FUEL PRODUCTION METHOD AND FUEL PRODUCTION DEVICE

Abstract

A fuel manufacturing method for producing CH4 by repeatedly performing step 1 and step 2 in this order, wherein step 1 comprises: charging an electrochemical cell comprising a positive electrode having Ni2O3H on a surface, a negative electrode containing a hydrogen-absorbing alloy, and an aqueous KHCO3 solution by an electric potential control device to accumulate hydrogen in the hydrogen-absorbing alloy at the negative electrode, the electric potential control device being connected to each of the positive electrode and the negative electrode; and then stopping the charging, wherein step 2 comprises: supplying a raw material containing at least one of aqueous CO2 and KHCO3 solutions to the electrochemical cell to produce CH4 at the negative electrode;and then stopping the supply of the raw material, and wherein the electrochemical cell is a used nickel-metal hydride secondary battery;

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention

[0001] The present disclosure relates to a fuel manufacturing method and a fuel manufacturing apparatus. 2. Description of the state of the art

[0002] Starting with the Sabatier reaction, which produces methane and water from hydrogen and carbon dioxide in the presence of nickel as a catalyst, various techniques have been developed to produce fuels, such as methane and hydrogen, using electrochemical reactions.

[0003] For example, there is a known method for producing hydrocarbons by reacting hydrogen contained in a hydrogen-absorbing alloy used for the negative electrode of an alkaline secondary battery with carbon dioxide (Japanese Patent Application Publication No. H10-008280).

[0004] In addition, there is a known system that generates hydrogen gas from an aqueous solution through an electrochemical reaction using a platinum electrode (Japanese Patent Application Publication No. 2021-001403). OVERVIEW OF THE INVENTION

[0005] Excellent safety, heat balance, cost performance, etc. are required when fuels such as methane are produced by electrochemical reactions.

[0006] For example, when methane and oxygen are generated within the same cell through an electrochemical reaction, there is a risk that methane and oxygen may react, and therefore some measures such as collecting oxygen must be taken (JP H10-008280 A).

[0007] Furthermore, if expensive platinum is used for an electrode, it may be difficult to reduce fuel manufacturing costs (JP 2021-001403 A).

[0008] The problem to be solved by an embodiment of the present disclosure is to provide a fuel manufacturing method and a fuel manufacturing apparatus that ensure excellent safety in the production of fuels.

[0009] Means of solving the problem include the following aspects. 1. A fuel manufacturing method for producing CH4 by repeatedly performing steps 1 and 2, wherein step 1 comprises: charging an electrochemical cell comprising a positive electrode having Ni2O3H on a surface, a negative electrode containing a hydrogen-absorbing alloy, and an aqueous KHCO3 solution through an electric potential control device to cause the hydrogen-absorbing alloy to absorb hydrogen at the negative electrode, the electric potential control device being connected to each of the positive electrode and the negative electrode; and then terminating the charging, wherein step 2 comprises: supplying a raw material containing at least one of CO2 and KHCO3 aqueous solutions to the electrochemical cell to produce CH4 at the negative electrode;and then stopping the supply of the raw material, and wherein the electrochemical cell is a used nickel-metal hydride secondary battery; 2. The fuel manufacturing method according to 1, comprising, prior to step 1, performing pretreatment to form Ni2O3H on the surface of the positive electrode, wherein the pretreatment comprises repeatedly and alternately applying mutually different first electric potential and second electric potential to the positive electrode in a state where the positive electrode containing Ni is immersed in an alkaline aqueous solution. 3. The fuel production method according to 1. or 2., comprising performing step 3 when step 2 is performed, wherein step 3 comprises: collecting a K2CO3 solution prepared in step 2; mixing the K2CO3 solution with the air to prepare an aqueous KHCO3 solution; and supplying the prepared aqueous KHCO3 solution as the raw material to the electrochemical cell. 4. A fuel manufacturing apparatus comprising a first unit for generating CH4 and a second unit for supplying a raw material for CH4 to the first unit, wherein the first unit comprises: an electrochemical cell comprising a positive electrode having Ni2O3H on a surface, a negative electrode containing a hydrogen-absorbing alloy and generating CH4, and an aqueous KHCO3 solution; and an electric potential control device connected to each of the positive electrode and the negative electrode, and the second unit comprises: a mixer that mixes a K2CO3 solution collected from the first unit with the air; and a supply device that supplies an aqueous KHCO3 solution produced by the mixer as the raw material to the first unit. 5. The fuel manufacturing apparatus according to claim 4, wherein the electrochemical cell is a used nickel-metal hydride secondary battery.

