WO2005078160A1

WO2005078160A1 - Process for producing hydrogen and apparatus therefor

Info

Publication number: WO2005078160A1
Application number: PCT/JP2005/002420
Authority: WO
Inventors: Tohru Kato; Ken Nozaki; Hiroshi Yokota; Chi Matsumura; Hiroyuki Yamada
Original assignee: Ebara Corporation; National Institute Of Advanced Industrial Science And Technology
Priority date: 2004-02-18
Filing date: 2005-02-17
Publication date: 2005-08-25
Also published as: US20070163889A1; DE112005000495T5

Abstract

An electrolytic cell of structure suited to a process for producing hydrogen through electrolysis of steam wherein in an electrolytic cell partitioned into an anode side and a cathode side by a diaphragm of solid oxide electrolyte, a reducing gas is fed into the anode side and steam into the cathode side with electric power applied to the anode and cathode electrodes. In one aspect, there is provided a hydrogen production apparatus through high-temperature steam electrolysis technique, comprising an electrolytic cell partitioned into an anode side and a cathode side by a diaphragm of solid oxide electrolyte, a conduit for feeding a reducing gas into the anode side of the electrolytic cell and a conduit for feeding steam into the cathode side of the electrolytic cell, characterized in that a metal cermet being stable in reducing atmosphere is used as the materials of the anode and cathode electrodes. In another aspect, there is provided a process for producing hydrogen through high-temperature steam electrolysis, comprising, with the use of a high-temperature steam electrolyzing apparatus having an electrolytic cell partitioned into an anode side and a cathode side by a diaphragm of solid oxide electrolyte, feeding steam into the cathode side and feeding a hydrocarbon-containing gas into the anode side so as to effect reaction with oxygen ions to thereby reduce the electrolytic voltage, characterized in that a waste gas discharged from the anode side of the electrolyzing apparatus is mixed in the hydrocarbon-containing gas fed into the anode side of the electrolyzing apparatus.

Description

Specification

Method and apparatus for producing hydrogen

Technical field

The present invention relates to a method and an apparatus for producing hydrogen by high-temperature steam electrolysis, and more particularly to an electrolysis apparatus in which an electrolytic cell is partitioned into an anode side and a force sword side by a solid oxide electrolyte membrane. The present invention relates to an electrolysis apparatus suitable for use in an electrolysis method in which electrolysis is reduced by supplying steam to a power source side and supplying a reducing gas to an anode side to perform electrolysis. Background art

[0002] Water electrolysis methods for the purpose of hydrogen production include alkaline water electrolysis, solid polymer water electrolysis, and high-temperature steam electrolysis. In alkaline water electrolysis and solid polymer water electrolysis, the electrolysis voltage is 1. Since 8V or more is required, the electrical efficiency is less than 80% and the amount of electricity required for hydrogen production is large. On the other hand, using a solid oxide electrolyte as a diaphragm, the electrolytic cell is divided into an anode side and a power source side, and high-temperature water vapor is supplied to the power source side, so that the water vapor is electrolyzed at a high temperature of about 800 ° C. In the high-temperature steam electrolysis method, heat energy can be used to decompose water due to the high temperature, and electrode overvoltage and resistance overvoltage can be suppressed low, so that an electrical efficiency of 90% or more can be expected. It can be reduced to 5V or less, and the amount of power required for hydrogen production can be reduced. Furthermore, recently, by supplying natural gas to the anode side of the electrolytic cell, oxygen ions which move to the anode side in the solid oxide electrolyte membrane are reacted on the anode side to reduce the chemical potential. An electrolysis method that can greatly reduce power consumption by using it for water decomposition has been proposed (US Pat. No. 6,051,125).

[0003] In the method proposed in the above US patent, natural gas is directly supplied to the anode side of the electrolytic cell to react with oxygen ions present on the anode side, and the reaction energy is converted to water on the power source side. This is used for disassembly. In this case, the theoretical electrolysis voltage is almost 0 because the depolarization effect of methane lowers the electrolysis voltage of water in principle. In a practical water electrolysis system, the voltage required to add this to the overvoltage is approximately 0.5 The above U.S. patent asserts that water electrolysis is possible with V.

[0004] The electrolytic cell used for ordinary high-temperature steam electrolysis has the same material and structure as the cell of a solid oxide fuel cell (SOFC), and is used as an electrode on the power source side on which steam is introduced to generate hydrogen. Ni cermet suitable for a reducing atmosphere is used, while conductive electrodes such as lanthanum cobaltite and lanthanum manganate are used as electrodes on the anode side where oxygen is generated. Figure 1 shows the concept of a normal high-temperature steam electrolyzer. In the device shown in Fig. 1, the electrolyzer (electrolyzer) is divided into a power source side and an anode side by a solid oxide electrolyte membrane, and high-temperature steam is supplied to the power source side to supply power source electrodes and By supplying power to the anode electrode, electrolysis of water vapor is performed on the power source side to obtain high-purity hydrogen. Oxygen ions o ² — generated by the electrolysis of water vapor move to the anode side through the solid oxide electrolyte diaphragm.

[0005] On the other hand, in a process in which a reducing gas is introduced into the anode side of an electrolytic cell in which oxygen is generated, and steam electrolysis is performed while reducing electrolysis power, both the power source and the anode are reduced to a reducing gas. Will be exposed. However, the metal may undergo steam oxidation at a high temperature until steam as a raw material is introduced on the power source side and hydrogen is generated. Water vapor may be introduced on the anode side to suppress carbon deposition, and acidic gas such as water is generated by the electrode reaction. Suitable electrolytic cells and process conditions have been proposed.

