JP2018069116A - Α-alumina granulated product for catalyst carrier and method for producing the same - Google Patents

Abstract

The present invention provides an inexpensive α-alumina granulated product having the BET specific surface area, crushing strength, powdering rate, pore volume, and bulk specific gravity required as a catalyst carrier, and a method for producing the same. [Solution] A first method for obtaining α-alumina mixed particles by mixing 50-70 wt% of α-alumina particles with an average particle size of 90-120 μm and 30-50 wt% of α-alumina fine particles with an average particle size of 0.4-0.7 μm. Step S01, a second step of kneading α-alumina mixed particles, 18 to 25 wt% of water, 2 to 5 wt% of binder, and more than 0 wt% to 7 wt% of a pore-forming agent, and obtaining a molded body by extrusion molding. A method for producing an α-alumina granulated product for a catalyst carrier, comprising: S02, a third step S03 of sizing a compact to obtain a granulated powder, and a fourth step S04 of firing the granulated powder. It is approximately spherical, has a BET specific surface area of 4.0 to 6.0 m2/g, a crushing strength of 9 kg or more, a pulverization rate of less than 1%, a pore volume of 0.25 to 0.45 cc/g, and a bulk specific gravity of 1. A granulated alpha alumina product for catalyst carriers having a particle size of .6 to 1.7. [Selection diagram] Figure 1

Description

  The present invention relates to an α-alumina granulated product used as a catalyst support and an efficient production method thereof.

  Alumina, which is a representative ceramic, includes transition alumina such as γ alumina and θ alumina, α alumina, and the like, and is widely used industrially according to various characteristics such as physical properties, shape, and manufacturing cost.

  A typical use of alumina may include a catalyst carrier, but generally, an appropriate BET specific surface area, crushing strength, pulverization rate, pore volume, bulk specific gravity and the like are required for the catalyst carrier. Here, for example, the BET specific surface area and the crushing strength are in a trade-off relationship with each other, and it is not easy to satisfy both requirements.

  On the other hand, for a catalyst carrier that requires a large BET specific surface area and high crushing strength, a granulated product mainly using transition alumina such as γ alumina or θ alumina is used.

  For example, in Patent Document 1 (Japanese Patent Application Laid-Open No. 2005-225696), water is added to a rehydratable alumina powder to form a rehydrated alumina molded body, and alcohol is present at a temperature of 130 ° C. or higher. There has been proposed a method for producing a transition alumina molded body characterized in that it is rehydrated by contact with water to form a rehydrated alumina molded body and then fired.

  The transition alumina molded body obtained by the production method disclosed in Patent Document 1 has a high specific surface area and high strength even when held at a high temperature, so that it can be suitably used for a catalyst carrier. .

  In Patent Document 2 (Japanese Patent Laid-Open No. 11-139865), a transition alumina powder having at least a part of rehydration is molded, rehydrated, and the molded body after rehydration is fired. In the method for producing a transition alumina molded body, after rehydration is performed in water vapor or a gas containing steam at 110 to 200 ° C., the molded body is brought into contact with water at 100 ° C. or less under normal pressure, and then separated from water. After that, a method for producing a transition alumina molded body characterized by firing the molded body after separation from water has been proposed.

  The transition alumina molded body obtained by the production method disclosed in Patent Document 2 has a low soda content and high strength, and includes a desiccant, an adsorbent, a catalyst, a catalyst carrier, and various chemical carriers. It can be used suitably for use.

JP 2005-225696 A JP-A-11-139865

  However, the production process of transition alumina is complicated, and the resulting catalyst carrier becomes expensive. In contrast, by firing aluminum hydroxide derived from the Bayer method, α-alumina can be produced at a relatively low cost. However, when the α-alumina is used, a catalyst carrier such as an appropriate BET specific surface area and crushing strength can be obtained. It is difficult to satisfy the above characteristics required as

  In view of the problems in the prior art as described above, the object of the present invention is to appropriately produce an α-alumina granulated product to obtain a BET specific surface area, a crushing strength, a pulverization rate, a pore volume required as a catalyst carrier. And an inexpensive α-alumina granulated product having all bulk specific gravity and an efficient production method thereof.

