JP3837482B2 - Catalyst for producing hydrogen and method for producing hydrogen using the same - Google Patents

Description

【００２２】
【発明の効果】
本発明によれば、炭化水素類を分解して水素を製造する反応において、二酸化炭素、水及び酸素等の酸化性ガス共存下においても、安定した触媒活性を有すると共に、長時間に亘って触媒寿命が維持される有用な触媒が提供される。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a hydrogen production catalyst used for hydrocarbon decomposition and a method for producing hydrogen using the same.
[0002]
[Prior art]
Hydrogen is widely used in the chemical industry as a raw material for ammonia and methanol, and in the future, it will be used in large quantities as an energy source for fuel cells and the like. Recently, it has been reported that iron-based catalysts are used as catalysts for producing hydrogen by cracking hydrocarbons (MAErmakova, DYErmakov, ALChuvilin, and GGKuvshinov, J. Catal., 201, 183-197 (2001); Serizawa Michio, Takenaka So, Yamanaka Ichiro, Otsuka Kiyoshi, 86th Catalytic Conference 3I05 (2000)). This iron-based catalyst exhibits an activity comparable to that of a Ni-based catalyst in a pure hydrocarbon decomposition reaction system in which an oxidizing gas such as oxygen is not present. It is also estimated that metal iron / iron carbide is involved in the reaction under the reaction conditions (reported by Ermakova et al.).
[0003]
However, when an appropriate amount of an oxidizing gas such as CO ₂ or H ₂ O, which is expected to react with by-product carbon, is added to the reaction system in order to extend the catalyst life in the hydrocarbon decomposition reaction, iron is further increased. There was a drawback that the state of oxidation was reduced and the activity of the iron-based catalyst was lowered. Therefore, in order to utilize the iron-based catalyst not only for hydrocarbon decomposition but also for hydrocarbon reforming, metallic iron / iron oxide is stable even in reaction systems containing these oxidizing gases. Therefore, it is important to develop an improved iron-based catalyst that maintains high activity.
[0004]
[Problems to be solved by the invention]
An object of the present invention is to provide an improved iron-based catalyst that is stable against a hydrocarbon decomposition reaction even in the presence of an oxidizing gas and that has a long-term catalytic activity, and a hydrocarbon using the catalyst. It is to provide a method for producing hydrogen from hydrogen.
[0005]
[Means for Solving the Problems]
As a result of intensive studies on the catalyst used in the catalytic cracking reaction of hydrocarbons in order to solve the above-mentioned problems, the present inventors have found that a catalyst comprising a specific component has good characteristics and completes the present invention. It came to.
That is, according to the present invention, an alumina-based support is loaded with an iron-containing substance and a substance containing at least one metal selected from Group IIa metal, Group VIIa metal and rare earth metal of the periodic table. A hydrogen production catalyst for use in the hydrocarbon decomposition reaction is provided.
Further, according to the present invention, the hydrocarbon is supported on the alumina carrier with an iron-containing substance and a substance containing at least one metal selected from Group IIa metal, Group VIIa metal and rare earth metal of the periodic table. A method for producing hydrogen by a hydrocarbon decomposition reaction is provided, wherein hydrogen is obtained by contacting the catalyst with a heated catalyst.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, in order to produce hydrogen by cracking hydrocarbons, an alumina-based catalyst support is provided with at least one metal selected from iron-containing materials and Group IIa metals, Group VIIa metals, and rare earth metals of the periodic table. A supported catalyst is used using the contained substance as an active ingredient.
[0007]
Examples of the alumina-based material used as the catalyst carrier in the present invention include various alumina structures conventionally known as catalyst carriers and their precursors, and are not limited in any way depending on their production method and raw materials. Examples of such alumina-based materials include α-alumina, β-alumina, γ-alumina, activated alumina, and the like. Moreover, as an alumina precursor, it becomes an alumina by baking, and organometallic aluminum compounds, such as aluminum isopropoxide, aluminum acetylacetonate, and triethylaluminum, are illustrated.
[0008]
The iron-containing substance used as the active component of the catalyst in the present invention includes any form, but those soluble in water and organic solvents are recommended. Specifically, inorganic substances such as iron nitrate and iron sulfate are recommended. Illustrative examples include iron acid salts, iron halides such as iron chloride and iron bromide, organic acid irons such as iron oxalate, iron stearate and iron acetate, and organometallic irons such as ferrocene and iron acetylacetonate . The amount of these iron-containing substances to be added is arbitrary, but is 0.01 to 100% by weight, preferably 1 to 70% by weight, based on the alumina carrier.
[0009]
The active component of the other catalyst used in combination with the iron-containing substance is a substance containing at least one metal selected from Group IIa metal, Group VIIa metal and rare earth metal of the periodic table (hereinafter referred to as this). Also referred to as “specific metal-containing material”). These are not limited as long as they are metals that do not themselves have hydrocarbon decomposition activity, but the Group IIa metal is preferably magnesium, the Group VIIa metal is preferably manganese or rhenium, and the rare earth metal is Lanthanum, cerium, europium and the like are preferable. Substances containing these metals include inorganic acid salts such as nitrates and sulfates, halides such as chlorides and bromides, organic acid salts such as oxalates and acetates, cyclopentadienyl metals, and acetylacetonate metals. And organometallic compounds such as Although these addition amounts are arbitrary, they are 0.01 to 80 weight%, preferably 1 to 20 weight% of a metal element with respect to an alumina type support | carrier.
[0010]
The catalyst preparation method of the present invention includes (1) a method of impregnating an alumina-based material as a support with an iron compound and a specific metal-containing material, and (2) precipitation of iron and a specific metal-containing material on an alumina-based support. A method, (3) a method of dropping a solution of iron and a specific metal-containing substance onto an alumina-based carrier (incipient wetness method), (4) a method of kneading an alumina-based carrier, an iron compound and a specific metal-containing substance, etc. Illustrated. In the case of (2) above, a combination of an inorganic salt of iron and a salt of a specific metal-containing substance and a basic precipitating agent is preferable, and ammonia water, potassium carbonate, sodium carbonate, etc. are used as the precipitating agent. Is preferred.
