JPH0640714A - High-oil-absorptive porous silica, production thereof and carrier - Google Patents

Abstract

PURPOSE:To improve oil absorptivity by drying a silica hydrogel obtained by the reaction of an alkali metal silicate having SiO2 of a specific conc. or below with a mineral acid at the critical temp. or above of a solution. CONSTITUTION:A mineral acid such as sulfuric acid is added into an aq. alkali metal silicate solution such as Na2SiO3 adjusted to >=60g/l SiO2 conc. by diluting with water at a prescribed temp. A SiO2 slurry produced by aging at the temp., raising the temp. and furthermore adding the mineral acid is adjusted in pH, is filtered, washed and suspended again in water. By-product Na2SO4 is removed by refilteration and washing to obtain a hydrogel. By suspending the hydrogel in a solvent such as methanol, filtering and cleaning, a silica methanogel is obtained. The silica methanogel is suspended in a solvent such as methanol, is heated up to the critical point of the solvent (Tc=240 deg.C, Pc=78.7atm) and is cooled to obtain the high-oil-absorptive porous SiO2 having >=350ml/100g oil absorption and >=5ml/g narrow pore volume by the mercury porosimeter.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to highly oil-absorbing porous silica, a method for producing the same, and a carrier for medicines, agricultural chemicals and the like.

[0002]

2. Description of the Related Art Conventionally, the problems to be solved by the invention
As a method for obtaining silica having a large pore volume and a high oil absorption capacity, for example, a method of controlling the reaction conditions of sodium silicate and sulfuric acid, or hydrothermally treating the produced silica hydrogel and treating with acid, and then drying is known. (JP-A-58-58)
135119).

However, the pore volume of conventional mercury porosimeters is about 4.5 ml / g at the maximum,
The oil absorption amount according to JIS-K-5101 method is 300 ml.
/ 100 g or less.

Silica has been conventionally used as a carrier for pharmaceuticals, agricultural chemicals, etc.
It is widely used as a powdering agent, various adsorbents, etc., but in such applications of silica, it has a higher oil absorption than silica obtained by the conventional technique and adsorbs and holds a large amount of various oily substances and the like. It is desired to provide a material having excellent fluidity even in cases.

[0005]

Means and Actions for Solving the Problems The present inventors have
As a result of earnestly studying in order to meet the above demand, SiO ₂
A silica hydrogel comprising agglomerates of fine primary particles is produced by the reaction of a relatively low concentration of an alkali metal silicate having a concentration of 60 g / l or less with a mineral acid, and the silica hydrogel is a critical point of its solvent. By the above supercritical drying, the oil absorption according to JIS-K-5101 method is 350
ml / 100 g or more, the pore volume by mercury porosimeter is 5 ml / g or more, which has a much larger oil absorption capacity than conventional silica (white carbon) and has a very large pore volume. It was found that porous silica (silica airgel) can be obtained. Further, this porous silica has excellent fluidity when adsorbing and holding a large amount of an oily substance such as n-butyl phthalate, and therefore, it is used as a carrier for pharmaceuticals, agricultural chemicals and the like, as a powdering agent, and for various adsorption. It is useful as an agent, and can be suitably used for applications such as heat insulating materials, sound deadening agents, thickeners, thixotropy imparting agents, and fillers for various functional papers (diazo photosensitive paper, inkjet paper, etc.). They have found out the present invention and made the present invention.

It has been known that the so-called sol-gel method is employed to supercritically dry silica produced by hydrolysis and gelation of alkoxysilane. However, according to such a method, the above-mentioned porous silica having an oil absorption of 350 ml / 100 g or more and a large oil absorption and pore volume of 5 ml / g or more by a mercury porosimeter cannot be obtained. is there. The porous silica having a large oil absorption and a large pore volume of the present invention is obtained only by supercritically drying a porous silica hydrogel obtained by reacting a low-concentration alkali metal silicate with a mineral acid. In this case, unless a porous silica hydrogel is obtained in the reaction stage, the above-mentioned porous silica having a large oil absorption and a large pore volume cannot be obtained even by supercritical drying. Further, even if a porous silica hydrogel is obtained at the reaction stage, the porous silica (silica aerogel) of the present invention cannot be obtained by drying it using a usual drying method. .

The present invention will be described in more detail below.

The porous silica (silica airgel) of the present invention has an oil absorption of 350 according to the JIS-K-5101 method.
ml / 100 g or more, more preferably 400 ml / 10
0g or more, the pore volume by mercury porosimeter is 5
ml / g or more, more preferably 5.5 ml / g or more. Further, the silica of the present invention has high transparency and high bulk.

