JPS6054917A - Production of molded uniform porous alumina article - Google Patents

Abstract

PURPOSE:To produce the titled molded article having high strength and sufficiently controlled porous structure, by adding an alumina hydrogel forming material to boehmite gel under specific conditions, and calcining the resultant alumina xerogel. CONSTITUTION:Alumina hydrogel is formed from an alumina hydrogel forming material, e.g. AlCl3, by the (heterogeneous) homogeneous precipitating method or ion exchange method, etc., and the pH of the resultant gel is fluctuated 1- 20 times alternately between the region of dissolving alumina hydrogel and region of precipitating boehmite hydrogel, and the alumina hydrogel forming material is added to the step of fluctuating the pH between the regions to afford boehmite gel of grown crystals. The alumina hydrogel forming material is then added continuously to the boehmite gel while keeping the pH thereof within the region of precipitating the alumina hydrogel to grow finally the crystals and give the aimed alumina hydrogel containing formed coarse aggregates. The resultant gel is subjected to combination of washing and drying operation to afford alumina xerogel, which is calcined and converted into alumina.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a porous alumina molded body, and more particularly to a method for producing a porous alumina molded body whose pore structure is adjusted to be suitable as a catalyst carrier.

Among porous inorganic oxides, alumina is widely used as a catalyst support, adsorbent, etc. due to its stable and active surface properties.
It is used as a base material for fillers, etc. For example, γ
-Alumina is widely used as a catalyst support, but
This is because it has a large specific surface area, high dispersion of active metal species, and excellent mechanical strength. In general, a catalyst carrier is required not only to have a large specific surface area, but also to have a pore size large enough to allow reaction molecules to easily approach the surface and to allow products to escape. In other words, catalytic action normally takes place on the surface of the catalyst, but if the reactant molecules or produced molecules are large in size, diffusion resistance may occur, or only molecules larger than a certain size can approach the surface. Therefore, not only the specific surface area of the catalyst but also the pore diameter and its distribution govern the performance of the catalyst. Generally, as the pore size increases, the surface area decreases. To compensate for this, the pore volume must be increased. However, if the pore volume is increased, the mechanical strength will be ignored, making it impractical.

In general, to control the pore structure such as pore diameter, pore volume, and pore size distribution of an alumina molded body, the size and shape of the constituent basic particles and their filling state are adjusted to This can be achieved by adjusting the size and amount of pores formed. For example, a molded body with a large pore size is produced from large basic particles, a molded body with a large pore diameter and a large pore volume is produced from a sparsely packed state, and a molded body with a large pore diameter is produced from a fibrous particle. A molded body with a large pore volume and a sharp pore size distribution can be obtained from a molded body with uniform particles. Therefore, in order to obtain a porous molded body with a controlled pore structure, it is necessary that the basic particles have a specific size and have a fibrous shape that facilitates loose filling. Regarding the manufacturing method of such alumina hydrogel, the present applicant has already published Japanese Patent Application Laid-open No. 56-1205.
This is disclosed in Publication No. 08. That is, in a method for producing a porous inorganic oxide using a hydrogel-forming substance as a raw material, the steps include (1) obtaining a seed hydrogel from the hydrogel-forming substance, and (2) transferring pl+ of the hydrogel to a hydrogel dissolution region and a hydrogel precipitation. A hydrogel-forming substance is added during the pH change to at least one of the hydrogel dissolution region and the hydrogel precipitation region 3- to obtain a crystal-grown hydrogel. It reveals how. By this method, a gel with relatively uniform basic particles can be obtained. Furthermore, the present applicant has disclosed a publication in Japanese Patent Application Laid-Open No. 55-27831 regarding alumina hydrosil having fibrous basic particles.
In addition to disclosing it in Publication No. 1, the alumina and dorosol made of boehmite particles, which are fibrous basic particles with very uniform particles, are specifically disclosed [11a57-
No. 97316.

To summarize the above facts, alumina hydrogel, which is the raw material for an alumina molded body consisting of fibrous basic particles whose basic particles have a specific size and are loosely packed, is (n) alumina hydrogel formation. (b) alternating the pl+ of the alumina hydrogel between a region of alumina hydrogel dissolution and a region of gel precipitation; 4- At least one of the precipitation regions is preferably obtained as a boehmite gel by adding an alumina hydrogel-forming substance and growing crystals during the pl+ fluctuation to the boehmite gel precipitation region.

