Chlorosilane carbon impurity removal system

Abstract

The utility model discloses a system for removing carbon impurities in chlorosilane, which belongs to the technical field of polycrystalline silicon production and comprises a first rectifying tower, the first rectifying tower is connected with a chlorosilane raw material pipe, a first silicon tetrachloride outlet pipe and a first connecting pipe, the first connecting pipe is connected with a second rectifying tower, and the second rectifying tower is connected with a second connecting pipe and a first discharge pipe. The second connecting pipe is connected with a third rectifying tower, the third rectifying tower is connected with a fourth connecting pipe and a fifth connecting pipe, the fourth connecting pipe is connected with a fourth rectifying tower, the fourth rectifying tower is connected with a second discharging pipe and a sixth connecting pipe, the sixth connecting pipe is connected with a fifth rectifying tower, and the fifth rectifying tower is connected with a product liquid outlet pipe and a seventh connecting pipe. According to the utility model, a chlorosilane raw material produced in a cold hydrogenation or trichlorosilane synthesis process is subjected to first rectification separation, second rectification separation, third rectification separation, fourth rectification separation and fifth rectification separation to obtain high-purity trichlorosilane.

Description

Technical Field

[0001] The utility model belongs to the technical field of polysilicon production, and in particular relates to a system for removing carbon impurities of chlorosilane. Background Art

[0002] The chlorosilane decarbonization process is a method for decarbonizing chlorosilane in polysilicon production. At present, the production of polysilicon mainly adopts the trichlorosilane reduction method. The trichlorosilane synthesis of this method uses industrial silicon powder, H2, hydrogen chloride and silicon tetrachloride as raw materials. Under the action of the catalyst in the hydrogenation furnace, a reaction occurs to generate trichlorosilane. In this process, carbon-containing impurities such as methyldichlorosilane, methyltrichlorosilane and dimethylchlorosilane will be produced. These carbon-containing impurities will be deposited in the silicon element, affecting the carbon index in the polysilicon to exceed the standard, and need to be separated before the trichlorosilane reduction reaction. The trichlorosilane purification process uses a distillation separation process, which uses the difference in boiling points between different substances for separation. Since the boiling point of methyldichlorosilane is 41°C, which is close to the boiling point of trichlorosilane (32°C), in order to reduce the content of methyldichlorosilane, a distillation tower with a higher theoretical plate number and reflux ratio is required, resulting in higher investment and operating costs for the distillation device. With the continuous development of science and technology, people have higher and higher requirements for the manufacturing process of chlorosilane decarbonization process.

[0003] The existing chlorosilane decarbonization process has certain drawbacks when used. The reactive distillation tower has the safety problem of stopping and overhauling when replacing the catalyst. The raw materials need to be pretreated before entering the reactor, and the decarbonization conversion rate is incomplete. The treated silicon tetrachloride and monomethyl trichlorosilane need to be further separated downstream. Patent CN109179426A proposes a method for reactive decarbonization, in which the pretreated silicon tetrachloride and carbon-containing trichlorosilane are sent to the reactive distillation tower, and the chlorine atom redistribution reaction is carried out. Through the separation effect of reactive distillation, the reaction product trichlorosilane is extracted from the top of the tower, and the tower bottom extracts excess silicon tetrachloride and the generated methyl trichlorosilane. The utility model converts the methyl dichlorosilane that is difficult to separate from trichlorosilane into methyl trichlorosilane that is easily separated by the conversion of reactive carbon, and realizes the decarbonization function of trichlorosilane. However, when the catalyst in the tower fails to be replaced, the tower needs to be stopped, which will affect the production stability of the system and bring safety risks. The excess silicon tetrachloride and monomethyltrichlorosilane are extracted from the bottom of the tower and need to be separated downstream, which brings a burden to the downstream separation. In order to prevent catalyst poisoning, a treatment device needs to be installed before entering the tower, which makes the decarbonization system more complicated.

