JP5107046B2 - Hydrocarbon steam reforming catalyst - Google Patents

Description

  The present invention relates to a steam reforming catalyst used for producing hydrogen from hydrocarbons. More specifically, the present invention relates to a steam reforming catalyst that is used for producing hydrogen by steam reforming an inexpensive petroleum hydrocarbon such as LP gas, naphtha, gasoline, and kerosene that is widely distributed in the market.

  In recent years, with increasing environmental awareness, attention has been focused on energy using hydrogen, which has a low environmental impact. As one of the energy technologies using hydrogen, fuel cells that can extract electrical energy from the reaction of hydrogen and oxygen without the direct emission of carbon dioxide, which is said to cause ozone depletion and global warming, are attracting attention. Yes. Various raw materials such as natural gas, liquid fuel, and petroleum hydrocarbons have been studied as hydrogen sources for fuel cells. In particular, petroleum hydrocarbons typified by LP gas, naphtha, gasoline, kerosene and the like are promising as hydrogen sources because they are widely distributed in large quantities.

  As a method for producing hydrogen using petroleum hydrocarbons as a raw material, a partial oxidation method or a steam reforming method is known, but the latter is considered to be able to produce hydrogen more economically. A reforming catalyst is used for these hydrogen productions. As a steam reforming catalyst for hydrocarbons, a nickel-based catalyst in which nickel is supported on a carrier such as alumina is known. However, a nickel-based catalyst has a drawback that it tends to cause a decrease in activity due to carbon deposition. When many hydrocarbons are used as raw materials, coexistence of a large amount of steam is required, and the steam unit increases the operating cost. Therefore, it is considered difficult to apply to petroleum hydrocarbons both technically and economically. On the other hand, noble metal-based catalysts using noble metals such as ruthenium and rhodium have recently attracted attention as reforming catalysts for hydrocarbons because they have an effect of suppressing carbon deposition and can reduce the amount of water vapor used. Examples include those in which ruthenium is supported on alumina (Non-Patent Document 1), those in which ruthenium is supported on alumina or silica (Patent Document 1), and alumina containing alkaline earth metal aluminate containing zirconia and a ruthenium component. What was carried (Patent Document 2) and the like. However, ruthenium-based reforming catalysts are susceptible to catalyst poisoning due to sulfur contained in the raw material hydrocarbons (Non-patent Document 2), and sulfur poisoning induces carbon deposition (Non-Patent Document 3). Therefore, it is difficult to effectively function the carbon deposition inhibiting effect. Therefore, when a petroleum hydrocarbon is used as a raw material, the catalyst is required to have not only catalytic activity for reforming but also a function of suppressing carbon deposition and suppressing sulfur poisoning. In order to solve this problem, the conventional method has proposed the formation of a complex carrier and the addition of a third component. For example, an alumina carrier on which zirconia having a zirconia sol as a precursor is supported, lanthanum oxide and cobalt are supported as promoters, and ruthenium is contained as an active component (Patent Document 3), Group IIa, Group IIIa and / or An activated alumina composite carrier containing an oxide of a lanthanoid metal, which has been subjected to a reduction treatment by supporting ruthenium (Patent Document 4), at least one selected from the group consisting of oxides of Group 2, Metal 3, Metal and Lanthanoid Metal A support obtained by calcining alumina containing 3 to 30% by weight of a seed at 800 to 900 ° C. on a catalyst basis, carrying 0.5 to 5% by weight of ruthenium, and reduced at 600 to 950 ° C. (Patent Document) 5) An alumina carrier carrying at least a ruthenium component, a zirconium component and an alkali metal component (patented) Document 6) methods, such as has been proposed.

However, so far, few catalysts have been designed so that the co-catalyst, the composite alumina support is designed to function in an effective form and arrangement with respect to ruthenium, and has excellent thermal stability.
JP-A 57-4232 Japanese Patent Laid-Open No. 5-220397 JP-A-7-88376 JP-A-8-52355 Japanese Patent Laid-Open No. 9-10586 JP 2001-276624 A “Journal of the Fuel Society” Vol. 59, p. 25 (1980) “Catalyst” Vol. 35, p. 224 (1993) “Journal of Fuel Association”, Vol. 68, p. 39 (1989)

  In the present invention, the co-catalyst introduced into the catalyst and the composite alumina carrier function effectively, respectively, and can suppress carbon deposition and suppress sulfur poisoning. An object of the present invention is to provide a steam reforming catalyst having excellent thermal stability that can maintain the catalytic function even when exposed to long-term use conditions in which high temperature steam coexists.

