Method for producing metal carbide and hydrocarbon

Abstract

The present invention is a method for manufacturing metal carbides using carbonate ions as a carbon source, comprising: a step of preparing a molten salt containing a first metal ion and the carbonate ion; a step of arranging a working electrode and a counter electrode in the molten salt, supplying a current between the working electrode and the counter electrode at a predetermined current density to generate the first metal carbide; and a step of restoring the carbonate ion concentration near the working electrode, wherein the generation of the first metal carbide and the restoration of the carbonate ion concentration are alternately repeated at least once.

Description

Technical Field

[0001] This invention relates to methods for manufacturing metal carbides and hydrocarbons. Background Technology

[0002] Acetylene is an important industrial substance as a raw material for various organic compounds. Acetylene is usually obtained by reacting metal carbides (mainly calcium carbides) with water.

[0003] Patent documents 1 and 2 disclose methods for producing metal carbides efficiently by rapidly reacting at relatively low temperatures. Non-patent document 1 discloses a method for obtaining a dense and uniform carbon film by electrolytic reduction of carbonate ions in a molten LiCl bath, where pulsed electrolysis is particularly useful.

[0004] Existing technical documents Patent documents Patent Document 1: Japanese Patent Application Publication No. 2023-054787 Patent Document 1: Japanese Patent Application Publication No. 2023-054788 Non-patent literature Non-patent document 1: Chongrui Zhuang et al. "Deposition and Morphology Control of Carbon Film through Electrochemical Reduction of Carbonate Ions in MoltenLiCl", October 2023, Journal of The Electrochemical Society 170(10) Summary of the Invention

[0005] The technical problem that the invention aims to solve The object of this invention is to provide a method for further improving current efficiency in the manufacture of metal carbides. This invention also provides a method for manufacturing hydrocarbons from the obtained metal carbides.

[0006] Technical solutions for solving technical problems The present invention includes the following solutions.

[0007] [1] A method for manufacturing metal carbides using carbonate ions as a carbon source, comprising: The step of preparing a molten salt containing a first metal ion and the above-mentioned carbonate ion; The steps of configuring a working electrode and a counter electrode in the aforementioned molten salt, supplying a current at a predetermined current density between the working electrode and the counter electrode, and generating a carbide of the aforementioned first metal; and The step of restoring the carbonate ion concentration near the working electrode. The formation of the carbide of the first metal and the recovery of the carbonate ion concentration alternate at least once.

[0008] [2] The method for manufacturing metal carbides as described in [1] above, wherein the restoration of the carbonate ion concentration is performed by stopping the current supply between the working electrode and the counter electrode.

[0009] [3] In the method for manufacturing metal carbides as described in [2] above, the current supply is stopped for 1 second to 1000 seconds during the recovery of the carbonate ion concentration.

[0010] [4] The method for manufacturing metal carbides as described in [2] or [3] above, wherein the current is supplied for 10 seconds to 1000 seconds during the formation of the carbides of the first metal.

[0011] [5] The method for manufacturing metal carbides as described in [1] above, wherein the recovery of the carbonate ion concentration is performed by supplying a current between the working electrode and the counter electrode at a current density lower than that supplied when the carbides of the first metal are generated.

[0012] [6] The method for manufacturing a metal carbide as described in any one of [1] to [5] above, wherein the molten salt as the first metal ion comprises at least one selected from alkali metal ions and alkaline earth metal ions.

[0013] [7] The method for manufacturing a metal carbide as described in any one of [1] to [6] above, wherein the molten salt as the first metal ion comprises one selected from lithium ion, sodium ion, potassium ion, rubidium and cesium and one selected from calcium ion and magnesium ion.

[0014] [8] The method for manufacturing metal carbides as described in any one of [1] to [7] above, wherein the molten salt as an anion further comprises at least one selected from halide ions and oxide ions.

[0015] [9] The method for manufacturing metal carbides as described in any one of [1] to [8] above, wherein the molten salt as an anion further includes both halide ions and oxide ions.

[0016]

[10] The method for manufacturing a metal carbide as described in any one of [1] to [9] above, wherein the metal carbide composition further comprises at least one selected from carbon, an elemental form of the first metal, a halide, a carbonate, an oxide, a hydride, and a peroxide.

[0017]

[11] A method for producing a hydrocarbon, comprising: The step of preparing a molten salt containing a first metal ion and a carbonate ion; The steps are as follows: 1. A working electrode and a counter electrode are disposed in the above molten salt, and a current is supplied between the working electrode and the counter electrode at a specified current density to generate the carbide of the first metal. The step of restoring the carbonate ion concentration near the working electrode; and The step of hydrolyzing the carbide of the first metal to obtain a hydrocarbon-containing gas. The formation of the carbide of the first metal and the recovery of the carbonate ion concentration are alternated and repeated more than once.

[0018]

[12] The method for manufacturing hydrocarbons as described in

[11] above, wherein the gas contains acetylene.

[0019]

[13] A method for producing hydrocarbons as described in

[11] or

[12] above, wherein the gas comprises acetylene and at least one selected from ethylene, ethane, methane, methylacetylene, propylene, butene and hydrogen.

[0020] Invention Effects According to the present invention, a method for manufacturing metal carbides with excellent current efficiency and a method for manufacturing hydrocarbons from the obtained metal carbides can be provided. Attached Figure Description

[0021] Figure 1 This is a flowchart illustrating the method for manufacturing metal carbides according to the first embodiment.