Disclosure of the invention

Problems to be solved by the invention

[0006] The present invention provides a reducing gas supplied to the anode side of an electrolytic cell, which is divided into an anode side and a cathode side by the above-described membrane of the solid oxide electrolyte, and is supplied to the power source side. An object of the present invention is to find a configuration of an electrolytic cell suitable for a method for producing hydrogen by electrolysis of water vapor by supplying water vapor and supplying power to an anode electrode and a power source electrode.

Means for solving the problem

[0007] As means for solving the above problems, one embodiment of the present invention provides an electrolytic cell separated into an anode side and a power source side by a membrane of a solid oxide electrolyte, and a reducing gas flowing through an electrolytic cell. This is a hydrogen production apparatus using a high-temperature steam electrolysis method equipped with a pipeline for supplying water to the cathode side and a pipeline for supplying water vapor to the power source of the electrolytic cell. The material of the anode electrode and the power source electrode is 400-1000 ° Provided is an apparatus characterized by using a cermet made of ceramic and metal which is stable in a reducing atmosphere at a temperature of C.

[0008] In the present invention, a reducing gas is supplied to the anode side of the electrolysis apparatus. Here, the reducing gas reacts with oxygen passing through the solid oxide electrolyte membrane to the anode side of the electrolytic cell in the steam electrolytic cell according to the present invention to lower the oxygen concentration on the anode side. And natural gas and hydrocarbon gas such as methane.

Brief Description of Drawings

FIG. 1 is a view showing the concept of a normal high-temperature steam electrolysis apparatus.

FIG. 2 is a view showing the concept of a high-temperature steam electrolysis apparatus according to the present invention.

FIG. 3 is a view showing an interconnector structure according to the present invention.

FIG. 4 is a view showing the concept of a high-temperature steam electrolysis apparatus used in the second embodiment of the present invention.

FIG. 5 is a flowchart showing the concept of an example of a hydrogen production method that works on the second aspect of the present invention.

FIG. 6 is a view showing the concept of a hydrogen production apparatus used in Example 1.

FIG. 7 is a view showing a structure of a hydrogen production experimental apparatus used in Example 2 of the present invention.

FIG. 8 is a graph showing the results of Example 2 of the present invention.

FIG. 2 shows the concept of one embodiment of a hydrogen production apparatus that is active in the present invention. In the hydrogen producing apparatus according to the present invention, a reducing atmosphere is provided on the power source side of the electrolysis apparatus (electrolyzer) by the generated hydrogen and on the anode side by the supply of reducing gas. Therefore, since both the anode electrode and the force electrode are exposed to the reducing gas, these materials also have stable ceramic and metallic power in a reducing atmosphere at a temperature of 400 to 1000 ° C. It is characterized by using cermet.

[0011] At the power source side of the electrolytic cell, the introduced steam is electrolyzed to generate hydrogen, so that the gas composition in the electrolytic cell changes from the entrance side to the exit side. At the entrance The outlet has the lowest hydrogen concentration, and the outlet has the highest hydrogen concentration. When only water vapor is supplied to the power source side of the electrolytic cell, metals such as Ni undergo steam oxidation at high temperatures. In order to prevent steam oxidation, it is effective to mix a reducing gas, but on the cathode side of the electrolytic cell of the present invention, since the purpose is to produce high-purity hydrogen, reduction is necessary. It is appropriate to mix hydrogen as a neutral gas. For Ni electrodes, which are widely used in electrolytic cells, the molar ratio of hydrogen to water vapor in the exposed atmosphere: H / HO is 0.01 or more.

twenty two

More preferably, if the concentration is 0.04 or more, steam concentration does not occur, so that the concentration becomes the necessary minimum hydrogen partial pressure.

[0012] The electrolysis voltage changes depending on the oxygen partial pressure on the anode side and the power source side of the electrolytic cell, and P (cathode)

It is effective to reduce the electrolytic voltage by making ZP02 (anode side) as large as possible.

[0013] Meanwhile, if the concentration of hydrogen mixed into the power source side of the electrolytic cell is increased, the oxygen partial pressure on the power source side decreases, which causes a voltage rise. It is preferable to keep it low only.

[0014] In particular, the molar ratio of reducing gas to acidic gas near the outlet on the anode side of the electrolytic cell: reducing gas Z Since acidic gas is 0.4 or less, it is necessary to reduce the electrolytic voltage. The H / HO at the inlet on the power source side of the electrolytic cell should be 0.4 or less, preferably 0.2 or less.

twenty two

It is better to support.

[0015] Hydrogen to be mixed is preferably circulated to a part of the hydrogen generated by steam electrolysis, since the system is simplified.

[0016] On the anode side of the electrolytic cell, the concentration of the reducing gas is highest at the entrance and decreases toward the exit. Thus, the oxygen partial pressure is lowest at the inlet and highest at the outlet. On the other hand, since hydrogen is generated on the power source side of the electrolytic cell, the hydrogen concentration increases toward the outlet, and the oxygen partial pressure decreases toward the outlet. When the flow of water vapor on the power source side of the electrolytic cell and the flow of reducing gas on the anode side are the same, the outlet with the largest P (power source side) / P (anode side) at the inlet Current density

02 02

The degree of non-uniformity increases, causing thermal stress and the like. For this reason, the flow of water vapor on the power source side of the electrolytic cell and the flow of reducing gas on the anode side are combined with the flow ( Countercurrent) is preferred.

[0017] It is possible to suppress the deposition of carbon by adding steam to the reducing gas supplied to the anode side of the electrolytic cell. In this case, the molar ratio of water to reducing gas is 0.4 or less, and preferably 0.2 or less.

