JP2694163B2 - Method for producing high-purity silica - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing high-purity silica.
Specifically, it is suitable for use as a packing material for chromatography, electronic material raw material, catalyst carrier, food additive, cosmetic additive (foundation), raw material of high-purity glass for optical fiber and optical glass, and further medical material. The present invention relates to a method for producing high-purity silica containing various impure metal components.

[Prior Art] Demand for highly purified silica has increased in many applications in recent years, but higher purity is desired. For example, when used as a packing material for chromatography, when trace metal impurities such as iron are mixed, the charge on the silica surface increases, which causes peak tailing of polar substances and facilitates adsorption of basic substances. However, the recovery rate and purity of the target substance deteriorate.

Further, when silica is used as a raw material for the semiconductor encapsulant filler, the incorporation of an alkali metal such as Na causes corrosion of the wiring, and the incorporation of radioactive elements such as U and Th causes a soft error. Therefore, high purification of silica filler is required in the field of IC and LSI.

On the other hand, when silica is used as the catalyst carrier, a decrease in purity due to the incorporation of various impure components easily causes a side reaction of the target catalytic reaction, which adversely affects the yield and purity of the target product.

In order to meet such demands in each field, high-purity silica containing various trace metal impurities is required.

Conventionally, silica production methods are generally roughly classified into a dry method and a wet method. The former is a vapor phase decomposition method such as a silicon halide or an alkoxysilane, and the latter is an alkali silicate or an alkoxysilane. Hydrolysis by acid.

As a method for producing high-purity silica by the dry method, for example, the following are known.

A method for producing high-purity silica by spraying a silicon halide, typified by silicon tetrachloride, with a fire onto a refractory target, depositing, melting and growing, and crushing. (JP
No. 58-140,313) A method for producing high-purity silica by further melting high-purity ultrafine silica particles produced by gas phase hydrolysis in a flame of a silicon halide in a flame. (Japanese Patent Laid-Open No. 59
However, these dry methods have the following problems.

 Silica raw materials such as silicon halides are expensive.

When a chlorosilane-based raw material is used as the silicon halide, chloro tends to remain in the product, and it is difficult to reduce chloro.

In the case of chlorosilane type, it is corrosive and flammable,
It is difficult to handle.

On the other hand, as a method for producing high-purity silica by the wet method,
For example, the following precipitation method is known.

An acidic silica sol obtained by treating an aqueous solution of sodium silicate with a cation exchange resin is converted to an alkaline silica sol with ammonia, and this solution is brought into contact with ammonium nitrate to produce coagulated precipitated silica gel, which is acid treated, washed with water, dried and melted. To obtain high-purity silica gel. (JP
60-180,911).

A method in which a sodium silicate aqueous solution is gradually added to a nitric acid aqueous solution to produce precipitated silica gel, and acid treatment, water washing, drying and firing are performed to obtain high purity silica. (JP-A-61-48,422
No.) A chelating agent such as ethylenediaminetetraacetic acid or oxalic acid is reacted with sodium silicate and a mineral acid in the presence of hydrogen peroxide to produce precipitated silica, which is treated with acid, washed with water, dried,
A method of obtaining high-purity silica by firing. (JP-A-61-178,
No. 414 and No. 62-12,608) Fluorine ion is contained in mineral acid or fluorine-containing compound is added to silica sol to produce precipitated silica, which is washed with water, treated with acid, washed with water, dried and fired to achieve high Method for obtaining pure silica. (JP-A-63-21,213 and 63-21,214
However, in all of these methods, alkali silicate is used as a raw material, but in general, since alkali silicate contains various metal impurities, these impurities are also contained in finally obtained silica. To some extent, it was difficult to produce a truly high purity product containing it. For example, although the above method is effective in removing Ti, when the concentration of mineral acid is high, hydrogen peroxide is easily decomposed and the effect of removing other metals is low. Further, in the above method, Al, although the effect of removing Fe is high, according to the additional test results of the present inventors, fluorine remains in the produced silica, the amount is 200ppm in high.
It is hard to call it high purity silica. In addition,
In the case of the method (1), since the produced form of silica is a precipitating silica and only fine particles can be obtained, the range of particle sizes that can be produced is narrow, and solid-liquid separation during dehydration is not good. Moreover, since these products have a remarkably small specific surface area, it was very difficult to use them as an adsorbent, for example.

