Method and device for removing metal byproducts in polycrystalline silicon slurry

Abstract

The invention relates to the field of polycrystalline silicon production, and discloses a method and a device for removing metal byproducts in polycrystalline silicon slurry. According to the method, in the presence of the organic reagent and the nitrogen-containing heterocyclic ring salt, the polycrystalline silicon slag slurry is subjected to flash evaporation treatment, meanwhile, gasified chlorosilane is controlled to account for 15-50 wt% of all chlorosilane in the polycrystalline silicon slag slurry, and the generated low-melting-point mixture is combined, so that metal by-products in the polycrystalline silicon slag slurry can be efficiently removed.

Description

Technical Field

[0001] The present invention relates to the field of polysilicon production, and particularly to a method and device for removing metal by-products from polysilicon slurry. Background Art

[0002] In the process of producing polysilicon by the improved Siemens method, a large amount of chlorosilane by-product slurry will inevitably be generated in the processes from silicon tetrachloride cold hydrogenation (trichlorosilane synthesis), trichlorosilane rectification and purification, reduction to reduction furnace tail gas recovery. The main components of polysilicon slurry are silicon powder (Si), silicon dioxide (SiO 2 ), trichlorosilane, silicon tetrachloride, hydrogen chloride and a small amount of high-boiling substances, etc. Among them, solid substances such as silicon dioxide and silicon powder are mainly generated due to side reactions in the silicon tetrachloride cold hydrogenation process, leakage in the process system, and incomplete deposition of silicon powder in the reduction furnace.

[0003] The mass proportion of liquid chlorosilanes (mainly including SiCl 4 , SiHCl 3 and a small amount of high-boiling substances) in polysilicon slurry reaches more than 80%. These substances are pollutants with strong toxicity and danger, and are extremely likely to react with water to generate flammable, explosive and toxic corrosive gas HCl. Therefore, the slurry must be reasonably treated. The metal by-products in chlorosilane slurry are mainly calcium chloride, ferric chloride and aluminum trichloride, and there are also a small amount of titanium salts, and they gradually accumulate in the slurry with the trichlorosilane synthesis and cold hydrogenation reactions. On the one hand, it will cause blockage of pipelines during the whole process, and on the other hand, it will also affect the catalytic activity of subsequent high-boiling treatment, and the presence of metal impurities will reduce the quality of polysilicon products.

[0004] At present, for the field of removing metal by-products from polysilicon slurry, relatively mature processes include: adding complexing agents, such as EDTA, alkali metal chlorides, etc., to form a mixed system of non-volatile aluminum compounds with aluminum-containing impurities, and then separating the remaining components of the slurry from this mixed system by distillation, so as to remove aluminum chloride impurities; by cooling, settling and crystallizing, aluminum trichloride exists in a stable solid form, and then filtering is used to achieve the purpose of removing aluminum; there is also a method of using organic complexing agents to complex and remove aluminum chloride, including additives containing groups such as N-, S- and -OH, to achieve the purification of chlorosilanes.

[0005] For example, Patent CN113149017A discloses a method for preparing chloroethylsilane from polysilicon by-products. First, high-boiling substances are crystallized at low temperature, and the crystallized substances are separated by filtration. Then, an auxiliary agent is added to the high-boiling substances from which the crystallized substances have been separated, and a metal aluminum complex is formed after heating. Finally, chloroethylsilane without aluminum trichloride is obtained by distillation. This method can effectively remove aluminum trichloride from high-boiling substances, but the aluminum removal process is relatively long. The crystallized substances formed require a precision filter with a filtration accuracy of 0.1-10 microns during filtration separation, which increases production costs. At the same time, the filter is prone to blockage, and frequent blockage cleaning causes unstable production. For another example, Patent CN101925532A discloses a method for removing aluminum and other metal chlorides from chlorosilane. In this method, a seed source is introduced into liquid chlorosilane, and aluminum trichloride crystallizes on the seeds in liquid chlorosilane through stirring to form solid slag, and then filtration separation is carried out. Patent CN108658082A discloses a method for removing aluminum trichloride from high-boiling substances. In this method, cooling crystallization is used to send high-boiling substances to a cooling and stirring tank, and after stirring at low temperature for 1-5 hours, it is sent to a normal-temperature sedimentation tank, and then the high-boiling substances are sedimented in a nitrogen environment for 1-20 hours to separate out a slurry including solid impurities and metal halides. However, this method has a long treatment process and the effect of removing aluminum chloride is not ideal.

