Method for manufacturing carbon materials

Abstract

Provided is a method for producing a carbon material that can produce a carbon material from carbon dioxide by molten salt electrolysis with high current efficiency. 【Solution means】A method for producing a carbon material that produces a carbon material from carbon dioxide by molten salt electrolysis, the method for producing a carbon material satisfying the following formula 1. 92 kJ / mol < ΔG 1 <165 kJ / mol Formula 1 In the formula 1, ΔG 1 is obtained by the following formula 2. ΔG 1 = ΔG CO - ΔG C Formula 2 In the formula 2, ΔG CO is the standard reaction Gibbs energy (kJ / mol) in the reaction in which carbon monoxide is generated by the decomposition reaction of the metal carbonate contained in the molten salt, and ΔG C is the standard reaction Gibbs energy (kJ / mol) in the reaction in which carbon is generated by the decomposition reaction of the metal carbonate contained in the molten salt.

Description

[Technical Field]

[0001] This invention relates to a method for producing carbon materials. [Background technology]

[0002] Carbon dioxide, methane, nitrous oxide, and chlorofluorocarbons (CFCs) are known as greenhouse gases. Carbon dioxide accounts for the majority of greenhouse gas emissions. Currently, the majority of carbon dioxide emissions are due to industrial activities. Reducing carbon dioxide emissions into the atmosphere is necessary to prevent the progression of global warming.

[0003] In addition to reducing carbon dioxide emissions, methods for the effective use of carbon dioxide are being considered. These methods involve using carbon dioxide as a raw material and producing useful substances by reacting it.

[0004] Patent Document 1 discloses a method for fixing carbon in carbon dioxide by an electrochemical process using a molten salt (molten salt electrolysis). The carbon dioxide fixing method involves (a) carbonate ions (CO3 2- The process includes (b) preparing an electrolytic bath consisting of a molten salt containing (c) (a), (b) arranging a cathode and an anode in the electrolytic bath, and (c) blowing carbon dioxide into the electrolytic bath and applying a voltage between the cathode and anode that reduces carbonate ions to produce an electric current. The carbon dioxide becomes carbonate ions in the electrolytic bath, and carbon material is produced when the carbonate ions are reduced at the negative electrode. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Patent No. 5557434 [Overview of the project] [Problems that the invention aims to solve]

[0006] In molten salt electrolysis, carbon monoxide may be by-produced. In this case, the current consumed by the by-production of carbon monoxide is not efficient. The present invention has been made in view of the above circumstances, and an object thereof is to provide a method for producing a carbon material capable of producing a carbon material from carbon dioxide by molten salt electrolysis with high current efficiency.

Means for Solving the Problems

[0007] In order to solve the above problems, the present invention has the following aspects. [1] A method for producing a carbon material by producing a carbon material from carbon dioxide by molten salt electrolysis, the method for producing a carbon material satisfying the following formula 1. 92 kJ / mol < ΔG 1 < 165 kJ / mol Formula 1 In the formula 1, ΔG 1 is obtained by the following formula 2. ΔG 1 = ΔG CO - ΔG C Formula 2 In the formula 2, ΔG CO is the standard reaction Gibbs energy (kJ / mol) in the reaction in which carbon monoxide is generated by the decomposition reaction of the metal carbonate contained in the molten salt, and ΔG C is the standard reaction Gibbs energy (kJ / mol) in the reaction in which carbon is generated by the decomposition reaction of the metal carbonate contained in the molten salt. [2] The ΔG CO is obtained by the following formula 3, and the ΔG C is obtained by the following formula 4, the method for producing a carbon material according to [1]. ΔG CO = ΔH CO - TΔS CO Formula 3 In the formula 3, ΔH CO is the enthalpy (kJ / mol) of the reaction in which carbon monoxide is generated by the decomposition reaction of the metal carbonate contained in the molten salt represented by the following formula 3A, and ΔS COis the entropy (kJ / K / mol) of the reaction in which carbon monoxide is produced by the decomposition reaction of the metal carbonate contained in the molten salt, and T is the reaction temperature (K). 2M (2 / m) CO3 → 2CO+2M (2 / m) O+O2 type 3A In the above formula 3A, M is the metal and m is the valence of the metal. ΔG C =ΔH C -TΔS C formula 4 In the above equation 4, ΔH C ΔS is the enthalpy (kJ / mol) of the reaction in which carbon is produced by the decomposition reaction of the metal carbonate contained in the molten salt, represented by the following formula 4A, and ΔS C is the entropy (kJ / K / mol) of the reaction in which carbon is produced by the decomposition reaction of the metal carbonate contained in the molten salt, and T is the reaction temperature (K). M (2 / m) CO3 → C+ M (2 / m) O+O2 type 4A In equation 4A, M and m are the same as in equation 3A. [3] The method for producing a carbon material according to [1] or [2], wherein the molten salt comprises at least one selected from the group consisting of alkali metal salts and alkaline earth metal salts. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a method for producing carbon materials from carbon dioxide by molten salt electrolysis with high current efficiency. [Brief explanation of the drawing]

