JP2000086201A - Production of hydrogen - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a production method of hydrogen in high yield keeping high catalytic activity by lowering reaction temperature in the production proc ess of hydrogen by catalytic pyrolysis of hydrocarbon using a carbon-based catalyst. SOLUTION: In the production of hydrogen by catalytic pyrolysis of hydrocarbons, a graphite material is used as the catalyst, and a reaction pipe having a double-pipe structure described below is used as the reactor. This pipe consists of an inner pipe and an outer pipe, the wall of the inner pipe having hydrogen permeability and the space between the inner pipe and the outer pipe being filled with the graphite material. Hydrocarbons in a gaseous state are supplied into the outer pipe, brought into contact with the graphite material and decomposed. Hydrogen produced by the decomposition of hydrocarbon is passed into the inner pipe through its wall. Since this method based on low temp. pyrolysis enables to produce hydrogen without CO2 emission from hydrocarbon while keeping the catalytic activity. The method can be applied to a fuel cell to be mounted on a car using hydrogen as the energy source.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing hydrogen by pyrolyzing hydrocarbons.

[0002]

2. Description of the Related Art Conventionally, hydrogen has been widely used in the chemical industry as a raw material for ammonia and methanol. It tends to be used in large quantities for fuel cells and the like. As methods for producing hydrogen from lower hydrocarbons such as methane, steam reforming and partial oxidation are known, but these methods produce a large amount of carbon dioxide, a substance causing global warming, as a by-product. There is a disadvantage that. Thus, development of a method for producing hydrogen from hydrocarbons without by-producing carbon dioxide has been desired. As a method for producing hydrogen without by-producing carbon dioxide from hydrocarbons, there is known a method for producing hydrogen and solid carbon by thermally decomposing methane or the like. Among these methods, 1) a method of using a catalyst in which a metal such as nickel is supported on an oxide of silica or the like, and 2) a method of using a specific carbonaceous substance as a catalyst (Japanese Patent No. 2767390) is proposed. Have been. Among them, in the method 1), for example, Miyashita et al. Have disclosed a method of decomposing methane using a silica-supported nickel catalyst [72th Catalyst Symposium Proceedings, p. 190 (1993)]. However, in this method, the poisoning of active metals such as nickel by co-produced solid carbon and the aggregation of the nickel metal itself tend to lower the catalytic activity, shorten the service life, and recycle when incinerated after use. There is a problem in that nickel oxide that remains difficult to remain remains and causes heavy metal contamination. In addition, the carbon catalyst of 2) has heat resistance, is easy to reuse by reactivation (because it is the same type of carbon as deposited carbon), and is incinerated after use (all can be gasified) or pulverized for other uses. Although it has advantages such as being usable, there is a problem that the reaction temperature is higher than the method using a nickel-based catalyst, and the activity of the catalyst is still reduced. Therefore, in hydrogen production using a carbon-based catalyst, there is a strong demand for lowering the reaction temperature and preventing the catalyst activity from lowering.

[0003]

SUMMARY OF THE INVENTION The present invention has been made in view of the above situation in the prior art. That is, an object of the present invention is to provide a method for producing hydrogen in a high yield while maintaining high catalytic activity by a low-temperature reaction when producing hydrogen by catalytic pyrolysis of a hydrocarbon using a carbon-based catalyst. It is in.

[0004]

