JP2001026664A - Preparation of porous product - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a process for preparing porous products with a low density and a large specific surface area by controlling the shrinkage of a wet gel to dry the gel. SOLUTION: A process for preparing a porous product uses a solvent having a melting point in the range of not lower than 0 deg.C to not higher than 60 deg.C as the drying solvent for a wet gel to obtain a dried gel. A process for preparing a porous product composed of a dried gel is constituted by a step of preparing a wet gel, a step of replacing the solvent of the wet gel with a drying solvent, a cooling step of coagulating the wet gel by cooling it to a temperature of lower than the melting point of the drying solvent, and a drying step of obtaining a dried gel by sublimation drying to reduce pressure to a pressure of less than the vapor pressure at the melting point of the drying solvent.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for obtaining a porous body having a low density and a large specific surface area.
The present invention relates to a method for producing a porous body that can be used as a heat insulating material, a soundproof material, a catalyst carrier, and the like.

[0002]

2. Description of the Related Art As a method for producing a porous metal oxide having a low density and a large specific surface area, a method using a sol-gel method is known. This is a method in which a wet gel obtained by dissolving a raw material of an oxide in a solvent at a low concentration and aggregating a sol of fine particles synthesized is dried to obtain a dry gel of a porous body. In this method, if natural drying, heating, and / or drying under reduced pressure are performed during the drying, the gel may shrink in the process to increase the density, or the gel may collapse depending on the drying conditions.

Therefore, a supercritical drying method is generally known as a drying method for obtaining a porous material having a low density and a large specific surface area in a sol-gel method (for example, Japanese Patent Laid-Open No. 7-13).
No. 8375). In this drying method, the wet gel is introduced into a high-pressure container, and the pressure is higher than the critical point of the solvent used for drying,
This is a method in which the solvent is removed from the wet gel after the temperature is set to the supercritical state. As the solvent, methanol, ethanol, carbon dioxide or the like is used.

As another drying method in the sol-gel method, a freeze-drying method is known. In this drying method, the gel in which the solvent is an aqueous solution is frozen, cooled by a vacuum device equipped with a freezing chamber, and directly sublimated in the frozen state to dry. Here, water is generally used as a solvent for drying. Since the triple point of water has a temperature of 0.0075 ° C. and a vapor pressure of 4.6 Torr,
In order to sublimate and dry from an aqueous solution in a frozen state, it is cooled to a temperature of 0 ° C. or less and frozen, and then the pressure is maintained at a temperature of 0 ° C. or less and a pressure of 4.6 Torr or less (usually 0.1 Torr).
Drying is performed under reduced pressure (Torr or less).

[0005]

In the above-mentioned supercritical drying method, the solvent used for drying is changed to the critical temperature of the solvent,
This is a drying method in which the pressure is released after a supercritical state at a critical pressure or higher. Therefore, in order to dry the wet gel, a high-pressure vessel is required as equipment. In addition, there is a problem that it is difficult to perform a continuous drying process, the process is a batch process, and the process is low in production efficiency. On the other hand, the above-mentioned freeze-drying method is a method of performing sublimation drying from an aqueous solution in a frozen state, and performing cooling at 0 ° C. or less and depressurization by evacuation. Therefore, in order to dry the wet gel, a vacuum container is required as equipment. In this method, unlike the supercritical drying method, a continuous drying process can be performed. However, there is a problem that the production efficiency is relatively low because it is necessary to keep cooling during drying, and it is necessary to evacuate to a high vacuum during the depressurization process.

In view of the above problems of the prior art, an object of the present invention is to provide a method for producing a porous body having a low density and a large specific surface area by drying a wet gel without using a high-pressure vessel as equipment. It is an object of the present invention to provide a production process that can perform a reduced-pressure drying process at around room temperature and has high production efficiency.

