JP3469285B2 - Method for producing granular alumina and spherical alumina particles - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing granular alumina. More specifically, the present invention relates to a method for directly producing granular alumina in the acid neutralization process of alkali aluminate, and a sharp particle size distribution which is unique. It relates to spherical, non-agglomerated spherical alumina particles having a shape.

[0002]

2. Description of the Related Art As alumina (Al ₂ O ₃ ), various crystal systems are known, and hydrated alumina, activated alumina, alpha-alumina, etc. are industrially produced in large quantities. Hydrated alumina is used for flame retardant aids, resin compounding agents, etc., activated alumina is used for adsorbents, catalyst carriers, etc.
α-Alumina is used for abrasives, ceramic raw materials, etc., respectively. These alumina particles generally have an indeterminate particle shape and generally have a broad particle size distribution.However, when they are handled or blended with resins, etc., the particles are shaped particles such as spherical particles and have a particle size distribution. It is also required to be sharp.

Conventionally, as a method for producing spherical alumina particles, a method of hydrolyzing organoaluminum (chemical review,
1985, No. 45, pp. 173 to 174). There is also known a method of obtaining fine alumina powder by spraying a mixed slurry of alumina sol and hydrogel of alumina in an air stream and drying the mixture (JP-A-61-174103). In addition, a method of spraying basic aluminum chloride or basic aluminum sulfate into a heated organic solvent is known.

[0004]

Although the method using organoaluminum is satisfactory in that it produces spherical alumina, it is expensive and its use is limited due to the use of expensive organoaluminum. At the same time, since the obtained alumina hydrate is ultrafine particles having a particle size of several tens of nm or less, it is likely to be aggregated during drying, and the aggregated particles are sintered and coarse secondary particles are formed when firing to α-alumina. There's a problem. Further, the granular alumina produced by the spray granulation method has a shape close to a true sphere, and the particle size is in the range of several μm, but the particle size distribution is quite broad, and the purpose is to produce alumina with a sharp particle size distribution. Is not yet fully satisfied with.

The present inventors have found that in the neutralization process of an alkaline aluminate solution with an acid, when a water-soluble acrylamide polymer is allowed to coexist among water-soluble polymers, spherical particles of a partially neutralized alkali aluminate are obtained. Was found to be deposited in high yield, and the present invention was completed.

That is, an object of the present invention is to provide a method for producing granular alumina capable of precipitating non-aggregating fine spherical alumina in a high yield in the neutralization process of alkali aluminate with acid. Another object of the present invention is to provide a method capable of inexpensively producing non-agglomerated regular-shaped granular alumina having spherical or nearly spherical regular particles and having a sharp particle size distribution. Still another object of the present invention is that the particles as a whole have a clear spherical shape, have a peculiar thread-like shape, have a sharp particle size distribution, and are non-aggregating granular alumina, particularly hydrated alumina, activated alumina, α -In providing the alumina.

[0007]

According to the present invention, an alkaline aluminate aqueous solution, a water-soluble acrylamide polymer having a molecular weight of 10,000 to 3,000,000 , and an aqueous acid solution are added.
In the mixed solution of M ₂ O · mAl ₂ O ₃ (M is potassium
Or represents a sodium atom. ) The aluminate represented by
The concentration of Al ₂ O ₃ in the alkali is 5.5 to 8 times.
The amount%, water-soluble acrylamide-based polymer to the Al ₂ O ₃
5 to 100% by weight, and the aqueous acid solution is partially
Add the mixture so that it becomes the same amount, and mix the mixture to obtain a warm solution.
After standing at a temperature of 2 to 50 ° C., a granular material consisting of a partially neutralized product of alkali aluminate is generated, and after the granular material is separated, it is neutralized with an acid, and if necessary, washed with water, dried and baked. A method for producing granular alumina is provided.

According to the present invention, the whole particle has a well-defined spherical shape and a thread-like particle structure, and has a specific crystal structure,
And the ratio of the particles of the major axis (D _L) and the minor axis (D _S) (D _S /
80% or more of particles having a sphericity of 0.90 to 1.00 represented by D _L ) have a formula D ₂₅ / D ₇₅ (wherein D ₂₅ is a volume-based cumulative particle size distribution curve by the Coulter counter method). 25
% Represents the particle size, and D ₇₅ represents the 75% particle size . Alumina spherical particles having a sharpness of a particle size distribution defined in (1 ) to 1.2 to 2.0 are provided.

