JP5816803B2 - Methanol generating apparatus, method for generating methanol, and electrode for methanol generation - Google Patents

Description

  The present disclosure relates to a methanol generator, a method of generating methanol, and an electrode for methanol generation.

  Patent Documents 1 to 4 and Non-Patent Document 1 disclose methods for reducing carbon dioxide.

  Patent Documents 1 and 2 disclose a method for reducing carbon dioxide using a gas phase reaction at a high temperature.

  Patent Document 3 discloses a method for electrochemically reducing carbon dioxide using a phthalocyanine-based metal complex.

  Patent Document 4 and Non-Patent Document 1 disclose a method of electrochemically reducing carbon dioxide using metallic copper or copper halide.

JP 2000-254508 A JP-A-1-313313 Japanese Patent Laid-Open No. 1-205088 JP 2004-176129 A

Y. Hori, “Modern Aspects of Electrochemistry”, 2008, vol. 42, p. p. 89-189

  The methods disclosed in Patent Literature 1 and Patent Literature 2 have problems such as a large amount of energy consumption and secondary generation of carbon dioxide.

  In the method disclosed in Patent Document 3, the reaction product is mainly carbon monoxide or formic acid, and there is a problem that alcohols cannot be generated.

  In the methods disclosed in Patent Document 4 and Non-Patent Document 1, generation of methanol was not recognized.

  The objective of this indication provides the novel methanol production | generation apparatus which produces | generates methanol, the method of producing | generating methanol, and the electrode for methanol production.

A methanol generator according to the present disclosure is a methanol generator that generates methanol by reducing carbon dioxide, and a tank for containing an electrolytic solution containing carbon dioxide, and the tank in contact with the electrolytic solution. Cu _1-x Au _x (0 <x <1) installed inside the tank
A cathode electrode having a region of the anode, an anode electrode having a metal or metal compound region disposed in contact with the electrolyte, and the cathode electrode having a negative potential with respect to the potential of the anode electrode And an external power supply for applying a voltage.

  The methanol production | generation apparatus which concerns on this indication can improve the production | generation efficiency of methanol.

It is the schematic which shows the methanol production | generation apparatus which concerns on this indication. It is the schematic which shows the methanol production | generation apparatus which concerns on this indication. It is the schematic which shows the methanol production | generation apparatus which concerns on this indication. It is a graph which shows the result of Example 1, the comparative example 1, and the comparative example 2. FIG. It is a graph which shows the result of Examples 1-7, the comparative example 1, and the comparative example 2. FIG.

A methanol generator according to a first aspect of the present disclosure is a methanol generator that generates methanol by reducing carbon dioxide, and a tank for containing an electrolytic solution containing carbon dioxide; and the electrolytic solution A cathode electrode having a region of Cu _1-x Au _x (0 <x <1), which is placed in contact with the electrolyte, and a metal or metal An anode electrode having a compound region; and an external power source for applying a voltage so that the cathode electrode has a negative potential with respect to the potential of the anode electrode.

  According to the first aspect, methanol can be obtained as the carbon dioxide reduction product.

In the methanol generation apparatus according to the second aspect of the present disclosure, in the first aspect, the Cu _1-x Au _x (0 <x <1) may be a solid solution or an intermetallic compound of Cu and Au.

  According to the second aspect, Cu and Au mixed at the atomic level promote the methanol formation reaction, and methanol can be obtained as a carbon dioxide reduction product.

  In the methanol generator according to the third aspect of the present disclosure, in the first aspect, the value of x may be 0.005 or more and 0.05 or less.

  According to the said 3rd aspect, the production | generation reaction of methanol is accelerated | stimulated by mixing Cu and Au with an appropriate density, and methanol can be obtained as a carbon dioxide reduction product.

  In the methanol generator according to the fourth aspect of the present disclosure, in the first aspect, the anode electrode may be carbon, platinum, gold, silver, copper, titanium, iridium oxide, or an alloy thereof.

  According to the said 4th aspect, it is suitable for the oxygen production | generation reaction on an anode electrode simply as an anode electrode which has in a tank inside.

  In the methanol generator according to the fifth aspect of the present disclosure, in the first aspect, the electrolytic solution may be an aqueous potassium chloride solution or an aqueous sodium chloride solution.