However, if such a gel is dried to form a xerogel and then converted to alumina by firing, it is not possible to obtain an alumina molded body with a sufficiently controlled pore structure as the object of the present invention. . If it is simply dried and fired, its mechanical strength will be very weak. This is thought to be because the sparsely aggregated structure is very weak. As a known method of increasing mechanical strength, it is possible to use a binder, but depending on the method of adding the binder, it is not possible to sufficiently increase the mechanical strength. A binder is usually effective in binding materials with a strong aggregate structure, but when the aggregate structure is weak, it is difficult to reinforce the inside of the aggregates even if the bonds between the aggregates are reinforced. Generally, when a binder is mixed for the purpose of reinforcing the inside of an aggregate, a kneading operation is performed to cause the agglomeration state of the basic particles to change due to shear force. When applied to the xerogel described above, the pore structure changes to something very undesirable. Furthermore, even when a binder is mixed into the nitrogel cake, no reinforcing effect is found. Therefore, in order to obtain an alumina molded body with strong mechanical strength, the alumina hydrogel used as a raw material must be one in which basic particles are firmly bonded together in loose aggregates.

The present inventors have developed a method of holding an alumina hydrogel consisting of intermediately crystal-grown boehmite particles obtained by the above steps (a) and (1)) in an alumina hydrogel precipitation region (1), and adding an alumina hydrogel forming substance thereto. When added in a continuous flow to grow crystals, an alumina hydrogel is obtained as a reinforced loose aggregate, and this is converted into an alumina xerogel and then calcined.
It was discovered that an alumina molded body with a well-controlled pore structure could be obtained, and the present invention was completed.

That is, according to the present invention, in a method for producing a porous alumina molded body using an alumina hydrogel-forming substance as a raw material, the steps include: (a) obtaining an alumina hydrogel from an alumina hydrogel-forming substance; Alternating the pH between an alumina hydrogel dissolution region and a boehmite gel precipitation region, and adjusting the pH to at least one of the alumina hydrogel dissolution region and the boehmite gel precipitation region.
Upon variation, an alumina hydrogel-forming substance is added,
Step of obtaining crystal-grown boehmite gel; (C) Adding an alumina hydrogel-forming substance in a continuous flow while holding the boehmite gel in the alumina hydrogel precipitation region, and finally crystal-growing the alumina to form loose aggregates. A step of obtaining a hydrogel; (d) a step of converting the alumina hydrogel into an alumina hydrogel by a combined operation of washing and drying, and then firing it to convert it into alumina; A method is provided.

In step (c) used in the present invention, the boehmite microcrystallite not only grows independently, but also because the boehmite microcrystallite already has a loosely aggregated structure. - The alumina hydrogel-forming substance is also deposited on the areas where the microcrystallites are in contact with each other, and as a result, these microcrystallites become integrated at the contact points. Therefore, the loosely aggregated structure seen as a whole becomes extremely strong as the contact points of the basic particles are reinforced. ] In the second step (C), the process ′pA
When the crystal growth of boehmite particles is promoted by (b), minute basic particles of alumina hydrogel are repeatedly dissolved due to pl+ fluctuations, and are further deposited and reinforced at the contact points of boehmite microcrystallites. The functional alumina hydrogel will also disappear, resulting in only weak loose aggregates. Also,
If all crystal growth is performed in step (c) instead of step (I)), the basic boehmite particles will be irregular,
Only alumina compacts with a broad pore structure can be obtained. The final crystal-grown and reinforced alumina hydrogel obtained in step (c) is converted into alumina xerogel by a combination of washing and drying, and then converted into alumina by firing. A porous alumina molded body can be formed by an operation including a step of.

The above steps (a), (b), (c), (d
), it becomes possible to produce a porous alumina molded body with strong mechanical strength and a well-controlled pore structure. It is completely impossible to easily and quickly obtain an alumina molded body with strong mechanical strength and a large concentration of pore volume in the desired pore size using conventional methods.

In the production of the porous alumina molded body of the present invention, the starting material used to form the alumina hydrogel is a compound containing aluminum as an element. For example, metal aluminum (A Q ), aluminum chloride (AΩc
u3, AQCQ 3・6H20), aluminum nitrate (
A Q (NO3) 3・9H203, aluminum sulfate CAB 2 (504) 3, AQ z (SO4) 34
8H20), polyaluminum chloride ([AQ 2 (O
ll)nC(16n)m(1<n<5, m<10
)), ammonium alum ((NH4)2504
・AQ2(504)3・241120), Sodium aluminate (NaAQOz), Potassium aluminate (KII02)
, aluminum isopropoxide (AQ (OCll(
CH2)2)3), aluminum oxide 1-oxide ([1
(QC2H6) 3 ), aluminum 7-broxide (AQ(QC(C1(3)3)3), aluminum hydroxide (A Q (011) 3 ), etc. Preferably, aluminum salts, e.g. , aluminum chloride (A
QCQ3, AQCQ3・61120), aluminum nitrate (A Q (NO3) 3・9820), aluminum sulfate (AQ2(S04)3, AQ2(S04)3・1
81120), aluminates such as sodium aluminate (NaA Q 02 ), and aluminum hydroxide (
A Q (Oll) 3), etc.

