Chlorosilane production method

Abstract

The present disclosure provides a method for producing chlorosilanes, the method including generating the chlorosilanes by reacting a silicon source with hydrogen chloride, or with tetrachlorosilane and hydrogen, the silicon source containing at least one selected from the group consisting of monocrystalline silicon and polycrystalline silicon each recovered from a solar panel. It is preferable that a content of the at least one selected from the group consisting of the monocrystalline silicon and the polycrystalline silicon be 1 part by mass to 99 parts by mass in 100 parts by mass of the silicon source.

Description

Method for producing chlorosilanes

[0001] The present invention relates to a method for producing chlorosilanes, and more particularly to a method for producing chlorosilanes including trichlorosilane by reacting a silicon source with hydrogen chloride or tetrachlorosilane and hydrogen.

[0002] Toward the realization of a low-carbon society, we are working to reduce CO2 emissions by utilizing renewable energy, including solar power generation. ２ The reduction of solar energy consumption is expected to accelerate. A typical solar cell module for solar power generation has a three-layer structure: a tempered glass surface, an encapsulating resin layer on the inside, and a backsheet on the back. Solar cell modules made of monocrystalline or polycrystalline silicon are arranged within the encapsulating resin layer and connected by electrical wires (interconnectors). The encapsulating resin must have transparency, flexibility, adhesiveness, tensile strength, and weather resistance, and ethylene vinyl acetate copolymer (hereinafter abbreviated as "EVA") is commonly used, which bonds the tempered glass, cells, and backsheet together by applying heat and pressure. While the adoption of solar power generation has progressed significantly, recycling solar cell modules at the time of disposal has been identified as an issue.

[0003] When this solar cell module is heated in an electric furnace or the like under an oxidizing atmosphere, the EVA melts at 80 to 120° C., a deacetylation reaction of the EVA occurs at around 350° C., and a thermal decomposition reaction of the polyethylene main chain occurs rapidly at around 450° C. Technologies for recycling solar cell modules by such thermal decomposition have been disclosed (see Patent Documents 1 and 2).

[0004] Furthermore, in order to prevent the EVA contained in solar cell modules from burning too quickly, a method has been proposed in which the resin components are slowly and steadily burned and removed, rather than lowering the oxygen concentration in the heating furnace, thereby recovering valuable resources efficiently and simply (see Patent Document 3).

[0005] By the above method, resin components such as the back sheet and sealing resin layer can be removed from the solar cell module, and the glass, cells, aluminum frame, etc. can be separated and recovered.

[0006] Japanese Patent Publication No. 11-165150 Japanese Patent Publication No. 2007-59793 International Publication No. WO2020 / 031661 Korean Patent Publication No. 20230033968 Chinese Patent Publication No. 115353111

[0007] The glass, aluminum frames, etc. recovered by the above method can be reused for solar cell modules and other uses. On the other hand, although the cells recovered by the above method are mainly composed of polycrystalline silicon or single-crystal silicon, they contain metal components such as wiring materials and resin components used in adhesives that were used to construct the solar cell module. Therefore, further purification measures are required to use the recovered cells as they are as cell materials.

[0008] For example, a method has been proposed (see Patent Document 4) that includes a primary acid leaching step in which an acid leaching solution is added to crushed waste solar silicon, and impurities contained in the waste solar silicon are leached and stirred. ３ One method that has been proposed is to immerse the silicon in a solution, pickle it with hydrochloric acid, and then thermally decompose a portion of the organic material at 330°C to 380°C, pulverize it into powder, purify it by melting and refining it, and then solidify it to obtain recycled silicon (see Patent Document 5).

[0009] These methods involve purifying silicon cells recovered from solar cell modules and reusing them for use in solar cell modules, but they require numerous purification steps, and a simpler recycling method has been desired.

[0010] Therefore, an object of the present invention is to provide a simple method for reusing silicon cells recovered from solar cell modules.

