JP4353657B2 - Method for separating hydrogen from hydrocarbon reformed gases using high temperature proton conductors - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention is a gas mixture containing carbon monoxide and hydrogen, to a hydrogen separation method for separating substantially only the hydrogen in particular immediately after synthesis hot synthesis gas.
[0002]
[Prior art]
In order to solve the global warming-causing problems such as carbon dioxide and exhaust gas harmful to living organisms, the problem can be reduced as much as possible from energy conversion technology that uses the combustion energy of fossil fuels as a mechanical energy source. The need for changes to energy conversion means that can be suppressed or to energy conversion means that do not substantially generate the gas in question has become a more pressing issue. Even in automobiles and the like, energy hybridization has been promoted, and the energy conversion means has been completely changed, and fuel cells are going to be changed to energy conversion means.
[0002]
Fuel cells have a long history of research and can convert the chemical energy of fuel directly into electrical energy through electrochemical reactions, and have the advantages of high conversion efficiency, clean exhaust, and low noise. It is attracting attention as an energy conversion means that can be installed in the department, and research into practical use is becoming more active. Among them, solid oxide fuel cells are expected to have much higher power generation efficiency than conventional heat engines, and are attracting attention as being able to solve future resource energy problems and the environmental problems.
In particular, a fuel using hydrogen as a fuel is attracting the most attention because a clean and fairly compact battery can be designed.
[0003]
However, in the battery that can be made compact at the present time, there is a problem that mixing of carbon monoxide into the hydrogen fuel causes poisoning to the noble metal catalyst, and causes adverse effects on the conversion means. It is an important issue to make the amount 100 ppm or less. The technology that has been proposed so far for removing carbon monoxide, etc., in the case of using reformed gas and synthesis gas as a hydrogen source,
1. Method using a porous body (filter).
2. A method of using palladium or a palladium alloy for hydrogen separation from the reformed gas.
3. There is a method using a solid electrolyte.
The method 3 is attracting attention as having few problems of separation performance and poisoning.
[0004]
Japanese Patent Application Laid-Open No. 10-297902 discloses production of synthesis gas by partial oxidation of hydrocarbons based on oxygen ion transport, and protons or proton alloys that use, for example, palladium or a palladium alloy as a hydrogen transport film from the generated synthesis gas. An invention of a process for producing hydrogen in which a transport membrane, for example, a step of separating only hydrogen using a high-temperature proton conductive solid electrolyte hydrogen transport membrane is integrated is described.
And although there is a principle explanation of the material and hydrogen production method that make up the solid electrolyte hydrogen transport membrane to be used, there is no specific explanation of hydrogen production, and it was confirmed that hydrogen was actually generated There is no data of what has been done. In addition, the present inventors tried to implement the technique within the range described in the above publication, but could not confirm the continuous separation of hydrogen.
[0005]
[Problems to be solved by the invention]
Therefore, the object of the present invention is to basically find the cause of the disadvantages of the prior art and establish a technique capable of separating pure hydrogen using a high-temperature proton conductive solid electrolyte that eliminates the disadvantages. The separation driving force depends only on the voltage, and the hydrogen separation technology that does not depend on the pressure difference and the concentration difference is established.
Then, it was estimated as follows why it did not operate | move by the principle only of the technical description of the said gazette. If the high-temperature proton conductive solid electrolyte has a stable chemical composition and structure, hydrogen separation must be realized from the proton conductive properties of the solid electrolyte. However, it is thought that the reason why it does not progress is that a stoichiometric change occurs in which the chemical composition and the crystal structure do not function as a proton conductor. Therefore, an experiment was attempted to examine how such a change can be prevented. At that time, since the reduction of oxygen is considered as a possibility, if it is attempted to supply oxygen by some method and the stoichiometric change can be eliminated, the proton conductivity of the solid electrolyte can be maintained. I thought. Based on this idea, when oxygen itself and a substance that can supply oxygen to the solid electrolyte, such as water (as steam), are supplied, hydrogen is supplied to the cathode side (some include hydrogen generated by electrolysis of the added steam) Has been confirmed to be stably transported by electrolysis. Thereby, the subject of the present invention was able to be solved.