Next, 11 of the present invention! ! The manufacturing method will be explained step by step.

Step (a): Production of seed alumina hydrogel slurry In the present invention, the seed alumina hydrogel slurry is
It is formed using the alumina hydrogel forming material described above. The particles (alumina hydrogel particles) contained in the alumina hydrogel slurry are used as seeds when an alumina hydrogel forming substance is added to grow the particles into a boehmite gel in the subsequent boehmite gel growth step [step (b)]. It is usually present in the form of hydroxide in alumina hydrogel slurry. This seed alumina hydrogel slurry is generally produced according to conventionally known methods. That is, conventional methods such as a heterogeneous precipitation method, a homogeneous precipitation method, an ion exchange method, a hydrolysis method, and a metal dissolution method can be employed.

The heterogeneous precipitation method is a method in which a hydrogel-forming substance is neutralized with an acidic or alkaline solution. For example, neutralizing by adding ammonia, sodium hydroxide, etc. as a neutralizing agent to a solution of aluminum nitrate or aluminum sulfate while stirring, or adding hydrochloric acid or sulfuric acid as a neutralizing agent to a solution of an alkali metal salt or ammonium salt. and converts it to aluminum hydroxide 11-. Specifically, it includes a method using a neutralization reaction using a combination of aluminum nitrate and sodium aluminate, or aluminum sulfate and sodium aluminate.

The homogeneous precipitation method is the same in principle as the heterogeneous precipitation method, but differs in that the concentration of the neutralizing agent during neutralization is kept uniform and precipitation is performed uniformly. For example, when carrying out homogeneous precipitation from a solution containing an alumina hydrogel-forming substance in the form of an acid salt,
As a neutralizing agent, an ammonia-releasing substance such as urea or hexamethylene lenti-l-lamin is used. Specifically, the required amount of urea is dissolved in a solution containing aluminum nitrate or aluminum sulfate, and this mixed solution is gradually heated while stirring to gradually decompose the neutralizing agent and release ammonia. The process involves gradual neutralization of the aluminum salt by released ammonia to convert it into an alumina hydrogel.

The ion exchange method is a method in which cations or anions coexisting in a solution of an alumina hydrogel-forming substance are ion-exchanged using an ion exchange resin to produce a colloidal gel. Commercially available colloidal aluminas are usually produced by these methods.

The hydrolysis method is a method in which a hydrolyzed alumina hydrogel forming substance is added to water to cause a hydrolysis reaction to produce an alumina hydrogel slurry. Specifically, it includes the reaction of an alcohol solution of aluminum isopropoxide.

As a metal dissolution method, there is a method in which basic aluminum hydroxide is generated by introducing aluminum or metal powder into a boiling aluminum nitrate or aluminum sulfate solution.

As in E-H, seeded alumina hydrogels can be produced by various methods familiar to those skilled in the art. In addition, there are various methods for modifying the produced alumina hydrogel, but the matters related to the production of these seed hydrogel slurries are well known to those skilled in the art, and the method of the present invention is based on these matters. It is not limited.

Therefore, the production of this seed hydrogel slurry may vary depending on the type of gel-forming substance used as a starting material and the physical properties of the desired product. In some cases, commercially available alumina hydrosils can be used as is. Moreover, the pH change in step (b) II! It is also possible to prepare in combination an I+ agent and an alumina hydrogel-forming substance. In this case, there is an advantage that step (a) and step (])) can be performed in consecutive operations without any troublesome operations such as separation operations in between. It can also be carried out under the same conditions using reagents.The concentration of this seed alumina hydrogel slurry is not particularly limited, as long as it can be stirred as a whole, and is usually +01'
It is less than Ii%, especially about 0.1 to 5%.

Step (b) Uniform growth of two seeds into one gel of boehmite microcrystals The method of the present invention involves the process of uniform growth of this alumina seed hydrogel into a boehmite gel and the process of uniform growth of the alumina seed hydrogel into a boehmite gel and the growth of fine alumina hydrogel particles that become non-uniform elementary particles. In this process, boehmite fine particles can be grown very uniformly.

In this step, the pl+ of the alumina seed hydrogel obtained above is alternately varied between the alumina hydrogel dissolution region and the permai 1 to gel precipitation region, and the alumina hydrogel dissolution region and/or the boehmite gel precipitation region. Preferably only during the transition to the boehmite gel precipitation region, the aforementioned alumina hydrogel-forming substances or pl+ modifiers are added alone or in the form of a mixture to obtain the precipitation of boehmite microcrystals. In addition, the alumina hydrogel referred to in the present invention is Boehmy 1
~, of course, refers to alumina hydrogels in general, such as pierite and amorphous alumina hydrogels.

