressure is 0.65-0.95 MPaG, the top operating temperature is 106-122℃, and the bottom operating temperature is 109-124℃; and / or,

[0093] In adsorption column 3, the operating temperature is 20-60℃ and the operating pressure is 0.5-1MPaG.

[0094] Specifically, in the first distillation column, the operating pressure can be within the range of any one or both of 0.15 MPaG, 0.17 MPaG, 0.19 MPaG, 0.25 MPaG, 0.28 MPaG, and 0.3 MPaG; the top operating temperature can be within the range of any one or both of 35°C, 38°C, 40°C, 41°C, 45°C, 50°C, and 52°C; and the bottom operating temperature can be within the range of any one or both of 93°C, 95°C, 98°C, 100°C, 105°C, and 110°C; and / or,

[0095] In the second distillation column 2, the operating pressure can be within the range of any one or both of 0.65 MPaG, 0.8 MPaG, and 0.95 MPaG; the top operating temperature can be within the range of any one or both of 106°C, 110°C, and 122°C; and the bottom operating temperature can be within the range of any one or both of 109°C, 110°C, 120°C, and 124°C; and / or,

[0096] In the adsorption column 3, the operating temperature can be any one of 20℃, 40℃, 50℃, 60℃ or any two of them, and the operating pressure can be any one of 0.5MPaG, 0.7MPaG, 1MPaG or any two of them.

[0097] Furthermore, in some embodiments of the present invention, the reflux ratio of the second distillation column 2 is (5-15):1.

[0098] The inventors discovered in their research that when the reflux ratio of the second distillation column 2 is (5-15):1, the processing efficiency of the second distillation column 2 can be improved while saving energy, and the methyl dichlorosilane in the second distillation column 2 can be further separated, thereby improving the purity of the crude trichlorosilane obtained from the second distillation column 2, and thus obtaining crude trichlorosilane with higher purity.

[0099] In a specific implementation, the reflux ratio is 10:1.

[0100] By setting the reflux ratio of the second distillation column 2, this invention can achieve efficient removal of methyldichlorosilane without loading a catalyst into the second distillation column 2. In practical applications, this not only eliminates the need for frequent catalyst replacement, saving production costs, but also avoids the introduction of impurities into the reaction system by the catalyst, thus improving product quality.

[0101] In some embodiments of the present invention, the top of the adsorption column 3 has a top feed inlet, and the top discharge outlet of the first discharge outlet and the top discharge outlet of the second distillation column 2 are respectively connected to the top feed inlet of the adsorption column 3.

[0102] Specifically, the crude trichlorosilane obtained from the first distillation column is output through the first outlet and enters the adsorption column 3 through the top inlet of the adsorption column 3. The crude trichlorosilane obtained from the second distillation column 2 is output through the top outlet and enters the adsorption column 3 through the top inlet of the adsorption column 3. Alternatively, the crude trichlorosilane obtained from the first distillation column is output through the first outlet and enters the adsorption column 3 through the top inlet of the adsorption column 3. The crude trichlorosilane obtained from the second distillation column 2 is output through the top outlet and mixed with the crude trichlorosilane output from the first distillation column. Then, it enters the adsorption column 3 through the top inlet of the adsorption column 3. In the adsorption column 3, impurities in the crude trichlorosilane are removed, thereby obtaining trichlorosilane with higher purity.

[0103] This invention allows crude trichlorosilane to enter the adsorption column 3 from the top and exit from the bottom, using a top-in, bottom-out method. This downward flow of material helps reduce resin wear, delays clogging of the adsorption column 3, and extends the service life of the system.

[0104] In some embodiments of the present invention, the feed to the disproportionation fixed-bed reactor 6 comprises silicon tetrachloride and silicon dichlorosilane, with a mass ratio of silicon tetrachloride to silicon dichlorosilane of (5-3):1. By ensuring that the feed to the disproportionation fixed-bed reactor 6 satisfies the above-mentioned relationship, the present invention can improve the conversion rate of the disproportionation reaction, resulting in the output material of the disproportionation fixed-bed reactor 6 containing a large amount of silicon tetrachloride, a large amount of trichlorosilane, and a small amount of silicon dichlorosilane, further improving the processing efficiency of the subsequent first distillation column and second distillation column 2. In some embodiments, the mass ratio of silicon tetrachloride to silicon dichlorosilane can be 4:1, and the specificity of the disproportionation reaction can be approximately 95%.