The granular alumina of the present invention has a bayerite type crystal structure in the case of hydrated alumina and η in the case of activated alumina.
-Alumina type crystal structure, and in the case of more advanced alumina, a θ-alumina type or α-alumina type crystal structure can be taken.

[0010]

In the present invention, among various water-soluble polymers, the water-soluble acrylamide polymer is used as a coagulant growth agent for growing a partially neutralized product of an alkali into a granular product, and the yield and the granular product. It is based on the finding that it acts specifically in terms of regularity.

Among the various water-soluble polymers, the water-soluble acrylamide polymer used in the present invention is dissolved in an alkaline aluminate solution having a high pH, and the solution state is stable. At the time of partial neutralization, the partially neutralized product is aggregated and grown into particles having a clear spherical shape and a string-like particle structure. Comparative Examples 1 to 7 described later
Describes the results of trying to produce granular alumina by adding various water-soluble polymers to an aqueous solution of alkali aluminate.

According to these results, when sodium alginate, which is a typical example of anionic polymer, and carboxymethyl cellulose (CMC) are used, starch, polyvinyl alcohol (PVA), gelatin and polyethylene glycol which are nonionic polymers are used. In the case where the polyamine-based flocculant which is a cationic polymer is used, the one added to the alkaline aluminate solution causes gelation or poor dispersion, and partial neutralization with acid becomes difficult. However, even if the product was forcibly washed with acid, the filterability was poor, and spherical particles having a uniform shape were not formed at all.

On the other hand, in the present invention in which a water-soluble acrylamide polymer is added to an alkali aluminate for partial neutralization, the alkali aluminate solution containing the water-soluble acrylamide polymer is not only stable. Nonetheless, this solution is stable to the addition of an acid, and the partially neutralized solution precipitates spherical particles of the partially neutralized product when left standing.

FIG. 1 is a scanning electron micrograph of hydrated alumina according to the present invention (magnification: 10000 times, the same applies hereinafter), FIG. 2 is a scanning electron micrograph of activated alumina according to the present invention, and FIG. 3 is according to the present invention. A scanning electron micrograph of .theta.-type alumina, and FIG. 4 is a scanning electron micrograph of .alpha.-alumina according to the present invention.

According to these scanning electron micrographs,
All of the granular aluminas according to the present invention have a distinctive spherical shape as a whole, and the extremely interesting fact that the spherical shape has a unique particle shape in which thread-shaped primary particles are aggregated in the shape of thread is It becomes clear. This fact indicates that, in the system of the present invention, hydrated alumina or its precursor is first produced in the form of filamentous primary particles in the reaction mother liquor, and then these filamentous primary particles undergo aggregate growth in the form of filament. Is teaching.

Even more surprisingly, the distinctive spherical particle structure and thread-like particle structure specific to this hydrated alumina and their underlying thread-like primary particle structure are such that -It is maintained even when calcined to alumina, and this fact shows the stability of the thread-like primary particle structure particles and the thread-like particle structure which is an aggregate thereof. Incidentally, FIG. 5 is an X-ray diffraction diagram of the hydrated alumina (bayerite) according to the present invention, and FIG. 6 is an X-ray diffraction diagram when the firing temperature of the hydrated alumina is changed.
According to these X-ray diffractograms, the alumina of the present invention shows a crystal structure of any one of bayerite type, η-alumina type, θ-alumina type, and α-alumina type, and even if the crystal structure changes. Regardless, it was truly other than that the above grain structure was maintained.

The granular alumina according to the present invention has a uniform shape and particle size distribution due to the formation of the above-mentioned thread-like particle structure, and the ratio of the major axis (D _L ) and the minor axis (D _S ) of the particles (D _S ). Sphericity expressed by _S / _DL ) 0.90 to 1.00
The particles have a constant particle shape of 80% or more.

Further, as a measure of the uniformity of the particle size, the formula D ₂₅
/ D ₇₅ (wherein, D ₂₅ represents a particle size of 25% of the cumulative particle size distribution curve of the volume-based by Coulter counter method,
D ₇₅ represents the particle size of the 75% value . Although there is a sharpness of the particle size distribution defined by ) , in the granular alumina of the present invention, this value is in the range of 1.2 to 2.0, and the particle size is extremely uniform.

In addition to the above characteristics, the alumina spherical particles according to the present invention are excellent in the independence of the particles, in which the individual particles (secondary particles) are scattered and there is little or no cohesiveness. This fact is clear from the result that the independence of the particles is not lost as shown in FIG. 4 even when it is fired in α-alumina, but this also shows that the filamentous primary particles become thread-penetrating and stable. It may be due to becoming.