Moreover, boehmite gel is composed of fine boehmite crystallites exhibiting a fibrous shape among alumina hydrogels, and when these crystallites aggregate, they form an aggregate that is significantly sparser than other alumina hydrogels. Therefore, the process (
The gel obtained in step b) is manufactured in the sense that it consists only of homogeneous boehmite microcrystallites with little contamination by other seed crystallites or particles such as Bayerai 1- or amorphous alumina hydrogel 15-. In the present invention, the boehmite gel precipitation region refers to the pl+ region under conditions that can cause the growth of boehmite microcrystallite, and the alumina hydrogel dissolution region refers to the range in which fine particles of aluminum hydrogel can be solubilized. 1) Refers to 11 areas. Therefore, in the boehmite gel precipitation region, fine alumina hydrogel particles dissolved in the dissolution region and pH
The alumina hydrogel-forming substances added during the fluctuation are rapidly occluded into large hydrogel particles, i.e., boehmite microcrystallites, and crystallize into larger boehmite +-f# crystallites, while in the alumina hydrogel dissolution region, the mixed The fine alumina hydrogel particles are dissolved, and only boehmite microcrystallites that have grown to a certain size are present. In step (b) of the present invention, an alumina hydrogel forming substance is added to the alumina hydrogel slurry (1), and the hydrogel slurry is repeatedly subjected to p+1 fluctuations to obtain a particle size of 16-. Obtain a homogenized precipitation of alumina hydrogel particles. In short, if the particles present in the alumina hydrogel slurry are non-uniform, the reaction system is alternately placed under dissolution conditions and growth conditions, taking advantage of the fact that fine particles are easily dissolved and grow easily. Further, by repeatedly varying the temperature, the seed alumina hydrogel can grow into uniform boehmite particles, that is, uniform growth into boehmite microcrystals can be realized.

The variation of the alumina hydrogel pl (to the dissolution region of the alumina hydrogel or the precipitation region of the boehmite gel is pl+
This is done using a regulator. The pl+ regulator may be an alumina hydrogel-forming material itself or a non-alumina hydrogel-forming material. However, it is preferred that the pl+ regulator used in the variation to at least one region is the alumina hydrogel-forming substance itself.

More preferably, the alumina hydrogel-forming material is used as a pl+ regulator only upon pl+ fluctuations into the boehmite gel precipitation region. That is, many alumina hydrogel-forming substances exhibit acidity or alkalinity when dissolved in water, and therefore can be used as pH regulators. For example, examples of acid f1 include aluminum chloride,
Examples of alkaline substances such as aluminum nitrate and aluminum sulfate include sodium aluminate. However, these materials tend toward the more neutral or boehmite gel precipitation region than their non-aluminum-containing acid or alkali counterparts. For example, when comparing aluminum sulfate and sulfuric acid, aluminum sulfate shows a higher pH, and when comparing sodium aluminate and caustic soda, sodium aluminate shows a lower pH. The pl+ regulator to be added is determined by the direction of the pl+ fluctuation.
C i.e. alumina hydrogel dissolution region or permium l
- Preferred substances differ depending on which region of the precipitation region Pl+ is to be varied.

Since the purpose of the fluctuation in the alumina hydrogel dissolution region is to dissolve microparticles, as a pl+ regulator,
When using a non-alumina hydrogel-forming substance and changing to the boehmite gel-forming region, the purpose is to stably grow boehmite crystallites, so by using an alumina hydrogel-forming substance as the Pl+ regulator, Very uniform agglomerates of boehmite crystallites can be obtained. That is, if the alumina hydrogel-forming material is an alkaline material such as, for example, sodium aluminate, this material is used as a pH adjuster upon transition to the boehmite gel-forming region, and an acidic non-alumina hydrogel-forming material, e.g. Nitric acid, hydrochloric acid, sulfuric acid, etc. can be used as pH adjusters to effect pl+ changes to the alumina hydrogel dissolution region. In addition, when the alumina hydrogel-forming substance is an acidic substance such as aluminum nitrate, aluminum sulfate, or aluminum chloride, this substance is used as a pH adjusting agent when changing to the boehmite gel-forming region, and an alkaline non-alumina hydrogel-forming substance, For example, caustic soda or the like can be used as a pH adjuster to change the pl+ to the alumina hydrogel dissolution region.

