JPH038710A - Production of fine silica gel powder having high filterability - Google Patents

Abstract

PURPOSE:To obtain silica gel having excellent filterability and large specific surface area by adding less than equivalent amount of a mineral acid to water- glass, adjusting the concentration of the formed sol, adding the sol to an aqueous solution of an NH4 salt, washing the formed precipitate with a mineral acid and then water and drying the product. CONSTITUTION:Silica sol is formed by adding >=0.05 and <1 equivalent (preferably 0.25-0.5 equivalent) (based on Na2O) of a mineral acid to water-glass (use of water-glass #3 on the market is convenient). The silica concentration in the sol is adjusted to 2-20wt.% (preferably 4-15wt.%) and the sol is added to an aqueous solution of an ammonium salt to precipitate silica gel. The ammonium salt is nitrate, chloride, sulfate, etc., and the amount is 0.5-2.0mol per 1mol of silica in the sol. The formed gel is first washed with a mineral acid to remove Na, Fe, Al, etc., and then with water and dried to obtain the objective silica gel useful as an adsorbent for removing the sediment of liquors, seasonings, etc.

Description

Detailed Description of the Invention 10.Objective of the Invention 1. The present invention is directed to the production of finely powdered silica gel that has excellent filtration properties, has a specific surface area similar to that of conventional silica gel adsorbents, and is considered to have a large adsorption capacity. It is about law.

1. Silica gel has excellent adsorption ability, and is used for draining in the fermentation industry. In this case, finely ground silica gel is often used in a batch process.

Adsorbent or silica gel for white carbon is produced by neutralizing water glass with acid to form a gel, and filtering, washing, and drying this gel.

However, the silica gel produced in this way has poor filterability, and when used as an adsorbent to remove impurities from the product liquid, it takes a lot of time and effort to separate the silica gel from the product liquid. This reduces production efficiency, so it is necessary to take measures such as using a filter aid such as Celite in order to improve filtration performance.Also, it has a large bulk density and is heavy, so it has poor dispersion in the liquid (therefore, it is difficult to adsorb It has drawbacks such as reduced efficiency.

Furthermore, since the silica gel obtained by the above method is in the form of hard granules, a pulverization step is required.

Although there are no patents aimed at producing silica gel with excellent filtration properties, there are
-42218 and JP-A-63-21212 disclose techniques for producing high-purity silica, and it is stated that silica gel produced by these methods has a small bulk density and excellent filterability. ing.

However, since all of these are aimed at producing high-purity silica, Na and Fe in water glass.

Ammonia and an ammonium salt are added to an acidic silica sol obtained by removing A1 and the like using an ion exchange resin to precipitate silica gel. Therefore, equipment for the ion exchange process is required, and since water glass contains about 10% Na20, a large amount of ion exchange resin and a large amount of chemicals for regenerating it are also required, which increases costs.

In addition, unless the water glass is diluted with water to bring the silica concentration to 6% or less and ion exchange is not performed, gelation will occur and blockage will occur, making it impossible to increase productivity.

An object of the present invention is to provide a method for producing silica gel having excellent filterability and a large specific surface area more easily than conventional methods.

1 Structure of the invention 1 The method for producing fine powder silica gel with good filterability according to the present invention for filtering is to add 0.05 equivalent to less than 1 equivalent of mineral acid to water glass based on its alkaline content. to produce silica sol and adjust the concentration of silica in the sol to 2 to 20% by weight, add this silica sol to an aqueous ammonium salt solution to precipitate silica gel, and precipitate mineral acid from this silica gel. It is characterized in that it is washed and then dried.

As the raw material water glass, it is convenient to use commercially available No. 3 water glass.

Examples of mineral acids added to water glass include nitric acid, hydrochloric acid, and sulfuric acid.

The amount of mineral acid added is 0.05 equivalent to less than 1 equivalent, preferably around 0925 equivalent to 0.5 equivalent, relative to the alkali content in water glass, that is, NaaO when No. 3 water glass is used. It's good.

Under acidic conditions in which the amount of mineral acid added is less than 1 equivalent relative to the alkaline content in water glass, no precipitate is formed and a silica sol is formed. The silica concentration in the silica sol is adjusted to 2 to 20% by weight, preferably 4 to 15% by weight.

When this sol is added to an aqueous ammonium salt solution, precipitation occurs instantly. This precipitation reaction proceeds on the basic side and produces a white, finely powdered precipitate.

Examples of ammonium salts include nitrates, chlorides, and sulfates.

The amount of ammonium salt used is 0.0% relative to the silica in the sol.
The range is preferably 5 to 2.0 (molar ratio).

The silica gel precipitate obtained as described above is washed with mineral acids such as nitric acid, hydrochloric acid, and sulfuric acid to remove Na.

Impurities such as Fe and A1 are removed. Washing with water alone is sufficient to remove impurities such as Na, and also reduces the specific surface area of silica gel.

After washing with mineral acid, it is washed with water and dried to form silica gel, but these steps are not particularly different from conventional methods.

In this way, the present invention provides silica gel with excellent filterability and a large specific surface area (Examples 1 to 7 described below).
reference).

