JPS6234683B2 - - Google Patents

Description

[Detailed description of the invention]

This invention relates to a method for producing activated alumina, and more particularly, to a method for producing activated alumina, which has excellent compressive strength, wear resistance, and large specific surface area, and which has pores of both relatively fine pore radius and relatively large pore radius. The present invention relates to a method for producing granular activated alumina, which has a radial distribution and is particularly suitable as a catalyst support or catalyst. Activated alumina is used for various purposes such as desiccants, adsorbents, catalysts, and catalyst carriers. Conventional methods for producing activated alumina include (1) powdered γ-alumina;
boehmite gel, boehmite or gypsite,
Add water or other binder and granulate it,
Next, this molded alumina is heated and activated at a temperature of about 300 to 900°C to produce molded γ- or η-alumina. (2) Alumina trihydrate (gypsite)
After partially calcining, it is mixed with water and granulated, and the granulated alumina is cured by immersing it in water or in water vapor or water vapor-containing gas at about 50 to 150°C, and then A method of producing activated alumina containing γ- and/or η-alumina by thermally activating shaped alumina is known. However, activated alumina produced by the method (1) is inferior in compressive strength, abrasion strength, and performance as a catalyst carrier. Furthermore, the performance and strength of activated alumina produced by method (2) are still unsatisfactory as a catalyst carrier. In view of these circumstances, the present inventors have conducted extensive research in order to obtain activated alumina with excellent quality and performance without the above-mentioned drawbacks, and have achieved high activity through a combination of certain conditions. It has been found that it is possible to produce activated alumina which has excellent compressive strength and abrasion resistance, as well as a large surface area and pore volume, without damage. The present invention maintains high activity, has excellent compressive strength, abrasion resistance strength, and large surface area, less than 100 Å.
The purpose of this paper is to provide a method for producing activated alumina which has a pore radius distribution in the range of 10,000 to 30,000 Å and is suitable as a catalyst or catalyst carrier, and its gist is at least partially In the method for producing activated alumina, the above-mentioned transition alumina or transition alumina-containing material is formed by adding water to the transition alumina or a transition alumina-containing material that can be rehydrated, and then rehydrating with steam, and further heating and activating the transition alumina or transition alumina-containing material. 2 to 70 parts by weight of water and 0 to 10 parts by weight of auxiliaries are added to 100 parts by weight of the product, molded into a desired shape, and the molded product is placed in steam or steam-containing gas at 0 to 50°C for 24 hours. Hold for more than an hour to partially rehydrate,
Then, the transition alumina particles are held in water vapor or a water vapor-containing gas at a temperature of 50 to 150°C and higher than the temperature during the partial rehydration for a time sufficient to substantially rehydrate the transition alumina particles. Twist and rehydrate.
The method of producing activated alumina is characterized in that the rehydrated alumina particles are then heated and activated at a temperature of 300 to 900°C. The present invention will be explained in detail below. In the process of the present invention, a partially rehydrated transition alumina or a transition alumina-containing material, usually having an average particle size of about 50 microns, i.e., χ-alumina or ρ-alumina, or an alumina containing these aluminas or aluminum hydroxide, is first treated with water. Add and shape. At this time, transition alumina or transition alumina-containing material 100
Water is used in an amount of 20 to 70 parts by weight, and an auxiliary agent may be added at this time. The amount of the auxiliary agent added may be 10 parts by weight or less. Examples of the auxiliary agents used in this case include crystalline cellulose, aluminum nitrate, aluminum chloride, acetic acid, nitric acid, acidic aluminum carbonate, polyethylene glycol, polyvinyl alcohol, and aqueous ammonia. That is, this auxiliary agent disappears during firing, leaving micropores in the fired and formed alumina. The shape of this molded product is granular, for example, spherical, cylindrical, tablet-like, etc., and its size may generally be about 3 to 10 mm. Examples of the granulation method include extrusion granulation, rolling granulation, and the like. Next, in the method of the present invention, a two-stage rehydration treatment is performed. First, in the first stage, the above-mentioned shaped transitional alumina is heated at 0 to 50°C, preferably 5 to 50°C, more preferably
Transition alumina particles are slowly regenerated in water vapor at a temperature of 10 to 30°C or in a water vapor-containing gas in the above temperature range, such as a mixture of water vapor and air (e.g., by generating water vapor and passing it in with air). It is maintained for a period of time during which it is hydrated and partially transformed into bayerite, that is, 24 hours or more, preferably 2 days or more, and more preferably 3 to 6 days. In the second stage of rehydration, the partially rehydrated alumina as described above is
in water vapor at a temperature higher than the first stage rehydration at 150°C, preferably from 80 to 130°C, more preferably from 100 to 120°C, or in a water vapor-containing gas (e.g. a mixture of water vapor and air) in the above temperature range. , the partially hydrated alumina particles are held for a period of time, such as 2 hours or more, until the partially hydrated alumina particles are substantially rehydrated and bayerite formation is substantially completed. After the two-step rehydration process is completed as described above, the rehydrated alumina is heated at a temperature of 300 to 900°C to activate it. Activated alumina is thus obtained with excellent compressive strength, abrasion strength and large surface area, and a pore radius distribution both below 100 Å and between 10,000 and 30,000 Å. This activated alumina has excellent activity not only as a catalyst carrier but also as a catalyst. Generally, improvement in strength and improvement in activity are contradictory, but the product produced by the method of the present invention has improved strength without deteriorating its performance as a catalyst carrier or catalyst. This is considered to be the result of the two-stage rehydration process consisting of the specific conditions mentioned above. However, the theoretical basis for this is not clear, but perhaps
When the two-stage rehydration process is carried out under the above-mentioned specific conditions, the initial slow rehydration creates a network that constitutes the basic structure, and the second stage
It is believed that rehydration of the stage results in further reinforcement around this network, completing substantial rehydration. On the other hand, if the rehydration is insufficient, of course, and even if the rehydration is sufficient, if the rehydration proceeds rapidly, it is presumed that structural destruction will occur and good physical properties will not be obtained. Next, examples of the method of the present invention and comparative examples will be shown to clarify the effects of the present invention. Example 1 Approximately 50 g of Avicel [Asahi Kasei Corporation] was added to 1 kg of transition alumina, which exhibits χ-alumina in X-rays and has an average particle size of approximately 50 μm.
Product, crystalline cellulose] was added and mixed for 1 hour in a mixer, and then molded in a rolling granulator while adding about 550 g of water to form spherical alumina with a diameter of 3 to 4 mm. After forming this transition alumina, it is immediately placed in a sealed container while still containing water and kept at approximately 25°C for 3 days, then placed in a sealed container with water coexisting and kept at 100 to 120°C for 2 hours to allow steam to form. I got cured. The rehydrated alumina was then dried and activated by heating at about 600° C. for 3 hours. This activated alumina is designated as sample A. Comparative Example 1 Molded transitional alumina produced in the same manner as in Example 1 was treated under the treatment conditions of Example 1 in a closed container with approximately
Activated alumina was obtained in the same manner as in Example 1 except that the step of "standing at 25°C for 3 days" was omitted. This is designated as sample B. Comparative Example 2 Molded transitional alumina produced in the same manner as in Example 1 was heated in a closed container at about 25°C for 30 minutes as in Example 1.
Activated alumina was obtained in the same manner as in Example 1 except that instead of holding it for 1 day, it was left in a closed container at about 25° C. for 12 hours. This material is designated as sample C. Comparative Example 3 Molded transitional alumina produced in the same manner as in Example 1 was cured in air by leaving it in the atmosphere for 3 days, and then cured in the same manner as in Example 1 for about 600 ml.
The mixture was activated by heating at ℃ for 3 hours. The obtained activated alumina is designated as Sample D. The compressive strength, abrasion resistance strength, performance of the catalyst using each sample as a carrier, specific surface area, pore volume, and mode pore radius of the above samples A to D were measured by the following methods, and the results are shown in Table 1. Shown below. (1) Compressive strength (Kg/piece) Using a Kiya type hardness tester, measure the breaking load of the grains (Kg/piece).
) was measured, and the average value of 20 was taken as the compressive strength. (2) Abrasion resistance strength (%) Measured in accordance with JIS K1474-1975. (3) Catalytic activity A 12c.c. sample carrier was immersed in a 42% vanadyl oxalate aqueous solution for 3 hours, and after draining, it was dried in a dryer to 100%
Dry at ℃ for 3 hours. The mixture was then fired in a firing furnace at 500°C for 3 hours under air circulation to produce a V ₂ O ₅ catalyst supported on activated alumina. This catalyst (12 c.c.) was packed into a denitrification reaction tube, and 8 volume% oxygen, 12 volume% carbon dioxide gas,
A NOx-containing gas consisting of 20% water vapor, 100ppm NOx (nitrogen oxides), 100ppm ammonia, and residual nitrogen (wet base) was passed under the conditions of SV20000Hr ^-1 and 270°C to determine the NOx decomposition rate (%). ) was measured and defined as catalyst performance. Note that the Nox decomposition rate is determined by the following formula. Nox amount (inlet, 100 ppm) - Nox amount (outlet) / Nox amount (inlet, 100 ppm)
×100 (4) Surface area This is the surface area (m ² /g) of the activated alumina support measured by the BET method N ₂ adsorption method. (5) Pore capacity (cc/g) and mode pore radius (Å) The volume (cc/g) with a pore radius of 40 Å or more measured by mercury intrusion method, and the pore radius (Å) distribution at the same time. I asked for it.