The porous silica usually has a pore volume of 1.5 ml / g or more, more preferably 2 ml / g or more by nitrogen adsorption, and a specific surface area (nitrogen adsorption method) of 200 by BET method. -700 m < ² > / g, More preferably, it is 400-600 m < ² > / g.

The porous silica of the present invention is an aggregate of primary particles, and the average primary particle diameter is usually 5 to 100 nm.
In addition, the average aggregate particle size is 1 to 50 μm.

The silica of the present invention has a SiO ₂ concentration of 60 g.
/ L or less, more preferably 40 g / l or less, by producing a silica hydrogel by a reaction with an alkali metal silicate and a mineral acid such as sulfuric acid, and drying the silica hydrogel at a temperature above the critical point of the solvent. You can

In this case, if the concentration of the alkali metal silicate is increased during the production of the silica hydrogel, the porous silica of the present invention cannot be obtained. The reaction between the alkali metal silicate and the mineral acid can be carried out according to a known method, but if the reaction temperature is too high, fine silica hydrogel may not be obtained.

The supercritical drying of the silica hydrogel is carried out by drying above the critical point of the solvent, and the method can be carried out according to the known supercritical drying method. In this case, it is obtained by the above reaction. The silica hydrogel thus obtained, that is, containing the water as it is, has a critical point (T _c
= 374.2 ° C., P _c = 218 atm) or more, or in order to lower the critical condition,
After replacing the water in the silica hydrogel with another solvent (for example, an organic solvent such as alcohol or carbon dioxide), the water may be supercritically dried.

As described above, the porous silica of the present invention has a large pore volume, a high oil absorption amount, and exhibits excellent fluidity while adsorbing and holding a large amount of an oily substance or the like. For this reason,
It has excellent performance as a carrier for pharmaceuticals, agricultural chemicals, etc., and as a powdering agent, and is effectively used as various adsorbents. Further, by utilizing such properties, it is suitably used for heat insulating materials, sound deadening materials, thickening agents, thixotropy imparting agents, and various functional paper fillers.

[0015]

EXAMPLES The present invention will be specifically described below by showing Examples and Comparative Examples, but the present invention is not limited to the following Examples.

Example 1 Commercially available No. 3 sodium silicate (SiO ₂ / Na ₂ O = 3.2) was diluted with water to obtain SiO _2.
142 ml of sulfuric acid having a concentration of 560 g / l was added while maintaining 5 liter of the solution having a concentration of 38 g / l at 60 ° C. Then, after aging at the same temperature for 30 minutes, the temperature was raised to 90 ° C., and 17 ml of sulfuric acid having the same concentration was further added.

The silica slurry obtained was adjusted to pH 5, filtered, washed with water, and then resuspended in water. PH to 4
Then, the mixture was filtered and washed again with water to remove the sodium sulfate as a by-product, and a silica hydrogel was obtained.

1 kg of this silica hydrogel (water content 90
%) Was suspended in 1 liter of methanol, filtered, and washed with methanol. Further, the obtained silica cake was suspended again in 1 liter of methanol, filtered and washed with methanol to obtain silica methanogel.

This silica methanogel was suspended in 1 liter of methanol, placed in an autoclave and sealed, and the critical point of methanol (T _c = 240 ° C., P _c = 78.7 at) was obtained.
m) until the autoclave is heated and then the temperature is raised to 2
While keeping the temperature at 40 ° C. or higher, the pressure was gradually reduced to atmospheric pressure and then cooled to obtain a silica airgel.

The apparent specific gravity of this silica airgel is 0.
10 ml / g, particle size D ₅₀ = 15.52 μm, D ₈₀ = 3
It was 0.51 μm and D ₉₇ = 49.55 μm.

Comparative Example 1 The silica hydrogel obtained in Example 1 was dried with hot air at 140 ° C. for 1 hour to obtain a silica xerogel.

Comparative Example 2 Commercially available No. 3 sodium silicate (SiO ₂ / Na ₂ O = 3.2) was diluted with water to obtain SiO _2.
While maintaining 5 liters of a solution having a concentration of 76 g / l at 90 ° C., 148 ml of sulfuric acid having a concentration of 560 g / l was added. Then, after aging at the same temperature for 30 minutes, 167 ml of sulfuric acid having the same concentration was further added.

The silica slurry obtained was adjusted to pH 5, filtered, washed with water, and then resuspended in water. PH to 4
Then, the mixture was filtered and washed again with water to remove the sodium sulfate as a by-product, and a silica hydrogel was obtained.