[0105] The inventors also discovered that by selecting the operating temperature and operating pressure of the disproportionation fixed-bed reactor 6, the conversion rate of the disproportionation reaction can be further improved while saving energy, thereby increasing the efficiency of removing high and low boiling points. Exemplarily, in some embodiments of the present invention, the operating temperature of the disproportionation fixed-bed reactor 6 is 50-60°C, and the operating pressure is 0.5-1 MPaG.

[0106] A second aspect of the present invention provides a method for removing high and low boiling points in polysilicon production, using the system of the first aspect.

[0107] Specifically, the low-boiling material enters the pre-fractionation section 13 of the first distillation column through the low-boiling material inlet. In the pre-fractionation section 13, the light components (mainly dichlorosilane and trichlorosilane) of the low-boiling material rise to the top rectification section 11. The light components are separated in the rectification section 11, and the trichlorosilane descends to the main fractionation section, thereby enriching the main fractionation section with crude trichlorosilane and the rectification section 11 with crude dichlorosilane. The crude dichlorosilane in the rectification section 11 is fed to the disproportionation fixed-bed reactor 6. The heavy components (mainly silicon tetrachloride, trichlorosilane, and a small amount of heavy components) of the low-boiling material descend to the bottom stripping section 12. In the stripping section 12, the trichlorosilane rises to the main fractionation section, thereby enriching the stripping section 12 with crude silicon tetrachloride and a small amount of heavy components, and enriching the main fractionation section with crude trichlorosilane.

[0108] The crude silicon tetrachloride and a small amount of heavy components in the stripping section 12 are discharged through the bottom outlet of the stripping section 12. They can be directly fed into the second distillation column 2 through the high-boiling material inlet, or they can be mixed with the high-boiling material and fed into the second distillation column 2 through the high-boiling material inlet. In the second distillation column 2, the crude silicon tetrachloride, a small amount of heavy components and high-boiling material are distilled. The crude trichlorosilane will rise and accumulate at the top of the second distillation column 2, while the silicon tetrachloride and some methyldichlorosilane will descend and accumulate at the bottom of the second distillation column 2. They are then discharged from the bottom of the second distillation column 2 to the slurry treatment process or sold externally.

[0109] The crude trichlorosilane from the main fractionation section of the first distillation column is discharged through the first outlet and can directly enter the adsorption column 3. The crude trichlorosilane produced at the top of the second distillation column 2 is discharged through the top outlet of the second distillation column 2 and can directly enter the adsorption column 3. Alternatively, the crude trichlorosilane from the main fractionation section of the first distillation column is discharged through the first outlet, and the crude trichlorosilane produced at the top of the second distillation column 2 is discharged through the top outlet of the second distillation column 2. The crude trichlorosilane produced in the first distillation column and the crude trichlorosilane produced in the second distillation column 2 are mixed and then directly enter the adsorption column 3. In the adsorption column 3, impurities in the crude trichlorosilane are adsorbed, thereby obtaining trichlorosilane with higher purity. This trichlorosilane can be further purified in the distillation unit to prepare high-purity polycrystalline silicon.

[0110] This preparation method uses the aforementioned system, thus removing high-boiling and low-boiling substances from polycrystalline silicon production to obtain high-purity trichlorosilane. Furthermore, this preparation method is simple to operate, low in cost, and suitable for widespread application.

