JPS5997526A - Manufacture of molded body of porous alumina - 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 The present invention enables rapid crystal growth of pseudo-boehmite in the production of porous alumina molded bodies, and also allows the pore volume and diameter to be adjusted and the pore distribution to be improved from the pseudo-boehmite. It concerns a method for obtaining extremely sharp and mechanically strong products. More specifically, the present invention uses alumina such as aluminum sulfate and aluminate as raw materials and a drogel-forming substance to produce a porous alumina molded body. Aluminum salt necessary for pseudo-boehmite growth is maintained at a temperature of 50° C. or above and stirred, and the slurry is kept at a pH of 6 to 11, which is the crystal growth region of pseudo-boehmite. At the same time, the aluminum salt and/or p I ( Crystal growth is performed to form an alumina hydrogel by selecting the control and adding aluminum at a rate of 20 to 500% aluminum atomic ratio/hi to aluminum hydroxide in the starting slurry, and 10 gels on this alumina are formed. The alumina xerogel powder is obtained by a combination of water washing and drying, and the alumina xerogel powder is mixed with a forming aid, the humidity is adjusted, the molding is performed, and the porous alumina is formed by drying and firing. Concerning how to get the body.

In particular, in the present invention, by mixing alumina xerogel powder with a molding aid and controlling the humidity during the molding operation, it is possible to obtain an alumina molded body with strong mechanical strength and a controlled pore structure. can.

Alumina is widely used as a catalyst support, and this is said to be due to its superior mechanical strength and specific surface area compared to other materials.

However, in recent years, controlled pore distribution, high pore volume, and strong mechanical strength have been cited as properties required for catalyst supports.

Normally, catalytic activity is controlled by the surface area of the catalyst, but if the size of the reacting molecules affects the catalytic reaction, for example if there is resistance to diffusion, the catalytic reaction may be carried out selectively with respect to molecules of a certain size. When tightening the material, the value and distribution of pore diameter becomes more important than the surface area. Its mechanical strength also depends on the pore diameter and pore volume. Therefore, various attempts have been made to control the pore size distribution of alumina and to obtain alumina with excellent mechanical strength.

Generally, in many catalytic reactions, the pore size of the catalyst is one of the important factors that greatly influences the activity and selectivity. As the pore diameter becomes smaller, the diffusion rate of reaction molecules in the pores becomes smaller, and the activity decreases due to a decrease in the catalytic effectiveness coefficient. Also, pore size! As the pore diameter is increased, the increase in the catalyst effectiveness reaches a certain level, and if the pore diameter is increased further, the surface area of the catalyst generally decreases, and the activity on a packed volume basis decreases. Furthermore, if an attempt is made to increase the pore diameter without reducing the specific surface area based on filling, the pore volume will become larger than necessary and the mechanical strength of the catalyst will decrease. Therefore, in order to create a catalyst that is sufficiently active for the desired reaction, it is necessary to adjust the average pore diameter to an optimal value and increase the pore volume to the extent that the mechanical strength does not decrease. It is necessary to obtain a support with a large effective specific surface area.

By the way, γ-alumina is one of the aluminas that are excellent in thermal stability and mechanical strength as a catalyst carrier.

It is known that this can be made by firing pseudo-boehmite, and γ-alumina can be transformed into other phases, such as α-alumina, by further firing.

Pseudo-boehmite is a gel of fibrous water-use boehmite microcrystals, also known as boehmite gel, and is generally made by aging amorphous aluminum hydroxide at a temperature of 50° C. or higher and a pH of 6 to 11.

Alumina support with controlled pore size distribution and pore volume (γ-
In order to obtain alumina (not only alumina but also other phases of alumina), the size and distribution of the pseudo-boehmite crystals must be adjusted to appropriate values. If the crystals are too large, the pore size of the alumina obtained by firing them will be large; if the crystals are too small, the pore size will be small, or excessive sintering of particles will occur during the firing process. As a result, the pore volume becomes small. Furthermore, if the crystals are irregular in size, the alumina crystals obtained by firing the alumina crystals will also be irregular, resulting in pore diameters being irregular and pore volume being smaller than necessary. In addition, if crystals other than fibrous pseudo-boehmite microcrystals are included, such as pseudo-boehmite microcrystals with poor fibrous properties or amorphous gels, the gels will aggregate densely, and the carrier obtained by firing may The pore volume becomes small. Therefore, in order to obtain alumina with sufficiently controlled pore size distribution and pore volume, it is necessary to create pseudo-boehmite whose crystallite size gives the desired pore size and whose particles are uniform in size. I have to.