  In order to solve the above-mentioned problems, the present inventors have conducted intensive research. As a result, at least one compound selected from a ruthenium compound and at least one compound selected from a cobalt compound are used as an alumina support containing a rare earth metal. In a steam reforming catalyst in which an alumina is supported, a specific amount of rare earth metal is contained in an alumina support by an impregnation method, and is added by firing at 600 to 800 ° C. in an oxygen atmosphere before supporting a ruthenium compound and a cobalt compound. The co-catalyst and composite carrier function synergistically with ruthenium to increase catalytic activity, and in addition, high performance not found in conventional catalysts that can suppress carbon deposition and suppress sulfur poisoning A novel steam reforming catalyst was found and the present invention was completed.

That is, the present invention is as follows.
[1] Water vapor obtained by containing a rare earth metal in an alumina support having a specific surface area of 60 to 120 m ² / g and further supporting at least one compound selected from ruthenium compounds and at least one compound selected from cobalt compounds. In the reforming catalyst, the rare earth metal is introduced into the alumina support by an impregnation method, the amount of the rare earth metal is less than 8.5 μmol / m ^{2 with} respect to the surface area of the alumina support, and at least one selected from the ruthenium compounds Before supporting at least one compound selected from the above compounds and cobalt compounds, the rare earth metal-containing alumina carrier is calcined at 600 to 800 ° C. in the presence of oxygen ,
And the steam reforming catalyst characterized by simultaneously carrying the ruthenium compound and the cobalt compound .
[ 2 ] The steam reforming catalyst according to [1], wherein the rare earth metal contains lanthanum or cerium.
[ 3 ] Rare earth metal is introduced into an alumina support having a specific surface area of 60 to 120 m ² / g by an impregnation method so that the surface area of the alumina support is less than 8.5 μmol / m ^2, and the rare earth metal is contained. A steam reforming catalyst characterized in that at least one compound selected from ruthenium compounds and at least one compound selected from cobalt compounds are simultaneously supported after calcining the alumina support in the presence of oxygen at 600 to 800 ° C. Manufacturing method.

  According to the present invention, the co-catalyst and composite alumina carrier are designed to function synergistically in an effective form and suitable arrangement with respect to ruthenium in order to suppress carbon deposition and suppress sulfur poisoning. In addition, it is possible to provide a steam reforming catalyst excellent in thermal stability that can maintain the catalytic function even when exposed to long-term use conditions in which high-temperature steam coexists.

The graph which shows the result of the experiment 1 which performed steam reforming using the catalyst obtained in Examples 1-2 and Comparative Examples 1-4. The graph which shows the result of having performed steam reforming by the method shown in Experiment 2.

The steam reforming catalyst of the present invention is a catalyst in which at least one compound selected from a ruthenium compound and a cobalt compound is supported on an alumina support containing a rare earth metal. It is carried out by an impregnation method, and the amount of the rare earth metal is less than 8.5 μmol / m ^{2 with} respect to the surface area of the alumina support, and is fired at 600 to 800 ° C. in an oxygen atmosphere before loading the ruthenium compound and the cobalt compound. is important.

In the steam reforming catalyst of the present invention, the alumina carrier is not particularly restricted by the composition or structure, but the specific surface area is 60 m ² / g or more, preferably so that the supported ruthenium and cobalt can be sufficiently dispersed. The pore volume is 80 to 120 m ² / g and the pore volume is 0.1 to 0.5 ml / g, preferably 0.2 to 0.5 ml / g. As an example, an aluminum isopropoxide or the like used as a precursor and a material added with a pore-controlling organic material and baked at 700 ° C. or higher can be used. If the specific surface area or the pore volume is smaller than this, the dispersibility of the supported ruthenium is deteriorated and a predetermined activity and catalyst life cannot be obtained. On the other hand, if the specific surface area and pore volume are larger, a sufficient carrier strength cannot be obtained.