[0006] Based on this, in the existing process of removing metals from polysilicon slurry, there are problems such as high energy consumption, complicated treatment steps, heavy treatment load, large loss of chlorosilane, and general effect of removing metal impurities. There is an urgent need to provide a method and device for simply, low-energy-consuming and efficiently removing metal impurities from the slurry. Summary of the Invention

[0007] The purpose of the present invention is to overcome the problems existing in the existing process of removing metals from polysilicon slurry, such as high energy consumption, complicated treatment steps, heavy treatment load, large loss of chlorosilane, and general effect of removing metal impurities, and to provide a device and method for removing metal by-products from polysilicon slurry. This method is simple to operate, low in energy consumption and can efficiently remove metal by-products from the slurry.

[0008] To achieve the above purpose, on the one hand, the present invention provides a method for removing metal by-products from polysilicon slurry, which includes:

[0009] Flash evaporation treatment is carried out on the polysilicon slurry in the presence of an organic reagent and a nitrogen-containing heterocyclic salt; the flash evaporation treatment includes: controlling the vaporized chlorosilane to account for 15-50 wt% of all the chlorosilane in the polysilicon slurry;

[0010] Wherein, the organic reagent is selected from at least one of choline chloride, urea, ethylene glycol, glycerol, acetamide, thiourea, N-methylimidazole, 1,3-dimethylurea and phenol, and the molar ratio of the amount of the organic reagent to the nitrogen-containing heterocyclic salt is 1:0.1-2.

[0011] In a second aspect of the present invention, there is provided an apparatus for removing metal by-products from polysilicon slurry, the apparatus comprising: an adiabatic flash tank (1), a normal temperature settling tank (2), a dryer (3), a dryer heat exchanger (5) and a buffer tank (6) connected in sequence through a first pipeline;

[0012] Moreover, the top of the adiabatic flash tank (1) is connected to the flash heat exchanger (4) and the buffer tank (6) in sequence through a second pipeline, so that 15-50 wt% of the chlorosilane in the polysilicon slurry is separated from the remaining polysilicon slurry after being flash-vaporized by the flash heat exchanger (4).

[0013] In a third aspect of the present invention, there is provided a method for removing metal by-products from polysilicon slurry by using the apparatus described in the second aspect of the present invention, wherein the method comprises the following steps:

[0014] (1-1): Placing the polysilicon slurry, an organic reagent and a nitrogen-containing heterocyclic salt into the adiabatic flash tank for flash treatment to obtain a first gas-phase product and the remaining polysilicon slurry;

[0015] (1-2): The first gas-phase product completes heat exchange in the flash heat exchanger through the second pipeline, and then flows into the buffer tank for separation from the remaining polysilicon slurry;

[0016] (2-1): The remaining polysilicon slurry flows into the normal temperature settling tank through the first pipeline for static phase separation treatment, and then a stratification reaction occurs; wherein, the upper layer is chlorosilane and the lower layer is a low melting point mixture;

[0017] (2-2): The upper-layer chlorosilane flows into the buffer tank through the third pipeline for separation from the lower-layer low melting point mixture; the lower-layer low melting point mixture flows into the dryer through the first pipeline for drying treatment to generate a second gas-phase product and a paste;

[0018] The second gas-phase product enters the dryer heat exchanger for heat exchange, and then flows into the buffer tank for separation from the paste; the paste is discharged through the fourth pipeline.

[0019] Through the above technical solutions, in the presence of an organic reagent and a nitrogen-containing heterocyclic salt, the polysilicon slurry is subjected to flash treatment, and at the same time, the vaporized chlorosilane is controlled to account for 15-50 wt% of all the chlorosilane in the polysilicon slurry. Combining with the generated low melting point mixture, the metal by-products in the polysilicon slurry can be efficiently removed. Description of the Drawings

[0020] Figure 1 It is an apparatus for removing metal by-products from polysilicon slurry in the specific embodiments and examples.