[0004] Patent CN110980742A proposes a method for reactive decarbonization. By side-drawing the unreacted chlorine donor and returning it to the tower for further reaction, monomethyl dichlorosilane can be obtained from the bottom of the tower, making full use of the chlorine donor. However, there are still a series of problems caused by replacing the catalyst after the reactive distillation catalyst fails. Moreover, it is difficult to completely separate the chlorine donor and monomethyl dichlorosilane from the side-stream material;

[0005] Patent CN114956092A proposes a method for decarbonizing trichlorosilane. The carbon-containing trichlorosilane material reacts under the catalysis of resin, and the reacted material is subjected to distillation separation to obtain silicon tetrachloride and monomethyl trichlorosilane at the bottom of the tower. In this process, the conversion of monomethyl dichlorosilane is not complete, and the subsequent separation of silicon tetrachloride and monomethyl trichlorosilane is still not thorough;

[0006] Patent CN 212740754 U proposes a method for trichlorosilane decarbonization reaction and rectification, including a reactive distillation column and a series of rectification columns. To improve the decarbonization conversion rate, multiple reactive distillation columns are set in series or parallel, further increasing the complexity of reactive distillation. We propose a decarbonization process for chlorosilanes in polysilicon production. Utility Model Content

[0007] To solve the above technical problems, the present utility model provides a system for removing carbon impurities from chlorosilanes. The chlorosilane raw materials produced in the cold hydrogeneration or trichlorosilane synthesis process are subjected to the first rectification separation, the second rectification separation, the third rectification separation, the fourth rectification separation, and the fifth rectification separation through the first rectification column, the second rectification column, the third rectification column, the fourth rectification column, and the fifth rectification column respectively to obtain high-purity trichlorosilane (the concentration of trichlorosilane needs to be greater than 99.9%); dichlorosilane and silicon tetrachloride in the chlorosilane raw materials react in a reactor to obtain trichlorosilane, further improving the utilization rate of chlorosilanes (the theoretical utilization rate of chlorosilane raw materials is 100%); the sixth rectification column separates the high-carbon chlorosilanes existing in the form of methylchlorosilanes discharged from the bottom of the third rectification column and the fifth rectification column, and the seventh rectification column further concentrates the high-carbon chlorosilanes discharged from the bottom of the sixth rectification column. The concentrated material is discharged from the bottom of the seventh rectification column. This part of the material has a very high carbon impurity content (it can be highly concentrated through process adjustment, such as adjusted to 5000 - 50000 ppm). This part of the high-carbon material undergoes high-pressure deep cooling to cool the methylchlorosilane into a solid state, and after filtration, the chlorosilane is recovered.

[0008] The object of the present utility model is achieved through the following technical solutions:

[0009] A system for removing carbon impurities from chlorosilane, comprising a first rectification column, wherein the first rectification column is connected to a chlorosilane raw material pipe, a first silicon tetrachloride outlet pipe and a first connecting pipe, the first connecting pipe is connected to a second rectification column, the second rectification column is connected to a second connecting pipe and a first external discharge pipe, the second connecting pipe is connected to a third rectification column, the third rectification column is connected to a fourth connecting pipe and a fifth connecting pipe, the fourth connecting pipe is connected to a fourth rectification column, the fourth rectification column is connected to a second external discharge pipe and a sixth connecting pipe, the sixth connecting pipe is connected to a fifth rectification column, and the fifth rectification column is connected to a product liquid outlet pipe and a seventh connecting pipe.

[0010] Preferably, after the fifth connecting pipe and the seventh connecting pipe are connected, they flow into a sixth rectification column. The sixth rectification column is connected to an eighth connecting pipe and a third external discharge pipe. The eighth connecting pipe is connected to a seventh rectification column. The seventh rectification column is connected to a fourth external discharge pipe and a ninth connecting pipe. The ninth connecting pipe is connected to a cryogenic filtration unit. The cryogenic filtration unit is connected to a tenth connecting pipe and a fifth external discharge pipe. The tenth connecting pipe is connected to a heat exchanger. The heat exchanger is connected to a sixth external discharge pipe. The third external discharge pipe, the fourth external discharge pipe and the sixth external discharge pipe are all connected to a chlorosilane raw material tank.