It is necessary that the anode electrode and the force sword electrode have gas diffusivity, have electron conduction, and have activity as an electrode catalyst.

Under the condition of H 2 / H 2 O <0.4, which is a preferable atmosphere in the electrolytic cell described above,

twenty two

It is preferable that the anode electrode and the force source electrode are mainly composed of a metal material which does not form a compound. Metals having electron conductivity and catalytic activity without forming oxides under such conditions include Ni, Fe, Co, Cu, Pt, Ag, Pd, Ru, and mixtures and alloys thereof.

The electrode material is generally used as a cermet mixed with a ceramic powder in order to suppress sintering at a high temperature.

twenty two

It is stable under the condition of O <0.4, and can be selected in consideration of reactivity with electrolyte material 'approximation of thermal expansion coefficient and oxygen ion conductivity or oxygen ion' electron conductivity .

[0021] In the apparatus working on the present invention, ZrO, CeO, LaCrO, LaTiO, LaGaO, etc.

It is preferable to use a material in which oxygen ion conductivity or electron conductivity is improved by partially substituting 222 3 33 for the material of the anode electrode and the force source electrode. In particular, when a material having conductivity of electrons and oxygen ions is used, the number of reaction sites increases when an electrode is used, and the area where oxygen ions can be diffused increases, which is effective in reducing the reaction overvoltage.

[0022] In a steam electrolyzer, when a plurality of electrolysis cells are connected in series to form a multistage, an interconnector for connecting an anode electrode and a force sword electrode is required. The gas contacts both the gas on the anode side and the gas on the power source side of the electrolytic cell, and also serves to separate (gas seal) these gases. In a normal SOFC cell or high-temperature water vapor electrolysis cell, one side has a reducing atmosphere and the other has an oxidizing atmosphere, so that it is difficult to select a material suitable for these, and it is also difficult to manufacture the cell. Specifically, at present, as a material for an interconnector suitable for both a reducing atmosphere and an oxidizing atmosphere, la Only limited ceramics, such as tin'chromite, have been found, and it has been difficult to produce dense structures from this material. For this reason, it has been difficult for an interconnector made of this material to ensure a gas seal at the junction of the electrodes.

In this process, since both the anode side and the power source side of the electrolytic cell are in a reducing atmosphere, a metal can be used as an interconnector material, which is easy to mold and join, and A highly reliable electrolytic device that can withstand stress can be manufactured. Examples of the interconnector material that can be used in the present invention include Ni, Ni-based alloys, Fe-based alloys, Co-based alloys, Cu-based alloys, and Ag-based alloys.

FIG. 3 shows a concept of an interconnector structure according to the present invention. The electrolytic cell 5 is divided into an outer anode side 12 and an inner power source side 11 by a cylindrical solid oxide electrolyte membrane 3, and an anode electrode 4 is provided outside the solid oxide electrolyte and an inner electrode side is provided inside. Force sword electrode 2 is arranged. In the apparatus shown in FIG. 3, the upper and lower two cylindrical electrodes 固体 the solid oxidant electrolyte composite are joined via the insulator 21, and the anode and the power source are connected by the interconnector 22. They are connected in series. Thus, by connecting a DC power supply to the anode and the power source, it is possible to secure the voltage required for electrolysis with a small amount of current and to advance the electrolysis reaction. High-temperature steam is supplied to the power source side 11 of the electrolytic cell, and reducing gas (indicated as CH) is supplied to the anode side 12, and power is supplied to both electrodes.

Four

As a result, electrolysis of water vapor occurs on the power source side to generate hydrogen. In addition, the generated oxygen ions move to the force sword side through the solid oxide electrolyte. On the anode side, the transferred oxygen ions react with the reducing gas to produce CO and H 2 O. Book

twenty two

In the apparatus according to the present invention, the above-mentioned metal material can be used as the interconnector material because both the anode side and the force source side of the electrolytic cell are in a reducing atmosphere.

[0025] The present inventors have been conducting research on the same technology as that of the above-mentioned US Patent No. 6,051,125 for some time. However, only the natural gas proposed in the above-mentioned US Patent was subjected to an electrolytic cell. It has been found that the method of supplying to the anode side has the following defects. In other words, at the beginning of the operation of the electrolyzer, almost the same data as those shown in the above-mentioned U.S. Patent can be obtained.However, if the operation is continued, the current value gradually decreases, and the operation cannot be continued. became. As a result of considering the reason, when methane is directly supplied to the anode side of the electrolytic cell, methane is decomposed on the high-temperature anode side, and carbon, which is a decomposition product, covers the electrode in a film form, and It was found that this was due to blockage.

[0026] A second aspect of the present invention is to provide a technique for preventing the above-described problem of electrode blocking due to generated carbon by a simple method without increasing the cost.

[0027] The present inventors have conducted intensive studies to find a means for solving the above-mentioned problems, and as a result, have found that natural gas (hydrocarbon-containing gas) supplied to the anode side of the electrolysis tank has water vapor or carbon dioxide. As a result, carbon produced by the decomposition of the hydrocarbon-containing gas on the anode side immediately reacts with water vapor and carbon dioxide to form CO or CO.

2

It has been found that body carbon can be prevented from depositing on the electrode surface. In a high-temperature steam electrolyzer using a solid oxide electrolyte membrane, carbon can be oxidized by oxygen ions that pass through the solid oxide electrolyte membrane and exist on the anode side of the electrolysis apparatus. Since the amount of reducing gas is larger than the amount of oxygen ions, this reaction alone cannot prevent the deposition of solid carbon. In addition, CO and hydrogen generated by the reaction between carbon and water vapor or carbon dioxide react with oxygen ions on the anode side as a reducing gas.

