JP3102082B2 - Production method of heat-resistant transition alumina - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat-resistant composition, particularly to a transitional alumina having heat resistance suitable for a catalyst carrier used for a catalytic combustion catalyst or a catalyst for purifying automobile exhaust, and a method for producing the same. .

[0002]

2. Description of the Related Art Application to chemical processes such as automobile exhaust gas removal, high-temperature steam reforming, catalytic combustion of hydrocarbons and hydrogen,
Further, recently, catalysts or catalyst carriers for the field of catalytic reaction under high temperatures such as gas turbines and boilers have been increasingly used in recent years.

As supports used in these fields, catalyst supports having a high specific surface area, usually transition alumina mainly composed of γ-alumina, are often used in view of effective use of catalyst components. ℃ or more, sometimes 1
In some cases, the temperature may exceed 200 ° C., and there is a demand for a catalyst carrier having a characteristic of excellent heat resistance with little decrease in specific surface area under use under such conditions.

However, as is well known, transition alumina is 10
When exposed to a high temperature of 00 ° C. or higher, crystal transition occurs to α-alumina crystals, and the specific surface area is significantly reduced.

When a transition alumina is coated on pellets or other shaped articles as a catalyst carrier and used, the structural change due to the crystal transition to α-alumina is caused by the falling off of the coating layer or the sintering of the catalyst component. May be a cause for promotion.

Heretofore, as a method for improving the thermal stability, for example, by preventing the specific surface area of the transition alumina from lowering, a rare earth element such as lanthanum, praseodymium, neodymium or the like, or an alkaline earth element such as calcium, strontium, barium or the like is added. It is known to do so.

[0007] For example, after impregnating an adsorbing gamma-alumina with a liquid of a barium compound, a heat treatment is performed and 3BaO · 1
Method for obtaining adsorptive alumina showing beta alumina in the crystal form of 6Al ₂ O ₃ (US Pat. No. 2,422,172)
Also, a method of depositing the above-mentioned rare earth substance on alumina or alumina hydrate having a particle size of 500 μm or less (Japanese Patent Application Laid-Open No. Sho 62-176542) is known, but heat treatment at a high temperature, for example, at 1200 ° C. for 3 hours Those having a BET specific surface area of more than 50 m ² / g after the heat treatment in the above have not been proposed.

[0008] Alumina having a high specific surface area is impregnated with an aqueous solution of barium oxide.
In baking the specific surface area is disclosed not less than 70m ² / g (JP 62-191043 JP) is, for barium oxide in this way is dissolved into the alumina, 1050 ° C. It is necessary to perform high-temperature sintering at a temperature of up to 1200 ° C. for a certain period of time, which makes the production equipment expensive and not economical.

A mixed solution of an aluminum alkoxide and a barium alkoxide is hydrolyzed in the presence of one or more oxygen-containing organic compounds having a plurality of functional groups to obtain a sol, which is then gelled. A method of drying and firing has a BET specific surface area of 97 m ² / g after firing for 3 hours at 1200 ° C.
242917), however, the production method using a metal alkoxide or an organic substance is expensive and the raw material is not economical.

On the other hand, it is known to thermally decompose aluminum sulfate to obtain transition alumina. (For example, Tokiko 4
No. 2-16934 and Journal of the Ceramic Industry Association, vol. 77 (2) 196
9, 60-65, Contemporary Chemistry 18 “Synthetic Inorganic Chemistry”
Kyoritsu Shuppan, page 113). The transition alumina obtained by the above method can be used, for example, in Modern Chemistry Course 18 “Inorganic Synthetic Chemistry”
As shown in page 113 of Kyoritsu Shuppan, when heated at about 1000 ° C., it shows a specific surface area of more than one hundred and several tens m ² / g.
When the temperature exceeds 00 ° C., it is described that the specific surface area rapidly decreases to 20 m ² / g or less. In the above-mentioned journal of the Ceramic Society of Japan, this transition alumina (γ-alumina) is a fine particle and the transition rate to α-crystal. Describes that sinterability is good.

