Method for producing chlorosilanes

Abstract

In order to prevent scale from depositing on the inner wall of an upstream portion of a heat exchanger provided in a transport path for transporting a reaction gas to a distillation column when preparing chlorosilanes by chlorination reaction of metal silicon, the present invention enables stable preparation of chlorosilanes, metal silicon is used in which the zirconium content (Zr%) is 35 mass ppm or less in terms of element, and the mass ratio (Ti% / Zr%) of the titanium content (Ti%) to the zirconium content (Zr%) is 8.0 or more.

Description

Technical Field

[0001] This invention relates to a novel method for preparing chlorosilanes. More specifically, it provides a method for the stable preparation of chlorosilanes via the chlorination reaction of metallic silicon. Background Technology

[0002] The chlorosilanes used in the preparation of high-purity polycrystalline silicon, exemplified by the Siemens process, are obtained by purifying chlorosilanes derived from the chlorination reaction of metallic silicon. For example, a common method is to feed metallic silicon powder and hydrogen chloride into a fluidized bed in a reactor to prepare trichlorosilane through the chlorination reaction of metallic silicon. Another known method is to feed metallic silicon powder, tetrachlorosilane, and, if necessary, hydrogen gas into a fluidized bed to prepare trichlorosilane through the chlorination reaction of metallic silicon.

[0003] The reaction can be represented by the following formula. It is known that at a reaction temperature of 300~360℃, the reactions of the following formula (1) and (2) occur, while at 500~550℃, the reaction of the following formula (3) occurs.

[0004] [Chemistry 1] Si + 3HCl → SiHCl3 + H2 (1) Si + 4HCl → SiCl4 + 2H2 (2) Si +3SiCl4+2H2→4SiHCl3 (3) The metallic silicon used as a raw material is generally silicon powder with a high degree of purification, known as metallurgical grade. A common method for preparing this metallurgical grade metallic silicon is as follows: a mixture of silicon raw materials, represented by silica, and reducing materials such as charcoal, coke, coal, and sawdust, is filled into an electric arc furnace as a raw material layer and heated at a high temperature of 2000~2500℃ to reduce the silica (see Non-Patent Literature 1).

[0005] Here, the purity of the aforementioned metallurgical-grade silicon is typically about 99% by mass conversion. More specifically, the silicon content is 98.5% to 99.4% by mass conversion, preferably 99.0% to 99.4%, and it is also mixed with metallic impurities such as Fe, Ca, Al, Mn, Ni, Zr, Zn, and Ti (Patent Documents 1 and 2). According to Patent Document 2, for example, the amount of metallic impurities is expressed as follows: iron 2300 to 3600 ppm by mass, aluminum 1400 to 1600 ppm by mass, zirconium less than 10 to 11 ppm by mass, and titanium 0.013 to 0.021 ppm by mass. It is well known that the silicon used in the preparation of such chlorosilanes contains zirconium and titanium, but it is known that titanium is less than zirconium in terms of their content ratio (Tables 1 and 2 of Patent Document 2).

[0006] By using this metallurgical-grade metallic silicon to prepare chlorosilanes, the target chlorosilanes can be obtained with high reactivity. However, in the purification process of the obtained chlorosilanes, the following problem exists: when the reaction solution is distilled, a considerable amount of scale deposits on the inner walls of the distillation column and its downstream tanks, piping, and other devices, causing blockages. However, analysis shows that the scale deposited downstream of the distillation column is mainly aluminum chloride, which is generated by the chlorination of aluminum components in the metal impurities contained in the aforementioned metallurgical-grade metallic silicon during the trichlorosilane formation reaction (paragraph 0005 of Patent Document 3).

[0007] As a measure to address the scale deposits formed by this aluminum chloride, the scale deposited in the distillation tower is extracted from the bottom of the tower. In addition, a solution has been proposed to remove the aluminum chloride by setting up a sodium chloride packed tower in the middle of the transport path of the reaction gas discharged from the chlorination reactor to the distillation tower, so that the aluminum chloride forms a double salt there (Patent Document 4).

