JP2654880B2 - Method for producing ceric oxide sol - Google Patents

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 ceric oxide sol, and provides a sol of ceric oxide useful as an industrial material used as an ultraviolet absorber, an abrasive, a catalyst, a ceramic raw material and the like. The present invention relates to a novel method for producing the ceric oxide sol.

[0002]

2. Description of the Related Art Conventionally, powdered ceric oxide is produced mainly by a thermal decomposition method of cerous oxalate. However, ceric oxide of this powder is naturally insoluble in water and other solvents, and thus it has been difficult to apply it to, for example, an ultraviolet absorber that requires transparency. Further, in order to improve the transparency, it has been studied to obtain ceric oxide as fine as possible. However, since the powder is a powder, there is a limit to the improvement.

In order to solve such a problem, a technique of supplying ceric oxide in a colloidal dispersion, that is, a sol form, has recently been developed. For example, JP-A-62-38235,
JP-A-62-275021 and JP-A-1-197316 disclose a method for producing the ceric oxide sol.

[0004] In these conventional production methods, a cerium nitrate aqueous solution is heated and destabilized to precipitate ceric oxide containing nitrate, which is redispersed in water to obtain a sol. The sol is obtained by partially neutralizing an aqueous ceric nitrate solution with a basic aqueous solution, but none of these methods is industrially advantageous, and the obtained sol is not satisfactory in quality.

In other words, according to the method described above, the aqueous solution of ceric nitrate as a raw material is used for electrolytic oxidation of cerous nitrate,
Alternatively, it must be obtained by reacting ceric oxide hydrate obtained from a solution of cerous salt with nitric acid, further hydrolyzing this aqueous solution for a long time, and separating the resulting precipitate by solid-liquid separation. Must be re-dispersed in water, and this method is not industrially advantageous. Further, there is also a problem that nitrate groups in the raw material are wastefully discarded as nitrate ions in solid-liquid separation.

According to the method described above, not only is there the same problem in that ceric nitrate is used as a raw material, but also when, for example, ammonia water is used in a basic aqueous solution, the obtained sol is used. There is a problem that ammonium nitrate is contained as a large amount of impurities in the solution. Furthermore,
In JP-A-1-197316, a sol obtained by these methods is used, which is once precipitated with a salt of a monovalent weak acid, and the precipitate is redispersed in water. Has been proposed, but this method is advantageous in that a sol stabilized with an acid other than nitric acid is produced, but the process becomes more complicated, and many by-product impurities are produced industrially. Is disadvantageous.

As described above, any of the conventionally known methods for producing ceric oxide sol requires complicated steps, and as a result, it is difficult to obtain a sol of stable quality. However, at present, it is not always an advantageous method for economic reasons.

[0008]

SUMMARY OF THE INVENTION The present inventors have conducted intensive studies on a method for obtaining a high-quality and stable ceric oxide sol which is economically advantageous through a simple process, and as a result, as a result, Using cerium and an oxidizing agent, a method for producing a sol from a gel obtained by reacting the cerium was found to provide a simple and stable ceric oxide sol, and the present invention was completed based on such findings. It has been done.

[0009]

That is, the present invention provides a method for producing a cerium oxide gel by reacting cerous carbonate with an oxidizing agent and then peptizing the gel with an acid. The present invention relates to a method for producing a cerium sol.

[0010]

The method for producing ceric oxide sol of the present invention will be described in more detail below. In the method for producing a ceric oxide sol of the present invention, first, as a first step, cerous carbonate is reacted with an oxidizing agent to obtain a ceric oxide gel. Cerous carbonate is a powder insoluble in water, but this reaction oxidizes trivalent cerium to tetravalent,
After the reaction, a gel of ceric oxide is formed. Conventionally,
As a method for obtaining ceric oxide, a method for obtaining from cerous carbonate by a reaction using an oxidizing agent is not known, and the present inventors have conducted various studies on this method and found that I got

First, as the raw material cerous carbonate, it is desirable to use as fine a powder as possible, and generally available commercially available cerous carbonate generally has a particle size of about several tens of microns. When this is used, it is preferable to use it after pulverizing it to 10 μm or less. Examples of the oxidizing agent include hydrogen peroxide, ozone, azides such as sodium azide, persulfates such as ammonium persulfate, dichromates such as potassium dichromate, and fluorine. However, among these oxides, it is most preferable to use hydrogen peroxide or ozone in that salts are not by-produced by the reaction. That is, these by-product salts require a separate removal operation in a later stage, and if they remain in the finally obtained sol solution, there arises a problem as impurities.

