JP2003165719A - Method for producing hydrophobic, lightweight and porous silica gel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a hydrophobic, lightweight and porous silica gel that is simple and allows low cost production. <P>SOLUTION: The method for producing a hydrophobic, lightweight and porous silica gel comprises a first step for preparing wet gel slurry that is flowable in a non-aqueous solvent by a sol-gel process, a second step for preparing hydrophobic wet gel by reacting the wet gel with a hydrophobic agent, and a third step for drying the hydrophobic wet gel. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing a hydrophobic and lightweight porous silica gel, and an object thereof is to provide a method for producing a hydrophobic and lightweight porous silica gel which can be produced simply and at low cost. To do.

[0002]

2. Description of the Related Art Hydrophobic and lightweight porous silica gel has been studied in various fields because of its unique optical properties, electrical properties, and extremely excellent heat insulating properties with small thermal conductivity. Porous silica gel can generally be produced by removing the dispersion medium from the wet gel. When the wet gel is heated or left at normal pressure to remove the dispersion medium, there is a problem that the gel contracts during drying and the fine structure collapses. The following manufacturing method is known as a manufacturing method in which the fine structure of the gel does not collapse even if the dispersion medium is removed from the wet gel.

[0003]

[Problems to be Solved by the Invention]
The 57120 discloses a sol - wet gel produced gel method and washed with liquid CO ₂ and volatile components of the gel body during was replaced with liquid CO _2, liquid CO ₂ through the supercritical state of the CO ₂ A method for producing porous silica gel characterized by being removed from the gel body is described. In addition, techniques for drying wet gel in a supercritical state are described in US Pat. No. 4,402,927, US Pat. No. 4,432,957, US Pat. No. 4,610,863, and the like.

However, the method of drying the wet gel under the supercritical conditions as described above is a method of drying the dispersion medium in the atmosphere at a critical point of the dispersion medium contained in the gel or at a temperature and pressure higher than the critical point. Therefore, in order to maintain a high temperature and high pressure atmosphere at or above the critical point (for example, when using CO ₂ as a dispersion medium, 40 ° C. and 80 atm), a reaction vessel capable of withstanding high temperature and high pressure is required. Excessive equipment was needed.

Further, in Japanese Patent No. 2840881, after exchanging water in the wet gel with a protic solvent / aprotic solvent, the wet gel is reacted with a surface modifier such as trimethylchlorosilane, and finally the wet gel is used. A method for producing a hydrophobic and lightweight porous silica gel is described, which comprises drying the porous silica gel.

In this method, the water content in the wet gel is exchanged with a protic solvent / aprotic solvent, so that the solvent replacement operation is complicated, the processing cost increases, and industrialization is difficult.

As described above, all the conventional methods require excessive facilities and are complicated in operation, so that there are problems that industrialization is difficult and manufacturing cost increases. It was The present invention is to provide a method for producing a hydrophobic and lightweight porous silica gel that can be produced simply and at low cost.

[0008]