In step (b) of the present invention, the pH of the alumina hydrogel slurry is adjusted to Boehmy 1 in order to obtain a gel consisting of Boehmy 1 particles with uniform crystal growth from alumina seed Hydrogel.・Includes an operation in which the periodic pl+ of the alumina hydrogel is varied from the gel precipitation region to the alumina hydrogel dissolution region, and then again varied from Beichimai 1 to the gel precipitation region, depending on the number of repetitions]: The size of the Boehmei 1-percent crystallites obtained from step (b) is controlled. The number of repetitions is one or more, and usually ranges from 2 to 20 times. The alumina hydrogel forming substance is added in portions according to the number of repetitions and when varying the pl+ of the alumina hydrogel slurry.

The amount of the alumina hydrogel-forming substance added at one time is within a range such that a uniform stirring state is maintained in one reaction vessel throughout the entire addition operation and a uniform alumina hydrogel concentration is obtained. If the alumina hydrogel particle concentration becomes too high, it becomes difficult to uniformly stir the alumina hydrogel slurry, and the uniform growth of alumina hydrogel particles becomes difficult.
11 It is not desirable because it will cause harm. Generally 1
120 = The amount of alumina hydrogel-forming material added, calculated as oxide, is between 2 and 20 per portion, calculated as oxide, relative to the hydrogel calculated as oxide contained in the alumina hydrogel slurry.
It is 0%.

The time the alumina hydrogel slurry is held in the alumina hydrogel dissolution zone is sufficient to dissolve the new fine alumina hydrogel resulting from the added alumina hydrogel forming material, and to eliminate unnecessary uniformly grown boehmite crystallites. It is necessary to take an appropriate length so that it does not dissolve. This holding time is closely related to the PH value of the dissolution region, and it is necessary to set an appropriate time corresponding to this. This retention time is usually in the range of about 1 minute to 60 minutes after the pH change; if the pH of the alumina hydrogel dissolution region is acidic, the smaller the pl+ value, the lower the pH value if it is alkaline. The longer the slurry is, the shorter the retention time will be.The time the slurry is retained in the boehmite gel precipitation region after the pH change is determined by the amount of time the slurry is retained in the boehmite gel precipitation region until the added alumina hydrogel forming substance and the fine alumina hydrogel particles dissolved in the dissolution region are uniformly sized. It is occluded by the gel particles and is sufficient for the crystal growth of new boehmite gel particles to occur, and is sufficient for the grown crystal particles to settle into a stable form.

Typically this time is longer than the time it is held in the dissolution zone;
The time is approximately 1 minute to 10 hours. However, in this case as well, holding it for a long time will have the opposite effect. Retention in the boehmite gel precipitation region for a long time will cause the growth of fine alumina hydrogel particles to be dissolved into boehmite gel microcrystallite in the alumina hydrogel dissolution region with the next pl+ fluctuation, and the boehmite gel particles will be It becomes uneven.

The alumina hydrogel dissolution region and boehmite gel precipitation region of an alumina hydrogel slurry are controlled by its PL (pH is controlled by the type of raw material of the alumina hydrogel forming material, the type and concentration of PL + regulator, temperature, and type of coexisting salt). Or it depends on the presence or absence of it.?
In the case of 1, the alumina hydrogel dissolution region is below p115 and above pi+12, and -mitogel stably grows crystals around p119 to 10. The temperature of the alumina hydrogel slurry affects the rate of dissolution of the alumina hydrogel particles and the rate of boehmite gel formation, as well as the crystalline form of the resulting particles. Alumina hydrogel gives amorphous aluminum hydroxide at room temperature and boehmite microcrystals above 50°C.

Therefore, it is preferable to operate at 50°C or higher.

Step 1(c): Reinforcement of loose aggregates by continuous flow The method of the present invention includes a step of reinforcing the aggregated structure of the uniform boehmite gel particles obtained in steps (a) and (b). In this step, while maintaining the pH of the boehmite gel obtained in step (b) in the alumina hydrogel precipitation region, an alumina hydrogel forming substance is added to the boehmite gel in a continuous flow, resulting in crystal growth and reinforcement. An alumina hydrogel is obtained as a loose aggregate. In this step, an alumina hydrogel forming substance and pl(
Addition method 1 in which the regulator is retained in the alumina hydrogel precipitation region 23- For example, by adding the regulator simultaneously and continuously, the uniform constituent particles of the boehmite gel grow and form loose aggregates. However, the structure of the sparsely flocculating tank will be reinforced. Addition of an alumina hydrogel-forming substance and a pH adjuster converts it to highly reactive active aluminum hydroxide. In a system where boehmite microcrystals coexist, this active aluminum hydroxide can be occluded by the boehmite microcrystals, causing them to grow, and forming loose aggregates of boehmite microcrystals. In such systems, it is occluded and reinforced at the contact points of microcrystals in a loosely aggregated structure.

