Methods for producing metal carbide and hydrocarbon, and metal carbide composition

Abstract

To provide: a method for producing a metal carbide using carbon dioxide as a carbon source and a metal oxide as a metal source; a method for producing a hydrocarbon from the metal carbide obtained using carbon dioxide as a carbon source and a metal oxide as a metal source; and a metal carbide composition.SOLUTION: A method for producing a metal carbide includes: preparing a molten salt containing an oxide of a first metal; adding carbon dioxide to the molten salt; applying a voltage to the molten salt containing the carbon dioxide; and obtaining a precipitate containing a carbide of the first metal. A method for producing a hydrocarbon includes hydrolyzing the carbide of the first metal to obtain a hydrocarbon-containing gas and a hydroxide of the first metal.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for producing metal carbides and hydrocarbons, and to a metal carbide composition. [Background technology]

[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] Calcium carbide is generally obtained by heating a mixture of quicklime (calcium oxide) and coke to a high temperature in an electric furnace (for example, Patent Document 1). Patent Document 2 proposes that coke is briquetted in advance and then mixed with quicklime. According to Patent Document 2, this makes it possible to obtain calcium carbide more effectively. Patent Document 3 proposes a method for producing lithium carbide by reacting metallic lithium obtained by melt electrolysis of lithium chloride with carbon powder such as carbon black. Non-Patent Document 1 proposes a method for producing lithium carbide by reacting metallic lithium obtained by molten salt electrolysis of lithium hydroxide with a carbon source such as carbon dioxide, and recycling the by-product lithium hydroxide to molten salt electrolysis. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Unexamined Patent Publication No. 178412 / 1983 [Patent Document 2] JP 2018-35328 A [Patent Document 3] Japanese Patent Application Publication No. 2-256626 [Non-patent literature]

[0005] [Non-Patent Document 1] McEnaney JM, Rohr BA, Nielander AC, Singh AR, King LA, Norskov JK, Jaramillo TF “A cyclic electrochemical strategy to produce acetylene from CO2, CH4, or alternative carbon sources.” Sustain Energy Fuels 4:2752-2759 (2020) Summary of the Invention [Problem to be solved by the invention]

[0006] To produce metal carbide, it is usually necessary to heat the raw material to 2000°C or higher. This results in low energy efficiency and generates a large amount of carbon dioxide. In addition, from the viewpoint of recent global warming countermeasures, there is a strong demand for using carbon dioxide as a carbon source, but in Patent Documents 1 to 3, carbon itself is simply used as the carbon source for metal carbide. Non-Patent Document 1 lists carbon dioxide as one of the carbon sources, but states that when carbon dioxide is used as a carbon source, a large amount of by-products are generated, and therefore, from the viewpoint of Faraday efficiency, it is desirable to use graphite carbon as the carbon source.

[0007] The present disclosure aims to provide a method for producing metal carbide using carbon dioxide as a carbon source and a metal oxide as a metal source. The present disclosure further provides a method for producing hydrocarbons from the metal carbide obtained using carbon dioxide as a carbon source and a metal oxide as a metal source. In addition, the present disclosure provides a metal carbide composition. [Means for solving the problem]

[0008] The present disclosure includes the following aspects. [1] preparing a molten salt containing an oxide of a first metal; adding carbon dioxide to the molten salt; and A method for producing metal carbide, comprising: applying a voltage to the molten salt containing carbon dioxide to obtain a precipitate containing carbide of the first metal.

[0009] [2] The method for producing metal carbide according to the above [1], wherein the molten salt further contains a halide of a second metal.

[0010] [3] The method for producing metal carbide according to [2] above, wherein the first metal and the second metal are the same.

[0011] [4] The method for producing a metal carbide according to the above [2] or [3], wherein the halogen in the halide includes chlorine.

[0012] [5] The method for producing a metal carbide according to the above [2] or [3], wherein the halogen in the halide includes fluorine.

[0013] [6] The method for producing metal carbide according to any one of the above [1] to [5], wherein the precipitate further contains at least one selected from the group consisting of carbon, an elemental form, a halide, a carbonate, an oxide, a hydride, and a peroxide of the first metal, and an elemental form, a halide, a carbonate, an oxide, and a carbide of a metal other than the first metal contained in the molten salt.

[0014] [7] The method for producing metal carbide according to any one of the above [1] to [6], wherein the first metal includes at least one selected from the group consisting of alkali metals and alkaline earth metals.

[0015] [8] The method for producing a metal carbide according to any one of the above [1] to [7], wherein the first metal includes at least one selected from the group consisting of lithium, sodium, potassium and calcium.

[0016] [9] preparing a molten salt containing an oxide of a first metal; adding carbon dioxide to the molten salt; applying a voltage to the molten salt containing carbon dioxide to obtain a precipitate containing a carbide of the first metal; and 11. A method for producing hydrocarbons, comprising hydrolyzing a carbide of the first metal to obtain a hydrocarbon-containing gas and a hydroxide of the first metal.

[0017]

[10] further comprising dehydrating the hydroxide to obtain an oxide of the first metal; and The method for producing hydrocarbons according to the above-mentioned [9], further comprising reusing the obtained oxide in preparing the molten salt.

[0018]

[11] The method for producing hydrocarbons according to the above [9] or

[10] , wherein the hydrocarbon is acetylene.

[0019]

[12] The method for producing hydrocarbons according to any one of the above [9] to

[11] , wherein the gas contains acetylene and at least one selected from the group consisting of ethylene, ethane, methane and hydrogen.

[0020]

[13] containing a first metal carbide as a main component; The metal carbide composition further comprises at least one selected from the group consisting of carbon, an elemental form, a halide, a carbonate, an oxide, a hydride, and a peroxide of the first metal, and an elemental form, a halide, a carbonate, an oxide, and a carbide of a metal other than the first metal. Effect of the Invention

[0021] According to the present disclosure, there are provided a method for producing metal carbide using carbon dioxide as a carbon source and a metal oxide as a metal source, a method for producing hydrocarbons from metal carbide obtained using carbon dioxide as a carbon source and a metal oxide as a metal source, and a metal carbide composition. [Brief description of the drawings]

[0022] [Figure 1] 1 is a flow chart illustrating a method for producing metal carbide according to the present disclosure. [Diagram 2] 1 is a flow chart illustrating a method for producing a hydrocarbon according to the present disclosure. [Diagram 3] 4 is a flow chart illustrating another hydrocarbon production method according to the present disclosure. [Figure 4A] 1 is a graph showing some of the results of GC-MS analysis of the hydrolysate obtained in Example 1. [Figure 4B] 1 is a graph showing the results of Raman spectroscopic analysis of the hydrolysate obtained in Example 1. [Figure 4C] 1 is a graph showing the results of XRD analysis of the hydrolysate obtained in Example 1. [Diagram 5] 1 is a graph showing the results of XRD analysis of the precipitate obtained in Example 2. [Figure 6] 1 is a graph showing some of the results of GC-MS analysis of the hydrolysate obtained in Example 3. [Figure 7] 1 is a graph showing some of the results of GC-MS analysis of the hydrolysate obtained in Example 4. [Figure 8] 1 is a graph showing the results of XRD analysis of the precipitate obtained in Example 5. [Figure 9] 1 is a graph showing the results of GC-MS analysis of the hydrolysate obtained in Example 6. [Figure 10] 1 is a graph showing the results of GC-MS analysis of the gases generated in Examples 7 to 9. [Figure 11] 13 is a graph showing the change in potential of the working electrode relative to the reference electrode when a current is applied to produce metal carbide in Example 10. [Figure 12] 1 is a photograph showing the appearance of a working electrode after current is passed therethrough for producing metal carbide in Example 10. [Figure 13] 1 is a photograph showing the appearance of a working electrode after current is passed therethrough for producing metal carbide in Example 11. [Figure 14] 1 is a graph showing the change in potential of a working electrode relative to a reference electrode when a current is applied to produce metal carbide in Examples 12 to 15. [Figure 15]13 is a photograph showing the appearance of a working electrode after current is passed therethrough for producing a metal carbide in Example 13. [Figure 16] 13 is a graph showing the change in potential of the working electrode relative to the reference electrode when a current is applied to produce metal carbide in Example 16. [Figure 17] 1 is a photograph showing the appearance of a working electrode after current is passed therethrough for producing metal carbide in Example 16. [Figure 18] 1 is a graph showing the results of XRD analysis of the precipitate obtained in Example 16. [Figure 19] 1 is a graph showing the results of XRD analysis of the metal oxide regenerated in Example 16. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] In the method for producing metal carbide disclosed herein, a voltage is applied to a molten salt containing a metal oxide and carbon dioxide (CO2) to obtain metal carbide. According to the method using this molten salt, the reaction proceeds quickly at a relatively low temperature of 800°C or less, and metal carbide can be obtained efficiently. In addition, since a metal oxide is used, the solubility of carbon dioxide in the molten salt is high. Therefore, the desired metal carbide can be obtained with higher productivity, selectivity, and safety in a smaller electrolytic bath. Furthermore, CO2, which is said to be the cause of global warming, can be effectively used as a carbon source.