That is, the invention according to claim 1 is the first step of preparing a wet gel slurry having fluidity in a non-aqueous solvent by a sol-gel method, the wet gel and hydrophobization. And a second step of preparing a hydrophobized wet gel by reacting with an agent, and a third step of drying the hydrophobized wet gel, and a method for producing a hydrophobic and lightweight porous silica gel. Regarding The invention according to claim 2 is characterized in that the preparation of the wet gel and the preparation of the hydrophobized wet gel are performed simultaneously by adding the hydrophobizing agent during the preparation of the wet gel. To a method for producing hydrophobic and lightweight porous silica gel. The invention according to claim 3 is characterized in that the boiling point of the non-aqueous solvent is higher than the boiling point of water.
And a method for producing the hydrophobic and lightweight porous silica gel described in 1. In the invention according to claim 4, in the third step, the hydrophobizing wet gel is heated at a temperature higher than the boiling point of water and a temperature lower than the boiling point of the non-aqueous solvent so that the components other than the hydrophobizing gel and the non-aqueous solvent are mainly contained. The method for producing a hydrophobic and lightweight porous silica gel according to claim 3, wherein the non-aqueous solvent is removed after being distilled off. In the invention according to claim 5, the surface tension (25 ° C) of the non-aqueous solvent is 40 mN.
/ M or less, It relates to the manufacturing method of the hydrophobic and lightweight porous silica gel according to any one of claims 1 to 4. The invention according to claim 6 is characterized in that the bulk density of the porous silica gel is 0.30 g / mL or less, and the production of the hydrophobic and lightweight porous silica gel according to any one of claims 1 to 5. Regarding the method.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION A method for producing a hydrophobic and lightweight porous silica gel according to the present invention will be described below. The first step is a step of preparing a wet gel slurry by a sol-gel method in a non-aqueous solvent. To prepare a wet gel slurry by the sol-gel method, a hydrolyzable silicon compound such as an alkoxysilane compound is used as a raw material, and this is obtained by hydrolysis and condensation in a non-aqueous solvent. You can

The hydrolyzable silicon compound (hereinafter, simply referred to as a silicon compound) is not particularly limited, but examples thereof include a chlorosilane compound, an alkoxysilane compound and derivatives thereof.

Specific examples thereof include tetrachlorosilane, tetramethoxysilane, tetraethoxysilane, tetraisopropoxysilane, tetraptoxysilane and the like. In addition, as derivatives of these compounds,
Examples thereof include low-condensation products obtained by partially hydrolyzing the silicon compound. Furthermore, two or more kinds of the silicon compounds described above can be mixed and used. Particularly in the present invention, as the silicon compound,
It is preferable to use an alkoxysilane compound, and tetramethoxysilane and tetraethoxysilane are particularly preferable.

The above silicon compound is hydrolyzed and condensed in a non-aqueous solvent containing water to form a wet gel. The non-aqueous solvent used is not particularly limited as long as it is a solvent that is insoluble in water and can be used. Particularly in the present invention,
Surface tension (25 ° C) is 40 mN / m or less, preferably 3
It is preferable to use a non-aqueous solvent of 0 mN / m or less. The reason for this is that when the solvent in the pores of the wet gel evaporates in the drying step (third step) described later, the capillary force acts and the pores shrink. This is because the capillary force is proportional to the surface tension and the pores shrink when the surface tension is large. Further, a non-aqueous solvent having a boiling point at atmospheric pressure higher than that of water (100 ° C.) is preferable, and 110 to 150 ° C. is particularly preferable. The reason is that when the boiling point of the non-aqueous solvent is 100 ° C. or lower, water is removed before the non-aqueous solvent is removed in the drying step (third step) described later. This is because the surface tension of water is large and causes pore contraction, which is not preferable. Also, if the boiling point of the non-aqueous solvent is too high, it becomes difficult to dry, which is not preferable. Examples of preferable non-aqueous solvent include toluene, xylene, ethylbenzene, octane and the like. In the present invention,
The above-mentioned non-aqueous solvent may be used alone or in combination of two or more kinds.

The amount of the non-aqueous solvent used is not particularly limited, but is 0.1 to 1 liter, preferably 0.2 to 0.5 liter, per mol of the raw material used. The reason is that if it is less than 0.1 liter, the fluidity of the wet gel is impaired and it becomes difficult to handle, and if it is used in excess of 1 liter, the productivity is lowered,
This is because neither case is preferable. The amount of water contained in the non-aqueous solvent is not particularly limited, but is 3 to 20 mol, preferably 6 to 12 mol per mol of the raw material. The reason for this is that if the amount of water is less than 3 mol, it takes time to hydrolyze the silicon compound, and if it exceeds 20 mol, it takes time in the drying step (third step) described later. This is because the case is not preferable.

