JPS643827B2 - - Google Patents

Description

[Detailed description of the invention]

TECHNICAL FIELD The present invention relates to a method for producing sintered alumina grains. Conventional technology Conventionally, sintered alumina granules used as aggregates for refractories and catalyst carriers were produced by adding water to a high-alumina powder raw material, granulating it, and then heating it to a high temperature to sinter it. It had been manufactured for some time. However, high alumina raw material powder generally has poor sinterability, and if it is granulated with water and then heated and sintered, sintered granules with sufficient strength cannot be obtained. High alumina raw material powder is mixed with a small amount of viscosity inorganic binder as a binder, granulated, and then sintered. However, blending a binder such as clay into the alumina raw material in this way not only reduces the purity of the obtained sintered grains, but also reduces the heat resistance, so it is not desirable. It was very difficult. In order to eliminate the above-mentioned drawbacks caused by blending binders such as clay with alumina raw materials, attempts have been made to produce strong alumina sintered granules without using binders. Publication No. 50930 describes the Bayer method alumina.
Calcined alumina obtained by firing to a temperature of 1250℃ or higher is ground so that particles with a particle size of 1μ or less account for 40% by weight or more, and this ground alumina is appropriately granulated with a small amount of water. A method is disclosed in which sintered alumina granules are produced by heating the granules to a temperature of 1700° C. or higher and sintering them. However, the method described in this patent publication requires (a) sintering the alumina at a temperature of 1250°C or higher prior to sintering, and (b) high strength sintered alumina particles unless the sintering temperature is 1700°C or higher. (c) Since no binder is used during granulation and only water is used, the granules have low strength before sintering and cannot be broken by impact etc., resulting in spherical sintered alumina particles. There are disadvantages such as not having OBJECTS OF THE INVENTION It is an object of the present invention to provide a method for producing sintered alumina grains that improves the drawbacks of the prior art described above and has advantages in terms of production operations and product quality. Summary of the Invention The method for producing sintered alumina particles of the present invention includes adding an organic binder made of a water-soluble polymer and an inorganic binder made of a water-soluble aluminum salt to alumina and/or aluminum hydroxide powder in the presence of water. , a step of mixing to obtain granules, and a step of heating and sintering the granules obtained in the previous step at a temperature of 1400 to 1900°C to obtain sintered alumina granules. Preferred Embodiments for Carrying Out the Invention Alumina is used as a raw material in the method for producing sintered alumina particles of the present invention.
As this alumina, for example, aluminum hydroxide obtained by the Bayer method is preferably calcined so that the α crystal size is 0.3 to 0.5 μm, and this alumina is ground into single particles (α crystals). Note that since aluminum hydroxide is converted to alumina under the alumina sintering conditions employed in the method of the present invention, aluminum hydroxide can be used together with or in place of the alumina, but for convenience, the following The explanation will be made regarding an embodiment using alumina powder as a raw material. The method of the present invention will be explained in detail below. (Pelletization step) According to the method of the present invention, first, an organic binder made of a water-soluble polymer and an inorganic binder made of a water-soluble aluminum salt are added to alumina powder in the presence of water, and then mixed to form an alumina powder. Obtain granules. A specific method for obtaining alumina granules by adding the organic binder and inorganic binder to alumina powder in the presence of water and then mixing them is as follows:
These include: (b) A binder aqueous solution obtained by dissolving both an organic binder and an inorganic binder in water is added to alumina powder and mixed in advance with a kneader and granulated, or the alumina powder is granulated while being sprayed with the binder aqueous solution. do. (b) After adding one of the organic binder and the inorganic binder to the alumina powder as a powder, then add the aqueous solution of the other binder and granulate it (for example, add the inorganic binder powder to the alumina powder, then add the organic binder aqueous solution It is preferable to add and granulate). (c) Water is added to the alumina powder and mixed, and an organic binder and an inorganic binder are added to this in the form of both powders, or one of them is added as a powder, and the other is added as an aqueous solution, and the mixture is granulated. (d) Add an organic binder and an inorganic binder to alumina powder in the form of powders, and granulate while spraying water. (e) A core material made of alumina, such as small grains of sintered alumina, is used, an aqueous binder solution is sprayed onto it, and alumina powder is adhered to the core material, which is then granulated. The presence of water is essential in the mixing process of the alumina powder and both binders and the alumina granulation process of the present invention, but if the presence of water is ensured, the above (a)
It goes without saying that methods other than the methods of ~(e) may be used. As the granulator, a stirring and mixing type granulator, a pan-type granulator, etc. are used. Alternatively, a spherical sizing machine may be used after extrusion granulation. In order to obtain alumina granules with a particle size of 0.1 to 3 m/mφ, it is preferable to use a stirring-mixing type granulator, and alumina granules that are compacted and have sphericity can be obtained. Further, in order to obtain alumina granules having a particle size of 3 m/mφ or more, a centrifugal fluid coating device (CF coater), a combination of an extrusion granulator and a spherical granulator, etc. can be used. In order to facilitate the granulation operation and further improve the sphericity and strength, 1~
10wt% crystalline cellulose can also be added. In addition, the reason why both an organic binder and an inorganic binder are used together in the present invention is that the organic binder increases the mechanical strength of the granulated material after granulation of the alumina powder and before heat treatment, and the granulated material becomes impact-resistant before the heat treatment. The inorganic binder works to prevent the alumina granules from being chipped or broken due to heating and before the alumina is sintered (usually 300 to 1000°C). This is because they function to prevent the granules from collapsing, and if one of these is absent, the following drawbacks will occur. (i) If only an organic binder is used, the mechanical strength of the alumina granules before the heat treatment is maintained as described above, but the organic binder does not maintain the mechanical strength of the alumina granules after heating the alumina granules at the temperature before the alumina sintering. Since it burns, it is not possible to prevent the alumina granules from collapsing before sintering of the alumina occurs. (ii) Since inorganic binders have inferior adhesive properties compared to organic binders, using only inorganic binders will reduce the mechanical strength of alumina granules before heat treatment.
Since it cannot be increased as much as when only an organic binder is used, the granules are likely to be damaged or destroyed before heating. In other words, the combined use of an organic binder and an inorganic binder in the present invention skillfully overcomes the drawbacks of using each alone. Examples of organic binders made of water-soluble polymers used in the present invention include polyvinyl alcohol (PVA), carboxymethyl cellulose (CMC),
Examples include dextrin, gum arabic, alginate (especially sodium salt), lignin sulfonate (especially sodium salt), glue, and gelatin. Two or more of these organic binders may be used in combination. As the inorganic binder made of water-soluble aluminum salt, it is preferable to use aluminum oxychloride, aluminum phosphate, aluminum formacetate, alumina sol, aluminum sulfate, polyaluminum chloride, aluminum hydroxychloride, and the like. According to the present invention, using an inorganic binder consisting of a water-soluble aluminum salt,
Since these inorganic binders are decomposed and converted into alumina under the alumina sintering conditions in the method of the present invention, impurities are prevented from being mixed into the obtained sintered alumina particles, resulting in high purity (for example, 99% or more alumina). This method has the advantage of producing sintered alumina grains. Two or more of these inorganic binders may be used in combination. (Sintering process) The alumina granules obtained above were then heated to 1400~
Alumina sintered grains are obtained by heating and sintering at a temperature of 1900℃. As the sintering furnace, any of Matsufuru furnace, shuttle kiln, tunnel kiln, rotary kiln, etc. can be used, but in order to increase productivity and achieve uniform firing, it is preferable to use a rotary kiln. Furthermore, by using a rotary kiln, the granules roll and rub against each other inside the kiln, resulting in the effect of so-called tomozuri (co-rubbing), and alumina sintered granules with high sphericity can be obtained. 0.05 to alumina to promote sintering
1.0 wt% MgO, NiO, MnO, MnO ₂ , CuO,
Fe ₂ O ₃ , ZrO ₂ , TiO _{2 ,} etc. may be added as a sintering aid. By granulating and sintering in this manner, dense and strong sintered granules can be obtained without losing the shape at the time of granulation. The present invention will be further explained below with reference to Examples, but the present invention is not limited to these Examples. Example 1 Alumina consisting of α crystals 0.3 to 0.5μ has an internal volume of 34
Small vibration mill (alumina balls 20m/mφ)
60Kg packed) and continuous pulverization at 7.5Kg/Hr. The particle size distribution of the alumina obtained was as follows.

