JPS59232911A - Manufacture of silica gel - Google Patents

Abstract

PURPOSE:To manufacture silica gel having >=about 400m<2>/g specific surface area and absorbing oil by >=about 130ml/100g by reacting an alkali metallic silicate with a mineral acid under specified conditions in two steps. CONSTITUTION:An aqueous soln. of an alkali metallic silicate such as sodium silicate is reacted with a mineral acid such as sulfuric acid at 30-100 deg.C, 1.5- 5pH and 12-25wt% concn. of SiO2 in the reactive liq. for about 5-30min. An alkali metallic silicate soln. is further added, and they are reacted at 30-100 deg.C, 6-10pH and 12-25wt% concn. of SiO2 for about 5-30min. The resulting reaction product is separated by filtration, washed, dried, and pulverized to obtain silica gel.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for obtaining silica gel by the reaction of an alkali silicate with a mineral acid, in particular its specific surface area.

The present invention relates to a method for obtaining silica gel with high oil absorption.

The chemical formula of silica gel is 5in2-XH2O (X=0.
1 to 04), and structurally it is classified as gel-like silica like white carbon, and is used for various purposes. These silica gels are required to have desired physical properties suitable for each use. For example, for toothpastes, emphasis is placed on abrasiveness and refractive index, for pigments, thixotropic properties and apparent specific gravity are important, and for fillers for rubber and plastics, of course, improvement of physical strength is important. For use, specific surface area is a measure of physical properties and potassium,
This allows approximately the drying properties to be adjusted. In this way, the physical properties required for each type of Ti are different depending on their use, but in general, quality is determined by the apparent specific gravity of 1.
Determined based on surface area, oil absorption, etc.

There are primary factors that govern the physical properties described above, including specific surface area and oil absorption.

■ Raw material concentration and B102 concentration in the reaction solution O Reaction temperature, pH during reaction 1 puO neutralization rate at the end of reaction O Type and concentration of electrolyte ■ Stirring speed θ Reaction method For example, adjusting the specific surface area is a factor of eD-○ All of these have an influence, but the @ items, reaction temperature and T)H at the end of the reaction, are particularly dominant. If the reaction temperature and other conditions are the same, and the reaction temperature and other conditions are the same, 'p' and 'I' at the end of the reaction are 500 to 700 I/S'.

300-400 m/? at pH 6-7? , it becomes 200-300 mi'/fI when finished at pH 8-9. These values vary slightly depending on factors other than pH at the end of the reaction, but in general, the specific surface area is high when the reaction is completed in an acidic state, while it is moderate when the reaction is completed in an acidic state.
On the alkali side, silica with a low specific surface area is obtained. This is thought to be due to the fact that when produced on the acidic side, dense silica containing very small primary particles is obtained, and small pores are formed at the contact points between these missing particles. Also.

It is thought that the silica produced on the alkaline side produces larger primary particles than the silica produced on the acidic side, and these aggregate to form secondary particles.

Therefore, it is considered that the number of pores is greater on the acidic side per unit weight, and silica with a larger specific surface area is inevitably obtained.

Based on the above considerations, when considering oil absorption, which is a physical property that affects the specific surface area and the properties of silica, it can be easily inferred that silica with a larger specific surface area will have less oil absorption if the particle size is the same.

In other words, silica with a large specific surface area has a small pore diameter, so oil and other liquid molecules cannot be adsorbed.

It is thought that the oil absorption amount increases simply because the surface of the secondary particles is wetted.

This is clearly shown in FIG. 1, which shows the results of an investigation of the relationship between the specific surface area and oil absorption of each commercially available silica. That is, although there is not necessarily a correlation between the specific surface area and the oil absorption amount, when the oil absorption amount is 140 m1/100f or more, the specific surface area is 250 to 550 m'/g.

In addition, according to Japanese Patent Publication No. 56-22809, the pH of the mixed system remains constant for most of the time from the start of mixing of the silicate to the monobasic acid above the current level. 1. React under conditions such as 3 to 5,
A method has been shown in which a solution containing a water-soluble polyvalent metal salt and insoluble finely powdered silicic acid are generated, and then the insoluble finely powder is separated and washed if necessary.The physical properties of the silica obtained by this method are Is the specific surface area 130~250rr? /Y
The oil absorption amount is 105 to 185 d/1009, and although the oil absorption amount is relatively large, the specific surface area is small.

