JP2011068520A - Method for producing silicon for solar cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To stably and inexpensively provide silicon for solar cells. <P>SOLUTION: An aspect of the method for producing silicon for solar cells comprises a step (1) of obtaining silicon tetrachloride by chlorinating a silicon-containing substance that contains zeolite in the presence of a carbon-containing substance, a step (2) of separating and purifying silicon tetrachloride obtained by the step (1), and a step (3) of obtaining polycrystalline silicon by reacting silicon tetrachloride purified in the step (2) with gaseous zinc. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for producing silicon for solar cells.

  In recent years, in order to prevent global warming, reducing carbon dioxide emissions, which is one of the causative substances, has become a major issue. Solar cells are attracting attention as a solution to this problem, and demand is growing significantly. Currently, the mainstream solar cell is a solar cell using silicon as a power generation layer, so that the demand for silicon for solar cells is tight as the demand for solar cells grows.

  On the other hand, the current solar cell is still expensive, and the price of the electric power obtained by the solar cell is several times that of the electricity cost of commercial power, and it is desired to reduce raw material costs and manufacturing costs. Yes.

  As a method of manufacturing silicon for solar cells, (1) Siemens method: a method of manufacturing polycrystalline silicon by reducing trichlorosilane with hydrogen, (2) Fluidized bed method: flowing silicon fine powder into the reactor A technique for producing polycrystalline silicon by introducing a mixed gas of monosilane and hydrogen into the mixture; (3) zinc reduction method: a technique for producing polycrystalline silicon by reducing silicon tetrachloride with molten zinc The above three methods can be mentioned. There are basic problems that the production efficiency of high purity metal silicon is low in (1) Siemens method and (2) fluidized bed method as the manufacturing method of solar cell silicon that is aimed at lowering the price. (3) It is considered preferable to use a zinc reduction method.

  FIG. 1 shows a general process for producing silicon for solar cells by a zinc reduction method currently proposed (see Patent Document 1).

  First, as shown in the following reaction formula (a) or (b), silicon dioxide such as silica is reduced with carbon to produce metal silicon having a purity of about 97 to 99%.

SiO ₂ + C → Si + CO ₂ (A)
SiO ₂ + 2C → Si + 2CO (i)
However, this manufacturing process has a problem that the reaction temperature needs to be 2000 ° C. or higher, which requires a large amount of electric power, and the price of metal silicon increases.

  Silicon tetrachloride having a purity of about 97 to 99% obtained by the above reaction is reacted with hydrogen chloride as shown in the following reaction formula (c) to produce silicon tetrachloride.

Si + 4HCl → SiCl ₄ + 2H ₂ (U)
As described above, the production process of silicon tetrachloride used in the zinc reduction method has problems such as being produced through a two-step reaction and requiring a large amount of electric power, leaving room for improvement. ing.

  High-purity polycrystalline silicon is produced by purifying silicon tetrachloride produced by the above-described method and reducing it with zinc gas based on the following reaction formula (d).

SiCl ₄ + 2Zn → Si + 2ZnCl ₂ (D)
Zinc chloride, which is a reaction by-product, is divided into metallic zinc and chlorine by electrolysis, and metallic zinc is reused as a raw material for the reaction (d). Chlorine is made hydrogen chloride by reacting with hydrogen (reaction formula (c)) produced in the process of producing silicon tetrachloride, and is reused as a raw material in the process of producing silicon tetrachloride.

Japanese Patent Laid-Open No. 11-092130 JP 58-055330 A Japanese Patent Publication No. 3-055407 Japanese Examined Patent Publication No. 4-072765

In light of the above-described present situation, it is desired to supply silicon for solar cells more stably and inexpensively. Therefore, in the present invention, by using raw materials that can be supplied stably and inexpensively, the manufacturing process is simplified and the reaction temperature is lowered as compared with the conventional manufacturing method, and silicon for solar cells is stably and inexpensively manufactured. Provide new manufacturing methods that can continue to be supplied.
As a method for producing silicon tetrachloride, a method using a two-step reaction is generally used, in which silicon-containing material is made into metal silicon, and silicon tetrachloride is produced by a reaction between the produced metal silicon and hydrogen chloride. There is also a method of producing directly from a silica-containing material such as silica.
SiO ₂ + 2C + 2Cl ₂ → SiCl ₄ + 2CO (e)

  In this method, as shown in the above reaction formula (e), silicon tetrachloride can be obtained by reacting a silicon-containing substance such as silica with carbon and chlorine. Therefore, the number of reaction processes is smaller than that in the conventional method. Can be reduced. However, the reactivity of a mixture of silica and the like with carbon and chlorine is low, and it is necessary to perform the reaction under a high temperature condition of 1300 ° C. or higher.