[0009] [Figure 1] This is a diagram showing a carbon material manufacturing apparatus according to one embodiment of the present invention. [Modes for carrying out the invention]

[0010] The embodiments of the present invention will be described in detail below, but the following description is merely one example of an embodiment of the present invention, and the present invention is not limited to these contents and can be modified and implemented within the scope of its gist.

[0011] ≪Method for manufacturing carbon materials≫ The carbon material manufacturing method of this embodiment is a method for manufacturing carbon material from carbon dioxide by molten salt electrolysis.

[0012] Figure 1 is a configuration diagram showing a carbon material manufacturing apparatus according to one embodiment of the present invention. The carbon material manufacturing apparatus 10 of this embodiment comprises a reaction vessel 1 for containing molten salt 2, a negative electrode 3, a positive electrode 4, a power supply 5 to which the negative electrode 3 and the positive electrode 4 are connected, and a carbon dioxide supply unit 6. The carbon material manufacturing apparatus 10 may also include an inert gas supply unit (not shown) for supplying an inert gas to the molten salt. Furthermore, the carbon material manufacturing apparatus 10 may also include a flow straightening plate (not shown) between the negative electrode 3 and the positive electrode 4 to stabilize the flow of the molten salt.

[0013] The method for producing the carbon material in this embodiment includes supplying carbon dioxide from a carbon dioxide supply unit 6 to the molten salt 2 in the reaction vessel 1, and applying a voltage between the negative electrode 3 and the positive electrode 4 to energize it. As a result, carbonate ions contained in the molten salt 2 are reduced by electrons, and the carbon material is generated on the negative electrode 3. The molten salt may also be stirred by supplying an inert gas to the molten salt from an inert gas supply unit.

[0014] The reactions at negative electrode 3 and positive electrode 4 are represented by equations (i) and (ii) below, respectively. Negative electrode: CO3 2- +4e - →C+3O2 formula (i) Positive electrode: 2O 2- →O2+4e - Formula (ii)

[0015] Furthermore, the reaction in molten salt 2 due to the supply of carbon dioxide is represented by the following equation (iii). CO2 (supplied from the carbon dioxide supply unit) + O 2- →CO32- Formula (iii)

[0016] Combining equations (i) to (iii) above, we obtain equation (iv) below. CO2→C+O2 formula (iv) In other words, in the carbon material manufacturing method of this embodiment, a reaction occurs in which carbon dioxide decomposes and carbon material and oxygen are produced.

[0017] In order for the reactions of equations (i) to (iii) above to proceed, carbonate ions (CO3) must be added to the molten salt at the start of the reaction. 2- ) and oxide ions (O 2- It is necessary that one or both of the following are included. Examples of carbonate ion sources include metal carbonates, which will be described later. Examples of oxide ion sources include metal oxides, which will be described later.

