JP3989228B2 - Method for producing alumina carrier with excellent heat resistance - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing an alumina carrier excellent in heat resistance, and particularly relates to a method for producing an alumina catalyst carrier excellent not only in mechanical strength but also in durability at high temperatures.
[0002]
[Prior art]
A catalyst body is known in which an aluminum plate is anodized, the resulting porous anodic oxide coating is hydrothermally treated to increase its BET surface area, and a catalyst is supported on the surface (Japanese Patent Laid-Open No. 2-144154). .
Since such a planar catalyst body is excellent in thermal conductivity, it is suitable for use as a wall material of a reaction chamber having heat exchange ability, but since its base material is aluminum, its upper melting point is low in strength. , The heat resistance is inferior, and the use limit is usually up to 200 ° C. Further, when aluminum is exposed on the outer surface, there is also a problem that corrosion proceeds from that portion.
[0003]
Therefore, in order to improve the strength and heat resistance, it has been attempted to use an anodized substrate obtained by rolling aluminum directly to stainless steel by a clad method and directly bonding it. However, in this case, stainless steel and aluminum often peel off during anodization, and the success rate of anodization is low. Even if anodization is successful, the strength of the substrate will increase, but due to the difference in thermal expansion coefficient between alumina and stainless steel, the alumina coating will peel off from the stainless steel plate when exposed to high temperatures, so the heat resistance is not sufficient. There was a drawback.
[0004]
Therefore, in order to improve the above-mentioned drawbacks, it has been attempted to use a substrate in which aluminum is sprayed on a stainless steel plate. In this case, however, a large-scale apparatus is required for manufacturing, and a uniform thickness is required. A porous alumina cortex with uniform pores on the surface cannot be formed. Accordingly, there is a drawback that not only the amount of catalyst supported is reduced, but also the heat resistance is not sufficient.
[0005]
These disadvantages are a plate-like alumina carrier having an alumina layer on at least one surface of a stainless steel plate, having a diffusion layer in which an aluminum component and an iron component are present at the interface between the stainless steel plate and the alumina layer, and the diffusion This was greatly improved by a plate-like alumina support (Japanese Patent Laid-Open No. 8-281125) having excellent heat resistance, characterized in that the contents of aluminum and iron in the layer changed gently. This improvement in heat resistance is particularly remarkable when the hydration treatment is performed before post-baking. However, the heat resistance of the alumina carrier is limited to about 700 ° C., and the reforming reaction of methane, which has become more important with the progress of practical technology of fuel cells in recent years, is used at a high temperature of 700 ° C. or higher. The important reaction carried out has the disadvantage that it cannot be used.
[0006]
[Problems to be solved by the invention]
Therefore, as a result of intensive studies to further improve the heat resistance of the aluminum clad material, the present inventors have carried out pore enlargement treatment on the anodized surface before hydration treatment , and thus the heat resistance of the obtained alumina support. Has been found to be further improved, and the present invention has been achieved.
Accordingly, an object of the present invention is to provide a heat-resistant catalytic reactor that not only has excellent mechanical strength but can withstand use at a high temperature of 700 ° C. or higher.
[0007]
[Means for Solving the Problems]
The above object of the present invention is to provide a catalytic reactor having the catalytic surface of a catalytic material formed by supporting a catalyst on a metal surface via an alumina layer as the inside of the reactor, wherein the catalytic material is Mg, Cr, Mo , W, Mn, Fe, Co, Ni, Ti, Zr, V, Cu, Ag, Zn, Bi, Sn, Pb, Sb, or a metal obtained by polymerizing these metals. An aluminum layer is provided on a metal surface selected from the group consisting of the following, followed by pre-baking at 400 to 600 ° C. for 1 to 10 hours , anodizing the aluminum surface of the fired metal , and then adding an acidic aqueous solution. after enlarging treatment of the surface pores caused by anodising using, instead of washing, or washing after, and hydrated with steam or 5 to 100 ° C. water, then with 350 ° C. or higher 1 More than an hour later This is a catalyst material obtained by supporting a catalyst on the surface of an alumina formed by calcination, and has been achieved by a heat-resistant catalyst reactor characterized by being able to withstand use at a high temperature of 700 ° C. or higher . In the present invention, the surface pore enlargement treatment is particularly preferably performed by immersing in an acidic bath having a pH of 3 to 6.5 and a temperature of 5 ° C. to 80 ° C. for 1 to 6 hours, It is preferable to perform pre-baking performed before anodizing under a load. The catalyst material is preferably formed in a honeycomb shape or a corrugated fin shape .
