JPH0986924A - Spherical agglomerated particle and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an inorganic filler for resin, consisting of a spherical agglomerated particle composed of fine particles of aluminum hydroxide, having an average secondary particle diameter falling within a prescribed range, the average minor diameter and the average major diameter/minor diameter ratio of primary particle restricted within respective specific ranges and excellent dimensional stability and to obtain a carrier for a fluidized layer catalyst having excellent flowability and high strength. SOLUTION: The spherical agglomerated particle has an average secondary particle diameter (A) of 0.5-200μm, a minor diameter of an average primary particle of 1/20 of the diameter A and a major diameter/minor diameter ratio of <=10. The particle can be produced by adding water to a solution of sodium aluminate having an Na2 O concentration of >=100g/L and an Na2 /Al2 O3 molar ratio of <=1.3 under stirring to lower the Na2 O concentration to <=70g/L, depositing aluminum hydroxide at <=40 deg.C and subjecting the precipitate to filtration, washing and drying. The produced spherical agglomerated particle is baked at 400-1200 deg.C for several sec to 24hr to obtain a transition alumina keeping the form of the spherical agglomerated particle.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to spherical particles composed of agglomerated fine particles, and more specifically, aluminum hydroxide used for flame retardants, various fillers, catalyst carriers, pigments, adsorbents, etc. TECHNICAL FIELD The present invention relates to spherical agglomerated particles made of transition alumina and α-alumina and a method for producing the same.

[0002]

2. Description of the Related Art Aluminum hydroxide has hitherto been widely used as a flame retardant, a filler and the like by taking advantage of physical properties and crystallographic properties. The aluminum hydroxide used for these purposes is usually obtained by the Bayer method in which finely grained aluminum hydroxide as seeds is added to a supersaturated sodium aluminate solution for crystallization. The shape of the aluminum hydroxide particles obtained by the Bayer method is from hexagonal columns having gibbsite crystal habit to plate-like particles or aggregates of the particles. Generally, when a resin is filled with particles having such an anisotropic shape as a feeler, the mechanical strength of the molded body is improved, but warping or deformation occurs, which makes the material unsuitable for precision parts. In order to suppress such warpage and deformation of the molded body, it is desirable to fill the spherical particles. As a method for obtaining spherical aluminum hydroxide, JP-A-63-21550
No. 9 publication is disclosed. The publication discloses that while precipitating aluminum hydroxide from an alkali metal aluminate, the pH of the alkali metal aluminate is changed, and monohydric and polyhydric alcohols are added to the alkali metal aluminate solution to obtain spherical water. This is to obtain aluminum oxide particles. However, the particles obtained by the method disclosed in this publication are hexagonal columnar particles that are radially aggregated and have an apparently spherical appearance, but are not substantially spherical. Therefore, the particles have poor packing properties, and the strength of the particles is low, so that physical properties that are satisfactory as a resin filler cannot be expected.

On the other hand, spherical particles having a particle size of about 100 μ are suitable for the activated alumina used as a fluidized bed catalyst carrier for crude oil cracking. Currently, spherical particles used for catalyst carrier applications are manufactured through a process in which fine aluminum hydroxide obtained by pulverization or the like is granulated using a spray dryer or the like and then fired. However, granulation with a spray dryer is a costly process, raising the cost of producing the resulting activated alumina. Japanese Patent Application Laid-Open No. 63-215509 also discloses a spherical activated alumina and a method for producing the same, but since the shape of the particles is a structure in which hexagonal columnar particles are radially aggregated,
When the particles are used together with the catalyst carrier, they have a drawback that they are crushed by mutual collision and chipping is likely to occur and the life of the catalyst carrier is shortened.

[0004]

The first object of the present invention is to provide an inexpensive inorganic filler for resin filling which gives excellent dimensional stability, and a second object thereof is excellent fluidity. Another object of the present invention is to provide a coarse spherical activated alumina of about 30 μm to about 200 μm, which has a high strength and is suitable for a carrier for a fluidized bed catalyst, at a low cost. In view of such circumstances,
As a result of intensive studies to develop substantially spherical particles that are easy to operate and low cost, the present inventors have allowed a specific sodium aluminate solution to be precipitated under specific conditions according to the Bayer method, and further if necessary. It was found that aluminum hydroxide and alumina satisfying the above-mentioned object can be obtained when calcination is carried out, and the present invention has been completed.