  On the other hand, when the carbonized product of silicate biomass is used as the silicon-containing substance that is the raw material of the reaction formula (e), the reactivity with chlorine is dramatically improved and the temperature is lower than the conventional temperature of 400 to 1100 ° C. There is a report example that silicon tetrachloride was obtained in high yield even under conditions (see Patent Document 2). The reason for this is that silica and carbon contained in the carbonized product are each fine particles in a highly dispersed state, porous and have a large surface area.

In addition, there is a report example of improving the reaction conversion rate by adding potassium compound, sulfur or sulfur compound to the carbonization product of raw material silicate biomass, and potassium content and sulfur content act as a catalyst for chlorination reaction Has been suggested (see Patent Documents 3 and 4).
However, since the specific gravity of silicate biomass is small, enormous costs are required to collect and transport a large amount of silicate biomass during industrialization. In addition, it is difficult to stably supply a large amount of silicate biomass, and it is difficult to say that silicate biomass is a useful material when mass production is considered.

  On the other hand, zeolite has a large surface area because it is a porous material. Also, since it has an acid point, when mixed with a carbon-containing material, it can be expected that silica and carbon will be highly dispersed, similar to biomass-derived silica and carbon compounds, due to the interaction between the acid point and the carbon-containing material. It can be expected to lower the reaction temperature.

  In addition, zeolite is industrially used in many fields for applications such as reaction catalysts, adsorbents, and ion exchange membranes, so that it can be expected to be supplied inexpensively and stably. Furthermore, most of the industrially used waste zeolite is treated as industrial waste without being recovered and reused. In view of the above-described contents, when a silicon-containing material containing at least zeolite is used, it is expected that silicon tetrachloride can be produced in a high yield even under low temperature conditions by a one-step reaction. In addition, it can be expected to reduce raw material costs and waste zeolite processing costs that were conventionally required. Furthermore, since industrial waste can be reduced, it can be expected to reduce the environmental load.

  One embodiment of the present invention is a method for producing silicon for solar cells. The method for producing silicon for solar cells includes a step (1) of obtaining silicon tetrachloride by chlorinating a silicon-containing material containing zeolite in the presence of a carbon-containing material, and a tetrachloride produced by the step (1). A step (2) for separating and purifying silicon; and a step (3) for obtaining polycrystalline silicon by reacting the silicon tetrachloride purified in step (2) with zinc gas.

  According to the method for producing silicon for solar cells of this embodiment, by using silicon-containing material containing zeolite and directly producing silicon tetrachloride by the reaction shown in (e) above, the conventional production method can be obtained. However, since the number of reaction steps can be reduced and the reaction temperature can be lowered, it is possible to continue supplying silicon for solar cells stably and inexpensively.

  According to the present invention, silicon for solar cells can be provided stably and inexpensively.

It is a process figure which shows the manufacturing method of the general silicon for solar cells using the conventional zinc reduction method. It is a process figure showing a manufacturing method of silicon for solar cells concerning an embodiment.

  Hereinafter, although the best mode for carrying out the present invention is shown, this is not restrictive.

  The method for producing silicon for solar cells according to the embodiment includes a step (1) of obtaining silicon tetrachloride by chlorinating a silicon-containing material containing zeolite in the presence of a carbon-containing material, and the step (1). The step (2) for separating and purifying the silicon tetrachloride obtained by the step (2) and the step (3) for obtaining polycrystalline silicon by reacting the silicon tetrachloride purified in the step (2) with zinc gas are provided. FIG. 2 is a process diagram showing a method for manufacturing silicon for solar cells according to an embodiment.