Next, regarding the use ratio of cerous carbonate and the oxidizing agent, the stoichiometry of the reaction varies depending on the particle size of the cerous carbonate used and the type of the oxidizing agent, although it cannot be said unconditionally. The formula is represented by the following formula Ce ₂ (CO ₃ ) ₃ + XO → 2CeO ₂ + 3CO ₂ + X (where XO indicates an oxidizing agent). What is necessary is just to use so that it may become the ratio of 10 equivalents. In particular, when hydrogen peroxide is used as the oxidizing agent, the reaction equivalent is generally 1 to 20 due to the self-decomposability of hydrogen peroxide.
It is preferable to use in an equivalent range.

Cerous carbonate is insoluble in water, and this powder is slurried with water and subjected to a reaction. Regarding the concentration at that time, the slurry is generally 5 to 20% by weight as CeO ₂ . The temperature during the reaction is not particularly limited, but is generally
In general, the higher the reaction temperature, the shorter the reaction time.However, when the above-mentioned hydrogen peroxide is used, the starting temperature of the reaction is set at 40 to prevent self-decomposition.
It is desirable to carry out the reaction at a temperature of not more than ° C., and to gradually raise the temperature later.

It is most preferable to complete the reaction between the cerous carbonate and the oxidizing agent. However, even if the reaction is not completed, after the subsequent peptization step with an acid, the unreacted residue in the gel is removed. Cerous carbonate can be separated and removed as a cerium salt by using means such as ultrafiltration.

As described above, the reaction between cerous carbonate and the oxidizing agent is performed, and the gel formed by the reaction is then peptized with an acid in the next step. The type of acid used is an inorganic acid such as hydrochloric acid, nitric acid, perchloric acid, or formic acid, acetic acid,
Organic acids such as lactic acid can be used alone or in combination.

The amount of the acid used depends on the type of the acid used, and cannot be unequivocally determined. However, when a strong acid such as hydrochloric acid is used, the amount may be relatively small, and when a weak acid such as acetic acid is used. In this case, the amount becomes large, and the ceric oxide gel is peptized to become a transparent sol. The amount is based on 1 mol of CeO ₂ in the gel.
It is generally in the range of 0.2 to 5.0 moles.

If the amount of the acid used is insufficient,
If the peptization of the ceric oxide gel does not proceed sufficiently and the amount of the acid used is too large, the ceric oxide gel is completely decomposed and a cerium salt is generated, which is not preferable. The resulting sol yield is low.

Regarding the conditions for peptizing with this acid, the reaction is preferably carried out at a reaction temperature of about 50 ° C. or higher, and desirably at about 90 ° C. for a reaction time of 0.1 to 1
0 hours. Further, There is no particular limitation with respect to the concentration of the oxide second Seriumugeru, but the reaction is carried out 1 to 15 wt% as a normal CeO _2, to carry out the reaction at a high concentration as possible is effective. By the method of the present invention described above, a ceric oxide sol can be obtained.

[0019]

The present invention will be further described below with reference to examples of the present invention, but the present invention is not limited to these examples. still,
In the examples, all percentages are by weight unless otherwise specified.

Example 1 Cerous carbonate (CeO ₂ 32.7)
%, Particle size 5 ~ 10μ), water 2139g and hydrogen peroxide water
131 g of (H ₂ O ₂ 34.5%) were added. After stirring at room temperature for 1 hour, the solution was heated to a temperature of 93 ° C., and the reaction was carried out with stirring for another 1 hour.

After the reaction, the product became a yellow-white gel slurry, and the cerium concentration was CeO ₂ 11.4%. The slurry was dried at 60 ° C., and the X-ray diffraction of the obtained powder was measured. As a result, the d values of the main peaks were 3.12, 1.91, and 1.6, respectively.
3 angstroms, and its crystal form is ceric oxide (Cerium oxide).
ianite).

Next, 1239 g of water and 41 g of hydrochloric acid (HCl 35.4%) were added to 1000 g of the ceric oxide gel slurry, and the mixture was heated at a temperature of 90 ° C. for 1.5 hours to perform a deflocculation treatment to thereby oxidize. A second cerium sol was obtained. As a result of analyzing this sol, it was CeO ₂ 5.2% and HCl 0.66%, and it was a transparent and extremely stable sediment-free sol solution.
There was no change after one month.

