JPH0283033A - Method for producing heat-resistant alumina carrier - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] (Field of Industrial Application) The present invention relates to a method for producing a heat-resistant composition, particularly a heat-resistant alumina carrier suitable for a catalyst carrier used in a catalytic combustion catalyst or a catalyst for automobile exhaust purification. It is something.

<Conventional technology> Applications to chemical processes such as automobile exhaust gas removal, high-temperature steam reforming, catalytic combustion of hydrocarbons and hydrogen, and more recently, catalytic reactions at high temperatures such as gas turbines and boilers.
There is a tendency for it to be used more and more frequently.

Catalyst carriers used in these fields are used at temperatures of 1000°C or higher, sometimes exceeding 1100°C, and under such conditions the specific surface area of the carriers used has excellent heat resistance with little loss. A catalyst support is required, and transitional alumina is often used as such a support.

However, as is well known, the disadvantage of this metastatic alumina is 10
When exposed to high temperatures of 00° C. or higher, a transition to an α-alumina form occurs, and the specific surface area substantially decreases significantly.

Particularly when using Type B, in which transitional alumina is coated on pellets or other molded objects as a catalyst carrier, the structural change due to this transition to α-alumina promotes shedding of the coating layer or sintering of the catalyst components. cause it to happen.

Conventionally, it has been known to add alkaline earth elements or rare earth elements as a method of improving the thermal stability of metastatic alumina, such as preventing a decrease in specific surface area. (
For example, JP-A No. 4417737, JP-A No. 48-146
No. 00, JP-A-54-117387, JP-A-59-8
No. 0752, JP-A-62-176542, JP-A-62
-180751, JP-A-62-191043, etc.).

However, if the carrier powder obtained by these known methods is pulverized so that it can be easily molded or coated on other molded products, the heat resistance function imparted to it will be extremely reduced, and it will be used as a combustion catalyst for gas turbines or for automobiles. It cannot be used as a carrier for catalysts that are exposed to high temperatures of 1000°C or higher.

On the other hand, using fine grained and highly pure transitional alumina in advance,
There is also a method of impregnating this with lanthanum to obtain a heat-resistant alumina carrier (Japanese Patent Application Laid-open No. 62-180751), but with this method, it is not possible to obtain a cheap catalyst carrier because the raw material, fine-grained transitional alumina, is expensive. .

(Problems to be Solved by the Invention) In view of the above circumstances, the present inventors have developed a material that is inexpensive, has a particle size that is excellent in molding and coating properties, and has a sufficient specific surface area even at high temperatures of 1000°C or higher. As a result of extensive research aimed at finding a method for producing an alumina carrier with excellent heat resistance (with little reduction in specific surface area), the method of the present invention was finally completed.

(Means for Solving the Problems) The method of the present invention is a method for producing a heat-resistant alumina carrier obtained by impregnating a powder of transitional alumina or alumina hydrate with a lanthanum compound and then calcining the powder. The powder of transitional alumina or alumina hydrate before being impregnated with the compound has an average secondary particle size of 3.
After grinding to 0μm or less, 300℃ or more ~ α
It is an object of the present invention to provide a method for producing a heat-resistant alumina carrier, which is characterized in that it is calcined at a temperature below the transition temperature to alumina, then impregnated with a lanthanum compound, and then calcined.

The method of the present invention will be explained in more detail below.

In the present invention, the powder of transitional alumina or alumina hydrate (hereinafter sometimes simply referred to as raw alumina) includes gamma (γ), delta (δ), eta (
Transitional alumina with morphologies such as η), chi (χ), theta (θ), kappa (ni), and rho (ρ), and hydrated alumina such as bayerite, norstrandite, gibbsite, pseudoboehmite, and boehmite. One or more of these may be used.

In addition to commercially available products, the transitional alumina or alumina hydrate may be one co-precipitated from a water-soluble aluminum solution such as aluminum nitrate, aluminum halide, or aluminum sulfate.

These raw aluminas are usually formed from secondary particles with an average particle size of several μm to several hundred μm, which are agglomerated primary particles with an average particle size of sub-μm to several tens of μm, although it depends on the manufacturing method or manufacturing conditions. These raw aluminas, whose secondary particle size is controlled to a few micrometers or less, are generally significantly more expensive than alumina obtained by the normal Bayer method, etc., because some manufacturing conditions are controlled. .