[Step (1)]
In the step (1), silicon tetrachloride is obtained by chlorinating a silicon-containing material (S10) containing at least zeolite in the presence of a carbon-containing material (S20) (S30) (S40).

  Here, “zeolite” is a crystalline inorganic porous material containing silica. Specifically, zeolite A, zeolite X, zeolite Y, zeolite L, zeolite Ω, USY zeolite, ZK, ZSM, silicalite , Shabasite, erionite, offretite, mordenite, nitrolite, faujasite, sodalite, tomsonite, etc., but not limited thereto.

  As a feature of zeolite, since it is a porous material, it has a large surface area and has acid sites. When using a material with a small surface area, such as silica, as the silicon-containing material, a pulverization step is required to increase the surface area, but since the zeolite has a large surface area, the pulverization step is unnecessary and the manufacturing process when industrialized Can be reduced. Moreover, when mixed with a carbon-containing substance, carbon can be highly dispersed in silica by the interaction between the acid sites in the zeolite and the carbon-containing substance, and silicon tetrachloride can be obtained in high yield even at low temperatures. .

Moreover, although it is desirable that the zeolite has the following characteristics, this is not restrictive. The surface area (BET method) is suitably ^{1 to} 1000 m ² / g, preferably 10 to 700 m ² / g, more preferably 300 to 600 m ² / g, but is not limited thereto. The average pore diameter is suitably 2 to 100 mm, preferably 10 to 70 mm, and more preferably 30 to 50 mm, but is not limited thereto. As the pore volume, 0.1 to 2.0 mL / g, preferably 0.3 to 1.5 mL / g, more preferably 0.5 to 1.0 mL / g is suitable. is not. The acid point is suitably 0.01 to 1.0 mol / kg, preferably 0.1 to 0.8 mol / kg, more preferably 0.3 to 0.6 mol / kg. is not. Further, the caivan ratio (molar ratio of silica to alumina) is 2 or more, preferably 2 to 1000, more preferably 10 to 1000, but is not limited thereto.

  The silicon-containing material used in the present embodiment only needs to contain at least zeolite, and may contain a silicon-containing compound in addition to zeolite. Specific examples of the silicon-containing compound include, but are not limited to, silica, silica sand, silicon accumulation biomass, amorphous silica alumina, and the like. The amount of silicon contained in the silicon-containing compound is 15 to 46% by mass, preferably 20 to 45% by mass, and more preferably 20 to 35% by mass. is not.

  Furthermore, the silicon-containing material used in the present embodiment may contain subcomponents other than the main components composed of the zeolite and the silicon-containing compound described above. Specific examples of subcomponents include noble metals supported in zeolites such as gold, silver, platinum, palladium and molybdenum, and binders used for forming zeolites such as clay minerals, silica sols and alumina sols. This is not the case.

  It is preferable to use waste zeolite as the zeolite. In addition, “waste zeolite” refers to zeolite after use industrially, and specifically includes zeolite after use in reaction catalyst, adsorbent, ion exchange membrane, etc. Absent. In addition, the waste zeolite may contain substances other than zeolite.

  Since zeolite is industrially used in many fields for applications such as reaction catalysts, adsorbents, and ion exchange membranes, waste zeolite can be supplied in large quantities and stably. Furthermore, most of the waste zeolite is treated as industrial waste without being recovered and reused. When a silicon-containing substance containing at least waste zeolite as a raw material is used, not only the raw material cost can be reduced, but also the ash treatment cost that has been conventionally required can be reduced. Furthermore, since industrial waste can be reduced, the burden on the environment can also be reduced.

  In particular, it is suitable to use a waste catalyst as waste zeolite, preferably a waste catalyst used for crude oil treatment, but this is not a limitation. Some waste catalysts used for crude oil treatment have carbon-containing substances in the crude oil attached to them, so that silica and a carbon-containing substance described later are in a highly dispersed state. Therefore, a high chlorination reaction conversion rate can be achieved under lower temperature conditions. In addition, the amount of carbon-containing material added can be reduced, further reducing costs. Furthermore, some waste catalysts used for crude oil treatment have sulfur components in the crude oil attached thereto, and the reaction conversion rate is further improved by the catalytic action of the sulfur content.