[0018] <molten salt> In the carbon material manufacturing method of this embodiment, a molten salt is used. Compared to using an aqueous solution, the molten salt has advantages such as higher carbon dioxide solubility and current efficiency, a faster reaction rate, and no need for a catalyst. Furthermore, compared to using an ionic liquid, the molten salt has advantages such as lower cost and a faster reaction rate.

[0019] Examples of molten salts include metal halides, metal oxides, and metal carbonates. Among these, metal halides are preferred. As for the metal, alkali metals and alkaline earth metals are preferred, with alkali metals being more preferred. Metal halides may be used individually or in combination of two or more types. Metal oxides may be used individually or in combination of two or more types. Metal carbonates may be used individually or in combination of two or more types.

[0020] Examples of alkali metal halides include LiF, NaF, KF, RbF, CsF, LiCl, NaCl, KCl, RbCl, CsCl, LiBr, NaBr, KBr, RbBr, CsBr, LiI, NaI, KI, RbI, and CsI, with LiCl, NaCl, KCl, RbCl, and CsCl being preferred, and LiCl, NaCl, and KCl being more preferred. Alkali metal halides may be used individually or in combination of two or more types.

[0021] Examples of alkaline earth metal halides include MgF2, CaF2, SrF2, BaF2, MgCl2, CaCl2, SrCl2, BaCl2, MgBr2, CaBr2, SrBr2, BaBr2, MgI2, CaI2, SrI2, and BaI2, with MgCl2, CaCl2, SrCl2, and BaCl2 being preferred. Alkaline earth metal halides may be used individually or in combination of two or more types.

[0022] Examples of alkali metal oxides include Li2O, Na2O, and K2O. Examples of alkaline earth metal oxides include MgO, CaO, and BaO. Alkali metal oxides may be used individually or in combination of two or more types. Alkaline earth metal oxides may be used individually or in combination of two or more types.

[0023] When using either alkali metal oxides or alkaline earth metal oxides, or both, the ratio of the total amount (moles) of alkali metal oxides and alkaline earth metal oxides used to the total amount (moles) of molten salt is preferably greater than 0 mol% and 50 mol%, more preferably greater than 0 mol% and 30 mol%, and even more preferably greater than 0 mol% and 20 mol%.

[0024] Examples of alkali metal carbonates include Li2CO3, Na2CO3, and K2CO3. Examples of alkaline earth metal carbonates include MgCO3, CaCO3, and BaCO3. Alkali metal carbonates may be used individually or in combination of two or more types. Alkaline earth metal carbonates may be used individually or in combination of two or more types.

[0025] When using either alkali metal carbonates or alkaline earth metal carbonates, or both, the ratio of the total amount (moles) of alkali metal carbonates and alkaline earth metal carbonates used to the total amount (moles) of molten salt is preferably 0 to 100 mol%, more preferably 0.5 to 50 mol%, and even more preferably 1 to 10 mol%.

[0026] <Negative electrode> The negative electrode material is preferably a material that is conductive at the reaction temperature. Examples of such materials include elemental metals such as nickel, iron, molybdenum, tantalum, tungsten, zinc, gallium, lead, and tin, alloys of such metals, carbon materials such as graphite, and elemental metals such as liquid metals and alloys of such metals.

[0027] <Positive electrode> The material for the positive electrode is preferably a material that can oxidize the oxide ion of formula (ii) above. Examples of such materials include carbon materials such as graphite, glassy carbon, diamond, and amorphous carbon, conductive ceramic electrodes, precious metals such as platinum and gold, and insoluble anodes such as nickel ferrite.

[0028] <ΔG 1 > The method for producing the carbon material of this embodiment satisfies the following equation 1. 92 kJ / mol < ΔG 1 <165kJ / mol Equation 1 In the above formula 1, ΔG 1 This can be calculated using equation 2 below.