[0024] The present disclosure includes a method for obtaining a hydrocarbon by hydrolyzing the metal carbide obtained by the above-mentioned method. According to this method, a high-purity hydrocarbon can be obtained efficiently. Furthermore, since it is possible to produce industrially important hydrocarbons (typically acetylene) from CO2, the method of the present disclosure is also very useful from the viewpoint of environmental conservation.

[0025] The present disclosure encompasses the reuse of metal hydroxides, which are by-produced during the production of hydrocarbons, as a metal source for producing the above-mentioned metal carbides. This allows the construction of a recycling system that includes the production of a first metal carbide using an oxide of a first metal, and the production of hydrocarbons using the first metal carbide. This allows for the effective use of resources.

[0026] The present disclosure encompasses a carbide composition comprising a carbide of a first metal, the carbide composition being useful in the production of hydrocarbons.

[0027] [Metal carbide manufacturing method] The method for producing a metal carbide according to the present disclosure includes preparing a molten salt containing an oxide of a first metal, adding carbon dioxide to the molten salt, and applying a voltage to the molten salt containing carbon dioxide to obtain a precipitate containing a carbide of the first metal. Figure 1 is a flow chart showing the method for producing a metal carbide according to the present disclosure.

[0028] (I) Preparation of molten salt (S11) First, a molten salt containing an oxide of a first metal is prepared. The oxide of the first metal is a metal source for the target metal carbide. For convenience, the metal salt (including the metal oxide) contained in the electrolytic bath is called a molten salt, even if it is not completely ionized.

[0029] (Oxide of the first metal) The oxide of the first metal is not particularly limited and is appropriately selected according to the target metal carbide. Among them, the first metal is preferably at least one selected from the group consisting of alkali metals and alkaline earth metals. This is because alkali metals and alkaline earth metals have smaller ionization energy than other metals and are easily ionized.

[0030] 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). A preferred alkali metal may be at least one selected from the group consisting of Li, Na, K, Rb and Cs. In particular, at least one selected from the group consisting of Li, Na, K and Cs is preferred.

[0031] The alkaline earth metal includes at least one selected from the group consisting of beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba) and radium (Ra). The preferred alkaline earth metal includes at least one selected from the group consisting of Mg, Ca, Sr and Ba.

[0032] Among these, taking into consideration the reactivity of the oxide of the first metal to water, the first metal is preferably Li, Na, K, or Ca. Na and Ca are more preferable in terms of low cost, and Li and Ca are more preferable in terms of safety, toxicity, and other handling properties.

[0033] The first metal is preferably Li, Na, K, or Cs in terms of the high solubility of the hydroxide in water. When the hydroxide of the first metal is highly soluble in water, the recycling efficiency of the first metal in the subsequent process is increased. In the method for producing hydrocarbons, metal carbide is hydrolyzed. At this time, the hydroxide of the first metal is by-produced together with the hydrocarbon. Since the hydrocarbon is generally difficult to dissolve in water, it can be easily extracted as a gas. In addition, carbon contained in the precipitate precipitates or floats in water. If the by-produced hydroxide of the first metal is dissolved in water, it becomes possible to efficiently remove the carbon by filtration. The hydroxide of the first metal can be recovered by removing water from the filtrate. The oxide of the first metal is obtained by dehydrating the hydroxide of the first metal. In other words, the higher the solubility of the hydroxide of the first metal in water, the easier it is to recover the oxide of the first metal. The obtained oxide of the first metal is reused in the preparation of the above-mentioned molten salt. On the other hand, the lower the solubility of the hydroxide of the first metal in water, the more energy required for its recovery can be reduced. From the viewpoint of energy reduction, the first metal is preferably Ca.

[0034] The amount of the oxide of the first metal contained in the molten salt is not particularly limited. From the viewpoint of reaction efficiency, the number of moles of the oxide of the first metal is preferably 1 mol% or more, more preferably 2 mol% or more, and particularly preferably 3 mol% or more, based on the total number of moles of the molten salt in the electrolytic bath. The number of moles of the oxide of the first metal is preferably 20 mol% or less, more preferably 15 mol% or less, and particularly preferably 10 mol% or less, based on the total number of moles of the molten salt in the electrolytic bath. In one embodiment, the number of moles of the oxide of the first metal is 1 mol% or more and 20 mol% or less, based on the total number of moles of the molten salt in the electrolytic bath.

[0035] (Other metal salts) The molten salt preferably contains a metal salt other than the oxide of the first metal. The other metal salt mainly functions as an electrolyte in the electrolytic bath. The other metal salt also makes it easier to melt the oxide of the first metal. The other metal salt includes a salt of an ion of a metal (hereinafter referred to as the second metal) and its counter ion (hereinafter referred to as the second anion).

[0036] The second metal and the first metal may be the same or different. When the second metal is the same as the first metal, carbide of the first metal is easily produced. When the second metal is the same as the first metal, the second anion is other than an oxide ion.

[0037] The other metal salt is not particularly limited as long as it can stably precipitate the target metal carbide. In particular, the other metal salt is preferably one that melts at a temperature of 800° C. or less.

[0038] Examples of the second metal include alkali metals, alkaline earth metals, rare earth elements, aluminum (Al), gallium (Ga), indium (In), thallium (Tl), zinc (Zn), cadmium (Cd), gold (Au), silver (Ag), and copper (Cu). The alkali metals and alkaline earth metals are as described above. Examples of rare earth elements include scandium (Sc), yttrium (Y), lanthanoid elements, and actinoid elements. Among these, at least one selected from the group consisting of alkali metals and alkaline earth metals is preferred because it tends to lower the melting temperature of other metal salts.

[0039] The second anion may be, for example, a carbonate ion (CO 2- ), sulfate ion, phosphate ion, nitrate ion, acetate ion, carboxylate ion, oxide ion (O2 - ) and halogen ions. Among these, halogen ions are preferred because they tend to lower the melting temperature of other metal salts. Halogens have a large electron affinity.

[0040] The halogen may be at least one selected from the group consisting of fluorine (F), chlorine (Cl), bromine (Br), iodine (I) and astatine (At). A preferred halogen may be at least one selected from the group consisting of F, Cl, Br and I. In particular, F and / or Cl are preferred. F is preferred in that it can improve the solubility of the oxide of the first metal and / or CO2.

[0041] In view of the ease with which CO2 is ionized, it is preferable that the second anion contains an oxide ion. Examples of the oxide of the second metal include an oxide of at least one metal selected from the group consisting of alkali metals and alkaline earth metals different from the first metal.

