JP2001220103A - Hydrogen producing method by decomposition of hydrocarbon - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a small-sized catalytic process for hydrogen production to replace of steam reforming reaction, small in energy consumption and for producing high purity hydrogen containing no CO and compatible with a fuel production process for a solid high molecular fuel cell. SOLUTION: A Ni/SiO2 catalyst is arranged on a Pd-Ag film in a reactors A and B. In the initial operation, a city gas and combustion air are introduced into the reactor A respectively from V1 and V2 to combust and exhausted from V5. Steam is generated by using the resultant heat by the combustion and the sweep steam is introduced into a hydrogen manifold. After the introduction of the sweep steam, the city gas is introduced into the reactor B from V2 to cause the methane decomposition reaction to obtain gaseous hydrogen and carbon. The resultant gaseous hydrogen in the reactor B penetrated through the Ps-Ag film and is discharged with steam from the hydrogen manifold. When the carbon generation in the reactor B reaches a certain stage, V2 is closed, V4 and V6 are opened and the combustion reaction of the carbon is performed and in the reaction A, V4 is closed, the introduction of the combustion air is stopped and successively V5 is closed to perform the methane decomposition reaction with the city gas from V1. After that, the reactors A and B are switched to each other to produce hydrogen.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing hydrogen in a solid polymer electrolyte fuel cell and various chemical processes by the catalytic cracking reaction of hydrocarbons, particularly natural gas and CH ₄ , and the combustion of generated carbon. The present invention relates to a process for producing high-purity hydrogen containing no carbonaceous material. The process of the present invention operates at a low temperature of about 500 ° C. and can produce hydrogen gas having a purity of 99.999% or more, which is useful as a high-purity hydrogen production process.

[0002]

2. Description of the Related Art Conventionally, methods for producing hydrogen from hydrocarbons include steam reforming, coal gasification, partial oxidation,
An autothermal reforming method is used. In particular, a steam reforming method in which steam reacts with a hydrocarbon is widely used as the most general method for producing hydrogen.

[0003] The steam reforming method is a large endothermic reaction under a pressurized condition, and requires an extremely high reaction temperature of 700 ° C or more and a large amount of heat energy accompanying the endothermic reaction. In addition, the generated hydrogen contains
It is a hydrogen production method which includes CO and CO ₂ , which must be separated and removed by a membrane separation or a pressure swing method in a post-process, and which is expensive in terms of equipment and energy.

[0004] Impurity CO in hydrogen obtained by the steam reforming process is removed by a shift reaction (CO + H ₂ O → CO ₂ + H ₂ ). CO cannot be completely removed from the hydrogen produced in the above.

On the other hand, a fuel cell (PEFC) using a polymer solid electrolyte has been developed as a new power generation method. However, impurity CO in H ₂ used as a fuel deactivates the activity of the electrode, and the performance of the cell is reduced. Therefore, in order to perform stable power generation for a long period of time, it is necessary to remove impurity CO in fuel as much as possible.

A small amount of oxygen is added to H ₂ containing a small amount of CO,
Oxidizing CO, but be removed has been studied, in the oxidation process, H ₂ is also part of the same time, since it is oxidized, H ₂ is consumed partially.

[0007]

SUMMARY OF THE INVENTION The present invention provides a membrane reactor having a hydrogen permeable membrane instead of the steam reforming method which has been used as a general hydrogen production method.
Hydrocarbons, in particular performs decomposition of CH _4, hydrogen free of CO in high purity with obtaining at a low temperature of about 500 ° C., obtained by carbon burnoff that generated the heat energy required for this reaction, high purity The purpose is to produce hydrogen and supply it to various chemical processes including fuel cells.

[0008]

The present inventors have SUMMARY OF THE INVENTION, for the purpose of solving the above problems, a hydrocarbon, particularly focusing on the CH ₄ decomposition reaction represented by CH ₄ → C + H _2. This reaction does not proceed from the constraints of thermodynamic chemical equilibrium at low temperatures, using a hydrogen-permeable membrane made of Pd-based alloy, the generated H ₂ from the reaction system, the separation and removal, low temperature of about 500 ° C. However, they found that the decomposition reaction proceeded. On the other hand, in this reaction, carbon is deposited on the catalyst and the catalyst is deactivated, but the generated carbon is burned in a membrane reactor, which can be used as a heat source for the decomposition reaction and the catalyst can be regenerated. The invention has been reached.