If the silica concentration in the silica sol is outside the range of 2 to 20% by weight, the above-mentioned silica gel cannot be obtained. That is, if the amount is less than 2% by weight, the filterability becomes extremely poor (see Comparative Example 3 below). On the other hand, if the amount is 20% by weight or more, the addition of mineral acid does not result in a silica sol, but a lump-like precipitate occurs (see Comparative Example 4 below).

Examples 1 to 3 The equivalent ratio of HNO3/Na2O to No. 3 water glass was 0.
Nitric acid was gradually added dropwise while stirring to give a final silica concentration of 4% by weight. This solution was gradually added dropwise to a 1 mo 1 /Q ammonium nitrate aqueous solution while stirring to form a precipitate, followed by stirring and subsequent ripening. The molar ratio of ammonium nitrate and silica was set to 1.0. Note that these operations were performed at room temperature.

The precipitate was filtered, suspended in 2N nitric acid, filtered, and washed. Next, after suspending in water, filtration and washing are performed, and 120
Silica gel was obtained by drying at °C.

Table 1 shows the properties of the silica gels obtained in Examples 1 to 3.

In Table 1, the filterability is No, 5CM paper, filtration area 10
It is expressed as the time required to filter a slurry of finely powdered silica gel Log in 200 mρ of water under conditions of Cm2 and suction pressure of 5 mmHg.

The shorter the time, the better the filterability.

Comparative Example 1 Table 1 shows the properties of silica gel obtained in the same manner as in Example 1 except that the HN O3 / Na s O equivalent ratio was changed to Ol, that is, no nitric acid was added.

However, this silica gel did not become a fine powder after drying, but was agglomerated granules.

Comparative Example 2 The same process as in Example 1 was carried out except that the HNO3/Na, O equivalent ratio was set to 1.0. However, in this case no precipitate was obtained instantly.

When Celite, which is known for its good filterability, was measured in a similar manner, the value was about 0.2 m1n.

Examples 4 to 7 Nitric acid (HNO3/Na) was added to No. 3 water glass so that the silica concentration was 4.8.1520% by weight, respectively.

(equivalent ratio fixed at 0.25) was gradually added dropwise while stirring.

The steps after dropping this solution into an aqueous ammonium nitrate solution were carried out in the same manner as in Examples 1 to 3, and the properties of the silica gel obtained are shown in Table 2.

Note that Example 4 and Example 2 are the same.

Comparative Example 3 Example 4 except that the silica concentration was 1% by weight
Table 2 shows the properties of the silica gel obtained in the same manner as above.

However, this silica gel was in the form of granules as in Comparative Example 1.

Comparative Example 4 Silica: Processed in the same manner as in Example 4 except that the agricultural content was 25% by weight. However, in this case, the addition of nitric acid caused a lump-like precipitate.

As is clear from Examples 1 to 7, the fine powder silica gel obtained by the method of the present invention has excellent filterability and a large specific surface area.

Comparative Example 5 Silica gel was obtained in the same manner as in Example 2, except that acid washing was not performed after precipitation filtration.

Comparative Example 6 Silica gel was obtained in the same manner as in Example 2, except that after precipitation filtration, acid washing (water washing was performed instead of acid washing).

Table 3 shows the results of measuring the impurity concentrations in the silica gels of Comparative Example 5, Comparative Example 6, and Example 2.

Table 3 ← Beat It can be seen that impurities are significantly reduced by acid washing.

C8 Effect of the invention 1. The white fine powder silica gel obtained by the method of the present invention (1) has excellent filterability, and exhibits filterability equivalent to that of Celite.

■It has a large specific surface area (and is expected to have a large adsorption capacity.

■It is in the form of a fine powder and has a low bulk density, so it has good dispersibility in solutions.

■Low content of impurities such as iron.

Because of these characteristics, it is an adsorbent suitable for removing the liquid in the food field, especially in the fermentation industry of sake, beer, wine, soy sauce, vinegar, mirin, etc.

2. According to the method of the present invention, there is no need for special pretreatment such as desalination using an ion exchange resin or ultrafiltration, so that the manufacturing cost can be significantly reduced.

In addition, in the conventional method, the silica concentration in the water glass must be diluted to 6% by weight or less for ion exchange, but in this paper, the silica concentration can be reduced to as high as 20% by weight, resulting in high productivity. .

3. Since the silica gel produced by the method of the present invention is a fine powder precipitate, it hardly aggregates even when dried, and is dispersed simply by adding it to a solution and stirring it. Therefore, the pulverization process required to make silica gel into a fine powder using the conventional method can be omitted, resulting in a reduction in manufacturing costs.

Claims (1)

[Claims] A mineral acid of 0.05 equivalent to less than 1 equivalent relative to the alkali content is added to water glass to generate a silica sol, and the concentration of silica in the sol is adjusted to 2 to 20% by weight, A method for producing fine powder silica gel with good filterability, which comprises adding this silica sol to an aqueous ammonium salt solution to precipitate silica gel, washing the silica gel precipitate with mineral acid, and then drying it.