Method for utilizing carbon dioxide as a resource and method for producing silicon carbide

Abstract

To provide a method for recycling carbon dioxide as silicon carbide which is a solid carbide at a low energy cost.SOLUTION: Provided are a method for recycling carbon dioxide and a method for producing silicon carbide, comprising reacting silicon with carbon dioxide through an exothermic reaction to combine carbon of the carbon dioxide with the silicon to obtain silicon carbide, wherein the exothermic reaction is carried out in a heating furnace.SELECTED DRAWING: None

Description

【Technical Field】 【0001】 The present invention relates to a method for resource utilization of carbon dioxide and a method for producing silicon carbide. 【Background Art】 【0002】 In order to realize a sustainable global environment and society, efforts to achieve a decarbonized society are accelerating internationally. For example, a large amount of carbon dioxide is emitted in thermal power generation using fossil fuels such as coal, oil, and natural gas as energy sources. Carbon dioxide accounts for most of the greenhouse gases and is considered the main cause of global warming, and technological development for reducing its emissions is underway. As an effort to reduce the emissions into the atmosphere by using carbon dioxide as a resource, for example, "CCUS (Carbon dioxide Capture, Utilization and Storage)" can be mentioned. In "CCUS", chemicals, fuels, minerals, etc. are listed as the utilization destinations of carbon dioxide. 【0003】 In addition, in order to realize a sustainable society, it is also important to effectively utilize resources and promote the reduction and reuse of waste. For example, under the situation where the digitalization of society is rapidly progressing, the semiconductor market is booming with the construction of digital infrastructure and the like. It is said that about 90,000 tons of silicon sludge are generated annually in the production of silicon wafers (semiconductor silicon), which are the base materials of semiconductor products, and research and development for effectively utilizing this silicon sludge are being carried out. For example, Non-Patent Document 1 describes a technique for obtaining silicon carbide from silicon chips (silicon sludge) using activated carbon as a carbon source. 【Prior Art Documents】 【Non-Patent Documents】 【0004】 【Non-Patent Document 1】 Powder Technology, December 2017, Vol. 322, p. 290-295 [Overview of the project] [Problems that the invention aims to solve] 【0005】 The effective use of carbon dioxide as a carbon source in chemical reactions is being widely explored. For example, if carbon dioxide can be used as a raw material for solid compounds, it would have the advantage of significantly reducing the volume of carbon dioxide. As part of such technologies, it is conceivable that minerals could be synthesized using carbon dioxide as a raw material and used as fine ceramics, etc. However, currently, the only proposed technology for mineralizing carbon dioxide is the reaction of carbon dioxide with calcium oxide to obtain calcium carbonate. 【0006】 The object of this invention is to provide a method for utilizing carbon dioxide as a resource, specifically silicon carbide, a solid carbide, at a low energy cost. [Means for solving the problem] 【0007】 In view of the above problems, the inventors of this invention conducted extensive research and found that when carbon dioxide and silicon are brought into contact and heated, an exothermic reaction occurs rather than an endothermic reaction, and silicon carbide is obtained as a reaction product. In other words, using carbon dioxide as a carbon source, silicon carbide, a solid carbide, is produced by an exothermic reaction. This invention was completed based on this finding and further research. 【0008】 The problems of the present invention were solved by the following means. [1] This method includes reacting silicon with carbon dioxide via an exothermic reaction to bond the carbon in the carbon dioxide with the silicon and obtain silicon carbide. A method for utilizing carbon dioxide as a resource, wherein the aforementioned exothermic reaction is carried out in a heating furnace. [2] A method for utilizing carbon dioxide as a resource, comprising reacting silicon with carbon dioxide via an exothermic reaction to bond the carbon of the carbon dioxide with the silicon to obtain a solid reaction product containing silicon carbide, and washing this solid reaction product to obtain silicon carbide with a purity of 99.00% or higher. [3] This method includes reacting silicon with carbon dioxide via an exothermic reaction to bond the carbon in the carbon dioxide with the silicon and obtain silicon carbide. A method for utilizing carbon dioxide as a resource, using silicon powder with a particle size of 0.2 to 4.0 μm as the silicon. [4] This method includes reacting silicon with carbon dioxide via an exothermic reaction to bond the carbon in the carbon dioxide with the silicon and obtain silicon carbide. A method for producing silicon carbide, wherein the aforementioned exothermic reaction is carried out in a heating furnace. [5] A method for producing silicon carbide, comprising reacting silicon with carbon dioxide via an exothermic reaction to bond the carbon of the carbon dioxide with the silicon to obtain a solid reaction product containing silicon carbide, and washing this solid reaction product to obtain silicon carbide with a purity of 99.00% or higher. [6] This method includes reacting silicon with carbon dioxide via an exothermic reaction to bond the carbon in the carbon dioxide with the silicon and obtain silicon carbide. A method for producing silicon carbide, wherein silicon powder with a particle size of 0.2 to 4.0 μm is used as the silicon. 