The granular alumina of the present invention is characterized in that it is relatively porous due to the above-mentioned thread structure.
That is, the activated alumina according to the present invention has a pore volume of 0.3 ml / g or more. The pores are macropores, and function effectively as a passage for adsorbing an adsorbent, a passage for adsorbing a catalytically active component of a catalyst carrier, and a passage for a reactant. Also, when used as a resin compounding agent, it gives an anchoring action to the interface with the resin.

[0021]

Preferred Embodiment of the Invention

[Production Method] (Alkali Aluminate) In the present invention, various salts such as K salt or Na salt of aluminate can be used as the alkali aluminate. From the viewpoint of size and the like, sodium aluminate having a composition represented by the following formula (1) is preferably used as the alkali aluminate. “Chemical formula 1” Na ₂ O · mAl ₂ O ₃ (1) In the formula, m is a number of 0.1 to 0.9, particularly 0.6 to 0.
It is a number of eight.

The composition of this sodium aluminate is related to the stability of the mixed solution and the yield and particle size of the formed granular material. When the molar ratio (m) of Al ₂ O ₃ is smaller than the above range, precipitation of partially neutralized particles becomes difficult to occur, yield tends to decrease, and particle shape and particle morphology are likely to be uneven, and partial neutralization is also performed. It requires a large amount of acid, which is not preferable. On the other hand, if the molar ratio of Al ₂ O ₃ is larger than the above range, the stability of the mixed solution is lowered and the particle morphology deviates from the true spherical shape, and the particle size distribution is not sharp. It is not preferable because it exists.

The concentration of sodium aluminate is preferably such that the concentration of Al ₂ O ₃ in the mixed solution is in the range of 5.5 to 8 % by weight. This is not preferable because it lowers the stability.

(Acrylamide Polymer) In the present invention, an acrylamide polymer used as a coagulant growth agent for alumina particles has the formula:

[Chemical 2] The acrylamide repeating unit represented by
This acrylamide polymer is preferably a homopolymer of acrylamide, but can be copolymerized with acrylamide repeating units within the range of 70 mol% or more, particularly 90 mol% or more of the total acrylamide repeating units. It may contain repeating units of various monomers, for example, ethylenically unsaturated carboxylic acids such as acrylic acid, methacrylic acid, maleic acid and fumaric acid, vinyl ethers, (meth) acrylic acid esters and the like. Further, the acrylamide polymer may contain an anionic unit modified to a carboxyl group by hydrolysis or a cationic unit esterified with an aminoalkyl group or a quaternary ammonium alkyl group.

The acrylamide polymer used in the present invention is preferably one having a not very high molecular weight, and its weight average molecular weight (Mw) is generally 10,000 to 3,000,000, particularly 1
It is desirable to be in the range of 0,000 to 2,000,000. If the molecular weight of the acrylamide polymer is too high, it tends to be difficult to form and precipitate the particulate matter. This is considered to be because when the molecular weight becomes too high, the entanglement of the molecular chains increases, and it becomes difficult to form the tufted aggregate structure described above.

In the acrylamide polymer, the relationship between the weight average molecular weight (Mw) and the intrinsic viscosity (η) is

[Equation 2] η = 3.73 × 10 ⁻⁴ × (Mw) 0.66 However, the intrinsic viscosity η is given by being measured in a 1N sodium nitrate solution at 30 ° C.

The acrylamide polymer preferably used in the present invention has a carboxyl group in a free or salt form in an amount of 0.2 to 500 mmol per 100 g of the polymer, particularly 0.1.
It is desirable to contain it at a concentration of 5 to 200 mmol.
The anionic group in the polymer chain acts to stretch the molecular chain in water by the electrostatic repulsion force of the same polar group, and facilitates the formation of tufted aggregate structure of alumina primary particles. Seem.

The acrylamide polymer is Al ₂ O.
₃ to 5% by weight, especially 10 to 40% by weight
It is preferable to add it in an amount of less than the above range, and if it is less than the above range, the precipitation yield of the particulate matter will be poor, such being undesirable. on the other hand,
Even if it is used in a larger amount than the above amount, there is no particular effect and it is economically rather disadvantageous.

As the (acid) acid, various inorganic acids and organic acids are used. From the economical point of view, it is preferable to use mineral acids such as sulfuric acid, hydrochloric acid, nitric acid and phosphoric acid. However, sulfuric acid is the most excellent in terms of the yield of granules and the uniformity of particle size and morphology.