[0022] 1 Adiabatic flash tank; 2 Normal temperature sedimentation tank; 3 Dryer; 4 Flash heat exchanger; 5 Dryer heat exchanger; 6 Buffer tank; 7 Slurry feed inlet; 8 Reagent feed inlet. Specific embodiments

[0023] In the ranges disclosed herein, the endpoints and any values are not limited to the exact ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0024] On the one hand, the present invention provides a method for removing metal by-products from polysilicon slurry, and the method includes:

[0025] Under the presence of an organic reagent and a nitrogen-containing heterocyclic salt, subjecting the polysilicon slurry to flash treatment; the flash treatment includes: controlling the vaporized chlorosilane to account for 15-50 wt% of all the chlorosilanes in the polysilicon slurry;

[0026] Wherein, the organic reagent is selected from at least one of choline chloride, urea, ethylene glycol, glycerol, acetamide, thiourea, N-methylimidazole, 1,3-dimethylurea, and phenol, and the molar ratio of the amount of the organic reagent to the nitrogen-containing heterocyclic salt is 1:0.1-2.

[0027] According to the present invention, in order to improve the efficiency of removing metal by-products from polysilicon slurry, preferably, the flash treatment includes: controlling the vaporized chlorosilane to account for 20-40 wt% of the chlorosilanes in the polysilicon slurry, for example, it can be values such as 20 wt%, 28 wt%, 30 wt%, 32 wt%, 34 wt%, 40 wt% and the ranges between any of these values.

[0028] In the present invention, in order to improve the cooperative effect of the organic reagent and the nitrogen-containing heterocyclic salt, preferably, the molar ratio of the amount of the organic reagent to the nitrogen-containing heterocyclic salt is 1:0.4-1. For example, it can be values such as 1:0.4, 1:0.6, 1:0.8, 1:1 and the ranges between any of these values.

[0029] According to the present invention, in order to further improve the coordination effect between the organic reagent and the nitrogen-containing heterocyclic salt, preferably, the nitrogen-containing heterocyclic salt is a nitrogen-containing heterocyclic hydrochloride. More preferably, the nitrogen-containing heterocycle in the nitrogen-containing heterocyclic hydrochloride is selected from at least one of imidazole, pyridine, morpholine, benzimidazole, 1,8-diazabicyclooctane, and 1,5-diazabicycloheptane. For example, the nitrogen-containing heterocyclic hydrochloride may be selected from at least one of 1,8-diazabicyclooctane hydrochloride, 1,5-diazabicycloheptane hydrochloride, and 1-ethylpyridine hydrochloride.

[0030] According to the present invention, in order to efficiently remove metal by-products in the polysilicon slurry, preferably, the organic reagent is selected from at least two of choline chloride, urea, ethylene glycol, glycerol, acetamide, thiourea, N-methylimidazole, 1,3-dimethylurea, and phenol.

[0031] According to a preferred embodiment, the organic reagent is selected from N-methylimidazole and 1,3-dimethylurea. More preferably, the molar ratio of the amounts of N-methylimidazole and 1,3-dimethylurea used is 1:0.5 - 3.0, more preferably 1:1 - 2.

[0032] According to another preferred embodiment, the organic reagent is selected from choline chloride and 1,3-dimethylurea; the molar ratio of the amounts of choline chloride and 1,3-dimethylurea used is preferably 1:0.5 - 3.0, more preferably 1:1 - 2.

[0033] According to the present invention, preferably, based on the mass of the polysilicon slurry used, the total mass of the organic reagent and the nitrogen-containing heterocyclic salt used is 0.1 - 3 wt%, preferably 0.5 - 2 wt%, and for example, it can be values such as 0.5 wt%, 0.9 wt%, 1 wt%, 1.2 wt%, 1.5 wt%, 1.9 wt%, 2.0 wt%, etc. and the ranges between any of these values.