[0010] According to the embodiment of the present disclosure, the fuel manufacturing method and the fuel manufacturing apparatus are provided which ensure excellent safety in the production of fuels. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Features, advantages and technical and industrial significance of exemplary embodiments of the invention will now be described with reference to the accompanying drawings, in which like reference numerals designate like elements, and wherein: Fig. 1 is an explanatory view for explaining the configuration of a first unit; Fig. Fig. 2 is an explanatory view for explaining the configuration of a fuel manufacturing apparatus; and Fig. 3 is an explanatory view for explaining the configuration of a second unit. DETAILED DESCRIPTION OF EMBODIMENTS

[0012] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.

[0013] In the present disclosure, when an embodiment is described with reference to drawings, the configuration of the embodiment is not limited to the configuration shown in the drawings. A component denoted by the same reference numeral in the drawings represents the same component. In the drawings, only some components may be denoted by reference numerals. The dimensional relationships in the drawings do not necessarily represent the actual dimensional relationships.

[0014] In the present disclosure, a numerical range indicated using “to” means a range including the numerical values ​​before and after “to” as the minimum value and the maximum value, respectively.

[0015] In the numerical ranges described step by step in the present disclosure, an upper limit or a lower limit described in one numerical range may be replaced with another upper limit or lower limit of another numerical range described step by step. In the numerical ranges described step by step in the present disclosure, an upper limit or a lower limit described in one numerical range may be replaced with a value shown in an example.

[0016] In the present disclosure, the word "step" includes not only an independent step, but also a step as long as the intended purpose of the step is achieved, even if the step cannot be clearly distinguished from other steps.

[0017] In the present disclosure, a combination of two or more preferred aspects is a preferred aspect.

[0018] In the present disclosure, unless otherwise specified, when there are plural kinds of substances corresponding to each component, the amount of each component means the total amount of the plural kinds of substances. Fuel production device

[0019] A fuel manufacturing apparatus of the present disclosure includes a first unit.

[0020] As in Fig. 1, the first unit 10 includes an electrochemical cell 11 and an electric potential control device 12. The electrochemical cell 11 comprises: a positive electrode 13 having Ni2O3H on a surface, a negative electrode 14 containing a hydrogen-absorbing alloy, and an aqueous KHCO3 solution 15 as an electrolyte.

[0021] The electrochemical cell 11 preferably further includes a collection port 16 for collecting produced CH4, K2CO3 solution, etc., and a supply port 17 for supplying a raw material for CH4 to be produced.

[0022] The electrochemical cell 11 is a used nickel-metal hydride secondary battery. The fuel production apparatus of the present disclosure uses the used nickel-metal hydride secondary battery as a flow reactor.

[0023] The positive electrode 13 has Ni2O3H on its surface. For the positive electrode 13, it is possible to use a positive electrode conventionally used for nickel-metal hydride secondary batteries, which contains Ni as the positive electrode active material. As described later, the positive electrode 13 with Ni2O3H on its surface can be obtained by performing a pretreatment step on the positive electrode 13 containing Ni.

[0024] For the negative electrode 14, it is possible to use a negative electrode conventionally used for nickel-metal hydride secondary batteries, which contains a hydrogen-absorbing alloy as the negative electrode active material. Types of hydrogen-absorbing alloy are not limited, and various types of hydrogen-absorbing alloy can be used as long as the hydrogen-absorbing alloy reversibly absorbs and releases hydrogen. Specifically, examples include mixed metals such as MmNi5 and highly active metals including Ni, Co, Mn, Al, etc. Note that Mm is a mixture of rare earth elements such as Ce and La.