1 kg of this silica hydrogel (water content 90
%) Was suspended in 1 liter of methanol, filtered, and washed with methanol. Further, the obtained silica cake was suspended again in 1 liter of methanol, filtered and washed with methanol to obtain silica methanogel.

After suspending this silica methanogel in 1 liter of methanol, supercritical drying was carried out in the same manner as in Example 1 to obtain a silica aerogel.

Next, properties of silica of Example 1 and Comparative Examples 1 and 2 (pore volume by mercury porosimeter, specific surface area by BET method, pore volume by nitrogen adsorption, pore peak diameter,
The oil absorption amount according to JIS-K-5101) was measured. The results are shown in Table 1. In addition, Table 1 also shows properties of commercially available wet silica.

[0027]

[Table 1] Vp (Hg): Pore volume by mercury porosimeter (ml / g) SN ₂ : Specific surface area by BET method (m ² /
g) Vp (N ₂ ): Pore volume due to nitrogen adsorption (ml /
g) D peak: Pore peak diameter (nm) O.D. A. : Oil absorption according to JIS-K-5101 (ml / 100g)

From the results shown in Table 1, the porous silica (silica aerogel) of the example prepared by supercritically drying the silica hydrogel obtained by the reaction of a relatively low concentration of alkali metal silicate and sulfuric acid. It has a very large pore volume as compared with commercially available wet silica, and it is recognized that it has a high oil absorption capacity. It is considered that this is because fine silica hydrogel was obtained by the above reaction and porous silica (silica airgel) was obtained while maintaining the void structure of the fine silica hydrogel.

On the other hand, as can be seen from Comparative Example 1, even if a fine silica hydrogel is obtained by the reaction, in the usual drying method, contraction of the silica particles occurs due to the surface tension of water during the drying process and pores are formed. Although it is thought that the cause is destruction, only dense silica gel having a small pore volume and a small oil absorption amount can be obtained, and as can be seen from Comparative Example 2, even if supercritical drying is used, If silica hydrogel having a fine structure was not formed in the reaction, similarly highly oil-absorbing silica gel could not be obtained.

Next, regarding the fluidity of the porous silica of Example 1 and the commercially available wet silica, 0 ml (0 v / w) of n-butyl phthalate (DBP) was added to 150 g of these silicas.
%), 150 ml (50 v / w%), 300 ml (6
6.7 v / w%) added, and tabletop kneader (Irie Shokai, PN
(V-2H) mixed for 15 to 25 minutes,
It was evaluated by measuring the fluidity index. The result is shown in Figure 1.
~ 2. In the figure, A to D are the results of commercially available wet silicas A to D, respectively.

FIG. 1 shows the relationship between the amount of DBP added and the degree of compression. The degree of compaction is a factor that is most closely related to the flow characteristics of the powder, and is 1 from the apparent apparent specific gravity X and the apparent apparent specific gravity Y.
It is calculated by the formula of 00 · (Y−X) / X, and the larger the value, the worse the fluidity. Also, in FIG.
The relationship between the DBP addition amount and the fluidity index is shown. The fluidity index (NF) has a relationship of compressibility (C) and NF = 100-1.35C. The larger this value, the better the fluidity. From the results of FIGS. 1 and 2, the silica of Example 1 is D
It is recognized that, in a state in which a large amount of BP is contained and adsorbed, it has much better fluidity than conventional silica. Therefore, from this, it is found that the silica of the present invention is very useful as a carrier for agricultural chemicals and the like.

[0032]

INDUSTRIAL APPLICABILITY The porous silica of the present invention has a very large pore volume and a high oil absorption capacity as compared with conventional wet process silica, and is in a state of adsorbing and retaining a large amount of oily substances. It exhibits excellent fluidity and is suitable for use as a carrier for pharmaceuticals, agricultural chemicals, and the like.

Further, according to the production method of the present invention, such porous silica can be produced reliably and easily.

[Brief description of drawings]

FIG. 1 is a graph showing the degree of compression when DBP is adsorbed and held on various silicas.

FIG. 2 is a graph showing a fluidity index when DBP is adsorbed and held on various silicas.

Claims (3)

[Claims] 1. A highly oil-absorbing porous silica having an oil absorption of 350 ml / 100 g or more according to the JIS-K-5101 method and a pore volume of 5 ml / g or more according to a mercury porosimeter. 2. The silica hydrogel obtained by the reaction between an alkali metal silicate having a SiO ₂ concentration of 60 g / l or less and a mineral acid is dried at a temperature above the critical point of the solvent. Method for producing silica. 3. A carrier comprising the silica according to claim 1.