JPS61158810A - Production of high-purity silica sol - Google Patents

Abstract

PURPOSE:To obtain a high-purity silica sol, by dealkalinizing a dilute aqueous solution of an alkali metal silicate with an ion exchange resin, removing impurities from the resultant silica liquid by ultrafiltration after acid treatment, and carrying out the growth of silica colloid particles. CONSTITUTION:A 0.5-7wt% aqueous solution of an alkali metal silicate is dealkalinized by contacting with a strongly acidic cation exchange resin to obtain a silica liquid.l An acid is added to the liquid and the silica liquid is subjected to the acid-treatment at <= 2.5pH and 0-98 deg.C. The impurities in the obtained acidic silica colloid liquid are removed with an ultra-filtration membrane having a critical molecular weight of 500-10,000 to obtain a solution of an oligosilicic acid. A part of the solution is added with ammonia or an amine and heated at 7-10pH and 60-98 deg.C to produce a heal sol, and the remaining part of the oligosilicate solution is added slowly and dropwise to the sol to effect the growth of the colloid particles. A silica colloid having a purity of higher than four-nines can be produced from an alkali metal silicate by this process.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for producing a high-purity silica sol that is substantially free of alkali and other impurities, even though it uses an alkali silicate as a raw material.

[Conventional technology and its problems]

Conventionally, what is called high-purity silica contains crystals and silica.
-m treatment, and those obtained by converting these into metal silicon and then chlorinating*1 are known. The former is inexpensive, but has a purity of 99.9% (three nines) at most, while the latter has a high purity of 7 o's and nines or more, but the purification process is complicated and the yield is very low. The cost is high. In order to produce silica sol from these, it is necessary to convert them into alkali silicates by alkali melting. However, the above-mentioned high-purity silica not only has poor alkali bath solubility, but also contains impurities during alkali melting, so this method is not suitable. It is almost impossible to obtain a high purity silica sol.

On the other hand, although white casen and aerosilha have good alkaline bath decomposition properties, their silica purity is about 99%, so even if they are used as raw materials, high purity silica sol cannot be obtained.

In addition, silica sol, which is produced from alkali silica salt by the usual method, such as the silica sol currently on the market,
It is possible to refine the silica by acid treatment and to improve its silica purity to some extent. However, in this type of silica sol, the particle size of the dispersed colloidal particles is about 20 to 100X, and therefore impurities contained in the colloidal particles cannot be removed to a high degree. Therefore, even with this method, it is impossible to improve the silica purity beyond three nines.

The only possible method for obtaining high-purity silica sol is to convert silicon tetrachloride to an alkoxide (e.g., ethyl silicate) and then hydrolyze it in aqueous ammonia, but this method requires a complicated process for raw material preparation. Since this method requires a large amount of alcohol and a large amount of alcohol gold, there is a disadvantage that the cost is extremely high. In addition, in this method, no means has been found to date to adjust the particle size of the colloidal particles as desired, so the reality is that only precipitated silica can be obtained.

[Means for solving problems]

The present inventors used an alkali silicate as a raw material, for which it is impossible to obtain a silica sol of high purity by conventional conventional methods, and dealkalized the dilute aqueous solution with an ion exchange resin to obtain a silicic acid solution. It was then discovered that by treating this with an acid, removing impurities by ultrafiltration, and then growing the silica colloid particles, a silica colloid with a silica purity higher than that of four nines could be obtained.

That is, the method for producing high purity silica sol according to the present invention is as follows:
(1) A silicic acid solution is prepared by dealkalizing an aqueous solution of an alkali silicate with a concentration of 0.5 to 7% by weight by bringing it into contact with a strong cation exchange resin, and was added, and the silicic acid solution was acid-treated under conditions of pH 2.5 and temperature θ to 98°C, and (c) impurities in the obtained acidic silicic acid colloid solution were separated into molecules! 500 to 10,000 (7) Prepare an oligosilicic acid solution by removing it with an ultrafiltration membrane, (d) Add ammonia or amine to a part of this oligosilicic acid Hf8 solution, and heat at a temperature of 60 to 98°C at pH 7 to 10. (e) The remainder of the oligosilicate solution is gradually added dropwise to the heel sol to grow and heat the colloidal particles.

In the method of the present invention, the alkali silicate used as a raw material is not particularly limited, but alkali metal silicates are advantageous in terms of cost and other aspects. Among them, water glass is the most preferred as a starting material because it is produced in large quantities and its chemical and physical properties have been well studied.

