JPH07138013A - Silica gel having high specific surface area and controlled high structural property and its production - Google Patents

Abstract

PURPOSE:To obtain a new silica gel having a high specific surface area and a controlled high structural property and useful as an adsorbent for low molecular organic compounds, a separator for chromatography, a filtering material for beers, etc. CONSTITUTION:A silica gel has a BET specific surface area of 700-1100m<2>/g, a pore volume of 0.5-2.5cc/g, a pore diameter of 20-50Angstrom in the pores occupying 90% of the pore volume, and a relation: AXB>=25000 wherein A (m<2>/g) is the BET specific surface area and B (Angstrom ) is the median pore diameter.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel silica gel having a high specific surface area and a controlled high structural property, and a method for producing silica gel having the physical properties.

The novel silica gel is useful as an adsorbent for low molecular weight organic compounds, a separating agent for chromatography, and a filtering agent for beer.

[0003]

2. Description of the Prior Art US Pat.
No. 2,466,842. That is, silica hydrogel is obtained by quantitatively mixing sodium silicate and sulfuric acid under the condition that the amount of excess sulfuric acid is 0.5 N using a mixing nozzle,
It can then be gelled to give a silica hydrogel.

Such silica hydrogel is disclosed in USP 1,9
As described in No. 00,859, various specific surface areas are adjusted by hydrothermal treatment.

Further, the silica hydrogel is dried to give silica gel having various pore volumes.

Regarding the drying method, USP 2,85
As described in No. 6,268, a method of instantaneously drying under superheated steam is known.

The silica gel thus obtained can be adjusted to a desired particle size by pulverization, or can be adjusted to various particle sizes by simultaneously performing drying and pulverization by the method as described above.

Generally, those having a fine average secondary particle diameter of 5 μm or less are used as a delustering agent for paints, an antiblocking agent for films, a viscosity modifier, and the like.
Those having an average secondary particle size of 5 μm or more are used as a separating agent for chromatography and a filtering agent for beer.

The adsorption function of the above-mentioned one silica gel is explained by the function of the silanol groups present on the surface and the adsorption function of the pores. For this reason, silica gel having a high specific surface area and a controlled high structure is also desired. The highly structured silica gel controlled here has a pore volume of 0.5 to
2.5 cc / g, 90% or more of the pore volume has a pore diameter of 20
What is ~ 50Å.

However, silica gel having a controlled high structure while having the above-mentioned high specific surface area, for example, BET specific surface area is A (m ² / g) and median pore diameter is B (Å). At times, silica gel having these relationships represented by the following formula A × B ≧ 25000 has not been provided so far.

Silica gel having such a high specific surface area and a high structural property is more excellent in adsorptivity by surface silanol groups than silica gel having A × B of less than 25,000 and further has a specific pore diameter, so that it is selectively adsorbed. It has excellent properties.

[0012]

The following points can be considered as the reason why silica gel having a high specific surface area and controlled high structure has not been obtained in the past.

In general, silica gel is obtained by reacting sodium silicate and sulfuric acid on the acidic side having a pH of about 2 using a mixing nozzle or the like to obtain a silica hydrosol. At this time, 2-3n
m primary particles of silica are deposited. Such primary particles have a specific surface area of 1000 to 1500 m ² / g. The primary particles form a three-dimensional network structure and become silica hydrogel. Silica hydrogel contains about 70 to 90 wt% of water, and its total pore volume is about 2.0 to 9.0.
cc / g is also present.

When such a silica hydrogel is washed with water and hydrothermally treated, the specific surface area is reduced.

Washing with water is usually carried out continuously. The form is performed by packing silica hydrogel in a column and continuously pouring washing water from the upper part or the lower part. Further, by controlling the temperature and pH of the washing water, the effect of hydrothermal treatment can be obtained together with the washing.

At this time, in order to maintain a specific surface area of about 700 m ² / g, it is known to wash with water at a low temperature of about 30 ° C. as described in USP 1,900,859. .