A common method for adjusting the pore diameter and pore volume of a carrier is to adjust the size and amount of pores formed between the particles by adjusting the size and filling state of the constituent basic particles. It is something.

However, from the point of view of mechanical strength, the filling state cannot be changed once the basic particles are determined. In many cases, the pore size and pore volume are
cannot be adjusted independently. This tendency also applies to alumina; in general, it is possible to increase the particle size of alumina, but on the other hand, the pore volume does not increase.
The disadvantage is that the specific surface area decreases and freezing occurs. Therefore, various methods have been proposed for obtaining alumina, particularly γ-alumina, carriers having a large pore volume in order to maintain the specific surface area at a high value and adjust the average pore diameter. For example, various methods have been proposed for controlling the degree of shrinkage of the gel structure during the drying and firing process of pseudo-boehmite. In this method, since the specific surface area of alumina is approximately constant, adjusting the average pore diameter is equivalent to adjusting the pore volume. Method for changing the drying rate of pseudo-boehmite (J.

Polymer 5science Vol 34, 1
(p. 29) are one example, but these methods have a very narrow range of pore volume that can be adjusted without reducing mechanical strength.
There is a drawback of loss. As a method of adjusting the pore volume within a wide range, a method of adding a water-soluble polymer compound such as polyethylene glycol to pseudoboehmite (Japanese Patent Laid-Open No. 52-10
4498, JP-A-52-77891) or a method of replacing part or most of the water in pseudo-boehmite with alcohol (
JP-A-507123588) and the like have been proposed.

The former method prevents the dense aggregation of pseudo-boehmite microcrystals due to the surface tension of water acting during drying and changes the pore volume depending on the amount added, while the latter method changes the amount of alcohol substitution. This changes the surface tension of water and changes the degree of aggregation of pseudo-boehmite particles, thereby ultimately controlling the pore volume of alumina. The carriers obtained using these methods avoid the problem of mechanical strength due to the surface tension of water, which is the so-called aggregation state of particles, and therefore do not have the drawbacks of being extremely mechanically weak or having poor water resistance. Motsu.

As a method that does not use such additives, there is also a known method (Japanese Patent Publication No. 37517/1973) in which a portion of pseudo-boehmite is converted into xerogel in advance and the pore volume is increased by mixing this into a slurry of pseudo-boehmite. However, the small pores between the pseudoboehmite microcrystals and the large pores between the xerogels simply coexist, resulting in a so-called dazol peak-type pore distribution, and it is difficult to create pores in the desired pore size. It is not possible to create a catalyst support with a large surface area due to concentration.

Therefore, the catalyst has the disadvantage of low activity.

In order to control the size of the basic particles constituting the alumina carrier, it is necessary to adjust the size of the basic particles of pseudoboehmite, which is the raw material. The usual method for producing pseudo-boehmite involves ripening seed aluminum hydroxide. In other words, the pH is maintained in a range of 6 to 11, which is convenient for the formation of pseudoboehmite, so the dissolution rate of microcrystals is extremely low, and the so-called Ostowall 1♂ particles, in which microcrystals dissolve and larger crystals grow, are formed. The rate of growth becomes extremely slow. Therefore, it takes a long time for the growth of boehmite particles.

As a method to overcome the drawbacks of the above methods,
27830, a method is disclosed for producing alumina supports, in particular γ-alumina, with significantly higher surface areas and controlled pore volumes by rapid crystal growth of pseudoboehmite. In this method, a slurry of aluminum hydroxide, which serves as crystal seeds, is kept at 50°C or higher, and aluminum salt and pI-
By alternately adding 1 control agent, active aluminum hydroxide is generated, and this is occluded in the seed aluminum hydroxide to promote its crystal growth, and the pseudo-boehmite particles that have grown are bound together to generate active aluminum hydroxide. By generating boehmite loose aggregates and changing the aggregation state, the degree of shrinkage of pseudo-boehmite during drying is controlled, and a carrier having controlled pore volume, pore diameter, and large surface area is provided. However, in the case of this method, since the aluminum salt and the PL-1 control agent are added alternately, the addition operation is complicated, and when used as an industrial method,
I am still not satisfied. Furthermore, it is difficult to obtain stable mechanical strength.