[0008]
DETAILED DESCRIPTION OF THE INVENTION
The clad material of the present invention is a carrier formed by providing an aluminum layer on a metal surface on which an aluminum layer can be provided. The shape may be any shape such as a plate shape, a rod shape, a cylinder shape, a ribbon shape, and a honeycomb shape. The metals that can provide an aluminum layer on the surface are Mg, Cr, Mo, W, Mn, Fe, Co, Ni, Ti, Zr, V, Cu, Ag, Zn, Bi, Sn, Pb, and Sb. From the standpoint of heat resistance, stainless steel or nickel-chromium alloy is particularly preferable in the present invention.
[0009]
The method for forming the aluminum layer on these metal surfaces may be any known method such as non-water plating, pressure bonding, vapor deposition, dripping, thermal spraying, rolling (clad method), etc. From the viewpoint of manufacturability, it is preferable to use a rolling method and attach an aluminum plate or aluminum foil to the metal surface. The thickness of the aluminum layer may be 5 μm or more, preferably 10 to 300 μm, particularly preferably 30 to 200 μm. However, the aluminum in the present invention includes an aluminum alloy that can be anodized. A clad material having a cylindrical shape or a honeycomb shape can be obtained by processing a plate-like clad material into those shapes.
[0010]
The clad material prepared as described above (not limited to the case where the clad method is used) has a very clear interface between the metal layer and the aluminum layer and is easily peeled off. Therefore, in the present invention, the cladding material to 400 ° C. to 600 ° C., preferably at form sintered between 1-10 hours at 450 ° C. to 550 ° C. (before firing), the metal layer side atoms and the aluminum layer side atoms is diffused to each other, Ru to form a diffusion layer around the interface. If the pre-baking temperature is less than 400 ° C., a good diffusion layer cannot be formed. Also, the firing time is less than 1 hour, and the effect of preventing peeling is poor, and firing for 10 hours or more is uneconomical, so it is particularly preferably about 5 to 9 hours. The firing may be performed in air or in an inert gas.
[0011]
Anodization of the aluminum surface can be easily performed using a known anodization technique. In general, immediately before anodization, in order to clean the aluminum surface, a surface treatment is performed using an alkaline aqueous solution, and then a treatment is performed using an acidic aqueous solution.
In the anodic oxidation in the present invention, it is preferable to use a highly oxidizing acid such as chromic acid or sulfuric acid as the treatment liquid. This makes it easy to change all the aluminum layers to alumina layers and to advance anodic oxidation to the inside of the diffusion layer provided as necessary, thereby diffusing oxygen atoms to the inside of the diffusion layer. In addition, what is necessary is just to determine the acid concentration of a process liquid suitably, For example, when using chromic acid, it is preferable to set it as 2 to 4 weight%.
[0012]
The anodizing conditions may be set as appropriate so that the BET surface area of the alumina layer is increased, but in the present invention, the anodizing treatment liquid temperature is set to 0 to 50 ° C., particularly normal temperature to 40 ° C. preferable. If it is less than 0 ° C., the BET surface area does not become very large, and if it exceeds 50 ° C., the dissolution becomes severe and it becomes difficult to economically form an oxide film. The treatment time for this anodic oxidation varies depending on the treatment conditions. For example, when a 2.5% by weight chromic acid aqueous solution is used as the treatment liquid, the treatment bath temperature is 38 ° C., and the current density is 19.0 A / m ^2. Is preferably 2 hours or more, particularly 4 hours or more.
