JPH08268715A - Production of high purity pseudo-boehmite powder - Google Patents

Abstract

PURPOSE: To obtain high purity pseudo-boehmite powder by adding a specified compd. in a washing process when pseudo-boehmite powder is produced by a neutralization decomposition method. CONSTITUTION: An aluminum salt soln. is mixed with an alkali aluminate soln., an aluminum salt soln. is mixed with an alkali soln. or an alkali aluminate soln. is mixed with an acidic soln. and the resultant mixture is aged, washed and dried to synthesize pseudo-boehmite powder. At this time, one or more among ammonium nitrate, ammonium hydrogencarbonate, a surfactant and a polymer are added at the time of the washing and the objective high purity pseudo-boehmite powder is obtd. This powder is suitable for use as a catalyst carrier.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing high-purity pseudo-boehmite powder, and more particularly to a method for producing high-purity pseudo-boehmite powder used as a catalyst carrier.

[0002]

2. Description of the Related Art Aluminum compounds such as aluminum hydroxide, aluminum oxyhydroxide, and alumina are widely used as raw materials or products for catalyst carriers. In general, γ-alumina, which is excellent in thermal stability and excellent in mechanical strength, is often used as a catalyst carrier, and this generally calcinates pseudo-boehmite (boehmite gel) obtained by aging boehmite gel. It is manufactured by
In order to produce this boehmite gel, a neutralization decomposition method of an aluminum salt or a hydrolysis method of an aluminum alkoxide is generally used.

A general neutralization decomposition method is to mix an aluminum salt solution and an alkali aluminate, an aluminum salt solution and an alkali, or an alkali aluminate solution and an acid. The boehmite gel prepared in Step 1 is heat-aged if necessary. The obtained slurry is filtered by a filter press or the like, the steps of dispersing the aluminum hydroxide cake in pure water and washing are repeated, and then dried by spray drying or the like to obtain pseudo-boehmite powder. Consists of In addition, in the hydrolysis method of aluminum alkoxide, water is added to and mixed with aluminum alkoxide. The same as the steps of the above-mentioned neutralization decomposition method. Is. The obtained pseudo-boehmite powder was added with an aqueous solution containing a peptizer such as nitric acid and acetic acid, kneaded, extruded, and dried.
It becomes an alumina catalyst carrier through a firing process.

Generally, the properties as a catalyst carrier are as follows: large specific surface area, appropriate pore size and pore distribution, large pore volume,
It has strong mechanical strength, good dispersibility of active metal species, and good moldability. These conditions are largely controlled by the manufacturing conditions of the powder and the catalyst carrier. In particular, the pH, temperature, aluminum concentration, salt concentration, time, etc. of the solution at the time of precipitation formation and precipitation aging are important parameters. In the case of the neutralization decomposition method, generally, at the time of forming a precipitate and at the time of aging the precipitate, the pH is 4 to 11, the temperature is room temperature to 100 ° C, and the treatment is carried out in a temperature range of 100 ° C to 200 ° C if necessary. However, it is possible to simultaneously obtain the above-mentioned properties (specific surface area, pore diameter and pore distribution, pore volume, mechanical strength, dispersibility of active metal species, moldability, etc.) as a catalyst carrier adjusted to an appropriate value. Is very difficult. As one of the improved techniques, a method is known in which a carboxylic acid, a hydroxycarboxylic acid, an alcohol and the like are allowed to exist in a solution for neutralization decomposition or hydrolysis.

Japanese Patent Publication No. 6-8174 discloses a method for preparing an alumina carrier having a sharp pore size distribution, in which an aluminum salt solution is adjusted to pH 7 to 10 in the presence of hydroxycarboxylic acid (gluconic acid, tartaric acid, citric acid, etc.). And a step of adding an alkali metal aluminate salt solution to obtain an aluminum hydroxide slurry, and a step of simultaneously adding an aluminum salt solution and an alkali metal aluminate salt solution while maintaining pH 7 to 10 of the slurry. A method for producing a pseudo-boehmite powder is disclosed. Further, in Japanese Patent Laid-Open No. 5-317706, a solution of alcohol (methanol, ethanol, and isomer alcohol containing propanol, butanol, pentanol, hexanol, etc.
It is disclosed that by coexisting two or more species in a dissolved state, the viscosity is changed by changing the type of alcohol or the molar ratio of alcohol and water to control the pore diameter.