【0009】 In this invention and specification, numerical ranges represented by "~" mean ranges that include the numerical values ​​before and after "~" as the lower and upper limits. In this specification, when describing the content, physical properties, etc. of components by setting multiple numerical ranges in stages, the upper and lower limits that form the numerical range are not limited to the specific combinations described before and after "~", and the numerical values ​​of the upper and lower limits that form each numerical range can be combined as appropriate. [Effects of the Invention] 【0010】 According to the carbon dioxide resource utilization method of the present invention, carbon dioxide can be efficiently utilized as a resource. Furthermore, according to the silicon carbide production method of the present invention, silicon carbide, which is a solid carbide, can be efficiently obtained using carbon dioxide as a carbon source. [Modes for carrying out the invention] 【0011】 [Method for utilizing carbon dioxide as a resource and method for producing silicon carbide] The present invention provides a method for utilizing carbon dioxide as a resource and a method for producing silicon carbide (hereinafter, "the present invention's method for utilizing carbon dioxide as a resource and a method for producing silicon carbide" will be collectively referred to simply as "the present invention's method"), which involves reacting silicon and carbon dioxide via an exothermic reaction to bond the carbon in the carbon dioxide with the silicon and produce silicon carbide. It has not been previously known that an exothermic reaction occurs when silicon and carbon dioxide are brought into contact and heated, and the present invention's method is essentially characterized by having this exothermic reaction as a constituent element. Based on this characteristic, the present invention provides the following three forms of methods. 【0012】 <First form> This method includes reacting silicon with carbon dioxide via an exothermic reaction to bond the carbon in the carbon dioxide with the silicon and obtain silicon carbide. A method for utilizing carbon dioxide as a resource or for producing silicon carbide, wherein the aforementioned exothermic reaction is carried out in a heating furnace. 【0013】 <Second form> A method for utilizing carbon dioxide as a resource or a method for producing silicon carbide, comprising reacting silicon with carbon dioxide via an exothermic reaction to bond the carbon of the carbon dioxide with the silicon to obtain a solid reaction product containing silicon carbide, and washing this solid reaction product to obtain silicon carbide with a purity of 99.00% or higher. 【0014】 <3rd form> This method includes reacting silicon with carbon dioxide via an exothermic reaction to bond the carbon in the carbon dioxide with the silicon and obtain silicon carbide. A method for resource recovery of carbon dioxide or a method for producing silicon carbide, using silicon powder with a particle size of 0.2 to 4.0 μm as the silicon. 【0015】 In the method of the present invention, the term "exothermic reaction" is used to mean a combustion synthesis reaction in which combustion propagates spontaneously and the synthesis reaction proceeds. In the present invention, the resource recovery of carbon dioxide means using carbon dioxide as a carbon source and resource recovering it as silicon carbide, which is a solid carbide. Examples of the form of resource recovery of carbon dioxide include recycling of carbon dioxide generated in industrial activities, etc., and a form in which carbon dioxide in the air is concentrated and used for resource recovery as needed. 【0016】 The above-mentioned features common to the first form, the second form, and the third form, that is, the reaction of bonding the carbon of the carbon dioxide and the silicon through an exothermic reaction between silicon and carbon dioxide to produce silicon carbide will be described, and in the description of the embodiments thereof, technical matters specific to each form will also be described. 【0017】 In the method of the present invention, an exothermic reaction between silicon and carbon dioxide is used. Silicon and carbon dioxide are made to coexist, and usually, an exothermic reaction is caused by heating. The method of the present invention is characterized in that it utilizes an exothermic reaction, whereby the energy supplied from the outside can be suppressed and the energy cost can be reduced. The reaction mechanism of this exothermic reaction will be examined below. 