JP2001104744A - Hydrophilic nano-porous material and method for production thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a material for producing a dehumidifying element large in adsorbing quantity and showing no hysteresis in an adsorbing/regenerating cycle. SOLUTION: This nano-porous material is substantially composed of silica and has a nano-porous structure uniform in pore size over a range from sub- nanometer to ten several nanometer and having a specific surface area of 400-1,300 m2/g and the inner surface of the nano-porous structure is made hydrophilic.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to, for example, a nanoporous material used as a material for a dehumidifying element used in an air conditioner, and a method for producing the same.

[0002]

2. Description of the Related Art In a desiccant air-conditioning system utilizing exhaust heat, an adsorption cooling system, and the like, various combinations of working fluids and adsorbing materials are conceivable. Assuming that the relative humidity is 50% RH in terms of P / Ps and the water content of the regenerated air is 10% RH, as shown in the image diagram of FIG. ~ 50% R
An adsorbent material having a change in the amount of adsorption as large as possible between H is required.

[0003] In the conventional zeolite, the adsorption amount is large at a low steam pressure, and the change in the adsorption amount in the target pressure range is not so large. Similarly, existing silica gel is in a linear form and may be better than zeolite, but the change in adsorption in the target pressure range is not yet large. Ideally, a dehumidifying material having an S-shaped adsorption equilibrium and capable of obtaining a large change in adsorption amount in a target pressure range is desirable. Activated carbon is a hydrophobic adsorption material by nature, but it is known that it exhibits S-shaped adsorption at a relatively high water vapor pressure due to the contribution of surface oxides. However, since the pressure corresponding to a large change in the adsorption amount is outside the target pressure range, it is not suitable for use in continuous dehumidification.

A typical known dehumidifying element is a dehumidifying element mainly composed of silica gel. The characteristics of the dehumidification characteristics of the silica gel element are that the adsorption isotherm is almost linear in a dehumidification operation range of 50% RH (relative humidity) or less, and has a large change in adsorption amount at 5% RH (relative humidity) or less. . This means that in the case of silica gel, regeneration of the dehumidifying element must be performed at a low RH% (relative humidity), that is, at a higher temperature (for example, 80 ° C. or higher).

However, in systems such as desiccant air conditioning, it is necessary to lower the regeneration temperature as much as possible in order to respond to demands such as energy saving and cost reduction.
For example, when the regeneration temperature is reduced to 70-60 ° C,
Silica gel cannot sufficiently restore the dehumidifying ability of the dehumidifying element, and the efficiency of the entire air conditioning system decreases. In other words, in a conventional dehumidifying element such as silica gel,
It is easy to understand that it is difficult to respond to energy conservation.

[0006] Adsorption is accompanied by heat generation. The heat of adsorption of the existing silica gel dehumidifying element is about 1.3 to 1.6 of the heat of aggregation of water.
There is a problem in that the relative humidity of the material is reduced due to heat generation during adsorption and the amount of water that can be dehumidified is also reduced. In addition, when the heat of adsorption is large, the amount of heat required for desorption of adsorbed molecules (regeneration of material) is large. Therefore, unless the regeneration temperature is further increased, continuous dehumidification operation is difficult to be achieved, and a decrease in efficiency of the dehumidification system can be avoided. Disappears.

[0007]

As a dehumidifying element replacing such silica gel, AlPO ₄ has been developed.
This basically has an S-shaped adsorption characteristic showing a large change in the amount of adsorption in the dehumidifying operation, but has a small amount of adsorption per unit weight and has a large hysteresis in the adsorption / regeneration cycle. In addition, when performing a continuous dehumidifying operation, similarly, there is a disadvantage that the regeneration of the element becomes difficult and the dehumidifying ability is lost. Therefore, the desiccant dehumidifying element is required to have a large amount of adsorption and not exhibit hysteresis in the adsorption / regeneration cycle.

[0008]

SUMMARY OF THE INVENTION The present invention provides a method for constructing a uniform nanopore structure and controlling the size of the nanopore based on the correlation between the pore diameter and the relative pressure based on the capillary condensation mechanism. S-shaped suction, close to the ideal material shown in 9
We have succeeded in developing a hydrophilic nanoporous material that has desorption characteristics and a very low heat of adsorption.

The invention according to claim 1 is a nanoporous material which is substantially made of silica and has a nanopore structure with a uniform diameter from sub-nanometer to ten-odd nanometer, and has a specific surface area of 400 nm. １1300 m ² / g, wherein the inner surface of the pore structure is hydrophilized. The material may be pure silica or a nanoporous silica material modified with a metal or metal oxide.

[0010] The "nanopore" specifically means a pore diameter in the range of 0.5 to 10.0 nm, and more specifically, 0.5 to 5.0 nm. In the present invention, when used for a dehumidifying element, 0.8 to 3.0 nm is preferable.
Also, because the pores are densely formed in the silica skeleton,
Its specific surface area shows a large value of 400 to 1300 m ² / g.

In the nanopores, the contact angle of polar molecules of water becomes smaller due to hydrophilicity, and the relative vapor pressure at which adsorption rises also becomes lower. One of the features of the present invention is that an excellent adsorbent material capable of adsorbing a large amount of a polar gas from a lower relative vapor pressure in the range of 0.05 to 0.5 in a large amount has been firstly produced.

[0012] The invention according to claim 2 is characterized in that the nanoporous material exhibits absorption / desorption characteristics with small hysteresis and controls the pore diameter, so that the relative vapor pressure is 5 to 5 in water adsorption.
2. The hydrophilicity according to claim 1, having an adsorption characteristic having a change in the amount of adsorption of 20 to 60% by weight for a specific vapor pressure range of 10 and several percent set in the range of 0%. It is a nanoporous material. However, the object to be adsorbed includes a polar substance such as alcohol, and is not limited to water. In a continuous dehumidification system such as a desiccant air conditioner, a small hysteresis indicates that the element can be easily regenerated, the continuous dehumidification capacity is increased, and the system efficiency can be improved.

