Method for producing metal carbide, carbide composition, and electrolytic apparatus

Abstract

To provide a method for further improving the effective current efficiency when manufacturing metal carbides, a carbide composition that can be manufactured by the above method, and an electrolytic apparatus for efficiently manufacturing metal carbides. [Solution] A method for producing metal carbide, comprising: preparing a molten salt containing a first metal ion and carbonate ions; arranging a working electrode and a counter electrode in an electrolytic cell, supplying an electric current between the working electrode and the counter electrode to obtain a carbide composition containing the carbide of the first metal; and recovering the carbide composition in a recovery unit provided in the electrolytic cell.

Description

[Technical Field]

[0001] This invention relates to a method for producing metal carbides, a carbide composition, and an electrolytic apparatus. [Background technology]

[0002] Acetylene is an industrially important substance used as a raw material for various organic compounds. Acetylene is usually obtained by the reaction of metal carbides (mainly calcium carbide) with water.

[0003] Patent documents 1 and 2 disclose a manufacturing method in which the reaction proceeds rapidly at relatively low temperatures and in which metal carbides can be efficiently obtained. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2023-054787 [Patent Document 2] Japanese Patent Publication No. 2023-054788 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] However, conventional methods for manufacturing metal carbides have the problem that, when electrolysis is performed for a long time, some of the composition containing the metal carbide is not retained on the electrode surface, resulting in a decrease in effective current efficiency.

[0006] This disclosure aims to provide a method for further improving the substantial current efficiency when manufacturing metal carbides. This disclosure further aims to provide a carbide composition that can be manufactured by the above method. This disclosure further aims to provide an electrolytic apparatus for efficiently manufacturing metal carbides. [Means for solving the problem]

[0007] This disclosure includes the following aspects: [1] To prepare a molten salt containing a primary metal ion and a carbonate ion, A working electrode and a counter electrode are placed in an electrolytic cell, and an electric current is supplied between the working electrode and the counter electrode to obtain a carbide composition containing the carbide of the first metal. In the recovery section provided within the electrolytic cell, the carbide composition is recovered. A method for producing metal carbide, including [2] The method for producing a metal carbide according to claim 1, wherein the method for preparing a molten salt containing the first metal ion and carbonate ions is to add a gas containing carbon dioxide to a molten salt containing an oxide of the first metal. [3] The method for producing a metal carbide according to item 1 or 2, wherein the working electrode is a carbon-containing electrode. [4] The method for producing metal carbide according to any one of claims 1 to 3, wherein the recovery unit is a receiver provided in the electrolytic cell. [5] The method for producing metal carbide according to any one of items 1 to 3, wherein the recovery unit is composed of a part of the electrolytic cell body. [6] The manufacturing method according to item 5, wherein the electrolytic cell body has a conical bottom, and the bottom constitutes the recovery section. [7] The manufacturing method according to item 5, wherein the electrolytic cell body has a curved bottom, and the bottom constitutes the recovery section. [8] A method for producing metal carbide according to any one of claims 1 to 7, wherein the working electrode is provided on the wall surface of the electrolytic cell body. [9] The method for producing a metal carbide according to any one of claims 1 to 8, wherein the carbide composition is a viscous body that is fluid at the electrolysis temperature.

[10] The production method according to any one of items 1 to 9, wherein the electrolytic cell main body includes a member that is in contact with the working electrode and is operable relative to the working electrode.

[11] The method for producing a metal carbide according to any one of items 1 to 10, further comprising withdrawing the carbide composition recovered in the recovery unit from a withdrawal part provided in the recovery unit.

[12] An electrolytic apparatus for producing a metal carbide, comprising: an electrolytic cell; a working electrode; a counter electrode; and a recovery unit for recovering the metal carbide; the electrolytic apparatus.

[13] The electrolytic apparatus according to item 12, wherein the recovery unit is a receiver provided inside the electrolytic cell.

[14] The electrolytic apparatus according to item 12, wherein the recovery unit is constituted by a part of the electrolytic cell main body.

[15] The electrolytic apparatus according to item 12, wherein the working electrode is provided on a wall surface of the electrolytic cell main body.

[16] The electrolytic apparatus according to item 12, further comprising a withdrawal part for withdrawing the metal carbide recovered in the recovery unit. [Effects of the Invention]

[0008] According to the present disclosure, it is possible to provide a production method capable of further improving the substantial current efficiency when producing a metal carbide, a carbide composition produced by the above production method, and an electrolytic apparatus for efficiently producing a metal carbide. [Brief Description of the Drawings]

[0009] [Figure 1] This is a flowchart showing the method for producing a metal carbide according to the present disclosure. [Figure 2] This is a schematic diagram showing an embodiment of the electrolytic apparatus according to the present disclosure. [Figure 3]This is a schematic diagram showing one embodiment of the electrolytic device relating to this disclosure. [Figure 4] This is a schematic diagram showing one embodiment of the electrolytic device relating to this disclosure. [Figure 5] This graph shows the change in the working electrode potential over time during the manufacturing of the metal carbide related to this disclosure. [Modes for carrying out the invention]

[0010] A method for manufacturing metal carbide according to one embodiment of this disclosure is: To prepare a molten salt containing a primary metal ion and a carbonate ion, A working electrode and a counter electrode are placed in an electrolytic cell, and an electric current is supplied between the working electrode and the counter electrode to obtain a carbide composition containing the carbide of the first metal. This includes recovering the carbide composition in a recovery unit provided within the electrolytic cell.

[0011] According to the method disclosed herein, the carbide composition that has fallen off without being retained by the electrodes as a result of prolonged electrolysis can be recovered without loss, thus enabling the acquisition of the desired metal carbide with high effective current efficiency.

[0012] This disclosure includes an electrolytic apparatus for efficiently producing metal carbides.