[0022] Figure 2 This is a flowchart illustrating the method for manufacturing hydrocarbons according to the first embodiment.

[0023] Figure 3 This is a flowchart illustrating a method for manufacturing metal carbides according to the second embodiment.

[0024] Figure 4 This is a flowchart illustrating the method for manufacturing hydrocarbons according to the second embodiment.

[0025] Figure 5 This is a spectrum representing the X-ray diffraction analysis results of the precipitate obtained in Example 1.

[0026] Figure 6 It is a graph showing the change over time of the working electrode potential when energized in Example 1 for manufacturing metal carbides. Detailed Implementation

[0027] Electrolysis of molten salts containing first metal ions and carbonate ions for an extended period of time will decrease the current efficiency. This decrease in current efficiency is believed to be due to the excessively low concentration of carbonate ions near the working electrode, which serve as the carbon source for the metal carbide.

[0028] During the supply of current between the working electrode and the counter electrode, carbonate ions (CO3-) are generated near the working electrode. 2- The reduction reaction of CO3 2- CO3 is consumed near the working electrode. 2- The concentration gradually decreases. This results in the generation of CO3 within the diffusion layer, the area between the working electrode and the edge of the electrolytic bath. 2- Concentration gradient. To mitigate the concentration gradient, CO3 is produced. 2- Diffusion from the edge of the electrolytic bath to the vicinity of the working electrode. However, under high current density, CO3 in the diffusion layer... 2- The diffusion rate is difficult to keep up with the CO3 at the working electrode. 2- The consumption of CO3 near the working electrode. 2- The concentration was too low. As a result, it was considered that CO3... 2- The reduction reaction becomes difficult to carry out (or even stops), and the current efficiency decreases.

[0029] In this invention, the carbonate ion concentration near the working electrode is restored during electrolysis, thereby improving current efficiency. This increased current efficiency leads to increased productivity.

[0030] Near the working electrode refers to the area where CO3 can be generated. 2- The space for the reduction reaction. Near the working electrode refers to the space inside the so-called Helmholtz layer, for example, the space between the surface of the working electrode and a location 1 nm away from that surface.

[0031] The recovery of carbonate ion concentration refers to an increase in carbonate ion concentration compared to the concentration near the working electrode immediately after the current supply is stopped; that is, a easing of the concentration gradient within the diffusion layer. The recovery of carbonate ion concentration near the working electrode can be achieved by stopping or inhibiting CO32-. 2- The reduction reaction is carried out.

[0032] First Implementation Method In this embodiment, during constant current electrolysis, the carbonate ion concentration can be restored by stopping the current supply between the working electrode and the counter electrode.

[0033] By stopping the current supply to the working electrode and the counter electrode, carbonate ions (CO3) 2- The reduction reaction of CO32- (CO32-) stops, and the CO32- near the working electrode... 2-Consumption ceases. During this period, CO3... 2- Diffusion, CO3 near the working electrode 2- Concentration restored.

[0034] [Methods for manufacturing metal carbides] The method for manufacturing metal carbides according to this embodiment includes: a step of preparing a molten salt containing a first metal ion and carbonate ions; a step of arranging a working electrode and a counter electrode in the molten salt, supplying a current between the working electrode and the counter electrode at a predetermined current density, and generating a carbide of the first metal; and a step of stopping the current supply between the working electrode and the counter electrode. The current supply and the current supply stop are alternately repeated at least once.

[0035] Figure 1 This is a flowchart illustrating a method for manufacturing metal carbides according to this embodiment.

[0036] In this embodiment, carbonate ions derived from carbon dioxide are used. CO2, which is identified as a cause of global warming, can be effectively utilized as a carbon source to obtain a carbide composition containing a first metal.

[0037] In this embodiment, the repetitive current supply and current supply cessation differ from the supply of so-called pulsed current. In pulsed current, the pulse width (current supply time) is typically less than 1 second, the pulse interval (period) is less than 1 second, the repetition frequency is 10 Hz or higher, and the duty cycle is 2 to 8. The CO3-containing... 2- In the molten salt electrolysis, the pulse width is 25 milliseconds, the current stop time is 475 milliseconds, the pulse interval (period) is 500 milliseconds, the repetition frequency is 2 Hz, and the duty cycle is 0.05.

[0038] In this embodiment, the current is not supplied in a way that involves instantaneous switching between on and off, as with pulsed current. Regarding the current in this embodiment, the duty cycle is 0.5 or more and less than 1, and the repetition frequency is 1 MHz or more and less than 4 MHz. In this embodiment, the current supply time is, for example, 10 seconds or more, and the current supply stop time is 1 second or more.

[0039] (i) Preparation of molten salt (S11) A molten salt comprising a first metal ion and carbonate ions from carbon dioxide is prepared. The carbonate ions are generated by absorbing a carbon dioxide-containing gas into an electrolytic bath. The first metal ion is generated by the ionization of a salt of the first metal.

[0040] In the molten salt, it is not necessary for both the first metal salt and carbon dioxide to ionize. In this embodiment, for convenience, the salt of the first metal contained in the electrolytic bath, including the case where it is completely ionized, is referred to as the first metal salt, and the molten salt prepared from the first metal salt and carbon dioxide, including the case where they are not completely ionized, is referred to as the molten salt.

[0041] (Carbonate ions from carbon dioxide) Carbonate ions are generated by absorbing carbon dioxide-containing gas into an electrolytic bath.

