JPH0258205B2 - - Google Patents

Description

BACKGROUND OF THE INVENTION Technical Field The present invention relates to a method for producing ammonium dawsonite (NH ₄ Al(OH) ₂ CO ₃ ) (hereinafter abbreviated as AACH). More specifically, by reacting water-insoluble basic aluminum sulfate with ammonium hydrogen carbonate, it is possible to obtain isolated acicular or rod-like crystals with a ratio of short axis to long axis of 5 or more, which is effective for various fillers, etc. Regarding the manufacturing method of AACH.

Prior art and its problems AACH has traditionally been used as a raw material for easily sinterable alumina powder, as a raw material for antacids, and as a raw material for single-crystal alumina. different ones are used.

AACH is generally obtained by reacting an aluminum salt aqueous solution or an aluminum hydroxide gel obtained by neutralizing the same with ammonium hydrogen carbonate or ammonium carbonate. can get
The crystallinity of AACH, the shape of crystal particles depends on the reaction method,
Although it varies depending on the ripening conditions, granular, plate-like, burr-like, and needle-like types are known as those with good crystallinity.

In general, isolated needle-like or rod-like crystals are excellent as fillers because of their large aspect ratio, and because they are isolated, they have good dispersibility. Therefore, it consists of a crystal shape like this.
AACH has excellent properties as a filler and is expected to open up new uses for AACH.

A known method for obtaining needle-like crystals of AACH is to gradually react concentrated ammonium bicarbonate with a dilute aqueous aluminum chloride solution (Japanese Patent Application Laid-open No. 58-26029). However, this method was not an economical or practical method because the concentration of the aluminum chloride aqueous solution used was as low as 0.02 mol/liter, resulting in a low unit yield, and because an ammonium bicarbonate aqueous solution of 2 mol/liter or more was required.

Further, as a method for efficiently obtaining AACH, there is a method of reacting aluminum hydroxide gel with ammonium hydrogen carbonate (US Pat. No. 2,783,124). However, since the purpose of this method is to produce antacids, the AACH obtained has poor crystallinity in order to improve reactivity with acids. The present inventors tried changing a number of reaction conditions such as reaction temperature, reaction time, and molar ratio of both components in order to improve crystallinity, but only a slight improvement in crystallinity was observed. Therefore, even with this method, needle-like or rod-like crystals could not be obtained.

In addition, even if an attempt is made to obtain needle-like crystals by crushing the burr-like AACH, which has a form of agglomerated needle-like crystals, the hardness of AACH is low, so the needle-like crystals themselves are destroyed during crushing and remain in the needle-like form. I couldn't do anything.

Summary of the Invention The present inventor has conducted research in order to achieve the purpose of the present invention, which is to provide a method for producing AACH consisting of needle-shaped or rod-shaped crystals with excellent properties in an efficient and isolated state. As a result of repeated experiments, it was discovered that the above object could be achieved by using a gel obtained by neutralizing aluminum sulfate, alum, etc. with an alkali in the acidic and neutral ranges, that is, a water-insoluble basic aluminum sulfate, as a starting material, and the present invention was realized. I have come to complete it.

That is, the method for producing crystalline ammonium dawsonite of the present invention is characterized by reacting water-insoluble basic aluminum sulfate with ammonium hydrogen carbonate.

Actions and Effects Because sulfate ions are bound to the water-insoluble basic aluminum sulfate gel of the present invention, crystals grow more slowly than when pure aluminum hydroxide gel is used, and as a result, isolation It is assumed that the crystals tend to form rod-shaped crystals. The above description is for the purpose of understanding the present invention more clearly, and is not intended to limit the scope of the present invention.

The manufacturing method of the present invention has the following advantages compared to conventional methods.

AACH needle crystals, which could only be synthesized at an aluminum concentration of 0.02 mol/liter or less, can now be synthesized at an aluminum concentration of 0.2 to 0.4 mol/liter by increasing the concentration of water-insoluble basic aluminum sulfate, increasing the unit yield. is 10x to 20
It can be doubled.

