JP2011098861A - Method and apparatus for producing solar cell silicon - Google Patents

Abstract

A method and apparatus for manufacturing silicon for solar cells that can be manufactured consistently from raw materials to products, require less energy, and generate less CO ₂ .
A method for producing silicon for solar cells from a raw material comprising silicon oxide containing impurities, wherein the raw material is electrochemically reduced in molten salt to separate oxygen. The molten salt electrolytic reduction step and the product obtained by the molten salt electrolytic reduction step are electrolytically purified in molten salt to produce chloride electrochemically, and chlorinate silicon while isolating some of the impurities. The molten salt electrolytic purification process recovered as a product, the distillation purification process for separating impurities entrained in the chloride recovered by the molten salt electrolytic purification process and separating them from silicon chloride, and the purification by the distillation purification process A reduction step of chemically reducing silicon chloride to obtain silicon.
[Selection] Figure 1

Description

  The present invention relates to a method and apparatus for manufacturing silicon for solar cells, and more specifically, silicon for solar cells that manufactures silicon for solar cells by reducing and purifying silicon oxide using a molten salt electrolysis method. The present invention relates to a manufacturing method and a manufacturing apparatus.

  In recent years, in consideration of the global environment, renewable energy such as sunlight, solar heat, wind power, etc., which generate less greenhouse gases has attracted attention. Among them, solar power generation is planned to build a large-scale power plant called Mega Solar, and it is known that the demand for solar cells serving as the base of this power generation facility will increase.

  As for solar cells, those using single crystal or polycrystalline silicon are mainly used. Silicon for solar cells (solar grade silicon) is required to have a purity of 99.9999% (6N) or higher, and as a material there is currently a non-standard product for silicon for semiconductors (purity 99.999999999% (11N)). in use. However, considering fluctuations in semiconductor demand and the future increase in demand for solar grade silicon, there is a high possibility that there will be obstacles to stable material supply. For this reason, it is necessary to develop a manufacturing system capable of supplying 6N solar grade silicon.

In addition, the current silicon production method requires a lot of energy in the raw material production process and generates CO ₂ as exhaust gas. For this reason, there has been a problem that EPT (energy payback time) becomes long compared to other renewable energies.

  In the conventional silicon manufacturing method, raw silicon dioxide is heated together with carbon to obtain roughly purified silicon. Thereafter, a method of converting this silicon into a silane-based gas and obtaining high-purity silicon by distillation purification is often used. This method is a technique for obtaining semiconductor grade silicon, and requires a lot of energy and complicated processes for obtaining a purity of 11N.

  On the other hand, regarding the manufacture of solar grade silicon, many simple manufacturing methods have been developed in anticipation of an increase in demand, but few technologies have been established. A method for producing solar grade silicon by electrochemical reduction of silicon dioxide has also been proposed (see, for example, Patent Document 1 and Patent Document 2). However, these methods are not consistently manufactured by electrochemical techniques from raw materials to products.

JP 2006-321688 A JP 2007-16293 A

Conventionally, as described above, a silicon non-standard product manufactured by a method for manufacturing silicon for semiconductor (11N) that requires a large amount of energy and generates a large amount of CO ₂ is often used as solar cell silicon. There was no method that could consistently manufacture solar silicon from raw materials to products. For this reason, solar cell silicon can be manufactured consistently from raw materials to products, and the development of solar cell silicon manufacturing method and manufacturing apparatus that requires less energy and generates less CO ₂ Was demanded.

The present invention has been made in response to the above-described conventional circumstances, and can be manufactured consistently from raw materials to products, and also requires less energy and generates less CO _2. It is intended to provide a manufacturing method and a manufacturing apparatus.

  One aspect of a method for producing silicon for solar cells of the present invention is a method for producing silicon for solar cells from a raw material made of an oxide of silicon containing impurities, wherein the raw material is a molten salt. A molten salt electroreduction step in which oxygen is separated by electrochemical reduction therein, and a product obtained by the molten salt electroreduction step is electrolytically purified in molten salt to electrochemically produce chloride, Molten salt electrorefining process for recovering silicon as chloride while separating a part of impurities, and distillation for separating impurities entrained in the chloride recovered by the molten salt electrorefining process to separate from silicon chloride And a reduction step of obtaining silicon by chemically reducing a chloride of silicon purified by the distillation purification step.