【0018】 When the reaction between silicon and carbon dioxide is represented by a reaction formula, the following reaction formula (1) can be recalled. Si + CO2→ SiC+O2(1) However, in the above reaction formula (1), the change in Gibbs free energy (ΔG (kJ / mol)) exceeds 300 within the range of 0 to 2500 K (0 to 2500 °C) under 1 atm. That is, this reaction is an endothermic reaction and cannot be an exothermic reaction. However, the fact that the reaction between silicon and carbon dioxide can be carried out via an exothermic reaction has been experimentally demonstrated in the examples described later. Furthermore, it has been confirmed that SiO2 is produced in addition to SiC in this reaction. Thus, it is presumed that the reaction between silicon and carbon dioxide proceeds, for example, according to the following reaction equations (2) to (4), and it is thought that SiC can be obtained in the method of the present invention according to the following reaction equations (2) and / or (3). 2Si + CO2 → SiO2 + SiC (2) 3Si + 2CO2→ 2SiC + SiO2+ O2(3) Si + CO2 → SiO2 + C (4) In reaction equation (2) above, ΔG is less than 0 in the range of 0 to 2500 K at 1 atmosphere. Also, in reaction equation (3) above, ΔG is less than 0 in the range of 0 to 1200 K at 1 atmosphere. In other words, reaction equations (2) and (3) are exothermic reactions even in the high-temperature range. Also, in reaction equation (4) above, ΔG is less than 0 in the range of 0 to 2500 K at 1 atmosphere. 【0019】 In the above reaction equation, SiC may be α-SiC or β-SiC. Normally, β-SiC is produced when an exothermic reaction is carried out at a temperature of around 500 to 1500°C, but this β-SiC can be subjected to a phase transition to α-SiC by heating it to a temperature exceeding 2000°C. 【0020】 In the method of the present invention, silicon itself (elementary silicon) may be used as the silicon source (raw material) for the exothermic reaction, or silicon-containing compounds (compounds containing the element silicon, such as silicon nitrides, borides, chlorides, fluorides, and hydrides) may be used. From the viewpoint of reaction efficiency, these silicon sources are preferably in powder form. Smaller particle sizes of the silicon source can further increase the yield of the desired silicon carbide. From this viewpoint, the particle size of the silicon source is preferably 0.2 to 4.0 μm, more preferably 0.3 to 3.0 μm, even more preferably 0.3 to 2.0 μm, and particularly preferably 0.4 to 1.5 μm. In the present invention, "particle size" means median diameter (d50). The median diameter is the particle size at which the cumulative distribution reaches 50% when the total volume of the particles is taken as 100%, as measured by laser diffraction and scattering. The silicon source consisting of the desired fine particles described above can be prepared by grinding processes such as using a mortar and pestle, ball mill, crush mill, and hammer mill. The silicon source is preferably silicon powder. It is also preferable to use silicon sludge or pulverized silicon sludge as the silicon powder. 【0021】 In the method of the present invention, carbon dioxide can be used without being limited by its source (emission source). For example, carbon dioxide from the air can be concentrated as needed. Carbon dioxide emitted from thermal power plants, cement plants, and blast furnaces of steel mills can also be used. Furthermore, carbon dioxide generated from various manufacturing plants such as waste incineration facilities, transport equipment, chemical manufacturing, pulp manufacturing, paper manufacturing, paper product manufacturing, food and beverage manufacturing, and machinery manufacturing may also be used. 【0022】 Furthermore, within the limits that do not impair the effects of the present invention, the reaction system of the exothermic reaction described above may contain atoms, molecules, or compounds other than carbon dioxide and silicon sources. Examples of such atoms, molecules, or compounds include nitrogen, noble gases, methane, ethylene, oxygen, carbon monoxide, carbon, and organic substances. In the above reaction system, the proportion of silicon source among the raw materials other than carbon dioxide is, for example, 50% by mass or more, preferably 60% by mass or more, and more preferably 70% by mass or more. 【0023】 In the method of the present invention, in order to control the temperature rise of the exothermic reaction, the material may be mixed with a diluent and reacted with carbon dioxide to cause an exothermic reaction. Examples of such diluents include oxides, nitrides, carbides, and complex oxides. The amount of diluent used is not particularly limited; for example, it can be used in amounts of 90 parts by mass or less per 100 parts by mass of carbide-forming raw material, preferably 80 parts by mass or less, and more preferably 75 parts by mass or less. 【0024】 In the method of the present invention, silicon and carbon dioxide are reacted via an exothermic reaction. Typically, a silicon source and carbon dioxide are introduced into a reaction vessel and heated to produce an exothermic reaction. The silicon source is usually a solid, but the present invention is not limited to the form in which the silicon source is a solid. 【0025】 The above-mentioned reaction vessel is preferably heat-resistant, and for example, a reaction vessel made of quartz, ceramics, or metal is preferred. 