[0013] In this disclosure, "effective current efficiency" refers to the current efficiency calculated for the portion of the total metal carbide produced by electrolysis that has been removed, excluding the lost metal carbide.

[0014] First Embodiment [Method for manufacturing metal carbide] The method for manufacturing metal carbide according to this embodiment is: To prepare a molten salt containing a primary metal ion and a carbonate ion, A working electrode and a counter electrode are placed in an electrolytic cell, and an electric current is supplied between the working electrode and the counter electrode to obtain a carbide composition containing the carbide of the first metal. This includes recovering the carbide composition in a recovery unit provided within the electrolytic cell, The recovery unit is a receiver provided within the electrolytic cell. Figure 1 is a flowchart showing the method for manufacturing metal carbide according to this disclosure.

[0015] Figure 2 shows a schematic diagram of the electrolytic apparatus according to this embodiment. The method for producing metal carbide and the electrolytic apparatus for producing metal carbide according to this embodiment will be described below with reference to Figure 2.

[0016] (i) Preparation of molten salt (S11) A molten salt 11 containing a first metal ion and carbonate ions is prepared in the electrolytic cell 19 that constitutes the electrolytic device 10. The first metal ion is the metal source for the target metal carbide and is generated by the ionization of the salt of the first metal.

[0017] In the molten salt 11, it is not necessary for all of the first metal salt and the carbonate ion source to be ionized. In this embodiment, for convenience, the first metal salt contained in the electrolytic bath is referred to as the first metal salt, including when it is completely ionized, and the molten salt prepared by the first metal salt and carbon dioxide is referred to as the molten salt, including when they are not completely ionized.

[0018] (First metal ion) The first metal ion may be at least one selected from the group consisting of, for example, alkali metal ions and alkaline earth metal ions. Alkali metal and alkaline earth metal carbides, also known as acetylides, readily produce acetylene through hydrolysis and have high industrial value.

[0019] Examples of alkali metals include at least one selected from the group consisting of lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and francium (Fr). The alkali metal may be at least one selected from the group consisting of Li, Na, K, Rb, and Cs. The alkali metal may be at least one selected from the group consisting of Li, Na, K, and Cs, with Li, Na, or K being particularly preferred.

[0020] Examples of alkaline earth metals include at least one selected from the group consisting of beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra). The alkaline earth metal may be at least one selected from the group consisting of Mg, Ca, Sr, and Ba, with Ca being particularly preferred.

[0021] From an industrial value standpoint, the first metal ion may contain alkaline earth metal ions. The first metal ion may contain alkali metal ions together with alkaline earth metal ions. This is because alkali metal ions have excellent functions as electrolytes, such as facilitating the ionization of alkaline earth metal salts, promoting the formation of alkaline earth metal ions, and lowering the melting point of the molten salt, enabling electrolysis at lower temperatures. The first metal ion may contain at least one alkali metal ion selected from the group consisting of Li, Na, K, Rb, and Cs ions, and at least one alkaline earth metal ion selected from the group consisting of Be, Mg, Ca, Sr, and Ba ions. In particular, it may contain at least one of Li, Na, and K ions, and a Ca ion.

[0022] Other primary metal ions include, for example, at least one selected from the group consisting of aluminum (Al), gallium (Ga), indium (In), thallium (Tl), zinc (Zn), cadmium (Cd), gold (Au), silver (Ag), and copper (Cu). Rare earth elements include scandium (Sc), yttrium (Y), lanthanide elements, and actinide elements. In particular, Al ions may be included.

[0023] The amount of primary metal ions contained in the molten salt 11 is not particularly limited. From the viewpoint of reaction efficiency, the number of moles of primary metal ions is preferably 1 mol% or more, more preferably 2 mol% or more, and particularly preferably 3 mol% or more, relative to the total number of moles of cations in the electrolytic bath.

[0024] The first metal salt is preferably ionized in a molten salt at a temperature of 800°C or lower. Specific examples of the first metal salt include alkali metal halides such as LiF, NaF, KF, RbF, CsF, LiCl, NaCl, KCl, RbCl, CsCl, LiBr, NaBr, KBr, RbBr, CsBr, LiI, NaI, KI, RbI, CsI; alkaline earth metal halides such as MgF2, CaF2, SrF2, BaF2, MgCl2, CaCl2, SrCl2, BaCl2, MgBr2, CaBr2, SrBr2, BaBr2, MgI2, CaI2, SrI2, BaI2; and Li2O and Na2O. Examples include metal oxides such as K2O and CaO; metal carbonates such as Li2CO3, Na2CO3, and K2CO3; metal nitrates such as LiNO3, NaNO3, and KNO3; rare earth element halides such as ScCl3, YCl3, LaCl3, CeCl3, PrCl3, NdCl3, PmCl3, SmCl3, EuCl3, GdCl3, TbCl3, DyCl3, HoCl3, ErCl3, TmCl3, YbCl3, and LuCl3; and earth metal halides such as AlCl3, GaCl3, InCl3, and TlCl3. These can be used individually or in combination of two or more. In particular, two or more metal salts may be combined because they tend to lower the melting temperature.

[0025] (Other metal ions) The molten salt 11 may contain other metal ions (tertiary metal ions) besides the primary metal ion. The tertiary metal ion is not particularly limited as long as the carbide of the primary metal, which is the target substance, can be stably precipitated. It is preferable that the salt of the tertiary metal ion dissociates at a temperature of 800°C or lower.

[0026] Examples of third metals include at least one selected from the group consisting of rare earth elements, aluminum (Al), gallium (Ga), indium (In), thallium (Tl), silicon (Si), germanium (Ge), tin (Sn), lead (Pb), zinc (Zn), cadmium (Cd), iron (Fe), nickel (Ni), cobalt (Co), manganese (Mn), gold (Au), silver (Ag), and copper (Cu). Examples of rare earth elements include scandium (Sc), yttrium (Y), lanthanide elements, and actinide elements.

