JPS62226811A - Production of alumina carrier - Google Patents

Abstract

PURPOSE:To produce a boehmite gel having a uniform particle size distribution by using aluminium sulfate which is a cheap alumina material and sodium aluminate under specified conditions. CONSTITUTION:A soln. of an alkali metal aluminate, especially sodium aluminate, is added to a soln. of the salt of aluminum and a mineral acid, especially aluminum sulfate, is the presence of a hydroxycarboxylic acid, especially gluconic acid, to control the pH to 7-10, and an aluminum hydroxide slurry is obtained. The soln. of the salt of aluminum and a mineral acid and the soln. of an alkali metal aluminate are simultaneously added to the slurry while keeping the pH at 7-10, and the alumina carrier is produced.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention controls the crystal growth of boehmite, and adjusts the pore volume and pore diameter of the alumina support obtained therefrom, thereby improving the alumina support with a sharp pore distribution. The present invention relates to a method for manufacturing a carrier.

(Prior Art) In recent years, one of the properties required of catalyst carriers is to have a controlled pore distribution. Catalytic activity is usually controlled by the surface area of the catalyst, but when a catalytic reaction is carried out selectively with respect to molecules of a certain size, the value and distribution of pore diameter becomes more important than the surface area. Generally, in many catalytic reactions, the pore size of the catalyst is one of the important factors that greatly influences the activity and selectivity. When the pore diameter is decreased, the resistance to diffusion of reactive molecules in the pores increases, and the effectiveness coefficient decreases, resulting in a decrease in activity. Conversely, if the pore size is made larger than necessary, the effective coefficient increases, but
Activity decreases due to a decrease in surface area.

In addition, an unnecessarily large pore diameter also leads to molecules larger than the target reaction molecules to the active site, thereby reducing the selectivity of the reaction. Therefore, in order to produce a catalyst that is sufficiently active for a desired reaction, it is necessary to obtain a carrier that has many pores with the optimum pore size for the reaction, that is, a support that has a sharp pore distribution.

Incidentally, r-alumina, which has excellent thermal stability and mechanical strength, is often used as a catalyst carrier. It is made by calcining boehmite gel. Boehmite gel is a hydrated gel of fibrous boehmite microcrystals, also called pseudo-boehmite, and is generally obtained by aging amorphous aluminum hydroxide at a temperature of 50° C. or higher and a pH of 6 to 11. In order to set the average pore diameter to a desired value and obtain an alumina support with a sharp pore distribution in which the pore volume of pores with a pore diameter near the average pore diameter accounts for most of the total pore volume, it is necessary to use this pseudo-eemite crystal. The size and its distribution must be adjusted to appropriate values.

Generally, as a method of adjusting the pore diameter of an alumina carrier, a method of changing the firing temperature of a boehmite gel molded product is known. However, although it is possible to adjust the average pore diameter with this method, the pore distribution is determined by the particle size distribution of the boehmite gel initially used, so unless a boehmite gel with uniform particle sizes is used,
An alumina support with a sharp pore distribution cannot be obtained. Also,
A well-known method for growing boehmite gel particles is to age aluminum hydroxide produced by hydrolysis, but the commonly used hydrolysis box (
In cases 6 to 11), the dissolution rate of microcrystals is extremely low, and the rate of particle growth in which microcrystals are dissolved and larger crystals grow is extremely low. Therefore, it takes a long time for the boehmite gel particles to grow.

Japanese Patent Publication No. 57-44605 discloses a method of promoting the crystal growth of sibemite gel by using aluminum hydroxide as a seed crystal and alternately adding an aluminum salt and a neutralizing agent to the seed crystal. This method is characterized in that the boehmite gel particle size can be controlled and boehmite gel with uniform particle size can be obtained by changing the number of times the aluminum salt and the neutralizing agent are added alternately. Therefore, if the boehmite gel obtained by this method is molded and fired by a known method, an alumina carrier having an arbitrary average pore diameter and a sharp pore distribution can be obtained. However, when aluminum sulfate, which is inexpensive and industrially useful, is used as an alumina carrier, this method often exhibits nonuniformity in particle growth, which is presumed to be due to the loose aggregation effect of boehmite gel particles mediated by sulfate groups.