  The carbon-containing substance used in the present embodiment may be not only solids such as coke, activated carbon, and carbon black, but also gases such as carbon monoxide, carbon dioxide, and methane. Although carbon monoxide produced | generated by (1) may be reused, it is not this limitation. The amount of carbon-containing material added is 2 to 25 times, preferably 2 to 12 times, more preferably 2 to 12 times the number of moles of silicon and aluminum contained in the silicon-containing material. Although it is suitable to make it 3-6 times, it is not this limitation.

  As a method of mixing the carbon-containing material and the silicon-containing material, simple mixing may be performed, or carbonization may be performed. Carbonization treatment refers to carbonizing a silicon-containing material by mixing a silicon-containing material and a carbon-containing material and heating in an inert gas atmosphere. By simply carbonizing the zeolite, the zeolite and the carbon-containing material are simply carbonized. Silica and carbon can be further highly dispersed compared with the case of mixing. In addition, nitrogen, argon, helium etc. are mentioned as an inert gas used for carbonization processing, However It is not this limitation. Moreover, as heating temperature at the time of carbonization processing, 200-1200 degreeC, Preferably it is 400-1000 degreeC, More preferably, 600-800 degreeC is suitable, However It is not this limitation.

  In one embodiment, the carbon-containing material contains ash resulting from an industrial process. In addition, the ash produced from an industrial process refers to the ash containing carbon produced by combustion and incineration processing in a factory facility. Specific examples include ash produced at waste incineration facilities and power plants, but this is not a limitation. Ashes generated from industrial processes generally have a small particle size and a large surface area, silica and carbon are more highly dispersed.

The amount of carbon contained in the ash generated from the industrial process is 30 to 95 mass%, preferably 60 to 95 mass%, more preferably 70 to 90 mass%, based on the total mass of the ash. Is suitable, but not limited to this. The average particle size of carbon contained in the ash produced from the industrial process is 0.1 to 1000 μm, preferably 1 to 100 μm, more preferably 5 to 30 μm. Not as long. Furthermore, 0.01~100m ² / g as a surface area (BET method) ash resulting from industrial processes, suitable preferably 0.1 to 50 m ² / g, and more preferably are from 1-30 m ² / g This is not the case.

  When a substance with a large particle size such as coke or activated carbon is used as the carbon-containing material, a pulverization step was required to reduce the particle size. It can be simplified. Further, the ash generated from the industrial process can be supplied in a large amount and stably. Furthermore, most of the ash generated from the industrial process is treated as industrial waste without being recovered and reused. For this reason, when the ash generated from the industrial process is used as the carbon-containing material, not only the raw material cost can be reduced, but also the processing cost of the waste zeolite that has been conventionally required can be reduced. Furthermore, since industrial waste can be reduced, the burden on the environment can also be reduced.

  In one embodiment, the ash generated from an industrial process as the carbon-containing material, particularly the ash generated from a power generation facility that converts combustion energy into electric power by burning organic matter (hereinafter referred to as ash generated from the power generation facility). It is preferable to contain. The ash generated from the power generation facility refers to ash generated mainly in a thermal power plant or an integrated gasification combined cycle (hereinafter abbreviated as IGCC), but is not limited thereto. IGCC is an electric power production system that generates electricity from combined power generation facilities using synthetic gas mainly composed of carbon monoxide and hydrogen generated from fossil fuels such as heavy oil, petroleum residue oil, petroleum coke, orimulsion, and coal. There is a large amount of ash discarded.

  The characteristics of the ash generated from the power generation equipment include not only the small particle size and the large surface area, but also the fact that it contains sulfur because it uses fossil fuel as a raw material. Since sulfur acts as a catalyst for the chlorination reaction as described above, the conversion rate of the chlorination reaction is improved when ash generated from the power generation equipment is used as the carbon-containing material. The ash produced from the power generation equipment suitably contains 1 to 30% by mass of sulfur, preferably 2 to 20% by mass, more preferably 5 to 10% by mass, but this is not restrictive.