[0027] The amount of third metal ions contained in the molten salt 11 is not particularly limited.

[0028] (Carbonate ions) Carbonate ions may be incorporated into the molten salt 11 by mixing a salt of the first metal with a carbonate that can serve as a carbonate ion source, or by absorbing a gas containing carbon dioxide (hereinafter also referred to as CO2 gas) into the electrolytic bath.

[0029] The carbonate cations that can serve as a carbonate ion source include at least one selected from the group consisting of Li, Na, K, Rb, Cs, Fr, Mg, Ca, Sr, Ba, Ra, Fe, Zn, Pb, Mn, Cu, Al, Ga, In, Tl, Cd, Au, Ag, and NH4. It is preferable that the carbonate dissociates in the molten salt at a temperature of 800°C or lower.

[0030] When a carbonate of a primary metal is used as a carbonate ion source, ionization produces primary metal ions and carbonate ions. Primary metal carbonates can be synthesized, for example, by reacting a hydroxide of a primary metal with carbon dioxide.

[0031] In this embodiment, carbonate ions may be incorporated into the molten salt 11 by adding a gas containing carbon dioxide to the molten salt 11 containing a first metal ion (preferably an oxide of the first metal). The CO2 gas is brought into contact with the liquid first metal salt in a gaseous state. The CO2 gas may be blown into the gas phase of the electrolytic bath and brought into contact with the liquid surface of the first metal salt, or the CO2 gas may be blown into the first metal salt. The CO2 gas may be a mixture of CO2 and an inert gas (typically argon). A sufficient amount of CO2 gas may be added to the first metal salt before supplying current, or the CO2 gas may be added to the first metal salt while supplying current.

[0032] The amount of CO2 gas injected should be set appropriately according to the amount of the first metal ion. For example, considering the absorption efficiency of the gas into the first metal salt, the amount of CO2 gas injected should be equal to or greater than the equivalent amount of the first metal salt.

[0033] In order to promote the dissolution of CO2 into the first metal salt, it is desirable for the bubble diameter of the injected CO2 gas to be small. The bubble diameter of the CO2 gas is preferably 10 mm or less, and more preferably 1 mm or less. The bubble diameter of the CO2 gas may be 100 nm or more, and may be 1 μm or more. The bubble diameter of the CO2 gas can be made finer by, for example, bubbling through a porous material made of quartz glass or high-purity alumina, stirring with a stirrer, applying vibration, or irradiating with ultrasound.

[0034] It is preferable to preheat the CO2 gas to near the temperature of the first metal salt. Preheating helps to suppress the decrease in the temperature of the first metal salt, which can cause it to solidify.

[0035] In this embodiment, alternatively, an electrode containing carbon may be used as the working electrode 12 to incorporate carbonate ions into the molten salt 11. The carbon contained in the working electrode 12 can serve as a carbon source for the target metal carbide.

[0036] Carbon only needs to be present on at least the surface of the working electrode 12. The surface of the working electrode is the part that can come into contact with the first metal ion.

[0037] Examples of carbon materials included in the working electrode 12 include at least one carbon material selected from the group consisting of glassy carbon (GC), graphite, isotropic graphite, highly oriented pyrolysis graphite (HOPG), plastic-formed carbon (PFC), and conductive diamond. In particular, from the viewpoint of Faraday efficiency, it may be a carbon material having a high degree of crystallinity, and may be HOPG. Other examples of carbon materials having a high degree of crystallinity include graphene, carbon nanotubes, carbon nanohorns, and carbon fibers. In particular, the working electrode 12 may be porous or fibrous carbon, and may be at least one selected from the group consisting of porous carbon, porous graphite, activated carbon, carbon fibers, and carbon nanotubes. The working electrode 12 may be obtained by molding the above carbon material, for example, a woven fabric, nonwoven fabric, felt, etc.

[0038] The amount of carbonate ions contained in the molten salt 11 is not particularly limited.

[0039] (Other anions) The molten salt 11 may contain anions other than carbonate ions as counterions to the first and third metal ions. Other anions include, for example, halide ions, sulfate ions, phosphate ions, nitrate ions, acetate ions, carboxylate ions, and oxide ions (O 2- At least one selected from the group consisting of ) is included. Other anions may include halide ions derived from metal first halides. Metal first halides are commonly used as molten salts and are excellent as electrolytes.

[0040] The anion may contain at least one of a halide ion and an oxide ion. Alternatively, the anion may contain both a halide ion and an oxide ion. While oxides of the first metal are readily available, they tend to have high melting points. Halides of the first metal are commonly used as molten salts. However, halide ions can generate highly oxidizing halogen gases (which can cause corrosion) at the anode. When both halide ions and oxide ions are present, the melting point of the molten salt 11 can be lowered while suppressing the generation of halogen gases.

[0041] Examples of halogens include at least one selected from the group consisting of fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At). The halogen may be at least one selected from the group consisting of F, Cl, Br, and I, and in particular may be F and / or Cl.

[0042] The amount of other anions contained in the molten salt 11 is not particularly limited.

[0043] Examples of primary metal salts used in the preparation of the molten salt 11 include, specifically, CaO, CaCl2, CaF2, CaBr2, CaI2, CaH2, and Ca3P2 as primary metal salts containing alkaline earth metal ions. Specific examples of primary metal salts containing alkali metal ions include Li2O, Na2O, K2O, Rb2O, LiF, NaF, KF, RbF, CsF, LiCl, NaCl, KCl, RbCl, CsCl, LiBr, NaBr, KBr, RbBr, CsBr, LiI, NaI, KI, RbI, and CsI.