Example 2 Cerium carbonate (CeO ₂ 51.3)
%, Particle diameter of 50 to 70 μ), to which 2420 g of water was added to form a slurry, which was wet-pulverized for 2 hours using a vibration ball mill (ball diameter: 10 mm). After wet milling, the particle size of the cerous carbonate was 3-6 μm. Next, ozone-containing air (O ₃ 1.1%) generated by an ozonizer was blown into the crushed slurry 1000 g at a flow rate of 200 L / hr at room temperature for 25 hours to carry out a reaction to obtain a ceric oxide gel slurry. .

To this gel slurry, 500 g of water and 52 g of acetic acid were added, and deflocculation treatment was performed while heating at 97 ° C. for 6 hours to obtain ceric oxide sol. As a result of analysis of this sol, it was CeO ₂ 10.3% and acetic acid 3.6%, and it was a transparent sol solution that was extremely stable and free from sediment, and there was no change even if this sol solution was left for one month. Was.

Example 3 To 1000 g of ceric carbonate used in Example 1, 4709 g of water, 521 g of ammonium persulfate and 310 g of aqueous ammonia (NH ₃ 26.3%) were added. The reaction was carried out at 70 ° C. for 2 hours while stirring. In this reaction, the use of aqueous ammonia is intended to neutralize sulfuric acid, which is a decomposition product of ammonium persulfate, and to prevent the formation of a water-soluble cerium salt. After the completion of the reaction, the product was filtered and washed, and washed until no ammonium ion or sulfate ion was observed in the filtrate. The obtained wet cake was suspended in water to obtain 4671 g of a gel slurry of CeO ₂ 7.0% ceric oxide.

Next, nitric acid (HNO ₃ to 1000g of the slurry 6
(7.4%) was added, and the mixture was heated at a temperature of 85 ° C. for 1 hour to perform a peptization treatment to obtain a cerium oxide sol. As a result of analyzing this sol, CeO _{2 was} 7.1% and HNO _{3 was} 2.1%, which was a transparent sol.

Example 4 To 1000 g of cerous carbonate used in Example 2 was added water and hydrogen peroxide solution (H ₂ O ₂ 34.5%) at the ratios shown in Table 1, respectively. After stirring for 6 hours, the solution was heated to a temperature of 93 ° C., and the reaction was carried out with stirring for another 1 hour. After the reaction, the obtained ceric oxide gel slurry was diluted with water until the concentration became CeO ₂ 2.0%, and 461 g of hydrochloric acid (HCl 35.4%) was added thereto. By heating and peptizing, ceric oxide sol was obtained.

The sol conversion ratio of cerium in the sol thus obtained was determined. The method involves ultrafiltration of each ceric oxide sol (using an ultrafiltration membrane with a molecular weight cut off of 10,000), measurement of the Ce3 ⁺ concentration in the ultrafiltrate, and conversion of the cerium sol into sol according to the following equation. The rate was calculated. Solization rate (%) = (1- (Ce ³⁺ concentration in ultrafiltrate /
CeO ₂ concentration × 172/140)) × 100 The results are shown in Table 1.

[0029]

[Table 1]

Each of these sol solutions had an extremely stable and transparent feeling. Further, the sol obtained under the production conditions of No. 1 in Table 1 was subsequently subjected to ultrafiltration,
The concentration of the sol was concentrated to CeO ₂ 30%, and the concentrated sol was also a stable transparent sol.

[0031]

The method for producing ceric oxide sol of the present invention has a simple production process and is very economically advantageous. In addition, the simplicity of the production process makes it easier to obtain a sol of stable quality as a result.

Therefore, the ceric oxide sol obtained by this method is a stable sol solution composed of extremely fine colloidal particles, and is particularly suitable for various ultraviolet absorbing applications utilizing the sol-specific transparency and uniform sol-specific uniformity. It is expected to be used in various fields such as abrasives, catalysts, and ceramic raw materials that make use of fineness, and will create new uses as ceric oxide-based materials.

Claims (2)

(57) [Claims] 1. A method for producing ceric oxide sol, comprising reacting cerous carbonate with an oxidizing agent to produce ceric oxide gel, and pulverizing the gel with an acid. 2. The method for producing ceric oxide sol according to claim 1, wherein the oxidizing agent is hydrogen peroxide or ozone.