Means for Solving the Problems The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, have completed the present invention. That is, according to the present invention, in a method for producing hydrogen by catalytic pyrolysis of a hydrocarbon, a graphite-like substance is used as a catalyst, and an inner tube and an outer tube are used as a reactor, and the tube wall of the inner tube is hydrogen A double-walled reaction tube formed on the permeable tube wall and filled with a graphite-like substance in the space between the inner tube and the outer tube is used. A method for producing hydrogen, wherein the hydrogen is supplied to contact the graphite-like substance to be decomposed, and hydrogen generated by the decomposition of the hydrocarbon is transferred into the inner pipe through the pipe wall of the inner pipe. . Further, according to the present invention, in a method for producing hydrogen by catalytic pyrolysis of a hydrocarbon, a graphite-like substance is used as a catalyst, and an inner tube and an outer tube are used as a reactor. Using a double-walled reaction tube formed on the permeable tube wall and filled with a graphite-like substance in its inner tube, supplying hydrocarbon to the inner tube in a gaseous state and contacting the graphite-like material And a method for producing hydrogen, wherein hydrogen generated by the decomposition of the hydrocarbon is transferred into the outer tube through the inner wall of the inner tube.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, a graphite-like substance is used as a catalyst for producing hydrogen by catalytic pyrolysis of hydrocarbons. As the graphite-like substance used in the method for producing hydrogen in the present invention, any of natural substances and artificially synthesized substances can be used, and any shape may be used. There is no restriction. Among them, the crystal structure of the graphite-like substance is particularly preferably one having a plane spacing (d) of 0.345 nm or less.
phite Powder (plane spacing d = 0.338 nm), manufactured by Johnson Matthey, trade name: CarbonPowder (plane spacing d = 0.337n)
m), manufactured by Strem Chemical Co., and the like. here,
The surface distance (d) is defined by the following equation. d = λ / 2 sin θ In the formula, λ is the wavelength of the X-ray.

The graphite-like substance used for the catalyst in the present invention is preferably used in the form of a mixture with a heat-resistant substance. As the heat-resistant substance, a porous substance and a non-porous substance can be used, but a non-porous substance is preferably used. Specific examples of such a heat-resistant substance include quartz sand, fused silica, fused alumina, boron nitride, and the like. The heat-resistant substance is usually used in the form of particles having a particle size larger than that of the graphite-like substance used as a catalyst.
m, preferably 50 to 1000 μm. The proportion of the heat-resistant substance used is 0.1 to 99% by weight, preferably 10 to 99% by weight, based on the mixture of the graphite-like substance and the heat-resistant substance.
90% by weight. When a graphite-like substance is used as a catalyst in the form of a mixture with a heat-resistant substance, the following effects are expected. (1) When the hydrocarbon gas is passed through the catalyst layer, scattering of the graphite-like substance is prevented. (2) Clogging of the catalyst layer can be prevented. (3) Heat can be efficiently conducted to the graphite-like substance.

Next, the present invention will be described with reference to the drawings. FIG. 1 is a schematic view showing one example of a reaction tube having a double tube structure used in the method for producing hydrogen of the present invention. In FIG. 1, 1 is an inner pipe, 2 is an outer pipe, 3 is a gas supply pipe, and 4 is a gas discharge pipe. The tube wall of the inner tube 1 is formed as a hydrogen-permeable tube wall, and hydrogen existing in the outer tube 2
Through the inner wall of the inner tube 1. The hydrogen permeable tube wall is a tube wall through which hydrogen gas is selectively transmitted, and is formed of a hydrogen permeable material. As the hydrogen permeable material in this case, there are various conventionally known materials, such as the alloy itself (Pd, Pd
/ Ag alloy, Pd / Cu alloy, Pd / Pt alloy, Pd /
V alloy, Fe / Ti alloy, etc.) and a hydrogen-permeable metal film (Pd, P
d / Ag alloy, Pd / Cu alloy, Pd / Pt alloy, Pd
/ V alloy, metal film formed from Fe / Ti alloy), and the surface of a tubular body made of a ceramic porous body,
Examples thereof include those in which a thin film of Pd or Pd / Ag is formed by electroless plating or the like.