Many other methods for producing silica have been proposed, but most silicas have a small specific surface area when their oil absorption is high, and it is difficult to obtain silica with a large specific surface area and high oil absorption. It had been. There is no manufacturing method that simultaneously satisfies these two contradictory physical properties.
A method for producing silica with an oil absorption of 110 yl/100 f at rt/S' and a specific surface of s541 m''/?
Although methods for obtaining silica with high oil absorption and large specific surface area have been disclosed, these manufacturing methods are technically very complex or use expensive organic solvents. It had Therefore, the present inventors conducted extensive research into whether silica that simultaneously has a high oil absorption amount and a large specific surface area could be easily produced by a reaction between an alkali silicate and a mineral acid, and found that the 5102 concentration in the reaction solution was 12. ~
In the range of 25 wt%, the reaction temperature is 50°C or higher, and the pH during the reaction is
pH 1.5-5.0 in the first stage and pH 6-5.0 in the second stage
The specific surface area is 400 m by adjusting the method in two steps.
The present invention was achieved by discovering that silica gel having an oil absorption of r3o7/1oof or more can be easily obtained.

To explain the present invention in detail, first, an alkali metal silicate solution and a mineral acid are mixed in a reaction solution with an S1O of 9 degrees of 12 to 25 wt%,
The reaction mixture is blended so that the pH of the reaction solution is 1.5 to 5.0, and the reaction is carried out by mixing and stirring while keeping the temperature at 50° C. or higher.

After about 5 to 30 minutes, an alkali metal silicate solution is further added to adjust the pH of the reaction solution to 6 to 10, and
While adjusting the 5i02 concentration to be in the range of 12 to 25 wt%, mixing and stirring are continued for an additional 5 to 30 minutes, washed with filtered water, dried, and pulverized to obtain a product.

Initially, the reactant was in the form of a viscous gel.

When this is stirred and mixed, it gradually becomes a porridge-like gel, but when an alkali silicate is added and mixed, it becomes a dry gel-like mixture with reduced water content. When acid is added to this, it becomes a porridge-like gel-like substance again, and water leaches out. In this way, the reaction progresses in a viscous gel-like state, so it is preferable to use a powerful mixer of the kneader type, such as a kneader, double roll screw mixer, or high-speed mixer, to ensure uniform mixing. .

The reaction can be carried out either continuously or batchwise.

The alkali silicate base used in the present invention includes Na, K
, TJI are mentioned, but sodium silicate is generally used. Also, mineral acids are nitric acid and phosphoric acid.

There are hydrochloric acid, sulfuric acid, etc., but sulfuric acid is generally used.

Further, although the concentration of the raw materials used is not particularly specified, the mineral acid and the alkali silicate are diluted and used so that the SiO□ concentration during the reaction is 12 to 25 wt%.

In this case, when using an acid with a large heat of dilution such as sulfuric acid as the mineral acid, it is easier to control the reaction temperature if the sulfuric acid is diluted and cooled in advance. The concentration of 8102 during the reaction is preferably 15 to 20 wt% of the alkali silicate.

It is better to add mineral acid; if it is more or less than this, the mixability will be poor and the quality will not be constant. In particular, if it is less than 12 wt%, depending on the pH, silica gel, which is the object of the present invention, such as silica sol, cannot be produced. In addition, for 25wt or more, practically commercially available mineral acids,
and cannot be adjusted by the concentration of alkali silicate,
In this case, specially manufactured raw materials are required, resulting in high costs, which is not preferable.

