Method for producing metal carbide and hydrocarbon

Abstract

This method for producing a metal carbide using carbonate ions as a carbon source comprises: preparing a molten salt containing first metal ions and the carbonate ions; disposing a working electrode and a counter electrode on the molten salt, and supplying a current between the working electrode and the counter electrode at a predetermined current density to produce a carbide of the first metal; and recovering the concentration of the carbonate ions near the working electrode, wherein the production of the carbide of the first metal and the recovery of the concentration of the carbonate ions are alternately repeated at least one time.

Description

METHOD FOR PRODUCING METAL CARBIDE AND HYDROCARBON

[0001] The present invention relates to a method for producing metal carbides and hydrocarbons.

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

[0003] Patent Documents 1 and 2 disclose a production method in which the reaction proceeds rapidly at a relatively low temperature, enabling metal carbide to be obtained efficiently. Non-Patent Document 1 shows that pulse electrolysis is useful for obtaining a dense and uniform carbon film by electrolytic reduction of carbonate ions in a molten LiCl bath.

[0004] JP 2023-054787 A JP 2023-054788 A

[0005] Chongrui Zhuang et al. "Deposition and Morphology Control of Carbon Film through Electrochemical Reduction of Carbonate Ions in Molten LiCl", October 2023, Journal of The Electrochemical Society 170(10)

[0006] The present disclosure aims to provide a method for producing metal carbides that can further improve current efficiency. The present disclosure also provides a method for producing hydrocarbons from the resulting metal carbides.

[0007] The present disclosure includes the following aspects: [1] A method for producing metal carbide using carbonate ions as a carbon source, comprising: preparing a molten salt containing first metal ions and the carbonate ions; disposing 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 produce carbide of the first metal; and restoring the carbonate ion concentration near the working electrode, wherein the production of carbide of the first metal and the restoration of the carbonate ion concentration are alternately repeated one or more times.

[0008] [2] The method for producing metal carbide according to the above [1], wherein the carbonate ion concentration is restored by stopping the supply of current between the working electrode and the counter electrode.

[0009] [3] The method for producing metal carbide according to [2] above, wherein the current supply is stopped for 1 second or more and 1000 seconds or less during the recovery of the carbonate ion concentration.

[0010] [4] The method for producing metal carbide according to [2] or [3] above, wherein the current is supplied for 10 seconds or more and 1000 seconds or less in generating the carbide of the first metal.

[0011] [5] The method for producing metal carbide according to the above [1], wherein the recovery of the carbonate ion concentration is carried out by supplying a current between the working electrode and the counter electrode at a current density smaller than the current density supplied during production of the carbide of the first metal.

[0012] [6] The method for producing metal carbide according to any one of [1] to [5] above, wherein the molten salt contains, as the first metal ion, at least one selected from the group consisting of alkali metal ions and alkaline earth metal ions.

[0013] [7] The method for producing metal carbide according to any one of the above [1] to [6], wherein the molten salt contains, as the first metal ions, one selected from the group consisting of lithium ions, sodium ions, potassium ions, rubidium, and cesium ions, and one selected from the group consisting of calcium ions and magnesium ions.

[0014] [8] The method for producing metal carbide according to any one of the above [1] to [7], wherein the molten salt further contains, as an anion, at least one selected from the group consisting of a halide ion and an oxide ion.

[0015] [9] The method for producing metal carbide according to any one of the above [1] to [8], wherein the molten salt further contains both halide ions and oxide ions as anions.

[0016]

[10] The method for producing metal carbide according to any one of [1] to [9] above, wherein the metal carbide composition further contains at least one selected from the group consisting of carbon, an elemental substance, a halide, a carbonate, an oxide, a hydride, and a peroxide of the first metal.

[0017]

[11] A method for producing hydrocarbons, comprising: preparing a molten salt containing first metal ions and carbonate ions; disposing 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 produce carbide of the first metal; restoring the carbonate ion concentration near the working electrode; and hydrolyzing the first metal carbide to obtain a gas containing hydrocarbons, wherein the production of the carbide of the first metal and the restoration of the carbonate ion concentration are alternately repeated one or more times.

[0018]

[12] The method for producing hydrocarbons according to

[11] above, wherein the gas contains acetylene.

[0019]

[13] The method for producing hydrocarbons according to

[11] or

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

[0020] The present disclosure provides a method for producing metal carbides with excellent current efficiency, and a method for producing hydrocarbons from the resulting metal carbides.

[0021] Fig. 1 is a flowchart showing a method for producing metal carbide according to a first embodiment; Fig. 2 is a flowchart showing a method for producing hydrocarbons according to a first embodiment; Fig. 3 is a flowchart showing a method for producing metal carbide according to a second embodiment; Fig. 4 is a graph showing the results of X-ray diffraction analysis of the precipitate obtained in Example 1; Fig. 5 is a graph showing the change in working electrode potential over time when current is applied to produce metal carbide in Example 1.

[0022] When electrolysis of a molten salt containing first metal ions and carbonate ions is carried out for a long period of time, the current efficiency may decrease. The decrease in current efficiency is thought to be caused by an excessively low concentration of carbonate ions, which are a carbon source for metal carbide, near the working electrode.