After such a step, drying is subsequently carried out. At this time, the silica hydrogel shrinks violently and the pore volume is remarkably reduced to about 0.3 to 0.5 cc / g.

The reason for this is not clear, but since the silica hydrogel is washed with water at a low temperature in order to maintain its specific surface area, there is almost no dissolution / precipitation of silica, and siloxane bonds between the primary particles in the three-dimensional network structure. There are few,
It is considered that the structure becomes weak, and as a result, it contracts extremely due to the capillary cohesive force that is said to occur when water evaporates.

On the other hand, regarding the relationship between the specific surface area and the pore diameter, the pore diameter tends to decrease as the specific surface area increases, and in the high specific surface area as in the present invention, (BET specific surface area): A (m ² / G), (median pore diameter): B (Å) A × B ≧ 25000, the silica gel satisfying the condition was not obtained.

Therefore, the inventors of the present invention have been earnestly researching a novel silica gel which has a high specific surface area and which has a high pore volume and a high pore diameter, which has not been conventionally produced. As a result of systematic examination, it has been found that the method according to the present invention can solve the problems all at once.

That is, the object of the present invention is to provide a silica gel having a high specific surface area and a controlled high structural property.

Another object of the present invention is to provide a method for producing such a novel silica gel.

[0023]

Means for Solving the Problems As a result of intensive studies on the silica gel having the above-mentioned physical properties, the inventors of the present invention have achieved conventional production by carrying out hydrothermal treatment under the conditions specified in the present invention. The present inventors have completed the present invention by discovering the finding that a novel silica gel which could not be produced can be easily produced.

That is, the silica gel of the present invention has a BET specific surface area of 700 to 1100 m ² / g and a pore volume of 0.5 to
2.5 cc / g, 90% or more of the pore volume has a pore diameter of 20
~ 50Å, and has a BET specific surface area of A (m ² / g)
When the median pore diameter is B (Å), these relations have the characteristics represented by the following formula A × B ≧ 25000.

The silica gel having such characteristics is a silica hydrogel obtained by mixing sodium silicate and sulfuric acid at 80 ° C. for the purpose of increasing only the bond of primary particles without decreasing the specific surface area. ~ 200 ° C, preferably 90 ° C to 150 ° C, pH less than 4.0, preferably 3.
It can be obtained by hydrothermal treatment at less than 0, followed by washing with water and drying.

The silica gel of the present invention has a specific surface area of 70.
If it is less than 0 m ² / g, the adsorption function of the surface silanol groups is insufficient. On the other hand, if the amount exceeds 1100 m ² / g, the reason is not clear, but the adsorption function is not stable, and there is a problem that the physical properties of silica gel change remarkably during use, so that it is within the above range.

Further, the above silica gel needs to have a controlled high structural property and has a pore volume of 0.5.
If it is less than cc / g, the amount of adsorption is insufficient. On the contrary 2.5
Those exceeding cc / g cannot be obtained by the method according to the present invention. Furthermore, the pore volume of 20 to 50Å is 9
If it is less than 0%, the adsorption performance is remarkably deteriorated and the object of the present invention cannot be achieved. Then, the BET specific surface area is A (m ²
/ G) and the median pore diameter is B (Å), A
If xB is less than 25,000, the adsorption performance is not good, as described above.

Further, the above contents will be described in detail.

Silica hydrogels are, for example, SiO ₂
25 wt% sodium silicate with a molar ratio of 3.3 and H ₂
42% by weight of SO ₄ sulfuric acid was added to the pH using a mixing nozzle.
The silica hydrosol can be obtained by mixing under conditions of 0.5 to 2.0 and a temperature of 60 ° C. or lower, and the silica hydrosol can be gelated within 10 minutes to obtain a silica hydrogel. In a batch reactor, sodium silicate and sulfuric acid are added
It can also be obtained by dropping at the same time under the condition of H 0.5 to 2.0, or by adding sodium silicate to sulfuric acid. The present invention is not limited to these methods, and the specific surface area at the time of silica hydrogel formation may be 700 m ² / g or more.