[0011]
The hydrocarbon used as a hydrogen production raw material in the present invention is usually a gas or liquid hydrocarbon at normal temperature, specifically, an aliphatic hydrocarbon such as methane, ethane, ethylene, propane, etc .; cyclohexane, cyclohexane Cycloaliphatic hydrocarbons such as pentane; aromatic hydrocarbons such as benzene, toluene and xylene are preferred, but solid hydrocarbons such as paraffin wax can also be used. These hydrocarbons may be used alone or in combination of two or more.
[0012]
Hydrocarbons can be used pure as they are, but they can also be diluted with an inert gas such as argon, nitrogen, helium, etc. in order to thermally decompose efficiently and efficiently thermodynamically. The dilution rate at this time is arbitrary. The reaction temperature is 200 to 1,200 ° C., preferably 500 to 800 ° C., and the contact time between the catalyst surface and the hydrocarbon gas is 0.01 to 1000 seconds, preferably 0.1 to 50 seconds. desirable. Furthermore, oxygen, water, and carbon dioxide can coexist in the reaction system, and carbon deposited on the catalyst and carbon generated during the reaction are partially removed.
The reaction formula in this case is as follows.
C + H ₂ O → CO + H ₂
C + CO ₂ → 2CO
C + O ₂ → CO ₂
The supply of H ₂ O, O ₂ and CO _{2 to} the reaction system can be performed continuously or intermittently. Moreover, although the addition amount is arbitrary, all are 0.001-100 mol with respect to 1 mol of carbon contained in raw material hydrocarbon, Preferably it is the ratio of 0.01-10 mol.
[0013]
The thermal decomposition method of the present invention can employ either a batch method or a distribution method, but is preferably carried out by a distribution method. When the distribution method is used, a fixed bed method, a moving bed method, a circulating fluidized bed method (Kamiyama et al., “Chemical Engineering” P.27, December 1994 issue) and the like can be appropriately employed. When the method of the present invention is carried out in a fixed bed system, it is preferable to provide a catalyst packed bed by packing a catalyst in a tubular reactor. At that time, it is desirable to fix the catalyst layer by laminating filter layers having pores smaller than the particle size of the carbonaceous material on the upper and lower ends of the catalyst packed layer.
[0014]
Since the catalyst of the present invention contains a specific metal-containing substance in addition to the iron-containing substance, even if an oxidizing gas such as water coexists in the reaction system, the metallic iron closely related to the catalytically active species / Since iron carbide (existence is confirmed by powder X-ray diffraction after reaction in the catalyst system of the present invention) is stable, it has excellent catalytic activity and catalyst life. This suggests that this catalyst is not only useful for producing hydrogen by cracking hydrocarbons, but may be used for reforming reactions in the future.
[0015]
【Example】
Next, the present invention will be described more specifically with reference to examples.
Example 1
3.62 g of iron nitrate (10 wt% of iron supported on alumina) and 5.27 g of magnesium nitrate (10 wt%) were dissolved in 50 g of distilled water, and then 5 g of commercially available activated alumina was suspended in the aqueous solution. Is supported on alumina. Next, distilled water was evaporated to dryness, left at 100 ° C. overnight, and then calcined at 700 ° C. for 3 hours to obtain 6.30 g of an iron / Mg / alumina catalyst.
1 g of the catalyst thus obtained and 5 g of quartz sand having a particle diameter of 100 to 1000 μm were mixed well, and this was filled in the center of a quartz reaction tube having an inner diameter of 12 mm to form a catalyst layer. In this case, both ends of the catalyst layer were filled with quartz wool so that the catalyst would not move during the reaction. The reaction tube was loaded into an electric furnace, and the catalyst was reduced at 600 ° C. for 2 hours while flowing hydrogen through the reaction tube.
[0016]
Next, while passing a mixed gas of methane / carbon dioxide / nitrogen / oxygen (volume ratio: 65/8/4/21) through the reaction tube at a rate of 40 cm ³ / min, the internal temperature of the reaction tube was set to 5 ° C. / The reaction was started by raising the temperature to 800 ° C. at a rate of minutes.
When the obtained product gas composition was analyzed by gas chromatography after 2, 4 and 6 hours, the results shown in Table 1 were obtained for the methane addition rate and the hydrogen production rate. In addition, organic products such as ethane, ethylene, and benzene were not recognized at all.
Six hours after the start of the reaction, the methane conversion was 95.2% and the hydrogen production rate was 0.000823 mol / hour, and the catalytic activity was not lowered even after 6 hours. The methane conversion rate (%) is calculated by the following formula.
Methane conversion rate = [(decomposed carbon) + (CO generated amount)] × 100 / [(decomposed carbon) + (CO generated amount) + (unreacted methane)]
Here, cracked carbon = [(raw methane) + (raw CO2)] − [(unreacted methane) + (unreacted CO2) + (produced CO)]
[0017]
Comparative Example 1
Except not using manganese nitrate, the reaction was carried out using a catalyst (iron / alumina) prepared in the same manner as in Example 1. As shown in Table 1, methane conversion was 79.2%, hydrogen production rate The methane conversion rate after 6 hours was as low as 14% or more.
[0018]
Examples 2-6
A catalyst prepared by preparing a catalyst (iron / metal / alumina) with a loading rate of 10% using manganese, lanthanum, cerium, europium and yttrium nitrates instead of the magnesium nitrate used in Example 1 was used. When the reaction was conducted in the same manner as in Example 1, the results shown in Table 1 were obtained. All of these catalysts were found to have little decrease in activity.
[0019]
Comparative Examples 2-4
A catalyst prepared in the same manner as in Example 1 except that each of nitrates of chromium, vanadium and lithium was used instead of magnesium nitrate used in Example 1 was reacted in the same manner for 6 hours. The activity of methane conversion afterwards was remarkably reduced to around 20%.
[0020]
Comparative Example 5
A catalyst supporting 10% manganese was prepared from only manganese nitrate and alumina without using an iron-based compound and reacted in the same manner as in Example 1. As a result, the methane conversion was about 8% even after 2 hours. The catalyst containing no catalyst was remarkably low in activity.
[0021]
[Table 1]