[0007]

According to the present invention, there is provided (a) a step of forming a wet gel containing a dry solvent having a melting point higher than 0 ° C. and not higher than 60 ° C., and (b) converting the wet gel to a melting point of the dry solvent. And (c) subsequent to the step (b), drying the wet gel under a reduced pressure atmosphere below the vapor pressure at the melting point of the dry solvent. The present invention relates to a method for producing a porous body made of a dried gel, which comprises a step of: The ambient temperature in the drying step (c) is preferably equal to or higher than the melting point of the drying solvent.
Also, the present invention provides (a) a step of forming a wet gel containing a dry solvent having a melting point higher than 0 ° C. and 60 ° C. or lower, and (b) contacting the wet gel with a refrigerant having a medium temperature of less than 0 ° C. Coagulating the wet gel; (c) following the step (b), drying the wet gel at an atmosphere temperature equal to or higher than the melting point of the dry solvent under a pressure atmosphere reduced to less than the vapor pressure at the melting point of the dry solvent. The present invention relates to a method for producing a porous body made of a dried gel, which comprises a step of: At this time, the refrigerant having a medium temperature of less than 0 ° C. is preferably liquid nitrogen. Preferably, the dry solvent is tertiary butyl alcohol or cyclohexane. Further, the atmospheric pressure in the drying step (c) is preferably less than 40 Torr. Further, in the method for producing a porous body, the wet gel may contain a gelling solvent different from the dry solvent. In this case, the gelling solvent may be replaced with the dry solvent. Further, the dry gel constituting the obtained porous body has a porosity of at least 60.
%, The specific surface area is preferably at least 500 m ² / g.

[0008]

DETAILED DESCRIPTION OF THE INVENTION As described above, the present invention is to obtain a porous body having a low density and a large specific surface area by drying a wet gel using a production process having a high production efficiency. Since the porous body obtained by the method of the present invention has a low density and a large porosity, it can be applied to a heat insulating material and a soundproofing material having excellent performance. Further, since the catalyst has a large specific surface area, it can be used as an efficient catalyst carrier by supporting the catalyst in the voids.

An example of the method for producing a porous body of the present invention will be described in the order of steps with reference to the step explanatory diagram shown in FIG. In the present invention, first, in step (a), a wet gel containing a dry solvent having a melting point higher than 0 ° C. and 60 ° C. or lower is formed. Here, in order to form a low-density solid portion of the dry gel constituting the porous body, a wet gel is obtained from a raw material for synthesizing a skeleton of the solid portion through a conventionally known wet gel manufacturing process. Therefore, in the present invention, the wet gel may be formed using a gelling solvent different from the dry solvent. In this case, the step (a ′) of substituting the gelling solvent with the dry solvent is performed. Just do it.

Next, in step (b), the wet gel is cooled to a temperature lower than the melting point of the dry solvent to solidify the wet gel. Then, following the cooling step (b), in the step (c), the wet gel is dried under a pressure atmosphere reduced to a vapor pressure lower than the melting point of the dry solvent. That is, the dry solvent is sublimated. By this drying step (c), a dried gel that is a porous body is obtained.

Hereinafter, the production method of the present invention will be described more specifically. First, in step (a), a raw material to be a solid part constituting a skeleton of a wet gel is dissolved or dispersed in a solvent and reacted to form a gel skeleton by advancing the reaction and form a wet gel. I do. Examples of the skeleton material of the gel include metal oxides such as silica, alumina and titania, which are formed by a sol-gel method using a metal alkoxide as a raw material thereof, a water glass method using an alkali silicate such as sodium silicate, or the like. be able to.
In this case, if necessary, the surface of the porous body obtained by drying the obtained wet gel may be subjected to a hydrophobic treatment by a conventionally known method. Further, as the skeleton material of the gel, an organic polymer can also be used, and urethane resin, phenol resin, urea resin, polyimide, polyacrylamide, polyvinyl alcohol, polyamide, and the like can be used. These can be produced by advancing the polymerization of the polymer raw material or the crosslinking of the polymer in a solvent.

The gelling solvent for forming the wet gel may be appropriately selected depending on the material of the gel. For example, common organic solvents such as water, methanol, ethanol, isopropanol, acetone, tetrahydrofuran, dimethylformamide and dimethylacetamide are used. Solvents or mixtures thereof can be used. The solvent is not particularly limited as long as it is a solvent that can form a stable gel. Note that the wet gel may be manufactured by a conventional method.

Further, in the present invention, in order to obtain a wet gel containing a dry solvent having a melting point higher than 0 ° C. and not higher than 60 ° C., a dry gel having a melting point higher than 0 ° C. and not higher than 60 ° C. A solvent may be used. In this case, it becomes easy to remove the catalyst and the like used for gel formation by solvent replacement. The solvent replacement may be performed, for example, by mixing a wet gel containing a gelling solvent in a dry solvent and performing replacement by diffusion of the solvent from the wet gel. This treatment can be performed at normal temperature and normal pressure. Preferably, solvent replacement can be promoted by stirring or heating.