  In conventional methods, sulfur compounds are mixed directly with silicon-containing substances and carbon-containing substances, or raw materials and sulfur compounds are mixed by sending sulfur compounds directly into the reaction system, so that silica, carbon, and sulfur compounds are sufficiently highly dispersed. Therefore, it is difficult to say that the catalyst ability of sulfur can be fully exhibited. On the other hand, since the ash generated from the power generation facility is in a highly dispersed state of carbon and sulfur at the molecular level, the reaction conversion rate can be improved even if the sulfur content is small.

  In the production of silicon tetrachloride, a catalyst for promoting the chlorination reaction may be added. Examples of the catalyst for promoting the chlorination reaction include potassium and sulfur, but are not limited thereto. Specifically, potassium carbonate, potassium chloride, potassium hydroxide, potassium sulfate, potassium nitrate, etc. can be used as the potassium content, and sulfur, sulfur dioxide, hydrogen sulfide, carbon disulfide, etc. can be used as the sulfur content. Not as long. The amount of the catalyst to be added is 0.05 to 30% by mass, preferably 0.05 to 20% by mass, and more preferably 0.1 to 10% by mass with respect to the silicon content in the reaction mixture. Suitable but not limited to this. In addition, as a method of mixing a silicon-containing substance containing at least zeolite, a carbon-containing substance, and, if necessary, a solid or liquid catalyst, either a wet method or a dry method may be used, and various methods can be used. Moreover, you may supply a reactor directly, without mixing a catalyst.

(Chlorine-containing substances)
Examples of the chlorine-containing substance used in the present embodiment include chlorine, carbon tetrachloride, chlorinated carbon compounds such as tetrachloroethylene, phosgene, chlorine and carbon monoxide, carbon dioxide, methane, hydrogen chloride, carbon chloride hydrogen, inert gas, and the like. However, the present invention is not limited to this. Further, as will be described later, the chlorine-containing material that has not been reacted in step (1) may be reused, and further, chlorine produced by electrolysis of zinc chloride in step (4) may be reused. Good.

  In the production method of the present embodiment, the reaction between the silicon-containing material, the carbon-containing material, and the mixture to which a catalyst is added as necessary, and the chlorine-containing material may use any method such as a fixed bed or a fluidized bed. The reaction temperature is suitably 400-1500 ° C, preferably 600-1200 ° C, more preferably 700-900 ° C, but is not limited thereto.

[Step (2)]
In step (2), silicon tetrachloride is separated and recovered from a reaction product obtained by chlorinating a silicon-containing material containing zeolite in the presence of a carbon-containing material (S50).

  Since zeolite generally contains many aluminas, the reaction product mainly contains silicon tetrachloride, aluminum chloride, carbon monoxide, and chlorine. As a method for separating and purifying silicon tetrachloride, a generally well-known distillation method can be used.

  Specifically, carbon monoxide and chlorine in the reaction product gas are separated by condensing the reaction product with a condenser (S60). The condensed reaction product liquid mainly contains silicon tetrachloride and aluminum chloride. When the condensate is passed through a distillation column and heated with a distillation can, the boiling point of aluminum chloride at atmospheric pressure is about 183 ° C. and the boiling point of silicon tetrachloride is about 58 ° C. Therefore, silicon tetrachloride (S70) is introduced from the top of the distillation column. Aluminum chloride can be taken out from the bottom of the distillation column. Furthermore, purity can be improved by repeatedly distilling the obtained silicon tetrachloride.

  In order to obtain high solar cell performance, it is necessary to use high-purity silicon. However, the purity of silicon tetrachloride, which is an intermediate compound, depends greatly on the purity of the silicon to be produced. It is preferable to increase the purity of silicon tetrachloride more than necessary by increasing the number of times. In one embodiment, it is preferable that the purity of the silicon tetrachloride purified by the step (2) is 99.99% or more by repeating the above steps.

  In one embodiment, the reaction product gas separated and recovered in the step (2) may be directly used as a raw material in the step (1) without further separation and purification. Carbon monoxide in the reaction product gas can be reused as the carbon-containing material in step (1), and unreacted chlorine-containing material can be reused as the chlorine source required for the chlorination reaction. it can. In addition, this reaction product gas recycling step has a great advantage in that a reaction gas separation and purification step is not required.