[0022]
【The invention's effect】
According to the present invention, in the reaction of decomposing hydrocarbons to produce hydrogen, the catalyst has a stable catalytic activity even in the presence of an oxidizing gas such as carbon dioxide, water, and oxygen, and the catalyst is used for a long time. Useful catalysts are provided that maintain their lifetime.

Claims (5)

  Hydrocarbon decomposition reaction characterized by supporting an iron-containing substance and a substance containing at least one metal selected from Group IIa metal, Group VIIa metal and rare earth metal on an alumina-based support Catalyst for hydrogen production used in   The catalyst for hydrogen production used in the hydrocarbon decomposition reaction according to claim 1, wherein the Group IIa metal is magnesium.   The catalyst for hydrogen production used for the hydrocarbon decomposition reaction according to claim 1, wherein the Group VIIa metal is manganese or rhenium.   Hydrocarbon is contacted under heating conditions with a catalyst in which an alumina-containing support is loaded with an iron-containing substance and a substance containing at least one metal selected from Group IIa metal, Group VIIa metal and rare earth metal of the periodic table A method for producing hydrogen by a hydrocarbon decomposition reaction, wherein hydrogen is obtained. Method for producing hydrogen according to claim 4, characterized in that the coexistence of carbon dioxide and / or oxygen in the decomposition reaction.