Production units of ammonium bicarbonate start from 52.5
1.5, which is more than 30 times less, making it possible to significantly reduce costs.

Manufacturing time can be significantly reduced.

Moreover, the isolated rod-like shape obtained by the present invention
AACH has much better dispersibility than agglomerated needle-like crystals such as burr-like AACH, and has a higher aspect ratio than granular or plate-like AACH, making it an excellent filler. have. Therefore, it can be used not only for various purposes as it is, but also for the following purposes, making it a material with extremely high industrial value.

By thermally decomposing it by conventional methods to produce γ-alumina with a high specific surface area, and chemically stable and strong γ-alumina, its uses as fillers, modifiers, reinforcing agents, etc. can be further expanded. .

If necessary, an appropriate binder is added, molded, and then fired to produce a porous alumina sintered body, which is expected to be used as various catalyst supports, ceramic-reinforced metal preforms, and heat insulating agents.

Note that shaping and sintering can also be carried out after thermal decomposition to form alumina.

Detailed Description of the Invention The water-insoluble basic aluminum sulfate used as a starting material in the present invention contains aluminum ions,
Contains sulfate ions and hydroxide ions as ionic species, and SO ₄ /Al (molar ratio) is preferably 0.04 to 0.40.
It is an aluminum compound with a value of 0.05 to 0.30. Substances from which this compound can be prepared include:
For example, there are aluminum compounds such as aluminum sulfate, ammonium alum, potassium alum, and sodium alum, and alkalis such as ammonium, sodium hydroxide, and potassium hydroxide, and they can be prepared by reacting them. Water-insoluble basic aluminum sulfate can be prepared by conventional methods. For example, an aqueous aluminum sulfate solution and aqueous ammonia are mixed into an acidic material with a pH of 2.0 to 7.0, preferably 3.5 to 7.0.
Water-insoluble basic aluminum sulfate can be prepared by neutralizing it at room temperature. Additionally, a method of hydrolyzing a basic aqueous aluminum sulfate solution by heating, a method of reacting sulfuric acid or an aqueous aluminum sulfate solution with an alkali aluminate aqueous solution, a method of reacting an aqueous aluminum sulfate solution with an aqueous urea solution, an aqueous aluminum sulfate solution and sodium carbonate, etc. Al(OH) _n × _o (× indicates a monovalent anion, m+n=3), a method of reacting an aqueous solution with aluminum sulfate, Al× ₃ (× indicates a monovalent anion, ion)
It can be prepared by a known method such as a method of reacting an aluminum hydroxide gel obtained by neutralizing an alkali aqueous solution with an aqueous aluminum sulfate solution.

The water-insoluble basic aluminum sulfate used in the present invention can be used in various forms depending on the reaction conditions, such as amorphous gel, slurry, crystalline powder, and amorphous There are granular, etc.

In the present invention, AACH crystals can be produced by making a slurry of water-insoluble basic aluminum sulfate as it is, or by making it into a slurry again after filtering, washing and drying it, and then reacting it with ammonium hydrogen carbonate. For the reaction, ammonium bicarbonate powder or aqueous solution may be added to the slurry, or conversely, the slurry may be added to the ammonium bicarbonate aqueous solution, but when adding the slurry, if the addition rate is too slow, aggregates may form. Addition should be done within 6 hours, more preferably within 3 hours as this will make it easier.
Do it within the time limit. This reaction mixture can then be aged to allow sufficient crystal growth.
If the ripening temperature is too low, the needle-like crystals tend to become fine, so a temperature of room temperature or higher, for example 50 to 70°C, is preferable. Similarly, it is desirable to allow sufficient ripening time. For example, 0.5 to 24 hours.

Further, the concentration of ammonium hydrogen carbonate used in the reaction mixture is preferably 1 mol/liter or less. This is because when the ammonium hydrogen carbonate concentration is too high, the aspect ratio of AACH produced tends to become smaller. Furthermore, if the concentration is too low, the production rate will be slow and a long period of aging will be required, so the particularly preferred concentration is in the range of 0.7 to 0.3 mol/liter.