In the conventional method as described in 1., it was difficult to control the pore volume and pore diameter and to obtain an alumina hydrogel with high mechanical strength. Therefore, when molding alumina hydrogel obtained by conventional methods, if powder molding, which is widely used for catalyst molding, etc., is applied, the mechanical strength of the agglomerated structure of the basic particles is weak, so it shrinks during washing and drying. The pore volume may decrease, or even if alumina xerogel powder can be made into a low bulk density alumina xerogel powder, it will be compressed by the mechanical force applied during powder compaction, resulting in a small pore volume and pore diameter. . Therefore, these alumina hydrogels are formed by a gel forming method that does not apply compressive force, but even in this case, the mechanical strength of the molded product obtained is not high. Furthermore, gel molding is currently not a reliable technology in some respects, and it has been desired industrially to obtain an alumina carrier with a controlled pore structure by powder molding.

In forming an alumina gel, the present inventors first added aluminum hydroxide to an aluminum hydroxide-containing slurry that had been adjusted to pH 6 to 11 and maintained at a temperature of 50°C or higher. 2 in atomic ratio
pl-]6-11 at a rate of 0-500%/l+r
A very simple method for producing an alumina hydrogel characterized in that at least one of the aluminum salt and the pH control agent substantially contains a sulfate group is disclosed. (Patent Application No. 57-69911). The present inventors focused on the extremely strong mechanical strength of the agglomerated structure of the basic particles of this alumina gel itself, and conducted intensive research on a method for obtaining an alumina molded support with strong mechanical strength from this alumina gel. As a result, the alumina hydrogel was first converted into alumina xerogel powder and then mixed with a forming aid.
It was discovered that the alumina molded body obtained through the steps of humidity conditioning and molding has controlled pore volume and pore diameter, and extremely high mechanical strength, leading to the completion of the present invention.

That is, the present invention includes (a) an alumina hydrogel forming step;
This is a method for producing an alumina molded body, which comprises a (+)) molding step and (C) a drying and firing step. Next, the characteristics of each step will be explained in sequence.

First, the alumina hydrogel forming step (a) has the following characteristics.

Miko aluminum hydroxide slurry is kept at a reasonable temperature of 50℃ or higher, and aluminum salt and pH control agent (
This is a simple method that consists only of the operation of simultaneously and continuously adding the agents (11) and 11). Aluminum salt and pH
Addition of the control agent converts the aluminum salt to highly reactive active aluminum hydroxide. In a system where seed aluminum hydroxide coexists, this active aluminum hydroxide is occluded by the seed aluminum hydroxide, which then grows to form cercolate. However, if too much active aluminum hydroxide coexists with respect to seed aluminum hydroxide, a portion of the active aluminum hydroxide t;
A phenomenon similar to the so-called generation of secondary nuclei during crystal growth occurs, in which active aluminum hydroxides combine with each other to become seed aluminum hydroxide without being occluded by miko aluminum hydroxide. Pseudo-boehmite of various sizes are mixed in the boehmite slurry,
Therefore, it becomes difficult to control the pore structure of the resulting alumina support. Therefore, this phenomenon can be suppressed by adding an aluminum salt and a pH control agent (neutralizing agent) at a rate of 500%/hr or less in aluminum atomic ratio to seed aluminum hydroxide.

Also, if the addition rate is too slow, crystal growth will take too long. However, the speed needs to be 20%/hr or more. Even if a favorable amount of active aluminum hydroxide coexists with the seed aluminum hydroxide, if it is not occluded by the single-child aluminum hydroxide within a short time, the active aluminum hydroxide will coalesce with each other and break up. According to the method of the present invention, when polyvalent anions such as sulfate groups are present in the system, the sulfate groups tend to be adsorbed onto the surface of seed aluminum hydroxide, and the sulfate groups are activated aluminum hydroxide. By utilizing the property of Nosumyagana seeds to mediate occlusion into aluminum hydroxide, the coalescence of activated aluminum hydroxide is suppressed. Of course, this method results in faster crystal growth than a system in which sulfate groups are not present, such as a system in which nitrate groups or halogen ions are present instead of sulfate groups. In systems where ions of trivalent or higher valence, such as phosphate groups, exist instead of sulfate groups, the rate of precipitation is too fast, pseudo-boehmite crystals are not formed, and phosphate ions are not sufficient to cause precipitation. Since the particles are contained in the particles and cannot be easily removed, the molded product obtained by firing this precipitate has a small pore volume and, as a result, a small surface area. In other words, by selecting a sulfate radical as a polyvalent anion, it is possible to have the advantage that anions can be easily removed by operations such as washing and filtration during the process of producing an alumina compact by firing from precipitate. . Other crystals are likely to be mixed in the pseudo-boehmite crystal formation region, that is, in order to maintain the system at pH 6 to 11 and grow pseudo-boehmite crystals. In a system containing sulfate radicals, there is a region where amorphous alumina hydrate precipitates below pl-16, and conversely, there is a region where crystallization of payerite occurs above pi-111. Even if you look at the system microscopically, it is undesirable for the pH to swing to a value other than 6 to 11.