[0042] A gas containing carbon dioxide (hereinafter, sometimes referred to as CO2 gas) is brought into contact with a liquid first metal salt in a gaseous state. The CO2 gas can be blown into the gas phase section of the electrolytic bath to contact the liquid surface of the first metal salt, or it can be blown into the first metal salt. The CO2 gas can be a mixture of CO2 and an inert gas (typically argon). A sufficient amount of CO2 gas can be added to the first metal salt before voltage is applied, or it can be added while voltage is being applied.

[0043] The amount of CO2 blown in can be appropriately set according to the amount of the first metal ions. For example, if the absorption efficiency of CO2 in the first metal salt is taken into account, the amount of CO2 blown in can be greater than or equal to the amount of the first metal salt.

[0044] From the viewpoint of promoting the dissolution of CO2 in the first metal salt, it is desirable for the bubble diameter of the blown CO2 gas to be as small as possible. The bubble diameter of CO2 gas can be less than 10 mm or less than 1 mm. The bubble diameter of CO2 gas can be greater than 100 nm or greater than 1 μm. The CO2 gas bubbles can be miniaturized, for example, by bubbling through porous materials made of quartz glass or high-purity alumina, by stirring with a stirrer, by applying vibration, or by irradiating with ultrasound.

[0045] The CO2 gas is preferably preheated to near the temperature of the first metal salt. Preheating can prevent the temperature of the first metal salt from decreasing and solidifying.

[0046] (Other anions) Molten salts may contain anions other than carbonate ions. Examples of 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 of the following.

[0047] Other anions may include at least one of halide ions and oxide ions. Metal salts containing halide ions are commonly used as molten salts and are excellent electrolytes. Oxide ions readily ionize CO2.

[0048] Other anions can include both halide ions and oxide ions.

[0049] (First metal ion) The first metal ion is, for example, at least one selected from alkali metal ions and alkaline earth metal ions. Alkali metal ions and alkaline earth metal ions have excellent functions as electrolytes.

[0050] As an alkali metal, at least one can be selected from lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and francium (Fr). An alkali metal can be at least one selected from Li, Na, K, Rb, and Cs. In particular, an alkali metal can be at least one selected from Li, Na, K, and Cs.

[0051] Alkaline earth metals can be selected from at least one of beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra). Alkaline earth metals can be selected from at least one of Mg, Ca, Sr, and Ba.

[0052] From an industrial perspective, the first metal ion can include alkaline earth metal ions. The first metal ion can contain both alkaline earth and alkali metal ions. Alkali metal ions readily ionize alkaline earth metal salts, promoting the formation of alkaline earth metal ions, and can lower the melting point of the molten salt, enabling electrolysis at lower temperatures.

[0053] The first metal ion may comprise at least one ion selected from Li, Na, K, Rb, and Cs as an alkali metal ion and at least one ion selected from Be, Mg, Ca, Sr, and Ba as an alkaline earth metal ion. The first metal ion may comprise at least one ion selected from Li, Na, K, Rb, and Cs and at least one ion selected from Ca and Mg.

[0054] Other first metal ions can be listed as at least one selected from aluminum (Al), gallium (Ga), indium (In), thallium (Tl), zinc (Zn), cadmium (Cd), gold (Au), silver (Ag), and copper (Cu). Rare earth elements can be listed as scandium (Sc), yttrium (Y), lanthanides, and actinides.

[0055] There is no particular limitation on the amount of the first metal ion contained in the molten salt.

[0056] The first metal salt preferably ionizes at a temperature below 800°C. 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, and CsI; alkaline earth metal halides such as MgF2, CaF2, SrF2, BaF2, MgCl2, CaCl2, SrCl2, BaCl2, MgBr2, CaBr2, SrBr2, BaBr2, MgI2, CaI2, SrI2, and BaI2; and Li Metal oxides such as O₂ and CaO; metal carbonates such as Li₂CO₃, Na₂CO₃, and K₂CO₃; metal nitrates such as LiNO₃, NaNO₃, and KNO₃; halides of rare earth elements such as ScCl₃, YCl₃, LaCl₃, CeCl₃, PrCl₃, NdCl₃, PmCl₃, SmCl₃, EuCl₃, GdCl₃, TbCl₃, DyCl₃, HoCl₃, ErCl₃, TmCl₃, YbCl₃, and LuCl₃; and halides of rare earth metals such as AlCl₃, GaCl₃, InCl₃, and TlCl₃. These can be used individually or in combination of two or more. Considering the ease with which the melting temperature decreases, combinations of two or more metal salts are possible.

[0057] (II) Current supply (S12) A working electrode and a counter electrode are placed in a molten salt, and a current is supplied between the working electrode and the counter electrode at a specified current density. Thus, CO3... 2- The material is reduced to obtain a precipitate containing a carbide of the first metal (the first metal carbide). This precipitate containing the first metal carbide is deposited on the surface of the electrode with the lower potential (here, the working electrode). As byproducts, carbon and oxygen are generated on the working electrode.

[0058] When the first metal is Ca, calcium carbide (CaC2) can be precipitated at the working electrode (Equations 1 and 2). Metallic calcium can also be generated at the working electrode (Equation 3). Some or all of the metallic calcium produced by this side reaction can further react to form calcium carbide (Equation 4). Alternatively, metallic calcium can react with carbon dioxide physically dissolved in the molten salt to form calcium carbide (Equation 5). Sometimes, fine carbon powder is generated, and the molten salt becomes turbid (Equation 6). The CaO generated in (Equations 5) and (Equations 6) above immediately dissolves in the molten salt, generating calcium ions and oxide ions (Equation 7).