In the present invention, since the purpose is to provide an inexpensive catalyst carrier, a general-purpose raw material alumina for boat fishing, such as alumina hydrate obtained by the Bayer method with an average secondary particle size of 108 m or more, or α- It is recommended to use transitional alumina obtained by calcining at a temperature below the temperature that transforms into alumina, or by-product boehmite gel obtained by neutralization, but pulverize those with a smaller average secondary particle size. By doing so, finer particles than the starting material alumina are obtained, and when the method of the present invention is applied to this, it exhibits a superior heat resistance improvement effect compared to a method of simply pulverizing.
There is no limitation on the average secondary particle size of the raw material alumina.

In the method of the present invention, raw alumina is first pulverized.

Although the degree of pulverization is not limited, the powder obtained by calcining after lanthanum treatment is usually formed into granules, pellets, honeycomb shapes, etc., or the surface of the already formed object is impregnated, Since it is often used by coating by spraying, coating, etc., it is usually ground to about 30 μm or less, preferably about 20 μm or less. If the average secondary particle diameter after pulverization is larger than the above range, the strength of the obtained molded product will be weak, and in the coating layer, the slurry in which alumina is dispersed will be unstable and will quickly settle. It is difficult to work with and cannot be produced industrially at low cost, and it also has weak adhesion to molded bodies, causing problems such as falling off. Therefore, it is desirable that the particle size be as small as possible, but pulverization into finer particles exceeding 30 μm or less may be determined based on the balance with the pulverization cost.

The pulverization method may be any method that can pulverize the powder of metastatic alumina or alumina hydrate to an average secondary particle size of 30 μm or less, such as ball mill pulverization, vibration mill pulverization, crusher pulverization, jet mill pulverization. Methods such as the following can be adopted, and these methods may be dry pulverization methods or wet pulverization methods.

The raw material alumina after pulverization is then calcined at a temperature of about 300° C. or above and below the α-alumina transition temperature for 30 minutes or more, preferably at about 00° C. to about 1000° C. for 1 hour to 20 hours. The firing atmosphere is usually air, but may also be a vacuum, an inert atmosphere, etc., and is not particularly limited.

In the above, if the calcination temperature is lower than about 300° C., no effect of improving the high temperature heat resistance of the obtained alumina support is observed even if it is impregnated with a lanthanum compound.

In the present invention, the raw material alumina after being crushed and calcined is then impregnated with a lanthanum compound. The amount of the lanthanum compound impregnated into the raw material alumina may be in the range of about 0.5% by weight to about 10% by weight, preferably about 1% to about 7% by weight as lanthanum element based on A 1203.
．． If the impregnated amount of lanthanum is less than about 0.5% by weight, the effect of suppressing the decrease in specific surface area during high-temperature use will not be sufficient; on the other hand, if the impregnated amount is too large, lanthanum and Al
．． The specific surface area decreases probably because a composite oxide is formed and grain growth occurs.

The method of impregnating raw material alumina with lanthanum is not particularly limited, but for example, lanthanum acetate [La (CH
s Coo)s ・3/2Hz OF, lanthanum nitrate [
L a (Now) s ・6 Hz OF, lanthanum oxalate [L at (Cx Oa) 3 98
Using an aqueous solution containing lanthanum such as lanthanum chloride [LaC1, 7H1O], the raw material alumina (transferable alumina or alumina hydrate) is immersed in the lanthanum aqueous solution, stirred thoroughly, and then water removed. An example is a method of evaporating and drying and then calcining.

Calcination may be performed at a temperature below the temperature at which the above raw material alumina transforms into α-alumina, usually at about 300°C or higher in the atmosphere.
It may be carried out at 800° C. for about 1 hour to IO hours.

The thus obtained transitional alumina has a BET specific surface area of approximately 10
If 0rrr/g or more is used, 1100℃,
It has excellent heat resistance with a specific surface area of at least 60 rrr/g even after heating for 3 hours, and can be used as a catalyst carrier as it is, or as a raw material for forming catalyst carriers of various shapes, or as a catalyst to be coated on the surface of a pre-formed product. It can be used as a carrier.

<Effects of the Invention> As detailed above, the method of the present invention uses inexpensive transitional alumina or alumina hydrate with average secondary particles of about 10 μm or more obtained by the Bayer method etc. as the raw material alumina, and grinds it → By adding the operations of calcination, lanthanum impregnation, and calcination, we can supply a heat-resistant alumina carrier that has good formability and coating properties, maintains substantially the initial transitional alumina morphology even at high temperatures, and is resistant to a decrease in specific surface area. This product can be used as a heat-resistant catalyst carrier at high temperatures for automobile exhaust purification catalysts, combustion catalysts, etc., and its industrial value is extremely large.