[0034] In the present invention, preferably, the conditions of the flash evaporation treatment include: a pressure of 0.05 - 1.2 MPa, a temperature of 60 - 110 °C, and a time of 1 - 6 h. More preferably, the conditions of the flash evaporation treatment include: a pressure of 0.1 - 1.0 MPa, a temperature of 70 - 100 °C, and a time of 2 - 4 h.

[0035] According to a preferred embodiment, the method further includes: sequentially performing static phase separation treatment and drying treatment on the remaining polysilicon slurry after the flash evaporation treatment.

[0036] In the present invention, preferably, the conditions for the static phase separation treatment include: a temperature of -20 to 40 °C and a time of 3 - 10 h. When the polysilicon slurry is in a low-temperature environment, the effect of static phase separation is more excellent. More preferably, the conditions for the static phase separation treatment include: a temperature of -20 to 10 °C and a time of 5 - 8 h.

[0037] In the present invention, preferably, the conditions for the drying treatment include: a temperature of 45 - 95 °C and a time of 3 - 8 h. More preferably, the conditions for the drying treatment include: a temperature of 60 - 80 °C and a time of 4 - 7 h.

[0038] In the present invention, preferably, the content of chlorosilane in the polysilicon slurry is 87 - 98 wt%, preferably 92 - 97 wt%; the polysilicon slurry may further include 0.1 - 5.0 wt% of silicon powder and 0.02 - 0.3 wt% of metal chloride, preferably 0.3 - 3.0 wt% of silicon powder and 0.03 - 0.25 wt% of metal chloride. The metal chloride may include one or more of aluminum chloride, iron chloride, calcium chloride, and titanium chloride.

[0039] In the present invention, preferably, the chlorosilane contains 78 - 90 wt% of silicon tetrachloride, 8 - 16 wt% of trichlorosilane, 1 - 3 wt% of dichlorosilane, and the balance is 1 - 5 wt% of high-boiling substances. More preferably, the chlorosilane contains 85 - 88 wt% of silicon tetrachloride, 10 - 12 wt% of trichlorosilane, 1.2 - 2 wt% of dichlorosilane, and the balance is 1 - 3 wt% of high-boiling substances.

[0040] The second aspect of the present invention provides a device for removing metal by-products from a polysilicon slurry, which includes: an adiabatic flash tank 1, a normal-temperature settling tank 2, a dryer 3, a dryer heat exchanger 5, and a buffer tank 6 connected in sequence through a first pipeline;

[0041] Moreover, the top of the adiabatic flash tank 1 is connected to the flash heat exchanger 4 and the buffer tank 6 in sequence through a second pipeline, so that 15 - 50 wt% of the chlorosilane in the polysilicon slurry is separated from the remaining polysilicon slurry after being flash-vaporized by the flash heat exchanger 4.

[0042] In the present invention, preferably, the normal-temperature settling tank 2 and the buffer tank 6 are connected through a third pipeline, so that the upper-layer chlorosilane statically phase-separated in the normal-temperature settling tank 2 is separated from the lower-layer low-melting-point mixture;

[0043] Another fourth pipeline is provided downstream of the dryer 3, so that the remaining paste after being dried by the dryer 3 is discharged through the fourth pipeline.

[0044] According to a preferred embodiment, a slurry feed port 7 and a reagent feed port 8 with valve devices are provided at the lower part of the outer wall of the adiabatic flash tank 1.

[0045] The present invention provides a device for removing metal by-products from polysilicon slurry as shown in Figure 1 wherein the polysilicon slurry enters the adiabatic flash tank 1 from the slurry feed port 7, and the organic reagent and the nitrogen-containing heterocyclic salt enter the adiabatic flash tank 1 from the reagent feed port 8.

[0046] In the adiabatic flash tank 1, part of the chlorosilane in the polysilicon slurry is vaporized and then enters the flash heat exchanger 4 through the second pipeline for heat exchange, and finally flows into the buffer tank 6. At the same time, metal by-products such as aluminum chloride, iron chloride and calcium chloride in the polysilicon slurry can react with the organic reagent and the nitrogen-containing heterocyclic salt to form a low-melting-point mixture. This low-melting-point mixture actually refers to a solvent system with a reduced melting point after mixing, which is partially formed by complexation caused by electron migration or attraction, and covalent and hydrogen bond interactions between molecules. This mixture often has a high viscosity and density, so it can wrap the silicon powder in the chlorosilane and be distinguished from the remaining chlorosilane in the polysilicon slag liquid.

