JPH0132169B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an industrially advantageous method for producing alumina powder having a low bulk density, particularly an alumina powder having a high surface area, high pore volume, low bulk density, and high oil absorption. γ-alumina, δ or θ-alumina are dehydration transfer products of pseudoboehmite, and have a wide range of uses such as adsorbents, additives, retention agents, catalysts, catalyst supports, forming aids, and coating agents. I have it.
Many of these uses include alumina's porosity, water absorption, oil absorption, adsorption, bulk density, water retention, oil retention,
This is due to purity etc. Therefore, it is desired to bring the pore volume, surface area, and bulk density of alumina to specific preferred ranges, particularly high pore volume, high surface area, and low bulk density. Methods for producing such alumina can be roughly divided into a gas phase production method and a hydrogel production method. The gas phase production method involves oxidation of metallic aluminum and thermal decomposition reaction of aluminum chloride, but the production method is accompanied by significant difficulties and has the drawbacks of high production cost. On the other hand, the hydrogel production method is a method in which pseudo-boehmite is produced once, and porous alumina is obtained by drying and firing it. Regarding this method, a method has been proposed in which the physical properties of the obtained alumina are controlled by adjusting the degree of contraction of the gel structure during the drying and firing process. There are methods such as replacing some or most of the water in the boehmite gel with an organic solvent such as alcohol, etc., but the alumina obtained by these methods has a low pore volume, high bulk density, and , they tend to have poor water resistance and, moreover, tend to be expensive to manufacture. Special Public Service 1977-
According to Publication No. 13496, alkali aluminate and
A method has been proposed in which a special pseudo-boehmite is produced by reaction with a halohydrin such as ethylene chlorohydrin, and this is used to produce alumina having a high surface area and low bulk specific gravity. However, this method also has the disadvantage of high production costs due to the use of expensive halohydrins such as ethylene chlorohydrin. The present inventors have completed the present invention as a result of intensive research aimed at developing a method for industrially advantageously producing alumina having a high surface area, high pore volume, and low bulk density. That is, according to the present invention, an alumina hydrogel-forming substance is added to an alumina hydrogel formed under conditions of pH 6 to 11 and 50°C or higher under pseudo-boehmite-forming conditions and in the presence of sulfate groups, and crystal growth is caused. ,
A pseudo-boehmite gel that forms loose aggregates is obtained, and this pseudo-boehmite gel is washed with water, spray-dried, and fired to have a pore volume of 2 to 5 ml/
g, surface area 150-300m ² /g and bulk density 0.10-0.25
A method for producing alumina is provided, characterized in that it produces alumina of g/ml. The method of the present invention consists of a special pseudo-boehmite formation process and an alumina formation process in which the formed gel is washed, dried, and fired. In the pseudo-boehmite formation process, an alumina hydrogel-forming substance is used as a raw material, and an alumina hydrogel, so-called seed gel in crystal growth (hereinafter referred to as starting alumina hydrogel), is formed under conditions of pH 6 to 11 and 50°C or higher. Using this alumina hydrogel as a seed, an alumina hydrogel-forming substance is further added to the seed alumina hydrogel under pseudo-boehmite forming conditions in a state in which sulfate groups substantially coexist, and finally crystal growth occurs. And pseudo-boehmite is formed which forms loose aggregates. There is no need to use a special alumina hydrogel-forming substance, and general-purpose, inexpensive materials such as sodium aluminate, potassium aluminate, aluminum chloride, aluminum nitrate, and aluminum sulfate can be used. On the other hand, as a reagent for adjusting pH, an alumina hydrogel forming substance may be used.