810 of alkali silicates. /MtO (where M represents an alkali metal) molar ratio is one of the important factors that determines the particle size of the dispersed colloid in the silicic acid solution obtained in the above step (a). If the molar ratio is less than 0.5, it tends to become ionic silicic acid, making it difficult to separate silicic acid from impurities in the ultrafiltration step (d). Furthermore, if the molar ratio exceeds 4.5, the stability of the silicic acid solution obtained in the step will deteriorate (however, lithium silicate is an example).

Therefore, the si of the alkali silicate used as the starting material
The molar ratio o, , /M, 0 may be in the range of 0.5 to 4.5, preferably 1 to 3.

According to the method of the present invention, the raw material alkali silicate is 0.
It is diluted with water to a concentration of 5-7% by weight and subjected to dealkalization. If the concentration of the alkali silicate aqueous solution is less than 0.5% by weight, the silicic acid solution after dealkalization tends to undergo hydrolysis and form a gel, which is undesirable.If it exceeds 7% by weight, the ion exchange resin Gelation may occur within the layer, making stable operation difficult. The dealkalization treatment is carried out using a strong acid type cation exchange resin, and examples of the ion exchange resin that can be used include Diaion 8-113 and PK208 manufactured by Mitsubishi Chemical Industries, Ltd.

When a weak acid type cation exchange resin is used, there is a large amount of alkali leakage and it is not possible to sufficiently dealkalize the aqueous alkali silicate solution.

Although a mason acid type cation exchange resin is normally used after being regenerated with a regenerating agent corresponding to about 1.5 times the exchange capacity, the ion exchange resin of the present invention can also be used at a regeneration rate of this level. playback
Even if an ion exchange resin with higher s is used, the alkali removal rate is only slightly improved and is not very effective. In addition, the impurities in the silicic acid solution obtained by dealkalization are strongly bound to the silicic acid, so even if it passes through the cation exchange resin layer many times, the amount of impurities cannot be reduced that much, and rather the resin Since multivalent ions are desorbed from the ion, the amount of impurities may increase.

The silicic acid solution obtained by dealkalization using a strong acid type cation exchange resin is then subjected to acid treatment.

In this acid treatment, acid is added to the SilicaR solution, and the pH is set to 2.5,
The colloidal particles in the silicic acid solution are estimated to grow to a size of about 3 mμ, and the impurities contained in the colloidal particles diffuse outside the particles. For acid treatment, hydrochloric acid, sulfuric acid,
Any organic acid such as nitric acid and pKa (5) can be used, but hydrochloric acid is particularly preferred. In the acid treatment of the present invention, the lower the pH, the more effective it is in removing impurities. There is a concern that impurities may come in from the container.
There is a concern that it may promote gelation.

In addition, in the case of acid treatment with I)H>2.5, impurities cannot be sufficiently removed in the next step of ultrafiltration, and the removal rate of trivalent or higher metals in particular decreases. Therefore, p during acid treatment
The H condition is 0 to 2.5, preferably 0.5 to 1.5. As for the temperature conditions, the higher the treatment temperature, the better the impurity removal rate in the next ultrafiltration step, but the lower the colloid stability, so it is appropriate to set it in the range of 0 to 98°C.

The acid-treated silicic acid solution (rR silicic acid colloidal solution) is then subjected to ultrafiltration, whereby ionic impurities in the silicic acid solution are removed. The ultrafiltration membrane used is one that is acid-resistant and does not allow impurities to be eluted from the membrane; for example, a polysulfone membrane manufactured by Asahi Kasei Industries, Ltd. can be used. The molecular weight cutoff is preferably 500 to 10,000, and if it is 10,000 or more, the silicic acid colloid will not be captured well in the membrane and the yield will decrease. When an alkali silicate with a small molar ratio of 810.7M and 0 is used as a raw material, the colloidal particles contained in the acidic silicic acid colloidal solution are also small, so the ultrafiltration membrane has a molecular weight cut-off of pebbles, for example, one with a molecular weight cut off of 500. It is possible to use However, generally speaking, the larger the molecular weight cutoff, the larger the amount of permeated water, and therefore the higher the filtration efficiency. The acidic silicic acid colloid liquid is circulated through, for example, a Holo 7 AINO-type ultrafiltration device, and is discharged from the system through a membrane.
While supplementing with the same amount of pure acidic liquid (pH 0.5 to 1.5) as liquid 1, continue this operation until the amount of pure acidic liquid supplied reaches 20 to 10,000 times the initial acidic silicate colloid liquid. Then, the dispersion medium of the acidic silicic acid colloid liquid is replaced with a pure acidic liquid. After that, the specific conductivity is 0.4μs/
Perform the same ultrafiltration operation as above using pure water of less than cm, and the amount of pure water replenished should be 20 to 100% of the original colloidal solution.
By continuing this operation until reaching 0x,
A highly pure oligosilicate bath solution is obtained.