[0011] The present inventors conducted extensive research to address the above-mentioned problems. Analysis of impurities in polycrystalline silicon and single-crystalline silicon recovered from solar cell modules revealed metallic components derived from wiring materials such as aluminum, and organic substances derived from resins. Therefore, methods for reusing such polycrystalline silicon and single-crystalline silicon were investigated. As a result, it was found that chlorosilanes such as trichlorosilane can be efficiently produced by using them as a silicon source for producing chlorosilanes by reacting silicon with hydrogen chloride or tetrachlorosilane with hydrogen. Furthermore, the obtained chlorosilanes were of the same quality as those produced from metal silicon. Therefore, it was found that impurities derived from the polycrystalline silicon and single-crystalline silicon (metallic impurities, carbon derived from resins) can be removed using conventional methods for purifying chlorosilanes, leading to the completion of the present invention.

[0012] That is, a production method according to one aspect of the present invention is a method for producing chlorosilanes, which comprises reacting a silicon source with hydrogen chloride or tetrachlorosilane with hydrogen to produce chlorosilanes, wherein the silicon source contains at least one of monocrystalline silicon and polycrystalline silicon recovered from solar panels.

[0013] According to a production method of one aspect of the present invention, polycrystalline silicon and single-crystalline silicon recovered from solar cell modules can be efficiently used as raw materials (i.e., silicon sources) for producing chlorosilanes. To use the polycrystalline silicon and single-crystalline silicon for cells in solar cell modules, it is necessary to thoroughly purify and remove metal components derived from wiring materials and organic substances derived from resins. In contrast, according to the present invention, chlorosilanes can be removed by known purification methods after production, and therefore the polycrystalline silicon and single-crystalline silicon can be used as silicon sources for producing chlorosilanes without thorough purification.

[0014] A production method according to one aspect of the present invention is a method for producing chlorosilanes by reacting a silicon source with hydrogen chloride or tetrachlorosilane and hydrogen to produce chlorosilanes, characterized in that the silicon source contains at least one of monocrystalline silicon and polycrystalline silicon recovered from solar panels. As described above, silicon cells recovered from solar cell modules are primarily composed of polycrystalline silicon and monocrystalline silicon. However, polycrystalline silicon and monocrystalline silicon contain impurities such as metal components such as aluminum used as wiring materials and organic components derived from resin materials. Therefore, when using the silicon cells as silicon for solar cell modules, these impurities must be thoroughly removed.

[0015] On the other hand, when producing polysilicon for semiconductors or solar cells, metallic silicon is converted to trichlorosilane by reacting it with hydrogen chloride or tetrachlorosilane and hydrogen. The trichlorosilane is then purified and reduced with hydrogen to obtain polysilicon. Furthermore, since the reaction between metallic silicon and hydrogen chloride produces tetrachlorosilane as a by-product in addition to trichlorosilane, the tetrachlorosilane is recovered and reacted with metallic silicon and hydrogen to produce trichlorosilane. Therefore, high-purity trichlorosilane can be obtained by using polycrystalline silicon or single-crystalline silicon recovered from solar cell modules instead of the metallic silicon.

[0016] Furthermore, metallic silicon contains metals such as iron, aluminum, or calcium, which act catalytically in the reaction between metallic silicon and hydrogen chloride or between tetrachlorosilane and hydrogen, thereby promoting the reaction. However, if these catalytic components are present in excess, they accumulate in the reaction vessel during the reaction, reducing the fluidity of the silicon source in the reaction vessel and affecting the purification efficiency of chlorosilanes after the reaction. Meanwhile, polycrystalline silicon or single-crystalline silicon recovered from solar cell modules contains aluminum derived from the wiring material on its surface, but contains no or very little iron or calcium. Therefore, when polycrystalline silicon or single-crystalline silicon recovered from solar cell modules is used as a silicon source for producing trichlorosilane or the like without undergoing advanced purification, the accumulation of iron and calcium in the reaction vessel can be suppressed, enabling stable production of chlorosilanes over an extended period of time.