In the present invention, in order to carry out a homogeneous reaction, it is preferable to use it in the form of a dilute aqueous solution, generally 1 to 1
It is preferable to use it at a concentration of 5% by weight. Further, the acid used may contain a neutral salt. The amount of the acid used in the mixing is such that a homogeneous mixed solution (initially transparent) is produced by partial neutralization, and the pH of the mixed solution is slightly lower than 14, but is higher than 13. It's like it doesn't fall.

(Precipitation of Granules) In the present invention, there is no limitation on the order of addition of the above components. For example, the acrylamide polymer may be added after the acid is added to the alkaline aluminate aqueous solution, or vice versa. It is also possible to add the acid after adding the acrylamide polymer to the alkaline aluminate aqueous solution. Of course, these may be added at the same time. In general, it is superior in terms of operability and uniformity of the mixture to add the acid after adding the acrylamide polymer to the alkaline aluminate aqueous solution. The obtained mixed liquid is well stirred so that the respective components are sufficiently mixed, homogenized, and then allowed to stand to precipitate particulates of the partially neutralized product.

The conditions for depositing the particulate matter are generally from 2 to
A suitable method is to leave it quietly at a temperature of 50 ° C. for about 1 to 50 hours. Generally, the lower the temperature, the larger the particle size of the deposited particles, and the higher the temperature, the smaller the particle size of the deposited particles. Thus, it is one of the advantages of the present invention that the particle size of the granules can be controlled by controlling the temperature.

The particles precipitated by leaving the mixed solution are then separated from the mother liquor. The particles obtained by the separation are neutralized by adding an acid, and then washed with water, dried, classified and the like to obtain a product. On the other hand, since the mother liquor from which the particles have been separated and the separated liquid after neutralization contain unprecipitated alumina components and acrylamide polymers, it goes without saying that these liquids can be effectively used again for mixing and precipitation. It is possible.

(Granular Alumina) The granular alumina according to the present invention is one in which all the particles are spherical and have a thread-like particle structure. The primary particle structure and the secondary particle structure are
It is deeply involved in the regularity of particles, the sharpness of particle size distribution, and the non-aggregation property of particles. The alumina particles, regardless of its crystal structure, a shaped particles close to spherical or spherical, the ratio of the major axis of the particle (D _L) and the minor axis (D _S) (D _S /
80% or more of the particles have a sphericity of 0.90 to 1.00 represented by D _L ).

The alumina particles according to the present invention have a uniform particle size, and have the formula D ₂₅ / D ₇₅ (wherein D ₂₅ is 25% of the volume-based cumulative particle size distribution line by the Coulter counter method).
And the particle diameter of D ₇₅ is 75%. The sharpness of the particle size distribution defined in () is in the range of 1.0 to 2.0. The average particle diameter (median diameter, D ₅₀ ) of the alumina particles according to the present invention can be freely adjusted, generally in the range of 0.5 to 20 μm.

According to the first aspect of the present invention, a bayerite type spherical hydrated alumina [Al ₂ (OH ₃ )] is provided. This spherical hydrated alumina has a flocculated precipitate at 200 ° C.
It is obtained by drying at a temperature not exceeding FIG. 1 shows the grain structure and FIG. 5 shows the crystal structure. Its refractive index is generally 1.6 or less.

According to the second aspect of the present invention, η type spherical activated alumina [Al ₂ O ₃ ] is provided. The spherical activated alumina is obtained by calcining the coagulated precipitate at a temperature of 200 ° C. or higher and not exceeding 800 ° C. FIG. 2 shows the grain structure, and FIG. 6 shows the crystal structure (400 ° C. and 60 ° C.).
(0 ° C. fired product). The specific surface area of this activated alumina is 150 to 350 m ² / g, especially 200 to 30
It is similar to that of ordinary activated alumina at 0 m ² / g, but has a relatively large pore volume of 0.3 ml / g or more, and since the pores are macropores, they bring significant advantages. It is a thing. Its refractive index is generally in the range of 1.60 to 1.66.

According to the third aspect of the present invention, θ type or α type activated alumina [Al ₂ O ₃ ] is provided. This θ-type spherical alumina has a cohesive precipitate of 12 at 800 ° C or higher.
It is obtained by firing at a temperature of 00 ° C. or lower. Figure 3
Shows its grain structure, and FIG. 6 shows its crystal structure (calcined products at 1000 ° C. and 1200 ° C.).