In the present invention, pH adjustment is carried out by adjusting the mixing ratio of mineral acid and alkali silicate, and this pH adjustment is the most important factor that influences the physical properties of silica. That is, even if the pH at the end of one reaction is the same, if the pH at the beginning of the reaction is different, silicas exhibiting different specific surface areas and oil absorption amounts can be obtained. Conversely, the same applies when the pH at the end of the reaction is different even if the initial stage of the reaction is the same. For example, the initial reaction pH is 1.5~
Comparing the case where the pu was adjusted to 2.0 and the pu at the end of the reaction was 6 to 7 and the case where it was 9 to 10, the former had a specific surface area of 680.
The oil absorption amount was 130 m''/100 f at m''/f, and the latter had an oil absorption amount of 260 m/100 f at a specific surface area of 540 mV.The relationship between this pH adjustment and the specific surface area oil absorption is shown in Figure 2.
It is shown in Figure 3. As described above, T)H at the initial stage of the reaction and pH at the end of the reaction greatly influence the physical properties of silica. next,
Let's talk about reaction temperature. Since this reaction generates heat due to the neutralization reaction of alkali and acid, it must be cooled if it is carried out at a high concentration as in the present invention. Therefore, if the temperature is set too low, there is an engineering problem in that the cooling area of the reactor must be large. In addition, in terms of silica physical properties, the pH at the time of reaction, the same pH, depending on the 5i02 concentration,
At the same -SiO□ concentration, when the temperature is below 30℃, it is 9
- BET surface area and oil absorption tend to be small at 30-40℃
When comparing temperatures around 80 to 90℃, if other conditions are the same, the oil absorption tends to be higher at 80 to 90℃, and the 5BET surface area tends to be smaller.This relationship is shown in Figures 4 and 5. show.

As described above, according to the method of the present invention, silica gel having a specific surface area of 400 m'/ or more and an oil absorption amount of 1'30+u/Ion' or more can be produced very easily by making slight changes to the reaction conditions. You will be able to get
This is an extremely industrially excellent invention. The silica gel obtained by the method of the present invention can be crushed to a particle size comparable to that of white carbon, and can be used as an adsorbent, a desiccant, a toothpaste base material, a rubber plastic filler, and a thickener for paint and ink.
Paper matte ring-opening conventional silica gel.

It can be used in all fields where white carbon is used.

Next, the present invention will be explained in more detail with reference to Examples.

-I〇- Example 1 Sodium silicate (SiOs/Naz, O molar ratio 3.I,
Sin.

The solution (concentration: 29% by weight) and sulfuric acid were continuously supplied. The sulfuric acid concentration at this time was adjusted so that the Sj, 02 slurry concentration at the beginning of one reaction was 16% and 2%. In addition, by changing the addition ratio of sodium silicate and sulfuric acid, the pH at the beginning of one reaction was 1.5.
, 3.0 and 5.0. Then, sodium silicate was added to the latter half of the continuous kneader, and T)H was added in amounts of 6 to 7, 7 to 8, and 9 to 10, and mixed well. Note that warm water was flowed through the jacket part of the continuous kneader to maintain a reaction temperature of 50°C.

The reaction product thus taken out from the continuous kneader was filtered, washed with water, dried and pulverized, and the specific surface area, oil absorption, and apparent specific gravity of the silica were measured. The results are shown in Table 1 and FIGS. 2 and 3.

The oil absorption was measured by the method of ASTM-D281-31, the specific surface area indicates the BIT surface area, and the measuring device was Shimadzu-Micromeritics specific surface area automatic measuring device 2.
Measured with a 200 model.

Table 1 Example 2 Sodium silicate (S i O! /Na!, O-E ratio 3.10
SiO, concentration 29% by weight) and 80% thiosulfuric acid were added simultaneously. At this time, the proportion of sodium silicate and sulfuric acid added was such that the pH of the reaction product was 2. When the number of reactants reached approximately 11, the addition of sodium silicate and sulfuric acid was temporarily stopped, and mixing was continued for 5 minutes. Thereafter, sodium silicate was added to obtain T)H9. The reaction temperature at this time was adjusted to 15°C, 40°C, and 80°C by flowing cold water or hot water through the jacket. After the addition of sodium silicate is complete,
After mixing for 0 minutes, the reaction product was taken out, filtered, washed with water, dried, and crushed, and the physical properties at that time were measured.
It is shown in the table, FIGS. 4 and 5. In addition, a part of the reaction product was collected, and 810. When slurry concentration was measured 2
It was 5wt%.