[0042] Specific examples of other metal salts 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; halides of rare earth elements such as AlCl3; oxides of metals other than the first metal such as Li2O and CaO; metal carbonates such as Li2CO3, Na2CO3, and K2CO3; and metal nitrates such as LiNO3, NaNO3, and KNO3. Among these, at least one selected from the group consisting of lithium salts, sodium salts, and potassium salts is preferred. In particular, chloride and / or fluoride of at least one element selected from the group consisting of Li, Na and K is preferred.

[0043] The other metal salts are used alone or in combination of two or more. In particular, it is preferable to use two or more other metal salts in combination, since the melting temperature is easily lowered. For example, a combination of multiple chlorides, a combination of multiple fluorides, and a combination of one or more chlorides and one or more fluorides can be mentioned. Specific examples include combinations of LiCl and KCl, LiCl, KCl, and CaCl2, LiF, NaF, and KF, NaF, and NaCl, and NaCl, KCl, and AlCl3.

[0044] In the combination of a plurality of metal salts, the compounding ratio of each metal salt is not particularly limited. For example, in the combination of LiCl and KCl, the moles of LiCl may be 30 mol% or more, 45 mol% or more, or 50 mol% or more, based on the total moles of LiCl and KCl. The moles of LiCl may be 90 mol% or less, 70 mol% or less, or 65 mol% or less, based on the total moles of LiCl and KCl. In one embodiment, the moles of LiCl are 45 mol% or more and 90 mol% or less, based on the total moles of LiCl and KCl.

[0045] (II) Addition of carbon dioxide (S12) Next, a gas containing carbon dioxide is added to the molten salt in a molten state. The gas containing carbon dioxide (hereinafter, may be referred to as CO2 gas) is brought into contact with the molten salt in a liquid state in a gaseous state. The CO2 gas may be blown into the gas phase of the electrolytic bath to contact the liquid surface of the molten salt, or the CO2 gas may be blown into the molten salt. The CO2 gas may be a mixed gas of CO2 and an inert gas (typically argon). A sufficient amount of CO2 gas may be added to the molten salt before the voltage is applied, or the CO2 gas may be added to the molten salt while the voltage is being applied.

[0046] The injected CO2 not only physically dissolves in the molten salt, but also ionizes to form carbonate ions (CO3 2- ) in the electrolytic bath. In the molten salt, the dissociation of the oxide of the first metal results in the formation of the first metal ion and oxide ion (O 2- ) is produced. For example, CO2 reacts with the oxide ions present in the molten salt to produce carbonate ions (CO3 2- That is, the amount of CO2 dissolved in the molten salt increases due to the oxide of the first metal, thereby improving productivity.

[0047] When the first metal is Li, in the molten salt, the oxide of the first metal dissociates to form lithium ions (Li + ) and oxide ions (O 2-) is produced (Equation 1). CO2 reacts with the above oxide ions to produce carbonate ions (CO3 2- ) (Equation 2). (Formula 1) Li2O → 2Li + + O 2- (Formula 2) CO2+O 2- →CO3 2-

[0048] The amount of CO2 gas injected may be appropriately set according to the amount of the oxide of the first metal. For example, the amount of CO2 gas injected is equal to or more than the equivalent of the oxide of the first metal contained in the molten salt, taking into consideration the efficiency of gas absorption into the molten salt. When the molten salt contains 29.9 g of lithium oxide as the oxide of the first metal, the amount of CO2 gas injected may be equal to or more than 44.0 g, or may be equal to or more than 440 g. By using an appropriate amount of CO2 gas, energy loss, a temperature drop of the molten salt, a decomposition reaction, etc. are suppressed, and the yield of the target carbide is improved.

[0049] In order to promote the dissolution of CO2 into the molten salt, it is desirable that the bubble diameter of the CO2 gas to be blown in is small. The bubble diameter of the CO2 gas is preferably 10 mm or less, more preferably 1 mm or less. The bubble diameter of the CO2 gas may be 100 nm or more, and may be 1 μm or more. The bubble diameter of the CO2 gas can be made fine 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.

[0050] It is preferable to preheat the CO2 gas to a temperature close to that of the molten salt, since preheating makes it easier to prevent the temperature of the molten salt from dropping and solidifying.

[0051] (III) Application of voltage (S13) Next, a voltage is applied to the molten salt. This causes CO3 2-is reduced to obtain a precipitate containing the carbide of the first metal (first metal carbide). The precipitate containing the first metal carbide is deposited on the surface of the electrode (cathode) with a lower potential. Carbon may be generated as a by-product on the cathode. Meanwhile, oxygen and halogen gases such as chlorine may be generated on the anode.

[0052] When the first metal is Li, lithium carbide (Li2C2) is deposited on the cathode as the first metal (Equation 3). Carbon and metallic lithium may be produced on the cathode through side reactions (Equations 4 and 5). Some or all of the carbon and metallic lithium produced in this side reaction may further react to form lithium carbide (Equation 6). Alternatively, metallic lithium may react with carbon dioxide physically dissolved in the molten salt to form lithium carbide (Equation 7). (Formula 3) 2Li + +2CO3 2- +10e - → Li2C2+6O 2- (Formula 4) 2CO3 2- +8e - → 2C+6O 2- (Formula 5) 2Li + +2e - → 2Li (Formula 6) 2Li+2C → Li2C2 (Equation 7) 2Li+2CO2 → Li2C2+2O2

[0053] Depending on the type of metal and conditions, the oxide of the first metal may further react with carbon dioxide to produce a carbide of the first metal. For example, when the first metal is Li, lithium carbide may be produced (Formula 8). (Formula 8) Li2O+2CO2→ Li2C2+5 / 2O2

[0054] On the other hand, O2 - is oxidized to produce oxygen (Equation 9). (Formula 9) 2O 2- → O2+4e -

[0055] When the first metal is Na, K or Ca, a similar reaction occurs to precipitate sodium carbide (Na2C2), potassium carbide (K2C2) or calcium carbide (CaC2). The same is true for other first metals.

[0056] On the anode, O2 - is oxidized to produce oxygen. The oxygen produced on the anode is released into the gas phase. This oxygen gas can be collected and used for other purposes.

[0057] The voltage is applied at a temperature at which the molten salt can be maintained in a molten state. The temperature of the electrolytic bath may be, for example, 350° C. or higher, or 400° C. or higher. The temperature of the electrolytic bath may be, for example, 800° C. or lower, or 700° C. or lower. According to the present disclosure, the reaction proceeds at such a relatively low temperature, and therefore the energy efficiency is high.

[0058] The applied voltage is set so that the cathode potential is between the potential (Ec) at which carbon precipitates and the potential (Em) at which the first metal precipitates. This can further improve the selectivity of the first metal carbide. If the cathode potential is excessively high (noble), mainly carbon precipitates, and the amount of the target first metal carbide produced is likely to decrease. If the cathode potential is excessively low (base), the first metal carbide is produced, but of the metals contained in the molten salt, the metal with the most noble redox potential in the molten salt mainly precipitates. If the molten salt contains multiple metals with similar redox potentials in the molten salt, an alloy of multiple metals may precipitate. For example, if the molten salt contains LiCl, KCl, and Li2O (5 mol%), the cathode potential is set to be 0.0 V or more and 1.0 V or less (Li + / Li standard). The voltage may be direct current, intermittent (pulse electrolysis), or superimposed with alternating current. The potentials Ec and Em can be determined by cyclic voltammetry measurements in the molten salt used, for example with a Ni electrode.

[0059] The current value may be appropriately set according to the amount of CO2 supplied per unit time. 2- The amount of CO2 and CO3 consumed per unit time at the cathode so that the concentration does not decrease 2- Therefore, CO2 and CO2 and O2 in molten salt - CO3 produced by reaction with 2- is set so that

[0060] The material of the cathode is not particularly limited. Examples of the material of the cathode include metals such as Ag, Cu, Ni, Pb, Hg, Tl, Bi, In, Sn, Cd, Au, Zn, Pd, Ga, Ge, Ni, 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.