[Table] Using a stirring mixer type granulator, for alumina
After adding and mixing 3.0% by weight polyaluminum chloride and 0.5% by weight magnesium oxide into the ground alumina,
A 1% aqueous solution of polyvinyl alcohol containing 25% by weight of alumina was added by spraying and granulated to obtain spherical alumina granules with an average diameter of 1 m/mφ. Next, the obtained granules were put in a rotary kiln.
Sintered alumina particles were obtained by heating and sintering at 1600°C. The disintegration of the sintered particles obtained by heating to 1600° C. in a rotary kiln was around 5%, and particles with uniform particle size and high sphericity were obtained. The obtained sintered grains had an apparent porosity of 2.5%, a bulk specific gravity of 3.65, and a crushing strength of 175 kg. Example 2 As in Example 1, alumina was continuously ground in a small vibrating mill and placed in a kneading machine with an internal volume of 10, and then 1% by weight of polyaluminum chloride and 0.5% by weight of oxidation were added to the alumina. Magnesium and
5% by weight of crystalline cellulose and 25% by weight of a 1% aqueous solution of polyvinyl alcohol were added and kneaded. Thereafter, it was granulated into a rod shape using an extrusion granulator, and then granulated into a spherical shape of about 5 m/mφ using a spherical granulator to obtain alumina granules. Next, this granulated material was heated in a rotary kiln for 1600 m
Alumina sintered grains were obtained by heating and sintering at ℃. The obtained sintered grains had an apparent porosity of 2.0%, a bulk specific gravity of 3.65, a crushing strength of 185 kg, and were highly spherical. Example 3 After alumina was continuously pulverized in a small vibrating mill in the same manner as in Example 1, 5.0% by weight of aluminum oxychloride was added to the alumina, and after mixing, a 23% by weight aqueous solution of 5% by weight of gum arabic was added by spraying. The granules are made into spherical particles with an average diameter of 2.0 using a stirring type granulator.
Alumina granules of m/mφ were obtained. Next, the obtained granules were put in a rotary kiln.
It was heated and sintered at 1600°C to obtain sintered alumina grains. The obtained sintered grains had an apparent porosity of 2.0%, a bulk specific gravity of 3.60, and a crushing strength of 180 kg. Comparative Example For comparison, only an organic binder was added without adding an inorganic binder consisting of a water-soluble aluminum salt to alumina powder that was continuously pulverized using a small vibrating mill in the same manner as in Example 1, and the same process as in Example 1 was carried out. After granulation using a stirring and mixing type granulator, the obtained alumina granules were heated and sintered at 1600°C in a rotary kiln to obtain sintered alumina granules. 60 to 70% of the obtained sintered granules were collapsed and did not retain their original shape at the time of granulation and were irregular, with an apparent porosity of 9.8%, bulk specific gravity of 3.45, and crushing strength of 130 kg. Example 4 After continuously grinding alumina in the same manner as in Example 1, 5% by weight of aluminum form acetate and 3% by weight of dextrin were added to the alumina and mixed.
While adding 23% by weight of water to the alumina by spraying, the mixture was granulated using a stirring type granulator to obtain alumina granules having a spherical shape and an average diameter of 2.0 m/mφ. The obtained granules were heated and sintered at 1600°C in a rotary kiln to obtain sintered alumina granules. The obtained sintered grains had an apparent porosity of 1.7%, a bulk specific gravity of 3.67, and a crushing strength of 185 kg. Effects of the Invention According to the present invention, since an organic binder and an inorganic binder are used together, the alumina granules will not be damaged or destroyed before the heat treatment, and after heating the aluminum granules, the alumina will not be sintered. Alumina granules do not collapse at temperatures before solidification (300 to 1300°C). Therefore, uniform sintered alumina particles having various properties such as high heat insulation properties and high strength can be obtained with a high recovery rate (yield). Furthermore, since the binder consisting of a water-soluble aluminum salt used as an inorganic binder is added to alumina under the heating conditions of the present invention, it has the advantage that the resulting sintered alumina particles are of high purity. Furthermore, as mentioned above, the alumina granules are
It has sufficient strength at temperatures up to 1300°C, so it can withstand rotational motion in a rotary kiln, and it also has sphericity and uniform particle size due to the shearing (co-rubbing) caused by rolling inside the kiln. Alumina sintered grains are obtained. A further advantage is that the sintering temperature can be lower than in conventional methods.