【0026】 The method of bringing silicon into contact with carbon dioxide is not particularly limited. For example, this could involve using a gas containing carbon dioxide in the reaction vessel or circulating carbon dioxide through the reaction vessel. In addition to carbon dioxide, other gases may be introduced into the reaction vessel. Examples of such gases include nitrogen gas, noble gases, carbon monoxide gas, and oxygen gas. The proportion of carbon dioxide in the gas introduced into the reaction vessel is not particularly limited, and the desired reaction can proceed even with low concentrations of carbon dioxide. Furthermore, by repeating the reaction or circulating the carbon dioxide supply in a flow system, it is possible to increase the yield of silicon carbide even with low concentrations of carbon dioxide. From the viewpoint of further improving reaction efficiency, the proportion of carbon dioxide in the gas introduced into the reaction vessel is preferably, for example, 1 volume% or more, preferably 5 volume% or more, and preferably 10 volume% or more. Furthermore, it is also preferable to carry out the reaction using an excess of carbon dioxide moles relative to the moles of silicon. 【0027】 The heating temperature when heating the reaction system is not particularly limited as long as an exothermic reaction occurs. For example, it can be 30°C or higher, more preferably 50°C or higher, even more preferably 100°C or higher, even more preferably 300°C or higher, even more preferably 500°C or higher, even more preferably 800°C or higher, even more preferably 1000°C or higher, even more preferably 1100°C or higher, and even more preferably 1150°C or higher. In addition, the above heating temperature can be, for example, 2500°C or lower, 2400°C or lower, 2300°C or lower, and 2200°C or lower. Therefore, the heating temperature of the reaction system can be 30 to 2500°C, preferably 300 to 2400°C, more preferably 500 to 2300°C, even more preferably 800 to 2200°C, even more preferably 1000 to 2200°C, even more preferably 1100 to 2200°C, and particularly preferably 1150 to 2200°C. 【0028】 The heating time is not particularly limited as long as the exothermic reaction has started. If heating continues after the start of the exothermic reaction, the heating time can be, for example, 0.1 to 5000 seconds, with 0.5 to 4000 seconds being more preferable. Furthermore, once the exothermic reaction has started, heating may be stopped or continued. For example, in a reaction where combustion propagates spontaneously and the synthesis reaction proceeds, the reaction will proceed efficiently even if heating is stopped. 【0029】 The means for heating the reaction system are not particularly limited. For example, heating devices that use heat conduction, such as heating furnaces (electric furnaces, gas heating furnaces, induction heating furnaces, etc.), can be used. It is also preferable to use laser irradiation, microwave irradiation, and halogen lamp light irradiation, which do not involve heat conduction. Microwave heating may be performed using single-mode standing waves or multi-mode microwave heating. 【0030】 The output of microwave irradiation can be, for example, 1 to 3000 W, with 5 to 1000 W being preferred. On the other hand, the output when irradiating with light (infrared) using a halogen lamp can be, for example, 1 to 1000 W, with 10 to 450 W being preferred. 【0031】 In the method of the present invention, the reaction between silicon and carbon dioxide may be carried out under atmospheric pressure, or under reduced or increased pressure with the reaction vessel sealed. Under increased pressure, the exothermic reaction can be accelerated. The reaction between silicon and carbon dioxide can be carried out, for example, under 0.01 to 200 MPa, or under 0.10 to 100 MPa. 【0032】 In the method of the present invention, the heating step may be repeated two or more times (preferably 2 to 5 times, more preferably 2 to 4 times) in a single reaction system. When the heating step of the reaction system is performed two or more times, typically, after the exothermic synthesis reaction of the previous step is completed, the reaction system is allowed to stand until it reaches room temperature before the next heating step is performed. Furthermore, if the particles constituting the reaction system have aggregated after the above-mentioned standing period, the aggregated particles may be crushed as needed. If the aggregated particles and the silicon source powder are present together, the silicon source powder may be removed by sieving (for example, a sieve with a mesh size of 45 μm) before crushing. This allows only the unreacted material in the aggregates to be subjected to the reaction with carbon dioxide again, thereby increasing the purity of the desired silicon carbide. 【0033】 Furthermore, in the method of the present invention, after the above-mentioned standing or crushing, it is preferable to wash the solid reaction product (crude product) after the exothermic reaction with a washing solution in order to remove unreacted silicon sources and by-products. The washing solution can be appropriately selected depending on the type of silicon source and by-product. For example, silicon carbide can be obtained in high purity by washing the solid reaction product after the exothermic reaction with a mixture of hydrofluoric acid and nitric acid or an aqueous sodium hydroxide solution. In the method of the present invention, it is particularly preferable to wash with an aqueous sodium hydroxide solution from the viewpoint of selectively dissolving and efficiently removing silicon and silicon dioxide. The above cleaning process can raise the purity of silicon carbide to, for example, 99.00% or higher, and can even