[0044] (ii) Current supply (S12) Next, the working electrode 12 and the counter electrode 13 are placed in the molten salt 11, and an electric current is supplied between the working electrode 12 and the counter electrode 13. As a result, CO3 is released on the working electrode 12. 2-is reduced, and a precipitate (carbide composition 16) containing a first metal carbide (first metal carbide) is obtained. The precipitate containing the first metal carbide precipitates on the surface of the working electrode 12. As by-products, carbon and oxygen can be generated on the working electrode 12.

[0045] When the first metal is Ca, calcium carbide (CaC2) can precipitate on the working electrode 12 (Formulas 1 and 2). Metal calcium can further be generated on the working electrode 12 (Formula 3). Part or all of the metal calcium generated by this side reaction can further react to form calcium carbide (Formula 4). Alternatively, metal calcium can react with carbon dioxide physically dissolved in the molten salt 11 to form calcium carbide (Formula 5). Fine carbon powder may be generated, and the molten salt 11 may turn black and turbid (Formula 6). The CaO generated in the above (Formula 5) and (Formula 6) immediately dissolves in the molten salt 11 to generate calcium ions and oxide ions (Formula 7). (Formula 1) CO3 2- +4e - → C+3O 2- (Formula 2) Ca 2+ +2C+2e - → CaC2 (Formula 3) Ca 2+ +2e - → Ca (Formula 4) Ca+2C → CaC2 (Formula 5) 2CO2+5Ca → CaC2+4CaO (Formula 6) 2Ca+CO2→ C+2CaO (Formula 7) CaO → Ca 2+ +O 2-

[0046] Also when the first metal is Na, K or Li, sodium carbide (Na2C2), potassium carbide (K2C2) or lithium carbide (Li2C2) precipitates together with carbon by a similar reaction. The same applies to other first metals.

[0047] On the counter electrode, O 2-The material is oxidized to produce oxygen (Equation 8). The oxygen produced on the counter electrode 13 is discharged into the gas phase. This oxygen gas can be recovered and used for other purposes. (Formula 8) 2O 2- → O2+4e -

[0048] The current is supplied at a temperature at which the molten state of the molten salt 11 can be maintained, that is, at a temperature approximately 10°C or more higher than the melting point of the molten salt 11. The temperature of the electrolytic bath may be 500°C or higher, or 550°C or higher, for example, in the case of NaCl-KCl-CaCl2 eutectic salt (melting point: 481°C). The temperature of the electrolytic bath may be 800°C or lower, or 700°C or lower. According to this disclosure, the reaction proceeds at such relatively low temperatures, resulting in high energy efficiency.

[0049] The electric current is supplied at a temperature that maintains the molten state of the molten salt 11. The temperature of the electrolytic bath may be, for example, 350°C or higher, or 400°C or higher. The temperature of the electrolytic bath may be, for example, 800°C or lower, or 700°C or lower. According to this disclosure, the reaction proceeds at such a relatively low temperature, resulting in high energy efficiency.

[0050] Current can be supplied by applying a voltage between the working electrode 12 and the counter electrode 13. The applied voltage is set so that the working electrode potential is lower (base) than the potential (Ec) at which carbon precipitates. The current value should be set appropriately according to the amount of CO2 supplied per unit time. If the working electrode potential is excessively high (noble), carbon will mainly precipitate, and the amount of the target first metal carbide produced will tend to decrease. If the working electrode potential is excessively low (base), the first metal carbide will be produced, but among the metals contained therein, the metal with the noblest oxidation-reduction potential in the molten salt 11 will mainly precipitate. If there are multiple metals with similar oxidation-reduction potentials in the molten salt 11, an alloy of multiple metals may precipitate. For example, if the molten salt 11 contains LiCl, KCl, and Li2O (5 mol%), the working electrode potential should be 1.0V or less (Li + (Li standard) is sufficient.

[0051] The current may be DC, intermittent (pulsed current), or superimposed AC. The potentials Ec and Em can be determined by cyclic voltammetry measurement in the molten salt 11 used, for example, using an Fe electrode. The working electrode potential is determined by the reference electrode (Ag + The potential between the galvanic acid (Ag) and the working electrode is measured and calibrated using the metal deposition potential as the reference. In the case of NaCl-KCl eutectic salt, the metal deposition potential is the deposition potential of the Na-Ca alloy.

[0052] The current supply time is not particularly limited. From an implementation standpoint, a longer supply time is preferable.

[0053] In this embodiment, the working electrode 12 is the cathode.

[0054] In this embodiment, a working electrode (cathode) made of SUS304 may be used. This improves the Faraday efficiency. Furthermore, SUS304 is desirable because it is relatively easy to obtain, inexpensive, and has excellent heat resistance. SUS304 is an austenitic stainless steel, and its composition is described in JIS G 4303, etc.

[0055] The material of the working electrode 12 is not limited to SUS304. Examples of materials for the working electrode 12 include metallic materials such as Ag, Cu, Ni, Pb, Hg, Tl, Bi, In, Sn, Cd, Au, Zn, Ga, Ge, Fe, Pt, Pd, Ru, Ti, Cr, Mo, W, V, Nb, Ta, Zr, and alloys thereof. Specifically, ferritic stainless steels such as SUS430 are used as alloys.

[0056] In particular, from the viewpoint of Faraday efficiency, the working electrode 12 may contain at least one selected from the group consisting of transition metals and alloys containing transition metals. Examples of transition metals include Ni, Fe, Mo, and Ti. The working electrode 12 may contain an iron alloy (typically stainless steel), or it may be a working electrode 12 made of an iron alloy. The working electrode 12 may contain SUS304, or it may be a working electrode 12 made of SUS304.