The invention according to claim 3 is characterized in that the heat of adsorption of water by the hydrophilic nanoporous material is 1.2 times or less the heat of condensation of water. It is a hydrophilic nanoporous material, preferably 1.1 times or less, more preferably 1.05 times or less. The heat of adsorption is smaller than that of silica gel, which is an existing adsorbent, and the amount of heat input and output during adsorption and regeneration is reduced, which has the effect of increasing the efficiency of the dehumidification system.

According to a fourth aspect of the present invention, a silica source and a surfactant are used in a molar ratio of silica: surfactant:
A step of preparing a uniform solution obtained by adding an acid to an aqueous solution or an aqueous alcohol solution of H ₂ O = 1: 0.1 to 0.5: 1 to 100, and casting the solution as a material by casting, coating, spraying or the like; And a step of removing a surfactant from the shape imparting body to form a porous body having regular nanopores, and a step of hydrophilizing the internal surface of the porous body. This is a method for producing a hydrophilic nanoporous material.

The surfactant is preferably a cationic surfactant. In the step of removing the surfactant, drying and baking at 350 ° C. or higher are usually performed. As the hydrophilization treatment, the steam treatment is effective because it can treat the inside of the pores at low cost.

Compared with the hydrothermal synthesis method, which is a conventional method for synthesizing zeolite, this method can synthesize a nanoporous material by a simple operation in a beaker and can synthesize from a solution state. In addition, bulk and thin films can be easily formed. In particular, a thin film having good adhesion to a substrate can be obtained. Thus, a nanoporous material having a regular pore structure can be synthesized by a simple process.

According to a fifth aspect of the present invention, the surfactant controls the diameter of the pores by selecting one or more linear alkyl groups having 8 to 22 carbon atoms. The method for producing a hydrophilic nanoporous material according to claim 4, characterized in that: Thereby, the required pore size can be selected according to the situation. Even when a plurality of surfactants are selected, the obtained pore diameter has a constant value according to the compounding ratio thereof, and the pore diameter can be controlled. As described above, in the present invention, the pore size can be easily and accurately controlled by selecting the raw material to be used.

As the silica source, water glass, silica colloid or tetraalkoxysilane may be used.
Suitable conditions for the hydrophilization treatment are, for example, a relative humidity of 3
The treatment is performed for 30 minutes to several days using 0 to 100% steam.

[0019]

Embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a dehumidifying element according to one embodiment of the present invention, which is configured by attaching a carrier paper formed in a corrugated shape to a frame-like frame. This carrier is
As shown in FIG. 2, the honeycomb structure is formed in a honeycomb shape having holes penetrating along the flow direction of the processing air, and a dehumidifying material made of a hydrophilic porous body is integrally fixed to an inner surface of the honeycomb structure. I have. Hereinafter, the dehumidifying material will be described in order.

FIG. 3 illustrates a process for producing a dehumidifying material composed of a hydrophilic silica porous material having regular nanopores. In step 1, a silica source, water, pH
A solution is prepared by mixing a regulator, a surfactant, ethanol and the like, and the mixture is stirred and aged in the presence of micelles of the surfactant while hydrolyzing the silica source. This forms a solution of the micelle-silicate complex after several tens of minutes.

As the Si source, tetraalkoxysilane, specifically, tetraethoxysilane, tetramethoxysilane, tetraisopropoxysilane or the like is used.
It is also possible to use an alkyl trialkoxysilane such as methyltrimethoxysilane together with the tetraalkoxysilane. Tetraalkoxysilanes can be used alone or in combination of two or more. An inexpensive Si source such as sodium silicate can also be used.

In the hydrolysis of the silica source, it is necessary to control the pH according to the type of the silica source. In the case of tetraalkoxysilane, it is carried out under acidic conditions, preferably at pH 1 to 4, and in the case of sodium silicate, it is carried out preferably at pH 2 to 9. The reason why the hydrolysis is performed under the control of the pH is to adjust the conditions under which the uniform nanostructure is hardened by controlling the hydrolysis and condensation rates. As a pH adjuster,
Any acid other than hydrofluoric acid can be used, and examples thereof include hydrochloric acid, hydrobromic acid, and sulfuric acid.

The amount of water to be added is preferably 0.5 to 100 mol, more preferably 5 to 10 mol, per 1 mol of the silica source. When the silica source is sodium silicate, it is preferably from 5 to 100 mol per mol. If the amount of water to be added is too large, hydrolysis and condensation may proceed too much to cause gelation, and if too small, there is a disadvantage that the subsequently added surfactant will not be dissolved. This hydrolysis is usually performed at room temperature for about several minutes to three hours. Immediately after adding water to the tetraalkoxysilane, that is, at the initial stage of hydrolysis, the mixture is in an emulsion state, but becomes a uniform solution as the hydrolysis proceeds.

The amount of ethanol to be added is preferably 1 to 10 mol, more preferably 5 to 7 mol, per mol of the silica source. The reason why an appropriate amount of alcohol is added is to obtain a viscous solution after mixing the surfactant, thereby improving coating properties and moldability.

One of the greatest features of the present invention in producing a hydrophilic porous silica material having regular nanopores is that a mixture of the above-mentioned silica source, surfactant, water and the like is used at room temperature. -It can be synthesized only by processing near normal pressure. The order of mixing is not particularly limited. After mixing
By stirring vigorously at room temperature for several minutes while appropriately adjusting the pH of the mixture, a clear, uniform and viscous solution is obtained. In the case of sodium silicate, a white precipitate forms immediately upon mixing with a micelle aqueous solution whose pH is controlled. In order to remove sodium and the like, it is necessary to add a step of filtering and washing.

If the mixture is allowed to react for a long time in a container after mixing the silica source, surfactant and water, the mixture gels,
Care must be taken because the nanopore structure of the resulting composite may be disrupted.