[0061] The material of the anode is not particularly limited. Examples of the material of the anode include Pt, conductive metal oxide, glassy carbon, natural graphite, isotropic graphite, pyrolytic graphite, plastic formed carbon, and boron-doped diamond. Examples of electrodes made of conductive metal oxide include transparent conductive electrodes called ITO electrodes in which a mixed oxide of indium and tin is formed on glass, electrodes called DSA electrodes (trademark of De Nora Permelec Electrodes, Inc.) in which oxides of platinum group metals such as ruthenium and iridium are formed on a substrate such as titanium, and La 1-x Sr x FeO 3-δ Among them, oxide-based anodes are preferred because they are less susceptible to consumption due to oxidation reactions.

[0062] (metal carbide) The obtained metal carbide is mainly a carbide of the first metal (first metal carbide). Considering hydrolysis in the subsequent steps, the first metal carbide is preferably at least one selected from the group consisting of Li2C2, Na2C2, K2C2, and CaC2.

[0063] According to the present disclosure, the first metal carbide can be obtained with high selectivity. The selectivity of the first metal carbide is expressed by the mass of the first metal carbide relative to the total mass of the first metal element, the compound containing the first metal (including the first metal carbide), and carbon contained in the deposit on the cathode. 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 embodiment, the selectivity of the first metal carbide is 90 mass% or more and 99.9 mass% or less.

[0064] Examples of compounds containing a first metal other than a first metal carbide include a salt of the first metal and a second anion (e.g., a halide of the first metal), a carbonate of the first metal, an oxide of the first metal, a hydride of the first metal, and a peroxide of the first metal.

[0065] (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 cathode 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, simple substances of the first metal, compounds containing the first metal other than the above-mentioned first metal carbide, and compounds containing the second metal.

[0066] 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. The compound containing the second metal may include at least one selected from the group consisting of the simple substance, halide, carbonate, oxide, and carbide of the second metal. The compound containing the metal material constituting the device may include at least one selected from the group consisting of the halide, oxide, carbonate, metal, and hydrates thereof of the metal.

[0067] For example, if the first metal is Li, the other metal salt is a mixture of LiCl and KCl, and the material constituting the device includes nickel, the precipitate may include at least one impurity selected from the group consisting of Li, KCl, LiCl, Li2CO3, K2CO3, LiKC2, HLiC2, K2C2, and NiCl2.

[0068] The amount of impurities is preferably 40% by mass or less, more preferably 20% by mass or less, and particularly preferably 10% by mass or less of the total precipitate on the cathode. 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 precipitate. In one embodiment, the amount of impurities is 0.1% by mass or more and 10% by mass or less of the total precipitate.

[0069] 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 spectroscopy and X-ray diffraction (XRD) analysis of the precipitate.

[0070] [Method of producing hydrocarbons] The present disclosure encompasses a method for producing hydrocarbons from metal carbides obtained by utilizing CO2. That is, the method for producing hydrocarbons according to the present disclosure includes preparing a molten salt containing an oxide of a first metal, adding carbon dioxide to the molten salt, applying a voltage to the molten salt containing carbon dioxide to obtain a precipitate containing the carbide of the first metal, and hydrolyzing the carbide of the first metal to obtain a hydrocarbon and a hydroxide of the first metal. Figure 2 is a flow chart showing the method for producing hydrocarbons according to the present disclosure.

[0071] (1) Preparation of molten salt (S21) The molten salt is prepared in the same manner as in the preparation of the molten salt (S11) in the above-mentioned method for producing metal carbide.

[0072] (2) Addition of carbon dioxide (S22) CO2 is added to the molten salt in the same manner as in the addition of carbon dioxide (S12) in the above-mentioned method for producing metal carbide.

[0073] (3) Application of voltage (S23) A voltage is applied to the molten salt in the same manner as in the voltage application (S13) in the above-mentioned method for producing a metal carbide, thereby obtaining a precipitate containing the first metal carbide.

[0074] (4) Hydrolysis of metal carbides (S24) Next, the first metal carbide is brought into contact with water to hydrolyze it. This produces a gas containing the target hydrocarbon. Hydrocarbons usually have low solubility in water. Therefore, the produced hydrocarbons are quickly released into the gas phase and are collected.

[0075] The first metal carbide may be isolated from the precipitate and then hydrolyzed. The isolation may be performed, for example, by crushing the precipitate and utilizing the difference in specific gravity. Alternatively, the precipitate may be directly hydrolyzed. In this case, the second metal carbide that may be contained in the precipitate is also hydrolyzed to generate hydrocarbons.

[0076] Examples of the obtained hydrocarbons include methane, ethane, ethylene, acetylene (C2H2), propane, propylene, butane, and butene. When an isolated first metal carbide is used or when the amount of impurities (particularly simple 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 gas recovered. Acetylene is an industrially important hydrocarbon.

[0077] The gas obtained 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 gas recovered. The amount of impurities may be 0.0001% by mass or more, or may be 0.001% by mass or more, of the gas recovered. In one embodiment, the amount of impurities is 0.0001% by mass or more and 1% by mass or less of the gas recovered.

[0078] The resulting gas may include, for example, acetylene and at least one selected from the group consisting of ethylene, ethane, methane, and hydrogen.

[0079] 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) of the recovered gas, Fourier transform infrared absorption spectrometry (FT-IR analysis) equipped with a gas cell, or ultraviolet-visible absorption spectrometry (UV-Vis analysis).

[0080] According to the present disclosure, the faradaic efficiency e of the production of hydrocarbons is improved. The faradaic efficiency e may be, for example, 50% or more, and 80% or more. The faradaic efficiency e may be, for example, 99.9% or less, and 99% or less. In one embodiment, the faradaic efficiency e is 50% or more and 99.9% or less.

[0081] For example, the Faradaic efficiency e for C2H2 production can be calculated as follows: First, the volumetric ratio of C2H2 contained in the collected gas is calculated from the total area of ​​the peaks obtained from the GC-MS analysis and the calibration curve. Next, the volume of C2H2 generated is calculated from the volume of the gas phase in the collection vessel and the calculated volumetric ratio of C2H2 in the gas. Finally, assuming that the generated C2H2 is in standard conditions (0°C, 101 kPa), the Faraday efficiency e (%) is calculated using the following formula.

[0082]

number

[0083] The amount of water to be brought into contact with the precipitate is appropriately set according to the mass of the precipitate. The amount of water is, for example, more than the amount necessary for hydrolysis of the metal carbide and metal contained in the precipitate. In addition, it is desirable to use an amount of water that can immerse the entire precipitate and takes into consideration evaporation due to heat generated during hydrolysis. In terms of making it easier to recover the hydroxide of the first metal, it is desirable to use an amount of water that is more than the amount that can dissolve all of the hydroxide produced. However, if an excessive amount of water is used, the load when recovering the hydroxide of the first metal tends to be large. When the first metal is lithium, the amount of water may be, for example, 10 times or more, or 20 times or more, relative to the mass of the precipitate. The amount of water may be, for example, 100 times or less, or 50 times or less, relative to the mass of the precipitate.

[0084] Hydrolysis of the first metal carbide produces a hydroxide of the first metal along with hydrocarbons. For example, hydrolysis of lithium carbide produces lithium hydroxide along with acetylene (Equation 9). (Formula 9) Li2C2+2H2O → C2H2+2LiOH

[0085] (Recycling System) The present disclosure further includes recovering the hydroxide of the first metal, which is a by-product of the hydrolysis, as an oxide and reusing it as a source of metal for producing the first metal carbide, thereby allowing the production of hydrocarbons in a cyclical manner.