[0008] Existing technical documents Patent documents Patent Document 1: Japanese Patent Application Publication No. 2012-534930 Patent Document 2: Japanese Patent Publication No. 2013-535399 Patent Document 3: Japanese Patent Application Publication No. 2013-010648 Patent Document 4: Japanese Patent Application Publication No. 2009-256197 Non-patent literature Non-patent literature 1: Industrial Heating, Vol. 46, No. 3 (2009), pp. 1-11, “Current Status and Issues of Small Electric Arc Furnaces”. Summary of the Invention

[0009] The problem that the invention aims to solve The aforementioned measures to address aluminum chloride deposition effectively alleviated the problem of scale buildup on the inner wall of the downstream distillation tower. However, from the perspective of stable industrial operation, even these measures are not sufficient to suppress scale deposition, especially in the transport path that sends the reaction gases to the distillation tower, where localized scale buildup still occurs, which is unsatisfactory.

[0010] More specifically, a cooling heat exchanger is installed midway through the transport path of the aforementioned reactant gas to the distillation column to liquefy the high-temperature reactant gas. Typically, the high-temperature reactant gas is cooled to 10-40°C and liquefied here. However, at this time, scale deposits locally form on the wall surface of the upstream portion of the heat exchanger where the gas flows in. (Hereinafter, the term "upstream portion of the wall surface of the heat exchanger" refers to the upper wall surface where the gas flows in). In particular, from the viewpoint of good cooling efficiency, when a shell-and-tube heat exchanger is used as the cooling heat exchanger, this scale will accumulate in large quantities on the perforated plate fixed to the inlet end of each cooling pipe within the heat exchanger, causing blockage of the small-diameter openings at the ends of the cooling pipes.

[0011] Based on the above, preventing scale buildup on the inner wall of the upstream section of the heat exchanger, which is installed in the transport path for sending the reaction gas to the distillation column, during the preparation of chlorosilanes via the chlorination reaction of metallic silicon, has become a major research topic, in order to achieve stable preparation of chlorosilanes.

[0012] Methods for solving problems In view of the above problems, the inventors have conducted in-depth research on measures to suppress scale deposition on the inner wall of the upstream portion of the heat exchanger located in the transport path of the aforementioned reactant gases. As a result, it was discovered that the scale deposited at this location has a special composition containing zirconium. Based on this insight, it was found that by using the aforementioned metallic silicon with low contents of zirconium and titanium within a specific range, scale deposition can be significantly suppressed, thus completing the present invention.

[0013] That is, the present invention relates to a method for preparing chlorosilanes, characterized in that, when preparing chlorosilanes by chlorination reaction of metallic silicon, the metallic silicon used is metallic silicon with a zirconium content (Zr%) of 35 ppm or less by mass conversion and a titanium content (Ti%) to zirconium content (Zr%) mass ratio (Ti%) / Zr%) of 8.0 or more.

[0014] The effects of the invention According to the present invention, by using metallic silicon with a zirconium content within a specific range and a titanium-to-zirconium mass ratio within a specific range, scale deposition on the inner wall of the upstream section of the heat exchanger can be significantly reduced when the reaction gas of chlorosilanes generated by their chlorination reaction is conveyed to the distillation column. As a result, the high cooling efficiency of the heat exchanger can be maintained, thereby enabling the stable production of chlorosilanes. Furthermore, when the heat exchanger is a shell-and-tube heat exchanger, blockage of the end openings of the cooling pipes connected to the fixed perforated plate on the reaction gas inflow side can be prevented, thus enabling the stable production of chlorosilanes, which is extremely useful industrially. Attached Figure Description

[0015] Figure 1 This is a representative process diagram of the preparation of chlorosilanes using the method of the present invention. Detailed Implementation

[0016] In the preparation of the chlorosilanes of this invention, any known method for chlorinating metallic silicon can be used, and there are no particular limitations. A fluidized bed reactor is generally used to carry out this chlorination reaction.

[0017] For example, a method for preparing chlorosilanes can be described by feeding the aforementioned metallic silicon and hydrogen chloride into a fluidized bed of a fluidized bed reactor to carry out a chlorination reaction of metallic silicon. Furthermore, in this invention, chlorosilanes include dichlorosilanes, trichlorosilanes, tetrachlorosilanes, etc., and the method for preparing trichlorosilanes is particularly preferred.

[0018] As for the aforementioned hydrogen chloride, various industrially available hydrogen chlorides can be used. Furthermore, regarding the supply of metallic silicon and hydrogen chloride, as long as the ratio is suitable for chlorination and the supply of metallic silicon and hydrogen chloride is at a rate corresponding to the flow rate that can form a fluidized bed, known conditions can be used, and there are no particular restrictions.