be increased to 99.10% or higher. This purity can be determined, for example, by inductively coupled plasma mass spectrometry (ICP-MS) or X-ray fluorescence analysis (XRD, XRF). The conditions for washing using an aqueous sodium hydroxide solution are not particularly limited. For example, the concentration of the aqueous sodium hydroxide solution can be 1 to 48% by mass, preferably 5 to 20% by mass, and more preferably 14 to 18% by mass. The temperature of the aqueous sodium hydroxide solution is not particularly limited. For example, it can be 10 to 180°C, preferably 50 to 180°C, more preferably 80 to 180°C, and even more preferably 120 to 160°C. Washing can be carried out, for example, by stirring the solid reaction product after the exothermic reaction in an aqueous sodium hydroxide solution for 1 minute to 72 hours (preferably 30 to 150 minutes). This dissolves silicon and silicon dioxide in the aqueous sodium hydroxide solution, and then high-purity silicon carbide can be obtained by solid-liquid separation such as filtration. 【0034】 The silicon carbide obtained by the method of the present invention can be applied to a variety of uses. For example, it can be used as a raw material for refractories, heating elements, setters, semiconductors, wafers, and semiconductor ingots. [Examples] 【0035】 The present invention will be described in more detail based on examples. Except as otherwise provided herein, the present invention is not limited to the following examples. 【0036】 [Example 1] A quartz cylinder (size: cross-sectional diameter 8 mm, length 70 mm) containing 0.15 g of silicon powder was placed along the central axis of the resonator. Under atmospheric pressure, carbon dioxide (CO2) gas was circulated through the cylinder at a flow rate of 0.14 L / min while microwaves were irradiated into the resonator at 70 W (frequency 2.45 GHz) for 10 seconds to form a single-mode standing wave, thereby electric heating of the silicon powder inside the cylinder. The temperature inside the reaction system was measured by thermography and found that the temperature reached 1800°C due to microwave irradiation. The reaction product was allowed to stand until it reached room temperature while the CO2 gas was still circulating. After standing, the reaction product was removed from the cylinder and crushed using an alumina mortar. Si and SiC were quantified using the RIR (reference intensity ratio) method based on the diffraction results obtained by XRD (X-ray diffraction) of the crushed reaction product. The quantitative results are shown in Table 1 below. The mass percentages in the table are based on the assumption that the sum of Si and SiC is 100 mass% (the same applies below). Furthermore, amorphous silica (SiO2) was confirmed as a reaction product by XRD. The same was true for the subsequent examples. 【0037】 [Example 2] The microwave irradiation time was set to 60 seconds, and the reaction product, which had been allowed to stand at room temperature in the same manner as in Example 1, was crushed using an alumina mortar. One cycle consisted of microwave irradiation followed by crushing, and this cycle was repeated three times. After three cycles, Si and SiC were quantified from the reaction product in the same manner as in Example 1. The quantitative results are shown in Table 1 below. 【0038】 [Example 3] In Example 2, the reaction product was obtained in the same manner as in Example 2, except that infrared radiation was irradiated with a halogen lamp at an output of 450 W for 10 seconds instead of microwave irradiation as the heating method. The quantitative results of Si and SiC are shown in Table 1 below. 【0039】 [Example 4] In Example 2, the reaction product (reaction product after 3 cycles) was obtained in the same manner as in Example 2, except that unreacted silicon powder was removed using a sieve (mesh size 45 μm) after "standing" and before "crushing" in each cycle. The quantitative results of Si and SiC are shown in Table 1 below. 【0040】 [Table 1] 【0041】 "Irradiation time (seconds)" refers to the time the reaction system was heated in one cycle. The same applies to the table below. "Reaction system temperature (°C)" is the temperature reached during the irradiation time. 【0042】 Table 1 shows that silicon carbide (solid carbide) can be efficiently obtained by the method of the present invention. In particular, a comparison between Examples 1 and 2 shows that increasing the number of cycles and thus the total irradiation time improves the yield of silicon carbide. 【0043】 [Example 5] In Example 1, the reaction product was obtained in the same manner as in Example 1, except that the amount of silicon powder was 0.5 g, a portion of the silicon powder in the cylinder was placed outside the resonator, and the CO2 gas flow rate was 1.05 L / min. Si and SiC were quantified in the same manner as in Example 1. The quantification results are shown in Table 2 below. "Placing a portion of the silicon powder inside the cylinder outside the resonator" means that the silicon powder was arranged so that a portion of the silicon powder inside the cylinder was irradiated with microwaves (in other words, so that a portion of the silicon powder was not irradiated with microwaves). 