[0047] In the adiabatic flash tank 1, the remaining polysilicon slag liquid enters the normal-temperature settling tank 2 through the first pipeline for static phase separation treatment. The low-melting-point mixture can settle at the bottom of the normal-temperature settling tank, causing the polysilicon slag liquid to be separated into upper and lower layers (wherein the upper layer is chlorosilane and the lower layer is the low-melting-point mixture).

[0048] The upper-layer chlorosilane exits from the sidewall opening of the normal-temperature settling tank 2, and then is separated from the lower-layer low-melting-point mixture. Then the chlorosilane flows into the buffer tank 6 through the third pipeline. The lower-layer low-melting-point mixture flows into the dryer 3 through the first pipeline for drying treatment to generate a second gas-phase product and a paste. Then, the second gas-phase product enters the dryer heat exchanger 5 for heat exchange and finally flows into the buffer tank 6. The paste is discharged through the fourth pipeline for hydrolysis treatment. This paste is mainly the low-melting-point mixture adhering with silicon powder.

[0049] In the present invention, the first gas-phase product and the second gas-phase product mainly include vaporized chlorosilane and a small amount of metal by-products.

[0050] The third aspect of the present invention provides a method for removing metal by-products from polysilicon slurry by using the device described in the second aspect of the present invention, wherein the method includes the following steps:

[0051] (1-1): After placing the polysilicon slurry, the organic reagent and the nitrogen-containing heterocyclic salt into the adiabatic flash tank (1) for flash treatment, a first gas-phase product and the remaining polysilicon slurry are obtained;

[0052] (1-2): The first gaseous product exchanges heat in the flash heat exchanger 4 through the second pipeline, and then flows into the buffer tank 6 for separation from the remaining polysilicon slurry;

[0053] (2-1): The remaining polysilicon slurry flows into the normal-temperature sedimentation tank 2 through the first pipeline for static phase separation treatment, and then a layering reaction occurs; among them, the upper layer is chlorosilane and the lower layer is a low-melting-point mixture;

[0054] (2-2): The upper-layer chlorosilane flows into the buffer tank 6 through the third pipeline for separation from the lower-layer low-melting-point mixture; the lower-layer low-melting-point mixture flows into the dryer 3 through the first pipeline for drying treatment to generate a second gaseous product and a slurry;

[0055] The second gaseous product exchanges heat in the dryer heat exchanger 5 and then flows into the buffer tank 6 for separation from the slurry; the slurry is discharged through the fourth pipeline.

[0056] According to the present invention, by using the method for removing metal by-products from polysilicon slurry, the metal by-products in the polysilicon slurry can be efficiently removed. According to some preferred embodiments, the total removal rate of the metal by-products is not less than 90%.

[0057] The present invention will be described in detail below through examples.

[0058] In the following examples, the metal content in the metal by-products was measured by the method described in Section 5.5 of "Industrial Silicon Tetrachloride (HG / T 5745-2020)": Determination Method of Iron, Aluminum, Chromium, Titanium, Copper, Manganese, Nickel, Boron, and Phosphorus Contents;

[0059] Metal by-product removal rate = 1 - (metal content in the material after removing metal by-products / metal content in the material before removing metal by-products) × 100% = 1 - (metal content before feeding the polysilicon slurry / metal content in the buffer tank) × 100%.

[0060] Preparation Example 1

[0061] Preparation Example 1 is used to illustrate the specific composition of polysilicon slurries A1 - A2, as shown in Tables 1 and 2:

[0062] Table 1 Composition and Content of Polysilicon Slurry

[0063] Preparation Example 1 Chlorosilane content / wt% Silicon powder content / wt% Metal chloride / wt% Polysilicon slurry A1 96.80 2.95 0.25 Polysilicon slurry A2 97.00 2.80 0.20

[0064] Table 2 Composition and Content of Chlorosilane in Polysilicon Slurry

[0065]