[0086] That is, the method for producing hydrocarbons according to the present disclosure further includes dehydrating the produced hydroxide of the first metal to obtain an oxide of the first metal, and reusing the obtained oxide of the first metal in the preparation of the molten salt (1) above. Figure 3 is a flowchart showing another method for producing hydrocarbons (recycle system) according to the present disclosure.

[0087] (5) Dehydration of the hydroxide of the first metal (S25) The hydroxide of the first metal produced together with the hydrocarbon is dehydrated to regenerate the oxide of the first metal.

[0088] The hydroxide of the first metal will either precipitate or dissolve in the water used for hydrolysis, depending on its solubility in water. Impurities contained in the precipitate will also precipitate or dissolve in the water. It is desirable to remove as many of the impurities as possible before dehydrating the hydroxide of the first metal.

[0089] When the solubility S of the hydroxide of the first metal in water at 20°C is 10 g / 100 gH2O or more, first, (i) impurities (typically carbon) precipitated in the water are removed by filtration or centrifugation, then (ii) water is removed from the remaining aqueous solution by heating or the like to obtain the hydroxide of the first metal, and the obtained hydroxide of the first metal is dehydrated by heating to produce the first metal as an oxide.

[0090] For example, the solubility S of lithium hydroxide is 12.8 g / 100 g H2O. Therefore, if the first metal is lithium, the precipitated impurities are first removed by filtration. After that, when the filtrate is heated sufficiently, lithium oxide is obtained according to the following reaction formula: 2LiOH → Li2O+H2O

[0091] Examples of the first metal having a hydroxide solubility S of 10 g / 100 g H2O or more include sodium, potassium, rubidium, and cesium, in addition to lithium.

[0092] When the solubility S of the hydroxide of the first metal is 10 g / 100 gH2O or more, and the solubility S of the carbonate of the first metal is half or less of the solubility S of the hydroxide of the first metal, an equivalent amount of CO2 may be blown into water containing the hydroxide of the first metal to precipitate the first metal as a carbonate. In this case, the oxide of the first metal can be obtained more efficiently by heating and pyrolyzing the precipitate. For example, the solubility S of lithium carbonate is 1.33 g / 100 gH2O, which is about one-tenth of the solubility S of lithium hydroxide. Therefore, lithium can be efficiently obtained as an oxide by first precipitating it as a carbonate. The lithium carbonate precipitated in water is easily pyrolyzed into lithium oxide by heating.

[0093] Examples of the first metal having a hydroxide solubility S of 10 g / 100 gH2O or more and a carbonate solubility S of half or less of the hydroxide solubility S include lithium, sodium, potassium, calcium, strontium, and barium.

[0094] When the solubility S of the hydroxide of the first metal is less than 10 g / 100 g H2O and the first metal can form a hydrogen carbonate, excess CO2 may be blown into water containing the hydroxide of the first metal to generate the hydrogen carbonate of the first metal. The hydrogen carbonate of the first metal is easily soluble in water. Next, as in (i) and (ii) above, the precipitate containing impurities is removed. The remaining aqueous solution is heated to thermally decompose the hydrogen carbonate of the first metal, thereby generating the hydroxide of the first metal again. Finally, the hydroxide of the first metal is dehydrated to generate the first metal as an oxide.

[0095] For example, the solubility S of calcium hydroxide (Ca(OH)2) is 0.17g / 100gH2O, and calcium forms hydrogen carbonate. Therefore, calcium hydroxide (Ca(OH)2) can be converted to calcium hydrogen carbonate (Ca(HCO3)2) and calcium hydroxide (Ca(OH)2) via the following reaction formula to produce calcium oxide (CaO). Ca(OH)2+2CO2 → Ca(HCO3)2 Ca(HCO3)2 → Ca(OH)2 + 2CO2 Ca(OH)2 → CaO+H2O

[0096] The above product containing the oxide of the first metal may contain, as impurities, an oxide of the second metal, hydroxides, peroxides, carbonates, hydrogencarbonates, and hydrates thereof of the first and second metals. The amount of impurities is preferably 20% by mass or less of the total amount of the above product, more preferably 10% by mass or less. The amount of impurities may be 0.1% by mass or more, or 1.0% by mass or more, of the total amount of the above product. In one embodiment, the amount of impurities is 0.1% by mass or more and 20% by mass or less of the total amount of the above product. When the amount of impurities is within the above range, side reactions in the recycling process (e.g., the precipitation process of the first metal carbide) are easily suppressed, and the Faraday efficiency can be further improved. The presence of the oxide of the first metal and the impurities and their quantification can be performed, for example, by Raman spectroscopy and X-ray diffraction (XRD) analysis of the precipitate.

[0097] (6) Reuse of the oxide of the first metal (S26) The obtained oxide of the first metal is reused in the preparation of the molten salt (1) above. This completes a cycle including the production of the first metal carbide using the oxide of the first metal and the production of hydrocarbons using the first metal carbide. The above product, which may contain impurities, may also be reused.

[0098] [Metal carbide composition] The present disclosure encompasses a metal carbide composition. The metal carbide composition includes a carbide of a first metal as a main component, and further includes 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, and an elemental substance, a halide, a carbonate, an oxide, and a carbide of a metal other than the first metal. The metal carbide composition is obtained, for example, by the method for producing a metal carbide of the present disclosure. In this case, the metal carbide composition is a precipitate formed on a cathode. The metal other than the first metal includes the above-mentioned second metal.

[0099] The main component of the metal carbide composition is the carbide of the first metal. The first metal is as described above. The main component is a component that occupies 50 mass% or more of the total mass of the metal carbide composition. The content ratio of the carbide of the first metal is preferably 80 mass% or more, more preferably 90 mass% or more of the mass of the metal carbide composition. The content ratio of the carbide of the first metal may be 99.9 mass% or less, or may be 99 mass% or less of the mass of the metal carbide composition. In one embodiment, the content ratio of the carbide of the first metal is 80 mass% or more and 99.9 mass% or less of the mass of the metal carbide composition.

[0100] Similarly, when the metal carbide composition is obtained by the method for producing metal carbide of the present disclosure, the metal carbide composition contains at least one selected from the group consisting of carbon, the simple substance, halide, carbonate, oxide, hydride, and peroxide of the first metal, and the simple substance, halide, carbonate, oxide, and carbide of the second metal, together with the carbide of the first metal. The metal carbide composition may also contain at least one selected from the group consisting of a solidified electrolyte (other metal salt), a halide, oxide, metal, and hydrate thereof of the material constituting the device. The carbon may contain at least one selected from the group consisting of graphite, amorphous carbon, glassy carbon, carbon nanotubes, diamond, nanodiamond, graphene, and other nanocarbon materials. EXAMPLES

[0101] [Example 1] (Metal Carbide Manufacturing) LiCl and KCl were mixed so that LiCl / KCl=58.5 mol% / 41.5 mol%, and vacuum dried at 200°C and 100 Pa or less for 24 hours or more. 5 mol% of Li2O was weighed out based on the total moles of LiCl and KCl, and added to the mixture to obtain a mixed salt. The mixed salt was placed in four glass containers, which were then set in an electric furnace, and heated to 450°C. In this way, a molten salt of LiCl-KCl-Li2O was obtained.

[0102] Then, a working electrode (a 1 cm × 1.5 cm nickel plate), a counter electrode (a coiled platinum wire), and a reference electrode (Ag + A lid (Ag / Ag) was attached to each of the four vessels and the vessels were sealed with the lid. CO2 was blown into each of the molten salts at 450°C in the four vessels at a flow rate of 100 mL / min for more than 30 minutes. Next, a voltage was applied using a potentio-galvanostat while maintaining the potential of the working electrode against the reference electrode at 0.09 V. The application times were 10 min, 30 min, 1 h, and 2 h, respectively. A deposit was confirmed on the working electrode. All experimental operations were performed in a glove box maintained in a high-purity argon atmosphere.