[0029] ΔG 1 =ΔG CO -ΔG C formula 2 In the above equation 2, ΔG COThis is the standard reaction Gibbs free energy (kJ / mol) for the reaction in which carbon monoxide is produced by the decomposition reaction of the metal carbonate contained in the molten salt, and ΔG C This is the standard reaction Gibbs free energy (kJ / mol) for the reaction in which carbon is produced by the decomposition reaction of the metal carbonate contained in the molten salt. The decomposition reaction of metal carbonates contained in the molten salt is represented by equation 3A below. Furthermore, the reaction in which carbon is produced by the decomposition reaction of metal carbonates contained in the molten salt is represented by equation 4A below. 2M (2 / m) CO3 → 2CO+2M (2 / m) O+O2 type 3A In the above formula 3A, M is the metal and m is the valence of the metal.

[0030] M (2 / m) CO3 → C+ M (2 / m) O+O2 type 4A In equation 4A, M and m are the same as in equation 3A.

[0031] ΔG 1 The value is greater than 92 kJ / mol and less than 165 kJ / mol, preferably greater than 106 kJ / mol and less than 150 kJ / mol, and more preferably greater than 110 kJ / mol and less than 140 kJ / mol. That is, ΔG 1 It is preferable to control the reaction temperature so that it falls within the aforementioned range. ΔG 1 When ΔG is above the aforementioned lower limit, carbon monoxide by-production is suppressed, and the carbon yield tends to improve. As a result, the current efficiency tends to increase. 1 If the value is below the aforementioned upper limit, carbon production is more likely to be promoted.

[0032] ΔG CO The ΔG is preferably 400 kJ / mol or higher, more preferably 500 kJ / mol or higher, and even more preferably 600 kJ / mol or higher. CO The upper limit of ΔG is not particularly limited, but for example, it may be 1100 (kJ / mol) or less. CO It is preferable to control the reaction temperature so that the value is equal to or greater than the lower limit. ΔG CO When the value is above the aforementioned lower limit, carbon monoxide by-production is suppressed, and the carbon yield tends to improve. As a result, the current efficiency tends to increase.

[0033] ΔG C The ΔG is preferably 600 kJ / mol or less, more preferably 550 kJ / mol or less, and even more preferably 520 kJ / mol or less. C The lower limit is not particularly limited, but for example, it may be 0 (kJ / mol) or greater. That is, ΔG C It is preferable to control the reaction temperature so that the value is below the upper limit mentioned above. ΔG C If the value is below the aforementioned upper limit, carbon production is more likely to be promoted.

[0034] Note that ΔG CO and ΔG C These can be calculated using equations 3 and 4 below, respectively. ΔG CO =ΔH CO -TΔS CO formula 3 In the above equation 3, ΔH CO ΔS is the enthalpy (kJ / mol) of the reaction in which carbon monoxide is produced by the decomposition reaction of the metal carbonate contained in the electrolytic salt represented by formula 3A, and ΔS CO is the entropy (kJ / K / mol) of the reaction in which carbon monoxide is produced by the decomposition reaction of the metal carbonate contained in the molten salt, and T is the reaction temperature (K).

[0035] ΔG C =ΔH C -TΔS C formula 4 In the above equation 4, ΔH C ΔS is the enthalpy (kJ / mol) of the reaction in which carbon is produced by the decomposition reaction of the metal carbonate contained in the molten salt represented by formula 4A, and ΔS C is the entropy (kJ / K / mol) of the reaction in which carbon is produced by the decomposition reaction of the metal carbonate contained in the molten salt, and T is the reaction temperature (K).

[0036] ΔH CO ΔS CO ΔH C , and ΔS C This value is determined by the type of metal in the metal carbonate. That is, ΔG CO ΔG C , and ΔG 1 This value is determined by the type of metal carbonate (i.e., the composition of the molten salt) and the reaction temperature. That is, ΔG CO ΔG C , and ΔG 1 This adjustment can be carried out by controlling either the composition of the molten salt or the reaction temperature, or both.