[0066] Preparation Example 2

[0067] Preparation Example 2 is used to illustrate the specific compositions of Reagents B1 - B8 and C1 - C2, which refer to organic reagents and nitrogen - containing heterocyclic salts, as shown in Table 3 specifically:

[0068] Table 3 Composition and Dosage Table of Organic Reagents and Nitrogen - containing Heterocyclic Salts

[0069]

[0070] Example 1

[0071] The example is used to illustrate the method for removing metal by - products from polysilicon slurry, including: using the device as shown in Figure 1 and proceeding according to the following steps:

[0072] (1 - 1): Put 500 g of polysilicon slurry A1 and 4.98 g of Reagent B1 into the adiabatic flash tank 1 for flash treatment, and then obtain the first gas - phase product and the remaining polysilicon slurry; among them, control the conditions of the flash treatment as pressure 0.15 MPa, temperature 80.0 °C, and time 3 h, so that the vaporized chlorosilane accounts for 30 wt% of all the chlorosilanes in the polysilicon slurry;

[0073] (1 - 2): The first gas - phase product completes heat exchange in the flash heat exchanger 4 through the second pipeline, and then flows into the buffer tank 6 for separation from the remaining polysilicon slurry;

[0074] (2 - 1): The remaining polysilicon slurry flows into the normal - temperature settling tank 2 through the first pipeline and is statically separated at 5 °C for 6 h, so that the remaining polysilicon slurry is phase - separated. After phase - separation, the upper layer is chlorosilane and the lower layer is a low - melting - point mixture;

[0075] (2 - 2): The upper - layer chlorosilane flows into the buffer tank 6 through the third pipeline for separation from the lower - layer low - melting - point mixture; the lower - layer low - melting - point mixture flows into the dryer 3 through the first pipeline and is dried at 65 °C for 5 h, and then a second gas - phase product and a paste are generated;

[0076] The second gas - phase product enters the dryer heat exchanger 5 for heat exchange and then flows into the buffer tank 6 for separation from the paste; the paste is discharged through the fourth pipeline.

[0077] Example 2

[0078] (1 - 1): Put 500 g of polysilicon slurry A2 and 4.98 g of Reagent B2 into the adiabatic flash tank 1 for flash treatment, and then obtain the first gas - phase product and the remaining polysilicon slurry; among them, control the conditions of the flash treatment as pressure 0.14 MPa, temperature 80 °C, and time 3.5 h, so that the vaporized chlorosilane accounts for 35 wt% of all the chlorosilanes in the polysilicon slurry;

[0079] (1-2): The first gaseous product exchanges heat in the flash heat exchanger 4 through the second pipeline, and then flows into the buffer tank 6 for separation from the remaining polysilicon slurry;

[0080] (2-1): The remaining polysilicon slurry flows into the normal-temperature settling tank 2 through the first pipeline, and is allowed to stand for phase separation treatment at 10°C for 6.5 h, so that the remaining polysilicon slurry undergoes phase separation. After phase separation, the upper layer is chlorosilane and the lower layer is a low-melting-point mixture;

[0081] (2-2): The upper-layer chlorosilane flows into the buffer tank 6 through the third pipeline for separation from the lower-layer low-melting-point mixture; the lower-layer low-melting-point mixture flows into the dryer 3 through the first pipeline and is dried at 75°C for 4.5 h, and then a second gaseous product and a slurry are generated;

[0082] The second gaseous product exchanges heat in the dryer heat exchanger 5 and then flows into the buffer tank 6 for separation from the slurry; the slurry is discharged through the fourth pipeline.

[0083] Example 3

[0084] A method similar to that of Example 1 is adopted, except that reagent B3 in the same weight part is used to replace reagent B1.

[0085] Example 4

[0086] A method similar to that of Example 1 is adopted, except that reagent B4 in the same weight part is used to replace reagent B1.

[0087] Example 5

[0088] A method similar to that of Example 1 is adopted, except that reagent B5 in the same weight part is used to replace reagent B1.

[0089] Example 6

[0090] A method similar to that of Example 1 is adopted, except that reagent B6 in the same weight part is used to replace reagent B1.

[0091] Example 7

[0092] A method similar to that of Example 1 is adopted, except that reagent B7 in the same weight part is used to replace reagent B1.