On the other hand, the α-type spherical alumina is obtained by calcining the aggregated precipitate at a temperature exceeding 1200 ° C. FIG. 4 shows the grain structure, and FIG. 6 shows the crystal structure (12
50 ° C. baked product). This alumina has a specific surface area of about 150 m ² / g for θ type and about 50 m ² / g for α type. Its refractive index is generally 1.6.
Greater than six.

The hydrated alumina spherical particles, activated alumina spherical particles or alumina spherical particles according to the present invention can be used, for example, in the following applications. That is, the bayerite-type hydrated alumina spherical particles are used as a filler for improving dehydration catalyst and further properties such as fire resistance, flame retardancy, whiteness and smoothness. Further, the η-alumina type activated alumina spherical particles have a wide range of applications as an adsorbent such as a desiccant, a catalyst carrier, a catalyst, dehydration of organic liquids, adsorption purification, removal of oil mist and the like. Since α-alumina type alumina spherical particles are used for catalysts, adsorbents, refractory materials, etc., they are excellent in chemical corrosion resistance, fire resistance, wear resistance, electrical insulation, mechanical strength, etc. It can be used for IC packages, spark plugs, yarn paths, bioceramics, high-alumina porcelain, abrasives and the like.

[0041]

The present invention will be described in detail by the following examples. The powdery physical properties of granular alumina and the evaluation test were carried out by the following methods. (1) Chemical composition JIS (2) Apparent specific gravity It was measured according to JIS K-6220.6. (3) Oil absorption amount Measured in accordance with JIS K-5101.19. (4) Specific surface area and pore volume Sorptomatic Series manufactured by Carlo Erba
s 1800 was used and measured by the BET method. (5) Particle size Measured by a Coulter counter (TA-II type manufactured by Coulter Electronics Co.) using an aperture tube of 50 μm. (6) Particle size by SEM Particle size scanning electron microscope (Hitachi S-570) Obtained from a photographic image, representative particles were selected, and the diameter of the particle image was measured using a scale and shown as the primary particle size. It was

(7) Representative particles are selected from photographic images obtained with a sphericity scanning electron microscope (S-570 manufactured by Hitachi), and the major axis and minor axis of the particle image are measured using a scale. It was calculated from the following formula. Sphericity = with minor (D _S) / long diameter (D _L) (8) refractive index previously Abbe refractometer, the refractive index known solvent (alpha-
Bromnaphthalene, kerosene). Then La
According to rsen's oil immersion method, a few mg of sample powder was placed on a slide glass, 1 drop of a solvent with a known refractive index was added, a cover glass was placed, and the solvent was sufficiently immersed, and then the Becke line was moved with an optical microscope. Observe and ask. (9) Yield The amount of Al ₂ O ₃ produced (calcined at 860 ° C.) was divided by the total amount of Al ₂ O ₃ in the sodium aluminate used in the reaction.

## EQU3 ## Yield (%) = [Al ₂ O ₃ weight produced (g) / total Al ₂ O ₃ amount reacted (g)] × 100

Example 1 A 2 L stainless beaker was placed in a commercially available sodium aluminate (Al ₂ O ₃ 21.4%, Na ₂ O 17.6%, Na
₂ O / Al ₂ O ₃ = 1.35) 706 g (8% as Al ₂ O ₃ concentration in the total liquid volume) Weigh out 212 ml of pure water, put in a thermostat controlled at 20 ° C. While stirring with a stirrer, 423 g of an acrylamide polymer aqueous solution (about 10% aqueous solution made by Wako Pure Chemical Industries, average molecular weight 500,000)
In addition (28% as polyacrylamide anhydride with respect to Al ₂ O ₃ content) was sufficiently dispersed. Then 5% sulfuric acid 545
g was added in about 1 minute (the pH after the end of addition was 14 <). After the end of addition, the stirring was stopped and the mixture was allowed to stand for 12 hours.

After standing for 12 hours, the precipitate and mother liquor were separated by filtration, and the obtained cake was redispersed in pure water to sufficiently disperse it, and then p
Add 5% sulfuric acid until H becomes 2.0 and stir for 1 hour when pH is almost stable at 2.0, then filter, wash with water, dry overnight in a constant temperature oven at 110 ° C, and pulverize with sample mill. And 400, 600, 1,000,
Firing was performed at 1200 and 1250 ° C. for 2 hours to obtain a filament-shaped fine particle spherical alumina powder. Table 1 shows the properties of this powder.
The electron micrograph (SEM) of the 110 ° C dry powder is shown in Fig. 1, the electron micrograph (SEM) of the 600, 1000, 1250 ° C calcined product is shown in Figs. 2 to 4, and the X-ray diffraction diagram of the dry powder product is shown. FIG. 5 shows an X-ray diffraction pattern of the fired product in FIG.