[Table] According to Table 1 above, sample A manufactured by the method of the present invention is a sample manufactured by omitting the step of slow steam curing at low temperature for a long time, in contrast to the method of the present invention. B, sample C produced by slow steam curing at low temperature for a short time, and sample D produced by hydration by air curing, both in compressive strength, abrasion resistance, and catalytic performance. It is clear that In addition, what has been explained above and shown in the examples is as follows.
These are examples to help understand the present invention, and the present invention is not limited by these examples.
The present invention is capable of other changes and modifications within the scope of the invention.

Claims (1)

[Claims] 1. A process for producing activated alumina in which transition alumina or a transition alumina-containing material that can be at least partially rehydrated is formed by adding water, then rehydrated with steam, and further activated by heating. or for 100 parts by weight of transition alumina-containing material
20 to 70 parts by weight of water and 0 to 10 parts by weight of auxiliary agents are added and molded into the desired shape, and the molded product is kept in water vapor or water vapor-containing gas at 0 to 50°C for 24 hours or more to partially heat the product. and then in water vapor or a water vapor-containing gas at a temperature of 50 to 150°C and higher than the temperature during the partial rehydration, sufficient to substantially rehydrate the transition alumina particles. A method for producing activated alumina, which comprises rehydrating the alumina particles by holding the particles for a period of time, and then heating and activating the rehydrated alumina particles at a temperature of 300 to 900°C.