[0037] The following describes, as an example, how to determine the reaction temperature when only LiCl is used as the molten salt. ΔH of Li2CO3 CO and ΔS CO These are 975 (kJ / mol) and 0.41 (kJ / K / mol), respectively. Therefore, from equation 3 above, ΔG CO Calculating this gives 975 - 0.40 × T(K). Also, the ΔH of Li2CO3 C and ΔS C These are 599 (kJ / mol) and 0.11 (kJ / K / mol), respectively. Therefore, from equation 4 above, ΔG C Calculating this gives 599 - 0.11 × T(K). The obtained ΔG CO and ΔG C From the above equation 2, ΔG 1 Calculating this gives us 376 - 0.29 × T(K). Therefore, we should select a reaction temperature where 376 - 0.29 × T(K) is within the range of 92 to 165 kJ / mol.

[0038] (When containing two or more types of molten salts) ΔG when two or more types of molten salts are included 1 The method for determining ΔG will be explained. Even if two or more types of molten salts are included, if only one type of metal is included in the molten salt, ΔG can be calculated using the method described above. 1can be obtained. Examples of such molten salts include those containing LiCl and Li₂CO₃. In this case, as described above, the ΔH of Li₂CO₃ CO and ΔS CO are obtained, and ΔG CO and ΔG C are obtained from the above formulas 3 and 4, and ΔG 1 is obtained from the above formula 2.

[0039] Next, the method for obtaining ΔG 1 when there are two or more metal species contained in the molten salt will be described. Hereinafter, it will be described separately for the case where the molten salt is only a carbonate and the case where the molten salt contains a salt other than a carbonate.

[0040] [When the molten salt is only a carbonate] Let the number of metal species contained in the molten salt be n, and assume that the metal species of M 1 ~M n are contained. In this case, for M 1 ~M n , ΔG C is obtained from the above formula 4. From the obtained ΔG C , the electrolysis voltage is obtained by the following formula 5. E C =(ΔG C -RTln[M t (2 / mt) CO₃]) / 4F Formula 5 In the above formula 5A, E C is the electrolysis voltage, R is the gas constant (kJ / (mol·K)), T is the reaction temperature (K), M t is any one of the metal species contained in M 1 ~M n . mt is the valence of M t . F is the Faraday constant (C / mol). [] means the activity of M t (2 / mt) CO₃ described therein. According to the above formula 5, for all of M 1 ~M n , E C is obtained, and for the metal species for which E C becomes the smallest, ΔG COFrom equation 4 above, ΔG C We find the value of ΔG obtained. CO and ΔG C From the above equation 2, ΔG 1 We seek.

[0041] [When the molten salt contains salts other than carbonates] Let x be the number of metal species contained in the molten salt, M 1 ~M x Assume that the following metal species are present. Also, assume that the molten salt is a halide. In this case, carbonate may also be present. In this case, M 1 ~M x Any two types of M included y and M z Regarding the standard reaction Gibbs free energy (kJ / mol) at the reaction temperature in equation 6A below, ΔG M We seek. M y (2 / my) CO3+(2 / mz)M z X mz →M z (2 / mz) CO3+(2 / my)M y X my formula 6A In the above formula 6A, X is a halogen atom, and M y and M z M 1 ~M x These are any two types of metals included in M. y The valence of is M, and mz is M z It is the valence of [the object]. M 1 ~M n ΔG in all combinations M We find ΔG M The metal species for which M is negative z1 Let's assume that ΔG M The M that is smallest in absolute value z1 M is a metal species for y1 Select the combination. ΔG at this time M ΔG M(min) Let's assume that.

[0042] ΔGM(min) The relationship between the equilibrium constant and the equilibrium constant is expressed by equation 6B below. ΔG M(min) =RTln(K) Equation 6B In equation 6B above, R is the gas constant (kJ / (mol·K)), T is the reaction temperature (K), and K is the equilibrium constant in equation 6A above. K is expressed in equation 6C below.