In order to remove the effects of these sulfate groups, it is necessary to first filter and wash the slurry during hydrolysis, then return the solids from which the sulfate groups have been removed to the hydrolysis process to continue hydrolysis. becomes. Therefore, the present inventors discovered that the non-uniformity of particle growth, which is presumed to be due to the loose agglomeration effect of the boehmite gel particles mentioned above, can be improved by the presence of hydroxycarboxylic acid in the reaction system.
It was previously proposed as No.-16,857.

(Problem to be Solved by the Invention) However, due to the force, the method of the above-mentioned Application No. 16,857/1985 is a particle that is thought to be due to the l1Jlii aggregation effect of boehmite gel particles generated when aluminum sulfate and sodium aluminate are used. Although the non-uniformity of the process can be improved and the complexity of the operation has been reduced, several steps are still required. With the intention of reducing the number of steps, we conducted further research focusing on the unique effects of hydroxycarboxylic acids. As a result, we were able to improve the non-uniformity of particle growth and obtain an alumina support with a sharp pore distribution. We succeeded in obtaining a boehmite gel with the necessary uniform particle size distribution, leading to the present invention.

(Means for Solving the Problem) That is, the present invention prepares an aluminum hydroxide slurry by adding an alkali metal aluminate solution to an aluminum mineral salt solution in the presence of a hydroxycarboxylic acid so that the pH thereof becomes 7 to 10. and a step of simultaneously adding an aluminum mineral salt solution and an alkali metal aluminate solution to the slurry while maintaining the pH of 7 to 10.

In the present invention, as a reaction in the first step, in the presence of a hydroxycarboxylic acid, an aqueous solution of an aluminum mineral salt, preferably aluminum sulfate, has a concentration of 7 to 10 p.p.
! (A slurry of aluminum hydroxide is obtained by adding an aqueous solution of an alkali metal salt of aluminate so as to give a concentration of -17 to 95.
A final slurry of aluminum hydroxide is obtained by simultaneously adding an aqueous solution of an aluminum mineral salt, preferably aluminum sulfate, and an aqueous solution of an alkali metal aluminate, preferably while maintaining the pH of 13 to 95. In both stages of the reaction, it is desirable to heat the reaction mixture to 50°C or higher, preferably 50 to 70°C.

The hydroxycarboxylic acid is usually used as an anti-aggregation agent, and includes gluconic acid, tartaric acid, citric acid, and the like. Hydroxycarboxylic acids may be used in acid form or in forms such as alkali metal or ammonium salts.

Therefore, in the present invention, hydroxycarboxylic acid includes its salt form. Although these acids can be used alone or in mixtures, the most preferred acid is gluconic acid.

The amount of hydroxycarboxylic acid added is equivalent to 1 mole of Ax2o5 in the aluminum hydroxide slurry! 70.01~0.15
It is a mole. If the amount added is too small, the desired effect will not be achieved, and even if it is used more widely than the above range, no particular effect can be expected. It is convenient to add all of these acids to the aluminum mineral salt before the reaction in the first step. It may be added. What is important is that the above amount of hydroxycarboxylic acid is present in the reaction system.

The aluminum mineral salt used in both steps of the reaction may be any strong salt such as hydrochloride or nitrate;
Sulfates are most preferred because they are inexpensive. Moreover, if the above reaction is carried out using aluminum sulfate and aluminum/acid alkali metal salt without adding hydroxycarboxylic acid, t
Although non-uniformity in particle growth appears, which is thought to be due to the presence of sulfate groups as described above, this is eliminated according to the present invention. As the alkali metal aluminate salt used together with the aluminum mineral salt, soda salt is preferred because it is inexpensive.

In the present invention, as a reaction in the first step, -1 is added to an aluminum mineral salt solution in the presence of a hydroxycarboxylic acid in a range of 7 to 1.
An aluminum hydroxide slurry gold is obtained by adding an alkali metal aluminate salt bath solution so that the aluminum hydroxide slurry is preferably -8 to 9.5. It is desirable to add the alkali metal aluminate in 5 to 15 minutes, preferably 5 to 10 minutes; if the addition time is too long, the uniformity of the boehmite gel particles will be impaired. The reaction of the second step is carried out by simultaneously adding an aluminum mineral acid salt solution and an aluminum/acid alkali metal salt to the aluminum oxide slurry while maintaining the pH of 7 to 10. The aluminum hydroxide slurry obtained in the reaction of the first step is heated for 5 to 120 minutes, preferably for 10 minutes.
It is more effective to perform the second step reaction after aging for ~60 minutes to improve the uniformity of the boehmite gel particles. Simultaneous addition of aluminum mineral salt solution and alkali metal aluminate solution in the reaction of the second step is 5 to 30%
Adding for 5 to 10 minutes is effective for uniform growth of boehmite gel particles. After completion of the reaction in the second step, it is preferable to further ripen for 5 to 120 minutes.