[0023] During the supply of current between the working electrode and the counter electrode, carbonate ions (CO ３ ２－ ) reduction reaction occurs, resulting in CO ３ ２－ is consumed, and CO ３ ２－ The concentration gradually decreases. Then, CO2 is generated between the vicinity of the working electrode and the offshore of the electrolytic bath, that is, in the so-called diffusion layer. ３ ２－ To alleviate the concentration gradient, CO is introduced from the offshore of the electrolytic bath to the vicinity of the working electrode. ３ ２－ However, when the current density is large, the diffusion of CO ３ ２－ The diffusion of CO ３ ２－ The CO ３ ２－ As a result, the CO ３ ２－ It is believed that the reduction reaction of the above-mentioned element becomes difficult to proceed (or even stops), resulting in a decrease in current efficiency.

[0024] In the present disclosure, the carbonate ion concentration near the working electrode is restored during electrolysis to improve current efficiency, which in turn improves productivity.

[0025] The vicinity of the working electrode is CO ３ ２－ The vicinity of the working electrode refers to a space within the so-called Helmholtz layer, for example, a space between the surface of the working electrode and a point 1 nm away from the surface.

[0026] The recovery of the carbonate ion concentration means that the carbonate ion concentration becomes higher than the concentration of carbonate ions near the working electrode immediately after the current supply is stopped, that is, the concentration gradient in the diffusion layer is alleviated. ３ ２－ This can be achieved by stopping or suppressing the reduction reaction of

[0027] First Embodiment In this embodiment, when constant current electrolysis is performed, the carbonate ion concentration is restored by stopping the supply of current between the working electrode and the counter electrode.

[0028] When the current supply between the working electrode and the counter electrode is stopped, carbonate ions (CO ３ ２－ ) reduction reaction stops, and CO ３ ２－ During this time, CO ３ ２－ is diffused and CO ３ ２－ The concentration is restored.

[0029] [Method for Producing Metal Carbide] The method for producing metal carbide according to this embodiment includes preparing a molten salt containing first metal ions and carbonate ions, placing a working electrode and a counter electrode in the molten salt, supplying a current at a predetermined current density between the working electrode and the counter electrode to produce carbide of the first metal, and stopping the current supply between the working electrode and the counter electrode. The current supply and the current supply stop are alternately repeated one or more times. Figure 1 is a flowchart showing the method for producing metal carbide according to this embodiment.

[0030] In this embodiment, carbonate ions derived from carbon dioxide are used. ２can be effectively utilized as a carbon source to obtain a carbide composition containing a carbide of the first metal.

[0031] In this embodiment, current supply and stop are repeated, but this is different from supplying a so-called pulse current. In a pulse current, the pulse width (current supply time) is generally less than 1 second, the pulse interval (period) is less than 1 second, the repetition frequency is 10 Hz or more, and the duty ratio is 2 to 8. ３ ２－ In the molten salt electrolysis including the above, 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 ratio is 0.05.

[0032] In this embodiment, the current is not supplied in a manner that switches on and off instantaneously, as in the case of a pulse current. Regarding the current in this embodiment, the duty ratio is 0.5 or more and less than 1, and the repetition frequency is 1 mHz or more and 4 mHz or less. 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.

[0033] (i) Preparation of Molten Salt (S11) A molten salt containing first metal ions and carbonate ions derived from carbon dioxide is prepared. The carbonate ions are generated by absorbing a gas containing carbon dioxide into an electrolytic bath. The first metal ions are generated by ionizing a salt of the first metal.

[0034] In the molten salt, it is not necessary that the first metal salt and carbon dioxide are all ionized. In this embodiment, for convenience, the salt of the first metal contained in the electrolytic bath will be referred to as the first metal salt, even if it is completely ionized, and the molten salt prepared from the first metal salt and carbon dioxide will be referred to as the molten salt, even if they are not completely ionized.

[0035] (Carbonate ions derived from carbon dioxide) Carbonate ions are generated by absorbing a gas containing carbon dioxide into an electrolytic bath. ２The CO is contacted in its gaseous state with the first metal salt in its liquid state. ２ The gas may be blown into the gas phase of the electrolytic bath to contact the liquid surface of the first metal salt, or CO ２ A gas may be bubbled through the first metal salt. ２ The gas is CO ２ and an inert gas (typically argon). ２ A gas may be added to the first metal salt, or CO ２ A gas may be added to the first metal salt.

[0036] CO ２ The amount of CO to be blown into the reactor may be appropriately determined depending on the amount of the first metal ions. ２ The amount of CO ２ Considering the absorption efficiency of the first metal salt, the amount is equal to or greater than the equivalent amount of the first metal salt.

[0037] CO to first metal salts ２ The dissolution of CO is promoted. ２ The smaller the gas bubble diameter, the better. ２ The gas bubble diameter may be 10 mm or less, or may be 1 mm or less. ２ The gas bubble diameter may be 100 nm or more, or may be 1 μm or more. ２ The gas bubbles 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 ultrasonic waves.