Here, in order to use the α-alumina granulated product as a catalyst carrier, BET (specific surface area): 4.0 to 6.0 m ² / g, crushing strength:> 9 kg, pulverization rate: <1%, pores The volume is preferably 0.25 to 0.45 cc / g, and the bulk specific gravity is preferably 1.6 to 1.7.

  In order to achieve the above object, the present inventors have conducted extensive research on α-alumina granulated products and production methods thereof. As a result, α-alumina particles having an appropriate particle size are mixed and granulated by extrusion. Etc. were found to be extremely effective and reached the present invention.

That is, the present invention
Α-alumina particles having an average particle size of 90 to 120 μm and α-alumina particles having an average particle size of 0.4 to 0.7 μm are mixed, and the contents of the α-alumina particles and the α-alumina particles are 50 to 50 respectively. A first step of obtaining α-alumina mixed particles of 70 wt% and 30-50 wt%;
The second step of kneading the α-alumina mixed particles, 18 to 25 wt% water, 2 to 5 wt% binder, and more than 0 wt% to 7 wt% or less pore former and obtaining a molded body by extrusion molding. When,
A third step of sizing the molded body to obtain a granulated powder; and
Having a fourth step of firing the granulated powder,
A method for producing an α-alumina granulated product for a catalyst carrier is provided.

  In the method for producing an α-alumina granulated product for a catalyst carrier of the present invention, an α-alumina particle having an average particle size of 90 to 120 μm and an α-alumina fine particle having an average particle size of 0.4 to 0.7 μm are mixed, By adjusting the α-alumina mixed particles in which the content of α-alumina particles and α-alumina fine particles is 50 to 70 wt% and 30 to 50 wt%, respectively, compared with the case where α alumina particles or α alumina fine particles are used alone. An α-alumina granulated product having both a large BET specific surface area and a high crushing strength can be obtained.

  Further, the mixing density of the α alumina particles and the α alumina fine particles increases the particle packing density. In addition, an external pressure can be applied by using extrusion molding instead of rolling granulation in the granulation process, and α-alumina particles and α-alumina fine particles are more highly filled, resulting in a large BET specific surface area and high crushing. An α-alumina granulated product having both strengths can be obtained.

  Further, by adding a pore forming agent of more than 0 wt% and not more than 7 wt% to the granulated powder before firing, voids can be formed in a region other than the bonded (sintered) portion between the α alumina particles. As a result, the BET specific surface area, bulk specific gravity, and the like can be adjusted without greatly reducing the crushing strength of the α-alumina granulated product.

In the method for producing an α-alumina granulated product for a catalyst carrier of the present invention, it is preferable that the firing temperature in the fourth step is 1200 to 1400 ° C. By setting the sintering temperature to 1200 ° C. or higher, the crushing strength of the α-alumina granulated product can be ensured (for example,> 9 kg), and by setting the sintering temperature to 1400 ° C. or lower, the decrease in the BET specific surface area is suppressed. (For example, 4.0 to 6.0 m ² / g).

  In the method for producing an α-alumina granulated product for a catalyst carrier of the present invention, it is preferable that the granulated powder is allowed to stand and dry as a pretreatment in the fourth step. By allowing the granulated powder to stand and dry, the rearrangement of α-alumina particles and α-alumina fine particles proceeds and the binder becomes familiar with the whole, so the granulated powder becomes dense and the crushing strength of the resulting α-alumina granulated product Can be improved.

  Furthermore, in the method for producing an α-alumina granulated product for a catalyst carrier of the present invention, it is preferable to use wheat flour or rice flour as the pore former. In addition to being easily available and inexpensive, they can be almost completely burned down by the firing process in the fourth step, and appropriate voids can be introduced into the α-alumina granulated product.

The present invention also provides:
a sintered body of α-alumina particles,
The sintered body has a substantially spherical shape,
The BET specific surface area is 4.0-6.0 m ² / g,
Crushing strength is greater than 9kg,
The powdering rate is less than 1%,
The pore volume is 0.25 to 0.45 cc / g,
The bulk specific gravity is 1.6 to 1.7,
An α-alumina granulated product for a catalyst support characterized by the above is also provided.

  The crushing strength of the α-alumina granulated product for a catalyst carrier of the present invention is greater than 9 kg, and it is possible to suppress the occurrence of cracks and a decrease in efficiency as a catalyst carrier when used in a reaction tower. Moreover, the powdering rate is less than 1%, and it can be suppressed that the surface of the catalyst carrier is peeled off to generate fine powder and the efficiency as the catalyst carrier is lowered.