  Examples of the shape of the alumina carrier include a spherical shape, a cylindrical shape, a prismatic shape, a tableting shape, a needle shape, a membrane shape, and a honeycomb structure shape. For molding the carrier, for example, molding methods such as pressure molding, extrusion molding, rolling granulation molding, and press molding can be used. Neither is particularly limited to limit the present invention, and a known method can be used.

  By using a rare earth metal, the catalytic activity is increased and the catalyst life is improved. As the rare earth metal, lanthanum, cerium, praseodymium, neodymium, promethium, samarium, ytterbium, and the like can be used. In particular, lanthanum and cerium are preferably used. These rare earth metals may be used alone or in combination of two or more. These rare earth metals can use rare earth metal compounds such as chlorides, nitrates and acetates as precursors in addition to oxides.

The alumina support containing the rare earth metal can be selectively distributed on the surface of the support by introducing the rare earth metal into the alumina support by an impregnation method. By selectively distributing the rare earth metal on the alumina surface, a large effect can be obtained with a small amount of addition, and the mechanical strength and heat resistance of the carrier are improved by the rare earth metal covering the alumina surface. In the physical mixing method and the kneading method, rare earth metal is distributed inside the alumina support, and the rare earth metal distributed inside the alumina carrier is wasted, so that an effective additive effect (hereinafter referred to as an additive amount effect) cannot be obtained. Negative effects such as increase in raw material cost due to a large relative decrease in the amount of alumina, lowering the mechanical strength of the support, and the rare earth metal forming a complex oxide with alumina and greatly reducing the specific surface area of the support Is not preferred because it tends to appear.
In order to introduce the rare earth metal into the alumina support by the impregnation method, the alumina support may be immersed in a solution containing the rare earth metal compound. At this time, the solvent is preferably water. Moreover, when impregnating, the pore filling method is preferable.

It is also important to coat the rare earth metal on the alumina surface so that the active metal can come into direct contact with the alumina when the rare earth metal is introduced into the alumina carrier by the impregnation method and distributed on the surface of the carrier. When the rare earth metal covers the entire surface area of the alumina support with a single layer, the amount of the rare earth metal contained in the alumina support is 8.5 μmol / m ² with respect to the surface area of the alumina support as its oxide. If the amount of the rare earth metal exceeds 8.5 μmol / m ² , it cannot be distributed in a single layer on the surface of the alumina support, and the excess forms a multimolecular layer. If the rare earth metal covers the entire surface area of the alumina support with a single layer, or forms a multi-molecular layer, the alumina support and active metal cannot be in direct contact, so the interaction between the support and active metal. This is not preferable because the decrease in the stability of the active metal on the catalyst surface and the decrease in the activity are liable to occur. Therefore, the amount of rare earth metal is less than 8.5 μmol / m ^{2 with} respect to the surface area of the alumina support so that the active metal can be in direct contact with the alumina. In addition, if the amount of rare earth metal is small, the effect of addition becomes low, which is not preferable. More preferably, it is 0.8 μmol / m ² or more and less than 8.5 μmol / m ² .
The amount of rare earth metal contained in the alumina support can be adjusted to the above range by adjusting the concentration of the rare earth metal compound in the solution impregnated in the alumina support.

  After the rare earth metal is contained in the alumina support by the impregnation method, before firing the ruthenium compound and the cobalt compound, firing is performed at 600 to 800 ° C., preferably 650 to 750 ° C., more preferably 700 to 750 ° C. in the presence of oxygen. The rare earth metal is fixed to the alumina support as an oxide by treatment. Firing in the presence of oxygen may be performed in the air. At this time, when the firing temperature is lower than 600 ° C., the introduced rare earth metal is not stabilized on the surface of the support, and the alumina support becomes susceptible to deterioration due to thermal history under the conditions of use of the water vapor reaction. The rare earth metal reacts with the alumina support to form a complex oxide (aluminate), which not only significantly impairs the specific surface area of the support but also the active metal that is incorporated into the support skeleton and distributed on the support surface. Since ruthenium does not function effectively compared to ruthenium, it is not preferable.