[0093] Example 8

[0094] A method similar to that of Example 1 is adopted, except that reagent B8 in the same weight part is used to replace reagent B1.

[0095] Example 9

[0096] A method similar to that of Example 1 was adopted, except that in step (1-1): the conditions of the flash treatment were controlled as a pressure of 0.15 MPa, a temperature of 75 °C, and a time of 2.5 h, such that the vaporized chlorosilane accounted for 20 wt% of all the chlorosilanes in the polysilicon slurry, and the remaining steps were the same as those in Example 1.

[0097] Example 10

[0098] A method similar to that of Example 1 was adopted, except that in step (1-1): the conditions of the flash treatment were controlled as a pressure of 0.13 MPa, a temperature of 85 °C, and a time of 3.5 h, such that the vaporized chlorosilane accounted for 40 wt% of all the chlorosilanes in the polysilicon slurry, and the remaining steps were the same as those in Example 1.

[0099] Comparative Example 1

[0100] A method similar to that of Example 1 was adopted, except that reagent C1 in the same weight portion was used to replace reagent B1.

[0101] Comparative Example 2

[0102] A method similar to that of Example 1 was adopted, except that reagent C2 in the same weight portion was used to replace reagent B1.

[0103] Comparative Example 3

[0104] A method similar to that of Example 1 was adopted, except that in step (1-1): the conditions of the flash treatment were controlled as a pressure of 0.17 MPa, a temperature of 75 °C, and a time of 0.5 h, such that the vaporized chlorosilane accounted for 10 wt% of all the chlorosilanes in the polysilicon slurry, and then a static phase separation treatment was carried out at room temperature for 12 h, and the remaining steps were the same as those in Example 1.

[0105] Comparative Example 4

[0106] A method similar to that of Example 1 was adopted, except that in step (1-1): the conditions of the flash treatment were controlled as a pressure of 0.13 MPa, a temperature of 85 °C, and a time of 8 h, such that the vaporized chlorosilane accounted for 70 wt% of all the chlorosilanes in the polysilicon slurry, and the remaining steps were the same as those in Example 1.

[0107] The metal content before feeding and the metal content in the buffer tank of the test examples and comparative examples were tested, and the removal rate of metal by-products was calculated, as specifically shown in Table 4.

[0108] Table 4 List of removal rates of metal by-products

[0109]

[0110] As can be seen from the results in Table 1, compared with Comparative Examples 1-4, the method for removing metal by-products from polysilicon slurry in Examples 1-10 of the present invention has a relatively high removal rate of metal by-products. In particular, the total removal rate of metal by-products in Examples 1-6 and 9-10 is not less than 90%.

[0111] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. A method for removing metal byproducts from polysilicon slurry, characterized in that: The method includes: In the presence of an organic reagent and a nitrogen-containing heterocyclic salt, the polycrystalline silicon slurry is flash-evaporated; the flash-evaporation treatment comprises: controlling the gasified chlorosilane to account for 15-50wt% of all the chlorosilane in the polycrystalline silicon slurry; The organic reagent is selected from at least one of choline chloride, urea, ethylene glycol, glycerol, acetamide, thiourea, N-methylimidazole, 1,3-dimethylurea and phenol, and the molar ratio of the organic reagent to the nitrogen-containing heterocyclic salt is 1:0.1-2.

2. The method according to claim 1, wherein: The flash treatment comprises: controlling the gasified chlorosilane to account for 20-40 wt % of the chlorosilane in the polycrystalline silicon slurry.

3. The method according to claim 1 or 2, wherein: The molar ratio of the organic reagent to the nitrogen-containing heterocyclic salt is 1:0.4-1; Preferably, the nitrogen-containing heterocyclic salt is a nitrogen-containing heterocyclic hydrochloride; More preferably, the nitrogen-containing heterocycle in the nitrogen-containing heterocycle hydrochloride is at least one selected from imidazole, pyridine, morpholine, benzimidazole, 1,8-diazabicyclooctane and 1,5-diazabicycloheptane.