As the surfactant, a compound having a long-chain alkyl group and a hydrophilic group is usually used. As the long-chain alkyl group, those having 8 to 22 carbon atoms are preferable. As the surfactant, specifically, an alkylammonium salt represented by the following general formula (1) (for example, cetyltrimethylammonium bromide) is preferable. [C _n H _{2n + 1} N (CH ₃ ) ₃ ] X (1) In the formula, n is an integer of 8 to 22, X is a halide ion such as a bromide ion or a chloride ion, or HSO ₄ ^−.
Or an organic anion such as an acetate ion. Other examples include alkyl alcohols such as acetyl alcohol, and fatty acids such as palmitic acid. Of these, alkyl ammonium salts represented by the above general formula (1) are preferable.

The surfactant is used as a template (molecular template) for forming micelles in an aqueous solution.
The size of this micelle is the number of carbon atoms (chain length) of the long-chain alkyl group.
It is the most important factor that ultimately determines the size of the uniform pore diameter of the porous body. FIG. 4 shows an X-ray diffraction pattern of the micelle formed by the surfactant. The size of micelles can be controlled by the type of surfactant (the size of the chain length) and the mixing ratio (in the case of multiple types of surfactants).

The thickness and the thermal stability of the silica layer of the hydrophilic porous silica having regular nanopores can be controlled by changing the charged composition of the surfactant and the silica source. The charge ratio (mol) of the surfactant and the silica source is preferably from 1:10 to 1: 1 and more preferably from 1: 7 to 1: 1.
1: 4 is preferred. If the amount of the surfactant is too large, there is a disadvantage that excessive surfactant crystals that do not contribute to the formation of the complex are mixed in the sample.If the amount is too small, excess silica that does not contribute to the formation of the micelle-silicate composite is mixed. In addition, there are inconveniences such as the silica layer being thickened and the regularity of the structure being reduced.

Next, in step 2 (see FIG. 3),
This solution is coated on the surface of a suitable substrate or molded by casting into a mold, and the surfactant is removed by drying to form a micelle-silicate composite in a film, powder or gel mass. To manufacture.

As the substrate for forming the micelle-silicate composite, any one can be used as long as it is generally used, and examples thereof include glass, quartz, and an acrylic plate. Any shape such as a plate shape and a dish shape can be used. Examples of the method for coating the substrate with the solution include a spin coating method, a casting method, and a dip coating method.

When a thin film is formed, a spin coating method is used. A substrate is placed on a spinner, a sample is dropped on the substrate, and 50 to 5000 rpm, preferably 2000 to 5000 rpm.
By rotating at 000 rpm, a uniform film can be formed. The thickness of the obtained spin-coated film can be adjusted to 1 μm to 500 μm depending on the spin-coating conditions. In the case of forming a thick film, a casting method is used. For example, the solution is poured into a container such as a Petri dish and dried to have a thickness of 1 μm to 500 μm.
It is possible to obtain m cast films.

Although the regularity of the structure of the formed micelle-silicate composite and the size of the composite are basically the same, it can be seen that there are some differences depending on the molding method. FIG. 5 shows X of the spin-coated film of the micelle-silicate composite.
3 shows a line diffraction pattern. FIG. 6 shows an X-ray diffraction pattern of the dried micelle-silicate composite casting powder. The structure of spin coating is somewhat more regular than that of casting, and the size of the micelle-silicate composite is also slightly smaller.

From the result of X-ray diffraction analysis of this nanocomposite, it was found that a periodic crystal structure in which a rod-like micelle (diameter: 2 to 4 nm) formed by a surfactant was surrounded by a silica layer having a thickness of 1 to 2 nm was obtained. It was confirmed that it had.
This nanocomposite was confirmed to belong to the hexagonal system.

Further, by firing this in step 3, a porous silica having a periodic nanostructure can be manufactured as shown in FIG. The heating temperature for firing is preferably 400 to 1000.
° C, more preferably 500-600 ° C. When the film-like micelle-silicate composite is used as it is, a film-like porous silica can be obtained,
Further, a powdery silica porous material can be obtained by making the micelle-silicate composite into a powder and firing it. As shown in Table 1, the porous silica has a Brunauer-Emmett-Taylor (BET) surface area of 500 to 500.
It is as high as 1200 m ² / g or more, and the average pore diameter is 0.8 to 2.3.
nm, and the pore diameters are uniform.

[0036]

[Table 1]

Further, in Step 4, a steam treatment (steaming with boiling water for 30 minutes to 5 hours) for hydrophilizing the pure silica porous body obtained by the calcination is carried out, thereby obtaining a silica porous material having hydrophilicity. You can get the body.

Using these porous materials, a water vapor adsorption isotherm was determined using a BELSORP18 automatic vapor adsorption measuring device.
It was measured at each temperature between 20 and 50 ° C.
FIG. 8 shows water vapor adsorption isotherms of three kinds of porous materials having different nanopore diameters. The adsorption isotherms exhibited S-shaped adsorption / desorption characteristics showing a large change in adsorption amount (a phenomenon that rapidly rises at a certain humidity) in a narrow humidity range between 10 and 50%. FIG. 9 shows a water vapor adsorption isotherm required for a current continuous dehumidifying material as a control example and a material considered as an ideal material of the continuous dehumidifying material. Thus, it can be seen that the S-shaped absorption / desorption characteristics shown in FIG. 8 have continuous dehumidification characteristics closer to an ideal material than conventional materials. This is a remarkable feature of the present invention.

Further, as shown in FIG. 10, the rise of the S-shaped adsorption isotherm greatly shifted to low humidity by the hydrophilization treatment indicates that the silica nanoporous material, which is originally hydrophobic, is hydrophilic. Has changed. that is,
As shown in FIG. 11, silicon atoms on the surface of silica combine with water oxygen to generate OH ⁻ of a hydrophilic group, and the formation of the hydrophilic group reduces the contact angle of water on the silica surface, thereby reducing the capillary. It is considered that the cause is that the condensing pressure decreases.