The silica hydrogel thus obtained is then washed with water and hydrothermally treated.

What is important here is that the structure of the primary particles in the three-dimensional network structure is strengthened without reducing the specific surface area,
The next step is to prevent the shrinkage from being affected in the subsequent drying step.

As described above, the washing with water and the hydrothermal treatment can be performed at the same time, but in such an operation, the influence of the hydrothermal treatment may be non-uniform. Considering the control of the distribution of pores, it is preferable to carry out the water washing and the hydrothermal treatment separately, preferably by carrying out the hydrothermal treatment and then the water washing or the water washing and the hydrothermal treatment. For example, it is desirable to carry out hydrothermal treatment in a batch system and then wash with water.

Here, the hydrothermal treatment means holding the silica hydrogel in the presence of water for a certain period of time at a constant temperature and pH condition.

At this time, if the pH is 4.0 or higher, the primary particles of silica gel grow and the high specific surface area cannot be maintained. It is possible to maintain a high specific surface area by lowering the temperature, but at temperatures below 80 ° C,
Subsequent drying causes excessive shrinkage of the silica gel, making it impossible to maintain a high pore volume and a high pore diameter.

In order to prevent the specific surface area from changing, it is important to wash with water at a pH of less than 4, as is clear in Comparative Examples 1 and 2 below, but only such an operation gives a high specific surface area. However, it does not have the controlled high structural property according to the present invention, and the diameter of the formed pores is very small, probably because of the relatively weak structure.

On the other hand, as is clear from Examples 1 to 3 shown below, those hydrothermally treated under the conditions according to the present invention maintained a sufficient pore volume and had a very fine pore distribution. Exists in a narrow distribution.

The reason for this is not clear, but as described above, if the temperature is insufficient at a pH of less than 4.0, the effect of increasing the binding of the primary particles becomes insufficient, and it is affected by shrinkage during drying. it is conceivable that.

On the other hand, in the case of hydrothermal treatment under the conditions according to the present invention, the influence of shrinkage during drying occurs uniformly, probably because the bond of primary particles is increased and the structure is strengthened. It is considered to have a high structural property.

On the other hand, when the pH is 4 or more, the specific surface area cannot be maintained although the pore volume, the pore diameter and the pore distribution according to the present invention are present.

[0040]

The silica gel thus obtained is BET
Specific surface area 700 to 100 m ² / g, pore volume 0.5 to
2.5 cc / g, 90% or more of the pore volume has a pore diameter of 20
˜50Å, and the relationship between the BET specific surface area and the median pore diameter is the following formula (BET specific surface area): A (m ² / g), (median pore diameter): B (Å) A × B ≧ 25000 It is a novel silica gel having the characteristics represented by and can be easily obtained by the above-mentioned production method.

The silica gel having the above characteristics of the present invention is
It is suitable for applications that make use of its strong adsorption performance.For example, when it is used as an anti-blocking agent for films, it exerts an effect in adsorbing the monomer component of the resin that deteriorates film performance, and is used as a chromatographic separation agent. Then, it is effective as an adsorbent for organic substances having a molecular diameter of 10 to 30Å, and as a filter agent for beer, it is effective in adsorbing proteins and the like that impair the storage stability of beer.

The novel silica gel according to the present invention is remarkably excellent in the adsorption property of the above-mentioned organic substances and is industrially very useful.

[0043]

According to the present invention, the BET specific surface area of 700
~ L100 m ² / g, pore volume 0.5-2.5 cc /
g, 90% or more of the pore volume is in the pore diameter 20 to 50Å, and the relationship between the BET specific surface area and the median pore diameter is expressed by the following formula (BET specific surface area): A (m ² / g), (median Pore diameter): B (Å) A × B ≧ 25000 can be obtained to obtain a novel silica gel, which is an adsorbent for a low-molecular organic compound, a chromatographic separation agent, It is useful as a filtering agent for beer.

[0044]

EXAMPLES Specific embodiments of the present invention will be shown below.