  According to the said 5th aspect, as electrolyte solution accommodated in the inside of a tank, it is suitable as simple and methanol-forming electrolyte solution.

  In the methanol generator according to the sixth aspect of the present disclosure, the absolute value of the voltage may be 2.5 V or more in the first aspect.

  According to the sixth aspect, by applying a potential sufficient for methanol production to the cathode electrode, the methanol production reaction is promoted, and methanol can be obtained as a carbon dioxide reduction product.

  The methanol generator according to a seventh aspect of the present disclosure is the above first aspect, wherein the methanol generator is further installed in the tank so as to be in contact with the electrolytic solution, and has a region of Ag / AgCl. The external power supply may have a potential of the cathode electrode of −1.7 V or less with respect to the potential of the reference electrode.

  According to the said 7th aspect, the production | generation reaction of methanol is accelerated | stimulated by giving a sufficient electric potential for methanol production | generation to a cathode electrode, and methanol can be obtained as a carbon dioxide reduction product.

  A methanol generator according to an eighth aspect of the present disclosure is the methanol generator according to the first aspect, wherein the methanol generator further includes a tank for accommodating the first electrolytic solution containing the carbon dioxide, You may provide the solid electrolyte membrane isolate | separated into the anode tank for accommodating a 2nd electrolyte solution.

  According to the said 8th aspect, the spreading | diffusion to the anode electrode of the methanol produced | generated on the cathode electrode can be prevented, and the oxidation reaction of methanol on an anode electrode can be prevented.

  In the methanol generator according to the ninth aspect of the present disclosure, in the eighth aspect, the first electrolytic solution is an aqueous potassium chloride solution or an aqueous sodium chloride solution, and the second electrolytic solution is an aqueous potassium bicarbonate solution, an aqueous hydrogen carbonate solution. It is good also as sodium aqueous solution or potassium sulfate aqueous solution.

  According to the ninth aspect, the first electrolytic solution is convenient and suitable as an electrolytic solution for producing methanol as the electrolytic solution housed in the cathode chamber. Further, the second electrolytic solution is suitable as an electrolytic solution that is contained in the anode tank and is simple and suitable for generating oxygen.

The method for producing methanol according to the tenth aspect of the present disclosure is a method for producing methanol using an apparatus for producing methanol, which has the following steps: Step of preparing a methanol production device having: (A) A tank, a cathode electrode, and an anode electrode, wherein the cathode electrode has a region of Cu _1-x Au _x (0 <x <1), and the anode electrode is a metal or a metal compound The electrolytic solution is held in the tank, the cathode electrode is in contact with the electrolytic solution, the anode electrode is in contact with the electrolytic solution, and the electrolytic solution is the carbon dioxide. And by applying a voltage so that the cathode electrode has a negative potential with respect to the potential of the anode electrode and reducing carbon dioxide contained in the electrolyte solution, Step (b) of producing methanol on the cathode electrode.

  According to the tenth aspect, a novel method for producing methanol as a carbon dioxide reduction product is provided.

  In the method for producing methanol according to the eleventh aspect of the present disclosure, in the step (b) of the tenth aspect, the methanol production apparatus may be placed at room temperature and atmospheric pressure.

  According to the eleventh aspect, methanol is obtained as a carbon dioxide reduction product without being installed in a special environment.

A methanol generation electrode according to a twelfth aspect of the present disclosure is a methanol generation electrode used in a methanol generation apparatus that generates methanol by reducing carbon dioxide, and includes Cu _1-x Au _x (0 <x < You may have the area | region of 1).

  According to the twelfth aspect, a novel electrode that generates methanol as a carbon dioxide reduction product is provided.

  Hereinafter, a methanol generator and a method for generating methanol according to an embodiment of the present disclosure will be described with reference to the drawings.

(Embodiment)
(Equipment for producing methanol)
FIG. 1A to FIG. 1C are schematic views of a methanol generator that generates methanol by reducing carbon dioxide.

  FIG. 1A is a basic configuration diagram of a methanol generator 10 for generating methanol according to the present disclosure. The methanol generator 10 includes a tank 11, a cathode electrode 12, an anode electrode 13, and an external power source 14. As shown in FIG. 1A, the methanol generator 10 may have a voltage measuring device 15 and a current measuring device 16 for monitoring the state of the carbon dioxide reduction reaction.