Therefore, when adding the aluminum salt and the pI-1 control agent (neutralizing agent), it is not preferable to add them alternately or intermittently at the same time, and sufficient stirring is not recommended. It is necessary to do both at the same time and continuously. Furthermore, since the pH in the system is not brought to the dissolution region of boehmite crystals, the crystal growth is faster than when the pH is brought to the dissolution region. In order for the sulfuric acid radicals to coagulate and bond the grown pseudo-boehmite crystal particles to each other using activated aluminum hydroxide as a binder, the aggregate will not break. When an alumina support is obtained, the molded product has a large pore volume and a large specific surface area, and has very strong mechanical strength. Based on the above characteristics, by selecting an appropriate value for the cumulative addition 1i of aluminum salt and pH control agent (medium hydroxide) to the initial seed aluminum hydroxide, #! The alumina hyalogel formed by J-J becomes extremely sparse and poorly aggregated. Characteristics of this alumina xerogel It can be done.

In the present invention, in connection with the alumina-on-alumina 1:' logel forming step (a), in the forming step (b), the alumina-on-I? Alumina xerogel powder is obtained by combining the alumina hydrogel from the logel forming process with water washing and drying operations, the powder is mixed with a molding aid, the humidity is adjusted, and molding is performed. The following points can be mentioned as characteristics and features of this process. It is easy to concentrate the solid content by filtration, which forms a wall aggregate. Since the basic particles of Ushida boehmite have grown to a certain size, it is difficult for sulfuric acid radicals and Na ions to be adsorbed to the surface, and they can be easily removed by washing with water and can be removed. Preparing alumina hydrogel powder by drying can be done very quickly. This means that when drying the alumina hydrogel that is the object of the present invention, it is possible to control the pore size to a relatively large enough size to avoid phenomena such as capillary condensation of water.
It is very suitable for simultaneous drying and powder preparation methods. In addition, the alumina xerogel powder obtained in this way has high water control properties and water retention properties, especially the amount of water that can be retained. This makes it easy for the molding aid to be dispersed uniformly and is easy to operate.
In other words, it is realized by humidity control and four-wire operation. Moreover, such water resistance and water retention properties widen the range in which humidity can be controlled during humidity control molding. In addition, even in the xerogel state, the strength of the aggregates in the hydrogel state is maintained, so the pore structure of the resulting alumina molded product is sufficient, without being destroyed by the shear force applied during kneading and molding. It will be adjusted. Moreover, products molded in this way do not lose their shape and have a very smooth appearance. In other words, the characteristics of alumina xerogel are:
Low bulk density, high purity, water retention, (high water control properties,
It has good humidity control properties, good vigor, and high mechanical strength. Depending on these characteristics, the type of molding aid,
By selecting appropriate values for the moisture content and moisture content during molding, the molded body obtained is easily converted into an alumina molded body in the next (C) drying and firing step, and the pore volume and average diameter of the alumina are reduced. It can be controlled and have high mechanical strength. Therefore, in the (C) drying and firing process, the following points are listed as the characteristics of B-light. The structure of the alumina xerogel in the present invention is highly resistant to condensation, and has the ability to overcome the condensation force during water evaporation, so there is no need to use special organic solvents in the drying process. There is no need to use an unnecessarily slow drying method. Firing can also include drying,
Even if I do it after drying, it won't change. Since the dried material has strong mechanical strength, it is possible to perform the firing while fluidizing it.

Due to the above characteristics, the product obtained by the method for producing an alumina molded body of the present invention can have the following properties. Pore volume 0.6-1.8ml/it', average pore diameter 1
00 to 1000 people, surface area 50 to 350 nI2/g, but 1] Surface crushing strength 2. OKg or more (pellet diameter 0.8-1
．． 6 mm, length 2 to 3 times the diameter), sodium content 0.05% by weight or less, sulfate content 0.05% by weight or less. Moreover, the pore distribution of the molded article of the present invention is very sharp. With such a simple and quick method, it has never been possible to obtain a highly pure alumina compact that concentrates the pore volume and surface area in the desired pore size and has strong mechanical strength using conventional methods. do not have.