Each physical property was measured by the following methods.

(L) BET Specific Surface Area After measuring the nitrogen adsorption-desorption isotherm using ASAP2400 (manufactured by Shimadzu Corp.), S. Brunauer, PHEmett, E. Tel
The ler method (J. Am. Chem. Soc., 60, 309 (1938)) was used.

(2) Pore Volume ASAP2400 (manufactured by Shimadzu Corporation) was used to measure adsorption and desorption isotherms of nitrogen, and then Barrett-Joyner-Halenda method (J. Am. Chem. Soc., 73,373 (1951) )).

(3) Pore Diameter The relationship between the relative pressure of nitrogen and the pore diameter was calculated by Barrett-Joyner-H
alenda method (J. Am. Chem. Soc., 73, 373 (1951)) was used to determine the relationship with the pore volume as shown in Table 2, and the median was defined as the pore diameter.

Example 1 Sodium silicate SiO ₂ 25 wt%, molar ratio 3.3
And 42 wt% of sulfuric acid H ₂ SO ₄ were mixed using a mixing nozzle under the conditions of a sodium silicate flow rate of about 15 l / min and a sulfuric acid flow rate of about 7.0 l / min to obtain a silica hydrosol. The temperature at this time was about 50 ° C.

The silica hydrosol gelled in about 5 minutes to obtain a silica hydrogel.

Next, the silica hydrogel was pulverized to about 10 mm using a sieve, and then hydrothermally treated for 4.0 hours under the conditions of 90 ° C. and pH 2.6.

Further, the hydrothermally treated silica hydrogel was washed with water and dried at 200 ° C. to obtain silica gel.

The relationship among the pore diameter, the cumulative pore volume, and the cumulative pore existence rate at this time is shown in Table 1 below.

The relationship between pore diameter and pore existence rate is shown in Table 2 below.

The specific surface area, pore volume and pore diameter of silica gel are shown in Table 3 below.

Further, 100 parts by weight of the polypropylene resin and 0.1 part by weight of the slip agent were pulverized with the silica gel of Example 1 and then 0.4 parts by weight of the silica gel was added. Was melt-blended to prepare pellets, and then the pellets were manufactured into a film using a water-cooled blown film manufacturing apparatus.

After the produced film was stored at 30 ° C. for 24 hours, the results of visually observing the amount of organic substances bleeding to the film surface are shown in Table 4 as a reference example.

[0058]

[Table 1]

[0059]

[Table 2]

[0060]

[Table 3]

[0061]

[Table 4]

Example 2 Silica gel was obtained in the same manner as in Example 1 except that the hydrothermal treatment was performed at 90 ° C., pH 2.6 for 1 hour.

The relationship between the pore diameter at this time, the cumulative pore volume, and the cumulative pore existence rate is shown in Table 1 above.

The relationship between the pore diameter and the pore existence rate is shown in Table 2 above.

The specific surface area, pore volume and pore diameter of silica gel are shown in Table 3 above.

Further, in the same manner as in Example 1 above, a film was produced from pellets prepared by adding, mixing and continuously mixing the silica gel of Example 2, and the produced film was heated at 30 ° C.
After storing for 24 hours in the above, the results of visually observing the amount of organic substances bleeding to the film surface are shown in Table 4 above as a reference example.

Example 3 Silica gel was obtained in the same manner as in Example 1 except that the hydrothermal treatment was performed at 90 ° C. and pH 2.8 for 2 hours.

The relationship between the pore diameter at this time, the cumulative pore volume, and the cumulative pore existence rate is shown in Table 1 above.

The relationship between the pore diameter and the pore existence rate is shown in Table 2 above.

The specific surface area, pore volume and pore diameter of silica gel are shown in Table 3 above.

Further, in the same manner as in Example 1 above, a film was produced from pellets prepared by adding, mixing and continuously mixing the silica gel of Example 3, and the produced film was heated at 30 ° C.
After storing for 24 hours in the above, the results of visually observing the amount of organic substances bleeding to the film surface are shown in Table 4 above as a reference example.