  One aspect of the solar cell silicon manufacturing apparatus of the present invention is a solar cell silicon manufacturing apparatus that manufactures solar cell silicon from a raw material made of an oxide of silicon containing impurities, wherein the raw material is a molten salt. A molten salt electroreduction means for electrochemically reducing and separating oxygen therein, and a product obtained by the molten salt electroreduction means is electrolytically purified in molten salt to electrochemically produce chloride, Molten salt electrolytic purification means for recovering silicon as chloride while separating a part of impurities, and distillation for separating impurities entrained in the chloride recovered by the molten salt electrolytic purification means to separate from silicon chloride It comprises a purification means, and a reduction means for obtaining silicon by chemically reducing the chloride of silicon purified by the distillation purification means.

According to the present invention, it can be produced consistently from raw material to finished products, and the required amount of energy is small, to provide a method and apparatus for manufacturing a silicon for even small solar cell generation amount of CO ₂ it can.

The figure for demonstrating the structure of the manufacturing method and manufacturing apparatus of the silicon for solar cells which concern on one Embodiment of this invention. The figure which shows schematic structure of the molten salt electrolytic reduction process of FIG. 1, and the apparatus to be used. The figure which shows schematic structure of the molten salt electrorefining process of FIG. 1, and the apparatus to be used. The figure which shows schematic structure of the distillation purification process of FIG. 1, and the apparatus to be used. The figure which shows schematic structure of the reduction | restoration process of FIG. 1, and the apparatus to be used.

  Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram for explaining a configuration of a method and an apparatus for manufacturing solar cell silicon according to an embodiment of the present invention. As shown in FIG. 1, in this embodiment, by combining five steps of a molten salt electrolytic reduction step 1, a molten salt electrolytic purification step 2, a distillation purification step 3, a reduction step 4 and a distillation step 5 Obtain battery silicon. As a result, the generation of CO ₂ due to the conversion reaction of the raw materials can be made zero, and a solar cell silicon production process that does not use any harmful gas can be achieved.

  That is, in this embodiment, a metal anode that is opposite to the cathode loaded with the raw material is immersed in molten salt and an electric current is passed between the electrodes to cause an electrochemical reaction, reducing the silicon dioxide of the raw material to obtain silicon. At the same time, oxygen is gasified at the anode and exhausted. Next, the silicon obtained by reduction is electrolytically purified in a molten salt to electrochemically convert the crudely purified silicon into chloride and to separate some of the impurities contained therein. Next, the chloride obtained by electrolytic purification is further distilled, the silicon chloride is refined using the difference in boiling point of each element, and further reduced by chemical reduction using an alkali metal or alkaline earth metal as a reducing agent. Thus, silicon for solar cells (solar grade silicon) is obtained.

  FIG. 2 schematically shows details of the apparatus used in the molten salt electroreduction step 1 and the molten salt electroreduction step 1 shown in FIG. As shown in the figure, in the molten salt electroreduction step 1, a conductor such as metal is contained in a molten salt (chloride) 8 loaded in an electrolytic cell 7 installed in an electric furnace 6 and maintained in a heated and molten state. An electrolytic reduction cathode 10 made of a net-like material made of metal and loaded with a raw material 9 therein and a metal electrolytic reduction anode 12 having an exhaust pipe 11 are installed. The raw material 9 is made of silicon oxide (silicon dioxide), and silica sand containing impurities can be used.

In this state, by passing a current between the electrolytic reduction cathode 10 and the electrolytic reduction anode 12, oxygen is electrochemically separated from the raw material 9 loaded on the electrolytic reduction cathode 10, and oxygen gas is generated at the electrolytic reduction anode 12. It is generated and discharged out of the system through the exhaust pipe 11. By this operation, the raw material 9 made of silicon oxide is reduced, and silicon can be obtained. According to this method, silicon can be produced without generating CO ₂ .

  Examples of the molten salt used as the electrolytic solvent for the reduction include, for example, a simple substance of alkali metal chloride such as lithium chloride, a simple substance of alkaline earth metal chloride such as calcium chloride, a simple substance of magnesium chloride, or these. What mixed 2 or more types can be used.

