Method for producing hydrocarbon and method for producing silicon carbide

Abstract

Provided is a method for producing a hydrocarbon with which it is possible to produce a high-purity hydrocarbon having a low content of hydrogen, nitrogen, oxygen, boron, aluminum, phosphorus, sulfur, titanium, vanadium, chromium, and molybdenum. A hydrocarbon production method provided with a hydrogen gas removal step in which hydrogen gas is removed from a crude hydrocarbon containing hydrogen gas and a hydrocarbon having 1-4 carbon atoms (inclusive) to obtain a low-hydrogen-content hydrocarbon having a hydrogen gas content of 100 ppm by volume or less, and an adsorption step in which the low-hydrogen-content hydrocarbon is brought into contact with an adsorbent to adsorb the low-hydrogen-content hydrocarbon and the adsorbent to obtain a low-hydrogen-content hydrocarbon having a hydrogen gas content of 100 ppm by volume or less. The content of hydrogen is 80 ppm by volume or less, the total content of nitrogen and oxygen is 5 ppm by volume or less, and the total content of boron, aluminum, phosphorus, sulfur, titanium, vanadium, chromium, and molybdenum is 250 ppb by mass or less. The adsorbent has crystals having pores having a pore diameter of more than 0.3 nm and 3.5 nm or less, and the crystal form of the crystals is not a mordenite type.

Description

Technical Field

[0001] The present invention relates to a method for producing hydrocarbons and a method for producing silicon carbide. Background Art

[0002] Single-crystal silicon carbide (SiC) is useful as a material for power semiconductors because it has an excellent electrical property with a bandgap about three times that of silicon (Si) and an insulation breakdown electric field strength ten times that of silicon. Among the raw materials used to produce single-crystal silicon carbide, high-purity hydrocarbons are used. For example, Patent Document 1 discloses a purification method for propane in which impurities are removed from low-purity propane (C3H8) to make it highly pure. According to the technique disclosed in Patent Document 1, high-purity propane with a purity of 99.99% by volume or more can be obtained, and such high-purity propane is useful as a raw material for single-crystal silicon carbide.

[0003] Patent Document 1 shows, as impurities removed from low-purity propane, ethane (C2H6), propylene (C3H6), n-butane (C4H 10 ) and isobutane (C4H 10 ), water (H2O), nitrogen (N2), oxygen (O2), and carbon dioxide (CO2). However, low-purity propane sometimes contains impurities other than these.

[0004] Prior Art Documents

[0005] Patent Documents

[0006] Patent Document 1: Japanese Patent Publication No. 5822299

[0007] Patent Document 2: WO 2016 / 121622 Summary of the Invention

[0008] Problems to be Solved by the Invention

[0009] For example, since hydrogen (H2) is used as a raw material when synthesizing propane from propylene, there is a risk that a large amount of hydrogen is contained in the resulting propane (see Patent Document 2). If hydrogen is contained in propane, there is a risk that it is difficult to remove nitrogen or oxygen from propane.

[0010] In addition, if elements such as nitrogen (N), oxygen (O), boron (B), aluminum (Al), phosphorus (P), sulfur (S), titanium (Ti), vanadium (V), chromium (Cr), and molybdenum (Mo) are contained in single-crystal silicon carbide, these elements become dopants, or there is a risk that oxides of these elements oxidize silicon carbide. As a result, since the electrical properties of silicon carbide change, there is a risk of adversely affecting the quality of the semiconductor.

[0011] Therefore, as the hydrocarbon used as a raw material for manufacturing single-crystal silicon carbide, it is desirable that the contents of hydrogen, nitrogen, oxygen, boron, aluminum, phosphorus, sulfur, titanium, vanadium, chromium, and molybdenum are low.

[0012] The object of the present invention is to provide a method for manufacturing a hydrocarbon that can produce a high-purity hydrocarbon with low contents of hydrogen, nitrogen, oxygen, boron, aluminum, phosphorus, sulfur, titanium, vanadium, chromium, and molybdenum, and a method for manufacturing silicon carbide that can produce silicon carbide with excellent electrical properties.

[0013] [Means for Solving the Problem]

[0014] To solve the above problems, the solutions of the present invention are shown in the following [1] to [8].

[0015] [1]. A method for manufacturing a hydrocarbon, comprising a hydrogen removal step and an adsorption step,

[0016] In the hydrogen removal step, hydrogen is removed from a crude hydrocarbon containing a hydrocarbon having 1 or more and 4 or less carbon atoms and hydrogen to obtain a low-hydrogen-content hydrocarbon having a hydrogen content of 100 volume ppm or less.

[0017] In the adsorption step, the low-hydrogen-content hydrocarbon is brought into contact with an adsorbent to obtain a high-purity hydrocarbon having a hydrogen content of 80 volume ppm or less, a total content of nitrogen and oxygen of 5 volume ppm or less, and a total content of boron, aluminum, phosphorus, sulfur, titanium, vanadium, chromium, and molybdenum of 250 mass ppb or less.

[0018] The adsorbent has crystals, and the crystals have pores with a pore diameter greater than 0.3 nm and 3.5 nm or less, and the crystal form of the crystals is not a mordenite type.

[0019] [2]. The method for manufacturing a hydrocarbon according to [1], wherein the hydrocarbon is at least one of methane, ethane, ethylene, propane, n-butane, and isobutane.

[0020] [3]. The method for manufacturing a hydrocarbon according to [1], wherein the hydrocarbon is at least one of propane and ethylene.

[0021] [4]. The method for manufacturing a hydrocarbon according to [1], wherein the adsorption step is a step of adsorbing at least one of the nitrogen and the oxygen from the low-hydrogen-content hydrocarbon using the adsorbent.

[0022] [5]. The method for manufacturing a hydrocarbon according to [1], wherein the adsorption step is a step of adsorbing at least one of boron, aluminum, phosphorus, sulfur, titanium, vanadium, chromium, and molybdenum from the low-hydrogen-content hydrocarbon using the adsorbent.

[0023] [6]. The method for manufacturing a hydrocarbon according to [1], wherein the hydrogen removal step is a step of removing the hydrogen from the crude hydrocarbon using a separation membrane.

[0024] [7]. The method for producing hydrocarbons as described in [1], which further includes a filtration step,

[0025] In the filtration step, the crude hydrocarbons, the low-hydrogen-content hydrocarbons, or the high-purity hydrocarbons are passed through a filter medium, thereby removing at least one of boron, aluminum, phosphorus, sulfur, titanium, vanadium, chromium, and molybdenum from the crude hydrocarbons, the low-hydrogen-content hydrocarbons, or the high-purity hydrocarbons.

[0026] The filter medium is at least one filter selected from a membrane filter, a sintered metal filter, and a filter having a plurality of particles made of metal halide.

[0027] [8]. A method for producing silicon carbide, which uses the high-purity hydrocarbons produced by the method for producing hydrocarbons according to any one of [1] to [7] as a raw material to produce silicon carbide.

[0028] Advantages of the Invention

[0029] According to the method for producing hydrocarbons of the present invention, high-purity hydrocarbons with low contents of hydrogen, nitrogen, oxygen, boron, aluminum, phosphorus, sulfur, titanium, vanadium, chromium, and molybdenum can be produced. In addition, according to the method for producing silicon carbide of the present invention, silicon carbide having excellent electrical properties can be produced. Description of the Drawings

[0030] Figure 1 is a schematic diagram illustrating an example of the membrane separation device used in the hydrogen removal step.

[0031] Figure 2 is a schematic diagram illustrating an example of the adsorption device used in the adsorption step.

[0032] Figure 3 is a schematic diagram illustrating an example of the filtration device used in the filtration step.

[0033] Figure 4 is a schematic diagram illustrating an example of the preparation device for preparing a sample for analysis.

[0034] Figure 5 is a schematic diagram illustrating an example of the hydrocarbon production device for continuously performing the hydrogen removal step, the adsorption step, and the filtration step. Detailed Description of the Invention

[0035] An embodiment of the present invention will be described below. Furthermore, this embodiment only shows an example of the present invention, and the present invention is not limited to this embodiment. In addition, various changes or improvements can be made to this embodiment, and such modified forms can also be included in the present invention.