  The electrolytic solution 17 is held inside the tank 11. The electrolyte solution 17 is, for example, a potassium chloride aqueous solution, a sodium chloride aqueous solution, a sodium hydrogen carbonate aqueous solution, or a sodium sulfate aqueous solution having a predetermined concentration. In particular, an aqueous potassium chloride solution or an aqueous sodium chloride solution is preferred. The concentration of the electrolytic solution 17 is preferably 0.05 mol / L or more and 5.0 mol / L or less.

The cathode electrode 12 has CuAu, which is an alloy of copper (hereinafter described as “Cu”) and gold (hereinafter described as “Au”), on the surface. Here, the composition formula of CuAu is Cu _1-x Au _x (where 0 <x <1).

CuAu is preferably a state of solid solution or intermetallic compound. Here, the solid solution means a solid phase in which the entire alloy is uniform as a result of the elements constituting the alloy being dissolved at the atomic level. Further, the intermetallic compound refers to a compound in which elements constituting the alloy are regularly arranged at the atomic level.

As a method for producing the solid solution CuAu, for example, a vacuum melting method or an arc melt method is used. When the composition ratio of Cu and Au constituting CuAu is expressed as Cu _1-x Au _x , the value of x is preferably in the range of 0.001 to 0.10. In particular, the value of x is preferably in the range of 0.005 to 0.05.

  CuAu constituting the cathode electrode 12 may contain elements other than Cu and Au to the extent that the crystal structure of CuAu is not disturbed. Specifically, CuAu may contain impurities at a level normally included in the process of preparing CuAu by a vacuum melting method or an arc melt method. The crystal structure of CuAu can be evaluated, for example, by performing X-ray diffraction measurement.

Although the cathode electrode 12 may be comprised only by CuAu, the laminated structure with the base material for hold | maintaining CuAu may be sufficient. The cathode electrode 12 may be formed, for example, by forming a thin film of CuAu on a base material such as glass or glassy carbon (registered trademark) or by supporting a large number of particulate CuAu on a conductive substrate. The configuration of the cathode electrode 12 is not particularly limited as long as it is in the form of a cathode electrode having an action of reducing carbon dioxide and generating methanol.

  The cathode electrode 12 is in contact with the electrolytic solution 17. More precisely, CuAu provided in the cathode electrode 12 contacts the electrolytic solution 17. As long as CuAu is in contact with the electrolytic solution 17, only a part of the cathode electrode 12 needs to be immersed in the electrolytic solution 17.

  The anode electrode 13 has a conductive material. The conductive substance is, for example, carbon, platinum, gold, silver, copper, titanium, iridium oxide, or an alloy thereof. The material of the conductive substance is not particularly limited as long as the conductive substance is not decomposed by its own oxidation reaction.

  The oxidation reaction of water at the anode electrode 13 and the reduction reaction of carbon dioxide at the cathode electrode 12 are separate and independent reaction systems, and the reaction occurring on the cathode electrode 12 side is not affected by the material of the anode electrode 13.

  The anode electrode 13 is also in contact with the electrolytic solution 17. More precisely, the conductive material provided in the anode electrode 13 is in contact with the electrolytic solution 17. As long as the conductive substance is in contact with the electrolytic solution 17, only a part of the anode electrode 13 needs to be immersed in the electrolytic solution 17.

  As shown in FIG. 1A, the methanol generator 10 may have a pipe 18 in the tank 11. Carbon dioxide is supplied to the electrolyte solution 17 through the pipe 18. One end of the tube 18 is immersed in the electrolytic solution 17.

  As shown in FIG. 1B, the methanol generator 100 may be provided with a solid electrolyte membrane 19 inside the tank 11. As a result, the solid electrolyte membrane 19 divides the electrolyte solution 17 into an anode-side electrolyte solution 17L and a cathode-side electrolyte solution 17R. In other words, the solid electrolyte membrane 19 separates the tank 11 into a cathode tank for containing the electrolytic solution 17L and an anode tank for containing the electrolytic solution 17R.

  The solid electrolyte membrane 19 prevents each electrolyte component from being mixed. In addition, since the solid electrolyte membrane 19 passes protons, the electrolyte solution 17R on the cathode electrode side and the electrolyte solution 17L on the anode electrode side are electrically connected. The solid electrolyte membrane 19 is, for example, a Nafion (registered trademark) membrane available from DuPont. The reason why the electrolyte solution 17 is divided by the solid electrolyte membrane 19 will be described later.