  FIG. 3 schematically shows details of the apparatus used in the molten salt electrolytic purification step 2 and the molten salt electrolytic purification step 2 shown in FIG. As shown in the figure, the silicon (including impurities) reduced in the molten salt electroreduction step 1 is used by extracting the molten salt electrorefined anode 13 (electrolytic reduction cathode 10 loaded with raw materials by molten salt electroreduction). And placed in the molten salt 15 heated and melted together with the metal cathode 14. A current is passed between the electrolytically purified anode 13 and the metal cathode 14.

  By this operation, Si is ionized in the electrolytically purified anode 13 and dispersed as silicon tetrachloride in the molten salt 15. However, since silicon tetrachloride has a boiling point as low as 57.6 ° C., it is immediately vaporized and released as a gas outside the molten salt 15. At this time, impurities, Fe, Ti, Al, C, etc. contained in the reduced silicon remain in the molten salt 15 or as an anode residue and are separated. On the other hand, at the metal cathode 14, metal (calcium, lithium, magnesium, or the like) is recovered as a precipitate 16 due to a molten salt component generated along with the generation of silicon chloride.

  FIG. 4 schematically shows details of a distillation purification process 3 for cooling and recovering the vapor of silicon tetrachloride generated in the electrolytic purification process 2 shown in FIG. 1 and an apparatus used for the distillation purification process 3. . The silicon tetrachloride vapor generated in the molten salt electrorefining step 2 is transferred to the agglomeration section 18 through the conduit 17 heated to about 100 ° C.

  A plurality of stages of cooling recovery plates 19 each set at a predetermined temperature are installed in the aggregation unit 18. In the example shown in FIG. 4, the first-stage cooling recovery plate 19 is higher than 60 ° C., the second-stage cooling recovery plate 19 is 50 to 60 ° C., and the third-stage cooling recovery plate 19 is lower than 50 ° C. It has become. The silicon tetrachloride 20 contained in the gas and the impurities boron chloride 21 and phosphorus chloride 22 are separated and aggregated and recovered due to the difference in freezing point. Specifically, phosphorus chloride 22 is recovered by the first-stage cooling recovery plate 19, silicon tetrachloride 20 is recovered by the second-stage cooling recovery plate 19, and boron chloride 21 is recovered by the third-stage cooling recovery plate 19. Is recovered. Silicon tetrachloride separated by this method is repeatedly distilled and agglomerated until the target purity is reached, thereby obtaining silicon tetrachloride having the target purity.

  FIG. 5 schematically shows details of the reduction step 4 for reducing again the silicon tetrachloride purified and recovered in the distillation purification step 3 shown in FIG. 1 and the apparatus used in the reduction step 4. In the reduction process 4, the highly purified silicon tetrachloride 23 is loaded on the vaporizing section 24 and heated to be vaporized. On the other hand, the metal deposit (calcium, lithium, magnesium, or the like) 16 deposited on the metal cathode 14 in the molten salt electrorefining process 2 is loaded into the reaction vessel 25, and this is heated and melted to melt the molten metal 29. Keep in state.

When the silicon tetrachloride 26 vaporized in this state is discharged into the molten metal 29 through the conduit 27, when the molten metal 29 is, for example, Mg, the molten metal 29
SiCl ₄ + 2Mg → Si + 2MgCl ₂
Thus, high-purity silicon 28 can be obtained from silicon tetrachloride.

  Further, as shown in FIG. 1, the obtained high-purity silicon is sent to the distillation step 5, where metal chloride and metal and high-purity silicon (silicon) are distilled and separated. The obtained high-purity silicon is evaluated for purity, and if it satisfies the conditions for purity as silicon for solar cells, it is regarded as a product. On the other hand, when the conditions for purity as solar cell silicon are not satisfied, high-purity silicon that satisfies the conditions for purity as solar cell silicon by repeating the purification step from electrolytic purification step 2 Can be obtained.

According to the manufacturing method and manufacturing apparatus of silicon for solar cell of the embodiment as described above, CO ₂ other than CO ₂ due to the power used in the preparation does not occur. In addition, since the use of harmful gases such as chlorine gas used for chloride conversion can be suppressed, it is possible to more efficiently manufacture silicon for solar cells.