[0036] The method for producing a hydrocarbon according to this embodiment includes a hydrogen removal step and an adsorption step. In the hydrogen removal step, hydrogen is removed from a crude hydrocarbon containing a hydrocarbon having 1 to 4 carbon atoms and hydrogen to obtain a low-hydrogen hydrocarbon having a hydrogen content of 100 volume ppm or less. In the adsorption step, the low-hydrogen hydrocarbon is brought into contact with an adsorbent to obtain a high-purity hydrocarbon having a hydrogen content of 80 volume ppm or less, a total content of nitrogen and oxygen of 5 volume ppm or less, and a total content of boron, aluminum, phosphorus, sulfur, titanium, vanadium, chromium, and molybdenum of 250 mass ppb or less. The adsorbent has a crystal having pores with a pore diameter greater than 0.3 nm and 3.5 nm or less, and the crystal form of the crystal is not a mordenite type.

[0037] According to the method for producing a hydrocarbon of this embodiment, a high-purity hydrocarbon with low contents of hydrogen, nitrogen, oxygen, boron, aluminum, phosphorus, sulfur, titanium, vanadium, chromium, and molybdenum can be produced. Specific description is given below.

[0038] Hydrocarbons having 1 to 4 carbon atoms may contain hydrogen, nitrogen, and oxygen as impurities. When a hydrocarbon contains hydrogen, it is difficult to remove nitrogen and oxygen from the hydrocarbon. Therefore, if the treatment for removing nitrogen and oxygen is carried out after reducing the hydrogen content, it is easy to remove nitrogen and oxygen from the hydrocarbon.

[0039] In the method for producing a hydrocarbon of this embodiment, since the adsorption step is carried out after the hydrogen removal step of removing hydrogen from the crude hydrocarbon to obtain a low-hydrogen hydrocarbon, nitrogen and oxygen in the hydrocarbon can be effectively adsorbed by the adsorbent to obtain a high-purity hydrocarbon.

[0040] The obtained high-purity hydrocarbon is suitable as a raw material for producing silicon carbide due to its low contents of hydrogen, nitrogen, oxygen, boron, aluminum, phosphorus, sulfur, titanium, vanadium, chromium, and molybdenum, and is particularly suitable as a raw material for producing single-crystal silicon carbide useful as a material for power semiconductors.

[0041] In addition, since the obtained high-purity hydrocarbon has a low oxygen content, it is not likely to catch fire or explode. Furthermore, since the obtained high-purity hydrocarbon has a low hydrogen content, it is not likely to cause hydrogen embrittlement of metals. For example, hydrogen embrittlement is not likely to occur in the metal forming the container for storing the high-purity hydrocarbon or the metal forming the pipe for supplying the high-purity hydrocarbon, so the storage container or the pipe is not likely to deteriorate.

[0042] In addition, the method for manufacturing silicon carbide according to this embodiment is a method for manufacturing silicon carbide using the high-purity hydrocarbon produced by the method for manufacturing hydrocarbon according to this embodiment as a raw material. Since the content of various impurities in the high-purity hydrocarbon is low as described above, if the high-purity hydrocarbon produced by the method for manufacturing hydrocarbon according to this embodiment is used as a raw material to manufacture silicon carbide, silicon carbide with a low content of the above elements (hydrogen, nitrogen, oxygen, boron, aluminum, phosphorus, sulfur, titanium, vanadium, chromium, and molybdenum) can be manufactured. Therefore, the silicon carbide produced by the method for manufacturing silicon carbide according to this embodiment has excellent electrical properties, and thus, if this silicon carbide is used, a semiconductor with excellent properties can be manufactured.

[0043] [Type of hydrocarbon]

[0044] The type of hydrocarbon is not particularly limited as long as the number of carbon atoms is 1 or more and 4 or less. However, from the viewpoint of high vapor pressure and easy supply, alkanes with 1 or more and 4 or less carbon atoms, or alkenes and alkynes with 2 or more and 4 or less carbon atoms are preferred.

[0045] Examples of alkanes include methane, ethane, propane, n-butane, and isobutane. Examples of alkenes include ethylene, propylene, 1-butene, 2-butene (including cis and trans isomers), and isobutene. Examples of alkynes include acetylene, propyne, 1-butyne, and 2-butyne.

[0046] These hydrocarbons can be used alone or in combination of two or more. In addition, among these hydrocarbons, from the viewpoint of easy availability, methane, ethane, propane, n-butane, isobutane, and ethylene are preferred.

[0047] [Impurities]

[0048] Examples of impurities contained in the hydrocarbon include compounds (excluding hydrocarbons with 1 or more and 4 or less carbon atoms) or simple substances composed of elements in the first to fifth periods of the periodic table. In particular, gaseous impurities such as hydrogen, nitrogen, and oxygen, or solid impurities such as compounds or simple substances having at least one of boron, aluminum, phosphorus, sulfur, titanium, vanadium, chromium, and molybdenum in the molecule are likely to be mixed into the hydrocarbon. Examples of compounds having these elements in the molecule include oxides, nitrides, halides, hydrides, hydroxides, etc. These compounds can exist in the form of particles, clusters, coordination compounds, etc.

[0049] Among these impurities, if hydrogen is contained in a hydrocarbon, it may cause deterioration of the storage container or piping for the hydrocarbon. In addition, if these impurities are contained in a hydrocarbon, in cases where high purity of the hydrocarbon is required, such as in the film formation process of silicon carbide or diamond wafers when manufacturing semiconductors using the hydrocarbon, it may cause deterioration of the characteristics of the product. Therefore, it is desirable to remove impurities from the hydrocarbon as much as possible through purification. On the other hand, since excessive purification increases the manufacturing cost of the hydrocarbon, it is acceptable to contain a small amount of impurities. The impurities in the hydrocarbon can be quantified using methods such as gas chromatography or inductively coupled plasma-mass spectrometry (ICP-MS).

[0050] [Crude hydrocarbon]

[0051] The crude hydrocarbon contains hydrocarbons having 1 to 4 carbon atoms and hydrogen. In the crude hydrocarbon, sometimes in addition to hydrogen, the above-mentioned impurities are also contained. As an example of the crude hydrocarbon, there can be cited crude propane synthesized by reacting hydrogen with propylene, and there is a risk that a large amount of hydrogen is contained in this crude propane.

[0052] When the content of hydrogen in the crude hydrocarbon is greater than 100 volume ppm, a hydrogen removal process is performed on the crude hydrocarbon to make the content of hydrogen 100 volume ppm or less.

[0053] Furthermore, when the content of hydrogen in the crude hydrocarbon is greater than 100 volume ppm, a hydrogen removal process must be performed to make the content of hydrogen 100 volume ppm or less. However, when the content of hydrogen is 100 volume ppm or less, the hydrogen removal process may not be performed. That is, when the content of hydrogen is 100 volume ppm or less, since the crude hydrocarbon can be said to be a low-hydrogen-content hydrocarbon, the implementation of the hydrogen removal process can be omitted, and an adsorption process is performed on the crude hydrocarbon.

[0054] [Low-hydrogen-content hydrocarbon]

[0055] A low-hydrogen-content hydrocarbon is a hydrocarbon in which the content of hydrogen is 100 volume ppm or less. By performing a hydrogen removal process on the crude hydrocarbon to remove hydrogen from the crude hydrocarbon, a low-hydrogen-content hydrocarbon can be obtained.

[0056] [High-purity hydrocarbon]

[0057] A high-purity hydrocarbon is a hydrocarbon in which the content of hydrogen is 80 volume ppm or less, the total content of nitrogen and oxygen is 5 volume ppm or less, and the total content of boron, aluminum, phosphorus, sulfur, titanium, vanadium, chromium, and molybdenum is 250 mass ppb or less. By bringing the low-hydrogen-content hydrocarbon into contact with an adsorbent and performing an adsorption process, impurities can be removed from the low-hydrogen-content hydrocarbon, thereby obtaining a high-purity hydrocarbon.

[0058] The hydrogen content in the high-purity hydrocarbon must be 80 volume ppm or less, preferably 5 volume ppm or more and 80 volume ppm or less, more preferably 40 volume ppm or more and 74 volume ppm or less.