However, when too much active aluminum hydroxide 11 coexists with boehmite microcrystals, a part of the active aluminum hydroxide is not occluded in the boehmite microcrystals themselves or in the contact points between the microcrystals, and instead is absorbed into the active water. Due to the coalescence of aluminum oxide, very fine boehmite particles become non-uniform, a phenomenon similar to the generation of secondary nuclei during crystal growth, and as a result, boehmite forms loose aggregates. The particles become non-uniform, and although the resulting alumina molded body has high mechanical strength, it becomes difficult to control the pore structure. There are also disadvantages if the rate of addition of the alumina hydrogel-forming material is too low. That is, when the amount of activated aluminum hydroxide in the system is insufficient to form loose aggregates, only partial loose aggregates are formed, and the growth and reinforcement of loose aggregates becomes uneven. . Therefore, the rate at which the alumina hydrogel-forming substance is added should be selected within a range that is appropriate for achieving growth of boehmite microcrystals and reinforcement of the formation of loose aggregates, and at the same time that the formation of new boehmite microcrystals is minimized. It is. This value is usually 5% aluminum molar ratio per hour for the boehmite obtained in step (b).
~500% (i.e., a ratio of 0.05 to 5 moles per hour per 11 moles in the boehmite gel).

Further, the total amount of the alumina hydrogel-forming substance added in step (c) is determined to be an appropriate value depending on the amount of boehmite gel obtained in step (b). If the total amount added is too large, it will not only cause the growth of boehmite gel consisting of uniformly aligned particles, agglomeration, and reinforcement of aggregates, but also lead to the formation of separate alumina hydrogel fine particles, which will affect the pore structure of the resulting alumina compact. To control *c L
It becomes. If the total amount added is too small, the mechanical strength of the alumina molded product obtained will be extremely weak because the boehmite gel will only grow and agglomerate, and will not work to reinforce the coagulum. Therefore, the total amount of the alumina hydrogel-forming substances added in step (c) is a value sufficient to realize the formation and reinforcement of linear film aggregates of boehmite microcrystals, and the generation of new boehmite microcrystals is small. This value should be selected within the range of usually 20 to 200'xl in terms of aluminum molar ratio to the boehmite gel obtained in step (1)). Of course, the engineering f.
! 7. The total amount of alumina hydrogel-forming substances introduced into the system in (a), (b) and (C) is 3:11:1, and the inside of the tank is kept in a uniform stirring state throughout the entire process. should be selected within a range that allows a uniform alumina hydrogel concentration to be obtained; for example, when carrying out the method of the present invention by gentle stirring with a general-purpose rotary blade, AQ2
03, it is preferable to keep it at 5% by weight or less.

The alumina hydrogel forming material and pl+ modifier used in step (c) may be the same as those used in step (b) or different. That is, the pH adjuster may be an alumina hydrogel-forming substance or a non-alumina hydrogel-forming substance. However, when using a non-alumina hydrogel-forming substance as a pl+ regulator, care must be taken to ensure that the inside of the system meets the objectives of the present invention even when viewed microscopically. For example, use a weak acid or alkali.

When using a strong acid or alkali, sufficient stirring is required. Therefore, it is preferable to use an alumina hydrogel-forming material also as a pl+ regulator. In general, when alumina hydrogel-forming materials are used, there is a tendency towards a more neutral or alumina hydrogel precipitation region than when using a corresponding non-aluminum containing acid or alkali. Therefore, by using this, the inside of the system can be maintained in the alumina hydrogel precipitation region even when viewed microscopically, and a phenomenon in which loosely aggregated boehmite microcrystals are partially redispersed occurs. 1, which is preferable for the purpose of the present invention because it is held as a uniform linear film aggregate.
In other words, the process +ra<c) can be performed by combining aluminum nitrate and sodium aluminate, or aluminum sulfate and sodium aluminate.

The alumina hydrogel precipitation region includes not only the boehmite gel precipitation region but also the precipitation regions of amorphous alumina hydrogels, Bayerai 1 and the like. The alumina hydrogel precipitation region is controlled by its pH, and its pl+ varies depending on the type of raw material of the alumina hydrogel forming substance, the type and concentration of the pl+ regulator, temperature, the type or presence or absence of coexisting ions, etc. In normal cases, the alumina hydrogel precipitation region is pl+5 or higher and pH 12 or lower.

Note that step (C) is industrially carried out in a flow reactor, such as by continuous addition of a hydrogel-forming substance to a continuous flow of pseudo-28-Boehmai 1 obtained in step (b). preferable.