【0044】 [Table 2] 【0045】 Fifty seconds after stopping microwave irradiation, the temperature of the reaction system outside the resonator was measured using thermography and found to have reached a high temperature of 1320°C. This revealed that in the above reaction, the heat of reaction from the exothermic reaction caused by microwave irradiation was propagated to the silicon powder that was not irradiated by microwaves, and the synthesis reaction proceeded (the exothermic reaction proceeded like a combustion synthesis reaction). 【0046】 [Example 6] In Example 1, the reaction product was obtained in the same manner as in Example 1, except that the microwave irradiation time was set to 1 second and the CO2 gas flow rate was set to 0.35 L / min. The quantitative results of Si and SiC are shown in Table 3 below. 【0047】 [Example 7] In Example 6, the reaction product was obtained in the same manner as in Example 6, except that the irradiation time was changed to 10 seconds. The quantitative results of Si and SiC are shown in Table 3 below. 【0048】 [Example 8] In Example 6, the reaction product was obtained in the same manner as in Example 6, except that the microwave irradiation time was changed to 100 seconds. The quantitative results of Si and SiC are shown in Table 3 below. 【0049】 [Example 9] In Example 6, the reaction product was obtained in the same manner as in Example 6, except that the microwave irradiation time was changed to 1000 seconds. The quantitative results of Si and SiC are shown in Table 3 below. In Example 9, XRD confirmed that the sample contained a crystalline phase of silica (SiO2). 【0050】 [Example 10] In Example 6, the reaction product was obtained in the same manner as in Example 6, except that the microwave irradiation time was changed to 3000 seconds. The quantitative results of Si and SiC in the sample after standing are shown in Table 3 below. In Example 10, XRD confirmed that the sample contained a crystalline phase of silica (SiO2). 【0051】 [Table 3] 【0052】 A comparison with Examples 6-8 shows that the yield of silicon carbide can be improved by increasing the heating time of the reaction system. On the other hand, the results of Examples 9 and 10 show that crystalline silica can also be produced by increasing the heating time at 1800°C. 【0053】 [Example 11] In Example 2, the reaction product was obtained in the same manner as in Example 2, except that a mixed gas of nitrogen and carbon dioxide (nitrogen:carbon dioxide = 50:50 by volume) was passed through the system instead of carbon dioxide gas. The quantitative results of Si and SiC are shown in Table 4 below. 【0054】 [Example 12] In Example 11, the reaction product was obtained in the same manner as in Example 11, except that the ratio of nitrogen to carbon dioxide in the mixed gas was changed to nitrogen:carbon dioxide = 90:10 (volume ratio), and the microwave irradiation time per cycle was changed to 10 seconds. The quantitative results of Si and SiC are shown in Table 4 below. 【0055】 [Example 13] In Example 12, the reaction product was obtained in the same manner as in Example 12, except that the ratio of nitrogen to carbon dioxide in the mixed gas was changed to nitrogen:carbon dioxide = 80:20 (volume ratio). The quantitative results of Si and SiC are shown in Table 4 below. 【0056】 [Example 14] In Example 12, the reaction product was obtained in the same manner as in Example 15, except that the ratio of nitrogen to carbon dioxide in the gas mixture was changed to nitrogen:carbon dioxide = 70:30 (volume ratio). The quantitative results of Si and SiC are shown in Table 4 below. 【0057】 [Table 4] 【0058】 The results from Examples 11-14 show that the method of the present invention can produce the desired solid carbide (silicon carbide) even when a gas other than carbon dioxide is mixed with the gas that comes into contact with silicon in the exothermic reaction (even when the mole fraction of carbon dioxide is low). 【0059】 [Example 15] 50 g of silicon powder was irradiated with a multimode microwave at an output of 300 W for 100 seconds while blowing carbon dioxide gas (blow rate 6 L / min). The resulting sample was allowed to stand at room temperature. Si and SiC were quantified from the sample after standing in the same manner as in Example 1. The quantification results are shown in Table 5 below. 【0060】 [Table 5] 【0061】 Table 5 shows that, by the method of the present invention, the desired silicon carbide can be efficiently obtained even when the amount of silicon powder is increased. 【0062】 [Example 16] 54 g of silicon sludge powder (purity: 99%, average particle size: 2.0-3.0 μm) was irradiated with multimode microwaves at an output of 1000 W for 60 seconds while blowing carbon dioxide gas (blowing rate: 6 L / min). The resulting sample was allowed to stand at room temperature. The reaction product, which had been allowed to stand at room temperature, was crushed using an alumina mortar. One cycle consisted of microwave irradiation followed by crushing, and this cycle was repeated three times. Si and SiC were quantified from the reaction product after three cycles in the same manner as in Example 1. The quantitative results are shown in Table 6 below. The amount of silicon sludge powder used is indicated in the "Silicon Powder" column in the table (the same applies below). 