[0038] CO ２ The gas is preferably preheated to a temperature close to that of the first metal salt, which prevents the first metal salt from being solidified due to a drop in temperature.

[0039] (Other Anions) The molten salt may contain anions other than carbonate ions. Examples of other anions include 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

[0040] The other anions may include at least one of halide ions and oxide ions. Metal salts containing halide ions are generally used as molten salts and are excellent as electrolytes. Oxide ions are CO ２ This makes it easier to ionize.

[0041] Other anions may include both halide and oxide ions.

[0042] (First Metal Ion) The first metal ion is, for example, at least one selected from the group consisting of alkali metal ions and alkaline earth metal ions. The alkali metal ions and alkaline earth metal ions have excellent electrolyte functions.

[0043] The alkali metal may be 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 particularly be at least one selected from the group consisting of Li, Na, K, and Cs.

[0044] The alkaline earth metal may be 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.

[0045] From the viewpoint of industrial value, the first metal ion may include an alkaline earth metal ion. The first metal ion may include an alkali metal ion together with the alkaline earth metal ion. The alkali metal ion facilitates ionization of the alkaline earth metal salt, promoting the generation of the alkaline earth metal ion and lowering the melting point of the molten salt, enabling electrolysis at a lower temperature.

[0046] The first metal ions may include 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. The first metal ions may include at least one Li, Na, K, Rb, and Cs ions, and at least one Ca and Mg ions.

[0047] Examples of other first metal ions include 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). Examples of rare earth elements include scandium (Sc), yttrium (Y), lanthanoid elements, and actinoid elements.

[0048] The amount of the first metal ions contained in the molten salt is not particularly limited.

[0049] The first metal salt preferably ionizes at a temperature of 800° C. or less. 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; MgF ２ , CaF ２ , SrF ２ , BaF ２ , MgCl ２ , CaCl ２ , SrCl ２ , BaCl ２ , MgBr ２ , CaBr ２ , SrBr ２ , BaBr ２ , MgI ２ , CaI ２ , SrI ２ , BaI ２ Alkaline earth metal halides such as Li ２ metal oxides such as O and CaO; ２ CO ３ , Na２ CO ３ , K. ２ CO ３ Metal carbonates such as LiNO ３ , NaNO ３ , KNO ３ Metal nitrates such as ScCl ３ , YCl ３ , LaCl ３ , CeCl ３ , PrCl ３ , NdCl ３ , PmCl ３ , SmCl ３ , EuCl ３ , GdCl ３ , TbCl ３ , DyCl ３ , HoCl ３ , ErCl ３ , TmCl ３ , YbCl ３ , LuCl ３ Halides of rare earth elements such as AlCl ３ , GaCl ３ , InCl ３ , TlCl ３ These may be used alone or in combination of two or more. In particular, two or more metal salts may be combined in order to facilitate a decrease in the melting temperature.

[0050] (II) Current Supply (S12) A working electrode and a counter electrode are placed in the molten salt, and a current is supplied between the working electrode and the counter electrode at a predetermined current density. ３ ２－ is reduced to obtain a precipitate containing a carbide of the first metal (first metal carbide). The precipitate containing the first metal carbide is deposited on the surface of the electrode with a lower potential (here, the working electrode). Carbon and oxygen may be generated as by-products on the working electrode.

[0051] When the first metal is Ca, the working electrode is made of calcium carbide (CaC ２) may precipitate (Equations 1 and 2). Metallic calcium may also be produced on the working electrode (Equation 3). Part or all of the metallic calcium produced in this side reaction may further react to form calcium carbide (Equation 4). Alternatively, metallic calcium may react with carbon dioxide physically dissolved in the molten salt to form calcium carbide (Equation 5). Fine carbon powder may be produced, causing the molten salt to become cloudy (Equation 6). The CaO produced in the above (Equation 5) and (Equation 6) immediately dissolves in the molten salt, producing calcium ions and oxide ions (Equation 7). (Equation 1) CO ３ ２－ +4e － → C + 3O ２－ (Formula 2) Ca ２＋ +2C+2e － → CaC ２ (Formula 3) Ca ２＋ +2e － → Ca (Formula 4) Ca+2C → CaC ２ (Formula 5) 2CO ２ +5Ca → CaC ２ +4CaO (Formula 6) 2Ca+CO ２ → C+2CaO (Formula 7) CaO → Ca ２＋ +O ２－

[0052] When the first metal is Na, K, or Li, a similar reaction occurs to produce sodium carbide (Na ２ C ２ ), potassium carbide (K ２ C ２ ) or lithium carbide (LiC ２ The same applies to the other first metals.

[0053] On the other hand, O ２－ is oxidized to generate oxygen (Equation 8). The oxygen generated on the counter electrode is released into the gas phase. This oxygen gas can be collected and used for other purposes. (Equation 8) 2O ２－ → O ２ +4e －

[0054] The current is supplied at a temperature at which the molten salt can be maintained in a molten state, i.e., a temperature that is approximately 10°C or higher than the melting point of the molten salt. For example, in the case of NaCl-KCl eutectic salt (melting point: 503.8°C), the temperature of the electrolytic bath may be 510°C or higher, or 550°C or higher. The temperature of the electrolytic bath may be, for example, 800°C or lower, or 700°C or lower. According to the present disclosure, the reaction proceeds at such a relatively low temperature, resulting in high energy efficiency.