[0017] In this specification, unless otherwise specified, the notation "A to B" for numerical values ​​A and B means "A or more and B or less." In such notation, when a unit is assigned only to numerical value B, the unit also applies to numerical value A. Hereinafter, a method for producing chlorosilanes according to one embodiment of the present invention will be described in detail.

[0018] <Method for Producing Chlorosilanes> In a method for producing chlorosilanes according to one aspect of the present invention, chlorosilanes are produced by reacting a silicon source with hydrogen chloride. This production reaction is represented by the following formula (1): Si + 3HCl → SiHCl ３ +H ２ (1) In addition, a side reaction occurs according to the following formula (2): Si + 4HCl → SiCl ４ +2H ２ As shown in (2), tetrachlorosilane is produced as a by-product, and further, a small amount of dichlorosilane is also produced as a by-product.

[0019] On the other hand, tetrachlorosilane (SiCl), a by-product of polysilicon production, ４) is converted to trichlorosilane and reused in the production of polysilicon. In this production method, trichlorosilane is produced from metallic silicon, tetrachlorosilane, and hydrogen according to the following reaction formula (3): ４ +2H ２ +Si → 4SiHCl ３ (3) The method for producing chlorosilanes according to one embodiment of the present invention can be used in any of the above production methods.

[0020] <Silicon Source> The production method according to one aspect of the present invention is characterized in that the silicon source contains at least one of monocrystalline silicon and polycrystalline silicon (hereinafter collectively referred to as "recovered silicon") recovered from solar panels. As a method for recovering monocrystalline silicon and polycrystalline silicon from solar panels, monocrystalline silicon and polycrystalline silicon recovered by known methods can be used. Among these, it is preferable to use polycrystalline silicon recovered from solar panels due to the reactivity of the reaction of chlorosilanes. Specific examples of the method for recovering monocrystalline silicon and polycrystalline silicon include the method described in Patent Document 3. The method described in Patent Document 3 involves heating waste solar panels containing monocrystalline silicon or polycrystalline silicon to heat-melt the resin in the waste solar panels, burning the heat-melted resin, and then recovering monocrystalline silicon or polycrystalline silicon from the waste solar panels.

[0021] Furthermore, the recovered silicon contains impurities such as metal components such as aluminum and organic components derived from the resin material, but in the production method according to one embodiment of the present invention, the recovered silicon containing impurities can be used as is. However, if the content of these impurities is too high, there is a risk that they will not be sufficiently removed during the purification operation after the reaction, so the content of at least one impurity in the recovered silicon is preferably one of the following. Note that the content in the following description is the content per 100 parts by mass of at least one type of recovered silicon.

[0022] Aluminum: preferably 50 to 3,000,000 ppm by mass, more preferably 50 to 300,000 ppm by mass, even more preferably 50 to 10,000 ppm by mass, and particularly preferably 50 to 1,000 ppm by mass. Iron: preferably 100 ppm by mass or less, more preferably 50 to 90 ppm by mass, and particularly preferably 60 to 90 ppm by mass. Calcium: preferably 100 ppm by mass or less, more preferably 1 to 90 ppm by mass, and particularly preferably 1 to 80 ppm by mass. Carbon: preferably 500 ppm by mass or less, more preferably 1 to 300 ppm by mass, and particularly preferably 1 to 100 ppm by mass.

[0023] The content of metal components, i.e., aluminum, iron, and calcium, in the silicon source or recovered silicon can be measured by X-ray fluorescence spectroscopy (XRF). Furthermore, for low concentrations of the above metal elements (100 mass ppm or less), the silicon source can be dissolved in nitric acid and then filtered, and the filtrate can be measured by inductively coupled plasma optical emission spectroscopy (ICP-OES). The carbon content of the silicon source or recovered silicon can be measured by measuring CO and CO by combustion-infrared absorption spectroscopy. ２ It can be determined by measuring

[0024] If the content of the above-mentioned impurities in the recovered silicon is too high, for example, the surface of the recovered silicon recovered from waste solar panels may be washed with an acid such as hydrochloric acid, nitric acid, sulfuric acid, or hydrofluoric acid, or an alkali such as sodium hydroxide or potassium hydroxide. After the washing, the impurities can be reduced to a desired range by washing with pure water and drying.