[0043] K={[M z1 (2 / mz1) CO3 [M] y1 X my1 ] (2 / my1)} / {[M y1 (2 / my1) CO3 [M] z1 X mz1 ] (2 / mz1)} Formula 6C In the above formula 6C, X, M y1 M z1 As stated above, my1 is M in equation 6A above. y to M y1 When this is the case, my is and mz1 is, in the above equation 6A, M z to M z1 This is the mz when [ ] is set to [ ]. [ ] represents the activity of each substance listed within the brackets. Below, [M y1 (2 / my1) CO3 and [M z1 (2 / mz1) Assume that CO3 is the same.

[0044] From the initial concentration in the molten salt, [M y1 X my1 ] (2 / my1) / [M z1 X mz1 ] (2 / mz1) Calculate and compare with K. K>[M y1 X my1 ] (2 / my1) / [M z1 X mz1 ] (2 / mz1) In the case of M y (2 / my) CO3+(2 / mz)M z X mz →M z (2 / mz) CO3+(2 / my)My X my The reaction proceeds in the direction of M z1 Regarding this, from equation 3 above, ΔG CO From equation 4 above, ΔG C We find the value of ΔG obtained. CO and ΔG C From the above equation 2, ΔG 1 We seek. K<[M y1 X my1 ] (2 / my1) / [M z1 X mz1 ] (2 / mz1) In the case of M z (2 / mz) CO3+(2 / my)M y X my →M y (2 / my) CO3+(2 / mz)M z X mz The reaction proceeds in the direction of M y1 Regarding this, from equation 3 above, ΔG CO From equation 4 above, ΔG C We find the value of ΔG obtained. CO and ΔG C From the above equation 2, ΔG 1 We seek. K=[M y1 X my1 ] (2 / my1) / [M z1 X mz1 ] (2 / mz1) In the case of M y1 and M z1 Let be a carbonate, and from equation 5 above, the electrolytic voltage is E C Find E C The smaller metal type (M y1 Or M z1 Regarding ), from equation 3 above, ΔG CO From equation 4 above, ΔG C We find the value of ΔG obtained. CO and ΔG C From the above equation 2, ΔG 1 We seek.

[0045] If the molten salt is an oxide, the same calculation as above can be performed in equation 7A below. In this case, carbonates may also be included as part of the molten salt. M y (2 / my) CO3+ M z (2 / mz) O→M z (2 / mz) CO3+ M y (2 / my) Type O 7A In this case, the initial concentration in the molten salt is calculated as follows: [M y1 (2 / my1) O] / [M z1 (2 / mz1) Calculate O and compare it with K. Note that K = [M y1 (2 / my1) O] / [M z1 (2 / mz1) In the case of O], M is the same as above. y1 and M z Let be a carbonate, and from equation 5 above, the electrolytic voltage is E C Find E C The smaller metal type (M y1 Or M z1 Regarding ), from equation 3 above, ΔG CO From equation 4 above, ΔG C We find the value of ΔG obtained. CO and ΔG C From the above equation 2, ΔG 1 We seek.

[0046] If the molten salt is an oxide or halide, the same calculation as above can be performed in equation 8A below. In this case, carbonates may also be included as part of the molten salt. M y (2 / my) CO3+(2 / mz)M z X mz +M z (2 / mz) O→M z (2 / mz) CO3+(2 / my)M y X my +M y (2 / my) O formula 8A In this case, the initial concentration in the molten salt is calculated as follows: {[My1 (2 / my1) O][M y1 X my1 ] (2 / my1)} / {[M z1 (2 / mz1) O][M z1 X mz1 ] (2 / mz1) Calculate} and compare it with K. Note that K = {[M y1 (2 / my1) O][M y1 X my1 ] (2 / my1)} / {[M z1 (2 / mz1) O][M z1 X mz1 ] (2 / mz1) In the case of}, M is the same as above. y1 and M z Let be a carbonate, and from equation 5 above, the electrolytic voltage is E C Find E C The smaller metal type (M y1 Or M z1 Regarding ), from equation 3 above, ΔG CO From equation 4 above, ΔG C We find the value of ΔG obtained. CO and ΔG C From the above equation 2, ΔG 1 We seek.