[0055] The current value can be appropriately set so that the working electrode potential during electrolysis is between the potential (Ec) at which carbon deposits and the potential (Em) at which the first metal deposits. This can further improve the selectivity of the first metal carbide. If the potential of the working electrode is excessively high (noble), carbon mainly deposits, and the amount of the target first metal carbide produced tends to decrease. If the potential of the working electrode is excessively low (base), the first metal carbide is produced, but the metal contained in the molten salt that has the most noble redox potential in the molten salt mainly deposits. If the molten salt contains multiple metals with similar redox potentials, an alloy of multiple metals may also deposit. For example, if the molten salt contains LiCl, KCl, and Li, ２ When the electrolyte contains O (5 mol%), the working electrode potential is 0.0 V or more and 1.0 V or less (Li ＋ / Li standard).

[0056] The current may be direct current, intermittent (pulse current), or superimposed with alternating current. The potentials Ec and Em can be determined by cyclic voltammetry measurement using, for example, an Fe electrode in the molten salt used. The working electrode potential is measured by the reference electrode (Ag ＋ The potential between the electrode and the working electrode (Ag / Ag) was measured and calibrated using the metal deposition potential as a reference. In the case of NaCl-KCl eutectic salt, the metal deposition potential is the deposition potential of the Na-Ca alloy.

[0057] The current supply time is not particularly limited. From the viewpoint of current efficiency, the current supply time may be 10 seconds or more and 1000 seconds or less. The current supply time may be 250 seconds or more, or 500 seconds or more. The current supply time may be 1000 seconds or less, or 500 seconds or less.

[0058] The material of the working electrode is not particularly limited. Examples of the material of 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 alloys thereof, as well as carbon materials such as glassy carbon, natural graphite, isotropic graphite, pyrolytic graphite, plastic-formed carbon, and conductive diamond.

[0059] The material of the counter electrode is not particularly limited. Examples of the material of the counter electrode include Pt, conductive metal oxide, glassy carbon, natural graphite, isotropic graphite, pyrolytic graphite, plastic formed carbon, and conductive diamond. Examples of the electrode made of conductive metal oxide include a transparent conductive electrode called an ITO electrode, in which a mixed oxide of indium and tin is formed on glass; a DSA electrode (trademark of De Nora Permelec Electrodes Co., Ltd.), in which an oxide of a platinum group metal such as ruthenium or iridium is formed on a substrate such as titanium; and a La electrode. １－ｘ Sr ｘ CoO ３－δ , La １－ｘ Sr ｘ FeO ３－δ Among them, oxide-based electrodes are preferable because they are less likely to be consumed by oxidation reactions.

[0060] (III) Stopping the current supply (S13) By stopping the current supply between the working electrode and the counter electrode, CO ３ ２－ The reduction reaction of CO ３ ２－ During this time, the consumption of CO ３ ２－ is diffused, and CO ３ ２－ The concentration is restored. ３ ２－ The recovery of the concentration is due to the next current supply. ３ ２－ Promotes the reduction reaction of

[0061] The current supply stop time is not particularly limited. From the viewpoint of current efficiency, the current supply stop time may be 1 second or more and 1000 seconds or less. The current supply stop time may be 1 second or more, or 30 seconds or more. The current supply stop time may be 300 seconds or less, or 50 seconds or less.

[0062] (IV) Current Supply and Stop The current supply and stop are alternately repeated one or more times. The phrase "alternately repeated one or more times" means that, after the initial current supply, the current is stopped and then supplied, and this cycle is repeated one or more times.

[0063] The current supply and current supply stop may be repeated alternately two or more times (supply → stop → supply → stop → supply), three or more times (supply → stop → supply → stop → supply → stop → supply), or four or more times (supply → stop → supply → stop → supply → stop → supply → stop → supply).

[0064] The current supply is stopped between the current supplies. The current supply stop time is the time between the current supplies.

[0065] The density of the current supplied initially and the density of the current supplied second or later may be the same or different. The densities of the currents supplied second or later may be the same or different.

[0066] The supply time of the first current and the supply time of the second and subsequent currents may be the same or different. The supply times of the second and subsequent currents may be the same or different.

[0067] The durations of the current supply interruptions may be the same or different.

[0068] In one aspect of the first embodiment, a method for producing metal carbide includes the steps of: preparing a molten salt containing, as first metal ions, one selected from the group consisting of lithium ions, sodium ions, potassium ions, rubidium, and cesium ions, one selected from the group consisting of calcium ions and magnesium ions, and the carbonate ions; disposing a working electrode and a counter electrode in the molten salt; and applying a current of 200 mA / cm between the working electrode and the counter electrode. －２ supplying a current at a current density of 0.1 to 0.5 for 300 to 500 seconds to generate carbide of the first metal; and stopping the current supply between the working electrode and the counter electrode for 1 to 300 seconds, wherein the current supply and the current supply stop are alternately repeated twice under the same conditions.