[0059] (Formula 1) CO3 2- +4e - → C+3O 2- (Equation 2) Ca2＋ +2C+2e - → CaC2 (Equation 3) Ca 2＋ +2e - → Ca (Equation 4) Ca + 2C → CaC2 (Equation 5) 2CO2 + 5Ca → CaC2 + 4CaO (Equation 6) 2Ca+CO2 → C+2CaO (Equation 7) CaO → Ca 2＋ +O 2- When the first metal is Na, K, or Li, sodium carbide (Na₂C₂), potassium carbide (K₂C₂), or lithium carbide (LiC₂) is precipitated together with carbon through the same reaction. The same applies to other first metals.

[0060] On the counter electrode, O 2- Oxygen is produced by oxidation (Equation 8). The oxygen produced at the counter electrode is discharged into the gas phase. This oxygen can be recovered and used for other purposes.

[0061] (Equation 8) 2O 2- → O2 + 4e - The current is supplied at a temperature that maintains the molten state of the molten salt, i.e., at a temperature approximately 10°C or higher than the melting point of the molten salt. The temperature of the electrolytic bath, for example, in the case of NaCl-KCl eutectic salts (melting point: 503.8°C), can be 510°C or higher, or 550°C or higher. The temperature of the electrolytic bath can, for example, be below 800°C, or below 700°C. According to the present invention, since the reaction is carried out at such a relatively low temperature, the energy efficiency is high.

[0062] The current value can be appropriately set such that the working electrode potential during electrolysis lies between the carbon deposition potential (Ec) and the first metal deposition potential (Em). This further improves the selectivity of the first metal carbide. If the working electrode potential is too high (expensive), carbon is mainly deposited, and the amount of the target first metal carbide formed is easily reduced. If the working electrode potential is too low (inexpensive), although the first metal carbide is formed, among the metals contained in the molten salt, the metal with the highest redox potential in that molten salt is mainly deposited. When multiple metals with similar redox potentials are present in the molten salt, alloys of multiple metals sometimes precipitate. For example, when the molten salt contains LiCl, KCl, and Li₂O (5 mol%), the working electrode potential is between 0.0 V and 1.0 V (LiCl, KCl, and Li₂O (5 mol%)). ＋ ( / Li reference) is sufficient.

[0063] The current can be direct current, intermittent (pulse current), or superimposed alternating current. Potentials Ec and Em can be determined using cyclic voltammetry with, for example, an Fe electrode in the molten salt being used. The working electrode potential is the reference electrode for measurement (Ag). ＋ The potential between the ( / Ag) electrode and the working electrode is a value corrected based on the metal deposition potential. In the case of NaCl-KCl eutectic salts, the metal deposition potential is the deposition potential of Na-Ca alloys.

[0064] There is no particular limitation on the current supply time. From the perspective of current efficiency, the current supply time can be more than 10 seconds and less than 1000 seconds. The current supply time can be more than 250 seconds or more than 500 seconds. The current supply time can be less than 1000 seconds or less than 500 seconds.

[0065] There are no particular limitations on the material of the working electrode. Examples of materials that can be used as the working electrode include metals 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 their alloys, as well as carbon materials such as glassy carbon, natural graphite, isotropic graphite, thermally decomposed graphite, plastically formed carbon, and conductive diamond.

[0066] There are no particular limitations on the material of the electrode. Examples of materials for the counter electrode include Pt, conductive metal oxides, glassy carbon, natural graphite, isotropic graphite, thermally decomposed graphite, plastically formed carbon, and conductive diamond. Examples of electrodes made of conductive metal oxides include, for instance, ITO electrodes (transparent conductive electrodes obtained by forming a film of a mixed oxide of indium and tin on glass), DSA electrodes (trademark of De-Nora-Permelec Electrode Co., Ltd.) (electrodes obtained by forming a film of oxides of platinum group metals such as ruthenium and iridium on a substrate such as titanium), and La... 1-x Sr x CoO 3-δ La 1- x Sr x FeO 3-δ Oxide electrodes, etc. Among them, oxide systems can also be used in aspects where oxidation reactions do not easily lead to consumption.

[0067] (III) Stopping of current supply (S13) By stopping the current supply to the working electrode and the counter electrode, CO3 2- The reduction reaction stops, and CO3 near the working electrode 2-Consumption ceases. During this period, CO3... 2- Diffusion, CO3 near the working electrode 2- Concentration restored. CO3 2- The restoration of concentration will promote the CO3 generated by the next current supply. 2- The reduction reaction.

[0068] There is no particular limitation on the current supply interruption time. From the perspective of current efficiency, the current supply interruption time can be more than 1 second and less than 1000 seconds. The current supply interruption time can be more than 1 second or more than 30 seconds. The current supply interruption time can be less than 300 seconds or less than 50 seconds.

[0069] (IV) Current supply and shutdown The current supply and stop are alternated and repeated more than once. Alternating and repeating more than once means that after the initial current supply, the cycle of stopping and supplying is performed more than once.

[0070] The current supply and current supply stop can be repeated alternately more than 2 times (supply → stop → supply → stop → supply), more than 3 times (supply → stop → supply → stop → supply → stop → supply), or more than 4 times (supply → stop → supply → stop → supply → stop → supply → stop → supply).

[0071] The supply of current stops between current supply and current supply. The time during which the supply of current stops is the time between current supply and current supply.

[0072] The density of the initial current supplied can be the same as or different from the density of the current supplied after the second supply. The density of the current supplied after the second supply can also be the same or different.