  1 ... Molten salt electrolytic reduction process, 2 ... Molten salt electrolytic purification process, 3 ... Distillation purification process, 4 ... Reduction process, 5 ... Distillation process, 6 ... Electric furnace, 7 ... Electrolyzer, 8 ...... Molten salt, 9 ... Raw material, 10 ... Electrolytic reduction cathode, 11 ... Exhaust pipe, 12 ... Electrolytic reduction anode, 13 ... Electrolytic purification anode, 14 ... Metal cathode, 15 ... Molten salt, 16 …… Precipitate, 17 …… Conduit, 18 …… Agglomerate, 19 …… Cooling recovery plate, 20 …… Silicon tetrachloride, 21 …… Phosphorus chloride, 22 …… Boron chloride, 23 …… High purity silicon tetrachloride , 24 ... vaporization section, 25 ... reaction vessel, 26 ... silicon tetrachloride gas, 27 ... conduit, 28 ... high-purity silicon, 29 ... molten metal.

Claims (7)

A method for producing silicon for solar cells, comprising producing silicon for solar cells from a raw material consisting of oxides of silicon containing impurities,
A molten salt electrolytic reduction process in which the raw material is electrochemically reduced in molten salt to separate oxygen;
Electrolytic purification of the product obtained by the molten salt electroreduction step in a molten salt to produce chloride electrochemically, and recovering silicon as chloride while separating a part of impurities Process,
A distillation purification step of distilling impurities entrained in the chloride recovered by the molten salt electrolytic purification step and separating it from silicon chloride;
A reduction step of obtaining silicon by chemically reducing silicon chloride purified by the distillation purification step;
The manufacturing method of the silicon for solar cells characterized by comprising. It is a manufacturing method of the silicon for solar cells of Claim 1,
In the molten salt electrolytic reduction step,
Oxygen is removed from the raw material by flowing an electric current between an electrolytic reduction anode having an exhaust pipe for exhausting gas and an electrolytic reduction cathode configured in a container shape with a conductive mesh material and holding the raw material therein. A method for producing silicon for solar cells, characterized in that silicon is obtained by separating the components. A method for producing silicon for solar cells according to claim 1 or 2,
In the molten salt electrolytic reduction step,
A method for producing silicon for solar cells, wherein the molten salt is lithium chloride, calcium chloride, or magnesium chloride, or a mixture of two or more thereof. It is a manufacturing method of silicon for solar cells given in any 1 paragraph of Claims 1-3,
In the molten salt electrolytic purification process,
The reduction product obtained in the molten salt electrolytic reduction step is electrolytically purified as an anode and dissolved in an anode, thereby separating impurities from the molten salt and recovering silicon chloride as a gas, and the molten salt is removed on the cathode side. A method for producing silicon for solar cells, comprising reducing and precipitating a metal on the cathode. It is a manufacturing method of the silicon for solar cells of any one of Claims 1-4,
In the distillation purification step,
A method for producing silicon for solar cells, wherein silicon chloride and impurities having different boiling points are separated by bringing the gas recovered in the electrolytic purification step into contact with a plurality of aggregate plates set at different temperatures. It is a manufacturing method of silicon for solar cells given in any 1 paragraph of Claims 1-5,
In the reduction step, the silicon chloride purified to a high purity obtained in the distillation purification step is brought into contact with the metal deposited on the cathode in the molten salt electrolytic purification step to chemically reduce to obtain silicon. A method for producing silicon for batteries. An apparatus for producing silicon for solar cells, which produces silicon for solar cells from a raw material consisting of oxides of silicon containing impurities,
Molten salt electrolytic reduction means for electrochemically reducing the raw material in molten salt to separate oxygen;
Electrolytic purification of the product obtained by the molten salt electroreduction means in the molten salt to electrochemically generate chloride, and recovering silicon as chloride while separating a part of impurities, the molten salt electrolytic purification Means,
A distillation purification means for distilling impurities entrained in the chloride recovered by the molten salt electrolytic purification means and separating it from silicon chloride;
A reducing means for chemically reducing silicon chloride purified by the distillation purification means to obtain silicon;
An apparatus for producing silicon for solar cells, comprising:

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