In the reaction tube shown in FIG. 1, a graphite-like substance as a catalyst is filled in an annular space between the outer peripheral surface of the inner tube 1 and the inner peripheral surface of the outer tube 2 to form a catalyst layer. Let it. Next, in order to produce hydrogen using the reaction tube shown in FIG. 1, a sweep gas (hydrogen gas, nitrogen gas, or the like) is allowed to flow through the inner tube 1 and gaseous hydrocarbon is reacted as a reaction gas. It is introduced into the outer tube 2 via the supply tube 3. This hydrocarbon gas is decomposed into hydrogen by passing through the catalyst layer and contacting the graphite-like substance. Hydrogen generated by the decomposition reaction of the hydrocarbon gas permeates into the inner pipe 1 through the pipe wall of the inner pipe 1 having hydrogen permeability, and is discharged and recovered together with the sweep gas. On the other hand, substances other than hydrogen are discharged through the gas discharge pipe 4. for that reason,
Since generated hydrogen and carbon do not react again on the catalyst, by-products of hydrocarbons such as methane can be suppressed. When the reaction is carried out in a usual fixed bed flow reactor, a reaction between hydrogen and carbon occurs, so that by-products such as methane significantly increase.

When the catalytic cracking reaction of hydrocarbons is performed as described above, carbon generated by the decomposition of hydrocarbons is captured by the graphite-like substance used as a catalyst first.
In addition, since the generated carbon is a similar graphite-like carbon, it effectively acts as a catalyst. Therefore, in the present invention, the activity of the catalyst does not decrease even if the decomposition reaction proceeds. However, if the reaction proceeds using carbon such as activated carbon as a catalyst instead of the graphite-like substance, graphite-like carbon having a different structure accumulates on the activated carbon. Activity will be reduced.

[0010] Hydrogen generated by the decomposition of hydrocarbons permeates from the outer tube 2 into the inner tube 1 and is continuously removed from the reaction system. As a result, the equilibrium of the hydrocarbon decomposition reaction is greatly inclined to the product side, so that the hydrocarbon decomposition reaction is smoothly promoted, and the reaction temperature is remarkably lowered.

FIG. 2 is a schematic view showing another example of a double-tube reactor used in the hydrogen production method of the present invention. In this reaction tube, the sweep gas is introduced through the sweep gas supply pipe 5 to the bottom of the inner pipe 1, from which the inner pipe 1
, Rises in the inner pipe 1 and is discharged through the sweep gas discharge pipe 6.

In the above-described method, the sweep gas is supplied into the inner tube 1. However, the use of such a sweep gas is not always necessary.
For example, the pressure may be maintained at 10 Torr or less, preferably 0.5 Torr or less. Thereby, permeation of hydrogen present in the outer tube 2 into the inner tube can be greatly promoted.

The graphite-like substance as a catalyst is shown in FIG.
As shown in FIG. 2 and FIG. 2, it is not always necessary to fill the space between the inner pipe 1 and the outer pipe 2; Can be supplied into the inner tube and brought into contact with the graphite-like substance to be decomposed. In this case, hydrogen generated by the decomposition of the hydrocarbon moves into the outer pipe 2 through the pipe wall of the inner pipe 1 and is discharged from the outer pipe 2 together with the sweep gas supplied to the outer pipe. In the above method, the sweep gas was supplied into the outer tube 2; however, the use of such a sweep gas is not always necessary, and the inside of the outer tube 2 is kept under vacuum conditions, for example, 10 torr or less, preferably 0 to 0. It may be kept below 0.5 torr. Thereby, permeation of hydrogen present in the inner tube 1 into the outer tube 2 can be greatly promoted.

The hydrocarbons used as a raw material for producing hydrogen in the present invention are preferably gaseous or liquid hydrocarbons having a large hydrogen / carbon ratio at room temperature. Specifically, aliphatic hydrocarbons such as methane, ethane, ethylene, and propane;
Alicyclic hydrocarbons such as cyclohexane and cyclopentane;
Aromatic hydrocarbons such as benzene, toluene and xylene are preferred. In addition, a liquid mixture such as gasoline, light oil, and kerosene, and a normal-temperature solid hydrocarbon such as paraffin and wax can also be used. The liquid or solid hydrocarbon at room temperature may be heated and converted into a gaseous substance, and then supplied to the reactor. These hydrocarbons may be used alone or in combination of two or more. At the time of this thermal decomposition reaction, water, carbon dioxide, and the like may coexist in the reaction system. The coexistence amount is 0.01 to 100 mol, preferably 0.1 to 50 mol, per 1 mol of carbon contained in the starting hydrocarbon. The supply of H ₂ O or CO ₂ to the reaction system can be performed continuously or intermittently.

