JPS62113713A - Production of silica gel - Google Patents

Abstract

PURPOSE:To produce silica gel having narrow pore size distribution and uniform and stable quality, in high reproducibility, by treating a specific silica hydrogel with an acid, washing with water and subjecting to hydrothermal treatment in a buffering aqueous solution under controlled pH condition. CONSTITUTION:An aqueous solution of sodium silicate of JIS No.3 grade is made to react with a mineral acid such as sulfuric acid, phosphoric acid, etc., at 0-30 deg.C to obtain a silica hydrosol having a pH of 3.0-6.0 and an SiO2 concentration of 4-20wt%. The sol is converted to a silica hydrogel by leaving stand at room temperature for >=10hr or dispersing in a non-aqueous organic solvent to effect the gelation of the sol. The silica hydrogel is optionally crushed, treated with an acid in a mineral acid solution of <=2.5 pH at >=50 deg.C for 1-5hr and washed with water until the pH of washing water becomes >=3.5. The obtained silica hydrogel is adjusted to 4-9 pH in a buffering aqueous solution of a phosphate or a citrate, subjected to hydrothermal treatment at 50-200 deg.C for 0.5-100hr, washed with deionized water to completely remove salts, etc., and dried at 100-150 deg.C.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a method for producing silica gel of stable quality.

(Prior Art) Silica gel has been widely used as a moisture absorbent, a desiccant, etc. since ancient times, and recently, as it has been used as a catalyst carrier, a chromatography filler, etc., the quality required for it has become stricter. For example, when used as a packing material for chromatography, the pore diameter, pore size distribution, pore volume, etc. of silica gel greatly influence the separation performance of chromatography, and the mechanical strength is related to the life of the packing material. In particular, since silica gel is an amorphous substance, its physical properties such as surface area, pore volume, and pore diameter/mechanical strength can be easily adjusted by changing the manufacturing method and conditions. However, because there are so many factors that control these physical property values, it has been extremely difficult to produce silica gel with constant performance with good reproducibility.

Generally, silica gel is produced by gelling a silica sol produced by a reaction between sodium silicate and a mineral acid, and then washing, filtering, and drying the silica sol. At this time, in order to produce silica gel with large pore capacity, silica hydrogel is heated at high temperature and high pH.
A method of hydrothermally treating silica hydrogel in water, a method of treating silica hydrogel with an organic acid (Japanese Unexamined Patent Publication No. 44-23011), and a method of treating silica hydrogel with an acid after hydrothermal treatment (Japanese Unexamined Patent Publication No. 58/1989)
-135119) are known, but they are still insufficient in terms of stabilizing quality.

(Object of the Invention) In view of the above points, an object of the present invention is to provide a method for producing a homogeneous, stable, and reproducible silica gel with a narrow pore distribution.

(Structure of the Invention) The present invention consists of gelling a silica hydrosol produced by a reaction between an aqueous alkali silicate solution and a mineral acid, and treating the obtained silica hydrogel with an acid solution having a pH of 2.5 or less.
This is a method for producing silica gel of stable quality, which is characterized in that after washing with water, the pH is adjusted to 4 to 9 in an aqueous solution having a buffering action and hydrothermal treatment is performed.

As the alkali silicate used in the present invention, an aqueous solution of sodium silicate or potassium silicate is preferable, and the most preferable one is an aqueous solution of sodium silicate of JIS3@ from the viewpoint of cost and the small amount of acid required for neutralization. . As the mineral acid to be reacted with the alkali silicate, polybasic acids such as sulfuric acid and phosphoric acid are preferred, and more stable hydrosils can be obtained.

If organic acids remain in the final product and are used, for example, in the filling of chromatography, they may cause noise in the graph of Chlore 1, so they are not suitable. The final pH of the silica hydrosol produced by this reaction is 3.0-6. O9
Preferably it is adjusted to 4.0 to 5.5. If it is less than this range, it will take a long time for the silica hydrogel to develop its mechanical strength, making it difficult to handle in subsequent steps. Moreover, if it exceeds this range, the gelation time becomes extremely short, which tends to produce partially non-uniform areas, making it difficult to produce homogeneous hydrosil.

The generation temperature of hydrosil is 0 to 30°C, especially 5 to 20°C.
A range of is preferred.

The SiO2 concentration in the final hydrosil state is 4-20
The raw material concentration is adjusted to be 5% to 10% by weight, preferably 5% to 10% by weight. S! If the 02 IiI degree is too small, the mechanical strength of the hydrogel will decrease and the strain of the gel matrix will increase, making the final silica gel product brittle, and the Si
If 026 degrees is too large, heterogeneous hydrosils are likely to be produced.

The silica hydrosol thus produced can be dispersed in a non-aqueous organic solvent to form a spherical silica hydrogel. Alternatively, the silica hydrosol can be left as it is to form a block-shaped silica hydrogel, and the shape of the hydrogel can be varied depending on the use of the product.