[0006]

However, in the method as described above, in the step of washing the electrolyte component adsorbed on the precipitate, if the electrolyte concentration during washing becomes low, the filterability of the aluminum hydroxide slurry deteriorates, There is a problem that solid-liquid separation becomes difficult and electrolyte components as impurities (in particular, alkali ions such as Na and K, chloride ions, and sulfate ions) cannot be completely removed.

[0007]

Therefore, the present inventor has found that the aluminum hydroxide slurry produced by the neutralization decomposition method has better dispersibility as the electrolyte component as an impurity decreases, so that the aluminum hydroxide is filtered. It was thought that the cloth would be clogged, the filterability would be poor, solid-liquid separation would be difficult, and separation of impurities would not be easy, and as a result of intensive studies to solve the above problems, the present invention has been accomplished.

That is, according to the present invention, a pseudo-boehmite powder is prepared by mixing, aging, washing and drying an aluminum salt solution and an alkali aluminate solution, an aluminum salt solution and an alkali solution, or an alkali aluminate solution and an acidic solution. A method for producing a high-purity pseudo-boehmite powder, which comprises adding one or more of ammonium nitrate, ammonium hydrogen carbonate, a surfactant, and a polymer in combination during the washing. ,
The high-purity pseudo-boehmite powder is a high-purity pseudo-boehmite powder for a catalyst carrier.

[0009]

DETAILED DESCRIPTION OF THE INVENTION According to the present invention, any one or more of ammonium nitrate, ammonium hydrogen carbonate, a surfactant and a polymer can be used at the time when the electrolyte concentration is lowered during washing and the dispersibility of particles is improved. Is added in combination to bring about a weak aggregation state (a binding state due to a weak van der Waals force) to improve the filterability. These components evaporate and scatter in the process of manufacturing a powder (pseudo-boehmite powder) that has been washed, filtered, and dried (pseudo-boehmite powder) (the process of molding and firing), so that it does not remain as an impurity in the catalyst carrier and is high A pure alumina catalyst carrier can be easily obtained.

The additives used in the present invention are preferably added in the form of a solution. The surfactant and polymer may be ionic or nonionic, but are compatible with the mother liquor,
Those that decompose at the lowest temperature possible are desirable. Specifically, as the surfactant, various fatty acid esters, glycerin esters, fatty acid amides, higher alcohols, alkyl amino acid salts, alkyl ether acetates, alkyl sulfocarboxylates, alkyl ammonium salts and the like are used. As the polymer, polyvinyl alcohol (PVA), acrylic copolymer, cellulose copolymer, polyethylene glycol, waxes, etc. are used.

The degree of aggregation (dispersibility) of aluminum hydroxide can be judged by the degree of settling of aluminum hydroxide particles when the aluminum hydroxide slurry is collected in a settling tube and allowed to stand. The smaller the volume of sediment, the better the dispersibility,
On the contrary, when the volume of sediment is large, it can be judged that the dispersibility is poor. As described above, the time when the electrolyte concentration is lowered during the washing and the dispersibility of the particles is improved is the time when the aluminum hydroxide is dispersed such that it is dispersed without settling for several days. The weak aggregation state is a binding state due to weak van der Waals force, and the powder that is washed, filtered, and dried after weak aggregation and sedimentation again contains a deflocculant such as water, nitric acid, or acetic acid. It is an agglomerated state that can be dispersed in an aqueous solution. That is, the powder can be dispersed again during the kneading for producing the catalyst carrier.

As the aluminum salt solution, the acidic solution, the alkaline aluminate solution, and the alkaline solution, salts generally used in the neutralization method are used. Typically, as the aluminum salt solution, aluminum chloride, aluminum sulfate, aluminum nitrate solution and the like, as the aluminate alkali, sodium aluminate and the like, as the alkali, ammonia, caustic soda and the like, as the acid, sulfuric acid, Hydrochloric acid, nitric acid, etc. are used. An aluminum salt solution is mixed with an alkali aluminate solution, an aluminum salt solution is mixed with an alkali solution, or an alkali aluminate solution is mixed with an acidic solution, and the mixture is aged, washed, and dried. Note that additives such as alcohol and carboxylic acid may coexist in the solution that undergoes neutralization decomposition. Aging, washing, and cleaning of this aluminum hydroxide slurry
The drying conditions are operating conditions that give the desired catalyst carrier characteristics, and a general method for preparing a neutralization decomposition method is used.