An acid or alkali that does not contain aluminum may be used. For example, in addition to the above-mentioned alumina hydrogel-forming substances, sulfuric acid, nitric acid, hydrochloric acid, ammonia, caustic soda, caustic potash, etc. may be used. In order to substantially coexist sulfate groups in the system, it is natural to use aluminum sulfate as one of the alumina hydrogel substances, or sulfuric acid as a PH regulator. In this combination, it is also possible to make sulfuric acid and/or aluminum sulfate coexist in the acidic solution. Preferable combinations of alumina hydrogel-forming substance and PH regulator to be added include aluminum sulfate-sodium aluminate, sulfuric acid-sodium aluminate, and aluminum sulfate-caustic soda. Among these, particularly preferred is aluminum sulfate-sodium aluminate. Because in this combination,
This is because it is a system that can be easily controlled within the PH range of 6 to 11, ie, pseudo-boehmite production conditions, even when looking at the inside of the system microscopically. The amount of sulfate radicals present in the system is 12 to 300%, preferably 20 to 100%, in terms of equivalent ratio to aluminum present in the system. A suitable range exists for the rate of addition of the alumina hydrogel forming material. The small addition rate not only does not achieve the rapid growth of pseudoboehmite;
Uniform growth of pseudo-boehmite crystal size as a result of competitive growth between fine pseudo-boehmite crystals and relatively grown pseudo-boehmite crystals, which occurs when a certain addition rate exists, also does not occur. In general, the finer the crystal, the easier it is to grow.
When growth is performed by addition operation in a system where fine crystals and relatively large crystals coexist, the crystals tend to become uniform as they grow. Therefore, the rate of addition of the alumina hydrogel-forming substance must be relatively high. However, there are also disadvantages if the addition rate is too high. In other words, if the amount of the alumina hydrogel-forming substance newly added to the system is too large compared to the amount of alumina hydrogel at the beginning, even if sulfate groups exist, they will not be occluded by the growing boehmite and will combine with each other and form new ones. This results in the generation of fine pseudo-boehmite crystals. Therefore, adding the alumina hydrogel-forming material too quickly will only result in non-uniform growth of pseudo-boehmite crystals. That is, the rate of addition of the alumina hydrogel-forming substance should be selected within a range that is appropriate for achieving selective growth of pseudo-boehmite crystals and does not generate new pseudo-boehmite crystals. This value corresponds to a molar ratio of aluminum of 20 to 500% per hour relative to the starting alumina hydrogel (i.e., a rate of 0.2 to 5 mol per hour for each mol of Al in the starting alumina hydrogel). It's inside. The amount of the alumina hydrogel-forming substance added is determined depending on the pore volume, surface area, and bulk density of the alumina to be obtained. When the amount of the alumina hydrogel-forming substance added increases, the pore volume of the resulting alumina tends to increase, the surface area decreases, and the bulk density tends to decrease. The starting alumina hydrogel is 10–20 Å
has a diameter of If an alumina hydrogel substance is added to this to grow pseudo-boehmite crystals with a diameter of 30 to 40 Å or more, it is necessary to add several times more of the alumina hydrogel-forming substance than the starting alumina hydrogel. Therefore, the amount of addition required to obtain alumina with the desired pore volume, surface area, and bulk density is an amount that is greater than the amount that makes the presence of pseudo-boehmite crystals obvious on X-ray diffraction, and that can be obtained. It can be said that the amount is such that the pore volume of alumina is 2 ml/g or more and the bulk density is 0.25 g/ml or less. Typically such amount is about 4 times or more the molar ratio of alumina to the starting alumina hydrogel. On the other hand, the upper limit of the amount added must be set so that the surface area of the alumina obtained does not become less than 50 m ² /g, although there is no specific limit. Normally, it is appropriate that it is 30 times or less. The alumina hydrogel-forming substance and the PH regulator are naturally added as an aqueous solution, but there are no particular limitations on their concentrations. However, it is undesirable to dilute it more than necessary