Here, the present invention according to claim 1 comprises two catalytic reactors using a hydrogen permeable membrane made of a Pd-based alloy membrane, wherein one of the reactors performs a decomposition reaction of hydrocarbons, particularly CH _4. In other reactors, catalytic combustion of carbon produced by air generates catalysts and generates heat of reaction for cracking hydrocarbons. The two reactors are switched periodically,
Repeat hydrocarbon decomposition and carbon combustion.

[0010] In the above-mentioned membrane reactor, in order to sweep generated hydrogen and promote the reaction efficiently, steam which is easily separated is used as a sweep gas. The water vapor of the sweep gas can be obtained by catalytic combustion of carbon, and it can be easily separated and removed from hydrogen only by cooling at the reactor outlet,
High-purity hydrogen can be easily obtained.

According to the present invention, high-purity hydrogen free of CO and CO ₂ can be easily obtained, so that fuel for a fuel cell using a polymer electrolyte and various chemical processes and chemical raw materials for a semiconductor manufacturing process can be obtained. Can be used as

In the present invention, by disposing two reactors for performing an endothermic reaction of catalytic cracking of hydrocarbons and an exothermic reaction of burning carbon in parallel, heat can be easily transmitted and the reactor can be reduced in size. It can be operated at a reaction temperature as low as about 500 ° C.

The catalyst used in the invention according to claims 5 and 6 includes Ni and Co supported on a metal oxide.
A system-based metal catalyst is effective, and a catalyst in which one or more metals are added as an additive based on Ni or Co is effective. As the carrier oxide, SiO ₂ or Al ₂ O ₃ based metal oxide is effective.

[0014] Further, as the catalyst, the Ni / SiO ₂ catalyst alone has sufficiently high activity for both the decomposition of hydrocarbons and the catalytic combustion of generated carbon, and can maintain high activity even in repeated operations.

In the hydrogen production process of the present invention, it is not necessary to supply excessive steam for the reaction, and the process can be simplified and the reactor can be made compact as compared with the steam reforming reaction process.

On the other hand, the conventional steam reforming reaction requires a reaction temperature of 700 ° C. or higher, whereas the hydrogen production process of the present invention requires a reaction temperature of 500 ° C.
Since the reaction temperature can be lowered, the durability of the constituent materials of the process can be extended, and the life of the catalyst can be extended.

[0017]

Next, an embodiment of the present invention will be described. FIG. 1 shows an example of a hydrogen production process by hydrocarbon cracking in the present invention. In the illustrated process, in the reactors A and B, a Ni / SiO ₂ catalyst is disposed on a Pd-Ag film. During the first operation, city gas is introduced into reactor A from V1, combustion air is introduced from V2 and burned, and exhausted from V5. Utilizing the heat obtained by the combustion, steam is generated and the sweep steam is introduced into the hydrogen manifold. After the introduction of the sweep steam, city gas is introduced into reactor B from V2, and a methane decomposition reaction is performed to obtain hydrogen gas and carbon. The hydrogen gas obtained in the reactor B passes through the Pd-Ag membrane and is discharged from the hydrogen manifold together with the vapor. When the production of carbon in the reactor B reaches a certain stage, V2 is closed and V4 and V6 are opened to perform a carbon combustion reaction.In the reactor A, V4 is closed, the introduction of combustion air is stopped, and then V5 is A methane decomposition reaction is performed with the city gas from V1. After that, the reactors A and B are alternately switched,
Generates hydrogen. After the completion of hydrogen production, V1 to V6 are all closed to terminate the reaction.

FIG. 2 shows the results of searching for a catalyst active in the present invention. Here, a 250 mm thick hydrogen permeable membrane made of 90Pd-10Ag was used. CH ₄ decomposition activity of various Ni catalysts was studied. This one of the Ni-based catalyst as is apparent in FIG. Also has a high activity to degradation activity of CH _4, it is found to be a good CH ₄ cracking catalyst. Further, when the concentration of the generated hydrogen was analyzed, no impurities were recognized by gas chromatography, and it was found that the purity was 99.999% or more in view of the analysis accuracy.