[0047] <Electrolytic conditions other than reaction temperature> The reaction atmosphere should preferably be moisture-free to prevent a decrease in electrolysis efficiency and deterioration of the electrolytic bath. Furthermore, since oxygen can also cause deterioration, an inert gas or carbon dioxide gas atmosphere is preferred. Examples of inert gases include helium, nitrogen, and argon. The reaction pressure can be atmospheric pressure.

[0048] The electrolysis voltage should be set to a potential at which carbonate ions are reduced. That is, it is preferable to set the voltage to a potential lower than the potential at which carbonate ions are reduced, and higher than the potential at which metals in the molten salt do not precipitate. The electrolysis voltage is preferably 1.2 to 8V, more preferably 1.4 to 6V, and even more preferably 1.6 to 4V. If the electrolysis voltage exceeds the upper limit, metals in the molten salt may precipitate. If the electrolysis voltage is below the lower limit, carbon is less likely to precipitate.

[0049] The reaction represented by formula (iii) proceeds at the gas-liquid interface. Therefore, it is preferable to increase the contact area between the supplied carbon dioxide and the molten salt. A preferred method for increasing the contact area is to reduce the size of the carbon dioxide bubbles.

[0050] <Carbon material recovery> The generated carbon material adheres to the negative electrode. The carbon material may also be dispersed in the molten salt. The carbon material dispersed in the molten salt can be separated by solid-liquid separation. After that, washing is preferable. Furthermore, it is preferable to peel off and wash the carbon material adhering to the negative electrode. Examples of peeling and washing include washing using ultrasound in water and washing with an acidic aqueous solution. Hydrochloric acid can be used as the acidic aqueous solution.

[0051] <Carbon materials> Examples of carbon materials produced by the carbon production method of this embodiment include amorphous carbon materials, graphite carbon materials, carbon nanotube carbon materials, carbon nanofiber carbon materials, graphene carbon materials, and diamond carbon materials. [Examples]

[0052] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0053] [Example 1] 300 g of a eutectic salt of LiCl and KCl was added to the reaction vessel as the molten salt. The composition of the eutectic salt was LiCl:KCl = 58.5:41.5 in molar ratio. The temperature in the reaction vessel was heated to 500°C, and the molten salt was melted under atmospheric pressure in an argon gas atmosphere. 15.2 g of potassium carbonate (2 mol%) was added to the reaction vessel, and argon gas was introduced to create an inert atmosphere. Note that in the above formula 6A, M z1 =Li, M y1 ΔG when =K M The result was negative. The obtained ΔG M From this, the equilibrium constant was determined using equations 6B and 6C. As a result, K > [M y1 X my1 ] (2 / my1) / [M z1 X mz1 ] (2 / mz1) Therefore, Li was selected as M in the above formulas 3A and 4A. A nickel plate measuring 20 mm x 20 mm with a thickness of 0.1 mm was used as the negative electrode. A graphite rod was used as the positive electrode. Electrolysis was performed for 1 hour at an applied potential of 0.4 V. After the electrolysis was completed, the generated carbon material was removed by ultrasonic cleaning of the negative electrode, and the obtained carbon material was sequentially washed with 1 M hydrochloric acid and water, and dried at 80°C for 24 hours to obtain the carbon material. Table 1 shows the reaction temperature, applied potential, electrolysis voltage, amount of electricity, and ΔG in Equation 2. CO ΔG C , and ΔG 1 This shows the carbon material yield and current efficiency. Current efficiency is the ratio of the actual carbon material yield to the theoretical carbon (C) yield that would be produced if all the electricity listed in Table 1 were used in the reaction represented by equation (i), expressed as a percentage. High current efficiency indicates that side reactions are suppressed. In Example 1, carbon dioxide was not supplied, but due to the short reaction time, carbon material was generated by carbonate ions derived from potassium carbonate. If the reaction is to be carried out for a longer period, carbon dioxide should be supplied.