As an adsorption mechanism, it is considered that the adsorption by a hydrogen bonding force with a small amount of the surface silanol hydrophilic group is larger than the micropore potential.
Considering that it is very small at 8 °, it is considered that the first layer adsorption of water is hydrogen bond adsorption to silanol groups on the entire surface including the micropores. Therefore, approximately BET
Dividing the amount of single molecule water adsorbed using the theory by the total specific surface area obtained from nitrogen adsorption gives the amount of adsorbed water per unit surface area on all surfaces. In this case, assuming that one adsorbed water molecule is coordinated with one silanol hydrophilic group, the surface concentration of the silanol group is determined. Using such a method, the change in the surface concentration of the silanol hydrophilic group due to the hydrophilization treatment was evaluated, and it was found that the number of silanol groups increased several times by the hydrophilization treatment.

Further, based on the results of the adsorption isotherms measured at different temperatures, the isosteric heat of adsorption of the adsorbent was calculated as follows:
It was determined using the Hoff integral equation (2). Q = R (lnP ₁ -lnP ₂ ) / (1 / T ₁ -1 / T ₂ ) (2) where R is a gas constant, P is an absolute pressure, and T is an adsorption temperature. Table 2 shows an example of the result. In the hydrophilic nanoporous material of the present invention, the heat of adsorption is small, about 1.03 to 1.1 times the heat of coagulation of water, and the conventional silica gel material (1.3 to 1.6 of the heat of coagulation of water). About twice as small). The small heat of adsorption means that the energy required for the dehumidifying operation is small and that the adverse effect of increasing the temperature of the dehumidifying material due to the heat of adsorption and decreasing the dehumidifying performance during continuous dehumidifying operation is small. It shows that the COP of the dehumidification system increases. This is a remarkable feature of the present invention.

[Table 2]

In addition, the hydrophilic treatment increases the number of water adsorption sites in the monomolecular layer of the dehumidifying material, reduces the contact angle of water, and greatly improves the hydrophilicity. Also, the hysteresis of absorption / desorption was sharply reduced. The above indicates that for a continuous dehumidification system, the dehumidification / regeneration cycle that can be continuously performed under as narrow a humidity condition as possible, that is, the dehumidification operation that can absorb and desorb a large amount in a certain narrow humidity range can be performed under well-balanced conditions. Means the improvement of the system efficiency. The absence of absorption / desorption hysteresis is a remarkable feature of the present invention.

A preferred embodiment of the porous material of the present invention is a dehumidifier. This is produced by attaching a porous material to a suitable carrier, forming the porous material, and performing a hydrophilic treatment. The carrier is not particularly limited as long as it can withstand a temperature of 600 ° C., but in order to form a ventilation path, it is preferable to use a honeycomb structure that is a macroscopic porous body. Depending on the use of the product, for example, papermaking or nonwoven fabric of inorganic fibers such as ceramic fibers, glass fibers or a mixture thereof, formed into an appropriate shape and size can be arbitrarily selected and used. In addition, in order to obtain a product with good mechanical strength and durability, a honeycomb structure made of glass fiber of almost the same component that is compatible with silica as an adsorbent in the manufacturing process and easy to integrate is used. It is desirable to use.

The honeycomb structure is impregnated with the solution of the micelle-silicate composite, and the operation of impregnation and drying is repeated until the target amount is applied to the honeycomb by ventilation drying at a temperature of 10 ° C. to 80 ° C. Then, 400-600 ° C, 1-
By baking for 5 hours and removing the micelles serving as molecular templates, a strong porous element using a honeycomb structure as a skeleton and silica having regular nanopores as a dehumidifying material is produced. Finally, a hydrophilic dehumidifying element is obtained by steaming on boiling steam for about 30 minutes. Also,
It is possible to leave (aging) for a long time in the air or to obtain a hydrophilic effect. By such a simple process, a dehumidifying element can be obtained, and reduction in manufacturing cost can be expected.

[0045]

The present invention will be described in more detail with reference to the following examples, which should not be construed as limiting the present invention. Table 1 summarizes the materials used in the examples, the measurement test results, and the like. The contents of each column in Table 1 are as follows. Silica source: tetraethoxysilane surfactant (Cn): trimethylammonium bromide _{[C n H 2n + 1 N} (CH 3) 3] Br pore diameter (d): calculated hexagonal structure from Horvath-Kawazoe pore size distribution curve than nitrogen adsorption Size (a): Center distance between both neighboring pores a =
2d100 / √3 Specific surface area (S): BET surface area Pore volume (V): Volume calculated from monolayer adsorption at a relative pressure of 0.99% Capillary condensation pressure (P / P ₀ ): Fineness by capillary condensation mechanism Relative humidity corresponding to pore size

Example 1 Tetraethoxysilane (TE)
13.7 g of ethanol was added to 10.42 g of (OS) (the molar ratio of TEOS: ethanol was 1: 6).
- ethanol solution was prepared, and hexadecyltrimethylammonium bromide (C ₁₆ H as the surfactant at the same time
₃₃ N (CH ₃ ) ₃ Br, hereinafter referred to as C16) 3.64
g (TEOS: C16 (molar ratio: 4: 1)) in pure water 1
3.5 g (TEOS: water molar ratio is 1: 1)
5) The mixture was stirred at room temperature for about 10 minutes. X-ray diffraction analysis was performed on the solution obtained by stirring and mixing the surfactant and pure water, and it was confirmed that micelles having a uniform size were formed (see FIG. 4). It turns out that the size of the micelle is 2.57 nm. A TEOS-ethanol solution was added to the micelle solution and mixed. Immediately after mixing, the emulsion was an emulsion, but became a clear and uniform solution within a few minutes. pH
In 3 (adjusted with hydrochloric acid), hydrolysis was carried out while stirring at room temperature for about 3 hours. In this way, a transparent, uniform and viscous micelle-silicate composite solution was obtained.