【0063】 [Table 6] 【0064】 [Example 16 - Washing (1)] The reaction product obtained in Example 16 after 3 cycles was placed in a 10% by mass NaOH aqueous solution and heated in an electric furnace at 140°C for 60 minutes. The liquid was then removed by filtration, and Si and SiC were quantified in the resulting washed reaction product in the same manner as in Example 1. The quantitative results are shown in Table 7 below. Amorphous silica (SiO2) was confirmed by XRD measurement of the washed reaction product. 【0065】 [Example 16 - Washing (2)] In Example 16-Washing (1), the reaction product was washed after 3 cycles in the same manner as in Example 16-Washing (1), except that the washing conditions were changed to those described in Table 7 below. Si and SiC were quantified from the resulting reaction product after washing in the same manner as in Example 1. The quantitative results are shown in Table 7 below. Notably, amorphous silica (SiO2) was not detected in the XRD measurement of the reaction product after washing. Therefore, it can be concluded that substantially single-phase SiC was obtained. 【0066】 [Example 16 - Washing (3)] In Example 16-Washing (1), the reaction product was washed after 3 cycles in the same manner as in Example 16-Washing (1), except that the washing conditions were changed to those described in Table 7 below. Si and SiC were quantified from the resulting reaction product after washing in the same manner as in Example 1. The quantitative results are shown in Table 7 below. Amorphous silica (SiO2) was confirmed by XRD measurement of the reaction product after washing. 【0067】 [Table 7] 【0068】 The results in Table 7 show that, in the method of the present invention, high-purity silicon carbide can be obtained by washing the mixture after the exothermic reaction with an aqueous sodium hydroxide solution. 【0069】 [Example 16 - Purity] ICP measurements were performed on the silicon sludge powder (Sample 3) from Example 16, the reaction product obtained after 3 cycles in Example 16 (Sample 2), and the reaction product after washing obtained in Example 16-Washing (2) (Sample 1). Specifically, each sample was dissolved in a mixed acid consisting of hydrochloric acid, nitric acid, hydrofluoric acid, and sulfuric acid using a microwave sample decomposition apparatus, and the results were measured using an ICP-MS instrument to determine the elemental composition of each sample. The results are shown in Table 8, and the purity is shown in Table 9. The purity (%) in Table 9 is the percentage of the silicon concentration (C2) relative to the total concentration of all elements (C1) ((C2 / C1) × 100). 【0070】 [Table 8] 【0071】 [Notes in Table 8] Units of values ​​in the table: μg / mg 【0072】 [Table 9] 【0073】 The results in Tables 8 and 9 show that high-purity silicon carbide can be obtained with high efficiency by washing under the conditions of Example 16-Washing (2). 【0074】 [Example 16-XRF] The elemental composition of the reaction product obtained after washing in Example 16-Washing (2) was investigated by XRF (X-ray Fluorescence) measurement. The results are shown in Table 10. 【0075】 [Table 10] 【0076】 The results in Table 10, as well as the XRF measurements, show that high-purity and highly efficient silicon carbide can be obtained by washing under the conditions of Example 16-Washing (2). 【0077】 [Example 17] The reaction product was obtained in the same manner as in Example 1, except that the microwave irradiation time was set to 60 seconds and an agate mortar was used instead of an alumina mortar for crushing the reaction product. The quantitative results of Si and SiC are shown in Table 11 below. 【0078】 [Example 18] The reaction product, which had been allowed to stand at room temperature in the same manner as in Example 17, was crushed using an alumina mortar. The process from microwave irradiation to crushing was considered one cycle, and this cycle was repeated twice. After two cycles, the Si and SiC content of the reaction product was quantified in the same manner as in Example 1. The quantitative results are shown in Table 11 below. 【0079】 [Example 19] In the same manner as in Example 17, the reaction product, which had been allowed to stand at room temperature, was crushed using an alumina mortar. The process from microwave irradiation to crushing constituted one cycle, and this cycle was repeated three times. After three cycles, the Si and SiC content of the reaction product was quantified in the same manner as in Example 1. The quantitative results are shown in Table 11 below. 【0080】 [Table 11] 【0081】 A comparison of Examples 17-19 shows that even with a relatively low microwave output of 70W, silicon carbide can be obtained efficiently from powdered silicon raw materials, and the yield can be further increased by increasing the number of cycles. 【0082】 [Example 20] A quartz cylinder (cross-sectional diameter: 8 mm) containing 0.15 g of silicon powder (purity: 99.99%, particle size: 1.3 μm) was placed in a tubular furnace. The cylinder was heated while carbon dioxide gas was circulated through it at a flow rate of 1.5 L / min. The furnace temperature was set to 1200°C using a thermocouple. The holding time was 60 minutes. The reaction product was removed from the furnace along with the cylinder and allowed to stand at room temperature while CO2 was circulated through it. The reaction product after standing was crushed using an agate mortar. Si and SiC were quantified using the RIR (reference intensity ratio) method based on the diffraction results obtained by XRD (X-ray diffraction) of the reaction product after crushing. The quantitative results are shown in Table 12 below. Amorphous silica (SiO2) was confirmed in the reaction product by XRD. 