[0069] In another aspect of the first embodiment, a method for producing metal carbide includes the steps of: preparing a molten salt containing, as first metal ions, one selected from the group consisting of lithium ions, sodium ions, potassium ions, rubidium, and cesium ions, one selected from the group consisting of calcium ions and magnesium ions, and the carbonate ions; disposing a working electrode and a counter electrode in the molten salt; and applying a current of 200 mA / cm between the working electrode and the counter electrode. －２ supplying a current at a current density of 0.1 to 0.5 for 250 seconds to produce carbide of the first metal; and stopping the current supply between the working electrode and the counter electrode for 30 seconds, wherein the current supply and the current stop are alternately repeated four times under the same conditions.

[0070] (Metal Carbide) The obtained metal carbide is mainly a carbide of the first metal (first metal carbide). Considering hydrolysis in the subsequent process, the first metal carbide is preferably a carbide of Li ２ C ２ , Na ２ C ２ , K. ２ C ２ and CaC ２ It may be at least one selected from the group consisting of:

[0071] According to the present disclosure, the first metal carbide can be obtained with 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 alone, the compound containing the first metal (including the first metal carbide), and carbon contained in the deposit on the working electrode. The selectivity of the first metal carbide is 60 mass% or more, and can be 80 mass% or more. The selectivity of the first metal carbide may be 99 mass% or less, and can be 90 mass% or less. In one aspect, the selectivity of the first metal carbide is 90 mass% or more and 99.9 mass% or less.

[0072] Examples of compounds containing the first metal other than the first metal carbide include salts of the first metal with 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.

[0073] (Impurities) The deposit may contain impurities. The impurities are deposits other than the first metal carbide. Examples of impurities contained in the deposit on the working electrode include at least one selected from the group consisting of carbon, solidified electrolyte (other metal salts), compounds containing metal materials constituting the device such as electrode materials, trace components contained in molten salts and oxides of the first metal, the first metal itself, compounds containing the first metal other than the above-mentioned first metal carbide, and compounds containing the first metal.

[0074] The carbon 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.

[0075] The compound containing the first metal may be at least one selected from the group consisting of an elemental substance, a halide, a carbonate, an oxide, and a carbide of the first metal.

[0076] The compound containing the metal material constituting the device may be at least one selected from the group consisting of halides, oxides, carbonates, metals, and hydrates thereof.

[0077] For example, when the first metal is Na, a mixture of NaF and NaCl is used as another metal salt, and the constituent material of the device contains nickel, the precipitate contains impurities such as Na, NaCl, and Na ２ CO ３ , Ni, NiCl ２ At least one selected from the group consisting of:

[0078] The amount of impurities is, for example, 40% by mass or less, 20% by mass or less, or 10% by mass or less of the total precipitates on the working electrode. The amount of impurities may be 10% by mass or more, 1% by mass or more, or 0.1% by mass or more of the total precipitates. In one aspect, the amount of impurities is 0.1% by mass or more and 10% by mass or less of the total precipitates.

[0079] The presence of the first metal carbide, the first metal itself, compounds containing the first metal, and other impurities can be confirmed and their quantities can be determined, for example, by Raman spectroscopic analysis and X-ray diffraction (XRD) analysis of the precipitate.

[0080] [Method for Producing Hydrocarbons] The present disclosure includes obtaining hydrocarbons by hydrolyzing the metal carbides obtained by the above-mentioned method. This method makes it possible to efficiently obtain high-purity hydrocarbons.

[0081] A method for producing hydrocarbons according to the present disclosure includes preparing a molten salt containing first metal ions and carbonate ions, disposing 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 produce carbide of the first metal, restoring the carbonate ion concentration near the working electrode, and hydrolyzing the first metal carbide to obtain a gas containing hydrocarbons. The production of the first metal carbide and the restoration of the carbonate ion concentration are alternately repeated one or more times. Figure 2 is a flowchart showing the method for producing hydrocarbons according to this embodiment.

[0082] (1) Preparation of Molten Salt (S21) A molten salt is prepared in the same manner as in (I) Preparation of Molten Salt in the above-described method for producing metal carbide.

[0083] (2) Current Supply (S22) In the same manner as in (II) Current Supply in the above-described method for producing a metal carbide, a current is supplied between the working electrode and the counter electrode, thereby obtaining a deposit containing the first metal carbide.

[0084] (3) Stopping the current supply (S23) The current supply between the working electrode and the counter electrode is stopped in the same manner as in (III) Stopping the current supply in the above-mentioned method for producing metal carbide. ３ ２－ The concentration is restored.

[0085] (4) Current Supply and Stoppage Similar to (IV) Current Supply and Stoppage in the above-described method for producing metal carbide, current supply and current supply stoppage are alternately repeated one or more times.