This micelle-silicate composite solution was spin-coated on a glass substrate and dried in air to form a transparent film on the substrate. X-ray diffraction analysis was performed on the transparent film. FIG. 12 shows the X-ray diffraction pattern. As shown in FIG. 12A, this low-angle X-ray diffraction pattern shows a very sharp diffraction peak with a d value of 3.88 nm near 2θ = 2 °. From this d value, the regular center distance between both neighboring nanostructures a = 2d1
00 / $ 3 is found to be 4.48. FIG.
As shown in FIG. 12B in which the vertical axis of FIG.
It exhibited weak reflection in a 2θ range of 4.0 to 7.0 ° other than θ = 2 °. 2.57, 1.96 and 1.30 nm d values
Peak is seen. They can be indexed in a hexagonal structure with a combined d-value of 3.88. These are (100), (110), (200) and (30)
0). That is, from the X-ray diffraction pattern, it was found that the silica-surfactant nanocomposite belonging to the hexagonal system was formed on the substrate.

The above silica-C16 nanocomposite was heated at 873 K for 5 hours in air to remove C16 from the composite. By analyzing the X-ray diffraction pattern, it was confirmed that the product formed by firing was a regular nanoporous material (see FIG. 7). The diffraction pattern did not change upon firing, indicating that a regular structure was maintained even after removal of the surfactant. D10 of calcined product
The 0 value (3.01 nm) is about 0.87 nm smaller than the d100 value before baking, and it seems that there is also shrinkage of silica due to baking.

The specific surface area, pore size distribution and pore volume of this nanoporous material were evaluated by a nitrogen adsorption test. Prior to measurement of the nitrogen adsorption isotherm, the nanoporous body was pretreated at 493K for 3 hours. Nitrogen absorption at 77K of nanoporous material
The desorption isotherm is shown in FIG. Brunauer-Emmet-
The tailor (BET) surface area was 1282 m ² / g. Horvath-Kawazoe pore size distribution curve for the calcined product (Horvath, G. and Kawazoe, KJ, J. Chem. En
g. Jpn., 16, 470-475 (1983)), the average pore size was determined to be about 1.8 nm. These measurement results indicated that the periodic silica-surfactant nanocomposite obtained by the method of the present invention was converted to a porous solid. From the d value of 3.01, the repetition distance between the pore centers is a = 3.4.
The thickness of the frame structure (thickness of the silica layer) was calculated to be about 1.6 nm by subtracting the Horvath-Kawazoe pore size from the pore center distance, which was calculated to be 7 nm (calculated using a = 2d100 / √3). It was estimated.

Steam treatment for hydrophilizing the pure silica porous body obtained by firing (steaming with boiling water for 30 minutes)
Was done. In addition, the water vapor adsorption characteristics before and after the hydrophilic treatment,
Using a BELSORP18 automatic vapor adsorption measuring device,
The tests were performed at temperatures such as 25, 30, 35, 40, 45, and 50 ° C. Before the measurement, the porous material powder was pretreated at 493K for 3 hours. At each temperature, the adsorption isotherm exhibited an S-shaped characteristic having a large change in adsorption amount (a phenomenon that rapidly rises at a certain humidity) in a certain narrow humidity range. FIG. 10 shows an example of the measurement results of the adsorption and desorption isotherms of water vapor at 298 K before and after the hydrophilic treatment.
The porous silica body before and after the hydrophilization treatment exhibits an S-shaped absorption / desorption characteristic showing a large change in the amount of adsorption (a phenomenon that rapidly rises at a certain humidity) in a narrow humidity range. The silica porous material before the hydrophilization treatment has an adsorbed amount of 140 ml (STP) / g at a relative pressure of 50% RH, and a residual water amount of 70 ml (STP) / g when regenerated to a relative pressure of 10% RH. However, the steep slope of the S-shape was slightly higher than the relative pressure of 50% RH.

Before the hydrophilization treatment, the silica porous material should be 10 to 5
It is not suitable as a dehumidifying material under continuous dehumidifying conditions of 0% RH. However, the silica porous body after the hydrophilic treatment is
At a relative pressure of 50% RH, the adsorption amount was 600 ml (S.
TP) / g, when the relative pressure is regenerated up to 10% RH,
The residual water content was 50 ml (STP) / g. Moreover,
The S-shaped steep slope could be controlled within a relative vapor pressure of 10 to 50% RH. Under the continuous dehumidifying condition, almost the ideal material described above was obtained.

The large shift of the rise of the S-shaped adsorption isotherm to low humidity indicates that the originally hydrophobic silica nanoporous body has been changed to a hydrophilic one.
The relative humidity corresponding to the pore diameter by the capillary condensation mechanism was 0.47 before the hydrophilic treatment, and 0.2 after the hydrophilic treatment.
By nine. This is because, by the hydrophilization treatment, silicon atoms on the surface of the silica are connected to oxygen of water to form OH ^{− of} a hydrophilic group, whereby the contact angle of water on the silica surface is reduced and the capillary condensation pressure is also reduced. It is thought that this is the cause. When the amount of adsorption of the monolayer was compared with the amount of vapor adsorption when the relative humidity was 10%, the amount before the hydrophilic treatment was 0.12 g / g, and that after the hydrophilic treatment was 0.42 g / g.
At 8 g / g, it was found to be increased about 4 times as compared with that before the treatment. That is, it is considered that the number of hydrophilic groups on the surface of the porous body increased several times by the hydrophilization treatment.