[0011]

In view of such circumstances,
We have a high BET specific surface area and 100
Has excellent heat resistance with little decrease in specific surface area even at high temperatures of 0 ° C or higher, and also exhibits excellent coating strength when coated on the surface of other catalyst supports, etc., and also has low production cost As a result of intensive studies for the purpose of finding a heat-resistant transition alumina, the present invention has finally been completed.

[0012]

That is, the present invention relates to a mixed solution of aluminum sulfate and a barium compound comprising 1 to 20 parts by weight of barium with respect to 100 parts by weight of alumina, or 20 parts by weight of water of crystallization of aluminum sulfate. It is another object of the present invention to provide a method for producing a heat-resistant transition alumina, which comprises subjecting a mixture containing water equal to or greater than water salt to thermal decomposition after heating.

Hereinafter, the present invention will be described in more detail. The aluminum sulfate used in the present invention has a BET specific surface area of at least 90 m ² / g of transition alumina obtained after thermal decomposition,
It is not particularly limited as long as it is preferably 100 m ² / g or more, and a commercially available product represented by the general formula Al ₂ (SO ₄ ) ₃ .nH ₂ O (where n = 0 to 27) Solid or liquid aluminum sulfate is used.

In the range where the transition alumina having the above physical properties can be obtained, aluminum sulfate may be replaced with other aluminum salts such as aluminum chloride, aluminum nitrate, aluminum formate, aluminum lactate, aluminum acetate, alumina hydrate or aluminum alkoxide. May be used together.

The barium compound used in the present invention may be any compound that can be uniformly dispersed or dissolved when mixed with aluminum sulfate, and examples thereof include barium oxide, barium acetate, barium nitrate, and barium sulfate.

The mixing ratio of aluminum sulfate and barium compound is about 1 to about 20 as barium with respect to 100 parts by weight of alumina in transition alumina obtained by firing to a desired temperature.
Part by weight, preferably in the range of about 2 to about 18 parts by weight.

When the amount of barium added to 100 parts by weight of alumina is less than 1 part by weight, the effect of suppressing the decrease in specific surface area at the time of use at high temperatures is not sufficient. Crystal growth of the composite oxide of alumina is remarkable, and the specific surface area is greatly reduced.

In practicing the present invention, the raw material aluminum sulfate and barium compound are wet-mixed in an aqueous solution to uniformly disperse alumina and barium, or the raw material aluminum sulfate and barium compound are converted to water of crystallization of aluminum sulfate. When the water contains more than 20 water salts, the aluminum sulfate and the lanthanum compound are dry-mixed with a V-type blender or the like to uniformly disperse alumina and barium.

The mixing operation is preferably performed by heating and stirring the solution. Therefore, the mixture of the aluminum sulfate and the barium compound may be prepared by converting one or both of them into an aqueous solution when both are solid, and adding the other to the mixture, or by simultaneously adding and mixing in water. If liquid aluminum sulfate is used, a solid or liquid barium compound may be added thereto and mixed.Additionally, sulfuric acid is added to aluminum hydroxide to prepare an aluminum sulfate solution, and the barium compound is added thereto. The wet mixing method is not particularly limited as long as the two form a liquid in which both are uniformly mixed and dispersed.

In the practice of the present invention, one or more of a lanthanum compound, a cerium compound, a zirconium compound and a silicon compound may be used in a mixing step.

In the practice of the present invention, the mixed solution or mixture is then heated to evaporate water. In this case, the mixed solution or the mixture gradually increases in viscosity, foams, and if further heated, becomes porous masses or aggregated particles. Since the degree of porosity at this point depends on the evaporation rate of water, a more porous product can be obtained by causing rapid evaporation of water.