[0086] (5) Hydrolysis of Metal Carbide (S24) The first metal carbide is brought into contact with water to be hydrolyzed. This produces a gas containing the target hydrocarbon. Hydrocarbons generally have low solubility in water. Therefore, the produced hydrocarbons are quickly released into the gas phase and recovered.

[0087] The first metal carbide may be isolated from the precipitate and then hydrolyzed. Isolation is performed, for example, by crushing the precipitate and utilizing the difference in specific gravity. Alternatively, the precipitate may be hydrolyzed directly. In this case, the first metal carbide that may be contained in the precipitate is also hydrolyzed to produce hydrocarbons.

[0088] The hydrocarbons obtained include, for example, methane, ethane, ethylene, acetylene (C ２ H ２ ), propane, propylene, butane, and butene. When an isolated first metal carbide is used or when the amount of impurities (particularly elemental metals) contained in the precipitate is small, acetylene is obtained as the main component. The main component is a component that accounts for 50% by mass or more of the total mass of the recovered gas. Acetylene is an industrially important hydrocarbon.

[0089] The resulting gas may contain impurities such as water vapor, hydrogen, nitrogen, and oxygen in addition to hydrocarbons. The amount of impurities is preferably 10% by mass or less, more preferably 1% by mass or less, of the recovered gas. The amount of impurities may be 0.0001% by mass or more, or even 0.001% 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.

[0090] The resulting gas may include, for example, acetylene and at least one selected from the group consisting of ethylene, ethane, methane, and hydrogen.

[0091] The presence of hydrocarbons and impurities can be confirmed and their quantity can be determined, for example, by gas chromatography-mass spectrometry (GC-MS analysis), Fourier transform infrared absorption spectrometry (FT-IR analysis) equipped with a gas cell, or ultraviolet-visible absorption spectrometry (UV-Vis analysis) of the recovered gas.

[0092] The amount of water to be brought into contact with the composition is appropriately determined depending on the mass of the composition. The amount of water is, for example, at least the amount necessary for hydrolysis of the metal carbide and metal contained in the composition. In addition, it is desirable to use an amount of water that allows the entire composition to be immersed and that takes into account evaporation due to heat generated during hydrolysis.

[0093] According to the present disclosure, the current efficiency e for producing hydrocarbons is improved. The current efficiency e is, for example, 8% or more, and may be 10% or more.

[0094] C ２ H ２ The current efficiency e for generation can be calculated as follows: First, the C contained in the recovered gas is calculated from the total area of ​​the peaks obtained from the GC-MS analysis and the calibration curve. ２ H ２ Next, the volume occupied by the gas phase in the collection vessel and the volume ratio of C in the calculated gas are calculated. ２ H ２ From the volume ratio of C ２ H ２ Finally, calculate the volume of generated C ２ H ２is assumed to be in standard conditions (0°C, 101 kPa), and the current efficiency e (%) is calculated using the following formula.

[0095]

[0096] Hydrolysis of the first metal carbide produces hydrocarbons as well as hydroxides of the first metal. For example, hydrolysis of calcium carbide produces calcium hydroxide along with water. CaC ２ +2H ２ O → C ２ H ２ + Ca(OH) ２

[0097] Second Embodiment This embodiment differs from the first embodiment in that ３ ２－ The difference is in the method for recovering the concentration. This difference will be explained below. In this embodiment, the other configurations of the method for producing metal carbide are the same as those in the first embodiment, so their explanation will be omitted. In this embodiment, the method for producing hydrocarbons is the same as that in the first embodiment, so their explanation will be omitted.

[0098] In this embodiment, the carbonate ion concentration is restored by supplying a current between the working electrode and the counter electrode at a current density (second current density) that is smaller than the current density (first current density) supplied during the generation of the carbide of the first metal. ３ ２－ The reduction reaction of is suppressed, resulting in an improvement in current efficiency.

[0099] 3 and 4 are flowcharts showing a method for producing metal carbide and hydrocarbons according to the present embodiment, respectively.

[0100] The second current density may be smaller than the first current density supplied immediately before.

[0101] The ratio (first / second) of the first current density to the second current density is the ratio of CO ３ ２－There are no particular limitations as long as the consumption of the current density is sufficiently suppressed. From the viewpoint of current efficiency, the current density ratio (first / second) may be 2 or more. The current density ratio (first / second) may be 5 or more, 6.5 or more, or 10 or more.

[0102] The supply time of the current at the first current density (first supply time) is not particularly limited. From the viewpoint of current efficiency, the first supply time may be 10 seconds or more and 1000 seconds or less. The first supply time may be 250 seconds or more, or 500 seconds or more. The first supply time may be 1000 seconds or less, or 800 seconds or less.

[0103] The supply time of the current of the second current density (second supply time) is not particularly limited. The second supply time may be shorter than the first supply time. From the viewpoint of current efficiency, the second supply time may be 10 seconds or more and 1000 seconds or less. The second supply time may be 1 second or more, 3 seconds or more, or 30 seconds or more. The second supply time may be 50 seconds or less, or 300 seconds or less.