To determine the heat of adsorption, the samples after the hydrophilization treatment were used to obtain 20, 25, 30, 35, 40, 45, 5
Water vapor adsorption isotherms were measured at each temperature of 0 ° C. In the case of the adsorption isotherm expressed by the relative pressure and the adsorption / desorption amount,
The adsorption isotherms measured at each temperature appear in the same form regardless of the temperature. From this phenomenon, it is considered that the heat of adsorption in the nanoporous material is almost the same as the heat of aggregation of water vapor. Based on the measurement results of the adsorption isotherms at different temperatures, the isosteric heat of adsorption of the adsorbent was obtained from the above-mentioned integral formula of the Van Hoff formula. The average value of the heat of equivalent adsorption is small, 1.1 times or less the heat of aggregation of water (see Table 2), and is about 1.3 to 1.6 times the conventional silica gel material (1.3 to 1.6 times the heat of aggregation of water). )
Turned out to be much smaller than that.

Example 2 In this example, decyltrimethylammonium bromide (C ₁₀ H ₂₁ N (C
H ₃ ) ₃ Br (hereinafter referred to as C10), dodecyltrimethylammonium bromide (C ₁₂ H ₂₅ N (CH ₃ ) ₃
Br, hereinafter referred to as C12), tetradecyl trimethyl ammonium bromide _{(C 14 H 29 N (CH} 3) 3 B
r, hereinafter referred to as C14) or octadecyltrimethylammonium bromide (C ₁₈ H ₃₃ N (CH ₃ ) ₃ B
r, hereinafter referred to as C18) alone or in combination of various kinds, in the same manner as in Example 1 to obtain transparent silica-C10 nanocomposite film, silica-C12 nanocomposite film, and silica-C14 nanocomposite, respectively. Film and silica-C18 nanocomposite film, silica-C
_{12 + 14 + 16 + 18} (that is, C12 + C14 + C
A mixture of 16 + C18 four surfactants) or a complex thereof was obtained.

An X-ray diffraction analysis was performed on each of the obtained nanocomposite films. The X-ray diffraction pattern
These are shown in FIGS. 14 to 18, respectively. All of the films exhibited X-ray reflections attributed to the hexagonal phase. d100
Values (C10, C12, C14, C18, and C
3.00, 3.32, 3.67, 4.04 and 3.5 for nanocomposites such as _{12 + 14 + 16 + 18} , respectively
0 nm) varies depending on the alkyl chain length of the surfactant. The interesting thing is that with a mixture of four surfactants,
The d100 value was not one of four values but one intermediate value. That is, mixing of the four types of surfactants did not form four types of micelles, but formed only micelles having an intermediate size. This means that by mixing the various surfactants, the size of the silica-micellar complex in the intermediate region of the different surfactant can be precisely controlled by the ratio of the amount of the different surfactant used. It confirms that surfactant micelles play an important role in the precise control of nanocomposite structure and size.

The above various silica-micellar nanocomposites were heated in air at 773 K for 5 hours to remove the respective surfactants from the composites. By analyzing the X-ray diffraction pattern, it was confirmed that the product formed by firing was a regular nanoporous material. The X-ray diffraction patterns are shown in FIGS. d100 value (C1
0, C12, C14, C18, and C
For the nanoporous material of _{12 + 14 + 16 + 18} , 2.22, 2.25, 2.86, 3.17 and 2.7, respectively.
(5 nm) was slightly changed by baking, but the diffraction pattern representing the ordered structure did not change in shape, indicating that the ordered structure was maintained even after the removal of the surfactant. Also, Brunauer-Emmett-Taylor (BE
T) Values such as surface area and average pore size were determined. Table 1 shows the results.
Are shown together.

These were subjected to a steam treatment (steaming with boiling water for 30 minutes) to make the pure silica porous body obtained by calcination hydrophilic. The adsorption isotherm of the water vapor adsorption characteristic before and after the hydrophilic treatment showed an S-shaped characteristic as in the previous example. Regarding the porous silica before and after the hydrophilic treatment, 29
The absorption and desorption isotherms of water vapor at 8K were measured, and FIG.
Shows the results of C10, and FIG. 25 shows the results of C12. Both of the porous silica bodies before and after the hydrophilic treatment show S-shaped absorption / desorption characteristics.

When the molecular template is C10 (FIG. 24), the adsorption amount of the porous silica before the hydrophilization treatment is 32 ml (STP) / g at a relative pressure of 25% RH, and the relative pressure is 10%.
% RH, the residual water content is 88 ml (S.
TP) / g, but the S-shaped steep slope was 30.
It is between 50% RH. Although the porous silica before the hydrophilization treatment is not necessarily suitable as a dehumidifying material under the continuous dehumidifying condition of 10.50% RH, it is more ideal that the steep gradient is close to the regeneration condition. it is conceivable that. Therefore, in the C10 silica porous body after the hydrophilization treatment, the steep gradient is between the relative pressures of 10.30% RH, which is considered to be a more ideal material for the continuous dehumidification regeneration condition of 10% RH. Can be

When the molecular template is C12 (FIG. 25), the adsorption amount of the porous silica before hydrophilization treatment is 40 ml (STP) / g and the relative pressure is 10% RH at a relative pressure of 30% RH.
When regenerated to H, the residual water content is 68 ml (STP)
/ G, but the S-shaped steep slope is 30.50% relative pressure
Between RH. Since the steep gradient of the C12 porous silica after the hydrophilization treatment is between the relative pressures of 20.40% RH, both materials are considered to be more ideal materials under the continuous dehumidification regeneration condition of 10% RH. Can be

The rise of the S-shaped adsorption isotherm is large to low humidity
The sharp shift is due to the inherent hydrophobic nature of silica nano
Already show that the porous body has changed to a hydrophilic one
This has been described in the first embodiment. C10, C12, C1 of this embodiment
4, C16 also showed the same hydrophilizing effect. example
For example, in the case of C10, the rising humidity before the hydrophilic treatment is 0.2
7, after the hydrophilization treatment, it decreased to 0.10. Hydrophilic treatment
OH of the hydrophilic group ⁻Formed on the silica surface
Contact angle and capillary condensation pressure
Call In addition, due to changes in the amount of monolayer adsorbed,
Therefore, the number of hydrophilic groups on the porous body surface increased several times.
I understand.