As a heating method, an oven, an oil bath,
Known methods such as spray drying, fluidized drying, vacuum drying, kneader, ribbon dryer, and paddle dryer can be used. The heating temperature is not particularly limited, but the heating is performed at about 100 ° C. to the thermal decomposition temperature of aluminum sulfate or lower. Usually, the heating is performed when the mixed solution or mixture is converted to water of crystallization of aluminum sulfate.
What is necessary is just to carry out to about salt. The heated barium substance-containing aluminum sulfate is then thermally decomposed and fired as necessary to obtain transition alumina.

The temperature at which aluminum sulfate is thermally decomposed is
The temperature is not less than the thermal decomposition temperature of barium-containing aluminum sulfate and not more than the temperature at which the transition alumina generated by decomposition does not undergo crystal transition to α-crystal. 24 hours, preferably about 90
It may be performed at 0 ° C. or higher to 1300 ° C. for about 0.5 seconds to 15 hours.

In the present invention, the transition alumina does not exceed the range usually used in the nuclear field, but refers to a process in which aluminum hydroxide is heated to become α-alumina. δ, η, θ, κ, ρ,
It has a crystal form such as χ, and is a transition alumina of θ, κ, and γ crystals.

In the practice of the present invention, heating and pyrolysis of the mixed solution or mixture of the barium compound and aluminum sulfate may be carried out as a continuous operation, but a method of crushing the heating prior to pyrolysis after heating is recommended. Is done.

Although the purpose of the crushing treatment varies depending on the heating method, the powder which has been foamed by heating and has become agglomerated or agglomerated particles is loosened, and the S which is generated at the time of the next thermal decomposition is generated.
Ox is easily volatilized.

In the pulverization, pulverization without using a pulverizing medium such as a ball mill or a vibration mill, for example, using a pulverizer having a low impact strength such as a free pulverizer or a jet mill, having an average secondary particle diameter of about 20 μm or less. It is preferable to disintegrate to about 70 μm.

Although the reason why the barium-containing aluminum sulfate heated product is subjected to the crushing treatment prior to the thermal decomposition is not clear, the obtained transition aluminum has a smaller average primary particle diameter as compared with the untreated product. The heat resistance is excellent, and the amount of SOx remaining in the transition alumina is reduced.

The heated product after the crushing is then thermally decomposed. The pyrolysis condition is, as described above, at a temperature not lower than the temperature at which barium-containing aluminum sulfate is thermally decomposed, and at a temperature at which conversion to α-alumina does not occur. Often, the water and SOx contained in the heated product are rapidly desorbed from the dried product particles by thermal decomposition, whereby the transition alumina foams and has a high specific surface area.

The pyrolysis methods include a rotary kiln,
Known methods such as instantaneous calcination, fluidized firing, stationary firing, a tunnel furnace, a batch furnace, and an atmosphere furnace may be used.

The alumina after pyrolysis can be formed into a transition alumina having a desired crystal form by selecting the pyrolysis conditions (pyrolysis temperature and time). It is also possible to adopt a method of forming transition alumina in a crystalline form.

The transition alumina thus obtained is
The BET specific surface area after firing at 1100 ° C. for 3 hours is 100 m ²
/ G or more and BE after firing at 1200 ° C. for 3 hours
It has excellent heat resistance with a T specific surface area of 60 m ² / g or more, usually about 80 m ² / g or more, and as it is or after being pulverized, as a catalyst carrier or a resin filler, or a catalyst carrier of various shapes. It can be used as a raw material for molding and as a catalyst carrier for coating the surface of an existing molded body such as a ceramic honeycomb.

[0033]

As described in detail above, the heat-resistant transition alumina of the present invention is finely divided into particles and has excellent coatability by a simple operation of mixing, heating, and thermal decomposition using an inexpensive raw material such as aluminum sulfate. The present invention provides a heat-resistant transition alumina having a high specific surface area with substantially no decrease in the specific surface area while substantially maintaining the initial form of the transition alumina, and its industrial value is extremely large.

[0034]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the following Examples.