In the present invention, the melting point is higher than 0 ° C. and 60 ° C.
The following dry solvents are used: drying can be performed at around room temperature, drying time is short because there are relatively many solvents having a high vapor pressure at the melting point, and equipment is simple. The reason for this is that an efficient drying process can be performed, for example, because the drying process can be simply performed. Examples of such a dry solvent include tertiary butyl alcohol (25 ° C., 41.5 Torr), glycerin (1
7.8 ° C., 3.6 × 10 ⁻⁶ Torr, cyclohexane (6.5 ° C., 39.6 Torr), cyclohexanol (21 ° C., 1 Torr), para-xylene (13.3)
° C, 4.3 Torr), benzene (5.5 ° C, 35.8).
Torr), phenol (41 ° C., 1.3 Torr) and the like. The values in parentheses are the melting point of each solvent and the vapor pressure of the solvent at that melting point.

Of these, tertiary butyl alcohol and cyclohexane are particularly preferred because of their high vapor pressure at the melting point. Using these, 4
Drying can be performed under a pressure atmosphere of less than 0 Torr. Therefore, since the sublimation speed is high and a vacuum pumping device for high vacuum is not required, it is easy to handle in terms of workability and equipment cost, and the process becomes very efficient.

Next, the wet gel obtained in the step (a) is cooled to a temperature lower than the melting point of the dry solvent contained in the wet gel to solidify the wet gel (step (b)). Here, a wet gel composed of a dry solvent having a melting point higher than 0 ° C. and equal to or lower than 60 ° C. is solidified by cooling to a temperature lower than the melting point of the dry solvent.
The cooling temperature may be lower than the melting point of the dry solvent, but is not particularly limited, and may be determined in consideration of the production efficiency of a refrigerator or a refrigerator. Preferably, the cooling is performed at a cooling temperature of about −20 ° C. Also, as in the case of using water, be sure to use 0
It is not necessary to cool to below ℃.

Further, the wet gel solidified in the step (b) is dried in the step (c). In the wet gel solidified in the cooling step (b), the dry solvent exists in the skeleton structure of the wet gel. Therefore, the wet gel is dried without greatly destroying the gel skeleton structure by vaporizing by sublimation from the frozen solid state. That is, unlike the case where the liquid dry solvent is simply dried and removed, if drying is carried out by sublimation, there is no gas-liquid interface in the gel skeleton structure, so that drying stress due to meniscus does not work. Therefore, when the dry solvent is removed, no contraction force acts on the gel skeleton structure, and the wet gel can be provided with a low-density dry gel porous body without being largely shrunk by the drying step.

In the drying step (c), the coagulated wet gel is dried under a reduced pressure atmosphere in order to sublimate the coagulated dry solvent. At this time, the atmospheric pressure is reduced to a pressure lower than the vapor pressure at the melting point of the dry solvent. The degree of vacuum in the container which can be reached by reducing the pressure varies depending on the type of the dry solvent, but it is necessary to set it to at least 50 Torr or less. However, as described above, when tertiary butyl alcohol or cyclohexane is used, 4
The pressure may be reduced to less than 0 Torr. Furthermore, since the drying rate by sublimation increases as the degree of vacuum decreases, it is effective to reduce the pressure to the order of 10 Torr or less, preferably 1 Torr or less.

The decompression operation can be performed using a general vacuum exhaust device such as a vacuum pump. For example, an oil rotary pump, an oil diffusion pump, a mechanical booster, a turbo molecular pump, a multistage ejector, and the like can be used.
These evacuation devices require a trap for collecting the vapor of the dry solvent generated from the coagulated wet gel. Usually, a low-temperature trap is used, and the vapor of the dry solvent is recovered as a solution by cooling using a cooler or a refrigerator using a dry ice cryogen or a refrigerant.

At the time of drying, a heating device or a cooling device
A freezing device is provided to control the temperature. As a heating device, a device using heater heating, radiation heating, convection heating, high-frequency heating, or the like may be used. In addition, the cooling / freezing device can be performed by a refrigeration device using a refrigerant, a refrigerating device, an electronic cooling device using a Peltier element, or the like. Usually, the drying temperature in the drying step is set lower than the melting point of the dry solvent in order to maintain the frozen state of the coagulated wet gel. However, in order to increase the drying speed and perform drying efficiently, it is preferable that the ambient temperature in the drying step is equal to or higher than the melting point of the drying solvent.