[Step (3)]
In step (3), as shown in the above reaction formula (d), silicon tetrachloride is reduced by performing a gas phase reaction between the silicon tetrachloride purified in step (2) and zinc gas (S80), High purity polycrystalline silicon is produced. In carrying out the method for producing silicon for solar cells according to the embodiment, the reaction temperature of the reduction reaction is preferably 600 to 1400 ° C., but is not limited thereto. In addition, as described later, the zinc used in the present embodiment may reuse the zinc gas that has not been reacted in the step (3), and the zinc separated and recovered in the later-described step (4). It may be reused.

  The produced polycrystalline silicon can be increased to a purity (99.99% or more, preferably 99.99999% or more) that can be used for a solar cell by repeating the evaporation separation method. Other reaction products include zinc chloride, unreacted zinc, silicon tetrachloride, and the like. By reducing the temperature to about 732 ° C., which is the boiling point of zinc chloride, zinc chloride becomes liquid and zinc becomes powder or liquid. Collected. Unreacted zinc and silicon tetrachloride can be reused as raw materials for the step (3).

[Step (4)]
One embodiment includes a step (4) of separating and recovering zinc chloride (S90) produced by the step (3) into zinc (S110) and chlorine (S120) by electrolysis (S100). The zinc separated and recovered in step (4) may be reused as the raw material for step (3), and the chlorine separated and recovered in step (4) may be reused as the raw material for step (1). By reusing the reaction by-products as reaction raw materials without leaving them, the production cost can be further reduced. Further, in the conventionally proposed manufacturing process, the process of converting to chlorine chloride is necessary for the reuse of the chlorine obtained in step (4). In the present embodiment, the process obtained in step (4) is required. It is possible to reuse the chlorine directly. Therefore, the manufacturing process can be simplified more than before, and the manufacturing cost can be further reduced.

  Hereinafter, the effect of the present invention will be specifically described based on examples. In the following description, a comparison / examination example of the manufacturing process of silicon tetrachloride in the step (1) is shown.

Example 1
100 mg of USY zeolite (manufactured by Catalyst Kasei Co., Ltd., Keiban ratio: 150) was used as the silicon-containing substance, and 39 mg of coke (manufactured by Nippon Oil Corporation, carbon content: 99.9% by mass or more) was used as the carbon-containing substance. The surface area (BET method) of the USY zeolite used was 570 m ² / g, the average pore diameter was 48 mm, the pore volume was 1.1 mL / g, the acid point was 0.5 mol / kg, and the coke was a commercially available ball mill. Used after grinding. The carbon-containing material was added to and mixed with the silicon-containing material to obtain a reaction mixture. The amount of carbon-containing material added was such that the number of moles of C contained in the reaction mixture satisfied the following formula (f).

Number of moles of C contained in the reaction mixture = 2A + 3B (f)
A: Number of moles of Si contained in silicon-containing material B: Number of moles of Al contained in silicon-containing material The reaction mixture was brought into contact with pure chlorine gas at 800 ° C., 900 ° C. or 1000 ° C. for 1 hour. Chlorination reaction was performed. Thereafter, the reaction product is condensed with a condenser to separate carbon monoxide and hydrogen chloride as reaction product gases, and the condensate is passed through a distillation column and heated with a distillation can. Got. The reaction conversion rate to silicon tetrachloride was calculated by the following formula (I).

Reaction conversion rate (%) = X / Y × 100 (ki)
X: Number of moles of silicon tetrachloride produced Y: Number of moles of Si contained in the silicon-containing material As a result, the reaction conversion ratio to silicon tetrachloride was 56.2% at a reaction temperature of 800 ° C., 900 It was 71.9% at 1000 ° C. and 71.0% at 1000 ° C.

(Example 2)
Waste USY zeolite 100 mg was used as the silicon-containing material, and coke 36 mg was used as the carbon-containing material. The waste USY zeolite used in this example was a waste catalyst used for crude oil treatment, and the carbon content in the crude oil was 1.9% by mass and the sulfur content was 0.3% by mass. The reaction mixture was prepared using the same method as in Example 1, and a chlorination reaction was performed by contacting with pure chlorine gas at 700 ° C., 800 ° C. or 900 ° C. for 1 hour. As a result, the reaction conversion rate to silicon tetrachloride was 74.1% at a reaction temperature of 700 ° C, 81.1% at 800 ° C, and 80.5% at 900 ° C.