Example 1 A 500 ml beaker was charged with 50 ml of purified water.
Aluminum sulfate [Al_Two(SO_Four)_Three・ 18H_Two
O] and 30 g of Al in the final desired transition alumina. _TwoO_Three1
1.0 part by weight as a barium element with respect to 00 parts by weight
Add barium acetate and stir at room temperature for 1 hour.
The resulting cloudy barium sulfate was completely dispersed. this
Dispersion (80 water salts in terms of water of crystallization of aluminum sulfate)
Boiled with an electric heater until viscous, and concentrated
After drying, put in an air bath at 180 ° C and evaporate to dryness for 1 hour
did. 100 g of the dried product obtained in this manner was quenched with juicer.
(VA-W35 manufactured by Hitachi Home Appliance Sales Co., Ltd.) for 3 minutes
To obtain a pulverized product having an average secondary particle diameter of 50 μm.
Was. 250 ° C / hour from room temperature to 1050 ° C
After heating at a heating rate between 1050 ° C for 16 hours, heat
Transition alumina (mostly γ-Al
Was Mina). Transition aluminum obtained in this way
Put 2 g of each in a mullite crucible,
110 ° C under a steam flow of 1.5 l / min at a steam temperature of 15 ° C.
Heat at 0 ° C and 1200 ° C for 3 hours for heat resistance test
And measure the specific surface area (by BET method) after heating.
Specified. Table 1 shows the results.

Examples 2 to 3 In the same manner as in Example 1, ₃ parts per 100 parts by weight of Al ₂ O ₃ as barium element in the final desired transition alumina was used.
Transition alumina was obtained by using barium acetate to be 5 parts by weight (Example 2) and 5 parts by weight (Example 3), and a decrease in specific surface area due to heating was examined in the same manner as in Example 1. Table 1 shows the results.

Example 4 330 ml of purified water was placed in a 500 ml beaker.
To this, aluminum sulfate [Al ₂ (SO ₄ ) ₃ · 18H
₂ O] 184 g and Al ₂ O in the final desired transition alumina
₃ Barium acetate was added so as to be 10 parts by weight as a barium element with respect to 100 parts by weight, and the resulting cloudy barium sulfate was completely dispersed while stirring at room temperature for 1 hour. This dispersion (corresponding to 84 hydrate in terms of water of crystallization of aluminum sulfate) was evaporated to dryness in a 130 ° C. air bath for 10 hours. 100 g of this dried product was ground with a juicer for 3 minutes to obtain a ground product having an average secondary particle diameter of 50 μm.
This pulverized product was heated at a heating rate of 250 ° C./hour from room temperature to 1000 ° C., calcined at 1050 ° C. for 16 hours, thermally decomposed, and transition alumina was obtained (as a result of X-ray diffraction, most was γ-alumina). I got As in Example 1, the decrease in specific surface area due to heating was examined. Table 1 shows the results.

Examples 5 to 6 In the same treatment as in Example 4, the final desired transition alumina is adjusted to be 15 parts by weight (Example 5) and 20 parts by weight (Example 6) with respect to Al ₂ O ₃ as a barium element. Then, transition alumina was obtained using barium acetate, and the decrease in specific surface area due to heating was examined in the same manner as in Example 1. Table 1 shows the results.

Example 7 A 500 ml beaker was charged with 330 ml of purified water.
To this, aluminum sulfate [Al ₂ (SO ₄ ) ₃ · 18H
₂ O] 184 g and Al ₂ O in the final desired transition alumina
₃ Barium chloride was added so as to be 5 parts by weight as a barium element with respect to 100 parts by weight, and the resulting cloudy barium sulfate was completely dispersed while stirring at room temperature for 1 hour. This dispersion was put into an air bath at 400 ° C. and evaporated to dryness for 10 hours while stirring by rapid boiling. This dried product 100
g was ground with a juicer for 3 minutes to obtain a ground product having an average secondary particle diameter of 50 μm. This pulverized product is cooled from room temperature to 10
1050 after heating up to 50 ° C at a heating rate of 250 ° C / hour
The mixture was calcined at 15 ° C. for 15 hours and thermally decomposed to obtain transition alumina (mostly γ-alumina as a result of X-ray diffraction). As in Example 1, the decrease in specific surface area due to heating was examined. Table 1 shows the results.