Step (d): Conversion of alumina hydrogel to alumina The alumina hydrogel as a crystal-grown and reinforced linear membrane aggregate is made into alumina xerogel by washing and drying silk-combining operations, and then fired to form the desired shape. It is said to be a porous alumina molded body with strong mechanical strength and characteristics. In order to remove coexisting unnecessary ions or impurities, a cleaning operation is performed as necessary in the alumina hydrogel state or alumina xerogel state. Conversion from alumina hydrogel to alumina xerogel can be carried out by drying, and this drying method is generally carried out at a temperature below room temperature to 200°C under conditions such that water in the alumina hydrogel is sufficiently evaporated. . Calcining is generally carried out at a temperature of 300 to 1200°C, depending on the desired crystalline form of alumina. For example, if γ-alumina is required, it is fired at a temperature of 400 to 800°C.

In step (d), in order to form an alumina molded body in a shape corresponding to the shape used in step (d), molding is performed in the state of alumina hydrogel or xerogel, or in rare cases, in the state of a fired product. The method may be a gel molding method by controlling the humidity of alumina hydrogel, or a molding method using alumina xerogel powder and a binder. Also, step (d)
Washing, drying and baking as operations in [1] may be omitted depending on the procedure. That is, step (1) is a method for converting alumina hydrogel into alumina, and a conventionally known method can be adopted.

The industrial production of porous alumina molded bodies according to the present invention is advantageously carried out by the method described above, and in particular, in the method of the present invention, a special By employing the alumina hydrogel formation process, there are great advantages in that the mechanical strength of the porous alumina molded body can be increased and the pore structure can be easily controlled.

Next, in order to explain the present invention in more detail, one specific example will be given below. These specific examples are for specifically explaining the principle of the present invention, and the present invention should not be limited to these specific examples.

Note that the mechanical strength will be explained in terms of the side crushing strength of the cylindrical molded body, but the mechanical strength in the present invention is
It refers to the mechanical strength resulting from the structure of porous alumina itself, including not only the side crushing strength but also the degree of abrasion and pulverization. In order to clarify the detailed description of the present invention, the side crushing strength will be used as a representative example. The pore distribution of the alumina molded body was measured by the so-called mercury intrusion method using a Mercury Pressure Porosimeter Model 70 (manufactured by Carse Erba, Milan, Italy). The surface tension of mercury is 474 dyne/cm at 25°C, and the contact angle is 1.
Measurements were made at an angle of 40° and with the absolute mercury pressure varied from 1 to 2000 Kg/cJ.

Comparative Example I 0.10 fl of an aluminum nitrate aqueous solution with an AQ 203 concentration/10 g IQ and 10 ρ of deionized water were heated to 90°C in an enameled container, and then AQ2 was heated with vigorous stirring.
03 Sodium aluminate aqueous solution with concentration 60g/Q 0.3
When 5Q was added instantaneously, it became cloudy, and an aqueous alumina hydrogel solution of pH 5 was found to be h<'H1 et al. While stirring this alumina hydrogel aqueous solution, after 10 minutes, as a first stage operation, an aluminum nitrate aqueous solution was added to the alumina hydrogel solution.
When toQ was added, Tll+ showed 3.5. This solution was kept at 90°C while stirring was continued, and after 5 minutes, 0.35 Q of the sodium aluminate aqueous solution described in -I was added.
u became 10. This operation of adding aluminum nitrate and sodium aluminate alternately after a certain period of time was repeated five times to prepare an alumina hydrogel slurry, filtered, redispersed in 1 fLQ of deionized water, and filtered and washed three times to form an alumina hydrogel cake. I got it. This cake was molded to 1.61φ with an extrusion molding machine, and the extruded product was
After drying at 20°C for 6 hours.

Alumina R1 was obtained by firing at 500° C. for 3 hours.

In the above operation, other operations were the same and pl+ was swung 11 times to obtain alumina R2.

The properties of each alumina obtained are shown in Table 1.32- vinegar.

Comparative Example 2 AQ203'a degree 40g IQ aluminum nitrate aqueous solution 0.10Q and deionized water 1i were placed in an enameled container, heated to 90°C, and while vigorously stirring, AQ2
03 Sodium aluminate aqueous solution with concentration 69g/fi 0.
When 35 Q was added instantly, it became cloudy and the pH was 9.5.
A slurry-like aluminum hydroxide aqueous solution was obtained. This is used as seed aluminum hydroxide, and AQ203 is added to this.
#0.29Q aluminum nitrate aqueous solution of 8gIQ
/hr, an aqueous sodium aluminate solution having an AQ 203 concentration of 69 g/Q was continuously added at a rate of 0.200/hr from different injection ports using a constant rate syringe. During the 6 hours during which the addition operation continued, the temperature was 90°C and the pH was 9 to 10. At 3 and 6 hours after the start of injection, samples of 0.3Q were collected, filtered, washed with deionization, extruded into a cake of 1.6 mm diameter, dried at 120°C for 6 hours, and then heated to 500°C. The mixture was fired for 3 hours to obtain alumina carriers R3 (3 hours after the start of injection) and R4 (6 hours after the start of injection). Its properties are shown in Table-1.