  Further, as shown in FIG. 1C, the methanol generator 200 may have a reference electrode 20 in the vicinity of the cathode electrode 12. The reference electrode 20 is in contact with the electrolyte solution 17R on the cathode side. The reference electrode 20 measures the potential of the cathode electrode 12 and is connected to the cathode electrode 12 via the voltage measuring device 15. The reference electrode 20 is, for example, a silver / silver chloride electrode (hereinafter referred to as “Ag / AgCl electrode”).

(Method of producing methanol)
A method for producing methanol using the above-described methanol production apparatus will be described.

  The methanol generator can be placed at room temperature and atmospheric pressure.

The external power supply 14 applies a voltage to the cathode electrode 12 so as to be negative with respect to the potential of the anode electrode 13. The value of the voltage applied by the external power source 14 has a threshold value necessary for obtaining a methanol production reaction. This threshold value varies depending on the distance between the cathode electrode 12 and the anode electrode 13, the type of material constituting the cathode electrode 12 or the anode electrode 13, the concentration of the electrolytic solution 17, and the like, but is preferably 2.5 V or more. .

  Part of the voltage applied to the cathode electrode 12 with respect to the anode electrode 13 is consumed in the oxidation reaction of water on the anode electrode 13. For this reason, in the case of the configuration shown in FIGS. 1A and 1B, it is difficult to grasp the voltage actually applied to the cathode electrode. On the other hand, in the case of the configuration shown in FIG. 1C, the voltage actually applied to the cathode electrode 12 can be obtained more accurately. The potential of the cathode electrode 12 with respect to the potential of the reference electrode 20 varies depending on the type of material constituting the reference electrode 20, but is preferably −1.7 V or less.

  As described above, carbon dioxide contained in the electrolytic solution 17 is reduced at the cathode electrode 12 by applying an appropriate voltage to the cathode electrode 12. As a result, methanol is generated on the surface of the cathode electrode 12.

  On the other hand, oxygen is generated by the oxidation reaction of water at the anode electrode 13, but when methanol is mixed in the electrolyte solution 17, methanol is also oxidized in addition to water. That is, part of the methanol produced at the cathode electrode 12 is oxidized at the anode electrode 13 when it reaches the anode electrode 13. As a result, the produced methanol returns to carbon dioxide. In order to suppress this reverse reaction, as shown in FIG. 1B and FIG. 1C, it is preferable to separate the electrolyte solution on the cathode side and the anode side using a solid electrolyte membrane 19.

  In response to the reduction reaction of carbon dioxide on the surface of the cathode electrode 12 using the methanol generator and the oxidation reaction of water on the surface of the anode electrode 13, a reaction current flows through the cathode electrode 12. As shown in FIGS. 1A to 1C, if the current measuring device 16 is incorporated, the amount of reaction current can be monitored.

  The invention is described in more detail with reference to the following examples.

Example 1
(Preparation of cathode electrode)
A CuAu cathode electrode according to the present disclosure was prepared.

  First, Au was dissolved in Cu using a vacuum melting method so that x = 0.167. Then, CuAu was obtained by solidifying the dissolved material. After processing the obtained CuAu into a 20 mm square and a thickness of 2 mm, the surface was washed with an organic solvent.

  The composition of CuAu was confirmed using an X-ray diffractometer. As a result, the peak of Au in a single state was not observed, and it was confirmed that CuAu in which Au was dissolved in Cu was formed.

  Thereafter, the obtained CuAu was bonded onto a glass plate to produce a cathode electrode according to the present disclosure.

(Assembly of the device)
The methanol generator shown in FIG. 1C was manufactured using the cathode electrode as described above. The configuration of the methanol generator is as follows.

Cathode electrode: CuAu (composition formula: Cu _0.9833 Au _0.0167 )
Anode electrode: Platinum Distance between electrodes: About 8cm
Reference electrode: Ag / AgCl
Anode-side electrolyte: potassium bicarbonate aqueous solution having a concentration of 0.5 mol / L Cathode-side electrolyte: potassium chloride aqueous solution having a concentration of 0.5 mol / L Solid electrolyte membrane: Nafion membrane (Nafion 117, manufactured by DuPont)
Carbon dioxide was supplied to the cathode side electrolyte solution by bubbling carbon dioxide gas through the tube for 30 minutes (carbon dioxide flow rate: 200 mL / min).