[0019] In addition, the reaction temperature can be appropriately determined according to the material and capacity of the reaction apparatus and the catalyst, etc. It is generally set in the range of 200~500℃, and preferably in the range of 250~450℃.

[0020] Furthermore, as another method for preparing chlorosilanes, one could mention a method in which metallic silicon powder, tetrachlorosilane, and hydrogen are fed together with a catalyst, such as copper silicide, into a fluidized bed to carry out the chlorination reaction of metallic silicon.

[0021] In the above method, the supply amounts of metallic silicon, tetrachlorosilane, and hydrogen can be determined under known conditions, without particular limitations, as long as they are in a ratio suitable for chlorination and can be supplied at a rate corresponding to the flow rate that can form a fluidized bed. Furthermore, the reaction temperature can be appropriately determined based on the material and capacity of the reaction apparatus and the catalyst, generally set in the range of 400–700°C, preferably in the range of 450–600°C.

[0022] The metallic silicon used in this invention is preferably metallic silicon of the aforementioned metallurgical grade. Typically, metallic silicon obtained in the following manner is used: a mixture of silicon raw materials, represented by silica, and reducing materials such as charcoal, coke, coal, and sawdust, is filled into an electric arc furnace as a raw material layer and heated at a high temperature of 2000-2500°C to reduce the silica. The reduction process yields relatively large blocks, each weighing approximately 1000-2000 kg. However, for the preparation of chlorosilanes, metallic silicon of a size suitable for the reaction can be used, obtained by pulverizing the silane.

[0023] As described above, the preparation of chlorosilanes is typically carried out in a fluidized bed manner, therefore the aforementioned metallic silicon is required to have a size suitable for flow in the fluidized bed. A metallic silicon with an average particle size of 150-400 μm, particularly 180-300 μm, is preferred. The average particle size of the metallic silicon can be measured according to the method described in the examples. By setting the average particle size of the metallic silicon within the above range, a stable fluidized bed can be obtained, and therefore this is preferred.

[0024] In the method for preparing chlorosilanes of the present invention, the zirconium content (Zr%) in the metallic silicon used as the above-mentioned raw material is low, preferably 35 ppm by mass or less, more preferably 25 ppm by mass or less, and even more preferably 25 ppm by mass or less. Furthermore, the mass ratio (Ti% / Zr%) of the titanium content (Ti%) to the zirconium content (Zr%) in this metallic silicon is 8.0 or more, preferably 9.0 or more, and even more preferably 9.0 or more. By using this metallic silicon with a low zirconium content and a specific high mass ratio of titanium to zirconium as the reaction raw material, scale deposition on the inner wall of the heat exchanger installed in the transport path to the distillation column can be effectively reduced. Additionally, in the method for preparing chlorosilanes of the present invention, the zirconium content (Zr%) in the metallic silicon used as the above-mentioned raw material is preferably 1 ppm by mass or more, more preferably 5 ppm by mass or more, and even more preferably 15 ppm by mass or more. Since the purification process for preparing this metallic silicon with a certain amount of zirconium is relatively simple, it is readily available as a reaction raw material. Furthermore, in this metallic silicon, the mass ratio (Ti %) of titanium content (Ti %) to zirconium content (Zr %) is low, preferably 30.0 or less, more preferably 20.0 or less, and even more preferably 15.0 or less. By using metallic silicon with the aforementioned low mass ratio as a reaction raw material, the titanium impurity content in the liquefaction products of the reaction gas can be reduced.

[0025] That is, according to the inventors' research, the composition of the scale deposited on the inner wall of the upstream section of the heat exchanger in the aforementioned reaction gas transport path is different from the aluminum chloride content of the scale deposited on the inner wall of the downstream device of the distillation column, which is conventionally known. The aluminum content in the scale is only trace (typically less than 0.3% by mass). On the other hand, the scale deposited on the inner wall of the upstream section of the heat exchanger is characterized by a high zirconium content, reaching 30-40% by mass, which is a unique component. Therefore, by using metallic silicon with the lowest possible zirconium content, the amount of scale deposited on the inner wall of the upstream section of the heat exchanger can be effectively reduced to a certain extent.