Table 2 Example 3 Capacity 2I1. Kneader (with jacket) and potassium silicate (
S 10. / to 20 molar ratio: 3. I, SiO, concentration 25
h) and 98 thiosulfuric acid were added continuously.

13- The ratio of potassium silicate and sulfuric acid added at this time is P of the reaction product.
It was added so that H was 2. When the number of reaction products reached about 12, the addition of potassium silicate and sulfuric acid was temporarily stopped and mixing was continued for 5 minutes. The temperature during the reaction was maintained at 25° C. by flowing cold water through the jacket. Thereafter, potassium silicate was added to adjust the pH at the end of the reaction to 9.5, and the reaction was carried out for 15 minutes while keeping the temperature at 90°C. At this time, the concentration of Sin in the reaction product and the slurry was 25 wt%. After that, it was washed in a pot, washed with water, dried, and crushed to have a specific surface area of 510 m/f and an oil absorption amount of 500 w1.
/ 100 f.

Silica gel with an apparent specific gravity of 0 and 15 f'/Co was obtained.

As in Examples 1 and 2, the condition during the reaction of Gao 1 was like a mound when the pH was low, and the mixing was about 100% good.
As the rH was increased, the viscosity increased and the mixture became sticky and the mixability deteriorated. Therefore, the kneader was designed to have a residence capacity and residence time that would allow sufficient mixing.

14- Example 4 The reaction was carried out under the same conditions as in Example 3, except that potassium silicate and sulfuric acid were diluted so that the Sin and slurry concentration at the end of the reaction were 13%. As a result, the specific surface area was 530%.
m/f oil absorption 2 pieces 5 pieces were obtained.

Comparative example! The reaction was carried out in the same manner as in Example 3, except that potassium silicate was added to adjust the pH to 11 at the end of the reaction.

5t-O at this time! The measurement results of slurry concentration, oil absorption, and specific surface area are shown.

S10, slurry concentration 23, 5 wt% specific surface area 350yl/f oil absorption 3
1 5 ml/100 f Comparative Example 2 Sodium silicate (Sin,/N a
, 0 molar ratio 5.1, EIiO, concentration 15%) and 1
0.03 sulfuric acid was added at the same time. At this time, the ratio of sodium silicate and sulfuric acid was adjusted so that the pH of the reaction product was 2.0. Further, the reaction temperature was 40°C. The state at this time was completely different from that in the example; at the start of the reaction, it was in a di-solution state of silica sol, but as time passed, it became gel-like. Thereafter, while maintaining the reaction temperature at 40° C., sodium silicate was added to adjust the pH to 8, and the mixture was mixed for 15 minutes.The resulting mixture was starch syrup-like. In this case, the Sin slurry concentration was 9 wt%.

As in the example, the specific surface area was determined by wading, washing with water, drying, and pulverizing.
When I measured the oil absorption amount, it was 450rr each. /f
, 120m/1oor.

Comparative Example 3 Same as Comparative Example 2, but the pH at the end of one reaction was set to 5.0. At this time, the Sin and slurry concentrations were 8.7 t, and when the specific surface area and oil absorption were measured, they were 64.
It was 9m7f, 110d/100IF.

[Brief explanation of drawings]

Figure 1 is a graph showing the relationship between specific surface area and oil absorption of commercially available silica, Figure 2 is a graph showing the relationship between specific surface area and reaction pH, Figure 3 is a graph showing the relationship between oil absorption and reaction pH, and Figure 3 is a graph showing the relationship between oil absorption and reaction pH. FIG. 4 is a graph showing the relationship between reaction temperature and specific surface area, and FIG. 5 is a graph showing the relationship between reaction temperature and oil absorption. Patent applicant: Central Glass Co., Ltd.

Claims (1)

[Claims] In a method for producing silica gel by the reaction of an alkali metal silicate and a mineral acid, B10. Concentration 12-2
5wt Chi 1 reaction temperature 50~! A method for producing silica gel, which comprises carrying out the reaction at 00°C and adjusting the pH of each reaction solution in two stages such that the pH of each reaction solution is 1.5 to 5.0° in the first stage and 6 to 10 in the second stage.