[0025] The electrolyte contained in the electrochemical cell 11 is the aqueous KHCO3 solution 15. The aqueous KHCO3 solution 15 not only serves as an electrolyte but is also a raw material for CH4, since the aqueous KHCO3 solution 15 generates CH4 by reacting with hydrogen accumulated in the hydrogen-absorbing alloy of the negative electrode 14.

[0026] The electric potential control device 12 is a device for controlling the electric potential of the positive electrode 13 and the negative electrode 14 and has a function similar to the function of a so-called potentiostat.

[0027] It is possible to synthesize methane using the first unit 10. Since the first unit 10 uses a used nickel-hydrogen secondary battery, the first unit 10 is a device capable of reducing the cost of synthesizing methane.

[0028] The fuel production apparatus of the present disclosure may include a second unit in addition to the first unit 10.

[0029] As in Fig. 2, a fuel production apparatus 100 of the present disclosure includes the first unit 10 and a second unit 20. The first unit 10 produces CH4, and the second unit 20 supplies a raw material for CH4 to the first unit 10.

[0030] As in Fig. As shown in Figure 3, the second unit 20 includes: a mixer 21 that mixes a K2CO3 solution collected by the first unit 10 with the air, and a feeder 22 that feeds an aqueous KHCO3 solution prepared by the mixer 21 as the raw material to the first unit 10. The mixer 21 can capture carbon dioxide in the air.

[0031] The second unit 20 preferably further includes a supply port 23 for supplying the aqueous K2CO3 solution collected from the first unit 10 and the air to the mixer 21, and a discharge port 24 for supplying the prepared aqueous KHCO3 solution as the raw material from the supply device 22 to the first unit 10.

[0032] In the fuel manufacturing apparatus 100 of the present disclosure, the electrochemical cell 11 of the first unit 10 uses the used nickel-metal hydride secondary battery as a flow reactor, thereby not only reducing the cost of the apparatus but also contributing to a reduction in the cost associated with the disposal of the used nickel-metal hydride secondary battery.

[0033] Furthermore, the second unit 20 uses air as the raw material to be fed to the first unit 10 and also performs the function of capturing CO2 contained in the air. Consequently, there is no cost for using captured CO2, thereby contributing to a reduction in fuel production costs.

[0034] As described above, the fuel manufacturing apparatus 100 of the present disclosure is a fuel manufacturing apparatus capable of reducing fuel manufacturing costs. Fuel production processStep 1 and Step 2

[0035] A fuel production method of the present disclosure is a fuel production method for producing CH4 by repeatedly performing Step 1 and Step 2 described later in this order. In the fuel production method, Step 1 is performed first. Step 1

[0036] Step 1 is a step of charging the electrochemical cell 10 (see Fig. 1) by the electrical potential control device 12.

[0037] During charging, it is preferable to keep the current density substantially constant at 0 to 1 A / cm 2 and to perform constant current charging until an open circuit voltage (OCV) detected by a voltage sensor included in the electric potential control device 12 reaches 1.4 V.

[0038] Furthermore, the temperature of the electrolyte is preferably 50°C or lower. If the temperature of the electrolyte is detected, the electrochemical cell 10 may include a temperature sensor.

[0039] As described above, it is preferable to perform charging until the open circuit voltage (OCV) detected by the voltage sensor included in the electric potential control device 12 reaches 1.4 V, and then stop charging when it reaches 1.4 V.

[0040] During charging, hydrogen accumulates in the hydrogen-absorbing alloy at the negative electrode 14. O2 is generated at the positive electrode 13. The generated O2 is preferentially released into the atmosphere. Step 2

[0041] Step 2 is performed after step 1. Step 2 involves supplying a raw material containing at least one of aqueous CO2 and KHCO3 solutions to the electrochemical cell 10 to produce CH4 at the negative electrode 14. The produced CH4 is collected and used as fuel.