The hydrocarbons are preferably used after being diluted with an inert gas such as argon, nitrogen, helium or the like in order to perform the thermal decomposition more advantageously thermodynamically. 1 to 50% by volume, preferably 0.8 to
The range is 10% by volume. The reaction temperature is at least room temperature, preferably at least 100 ° C., more preferably at least 30 ° C.
The temperature is 0 ° C. or more, and the upper limit is about 1500 ° C. Generally, 100 to 1,500 ° C, preferably 300 to 1,000 ° C, more preferably 500 to 800 ° C.
A temperature of ° C is employed. The contact time between the catalyst surface and the hydrocarbon gas is 0.01 to 1000 seconds, preferably 0.1 to 5 seconds.
0 seconds. The oxygen concentration in the reaction system is 0.1% by volume or less,
Preferably it is 0%. As the sweep gas, an inert gas such as argon, nitrogen, and helium is usually used.
The flow rate of the sweep gas is 1 to 1 of the flow rate of the reaction gas.
1000 times, preferably <10 to 200 times.

The method of using the double-tube reactor and the graphite-like substance catalyst of the present invention in combination uses the activated carbon catalyst or the like in a conventional fixed-bed flow type reactor in comparison with the conventional method in which the generated hydrogen is used successively. By shifting the chemical equilibrium to the product side by flowing out of the reaction system, hydrocarbons can be thermally decomposed under the reaction conditions at low temperature, and the produced graphite-like carbon also acts as a catalyst, so the activity of the catalyst This method has the advantage that no reduction occurs, and is an extremely excellent method for producing hydrogen by pyrolysis of hydrocarbons.

[0017]

EXAMPLES Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited thereto. Example 1 Commercial graphite pulverized to a particle size of 1 to 10 μm (manufactured by Johnson Matthey; trade name: Carbon Graph)
item Powder, spacing d = 0.338 nm) 2 g
And 10 g of quartz sand having a particle size of 100 to 1000 μm are mixed well, and the mixture is mixed with a 90 w
The catalyst layer was filled between a double tube type reaction tube consisting of an inner tube made of an alloy of t% Pd / 10 wt% Ag and an outer tube made of quartz having an inner diameter of 19.5 mm. At that time, both ends of the catalyst layer were filled with quartz wool to prevent the catalyst from moving during the reaction.
This double tube type reaction tube is charged into an electric furnace, and a mixed gas of ethane and nitrogen (ethane / nitrogen = 2/98 (volume ratio)) is
The reaction tube was heated to 650 ° C. (923 K) at a rate of 6 ° C./min while passing at a rate of 20 cm ³ / min to start the reaction. In addition, sweep gas (flow rate 1700 cm ³ /
(Minute), argon was used to flow in the same direction as the reaction gas. At 650 ° C. (92
After reaching 3K), the product gas was sampled at predetermined time intervals and the gas composition was analyzed by gas chromatography. The ethane conversion was about 35% immediately after the start of the reaction, and the conversion was up to about 2 hours. Decreased slightly, but the catalytic activity increased with the accumulation of graphite-like carbon, and 8
After time, the conversion of ethane reached about 70% (see line 1 in FIG. 3). On the other hand, the yield of organic products (methane, ethane, ethylene, benzene, etc.) is 2 hours after the start of the reaction.
From about 0% to about 5% or less after 6 hours (see line 2 in FIG. 3), and correspondingly, the ratio of the total amount of generated hydrogen to the generated carbon is represented by the stoichiometric formula. About 1.
5 (the ratio of the total amount of generated hydrogen to the generated carbon is shown as an inset in FIG. 3).