Next, the method of the present invention will be explained in more detail.

[Alumina hydrogel forming step (a)] The aluminum hydroxide-containing slurry serving as a raw material in step (a) of the method of the present invention acts as a seed aluminum hydroxide, and is produced by a generally known method. That is, by adding an alkali to an aqueous solution of a strong acid salt of aluminum, such as aluminum nitrate, aluminum chloride, or aluminum sulfate, or by adding an acid or the above-mentioned strong aluminum acid salt to an aqueous solution of aluminate or potassium aluminate. It is made in the range of pl-16 to 11.

Therefore, in the combination of aluminum salt and pH control agent (neutralizing agent) in step (a) of the method of the invention, prior to the operation of growing the seed aluminum hydroxide,
Seed aluminum hydroxide can also be prepared. In this case, there is an advantage that the preparation and growth of seed aluminum hydroxide can be performed in a continuous operation without complicated operations such as separation operations in the middle. According to microscopic observation, the yuzu aluminum hydroxide produced by this neutralization reaction has a fiber shape with a diameter of 10 to 20 people and a length of about iooλ. It is thought to have a structure similar to pseudobaelite, but because the particle size is so small that it appears amorphous in X-ray diffraction.When aluminum hydroxide in this state is washed, dried, and fired at 400°C, the pore volume is 0.4CC
, # or less amorphous alumina can only be obtained. Naturally, even if this seed aluminum hydroxide is simply kept at 50°C or above with a pH within the range of 6 to 11 for more than one day and night, no crystal growth is observed, and no crystal growth is observed.
The pore volume of the alumina molded body obtained by firing is 0.4 CC/
It remained below f, an extremely low value.

Step (a) of the method of the present invention is to maintain the seed aluminum hydroxide slurry obtained by the above-mentioned conventional method at a temperature of 50°C or higher, preferably 70°C or higher, and add aluminum salt and pH control side to the slurry while stirring. This is done by simultaneously and continuously adding a neutralizing agent (neutralizing agent). The pore distribution of γ-alumina obtained when operating at lower temperatures tends to be blow 1. If the addition operation is performed under atmospheric pressure, the slurry temperature will be io
Do not exceed 0°C. This operation can also be carried out at 100° C. or higher by using a pressure cooker. However, in that case the pore distribution tends to be rather zorodoid.

The pore distribution of the finally obtained γ-alumina is thus influenced by the slurry temperature. However, this effect is 50
If it's above ℃, it's not a big deal.

As long as the aluminum salt to be added is a water-soluble salt, it may be aluminum sulfate, or it may be an alkaline salt such as sodium aluminate or potassium aluminate. p I to add
- As the J control agent, when aluminum sulfate is used as the aluminum salt, alkaline aluminum salts such as sodium aluminate and potassium aluminate may be used, and strained ammonia, caustic soda, and caustic potash may also be used. When an alkali salt such as sodium aluminate or potassium aluminate is used as the aluminum salt, an acid such as sulfuric acid is used. Crushed aluminum salt and p I-1
In the combination of control agents, sulfuric acid and/or aluminum sulfate may be present in the acidic solution.

For example, a combination of a mixed aqueous solution of aluminum nitrate and sulfuric acid and an alkali or alkaline salt solution may be used. Preferable combinations of aluminum salt and pH control agent (neutralizing agent) 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. This is because, in this combination, the pH of the system can be easily controlled within the range of 6 to 11 even when viewed microscopically.

The amount of sulfate radicals present in the system is 12 to 300%, preferably 2% in molar ratio to aluminum present in the system.
It is 0-100%.

There is a suitable range of aluminum salt addition rates.