[0103] (Hydrocarbon production) The precipitates were placed in four sealed test tubes. Pure water was added to these test tubes in small amounts at room temperature (23°C) to hydrolyze the precipitates. The total amount of water added was 2.5 ml for each test tube. After confirming that bubbles were being generated in the test tubes, the test tubes were left to stand until the bubbles were no longer observed. Next, 100 μl (microliters) of gas was collected from the test tubes using a gas-tight syringe.

[0104] Using a gas chromatograph (GC), GC-MS analysis of the resulting gas confirmed that C2H2 was produced as the main component. It was also confirmed that methane, ethane, and hydrogen were by-produced. Other impurities included water, carbon dioxide, nitrogen, oxygen, and argon. The amount of each component produced was also confirmed. The mass percentage of C2H2 in the recovered gas was well above 50 mass%.

[0105] The results of GC-MS analysis of the gas obtained by hydrolysis of the precipitate obtained by applying voltage for 1 hour are shown in Figure 4A. The faradaic efficiency of the C2H2 gas generation was calculated to be about 25.2%. The average current value at this time was 359.4 mA.

[0106] Raman spectroscopy and XRD analysis were performed on each of the four hydrolysates. The analysis results are shown in Figure 4B and Figure 4C. Figure 4B and Figure 4C show the analysis results of the precipitates obtained with the voltage application times of 10 minutes, 30 minutes, 1 hour, and 2 hours. From these analyses, it was confirmed that all of the hydrolysates contained at least KCl, Ni, carbon, and Li2CO3. Therefore, it is considered that the precipitates before hydrolysis contained the above-mentioned KCl, Ni, carbon, and Li2CO3 in addition to Li2C2. The mass ratio of impurities in the hydrolysates was sufficiently less than 50 mass%.

[0107] (Regeneration of metal oxides) The liquid remaining after the hydrolysis was filtered to remove the precipitate. The filtrate was then heated sufficiently to remove water and perform a dehydration reaction to obtain a solidified product. XRD analysis was performed on this solidified product to confirm that Li2O was regenerated as the main component. The precipitate obtained by the filtration was dried and subjected to Raman spectroscopy and XRD analysis. These analyses confirmed that the main component of the precipitate was carbon, with a trace amount of nickel included.

[0108] [Example 2] (Metal Carbide Manufacturing) A deposit was obtained in the same manner as in Example 1, except that a voltage was applied for 30 minutes while maintaining the potential of the working electrode relative to the reference electrode at 0.225 V. The average current value at this time was 570 mA. From the XRD analysis of the obtained deposit, it was confirmed that the deposit contained Li2C2 and at least KCl, LiCl, Ni, carbon, Li2O, and Li2CO3 as impurities. The result of the XRD analysis of the obtained deposit is shown in FIG. 5. The mass ratio of the impurities in the deposit was sufficiently less than 50 mass%.

[0109] (Hydrocarbon production) The precipitate was hydrolyzed in the same manner as in Example 1. GC-MS analysis confirmed that the main component of the generated gas was C2H2. Furthermore, it was confirmed that ethane and hydrogen were by-produced. In addition, water, carbon dioxide, nitrogen, oxygen, and argon were contained as impurities. The mass ratio of C2H2 in the collected gas was sufficiently more than 50 mass%.

[0110] (Regeneration of metal oxides) A solidified material was obtained in the same manner as in Example 1. From the XRD analysis of the obtained solidified material, it was confirmed that the solidified material contained Li2O as a main component.

[0111] [Example 3] (Metal Carbide Manufacturing) A deposit was obtained in the same manner as in Example 1, except that a voltage was applied for 1 hour while maintaining the potential of the working electrode relative to the reference electrode at 0.3 V. The average current value at this time was 684 mA. From the results of Raman spectroscopy and XRD analysis of the obtained deposit, it was confirmed that the deposit contained Li2C2 and at least KCl, LiCl, Ni, carbon, Li2O, and Li2CO3 as impurities. The mass ratio of the impurities in the deposit was sufficiently less than 50 mass%.

[0112] (Hydrocarbon production) The precipitate was hydrolyzed in the same manner as in Example 1. GC-MS analysis confirmed that the main component of the generated gas was C2H2. The results of the GC-MS analysis are shown in FIG. 6. Furthermore, it was confirmed that ethane and hydrogen were by-produced. Other impurities included water, carbon dioxide, nitrogen, oxygen, and argon. The mass ratio of C2H2 in the collected gas was sufficiently more than 50 mass%. The Faraday efficiency of C2H2 gas generation was calculated to be about 54.7%.

[0113] (Regeneration of metal oxides) A solidified material was obtained in the same manner as in Example 1. From the XRD analysis of the obtained solidified material, it was confirmed that the solidified material contained Li2O as a main component.

[0114] [Example 4] (Metal Carbide Manufacturing) A deposit was obtained in the same manner as in Example 1, except that a voltage was applied for 1 hour while maintaining the potential of the working electrode relative to the reference electrode at 0.75 V. The average current value at this time was 75 mA. From Raman spectroscopy and XRD analysis of the obtained deposit, it was confirmed that the deposit contained Li2C2 and at least KCl, LiCl, Ni, carbon, Li2O, and Li2CO3 as impurities. The mass ratio of the impurities in the deposit was sufficiently less than 50 mass%.

[0115] (Hydrocarbon production) The precipitate was hydrolyzed in the same manner as in Example 1. GC-MS analysis confirmed that the generated gas contained C2H2. A portion of the results of the GC-MS analysis are shown in Figure 7.

[0116] (Regeneration of metal oxides) A solidified material was obtained in the same manner as in Example 1. From the XRD analysis of the obtained solidified material, it was confirmed that the solidified material contained Li2O as a main component.

[0117] [Example 5] (Metal Carbide Manufacturing) LiCl, KCl, and CaCl2 were mixed so that LiCl / KCl / CaCl2=52.3 mol% / 11.6 mol% / 36.1 mol%. 3 mol% of CaO was weighed out based on the total moles of LiCl, KCl, and CaCl2, and added to the mixture to obtain a mixed salt. The mixed salt was placed in a container and set in an electric furnace, and the mixed salt was heated to 450°C. In this way, a molten salt of LiCl-KCl-CaCl2-CaO was obtained.

[0118] A precipitate was obtained in the same manner as in Example 1, except that this molten salt was used and a voltage was applied for 30 minutes while maintaining the potential of the working electrode relative to the reference electrode at 0.4 V. From Raman spectroscopic analysis and XRD analysis of the obtained precipitate, it was confirmed that the precipitate contained CaC2 and at least LiCl, KCl, CaCl2, Ni, carbon, CaO, and CaCO3 as impurities. The result of the XRD analysis of the obtained precipitate is shown in FIG. 8. The mass ratio of the impurities in the precipitate was sufficiently less than 50 mass%.

[0119] (Hydrocarbon production) The precipitate was hydrolyzed in the same manner as in Example 1. GC-MS analysis confirmed that the main component of the generated gas was C2H2. Furthermore, it was confirmed that ethane and hydrogen were by-produced. In addition, water, carbon dioxide, nitrogen, oxygen, and argon were contained as impurities. The mass ratio of C2H2 in the collected gas was sufficiently more than 50 mass%.

[0120] (Regeneration of metal oxides) CO2 was blown into the liquid remaining after the hydrolysis. The precipitate was then removed by filtration. The remaining filtrate was heated sufficiently to remove water and perform a dehydration reaction to obtain a solidified product. XRD analysis of the obtained solidified product confirmed that it contained CaO as the main component.

[0121] [Example 6] (Manufacturing of metal carbides) A deposit was obtained in the same manner as in Example 5, except that a voltage was applied for 1 hour while maintaining the potential of the working electrode relative to the reference electrode at 0.15 V. From Raman spectroscopic analysis and XRD analysis of the obtained deposit, it was confirmed that the deposit contained CaC2 and at least CaCl2 as an impurity. The mass ratio of the impurities in the deposit was sufficiently less than 50 mass%.