[0025] There are no particular restrictions on the particle size of the recovered silicon when it is used as a silicon source. From the viewpoint of reactivity with hydrogen chloride or tetrachlorosilane and hydrogen, the particle size is preferably 30 to 2000 μm, more preferably 50 to 1000 μm, and particularly preferably 50 to 500 μm.

[0026] In a production method according to one aspect of the present invention, the silicon source may contain at least one of the recovered silicon types described above, and the entire amount of the silicon source may be the recovered silicon. The recovered silicon may also be a combination of the washed recovered silicon described above and unwashed recovered silicon. Alternatively, the recovered silicon may be mixed with metallic silicon, as described below. As described above, in the reaction between metallic silicon and hydrogen chloride, or between tetrachlorosilane and hydrogen, metal components such as iron, aluminum, and calcium act catalytically to promote the reaction. Therefore, when using these as the silicon source, the content of the metal components such as iron, aluminum, and calcium in the silicon source may be appropriately adjusted. Specifically, when a mixture of recovered silicon and metallic silicon described below is used, the content of recovered silicon per 100 parts by mass of the silicon source is preferably 1 to 99 parts by mass, more preferably 50 to 99 parts by mass, and particularly preferably 80 to 95 parts by mass.

[0027] <Metallic silicon> As the metallic silicon used in the above reaction, known materials such as metallurgical metallic silicon or silicon iron can be used without any limitation. Furthermore, there are no particular limitations on the components or contents of impurities such as iron compounds contained in such metallic silicon. Such metallic silicon is usually used in the form of a fine powder with an average particle size of about 100 to 500 μm.

[0028] <Hydrogen Chloride> The hydrogen chloride used in the reaction with the silicon source may be contaminated with hydrogen or the like without any restrictions. However, chlorosilanes such as trichlorosilane, tetrachlorosilane, and dichlorosilane are generally highly hydrolyzable and therefore react with moisture. Therefore, if the hydrogen chloride contains moisture, the yield of the produced trichlorosilane may decrease. Therefore, it is preferable that the hydrogen chloride be in a dry state.

[0029] <Hydrogen> The hydrogen used in the reaction with the silicon source is not particularly limited, and pure hydrogen, hydrogen recovered after the reaction of the silicon source with hydrogen chloride, or tetrachlorosilane with hydrogen, etc. can be used. As with the hydrogen chloride, it is preferable that this hydrogen be in a dry state.

[0030] <Reaction of Silicon Source with Hydrogen Chloride or Tetrachlorosilane and Hydrogen> From the viewpoint of efficiently producing trichlorosilane, it is preferable to use a catalyst in the reaction of a silicon source with hydrogen chloride or tetrachlorosilane and hydrogen. As such a catalyst, any known catalyst component for the reaction of a silicon source with hydrogen chloride or tetrachlorosilane and hydrogen can be used without particular limitation.

[0031] Specific examples of such catalyst components include, in addition to the aluminum, iron, and calcium mentioned above, metals of Groups 8 to 10, such as cobalt, nickel, palladium, and platinum, or chlorides thereof, and metals or chlorides of copper, titanium, and the like. These catalysts can be used alone or in combination with multiple catalysts. The amount of the catalyst component used is not particularly limited as long as it is an amount that efficiently produces trichlorosilane, and can be determined appropriately taking into account the capacity of the production equipment, etc. Generally, it is sufficient to use 0.05 to 40 wt %, particularly 0.1 to 5 wt %, of the metal element equivalent relative to the metallic silicon.

[0032] As described above, the recovered silicon contains aluminum, and when metallic silicon is used in combination, the metallic silicon contains aluminum, iron, and calcium. Therefore, in the production method according to one aspect of the present invention, it is preferable to use a silicon source containing catalyst components in a blend such that the content of the catalyst components falls within the following range. The content in the following description is the content per 100 parts by mass of the silicon source.