Example 3 Instead of the silica source of tetraethoxysilane (TEOS) of Example 1, 4.555 g of low-value water glass (sodium silicate solution) was added to hexadecyltrimethylammonium bromide (surfactant) as a surfactant. 2.278 g of C ₁₆ H ₃₃ N (CH ₃ ) ₃ Br (hereinafter referred to as C16) [water glass: C16 (molar ratio) is 8:
1) (water glass: water molar ratio is 1:15), and the mixture was stirred at room temperature for about 10 minutes to mix water glass and micelles. The silicate solution initially exhibited strong alkalinity, but hydrochloric acid was added to the silicate solution to adjust the pH to 3.
When the mixture is adjusted to 加 水 9 and hydrolyzed with stirring at room temperature for about 3 hours, a white precipitate is formed. The obtained precipitate is filtered, washed with water, dried (100 ° C. for 12 hours), and then calcined at 500 ° C. in air for 5 hours. Thus, a porous body having a nanopore structure was obtained.

Example 4 A micelle-silicate solution prepared in the same manner as in Example 1 was cast on a glass substrate and dried at 60 ° C. for 1 hour to obtain a film having a thickness of 5%.
A μm gel product was obtained. The product cracked into small pieces averaging about 3-5 mm. Next, the gel-like product was removed from the substrate and crushed to a powder. The X-ray diffraction pattern of the powdered silica-C16 nanocomposite is shown in FIG. The X-ray diffraction pattern was also indexed to a hexagonal phase with a d100 value of 3.94 nm.

Example 5 A micelle-silicate solution obtained in the same manner as in Example 1 was poured into a Petri dish and dried at room temperature (25 to 27 ° C.) for 24 hours to obtain a transparent film having a thickness of about 30 μm. A self-holding film was obtained.
The X-ray diffraction pattern of the film has a d value of about 4.03 nm.
Showed a broad diffraction peak. The fact that the composite of this example shows a broad diffraction peak suggests that the composite is composed of C16 cylindrical micelles in which the orientation of the array surrounded by silica is statistically slightly scattered. . The morphology and transparency of the film were maintained even after baking this film at 500 ° C. in air.
Further, the X-ray diffraction pattern of the fired sample also showed one diffraction peak having a d value of 3.0 nm. BET surface area is 1100m
² / g. Thus, a transparent self-holding porous film was obtained.

[Embodiment 6] An embodiment in which the above porous material is used as a dehumidifying element will be described below. As described in Example 2, when the molecular template is C10, the steep slope of the S-shape is between 10-30% RH, so that the regeneration condition for continuous dehumidification is 10% RH. , Considered more ideal material. In this example, a dehumidifying element was prototyped using C10 as a micelle-silicate composite solution. Honeycomb structure made of glass fiber (the weight of the honeycomb is 9.
445 g, very low specific gravity of apparent specific gravity of 0.12 g / cm ³ , through holes having a thickness of 0.1 mm, and a pitch of 3 × 1.8 m
The waveform is about m. 1 and 2), impregnated with micelle-silicate, and then heated with hot air at 80 ° C.
Airflow drying was performed for 0 minutes. This operation was repeated until a predetermined amount of the solution adhered to the honeycomb. Next, baking was performed at a temperature of 500 ° C. for 5 hours in an air atmosphere. The total weight of the fired honeycomb was 18.560 g. The honeycomb with the porous porous silica is washed with boiling water for 30 minutes.
Hydrophilic treatment was performed by steaming for minutes.

In the obtained dehumidifying element, from the change in weight,
It can be seen that 100% of the silica adsorbent (substrate to hygroscopic material 1: 1) was fixed to the substrate. In this silica adsorbing material, the pore diameter was 1.1 nm,
The pore volume was 0.49 cm / g (see Table 1). When a water vapor adsorption test was performed at a temperature of 25 ° C. using a BELSORP18 automatic vapor adsorption amount measuring device, the relative humidity was 1%.
It showed a moisture absorption of 7.2 g / g at 0%, 16 g / g at 20% relative humidity, and 25 g / g at 30% relative humidity. (FIG. 24
reference). The above-described nanoporous moisture absorbent of the present invention has a high affinity with the glass fiber of the honeycomb, and not only wets the honeycomb surface of the glass fiber well, but also penetrates well into the honeycomb fiber gap and becomes integral with the honeycomb after drying. In addition, the honeycomb can be strengthened as a reinforcing material, and a dehumidifying element having high mechanical strength can be obtained.

The dynamic adsorption characteristics of the dehumidifying element prepared as described above were compared with that of a conventional dehumidifying element made of silica gel (a silica gel adsorbent of 150% was fixed to a honeycomb substrate). Was evaluated. The dehumidifying performance of a dehumidifying element in which a silica adsorbent having 100% nanopores was fixed to a honeycomb substrate was evaluated. Evaluation method is length 6
Using a 0 mm honeycomb, processing air and regeneration air were alternately fed from the front surface of the element at a wind speed of 2 m / sec for a certain period of time.

First, the treated air had a water content of 11 g / kg.
The air having a constant temperature and humidity of 27 ° C. was flowed, and the moisture content, temperature, and moisture content of the treated air before and after passing through the dehumidifying element were measured, and a dynamic dehumidifying ability evaluation test was performed. Similarly,
Air having a water content of 14 g / kg at a constant temperature and constant humidity of 60 ° C. and 65 ° C. is flowed as the regenerating air. The ability was evaluated. As a control example, a similar evaluation test of dehumidifying performance was performed under the same conditions using a conventional silica gel dehumidifying element.