[0011] Preferably, the first silicon tetrachloride outlet pipe is connected to a silicon tetrachloride raw material system.

[0012] Preferably, the first external discharge pipe is connected to a dichlorosilane treatment unit.

[0013] Preferably, the second external discharge pipe is connected to a light component treatment unit.

[0014] Preferably, the fifth external discharge pipe is connected to a methylchlorosilane treatment unit.

[0015] Preferably, the cryogenic filtration unit adopts a low-temperature freezing device.

[0016] The beneficial effects of this technical solution are as follows:

[0017] 1. A system for removing carbon impurities from chlorosilanes provided by the present utility model. The chlorosilane raw materials produced in the cold hydrogeneration or trichlorosilane synthesis process are respectively subjected to the first rectification separation, the second rectification separation, the third rectification separation, the fourth rectification separation and the fifth rectification separation through the first rectification column, the second rectification column, the third rectification column, the fourth rectification column and the fifth rectification column to obtain high-purity trichlorosilane (the concentration of trichlorosilane needs to be greater than 99.9%); dichlorodihydrogen silane and silicon tetrachloride in the chlorosilane raw materials react in a reactor to obtain trichlorosilane, further improving the utilization rate of chlorosilanes (the theoretical utilization rate of chlorosilane raw materials is 100%); the sixth rectification column separates the high-carbon chlorosilanes existing in the form of methylchlorosilanes discharged from the bottom of the third rectification column and the fifth rectification column, and the seventh rectification column further concentrates the high-carbon chlorosilanes discharged from the bottom of the sixth rectification column. The concentrated material is discharged from the bottom of the seventh rectification column. This part of the material has a very high carbon impurity content (it can be highly concentrated through process adjustment, such as adjusted to 5000 - 50000 ppm). This part of the high-carbon material undergoes high-pressure deep cooling to cool the methylchlorosilane into a solid state, and after filtration, the chlorosilane is recovered.

[0018] 2. A system for removing carbon impurities from chlorosilanes provided by the present utility model utilizes the difference in the freezing point temperatures of chlorosilanes and methylchlorosilanes. At an ultra-low temperature of -150~-160°C, the methylchlorosilane preferentially solidifies into solid particles, and the solid-liquid separation can be better; the present utility model can remove more than 98% of the carbon-containing methylchlorosilanes in the trichlorosilane, and the carbon in the polysilicon produced by the reduction of trichlorosilane reaches the electronic grade level, and can be at least better than the electronic special grade level. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is a schematic structural diagram of the present utility model;

[0020] Wherein: 1. The first rectification column; 2. The second rectification column; 3. The third rectification column; 4. The fourth rectification column; 5. The fifth rectification column; 6. The sixth rectification column; 7. The seventh rectification column; 8. The deep cooling and filtration unit; 9. The heat exchanger; 10. The chlorosilane raw material tank; 11. The silicon tetrachloride raw material system; 12. The dichlorodihydrogen silane treatment unit; 13. The light component treatment unit; 14. The methylchlorosilane treatment unit; 101. The chlorosilane raw material pipe; 102. The first silicon tetrachloride outlet pipe; 103. The first connecting pipe; 104. The second connecting pipe; 105. The first external discharge pipe; 106. The fourth connecting pipe; 107. The fifth connecting pipe; 108. The second external discharge pipe; 109. The sixth connecting pipe; 110. The product liquid outlet pipe; 111. The seventh connecting pipe; 112. The eighth connecting pipe; 113. The third external discharge pipe; 114. The fourth external discharge pipe; 115. The ninth connecting pipe; 116. The tenth connecting pipe; 117. The fifth external discharge pipe; 118. The sixth external discharge pipe. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0021] The present utility model will be further described in detail below in conjunction with embodiments, but the implementation manners of the present utility model are not limited thereto.