There is no particular limitation on the quantitative ratio of aluminum hydroxide produced in the reaction of the first step and the reaction of the second step, but Aλ20
5 conversion weight ratio: 1; 9 to 9; 1 preferably 2; 8 to 8:
It is convenient to carry out both reactions in the range of 2, and it is possible to produce an alumina support with a large average pore diameter by increasing the proportion of aluminum hydroxide produced in the reaction of the second step.

As mentioned above, the present invention is characterized in that the production of aluminum hydroxide is carried out in two steps in the presence of a hydroxycarboxylic acid. In the presence of hydroxycarboxylic acid, a method of adding an alkali metal aluminate salt solution to an aluminum mineral salt solution (reaction in the first step) or a method of adding an aluminum mineral salt solution and an alkali metal aluminate solution An alumina support with a sharp pore distribution can be obtained even if the method of simultaneously adding (reaction in the second step) is carried out individually. However, when the two reactions are combined as in the present invention, an alumina support with a sharper pore distribution can be obtained than the alumina support obtained from the single reaction. Furthermore, it is difficult to change the average pore diameter of the alumina support from a single reaction, but in the present invention, the ratio of the amounts of aluminum hydroxide produced in the reaction in the first step and the reaction in the second step is changed. This is also possible by doing so.

(Example) Specific examples and comparative examples of the present invention will be shown below.

Example 1 54 ml of water was placed in a stainless steel reaction tank with an internal volume of 130λ and equipped with a stirrer.
2, an aluminum sulfate solution 51BOf with an Al2O3 concentration of a1% by weight, and a gluconic acid solution 50F with a concentration of 50% by weight were added and kept heated to 70°C. Next, add Aj & 20g to this solution as a reaction in the first step.
3760 g of sodium aluminate solution (wt%) was added over 5 minutes, and aged for an additional 30 minutes, p! (An aluminum hydroxide slurry of 9,5 was obtained.Next, as a reaction in the second step, the aluminum sulfate solution 5180F to which the gluconic acid bath V[s o y was added and the aluminum hydroxide solution 37609 and +) were simultaneously added for 5 minutes while maintaining Ha2 to &8, and then aged for 30 minutes. During this time, the temperature of the slurry was maintained at 70°C. The amount of gluconic acid used in this case is AQ20 contained in all the alumina raw materials used! 1 mole win! The amount was 70.013 mol, and the physical ratio of aluminum hydroxide produced in the reaction of the first step and the reaction of the second step was 5:5. The obtained slurry was filtered and washed, and then heated and kneaded in a negoo machine equipped with a heating mechanism to obtain a 40% by weight slurry having a temperature of 11,205 m degrees. This paste was molded using an extrusion molding machine with a die of 1 mm diameter, and then heated to 18° C.
It was dried for an hour and then fired in an electric furnace at 700°C for 2 hours.

The obtained alumina carrier is designated as A, and its properties are shown in the table.

The amount of gluconic acid used was changed to 0.032 mol, 0.078 mol, and 0.15 mol per mol of AQ20 contained in the total alumina raw material used, respectively, and the alumina carriers B, C, and D were prepared by the above method. I got it. Its properties are shown in the table.

In the table, the sharpness of the pore distribution is expressed as the ratio of the pore volume occupied by pores having an average pore diameter of ±10X to the total pore volume @-). It can be seen from this table that as the amount of gluco/acid added increases, the sharpness of the pore distribution increases. In addition, the amount of A contained in the total alumina raw material using the added amount of gluconic acid
Even if the amount is increased by 0.15 mol per 1 mol of l2O5, no better effect can be expected.

Example 2 0.03 mol of AR20s contained in total alumina feedstock using ammonium tartrate as anti-agglomeration agent
Alumina carrier Z was obtained in exactly the same manner as described in Example 1, except that 3 mol was added. Its properties are shown in the table.

Ammonium tartrate shows almost the same improvement effect on pore distribution sharpness as gluconic acid.