Comparative Examples 1 to 7 4% sodium alginate (manufactured by Wako Pure Chemical Industries) solution, 5% starch (Japan Food Processing MS-4600) solution, 5% gelatin (Wako Pure Chemical Industries) in place of the polyacrylamide aqueous solution of Example 1 Solution), 4% CMC (Wako Pure Chemical Industries) solution, 4% P
VA (Kuraray Co., Ltd. PVA-117) solution, polyethylene glycol # 400 (manufactured by Wako Pure Chemical Industries) 1: 3 aqueous solution, and a 1% solution of polyamine-based polymer flocculant (Mw = 8,000,000) was added to neutralize the acid. Alumina particles were prepared in the same manner as in Example 1 except that washing with water, washing with dilute acid, and washing with warm water were repeated without using any of them, but all had very poor filterability, and spherical particles having a uniform shape could not be obtained. There wasn't.

Comparative Example 8 Same as Example 1 except that the amount of the acrylamide polymer aqueous solution added was 3% in terms of anhydride relative to Al ₂ O ₃ and the total amount was adjusted to 1886 g by adjusting the amount of water. However, spherical particles having a uniform shape were not obtained, and the yield was extremely low.

Examples 2 to 3 In the same manner as in Example 1 except that the standing temperature was set to 2 ° C. and 50 ° C., filament-shaped fine particle spherical alumina powder was prepared.
The properties of this powder are shown in Table 2.

Example 4 In Example 1, the standing temperature was 2 ° C., and the addition amount of the acrylamide polymer aqueous solution was 10 in terms of anhydride with respect to Al ₂ O ₃ minutes.
%, The standing time is 48 hours, and the total amount is 1886g
A filamentous fine particle spherical alumina powder was prepared in the same manner as in Example 1 except that the amount of water was adjusted so that. The properties of this powder are shown in Table 2.

Example 5 The amount of sodium aluminate used in Example 1 was 485 g (Al ₂ O).
_A thread-like fine particle spherical alumina powder was prepared in the same manner as in Example 1 except that the amount of water was adjusted so that the total amount was 1886 g at ₃ concentrations of 5.5%). The properties of this powder are shown in Table 2.

Example 6 The chemical composition is Al ₂ O ₃ concentration 18.8%, Na ₂ O 1
786 g of sodium aluminate of 8.2% (Na ₂ O / Al ₂ O ₃ = 1.66) and 633 g of 5% sulfuric acid added
In the same manner as in Example 1 except that the amount of water was adjusted so that the total amount was 1886 g, a spherical alumina powder having a filament shape was prepared. The properties of this powder are shown in Table 2.

Comparative Examples 9 to 10 In Example 1, the amount of sodium aluminate was 964 g (Al ₂ O
₃ concentration 11%), 264g (Al ₂ O ₃ concentration 3%)
The total amount was adjusted to 1886 g by adjusting the amount of water, but the substance whose Al ₂ O ₃ concentration was adjusted to 11% gelled when sulfuric acid was added to form an aggregate, and the Al ₂ O ₃ concentration was adjusted to 3%. The product did not become spherical particles because of weak gelation after 48 hours.

Comparative Example 11 Example 1 The temperature of the mixed solution was adjusted to 70 ° C. and mixed, and then 70
When it was allowed to stand at ℃, spherical particles having a uniform shape could not be obtained.

Examples 7 to 8 The same as Example 1 except that the aqueous solution of polyacrylamide used in Example 1 had a molecular weight of 300,000 and 1.2 million and the anion degree of each was 0.3 mol%. Was prepared in the same manner as described above to obtain spherical aluminum powder having fine filaments. The powder properties of this product are shown in Table 2.

Comparative Example 12 The same procedure as in Example 1 was carried out except that polyacrylamide having a molecular weight of 8 million and a concentration of 1% was used in Example 1 and the amount of water was adjusted so that the total amount was 1886 g. Spherical particles having a uniform shape could not be obtained because filtration was impossible.

[0055]

[Table 1]

[0056]

[Table 2]

Application Example 1 Average particle size obtained in Example 8 1.5 μm BET method specific surface area is 0 m ² / g, D ₂₅ / D ₇₅ is 1.7 liter. Microsphere Bayerite (Sample No. 1) having a particle structure was mixed with an olefin resin, and the tensile strength and flame retardancy of the resin sheet were evaluated. The resin selected in this example is E manufactured by Toso Co., which is commercially available for industrial use.
VA (EthyleneVinyl Acetate: Ultrasen 63
0) and EEA (Ethylene Ethyl Acryl manufactured by Nippon Unicar Co., Ltd.)
ate: DPDJ 6169).