This contributes to lowering the electrolysis voltage of the electrolyzer.

[0028] Further, the present inventors described that water vapor was applied to the power source side of a high-temperature steam electrolyzer in which the electrolytic cell was partitioned into an anode side and a power source side using a solid oxide electrolyte as a diaphragm as described above. In the high-temperature steam electrolysis method that reduces the electrolysis voltage by supplying a hydrocarbon-containing gas to the anode side and reacting it with oxygen ions, the exhaust gas discharged from the anode side of the electrolysis device Focusing on the fact that water and carbon dioxide generated by the reaction between hydrocarbons and the like in the supplied gas and oxygen passing through the solid oxidant electrolyte membrane are included, the anode-side exhaust gas is It has been found that water vapor and Z or carbon dioxide can be easily mixed by mixing with a hydrocarbon-containing gas supplied to the anode side of the electrolysis apparatus.

That is, in the second embodiment of the present invention, a steam is supplied to a power source side of a high-temperature steam electrolysis apparatus in which an electrolytic cell is partitioned into an anode side and a power source side using a solid oxide electrolyte as a diaphragm, By supplying hydrocarbon-containing gas to the side and reacting with oxygen ions A method for producing hydrogen by high-temperature steam electrolysis for reducing the electrolysis voltage is characterized in that exhaust gas discharged from the anode side of the electrolysis apparatus is mixed with hydrocarbon-containing gas supplied to the anode side of the electrolysis apparatus. The present invention relates to a method for producing hydrogen.

[0030] The second aspect of the present invention also relates to an apparatus for performing a brute force method. Therefore, in still another embodiment of the present invention, an electrolytic cell partitioned into an anode side and a cathode side by a membrane of a solid oxide electrolyte, and a hydrocarbon-containing gas supplied to the anode side of the electrolytic cell. And a conduit for supplying water vapor to the force sword of the electrolytic cell. Further, the exhaust gas discharged from the anode side of the electrolytic cell is provided with a hydrocarbon-containing gas supplied to the anode side of the electrolytic cell. The present invention relates to an apparatus for producing hydrogen, which is provided with a conduit for mixing hydrogen therein.

[0031] In the method of the present invention, a hydrocarbon-containing gas is supplied to the anode side of the electrolysis apparatus. Here, the hydrocarbon-containing gas means a gas containing a hydrocarbon such as natural gas or methane. Further, the expression “reducing gas” used in the present specification means that in the steam electrolytic cell according to the present invention, oxygen reacts with oxygen passing through the solid oxide electrolyte membrane to the anode side of the electrolytic cell, and It means a gas that can lower the oxygen concentration.

[0032] The basic principle of an apparatus for producing hydrogen by high-temperature water vapor electrolysis using a solid oxidant electrolyte membrane used in the second embodiment of the present invention will be described with reference to FIG.

The high-temperature steam electrolyzer 113 is divided into an anode side 115 and a force sword side 116 by a membrane 114 of a solid oxide electrolyte. When high-temperature steam 119 is supplied to the power source side 116 of the electrolytic cell, and the hydrocarbon-containing gas 110 is supplied to the anode side 115 of the electrolytic cell, and the electric power 117 is converted to direct current by the AC-DC converter 18 and the electricity is supplied to the electrolytic cell. The high temperature steam 119 supplied to the power source side 116 is decomposed into hydrogen and oxygen by the electrolytic action. The produced hydrogen 120 is recovered as high-purity hydrogen. On the other hand, the generated oxygen 121 becomes oxygen ions and selectively passes through the solid oxide electrolyte diaphragm 114 and moves to the anode side 115. Here, when the hydrocarbon-containing gas 110 is supplied to the anode side 115, oxygen ions 121 are consumed in reaction with the hydrocarbon-containing gas and contribute to the formation of a concentration gradient of oxygen ions. Voltage and power consumption is greatly reduced.

[0034] The second embodiment of the present invention is directed to a hydrocarbon-containing solution supplied to the anode side of a high-temperature steam electrolyzer. An exhaust gas discharged from the anode side of the electrolytic cell is mixed with the gas. The method according to the present invention will be described with reference to FIG. In the following, methane will be described as an example of the hydrocarbon gas as appropriate, but the present invention is not limited to this description, and can be applied to other hydrocarbon gases.

[0035] In the system shown in Fig. 5, a hydrocarbon-containing gas is supplied to the anode side of the high-temperature steam electrolysis tank described above, and high-temperature steam is supplied to the cathode side of the electrolysis tank to supply power. To electrolyze high-temperature steam. High-temperature exhaust gas is generated from the anode side of the electrolytic cell, and high-temperature hydrogen-containing gas (including hydrogen and water vapor) is generated from the power source side. In the system of the present invention, the high-temperature exhaust gas discharged from the anode side of the electrolytic cell is mixed with the hydrocarbon-containing gas supplied to the electrolytic cell anode side.

[0036] As described above, the method according to the second aspect of the present invention comprises mixing the exhaust gas discharged from the anode side of the electrolytic cell with the hydrocarbon-containing gas supplied to the anode side of the electrolytic cell. Is supplied to the anode side of the electrolytic cell. As a result, water vapor and carbon dioxide contained in the mixed exhaust gas immediately react with carbon generated by thermal decomposition of hydrocarbons such as methane on the anode side of the electrolytic cell, and CO or CO

As a result, the generation of solid carbon on the anode side of the electrolytic cell can be prevented, and the contamination of the electrode by carbon can be prevented.