The reason is as follows. That is, the pressure in the drying container containing the coagulated dry solvent,
If the atmosphere pressure is maintained at or below the saturated vapor pressure at the melting point of the dry solvent, the solid state of the skeleton of the wet gel containing the solidified dry solvent is maintained even if the temperature is raised to the melting point temperature of the dry solvent or higher. As it is, only the dry solvent sublimes. Then, the higher the ambient temperature is, the higher the drying speed by sublimation is, and the more efficient the drying is. Furthermore, if a drying solvent having a melting point of room temperature or lower is used, drying can be performed at room temperature without particularly controlling the temperature, so that there is a merit that energy can be efficiently saved.

Further, in the method for producing a porous body of the present invention, a wet gel containing a dry solvent having a melting point higher than 0 ° C. and 60 ° C. or lower is formed in step (a), and thereafter, in step (b). The formed wet gel may be solidified by contact with a refrigerant having a medium temperature of less than 0 ° C. This procedure allows the dry solvent in the wet gel to be quickly frozen. For example, as a method for contacting a refrigerant, methanol /
It can be performed by directly immersing in dry ice, acetone / dry ice cryogen, liquid nitrogen, or the like.
The freezing due to this rapid cooling causes the dry solvent not to crystallize greatly, forming minute crystals in the skeleton of the wet gel,
Since it hardens in an amorphous state, the stress on the wet gel skeleton at the time of solidification of the solvent is reduced, and an effect is obtained that a good dry gel can be obtained. Subsequently, in step (c),
After the pressure is reduced to a pressure lower than the vapor pressure at the melting point of the solidified dry solvent, the wet gel is dried while maintaining the temperature of the atmosphere equal to or higher than the melting point of the dry solvent. In this step (c), sublimation with a high drying rate is performed, and efficient production can be performed.

According to the manufacturing method of the present invention as described above,
A porous body composed of various dried gels having excellent physical properties can be obtained. Among the porous bodies obtained in the present invention,
As the obtained physical properties, it is preferable that the porosity of the dried gel is at least 60% by volume and the specific surface area of the dried gel is at least 500 m ² / g. The porosity is
It is the ratio of the space occupied by the space other than the gel skeleton in the porous dry gel, and is expressed as a percentage obtained by dividing the difference between the true density of the solid portion of the gel skeleton and the apparent density of the dry gel by the true density.

Further, according to the present invention, it is preferable to use a heat-insulating material, a sound-insulating material, a catalyst carrier, etc. to which the dried gel can be applied.
A porous body having a porosity of 0% or more can be favorably obtained.
In particular, the specific surface area is 500 according to the Brunauer-Emmett-Teller (BET) method, which is a measurement method based on nitrogen adsorption.
A porous body having a value of m ² / g or more can be obtained favorably.

Further, it is possible to obtain one having an apparent density of 1000 kg / m ³ or less and an average pore size of 1 μm or less. In particular, the apparent density of the porous body is 500k
g / m ³ or less and an average pore size of 1 μm or less can provide a dried gel having excellent heat insulating performance. These densities can be controlled by adjusting the solid content ratio when mixing the raw materials during the formation of the wet gel. As the shape of the porous body made of dried gel, monolithic board shape, granular shape such as beads,
It can be used in the form of a powder or a shape obtained by molding them.

[0026]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, but it should not be construed that the present invention is limited thereto. The shrinkage rate, which indicates the degree of shrinkage, is expressed as a percentage obtained by dividing the linear size of the gel after drying by the linear size of the wet gel before drying. << Example 1 >> A silica sol solution was prepared by mixing tetramethoxysilane as a metal alkoxide, ethanol as a gelling solvent, and 0.01 N ammonia water as a catalyst at a molar ratio of 1: 5: 4, respectively. . In order to obtain a wet gel from this solution, a silica sol solution was dropped into a hexane solution to perform gelation, thereby obtaining a bead-like silica wet gel having a diameter of about several mm. This was filtered through a sieve with a mesh size of 500 μm to separate the wet gel from the hexane solution. Next, ethanol as a gelling solvent contained in the bead-shaped wet gel was replaced with a dry solvent. The wet gel was placed in tertiary butyl alcohol and left at 40 ° C., and the solvent was replaced three times.