Moreover, the BET specific surface area and the pore volume of the α-alumina granulated product for a catalyst carrier of the present invention are 4.0 to 6.0 m ² / g and 0.25 to 0.45 cc / g, respectively, and a sufficient reaction field Can be provided. The bulk specific gravity has a correlation with the pore volume, and is an index for adjusting the pore volume to the above range.

  The α-alumina granulated product for a catalyst carrier of the present invention has the above-mentioned characteristics and can be suitably used as a catalyst carrier. In particular, a process for producing dimethyl oxalate from a mixed gas of carbon monoxide and methanol. Can be suitably used.

The α-alumina granulated product for a catalyst carrier of the present invention preferably has a void due to the pore forming agent, and the void is more preferably a substantially spherical shape having a diameter of 3 to 50 μm. The voids due to the pore forming agent are formed in regions other than the bonded (sintered) portion of the α alumina particles and do not cause a significant decrease in strength. Therefore, the crush strength (> 9 kg) of the α alumina granulated product and the BET A specific surface area (4.0-6.0 m ² / g) and bulk specific gravity (1.6-1.7) can be realized simultaneously.

According to the present invention, an inexpensive α-alumina granulated product having all the BET specific surface area, crushing strength, pulverization rate, pore volume and bulk specific gravity required as a catalyst carrier and an efficient production method thereof are provided. Can do. More specifically, the α-alumina granulated product has a BET specific surface area of 4.0 to 6.0 m ² / g, a crushing strength of> 9 kg, a powdering rate of <1%, and a pore volume of 0.25 to 0.25. 0.45 cc / g and bulk specific gravity: 1.6 to 1.7.

It is process drawing regarding the manufacturing method of the alpha alumina granulated product of this invention. 2 is a scanning electron micrograph of a cross section of an α-alumina granulated product obtained in Comparative Example 1. 2 is a scanning electron micrograph of a cross section of an α-alumina granulated product obtained in Comparative Example 2. 2 is a scanning electron micrograph of a cross section of an α-alumina granulated product obtained in Example 2.

  Hereinafter, typical embodiments of the α-alumina granulated product for catalyst and the method for producing the same according to the present invention will be described in detail with reference to the drawings, but the present invention is not limited thereto.

1. Process for Producing α-Alumina Granulated Product for Catalyst Support FIG. 1 shows a process chart relating to the method for producing an α-alumina granulated product of the present invention. The production method of the α-alumina granulated product of the present invention includes a first step (S01) for obtaining α-alumina mixed particles, a second step (S02) for obtaining a molded product by extrusion molding, and granulating the molded product for granulation. It has the 3rd process (S03) which obtains granule powder, and the 4th process (S04) which bakes granulated powder. Hereinafter, each step will be described.

(1) Preparation of α-alumina mixed particles (first step: S01)
The first step (S01) is a step for adjusting α-alumina mixed particles by mixing α-alumina particles and α-alumina fine particles.

  By setting the average particle diameter of α-alumina particles to 90 to 120 μm and the average particle diameter of α-alumina particles to 0.4 to 0.7 μm, the voids formed between the α-alumina particles are filled with α-alumina particles, Α-alumina mixed particles having a high packing density can be obtained. In addition, since the α-alumina fine particles have sinterability superior to that of the α-alumina particles, the crushing strength of the α-alumina granulated product can be improved.

  In addition, the content of α-alumina particles is 50 to 70 wt%, and the content of α-alumina particles is 30 to 50 wt%, so that α-alumina particles can be sufficiently filled between α-alumina particles, Uniform dispersibility of each particle can be ensured.

  The mixing method of α alumina particles and α alumina particles is not particularly limited as long as the effects of the present invention are not impaired, and various conventionally known mixing methods can be used. In addition, since it knead | mixes with another raw material in a 2nd process (S02), the uniform dispersion | distribution of alpha alumina particle and alpha alumina fine particle may be achieved by the said kneading.

(2) Kneading and extrusion molding (second step: S02)
The second step (S02) is a step of kneading α-alumina mixed particles, water, a binder, and a pore former, and obtaining a molded body by extrusion molding.