If the addition rate is low, rapid growth of yuzu aluminum hydroxide will not be achieved, and selective growth will not occur with respect to fine seed aluminum hydroxide. In general, fine crystals have the property of being easy to grow. Therefore, in a system where fine crystals and relatively large crystals exist, when crystal growth occurs competitively, that is, when the seed aluminum hydroxide When active aluminum hydroxide is present, crystals grow and become uniform. Therefore, the rate of addition of aluminum salt must be high to some extent. However, there are also disadvantages if the addition rate is too high. In other words, if the amount of active aluminum hydroxide in the system is too large compared to the amount of seed aluminum hydroxide at the beginning, even if sulfate groups exist, they will not be occluded by the seed aluminum hydroxide or the pseudoboehmite in the middle of growth, and they will become intercalated with each other. They combine to generate new seed aluminum hydroxide. Therefore, addition of aluminum salts too quickly will cause the presence of minute pseudoboehmite particles that will continue to grow and form from the generation of new seed aluminum hydroxide.
This results in non-uniformity in pseudo-boehmite particle size. Therefore, the rate of addition of aluminum salt should be selected within a range that is appropriate for achieving selective growth of seed aluminum hydroxide and does not generate new seed aluminum hydroxide. This value is 20 to 1 hour based on the atomic ratio of aluminum to seed aluminum hydroxide.
500% (i.e. Aj? in seed aluminum hydroxide)
90.2 to 5 moles per hour per mole). When the amount of aluminum salt added to the seed aluminum hydroxide is small, the growth potential of the seed aluminum hydroxide is extremely large, so even at an addition rate of 500%/hr, new seed aluminum hydroxide is hardly formed. . However, as the amount of addition increases, the seed aluminum hydroxide becomes pseudo-boehmite particles and the growth ability slows down, so it is preferable to slow down the addition rate.

The amount of aluminum salt added is determined depending on the pore diameter and pore volume of the molded product to be obtained. About 1 prepared at the beginning
If seed aluminum hydroxide with a diameter of 0 to 20 Å occludes active aluminum hydroxide and grows into pseudoboehmite particles with a diameter of 30 to 40 Å or more, the aluminum salt of yuzu aluminum hydroxide is several times larger than that of yuzu aluminum hydroxide. It is necessary to add Therefore, the alumina with the desired pore diameter and pore volume is 44! It can be said that the amount of aluminum salt added to the seed aluminum hydroxide is greater than the amount at which the presence of pseudo-boehmite crystallites in the slurry becomes clear on X-ray diffraction.

Usually such amount is about three times or more the molar ratio of alumina to seed aluminum hydroxide. On the other hand, the upper limit of the amount added cannot be determined considering the ratio of seeds to growing parts, but the pore diameter of the resulting alumina compact,
Considering the pore distribution and pore volume, 30 times 1 is appropriate.

The aluminum salt and p I-1 control agent (neutralizing agent) are
Naturally, they are added as an aqueous solution, but their concentration is not particularly limited. However, it is undesirable to dilute it more than necessary or to make it more concentrated, as this will bring disadvantages to stirring and control within the system. Also, the concentrations of seed aluminum hydroxide and alumina salt should be adjusted so that the solids concentration in the slurry does not become too palatable. If these concentrations are too high, the slurry cannot be stirred sufficiently, and the added aluminum salt or pI control agent may become partially concentrated, resulting in lower pI control agent, which is one of the constituent elements of the present invention.
This is not desirable because it becomes impossible to maintain I within the range of 6 to 11 microscopically. Therefore, it is desirable to select a concentration that will allow uniform stirring within the system, and a stirring method that will constantly maintain uniformity within the system. For example, if Δ1203 is maintained at about 5% by weight or less, step (a) of the method of the present invention can be performed even under gentle stirring using a general-purpose rotary blade.

[Forming process (1))] The slurry-like pseudo-boehmite that has grown and aggregated to a size that provides the desired pore structure of the carrier is filtered to remove sulfate ions, sodium ions, etc. coexisting in the system together with the solution. Cleaned as necessary.

At this time, it is also possible to use a method in which the liquid containing these ions is evaporated and dried without filtration or washing operations, such as a spray drying method, followed by washing.

That is, since washing can be easily carried out in the state of alumina hydrogel or alumina xerogel, it is preferable to carry out washing depending on the purpose.