[0042] The aqueous CO2 or KHCO3 solution is the raw material for CH4 to be produced at the negative electrode 14. When CO2 is present as the raw material for CH4, a reduction reaction of CO2 occurs at the negative electrode 14, and CH4 is produced. Furthermore, when an aqueous KHCO3 solution is present as the raw material for CH4, a reaction represented by equation (1) below occurs using H absorbed by the negative electrode 14. 2KHCO3 + 8MH → CH4 + K2CO3 + 3H2O + 8M Equation (1)

[0043] Since there is no need to use CO2, an aqueous KHCO3 solution is preferred as the raw material for CH4 to be supplied to the electrochemical cell 10.

[0044] In step 2, the electric potential control device 12 applies no voltage to the electrochemical cell 10 and monitors the voltage of the positive electrode 13 and the negative electrode 14. It is preferable to supply the raw material until the voltage reaches 0.6 V while monitoring the voltage and generate CH4. It is preferable to stop supplying the raw material when the voltage reaches 0.6 V. This makes it possible to prevent an oxygen-absorbing alloy in the negative electrode 14 from being completely oxidized.

[0045] After step 2, loading is performed again in step 1 and then step 2 is performed. Thus, steps 1 and 2 can be performed repeatedly in this order.

[0046] Since the fuel production method of the present disclosure is configured as described above, O2 and CH4 are not produced simultaneously, and therefore this method is very safe, uses a thermodynamically favorable reaction, and can produce CH4 very efficiently. Pretreatment step

[0047] It should be noted that a pretreatment step for forming Ni2O3H on the surface of the positive electrode may be performed prior to step 1. This pretreatment step is preferably performed when the surface of the positive electrode is not coated with Ni2O3H, or when the amount of Ni2O3H coating on the surface is small when the surface is coated with Ni2O3H.

[0048] The pretreatment step involves repeatedly and alternately applying mutually different first electric potentials and second electric potentials to the positive electrode while the positive electrode containing Ni is immersed in an alkaline aqueous solution. The first electric potential is an electric potential at which Ni is tetravalent in a Ni-H2O system, and the second electric potential is an electric potential at which Ni is divalent in the Ni-H2O system.

[0049] The electric potential control device 12 can apply the first electric potential and the second electrode potential, controlled as described above.

[0050] For the formation of Ni2O3H on the surface of the positive electrode containing Ni by such a method, it is possible to apply a method described in Japanese Patent Application Publication No. 2022-45695.

[0051] It is possible to sufficiently form Ni2O3H on the surface of the positive electrode through the pretreatment step. Since Ni2O3 exhibits both corrosion resistance and electrical conductivity, the positive electrode 13 with Ni2O3H on the surface can be used stably for a long time. Step 3

[0052] Note that step 3 can be performed when step 2 is performed. Step 3 includes collecting a K2CO3 solution prepared in step 2; mixing the K2CO3 solution with the atmosphere to prepare an aqueous KHCO3 solution; and supplying the prepared aqueous KHCO3 solution as the raw material to the electrochemical cell. Step 3 is performed in unit 2 (see FIG. 2).

[0053] In step 3, the K2CO3 solution produced in step 2 is first collected. As shown by equation (1), K2CO3 is produced when CH4 is produced. K2CO3 is collected as a solution.

[0054] The collected K2CO3 solution is mixed with the air in the mixer 21 (see Fig. 3). At this time, a reaction of the following equation (2) takes place using CO2 in the air. Atmosphere (CO2) + K2CO3 + H2O → 2KHCO3 (2)

[0055] The produced aqueous KHCO3 solution can be used as raw material for CH4, as shown in equation (1), and is therefore fed to the electrochemical cell 10.