  Here, paste suitable for extrusion molding by kneading α-alumina mixed particles, 18 to 25 wt% water, 2 to 5 wt% binder, and more than 0 wt% to 7 wt% or less pore former. Can be obtained. In addition, you may add a suitable plasticizer etc. as needed. The kneading method is not particularly limited as long as the effects of the present invention are not impaired, and various conventionally known kneading methods can be used, for example, kneading using a general kneader (kneading machine). can do.

  By making the addition amount of the binder 1 wt% or more, it is possible to impart an appropriate viscosity to the paste for extrusion molding, and the BET specific surface area of the α-alumina granulated product is sufficiently large due to voids formed by burnout of the binder can do. On the other hand, when the addition amount of the binder is 5 wt% or less, an appropriate viscosity can be imparted to the extrusion paste, and the crushing strength of the α-alumina granulated product can be sufficiently increased.

  In addition, the more preferable addition amount of a binder is 2-4 wt%. By setting the addition amount of the binder to 2 wt% or more, an appropriate strength can be imparted to the molded body after extrusion, and the formation of an ellipse at the time of sizing can be suppressed. On the other hand, by setting the addition amount of the binder to 4 wt% or less, an appropriate deformability can be imparted to the molded body after extrusion, and it can be made spherical at the time of sizing.

  The binder is not particularly limited as long as the effects of the present invention are not impaired, and various conventionally known binders can be used. For example, hydroxypropylmethylcellulose is preferably used. The binder is used to bond the α alumina particles and the α alumina fine particles. When the α alumina particles and the α alumina fine particles are appropriately bonded, molding in the extrusion process becomes possible. When the amount of the binder added increases, the moldability improves and the shape retention of the granulated powder improves, but when the amount added is too large, the elasticity of the granulated powder increases, and the particle size in the third step is spherical. Difficult to do. Further, since the binder is burned off during firing to form voids, when the amount added is too large, the strength of the granulated product is lowered.

  As the pore-forming agent, it is preferable to use wheat flour or rice flour. In addition to being easily available and inexpensive, they can be almost completely burned down by the firing process in the fourth step, and appropriate voids can be introduced into the α-alumina granulated product.

  The apparatus used for extrusion is not particularly limited as long as the effects of the present invention are not impaired, and various conventionally known extruders can be used. However, by applying pressure, the gap between α-alumina particles is reduced and dense molding is performed. What can obtain a body is preferable. By cutting the kneaded body extruded from the extruder into an appropriate size, a molded body used in the third step (S03) can be obtained.

(3) Sizing of granulated powder (third step: S03)
The third step (S03) is a step of producing granulated powder by sizing the shaped body obtained in the second step (S02).

  The granulator used for granulation is not particularly limited as long as the effects of the present invention are not impaired, and various conventionally known granulators can be used. Here, the shape of the granulated powder is preferably substantially spherical, and the particle size can be arbitrarily set according to the application. Note that the particle size does not change significantly before and after firing.

(4) Firing of granulated powder (fourth step: S04)
The fourth step (S04) is a step for firing the granulated powder obtained in the third step (S03) to obtain an α-alumina granulated product that can be suitably used as a catalyst carrier.

  The firing conditions for the granulated powder are not particularly limited as long as the effects of the present invention are not impaired, but the properties such as the crushing strength and the BET specific surface area of the α-alumina granulated product vary depending on the firing conditions. Here, in order to achieve both high crushing strength and a large BET specific surface area, the firing temperature is preferably 1200 to 1400 ° C, and more preferably 1250 to 1350 ° C. In addition, the holding time at the firing temperature is preferably 0.25 to 10 hours, and more preferably 0.25 to 5 hours.

  Moreover, it is preferable that the granulated powder is allowed to stand and dry as a pretreatment for firing. By allowing the granulated powder to stand and dry, the rearrangement of α-alumina particles and α-alumina fine particles proceeds and the binder becomes familiar with the whole, so the granulated powder becomes dense and the crushing strength of the resulting α-alumina granulated product Can be improved.

2. Α-alumina granulated product for catalyst carrier The α-alumina granulated product for catalyst carrier of the present invention can be suitably produced by the production method of α-alumina granulated product for catalyst carrier of the present invention, and BET specific surface area, crushing strength The powdering rate, pore volume and bulk specific gravity are controlled to appropriate values. Hereinafter, the characteristics of the α-alumina granulated product will be described.