[0033] Aluminum: preferably 50 to 20,000 ppm by mass, more preferably 500 to 10,000 ppm by mass, and particularly preferably 600 to 6,000 ppm by mass. Iron: preferably 50 to 10,000 ppm by mass, more preferably 50 to 5,000 ppm by mass, and particularly preferably 1,000 to 3,000 ppm by mass. Calcium: preferably 50 to 5,000 ppm by mass, more preferably 50 to 3,000 ppm by mass, and particularly preferably 50 to 500 ppm by mass.

[0034] As described above, the content of metal components, i.e., aluminum, iron, and calcium, in the silicon source or recovered silicon can be measured by X-ray fluorescence spectroscopy (XRF). For low concentrations of the above metal elements (100 mass ppm or less), the silicon source can be dissolved in nitric acid and then filtered, and the filtrate can be measured by inductively coupled plasma optical emission spectroscopy (ICP-OES). The carbon content of the silicon source or recovered silicon can be measured by the combustion-infrared absorption method using CO and CO ２ It can be determined by measuring

[0035] The above-mentioned catalytic components may be present in the reaction system by being added thereto, but when the silicon source used contains catalytic components such as aluminum, iron, calcium, etc. as impurities, these impurities can be effectively used as catalytic components. Of course, even when metallic silicon containing catalytic components as impurities is used, there is no problem in further adding catalytic components to the reaction system in order to increase the reactivity of the silicon source with hydrogen chloride or tetrachlorosilane and hydrogen.

[0036] In the reaction of the silicon source with hydrogen chloride or tetrachlorosilane and hydrogen, any known reactor can be used without any particular limitation. Specific examples of such reactors include fixed-bed reactors and fluidized-bed reactors. Among the above reactors, a fluidized-bed reactor is preferred because it allows continuous supply of the silicon source and hydrogen chloride, or tetrachlorosilane and hydrogen, to continuously produce trichlorosilane. Furthermore, since the reaction is an exothermic and endothermic reaction, a fluidized-bed reactor is preferred from the viewpoint of achieving a uniform temperature distribution in the reaction region.

[0037] The reaction temperature in the reaction between a silicon source and hydrogen chloride, or between tetrachlorosilane and hydrogen, may be appropriately determined taking into consideration the material and capacity of the production equipment. If the reaction temperature is higher than necessary, the selectivity for trichlorosilane decreases, and the amount of chlorosilane by-products other than trichlorosilane, such as tetrachlorosilane and dichlorosilane, increases. The reaction between a silicon source and hydrogen chloride is an exothermic reaction, and the reaction temperature is generally set in the range of 250 to 400°C.

[0038] On the other hand, the reaction temperature between the silicon source and tetrachlorosilane and hydrogen is an endothermic reaction, and the reaction temperature is generally set in the range of 400 to 700°C, particularly 450 to 600°C.

[0039] <Condensation, Separation, and Distillation of Chlorosilanes> The reaction of the silicon source with hydrogen chloride or tetrachlorosilane and hydrogen generates a reaction product gas containing trichlorosilane. This reaction product gas contains by-product chlorosilanes other than trichlorosilane, such as tetrachlorosilane or dichlorosilane, as well as by-product hydrogen and boron and other unavoidable impurities contained in the silicon source.

[0040] Therefore, when recovering trichlorosilane from the reaction product gas, the reaction product gas may first be passed through an appropriate filter to remove solid matter such as silicon source particles, and then subjected to condensation and separation. Chlorosilanes including trichlorosilane are condensed and separated from the reaction product gas after passing through the filter.

[0041] In this condensation and separation step, the reaction product gas is cooled, and the cooling temperature need only be equal to or lower than the temperature at which various chlorosilanes condense, and may be appropriately determined taking into consideration the cooling capacity of the cooling device, etc. The lower the cooling temperature, the more effective the chlorosilane removal tends to be, but generally, a temperature of -10°C or lower, particularly -30°C or lower, is sufficient. The pressure in the condensation and separation is also not particularly limited as long as the chlorosilanes can be sufficiently removed, and may be appropriately determined taking into consideration the capacity of the condensation and removal device, etc. A pressure of 300 kPaG or higher, particularly 500 kPaG or higher, is generally sufficient.