[0006]
[Means for Solving the Problems]
In the present invention, electrodes capable of oxidizing hydrogen and reducing protons are attached to both surfaces of a membrane made of a high-temperature proton conductive solid electrolyte, one being an anode chamber (anode chamber) and the other being a cathode chamber (cathode chamber). At least carbon monoxide and / or in the anode chamber of an electrochemical cell in which a voltage is applied to the electrode so as to constitute and the high temperature proton conductive solid electrolyte is maintained to have sufficient ionic conductivity. A mixed gas containing carbon dioxide and hydrogen is supplied, and the cathode chamber is supplied with moisture at a ratio of 0.1-0.4 mol / generated H ₂ mol or a sweep gas containing moisture to the cathode chamber. This is a method for obtaining hydrogen separated from a gas. Preferably, it is a method for obtaining hydrogen separated from the mixed gas, characterized in that a membrane comprising a high-temperature proton conductive solid electrolyte is maintained at 700 ° C. or higher and 1000 ° C., and more preferably generated as a mixed gas A method for obtaining the separated hydrogen, characterized by using a high temperature reformed gas.
[0007]
[Embodiments of the present invention]
The present invention will be described in more detail.
A. A schematic structure of an electrochemical cell used in the present invention will be described with reference to FIG. In FIG. 1, [A] constitutes an anode chamber, to which a mixed gas G _MIX containing carbon monoxide (CO) such as a reformed gas is supplied, and a DC voltage D.V. C. Anode electrode EL _A , cathode electrode EL _C, and high-temperature proton conductive solid electrolyte S. E. Gas G _co having an increased CO concentration as a result of separation of hydrogen by an electrochemical cell composed of a film made of is taken out outdoors. [C] constitutes a cathode chamber from which separated hydrogen gas that has moved to the surface of the cathode electrode EL _C and a sweep gas that is supplied to separate the separated hydrogen gas from the electrode surface. moisture in G _SW is the hydrogen gas generated is electrolyzed is taken out together with the sweep gas G _SW. With such a configuration, hydrogen is separated.
[0008]
Here, only moisture may be supplied without using the sweep gas.
The concept of the membrane includes a relatively thick several mm thickness, and the shape is also plate-like, tube-like (in this case, it can be a cylindrical electrolytic cell), and the main points are hydrogen separation based on the above principle. Any device that exhibits its function may be used.
Further, as a raw material mixed gas for hydrogen separation, for example, a mixed gas of hydrogen and carbon monoxide (ratio 2/1) generated by a reaction of 1, CH ₄ + 1 / 2O ₂ → CO + 2H ₂ , 2, CO + H ₂ O → CO Examples thereof include a mixed gas of hydrogen and carbon dioxide (ratio is 3/1) obtained by reacting carbon monoxide produced in 1 with water vapor from the reaction of ₂ + H ₂ .
[0009]
B. The electrochemical cell is formed by attaching an electrode capable of causing the oxidation-proton reduction reaction of hydrogen on either side of the high-temperature proton conductors solid electrolyte. The reaction at the electrode of the electrochemical cell is theoretically H ₂ → 2H ⁺ + 2e ⁻ (anode) (1)
2H ⁺ + 2e ⁻ → H ₂ (cathode) (2)
However, since the reaction cannot be stably maintained, a small amount of oxygen replenisher, for example, water vapor is supplied to the cathode side, and a current caused by a small amount of oxide ions is generated in the solid electrolyte. The hydrogen separation of the present invention was realized.
[0010]
C. Examples of the high-temperature proton conductor solid electrolyte include SrCe _0.95 Yb _0.05 O _3-α , BaCe _0.80 Y _0.20 O _3-α , CaZr _0.90 In _0.10 O _3-α ( α is a value that neutralizes the charge of the mixed oxide) . Basically, any proton conductive oxide solid electrolyte can be used.