or make it more concentrated, as this will bring disadvantages to stirring and control within the system. Also, the concentrations of the starting alumina hydrogel and the added alumina hydrogel forming substance should be adjusted so that the solids concentration in the slurry does not become too high. If these concentrations are too high, the slurry cannot be stirred sufficiently, and the added alumina hydrogel-forming substance or PH regulator may become partially concentrated, resulting in pseudo-boehmite, which is one of the constituent elements of the present invention. This is not preferable since it becomes microscopically impossible to maintain the production conditions. Therefore, it is desirable to select a concentration that will ensure uniform stirring within the system, and a stirring method that will constantly maintain uniformity within the system. For example, the method of the present invention can be carried out even under gentle stirring using a general-purpose rotary blade, provided that Al ₂ O ₃ is kept at about 5% by weight or less. The conditions for producing pseudo-boehmite in the present invention are usually 50°C or higher and a pH of 6 to 11, and if the addition operation is performed under atmospheric pressure, the slurry concentration will not rise to 100°C or higher. The generated pseudo-boehmite is washed with water, filtered, and dried, but the pseudo-boehmite of the present invention does not require any special washing method, and can be washed with water several times to remove soluble metal ions such as Na and
It can be made substantially free of ions such as SO ₄ ^2- and NO ₃ ^- . The pseudo-boehmite obtained in this way has the following characteristics. That is, the pseudo-boehmite basic particles are fibrous and difficult to form a close-packed structure. Since the basic particle size is uniform, fine particles do not become densely packed in the spaces between particles. Since the pseudo-boehmite microcrystals are reinforced in a loosely agglomerated state, when compared after drying, the agglomerated state changes less than in a packing made of ordinary fibrous basic particles. Due to these characteristics, an alumina powder with a very low bulk density, high surface area, and high pore volume can be obtained by subjecting this pseudoboehmite to a spray drying process. The present invention is based on the discovery that pseudo-boehmite, which has the characteristics that the size, shape, and aggregates of the basic particles of alumina powder are reinforced, can be used as a stable raw material for low bulk density alumina. It was completed. In particular, this pseudo-boehmite has the strength to resist the condensation force that acts during drying in an aqueous solvent, so the alumina xerogel obtained by drying,
When the alumina obtained by firing is re-wetted with water or an oil-based solvent, it has an oil retention property that is almost comparable to the water retention property before drying or the pore volume after drying and firing. In general, a method of preventing condensation during the drying process using an organic solvent or the like results in alumina having a low bulk density, but often has poor water and oil retention properties. In this respect, since the alumina obtained by the process of the present invention has undergone a direct water drying process, it is very advantageous in terms of the use of alumina powder. In the present invention, in order to obtain alumina powder, drying and powdering are performed simultaneously by spray drying. Although the drying step and the powdering step can be performed separately, a separate sizing step is required. In this respect, the spray drying method is advantageous because it can easily produce spherical powder with uniform particle size. In addition, alumina powder with a lower bulk density can be obtained by treating it with an organic solvent before drying, but it is converted to alumina with a sufficiently low bulk density even without treatment, so the bulk density is lower than necessary. There is no need for bulk density, and treatment with organic solvents may be used only for special purposes. According to the present invention, the washed pseudoboehmite is subjected to a spray drying treatment after adjusting the solid content concentration by filtration or the like. The drying temperature for an aqueous solution is
The temperature is 100°C to 200°C, and any conditions such as ventilation, reduced pressure, or atmospheric conditions may be used. Usually done under ventilation. After spray drying, further drying at 100℃ to 200℃ if necessary.