[0057] The working electrode 12 may be made of a porous material. In this disclosure, "porous material" means a material having multiple pores. The material of the porous material is not particularly limited as long as it has the conductivity necessary for an electrode material and sufficient heat resistance and corrosion resistance to the molten salt used, and examples include sintered bodies of various metals or alloys, conductive ceramics, etc. The average pore diameter of the porous material is not particularly limited and may be a microporous material with a small average pore diameter (e.g., less than 2 nm), a mesoporous material with a medium average pore diameter (e.g., 2 nm to 50 nm), or a macroporous material with a large average pore diameter (e.g., greater than 50 nm), and may also be a mesh-like or sponge-like material in which each pore is visible (e.g., 1 mm or more).

[0058] An example of a porous material is porous stainless steel.

[0059] Furthermore, the working electrode 12 may be made of a fibrous material. In this disclosure, "fibrous material" refers to a material which is an aggregate of multiple monofilaments formed by weaving, bundling, spinning, laminating, etc., of fibrous elements (monofilaments) whose length is larger than their width (not particularly limited, but for example, 10 times or more, or 100 times or more). The material of the fibrous material is not particularly limited as long as it has the conductivity necessary for an electrode material and sufficient heat resistance and corrosion resistance to the molten salt used, and in addition to the metal materials and alloy materials mentioned above, other fibrous materials such as carbon fibers, carbon nanofibers, carbon nanotubes, and conductive ceramic fibers can be used. Furthermore, the fibrous material may be a woven fabric, nonwoven fabric, felt-like fibrous material, a porous fibrous material, or a fibrous material formed by processing monofilaments on a base material into a comb-like, brush-like, pile-like, etc.

[0060] Examples of fibrous materials include steel wool and stainless steel wool.

[0061] The working electrode 12 being made of a porous or fibrous material increases the contact area between the working electrode 12 and the molten salt 11, thereby improving the Faraday efficiency.

[0062] The material of the counter electrode 13 (anode) is not particularly limited. Examples of counter electrode materials include Pt, conductive metal oxides, glassy carbon, natural graphite, isotropic graphite, pyrolytic graphite, plastic-formed carbon, and boron-doped diamond. Examples of electrodes made of conductive metal oxides include transparent conductive electrodes called ITO electrodes, which are made by depositing a mixed oxide of indium and tin on glass, electrodes called DSA electrodes (trademark of Denora Permelec Electrodes Co., Ltd.), which are made by depositing oxides of platinum group metals such as ruthenium and iridium on a substrate such as titanium, and La 1-x Sr x FeO 3-δ Examples include conductive metal oxide electrodes having compositions such as (0≦x≦0.5 (particularly 0.1≦x≦0.5), 0≦δ≦0.5). Among these, oxide-based counter electrodes are preferred because they are less prone to wear due to oxidation reactions.

[0063] The working electrode 12 and the counter electrode 13 may be connected to an external power supply 14. Furthermore, the working electrode 12 and the counter electrode 13 may be used as a single pair or as multiple pairs.

[0064] During the supply of current, new electrodes may be sequentially added to the electrodes that are being consumed. For example, if the electrodes are rod-shaped electrodes, an electrode extension device may be provided on the working electrode 12 to automatically or manually insert electrodes with screws or the like onto the top of the electrodes that are being consumed. Alternatively, electrodes may be covered with a mesh container, and the chipped electrodes may be added to the container. In this case, the mesh container may also serve as a collection section for the carbide composition 16 generated on the working electrode.

[0065] (iii) Recovery of the carbide composition (S13) Next, the carbide composition 16 generated on the working electrode is recovered in a recovery unit provided in the electrolytic cell 19. In this embodiment, the recovery unit is a receiver 15 provided in the electrolytic cell 19.

[0066] In this embodiment, if electrolysis is performed for a long period of time, a portion of the carbide composition containing metal carbide will not be retained on the electrode surface and will detach from the electrode. By providing a receiver in the electrolytic cell 19 that can recover the detached carbide composition, the loss of the generated carbide composition is prevented, and as a result, the decrease in effective current efficiency can be suppressed.

[0067] In this disclosure, the carbide composition may fall vertically downward from the working electrode during electrolysis. Therefore, in this embodiment, if the receiver is positioned so that its bottom is located vertically below the working electrode, most of the fallen carbide composition can be recovered.

[0068] In this embodiment, the receiver 15 can be placed at the bottom of the electrolytic cell 19 body, vertically below the working electrode 12. However, the method of installing the receiver 15 in this embodiment is not limited to the above; it may be suspended from the ceiling or the like, or suspended from a structure extending from the side wall of the electrolytic cell 19 body. Furthermore, in order to further improve the recovery rate of the carbide composition 16 that has fallen off the working electrode 12, the receiver 15 may be installed so that its side wall covers the working electrode 12.

[0069] The side walls of the receiver 15 may take any form, for example, they may cover the working electrode 12. The shape and capacity of the receiver 15 are not particularly limited and may be appropriately selected according to the scale and shape of the electrolysis system. The material of the receiver 15 is not particularly limited as long as it can exist stably in the molten salt 11 at about 800°C, and may be made of iron, copper, bronze, stainless steel, ceramic, etc.

[0070] To more efficiently recover the carbide composition 16 deposited on the working electrode 12, the electrolytic cell 19 body may include a member that contacts the working electrode 12 and is operable relative to the working electrode 12. For example, the working electrode 12 may have a wiping means capable of wiping the working electrode 12. For example, the working electrode 12 may be equipped with a wiper member (e.g., a wiper blade) as a wiping means, and the working electrode surface may be wiped by moving the wiper member relative to the working electrode 12. The material of the wiper member is not particularly limited as long as it can withstand the high temperature (about 800°C) during electrolysis. Wiping is preferably performed so that the carbide composition 16 is recovered in the recovery section.

[0071] (iv) Extraction of carbide composition (S14) In this embodiment, as shown in Figure 2, the carbide composition 16 collected in the collection unit may be further extracted from an extraction unit provided in the collection unit.