(1) Shape, Size and Composition The α-alumina granulated product of the present invention is a mixture of α-alumina particles having an average particle size of 90 to 120 μm and α-alumina particles having an average particle size of 0.4 to 0.7 μm. Sintered into a substantially spherical shape. Here, these average particle diameters can be measured directly using a scanning electron microscope or the like, or using a laser diffraction particle size distribution measuring apparatus. In addition, what is necessary is just to determine the diameter of alpha alumina granulated material suitably according to a use.

  Here, the α alumina particles constituting the α alumina granulated product are not particularly limited as long as the effects of the present invention are not impaired, and various conventionally known α alumina particles can be used, but obtained by the Bayer method. It is preferable to use α-alumina particles obtained by firing aluminum hydroxide.

  In addition, the α-alumina granulated product of the present invention is basically a product of α-alumina particles sintered together, but a slight amount of carbon or the like that has not been completely removed by firing in the fourth step (S04) remains. It is permissible. Here, since the α-alumina granulated product has a large number of minute voids, the BET specific surface area has a high value.

(2) BET specific surface area The BET specific surface area of the α-alumina granulated product of the present invention is 4.0 to 6.0 m ² / g. Since the BET specific surface area is 4.0 to 6.0 m ² / g, the α-alumina granulated product can be sufficiently loaded with platinum or the like having a function as a catalyst. The BET specific surface area can be measured by a nitrogen gas adsorption method in which nitrogen gas is adsorbed on the sample surface and the surface area of the sample is obtained from the adsorption amount.

(3) Crushing strength The α-alumina granulated product of the present invention has a crushing strength higher than 9 kg. When the crushing strength is higher than 9 kg, breakage or the like when used as a catalyst carrier can be suppressed. The crushing strength is obtained by a Kiyama altimeter that collects one α-alumina granulated product on a sample stage, presses it with a pressure attachment, and reads the numerical value when a crack occurs in the α-alumina granulated product. Can do.

(4) Powdering rate The powdering rate of the α-alumina granulated product of the present invention is a value smaller than 1%. When the pulverization rate is smaller than 1%, a region that can be used as a catalyst carrier can be sufficiently secured.

  The pulverization rate can be measured by using a cylindrical container having a diameter of 254 mm and a height of 152 mm, and having one jammer plate having a width of 51 mm and a height of 152 mm inside the container. Specifically, the sample weighed 100.00 g is inserted into the container, and after capping, it is rubbed at 60 rpm for 30 minutes. The sample is taken out from the container after being rubbed, and after the powder on the sample surface is removed with a 1 mm sieve, the weight of the sample is measured to the second decimal place. The powdering rate can be calculated from the weight difference before and after the measurement. Powdering rate = (weight before rubbing−weight after rubbing) / weight before rubbing × 100

(5) Pore volume The pore volume of the α-alumina granulated product of the present invention is 0.25 to 0.45 cc / g. When the pore volume is 0.25 to 0.45 cc / g, the α-alumina granulated product can be sufficiently loaded with platinum or the like having a function as a catalyst. The pore volume can be determined by a mercury porosimeter that applies pressure to mercury and press-fits into the pores of the sample, and measures the relationship between the pressure applied at that time and the volume of mercury pushed in.

  Here, the α-alumina granulated product preferably has voids due to the pore forming agent. In the firing step for obtaining the α-alumina granulated product, when the binder that bonds the α-alumina particles is burned out, a gap is formed in the bonded portion, so that the strength is greatly reduced. On the other hand, when the pore forming agent is burned out, a hole is formed. However, since the formation of the hole is local, a decrease in strength can be suppressed.

(6) Bulk specific gravity The bulk specific gravity of the α alumina granulated product of the present invention is 1.6 to 1.7. The bulk specific gravity has a correlation with the pore volume, and the pore volume can be adjusted to 0.25 to 0.45 cc / g by being within the above range. Further, when the bulk specific gravity is low, it is difficult to support the catalyst component, and when the bulk specific gravity is high, the strength is low.