[0042] The cooling means for condensation is not particularly limited, and any known cooling means can be used as long as it can cool the reaction product gas to the above-mentioned cooling temperature. Specific examples of such cooling means include a cooling means that cools the reaction product gas by passing it through a cooled heat exchanger, or a cooling means that cools the reaction product gas using a condensate that has been condensed and cooled. These methods can be used alone or in combination.

[0043] Furthermore, a pressurizer can be installed prior to the condensation and removal of chlorosilanes in order to increase the gas pressure. To protect the pressurizer, a preliminary chlorosilane condenser or filter can also be installed upstream of the pressurizer. These points can be adopted as standard practices in industrial process design.

[0044] The condensate obtained from the reaction product gas by the above-described condensation separation is a mixture of various chlorosilanes, and trichlorosilane is isolated by distillation. The recovered trichlorosilane is used as a deposition raw material in the process of producing polysilicon.

[0045] Furthermore, the exhaust gas after condensation and separation of chlorosilanes contains hydrogen gas as a main component and can be used as a hydrogen source for various production processes such as hydrogen in the production of the above-mentioned chlorosilanes.

[0046] [Summary] A method for producing chlorosilanes according to Aspect 1 of the present invention is a method for producing chlorosilanes by reacting a silicon source with hydrogen chloride or tetrachlorosilane with hydrogen to produce chlorosilanes, wherein the silicon source contains at least one of monocrystalline silicon and polycrystalline silicon recovered from solar panels.

[0047] In the method for producing chlorosilanes according to Aspect 2 of the present invention, in the above-mentioned Aspect 1, it is preferable that the content of at least one of the monocrystalline silicon and the polycrystalline silicon per 100 parts by mass of the silicon source is 1 to 99 parts by mass.

[0048] In the method for producing chlorosilanes according to Aspect 3 of the present invention, in the above-mentioned Aspect 1 or 2, the content of aluminum in 100 parts by mass of the silicon source is preferably 50 to 20,000 ppm by mass.

[0049] A fourth aspect of the present invention relates to the method for producing chlorosilanes, and is preferably the method for producing chlorosilanes according to any one of the first to third aspects, wherein the iron content in 100 parts by mass of the silicon source is 50 to 10,000 ppm by mass.

[0050] A fifth aspect of the present invention relates to the method for producing chlorosilanes, and in any one of the first to fourth aspects, the calcium content in 100 parts by mass of the silicon source is preferably 50 to 5,000 ppm by mass.

[0051] A sixth aspect of the present invention relates to the method for producing chlorosilanes, and in any one of the first to fifth aspects, the carbon content in 100 parts by mass of the silicon source is preferably 10 to 10,000 ppm by mass.

[0052] A seventh aspect of the present invention relates to the method for producing chlorosilanes, and is preferably the method for producing chlorosilanes according to any one of the first to sixth aspects, wherein the silicon source has an aluminum content of 50 to 300,000 ppm by mass per 100 parts by mass of at least one of the monocrystalline silicon and the polycrystalline silicon.

[0053] Aspect 8 of the present invention is the method for producing chlorosilanes according to any one of Aspects 1 to 7, wherein the silicon source preferably has an iron content of 100 ppm by mass or less per 100 parts by mass of at least one of the monocrystalline silicon and the polycrystalline silicon.

[0054] A ninth aspect of the present invention is directed to the method for producing chlorosilanes according to any one of the first to eighth aspects, wherein the silicon source preferably has a calcium content of 100 ppm by mass or less per 100 parts by mass of at least one of the monocrystalline silicon and the polycrystalline silicon.

[0055] A tenth aspect of the present invention relates to the method for producing chlorosilanes, in any one of the first to ninth aspects, wherein the silicon source preferably has a carbon content of 500 ppm by mass or less per 100 parts by mass of at least one of the monocrystalline silicon and the polycrystalline silicon.