[0026] However, even so, there is an inherent limit to the reduction of zirconium content in the aforementioned metallic silicon. In fact, even when using commercially available metallic silicon with the lowest zirconium content as the reaction raw material, the suppression of scale deposition on the inner wall of the upstream section of the heat exchanger is still unsatisfactory. In this case, if the aforementioned metallic silicon not only satisfies the requirement of a low zirconium content as described above, but also satisfies the requirement of a high titanium content within a specific range compared to the zirconium content, then an excellent effect of significantly improving the suppression of scale deposition on the inner wall of the heat exchanger can be obtained.

[0027] The reason is not entirely clear, but the inventors speculate that it may be due to the following effect: Regarding the metallic impurities contained in metallic silicon, including the aforementioned aluminum, zirconium, and even titanium, in most metal types, these metal types are chlorinated to form chlorides during the formation reaction of chlorosilanes such as trichlorosilanes. Then, in these metal chlorides, the main component of the aforementioned metallic impurities, namely aluminum chloride (aluminum chloride), has a melting point of 192°C. Although this is a fairly high melting point, it is significantly lower than the high reaction temperature of the chlorination reaction of metallic silicon that forms the aforementioned chlorosilanes. Therefore, if it is aluminum chloride, its deposition is suppressed to a state that is not too active in the upstream part of the heat exchanger in the middle of the transport path leading to the aforementioned distillation column into which the high-temperature reaction gas generated in this chlorination reaction flows. On the other hand, since the melting point of the zirconium chloride (zirconium tetrachloride) exceeds 400°C, it can be assumed that it has solidified in the reaction gas that has flowed into the upstream part of the heat exchanger. Furthermore, in the early stage of cooling, due to exposure to the environment of decreasing temperature, this substance will selectively adhere to the inner wall surface of the upstream part of the heat exchanger and form scale.

[0028] In this case, when the metallic silicon contains the aforementioned specific amount of titanium, the titanium chloride (titanium tetrachloride) has a melting point as low as -25°C and a boiling point as low as 136.4°C. Therefore, it can be assumed that it will be liquefied in the upstream section of the aforementioned heat exchanger, which is used to cool the aforementioned high-temperature reaction gases to 10~40°C and liquefy them. Thus, the liquid titanium chloride has good affinity with the aforementioned solid zirconium chloride, effectively reducing its adhesion to the inner wall of the device. As a result, it can be presumed that it has a significant effect on inhibiting scale deposition on the inner wall of the heat exchanger as described above.

[0029] Furthermore, when metallic silicon containing the aforementioned specific amount of titanium is used as a reactant as described above, it is cooled and condensed in a heat exchanger and then transported to… Figure 1 The reaction liquid in the distillation column 5 shown contains titanium chloride corresponding to the titanium content in the reaction raw materials. However, the titanium chloride can be separated and discharged into high-boiling substances through distillation in the distillation column 5, and thus most of it can be easily removed.

[0030] Here, if the zirconium content (Zr%) in the silicon metal used as a raw material exceeds 35 ppm by mass, scale deposition on the inner wall of the upstream section of the heat exchanger will increase significantly. Furthermore, if the zirconium content (Zr%) in the silicon metal is less than 1 ppm by mass, the purification level increases, making it difficult to obtain.

[0031] Furthermore, when the mass ratio (Ti % / Zr %) of the titanium content (Zr %) in the silicon metal used is below 8.0, scale deposition on the inner wall of the upstream section of the heat exchanger will increase significantly. Additionally, when this value exceeds 30.0, the titanium impurity content in the liquefaction products of the reaction gas will be excessively high.

[0032] In metallic silicon, when the titanium content meets the above-mentioned mass ratio (Ti % / Zr%) relative to the zirconium content (Zr %), generally, the titanium content expressed in element-converted mass is 10 ppm or more and 600 ppm or less, more preferably 10 ppm or more and 400 ppm or less, and even more preferably 10 ppm or more and 300 ppm or less.

[0033] Here, although metallurgical-grade silicon has a high purity as described above, it still contains various metallic impurities, and the specific content of each metal varies within a certain range depending on the purification degree of the silicon raw material and the purification method of the obtained silicon. The zirconium and titanium contents specified in this invention are also within the range of variation of metallic impurities in this type of metallurgical-grade silicon. As silicon that satisfies these relationships as specified above, it can be prepared by those skilled in the art by adjusting the selection of silicon raw materials and the degree of purification performed. In addition, even among commercially available silicon products, there are actually a small percentage that meet the specified contents of zirconium and titanium, and these products can be selected through analysis and identification.