[0037] Even in this case, if the amount of added steam is insufficient, a carbon film is formed on the electrode, causing trouble. Theoretically, in order to prevent the formation of a carbon film, the total amount of water vapor or carbon dioxide added is determined by the amount of carbon (carbon equivalent If the amount is equimolar to (number), the carbon in the hydrocarbon-containing gas is all converted to CO, so that carbon precipitation hardly occurs. In order to prevent carbon precipitation more surely, the total amount of water vapor or carbon dioxide mixed into the hydrocarbon-containing gas depends on the amount of hydrocarbons supplied to the anode side of the electrolytic cell. It is preferably at least equimolar to the amount of carbon (moles of carbon atoms) in the gas. When water vapor is added in excess of the equimolar amount of hydrocarbon carbon, methane carbon is oxidized to dioxygenated carbon, but up to twice the molar amount of dioxinated carbon is generated. As a result, hydrogen is generated, and the hydrogen reacts with oxygen ions as a reducing agent. There is almost no waste. The reaction of CO + H0 → CO + H is an exothermic reaction,

2 2 2

There is no need to supply energy to make it go. The reaction of CH + 2H 0 → CO + 4H, which is the total reaction of methane and water, and the reaction of CH + CO → 2CO + 2H are slightly endothermic.

4 2 2 2 4 2 2

Therefore, it is necessary to supply heat in order to make the whole reaction proceed.Because this thermal energy is smaller than the electric energy that can be obtained as an overvoltage during electrolysis, it is not necessary to heat it from outside. Absent.

[0038] The energy required to add twice as much water vapor as methane is considerably large. To suppress energy consumption, high-efficiency heat exchange ^^ also releases the power of the electrolytic cell. ) Heat must be used. On the other hand, the off-gas component contains water generated by methane oxidation and carbon dioxide in a ratio of 2: 1 and contains unburned reducing gas components (hydrocarbons such as methane). Therefore, according to the method of the present invention, instead of adding water vapor from the outside, if the offgas discharged from the anode side of the electrolytic cell is added to the supplied hydrocarbon-containing gas, the high-temperature offgas can be used as it is. The steam contained in the off-gas and the carbon dioxide both have the effect of suppressing the precipitation of carbon, and also have the effect of depolarizing together with the unburned reducing gas component catalyst, thus making energy more effective. Can be used for

[0039] The mixed gas of methane, water vapor, and carbon dioxide easily reacts with the catalyst at the temperature (about 650 ° C to 1000 ° C) used in the high-temperature steam electrolysis that is effective in the present invention. CO and hydrogen, or CO and hydrogen. If this reaction is actively used, methane will touch the electrode

2

Before being converted into CO, CO, and H, methane decomposes and contaminates the electrodes.

twenty two

Disappears. Therefore, in a preferred aspect of the present invention, in the method described above, the mixed gas of the hydrocarbon-containing gas and the exhaust gas on the anode side supplied to the anode side of the electrolysis apparatus is subjected to a hydrogen reaction by a thermal reaction before coming into contact with the anode of the electrolysis apparatus. And converting the gas into a mixed gas containing carbon monoxide as a main component, and then bringing the mixed gas into contact with the anode. In order to achieve this, if the structure is such that the mixed gas of methane, water vapor and carbon dioxide supplied to the electrolytic cell passes through the catalyst layer before hitting the electrode, the methane will not directly hit the electrode. The purpose of pollution prevention can be sufficiently achieved. That is, in the electrolysis apparatus according to the present invention, a mixed gas of steam and the exhaust gas on the anode side of the electrolysis tank is used for the electrolysis apparatus. A catalyst layer is placed in the pipeline that supplies the anode side, and the mixed gas of the hydrocarbon-containing gas and the exhaust gas on the anode side mainly converts hydrogen and carbon monoxide by a thermal reaction before coming into contact with the anode of the electrolyzer. It is more preferable to be configured to be converted to a mixed gas as a component.

[0040] As described above, the generation of hydrogen by the reaction between methane and water is a slightly endothermic reaction, and the high-temperature steam electrolyzer used in the present invention maintains a high temperature of 650-1000 ° C. Energy may be insufficient at an overvoltage of about 0.5V. In particular, when overvoltage is reduced by adopting a thin YSZ (yttrium-stabilized zirconia) film as a solid oxide electrolyte diaphragm, energy injection is required to maintain the temperature required for the steam electrolysis reaction. . It is not advisable to supplement this with electric energy, so it is preferable to use the combustion energy of methane. In this case, the simplest and most efficient method is to add partial oxygen to methane and supply it to the electrolyzer to cause a partial oxidation reaction of methane, and use the heat of this reaction. Since the amount of oxygen required for this reaction is not very large, there is little danger from oxygen contamination. Also, the use of air instead of oxygen does not increase the increase in waste heat due to nitrogen. Furthermore, the water vapor and CO generated by this reaction are more preferable because they are used to prevent carbon deposition on the electrode.

Therefore, still another embodiment of the present invention relates to the above-described method for producing hydrogen, wherein oxygen or air is mixed with the exhaust gas on the anode side of the electrolysis apparatus, and the obtained mixed gas is mixed on the anode side of the electrolysis apparatus. The present invention further relates to a method characterized by mixing with a hydrocarbon-containing gas supplied to a gas, and converting the mixture into a mixed gas containing hydrogen and carbon monoxide as main components by heat of partial oxidation reaction of the hydrocarbon-containing gas.