D. As an electrode constituent material, metals such as Pt and Ni, and electron conductive oxides can be used.
[0011]
【Example】
Example 1
A porous platinum electrode is attached to a proton conductive electrolyte SrCe _0.95 Yb _0.05 O _3-α processed into a disk shape having a diameter of 13 mm and a thickness of 0.5 mm, and a magnetic material constituting an anode chamber and a cathode chamber An electrochemical cell was constructed by being hermetically sandwiched with a member made of metal. A gas obtained by diluting a 2: 1 mixed gas of hydrogen and carbon monoxide with a diluent gas Ar is introduced into the anode chamber, and direct current is applied. The amount of hydrogen generated in the other electrode chamber is measured by a gas chromatograph (Shimadzu Corporation). GC-8A) manufactured. In this experiment using a wet argon as the sweep gas G _SW is high current efficiency to a relatively high current density by introducing steam into the cathode compartment is obtained. As a result of conducting an experiment at 900 ° C., it was confirmed that hydrogen was generated in the cathode chamber while being energized, and hydrogen was separated from the reformed gas by such a method. As shown in FIG. 2, the generation amount of hydrogen coincided with the value calculated from the current up to a current density of about 120 mA / cm ² . This indicates that all of the energized electricity was used for hydrogen generation in the cathode chamber, and the current efficiency is approximately 1.
[0012]
As shown in FIG. 3, was examined changes due to energization of the concentration of hydrogen and carbon monoxide in the anode chamber outlet gas G _CO, the concentration of carbon monoxide hardly changes with respect to current, whereas, hydrogen Monotonically decreasing, indicating that hydrogen has been separated.
Here, although the reduction amount of hydrogen is small, it is obvious that the hydrogen separation efficiency can be increased by increasing the electrode area and current.
[0013]
Comparative Example Here, argon without adding water vapor was used as the sweep gas G _SW , and when the relationship between the hydrogen generation rate in the cathode chamber and the current value was examined, the hydrogen generation rate was saturated at a current density of 25 mA / cm ² and hydrogen. It can be seen that the separation of is not proportional to the amount of current (FIG. 4). Further, FIG. 5 shows the results of measuring the hydrogen reduction rate in the anode chamber. Compared with FIG. 3, it is understood that the performance of hydrogen separation by the electrolytic cell is clearly poor.
[0014]
【The invention's effect】
As described above, hydrogen separation technology that can obtain hydrogen that does not contain CO by the method of the present invention and that can be designed to produce high-purity hydrogen by combining with the production of reformed gas. It is possible to provide an excellent effect.
[Brief description of the drawings]
FIG. 1 shows an example of a hydrogen separator according to the present invention. FIG. 2 shows current density and hydrogen generation rate by the method of the present invention. FIG. 3 shows hydrogen separation efficiency by the method of the present invention. Comparative example (cathode chamber)
FIG. 5: Comparative example using non-wet sweep gas (anode chamber)
[Explanation of symbols]
[A] Anode chamber [C] Cathode chamber EL _A Anode electrode EL _C Cathode electrode E High-temperature proton conductive electrolyte G _MIX mixed gas G _CO cathode chamber exhaust gas G _SW sweep gas

Claims (3)

Electrodes capable of oxidizing hydrogen and reducing protons are attached to both surfaces of a membrane composed of a high-temperature proton conductive solid electrolyte, one of which constitutes an anode chamber (anode chamber) and the other constitutes a cathode chamber (cathode chamber). voltage is applied to the electrodes as, and of maintaining electrochemical cell such that the high temperature proton conducting solid electrolyte has a sufficient ionic conductivity, a mixed gas containing carbon monoxide and hydrogen in the anode chamber A method for obtaining hydrogen separated from the mixed gas, characterized in that the cathode chamber is supplied with moisture or a sweep gas containing moisture at a ratio of 0.1-0.4 mol / generated H ₂ mol to the cathode chamber. .   2. The method for obtaining hydrogen separated from a mixed gas according to claim 1, wherein the membrane comprising the high-temperature proton conductive solid electrolyte is maintained at 700 ° C. or more and 1000 ° C.   The method for obtaining separated hydrogen according to claim 1 or 2, wherein the mixed gas is a high-temperature reformed gas produced.

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