  The bulk specific gravity can be measured by the Archimedes method. Specifically, after putting a sample in pure water and making it saturated, the mass in the water is measured, the saturated sample is taken out from the water, and water droplets on the sample surface are wiped off, and then the saturated water weight is measured. Next, the sample is dried at 105 ° C., and the weight after drying is measured. The bulk specific gravity can be calculated by the dry weight of the sample / (the saturated water weight of the sample−the weight of the sample in water).

  As mentioned above, although typical embodiment of this invention was described, this invention is not limited only to these, Various design changes are possible and these design changes are all contained in the technical scope of this invention. It is.

<Example>
After mixing α-alumina particles and α-alumina fine particles at the ratios described in Example 1 and Example 2 in Table 1 to prepare α-alumina mixed particles (first step), Example 1 and Example 2 in Table 2 Each component (wt%) described in 1 was kneaded and a molded body was obtained by extrusion molding (second step). Next, after the obtained compact was sized to obtain a granulated powder (third step), firing was performed under the conditions shown in Table 2 (fourth step). The obtained α-alumina granulated product has a spherical shape of φ5 mm.

  In addition, Shin-Etsu Chemical Co., Ltd. hydroxypropyl methylcellulose (65SH-4000) was used for the binder, and rice flour was used for the pore-forming agent.

≪Comparative example≫
After mixing α-alumina particles and α-alumina fine particles at the ratio described in Comparative Example 1 to Comparative Example 5 in Table 1 to prepare α-alumina mixed particles (first step), Comparative Example 1 to Comparative Example 5 in Table 2 Each component (wt%) described in 1 was kneaded, and a molded body was obtained by extrusion molding or rolling granulation (second step). In Comparative Example 1, no binder and pore former were added, and in Comparative Example 2, no pore former was added. In Comparative Example 1 and Comparative Example 2, an appropriate amount of water is added for rolling granulation and extrusion molding, respectively. Next, after the obtained compact was sized to obtain a granulated powder (third step), firing was performed under the conditions shown in Table 2 (fourth step). The obtained α-alumina granulated product has a spherical shape of φ5 mm.

[Evaluation]
(1) Crushing strength The crushing strength is obtained by collecting one α-alumina granulated product on a sample stage and pressing it with a pressure attachment to read the numerical value when a crack occurs in the α-alumina granulated product. Sought by. The obtained results are shown in Table 3. The average value was calculated with 10 test repetitions.

(2) BET specific surface area The BET specific surface area was measured by a nitrogen gas adsorption method in which nitrogen gas was adsorbed on the surface of the α-alumina granulated product, and the surface area of the sample was determined from the adsorption amount. The obtained results are shown in Table 3.

(3) Powdering rate The powdering rate was measured by using a cylindrical container having a diameter of 254 mm and a height of 152 mm, and having one jammer plate having a width of 51 mm and a height of 152 mm inside the container. Specifically, the α-alumina granulated product weighed 100.00 g is inserted into the container, and after capping, air-rubbed at 60 rpm for 30 minutes. The α-alumina granulated product was taken out from the container after being rubbed, and after the surface powder was removed with a 1 mm sieve, the weight was measured to the second decimal place. The powdering rate was calculated from the weight difference before and after the measurement (powdering rate = (weight before air-rubbing-weight after air scrubbing) / weight before air scrubbing × 100). The obtained results are shown in Table 3.

(4) Pore volume The pore volume is measured by a mercury porosimeter that applies pressure to mercury and press-fits into the pores of the α-alumina granulated product, and measures the relationship between the pressure applied at that time and the volume of mercury pushed in. Asked. The obtained results are shown in Table 3.

(5) Bulk specific gravity Bulk specific gravity was measured by the Archimedes method. Specifically, after putting α-alumina granulated product in pure water and making it saturated, measure the mass in water, take the saturated sample from the water, wipe off the water droplets on the surface, taking measurement. Next, the sample is dried at 105 ° C., and the weight after drying is measured. The bulk specific gravity was calculated by the dry weight of the sample / (saturated weight of the sample−weight of the sample in water). The obtained results are shown in Table 3.

The crushing strength, BET specific surface area, pulverization rate, pore volume and bulk specific gravity of the α-alumina granulated product obtained in Example 1 and Example 2 are the target values of the present invention (crushing strength> 9 kg, BET specific surface area). : 4.0 to 6.0 m ² / g, powdering rate: less than 1%, pore volume: 0.25 to 0.45 cc / g, bulk specific gravity: 1.6 to 1.7) .