[0034] Furthermore, as mentioned above, aluminum in metallic silicon is not a major component of the scale deposited on the inner wall of the upstream section of the heat exchanger, and reducing its content will not significantly affect the effectiveness of the present invention. However, the lower the content, the better. Furthermore, considering the effective prevention of scale deposition from aluminum chloride in subsequent processes of distillation, it is ideal to use metallic silicon with an aluminum content preferably between 50 ppm and 3000 ppm, more preferably between 1400 ppm and 1600 ppm, based on elemental mass conversion.

[0035] In this invention, the content of metallic impurities contained in metallic silicon is the value obtained by dissolving the metallic silicon with fluorinated nitric acid, filtering the filtrate, and then introducing the filtrate into a high-frequency inductively coupled plasma optical emission spectrometer (ICP-OES).

[0036] The representative process diagrams of the preparation method of chlorosilanes for implementing the present invention described above are as follows: Figure 1 As shown. In Figure 1In the preparation process, metallic silicon and hydrogen chloride are supplied to the fluidized bed of a fluidized bed reactor for chlorination of metallic silicon, thereby producing trichlorosilane. Specifically, metallic silicon is supplied to the fluidized bed reactor 1 through the metallic silicon powder inlet channel 2, and hydrogen chloride is supplied to the fluidized bed reactor 1 through the hydrogen chloride supply pipe 3, where the chlorination reaction is carried out. The reaction gas (temperature above 320°C) generated in the fluidized bed reactor 1 is discharged from the top of the device to the conveying pipe 4 and sent to the distillation column 5.

[0037] A filter 6 is installed midway through the conveying pipe 4. The filter 6 is used to remove the fine powder of metallic silicon contained in the reaction gas. In the conveying pipe 4, a portion upstream of the filter 6 is a double pipe, through which the filter 6 removes the fine powder of metallic silicon from the reaction gas.

[0038] In the delivery piping 4, a cooling heat exchanger 7 is installed downstream of the filter 6, where the reaction gas is cooled to 10-40°C, more preferably to 20-30°C, and then liquefied before being fed into the distillation column 5. As for the heat exchanger 7, a shell-and-tube type is generally preferred to increase the heat transfer area, but plate type, finned tube type, etc., can also be used. As mentioned above, in the heat exchanger 7, a special scale, mainly composed of zirconium, will deposit on the wall surface of its upstream portion. Especially when the heat exchanger is a shell-and-tube type, this scale will deposit on the fixed perforated plate located on the reaction gas inflow side or on the wall surface of the cooling pipe end at the opening therein. However, according to the present invention, its deposition is significantly suppressed.

[0039] When a shell-and-tube heat exchanger is used as heat exchanger 7, a preferred embodiment is to spray a liquid containing chlorosilanes such as trichlorosilane or tetrachlorosilane onto the aforementioned fixed perforated plate. This forms a chlorosilane liquid film on the wall surface of the fixed perforated plate, thereby more effectively inhibiting scale deposition.

[0040] The reaction liquid that has passed through the heat exchanger 7 is distilled in distillation column 5, and the purified gas containing trichlorosilane is recovered from the purified gas recovery pipe 8 above. In addition, high-boiling substances, including aluminum chloride, titanium tetrachloride, etc., are discharged from the bottom of the column to the high-boiling substance discharge pipe 9.

[0041] Example The following examples illustrate the invention in more detail, but the invention is not limited to these examples. In the examples and comparative examples, the following methods were used to measure the content of various metal impurities in metallic silicon, measure the silicon content, measure the average particle size of metallic silicon, and analyze the composition of scale.

[0042] 1) Content of various metallic impurities in metallic silicon Accurately weigh 0.5 g of metallic silicon as the sample and place it in a 50 ml Teflon (registered trademark) beaker. Add 30 ml of 7N-HNO3, then slowly add HF (50% by mass) to decompose the sample. After decomposition, place the sample solution on a heating plate and heat at 140°C for 2 hours, then at 160°C for 1 hour. Further adjust the heating plate temperature to 140°C and heat until a small amount of liquid remains. After heating, add 2 ml of HCl (35% by mass) as a recovery reagent to the residual liquid, then add 5 ml of pure water, and heat at 140°C for 5 minutes. Remove the beaker from the heating plate and allow it to cool to room temperature.

[0043] The sample solution in the beaker was filtered into a 100 ml polyethylene volumetric flask using a polyethylene funnel and filter paper, and then diluted to 100 ml with pure water. The solution was then introduced into an inductively coupled plasma optical emission spectrometry (ICP-OES) system—a dual-wavelength sequential Optima 8300 (trade name; manufactured by PerkinElmer)—for analysis.