In the method of the present invention, since the colloid particles dispersed in the acidic silicate colloid liquid are fine (estimated to be about 3 m or 3 g at the most), most of the impurities in the liquid can be removed by ultrafiltration. silica purity can be increased to at least four nines. If a very high purity gold is desired, the silica purity can be increased to five nines or higher by passing the oligosilicate bath solution at 8 V = 5 through a hot bed of anion exchange resin with a regeneration rate of 5 or higher. can be improved. Of course, Fe, AI, and Ti are difficult to remove because they are highly reactive with old metals and easily form solid strong acids.

However, such ions can also be removed by passing through the chelate resin layer.

The high purity oligosilicic acid solution obtained by the above ultrafiltration operation is adjusted to pH by adding high purity ammonia or amine to it.
By adjusting f to 7 to 10 and heating to 60 to 98"C, a heel sol with a colloidal particle size of 5 to 7 mμ is obtained. Highly purified oligosilicate f8 is added to this heel sol while keeping the pH constant. By adding a liquid, colloidal particles can be grown to a desired particle size. Therefore, a part of the high purity oligosilicate solution obtained by ultrafiltration is collected to prepare a seal sol. By adding the remaining high-purity oligosilicic acid solution Xt- to the silica, a high-purity silica sol having a silica purity of four nines or more can be obtained.

Incidentally, the particle size of the silicic acid colloid in the present invention was determined by applying a sample to a sample stand, freeze-drying it, observing it with a transmission electron microscope, and measuring the particle size.

Example 1 [Preparation of oligosilicic acid solution 'fiA] 853 g of No. 3 sodium silicate (silicate ratio 3.1) was mixed with 409 g of water.
This aqueous solution was diluted with 7 g of styrene-based strong acid type cation exchange resin (manufactured by Mitsubishi Kasei Co., Ltd.), which had been regenerated in advance with hydrochloric acid.
IB) A 5% silicic acid solution was obtained by passing the solution through a 117 tube at room temperature. 112,500 g of special reagent grade 35% salt was added to this silicic acid solution and heated at 95°C for 1 hour to obtain an acidic silicic acid colloid solution (
This operation is called f+footing). The pH at this time was approximately O. This liquid is filtered through a flow-type ultrafiltration membrane (made by Layakasei).
8IP-1013 (molecular weight cut off: 6000) was injected into a device incorporating the membrane, and the membrane was operated at an apparent passage speed of 0.9 m/% average filtration pressure of 2 kg/cm, and the amount of filtrated water was 581/cm. I missed it in hr. Oligosilicon Got a solution person.

[Preparation of oligosilicate bath solution B]

Bt was obtained in the same manner as the oligosilicate solution except that the liquid temperature during leaching was set to room temperature.

[Preparation of oligosilicic acid solution C]

An oligosilicic acid solution C4- was obtained in the same manner as the oligosilicic acid solution except that the amount of 35% hydrochloric acid added at the time of leaching was changed to 100 g.

[Preparation of oligosilicate bath liquid]

The liquid temperature during leaching is room temperature, and the acid added is reagent grade 9.
8% sulfuric acid is 150g, and the acid used in the ultrafiltration operation is 9
An oligosilicate solution was prepared in the same manner as the oligosilicate solution iA except that the specified sulfuric acid was used.

[Preparation of oligosilicic acid solution E]

Oligo-silicic acid solution Et was prepared in the same manner as oligo-silicic acid solution A, except that the t of 35% hydrochloric acid added during leaching was 10 g, and the normality of @acid used in the ultrafiltration operation was 0.1.
-I got it.

[Preparation of high purity silica sol]

The above oligosilicic acid solution A290- and specific conductivity o, 1t
Pure water below is/cm 100+114 and reagent special grade 28
%Ammonia water 2Ltt? A heel sol was prepared by mixing and heating to 85"C. Oligosilicate solution A3800
−, ammonia water obtained from ammonia gas 101jf
: The added liquid was added to the above-mentioned heel sol at a rate of 5 m/hr, and after the addition, the silica concentration was concentrated to 20% to obtain silica sol At-. The viscosity of this sol is 1.7 Cp
, specific gravity 1.109, turbidity o,ot cm-', specific surface area of silica 185 m"/g, and the amount of impurities is 2
It was 5 ppm/8 io.