[0111] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0112] Example 1

[0113] The system for removing high and low boiling points in polysilicon production in this embodiment is as follows: Figure 1 As shown, it includes:

[0114] Disproportionation fixed-bed reactor 6, first distillation column, second distillation column 2, adsorption column 3, first heat exchanger 4, second heat exchanger 5, third heat exchanger 7;

[0115] The first distillation column includes a top rectifying section 11, a bottom stripping section 12, and a separation section located between the rectifying section 11 and the stripping section 12. The rectifying section 11, the separation section, and the stripping section 12 are sequentially interconnected. The separation section includes a pre-fractionation section 13 arranged in parallel and not interconnected with each other, and a main fractionation section. The main fractionation section includes, from top to bottom, a first main fractionation section 141 and a second main fractionation section 142 that are interconnected. The pre-fractionation section 13 has a low-boiling material inlet, the stripping section 12 has a bottom outlet, the first main fractionation section 141 has a first outlet, the first distillation column has a rectifying section outlet, and the second main fractionation section 142 has a second outlet.

[0116] The outlet of the disproportionation fixed-bed reactor 6 is connected to the inlet of the low-boiling material, and the outlet of the rectification section is connected to the inlet of the disproportionation fixed-bed reactor 6. The inlet of the disproportionation fixed-bed reactor 6 is located at the top of the disproportionation fixed-bed reactor 6, and the outlet of the disproportionation fixed-bed reactor 6 is located at the bottom of the disproportionation fixed-bed reactor 6.

[0117] The second distillation column 2 has a high-boiling material inlet and a top outlet, and the bottom outlet of the stripping section 12 is connected to the high-boiling material inlet.

[0118] The second discharge port is connected to the heat source inlet of the first heat exchanger 4. The discharge port of the disproportionation fixed bed reactor 6 and the low-boiling material are respectively connected to the cold source inlet of the first heat exchanger 4. The cold source outlet of the first heat exchanger 4 is connected to the low-boiling material inlet. The heat source outlet of the first heat exchanger 4 is connected to the inlet of the disproportionation fixed bed reactor 6.

[0119] The top outlet of the second distillation column 2 is connected to the heat source inlet of the second heat exchanger 5, the bottom outlet of the first distillation column is connected to the cold source inlet of the second heat exchanger 5, the heat source outlet of the second heat exchanger 5 is connected to the heat source inlet of the third heat exchanger 7, the heat source outlet of the third heat exchanger 7 is connected to the adsorption column 3, and the cold source outlet of the second heat exchanger 5 is connected to the stripping section 12.

[0120] In the first distillation column, the feed by mass percentage includes: DCS: 6.72%, TCS: 43.05%, STC: 50.23%, operating pressure: 0.2 MPaG, reflux ratio: 60:1, top operating temperature: 41℃, bottom operating temperature: 102℃; the rectification section 11 has 30 trays, the stripping section 12 has 20 trays, the pre-fractionation section 13 has 80 trays, and the main fractionation section has 80 trays. The first outlet is located at the 40th tray of the main fractionation section, and the second outlet is located at the 70th tray of the main fractionation section.

[0121] In the second distillation column 2, the feed by mass percentage includes: TCS 99.4%, STC 0.6%, methyl dichlorosilane 10ppm, operating pressure 0.85MPaG, reflux ratio 10:1, column top operating temperature 116℃, column bottom operating temperature 120℃, the second distillation column 2 has 120 trays, and the high-boiling material feed inlet is located at the 90th tray of the second distillation column 2;

[0122] In adsorption column 3, the operating temperature is 20℃ and the operating pressure is 0.5MPaG;

[0123] In the disproportionation fixed-bed reactor 6, the feed consists of silicon tetrachloride and dichlorosilane, with a mass ratio of silicon tetrachloride to dichlorosilane of 4:1. The operating temperature is 60°C and the operating pressure is 0.8 MPaG.

[0124] The purity of trichlorosilane in the material output from adsorption column 3 can reach 99.99%. Compared with the system that uses a two-stage low-boiling tower, a two-stage high-boiling tower, and an anti-disproportionation separation tower, the system in this embodiment can reduce the investment in three towers and their auxiliary equipment. Taking an annual production scale of 50,000 tons of polysilicon as an example, it can save 6 million yuan in equipment costs, about 15 t / h of steam, and about 600 cubic meters / h of circulating water.

[0125] The various embodiments in this specification are described in a related manner. Similar or identical parts between embodiments can be referred to mutually. Each embodiment focuses on its differences from other embodiments. The above are merely preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention are included within the scope of protection of the present invention.