An acid catalyst such as an organic acid or an inorganic acid, or an alkali catalyst such as an organic alkali or an inorganic alkali can be added as a hydrolysis catalyst. When using a catalyst, it is preferable to use an alkali catalyst such as ammonia. The reason for this is that the use of an alkali catalyst is preferable because the pores of the gel become large and the pores are less likely to shrink in the drying step (third step) described later.

Further, in order to improve the compatibility between the raw material and water, it is preferable to add alcohols, acetone or the like. The reason for this is that the use of these compatible solvents accelerates the hydrolysis of the silicon compound and prepares a more uniform gel. When blending a compatible solvent, the amount of the compatible solvent to be blended is not particularly limited,
The amount is 0.05 to 0.5 liter, preferably 0.1 to 0.3 liter, per mol of the raw material used. The reason for this is that if the amount is less than 0.05 liter, the effect of the compatible solvent cannot be obtained, and even if the amount is more than 0.5 liter, no further effect can be obtained. This is because in any case, it is not preferable because it becomes fine powder and becomes difficult to handle.

To hydrolyze and condense a silicon compound in a non-aqueous solvent containing water, the raw materials are added to the non-aqueous solvent,
It may be gelled with stirring at 0 to 100 ° C, preferably 30 to 70 ° C. By doing so, it is possible to prepare a wet gel having fluidity dispersed in a non-aqueous solvent.

The second step is a step of preparing the hydrophobized wet gel by reacting the wet gel prepared in the first step with the hydrophobizing agent. The hydrophobizing agent is a compound having both a functional group capable of reacting with silanol groups on the surface of silica particles constituting the fine structure of the wet gel and a hydrophobic group. As the functional group capable of reacting with the silanol group, halogen, an amino group,
Examples thereof include imino group, carboxyl group and alkoxyl group. Examples of the hydrophobic group include an alkyl group, a phenyl group and their fluorides. Specific examples of the hydrophobizing agent include those represented by the following formula 1 (Chemical formula 1). Specifically, methyltrimethoxysilane, methyltriethoxysilane, hexamethyldisilazane, trimethylchlorosilane, Fluorooctylethyltrimethoxysilane, hexamethyldisiloxane, trimethylmethoxysilane, trimethylethoxysilane, triethylethoxysilane, triethylmethoxysilane, dimethyldichlorosilane, dimethyldiethoxysilane, diethyldiethoxysilane, methyltrichlorosilane, ethyltrichlorosilane, etc. Can be illustrated. Further, one of the above-mentioned hydrophobizing agents can be used alone, or two or more kinds of hydrophobizing agents can be mixed and used.

[Chemical 1] (However, R is a hydrophobic group such as an alkyl group or a fluoro group, M is Si, X is a functional group such as halogen or an alkoxy group, a is 1 to 3 and b is 4 to 2.)

The method for preparing the hydrophobized wet gel by reacting the wet gel and the hydrophobizing agent is not particularly limited. For example, a solvent for dissolving the hydrophobizing agent and the hydrophobizing agent is added to the wet gel to 0 to 100 ° C, preferably 30 to
Under conditions of 70 ° C., 30 minutes to 100 hours, preferably 2 to
A method of stirring for about 20 hours can be exemplified. Further, after preparing the wet gel as described above, a hydrophobizing agent may be added, but when the wet gel is prepared in the first step, the hydrophobizing agent is previously added to the non-aqueous solvent. Alternatively, the wet gel may be prepared and the wet gel may be made hydrophobic at the same time. By doing so, it is possible to save the trouble of adding a hydrophobizing agent again, and it is possible to manufacture the porous silica gel more simply and at low cost.

The amount of the hydrophobizing agent used is not particularly limited,
0.01 to 2 mol, preferably 0.0 per mol of the raw material
5 to 0.5 mol of hydrophobizing agent may be used.

The third step is a step of drying the hydrophobized wet gel prepared in the second step. The method for drying is not particularly limited as long as it can dry the hydrophobized wet gel, that is, a method that can reduce the amount of the dispersion medium of the hydrophobized wet gel.
For example, heating drying at normal pressure, freeze drying, reduced pressure drying, filtration treatment, or a method of decanting the dispersion medium by leaving a wet gel to stand can be exemplified.