Comparative Example 1 An alumina carrier was prepared in exactly the same manner as described in Example 1 except that no anti-aggregation agent was used. I got it. Its properties are shown in the table.

The sharpness of the pore distribution is significantly lower than that of an alumina support obtained when an anti-aggregation agent is added.

Comparative Example 2 A carrier was prepared in exactly the same manner as described in Example 1, except that in the first step reaction of adding a sodium aluminate solution to an aluminum sulfate solution, the addition time of the sodium aluminate solution was changed to 15 minutes. I got a G. In addition, in the reaction of the second step in which the aluminum sulfate solution and the sodium aluminate solution were added simultaneously, the carrier I got it. In both cases, the addition fFi of gluconic acid, Ax2o contained in the total alumina raw material used! per mole, 9
G, 032 mol. The properties of carriers G and H are shown in the table.

In either case, the value of the sharpness of the pore distribution is lower than that of the alumina support obtained when the same amount of gluconic acid is added and the addition time is 5 minutes in both the first and second steps.

Example 3 Using gluconic acid as an anti-agglomeration agent, using 0.052 mol of F) per 2031 mol of A°C contained in the total alumina raw material, aluminum hydroxide produced by the reaction in the first step and the reaction in the second step. The physical ratio of 8:2.5, respectively.
Carriers J and K were obtained in the same manner as described in Example 1 except that the ratio was changed to 2:8. In addition, each alumina raw material was divided at a set ratio so that the total amount of aluminum hydroxide produced by the reaction in the first step and the reaction in the second step was the same as in Example 1, and gluconic acid was also divided at the same ratio. It was added in portions to the aluminum sulfate solution used in each step of the reaction. The properties of the carrier and Jl are shown in the table.

It can be seen that as the reaction rate of the second step increases, the average pore diameter of the alumina support increases, but the sharpness of the pore distribution also remains at a high value.

Comparative Example 3 Using gluconate as an anti-agglomeration agent, using 20 g of Afi contained in the total alumina raw material and 32 moles of υ0D per 1 mole, only the reaction of the first step of adding a sodium aluminate solution to an aluminum sulfate solution was carried out to form a carrier. I got it.

Further, with the same amount of gluconic acid added, a carrier M was obtained by carrying out only the reaction of the second step in which the aluminum #L acid solution and the sodium aluminate solution were added at the same time. The properties of carrier L%M are shown in the table.

Regarding the sharpness of the pore distribution, even if the reaction in the first step and the reaction in the second step are carried out independently.

Although an alumina support with a relatively high value is obtained, it is found that the value of the sharpness of the pore distribution is low when compared with an alumina support that has approximately the same average pore diameter even though both reactions are combined. Further, the alumina carrier obtained only by the reaction in the first step has a small pore volume.

(Effects) According to the present invention, boehmite gel having a uniform particle size distribution can be obtained using TFT* aluminum and sodium aluminate, which are inexpensive and industrially useful alumina raw materials. Further, according to the present invention, the ratio between the reaction in the first step of adding sodium aluminate to the aluminum sulfate solution and the reaction in the second step of adding the aluminum sulfate solution and sodium aluminate simultaneously is changed. This allows the size of the boehmite gel particles to be changed without impairing the uniformity of the distribution.

An alumina carrier having an arbitrary average pore diameter and a sharp pore distribution can be produced from the Mitogel thus obtained by molding and firing by a known method.

Patent applicant Sumitomo Metal Mining Co., Ltd. Representative Patent attorney Tatsuo Sato
2 people outside

Claims (1)

[Claims] 1) A step of adding an alkali metal aluminate solution to an aluminum mineral salt solution in the presence of a hydroxycarboxylic acid so that the pH becomes 7 to 10 to obtain an aluminum hydroxide slurry; A method for producing an alumina carrier comprising the step of simultaneously adding an aluminum mineral salt solution and an alkali metal aluminate solution to a slurry while maintaining the pH of 7 to 10. 2) 0.01 to 0.1 per mole of Al_2O_3 contained in the total alumina raw material using hydroxycarboxylic acid
2. The method according to claim 1, wherein the compound is present in a 5 molar reaction system. 3) The method according to claim 1, wherein the hydroxycarboxylic acid is gluconic acid. 4) The method according to claim 1, wherein the aluminum mineral salt is aluminum sulfate and the alkali metal aluminate salt is sodium aluminate.