[0122] (Hydrocarbon production) The precipitate was hydrolyzed in the same manner as in Example 1. GC-MS analysis confirmed that the generated gas was C2H2. Furthermore, it was confirmed that ethane and hydrogen were by-produced. In addition, water, carbon dioxide, nitrogen, oxygen, and argon were generated as impurities. The mass ratio of C2H2 in the collected gas was sufficiently more than 50 mass%. The results of the GC-MS analysis are shown in FIG. 9.

[0123] (Regeneration of metal oxides) A solidified material was obtained in the same manner as in Example 5. From the XRD analysis of the obtained solidified material, it was confirmed that the solidified material contained CaO as a main component.

[0124] [Example 7] (Manufacturing of metal carbides) A precipitate was obtained in the same manner as in Example 5, except that iron was used as the working electrode and a voltage was applied for 2 hours while maintaining the potential of the working electrode relative to the reference electrode at 0.80 V. From Raman spectroscopic analysis and XRD analysis of the obtained precipitate, it was confirmed that the precipitate contained CaC2 and at least CaCl2 as an impurity. The mass ratio of the impurities in the precipitate was sufficiently less than 50 mass%.

[0125] (Hydrocarbon production) The precipitate was hydrolyzed in the same manner as in Example 1. GC-MS analysis confirmed that the generated gas was C2H2. Furthermore, it was confirmed that ethylene and hydrogen were by-produced. Other impurities generated included water, carbon dioxide, nitrogen, oxygen, and argon. The mass ratio of C2H2 in the collected gas was sufficiently more than 50 mass%. The results of the GC-MS analysis are shown in FIG. 10(1).

[0126] (Regeneration of metal oxides) A solidified material was obtained in the same manner as in Example 5. From the XRD analysis of the obtained solidified material, it was confirmed that the solidified material contained CaO as a main component.

[0127] [Example 8] (Metal Carbide Manufacturing) A precipitate was obtained in the same manner as in Example 5, except that the potential of the working electrode relative to the reference electrode was maintained at 0.40 V. From Raman spectroscopic analysis and XRD analysis of the obtained precipitate, it was confirmed that the precipitate contained CaC2 and at least CaCl2 as an impurity. The mass ratio of the impurities in the precipitate was sufficiently less than 50 mass%.

[0128] (Hydrocarbon production) The precipitate was hydrolyzed in the same manner as in Example 1. GC-MS analysis confirmed that the generated gas was C2H2. Furthermore, it was confirmed that ethane, ethylene, and hydrogen were by-produced. In addition, water, carbon dioxide, nitrogen, oxygen, and argon were generated as impurities. The mass ratio of C2H2 in the collected gas was sufficiently more than 50 mass%. The results of the GC-MS analysis are shown in FIG. 10(2).

[0129] (Regeneration of metal oxides) A solidified material was obtained in the same manner as in Example 5. From the XRD analysis of the obtained solidified material, it was confirmed that the solidified material contained CaO as a main component.

[0130] [Example 9] (Metal Carbide Manufacturing) A precipitate was obtained in the same manner as in Example 5, except that the potential of the working electrode relative to the reference electrode was maintained at 0.15 V. From Raman spectroscopic analysis and XRD analysis of the obtained precipitate, it was confirmed that the precipitate contained CaC2 and at least CaCl2 as an impurity. The mass ratio of the impurities in the precipitate was sufficiently less than 50 mass%.

[0131] (Hydrocarbon production) The precipitate was hydrolyzed in the same manner as in Example 1. GC-MS analysis confirmed that the generated gas was C2H2. Furthermore, it was confirmed that ethane, ethylene, and hydrogen were by-produced. In addition, water, carbon dioxide, nitrogen, oxygen, and argon were generated as impurities. The mass ratio of C2H2 in the collected gas was sufficiently more than 50 mass%. The results of the GC-MS analysis are shown in FIG. 10(3).

[0132] (Regeneration of metal oxides) A solidified material was obtained in the same manner as in Example 5. From the XRD analysis of the obtained solidified material, it was confirmed that the solidified material contained CaO as a main component.

[0133] [Example 10] (Metal Carbide Manufacturing) The current between the working electrode and the counter electrode was set to -100 mA, i.e., the current density was set to -50 mA / cm 2 A precipitate was obtained in the same manner as in Example 5, except that the current was maintained at 100 C until the current flow reached 100 C.

[0134] The potential change of the working electrode relative to the reference electrode when a current is applied is shown in Figure 11(1). The appearance of the working electrode after the current is applied is shown in Figure 12. A black precipitate can be seen on the surface of the working electrode. From Raman spectroscopic analysis and XRD analysis of the obtained precipitate, it was confirmed that the precipitate contained CaC2 and at least CaCl2 as an impurity. The mass ratio of the impurities in the precipitate was sufficiently less than 50 mass%.

[0135] (Hydrocarbon production) The precipitate was hydrolyzed in the same manner as in Example 1. GC-MS analysis confirmed that the gas produced was C2H2. Furthermore, it was confirmed that ethane, ethylene, and hydrogen were by-produced. Other impurities produced included water, carbon dioxide, nitrogen, oxygen, and argon. The Faraday efficiency of C2H2 gas production was calculated to be about 0.1%.

[0136] (Regeneration of metal oxides) A solidified material was obtained in the same manner as in Example 5. From the XRD analysis of the obtained solidified material, it was confirmed that the solidified material contained CaO as a main component.

[0137] [Example 11] (Manufacturing of metal carbides) A deposit was obtained in the same manner as in Example 10, except that iron was used as the working electrode. The potential change of the working electrode relative to the reference electrode during current application is shown in FIG. 11(2). The appearance of the working electrode after current application is shown in FIG. 13. A black deposit can be confirmed on the surface of the working electrode. From Raman spectroscopy and XRD analysis of the obtained deposit, it was confirmed that the deposit contained CaC2 and at least CaCl2 as an impurity. The mass ratio of the impurities in the deposit was sufficiently less than 50 mass%.

[0138] (Hydrocarbon production) The precipitate was hydrolyzed in the same manner as in Example 1. GC-MS analysis confirmed that the generated gas was C2H2. Furthermore, it was confirmed that ethane, ethylene, and hydrogen were by-produced. In addition, water, carbon dioxide, nitrogen, oxygen, and argon were generated as impurities. The mass ratio of C2H2 in the collected gas was sufficiently more than 50 mass%. The Faraday efficiency of C2H2 gas generation was calculated to be about 7.9%.

[0139] (Regeneration of metal oxides) A solidified material was obtained in the same manner as in Example 5. From the XRD analysis of the obtained solidified material, it was confirmed that the solidified material contained CaO as a main component.

[0140] [Example 12] (Manufacturing of metal carbides) NaCl, KCl, and CaCl2 were mixed so that NaCl / KCl / CaCl2 = 33.4 mol% / 11.6 mol% / 55.0 mol%, and vacuum dried at 200°C and 100 Pa or less for 24 hours or more. CaO was weighed out at 3 mol% relative to the total number of moles of NaCl, KCl, and CaCl2, and added to the above mixture to obtain a mixed salt. The mixed salt was placed in a Pyrex (trademark of Corning) container, set in an electric furnace, and heated to 550°C. In this way, a molten salt of NaCl-KCl-CaCl2-CaO was obtained.

[0141] By using this molten salt, the current density was reduced to -100mA / cm 2 A precipitate was obtained in the same manner as in Example 11, except that the temperature was maintained at 100° C. The potential change of the working electrode relative to the reference electrode during current application is shown in FIG. 14(1). From Raman spectroscopic analysis and XRD analysis of the obtained precipitate, it was confirmed that the precipitate contained CaC2 and at least CaCl2 as an impurity. The mass ratio of the impurities in the precipitate was sufficiently less than 50 mass%.