[0059] In addition, the total content of nitrogen and oxygen in the high-purity hydrocarbon must be 5 volume ppm or less, preferably 0.2 volume ppm or more and 3 volume ppm or less, more preferably 0.3 volume ppm or more and 2 volume ppm or less, further preferably 0.4 volume ppm or more and 1 volume ppm or less.

[0060] Furthermore, the total content of boron, aluminum, phosphorus, sulfur, titanium, vanadium, chromium, and molybdenum in the high-purity hydrocarbon must be 250 mass ppb or less, preferably 1 mass ppb or more and 100 mass ppb or less, more preferably 3 mass ppb or more and 50 mass ppb or less, further preferably 4 mass ppb or more and 15 mass ppb or less.

[0061] As long as the contents of these impurities are within the above numerical ranges, high-purity hydrocarbons can be produced without excessive manufacturing costs.

[0062] As a method for purifying the crude hydrocarbon by removing the impurities, a membrane separation method, an adsorption method, a filtration method, a distillation method, etc. can be used. However, in the method for producing hydrocarbons in the present embodiment, a hydrogen removal step of obtaining a low-hydrogen-content hydrocarbon by removing hydrogen from the crude hydrocarbon and an adsorption step of bringing the low-hydrogen-content hydrocarbon into contact with an adsorbent are performed to obtain a high-purity hydrocarbon. A purification step other than the hydrogen removal step and the adsorption step can be further combined, and a purification step using any purification method can be selected according to the type and amount of impurities to be removed, the production capacity of the hydrocarbon, etc.

[0063] [Hydrogen Removal Step]

[0064] The hydrogen removal step is a step of removing hydrogen from the crude hydrocarbon to obtain a low-hydrogen-content hydrocarbon having a hydrogen content of 100 volume ppm or less. There is no particular limitation on the method for removing hydrogen from the crude hydrocarbon in the hydrogen removal step. For example, a membrane separation method of passing the crude hydrocarbon through a separation membrane or a distillation method of distilling the crude hydrocarbon can be used.

[0065] Regarding the membrane separation method, it will be described in detail below. By passing the crude hydrocarbon through a separation membrane, hydrogen can be separated from the crude hydrocarbon. In addition, there are cases where nitrogen and oxygen can also be separated. The material, shape, pore diameter, etc. of the separation membrane used are not particularly limited as long as a difference in the permeation rate between the hydrocarbon and the impurities can be generated.

[0066] Examples of the material of the separation membrane include polyethylene, polypropylene, polyvinylidene fluoride, polysulfone, polyethersulfone, cellulose acetate, polyimide, alumina, mullite, titanium oxide, etc. Among these materials, polyimide is preferred from the viewpoint of ease of acquisition.

[0067] Examples of the shape of the separation membrane include hollow fiber shape, cylindrical shape, corrugated shape, etc. Among these shapes, the hollow fiber shape is preferred from the viewpoint of ease of acquisition.

[0068] Generally, since the permeation rate of hydrocarbons through the separation membrane is low and the permeation rate of gaseous impurities such as hydrogen through the separation membrane is high, the low-hydrogen-content hydrocarbons after removing impurities can be captured from the non-permeate gas outlet of the separation membrane. That is, the gas that does not permeate through the separation membrane in the crude hydrocarbons becomes low-hydrogen-content hydrocarbons.

[0069] The purification method using the separation membrane can also be applied to the removal of any impurities, but from the viewpoint of the fast permeation rate through the separation membrane, it is effective for the removal of hydrogen, nitrogen, and oxygen, and particularly effective for the removal of hydrogen.

[0070] The conditions of the membrane separation method such as temperature and pressure can be arbitrarily set as long as hydrocarbons and impurities can be separated and the temperature conditions and pressure conditions for the use of the separation membrane are satisfied.

[0071] The temperature condition is preferably, for example, -20°C or higher and 200°C or lower, more preferably 0°C or higher and 150°C or lower, further preferably 5°C or higher and 80°C or lower, and particularly preferably 10°C or higher and 40°C or lower.

[0072] In addition, the pressure condition is preferably 0.1 MPa or higher and 5 MPa or lower, more preferably 0.15 MPa or higher and 4 MPa or lower, and further preferably 0.2 MPa or higher and 3 MPa or lower.

[0073] [Adsorption process]

[0074] The adsorption process is a process in which low-hydrogen-content hydrocarbons are brought into contact with an adsorbent to obtain high-purity hydrocarbons with a hydrogen content of 80 volume ppm or less, a total content of nitrogen and oxygen of 5 volume ppm or less, and a total content of boron, aluminum, phosphorus, sulfur, titanium, vanadium, chromium, and molybdenum of 250 mass ppb or less. The adsorbent used in the adsorption process has a crystal containing pores with a pore diameter greater than 0.3 nm and 3.5 nm or less. Furthermore, the crystal form of the adsorbent is not the mordenite type.

[0075] In the adsorption process, at least one of nitrogen and oxygen can be adsorbed from low-hydrogen hydrocarbons using an adsorbent, and at least one of boron, aluminum, phosphorus, sulfur, titanium, vanadium, chromium, and molybdenum can also be adsorbed from low-hydrogen hydrocarbons using an adsorbent. Alternatively, all of nitrogen, oxygen, boron, aluminum, phosphorus, sulfur, titanium, vanadium, chromium, and molybdenum can be adsorbed from low-hydrogen hydrocarbons using an adsorbent.

[0076] The type of adsorbent is not particularly limited as long as it can adsorb the above impurities. However, if the pore diameter (average pore diameter) of the pores of the adsorbent is too small, desorption of nitrogen and oxygen is likely to occur. On the other hand, if the pore diameter (average pore diameter) of the pores of the adsorbent is too large, since hydrocarbons are adsorbed excessively, in addition to a decrease in the productivity of high-purity hydrocarbons, there is also a risk that the adsorption power of nitrogen and oxygen becomes insufficient.

[0077] Therefore, the pore diameter (average pore diameter) of the pores of the adsorbent must be greater than 0.3 nm and 3.5 nm or less, preferably 0.4 nm or more and 2.5 nm or less, more preferably 0.5 nm or more and 1 nm or less. If such an adsorbent is used, nitrogen and oxygen contained in low-hydrogen hydrocarbons can be adsorbed sufficiently. Furthermore, the pore diameter (average pore diameter) of the pores can be measured by a gas adsorption method (for example, BET adsorption method).

[0078] There is no particular limitation on the material forming the adsorbent, but from the viewpoints of economy or ease of acquisition, activated carbon, zeolite, silica gel, and alumina are preferred, and activated carbon and zeolite are more preferred. As the activated carbon, coconut shell activated carbon is preferred.

[0079] In addition, as the zeolite, zeolites having crystals with a crystal form of type A, X, Y, L, or ferrierite type can be used, and the crystal form is preferably type A and type X. On the other hand, zeolites having crystals with a crystal form of mordenite type are not suitable because their adsorption capacity for nitrogen and oxygen is insufficient even if the pore diameter (average pore diameter) of the pores is greater than 0.3 nm and 3.5 nm or less.

[0080] The adsorption conditions such as temperature and pressure are not particularly limited as long as impurities can be adsorbed. However, when the temperature is low and the pressure is high, nitrogen and oxygen are easily adsorbed by the adsorbent, and hydrocarbons are also easily adsorbed by the adsorbent. If the temperature is too high, there is a risk of desorption of nitrogen and oxygen from the adsorbent.

[0081] Therefore, the temperature condition is preferably, for example, -20°C or more and 200°C or less, more preferably 0°C or more and 150°C or less, further preferably 5°C or more and 80°C or less, and particularly preferably 10°C or more and 40°C or less.

[0082] In addition, the pressure condition is preferably 0.1 MPa or more and 5 MPa or less, more preferably 0.15 MPa or more and 4 MPa or less, and still more preferably 0.2 MPa or more and 3 MPa or less. As long as the pressure is within the above range, nitrogen, oxygen, boron, aluminum, phosphorus, sulfur, titanium, vanadium, chromium, and molybdenum contained in the low-hydrogen-content hydrocarbon are easily adsorbed by the adsorbent, and the content of these impurities can be easily and sufficiently reduced.