[0022] Embodiment 1

[0023] As Figure 1 shown, a system for removing carbon impurities from chlorosilane includes a first rectification tower 1, which is connected to a chlorosilane raw material pipe 101, a first silicon tetrachloride outlet pipe 102 and a first connecting pipe 103. The first connecting pipe 103 is connected to a second rectification tower 2. The second rectification tower 2 is connected to a second connecting pipe 104 and a first external discharge pipe 105. The second connecting pipe 104 is connected to a third rectification tower 3. The third rectification tower 3 is connected to a fourth connecting pipe 106 and a fifth connecting pipe 107. The fourth connecting pipe 106 is connected to a fourth rectification tower 4. The fourth rectification tower 4 is connected to a second external discharge pipe 108 and a sixth connecting pipe 109. The sixth connecting pipe 109 is connected to a fifth rectification tower 5. The fifth rectification tower 5 is connected to a product liquid outlet pipe 110 and a seventh connecting pipe 111.

[0024] Embodiment 2

[0025] The difference between this embodiment and Embodiment 1 is that after the fifth connecting pipe 107 and the seventh connecting pipe 111 are connected, they flow into a sixth rectification tower 6. The sixth rectification tower 6 is connected to an eighth connecting pipe 112 and a third external discharge pipe 113. The eighth connecting pipe 112 is connected to a seventh rectification tower 7. The seventh rectification tower 7 is connected to a fourth external discharge pipe 114 and a ninth connecting pipe 115. The ninth connecting pipe 115 is connected to a cryogenic filtration unit 8. The cryogenic filtration unit 8 is connected to a tenth connecting pipe 116 and a fifth external discharge pipe 117. The tenth connecting pipe 116 is connected to a heat exchanger 9. The heat exchanger 9 is connected to a sixth external discharge pipe 118. The third external discharge pipe 113, the fourth external discharge pipe 114 and the sixth external discharge pipe 118 are all connected to a chlorosilane raw material tank 10.

[0026] Among them, the first silicon tetrachloride outlet pipe 102 is connected to a silicon tetrachloride raw material system 11. The silicon tetrachloride raw material system 11 is a prior art, such as including a silicon tetrachloride raw material tank, a silicon tetrachloride connecting pipe and a silicon tetrachloride transfer pump.

[0027] Among them, the first external discharge pipe 105 is connected to the dichlorosilane treatment unit 12. The dichlorosilane treatment unit 12 includes a mixer for dichlorosilane and silicon tetrachloride. After the mixed material is pressurized to 0.8 - 1.2 Mpa by a machine pump and heated to 50 - 65 °C by a heat exchanger 9, it undergoes a reverse disproportionation reaction SiH2Cl2 + SiCl4 → SiHCl3 in a reaction column. After the reaction, the raw material trichlorosilane generated and the unreacted silicon tetrachloride and dichlorosilane enter a cooler in the next process for cooling. After the temperature is reduced to 10 - 20 °C, they enter an adsorption column for impurity adsorption. The adsorbed material enters the original chlorosilane storage tank and serves as the raw material for rectification.

[0028] Among them, the second external discharge pipe 108 is connected to the light component treatment unit 13. The light component treatment unit 13 includes a condenser and an adsorber. After the light components are cooled, the light component impurities are adsorbed and removed, and it can also be returned to the raw material tank as raw material. The light component treatment unit 13 is a prior art and will not be described in detail here.

[0029] Among them, the fifth external discharge pipe 117 is connected to the methylchlorosilane treatment unit 14. The methylchlorosilane treatment unit 14 includes a methylchlorosilane storage tank and a heating system to melt the solidified methylchlorosilane into a liquid. The methylchlorosilane treatment unit 14 is a prior art and will not be described in detail here.