[0005]

That is, according to the present invention, the average secondary particle diameter is 0.5 to 200 μm, and the short diameter of the average primary particles constituting the secondary particles is 20 minutes of the average secondary particle diameter. Of 1 or less and a ratio of major axis / minor axis of 10 or less, the spherical agglomerate particles are characterized by being composed of a fine particle agglomerate of aluminum hydroxide, and a transition having the above-mentioned skeleton obtained by firing these agglomerate particles Provide spherical agglomerated particles of alumina or α-alumina. Furthermore, the Na ₂ O concentration is 100
While stirring a sodium aluminate solution having a molar ratio of g / l or more and Na ₂ O / Al ₂ O ₃ of 1.3 or less, the Na ₂ O concentration was 7 or less.
Water is added so as to be 0 g / l or less, aluminum hydroxide is precipitated at a liquid temperature of 40 ° C. or less, and then the precipitate is filtered, washed, and dried to have an average secondary particle diameter of 0. Spherical aggregated particles having a diameter of 5 to 200 μm, a minor axis of the average primary particles constituting the secondary particles being 1/20 or less of the average secondary particle diameter and a major axis / minor axis ratio of 10 or less, and The present invention provides a method for producing transition alumina or α-alumina spherical agglomerated particles having the above skeleton obtained by firing these agglomerated particles.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below.
The average secondary particle diameter of the spherical aggregated particles in the present invention is about 0.
5 μm to about 200 μm, and further according to the application, as a resin filling filler, about 0.5 to 50 mμ, preferably about 1 to 30 μm, and a catalyst carrier, about 30 μm to about 20.
It is 0 μm, preferably about 40 μm to about 150 μm.
When applied as a filler for resin filling, if the average secondary particle size is less than about 0.5 μm, the kneading viscosity at the time of resin filling becomes too high and the kneading is difficult, and if it exceeds 50 μm, the strength of the molded product decreases. To do. When applied as a catalyst carrier, if it is less than 30 μm, the loss due to scattering becomes large when used as a fluidized bed catalyst.

Further, in the spherical agglomerated particles of the present invention, the short diameter of the primary particles is 1/20 or less of that of the secondary particles, preferably 1/2.
Spherical aluminum hydroxide composed of agglomerates of 5 to 1/500 and a ratio of major axis / minor axis of 10 or less, preferably 2 to 8, or transition alumina (activated alumina) or α-alumina obtained by firing the spherical aluminum hydroxide. Is mandatory. In the present invention, when the particle size of the primary particles forming the agglomerates is larger than 1/20 of the particle size of the secondary particles, the surface irregularities of the secondary particles become large and the fluidity, mechanical strength, etc. decrease. Good packing properties and catalyst properties cannot be obtained. Since the same phenomenon occurs in the shape of the primary particles, the ratio of major axis / minor axis needs to be 10 or less.

The crystal form of the spherical aggregated aluminum hydroxide particles of the present invention is gibbsite, bayerite or a mixed crystal thereof. When the particles are composed of amorphous crystals, the decomposition temperature during heating becomes low, which may cause thermal decomposition and dehydration reaction during resin molding, resulting in poor appearance of the product and insufficient strength. Further, when it is used for a catalyst, it is used as transition alumina or activated alumina by firing aluminum hydroxide having the form.

The method for producing the spherical agglomerated particles having the above-mentioned physical properties of the present invention is not particularly limited, but the spherical agglomerated particles can be obtained, for example, by a simple method as shown below. Water is added quickly while stirring the highly supersaturated aqueous sodium aluminate solution. The liquid temperature after adding water is 40 ° C or lower, preferably 0 ° C to
The temperature is 35 ° C., more preferably 5 ° C. to 30 ° C., and in that state, the spherical aluminum hydroxide of the present invention can be obtained by allowing the precipitated aluminum hydroxide to be filtered, washed and dried. It is desirable that the sodium aluminate solution used in the manufacturing method has a molar ratio of 1.3 or less and the sodium concentration in terms of Na ₂ O is 100 g / l or more. The soda concentration in the sodium aluminate aqueous solution after diluted with water is 70 g / l or less in terms of Na ₂ O, and the liquid temperature is about 4
The temperature is 0 ° C or lower, preferably about 35 ° C or lower. Therefore, the sodium aluminate solution may be preliminarily cooled to about 40 ° C. or below 40 ° C., and then water may be added to cause precipitation, or a dilute sodium aluminate solution may be used in place of water. It is preferable to add water to the aqueous solution of sodium aluminate as quickly as possible, and it is not particularly limited, but when carrying out on an industrial scale, the sodium aluminate solution and water are put in a container. A method of simultaneously adding, supplying and precipitating with stirring is recommended. The precipitation time depends on the concentration of the sodium aluminate solution, the liquid temperature at the time of precipitation, etc., but is usually about 5 hours to about 10 days, usually about 10 hours under stirring.
After holding for about 5 days, the precipitated aluminum hydroxide may be held in the solution (aged) if necessary, and the precipitate may be filtered, washed and dried. For filtration, washing, and drying, known methods in ordinary Bayer method are applied.

By adopting such a method, the average secondary particle diameter is usually 0.5 to 200 μm, and the short diameter of the average primary particles constituting the secondary particles is 2 of the average secondary particle diameter.
Spherical agglomerated particles of aluminum hydroxide in which fine particles having a ratio of major axis / minor axis of 10 or less and 10 or less are aggregated are obtained.