[Problems and Solutions of the Invention] In view of the above situation, the present inventors efficiently remove various metal impurities when producing high-purity silica using a solution of a silicic acid compound as a raw material, and obtain a truly high-purity silica. As a result of extensive studies on a method for obtaining silica, it was found that various trace metal impurities were removed very well by bringing the solution into contact with a specific chelating agent, resulting in high-purity silica. Found and completed the present invention. That is, the gist of the present invention is that a solution of a silicic acid compound, a silica sol or a silica hydrogel is brought into contact with a chelating agent having a phenolic hydroxyl group and a sulfonic acid group as a ligand, and then silica is obtained using this as a raw material. And a method for producing high-purity silica.

 Hereinafter, the present invention will be described in detail.

Examples of the silicic acid compound used as a raw material in the present invention include:
Examples thereof include alkali silicate, silica sol, silica hydrogel and the like. The case of alkali silicate will be described as an example. Examples of the alkali silicate to be used in the present invention include sodium silicate, potassium silicate, and ammonium silicate. For example, in the case of sodium silicate, commercially available sodium silicate, JIS features 1, 2, 3 No. 4, sodium orthosilicate, sodium metasilicate and the like. In these alkali silicates, Al is generally a few
100-several 1000 ppm, Fe several tens-several 1000 ppm, Ti several tens-several 100 ppm, and impurities such as U and Th, which are α emitters, are contained in the order of several tens-several 100 ppb.

The concentration of the alkaline silicate aqueous solution is usually 1 to 20% by weight, preferably 2 to 10% by weight, as the SiO ₂ concentration. If this concentration is too low, the volume of the alkali silicate aqueous solution to be treated increases, and the refining operation is difficult.
On the other hand, if it is too high, the solution gels when the pH is adjusted by adding an acid to the alkali silicate aqueous solution, which is not preferable. The gelation of this solution depends on the type and amount of the acid used, so the actual concentration of the aqueous alkali silicate solution is selected from the above range depending on the treatment method.

In the present invention, it is an essential requirement to bring the solution of the silicic acid compound as described above into contact with a chelating agent having a phenolic hydroxyl group and a sulfonic acid group as a ligand. That is, by the treatment of the present invention, various metal impurities that could not be sufficiently removed by the conventional purification method can be effectively removed. For example, in the case of Ti, it was possible to remove up to about 10 ppm by repeating the acid washing, but further purification was difficult. In the case of the present invention, it can be reproducibly reduced to an extremely low level.

Further, in the present invention, silica sol or silica hydrogel can be used instead of the silicic acid compound. As the silica sol and silica hydrogel, those obtained by a usual method can be used.

Specific examples of the chelating agent specified in the present invention generally include chromotropic acid, tyrone, 5-sulfosalicylic acid, oxine-5-sulfonic acid and the like and soluble salts thereof (sodium salt and the like). You may use together 2 or more types of these compounds. The amount of the chelating agent added is appropriately selected depending on the raw material silicic acid compound, the content of metal impurities in the silica sol or silica hydrogel and the target purity of silica, etc. It is selected from the range of 0.1 to 20% by weight with respect to the acid and alkali.

Furthermore, in the present invention, together with the chelating agent, ethylenediaminetetraacetic acid, thiomalic acid, oxalic acid, citric acid,
It is also effective to use a chelating agent such as salicylic acid and a soluble salt thereof (sodium salt, calcium salt, etc.) in combination. The amount of this chelating agent used cannot be generally stated, but it is usually relative to chelating agents such as chromotropic acid, tyrone, 5-sulfosalicylic acid, oxine-5-sulfonic acid and their soluble salts (such as sodium salts). 0.
It is about 2 to 2 times by weight, preferably about 0.3 to 1 times by weight.

The contact treatment between the solution of the silicic acid compound and the chelating agent is
Usually, a predetermined amount of the chelating agent is added to the solution and kept under stirring, but it is preferable that the chelating agent is dissolved in water and gradually added (for example, over 30 minutes) because the purification effect is large.

In the present invention, silica is produced from the raw material that has been subjected to the above contact treatment, but this method is not particularly limited,
Various methods can be adopted according to known methods. In short, the most important point of the present invention is to bring the raw material into contact with the chelating agent, and there is no particular feature in the subsequent steps. Therefore, in the case of an aqueous alkali silicate solution, a high purity silica can be obtained by mixing with a mineral acid to form a hydrogel and then washing and drying the same in a conventional manner. At this time, the method of mixing the alkaline silicate aqueous solution and the mineral acid is usually added with the alkaline silicate aqueous solution in the mineral acid and reacted in an acidic region,
Alternatively, a method in which both are simultaneously mixed so that the mixture is in the acidic region is desirable. The pH at this time is usually 2 to 6, preferably 3 to 5.