[0142] (Hydrocarbon production) The precipitate was hydrolyzed in the same manner as in Example 1. GC-MS analysis confirmed that the generated gas was C2H2. Furthermore, it was confirmed that ethane, ethylene, and hydrogen were by-produced. In addition, water, carbon dioxide, nitrogen, oxygen, and argon were generated as impurities. The mass ratio of C2H2 in the collected gas was sufficiently more than 50 mass%. The Faraday efficiency of C2H2 gas generation was calculated to be about 25%.

[0143] (Regeneration of metal oxides) A solidified material was obtained in the same manner as in Example 5. From the XRD analysis of the obtained solidified material, it was confirmed that the solidified material contained CaO as a main component.

[0144] [Example 13] (Manufacturing of metal carbides) Current density -200mA / cm 2A deposit was obtained in the same manner as in Example 12, except that the above condition was maintained. The potential change of the working electrode relative to the reference electrode during current application is shown in FIG. 14(2). The appearance of the working electrode after current application is shown in FIG. 15. A black deposit can be confirmed on the surface of the working electrode. From Raman spectroscopy and XRD analysis of the obtained deposit, it was confirmed that the deposit contained CaC2 and at least CaCl2 as an impurity. The mass ratio of the impurities in the deposit was sufficiently less than 50 mass%.

[0145] (Hydrocarbon production) The precipitate was hydrolyzed in the same manner as in Example 1. GC-MS analysis confirmed that the generated gas was C2H2. Furthermore, it was confirmed that ethane, ethylene, and hydrogen were by-produced. In addition, water, carbon dioxide, nitrogen, oxygen, and argon were generated as impurities. The mass ratio of C2H2 in the collected gas was sufficiently more than 50 mass%. The Faraday efficiency of C2H2 gas generation was calculated to be about 34%.

[0146] (Regeneration of metal oxides) A solidified material was obtained in the same manner as in Example 5. From the XRD analysis of the obtained solidified material, it was confirmed that the solidified material contained CaO as a main component.

[0147] [Example 14] (Manufacturing of metal carbides) Current density -300mA / cm 2 A precipitate was obtained in the same manner as in Example 12, except that the above-mentioned condition was maintained. The potential change of the working electrode relative to the reference electrode during current application is shown in FIG. 14(3). From the Raman spectroscopic analysis and XRD analysis of the obtained precipitate, it was confirmed that the precipitate contained CaC2 and at least CaCl2 as an impurity. The mass ratio of the impurities in the precipitate was sufficiently less than 50 mass%.

[0148] (Hydrocarbon production) The precipitate was hydrolyzed in the same manner as in Example 1. GC-MS analysis confirmed that the generated gas was C2H2. Furthermore, it was confirmed that ethane, ethylene, and hydrogen were by-produced. Other impurities generated included water, carbon dioxide, nitrogen, oxygen, and argon. The mass ratio of C2H2 in the collected gas was sufficiently more than 50 mass%. The Faraday efficiency of C2H2 gas generation was calculated to be about 22%.

[0149] (Regeneration of metal oxides) A solidified material was obtained in the same manner as in Example 5. From the XRD analysis of the obtained solidified material, it was confirmed that the solidified material contained CaO as a main component.

[0150] [Example 15] (Manufacturing of metal carbides) Current density -400mA / cm 2 A precipitate was obtained in the same manner as in Example 12, except that the above-mentioned condition was maintained. The potential change of the working electrode relative to the reference electrode during current application is shown in FIG. 14(4). From the Raman spectroscopic analysis and XRD analysis of the obtained precipitate, it was confirmed that the precipitate contained CaC2 and at least CaCl2 as an impurity. The mass ratio of the impurities in the precipitate was sufficiently less than 50 mass%.

[0151] (Hydrocarbon production) The precipitate was hydrolyzed in the same manner as in Example 1. GC-MS analysis confirmed that the generated gas was C2H2. Furthermore, it was confirmed that ethane, ethylene, and hydrogen were by-produced. In addition, water, carbon dioxide, nitrogen, oxygen, and argon were generated as impurities. The mass ratio of C2H2 in the collected gas was sufficiently more than 50 mass%. The Faraday efficiency of C2H2 gas generation was calculated to be about 8%.

[0152] (Regeneration of metal oxides) A solidified material was obtained in the same manner as in Example 5. From the XRD analysis of the obtained solidified material, it was confirmed that the solidified material contained CaO as a main component.

[0153] [Example 16] (Manufacturing of metal carbides) A precipitate was obtained in the same manner as in Example 13, except that a molten salt in which 7 mol% of CaCl2 was added to the total moles of NaCl, KCl, and CaCl2 was used as the NaCl-KCl-CaCl2-CaO molten salt.

[0154] The change in potential of the working electrode relative to the reference electrode when a current is applied is shown in Figure 16. The appearance of the working electrode after current is applied is shown in Figure 17. Black deposits can be seen on the surface of the working electrode. There was a large amount of deposit, and the working electrode had become larger overall due to the deposits. For reference, the original size of the working electrode is shown by a dashed line in Figure 17. The results of XRD analysis of the obtained deposits are shown in Figure 18. It was confirmed from Figure 18 that the deposits contained CaC2, and at least carbon and CaCl2 as impurities. The mass proportion of impurities in the deposits was well below 50 mass%.

[0155] (Hydrocarbon production) In the same manner as in Example 1, about 1 cc of water was added to the precipitate and hydrolyzed. GC-MS analysis confirmed that the generated gas was C2H2. Furthermore, it was confirmed that ethane, ethylene, and hydrogen were by-produced. Other impurities generated included water, carbon dioxide, nitrogen, oxygen, and argon. The mass ratio of C2H2 in the collected gas was sufficiently more than 50 mass%. The Faraday efficiency of C2H2 gas generation was calculated to be about 68%. It is considered that the dissolution of CaC2 precipitated on the electrode into the molten salt was suppressed by using a molten salt to which CaC2 had been added beforehand.

[0156] (Regeneration of metal oxide) 1.14 g of the aqueous solution remaining after the above hydrolysis was placed in an aluminum cup and heated at 80°C for 50 minutes, then heated at 200°C for 20 minutes to evaporate and dry. 0.156 g of the obtained black solid was placed in a nickel reaction tube, and heated to 500°C over 3 hours while flowing nitrogen gas at a flow rate of 500 ml / min, and held for 1 hour. The solid was cooled to room temperature while flowing nitrogen gas, and 0.100 g of the black solid was removed from the reaction tube. The obtained solid was quickly placed on a sample plate of an XRD and subjected to XRD analysis. The obtained results are shown in Figure 19. From Figure 19, it was confirmed that CaO, Fe as an electrode material, and NaCl as a component of the molten salt were contained.

[0157] Constant potential electrolysis was performed in Examples 1 to 9. Constant current electrolysis was performed in Examples 10 to 16. The desired carbide of the first metal was obtained by any of the electrolysis methods.

[0158] As shown in Example 16, the raw material metal oxide (CaO in Example 16) can be easily regenerated and recovered from the aqueous solution after hydrolysis. The recovered metal oxide can be reused as a raw material in the production of metal carbide. This allows the construction of a recycling system and provides an environmentally friendly process. [Industrial Applicability]

[0159] The production method of the present disclosure uses carbon dioxide, which causes global warming, as a carbon source, and is therefore useful in various fields, particularly in the environmental field.

Claims

[Claim 1] The main component is a carbide of a first metal, Further, a halide of a second metal other than the first metal is contained, the first metal includes at least one selected from the group consisting of alkali metals and alkaline earth metals, the second metal includes at least one selected from the group consisting of alkali metals and alkaline earth metals, The content of the first metal carbide is 80% by mass or more and 99% by mass or less of the metal carbide composition. Metal carbide compositions.

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