[0104] The current supply at the first current density (first current supply) and the current supply at the second current density (second current supply) are alternately repeated one or more times. "Alternately repeated one or more times" means that one cycle is composed of the first current supply, the second current supply, and the first current supply, and this cycle is repeated one or more times.

[0105] The second current supply is performed between the first current supplies. The second supply time is the time between the first current supplies during which a current of the second current density is supplied.

[0106] The first current supply and the second current supply may be repeated alternately two or more times (first supply → second supply → first supply → second supply → first supply), three or more times (first supply → second supply → first supply → second supply → first supply → first supply), or four or more times (first supply → second supply → first supply → second supply → first supply → second supply → first supply → first supply).

[0107] The first current density supplied initially and the first current density supplied second or later may be the same or different. The first current densities supplied second or later may be the same or different.

[0108] The initial first supply time and the second and subsequent first supply times may be the same or different. The first supply times from the second time onwards may be the same or different.

[0109] The second current densities supplied multiple times may be the same or different from each other, and the second supply times supplied multiple times may be the same or different from each other.

[0110] In one aspect of the second embodiment, a method for producing metal carbide includes the steps of: preparing a molten salt containing, as first metal ions, one selected from the group consisting of lithium ions, sodium ions, potassium ions, rubidium, and cesium ions, one selected from the group consisting of calcium ions and magnesium ions, and the carbonate ions; disposing a working electrode and a counter electrode in the molten salt; and applying a current of 200 mA / cm between the working electrode and the counter electrode. －２ supplying a current at a current density of 30 mA / cm between the working electrode and the counter electrode for 500 seconds to generate carbide of the first metal; －２ and supplying a current for 30 seconds at a current density of 1000 kJ / s, and supplying a current, wherein the current supply and the current supply stop are alternately repeated twice under the same conditions.

[0111] Although the embodiments of the present disclosure have been described in detail above, the present disclosure is not limited to these, and design changes are possible within the scope of the gist of the present disclosure.

[0112] In the above embodiment, carbon dioxide is used as the carbonate ion source, but this is not limiting. The carbonate ion source may be any metal carbonate. When a first metal carbonate is used, the first metal ion and carbonate ion are generated by ionization. The first metal carbonate can be synthesized, for example, by reacting the first metal hydroxide with carbon dioxide.

[0113] Example 1 (Production of Metal Carbide) NaCl, KCl, and CaCl ２ and NaCl / KCl / CaCl ２ The salt mixture was mixed to a ratio of 33.4 mol% / 11.6 mol% / 55.0 mol%, and then 3 mol% of CaO was added, followed by vacuum drying at 200°C and 100 Pa or less for 24 hours or more. Each of these mixed salts was placed in a glass container, placed in an electric furnace, and heated to 550°C. In this way, NaCl-KCl-CaCl ２ A molten salt of CaO was obtained.

[0114] Next, a working electrode (1 cm x 1.5 cm Fe plate), a counter electrode (coiled platinum wire), and a reference electrode (Ag ＋ The vessel was sealed with a lid. The molten salt in the vessel was heated to 550°C and CO ２ was blown in at a flow rate of 100 mL / min for 30 minutes or more.

[0115] Using a potentio-galvanostat, the current density was set to 200 mA / cm －２ The current was supplied for 500 seconds while maintaining the current density at 200 mA / cm. Thereafter, the current supply was stopped for 300 seconds. Subsequently, the current density was again increased to 200 mA / cm. －２ A current was supplied for 500 seconds while maintaining the voltage at this value.

[0116] Thereafter, the working electrode was taken out and it was confirmed that a precipitate had been deposited on the working electrode. X-ray diffraction measurement revealed that the precipitate consisted mainly of CaC ２ It was confirmed that the precipitate contained CuKα radiation. Figure 5 is a graph showing the results of X-ray diffraction analysis of the precipitate. The analysis was carried out by fixing the precipitate in an airtight sample holder in a glove box to avoid contact with moisture in the air.

[0117] All experimental operations were carried out in a glove box maintained in a high-purity argon atmosphere. Figure 6 is a graph showing the change in the working electrode potential over time when electricity was applied to produce metal carbide. The potential of the working electrode was measured using a reference electrode (Ag ＋ The potential between the electrode (Ag / Ag) and the cathode was measured and calibrated using the Na--K--Ca alloy deposition potential as a standard.

[0118] (Production of Hydrocarbons) The precipitate was placed in a sealed test tube. Pure water was added to the test tube in small amounts at room temperature (23°C) to hydrolyze the precipitate. The total amount of water added was 2.5 ml. After confirming that foaming had occurred in the test tube, the test tube was left to stand until foaming no longer occurred. Subsequently, 100 μl (microliters) of gas was collected from the test tube using a gas-tight syringe.

[0119] The obtained gas was analyzed by gas chromatography (GC) and the main components were found to be C ２ H ２ It was confirmed that methane, ethane, and hydrogen were produced as by-products. The gas also contained water, carbon dioxide, nitrogen, oxygen, and argon. The amount of each component produced was also confirmed. ２ H ２ The mass proportion of was sufficiently more than 50 mass %.