R3 and R4 have a large pore volume, but have a broad distribution and have a volume in the pore diameter portion of 400 or more, where the surface area is sometimes small. Moreover, its mechanical strength is low.

Example I AQ 203 Aluminum nitrate aqueous solution with concentration 4 h/Q 0
．． 10Q and deionized water Ill were placed in an enameled container, heated to 90°C, and then mixed with An 2 while stirring vigorously.
03 Sodium aluminate aqueous solution with concentration 69g/Q 0.3
When 5Ω was added instantly, it became cloudy and an alumina hydrogel aqueous solution with pl+9.5 was obtained. After 10 minutes with stirring, 0.10Q of aluminum nitrate aqueous solution was added to this alumina hydrogel aqueous solution, and pl (=3.5) was stirred while keeping this solution at 90°C. After 5 minutes, 0.350 of the above sodium aluminate aqueous solution was added, and pl+ became 10. This operation of adding aluminum nitrate and sodium aluminate alternately at a certain time interval was repeated 5 times to prepare the seed alumina hydrogel aqueous solution. To this, AQ203 concentration 8g/
Q aluminum nitrate aqueous solution at 0.2'JQ/hr,
A sodium aluminate aqueous solution having an AQ 203 concentration of 69 gIQ was added continuously for 3 hours from different injection ports using a constant rate syringe at a rate of 0.200/hr. During the 3 hours during which the addition operation continued, the temperature was 90° C. and the pH was 9 to 10. This liquid was filtered, and washing by redispersing in 10 fl of deionized water and filtering was repeated three times to obtain a cake.

This cake has a diameter of 1.61 mm with a solid content concentration of approximately 25%.
It was molded into a cylindrical shape using an extrusion molding machine having a die with holes of 100 to 100 cm, and dried at a temperature of 120° C. for 6 hours. Thereafter, it was placed in an electric furnace and fired at 500° C. for 3 hours while blowing air to obtain an alumina molded body A. As shown in Table 1, unlike the alumina of the comparative example, this material has a large pore diameter but a sharp pore distribution, and also has excellent mechanical strength.

Example 2 A nitric acid aqueous solution was prepared by dissolving 1652 g of commercially available special grade concentrated nitric acid in 5Q deionized water. This nitric acid aqueous solution 0.165Q
and 10Q of deionized water in an enamel container and heated to 95°C.
After heating, 0.4 Q of a sodium aluminate aqueous solution with a concentration of 611 g/Q of 35-AQ2O3 was instantly added while stirring vigorously, resulting in pHIO
An aqueous solution was obtained. This was used as a seed aluminum hydroxide, stirring was continued, and after 15 minutes, 0.1659 of the above nitric acid aqueous solution was added as the first operation, resulting in a PI+2.5
showed that. Continue stirring while keeping this solution at 95°C,
After a few minutes, 0.4Q of the above sodium aluminate aqueous solution was added, and pl+ was 11. Repeat this operation of adding nitric acid and sodium aluminate alternately after a certain period of time,
After completing the 8th stage and holding it for 15 minutes, add A11120 to this.
, 0.29Q aluminum sulfate aqueous solution with a concentration of 8g/ρ
/hr, an aqueous sodium aluminate solution having an AQ 203 concentration of 69 g/ff was continuously added at a rate of 0.20 Q/hr from different injection ports using a constant rate injector. During the 3 hours during which the addition operation continued, the temperature was 90°C and the pH was 9 to 10.
Met. Using this solution, an alumina opening was obtained in the same manner as in Example 1. The properties of this alumina 0 are shown in Table 1. This alumina has a sharp pore distribution and excellent mechanical strength.

−36=

Claims (2)

[Claims] (1) A method for producing a porous alumina molded body using an alumina hydrogel molded material as a raw material, including: (a) obtaining an alumina hydrogel from an alumina hydrogel forming material; (b) adjusting the pH of the alumina hydrogel to dissolve the alumina hydrogel; and the boehmite gel precipitation region, and at least one of the alumina hydrogel dissolution region and the boehmite gel precipitation region.
(c) Adding an alumina hydrogel forming substance in a continuous flow while maintaining the boehmite gel in the alumina hydrogel precipitation region, and finally (d) converting the alumina hydrogel into alumina xerogel by a combined operation of washing and drying, and then converting it into alumina by firing; A method for producing a uniformly porous alumina molded body. (2) In step (b), the alumina hydrogel-forming substance is added only when the pH changes to the boehmite gel precipitation region when the pH changes by [ρ]1.
The method described in section.