[0083] [Filtration step]

[0084] The method for producing a hydrocarbon according to this embodiment may further include a filtration step of filtering and removing solid impurities by passing the hydrocarbon through a filter medium. That is, it may further include a filtration step of passing the crude hydrocarbon, low-hydrogen-content hydrocarbon, or high-purity hydrocarbon through a filter medium and removing at least one of boron, aluminum, phosphorus, sulfur, titanium, vanadium, chromium, and molybdenum from the crude hydrocarbon, low-hydrogen-content hydrocarbon, or high-purity hydrocarbon.

[0085] By implementing the filtration step, the content of boron, aluminum, phosphorus, sulfur, titanium, vanadium, chromium, and molybdenum contained in the hydrocarbon can be further reduced.

[0086] As described above, the filtration step can be performed on the crude hydrocarbon, low-hydrogen-content hydrocarbon, or high-purity hydrocarbon, or on any one of these three hydrocarbons, or on two of them, or on all three of them. For example, the filtration step can be performed only after the adsorption step, or a total of three filtration steps can be performed before and after the hydrogen removal step and after the adsorption step.

[0087] The type of the filter medium is not particularly limited as long as it can remove at least one of boron, aluminum, phosphorus, sulfur, titanium, vanadium, chromium, and molybdenum. For example, filters, powders, granules, etc. that can increase the contact area between the impurities and the filter medium can be used as the filter medium.

[0088] Among these, it is preferable to use a filter medium in the shape of a filter with low pressure loss, and more preferably at least one of a membrane filter (for example, a resin-made membrane filter), a sintered metal filter, and a filter having a plurality of metal halide particles.

[0089] The type of the resin for forming the membrane filter is not particularly limited, and examples thereof include polyethylene, polypropylene, nylon, polytetrafluoroethylene (PTFE), poly(chlorotrifluoroethylene) (PCTFE), and tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA).

[0090] There is no particular limitation on the type of metal for forming the sintered metal filter, and examples thereof include stainless steel, nickel-based alloys, etc. As the stainless steel, austenitic stainless steel, martensitic stainless steel, ferritic stainless steel, etc. can be cited, but austenitic stainless steel that is easy to obtain is preferred, and SUS304, SUS304L, SUS316, SUS316L, etc. are more preferred. As the nickel-based alloy, nickel, Monel (registered trademark), Hastelloy (registered trademark), etc. can be cited, but nickel that is easy to obtain is preferred.

[0091] For a filter having a plurality of metal halide particles, as long as it can filter and remove solid impurities, its structure is not particularly limited.

[0092] There is no particular limitation on the type of metal halide for forming the particles of the filter having a plurality of metal halide particles, and examples thereof include metal fluorides, metal chlorides, metal bromides, and metal iodides. Among these, metal fluorides are preferred. As the types of metals contained in the metal halide, lithium (Li), sodium (Na), potassium (K), cesium (Cs), magnesium (Mg), calcium (Ca), iron (Fe), cobalt (Co), nickel (Ni), aluminum, etc. can be cited, but sodium, potassium, magnesium, and aluminum that are easy to obtain are preferred, and sodium is more preferred.

[0093] Regarding the filtration conditions such as temperature and pressure, as long as impurities can be filtered, there is no particular limitation, but the temperature conditions are preferably, for example, -20°C or higher and 200°C or lower, more preferably 0°C or higher and 150°C or lower, further preferably 5°C or higher and 80°C or lower, and particularly preferably 10°C or higher and 40°C or lower.

[0094] In addition, the pressure conditions are preferably 0.1 MPa or higher and 5 MPa or lower, more preferably 0.15 MPa or higher and 4 MPa or lower, and further preferably 0.2 MPa or higher and 3 MPa or lower.

[0095] As long as the temperature conditions and pressure conditions are within the above ranges, not much labor is required, and it is easy to remove solid impurities from the hydrocarbon.

[0096] Next, a method for manufacturing silicon carbide according to this embodiment will be described. As an example, a method for manufacturing a silicon carbide epitaxial wafer using high-purity hydrocarbon manufactured by the method for manufacturing hydrocarbon according to this embodiment as a raw material will be described. The method for manufacturing a silicon carbide epitaxial wafer described below includes a grinding process, a purification (gas etching) process, a film formation (epitaxial growth) process, and a cooling process. These processes will be described.

[0097] [Grinding process]

[0098] First, prepare a hexagonal silicon carbide single crystal substrate and polish it by a polishing method such as chemical mechanical polishing until the thickness of the lattice disorder layer on its surface becomes 3 nm or less. Furthermore, the "lattice disorder layer" refers to a layer in which the striped structure corresponding to the atomic layer (lattice) of the silicon carbide single crystal or a part of the stripe is unclear in the lattice image (an image capable of confirming the lattice) obtained by using a transmission electron microscope (TEM).

[0099] There is no particular limitation on the type of abrasive grains contained in the polishing liquid used for polishing, but particles that are insoluble and dispersed in the pH range of the polishing liquid are preferably used. The pH of the polishing liquid is preferably less than 2. In this case, particles such as diamond, silicon carbide, alumina, titanium oxide, and silicon oxide can be used as the abrasive grains.

[0100] There is no particular limitation on the average particle size of the abrasive grains, but it is preferably 1 nm or more and 400 nm or less, more preferably 10 nm or more and 200 nm or less, and still more preferably 10 nm or more and 150 nm or less.

[0101] In order to obtain a good final finishing surface, in terms of the fact that abrasive grains with a small average particle size are already commercially available at low cost, abrasive grains made of silica are preferred, and abrasive grains made of colloidal silica are more preferred. The average particle size of the abrasive grains made of colloidal silica can be appropriately selected according to processing characteristics such as processing speed and surface roughness.

[0102] When a higher polishing speed is required, abrasive grains with a large average particle size can be used. When a small surface roughness, that is, a highly smooth surface, is required, abrasive grains with a small average particle size can be used. Abrasive grains with an average particle size greater than 400 nm are expensive, but the polishing speed is not high and it is uneconomical. Abrasive grains with an extremely small average particle size, such as less than 1 nm, have a significantly reduced polishing speed.

[0103] There is no particular limitation on the content of the abrasive grains in the polishing liquid, but it is preferably 1% by mass or more and 30% by mass or less, more preferably 1.5% by mass or more and 15% by mass or less. If the content of the abrasive grains in the polishing liquid is within the above numerical range, the abrasive grains are not easily dried, so scratches are not easily generated, and it has the advantages of economy and high processing speed.

[0104] The polishing liquid can be an aqueous slurry, and its pH at 20 °C is preferably less than 2.0, more preferably less than 1.5, and still more preferably less than 1.2. As long as the pH of the polishing liquid is within the above numerical range, a sufficient polishing speed can be obtained. In addition, as long as the pH of the polishing liquid is within the above numerical range, even in a normal indoor environment, the chemical reactivity with respect to silicon carbide is significantly increased, so ultra-precise polishing can be performed.

[0105] It can be considered that silicon carbide is not directly removed or polished by the mechanical action of abrasive grains such as oxide particles in the polishing liquid, but is polished by a mechanism in which the polishing liquid chemically reacts with the surface of the silicon carbide single crystal to generate silicon oxide, and the generated silicon oxide is mechanically removed by the abrasive grains. Therefore, it is important to make the liquid property of the polishing liquid easily reactive with silicon carbide, make the pH less than 2, and select particles with appropriate hardness (for example, oxide particles) as abrasive grains to obtain a smooth surface without scratches or a processed and deteriorated layer.

[0106] The pH of the polishing liquid can be adjusted using acids such as hydrochloric acid, nitric acid, phosphoric acid, and sulfuric acid. The acid used can be one type, but it is preferably two or more types. Although the reason why it is effective to use multiple acids is not yet clear, experiments have confirmed that the interaction of multiple acids has the possibility of improving the effect.

[0107] The content of the acid in the polishing liquid, for example, in the case of hydrochloric acid, can be 0.5% by mass or more and 5% by mass or less, in the case of nitric acid, can be 0.5% by mass or more and 5% by mass or less, in the case of phosphoric acid, can be 0.5% by mass or more and 5% by mass or less, and in the case of sulfuric acid, can be 0.5% by mass or more and 5% by mass or less. The type and content of the acid can be determined within the above range so that the pH is less than 2.

[0108] Furthermore, inorganic acids are effective because they are strong acids compared to organic acids, and thus it is easy to adjust the liquid property of the polishing liquid to be strongly acidic. It is not easy to adjust the liquid property of the polishing liquid to be strongly acidic using organic acids.