[0013]
In the present invention, after the anodic oxidation 3 50 ° C. or higher for 1 hour or more, preferably, it intends row post baking further 450 ° C. to 550 ° C.. This makes the anodic oxide film a γ-alumina layer, which is preferable as the surface of the catalyst carrier, and makes the change in the concentration of diffusion atoms in the diffusion layer more gentle. However, heat resistance sufficient to withstand a reaction performed at 700 ° C. to 800 ° C. such as a reforming reaction of methane cannot be obtained by this alone.
[0014]
Therefore, in the present invention, in order to increase the BET surface area of the surface of the anodized film before post-baking and improve the heat resistance, a pore enlargement process for expanding the pores in the anodized film using an acidic aqueous solution is performed. Do. The acidic aqueous solution used here can be appropriately selected from the same treatment solution used during the anodic oxidation. Therefore, after anodic oxidation, the pore enlargement treatment can be continued in the same treatment liquid. What is necessary is just to set suitably the temperature and time of this pore expansion process according to the kind and density | concentration of the acid which are used as a process liquid. Preferred conditions are pH 3-6. For example, when 4% by weight of succinic acid is used at 20 ° C., about 90 minutes or more is necessary, but 120 minutes is sufficient.
[0015]
It is not always clear why the heat resistance is increased by introducing the pore enlargement treatment step, but the subsequent hydration treatment is carried out to the deep part in the pore by expanding the pore. As a result of the softening of the deep part of the alumina layer, it becomes possible to absorb the difference in thermal expansion coefficient between the metal and the alumina layer, and the alumina layer is prevented from peeling off from the metal surface even when heated to 700 ° C. or higher. It is considered a thing. The said hydration process is performed using water vapor | steam or 5-100 degreeC, Preferably it is 40-100 degreeC water. The processing temperature and processing time can be set as appropriate. The water is preferably distilled water or ion exchange water. After the hydration treatment, the post-baking is performed.
[0016]
A catalyst body can be obtained by supporting various catalyst fine particles on the alumina surface of the alumina support thus obtained, as is well known. Therefore, when the alumina carrier of the present invention is in the form of a plate, a catalyst such as a honeycomb or corrugated fin is formed so that the alumina surface becomes the inner surface, and then the catalyst is supported on the inner surface. It becomes a reactor. In addition, a reactor is formed with an aluminum layer of a pre-fired clad material as an inner surface, or after a reactor is formed with an aluminum layer of a clad material that is not pre-fired as an inner surface, and then pre-fired, anodization A catalytic reactor can also be obtained through each step of expansion treatment, hydration treatment, post-calcination, and catalyst support.
[0017]
【The invention's effect】
According to the production method of the present invention, there is provided an alumina carrier having an alumina layer obtained by anodizing, which can be used for a reaction at a high temperature such as 700 ° C. to 800 ° C. that cannot be conventionally achieved. can get. In addition, the pore enlargement treatment can be used as it is without any particular improvement of the conventional manufacturing apparatus because the treatment liquid used during anodization can be used as it is.
[0018]
【Example】
EXAMPLES Hereinafter, although an Example demonstrates this invention further in full detail, this invention is not limited by this.
[0019]
Example 1.
SUS430 with Al added (18% Cr, 4% Al) 290μm thick stainless steel as a base material, 40-50μm thick aluminum are laminated on both sides, and using a rolling mill, an aluminum / stainless steel clad substrate Got. The obtained clad substrate was cut out to 3.5 cm × 12.5 cm, heated from a normal temperature to 500 ° C. at 6 ° C./min using a gold furnace, and then at 500 ° C. for 3 hours, 0.83 g / Firing was performed in air with or without a load of cm ² .
[0020]
Masking was performed so as not to leak current from the cut surface of the clad substrate when anodizing. In order to improve the adhesion of masking, a substrate whose surface was covered with vinyl tape was immersed in a 20 wt% sodium hydroxide solution for 3 minutes and a 30 wt% nitric acid aqueous solution for 1 minute to perform surface treatment. Next, after anodizing for 2 minutes as a pretreatment to roughen the surface, it is washed with ion-exchanged water, dried, and a portion other than the anodized is coated with a masking agent and dried at room temperature for about half a day. It was.