In the present invention, two or more of these methods may be combined and used. For example, if a non-aqueous solvent having a boiling point higher than that of water is used, the hydrophobized wet gel is first heated to a temperature above the boiling point of water and below the boiling point of the non-aqueous solvent. This makes it possible to remove components other than the hydrophobized wet gel and the non-aqueous solvent, that is, the catalyst, the hydrophobizing agent, water, etc. used in the reaction. Then, the residual liquid is allowed to stand and the supernatant non-aqueous solvent is removed by decantation, and then the liquid is heated to the boiling point of the non-aqueous solvent or higher. By doing so, the non-aqueous solvent can be removed and porous silica gel can be obtained.

The morphology of the porous silica gel thus produced is granular or powdery, and its bulk density is 0.30 g /
It is as light as less than mL. It also has hydrophobicity.

As described above, the method for manufacturing the hydrophobic and lightweight porous silica gel according to the present invention, when drying the wet gel, is under the conditions of high temperature and high pressure such as a supercritical state when the wet gel is dried. Never need. Further, it does not require a complicated operation such as a solvent replacement operation. Therefore, the hydrophobic and lightweight porous silica gel can be easily produced at low cost without requiring expensive equipment.

[0024]

EXAMPLES The present invention will be described below based on examples.
The invention is in no way limited to these examples. <Example 1> 2.5 parts by weight of xylene, 0.5 parts by weight of water,
A mixed solution of 1 part by weight of methyl orthosilicate, 1 part by weight of methanol and 0.1 part by weight of hexamethyldisilazane (HMDS) was added dropwise to a mixed solution of 0.0067 parts by weight of ammonia, and the liquid temperature was changed while stirring. Was adjusted to 45 ° C. and the reaction was continued for 5 hours. Next, the liquid temperature is the boiling point of xylene (138
℃) is heated at atmospheric pressure, distilled, methanol,
Water, ammonia and unreacted HMDS were removed. After cooling the internal liquid, it was taken out and allowed to stand to remove the supernatant liquid, then at normal pressure, 1
It was dried at 50 ° C. to prepare porous silica gel.

<Example 2> The reaction temperature of Example 1 was set to 40.
Porous silica gel was prepared in the same manner except that the reaction temperature was 48 ° C. and the reaction time was 48 hours.

Example 3 A porous silica gel was prepared in the same manner as in Example 1, except that the amount of HMDS in Example 1 was 0.2 part by weight.

<Example 4> The reaction temperature of Example 1 was set to 55 ° C.
Porous silica gel was prepared in the same manner as in Example 1 except that

<Example 5> In a mixed solution of 2.5 parts by weight of xylene, 0.5 parts by weight of water and 0.0067 parts by weight of ammonia, 1 part by weight of methyl orthosilicate, 1 part by weight of methanol,
A mixed solution of 0.1 part by weight of hexamethyldisilazane (HMDS) was added dropwise, the liquid temperature was adjusted to 45 ° C. with stirring, and the reaction was continued for 5 hours. Then, methanol 0.2
After adding 1 part by weight and 0.1 part by weight of HMDS, the mixture was heated and the distillate was refluxed and reacted for 2 hours. Finally, heating at normal pressure until the liquid temperature reaches the boiling point of xylene (138 ° C),
Distilled to yield methanol, water, ammonia and unreacted H
The MDS was removed. After cooling the internal liquid, take it out,
It was dried at 0 ° C. to prepare porous silica gel.

Example 6 A mixed solution of 2.5 parts by weight of xylene, 0.5 parts by weight of water and 0.0067 parts by weight of ammonia was added dropwise with a mixed solution of 1 part by weight of methyl orthosilicate and 1 part by weight of methanol. Then, the liquid temperature was adjusted to 45 ° C. with stirring, and the reaction was continued for 5 hours. Then methanol 0.
After 2 parts by weight and 0.2 parts by weight of HMDS were added dropwise, the mixture was heated and the distillate was refluxed and reacted for 2 hours. Finally, heating at normal pressure until the liquid temperature reaches the boiling point of xylene (138 ° C),
Distilled to yield methanol, water, ammonia and unreacted H
The MDS was removed. After cooling the internal liquid, take it out,
It was dried at 0 ° C. to prepare porous silica gel.