[0073] The initial current supply time and subsequent current supply times can be the same or different. The subsequent current supply times can also be the same or different.

[0074] The current supply and stop times can be the same or different for each of the multiple current supply cycles.

[0075] In one embodiment of the first method, the method for manufacturing metal carbides is a method for manufacturing metal carbides using carbonate ions as a carbon source, comprising: The step of preparing a molten salt, wherein the molten salt comprises, as a first metal ion, one selected from lithium ion, sodium ion, potassium ion, rubidium and cesium ion and one selected from calcium ion and magnesium ion and contains the aforementioned carbonate ion; A working electrode and a counter electrode are configured in the above molten salt, and an electric current of 200 mA / cm is applied between the working electrode and the counter electrode. -2The step of supplying a current density of 300-500 seconds to generate the carbide of the first metal described above; and The step of stopping the current supply between the working electrode and the counter electrode for 1 to 300 seconds. The current supply and current supply stop alternate twice under the same conditions.

[0076] In another embodiment of the first embodiment, the method for manufacturing the metal carbide is a method for manufacturing the metal carbide using carbonate ions as a carbon source, including: The step of preparing a molten salt, wherein the molten salt comprises, as a first metal ion, one selected from lithium ion, sodium ion, potassium ion, rubidium and cesium ion and one selected from calcium ion and magnesium ion and contains the aforementioned carbonate ion; A working electrode and a counter electrode are configured in the above molten salt, and an electric current of 200 mA / cm is applied between the working electrode and the counter electrode. -2 The current density is supplied for 250 seconds to generate the carbide of the first metal; and The procedure involves stopping the current supply between the working electrode and the counter electrode for 30 seconds. The current supply and current supply stop alternate 4 times under the same conditions.

[0077] (Metal carbides) The resulting metal carbide is primarily a carbide of the first metal (first metal carbide). Considering hydrolysis in subsequent processes, the first metal carbide can be at least one selected from Li₂C₂, Na₂C₂, K₂C₂, and CaC₂.

[0078] According to the present invention, a first metal carbide can be obtained with a high selectivity. The selectivity of the first metal carbide is expressed as the mass of the first metal carbide relative to the total mass of the first metal contained in the deposit on the working electrode, the compound containing the first metal (including the first metal carbide), and carbon. The selectivity of the first metal carbide is 60% by mass or more, and can be 80% by mass or more. The selectivity of the first metal carbide can be 99% by mass or less, and can also be 90% by mass or less. In one embodiment, the selectivity of the first metal carbide is 90% by mass or more and 99.9% by mass or less.

[0079] Examples of compounds containing the first metal other than first metal carbides include, for example, salts of the first metal and other anions (e.g., halides of the first metal), carbonates of the first metal, oxides of the first metal, hydrides of the first metal, and peroxides of the first metal.

[0080] (Impurities) The precipitate may contain impurities. Impurities are precipitates other than the first metal carbide. Examples of impurities contained in the precipitate on the working electrode include, for example, carbon, solidified electrolyte (other metal salts), compounds containing metallic materials constituting the electrode material, trace components contained in molten salts or oxides of the first metal, elemental first metal, compounds containing the first metal other than the aforementioned first metal carbide, and compounds containing the first metal.

[0081] The carbon mentioned above may include at least one type selected from nano-carbon materials such as graphite, amorphous carbon, glassy carbon, carbon nanotubes, diamond, nanodiamond, and graphene.

[0082] As a compound containing a first metal, at least one can be selected from the first metal element, halide, carbonate, oxide and carbide.

[0083] As a compound containing a metallic material constituting the device, at least one can be selected from the following: halides, oxides, carbonates, metals, and hydrates of the metal.

[0084] For example, if the first metal is Na, and a mixture of NaF and NaCl is used as other metal salts, and the constituent materials of the device include nickel, the precipitate may contain at least one impurity selected from Na, NaCl, Na2CO3, Ni, and NiCl2.

[0085] The impurity content is, for example, less than 40% by mass, less than 20% by mass, or less than 10% by mass of all precipitates on the working electrode. The impurity content can be more than 10% by mass of the total precipitates, more than 1% by mass, or more than 0.1% by mass. In one embodiment, the impurity content is more than 0.1% by mass and less than 10% by mass of all precipitates.

[0086] The presence and quantification of the first metal carbide, the elemental form of the first metal, compounds containing the first metal, and other impurities can be confirmed, for example, by Raman spectrophotometry and X-ray diffraction (XRD) analysis of the precipitates.

[0087] [Methods for manufacturing hydrocarbons] This invention includes the step of hydrolyzing a metal carbide obtained by the above method to obtain hydrocarbons. This method enables the efficient production of high-purity hydrocarbons.

[0088] The method for producing hydrocarbons according to the present invention includes the following steps: preparing a molten salt containing a first metal ion and carbonate ions; arranging a working electrode and a counter electrode in the molten salt, and supplying a current at a predetermined current density between the working electrode and the counter electrode to generate a carbide of the first metal; restoring the carbonate ion concentration near the working electrode; and hydrolyzing the carbide of the first metal to obtain a gas containing hydrocarbons. The generation of the carbide of the first metal and the restoration of the carbonate ion concentration are alternately repeated at least once.

[0089] Figure 2 This is a flowchart illustrating the method for manufacturing hydrocarbons according to this embodiment.

[0090] (1) Preparation of molten salt (S21) The same procedure is followed as in the preparation of molten salt in (I) of the above-mentioned method for manufacturing metal carbides to prepare molten salt.