The compounding amount with respect to the resin is 100 parts by weight of the resin, 100 parts by weight of the sample powder is added, and the mixture is kneaded with a 3.5 inch kneading roll at 100 ° C. for 10 minutes, and the surface is made of Teflon-coated stainless steel. Sandwiched between press plates,
Press for 7 minutes at 130 ℃, each test sheet piece (for elongation residual rate test, dumbbell type (JIS K-7113) with a thickness of 1 mm,
6mm × 80mm × 1m for limit oxygen index measurement test
m) was prepared. Each physical property test was conducted using the above test sheet pieces, and the results are shown in Table 3.

The test measurement method for evaluating the physical properties of the resin product containing the flame retardant will be described below. Measurement method of tensile elongation residual rate test: -The test sheet prepared by the above method was measured according to the plastic tensile test method described in JIS-K-7113. It is indicated that the higher the elongation residual ratio is, the stronger the resistance of the sheet to pulling is. Measurement method of limit oxygen index (%) test: − Using a candle method combustion tester manufactured by Toyo Seiki Seisaku-sho, Ltd., a test was conducted according to the method A described in JIS-K-7201, and the limit oxygen index ( %), And the larger the index, the larger the flame retardant effect. For comparison, the same evaluation was performed on a commercially available normal hydroxide alumina (bayerite) powder (Sample No. H-1) having an irregular shape with an average particle size of 1 μm.

[0060]

[Table 3]

From the results shown in Table 3, comparing the two, the bayerite of the present invention is superior in tensile strength and flame retardancy because the non-aggregating property of the particle characteristics of the present application contributes to the dispersibility. Further, it is assumed that the thread-like particle structure as seen on the surface of the particles enhances the compatibility with the resin.

Application Example 2 Microsphere activated alumina having an average particle size of 6.7 μm and a uniform particle size distribution and a string-like particle structure obtained in Example 1-2 has an inner diameter of 2.5 mm and an outer diameter of 5 mm. , A glass tube which was molded into a ring shape having a height of 6 mm and was filled with the obtained molded product so that the inner diameter was 40 mm and the height of the packed bed was 50 mm, in which 1000 ml of water was added to an equal mixture of benzene and toluene. , Space velocity (LHS
V) Water was added at 20 hr ^-1 and the water content was measured by the Karl Fischer method.
It was pm. Similarly, commercially available activated alumina is classified, and those having an average particle size of about 6 μm are similarly molded into a ring shape,
The mixed solution was dehydrated under the same conditions, and the similarly measured water content was 170 ppm. This fact indicates that the particles formed by the spherical shaped particles having the thread-like particle structure of the present invention have high porosity due to the particle characteristics, so that the gas is well diffused inside the molded article and is efficiently dehydrated. is assumed.

Application Example 3 An iron plate and a stainless plate were polished using α-alumina spherical particles having the thread-like particle structure and the uniform particle size obtained in Example 1-5. At the same time, for comparison, a commercially available alumina hydroxide (bayerite) was fired at 1200 ° C. to obtain α-alumina, and the polishing degree was evaluated. Comparing the polishing properties of the two under constant polishing conditions for a certain period of time, the latter had a polishing degree of about 70% of the former α-alumina of the present invention. It is assumed that these differences are due to the uniformity of the particle size of the particles of the present application and the effect obtained from the particle characteristics exerted by the thread-like particle structure.

[0064]

EFFECTS OF THE INVENTION According to the present invention, in the neutralization process of an alkaline aluminate solution with an acid, coexistence of an acrylamide polymer, which is a kind of water-soluble polymer, allows spherical or near-spherical shaped particles to be formed. Non-agglomerated fixed-form granular alumina having a sharp particle size distribution can be produced at high yield with high productivity at low cost. Moreover, according to the present invention, the particles as a whole have a clear spherical shape, have a peculiar thread-like shape, and have a sharp particle size distribution, and non-aggregating granular alumina, particularly hydrated alumina, activated alumina, α- There is an advantage that alumina can be obtained.

[Brief description of drawings]

FIG. 1 is a scanning electron micrograph showing a particle structure of hydrated alumina according to the present invention (magnification: 10000 times, the same applies hereinafter).
Is.