Example 1

Using the experimental apparatus 1 shown in FIG. 6, an experiment for producing hydrogen by high-temperature steam electrolysis was performed. A cylindrical scandium-stabilized zirconia (SSZ) having a closed end was used as a solid oxide electrolyte diaphragm 3, and on both sides thereof, an anode 2 and a force sword 4 were provided with a Ni-zirconia cermet electrode. This was placed in the electrolytic cell 5, and the electrolytic cell 5 was partitioned into an anode side 12 and a force source side 11. An exhaust pipe 6 for discharging a mixed gas of hydrogen and water vapor is installed on the power source side 11, and a reducing gas (shown as CH) is introduced on the anode side 12 of the electrolytic cell. A gas inlet 7 for the gas inlet was formed.

[0042] Methane is supplied from the gas inlet 7 to the anode side 12 of the electrolysis apparatus, and steam is supplied from the power source side inlet 8, and power is supplied to the anode 2 and power source 4 from the DC power supply 13 at 700 ° C. Thus, high-temperature steam electrolysis was performed. It was confirmed that hydrogen was generated from the outlet 9 of the generated gas exhaust pipe 6.

Example 2

An experiment of hydrogen production by high-temperature steam electrolysis according to the second embodiment of the present invention was performed using the high-temperature steam electrolysis apparatus shown in FIG. The high-temperature steam electrolyzer 1 shown in FIG. 7 has electrodes (anode 2 and force source 4) attached to both sides of a cylindrical solid oxide electrolyte membrane 3 having one end closed, and an electrolytic cell 5 Is divided into an anode side 12 and a force sword side 11. An exhaust pipe 6 for discharging a mixed gas of generated hydrogen and water vapor is provided on the power source side 11. Further, a gas inlet 7 for introducing a hydrocarbon-containing gas is formed on the anode side 12 of the electrolytic cell. This structure is almost the same as that of the solid oxide fuel cell (SOFC) cell, and its manufacturing method is almost the same as that of the SOFC cell. In this embodiment, a thin film of YSZ (yttrium-stabilized zirconia) (thickness: 100 μm) is used as the solid oxide electrolyte diaphragm 3, and nickel cermet electrodes 2 and 4 are formed on both sides of the YSZ film 3. Attach, the outer electrode 2 was the anode and the inner electrode 4 was the force source.

[0043] The electrolysis test was performed by disposing the electrolysis tank 5 in an electric furnace, applying a DC voltage 13 to both electrodes while maintaining the temperature at 1,000 ° C. In the method of the present invention, only steam was supplied to the power source side 11 of the electrolytic cell at normal pressure, and a mixture of simulated exhaust gas having a gas volume ratio twice that of methane was supplied to the anode side 12. As the simulated exhaust gas, a mixture of steam, carbon dioxide, and methane at a ratio of 4: 2: 1 was supplied. The actual anode side exhaust gas contains hydrogen and CO generated by the reaction of methane instead of methane as unburned gas. Here, methane was substituted. The mixing ratio of methane was determined assuming a fuel utilization rate of about 85%. The reason why the outside of the electrolytic cell is set to the anode side is to make it easier to observe the state of carbon deposited on the anode.

As a comparative experiment, an experiment was conducted according to the method of the above-mentioned US Pat. No. 6,051,125 by flowing only steam at the cathode side 11 and flowing only methane at the anode side 12 at normal pressure. Was. Change Next, a comparative experiment was performed using the condition in which the anode side 12 was opened and methane was not flown, that is, the condition of a normal high-temperature steam electrolysis method. In the experiment, a DC voltage was applied to the electrode to observe the voltage versus current, and the state of the anode was observed after electrolysis was performed for an appropriate time.

[0045] In a normal steam electrolysis method in which methane is not supplied to the anode side 12, the open circuit electrolysis voltage, that is, the voltage at which a current starts to flow when the voltage is increased is about 0.9 V, which is practical steam electrolysis. Under the condition of the current value of lAZcm ² , an electrolysis voltage of 2 V was required. On the other hand, in the method of the above-mentioned U.S. Patent and the method of the present invention, the open-circuit voltage does not become a definite value, and the electrolytic current starts to flow at a very small voltage, and when the voltage is increased, the current value becomes almost linear. The electrolysis voltage was 1.3 V at lAZcm ² which is a practical current value. This value is considerably higher than the estimated value which is qualitatively described in the above-mentioned U.S. patent specification.The YSZ film thickness of the electrolytic cell used in this example is as large as 100 m. Therefore, it is considered to be a reasonable value. However, even the electrolysis voltage obtained in this example does not use natural gas! / ヽ It is considerably lower than that of high-temperature steam electrolysis! ヽ Electrolysis voltage is low. Suggests.

[0046] The effect of preventing electrode contamination by mixing steam and carbon dioxide into the hydrocarbon-containing gas supplied to the anode side of the electrolytic cell is to reduce the current value by keeping the electrolytic voltage 1.3V for a long time. It was checked by observation. The change in electrolysis current value between the case where only methane is supplied to the anode side 12 of the electrolytic cell and the case where simulated anode exhaust gas with a volume ratio twice that of methane is mixed and supplied to the anode side 12 of the electrolytic cell are as follows: As shown in the graph of Fig. 8, the current value continued to decrease when only methane was supplied, whereas the current value remained almost constant when the simulated anode side exhaust gas was mixed with methane and supplied. Met. In addition, visual observation of the electrode (anode) also showed that when methane was supplied only to the anode side 12 of the electrolytic cell, considerable carbon deposition occurred in the anode one hour later. However, when methane and the simulated waste gas were mixed and supplied to the anode side 12 of the electrolytic cell, the surface remained clean after 10 hours.