FIG. 3 shows the oxidizing activity of the produced carbon in the present invention. As can be seen from the figure, various Ni-based catalysts are active in catalytic combustion of carbon, especially Ni / SiO ₂ and Ni-
It can be seen that the activity of the Co / SiO ₂ catalyst is high. When combined with the results of the decomposition of CH ₄ shown in FIG. 2 in the preceding section, it can be seen that Ni / SiO ₂ shows activity in both reactions and is most suitable as the catalyst for the hydrogen production process of the present invention shown in FIG. However, Ni / S
In addition to iO ₂ , many Ni-based and Co-based catalysts show activity in both reactions, and any of them can be applied to the hydrogen production process of the present invention.

[0020] using a Ni / SiO ₂ catalyst which is considered optimal in FIG. 4, a membrane reactor having a hydrogen-permeable membrane having the composition 90Pd-10Ag, hydrogen production by CH ₄ decomposition at 500 ° C., with air combustion The results of repeated carbon combustion are shown. As is clear from the figure, even when hydrogen production and carbon combustion are repeatedly performed, the catalyst does not deteriorate, and high CH ₄ decomposition activity and carbon removal can be performed. Also, from the results of FIG. 4, it is desirable that the timing of switching between the two reactors in the present process shown in FIG. 1 is several hours to several tens of hours.

The effect of the composition of the hydrogen permeable membrane was examined, and the activity was improved as the Ag concentration increased, and the largest CH ₄ decomposition activity was obtained at an Ag content of 20%. Therefore, the composition of the hydrogen-permeable membrane applicable to this process is not limited to 90Pd-10Ag, but any Pd-Ag-based alloy, and eventually any Pd-based alloy and Ni-based hydrogen-absorbing alloy can be applied. It became clear.

Therefore, the hydrogen production process based on the hydrocarbon decomposition reaction according to the present invention is compact and simple, yet has an excellent energy balance,
It became clear that the process could generate more than 99.999% hydrogen.

The catalytic reactor applicable to the hydrogen production process of the present invention is not limited to a flat plate type as shown in FIG. 1, but a double tube type reactor as shown in FIG. Any of a tubular reactor and a flat reactor can be applied.

[0024]

Next, an embodiment of the present invention will be described. (Example 1) Ni (NO ₃ ) weighed to 10 wt% as Ni on high surface area SiO ₂ was evaporated to dryness, and then dried at 70 ° C.
The Ni / SiO ₂ catalyst was prepared by calcining in air at 00 ° C and hydrogen reduction at 500 ° C. After pressure molding, the catalyst was sized using a sieve so that the particles became particles of the specified size.

The obtained catalyst was used as a hydrogen separation membrane to a thickness of 25
The flat and membrane catalytic reactors shown in FIG. 1 or FIG. 5 were packed with a 0 mm 90Pd-10Ag membrane. As a sweep gas, steam was generated at 150 ° C. and supplied. Water vapor was removed by water cooling at the reactor outlet to obtain hydrogen. The compositions of the raw materials and products were all analyzed by gas chromatography, and the carbon exhaust gas was also analyzed by a chemiluminescence NOx meter.

A gas having a composition of CH ₄ : N ₂ = 1: 6.5 is contacted for a contact time of W /
F = 25 g-cat.h / mol. The CH ₄ decomposition activity with various catalysts is as shown in FIG. From this figure, it can be seen that many Ni-based catalysts are active in the CH ₄ decomposition reaction as described above. The most active catalysts was a Co-Ni, Ni but also have sufficient activity, the CH ₄ conversion at 500 ° C. in excess of 80%. The impurities in the hydrogen obtained at this time were less than the gas chromatography analysis sensitivity and had a purity of 99.999% or more. The combustion activity of the generated carbon is as shown in FIG. As a catalyst effective for the present invention, it is necessary to be active for both CH ₄ decomposition and carbon combustion, and it is understood that the Ni / SiO ₂ catalyst has excellent activity and repetition stability.