[0109] The polishing of silicon carbide is carried out by generating an oxide film on the surface of silicon carbide with a strongly acidic polishing liquid and removing it with abrasive grains. However, in order to accelerate the surface oxidation, an oxidizing agent can also be added to the polishing liquid. There is no particular limitation on the type of oxidizing agent, but examples include hydrogen peroxide, perchloric acid, potassium dichromate, ammonium persulfate sulfate, etc. For example, if hydrogen peroxide water is used, the polishing rate is increased by setting the content in the polishing liquid to 0.5% by mass or more and 5% by mass or less, preferably 1.5% by mass or more and 4% by mass or less.

[0110] In the polishing liquid, in order to inhibit the gelation of the abrasive grains, a gelation inhibitor can be added. There is no particular limitation on the type of gelation inhibitor, but for example, phosphoric acid ester-based chelating agents such as 1-hydroxyethylidene-1,1-diphosphonic acid and aminotriethylenephosphonic acid can be used. There is no particular limitation on the content of the gelation inhibitor in the polishing liquid, but it is preferably 0.01% by mass or more and 6% by mass or less, more preferably 0.05% by mass or more and 2% by mass or less.

[0111] [Cleaning process]

[0112] In the cleaning process, in a hydrogen atmosphere, the ground hexagonal silicon carbide single crystal substrate is maintained at a high temperature to clean (gas etch) its surface. An example of the cleaning process will be described below.

[0113] After cleaning the hexagonal silicon carbide single crystal substrate ground through the grinding process, it is placed in an epitaxial growth apparatus (for example, a mass-production multi-wafer planetary CVD apparatus). Hydrogen is introduced into the epitaxial growth apparatus, and the pressure inside the epitaxial growth apparatus is adjusted to 100 mbar or more and 250 mbar or less. The flow rate of hydrogen is 40 slm or more and 120 slm or less.

[0114] The temperature inside the epitaxial growth apparatus is raised so that the temperature of the hexagonal silicon carbide single crystal substrate becomes 1400 °C or more and 1600 °C or less, preferably 1480 °C or more and 1600 °C or less, and the surface of the hexagonal silicon carbide single crystal substrate is cleaned with hydrogen. The processing time is 5 minutes or more and 30 minutes or less. When cleaning under these conditions, the etching amount is 0.05 μm or more and 0.4 μm or less.

[0115] [Film deposition process]

[0116] In the film deposition process, the amount of silane (SiH4) gas and propane gas required for epitaxial growth of silicon carbide is supplied to the surface of the hexagonal silicon carbide single crystal substrate cleaned through the cleaning process, and silicon carbide is epitaxially grown.

[0117] The conditions of the film deposition process can be determined according to the desired film thickness and film growth rate. For example, the flow rate of silane gas can be set to 15 sccm or more and 150 sccm or less, the flow rate of propane gas can be set to 3.5 sccm or more and 60 sccm or less, the pressure can be set to 80 mbar or more and 250 mbar or less, and the substrate temperature can be set to 1400 °C or more and 1600 °C or less.

[0118] As a method for suppressing step bunching during the growth of the silicon carbide epitaxial film, a method of controlling the ratio of the supplied source gases to increase the migration of silicon atoms on the growth surface is known. In the present embodiment, it is preferable to control the ratio of the supply amounts of silane gas and propane gas so that the molar ratio C / Si of the carbon atoms in propane to the silicon atoms in silane becomes 0.7 or more and 1.2 or less.

[0119] In addition, the growth rate of the silicon carbide epitaxial film can be set to 3 μm / h or more and 20 μm / h or less. Generally, the film thickness of the grown silicon carbide epitaxial film is 5 μm or more and 20 μm or less.

[0120] [Cooling process]

[0121] In the film formation process, silane gas and propane gas are supplied into the epitaxial growth apparatus. However, when the formation of the epitaxial film of silicon carbide is completed, the supply of silane gas and propane gas is stopped simultaneously, and the supply of nitrogen gas introduced as a doping gas is also stopped.

[0122] Then, the temperature of the hexagonal silicon carbide single crystal substrate is maintained until the exhaust of silane gas and propane gas from the epitaxial growth apparatus is completed. After the exhaust is completed, the temperature of the hexagonal silicon carbide single crystal substrate is lowered (temperature reduction process).

[0123] However, during this temperature reduction process, gas etching also occurs on the surface of the epitaxial film of silicon carbide, and the surface morphology may deteriorate. In order to suppress the deterioration of the surface morphology, it is important the timing of stopping the supply of silane gas and propane gas and the timing of temperature reduction.

[0124] After simultaneously stopping the supply of silane gas and propane gas, the growth temperature is maintained until the supplied silane gas and propane gas disappear from the surface of the hexagonal silicon carbide single crystal substrate. After that, if the temperature is lowered to room temperature at an average rate of about 50 °C / min, the deterioration of the surface morphology of the epitaxial film of silicon carbide can be suppressed.

[0125] Examples

[0126] Examples and comparative examples are shown below to more specifically illustrate the present invention.

[0127] [Example 1-1]

[0128] Use Figure 1 The membrane separation device shown to purify propane (1) of crude hydrocarbons. The cylinder 1 (capacity 47 L, made of manganese steel) filled with propane (1) is connected to the gas inlet 11 of the separation membrane module 10 (CO-B01 manufactured by UBE Industries, Ltd.) via a pipe 100 made of SUS316. A pressure control device 101 and a mass flow controller 102 are sequentially arranged in series on the pipe 100 from the upstream side to the downstream side.

[0129] The separation membrane module 10 has a separation membrane (not shown), a non-permeate gas outlet 12 for discharging the gas that has not permeated through the separation membrane, and a permeate gas outlet 13 for discharging the gas that has permeated through the separation membrane. The permeate gas outlet 13 is connected to a combustion decontamination device (not shown) via an exhaust pipe 14. The non-permeate gas outlet 12 is connected to a cylinder 2 (capacity 47 L, made of manganese steel) via a trapping pipe 16 made of SUS316. A flowmeter 130 is provided on the trapping pipe 16.

[0130] From the portion between the separation membrane module 10 and the flowmeter 130 in the capture pipe 16, the branch pipe bifurcates into two and extends, and the tip of this branch pipe is connected to the pressure gauge 15. Further, from the portion between the flowmeter 130 and the cylinder 2 in the capture pipe 16, the vacuum suction pipe 18 made of SUS316 bifurcates into two and extends, and a vacuum pump connection valve 17 and a vacuum pump 19 are successively arranged in series on this vacuum suction pipe 18 from the upstream side to the downstream side.

[0131] Through the flowmeter 130, the flow rate of the gas flowing out from the non-permeating gas outlet 12 can be measured. The exhaust port of the vacuum pump 19 is connected to a local exhaust device (not shown). The cylinder 2 can be cooled to any temperature by a cooling tank (not shown).

[0132] Propane (1) filled in the cylinder 1 is caused to flow through the separation membrane module 10 under the conditions of a temperature of 30 °C, a pressure of 0.4 MPaG, and a flow rate of 1000 mL / min. 7 kg of the gas discharged from the non-permeating gas outlet 12 is filled into the cylinder 2 cooled to -78 °C by a cooling tank (not shown) and with the internal pressure reduced to 1 kPa or less, and becomes propane (2). This propane (2) is a low-hydrogen hydrocarbon obtained by purifying propane (1) through the separation membrane.

[0133] Furthermore, the flow rate of the gas flowing out from the non-permeating gas outlet 12 is 710 mL / min. The gas discharged from the permeating gas outlet 13 is processed in a combustion decontamination device (not shown) through the exhaust pipe 14 and then exhausted.

[0134] Next, use Figure 2 the adsorption device shown to purify propane (2). Figure 2 The structure of the adsorption device, except for replacing the cylinder 1 with the cylinder 2, replacing the cylinder 2 with the cylinder 3, and replacing the separation membrane module 10 with the adsorption tower 30, has substantially the same structure as Figure 1 the membrane separation device.