Washing with water is sufficient for washing. For example, washing with water in the state of alumina hydrogel is carried out by dispersing the gel in water or warm water several times to several times as much and repeating the operation of filtering and removing the liquid several times. 1. To obtain alumina xerogel powder from alumina hydrogel, drying and then pulverization can be used, but the operation is complicated, so spray drying is usually used to dry and powder at the same time. Do you want to do it? I-4□lJ. The alumina xerogel thus obtained is mixed with a molding aid, conditioned and then molded. As the molding aid, commonly used inorganic substances such as aluminol, silica sol, and silica alumina sol are used. In particular, when contamination with bristle force is to be avoided, aluminum hydroxide or amorphous aluminum hydroxide, generally called alumina sol, such as boehmite, which has very low crystallinity, is used. As a molding aid, the seed aluminum hydroxide used in step (21) of the present invention can also be used. Either way, baking! A molding aid having a high degree of i'i'A and high sinterability is preferable. When the catalyst is required to have good chemical properties, for example acidic properties, known acidic forming aids such as phosphoric acid and phosphoric acid can also be used. The amount of molding aid added in each of these molding aids varies depending on its type and the use of the molded product, but it is usually 0.1 to 20 ton (solid content) per 100 parts by weight of alumina xerogel. It is.

The moisture content of the molding mixture is normally adjusted to 50 to 80% by weight, preferably 55 to 70% by weight. This humidity control is performed by adjusting the amount of water added to the mixture or by dehumidifying it by drying or other means. Further, this mixing and humidity control can be performed using a molding machine.

The shape of the molded body may be a columnar shape, a hollow cylindrical shape, or a non-circular cross section, for example, a multilobed shape such as an ellipse, a tri-rope, or a four-lobed lobe. It may also be a granular molded product. In general, suitable methods for molding into these shapes include molding using a piston-type extruder or screw-type extruder, tabletting using a tablet machine or press, etc. ,
When molding into granules, for example, the IJ ring method,
Examples include dropping in oil method and wet granulation method. The size of the molded object,
The shape can be appropriately selected depending on the purpose of use.

[Drying and firing process of molded body (C)]

The molded body formed into the desired shape and dimensions is dried to remove free water, and fired to remove some bound water, resulting in 7.-alumina or δ or θ-
converted to alumina. By this drying and calcination, it is possible to obtain a porous alumina molded body that is stable and suitable as a catalyst carrier. Calcination is usually carried out at a higher temperature than the temperature at which the compact is used as a catalyst, but f
Preferred temperatures are 300 to 1000°C, 400 to 800°C to obtain γ-alumina, and 800 to 1000°C to obtain δ to θ-alumina. Further, drying prior to firing is performed at room temperature or higher, preferably at 100 to 200°C. As a specific example, the molded body is dried with hot air and then fired in a heating furnace, or the temperature is sequentially raised from 100° C. to a predetermined firing temperature in a heating furnace. The drying and baking time is usually within the range of 30 minutes to 10 hours.

The porous alumina molded body according to the present invention is advantageously produced by the method described above, and in particular, in the present invention, as described above, the xerogel powder is The important technical feature of "lJ=tomorrow, +1 (II) is that the pore structure is controlled and an alumina molded body with strong mechanical strength can be obtained, which is a great advantage.

EXAMPLES In order to explain the present invention in more detail, Examples and Comparative Examples will be given below. These Examples specifically illustrate the present invention, and the present invention is not limited by these Examples.

Comparative Example Aluminum nitrate aqueous solution o, to7? with Al2O3 concentration of 4.0 f/f? and 1 liter of deionized water in an enameled container, heated to 90°C, and stirred vigorously.
I 203 Sodium aluminate aqueous solution with a concentration of 69 g/l 0
．． When I added 351 instantly, it became cloudy and pi(9,
A slurry aluminum hydroxide aqueous solution of No. 5 was obtained.

This is used as seed aluminum hydroxide, and A1□0 is added to this.
3 Concentrated L 0.2 g/l aluminum nitrate aqueous solution
A sodium aluminate aqueous solution having an Al2O3IN degree of 69 f/l and 9 J/hr was continuously added at a rate of 0.20 J'/hr from different injection ports using a constant rate injector. While the addition operation was continued, the temperature was 90°C and the pH was 9-10. The injection was stopped 2.5 hours after the start of the stay, and after dilution with cold water, it was filtered and washed with deionized water.
Most of the Na″- and NO3- ions were removed.

The obtained filter cake was placed at a solid content of approximately 2%.
Redisperse in deionized water so that the stock solution feed rate is approximately 1.
2 CC/m i IT , gas-liquid mixing volume ratio 1.25
Sprayed under the conditions of 0, drying temperature 1so℃, approximately 40001
The mixture was dried under an air flow of /min to obtain alumina xerogel powder.