[0030] Among them, the cryogenic filtration unit 8 uses a cryogenic freezing device. The cryogenic freezing device solidifies the methylchlorosilane into a solid, thereby separating the liquid-solid phase of the liquid-phase chlorosilane. The cryogenic freezing device is a prior art and will not be described in detail here.

[0031] A method for removing carbon impurities from chlorosilane includes the following steps:

[0032] Step 1: The chlorosilane raw material enters the first rectification tower 1 for the first rectification separation. The bottom product of the first rectification tower 1 flows into the silicon tetrachloride storage tank, and the top product of the first rectification tower 1 flows into the second rectification tower 2;

[0033] Step 2: The top product of the first rectification tower 1 undergoes the second rectification separation in the second rectification tower 2. The bottom product of the second rectification tower 2 flows into the third rectification tower 3, and the top product of the second rectification tower 2 flows into the dichlorosilane treatment process;

[0034] Step 3: The bottom product of the second rectification tower 2 undergoes the third rectification separation in the third rectification tower 3. The top product of the third rectification tower 3 flows into the fourth rectification tower 4, and the bottom product of the third rectification tower 3 flows into the sixth rectification tower 6;

[0035] Step 4: The top product of the third rectification tower 3 undergoes the fourth rectification separation in the fourth rectification tower 4. The top product of the fourth rectification tower 4 flows into the light component treatment unit 13, and the bottom product of the fourth rectification tower 4 flows into the fifth rectification tower 5;

[0036] Step 5: The bottoms product of the fourth distillation column 4 is fed into the fifth distillation column 5 for the fifth distillation separation. The overhead product of the fifth distillation column 5 is high-purity trichlorosilane, and the bottoms product of the fifth distillation column 5 is fed into the sixth distillation column 6.

[0037] Among them, in Step 1, the temperature of the chlorosilane raw material is 80°C. The chlorosilane raw material produced in the cold hydrocracking synthesis process includes 70% SiCl4, 28.5% SiHCl3, and 1.5% SiH2Cl2.

[0038] Among them, the number of theoretical plates of the first distillation column 1 is 80, the overhead reflux ratio of the first distillation column 1 is 6, the column pressure of the first distillation column 1 is 0.8 MpaG, the temperature at the top of the first distillation column 1 is 112°C, and the temperature at the bottom of the first distillation column 1 is 147°C; the number of theoretical plates of the second distillation column 2 is 80, the feed reflux ratio of the second distillation column 2 is 5, the column pressure of the second distillation column 2 is 0.5 MpaG, the temperature at the top of the second distillation column 2 is 82°C, and the temperature at the bottom of the second distillation column 2 is 97°C; the number of theoretical plates of the third distillation column 3 is 80, the overhead reflux ratio of the third distillation column 3 is 7, the column pressure of the third distillation column 3 is 0.8 MpaG, the temperature at the top of the third distillation column 3 is 113°C, and the temperature at the bottom of the third distillation column 3 is 125°C; the number of theoretical plates of the fourth distillation column 4 is 60, the feed reflux ratio of the fourth distillation column 4 is 6, the column pressure of the fourth distillation column 4 is 0.8 MpaG, the temperature at the top of the fourth distillation column 4 is 113°C, and the temperature at the bottom of the fourth distillation column 4 is 125°C; the number of theoretical plates of the fifth distillation column 5 is 60, the reflux ratio of the fifth distillation column 5 is 5, the column pressure of the fifth distillation column 5 is 0.8 MpaG, the temperature at the top of the fifth distillation column 5 is 112°C, and the temperature at the bottom of the fifth distillation column 5 is 124°C.