  In contrast, the α-alumina granulated product obtained in Comparative Example 1 employing rolling granulation has an average crushing strength of 5.5 kg and does not meet the target value of crushing strength. Further, the α-alumina granulated product obtained in Comparative Example 2 to which α-alumina particles are not added does not satisfy the target value of the pore volume. Furthermore, the α-alumina granulated product obtained in Comparative Example 3 with a small amount of α-alumina fine particles does not meet the target values for the crushing strength and the BET specific surface area. From the results, it can be seen that the crushing strength, the BET specific surface area and the pore volume can be set to appropriate values by adding an appropriate amount of α-alumina fine particles to α-alumina particles and employing extrusion molding.

  Further, in the α-alumina granulated product obtained in Comparative Example 4 and Comparative Example 5 in which no pore forming agent is used, the crushing strength, the pulverization rate, and the bulk specific gravity cannot be set within the target value range at the same time. Here, since the stationary drying was not performed in Comparative Example 4 and the stationary drying was performed in Comparative Example 5, the α-alumina granulated product obtained in Comparative Example 5 was obtained in Comparative Example 4. Compared to the alumina granulated product, it has a clearly higher crushing strength.

  Regarding the cross section of the α-alumina granulated product obtained in Comparative Example 1 and Comparative Example 2, observed images obtained with a scanning electron microscope are shown in FIGS. 2 and 3, respectively. The scanning electron microscope used was a field emission scanning electron microscope S-4700 manufactured by Hitachi, Ltd. In the α-alumina granulated product obtained in Comparative Example 1 using rolling granulation, many voids are observed, whereas in the α-alumina granulated product obtained in Comparative Example 2 using extrusion molding, α Alumina particles are densely packed. From this result, it can be seen that by using extrusion molding in the second step, a denser compact is obtained, and the finally obtained α-alumina granulated product is also densified.

  Regarding the cross section of the α-alumina granulated product obtained in Example 2, an observation image obtained by a scanning electron microscope is shown in FIG. A substantially spherical void resulting from the burning of the pore-forming agent is formed, and the diameter of the void is 3 to 50 μm (the void surrounded by ○ is typical). In addition, the voids are formed in a region that is not a joint between the α-alumina particles, and it is considered that the strength reduction due to the formation of the voids is small.

Claims (7)

Α-alumina particles having an average particle size of 90 to 120 μm and α-alumina particles having an average particle size of 0.4 to 0.7 μm are mixed, and the contents of the α-alumina particles and the α-alumina particles are 50 to 50 respectively. A first step of obtaining α-alumina mixed particles of 70 wt% and 30-50 wt%;
The second step of kneading the α-alumina mixed particles, 18 to 25 wt% water, 2 to 5 wt% binder, and more than 0 wt% to 7 wt% or less pore former and obtaining a molded body by extrusion molding. When,
A third step of sizing the molded body to obtain a granulated powder; and
Having a fourth step of firing the granulated powder,
A process for producing an α-alumina granulated product for a catalyst carrier. The firing temperature in the fourth step is 1200 to 1400 ° C.,
The method for producing an α-alumina granulated product for a catalyst carrier according to claim 1. As the pretreatment in the fourth step, the granulated powder is allowed to stand and dry.
The method for producing an α-alumina granulated product for a catalyst carrier according to claim 1 or 2. Using wheat flour or rice flour for the pore-forming agent,
The method for producing an α-alumina granulated product for a catalyst carrier according to any one of claims 1 to 3. a sintered body of α-alumina particles,
The sintered body has a substantially spherical shape,
The BET specific surface area is 4.0-6.0 m ² / g,
Crushing strength is greater than 9kg,
The powdering rate is less than 1%,
The pore volume is 0.25 to 0.45 cc / g,
The bulk specific gravity is 1.6 to 1.7,
An α-alumina granulated product for a catalyst carrier characterized by Having voids due to the pore-forming agent,
The α-alumina granulated product for a catalyst carrier according to claim 5. The gap is a substantially spherical shape having a diameter of 3 to 50 μm,
The α-alumina granulated product for catalyst carrier according to claim 6.