Further, the wet gel collected by filtration was placed in a refrigerator set at 5 ° C., cooled, and the wet gel was frozen. After the coagulated wet gel is placed in a vacuum container set at 20 ° C., vacuum evacuation is performed by an oil rotary pump through a cooling trap immersed in liquid nitrogen, and drying is performed while evacuating to a degree of vacuum of 1 Torr or less. Was.
During this time, through the observation window of the vacuum container, it was confirmed that tertiary butyl alcohol was dried while sublimating from a state in which the wet gel was solidified. The resulting dried gel of silica had a shrinkage of about 85% in the diameter of the beads, and the shrinkage was suppressed. And the physical properties as a porous body are
The porosity was about 90%, the specific surface area by the BET method was about 900 m ² / g, and the average pore diameter was about 9 nm.

Comparative Example 1 A wet gel of silica in the form of beads having a diameter of several mm produced in the same manner as in Example 1 was allowed to stand at normal temperature and normal pressure and air-dried. The obtained dried gel of silica shrunk to about 35% in the diameter of the beads, and the gel skeleton structure was largely collapsed. The physical properties of the porous body are about 30% porosity, about 450 m ² / g as specific surface area by BET method,
An average pore diameter of about 4 nm was obtained. It was confirmed that the pore diameter was reduced by shrinkage, and the structure of the porous body was largely collapsed.

Example 2 Resorcinol and formaldehyde as phenolic resin raw materials and sodium carbonate as a catalyst were mixed at a molar ratio of 1: 2: 0.01, respectively, so that the solid content of the resin was about 8% by weight. The mixture was mixed with water as a chemical solvent to prepare a raw material mixture. In order to obtain a wet gel from this mixture, the mixture was placed in a thermostat at about 85 ° C. for 5 days to obtain a phenol resin wet gel. The shape was formed in a board shape. Next, the wet gel was subjected to solvent replacement with tertiary butyl alcohol used as a dry solvent three times.

Next, the wet gel replaced with a dry solvent was
The sample was placed in a refrigerator set at ℃ and cooled to freeze the wet gel. The coagulated wet gel was placed in a vacuum container set at 20 ° C., and then evacuated by an oil rotary pump through a cooling trap immersed in liquid nitrogen, and evacuated to an ultimate vacuum of 1 Torr or less. Vacuum is 40 Torr
While confirming the following, the temperature of the atmosphere in the vacuum vessel was raised to 65 ° C., and drying by sublimation was performed.

In the obtained dried gel of phenolic resin, the shrinkage of the size was about 85%, which was suppressed. The porous material has a porosity of about 93% and a specific surface area of about 620 m ² / BET method.
g, an average pore diameter of about 4 nm was obtained.

Comparative Example 2 A wet gel of a phenolic resin produced in the same manner as in Example 2 was allowed to stand at room temperature and normal pressure and air-dried. The size of the obtained dried gel of the phenolic resin was shrunk to about 30%, and the gel was significantly crushed. The porous material has a porosity of about 15%, a specific surface area of about 380 m ² / g by a BET method, and an average pore diameter of about 4 nm.
was gotten. Although the pore diameter is not changed, the size is largely shrunk and the specific surface area is greatly reduced. Therefore, it is considered that the structure of the porous body is broken and the number of pores is reduced.

Example 3 The heat insulation performance of a porous board made of a dried gel of phenolic resin prepared in Example 2 was measured. The apparent density of this porous body is about 90 kg / m ³
Met. The thermal insulation performance was 0.033 W / mK in thermal conductivity at an average temperature of 24 ° C. and atmospheric pressure, and a good thermal insulation performance equivalent to 0.035 W / mK of general glass wool was obtained. Furthermore, by filling this board-shaped porous body into an aluminum foil laminated film container and sealing it by vacuum, it was possible to obtain excellent vacuum heat insulating performance with a thermal conductivity of 0.010 W / mK or less. The vacuum in the vessel at this time was about 0.01 Torr.

Example 4 In the same manner as in Example 2, resorcinol and formaldehyde were used as phenol resin raw materials, and sodium carbonate was used as a catalyst at a molar ratio of 1: 2 to 0.01, respectively, and the resin solid content was about 8%. weight%
Was mixed with water as a gelling solvent so as to obtain a raw material mixture. To obtain a wet gel from this mixture, about 85
It was put in a thermostat at 5 ° C. for 5 days to obtain a wet gel of a phenol resin. The shape was formed in a board shape. This wet gel was subjected to solvent replacement three times with cyclohexane used as a dry solvent.