[0027]

The hydrogen production process based on the hydrocarbon decomposition reaction according to the present invention is a process that can be thermally independent, can produce high-purity hydrogen at a low temperature of about 500 ° C., and has a simple process. Despite its small size, it exhibits sufficient hydrogen production capacity.

Accordingly, the process for producing hydrogen based on the hydrocarbon decomposition reaction can be applied to various chemical processes requiring high-purity hydrogen. In particular, a fuel cell for a fuel cell using a solid polymer electrolyte as an electrolyte It has excellent characteristics as a generation process.

[Brief description of the drawings]

FIG. 1 is an apparatus flow chart showing a conceptual example of a process according to the present invention.

FIG. 2 is a diagram showing the temperature dependence of the activity of various catalysts for the CH ₄ decomposition reaction according to the present invention.

FIG. 3 is a diagram showing the temperature dependence of the combustion activity of carbon generated by the decomposition of CH _{4 of} various catalysts according to the present invention.

FIG. 4 is a graph showing changes in the catalytic activity of repeated decomposition of CH ₄ and carbon oxidation in the Ni / SiO ₂ catalyst according to the present invention.

FIG. 5 is a view showing an example of a tubular reactor applicable to CH ₄ decomposition and carbon oxidation according to the present invention.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) B01J 23/89 B01J 38/00 301C 38/00 301 C10G 11/02 C09K 5/16 B01J 23/74 321M C10G 11/02 C09K 5/00 J (72) Inventor Hidetoshi Shinkai 1-17-1 Chiyo, Hakata-ku, Fukuoka City, Fukuoka Prefecture F-term (reference) 4F006 GA41 KE16Q KE16R MA03 MA31 MB04 MC02 MC02X MC03 MC03 MC03 NA39 NA54 NA64 PB18 PB66 PC80 4G040 DA03 DB01 DB03 DB05 DC01 DC02 DC03 DC04 4G069 AA04 AA15 BA02A BA02B BA18 BC10A BC16A BC31A BC32A BC32B BC43A BC51A BC66A BC67A BC68A BC68B BC72A BC72B BC7529 DA05H07

Claims (7)

[Claims] 1. A process for decomposing hydrocarbons such as methane, ethane and ethylene (CnHm → nC + 1 / 2mH ₂ ) to produce hydrogen and burning the produced carbon (C + O ₂ → CO ₂ ) A high-purity hydrogen production process comprising a two-stage reactor for obtaining reaction heat of catalyst regeneration and decomposition reaction. 2. A hydrogen production process by a hydrocarbon decomposition reaction, wherein any hydrocarbon can be used as the hydrocarbon, and in particular, a city gas containing CH ₄ as a main component is used. 3. In order to remove the generated hydrogen and promote the reaction even at a low temperature in the hydrocarbon decomposition reaction, a hydrogen permeable alloy, particularly a hydrogen permeable membrane made of a Pd-based, preferably Pd-Ag-based, is used. Hydrocarbon cracking catalyst process using a reactor characterized in that the catalyst is shifted to the product side. 4. A hydrocarbon cracking reactor using a hydrogen separation membrane according to claim 3, wherein steam generated by using exhaust heat of a carbon combustion process is used as a gas for sweeping hydrogen permeated through the carbon separation membrane. Using a membrane-type reaction process. 5. A catalyst for cracking and burning hydrocarbons represented by the general formula Ni-M / AO or Co-N / AO. Where M is Co, F
One or two selected from the group consisting of e, Cu, Pd, Ag, Pt
More than one kind of metal element. N is one or more metal elements selected from the group consisting of Ni, Fe, Cu, Pd, Ag, and Pt. AO is Si,
A metal oxide comprising one or more metal elements selected from the group consisting of Mg, Zr, Ce or Al. Desirably
M is Fe, N is Ni, and AO is SiO ₂ . 6. A hydrogen production process using a Ni / SiO ₂ catalyst as a catalyst for hydrocarbon cracking and carbon combustion. 7. A method for producing a solid polymer electrolyte fuel cell using the hydrogen production method according to claim 1.