Also, instead of oligo silicic acid solution B,
4 types of silica sol B in the same manner as above.
-Bt-%. The following table shows the conditions for preparing the oligosilicic acid solution used and the amount of impurities in each silica sol.

(Left below) Table 1 Reference Example Example 2 Cation exchange resin regenerated in advance to a regeneration ratio of 5 (8 to -x
B)tA! and anion exchange resin (8 people - 10) 1.5
The oligosilicic acid solution Atl-8v-5f obtained in Example 1 was passed through the mixed bed in which the oligosilicic acid solution Atl-8v-5f was thoroughly mixed. It was lowered to .

When silica sol t' was prepared using this oligosilicic acid solution in the same manner as in Example 1, the amount of impurities was s ppm.
/5ift, and the average particle size of the colloid is 13.6m.
It was μ.

Example 3 Sodium metasilicate (silicon W ratio Q, 5) 853g? :, water 40
This water fB solution was diluted with 97 g and passed through a styrene-based strong acid type cation exchange resin 51 regenerated with all metallurgical hydrochloric acid at room temperature to obtain a 0.7% silicic acid solution. Add 200 g of reagent grade 35% hydrochloric acid to this silicic acid solution (pH at this time was about 0),
The mixture was heated at 5° C. for 1 hour to obtain an acidic silicate colloid solution. This liquid was supplied to a device equipped with a flow-through ultrafiltration membrane (Asahi Kasei 1sIP-1013, molecular weight cut off 500) 1&:, and the apparent passage speed inside the membrane was 0.9 m/s, and the average filtration pressure was 2'. When operated at 47 cm, the amount of filtrated water was 601/h.
Atatsumen with r. Solvent replacement was carried out by injecting 4N hydrochloric acid into a 201T apparatus at the same rate as the discharge rate of the filtrate, and then salt M was added with 501T of pure water with a specific conductivity of 0.1 μs/cm or less.
By substituting , oligosilicate bath liquid Fi was obtained. The average particle size of the colloid contained in this solution is 2 mμ, and the amount of impurities is 5 ppm/8i0. Met.

Next, using this oligosilicone 1w8 liquid, a silica sol was obtained in the same manner as in Example 1, and the impurity t was 7 ppm.
/8i0. The average particle size of the colloid is 14.7 m.
It was μ.

〔effect〕

Conventional silica sol binders used for ceramic phyno ζ-use insulation materials or lost wax are
There were many problems with strength reduction due to softening or cristonolite formation at high temperatures, but as shown in the examples, the silica sol obtained by the present invention has a silica purity of four nines or higher, so it can be used as Even when used as a reader, there is no problem as mentioned above. In addition, since the silica sol obtained in the present invention is of high purity, it can be used as a raw material for synthetic crystals, as an abrasive material for VLSI wafers, and as a raw material for quartz phi-1-1 quartz luze. be able to. Of course, high purity silica can be obtained from the silica sol of the present invention by drying and firing it.

Claims (1)

[Claims] 1. (a) A silicic acid solution is prepared by dealkalizing an aqueous solution of an alkali silicate having a concentration of 0.5 to 7% by weight by contacting it with a strong acid type cation exchange resin, (b) Add acid to this silicic acid solution, pH 2.5 or lower, temperature 0~
A silicic acid solution is acid-treated at 98°C, and (c) impurities in the obtained acidic silicic acid colloid solution are removed with a molecular weight cut-off of 500 to 100.
00 ultrafiltration membrane to prepare an oligosilicic acid solution, (d) Add ammonia or amine to a part of this oligosilicic acid solution, and heat to a temperature of 60 to 98°C at pH 7 to 10 to form a heel sol. (e) Gradually dripping the remainder of the oligosilicate solution into this heel sol to grow colloidal particles. 2. Alkaline silicate SiO_2 used in step (a)
2. The method according to claim 1, wherein the molar ratio /M_2O (where M represents an alkali metal) is in the range of 0.5 to 4.5. 3. The acids used in step (b) are hydrochloric acid, sulfuric acid, nitric acid and p
The method according to claim 1, wherein the organic acid is selected from organic acids having a Ka<5.