Next, the wet gel replaced with a dry solvent is
The sample was placed in a freezer set at 10 ° C., cooled, and the wet gel was frozen. After the coagulated wet gel is placed in a vacuum container set at 5 ° C., vacuum evacuation is performed by a mechanical booster (using an oil rotary pump as an auxiliary exhaust device) through a cooling trap immersed in liquid nitrogen, and the ultimate vacuum is reached. The air was evacuated to 1 Torr or less. Vacuum is 40 Torr
While confirming the following, the temperature of the atmosphere in the vacuum vessel was raised to 65 ° C., and drying by sublimation was performed. The resulting dried gel of phenolic resin has a size shrinkage of about 8
The shrinkage was 5%, which was suppressed. The physical properties of the porous body were a porosity of about 93%, a value of about 650 m ² / g as a specific surface area by a BET method and a value of about 5 nm as an average pore diameter.

Example 5 In the same manner as in Example 2, resorcinol and formaldehyde as phenol resin raw materials and sodium carbonate as a catalyst were used at a molar ratio of 1: 2: 0.01, respectively, and the resin solid content was about The raw material mixture was prepared by mixing with water as a gelling solvent so as to be 8% by weight. To obtain a wet gel from this mixture, about 8
It was placed in a 5 ° C. thermostat for 5 days to obtain a phenol resin wet gel. The shape was formed in a board shape. Next, the wet gel was subjected to solvent replacement with tertiary butyl alcohol used as a dry solvent three times. Next, the wet gel replaced with a dry solvent was cooled by immersing the wet gel in liquid nitrogen (−196 ° C.), and the wet gel was frozen. The coagulated wet gel was taken out of the liquid nitrogen and immediately placed in a vacuum vessel set at 20 ° C., and then evacuated to a vacuum of 0.1 Torr or less. Vacuum is 40 To
While confirming that the temperature was rr or less, the temperature of the atmosphere in the vacuum vessel was raised to 50 ° C., and drying by sublimation was performed.

The resulting dried gel of the phenolic resin had a size shrinkage of about 98%, and could be dried with almost no shrinkage. The porous material has a porosity of about 93%, a specific surface area of about 770 m 2 / g by a BET method, and an average pore diameter of about 4 nm.
Was obtained.

[0038]

As described above, according to the present invention, a porous body having a low specific density and a large specific surface area can be produced by drying a wet gel. Thus, it is possible to provide a production process which can perform a vacuum drying treatment and has high production efficiency.

[Brief description of the drawings]

FIG. 1 is a process explanatory view of an example of a method for producing a porous body of the present invention.

Claims (8)

[Claims] 1. A step of forming a wet gel containing a dry solvent having a melting point higher than 0 ° C. and 60 ° C. or lower, and (b) cooling the wet gel to a temperature lower than the melting point of the dry solvent. A step of coagulating the wet gel, and (c) a step of drying the wet gel in a pressure atmosphere reduced to a pressure lower than the vapor pressure at the melting point of the dry solvent following the step (b). How to make the body. 2. The method for producing a porous body according to claim 1, wherein the atmosphere temperature in the drying step (c) is equal to or higher than the melting point of the drying solvent. 3. A step of forming a wet gel containing a dry solvent having a melting point higher than 0 ° C. and 60 ° C. or lower, and (b) bringing the wet gel into contact with a refrigerant having a medium temperature lower than 0 ° C. A step of coagulating the gel, (c) following the step (b), drying the wet gel at an atmosphere temperature equal to or higher than the melting point of the dry solvent under a pressure atmosphere reduced to a vapor pressure at the melting point of the dry solvent. A method for producing a porous body comprising a dried gel having a step. 4. The method according to claim 3, wherein the refrigerant having a medium temperature of less than 0 ° C. is liquid nitrogen. 5. The method for producing a porous body according to claim 1, wherein the dry solvent is tertiary butyl alcohol or cyclohexane. 6. The atmosphere pressure in the drying step (c) is 4
The method for producing a porous body according to any one of claims 1 to 5, wherein the method is less than 0 Torr. 7. The porous body according to claim 1, wherein the wet gel contains a gelling solvent different from the dry solvent, and the gelling solvent is replaced with the dry solvent in the step (a). Production method. 8. A method for producing a porous body according to claim 1, wherein the porosity is at least 60%.
A porous body made of a dried gel having a specific surface area of at least 500 m ² / g.