(Example 3)
USY zeolite 100 mg was used as the silicon-containing material, and 46 mg of ash generated from the industrial process was used as the carbon-containing material. In this example, the ash produced from the waste incineration facility was used without being crushed as the ash produced from the industrial process. The carbon content of the ash produced from the industrial process used was 85.2% by mass, the average particle size was 17 μm, and the surface area (BET method) was 19 m ² / g. The reaction mixture was prepared using the same method as in Example 1, and a chlorination reaction was performed by contacting with pure chlorine gas at 700 ° C., 800 ° C. or 900 ° C. for 1 hour. As a result, the reaction conversion rate to silicon tetrachloride was 65.6% at 700 ° C, 72.5% at 800 ° C, and 72.8% at 900 ° C.

Example 4
100 mg of USY zeolite was used as the silicon-containing material, and 49 mg of ash generated from the power generation facility was used as the carbon-containing material. In this example, the ash generated from IGCC was used without pulverizing as the ash generated from the power generation equipment. The carbon content of the used IGCC ash was 79.0% by mass, the sulfur content was 5.9% by mass, the average particle size was 8 μm, and the surface area (BET method) was 23 m ² / g. The reaction mixture was prepared using the same method as in Example 1, and a chlorination reaction was performed by contacting with pure chlorine gas at 700 ° C., 800 ° C. or 900 ° C. for 1 hour. As a result, the reaction conversion rate to silicon tetrachloride was 74.3% at a reaction temperature of 700 ° C, 82.0% at 800 ° C, and 81.7% at 900 ° C.

(Comparative Example 1)
Silica 100 mg was used as the silicon-containing material, and coke 39 mg was used as the carbon-containing material. The silica was used after being pulverized by a ball mill. In addition, the surface area (BET method) of the silica stone after pulverization was 2160 cm ² / g, and the silica content was 95.2% by mass. The reaction mixture was prepared using the same method as in Example 1, and a chlorination reaction was performed by contacting with pure chlorine gas at 700 ° C., 800 ° C. or 900 ° C. for 1 hour. As a result, the reaction conversion rate to silicon tetrachloride was 3.9% at a reaction temperature of 700 ° C, 4.2% at 800 ° C, and 4.0% at 900 ° C.

  As mentioned above, although this invention was demonstrated based on the Example, this invention is not restrict | limited to these, A various change and improvement are possible.

Claims (7)

A step (1) of obtaining silicon tetrachloride by chlorinating a silicon-containing material containing zeolite in the presence of a carbon-containing material;
A step (2) of separating and purifying silicon tetrachloride produced by the step (1);
A step (3) of obtaining polycrystalline silicon by reacting the silicon tetrachloride purified in the step (2) with a zinc gas;
A method for producing silicon for solar cells.   The method for producing silicon for solar cells according to claim 1, wherein the zeolite is waste zeolite.   The method for producing silicon for solar cells according to claim 1 or 2, wherein the carbon-containing substance contains ash generated from an industrial process.   The method for producing silicon for solar cells according to claim 3, wherein the ash generated from the industrial process is ash generated from a power generation facility that converts combustion energy into electric power by burning organic matter.   The method for producing silicon for solar cells according to any one of claims 1 to 4, wherein the purity of silicon tetrachloride obtained in the step (2) is 99.99% or more.   The method for producing silicon for solar cells according to any one of claims 1 to 5, wherein the reaction product gas generated in the step (2) is reused as a raw material in the step (1). Further comprising a step (4) of separating and recovering zinc and chlorine by electrolyzing the zinc chloride produced in the step (3),
The zinc separated and recovered in the step (4) is reused as a raw material in the step (3), and the chlorine separated and recovered in the step (4) is reused as a raw material in the step (1). Item 7. The method for producing silicon for solar cells according to any one of Items 1 to 6.

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