It should be noted that by adding the crystalline AACH obtained in the present invention as seed crystals to the raw material or reaction mixture in advance and then ripening, a larger
Rod-shaped crystals of AACH can be obtained and the ripening time can be shortened.

Examples Example 1 Dilute 80 ml of 28% ammonia water to 500 ml, add this to 1 liter of 0.2 mol/liter ammonium alum aqueous solution, and add 1
The mixture was added dropwise over a period of time to obtain a slurry of water-insoluble basic aluminum sulfate. The final pH at this time was 5.2. In addition, after filtering, washing, and drying a portion of the slurry, Al and SO ₄ were measured, and SO ₄ /Al = 0.16.
It was hot. While maintaining this slurry at 60° C., 79 g of ammonium hydrogen carbonate was gradually added in powder form. After aging the reaction mixture at 60° C. for 10 hours, the resulting precipitate was filtered and washed to obtain 50 g of white powder. Observation using a scanning electron microscope showed that this powder was an isolated rod-shaped crystal with a minor axis of 0.3 microns and a major axis of 1.5 microns (Figure 1). Furthermore, it was confirmed to be AACH by powder X-ray diffraction measurement.

Example 2 95 ml of 28% ammonia water was diluted to 500 ml, and this was added to 1 liter of 0.2 mol/liter ammonium alum aqueous solution while keeping the liquid temperature at 50°C.
A slurry of water-insoluble basic aluminum sulfate was obtained dropwise over time. The final pH at this time was 6.9. After filtering and drying this slurry, Al and SO ₄ were measured and found that SO ₄ /Al (molar ratio) = 0.08.
It was hot. Pure water was added to this again to make 750 ml of slurry. This was heated to 60℃ in advance.
1 mol/liter ammonium bicarbonate aqueous solution
After dripping for 1 hour while maintaining the temperature at 750ml,
It was aged at 60°C for 10 hours. Filter the formed precipitate,
After washing, 50 g of white powder was obtained. This powder has a short diameter
Isolated rod shape with a diameter of 0.2 microns and a major diameter of 1.5 microns.
It was AACH.

Example 3 To a slurry of water-insoluble basic aluminum sulfate obtained in the same manner as in Example 2, 20 g of acicular AACH obtained in the same manner as in Example 1 was added and mixed. While keeping this solution at 60℃, add ammonium hydrogen carbonate.
After gradually adding 79 g, the mixture was aged at 60°C for 5 hours, and the resulting precipitate was filtered and washed to obtain 68 g of white powder. This powder was an isolated rod-shaped AACH with a minor axis of 0.5 microns and a major axis of 5.0 microns.

Comparative example 47g of ammonium hydrogen carbonate was made into a 300ml aqueous solution, and the reagent aluminum chloride hexahydrate 1g was made into a 750ml aqueous solution, while maintaining the temperature of the liquid at 55℃.
It was dropped in 20 hours. The obtained precipitate was filtered, washed and dried to obtain a white powder. This powder has a short diameter
Isolated needle shape of 0.3 micron, major axis 3.0 micron
Although it was AACH, the yield was small at 0.9g.

[Brief explanation of the drawing]

FIG. 1 is a scanning electron micrograph of a crystal of AACH obtained in Example 1 according to the present invention, magnified 10,000 times.

Claims (1)

[Claims] 1. A method for producing crystalline ammonium dawsonite, which comprises reacting water-insoluble basic aluminum sulfate with ammonium hydrogen carbonate. 2. The water-insoluble basic aluminum sulfate is obtained by reacting an aqueous solution of ammonium alum and/or aluminum sulfate with an alkali in a pH range of 3.5 to 7.0. A method for producing crystalline ammonium dawsonite according to scope 1. 3. The method for producing crystalline ammonium dawsonite according to claim 1 or 2, characterized in that ammonium hydrogen carbonate is reacted in the state of an aqueous solution with a concentration of 1 mol/liter or less.