[0021]
The substrate pretreated as described above was anodized using a 2.5% chromic acid aqueous solution at a liquid temperature of 30 ° C. and a current density of 15.0 A / m ² for 12 hours.
The success rate of anodic oxidation when pre-baked without applying a load was about 33%, and the success rate when applied with a load was about 91%. In the case where pre-firing was not performed, partial peeling was observed at the interface between the stainless steel layer and the alumina layer in the sample after anodization.
[0022]
The substrate after anodization was subjected to pore expansion treatment at 20 ° C. for 2 hours using 4% by weight of oxalic acid, and then dipped in ion exchange water at 80 ° C. for 1 hour to be hydrated. The total liquid volume was adjusted so that the liquid surface ratio (liquid volume per apparent surface) was constant at 7.2 in all treatments.
The obtained hydrated substrate was washed with water, dried at room temperature for 1 day, heated from room temperature at 6 ° C./min to 500 ° C., and calcined at 500 ° C. for 3 hours. A carrier was obtained.
[0023]
Comparative Example 1
A plate-like alumina support was obtained in the same manner as in Example 1 except that the pore enlargement treatment was not performed.
The carrier obtained in the examples and comparative examples was heated from room temperature to 820 ° C. at a heating rate of 20 ° C./min, and a heat resistance test was carried out 30 times at this temperature for 2 hours. In the case of the alumina carrier of the present invention, no peeling of the alumina layer was observed, whereas in the case of the carrier obtained in Comparative Example 1, the alumina layer was almost peeled off. This result demonstrates the effectiveness of the present invention.

Claims (5)

In a catalytic reactor having the catalytic surface of a catalytic material formed by supporting a catalyst on a metal surface via an alumina layer as the inner side of the reactor, the catalytic material is Mg, Cr, Mo, W, Mn, Fe, Co , Ni, Ti, Zr, V, Cu, Ag, Zn, Bi, Sn, Pb, Sb, selected from the group consisting of simple metals or alloys, or metals obtained by polymerizing these metals After the aluminum layer was provided on the metal surface, pre-fired at 400 ° C. to 600 ° C. for 1 to 10 hours, the aluminum surface of the fired metal was anodized, and then produced by the anodic oxidation using an acidic aqueous solution After expanding the surface pores, instead of washing, or after washing, hydrated with water vapor or water at 5 to 100 ° C. and then post-fired at 350 ° C. or higher for 1 hour or longer. Aluminum A heat-resistant catalytic reactor , characterized in that it is a catalyst material having a catalyst supported on its surface and can withstand use at a high temperature of 700 ° C to 800 ° C. The heat-resistant catalyst according to claim 1, wherein the surface pore enlargement treatment is performed by immersing in an acidic bath having a pH of 3 to 6.5 and a temperature of 5 ° C to 80 ° C for 1 to 6 hours. Reactor. The heat-resistant catalytic reactor according to claim 1 or 2, wherein the pre-calcination is performed under a load . The heat-resistant catalyst reactor according to any one of claims 1 to 3, wherein the catalyst material is formed in a honeycomb shape or a corrugated fin shape . A single element or alloy selected from Mg, Cr, Mo, W, Mn, Fe, Co, Ni, Ti, Zr, V, Cu, Ag, Zn, Bi, Sn, Pb, and Sb, or a metal thereof. After providing an aluminum layer on a metal surface selected from the group consisting of polymerized metals, the aluminum layer of the metal material obtained by pre-baking at 400 ° C. to 600 ° C. for 1 to 10 hours under the load is used as the inner surface After forming the reactor, the surface of the aluminum layer is anodized, and then the surface pores generated by the anodization are expanded using an acidic aqueous solution. was hydrated with 5 to 100 ° C. in water and then made by supporting a catalyst on the rear fired to form the alumina surface more than one hour at 350 ° C. or higher, according to claim 1, 2 or 4 by heat Catalytic reactor.