4. The method according to any one of claims 1 to 3, wherein: The organic reagent is selected from at least two of choline chloride, urea, ethylene glycol, glycerol, acetamide, thiourea, N-methylimidazole, 1,3-dimethylurea and phenol; Preferably, the organic reagent is selected from N-methylimidazole and 1,3-dimethylurea; the molar ratio of the N-methylimidazole to 1,3-dimethylurea is preferably 1:0.5-3.0, more preferably 1:1-2; And / or, the organic reagent is selected from choline chloride and 1,3-dimethylurea; the molar ratio of choline chloride to 1,3-dimethylurea is preferably 1:0.5-3.0, more preferably 1:1-2.

5. The method according to any one of claims 1 to 4, wherein: The flash treatment conditions include: pressure of 0.05-1.2 MPa, temperature of 60-110° C., and time of 1-6 h; Preferably, the flash treatment conditions include: pressure of 0.1-1.0 MPa, temperature of 70-100° C., and time of 2-4 h.

6. The method according to any one of claims 1 to 5, wherein: The method further comprises: sequentially performing a standing phase separation treatment and a drying treatment on the polysilicon slurry remaining after the flash evaporation treatment; Preferably, the conditions for the static phase separation treatment include: temperature of -20°C to 40°C, time of 3-10h; Preferably, the drying conditions include: temperature of 45-95° C. and time of 3-8 h.

7. The method according to any one of claims 1 to 5, wherein: The content of chlorosilane in the polysilicon slurry is 87-98wt%, preferably 92-97wt%; Preferably, the chlorosilane contains 78-90 wt% of silicon tetrachloride, 8-14 wt% of trichlorosilane, 1-3 wt% of dichlorosilane, and the remainder is 1-5 wt% of high boiling substances.

8. A device for removing metal byproducts from polysilicon slurry, characterized in that: The device comprises: an adiabatic flash tank (1), a normal temperature settling tank (2), a dryer (3), a dryer heat exchanger (5) and a buffer tank (6) which are sequentially connected via a first pipeline; Furthermore, the top of the adiabatic flash tank (1) is connected to the flash heat exchanger (4) and the buffer tank (6) in sequence through a second pipeline, so that 15-50wt% of the chlorosilane in the polycrystalline silicon slurry can be separated from the remaining polycrystalline silicon slurry after being flash vaporized in the flash heat exchanger (4).

9. The device according to claim 8, wherein: The normal temperature settling tank (2) and the buffer tank (6) are connected via a third pipeline, so that the upper layer of chlorosilane and the lower layer of low melting point mixture separated by static phase separation in the normal temperature settling tank (2) can be separated; A fourth pipeline is further provided downstream of the dryer (3) so that the slurry remaining after drying by the dryer (3) can be discharged externally through the fourth pipeline.

10. The device according to claim 8 or 9, wherein: The lower part of the outer wall of the thermal insulation flash tank (1) is provided with a slurry feed inlet (7) and a reagent feed inlet (8) with a valve device.

11. A method for removing metal byproducts from polysilicon slurry using the device according to any one of claims 8 to 10, wherein: The method comprises the following steps: (1-1): placing polycrystalline silicon slurry, organic reagent and nitrogen-containing heterocyclic salt into the adiabatic flash tank (1) for flash treatment to obtain a first gas phase product and remaining polycrystalline silicon slurry; (1-2): The first gas phase product completes heat exchange in the flash heat exchanger (4) through the second pipeline, and then flows into the buffer tank (6) to be separated from the remaining polysilicon slurry; (2-1): The remaining polysilicon slurry flows into the normal temperature settling tank (2) through the first pipeline for static phase separation treatment, and a stratification reaction occurs; wherein the upper layer is chlorosilane and the lower layer is a low melting point mixture; (2-2): the upper layer of chlorosilane flows into the buffer tank (6) through the third pipeline to be separated from the lower layer of low melting point mixture; the lower layer of low melting point mixture flows into the dryer (3) through the first pipeline to be dried to generate a second gas phase product and a slurry; The second gas phase product enters the dryer heat exchanger (5) for heat exchange, and then flows into the buffer tank (6) to be separated from the slurry; the slurry is discharged through a fourth pipeline.

Images