After gelation, in some cases, it is preferable to carry out a dipping treatment with a mineral acid solution for washing, and this treatment further elutes and removes metal impurities that could not be removed by chelation. Next, it is washed with ion-exchanged water. At this time, if ion-exchanged water containing a chelating agent is used, the washing effect is particularly large and desirable.
Note that these washing operations can be repeated twice or more as necessary.

High-purity silica can also be obtained by separately treating the silica sol and silica hydrogel with a chelating agent.

The silica thus obtained is dried and recovered as high-purity silica.

EFFECTS OF THE INVENTION According to the present invention, a solution of a silicic acid compound, silica gel or silica hydrogel is brought into contact with a specific chelating agent, and as a result, highly pure silica having extremely low content of various metal impurities is obtained. be able to. Therefore, the silica obtained in the present invention can be widely used as a packing material for chromatography, an electronic material raw material, a catalyst carrier, a food additive, a cosmetic additive, a high-purity glass for optical fiber and a raw material of an optical glass, and a medical material. it can. Further, since porous silica gel can be produced in the present invention, further,
It can be used for various purposes.

[Examples] Next, the present invention will be described more specifically, but the present invention is not limited to the description of the following examples unless it exceeds the gist.

Example 1 Commercially available sodium silicate aqueous solution (SiO ₂ concentration 27.0% by weight,
Na ₂ O concentration 8.2%) 30 ml was taken and stirred.

Separately, 0.5588 g of ETA (disodium ethylenediaminetetraacetate, Kanto Chemical Special Grade) and 0.6005 g of disodium chromotropic acid (Merck Special Grade) are ion-exchanged water 90.5 ml.
And was gradually added to the sodium silicate aqueous solution over 30 minutes. The stirring was continued for about 5 hours and the color changed to reddish brown.

This solution was added to 29.5 ml of (1 + 9) sulfuric acid aqueous solution, and NH
_The pH was adjusted to 3.0 with a ₄ OH aqueous solution and then raised to pH 4.0. After stirring well, this aqueous solution was kept at 80 ° C. for 1 hour for gelation.

This silica hydrogel was finely crushed, washed with about 5 parts of ion-exchanged water, and then put into 200 ml of 5N HCl for about 2 parts.
The temperature was kept at 80 ° C. and the mixture was stirred at room temperature for 8 hours. After washing with about 25 ion-exchanged water containing 1 mM oxalic acid, it was washed with about 25 ion-exchanged water and dried in an oven dryer.

 The content of impurities in silica is shown in Table 1 below.

As is clear from Table 1, each impurity element in silica was 25 ppm or less in total, and U.Th was 0.1 ppb or less, and low-radioactive high-purity silica was obtained.

When the pore distribution of this sample was examined by BET measurement, it was porous silica gel as shown in FIG. In the figure, SA is the specific surface area per 1 g of silica (m ² / g), and PV is the pore volume per 1 g of silica (ml / g).

Example 2 Commercially available sodium silicate aqueous solution (SiO ₂ concentration 27.0% by weight,
Na ₂ O concentration 8.2 wt%) 30 ml was taken and stirred.

Separately, 0.6149 g of calcium disodium ethylenediaminetetraacetate (manufactured by Wako Pure Chemical Industries, Ltd.) and 0.6012 g of disodium chromotropic acid (Merck special grade) are added to ion-exchanged water 90.5 m.
It was dispersed in 1 l and gradually added to an aqueous sodium silicate solution over 30 minutes. After stirring for 5 hours, the color changed to reddish brown.

This solution was added to 29.5 ml of (1 + 9) sulfuric acid aqueous solution and NH ₄ O was added.
The pH was adjusted to 3.0 with an aqueous H solution and then raised to pH 4.0. After stirring well, this aqueous solution was kept at 80 ° C. for 1 hour for gelation.

The silica hydrogel was finely pulverized, washed with about 5 of ion-exchanged water, and then placed in 200 ml of 5N HCl and immersed at room temperature overnight. Then, it was washed with about 40 ion-exchanged water and dried in an oven dryer.

 The content of impurities in silica is shown in Table 1 below.

Example 3 Commercially available sodium silicate aqueous solution (SiO ₂ concentration 27.0% by weight,
Na ₂ O concentration 8.2 wt%) 30 ml was taken and stirred.

Separately, 0.6005 g of disodium chromotropic acid (Merck special grade) was dispersed in 90.5 ml of ion-exchanged water and gradually added to the sodium silicate aqueous solution over 30 minutes. The stirring was continued for about 5 hours and the color changed to reddish brown.

This solution was added to 29.5 ml of (1 + 9) sulfuric acid aqueous solution and NH ₄ O was added.
The pH was adjusted to 3.0 with an aqueous H solution and then raised to pH 4.0. After stirring well, this aqueous solution was kept at 80 ° C. for 1 hour for gelation.