Further, the spherical agglomerated particles of aluminum hydroxide obtained as described above are heated at 400 ° C. for several seconds to 24 hours.
By calcining at a temperature of 1200 ° C., a transition alumina having the above-mentioned skeleton can be obtained. Further, when α-alumina is obtained, it may be calcined at a temperature of about 1000 ° C. to about 1200 ° C. for about 1 hour to about 48 hours. In the above, the transitional alumina refers to so-called intermediate alumina which has a crystal form of ρ, χ, δ, η, κ, γ and the like, and which is obtained by firing aluminum hydroxide to form α alumina. Further, as the firing device, a known firing device may be applied by a Bayer method such as an electric furnace, a tunnel kiln, a fluidized firing furnace, or a hydrolysis method of aluminum alkoxide.

[0012]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto.
In the present example, the size of the agglomerated particles was obtained by taking a scanning micrograph of the obtained particles and randomly selecting 20 particles from the particles in the field of view and using the average value thereof.

Example 1 800 ml of a sodium aluminate aqueous solution (molar ratio: Na ₂ O / Al ₂ O ₃ = 1.2, Na ₂ O content = 300 g / 1) cooled to 10 ° C. was separated into 2 liters of separable. Charge into a flask and stir at a speed of 200 rpm for 10
After adding 1120 ml of deionized water at 0 ° C for 2 seconds and stirring at 10 ° C for 16 hours for aging, the precipitated aluminum hydroxide was filtered and separated, and washed with deionized water.
Aluminum hydroxide was obtained by drying at 0 ° C. for 2 hours. When the obtained aluminum hydroxide was observed by a scanning micrograph, the minor axis of the primary particles was 0.2 μ, the major axis / minor axis was 6.5, and the particle size of the secondary particles was 8.1 μ. The particles were spherical aggregates.

Example 2 200 ml of an aqueous sodium aluminate solution (molar ratio: Na ₂ O / Al ₂ O ₃ = 1.2, Na ₂ O content = 300 g / 1) cooled to 10 ° C. was separated into 2 liters of separable. Charge into a flask and stir at a speed of 200 rpm for 10
Add 1800 ml of deionized water at ℃ for 2 seconds,
After stirring for 5 days and aging, the precipitated aluminum hydroxide was filtered and separated, and washed with deionized water.
Aluminum hydroxide was obtained by drying at 0 ° C. for 2 hours. When the obtained aluminum hydroxide was observed by a scanning micrograph, the minor axis of the primary particles was 1.8 μm, the major axis / minor axis was 2, and the particle diameter of the secondary particles was 41.2 μ, which was substantially spherical. It was an aggregated particle.

[0015]

The spherical agglomerated aluminum hydroxide obtained in the present invention and the transition alumina and activated alumina particles obtained by firing the spherical aluminium hydroxide are formed by agglomeration of fine particles, and the irregularities on the surface of the secondary particles are the secondary particles. Since it is smaller than the diameter, there is little warpage or deformation of the molded product when used as a filler for resin filling, and when used as a catalyst carrier for crude oil cracking, fluidity, pulverization resistance, etc. It also has excellent mechanical strength, and is simple and conforms to the Buyer method.
Since it can be obtained by a simple manufacturing method and is inexpensive, its industrial utility value is enormous.

Claims (7)

[Claims] 1. The average secondary particle diameter is 0.5 to 200 μm, and the short diameter of the average primary particles constituting the secondary particles is 1/20 or less of the average secondary particle diameter and the long diameter / short diameter. Ratio of 1
A spherical agglomerated particle comprising a fine particle of aluminum hydroxide of 0 or less. 2. The spherical agglomerated particles according to claim 1, wherein the aluminum hydroxide particles are composed mainly of at least bayerite or particles having a gibbsite crystal form. 3. A spherical agglomerated particle made of transition alumina which retains the form of the spherical agglomerated particle obtained by heat-treating the spherical agglomerated particle of aluminum hydroxide according to claim 1. 4. A spherical agglomerated particle made of α-alumina, which retains the form of the spherical agglomerated particle obtained by heat-treating the spherical agglomerated particle of aluminum hydroxide according to claim 1. 5. A Na ₂ O concentration of 100 g / l or more, Na ₂
While stirring a sodium aluminate solution having an O / Al ₂ O ₃ molar ratio of 1.3 or less, water was added so that the Na ₂ O concentration was 70 g / l or less, and aluminum hydroxide was added at a liquid temperature of 40 ° C. or less. The method for producing spherical agglomerated particles according to claim 1, wherein the particles are precipitated, then the precipitate is filtered, washed, and dried. 6. The spherical agglomerated particles of transition alumina according to claim 3, wherein the spherical agglomerated particles obtained by the method of claim 5 are fired at a temperature of 400 ° C. to 1200 ° C. for several seconds to 24 hours. Production method. 7. The spherical agglomerated particles obtained by the method of claim 5,
The method for producing spherical agglomerated particles of α-alumina according to claim 4, wherein the firing is performed at a temperature of 1000 ° C to 1200 ° C for a time of 48 hours.