[0056] Aspect 11 of the present invention is a method for producing chlorosilanes according to any one of Aspects 1 to 10, wherein the single crystal silicon and polycrystalline silicon recovered from the solar panels preferably include single crystal silicon or polycrystalline silicon recovered from the solar panels, and the surface of the obtained single crystal silicon or polycrystalline silicon washed with an acid.

[0057] The present invention will be further explained below with reference to examples, but the present invention is not limited to these examples in any way.

[0058] <Silicon Source> In the following examples, the following silicon sources were used. Unwashed recovered silicon: silicon obtained by heating a waste solar panel containing single crystal silicon to heat-melt the resin in the waste solar panel, burning the heat-melted resin, and then recovering it from the waste solar panel. Washed recovered silicon: silicon obtained by immersing the unwashed recovered silicon in 35% hydrochloric acid for 1 hour and then drying. Metallic silicon: commercially available product. Ferrosilicon: commercially available product. Copper silicon: a mixture of a commercially available product and metallic silicon.

[0059] The contents of aluminum, iron, calcium, and copper in each silicon source were measured by X-ray fluorescence spectroscopy (XRF) (ZSX Primus IV (Rigaku Corporation)). The low concentration range of the above metal elements (100 mass ppm or less) was measured by high-frequency inductively coupled plasma optical emission spectroscopy (ICP-OES) (Optima 8300 (PerkinElmer Co., Ltd.)). The carbon content was measured by CO and CO by combustion-infrared absorption spectroscopy (EMIA-110 (Horiba, Ltd.)). ２ The content of each element in each silicon source is shown in Table 1.

[0060]

[0061] <Reaction of silicon source with hydrogen chloride> 10 g of silicon source was packed into an SUS reaction tube with an inner diameter of 8 mm, and the reactor was maintained at 350°C. Then, hydrogen chloride gas and hydrogen gas were continuously supplied to the reactor at 50 ml / min each for 250 min. The exhaust gas from the reactor was cooled to -70°C to obtain a coolant.

[0062] The supply of hydrogen chloride gas and hydrogen gas was stopped, the temperature was lowered, the reaction residue was removed from the reactor and weighed, and the reaction rate (%) of the silicon source in Table 2 was calculated from the amount of silicon source charged into the reactor using the following formula: Reaction rate = ((amount of silicon source charged) - (amount of reaction residue)) / (amount of silicon source charged) x 100

[0063] After the reaction was completed, the reaction residue was visually observed to confirm the presence or absence of silicon lumps with a particle size of 1 mm or more. The methyldichlorosilane (MDCS) content of the obtained coolant was measured using a gas chromatograph. The remaining silicon lumps, which are agglomerates of silicon reaction residue, indicate a deterioration in fluidity and reactivity in the reactor during long-term operation.

[0064] Example 1 The above production was carried out using a mixture of 98 parts by mass of washed and recovered silicon and 2 parts by mass of unwashed and recovered silicon as the silicon source. As a result, the reaction rate was 16%, and almost no silicon lumps were observed. The methyldichlorosilane content was 0.3 ppma. Table 2 shows the iron, calcium, aluminum, and carbon contents of the silicon source used, the reaction rate, the presence or absence of silicon lumps, and the MDCS content.

[0065] Examples 2 to 5, Comparative Example 1 Production was carried out in the same manner as in Example 1, except that the silicon source shown in the table was used in the amount shown in Table 2. The reaction rate and MDCS content are shown as relative values, with the result of Example 1 set to 1. The results are shown in Table 2. Even when recovered silicon was used, the reaction rate could be improved to the same level as when metal silicon was used by adjusting the impurity content. On the other hand, since recovered silicon has a lower calcium content than metal silicon, it is presumed that the amount of silicon chunks that cause poor flow is smaller. Furthermore, since recovered silicon also has a lower carbon content than metal silicon, the amount of carbon-derived MDCS produced is also smaller, and higher purity chlorosilanes can be obtained.