It can be done with Firing is performed at a temperature of 400°C to 1100°C for 30 minutes or more. When the pseudo-boehmite in the present invention is fired at 400°C to 800°C, γ-alumina is
When fired at 800°C to 1100°C, δ or θ-alumina is mainly produced. For example, the BET surface area is 230 m ² /g at 500°C and 189 m 2 /g at 900°C.
m ² /g, which changes to 109 m ² /g at 1100°C. The firing temperature is closely related not only to the surface area but also to the size of the basic particles of alumina, the size of the gaps between the basic particles, and the properties of the surface. Generally, as the firing temperature increases, the surface area decreases, but the size of the basic alumina particles increases, the gap between the basic particles also increases, and as the surface hydroxyl groups decrease, hydrophobicity and lipophilicity increase. Therefore, it is necessary to determine the firing temperature depending on the purpose. Next, further explanation will be given by giving specific examples and comparative examples of the present invention. Comparative Example 1 Aluminum sulfate aqueous solution with Al ₂ O ₃ concentration of 80 g/
0.224 and deionized water were placed in an enameled container, heated to 90℃, and stirred vigorously.
Sodium aluminate aqueous solution with Al ₂ O ₃ concentration 69g/
1.55 was added instantly to obtain a slurry-like white liquid with a pH of 10. The liquid had a pH of 10 when it was held at 90°C for 3 hours and also when it was held for 6 hours. 0.3 samples were taken at each time point, filtered, washed with deionized water, and washed with Na ⁺
and most of the SO ₄ ^2- ions were removed. The resulting filter cake was redispersed in deionized water to a solids concentration of approximately 2% by weight, and dried at a drying temperature of 150°C.
°C, under air flow of approximately 4000/min, stock solution supply rate approximately 12
Spray drying was carried out under conditions of cc/min and gas-liquid volume ratio of 1250, and the alumina xerogel powder was dried at 120°C for 6 hours and then calcined at 500°C for 3 hours to obtain γ-alumina powder. This sample was subjected to R ₁ (retention time 3 hours), R ₂
(6 hours) and its properties are shown in Table 1. _R1 ,
It shows almost the same properties as R ₂ , and the bulk density is 0.65g/
It shows an extremely large value of cc, and the pore volume is also 0.7cc/
It shows only an extremely small value of less than g. Comparative Example 2 Aluminum nitrate aqueous solution with Al ₂ O ₃ concentration of 40 g/
Put 0.10 and deionized water 10 in an enameled container, heat it to 90℃, and stir vigorously.
Sodium aluminate aqueous solution with Al ₂ O ₃ concentration 69g/
When I added 0.35 instantly, it became cloudy and the pH was 9.5.
A slurry-like aluminum hydroxide aqueous solution was obtained. This was used as a seed aluminum hydroxide, and an aluminum nitrate aqueous solution with an Al ₂ O ₃ concentration of 8 g/h was added at a rate of 0.29/hr, and a sodium aluminate aqueous solution with an Al ₂ O ₃ concentration of 69 g/h was added at a rate of 0.20/hr using a constant-rate injector. It was added continuously from different injection ports using a . During the 6 hours that the addition operation continued, the temperature was 90℃ and the pH was 9 to 10.
It was hot. 3 hours and 6 hours after the start of injection, 0.3 samples were taken and filtered.
After washing with deionized water, the cake was spray-dried under the same conditions as Comparative Example 1, and the alumina xerogel powder was
Dry at 120°C for 6 hours, then sinter at 500°C for 3 hours to form alumina carrier R ₃ (3 hours after the start of injection), R ₄
(6 hours after the start of injection) was obtained. Show its properties.
Shown in 1. _R3 has a large bulk density and a small pore volume. R ₄ has a small bulk density, but a small pore volume and a small surface area. Example 1 Aluminum sulfate aqueous solution with Al ₂ O ₃ concentration of 80 g/
0.05 and deionized water were placed in an enameled container, heated to 90℃, and stirred vigorously.
Sodium aluminate aqueous solution with Al ₂ O ₃ concentration 69g/
When 0.35 was added instantly, it became cloudy and a slurry-like aluminum hydroxide aqueous solution with pH 10 was obtained.
This is used as a seed aluminum hydroxide.
An aluminum sulfate aqueous solution with an Al ₂ O ₃ concentration of 8 g/
A sodium aluminate aqueous solution having an Al ₂ O ₃ concentration of 69 g/hr was added continuously at a rate of 0.20/hr from different injection ports using a constant rate syringe. During the 6 hours that the addition operation continued, the temperature was 90℃ and the pH was 9 to 10.