  As a method for supporting the ruthenium compound and the cobalt compound on the alumina carrier containing the rare earth metal, a known impregnation method can be used. As the ruthenium compound, a compound such as ruthenium trichloride or ruthenium nitrate can be used as a precursor of the ruthenium active component. Particularly preferably, ruthenium trichloride (anhydride or hydrate) is used. The supported amount of the ruthenium compound depends on the surface area of the support, but is generally 0.3 to 5.0% by weight, preferably 0.5 to 3.0% by weight as a metal with respect to the catalyst weight. If the supported amount of ruthenium is less than this, the ruthenium functioning as the active site is reduced and sufficient catalytic activity cannot be obtained, and if the supported amount is too large, the dispersibility of ruthenium is lowered and it does not function effectively. . The cobalt compound serving as a cocatalyst can be supported on the support before or after the ruthenium compound is supported after the rare earth metal is fixed on the alumina support as an oxide, or simultaneously with the ruthenium compound. In particular, by carrying the cobalt compound simultaneously with the ruthenium compound, the effect of improving the dispersibility of ruthenium and remarkably improving the catalytic activity is exhibited. Moreover, it is thought that it suppresses crystallization of ruthenium by acting as a wedge with respect to ruthenium, and suppresses catalyst deterioration by suppressing aggregation of ruthenium that proceeds during the reforming reaction. Therefore, it is preferable to simultaneously carry a cobalt compound and a ruthenium compound since these effects are more emphasized. As the cobalt compound, one or more compounds such as cobalt nitrate, cobalt carbonate, cobalt acetate, cobalt hydroxide, and cobalt chloride are used as a precursor of the cobalt promoter component, and cobalt nitrate is particularly preferably used.

  The amount of cobalt is 0.1 to 3, preferably 0.1 to 1.0, and more preferably 0.2 to 0.5 in terms of an atomic molar ratio to ruthenium (hereinafter, Co / Ru ratio). When the Co / Ru ratio is less than 0.1, the cocatalyst effect does not sufficiently appear, and when it is 3 or more, the excess cobalt adversely impairs the catalytic function of ruthenium.

  The conditions for the drying treatment and the firing treatment after supporting the ruthenium compound and the cobalt compound are not particularly specified, but are, for example, in air at 100 ° C. or higher. In addition, the obtained catalyst may be reduced in a liquid phase for the purpose of reducing the load such as pretreatment reduction when using the reforming reaction or heat generation at the initial stage of the reaction. The reduction treatment method is, for example, preparing a 1-20% aqueous solution using a reducing agent such as formic acid, alkali metal salt of formic acid, formalin, hydrazine, sodium borohydride, etc., and heating to a temperature of room temperature to 60 ° C. After that, the catalyst is added.

  The steam reforming catalyst obtained by the above method is preferably subjected to a reduction treatment in advance before the reforming reaction, but is not necessarily because it is reduced as a result of contact with hydrogen in the reaction gas generated in the reforming reaction. I don't need it. In some cases, the catalyst performance may be improved by controlling the reduction temperature. When the reduction treatment is carried out, it is carried out at 700 ° C. or less, preferably 600 to 700 ° C. under a hydrogen gas flow. When the temperature exceeds 700 ° C., the dispersibility of ruthenium is lowered before the steam reforming reaction, and as a result, the catalyst performance is impaired.

  The steam reforming catalyst of the present invention can be used in a process for producing hydrogen from hydrocarbons in the presence of steam. There are no particular restrictions on the application to the hydrogen production process, and it can be applied to the production of hydrogen for hydrorefining at refineries and the like, and the production of hydrogen for fuel cells in a stationary distributed power source. The hydrocarbon is not particularly limited, and examples thereof include saturated aliphatic hydrocarbon compounds having 1 or more carbon atoms, such as methane, ethane, propane, butane, pentane, hexane, heptane, and octane, cyclopropane, cyclobutane, cyclopentane, Examples thereof include saturated alicyclic hydrocarbon compounds having 3 or more carbon atoms typified by cyclohexane and the like, and aromatic hydrocarbon compounds typified by benzene, toluene, xylene and the like. It may be a mixture containing one or more of these, and may be a petroleum fraction typified by LP gas, naphtha, gasoline, kerosene, light oil, etc. obtained by petroleum refining or a part of them. May be. The sulfur content contained in the hydrocarbon is 0.2 ppm by weight or less, preferably 0.05 ppm by weight or less. If the sulfur content exceeds 0.2 ppm by weight, the catalyst poisoning due to the sulfur compound becomes significant, and the catalyst activity is lowered and the catalyst life is likely to advance. Even for hydrocarbons with a sulfur content of more than 0.2 ppm by weight, pretreatment such as hydrodesulfurization and adsorptive desulfurization is performed before the reforming reaction, and the sulfur content is 0.2 ppm by weight or less in advance. The steam reforming catalyst of the present invention can be used by reducing to a low level. In this pretreatment, the lower the sulfur content of the hydrocarbon, the more preferable it is because the catalyst poisoning by sulfur can be reduced.