[0072] In Figure 2, a gate valve 17 is connected to a receiver 15 as an extraction port. For example, the gate valve 17 remains closed until a certain mass of carbide composition accumulates in the receiver. Once a certain mass of carbide composition has accumulated, the gate valve 17 can be opened to extract the carbide composition from the electrolytic device 10. The material of the gate valve 17 is not particularly limited as long as it can exist stably in the molten salt 11 at approximately 800°C.

[0073] The form of the extraction section is not limited to those described above. For example, the extraction section may be an intake valve, exhaust valve, motor valve, ball valve, air valve, diaphragm valve, check valve, butterfly valve, globe valve, etc., in addition to the gate valve 17. Furthermore, the extraction section may be in an "open" state at all times, and is not limited to the form of a valve; for example, it may be in the form of piping connected to the recovery section.

[0074] (Carbide composition) This disclosure includes carbide compositions that can be produced by the above-described manufacturing method.

[0075] The carbide compositions of this disclosure, A carbide of at least one first metal selected from the group consisting of alkali metals and alkaline earth metals, At least one selected from the group consisting of the elemental first metal, the oxide of the first metal, and the halide of the first metal, It may contain carbon.

[0076] The carbide composition relating to this disclosure can be used in the production of hydrocarbons.

[0077] The carbide composition contains a first metal carbide. Considering hydrolysis in subsequent processes, the first metal carbide may be at least one selected from the group consisting of Li2C2, Na2C2, K2C2, CaC2, and Al4C3.

[0078] The content of the first metal carbide in the carbide composition may be 5% by mass or more, 10% by mass or more, 20% by mass or more, 30% by mass or more, 50% by mass or more, etc., and may be 99% by mass or less, 95% by mass or less, 90% by mass or less, 80% by mass or less, etc. In one embodiment, the content of the first metal carbide is 10% by mass or more.

[0079] The carbide composition may contain compounds containing a primary metal other than the primary metal carbide. Examples of compounds containing a primary metal other than the primary metal carbide include salts of the primary metal with other anions (e.g., halides of the primary metal), elements of the primary metal, carbonates of the primary metal, oxides of the primary metal, hydrides of the primary metal, and peroxides of the primary metal. For example, if the primary metal is Ca, the carbide composition may contain CaO.

[0080] The carbon contained in the carbide composition may include at least one selected from the group consisting of nanocarbon materials such as graphite, amorphous carbon, glassy carbon, carbon nanotubes, diamond, nanodiamond, and graphene. In one embodiment, the carbide composition contains amorphous carbon.

[0081] The carbide composition may have a carbon coating on its surface. The carbon content of the carbon-coated portion of the carbide composition may be 50% by mass or more, 70% by mass or more, 90% by mass or more, or 95% by mass or more, relative to the entire carbon-coated portion. In one embodiment, the carbon content of the carbon-coated portion of the carbide composition is 90% by mass to 100% by mass, relative to the entire carbon-coated portion.

[0082] The carbide composition may also contain, as a precipitate other than those mentioned above, at least one selected from the group consisting of elemental metal 2, oxides of metal 2, and halides of metal 2. The metal 2 may be a metal other than the metal 1, and may be any of the metals listed as examples of the metal 1. The metal 2 may be a component derived from the working electrode 12 or the counter electrode; for example, if the working electrode 12 is iron, the metal 2 may be iron.

[0083] The content of at least one selected from the group consisting of elemental metals, oxides of metals, and halides of metals is, for example, 40% by mass or less, 20% by mass or less, or 10% by mass or less of the carbide composition. The amount of impurities may be 10% by mass or more of the total precipitate, 1% by mass or more, or 0.1% by mass or more. In one embodiment, the content of at least one selected from the group consisting of elemental metals, oxides of metals, and halides of metals is 0.1% by mass or more and 10% by mass or less of the carbide composition.

[0084] The presence and quantification of primary metal carbides, primary metals in their elemental form, compounds containing primary metals, and other precipitates can be performed, for example, by Raman spectroscopy and X-ray diffraction (XRD) analysis of the precipitates.

[0085] The carbide composition may be a viscous body that is fluid at the electrolysis temperature. The electrolysis temperature refers to the temperature of the electrolytic bath in the current supply (S12) step. Because the carbide composition is a viscous body that is fluid at the electrolysis temperature, the detachment of the carbide composition deposited on the working electrode is promoted, and it is easier to collect it in the recovery section provided within the working electrode.

[0086] For example, the carbide composition may be in a slurry state at the electrolysis temperature.

[0087] From the viewpoint of promoting the slurry formation of the carbide composition, the molten salt 11 may contain a first metal halide. Examples of halogens include at least one selected from the group consisting of fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At). The halogen may be at least one selected from the group consisting of F, Cl, Br, and I, and in particular, may be F and / or Cl.

[0088] The carbide composition does not have to be a viscous body that is fluid at non-electrolytic temperatures; for example, it may be an elastic body.

[0089] This disclosure also relates to the possibility of hydrolyzing the metal carbide obtained by the above method to obtain hydrocarbons. This method allows for the efficient acquisition of high-purity hydrocarbons.

[0090] For example, the metal carbide obtained by the above method is brought into contact with water to hydrolyze it. This yields a gas containing the desired hydrocarbon. Hydrocarbons typically have low solubility in water. Therefore, the generated hydrocarbon is quickly released into the gas phase and recovered.

[0091] The primary metal carbide may be isolated from the precipitate at the working electrode and hydrolyzed. Isolation can be carried out, for example, by crushing the precipitate and utilizing the difference in specific gravity. Alternatively, the precipitate may be hydrolyzed directly. In this case, the primary metal carbide that may be contained in the precipitate is also hydrolyzed to produce hydrocarbons.