It was hot. 3 hours, 4 hours, and 5 hours after the start of injection
After 6 hours, 0.3 samples were taken, filtered, redispersed in deionized water 2, and filtered. Washing was repeated three times to obtain four types of cakes. All of these cakes showed pseudo-boehmite on X-ray diffraction. The obtained filter cake was redispersed in deionized water so that the solid content concentration was about 2% by weight, and dried at a drying temperature of 150°C and about 4000% by weight.
The alumina xerogel powder was obtained by spray drying under the conditions of an air flow of 12 min, a stock solution supply rate of about 12 c.c./min, and a gas-liquid mixing volume ratio of 1250.
Dry for an hour. After that, it was placed in an electric furnace and fired at 500℃ for 3 hours while blowing air. The obtained γ
- For alumina powder, the time from the start of injection is 3 hours,
A for 4 hours, 5 hours, and 6 hours, respectively.
Let them be B, C, and D. Its properties are shown in Table 1 together with aluminas R ₁ to _{R 4} of comparative examples. A, B, C, D
As time goes by, the bulk density gradually decreases. In addition, the pore volumes all showed large values of 2.5 cc/g or more, and the surface areas also maintained values of 150 m ² /g or more.

[Table] Example 2 Aluminum nitrate aqueous solution with Al ₂ O ₃ concentration of 40 g/
Put 0.10 and deionized water 10 in an enameled container, heat it to 90℃, and stir vigorously.
Sodium aluminate aqueous solution with Al ₂ O ₃ concentration 69g/
When I added 0.35 instantly, it became cloudy and the pH was 9.5.
A slurry-like aluminum hydroxide aqueous solution was obtained. This was used as a seed aluminum hydroxide, and the same addition operation as in Example 1 was performed to obtain γ-alumina powders E and F for 3 hours and 6 hours after the start of addition. Its properties are shown in Table-2. E is the bulk density
The value is relatively large at 0.22g/cc, and the pore volume is
Although it is still in an undeveloped state at 2.53cc/g, the bulk density of F is 0.18g/cc and the pore volume is 3.0cc/g.
That's all.

[Table] Example 3 Place 0.15 of an 11.6 wt% sulfuric acid aqueous solution and 10 of deionized water in an enameled container, heat it to 80°C, and then instantaneously add 0.4 of a sodium aluminate aqueous solution with an Al ₂ O ₃ concentration of 69 g/h while stirring vigorously. When I put it into
A slurry-like aluminum hydroxide aqueous solution was obtained which was cloudy and had a pH of 10. This is used as seed aluminum hydroxide, and 11.6wt% sulfuric acid aqueous solution is added to it at 0.13%
An aqueous sodium aluminate solution having an Al ₂ O ₃ concentration of 69 g/hr was added continuously at a rate of 0.27/hr from different injection ports using a constant rate syringe. The temperature was maintained at 80°C during the 9 hours that the addition operation continued, and the pH was
It showed a value of 9.5 to 10. After 6 hours and 9 hours after the start of injection, 0.3 samples of the liquid were taken, and the same procedure as in Example 1 was carried out to obtain γ-alumina powders G and H. Its properties are shown in Table 3. It can be seen that even by this method, it is possible to produce a γ-alumina carrier H that has a low bulk density, a large pore volume, and a large surface area, as shown in the properties of the γ-alumina carrier H.

[Table] Example 4 Aluminum sulfate aqueous solution with Al ₂ O ₃ concentration of 80 g/
0.25 and deionized water were placed in an enamel container, heated to 70℃, and heated to 50℃ while stirring vigorously.