[0054] [Examples 2-6] The reaction was carried out in the same manner as in Example 1, except that the reaction temperature, applied potential, and amount of electricity were changed as shown in Table 1.

[0055] [Comparative Examples 1-6] The reaction was carried out in the same manner as in Example 1, except that the reaction temperature, applied potential, and amount of electricity were changed as shown in Table 1.

[0056] [Table 1] As shown in Table 1, ΔG 1 Examples 1-6, where the current was greater than 92 kJ / mol and less than 165 kJ / mol, showed high current efficiency. On the other hand, ΔG 1 Comparative Examples 1-3, where the current concentration was 165 kJ / mol or higher, and Comparative Examples 4-6, where it was 92 kJ / mol or lower, showed low current efficiency. [Industrial applicability]

[0057] The present invention's method for producing carbon materials is useful because it allows for the production of carbon materials from carbon dioxide by molten salt electrolysis with high current efficiency. [Explanation of Symbols]

[0058] 1…Reaction vessel, 2…Molten salt, 3…Negative electrode, 4…Positive electrode, 5…Power supply, 6…Carbon dioxide supply unit, 10…Carbon material manufacturing equipment

Claims

1. A method for producing carbon materials, which involves producing carbon materials from carbon dioxide by molten salt electrolysis, A method for producing a carbon material that satisfies the following equation 1. 92kJ / mol<ΔG １ <165 kJ / mol Equation 1 In the above formula 1, ΔG １ This can be calculated using equation 2 below. ΔG １ = ΔG ＣＯ −ΔG Ｃ Equation 2 In the above equation 2, ΔG ＣＯ This is the standard reaction Gibbs free energy (kJ / mol) in the reaction in which carbon monoxide is produced by the decomposition reaction of the metal carbonate contained in the molten salt, and ΔG Ｃ This is the standard reaction Gibbs free energy (kJ / mol) for the reaction in which carbon is produced by the decomposition reaction of the metal carbonate contained in the molten salt.

2. The above ΔG ＣＯ is obtained by the following formula 3, and the above ΔG Ｃ is obtained by the following formula 4, the method for producing a carbon material according to claim 1. ΔG ＣＯ = ΔH ＣＯ - TΔS ＣＯ Equation 3 In the above formula 3, ΔH ＣＯ ΔS is the enthalpy (kJ / mol) of the reaction in which carbon monoxide is produced by the decomposition reaction of the metal carbonate contained in the molten salt, represented by the following formula 3A, and ＣＯ is the entropy (kJ / K / mol) of the reaction in which carbon monoxide is produced by the decomposition reaction of the metal carbonate contained in the molten salt, and T is the reaction temperature (K). 2M （２／ｍ） CO ３ → 2CO + 2M （２／ｍ） O + O ２ Formula 3A In the above formula 3A, M is the metal and m is the valence of the metal. ΔG Ｃ = ΔH Ｃ - TΔS Ｃ Equation 4 In the above formula 4, ΔH Ｃ ΔS is the enthalpy (kJ / mol) of the reaction in which carbon is produced by the decomposition reaction of the metal carbonate contained in the molten salt, represented by the following formula 4A, and ΔS Ｃ is the entropy (kJ / K / mol) of the reaction in which carbon is produced by the decomposition reaction of the metal carbonate contained in the molten salt, and T is the reaction temperature (K). M （２／ｍ） CO ３ → C + M （２／ｍ） O + O ２ Formula 4A In formula 4A, M and m are the same as in formula 3A.

3. The method for producing a carbon material according to claim 1 or 2, wherein the molten salt comprises at least one selected from the group consisting of alkali metal salts and alkaline earth metal salts.

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