[0092] Examples of hydrocarbons that can be obtained include methane, ethane, ethylene, acetylene (C2H2), propane, propylene, butane, and butene. When isolated primary metal carbides are used, or when the amount of impurities (especially elemental metals) in the precipitate is small, acetylene can be obtained as the main component. The main component is defined as the component that accounts for 50% or more of the total mass of the recovered gas. Acetylene is an industrially important hydrocarbon.

[0093] The resulting gas may contain hydrocarbons as well as impurities such as water vapor, hydrogen, nitrogen, and oxygen. The amount of impurities is preferably 10% by mass or less of the recovered gas, and more preferably 1% by mass or less. The amount of impurities may be 0.0001% by mass or more of the recovered gas, and may be 0.001% by mass or more. In one embodiment, the amount of impurities is 0.0001% by mass or more and 1% by mass or less of the recovered gas.

[0094] The resulting gas may contain, in addition to acetylene, at least one selected from the group consisting of ethylene, ethane, methane, methylacetylene, propylene, butene, and hydrogen.

[0095] The presence and quantification of hydrocarbons and impurities can be performed, for example, by gas chromatography-mass spectrometry (GC-MS) of the recovered gas, Fourier transform infrared absorption spectroscopy (FT-IR) spectroscopy with a gas cell, or ultraviolet-visible absorption spectroscopy (UV-Vis spectroscopy).

[0096] The amount of water to be brought into contact with the composition is appropriately set according to the mass of the composition. The amount of water is, for example, greater than or equal to the amount necessary for the hydrolysis of the metal carbides and metals contained in the composition. In addition, it is desirable to use an amount of water that is sufficient to immerse the entire composition and that takes into account evaporation due to the heat generated during hydrolysis.

[0097] According to this disclosure, the current efficiency e for hydrocarbon production is improved. The current efficiency e is, for example, 8% or more, and may be 10% or more.

[0098] The current efficiency e for C2H2 generation can be calculated as follows. First, the volume percentage of C2H2 in the recovered gas is calculated from the total area of ​​peaks obtained from GC-MS analysis and the calibration curve. Next, the volume of C2H2 generated is calculated from the volume occupied by the gas phase in the recovery container and the calculated volume percentage of C2H2 in the gas. Finally, assuming that the generated C2H2 was under standard conditions (0°C, 101kPa), the current efficiency e(%) is calculated using the following formula.

[0099]

number

[0100] Hydrolysis of primary metal carbides produces hydrocarbons as well as primary metal hydroxides. For example, hydrolysis of calcium carbide produces calcium hydroxide along with water. CaC2 + 2H2O → C2H2 + Ca(OH)2

[0101] Second Embodiment This embodiment is the same as the first embodiment except that the recovery unit provided in the electrolytic cell is composed of a part of the electrolytic cell body. This difference will be explained below. In this embodiment, the other components of the method for manufacturing metal carbide are the same as in the first embodiment, so their explanation will be omitted.

[0102] Figure 3 shows a schematic diagram of the electrolytic apparatus according to this embodiment. The electrolytic apparatus for producing metal carbide according to this embodiment will be described below with reference to Figure 3.

[0103] In this embodiment, the bottom portion 18, which is part of the electrolytic cell body, plays the role of a recovery section, thus preventing the configuration of the electrolytic device 10 from becoming complicated.

[0104] The shape of the bottom portion 18 is not particularly limited and may be any shape depending on the properties of the carbide composition produced during electrolysis. For example, the shape of the bottom portion 18 may be conical or it may have a curved surface. Also, the extraction portion may be located at the bottom of the bottom portion 18.

[0105] The material of the bottom portion 18 is not particularly limited and may be the same material as the other parts of the electrolytic cell 19 body. Furthermore, the bottom portion may be polished to improve the slipperiness of the carbide composition accumulated therein.

[0106] Third Embodiment This embodiment is the same as the first embodiment except that the working electrode is provided on the wall surface of the electrolytic cell body. This difference will be explained below. In this embodiment, the other configurations of the method for manufacturing metal carbide are the same as in the first embodiment, so their explanation will be omitted.

[0107] Figure 4 shows a schematic diagram of the electrolytic apparatus according to this embodiment. The electrolytic apparatus for producing metal carbide according to this embodiment will be described below with reference to Figure 4.

[0108] In this embodiment, since the working electrode 12 is provided on the wall surface of the electrolytic cell 19 body, the entire electrolytic cell 19 body can be used as the working electrode 12, which in turn can lead to miniaturization of the electrolytic device and an increase in the contact area between the working electrode 12 and the molten salt 11.

[0109] The working electrode 12 may be physically attached to the wall of the electrolytic cell 19 using, for example, screws or bolts, or it may be provided by coating the wall of the electrolytic cell 19 with a coating. Alternatively, as shown in Figure 4, a container-shaped working electrode 12 may be provided by placing or fitting it along the wall of the electrolytic cell 19.

[0110] In this embodiment, the carbide composition is deposited on the working electrode portion of the electrolytic device 10. By making the working electrode 12 container-shaped, the working electrode 12 can also serve as a recovery unit. Furthermore, if the working electrode 12 is container-shaped, the extraction unit may be placed at the bottom of the working electrode 12.

[0111] In this embodiment, the shape of the working electrode 12 is not particularly limited and can be appropriately selected according to the shape of the electrolytic cell 19.

[0112] While embodiments of this disclosure have been described in detail above, this disclosure is not limited thereto, and design modifications are possible without departing from the gist of this disclosure. [Examples]

[0113] [Example 1] (Manufacturing of metal carbide) NaCl, KCl, and CaCl2 were mixed in the ratios NaCl / KCl / CaCl2 = 33.4 mol% / 11.6 mol% / 55.0 mol%, and then 3 mol% CaO was added. The mixture was then vacuum-dried at 200°C and below 100 Pa for at least 24 hours. Each of these mixed salts was placed in a glass container and set in an electric furnace, where it was heated to 550°C. In this way, molten salts of NaCl-KCl-CaCl2-CaO were obtained.