[0056] There is no need to use a separated compound such as CO2 in the feed stream in the fuel production process of the present disclosure (see Fig.2). Consequently, the fuel is produced in fewer steps. Furthermore, the heat generated in the Sabatier reaction, which produces CH4, is offset by heat absorption due to the decomposition of KHCO3, and this is an energy advantage.

[0057] Furthermore, since a used nickel-metal hydride secondary battery can be used as the electrochemical cell 10, it is possible to produce the fuel at a lower cost. Furthermore, O2 and CH4 are not produced simultaneously in this step.

[0058] Thus, the fuel manufacturing method of the present disclosure is a fuel manufacturing method that ensures excellent safety and can reduce fuel manufacturing costs.

[0059] In the following, the present disclosure is further described by experimental examples. Experimental Example 1

[0060] It was confirmed that the production of CH4 in step 2 was carried out as follows, using an aqueous KHCO3 solution as the electrolyte.

[0061] An electrochemical cell was used for testing. In this electrochemical cell, a fully charged 4 cm 2 MH battery negative electrode (LaNi5) was used as the negative electrode. Pt was used as the counter electrode and a voltage of 80 V was applied. Note that the current was 0.027 A / cm 2 fraud.

[0062] When the negative electrode was exposed to an aqueous saturated potassium carbonate solution (33.7 g / 100 mL), gas was produced from the negative electrode.

[0063] When the produced gas was collected in a package and analyzed by gas chromatography, it was confirmed that CH4 was produced. Experimental Example 2

[0064] Gas was generated from the negative electrode in the same manner as in Experimental Example 1, except that an aqueous KOH solution was used as the electrolyte.

[0065] When the produced gas was collected in a package and analyzed by gas chromatography, it was found that H2 and CO2 were produced, but the production of any fuel gas, including CH4, was not observed. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] JP 10-008280

[0003] JP 2021-001403 [0004, 0007] JP H10-008280 A

[0006] JP 2022-45695

[0050]

Claims

[1] A fuel production process for producing CH4 by repeatedly performing step 1 and step 2, wherein Step 1 comprises: charging an electrochemical cell having a positive electrode with Ni2O3H on a surface, a negative electrode containing a hydrogen-absorbing alloy, and an aqueous KHCO3 solution through an electric potential control device so that the hydrogen-absorbing alloy absorbs hydrogen at the negative electrode, wherein the electric potential control device is connected to both the positive electrode and the negative electrode, and then terminating the charging, Step 2 includes: feeding a raw material containing an aqueous CO2 and / or KHCO3 solution to the electrochemical cell to generate CH4 at the negative electrode, and then stopping the feeding of the raw material, and the electrochemical cell is a used nickel-metal hydride secondary battery. [2] A fuel manufacturing method according to claim 1, comprising, prior to step 1, performing a pretreatment for forming Ni2O3H on the surface of the positive electrode, the pretreatment comprising repeatedly and alternately applying a first electric potential and a second electric potential different from each other to the positive electrode in a state where the positive electrode containing Ni is immersed in an alkaline aqueous solution. [3] The fuel manufacturing method according to claim 1, comprising performing step 3 when step 2 is performed, wherein step 3 comprises: collecting a K2CO3 solution prepared in step 2, mixing the K2CO3 solution with air to prepare an aqueous KHCO3 solution, and supplying the prepared aqueous KHCO3 solution as the raw material of the electrochemical cell. [4] A fuel production apparatus comprising a first unit for producing CH4 and a second unit for supplying a raw material for CH4 to the first unit, wherein the first unit is an electrochemical cell comprising a positive electrode having Ni2O3H on a surface, a negative electrode containing a hydrogen-absorbing alloy and generating CH4, and an aqueous KHCO3 solution, and an electric potential control device connected to the positive electrode and the negative electrode, and the second unit comprises a mixer that mixes a K2CO3 solution collected by the first unit with air, and a feeding device that feeds an aqueous KHCO3 solution generated by the mixer as a raw material to the first unit. [5] The fuel manufacturing apparatus according to claim 4, wherein the electrochemical cell is a used nickel-metal hydride secondary battery.

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