[0013]

Example 1 Formic acid was added to an aqueous solution of aluminum chloride having a concentration of 0.5 mol / l in an amount of 5 wt% and mixed, and then an aqueous solution of sodium aluminate having a concentration of 0.5 mol / l was added to adjust the pH to 9.0. Formed a precipitate. After filtering 2 l of this aluminum hydroxide slurry, the step of dispersing the obtained gel in 10 l of pure water and filtering it was repeated twice.
The electric conductivity of the filtrate at this time was 0.57 mS / cm. After the gel was dispersed in pure water, a concentration of 0.2 mol / l ammonium nitrate aqueous solution was added, and the mixture was further filtered. After dispersion, filtration was repeated twice. The obtained filter cake was dried, then kneaded and extruded. The molded body was dried and then heated to 600 ° C. and calcined to obtain a catalyst carrier. Impurities in catalyst carriers
Table 1 shows (Na, Cl).

[0014]

[Table 1]

The catalyst carrier contained 5 ppm of Na and 50 ppm of Cl.

[0016]

Example 2 A process of filtering 2 l of aluminum hydroxide slurry synthesized in the same manner as in Example 1, dispersing in pure water and filtering was repeated several times. The electrical conductivity of the filtrate at this time is 0.65
It was mS / cm. The step of dispersing this gel in pure water, adding an 8 wt% aqueous solution of polyvinyl alcohol (PVA), further filtering, dispersing and filtering was repeated twice. The obtained filter cake was dried, then kneaded and extruded. This molded body was dried and then heated to 600 ° C. and calcined to obtain a catalyst carrier. The impurities (Na, Cl) in the catalyst carrier are shown in Table 1. The catalyst carrier contained 6 ppm of Na and 70 ppm of Cl.

[0017]

Comparative Example 1 In the washing step of Example 1, the steps of filtering, dispersing and filtering were repeated in the same manner without adding a 0.2 mol / l ammonium nitrate aqueous solution. When the electric conductivity of the aluminum hydroxide slurry reached 0.1 mS / cm, the aluminum hydroxide slurry could not be filtered and was dried by spray drying. After that, the dried powder is kneaded and extruded in the same manner, and the molded body is dried at 600 ° C.
The temperature was raised up to calcination, and the mixture was calcined to obtain a catalyst carrier. The impurities (Na, Cl) in the catalyst carrier are shown in Table 1. Na in this catalyst carrier is
110 ppm and Cl were 1200 ppm.

In this way, ammonium nitrate in the washing process,
By adding polyvinyl alcohol (PVA), in the absence of addition, Na; 110ppm, while Cl; 1200ppm, whereas ammonium nitrate, when adding polyvinyl alcohol (PVA), Na; 5 ~ 6ppm, Cl; 50 It can be seen that the amount is up to 70 ppm, and the impurities in the catalyst carrier are reduced.

[0019]

According to the present invention, by adding any one or a combination of ammonium nitrate, ammonium hydrogen carbonate, a surfactant and a polymer in the washing step of the neutralization decomposition method, a high purity can be obtained. Pseudo-boehmite powder and catalyst carrier can be obtained.

Claims (2)

[Claims] 1. An aluminum salt solution and an alkali aluminate solution, an aluminum salt solution and an alkali solution, or an alkali aluminate solution and an acidic solution are mixed and aged.
In the method of synthesizing pseudo-boehmite powder by washing and drying, any one of ammonium nitrate, ammonium hydrogen carbonate, a surfactant, and a polymer at the time of washing, or 2
A method for producing a high-purity pseudo-boehmite powder, which comprises adding three or more in combination. 2. A method for producing a high-purity pseudo-boehmite powder, which is a high-purity pseudo-boehmite powder for a catalyst carrier.