When 0.34 of the specified aqueous sodium hydroxide solution was added, a slurry of aluminum hydroxide that became cloudy and had a pH of 10.5 was obtained. This was used as a seed aluminum hydroxide, and an aluminum sulfate aqueous solution with an Al ₂ O ₃ concentration of 80 g/h was added at a rate of 0.25/hr, and a 5N sodium hydroxide aqueous solution was added at a rate of 0.31/hr using a constant-rate syringe. It was added continuously from the inlet. During the 3 hours that the addition operation continued, the temperature remained at 70°C.
The pH was kept at 9.5-10.5. The injection was stopped 3 hours after the start of the injection, and γ-alumina powder I was obtained by the same operation as in Example 1. This property is shown in Table-6. γ-Alumina powder I exhibits almost similar properties to γ-Alumina powder B of Example 1. Therefore, the method of the present invention can also be carried out using this combination of reagents.

[Table] Example 5 The spray-dried powder that gave γ-alumina powder B in Example 1 was fired at 1000°C for 3 hours instead of at 500°C to obtain θ-alumina powder J. Its properties are shown in Table-7. Theta-alumina powder has a small bulk density and a large pore volume. Although the surface area is reduced compared to γ-alumina powder B, it still has a large value exceeding 150 m ² /g.

[Table] Example 6 An aluminum nitrate/sulfuric acid mixed solution was prepared by mixing an aluminum nitrate aqueous solution with an Al ₂ O ₃ concentration of 80 g/1 and a 11.6 wt% sulfuric acid aqueous solution at a weight ratio of 1:1, and 0.25% of this solution and 10% of deionized water were mixed. was placed in an enamel container, heated to 70℃, and stirred vigorously for 5 minutes.
When 0.22 of the specified aqueous sodium hydroxide solution was added, a slurry of aluminum hydroxide that became cloudy and had a pH of 10 was obtained. This was used as a seed aluminum hydroxide, and the previously prepared aluminum nitrate/sulfuric acid mixture was added at a rate of 0.25/hr and the 5N sodium hydroxide aqueous solution was added at a rate of approximately 0.20/hr using a constant-rate syringe. It was added continuously from the inlet. During the 3 hours that the addition operation continued, the temperature remained at 70°C.
The pH was kept at 9.5-10.5. The injection was stopped 3 hours after the start of the injection, and γ-alumina powder K was obtained by the same operation as in Example 1. The properties are shown in Table 8. This powder exhibits properties almost similar to those of γ-alumina powder C of Example 1. Therefore, the method of the present invention can also be carried out using this combination of reagents.

[Table] Example 7 In Example 6, aluminum chloride was used instead of aluminum nitrate to prepare an aluminum chloride/sulfuric acid mixture, and this was used instead of the aluminum nitrate/sulfuric acid mixture. - Alumina powder L was obtained. The properties are shown in Table 8.
This γ-alumina powder L exhibits almost similar properties to the γ-alumina powders B to C of Example 1. Therefore, the method of the present invention can also be carried out using this combination of reagents.

【table】

Claims (1)

[Claims] 1. An alumina hydrogel-forming substance is added to an alumina hydrogel formed at a temperature of 50°C or higher, a pH of 6 to 11, and in the presence of a sulfate group. Then, by obtaining a pseudo-boehmite gel in which crystals grow and form loose aggregates, this pseudo-boehmite gel is washed with water, spray-dried, and fired to have a pore volume of 2 to 5 ml/g and a surface area of 150
A method for producing alumina, characterized in that it produces alumina of ~300 m ² /g and a bulk density of 0.10 to 0.25 g/ml. 2. The method according to claim 1, wherein the alumina hydrogel forming substance is aluminum sulfate and/or sodium aluminate. 3 After spray drying, calcination is performed at 400 to 800℃ to obtain γ-
A method according to claim 1 or claim 2 for forming alumina. 4 After spray drying, calcination is performed at 800 to 1100℃, and δ
or the method of claim 1 or 2 for obtaining θ-alumina.