<Examples> Hereinafter, the method of the present invention will be explained in more detail with reference to Examples, but the method of the present invention is not limited to the following Examples.

Example 1 Average secondary particle diameter 55 μm, BET surface area 190 rrr
/g of pseudoboehmite aluminum hydroxide is 20j!
Supply it to a ball mill and grind it for 30 minutes until the average secondary particle size is 1.
After reducing the thickness to 8 μm, it was calcined in a hot air circulation dryer at 490° C. for 18 hours.

Approximately 1.5 kg of 1 kg of alumina obtained in this way
Lanthanum acetate (L a (CHs C00) s
・3/2H□0) was immersed in an aqueous solution, thoroughly stirred, and then water was evaporated to impregnate 3% by weight of lanthanum based on the alumina.

Thereafter, the alumina impregnated with lanthanum was taken out and calcined in an electric furnace at 490° C. for 4 hours to obtain an alumina carrier.

This sample is referred to as sample mt.

Example 2 Average secondary particle diameter 50 μm, BET surface area 120rd/
γ-alumina (trade name KC512, manufactured by Sumitomo Chemical Industries, Ltd.) was supplied to a 201 ball mill, pulverized for 30 minutes to give an average secondary particle size of toIIm, and then pulverized in a hot air circulation dryer at 490°C for 18 hours. Fired.

1 kg of alumina obtained in this way costs about 1.5 kr.
Lanthanum oxalate [Latcctoa] x 9 Hz
O] It was immersed in an aqueous solution, thoroughly stirred, and then water was evaporated to impregnate 1% by weight of lanthanum based on the alumina.

Next, the alumina impregnated with lanthanum was taken out and calcined in an electric furnace at 490°C for 4 hours to obtain an alumina carrier. This sample is referred to as sample 11m2.

Comparative Example 1 The same procedure as in Example 1 (using the same raw materials and calcination, lanthanum impregnation, and calcination, except that the raw material alumina, pseudoboehmite aluminum hydroxide, was not pulverized before impregnation with lanthanum)
An alumina carrier was prepared by performing the same treatment. This is referred to as sample Il&lL3.

Comparative Example 2 An alumina carrier was prepared in exactly the same manner as in Example 1, except that the pulverized pseudoboehmite aluminum hydroxide was immersed in lanthanum without being calcined. This is called sample sample 4.

Comparative Example 3 The same pseudoboehmite aluminum hydroxide as in Example 1 was baked at 490°C for 18 hours in a hot air circulation dryer, and then impregnated with 3% by weight of lanthanum in the same manner as in Example 1.
After calcining at 0° C. for 4 hours, the mixture was pulverized in a 201 ball mill for about 30 minutes to obtain an alumina carrier having an average secondary particle size of 18 μm.

This is called sample magnet 5.

Comparative Example 4 An alumina carrier was prepared in exactly the same manner as in Example 2, except that the T-alumina after pulverization was immersed in a lanthanum aqueous solution without being calcined. This is called a sample sample 6.

Test Example 5 g each of the alumina carriers from sample 11ml to sample size 6 obtained by the above method were placed in a mullite crucible and heated in a siliconite furnace at 1100°C in the atmosphere for 3 hours to perform a heat resistance test. The surface area (by BET method) was measured. The results are shown in Table 1.

In addition, as a guide for the ease of handling the slurry used for coating the surface of a molded body made of a ceramic porous body, etc., 30 g of each of the above carrier particle samples was dispersed in 100 cc of water to form a slurry, and then the carrier particles were The settling time was measured. The results are shown in Table 1.

Claims (1)

[Claims] In a method for producing a heat-resistant alumina carrier obtained by impregnating a powder of transitional alumina or alumina hydrate with a lanthanum compound and then performing calcination, the transitional alumina or alumina hydrate before being impregnated with a lanthanum compound. After pulverizing the powder so that the average secondary particle size is 30 μm or less, it is calcined at a temperature of 300°C or higher and lower than the transition temperature to α-alumina, and then impregnated with a lanthanum compound and then calcined. A method for producing a characteristic heat-resistant alumina carrier.