Claims (1)

[Claims] 1. An organic binder made of a water-soluble polymer and an inorganic binder made of a water-soluble aluminum salt are added to alumina and/or aluminum hydroxide powder in the presence of water, and then mixed to form a granulated product. and the granules obtained in the previous step at 1400 to 1900℃.
A method for producing sintered alumina particles, the method comprising: heating and sintering the alumina sintered particles at a temperature of . 2. The method according to claim 1, further comprising adding crystalline cellulose to the alumina and/or aluminum hydroxide powder. 3 MgO, NiO, MnO, MnO ₂ , CuO, Fe ₂ O ₃ ,
2. The method according to claim 1, wherein 0.05 to 1.0% by weight of a sintering aid selected from the group consisting of ZrO ₂ and TiO ₂ is added to the alumina and/or aluminum hydroxide powder. 4 The organic binder is polyvinyl alcohol (PVA), carboxymethyl cellulose (CMC),
2. The method of claim 1, wherein the method is selected from the group consisting of dextrin, gum arabic, alginate, lignosulfonate, glue, and gelatin. 5 The inorganic binder is aluminum oxychloride,
The method of claim 1, wherein the method is selected from the group consisting of aluminum phosphate, aluminum formacetate, alumina sol, aluminum sulfate, polyaluminum chloride, and aluminum hydroxychloride. 6. The method according to claim 1, wherein the sintering is performed in a rotary kiln.