[0091] (2) Current supply (S22) The same operation as in (II) of the above-described method for manufacturing metal carbides involves supplying current between the working electrode and the counter electrode. This yields a precipitate containing the first metal carbide.

[0092] (3) Stop the current supply (S23) Similar to the current supply cessation step (III) in the aforementioned method for manufacturing metal carbides, the current supply between the working electrode and the counter electrode is stopped. As a result, CO3 near the working electrode... 2- Concentration restored.

[0093] (4) Current supply and stop The same operation as (IV) current supply and stop in the above-mentioned method for manufacturing metal carbides is repeated once or more alternately with the current supply and current supply stop.

[0094] (5) Hydrolysis of metal carbides (S24) The first metal carbide is brought into contact with water for hydrolysis. This yields a gas containing the target hydrocarbon. Hydrocarbons typically have low solubility in water. Therefore, the generated hydrocarbon is rapidly released into the gas phase for recovery.

[0095] The first metal carbide can be separated from the precipitate by hydrolysis. Separation can be carried out, for example, by crushing the precipitate and utilizing the difference in specific gravity. Alternatively, the precipitate can be hydrolyzed directly. In this case, the first metal carbide that may be contained in the precipitate is also hydrolyzed to generate hydrocarbons.

[0096] Examples of hydrocarbons obtained include methane, ethane, ethylene, acetylene (C₂H₂), propane, propylene, butane, and butene. When using the separated first metal carbide, or when the amount of impurities (especially elemental metal) in the precipitate is low, acetylene can be obtained as the main component. The main component is defined as the component that accounts for more than 50% by mass of the total recovered gas. Acetylene is an important hydrocarbon in industry.

[0097] In addition to hydrocarbons, the obtained gas may contain water vapor, hydrogen, nitrogen, and oxygen as impurities. The amount of impurities is preferably 10% by mass or less of the recovered gas, more preferably 1% by mass or less. The amount of impurities can be 0.0001% by mass or more of the recovered gas. In one embodiment, the amount of impurities is 0.0001% by mass or more and 1% by mass or less of the recovered gas.

[0098] The resulting gas may, for example, contain acetylene and at least one selected from ethylene, ethane, methane, and hydrogen.

[0099] The presence of hydrocarbons and impurities can be confirmed and their quantification can be performed, for example, by gas chromatography-mass spectrometry (GC-MS), Fourier transform infrared absorption spectrometry (FT-IR) with a gas cell, and ultraviolet-visible absorption spectrometry (UV-Vis).

[0100] The amount of water in contact with the composition is appropriately set according to the mass of the composition. For example, the amount of water is greater than or equal to the amount required for the hydrolysis of the metal carbides and metals contained in the composition. Furthermore, it is desirable to use water that is sufficient to impregnate the entire composition and takes into account the evaporation caused by the exothermic reaction during hydrolysis.

[0101] According to the present invention, the current efficiency e related to hydrocarbon generation is improved. The current efficiency e is, for example, 8% or more, and can be 10% or more.

[0102] The current efficiency e related to C2H2 generation can be calculated as follows.

[0103] First, the volume proportion of C2H2 in the recovered gas is calculated from the total peak area and standard curve obtained by GC-MS analysis. Next, the volume of C2H2 generated is calculated from the volume of the gas phase in the recovery container and the calculated volume proportion of C2H2 in the gas. Finally, assuming the generated C2H2 is under standard conditions (0°C, 101 kPa), the current efficiency e (%) is calculated using the following formula. Hydrolysis of the first metal carbide also produces hydroxides of the first metal along with hydrocarbons. For example, if a calcium carbide hydrolyzes, it produces calcium hydroxide along with water.

[0104] CaC2+2H2O → C2H2+Ca(OH)2 Second Implementation Method This implementation method, like the first implementation method, focuses on restoring CO3. 2- The methods for determining concentration differ. This difference will be explained below. In this embodiment, the other components of the method for manufacturing the metal carbide are the same as in the first embodiment, therefore their description is omitted. In this embodiment, the method for manufacturing the hydrocarbon is the same as in the first embodiment, therefore its description is omitted.

[0105] In this embodiment, the carbonate ion concentration is restored by supplying a current at a lower current density (second current density) than that supplied during the formation of the carbide of the first metal between the working electrode and the counter electrode. Thus, CO3... 2- The reduction reaction was suppressed, resulting in improved current efficiency.

[0106] Figure 3 This is a flowchart illustrating a method for manufacturing metal carbides according to this embodiment.

[0107] Figure 4 This is a flowchart illustrating the method for manufacturing hydrocarbons according to this embodiment.

[0108] The second current density should be smaller than the first current density supplied before it.

[0109] The ratio of the first current density to the second current density (first / second) is determined by the CO3 near the working electrode at the second current density. 2- The consumption needs to be sufficiently suppressed; there are no particular limitations. From the viewpoint of current efficiency, the ratio of current density (first / second) can be 2 or higher. The ratio of current density (first / second) can be 5 or higher, 6.5 or higher, or 10 or higher.

[0110] The supply time of the first current density (first supply time) is not particularly limited. From the viewpoint of current efficiency, the first supply time can be more than 10 seconds and less than 1000 seconds. The first supply time can be more than 250 seconds or more than 500 seconds. The first supply time can be less than 1000 seconds or less than 800 seconds.