Example 8 330 ml of purified water was placed in a beaker having a volume of 500 ml.
This Arimizu aluminum sulfate _{[Al 2 (SO 4) 3} · 1
8H ₂ O] and 184 g of barium chloride were added to the final desired transition alumina so as to be 5.0 parts by weight with respect to Al ₂ O ₃ as a barium element. Was dispersed. This dispersion was put into an air bath at 400 ° C. and evaporated to dryness for 10 hours while stirring by rapid boiling. The dried product was heated from room temperature to 1050 ° C. at a heating rate of 250 ° C./hour, and then calcined at 1050 ° C. for 15 hours to obtain transferable alumina. This was examined for the decrease in specific surface area due to heating in the same manner as in Example 1. Table 1 shows the results.

[0041] in addition to lanthanum sulfate of barium acetate in Example 9 Example 1 as lanthanum element in the final desired transition alumina Al ₂
Transition alumina was obtained in the same manner as above except that the amount became 1.0 part by weight with respect to O _3, and the decrease in specific surface area due to heating was examined in the same manner as in Example 7. Table 1 shows the results.

Example 10 Aluminum sulfate [Al ₂ (SO ₄ ) ₃ .16H ₂ O]
400 g was charged into a dish-type tumbling granulator and sprayed with 95 cc of an aqueous solution in which barium acetate was dissolved in an amount of 5 parts by weight as barium atoms with respect to 100 parts by weight of Al ₂ O ₃ in the final desired transition alumina. A granulated product of aluminum sulfate powder was obtained. This granulated product (equivalent to 22 hydrates in terms of aluminum sulfate crystal water) is cooled from room temperature to 1050 ° C. for 25 minutes.
After heating at a rate of 0 ° C./hour, calcined at 1050 ° C. for 16 hours and thermally decomposed to obtain transition alumina (mostly γ-alumina as a result of X-ray diffraction). Using this transition alumina, a decrease in the specific surface area due to heating was examined in the same manner as in Example 1. Table 1 shows the results.

Comparative Example 1 Transition alumina was obtained in the same manner as in Example 1 except that barium acetate was not added, and the decrease in specific surface area due to heating was examined in the same manner as in Example 1. Table 1 shows the results.

Comparative Example 2 300 ml of purified water was placed in a beaker having a volume of 500 ml.
To this, 30 g of the transition alumina obtained in Comparative Example 1 and barium acetate as a barium element so as to be 2.0 parts by weight based on Al ₂ O ₃ were added and dispersed at 90 ° C. for 1 hour with stirring. After the water was evaporated while heating the slurry, the slurry was dried at 400 ° C. for 10 hours. Next, the dried product is heated from room temperature to 1000 ° C. at a rate of 250 ° C./hour, and then calcined at 1000 ° C. for 15 hours to obtain transition alumina (mostly γ-alumina as a result of X-ray diffraction). Was. Using this transition alumina, the decrease in specific surface area due to heating was examined in the same manner as in Example 1. Table 1 shows the results.

Comparative Example 3 In the same treatment as in Example 7, transition alumina was obtained by using barium acetate so that the final desired transition alumina was 0.5 part by weight with respect to Al ₂ O ₃ as a barium element. In the same manner as described above, the decrease in specific surface area due to heating was examined. Table 1 shows the results.

[0046]

[Table 1]

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁷ , DB name) B01J 21/00-37/36 C01F 7/00

Claims (2)

(57) [Claims] 1. A mixed solution of aluminum sulfate and a barium compound comprising 1 to 20 parts by weight of barium based on 100 parts by weight of alumina or a mixture containing water of 20 hydrates or more in terms of water of crystallization of aluminum sulfate. A method for producing a heat-resistant transition alumina, comprising thermally decomposing and thermally decomposing a transition alumina. 2. The process for producing heat-resistant transition alumina according to claim 1, wherein the powder after heating is pulverized and then thermally decomposed.