Claims

1. A system for removing high and low boiling points during polysilicon production, characterized in that, It includes a first distillation column, a second distillation column, an adsorption column, a disproportionation fixed-bed reactor, and a second heat exchanger; The first distillation column includes a top rectifying section, a bottom stripping section, and a separation section located between the rectifying section and the stripping section. The rectifying section, the separation section, and the stripping section are sequentially interconnected. The separation section includes a pre-fractionation section and a main fractionation section arranged side by side and not interconnected. The main fractionation section includes, from top to bottom, a first main fractionation section and a second main fractionation section that are interconnected. The pre-fractionation section has a low-boiling material inlet, the stripping section has a bottom outlet, and the first main fractionation section has a first outlet. The outlet of the disproportionation fixed-bed reactor is connected to the low-boiling material inlet. The rectification section has 30-50 trays, the stripping section has 10-30 trays, the pre-fractionation section has 40-80 trays, and the main fractionation section has 40-80 trays. The second distillation column has a high-boiling material inlet and a top outlet, and the bottom outlet of the stripping section is connected to the high-boiling material inlet. The first discharge port and the top discharge port of the second distillation column are respectively connected to the adsorption column; Low-boiling-point materials include silicon tetrachloride, trichlorosilane, and dichlorosilane; High-boiling-point materials include trichlorosilane, silicon tetrachloride, and methyldichlorosilane; The first distillation column has a rectification section outlet, which is connected to the feed inlet of the disproportionation fixed-bed reactor; the feed inlet of the disproportionation fixed-bed reactor is located at the top of the disproportionation fixed-bed reactor, and the discharge outlet of the disproportionation fixed-bed reactor is located at the bottom of the disproportionation fixed-bed reactor. And / or, The top of the adsorption column has a top feed inlet, and the first discharge outlet and the top discharge outlet of the second distillation column are respectively connected to the top feed inlet of the adsorption column. The top outlet of the second distillation column is connected to the heat source inlet of the second heat exchanger, the bottom outlet of the first distillation column is connected to the cold source inlet of the second heat exchanger, the heat source outlet of the second heat exchanger is connected to the feed inlet of the adsorption column, and the cold source outlet of the second heat exchanger is connected to the stripping section.

2. The system according to claim 1, characterized in that, The first discharge port is located at the 30th-50th tray of the main fractionation section.

3. The system according to claim 1, characterized in that, The system also includes a first heat exchanger, and the second main fractionation section has a second discharge port; The second discharge port is connected to the heat source inlet of the first heat exchanger, the discharge port of the disproportionation fixed bed reactor and the low-boiling material are respectively connected to the cold source inlet of the first heat exchanger, the cold source outlet of the first heat exchanger is connected to the feed port of the low-boiling material, and the heat source outlet of the first heat exchanger is connected to the inlet of the disproportionation fixed bed reactor.

4. The system according to claim 3, characterized in that, The second discharge port is located at the 60th-75th tray of the main fractionation section.

5. The system according to claim 1, characterized in that, The second distillation column has 100-120 trays; and / or, The high-boiling material inlet is located at trays 80-100 of the second distillation column.

6. The system according to any one of claims 1-4, characterized in that, In the first distillation column, the operating pressure is 0.15-0.3 MPaG, the top operating temperature is 35-52℃, and the bottom operating temperature is 93-110℃; and / or, In the second distillation column, the operating pressure is 0.65-0.95 MPaG, the top operating temperature is 106-122℃, and the bottom operating temperature is 109-124℃; and / or, The adsorption column operates at a temperature of 20-60℃ and a pressure of 0.5-1 MPaG; and / or, The reflux ratio of the second distillation column is (5-15):1; and / or, The feed to the disproportionation fixed-bed reactor includes silicon tetrachloride and dichlorosilane, wherein the mass ratio of silicon tetrachloride to dichlorosilane is (5-4):1; and / or, The operating temperature in the disproportionation fixed-bed reactor is 50-60℃, and the operating pressure is 0.5-1MPaG.

7. A method for removing high and low boiling points in polycrystalline silicon production, characterized in that, The system described in any one of claims 1-6 shall be used.

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