[0111] The supply time of the second current density (second supply time) is not particularly limited. The second supply time can be shorter than the first supply time. From the point of view of current efficiency, the second supply time can be more than 10 seconds and less than 1000 seconds. The second supply time can be more than 1 second, more than 3 seconds, or more than 30 seconds. The second supply time can be less than 50 seconds or less than 300 seconds.

[0112] The supply of current at a first current density (first current supply) and the supply of current at a second current density (second current supply) are alternately repeated at least once. Alternating at least once means that after supplying the first current, the cycle of supplying the second current and supplying the first current is performed at least once.

[0113] The second current supply occurs between the first current supply and the first current supply. The second supply time is the time during which a second current density is supplied between the first current supply and the first current supply.

[0114] The first current supply and the second current supply can be alternated and repeated more than twice (first supply → second supply → first supply → second supply → first supply), more than three times (first supply → second supply → first supply → second supply → first supply → second supply → first supply → second supply → first supply), or more than four times (first supply → second supply → first supply → second supply → first supply → second supply → first supply → second supply → first supply → second supply → first supply).

[0115] The initial current density supplied can be the same as or different from the initial current density supplied after the second supply. The initial current density supplied after the second supply can also be the same as or different from the initial current density supplied after the second supply.

[0116] The initial first supply time can be the same as or different from the first supply time after the second. The first supply times after the second can also be the same as or different.

[0117] The second current density supplied multiple times can be the same or different. The duration of the second supply multiple times can also be the same or different.

[0118] In one embodiment of the second method, the method for manufacturing metal carbides is a method for manufacturing metal carbides using carbonate ions as a carbon source, comprising: The step of preparing a molten salt, wherein the molten salt comprises, as a first metal ion, one selected from lithium ion, sodium ion, potassium ion, rubidium and cesium ion and one selected from calcium ion and magnesium ion and contains the aforementioned carbonate ion; A working electrode and a counter electrode are configured in the above molten salt, and an electric current of 200 mA / cm is applied between the working electrode and the counter electrode. -2The step of supplying a current density of 500 seconds to generate the carbide of the first metal; and A current of 30 mA / cm is applied between the working electrode and the counter electrode. -2 The current density is supplied for 30 seconds, and the current supply steps are as follows: The current supply and current supply stop are alternated twice under the same conditions.

[0119] The embodiments of the present invention have been described in detail above, but the present invention is not limited thereto, and design changes can be made within the scope of the present invention without departing from the spirit of the present invention.

[0120] In the above embodiments, carbon dioxide is used as the carbonate ion source, but it is not limited to this. The carbonate ion source can be a carbonate of any metal. If a carbonate of a first metal is used, first metal ions and carbonate ions are generated by ionization. The carbonate of the first metal can be synthesized, for example, by reacting a hydroxide of the first metal with carbon dioxide.

[0121] Example [Example 1] (Manufacturing of metal carbides) NaCl, KCl, and CaCl2 were mixed in a ratio of 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. The resulting salt mixture was then placed in separate glass containers and heated to 550°C in an electric furnace. This yielded a molten salt of NaCl-KCl-CaCl2-CaO.

[0122] Next, the working electrode (a 1cm × 1.5cm Fe plate), the counter electrode (a coiled platinum wire), and the reference electrode (Ag) were installed on the lid of the container. ＋ / Ag), seal the container with the lid. Heat the molten salt in the container to 550°C, and blow CO2 in at a flow rate of 100 mL / min for at least 30 minutes.

[0123] Using a galvanostat, the current density was maintained at 200 mA / cm². -2 A current was supplied for 500 seconds. Then, the current supply was stopped for 300 seconds. Next, the current density was maintained at 200 mA / cm². -2 A current is supplied for 500 seconds at a time.

[0124] Then, the working electrode was installed, and it was confirmed that precipitates had formed on the working electrode. X-ray diffraction analysis confirmed that the precipitates contained CaC2 as the main component. Figure 5This is a spectrum representing the X-ray diffraction analysis results of the precipitate. To avoid contact with moisture in the atmosphere, the precipitate was fixed in an airtight sample holder inside a glove box, and the analysis was performed using CuKα diffraction.

[0125] All experimental procedures were carried out in a glove box with a high-purity argon atmosphere. Figure 6 This is a graph showing the change in the working electrode potential over time when an electric current is applied during the manufacture of metal carbides. The potential of the working electrode is used to measure the potential of the reference electrode (Ag). ＋ The potential between the anode and cathode ( / Ag) is a value corrected based on the precipitation potential of the Na-K-Ca alloy.

[0126] (Hydrocarbon manufacturing) The precipitate was collected in a sealed test tube. Pure water was added gradually in small amounts to the test tube at room temperature (23°C) to hydrolyze the precipitate. The total amount of water added was 2.5 ml. After confirming the formation of bubbles in the test tube, the tube was allowed to stand until no more bubbles were observed. Then, 100 μl (microliters) of gas was collected from the test tube using an airtight syringe.

[0127] GC analysis of the obtained gas confirmed that C2H2 was formed as the main component. Methane, ethane, and hydrogen were also confirmed as byproducts. Water, carbon dioxide, nitrogen, oxygen, and argon were also present. The amounts of each component formed were also confirmed. The mass percentage of C2H2 in the recovered gas was well greater than 50% by mass.

[0128] Regarding C2H2 gas generation, the calculated current efficiency is approximately 14.12%. A higher current efficiency associated with C2H2 gas generation can be said to correlate with a higher current efficiency associated with metal carbide formation.

[0129] [Examples 2-8] Except for changing the current supply and stop times as shown in Table 1, electrolysis and hydrolysis were performed in the same manner as in Example 1.