[0114] The working electrode was the inner surface of a nickel crucible (20 mL capacity, 38 mm outer diameter, 32 mm height, manufactured by Fisher Scientific). Approximately 100 g of molten salt of NaCl-KCl-CaCl2-CaO was placed in the nickel crucible, and the electrode surface area was 37 cm². 2 The following was done. A glassy carbon rod (3 mm in diameter, manufactured by Tokai Carbon Co., Ltd.) was used as the counter electrode. For the reference electrode, an Ag wire immersed in a bath containing 1.0 mol% AgCl was placed in an HB alumina tube (manufactured by Nikkatoh Co., Ltd.). Next, the working electrode, counter electrode, and reference electrode were attached to the lid of the container, and the container was sealed with this lid. The molten salt in the container was heated to 550°C, and CO2 was blown in at a flow rate of 100 mL / min for more than 30 minutes. During electrolysis, CO2 was constantly flowed into the gas phase at a flow rate of 100 mL / min to maintain a constant CO2 atmosphere.

[0115] Using a potentiometer-galvanostat, a current value of 4500 mA, i.e., a current density of 200 mA / cm², was achieved. 2 The current was supplied for 2222 seconds, maintaining the current until the electrical charge reached 10000C.

[0116] Subsequently, the counter electrode and reference electrode were removed, and the mixture was cooled and solidified to room temperature. All of the crucible contents were then removed. Precipitation was confirmed on the working electrode. X-ray diffraction measurements confirmed that the crucible contents contained carbon, CaC2, and molten salt components.

[0117] All experimental procedures were performed in a glove box maintaining a high-purity argon atmosphere. Figure 5 is a graph showing the change in the working electrode potential over time when current is applied to produce metal carbide. The potential of the working electrode is compared to the reference electrode (Ag + The potential between the silver (Ag) and the cathode was measured and calibrated using the Na-K-Ca alloy deposition potential as a reference.

[0118] (Hydrogen manufacturing) A portion of the crucible contents was placed in a sealed test tube. Pure water was added to this test tube in small amounts at room temperature (23°C) to hydrolyze the precipitate. A total of 2.5 ml of water was added. After confirming that foaming was occurring in the test tube, it was left to stand until foaming ceased. Next, 100 μl (microliters) of gas from the test tube was collected using a gas-tight syringe. This process was repeated for all of the crucible contents, and the sum of these measurements was calculated to determine the current efficiency. The entire volume of the liquid after hydrolysis was filtered, and the amount of carbon produced was calculated.

[0119] Using a gas chromatograph (GC) apparatus, GC analysis was performed on the obtained gas to confirm that C2H2 was produced as the main component. Furthermore, methane, ethane, and hydrogen were confirmed to be by-products. In addition, water, carbon dioxide, nitrogen, oxygen, and argon were also present. The amount of each component produced was also confirmed. The mass percentage of C2H2 in the recovered gas was well above 50% by mass.

[0120] The current efficiency for C2H2 gas production was calculated to be approximately 1.82%. Most of the by-products were carbon. [Industrial applicability]

[0121] The manufacturing method disclosed herein is useful in various fields because the reaction proceeds rapidly at relatively low temperatures. [Explanation of Symbols]

[0122] 10 Electrolyzer 11 Molten salt 12 Working electrode 13 Opposite 14 External power supply 15 Receiver 16 Carbide Compositions 17 Gate valve 18 Bottom 19 Electrolytic cell

Claims

1. To prepare a molten salt containing a primary metal ion and a carbonate ion, A working electrode and a counter electrode are placed in an electrolytic cell, and an electric current is supplied between the working electrode and the counter electrode to obtain a carbide composition containing the carbide of the first metal. In the recovery section provided within the electrolytic cell, the carbide composition is recovered. A method for producing metal carbide, including

2. The method for producing a metal carbide according to claim 1, wherein the method for preparing a molten salt containing the first metal ion and carbonate ions is to add a gas containing carbon dioxide to a molten salt containing an oxide of the first metal.

3. The method for producing a metal carbide according to claim 1 or 2, wherein the working electrode is an electrode containing carbon.

4. The method for producing metal carbide according to claim 1, wherein the recovery unit is a receiver provided in the electrolytic cell.

5. The method for producing metal carbide according to claim 1, wherein the recovery unit is composed of a part of the electrolytic cell body.

6. The manufacturing method according to claim 5, wherein the electrolytic cell body has a conical bottom, and the bottom constitutes the recovery section.

7. The manufacturing method according to claim 5, wherein the electrolytic cell body has a curved bottom, and the bottom constitutes the recovery section.

8. The method for producing metal carbide according to claim 1, wherein the working electrode is provided on the wall surface of the electrolytic cell body.

9. The method for producing a metal carbide according to claim 1, wherein the carbide composition is a viscous body that is fluid at the electrolysis temperature.

10. The manufacturing method according to claim 1, wherein the electrolytic cell body includes a member that contacts the working electrode and is operable relative to the working electrode.

11. A method for producing a metal carbide according to claim 1, further comprising extracting the carbide composition collected in the collection section from an extraction section provided in the collection section.

12. An electrolytic apparatus for producing metal carbide, Electrolytic cell; Working electrode; Opposite; and A recovery unit for recovering the aforementioned metal carbide; An electrolytic device having the following features.

13. The electrolytic apparatus according to claim 12, wherein the recovery unit is a receiver provided in the electrolytic cell.

14. The electrolytic apparatus according to claim 12, wherein the recovery unit is composed of a part of the electrolytic cell body.

15. The electrolytic apparatus according to claim 12, wherein the working electrode is provided on the wall surface of the electrolytic cell body.

16. Furthermore, the electrolytic apparatus according to claim 12, further comprising an extraction unit for extracting the metal carbide recovered in the recovery unit.

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