【0083】 [Example 21] Except for replacing the silicon powder in Example 20 with 0.15 g of silicon sludge powder (purity: 99.9%, particle size: 0.5 μm) and setting the furnace temperature to 1150°C, the reaction product was obtained in the same manner as in Example 20, and Si and SiC were quantified. The quantification results are shown in Table 12 below. Amorphous silica (SiO2) was confirmed in the reaction product by XRD. 【0084】 [Example 22] The reaction product was obtained in the same manner as in Example 20, except that the silicon powder was replaced with 0.15 g of silicon sludge powder (purity: 99.9%, particle size: 0.5 μm), and Si and SiC were quantified. The quantification results are shown in Table 12 below. Amorphous silica (SiO2) was confirmed in the reaction product by XRD. 【0085】 [Example 23] The reaction product was obtained in the same manner as in Example 20, except that the holding time was set to 180 minutes, and Si and SiC were quantified. The quantification results are shown in Table 12 below. Amorphous silica (SiO2) was confirmed in the reaction product by XRD. 【0086】 [Example 24] The reaction product was obtained in the same manner as in Example 20, except that the holding time was set to 10 minutes and the furnace temperature to 1300°C, and Si and SiC were quantified. The quantification results are shown in Table 12 below. Amorphous silica (SiO2) was confirmed in the reaction product by XRD. 【0087】 [Example 25] The reaction product was obtained in the same manner as in Example 24, except that the holding time was set to 30 minutes, and Si and SiC were quantified. The quantification results are shown in Table 12 below. Amorphous silica (SiO2) was confirmed in the reaction product by XRD. 【0088】 [Example 26] The reaction product was obtained in the same manner as in Example 24, except that the holding time was set to 60 minutes, and Si and SiC were quantified. The quantification results are shown in Table 12 below. Amorphous silica (SiO2) was confirmed in the reaction product by XRD. 【0089】 [Example 27] The reaction product was obtained in the same manner as in Example 26, except that the cycle from circulating carbon dioxide gas through the cylinder to crushing was performed three times, and Si and SiC were quantified. The quantification results are shown in Table 12 below. Amorphous silica (SiO2) was confirmed in the reaction product by XRD. 【0090】 [Example 28] The reaction product was obtained in the same manner as in Example 26, except that the carbon dioxide gas flow rate was set to 3.0 L / min, and Si and SiC were quantified. The quantification results are shown in Table 12 below. Amorphous silica (SiO2) was confirmed in the reaction product by XRD. 【0091】 [Example 29] The reaction product was obtained in the same manner as in Example 26, except that the furnace temperature was set to 1394°C, and Si and SiC were quantified. The quantification results are shown in Table 12 below. Amorphous silica (SiO2) was confirmed in the reaction product by XRD. 【0092】 [Table 12] 【0093】 Table 12 shows that silicon carbide can be obtained by heating the reaction system to 1150°C or higher. It was also found that the yield of silicon carbide can be effectively increased by reducing the particle size of the silicon raw material.

Claims

[Claim 1] A method for utilizing carbon dioxide, comprising: circulating carbon dioxide in a reaction vessel heated to 1150 to 2200°C by a heating furnace to bring silicon powder with a particle size of 0.2 to 4.0 μm placed in the reaction vessel into contact with the carbon dioxide; and reacting the silicon powder and the carbon dioxide through an exothermic reaction by this contact to obtain a solid reaction product containing silicon carbide and silicon dioxide, formed by the bonding of the carbon of the carbon dioxide and the silicon of the silicon powder. [Claim 2] The method for resource utilization of carbon dioxide according to Claim 1, further comprising washing the solid reaction product to obtain silicon carbide with a purity of 99.00% or higher. [Claim 3] The method for resource recovery of carbon dioxide according to claim 1 or 2, wherein the exothermic reaction is represented by at least the following reaction formula (2) and / or (3). 2Si + CO 2 → SiO 2 + SiC (2) 3Si + 2CO 2 → 2SiC + SiO 2 + O 2 (3) [Claim 4] A method for producing silicon carbide, comprising: circulating carbon dioxide in a reaction vessel heated to 1150 to 2200°C by a heating furnace to bring silicon powder with a particle size of 0.2 to 4.0 μm placed in the reaction vessel into contact with the carbon dioxide; and reacting the silicon powder and the carbon dioxide through an exothermic reaction by this contact to obtain a solid reaction product containing silicon carbide and silicon dioxide, formed by the bonding of the carbon of the carbon dioxide with the silicon of the silicon powder. [Claim 5] The method for producing silicon carbide according to claim 4, comprising washing the solid reaction product to obtain silicon carbide with a purity of 99.00% or higher. [Claim 6] The method for producing silicon carbide according to claim 4 or 5, wherein the exothermic reaction is represented by at least the following reaction formula (2) and / or (3). 2Si + CO 2 → SiO 2 + SiC (2) 3Si + 2CO 2 → 2SiC + SiO 2 + O 2 (3)