[0135] Propane (2) filled in the cylinder 2 is caused to flow through the adsorption tower 30 filled with an adsorbent under the conditions of a temperature of 30 °C, a pressure of 0.4 MPaG, and a flow rate of 1000 mL / min. Then, 2 kg of the gas passing through the adsorption tower 30 is filled into the cylinder 3 (with a capacity of 47 L and made of manganese steel) cooled to -78 °C by a cooling tank (not shown) and with the internal pressure reduced to 1 kPa or less, and becomes propane (3). This propane (3) is a high-purity hydrocarbon obtained by purifying propane (2) with the adsorbent.

[0136] Furthermore, the flow rate of the outlet gas of the adsorption tower 30 is 310 mL / min. The size of the adsorption tower 30 is an inner diameter of 100 mm and a length of 2000 mm. The adsorbent is molecular sieve 13X (type X zeolite, average pore diameter 1 nm) manufactured by Union Showa Corporation, and the filling amount of the adsorbent in the adsorption tower 30 is 7 kg.

[0137] The average pore diameter of the adsorbent is measured as follows.

[0138] Measuring instrument: Belsorp max manufactured by Nikkiso Co., Ltd.

[0139] Adsorbate: Nitrogen

[0140] Measuring temperature: 77 K

[0141] Sample pretreatment: Heat and dry at 300 °C for 6 h under vacuum conditions.

[0142] Sample amount: 0.10 g

[0143] Next, propane (3) is purified using the Figure 3 shown filtration device. Figure 3 The structure of the filtration device of Figure 1 is substantially the same as that of the membrane separation device of

[0144] except that the cylinder 1 is replaced with cylinder 3, the cylinder 2 is replaced with cylinder 4, and the separation membrane module 10 is replaced with the gas filter 40.

[0145] Furthermore, the flow rate of the outlet gas of the gas filter 40 is 1000 mL / min. The gas filter 40 is a PTFE membrane filter, which is Wafergard (registered trademark) manufactured by ENTEGRIS, Inc.

[0146] Next, the propane (1) to (4) are analyzed to measure the hydrogen content. The results are shown in Table 1. The measurement conditions are as follows.

[0147] Analytical instrument: Gas chromatography (Tracera manufactured by Shimadzu Corporation)

[0148] Detector: TCD

[0149] Temperature of the detector: 150 °C

[0150] Current value of the detector: 180 mA

[0151] Injection volume of the sample: 1.0 mL

[0152] Column: Micropacked ST

[0153] Temperature of the column: 200 °C

[0154] Carrier gas: Argon

[0155] Flow rate of the carrier gas: 20 mL / min

[0156] Analyses of propane (1) to (4) were performed to determine the nitrogen content and the oxygen content. The results are shown in Table 1. The measurement conditions are as described below.

[0157] Analytical instrument: Gas chromatograph (Tracera manufactured by Shimadzu Corporation)

[0158] Detector: BID

[0159] Temperature of the detector: 250 °C

[0160] Injection volume of the sample: 1.0 mL

[0161] Column: Micropacked ST

[0162] Temperature of the column: 200 °C

[0163] Carrier gas: Helium

[0164] Flow rate of the carrier gas: 9.0 mL / min

[0165] Analyses of propane (1) to (4) were performed to determine the contents of boron, aluminum, phosphorus, sulfur, titanium, vanadium, chromium, and molybdenum. The results are shown in Table 1. Regarding the measurement method, the case of propane (1) is described as an example, but it is also substantially the same for the cases of propane (2) to (4).

[0166] Remove cylinder 1 from the Figure 1 membrane separation device and install it on the Figure 4 modulation device. That is, valve 50 of cylinder 1 is connected to pressure control device 101 via pipe 51, and pressure control device 101 is connected to mass flow controller 102 via connecting pipe 52. Then, mass flow controller 102 is connected to nitric acid container 60 via connecting pipe 54. 100 g of a 1 mass% nitric acid aqueous solution 61 is contained in nitric acid container 60, and the tip of connecting pipe 54 is disposed in nitric acid aqueous solution 61. In addition, an exhaust port 70 is provided on nitric acid container 60.

[0167] While vaporizing the liquid-phase propane in the cylinder (1) at 20°C, propane gas is withdrawn from the gas phase portion inside the cylinder (1) and circulated at a flow rate of 100 mL / min into the aqueous nitric acid solution 61 in the nitric acid container 60 to cause bubbling. By bringing the propane gas into contact with the aqueous nitric acid solution 61, boron, aluminum, phosphorus, sulfur, titanium, vanadium, chromium, and molybdenum in the propane gas are absorbed by the aqueous nitric acid solution 61.

[0168] The mass (M1) of the aqueous nitric acid solution 61 after the propane gas has passed through is 96 g. The mass difference (M2) of the cylinder 1 before and after the propane gas has passed through is 10 g. After diluting the aqueous nitric acid solution 61 to 100 g (M3) with ultrapure water, the diluted aqueous nitric acid solution is collected and analyzed for metals using an inductively coupled plasma-mass spectrometer, and the signal intensities (y) of boron, aluminum, phosphorus, sulfur, titanium, vanadium, chromium, and molybdenum contained in the diluted aqueous nitric acid solution are measured respectively.

[0169] Then, using the calibration curve, the contents (M) of boron, aluminum, phosphorus, sulfur, titanium, vanadium, chromium, and molybdenum are calculated respectively from the signal intensities (y), and the sum of the contents of boron, aluminum, phosphorus, sulfur, titanium, vanadium, chromium, and molybdenum is obtained by summing them up.

[0170] The contents (M) of boron, aluminum, phosphorus, sulfur, titanium, vanadium, chromium, and molybdenum in the propane (1) can be calculated by the following formula.

[0171] M = [{(y - b) / a} × (M3 / M1)] / M2

[0172] In the above formula, a is the slope of the calibration curve, and b is the intercept of the calibration curve. The calibration curve used is made as follows. That is, nitric acid standard solutions with the contents of the above-mentioned respective impurities being 0 mass ppb (impurity-free), 10 mass ppb, 100 mass ppb, 300 mass ppb, and 700 mass ppb are prepared respectively, and analyzed using an inductively coupled plasma-mass spectrometer. Then, the content of the impurity in the nitric acid standard solution is plotted on the horizontal axis, and the signal intensity is plotted on the vertical axis to make the calibration curve, and its slope (a) and intercept (b) are obtained.

[0173] [Table 1]

[0174]

[0175] [Example 1-2]

[0176] Propane (5) is obtained by purifying propane (1) in the same manner as in Example 1-1, except that a filter cartridge (inner diameter 22.9 mm, length 100 mm) filled with 70 g of sodium fluoride particles (cylindrical particles with a diameter of 3 mm × length of 5 mm, manufactured by Morita Chemical Industries Co., Ltd.) is used as the gas filter 40 instead of the PTFE membrane filter.

[0177] Then, in the same manner as in Example 1-1, the contents of hydrogen, nitrogen, oxygen, boron, aluminum, phosphorus, sulfur, titanium, vanadium, chromium, and molybdenum in propane (5) were measured. The results are shown in Table 1.

[0178] [Example 1-3]

[0179] Propane (1) was purified in the same manner as in Example 1-1, except that a nickel membrane filter (Wafergard III manufactured by ENTEGRIS) was used instead of the PTFE membrane filter as the gas filter 40, to obtain propane (6).

[0180] Then, in the same manner as in Example 1-1, the contents of hydrogen, nitrogen, oxygen, boron, aluminum, phosphorus, sulfur, titanium, vanadium, chromium, and molybdenum in propane (6) were measured. The results are shown in Table 1.

[0181] [Example 1-4]

[0182] Propane (1) was purified in the same manner as in Example 1-1, except that a molecular sieve 4A (type A zeolite, average pore diameter 0.4 nm) manufactured by Union Showa Corporation was used as the adsorbent filled in the adsorption tower 30 and the filtration using the gas filter 40 was not performed, to obtain propane (7).

[0183] Then, in the same manner as in Example 1-1, the contents of hydrogen, nitrogen, oxygen, boron, aluminum, phosphorus, sulfur, titanium, vanadium, chromium, and molybdenum in propane (7) were measured. The results are shown in Table 1.

[0184] [Example 1-5]

[0185] Propane (1) was purified in the same manner as in Example 1-1, except that coconut shell activated carbon (average pore diameter 2.5 nm) manufactured by Osaka Gas Chemical Co., Ltd. was used as the adsorbent filled in the adsorption tower 30 and the filtration using the gas filter 40 was not performed, to obtain propane (8).