[0130] [Comparative Examples 1-3] Electrolysis was performed continuously for 1000 seconds, 600 seconds, or 250 seconds without setting a stop time for the current. Otherwise, electrolysis and hydrolysis were performed in the same manner as in Example 1.

[0131] Regarding the C2H2 gas generation in Comparative Example 1, the current efficiency was 7.55%. Comparing Example 1 with Comparative Example 1, by stopping the current supply, the current efficiency was 1.8 times higher than that of continuous electrolysis. In the comparison between Examples 3-8 and Comparative Example 1, CO3 generation was also performed... 2-The recovery rate was 1.3 to 2.6 times higher than that of Comparative Example 2. In a comparison between Example 2 and Comparative Example 2, the current efficiency was also 1.1 times higher. Comparative Example 3 had extremely low current efficiency.

[0132] [Table 1] Molten salt: NaCl-KCl-CaCl2-CaO [Example 9] Except for setting the current supply time and stop time to 250 seconds and 30 seconds respectively, and repeating the operation 4 times, the electrolysis and hydrolysis were performed in the same way as in Example 1.

[0133] Regarding C2H2 gas generation, the current efficiency was 13.41%. Comparing Example 9 with Comparative Example 1, the current efficiency was 1.7 times higher by stopping the current supply. As can be understood from Example 9, the current efficiency was also improved by alternately and repeatedly supplying and stopping the current.

[0134] [Table 2] Molten salt: NaCl-KCl-CaCl2-CaO [Example 10] In addition to replacing the cessation of current supply, the current supply density is 30 mA / cm². -2 In addition to the current, electrolysis and hydrolysis were performed in the same manner as in Example 4.

[0135] Regarding C2H2 gas generation, the current efficiency was 8.49%. Comparing Example 10 and Comparative Example 1, by supplying current at a low current density, the current efficiency was 1.1 times higher than that supplied at the same current density. Furthermore, by repeatedly supplying current at a lower current density and then at a higher current density, further improvements in current efficiency can be expected.

[0136] [Table 3] Molten salt: NaCl-KCl-CaCl2-CaO Industrial availability The manufacturing method of the present invention proceeds rapidly at relatively low temperatures, and is therefore useful in various fields.

[0137] This application claims priority based on Japanese Patent Application No. 2024-041238 filed on March 15, 2024, the entire contents of which are incorporated herein by reference.

Claims

1. A method for manufacturing metal carbides using carbonate ions as a carbon source, characterized in that, include: The step of preparing a molten salt comprising a first metal ion and the carbonate ion; The steps include: configuring a working electrode and a counter electrode in the molten salt, supplying a current between the working electrode and the counter electrode at a specified current density, and generating a carbide of the first metal. and The step of restoring the carbonate ion concentration near the working electrode. The formation of the first metal carbide and the recovery of the carbonate ion concentration are alternately repeated more than once.

2. The method for manufacturing metal carbides as described in claim 1, characterized in that: The restoration of the carbonate ion concentration is achieved by stopping the current supply between the working electrode and the counter electrode.

3. The method for manufacturing metal carbides as described in claim 2, characterized in that: During the recovery of the carbonate ion concentration, the current supply is stopped for more than 1 second and less than 1000 seconds.

4. The method for manufacturing metal carbides as described in claim 2 or 3, characterized in that: During the formation of the carbide of the first metal, the current is supplied for 10 seconds to 1000 seconds.

5. The method for manufacturing metal carbides as described in claim 1, characterized in that: The restoration of the carbonate ion concentration is carried out by supplying a current between the working electrode and the counter electrode at a lower current density than that supplied during the formation of the carbide of the first metal.

6. The method for manufacturing metal carbides according to any one of claims 1 to 5, characterized in that: The molten salt, as the first metal ion, comprises at least one selected from alkali metal ions and alkaline earth metal ions.

7. The method for manufacturing metal carbides according to any one of claims 1 to 6, characterized in that: The molten salt, as the first metal ion, comprises one selected from lithium ions, sodium ions, potassium ions, rubidium and cesium ions, and one selected from calcium ions and magnesium ions.

8. The method for manufacturing metal carbides according to any one of claims 1 to 7, characterized in that: The molten salt, as an anion, also includes at least one selected from halide ions and oxide ions.

9. The method for manufacturing metal carbides according to any one of claims 1 to 8, characterized in that: The molten salt, as an anion, also includes both halide ions and oxide ions.

10. The method for manufacturing metal carbides according to any one of claims 1 to 9, characterized in that: The metal carbide composition further comprises at least one selected from carbon, elemental form of the first metal, halide, carbonate, oxide, hydride, and peroxide.

11. A method for producing hydrocarbons, characterized in that, include: The step of preparing a molten salt containing a first metal ion and a carbonate ion; The steps include: configuring a working electrode and a counter electrode in the molten salt, supplying a current between the working electrode and the counter electrode at a specified current density, and generating a carbide of the first metal. The step of restoring the carbonate ion concentration near the working electrode; and The step of hydrolyzing the carbide of the first metal to obtain a hydrocarbon-containing gas. The formation of the first metal carbide and the recovery of the carbonate ion concentration alternately repeat at least once.

12. The method for producing hydrocarbons as described in claim 11, characterized in that: The gas contains acetylene.

13. The method for producing hydrocarbons as described in claim 11 or 12, characterized in that: The gas contains acetylene and at least one selected from ethylene, ethane, methane, methylacetylene, propylene, butene, and hydrogen.

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