[0066]

[0067] <Reaction of silicon source with tetrachlorosilane and hydrogen> 3.0 g of silicon source was packed into an SUS reaction tube with an inner diameter of 8 mm, and the reactor was maintained at 530° C. After that, tetrachlorosilane gas and hydrogen gas were continuously supplied to the reactor at 40 ml / min and 110 ml / min, respectively, for 300 min. The exhaust gas from the reactor was cooled to −70° C. to obtain a coolant.

[0068] The supply of tetrachlorosilane gas and hydrogen gas was stopped, the temperature was lowered, the reaction residue was removed from the reactor and weighed, and the reaction rate (%) of the silicon source in Table 3 was calculated from the amount of silicon source charged into the reactor using the following formula: Reaction rate = ((amount of silicon source charged) - (amount of reaction residue)) / (amount of silicon source charged) x 100

[0069] Example 6: The above production was carried out using a mixture of 98 parts by mass of washed and recovered silicon and 2 parts by mass of unwashed and recovered silicon as the silicon source. As a result, the reaction rate was 0.14%, meaning that almost no reaction occurred. Table 3 shows the contents and reaction rates of iron, calcium, aluminum, carbon, and copper in the silicon source used.

[0070] Examples 7 and 8, Comparative Examples 2 and 3 Production was carried out in the same manner as in Example 6, except that the silicon source was the one shown in Table 3 and the amount shown in Table 3. The reaction rate was shown as a relative value, with the result of Example 6 taken as 1. The results are shown in Table 3. Even when recovered silicon was used, the reaction rate could be improved to the same level as when metallurgical silicon was used by adjusting the impurity content.

[0071]

Claims

1. A method for producing chlorosilanes, comprising reacting a silicon source with hydrogen chloride, or tetrachlorosilane and hydrogen, to produce chlorosilanes, wherein the silicon source contains at least one of monocrystalline silicon and polycrystalline silicon recovered from solar panels.

2. The method for producing chlorosilanes according to claim 1, wherein the content of at least one of the monocrystalline silicon and polycrystalline silicon per 100 parts by mass of the silicon source is 1 to 99 parts by mass.

3. The method for producing chlorosilanes according to claim 1 or 2, wherein the aluminum content in 100 parts by mass of the silicon source is 50 to 20,000 ppm by mass.

4. The method for producing chlorosilanes according to claim 1 or 2, wherein the iron content in 100 parts by mass of the silicon source is 50 to 10,000 ppm by mass.

5. The method for producing chlorosilanes according to claim 1 or 2, wherein the calcium content in 100 parts by mass of the silicon source is 50 to 5,000 ppm by mass.

6. The method for producing chlorosilanes according to claim 1 or 2, wherein the carbon content in 100 parts by mass of the silicon source is 10 to 10,000 ppm by mass.

7. The method for producing chlorosilanes according to claim 1 or 2, wherein the aluminum content per 100 parts by mass of at least one of the monocrystalline silicon and polycrystalline silicon in the silicon source is 50 to 300,000 ppm by mass.

8. The method for producing chlorosilanes according to claim 1 or 2, wherein the iron content per 100 parts by mass of at least one of the monocrystalline silicon and polycrystalline silicon in the silicon source is 100 ppm by mass or less.

9. The method for producing chlorosilanes according to claim 1 or 2, wherein the calcium content per 100 parts by mass of at least one of the monocrystalline silicon and polycrystalline silicon in the silicon source is 100 ppm by mass or less.

10. The method for producing chlorosilanes according to claim 1 or 2, wherein the carbon content per 100 parts by mass of at least one of the monocrystalline silicon and polycrystalline silicon in the silicon source is 500 ppm by mass or less.

11. The method for producing chlorosilanes according to claim 1 or 2, wherein the single crystal silicon and polycrystalline silicon recovered from the solar panels comprises recovering single crystal silicon or polycrystalline silicon from the solar panels and washing the surface of the resulting single crystal silicon or polycrystalline silicon with an acid.