Comparative Example 1 Silica gel was obtained in the same manner as in Example 1 except that hydrothermal treatment was carried out at 30 ° C., pH 2.5 for 4 hours.

The relationship between the pore diameter at this time, the cumulative pore volume, and the cumulative pore existence rate is shown in Table 1 above.

The relationship between the pore diameter and the pore existence rate is shown in Table 2 above.

The specific surface area, pore volume and pore diameter of silica gel are shown in Table 3 above.

Further, in the same manner as in Example 1 above, the silica gel of Comparative Example 1 was added, mixed, and mixed to prepare a film, and a film was produced.
After storing for 24 hours in the above, the results of visually observing the amount of organic substances bleeding to the film surface are shown in Table 4 above as a reference example.

Comparative Example 2 Silica gel was obtained in the same manner as in Example 1 except that the hydrothermal treatment was carried out at 70 ° C., pH 2.5 for 4 hours.

The relationship between the pore diameter at this time, the cumulative pore volume, and the cumulative pore existence rate is shown in Table 1 above.

The relationship between the pore diameter and the pore existence rate is shown in Table 2 above.

The specific surface area, pore volume and pore diameter of silica gel are shown in Table 3 above.

Further, in the same manner as in Example 1 above, a film was produced from pellets prepared by adding, mixing and continuously mixing the silica gel of Comparative Example 2, and the produced film was heated at 30 ° C.
After storing for 24 hours in the above, the results of visually observing the amount of organic substances bleeding to the film surface are shown in Table 4 above as a reference example.

Comparative Example 3 Silica gel was obtained in the same manner as in Example 1 except that hydrothermal treatment was performed at 90 ° C., pH 4.5 for 4 hours.

The specific surface area, pore volume and pore diameter of the silica gel at this time are shown in Table 1 above. The relationships among the pore diameter, the cumulative pore volume, and the cumulative pore existence rate at this time are shown in Table 1 above.

Further, specific surface area of silica gel, pore volume,
The pore diameters are listed in Table 1 above.

The relationship between the pore diameter and the pore existence rate is shown in Table 2 above.

The specific surface area, pore volume and pore diameter of silica gel are shown in Table 3 above.

Further, in the same manner as in Example 1 above, a film was produced from pellets prepared by adding, mixing and continuously mixing the silica gel of Comparative Example 3, and the produced film was heated at 30 ° C.
After storing for 24 hours in the above, the results of visually observing the amount of organic substances bleeding to the film surface are shown in Table 4 above as a reference example.

Comparative Example 4 Silica gel was obtained in the same manner as in Example 1 except that the hydrothermal treatment was carried out at 90 ° C., pH 7.0 for 4 hours.

The relationship between the pore diameter at this time, the cumulative pore volume, and the cumulative pore existence rate is shown in Table 1 above.

The relationship between the pore diameter and the pore existence rate is shown in Table 2 above.

The specific surface area, pore volume and fine milk diameter of silica gel are shown in Table 3 above.

Further, in the same manner as in Example 1 above, a film was produced from pellets prepared by adding, mixing and continuously mixing the silica gel of Comparative Example 4, and the produced film was heated at 30 ° C.
After storing for 24 hours in the above, the results of visually observing the amount of organic substances bleeding to the film surface are shown in Table 4 above as a reference example.

Claims (2)

[Claims] 1. A BET specific surface area of 700 to 100 m ² /
g, pore volume 0.5 to 2.5 cc / g, pore volume 90
% Or more in the pore diameter of 20 to 50Å, and the BET specific surface area is A (m ² / g), and the median pore diameter is B (Å)
The silica gel is characterized in that these relationships are represented by the following formula A × B ≧ 25000. 2. A silica hydrogel obtained by mixing sodium silicate and sulfuric acid at 80 ° C. to 200 ° C., pH 4.0.
The method for producing silica gel according to claim 1, which comprises hydrothermally treating at a temperature lower than that, followed by washing with water and drying.