[0186] Then, in the same manner as in Example 1-1, the contents of hydrogen, nitrogen, oxygen, boron, aluminum, phosphorus, sulfur, titanium, vanadium, chromium, and molybdenum in propane (8) were measured. The results are shown in Table 1.

[0187] [Example 1-6]

[0188] For the propane (3) obtained in Example 1-1, it was purified again using Figure 2 the adsorption device to obtain propane (9). That is, propane (3) was passed through the adsorption tower 30 used in Example 1-1 to purify propane (3).

[0189] Then, in the same manner as in Example 1-1, the contents of hydrogen, nitrogen, oxygen, boron, aluminum, phosphorus, sulfur, titanium, vanadium, chromium, and molybdenum in propane (9) were measured. The results are shown in Table 1.

[0190] [Example 1-7]

[0191] Using Figure 5 the hydrocarbon production apparatus shown, propane (1) was purified to obtain propane (10) filled in cylinder 200. Figure 5 The production apparatus is Figures 1 - 3 an apparatus in which each of the apparatuses is connected in series, and membrane separation, adsorption, and filtration exactly the same as in Example 1-1 can be continuously performed (that is, it is not necessary to fill the propane purified through each process into a cylinder and then supply it to the next process for operation). Figure 1 The apparatus of Figure 2 is connected to the apparatus of Figure 2 by pipe 115, Figure 3 and the apparatus of

[0192] Then, in the same manner as in Example 1-1, the contents of hydrogen, nitrogen, oxygen, boron, aluminum, phosphorus, sulfur, titanium, vanadium, chromium, and molybdenum in propane (10) were measured. The results are shown in Table 1.

[0193] [Comparative Example 1-1]

[0194] Except that as the adsorbent filled in adsorption tower 30, molecular sieve 3A (type A zeolite, average pore diameter 0.3 nm) manufactured by Union Showa Co., Ltd. was used, and filtration using gas filter 40 was not performed, propane (1) was purified in the same manner as in Example 1-1 to obtain propane (11).

[0195] Then, in the same manner as in Example 1-1, the contents of hydrogen, nitrogen, oxygen, boron, aluminum, phosphorus, sulfur, titanium, vanadium, chromium, and molybdenum in propane (11) were measured. The results are shown in Table 1.

[0196] [Comparative Example 1-2]

[0197] Except that as the adsorbent filled in adsorption tower 30, coal activated carbon (average pore diameter 3.7 nm) manufactured by Osaka Gas Chemical Co., Ltd. was used, and filtration using gas filter 40 was not performed, propane (1) was purified in the same manner as in Example 1-1 to obtain propane (12).

[0198] Then, in the same manner as in Example 1-1, the contents of hydrogen, nitrogen, oxygen, boron, aluminum, phosphorus, sulfur, titanium, vanadium, chromium, and molybdenum in propane (12) were measured. The results are shown in Table 1.

[0199] [Comparative Example 1-3]

[0200] Propane (1) was purified in the same manner as in Example 1-1, except that membrane separation using the separation membrane module 10 was not performed and filtration using the gas filter 40 was not performed, to obtain propane (13).

[0201] Then, the contents of hydrogen, nitrogen, oxygen, boron, aluminum, phosphorus, sulfur, titanium, vanadium, chromium, and molybdenum in propane (13) were measured in the same manner as in Example 1-1. The results are shown in Table 1.

[0202] [Examples 2 to 6]

[0203] Purification was carried out in the same manner as in Example 1-1, except that ethylene, methane, ethane, n-butane, or isobutane was used instead of propane, respectively, to produce the purified hydrocarbons described above. Then, the contents of hydrogen, nitrogen, oxygen, boron, aluminum, phosphorus, sulfur, titanium, vanadium, chromium, and molybdenum in the purified hydrocarbons described above were measured in the same manner as in Example 1-1. The results are shown in Tables 2 to 6.

[0204] Furthermore, ethylene (1) described in Table 2 is a substance corresponding to propane (1) in Example 1-1 and is crude hydrocarbon ethylene. In addition, ethylene (2) described in Table 2 is a substance corresponding to propane (2) in Example 1-1 and is ethylene of low hydrogen content hydrocarbon obtained by subjecting ethylene (1) to membrane separation using the separation membrane module 10 and purification. Ethylene (3) described in Table 2 is a substance corresponding to propane (3) in Example 1-1 and is ethylene of high-purity hydrocarbon obtained by subjecting ethylene (2) to adsorption using the adsorption tower 30 and purification. Ethylene (4) described in Table 2 is a substance corresponding to propane (4) in Example 1-1 and is ethylene obtained by subjecting ethylene (3) to filtration using the ethylene gas filter 40 and purification. The same applies to methane, ethane, n-butane, and isobutane.

[0205] [Table 2]

[0206]

[0207] [Table 3]

[0208]

[0209] [Table 4]

[0210]

[0211] [Table 5]

[0212]

[0213] [Table 6]

[0214]

[0215] [Comparative Example 2]

[0216] Except that the hydrocarbon is methane, using synthetic zeolite HS-642 (cation type: sodium, mordenite-type zeolite, average pore diameter 0.7 nm) manufactured by Fujifilm Wako Pure Chemical Corporation as the adsorbent filled in the adsorption tower 30, and not performing the filtration using the gas filter 40, methane (2) was purified in the same manner as in Example 1-1 to obtain methane (5).

[0217] Then, in the same manner as in Example 1-1, the contents of hydrogen, nitrogen, oxygen, boron, aluminum, phosphorus, sulfur, titanium, vanadium, chromium, and molybdenum in methane (5) were measured. The results are shown in Table 3.

[0218] From the results of Example 1-1, the following was found. That is, by combining the membrane separation process (hydrogen removal process), the adsorption process, and the filtration process, hydrogen, nitrogen, oxygen, boron, aluminum, phosphorus, sulfur, titanium, vanadium, chromium, and molybdenum can be removed from propane.

[0219] Hydrogen, nitrogen, and oxygen can be removed by the membrane separation process and the adsorption process. The removal of hydrogen by the membrane separation process is more effective, and the removal of nitrogen and oxygen by the adsorption process is more effective.

[0220] On the other hand, boron, aluminum, phosphorus, sulfur, titanium, vanadium, chromium, and molybdenum can be removed by any of the membrane separation process, the adsorption process, and the filtration process. However, when removing boron, aluminum, phosphorus, sulfur, titanium, vanadium, chromium, and molybdenum using the filtration process, the impurities can be reduced to a lower concentration compared to the membrane separation process and the adsorption process. Furthermore, since the inlet flow rate and the outlet flow rate of the supplied propane are equal, that is, propane is purified quantitatively, from the viewpoints of productivity and the removal efficiency of the impurities, the removal by the filtration process is more effective.

[0221] From the results of Examples 1-2 and 1-3, the following was found. That is, by using metal fluoride or a metal membrane filter as the filter medium for filtration, boron, aluminum, phosphorus, sulfur, titanium, vanadium, chromium, and molybdenum can be removed. In particular, if a metal membrane filter is used, the contents of boron, aluminum, phosphorus, sulfur, titanium, vanadium, chromium, and molybdenum in propane can be further reduced.

[0222] From the results of Examples 1-4 and 1-5, the following was found. That is, not only when using molecular sieve 13X as the adsorbent, but also when using molecular sieve 4A or coconut shell activated carbon as the adsorbent, further reduction of the impurities can be achieved.

[0223] From the results of Examples 1-6, the following was found. That is, by passing the hydrocarbon purified once by the adsorbent through the adsorbent again, the contents of hydrogen, nitrogen, and oxygen can be further reduced. In addition, the contents of boron, aluminum, phosphorus, sulfur, titanium, vanadium, chromium, and molybdenum can also be reduced to a certain extent.

[0224] From the results of Examples 1-7, the following was found. That is, even when the membrane separation step, adsorption step, and filtration step are continuously carried out, the high-purification of propane can be achieved without problems.