The formed hydrogel is usually left standing at air temperature for 10 hours or more until its mechanical strength becomes sufficiently high.

The formed silica hydrogel is left as it is in the spherical form, and crushed into a predetermined size in the block form.
Acid treatment is performed in an acid solution of 2.5 or less at a temperature of 50°C or higher, preferably 80°C or higher for 1 to 5 hours.

The rR bath solution used is preferably a mineral acid such as hydrochloric acid or sulfuric acid. This acid treatment is performed for the purpose of suppressing the growth of primary particles and removing impurities in the hydrogel.Additionally, this acid treatment removes factors that affect the physical properties of the product silica gel before this process.

For example, it has the effect of suppressing the influence of fluctuations in silica concentration, pl-1 of silica sol, etc. If the pH exceeds 2.5, the effect of acid treatment will not be sufficient. The appropriate acid concentration is 0.01
~ION, preferably about 0.1 to 5N.

After acid treatment, the hydrogel is washed with water until at least 1) H3.5 or higher to remove eluted impurities. If this water washing is insufficient, it will be difficult to maintain pl-1 constant in the subsequent hydrothermal treatment step.

Although the acid treatment step described above is essential in the present invention, the hydrothermal treatment step that follows is the most important.

In other words, this hydrothermal treatment step is carried out to finally adjust the physical properties of silica gel, such as its surface area, pore diameter, and pore volume, to a predetermined range.In the present invention, silica hydrogel is treated in an aqueous solution with a buffering effect. By strictly adjusting the DH to a range of 4.0 to 9.0, preferably 5.5 to 8.5, it is said that homogenization of vesica gel products is significantly more effective than when such a buffer is not used. knowledge) has been evaluated.

As a liquid having such a buffering effect, a normal pH adjusting agent such as a phosphate-based or a citrate-based buffer is preferably used, or alternatively, it may be adjusted one by one with an aqueous solution of an alkali and an acid. good.

Hydrothermal treatment temperature is 50-200'C, preferably 70-1
The temperature is 80'C and the treatment time is 0.5 to 100 hours, with a practical range of 1 to 10 hours being appropriate.

If the pH during hydrothermal treatment is less than the above range, the effect of adjusting the silica gel pore size is lost, and if it exceeds the above range, the dissolved NU of the silica gel increases, the silica gel matrix is destroyed, and the homogeneity of the hydrogel is impaired.

Generally, the higher the temperature during hydrothermal treatment, the longer the treatment time, and the higher the pH, the smaller the surface area of silica gel and the larger the average pore diameter.

FIG. 1 shows the relationship between the pH of the hydrothermal treatment and the surface area and average pore diameter of the silica gel produced when the hydrothermal treatment was carried out at 80° C. for 2 hours according to the method of the present invention.

Further, FIG. 2 shows the relationship between the hydrothermal treatment time and temperature and the average pore diameter of the produced silica gel when the pH during the hydrothermal treatment is set to 6.2 by the method of the present invention.

After the hydrothermal treatment, the silica gel is washed with deionized water to completely remove salts, etc., dried at 100 to 150'C, and if necessary, pulverized and classified into products.

Figure 3 shows the pore distribution of the silica gel prepared by the method of the present invention and the conventional product.

The present invention will be explained below with reference to Examples and Comparative Examples.

All percentages in the examples are based on weight.

Example 1 A silica hydrosol with a DH of 4°5 was prepared by gradually adding JISa sodium silicate 1850C1 diluted 2.5 times with water to sulfuric acid 550a with a 20% ia degree.
8.9%). Hydrosil gels after about 10 minutes, but after being left overnight, it is crushed and washed in 1N sulfuric acid.
0℃, 2 hours r! After the acid treatment, the hydrogel was washed with water until the pH reached 5. This hydrogel was divided into three parts: Sample No. 1. No, 2. No, I set it as 3. Next, sample No. 1 was adjusted to pH 6 using a phosphate buffer (potassium dihydrogen phosphate/disodium hydrogen phosphate), and sample No. 2 was adjusted to pH 6 using a citrate buffer (sodium citrate/sodium hydroxide). , 80℃ while maintaining at 5
, water and heat treatment for 2 hours. Further, sample No. 003 was subjected to the same hydrothermal treatment while maintaining the pH at 6.5 by adding a small amount of sodium hydroxide solution and Wt acid in several portions. Table 1 shows the physical properties of the silica gel obtained by thoroughly washing the samples with deionized water and drying them at 120'C.