[0047] From the test results, according to the high-temperature steam electrolysis method in which a hydrocarbon-containing gas (methane) is supplied to the anode side of the electrolytic cell, the method of supplying only methane to the anode side of the electrolytic cell is as follows. The continuous operation is shown to be difficult as the electrodes begin to clog after a few hours of electrolysis. However, when the anode side exhaust gas containing water vapor and carbon dioxide is added to methane and supplied to the anode side of the electrolytic cell, the amount of the exhaust gas mixed is almost twice as large as the volume ratio of the catalyst. It was shown that practical long-term operation without any influence was possible. In another experiment, the ratio of water vapor and carbon dioxide mixed into methane supplied to the anode side 12 of the electrolytic cell was changed, and the amount of water vapor mixed was twice that of methane. Even if the volume ratio is less than or equal to the volume ratio, the electrode was not immediately clogged.However, when the ratio of methane to the sum of water vapor and the carbon dioxide in the exhaust gas was an equimolar ratio, the ratio was low. The onset of occlusion was observed in a relatively short time. In the tests so far, when the sum of the water vapor added to methane and the carbon dioxide was twice the molar ratio of methane, no carbon deposition was observed. Mixing of the anode side exhaust gas containing carbon dioxide is considered to be the most preferable amount for preventing the electrode from being clogged. Mixing a larger amount of exhaust gas is preferable in terms of clogging of the electrodes, but it is not preferable because the concentration of methane supplied to the anode side of the electrolytic cell decreases, so that a large electrolytic current value cannot be obtained.

Not good.

[0048] Incidentally, in the method of mixing water vapor from the outside instead of the exhaust gas on the anode side, it is possible to prevent the blockage of the anode. Energy is required to raise the temperature to about 1000 ° C), so extra energy is consumed when the electrolytic overvoltage is small. Further, in the method of the present invention, the unburned gas (residual methane) contained in the exhaust gas on the anode side is reused. It can be reduced by about 40%.

[0049] Various aspects of the present invention are as follows.

[0050] 1. Steam is supplied to a power source side of a high-temperature steam electrolysis apparatus in which an electrolytic cell is partitioned into an anode side and a power source side using a solid oxide electrolyte as a diaphragm, and a hydrocarbon-containing gas is supplied to the anode side. In the hydrogen production method using high-temperature water vapor electrolysis, which reduces the electrolysis voltage by supplying oxygen and reacting with oxygen ions, the hydrocarbon-containing gas supplied to the anode side of the electrolyzer discharges the gas from the anode side of the electrolyzer. Mixed exhaust gas Hydrogen production method.

[0051] 2. The anode side force is adjusted so that the sum of water vapor and carbon dioxide is equal to or greater than the molar number of carbon atoms in the hydrocarbon-containing gas supplied to the anode side of the electrolysis apparatus. 2. The method for producing hydrogen according to the above item 1, wherein exhaust gas is mixed.

[0052] 3. The anode-side force is set such that the sum of water vapor and carbon dioxide becomes about twice the molar number of carbon atoms in the hydrocarbon-containing gas supplied to the anode side of the electrolysis apparatus. 2. The method for producing hydrogen according to item 1, wherein the exhaust gas is mixed.

4. The mixed gas of the hydrocarbon-containing gas and the exhaust gas on the anode side to be supplied to the anode side of the electrolytic device is mixed with hydrogen and carbon monoxide as main components by a thermal reaction before contacting the anode of the electrolytic device. 4. The method for producing hydrogen according to any one of the above items 1 to 3, wherein the method is brought into contact with the anode after conversion to gas.

[0054] 5. Oxygen or air is mixed with the exhaust gas on the anode side of the electrolyzer, and the obtained mixed gas is mixed with the hydrocarbon-containing gas supplied to the anode side of the electrolyzer to partially oxidize the hydrocarbon-containing gas. 5. The method for producing hydrogen according to any one of the above items 1 to 4, wherein the reaction heat is converted into a mixed gas containing hydrogen and carbon monoxide as main components.

[0055] 6. An electrolytic cell separated into an anode side and a force source side by a membrane of a solid oxide electrolyte, a pipeline for supplying a hydrocarbon-containing gas to the anode side of the electrolytic cell, A conduit for supplying the power source, and a conduit for mixing exhaust gas discharged from the anode side of the electrolytic cell into a hydrocarbon-containing gas supplied to the anode side of the electrolytic cell. Hydrogen production equipment.

[0056] 7. A catalyst layer is arranged in a conduit for supplying a mixed gas of water vapor and the exhaust gas on the anode side of the electrolytic cell to the anode side of the electrolytic cell, and the mixed gas of the hydrocarbon-containing gas and the exhaust gas on the anode side is subjected to electrolysis. 7. The apparatus for producing hydrogen according to claim 6, wherein the apparatus is configured to convert into a mixed gas containing hydrogen and carbon monoxide as main components by a thermal reaction before coming into contact with an anode of the apparatus.

[0057] 8. An electrolytic cell separated into an anode side and a force source side by a membrane of a solid oxide electrolyte, a pipeline for supplying a reducing gas to the anode side of the electrolytic cell, A high-temperature steam electrolysis method for producing hydrogen, comprising An apparatus characterized in that a cermet which has a stable ceramic and metallic force in a reducing atmosphere at a temperature of 400 to 1000 ° C is used as a material for a cathode electrode and a force electrode.

9. As a cermet used as an electrode material, a temperature of 400 to 1000 ° C. and a molar ratio of hydrogen to water vapor in the atmosphere: H / H 0, or a mole of water to a reducing gas

twenty two

9. The apparatus according to the above item 8, wherein a cermet mainly composed of a metal which does not form an oxide as an equilibrium reaction is used under an atmosphere condition having a ratio of 0.4 or less.

[0059] 10. The apparatus according to the above item 8, wherein Ni cermet is used as the cermet used as the electrode material.