  The hydrocarbon reforming reaction performed using the steam reforming catalyst of the present invention has a steam / carbon ratio (hereinafter referred to as S / C ratio) of 1 to 10, preferably 2 to 5. When the S / C ratio is less than 1, the decrease in the catalyst activity is remarkably accelerated. When the S / C ratio is 10 or more, the amount of water vapor supplied is excessive, resulting in an increase in cost. The reaction temperature depends on the type of hydrocarbon, but is usually 400 to 800 ° C, preferably 500 to 750 ° C. Even if the reaction temperature is less than 400 ° C., the steam reforming reaction proceeds, but the ratio of hydrogen generated thermodynamically decreases and the hydrogen yield decreases, which is not preferable. On the other hand, if it exceeds 800 ° C., the thermal deterioration is accelerated and the catalyst life is remarkably reduced.

The reaction method using the steam reforming catalyst of the present invention is not particularly limited, such as a continuous flow method or a batch method, but is preferable because the former can efficiently perform the reforming reaction. Liquid hourly space velocity of hydrocarbons in this case (hereinafter, LHSV) is dependent on the type of hydrocarbon, typically 10 hr ^-1 or less, preferably ^{5 hr -1} or less. Depending on the type of hydrocarbon, the reforming reaction is possible even if the LHSV exceeds 10 hr ⁻¹ , but it is not economically preferable because a facility for supplying a large amount of hydrocarbon or steam is required. The reaction pressure depends on the type of hydrocarbon, but is usually 0 to 5 MPa, preferably 0 to 2 MPa. If the reaction pressure exceeds 5 MPa, an equipment using an expensive pressure-resistant material is required, which is not economically preferable.

  The reaction mode using the steam reforming catalyst of the present invention is not particularly limited, such as a fixed bed type, a moving bed type, and a fluidized bed type. The reactor using the steam reforming catalyst of the present invention is not particularly limited. The steam reforming catalyst of the present invention can be used alone or in combination with other catalysts.

  EXAMPLES Hereinafter, although this invention is demonstrated concretely based on an Example, this invention is not limited to this.

[Preparation of catalyst]
Example 1 (Catalyst A)
After impregnating 415 g of a ² mm diameter alumina carrier (specific surface area 120 m ² / g, pore volume 0.36 ml / g) with 150 ml of an aqueous solution in which 87.7 g of lanthanum nitrate hexahydrate was dissolved by a pore filling method, 110 ° C. For 16 hours, followed by baking at 650 ° C. for 3 hours in the presence of oxygen. The obtained lanthanum-containing support was impregnated with 150 ml of an aqueous solution in which 23.3 g of ruthenium trichloride and 10.2 g of cobalt (II) nitrate hexahydrate were dissolved, and then dried at 150 ° C. for 16 hours. The obtained catalyst was subjected to liquid phase reduction treatment at 40 ° C. using an aqueous hydrazine carbonate solution and dried at 150 ° C. for 10 hours to obtain Catalyst A.

Comparative Example 1 (Catalyst B)
In the method of Example 1, the catalyst B was prepared by the same preparation method as in Example 1 except that cobalt nitrate was not used.

Comparative Example 2 (Catalyst C)
In the method of Example 1, the catalyst C was prepared by the same preparation method as in Example 1 except that lanthanum nitrate was not used.

Comparative Example 3 (Catalyst D)
In the method of Example 1, the catalyst D was prepared by the same preparation method as in Example 1 except that the calcination treatment after supporting lanthanum nitrate was performed at 850 ° C. for 3 hours in the presence of oxygen.

Example 2 (Catalyst E)
A catalyst E was obtained in the same manner as in Example 1 except that 35.3 g of lanthanum nitrate hexahydrate was used in the method of Example 1.