[0044] 2) Silicon content in metallic silicon Take 3 g to 10 g of metallic silicon and place it in a mortar. Grind the silicon using a pestle. Place the resulting powdered sample on a fluorescent X-ray stage and measure the silicon content using a fluorescent X-ray analysis device (manufactured by Rigaku Corporation, product name: "ZSXPrimus II").

[0045] 3) Average particle size of metallic silicon <Collection Method> Approximately 1 kg of metallic silicon was collected from a 1-ton flexible container and placed in a glass container. After thorough mixing, the amount required for the following analysis was collected.

[0046] <Analytical Methods> Approximately 100 g of metallic silicon powder was classified using a vibrating sieve equipped with multiple sieves. Starting with the smallest sieve residue, the residues were sequentially accumulated, and the cumulative particle size at 50% by mass was defined as the average particle size (median diameter). The vibrating sieve used was a machine equipped with test sieves conforming to JIS Z 8801-1 and with nominal sieve aperture sizes of 500 μm, 355 μm, 250 μm, 212 μm, 150 μm, 106 μm, and 45 μm.

[0047] 4) Methods for analyzing the composition of scale deposited on the inner wall of the upstream section of the heat exchanger. <Collection Method> Disassemble the heat exchanger 7 located in the middle of the delivery piping 4, collect about 5 g of scale adhering to the upper surface of the fixed perforated plate on the inflow side of the shell-and-tube heat exchanger, place it in a glass bottle, and use it for the following analysis.

[0048] <Analytical Methods> Accurately weigh 2.0–5.0 g of the above scale sample into a 50 ml Teflon (registered trademark) beaker and add 30 ml of pure water. Place filter paper in a polyethylene funnel and filter the sample solution in the beaker. Add pure water to the filtrate using a 100 ml polyethylene volumetric flask and bring the volume to 100 ml to obtain the sample solution. Dilute the obtained sample solution with pure water according to the concentration of the target element to be measured. Introduce these solutions into an ICP-OES apparatus (Optima 8300 (trade name; manufactured by PerkinElmer)) for analysis.

[0049] Examples 1-3 and Comparative Examples 1 and 2 pass Figure 1 The preparation process shown is for the preparation of trichlorosilane. The silicon powder used has the silicon content and metal impurity content (zirconium content, titanium content, and aluminum content) shown in Table 1 below, and the average particle size is 250 μm.

[0050] [Table 1]

[0051] In addition, Figure 1 In the preparation process, the heat exchanger 7 is a shell-and-tube heat exchanger equipped with 110 cooling pipes (25mm in diameter). Moreover, the shell-and-tube heat exchanger 7 is configured such that a liquid containing chlorosilanes is sprayed onto a fixed perforated plate located on the side where the reaction gas flows in.

[0052] The aforementioned metallic silicon powder and hydrogen chloride are fed into a fluidized bed reactor 1, where a chlorination reaction is carried out at a reaction temperature of 350°C. A reaction gas containing 85% by volume of trichlorosilane and 15% by volume of tetrachlorosilane is introduced at a flow rate of 500 m³ / h. 3 The generated amount per hour is discharged into the delivery pipe 4. The aforementioned reaction gas flowing through the delivery pipe 4 into the heat exchanger 7 is condensed into a reaction liquid at 20°C and then transported to the distillation tower 5.

[0053] After the chlorination reaction was carried out for 8000 hours, the reaction was stopped, the heat exchanger 7 was disassembled, and the openings at the inflow end of the cooling pipes were observed. Openings completely blocked by scale deposits were identified as blocked, and their number was counted. The blockage rate was calculated using the following formula: Blockage rate (%) = (Number of blocked pipes / Total number of pipes) × 100 This is shown in Table 2. However, in Comparative Example 1, the pressure differential of the heat exchanger 7 increased around 3000 hours, rendering it unable to operate; therefore, the blockage rate at that time is recorded.

[0054] [Table 2]

[0055] In addition, analysis of the composition of the scale deposited in each embodiment and comparative example showed that the zirconium content [wt%] was 30 to 40% by mass.

[0056] The preferred embodiments of the present invention are described below.