FIG. 2 is a scanning electron micrograph showing the particle structure of activated alumina according to the present invention.

FIG. 3 is a scanning electron micrograph showing a particle structure of θ-type alumina according to the present invention.

FIG. 4 is a scanning electron micrograph showing a particle structure of α-alumina according to the present invention.

FIG. 5: Hydrated alumina according to the invention (bayerite)
2 is an X-ray diffraction diagram of FIG.

FIG. 6 is an X-ray diffraction diagram when calcination temperature of hydrated alumina is changed.

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshihiko Shibuya 4-1-21-2 Nihombashi Muromachi, Chuo-ku, Tokyo Mizusawa Chemical Industry Co., Ltd. (56) Reference JP-A-4-42809 (JP, A) JP JP-A-63-215509 (JP, A) JP-A-49-101299 (JP, A) JP-A-56-37207 (JP, A) JP-A-3-290312 (JP, A) JP-A-61-256921 (JP , A) (58) Fields surveyed (Int.Cl. ⁷ , DB name) C01F 7/14 C01F 7/02

Claims (8)

(57) [Claims] 1. An alkaline aluminate aqueous solution having a molecular weight of 1
Million to 3 million water-soluble acrylamide polymers , and
The aqueous solution of phosphoric acid in the mixed solution after addition has the general formula M ₂ O · mA.
l ₂ O ₃ (M represents a potassium or sodium atom)
Concentration as Al ₂ O ₃ in the alkali aluminate represented
The water-soluble acrylamide type having a degree of 5.5 to 8% by weight
The polymer is 5 to 100% by weight with respect to the Al ₂ O ₃ , and
And the acid aqueous solution are added so that they are partially neutralized and mixed.
The resulting mixed solution is allowed to stand at a temperature of 2 to 50 ° C. to form granules consisting of a partially neutralized product of alkali aluminate, the granules are separated, then neutralized with an acid, and then if necessary. A method for producing granular alumina, which comprises washing with water, drying and firing. _2. A sodium aluminate having a composition in which m in an alkali aluminate represented by the general formula M ₂ O.mAl ₂ O ₃ is 0.1 to 0.9. A method for producing the described granular alumina. 3. The acrylamide polymer has 0.2 to 500 mmol / 1 of carboxyl groups in free or salt form.
The manufacturing method according to claim 1, which has a concentration of 00 g. 4. The amount of the aqueous acid solution added is 13 at the pH of the mixed solution.
The manufacturing method according to claim 1, wherein the amount added is from 14 to 14. Entire wherein the particles have a thread Komari like particle structure with a clear sphere has a bayerite crystal structure, and the ratio of the particles of the major axis (D _L) and the minor axis (D _S) ( 80% or more of particles having a sphericity of 0.90 to 1.00 represented by D _S / D _L have the formula D ₂₅ / D ₇₅ (wherein D ₂₅ is a volume-based cumulative particle size by the Coulter counter method). represents a particle size of 25% of the distribution curve, D ₇₅ is the sharpness of the particle size distribution defined by representative.) the particle size of the 75% value is characterized in that 1.2 to 2.0 Non-cohesive hydrated alumina spherical particles. 6. The particles as a whole have a definite spherical shape and a thread-like particle structure, an η-alumina type crystal structure and a BET specific surface area in the range of 150 to 350 m ² / g. 80% or more of the particles having a sphericity of 0.90 to 1.00 represented by the ratio (D _S / D _L ) of the long diameter (D _L ) and the short diameter (D _S ) of the particles have the formula D ₂₅ / D ₇₅ (wherein, D ₂₅ represents a particle size of 25% of the cumulative particle size distribution curve of the volume-based by Coulter counter method, D ₇₅ represents. a particle size that 75% value) of the particle size distribution defined by A non-agglomerating activated alumina spherical particle having a sharpness of 1.2 to 2.0. 7. The activated alumina spherical particles according to claim 6 , wherein the pore volume is 0.3 ml / g or more. Overall 8. particles have a thread Komari like particle structure with a clear sphere has a θ- alumina or α- alumina type crystal structure, and said particles diameter (D _L) and the minor axis (D _s ) ratio (D _S / D _L ) having a sphericity of 0.90 to 1.00 is 80% or more, and the formula D ₂₅ / D ₇₅ (wherein , D ₂₅ is > The particle size of 25% value of the volume-based cumulative particle size distribution curve by the Luther counter method is represented, and D ₇₅ is the particle size of the 75% value thereof .) Non-aggregating alumina spherical particles, characterized in that it is 2.0.