Add commercially available alumina sol (Nissan Alumina Sol) to this alumina xerogel powder as a molding aid, and add alumina sol to the powder for approximately 50 minutes.
The mixture was mixed while controlling the humidity so that the weight was 1%. At this time, the water retention of alumina xerogel is extremely low, approximately 130% by weight.
Met. After kneading this humidity-adjusted material with a kneader, 1.6+n
+nφ, and the extruded product was dried at 1.2Q°C for 6 hours and then fired at 500°C for 3 hours to obtain an alumina molded body. This sample is designated as R and its properties are shown in Table 1.

This molded body has a small pore volume and a small average pore 7η. It also has very low mechanical strength. In addition, the alumina molded body obtained by gel-molding the filter cake obtained at this time at a water content of 320% by weight, drying, and firing has a pore volume of 1.02 CC/S' and an average fineness. Pore diameter is 207λ
showed a relatively large value.

This means that the pseudo-boehmite obtained by the method of this comparative example has an unreinforced wall structure, so structural destruction occurs during the process of conditioning and kneading the xerogel.
It is considered that the pore volume and average pore diameter of the alumina molded body obtained as a result became small.

Example A I 203 An aqueous solution of aluminum sulfate with a concentration of 80 g/l 0.01 and deionized water 10. Place the ff in an enameled container, heat it to 90°C, and stir vigorously.
Al2O3 concentration 69f//7? When 0.35e of sodium aluminate aqueous solution was added instantly, it became cloudy and pl-1
A slurry aluminum hydroxide aqueous solution of f
'1. is. Using this as a seed aluminum hydroxide, add an aluminum sulfate aqueous solution with an Al2O3 concentration of 8 g/l to it at a rate of 0.29 e/hrA+203 and an aluminic acid'/-da aqueous solution with a concentration of 69 f//l at a rate of 0.20 J/I+r. It was added continuously from different injection ports using a constant rate syringe. While the heating operation continued, the temperature was 90℃, pI-■9~1
It was 0. The injection was stopped 4 hours after the start of the injection, diluted with cold water, filtered, and diluted with deionized water 21
Washing by redispersing and filtering was repeated three times to obtain a cake. This cake showed pseudoboehmite on X-ray diffraction. The obtained filter cake was dispersed in deionized water so that the solid content concentration was about 2% by weight, sprayed at a stock solution supply rate of about 12 cc/min, and a gas-liquid mixing volume ratio of 1.250, and dried. Temperature 150℃, about 4000e
/n]■] to obtain alumina xerogel powder. A commercially available alumina sol (Nissan Alumina Sol) was mixed into this alumina xerogel powder as a molding aid while controlling the humidity so that the amount of alumina was about 5% by weight. The water retention capacity of the alumina xerogel at this time was approximately 200% by weight, which was a fairly large value.

After kneading this humidity-adjusted product in a kneading machine, it was molded into a columnar shape using an extrusion molding machine having a die with a hole of 1.6 mmφ, and the temperature was 1.
It was dried at 20°C for 6 hours. After that, it was placed in an electric furnace and air was blown into it. The properties of the alumina molded body a obtained by gel molding of the filter cake filter cake are also shown in Table 1 for comparison. Mochikatsu and surface area have the same value of X゛.Also, mechanical strength also shows an extremely large value.Furthermore, when compared with gel molded product (a), the pore structure is the same as in the comparative example. Nevertheless, it can be seen that the mechanical strength is improved. Therefore, it can be seen that the method of the present invention is an effective method for controlling the pore structure and obtaining an alumina support with high mechanical strength.

Margin table below -1 Molded object sample name 几 A Table (7M result (7712/S') 202 19
1 205 Pore volume (CC7g) 0.83
1.05 1.09 average, ■11 hole diameter townsman)
164 220 212 Bullet diameter (wnφ
) 1.4 1.3 1.1 Compressive strength N'
In town 7) 1.5 4.2 2.8*
Value based on a cylindrical pore model calculated using the formula 40,000 x pore volume/surface area.

4: 11111 measured by applying a load with I disk 2
Level of surface crushing.

Patent applicant: Chiyoda Corporation Agent Patent Attorney Toshiaki Ikeura

Claims (1)

[Claims] (1) In producing a porous alumina molded body, (a
) A -'<
Pi-
■Aluminum salt and pi-
an alumina hydrogel forming step, which comprises adding an i-control agent, and in which at least one of the aluminum salt and the pH control agent contains a sulfate group; (c) mixing the alumina xerogel powder and a molding aid, controlling the humidity, and molding; (c) drying and firing the molded body to convert it into an alumina molded body. A method for producing an alumina molded body.