[0057] [1] A method for preparing chlorosilanes, characterized in that, When preparing chlorosilanes by chlorination of metallic silicon, the metallic silicon used is metallic silicon with a zirconium content (Zr%) of 35 ppm or less by mass conversion and a titanium content (Ti%) to zirconium content (Zr%) mass ratio (Ti%) / Zr%) of 8.0 or more.

[0058] [2] According to the method for preparing chlorosilanes described in [1], wherein the mass ratio (Ti % / Zr %) of the titanium content (Ti %) to the zirconium content (Zr %) in the silicon metal used is 30.0 or less.

[0059] [3] According to the preparation method of chlorosilanes described in [1] or [2], wherein the zirconium content (Zr %) in the silicon metal used is more than 1 ppm by mass.

[0060] [4] The method for preparing chlorosilanes according to any one of [1] to [3], wherein the titanium content (Ti %) in the metallic silicon is 10 ppm by mass or more and 600 ppm by mass or less in elemental conversion.

[0061] [5] The method for preparing chlorosilanes according to any one of [1] to [4], wherein the chlorination reaction of metallic silicon is a reaction of metallic silicon with hydrogen chloride to prepare trichlorosilane.

[0062] [6] The method for preparing chlorosilanes according to any one of [1] to [5], wherein the average particle size of metallic silicon is 150 to 400 μm.

[0063] [7] The method for preparing chlorosilanes according to any one of [1] to [6], wherein the reaction gas obtained by the chlorination reaction of metallic silicon is conveyed to a distillation column for purification, and a heat exchanger is provided in the middle of the conveying path of the reaction gas to the distillation column, the heat exchanger being used to cool and liquefy the reaction gas.

[0064] [8] According to the method for preparing chlorosilanes described in [7], the heat exchanger cools the reaction gas to 10~40°C and liquefies it.

[0065] [9] The method for preparing chlorosilanes according to [7] or [8], wherein the heat exchanger is a shell-and-tube heat exchanger.

[0066]

[10] A method for preparing chlorosilanes, characterized in that, When preparing chlorosilanes by chlorination of metallic silicon, the metallic silicon used is one with a zirconium content (Zr%) of 1 ppm to 35 ppm by mass conversion and a titanium content (Ti%) to zirconium content (Zr%) mass ratio (Ti%) to Zr%) of 8.0 to 30.0.

[0067] Explanation of symbols 1: Fluidized bed reactor 2: Silicon powder introduction flow path 3: Hydrogen chloride supply pipe 4: Delivery piping 5: Distillation Column 6: Filter 7: Heat exchanger 8: Purified gas recovery tube 9: High-boiling-point discharge pipe

Claims

1. A method for preparing chlorosilanes, characterized in that, When preparing chlorosilanes by chlorination of metallic silicon, the metallic silicon used is metallic silicon with a zirconium content (Zr%) of 35 ppm or less by mass conversion and a titanium content (Ti%) to zirconium content (Zr%) mass ratio (Ti%) / Zr%) of 8.0 or more.

2. The method for preparing chlorosilanes according to claim 1, wherein, In the metallic silicon used, the mass ratio (Ti %) of the titanium content (Ti %) to the zirconium content (Zr %) is 30.0 or less.

3. The method for preparing chlorosilanes according to claim 1 or 2, wherein, The zirconium content (Zr%) in the silicon metal used is at least 1 ppm by mass.

4. The method for preparing chlorosilanes according to claim 1 or 2, wherein, The titanium content (Ti %) in metallic silicon is between 10 ppm by mass and 600 ppm by mass, calculated as an elemental equivalent.

5. The method for preparing chlorosilanes according to claim 1 or 2, wherein, The chlorination reaction of metallic silicon is a reaction that produces trichlorosilane by reacting metallic silicon with hydrogen chloride.

6. The method for preparing chlorosilanes according to claim 1 or 2, wherein, The average particle size of metallic silicon is 150 ~ 400 μm.

7. The method for preparing chlorosilanes according to claim 1 or 2, wherein, The reaction gas obtained by the chlorination reaction of metallic silicon is transported to a distillation column for purification. A heat exchanger is installed midway along the transport path of the reaction gas to the distillation column to cool and liquefy the reaction gas.

8. The method for preparing chlorosilanes according to claim 7, wherein, The heat exchanger cools the reaction gas to 10~40°C and liquefies it.

9. The method for preparing chlorosilanes according to claim 7, wherein, The heat exchanger is a shell-and-tube heat exchanger.

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