Comparative Example 4 (Catalyst F)
A catalyst F was obtained in the same manner as in Example 1 except that 147 g of lanthanum nitrate hexahydrate was used in the method of Example 1.

  Table 1 shows the composition measured by IPC mass spectrometry and the specific surface area by the nitrogen adsorption method for the catalysts A to F obtained by the above preparation.

[Experiment 1]
A SUS cylindrical reaction tube having an inner diameter of 30 mmφ filled with 15 cc of each catalyst adjusted to 1-3 mmφ and uniformly diluted with 35 cc of inert alumina having a diameter of 2 mmφ, and a hydrogen gas flow with a gas space velocity (hereinafter referred to as GHSV) = 2000 hr ⁻¹ . 10 ° C./min. After heating at 600 ° C. for 90 minutes at a rate of 600 ° C., LHSV = 5.0 hr ⁻¹ using kerosene (hereinafter referred to as desulfurized kerosene) obtained by desulfurizing commercially available JIS No. 1 kerosene to a sulfur concentration of 50 ppb, The steam reforming reaction was performed at a steam / carbon ratio of 3.0, a reaction pressure of 0.10 MPa-G, and 600 ° C. Table 2 shows the properties of the desulfurized kerosene used as the raw material oil.

The product obtained by the above steam reforming reaction was sampled in a gas state, and the product composition was analyzed by gas chromatography. The catalytic activity of the reforming catalyst obtained in each of the above examples was evaluated using the C1 conversion obtained by the following formula as an index.
C1 conversion (%) = a ÷ b × 100
a: C1 compound (methane, carbon monoxide, carbon dioxide) contained in the product at the outlet of the reactor
B: the total number of moles of carbon contained in the raw material hydrocarbon (desulfurized kerosene) The steam reforming reaction was carried out under the conditions described above using the catalysts obtained in Examples 1-2 and Comparative Examples 1-4. The results are shown in FIG. Catalyst A and Catalyst E obtained according to the present invention have a higher C1 conversion rate and higher activity than when the catalysts of Comparative Examples 1 to 4 are used, and maintain a high conversion rate even after a lapse of time. It can be seen that the catalyst is less deteriorated.

[Experiment 2]
Using the catalyst A obtained in Example 1, in the same manner as in Experiment 1, under a hydrogen stream of GHSV = 2000 hr ⁻¹ at 10 ° C./min. The temperature was raised at a rate of 600 ° C. for 90 minutes, and the same desulfurized kerosene as in Experiment 1 was used as the raw material LHSV = 0.5 hr ⁻¹ , steam / carbon ratio = 3.0, reaction pressure 0 The results of the steam reforming reaction at 0.000 MPa-G (atmospheric pressure) and 600 ° C. are shown in FIG. FIG. 2 shows that the catalyst of the present invention maintains a C1 conversion rate of 100% even after 4000 hours or more in the steam reforming reaction of kerosene, and has a highly active and long-lived catalyst performance that can meet practical use. Show.

Claims (3)

A steam reforming catalyst comprising a rare earth metal contained in an alumina support having a specific surface area of 60 to 120 m ² / g , and further supporting at least one compound selected from ruthenium compounds and at least one compound selected from cobalt compounds. In the method, the rare earth metal is introduced into the alumina support by an impregnation method, the amount of the rare earth metal is less than 8.5 μmol / m ^{2 with} respect to the surface area of the alumina support, and at least one compound selected from the ruthenium compound and Before supporting at least one compound selected from cobalt compounds, the alumina carrier containing the rare earth metal is fired at 600 to 800 ° C. in the presence of oxygen ,
And the steam reforming catalyst characterized by simultaneously carrying the ruthenium compound and the cobalt compound .   The steam reforming catalyst according to claim 1, wherein the rare earth metal contains lanthanum or cerium. An alumina support having a specific surface area of 60 to 120 m ² / g introduced into the alumina support by an impregnation method so that the rare earth metal is less than 8.5 μmol / m ^{2 with} respect to the surface area of the alumina support. Is calcined at 600 to 800 ° C. in the presence of oxygen, and then simultaneously supports at least one compound selected from ruthenium compounds and at least one compound selected from cobalt compounds. .

Images