The silica hydrogel was finely pulverized, washed with about 5 of ion-exchanged water, and then placed in 200 ml of 5N HCl and immersed at room temperature overnight. Then, it was washed with about 40 ion-exchanged water and dried in an oven dryer.

 The content of impurities in silica is shown in Table 1 below.

Examples 4 to 5 In the method of Example 1, the chelating agent of the present invention was changed to the same amount of Tyrone or 5-sulfosalicylic acid, and otherwise the content of impurities in silica when the silica was produced by exactly the same method. Is shown in Table 1 below.

Comparative Example Commercially available sodium silicate aqueous solution (SiO ₂ concentration 27.0% by weight,
Na ₂ O concentration 8.2 wt%) 30 ml was taken and stirred.

90.5 ml of ion-exchanged water was gradually added to the sodium silicate aqueous solution over 30 minutes. The stirring was performed for about 5 hours.

This solution was added to 29.5 ml of (1 + 9) sulfuric acid aqueous solution and NH ₄ O was added.
The pH was adjusted to 3.0 with an aqueous H solution and then raised to pH 4.0. After stirring well, this aqueous solution was kept at 80 ° C. for 1 hour for gelation.

The silica hydrogel was finely pulverized, washed with about 5 of ion-exchanged water, and then placed in 200 ml of 5N HCl and immersed at room temperature overnight. Then, it was washed with about 40 ion-exchanged water and dried in an oven dryer.

 The content of impurities in silica and others are shown in Table 1 below.

As is clear from Table-1, Ti53ppm, Al56p in silica
pm etc remained.

Example 6 1000 ml of pH 1.2 silica sol (5.0% by weight as SiO ₂ ) was stirred and aqueous ammonia was added to adjust the pH to 2.0.

After stirring well, this aqueous solution was kept at 80 ° C. for 2 hours for gelation.

Subsequent operations were the same as in Example 1 to produce silica.

Impurities in the silica at this time were Al 12ppm Ca 0.49p
pm Cr 0.081ppm Fe 2.3ppm Mg 0.16ppm Na 0.6
8ppm Ti 40ppm V 0.47ppm Zr 2.3ppm, but silica sol with pH 1.2 (5.0wt% as SiO ₂ ) 1000ml
Was added to 50 ml of a solution of sulfuric acid adjusted to pH 1.2 with 4,0011 g of disodium chromotropic acid salt and treated in the same manner.
10ppm Ca 0.43ppm Cr 0.065ppm Fe 1.9ppm Mg
0.086ppm Na 0.62ppm Ti 22ppm V 0.27ppm Z
r Reduced to 2.0 ppm.

Example 7 200 ml of silica hydrogel (5.0 wt% as SiO ₂ ) was washed with about 40 ion-exchanged water and dried at 180 ° C.
l 13ppm Ca 1.2ppm Cr 0.092ppm Fe 1.9ppm Mg
1.9ppm Na 2.2ppm Ti 6.0ppm V 0.076ppm Zr
It was 0.50 ppm.

200 ml of the same silica hydrogel (5.0 wt% as SiO ₂ )
10 mM of each was dissolved in about 25 ion-exchanged water in which disodium chromotropate and disodium calcium ethylenediaminetetraacetate were dissolved and brought into contact with each other. Then, it was washed with ion-exchanged water 15 and dried at 180 ° C., and then it was reduced to Al 8.7 ppm Ca 1.0 ppm Cr 0.090 ppm Fe 1.9 ppm Mg 0.27 ppm Na 1.9 ppm Ti 4.0 ppm V 0.052 ppm Zr 0.33 ppm.

[Brief description of the drawings]

FIG. 1 is a graph showing the pore size distribution of silica obtained in Example 1 of the present invention.

Claims (3)

(57) [Claims] 1. A method for producing high-purity silica, which comprises bringing a solution of a silicic acid compound into contact with a chelating agent having a phenolic hydroxyl group and a sulfonic acid group as a ligand, and then using this as a raw material to obtain silica. . 2. A method for producing high-purity silica, which comprises contacting silica sol or silica hydrogel with a chelating agent having a phenolic hydroxyl group and a sulfonic acid group as a ligand, and then using this as a raw material to obtain silica. 3. A chelating agent which is used in combination with at least one chelating agent selected from sodium ethylenediaminetetraacetate or calcium ethylenediaminetetraacetate, thiomalic acid, oxalic acid, citric acid and salicylic acid. The method for producing high-purity silica according to claim 1 or 2.