The conversion (%) of the ethane and the yield (%) of the organic product are represented by the following formulas. Ethane conversion (%) = (AB) / A × 100 A: Number of moles of starting ethane B: Number of moles of unreacted ethane Yield of organic product (%) = (total of organic product) (Mol number) / mol number of raw material ethane × 100 In the above formula, total mol number of organic product = (methane + (ethane + ethylene) × 2 + (propane + propylene) × 3 +
Benzene x 6)

Comparative Example 1 A commercial activated carbon (manufactured by Aldrich, trade name: AC Darco KB-) was used in place of the graphite used in Example 1.
A thermal decomposition reaction was carried out in the same manner as in Example except that B) was used and a fixed bed reaction tube was used instead of the double tube reaction tube, and the catalytic activity gradually decreased in a reaction for 5 hours. (See line 1 in FIG. 4). In addition, the amount of the organic product was constant at a little less than about 40%, which was 8 times or more that of the steady-state activity in Example 1 (see line 2 in FIG. 4). It was very different.

[0020]

According to the present invention, the advantages of the graphite-like substance as a catalyst (such as heat resistance, easy reuse by reactivation, and reusability for other uses by incineration or pulverization after use) are obtained. By utilizing it in combination with a double-tube reactor while maximizing its utilization, it is possible to carry out the thermal decomposition reaction of hydrocarbons at a lower temperature without lowering the catalytic activity compared to the conventional method. It is suitable as a production method. Further, the present invention can produce hydrogen while maintaining catalytic activity by pyrolysis at a low temperature without emitting carbon dioxide from hydrocarbons in a small-sized device. Applicable.

[Brief description of the drawings]

FIG. 1 is a schematic view showing an example of a double-structure reaction tube used in the present invention.

FIG. 2 is a schematic view showing another example of a reaction tube having a double tube structure used in the present invention.

FIG. 3 is a graph showing a reaction result obtained in Example 1.

FIG. 4 is a graph showing the reaction results obtained in Comparative Example 1.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Inner pipe 2 Outer pipe 3 Gas supply pipe 4 Gas discharge pipe 5 Sweep gas supply pipe 6 Sweep gas discharge pipe

(72) Inventor Kunio Suzuki 1-1-1, Higashi, Tsukuba, Ibaraki Pref., National Institute of Advanced Industrial Science and Technology (72) Inventor Satoshi Hamakawa 1-1-1, Higashi, Tsukuba, Ibaraki Pref. In the laboratory

Claims (2)

[Claims] 1. A method for producing hydrogen by catalytic pyrolysis of a hydrocarbon, wherein a graphite-like substance is used as a catalyst,
The reactor consists of an inner tube and an outer tube, and the tube wall of the inner tube is formed on the hydrogen permeable tube wall, and the space between the inner tube and the outer tube is filled with a graphite-like substance. Using a reaction tube having a double-tube structure, hydrocarbon is supplied in gaseous form to the outer tube of the reaction tube, and is brought into contact with the graphite-like substance to be decomposed. A method for producing hydrogen, wherein the method is transferred to an inner tube through a tube wall. 2. A method for producing hydrogen by catalytic pyrolysis of a hydrocarbon, wherein a graphite-like substance is used as a catalyst,
As a reactor, a reaction tube having a double tube structure comprising an inner tube and an outer tube, wherein the tube wall of the inner tube is formed on a hydrogen permeable tube wall, and the inner tube is filled with a graphite-like substance. Use
Hydrocarbon is supplied to the inner tube in a gaseous state and is brought into contact with the graphite-like substance to be decomposed, and hydrogen generated by the decomposition of the hydrocarbon is transferred into the outer tube through the tube wall of the inner tube. Method for producing hydrogen.