Comparative Example 1 A mixed solution of 1 part by weight of methyl orthosilicate and 1 part by weight of methanol was dropped into a mixed solution of 2.5 parts by weight of xylene, 0.5 parts by weight of water and 0.0067 parts by weight of ammonia. Then, the liquid temperature was adjusted to 45 ° C. with stirring, and the reaction was continued for 5 hours. Then, the liquid was heated and distilled at normal pressure until the liquid temperature reached the boiling point of xylene (138 ° C.) to remove methanol, water and ammonia. After cooling the internal liquid, it was taken out and allowed to stand to remove the supernatant liquid, and then the pressure was adjusted to 150 at atmospheric pressure.
It was dried at ℃, to prepare porous silica gel.

Comparative Example 2 In a mixed solution of 0.5 part by weight of water and 0.0067 part by weight of ammonia, 1 part by weight of methyl orthosilicate, 1 part by weight of methanol, 0.1 part by weight of hexamethyldisilazane (HMDS). When a part of the mixed solution was dropped, the whole liquid gelled and lost fluidity, and stirring could not be performed.

The bulk density, hydrophobicity and shape of the porous silica gel obtained by the above-mentioned preparation methods of Examples and Comparative Examples were evaluated by the following methods. The results are shown in Table 1. <Bulk Density> The bulk density of the porous silica gel was measured by the static method of the apparent density test method of JIS K5101. <Hydrophobicity> 5 g of a sample was put in 50 mL of water, mixed gently, and when the sample floated, it was judged to be hydrophobic, and when the sample settled, it was judged to be non-hydrophobic. <Shape> The shape of the porous silica gel was judged by observing the appearance.

[0033]

[Table 1]

[0034]

EFFECTS OF THE INVENTION The method for producing a hydrophobic and lightweight porous silica gel according to the present invention described above requires high temperature and high pressure conditions such as a supercritical state when drying a wet gel. Absent. Further, it does not require a complicated operation such as a solvent replacement operation. Therefore, it is possible to easily and inexpensively produce hydrophobic and lightweight porous silica gel without requiring expensive equipment.

Claims (6)

[Claims] 1. A first step of preparing a wet gel slurry having fluidity in a non-aqueous solvent by a sol-gel method,
Hydrophobic and lightweight, comprising a second step of preparing the hydrophobized wet gel by reacting the wet gel with a hydrophobizing agent, and a third step of drying the hydrophobized wet gel. Method for producing porous silica gel. 2. The hydrophobicity according to claim 1, wherein the hydrophobizing agent is added at the time of preparing the wet gel so that the wet gel and the hydrophobized wet gel are simultaneously prepared. And lightweight method for producing porous silica gel. 3. The method for producing a hydrophobic and lightweight porous silica gel according to claim 1, wherein the boiling point of the non-aqueous solvent is higher than the boiling point of water. 4. The third step mainly comprises distilling off components other than the hydrophobized gel and the non-aqueous solvent by heating the hydrophobized wet gel at a temperature higher than the boiling point of water and lower than the boiling point of the non-aqueous solvent. After that, the non-aqueous solvent is removed, and the method for producing a hydrophobic and lightweight porous silica gel according to claim 3. 5. The method for producing a hydrophobic and lightweight porous silica gel according to claim 1, wherein the surface tension (25 ° C.) of the non-aqueous solvent is 40 mN / m or less. . 6. The bulk density of the porous silica gel is 0.3.
It is 0 g / mL or less and is 1 to 5 characterized by the above-mentioned.
5. The method for producing a hydrophobic and lightweight porous silica gel according to any one of 1.