[0225] The results of Comparative Examples 1-1 and 1-2 showed that when the average pore diameter of the adsorbent was too small or too large, the contents of nitrogen and oxygen in propane increased. This result indicates that nitrogen and oxygen adsorbed by the adsorbent are released from the adsorbent by passing propane through. In addition, it is implied that when the average pore diameter of the adsorbent is large, the productivity of propane decreases because too much propane passing through is adsorbed. From the above results, it was shown that the average pore diameter of the adsorbent that can be used for the purification of propane has an appropriate size.

[0226] From the results of Comparative Example 1-3, it was found that when propane was treated only with an adsorbent having an average pore diameter greater than 0.3 nm and 3.5 nm or less, the total content of nitrogen and oxygen and the total content of boron, aluminum, phosphorus, sulfur, titanium, vanadium, chromium, and molybdenum in the hydrocarbon were not sufficiently reduced. From this, it was implied that when the hydrocarbon contains too much hydrogen, the efficiency of the adsorption step decreases.

[0227] From the results of Examples 2-6, the following was found. That is, through the membrane separation step, adsorption step, and filtration step, hydrogen, nitrogen, oxygen, boron, aluminum, phosphorus, sulfur, titanium, vanadium, chromium, and molybdenum can be removed from ethylene, methane, ethane, n-butane, and isobutane without problems.

[0228] From the results of Comparative Example 2, the following was found. That is, when mordenite-type zeolite is used as the adsorbent, even when the content of hydrogen in the hydrocarbon is reduced to 100 volume ppm or less by the membrane separation step, the adsorption of nitrogen and oxygen from the hydrocarbon is not sufficiently carried out.

[0229] [Example 7]

[0230] A method for forming a silicon carbide film using propane (4) will be described. The following steps are carried out to form a silicon carbide film on the surface of a hexagonal silicon carbide single crystal substrate.

[0231] First, a polishing step is carried out to polish the surface of the hexagonal silicon carbide single crystal substrate. This polishing step is carried out in two stages. The first-stage polishing is mechanical polishing, using abrasive grains with a diameter of 5 μm or less, at 350 g / cm 2It is polished under a processing pressure. The polishing in the second stage is chemical mechanical polishing. It is polished for 30 minutes using a slurry-like polishing liquid to make the surface roughness Ra of the hexagonal silicon carbide single crystal substrate less than 0.5 nm. The abrasive grains contained in the polishing liquid are silica particles with an average particle size of 10 to 150 nm. In addition, the polishing liquid contains sulfuric acid and has a pH of 1.9 at 20 °C.

[0232] Next, the polished hexagonal silicon carbide single crystal substrate is subjected to RCA cleaning and then set in an epitaxial growth apparatus. Furthermore, RCA cleaning is a wet cleaning method commonly used for silicon wafers. It is a cleaning method that uses a solution mixed with sulfuric acid and hydrogen peroxide water, a solution mixed with ammonia and hydrogen peroxide water, a solution mixed with hydrochloric acid and hydrogen peroxide water, and a hydrofluoric acid aqueous solution to remove organic substances, heavy metals, and particles on the surface of the substrate.

[0233] Next, a purification (gas etching) process is performed in the epitaxial growth apparatus. The purification process is carried out for 10 minutes under the conditions of a hydrogen flow rate of 90 slm, a pressure in the reactor of 200 mbar, and a substrate temperature of 1550 °C.

[0234] After the purification process, a silicon carbide epitaxial growth process is performed. In the silicon carbide epitaxial growth process, the flow rate of silane gas is 48 sccm, the flow rate of propane(4) gas is 17.6 sccm, and the molar ratio C / Si of carbon atoms in propane to silicon atoms in silane is 1.1. The pressure in the reactor is set to 200 mbar, the temperature of the substrate is set to 1550 °C, and a silicon carbide epitaxial growth process is performed for 2 hours to form a silicon carbide epitaxial film with a thickness of 10 μm.

[0235] Furthermore, as the epitaxial growth apparatus, Hot Wall SiC CVD manufactured by AIXTRON Corporation, a mass-production type multi-wafer planetary CVD apparatus, is used. Furthermore, a silicon carbide epitaxial film is grown on a silicon surface that is inclined 4° in the <11-20> axis direction with respect to the (0001) plane of the hexagonal silicon carbide single crystal. After that, the supply of silane gas and propane(4) is stopped, and after exhausting the two gases, the substrate temperature is lowered by 50 °C per minute until it reaches room temperature.

[0236] Secondary ion mass spectrometry (IMS 7f-Auto manufactured by CAMECA Corporation) is used to quantify the element concentrations of nitrogen, boron, aluminum, phosphorus, sulfur, titanium, vanadium, chromium, and molybdenum contained in the silicon carbide epitaxial film obtained by the above procedure. The results are shown in Table 7.

[0237] [Table 7]

[0238]

[0239] [Comparative Example 3]

[0240] Except for using propane (1) instead of propane (4), in the same manner as in Example 7, a silicon carbide epitaxial film was formed on the surface of a hexagonal silicon carbide single crystal substrate. Then, the elemental concentrations of nitrogen, boron, aluminum, phosphorus, sulfur, titanium, vanadium, chromium, and molybdenum in the silicon carbide epitaxial film were quantified. The results are shown in Table 7.

[0241] From the results of Example 7 and Comparative Example 3, the following can be known. That is, if the content of impurities contained in propane is reduced, the elemental concentrations of nitrogen, boron, aluminum, phosphorus, sulfur, titanium, vanadium, chromium, and molybdenum in the silicon carbide epitaxial film can be reduced.

[0242] Description of Reference Numerals

[0243] 1 to 4: cylinders

[0244] 10: separation membrane module

[0245] 12: non-permeating gas outlet

[0246] 13: permeating gas outlet

[0247] 30: adsorption tower

[0248] 40: gas filter

[0249] 200: cylinder

Claims

1. A method for manufacturing a hydrocarbon, comprising a hydrogen removal step and an adsorption step, in the hydrogen removal step, hydrogen is removed from a crude hydrocarbon containing a hydrocarbon having 1 to 4 carbon atoms and hydrogen to obtain a low-hydrogen-content hydrocarbon having a hydrogen content of 100 volume ppm or less, in the adsorption step, the low-hydrogen-content hydrocarbon is brought into contact with an adsorbent to obtain a high-purity hydrocarbon having a hydrogen content of 80 volume ppm or less, a total content of nitrogen and oxygen of 5 volume ppm or less, and a total content of boron, aluminum, phosphorus, sulfur, titanium, vanadium, chromium, and molybdenum of 250 mass ppb or less, the adsorbent has a crystal having pores with a pore diameter greater than 0.3 nm and 3.5 nm or less, and the crystal form of the crystal is not a mordenite type.

2. The method for manufacturing a hydrocarbon according to claim 1, wherein the hydrocarbon is at least one of methane, ethane, ethylene, propane, n-butane, and isobutane.

3. The method for manufacturing a hydrocarbon according to claim 1, wherein the hydrocarbon is at least one of propane and ethylene.

4. The method for manufacturing a hydrocarbon according to claim 1, wherein the adsorption step is a step of adsorbing at least one of the nitrogen and the oxygen from the low-hydrogen-content hydrocarbon using the adsorbent.

5. The method for manufacturing a hydrocarbon according to claim 1, wherein the adsorption step is a step of adsorbing at least one of boron, aluminum, phosphorus, sulfur, titanium, vanadium, chromium, and molybdenum from the low-hydrogen-content hydrocarbon using the adsorbent.

6. The method for manufacturing a hydrocarbon according to claim 1, wherein the hydrogen removal step is a step of removing the hydrogen from the crude hydrocarbon using a separation membrane.

7. The method for manufacturing a hydrocarbon according to claim 1, further comprising a filtration step, in the filtration step, the crude hydrocarbon, the low-hydrogen-content hydrocarbon, or the high-purity hydrocarbon is passed through a filter medium to remove at least one of boron, aluminum, phosphorus, sulfur, titanium, vanadium, chromium, and molybdenum from the crude hydrocarbon, the low-hydrogen-content hydrocarbon, or the high-purity hydrocarbon, the filter medium is at least one filter of a membrane filter, a sintered metal filter, and a filter having a plurality of metal halide particles.

8. A method for manufacturing silicon carbide, using the high-purity hydrocarbon manufactured by the method for manufacturing a hydrocarbon according to any one of claims 1 to 7 as a raw material to manufacture silicon carbide.

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