[0039] The number of theoretical plates of the sixth distillation column 6 is 80, the reflux ratio of the sixth distillation column 6 is 8, the column pressure of the sixth distillation column 6 is 0.5 MpaG, the temperature at the top of the sixth distillation column 6 is 95°C, and the temperature at the bottom of the sixth distillation column 6 is 96°C; the number of theoretical plates of the seventh distillation column 7 is 80, the reflux ratio of the seventh distillation column 7 is 15, the column pressure of the seventh distillation column 7 is 0.5 MpaG, the temperature at the top of the seventh distillation column 7 is 95°C, and the temperature at the bottom of the seventh distillation column 7 is 96°C; the pressure of the deep cooling and filtration unit is 0.5 MpaG, and the temperature of the deep cooling and filtration unit is -160°C.

[0040] The concentration of the high-purity trichlorosilane in the overhead product of the fifth distillation column 5 is >99.9%, and the content of carbon impurities (methylchlorosilanes) is <1 ppm.

[0041] The carbon impurity content of the trichlorosilane raw material is low, and the carbon in the polysilicon produced by the reduction of trichlorosilane reaches the electronic grade level, and can be lower than the electronic super special grade level at the lowest.

[0042] The above are only the preferred embodiments of the present invention, and do not impose any form of limitation on the present invention. Any simple modification or equivalent change made to the above embodiments based on the technical essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A system for removing carbon impurities from chlorosilanes, characterized in that: It includes a first rectification tower (1), and the first rectification tower (1) is connected to a chlorosilane raw material pipe (101), a first silicon tetrachloride outlet pipe (102) and a first connecting pipe (103). The first connecting pipe (103) is connected to a second rectification tower (2). The second rectification tower (2) is connected to a second connecting pipe (104) and a first external discharge pipe (105). The second connecting pipe (104) is connected to a third rectification tower (3). The third rectification tower (3) is connected to a fourth connecting pipe (106) and a fifth connecting pipe (107). The fourth connecting pipe (106) is connected to a fourth rectification tower (4). The fourth rectification tower (4) is connected to a second external discharge pipe (108) and a sixth connecting pipe (109). The sixth connecting pipe (109) is connected to a fifth rectification tower (5). The fifth rectification tower (5) is connected to a product liquid outlet pipe (110) and a seventh connecting pipe (111).

2. The system for removing carbon impurities from chlorosilane according to claim 1, wherein: After the fifth connecting pipe (107) and the seventh connecting pipe (111) are connected and flow into a sixth rectification tower (6), the sixth rectification tower (6) is connected to an eighth connecting pipe (112) and a third external discharge pipe (113). The eighth connecting pipe (112) is connected to a seventh rectification tower (7). The seventh rectification tower (7) is connected to a fourth external discharge pipe (114) and a ninth connecting pipe (115). The ninth connecting pipe (115) is connected to a cryogenic filtration unit (8). The cryogenic filtration unit (8) is connected to a tenth connecting pipe (116) and a fifth external discharge pipe (117). The tenth connecting pipe (116) is connected to a heat exchanger (9). The heat exchanger (9) is connected to a sixth external discharge pipe (118). The third external discharge pipe (113), the fourth external discharge pipe (114) and the sixth external discharge pipe (118) are all connected to a chlorosilane raw material tank (10).

3. The system for removing carbon impurities from chlorosilane according to claim 2, characterized in that: The first silicon tetrachloride outlet pipe (102) is connected to a silicon tetrachloride raw material system (11).

4. A system for removing carbon impurities from chlorosilane according to claim 2, characterized in that: The first external discharge pipe (105) is connected to a dichlorosilane treatment unit (12).

5. The system for removing carbon impurities from chlorosilane according to claim 2, characterized in that: The second external discharge pipe (108) is connected to a light component treatment unit (13).

6. The system for removing carbon impurities from chlorosilane according to claim 2, characterized in that: The fifth external discharge pipe (117) is connected to a methylchlorosilane treatment unit (14).

7. A system for removing carbon impurities from chlorosilane according to claim 2, characterized in that: The cryogenic filtration unit (8) adopts a low-temperature freezing device.

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