(Reduction of carbon dioxide)
After dissolving carbon dioxide in the cathode side electrolyte, the tank was sealed. Thereafter, a voltage was applied using a potentiostat so that the cathode electrode potential was negative with respect to the anode electrode potential. The value of the applied voltage was controlled by a potentiostat so that the potential of the cathode electrode with respect to the reference electrode was -1.9V.

After applying a voltage for a certain period of time, the type and amount of reaction product produced in the tank were measured using gas chromatography and liquid chromatography. As a result, carbon monoxide (CO), formic acid (HCOOH), methane (CH ₄ ), ethylene (C ₂ H ₄ ), aldehydes and ethanol were detected as reduction products of carbon dioxide. Furthermore, as shown in FIG. 2, in the product analysis by the head space type gas chromatography method, a peak was observed at the detection position (position of the arrow in the figure) indicating the production of methanol. That is, it was confirmed that methanol was produced by using CuAu for the cathode electrode.

In Example 1, the production amount of methanol per 1000 seconds of electrolysis time was 3.1 × 10 ⁻⁷ mol / cm ² . The electrolysis time is equal to the time when voltage is applied to the cathode electrode from the external power source.

  As a result of calculating the Faraday efficiency (production efficiency) of methanol production according to Example 1, it was 1.42%. The Faraday efficiency refers to the ratio of the amount of charge used for reaction product generation to the total reaction charge amount. (Faraday efficiency of methanol generation) = (reaction charge used for methanol generation) Amount) / (total reaction charge amount) × 100 [%].

(Comparative Example 1)
An experiment similar to that in Example 1 was performed except that a Cu electrode not containing Au was used as the cathode electrode.

As a result, as in Example 1, CO, HCOOH, CH ₄ , C ₂ H ₄ , aldehydes and ethanol were detected. However, as shown in FIG. 2, no signal was obtained at the detection position corresponding to methanol production. That is, in Comparative Example 1, methanol was not generated.

(Comparative Example 2)
An experiment similar to that in Example 1 was performed except that an Au electrode not containing Cu was used as the cathode electrode.

  As a result, CO and HCOOH were detected. However, as shown in FIG. 2, no signal was obtained at the detection position corresponding to methanol production. That is, in Comparative Example 2, methanol was not generated.

As described above, when a CuAu electrode, a single Cu electrode, or a single Au electrode was used as the cathode electrode, as shown in FIG. That is, it can be said that by using a CuAu electrode obtained by alloying Cu and Au as a cathode electrode, a unique effect that could not be expressed by Cu alone or Au alone was developed, and methanol was produced.

(Example 2)
The same experiment as in Example 1 was performed except that a 0.5 mol / L sodium chloride aqueous solution was used as the cathode electrolyte.

  As a result, it was confirmed that methanol was produced as a reduction product of carbon dioxide.

(Example 3)
The same experiment as in Example 1 was performed except that an electrode in which CuAu fine particles having the same composition ratio as in Example 1 were supported on the glassy carbon (registered trademark) substrate surface was used as the cathode electrode.

  As a result, the obtained reaction product was almost the same as in Example 1, and it was confirmed that methanol was produced. In addition, when using an electrode in which a CuAu thin film having the same composition ratio as in Example 1 was laminated on glassy carbon, the same results as in Example 1 were obtained.

Example 4
The same experiment as in Example 1 was performed except that a CuAu electrode represented by the composition formula: Cu _0.995 Au _0.005 was used as the cathode electrode.

  As a result, it was confirmed that methanol was produced as a reduction product of carbon dioxide.

(Example 5)
The same experiment as in Example 1 was performed except that a CuAu electrode represented by the composition formula: Cu _0.95 Au _0.05 was used as the cathode electrode.

  As a result, it was confirmed that methanol was produced as a reduction product of carbon dioxide.

(Example 6)
The same experiment as in Example 1 was performed except that the potentiostat was controlled so that the potential of the cathode electrode with respect to the reference electrode was −1.7 V.

  As a result, it was confirmed that methanol was produced as a reduction product of carbon dioxide.