[0120] C ２ H ２ The current efficiency for gas production was calculated to be about 14.12%. ２ H ２ It can be said that the higher the current efficiency for gas production, the higher the current efficiency for metal carbide production.

[0121] Examples 2 to 8 Electrolysis and hydrolysis were carried out in the same manner as in Example 1, except that the current supply time and stop time were changed as shown in Table 1.

[0122] Comparative Examples 1 to 3 Electrolysis and hydrolysis were carried out in the same manner as in Example 1, except that the electrolysis was carried out continuously for 1000 seconds, 600 seconds or 250 seconds without providing a time period for stopping the current.

[0123] Comparative Example 1 C ２ H ２ The current efficiency for gas generation was 7.55%. Comparing Example 1 with Comparative Example 1, the current efficiency was 1.8 times higher when the current supply was stopped than when continuous electrolysis was performed. Comparing Examples 3 to 8 with Comparative Example 1 also showed that CO ３ ２－By carrying out the recovery, the current efficiency increased by 1.3 to 2.6 times. The current efficiency also increased by 1.1 times when Example 2 was compared with Comparative Example 2. The current efficiency of Comparative Example 3 was extremely low.

[0124]

[0125] Example 9 Electrolysis and hydrolysis were carried out in the same manner as in Example 1, except that the current supply time and stop time were set to 250 seconds and 30 seconds, respectively, and this operation was repeated four times.

[0126] C ２ H ２ The current efficiency for gas generation was 13.41%. Comparing Example 9 with Comparative Example 1, stopping the current supply increased the current efficiency by 1.7 times. From Example 9, it can be seen that the current efficiency can be improved by alternately repeating the supply and stop of current.

[0127]

[0128] [Example 10] Instead of stopping the current supply, the current density was increased to 30 mA / cm －２ Electrolysis and hydrolysis were carried out in the same manner as in Example 4, except that a current of 1000 kJ / min was supplied.

[0129] C ２ H ２ The current efficiency for gas generation was 8.49%. Comparing Example 10 with Comparative Example 1, supplying current at a low current density resulted in a current efficiency 1.1 times higher than supplying current at the same current density. It is also expected that the current efficiency will improve by repeatedly supplying current at a lower current density and a higher current density.

[0130]

[0131] The production method of the present disclosure is useful in various fields because the reaction proceeds quickly at relatively low temperatures.

[0132] 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 producing metal carbide using carbonate ions as a carbon source, comprising: preparing a molten salt containing first metal ions and the carbonate ions; placing 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 produce carbide of the first metal; and restoring the carbonate ion concentration near the working electrode, wherein the production of carbide of the first metal and the restoration of the carbonate ion concentration are alternately repeated one or more times.

2. The method for producing metal carbide according to claim 1, wherein the carbonate ion concentration is restored by stopping the supply of current between the working electrode and the counter electrode.

3. The method for producing metal carbide according to claim 2, wherein the current supply is stopped for 1 second or more and 1000 seconds or less during the recovery of the carbonate ion concentration.

4. The method for producing metal carbide according to claim 2 or 3, wherein the current is supplied for 10 seconds or more and 1000 seconds or less in generating the carbide of the first metal.

5. The method for producing metal carbide according to claim 1, wherein the recovery of the carbonate ion concentration is carried out by supplying a current between the working electrode and the counter electrode at a current density lower than the current density supplied during the production of the carbide of the first metal.

6. A method for producing metal carbide according to any one of claims 1 to 5, wherein the molten salt contains, as the first metal ion, at least one ion selected from the group consisting of alkali metal ions and alkaline earth metal ions.

7. The method for producing metal carbide according to any one of claims 1 to 6, wherein the molten salt contains, as the first metal ions, one selected from the group consisting of lithium ions, sodium ions, potassium ions, rubidium, and cesium ions, and one selected from the group consisting of calcium ions and magnesium ions.

8. The method for producing metal carbide according to any one of claims 1 to 7, wherein the molten salt further contains, as an anion, at least one selected from the group consisting of halide ions and oxide ions.

9. The method for producing metal carbide according to any one of claims 1 to 8, wherein the molten salt further contains both halide ions and oxide ions as anions.

10. The method for producing metal carbide according to any one of claims 1 to 9, wherein the metal carbide composition further contains at least one selected from the group consisting of carbon, an elemental substance, a halide, a carbonate, an oxide, a hydride, and a peroxide of the first metal.

11. A method for producing hydrocarbons, comprising: preparing a molten salt containing first metal ions and carbonate ions; disposing 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 produce carbide of the first metal; restoring the carbonate ion concentration near the working electrode; and hydrolyzing the first metal carbide to obtain a gas containing hydrocarbons, wherein the production of the carbide of the first metal and the restoration of the carbonate ion concentration are alternately repeated one or more times.

12. The method for producing hydrocarbons according to claim 11, wherein the gas comprises acetylene.

13. The method for producing hydrocarbons according to claim 11 or 12, wherein the gas contains acetylene and at least one selected from the group consisting of ethylene, ethane, methane, methylacetylene, propylene, butene, and hydrogen.

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