Note that the surface area and pore volume of the silica gel were measured using QUANTASORe manufactured by Yuyuri Ionics Co., Ltd., and the average pore diameter was calculated using the following formula.

d=4XV/5X104 d: Average pore diameter (A) v: mpore capacity (rn1/g) S2 surface area (bottom/g) Table-1 □H □□ --■ Example 2 In sulfuric acid with a concentration of 20% JISa sodium silicate diluted 2.5 times was added to the solution, and the DH was 3.5.4 respectively.
．． A silica hydrosol of 0.5.0 was produced.

Hydrogels were produced from these under the same conditions as in Example 1.

After acid treatment and water washing, hydrothermal treatment was performed at 80°C for 2 hours in the same phosphate aqueous solution of pl-16,5 (sample 4,
5.6). The subsequent treatment was carried out in the same manner as in Example 1, and the physical properties of the obtained silica gel are shown in Table 2.

Table 2 According to Table 2, even if the DH of the silica sol produced by the reaction between sodium silicate and acid is different, if conditions such as pH during hydrothermal treatment are kept constant, silica gel with stable physical properties can be produced. It turns out that things are possible.

Example 3 S! in a silica hydrosol produced by the reaction of sulfuric acid at a temperature of 20% with No. 02 Three types of silica h 1-0 sols were prepared by adjusting the alkali silicate = i so that the concentrations were 8.3%, 12.3%, and 15%, respectively (sample 7.8.9). Table 3 shows the physical properties of the silica gel obtained in the same manner as in Example 1, except that the subsequent treatment of each sample was carried out in a phosphate solution with a pH of 6.5 and a hydrothermal treatment temperature of 90°C for 2 hours. Shown below.

Table 3 It can be seen from Table 3 that the physical properties of silica gel are hardly affected by the S +02 concentration in the silica sol if other conditions are held constant.

Comparative Example 1 The DH of the silica hydrosol produced in the same manner as in Example 2 was 3.
．． 5. Make three samples of 4.0.5.0 (sample No.
10.11.12> Table 4 shows the physical properties of silica gel obtained under the same conditions as in Example 3 except that these hydrosils were not treated with acid.

Table-4 In other words, r! If i treatment is omitted, p of hydrosil
H causes changes in physical properties, especially surface area and pore diameter, making it impossible to obtain stable quality.

Comparative Example 2 In the same manner as in Example 2, the pH was adjusted to 3.5° and 4.0°, respectively.
After generating and gelling a silica hydrosol with a pH of 5.0 and performing the same steps up to acid treatment, the hydrogel was divided into three parts and washed with water until the pH of the washing solution was 3.5, 4.0 and 5.5, respectively. Sample No. 013.14.15). Next, each sample was poured into deionized water until the DH of each slurry liquid was 6.
Table 5 shows the physical properties of the silica gel obtained by adding a sodium hydroxide solution to adjust the silica gel to a pH of 5, followed by hydrothermal treatment at 80° C. for 2 hours, washing with water, and drying.

Table 5 It can be seen that when a buffer solution is not used as described above, it is difficult to set conditions to obtain the desired physical property values of the product due to large changes in pH during hydrothermal treatment.

(Effects of the Invention) According to the method of the present invention, the silica sol produced by the reaction between an alkali silicate and a mineral acid is gelled, and the resulting silica gel is acid-treated at a pH of ~2.5. By adjusting the pH to 4 to 9 and performing hydrothermal treatment, it is possible to produce silica gel of stable quality and a sharp pore distribution as shown in FIG. In addition, since silica gel having desired physical properties can be obtained by arbitrarily adjusting the pH during hydrothermal treatment with a buffer, there is an advantage that silica gel with characteristics suitable for various uses can be easily produced. The method of the present invention is particularly useful as a method for producing silica gel used as a packing material for chromatography.

[Brief explanation of drawings]

Figures 1 and 2 are graphs showing the physical properties of silica gel obtained by the method of the present invention. Figure 1 is a diagram showing the relationship between surface area and pore diameter according to l)H during hydrothermal treatment, and Figure 2 is a diagram showing the relationship between hydrothermal treatment time and average pore size. It is a relationship diagram with a hole diameter. FIG. 3 is a graph showing a comparison (relationship between pore diameter and cumulative pore volume) between the silica gel produced by the method of the present invention and a conventional product. In Figure 3, 1...Product of the present invention (average pore diameter 59)
, 2... Same (average pore diameter 120A), 3... Conventional product (trade name: ieselgel 60), 4-...
Same (product name: Iese Igel 100).

Claims (2)

[Claims] (1) The silica hydrosol produced by the reaction between an aqueous alkali silicate solution and a mineral acid solution is gelled, the resulting silica hydrogel is treated with an acid solution with a pH of 2.5 or less, and after washing with water, it is placed in an aqueous solution with a buffering effect. A method for producing silica gel of stable quality, which comprises adjusting the pH to 4 to 9 and performing hydrothermal treatment. (2) A method for producing silica gel using a phosphate-based or citrate-based buffer as a buffer during hydrothermal treatment.