(Example 7)
The same experiment as in Example 1 was performed except that the potentiostat was controlled so that the potential of the cathode electrode with respect to the reference electrode was −2.1V.

  As a result, it was confirmed that methanol was produced as a reduction product of carbon dioxide.

  In FIG. 3, the figure which compared the methanol production amount obtained in Examples 1-7, the comparative example 1, and the comparative example 2 is shown. The graph shown in FIG. 3 is a graph relatively showing the amount of methanol produced in each of the examples and comparative examples, with the amount of methanol produced in Example 1 being “100”.

As shown in FIG. 3, the production | generation of methanol was confirmed in Examples 1-7, and the production | generation of methanol was not confirmed in the comparative example 1 and the comparative example 2. As shown in FIG.

  As described above, it was confirmed that methanol was efficiently generated as a reduction product of carbon dioxide on the cathode electrode by using the cathode electrode having a CuAu region.

  The present disclosure provides a novel apparatus and method for producing methanol using carbon dioxide as a reduction product by using a cathode electrode having CuAu.

10, 100, 200 Methanol generator 11 Tank 12 Cathode electrode 13 Anode electrode 14 External power supply 15 Voltage measuring device 16 Current measuring device 17, 17L, 17R Electrolyte 18 Tube 19 Solid electrolyte membrane 20 Reference electrode

Claims (12)

A methanol generator that generates methanol by reducing carbon dioxide,
A tank for containing an electrolyte containing carbon dioxide;
A cathode electrode installed in the tank so as to be in contact with the electrolytic solution and having a region of Cu _1-x Au _x (0 <x <1);
An anode electrode installed in the tank so as to be in contact with the electrolytic solution, and having a metal or metal compound region;
An external power source for applying a voltage so that the cathode electrode has a negative potential with respect to the potential of the anode electrode;
A methanol generator comprising: The _{Cu 1-x} Au _x is a solid solution or an intermetallic compound of Cu and Au, methanol generating apparatus according to claim 1.   The methanol generator according to claim 1, wherein the value of x is 0.005 or more and 0.05 or less.   The methanol generator according to claim 1, wherein the anode electrode is carbon, platinum, gold, silver, copper, titanium, iridium oxide, or an alloy thereof.   The methanol production | generation apparatus of Claim 1 whose said electrolyte solution is potassium chloride aqueous solution or sodium chloride aqueous solution.   The methanol generator according to claim 1 whose absolute value of said voltage is 2.5V or more. The methanol generator further comprises:
A reference electrode installed in the tank so as to be in contact with the electrolytic solution and having a region of Ag / AgCl,
The methanol generator according to claim 1, wherein the external power source has a potential of the cathode electrode of −1.7 V or less with respect to a potential of the reference electrode. The methanol generator further comprises:
A solid electrolyte membrane that separates the tank into a cathode tank for containing the first electrolyte containing carbon dioxide and an anode tank for containing the second electrolyte;
The methanol production | generation apparatus of Claim 1 provided with these. It said first electrolyte is an aqueous potassium chloride solution or chloride sodium c anhydrous solution,
The second electrolytic solution is a potassium hydrogen carbonate aqueous solution, a sodium hydrogen carbonate aqueous solution, or a potassium sulfate aqueous solution.
The methanol production | generation apparatus of Claim 8. A method for producing methanol using an apparatus for producing methanol comprising the following steps:
A step (a) of preparing a methanol generator having:
Tank,
A cathode electrode, and
Anode electrode, where
The cathode electrode has a region of Cu _1-x Au _x (0 <x <1),
The anode electrode has a region of metal or metal compound,
In the tank, an electrolyte is held,
The cathode electrode is in contact with the electrolyte;
The anode electrode is in contact with the electrolyte;
The electrolyte is contained carbon dioxide, and,
A step (b) of generating methanol on the cathode electrode by applying a voltage so that the cathode electrode has a negative potential with respect to the potential of the anode electrode and reducing carbon dioxide contained in the electrolyte solution;   The method for producing methanol according to claim 10, wherein in the step (b), the methanol production apparatus is placed at room temperature and atmospheric pressure. An electrode for methanol production used in a methanol production device for producing methanol by reducing carbon dioxide,
An electrode for methanol generation having a region of Cu _1-x Au _x (0 <x <1).

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