[0060] 11. The metal cermet used as an electrode material according to any one of the above items 8 to 10, wherein a material which is an oxygen ion conductor or an oxygen ion 'electron conductor is mixed with a metal. Equipment.

[0061] 12. The apparatus according to any one of the above items 8 to 10, wherein scandium-stabilized zirconia (SSZ) or yttrium-stabilized zirconia (YSZ) is used as the solid oxidant electrolyte.

13. The above-mentioned item 8, further comprising a conduit for mixing a part of the hydrogen gas generated on the power source side of the electrolytic cell with the steam supplied to the power source side of the electrolytic cell. The apparatus according to any one of paragraphs 12 to 12.

[0063] 14. The flow of water vapor on the power source side of the electrolytic cell and the flow of reducing gas on the anode side of the electrolytic cell are configured to be countercurrent to each other. The device according to item 8/13, item 13 /!

15. The apparatus according to any one of the above items 8 to 14, wherein the plurality of anode electrodes and force source electrodes are connected in series by a metal interconnector.

[0065] 16. A reducing gas is supplied to the anode side of an electrolytic cell separated into an anode side and a force sword side by a membrane of a solid oxide electrolyte, and steam is supplied to the force sword side. A method for producing hydrogen by electrolysis of steam by supplying electric power to an electrode and a force sword electrode, wherein hydrogen is mixed into steam supplied to a force sword side of an electrolytic cell.

17. Hydrogen is added to steam supplied to the power source side of the electrolytic cell, Ratio: H / HO is mixed in an amount of 0.4 or less and 0.01 or more,

twenty two

The method described in the section.

18. The flow of water vapor on the power source side of the electrolytic cell and the flow of reducing gas on the anode side of the electrolytic cell are converted into the above-described 16 Or the method of paragraph 17.

Industrial applicability

According to the present invention, the present invention relates to a method and an apparatus for producing hydrogen by high-temperature steam electrolysis, and in particular, an electrolytic cell is divided into an anode side and a force source side by a solid oxide electrolyte membrane. An electrolysis apparatus suitable for use in an electrolysis method in which electrolysis power is reduced by supplying steam to the power source side of the electrolysis apparatus and supplying a reducing gas to the anode side to perform electrolysis. The optimal driving method is provided.

[0069] Further, according to the second aspect of the present invention, a hydrocarbon-containing gas is supplied to the anode side of an electrolyzer in which an electrolytic cell is divided into an anode side and a power source side by a solid oxide electrolyte membrane. The method of producing hydrogen by supplying high-temperature steam to the power source side and performing steam electrolysis to prevent clogging of electrodes due to solid carbon precipitated by the thermal decomposition of hydrocarbons In addition, hydrogen can be efficiently produced by effectively utilizing the heat of the anode-side exhaust gas after the reaction and the unburned gas components contained therein.

Claims

The scope of the claims

[1] Steam is supplied to the power source side of a high-temperature steam electrolyzer in which an electrolytic cell is partitioned into an anode side and a power source side using a solid oxide electrolyte as a diaphragm, and hydrocarbon-containing gas is supplied to the anode side. In the hydrogen production method using high-temperature steam electrolysis to reduce the electrolysis voltage by reacting with oxygen ions, the exhaust gas discharged from the anode side of the electrolysis apparatus is supplied to the hydrocarbon-containing gas supplied to the anode side of the electrolysis apparatus. A method for producing hydrogen, characterized by being mixed.

[2] Exhaust gas on the anode side so that the sum of water vapor and carbon dioxide is equal to or greater than the molar number of carbon atoms in the hydrocarbon-containing gas supplied to the anode side of the electrolysis apparatus. 2. The hydrogen production method according to claim 1, wherein the hydrogen is mixed.

[3] Exhaust gas from the anode side such that the sum of water vapor and carbon dioxide is about twice the molar number of carbon atoms in the hydrocarbon-containing gas supplied to the anode side of the electrolyzer. 2. The hydrogen production method according to claim 1, further comprising mixing hydrogen.

[4] A mixed gas of hydrocarbon-containing gas and exhaust gas on the anode side supplied to the anode side of the electrolyzer is converted to a mixed gas containing hydrogen and carbon monoxide as main components by a thermal reaction before contacting the anode of the electrolyzer. 14. The method for producing hydrogen according to claim 13, wherein the anode is brought into contact with the anode after performing the above.

[5] Oxygen or air is mixed with the exhaust gas on the anode side of the electrolyzer, and the resulting mixed gas is mixed with the hydrocarbon-containing gas supplied to the anode side of the electrolyzer, and the heat of the partial oxidation reaction of the hydrocarbon-containing gas is 15. The method for producing hydrogen according to claim 14, wherein the gas is converted into a mixed gas containing hydrogen and carbon monoxide as main components.

[6] An electrolytic cell separated into an anode side and a force source side by a membrane of solid oxide electrolyte, a pipeline for supplying a hydrocarbon-containing gas to the anode side of the electrolytic cell, and a vapor for supplying cathode gas to the electrolytic cell. And a pipe for mixing exhaust gas, which also discharges the anode side force of the electrolytic cell, into the hydrocarbon-containing gas supplied to the anode side of the electrolytic cell. Hydrogen production equipment.

[7] Supply a mixed gas of steam and the exhaust gas on the anode side of the electrolytic cell to the anode side of the electrolytic cell. A catalyst layer is placed in the pipeline, and the mixed gas of the hydrocarbon-containing gas and the exhaust gas on the anode side is subjected to electrolysis. 7. The hydrogen producing apparatus according to claim 6, wherein the apparatus is configured to be converted into a mixed gas containing hydrogen and carbon monoxide as main components by a thermal reaction before coming into contact with an anode of the apparatus.