[0068] FIG. 26 (a) moisture content of the air due to the adsorption time before and after passing through the honeycomb (inlet side: chi _in, outlet:. Showing the change in the chi _out FIG. 26 (b) moisture process 5 shows the change in the amount of moisture absorption (m _W ) of the honeycomb of Example 1. It can be seen that the embodiment of the present invention absorbed more moisture than the material of the control example (see FIG. 27). The water content of the air before passing through (before the entrance) is 11g
/ Kg, but the water content of the air after passing through (near the outlet) drops sharply at first, and then returns to the state before the inlet. In the present invention, the initial minimum is slightly lower than the control. The material of the present invention has a lower moisture content of the treated air at the outlet than the conventional material,
It was found that more moisture had been dehumidified.

Table 3 summarizes the results of a comparison test between the dehumidifier of the present invention having regular nanopores shown in FIGS. 26 and 27 and a control (commercial silica gel dehumidifier).

[Table 3]

In the conventional method for producing a continuous dehumidifying element or a total heat exchange element, it was necessary to apply an organic or inorganic adhesive having no hygroscopic property at the time of molding. However, there is a problem that the effective area for performing the moisture absorbing action is reduced. According to the production method of the present invention, the application of only silica is used at the time of molding the element, so that the moisture absorption performance of the element is improved by about several% to several tens% compared to the case where an adhesive is used, Moreover, as described above, the strength of the element has been greatly improved.

The moisture exchange element obtained according to the present invention can be used not only in a rotary type as shown in FIG. 1, but also in a cross-current type and a counter-current type.

Further, the porous material of the present invention can be used not only for dehumidifying elements but also for applications such as total heat exchange type heat exchangers, adsorption type abatement apparatuses, adsorption cooling apparatuses, etc. Can be used as a catalyst tank by adding a small amount of additives.

[0073]

As described above, according to the present invention,
For example, an energy-saving air conditioner that has a large absolute adsorption amount in the humidity range of the dehumidification adsorption / regeneration conditions, is easy to regenerate, has low hysteresis in the adsorption / regeneration cycle, and can perform continuous dehumidification efficiently. It is possible to provide a material for producing a suitable dehumidifying element by using the material.

[Brief description of the drawings]

FIG. 1 is a perspective view illustrating an example of a dehumidifying element according to a first embodiment of the present invention.

FIG. 2 is an enlarged view showing a main part of a single-wave honeycomb.

FIG. 3 is a flowchart illustrating the steps of the embodiment of the present invention.

FIG. 4 is a graph showing an X-ray diffraction pattern of a micelle nanostructure.

FIG. 5 is a graph showing an X-ray diffraction pattern of a spin-coated film of a micelle-silicate composite.

FIG. 6 is a graph showing an X-ray diffraction pattern of the dried micelle-silicate composite casting powder.

FIG. 7 is a graph showing an X-ray diffraction pattern of a porous silica powder having a regular nanopore structure.

FIG. 8 is an adsorption isotherm of a hydrophilic nanoporous material exhibiting S-shaped adsorption characteristics.

FIG. 9 is a graph showing a comparison between a current material and an ideal material as a control example of FIG. 8;

FIG. 10 is an adsorption isotherm before and after a hydrophilization treatment of the nanoporous body of Example 1.

FIG. 11 is a chemical formula showing a surface reaction during a hydrophilic treatment.

FIG. 12 is a graph showing an X-ray diffraction pattern of the nanoporous material of Example 1.

FIG. 13 is a graph showing a nitrogen adsorption isotherm of the nanoporous material of Example 1.

FIG. 14 is a graph showing an X-ray diffraction pattern (C10) of the micelle-silicate composite of Example 2.

FIG. 15 is a graph showing an X-ray diffraction pattern (C12) of the micelle-silicate composite of Example 2.

FIG. 16 is a graph showing an X-ray diffraction pattern (C14) of the micelle-silicate composite of Example 2.

FIG. 17 is a graph showing an X-ray diffraction pattern (C18) of the micelle-silicate composite of Example 2.

FIG. 18 is a graph showing an X-ray diffraction pattern (C _{12 + 14 + 16 + 18} ) of the micelle-silicate composite of Example 2.

FIG. 19 is a graph showing an X-ray diffraction pattern (C10) of the nanoporous material of Example 2.

FIG. 20 is a graph showing an X-ray diffraction pattern (C12) of the nanoporous material of Example 2.

FIG. 21 is a graph showing an X-ray diffraction pattern (C14) of the nanoporous material of Example 2.

FIG. 22 is a graph showing an X-ray diffraction pattern (C18) of the nanoporous material of Example 2.

FIG. 23 is a graph showing an X-ray diffraction pattern (C _{12 + 14 + 16 + 18} ) of the nanoporous material of Example 2.

FIG. 24 shows adsorption isotherms of a nanoporous material (C10) of Example 2 before and after a hydrophilization treatment.

FIG. 25 shows adsorption isotherms of the nanoporous material (C12) of Example 2 before and after a hydrophilization treatment.

FIG. 26 is a graph showing one of the results of a dynamic adsorption experiment in Example 6.

FIG. 27 is a graph showing a control example of the results of the dynamic adsorption experiment in Example 6.

────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] November 9, 1999 (1999.11.
9)

[Procedure amendment 1]

[Document name to be amended] Drawing

[Correction target item name] Figure 3

[Correction method] Change

[Correction contents]

FIG. 3

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4D052 AA08 CB01 FA01 GA01 GA03 GA04 GB03 GB13 GB14 GB16 GB17 GB18 HA01 HA17 HA49 HB02 4G066 AA22B AA71A AB09D AB18A BA03 BA05 BA07 BA20 BA23 BA25 BA26 BA31 BA36 CA43 DA03 FA03 FA14 FA22 FA FA36 FA37 4G072 AA28 AA41 BB09 BB15 CC13 GG01 GG03 HH30 JJ11 JJ33 LL06 LL14 MM01 MM02 MM31 NN21 QQ06 RR05 RR12 RR05 TT05 UU11

Claims (5)

[Claims] 1. A nanoporous material which is substantially made of silica and has a uniform nanopore structure having a uniform diameter from sub-nanometers to ten and several nanometers, having a specific surface area of 400
-1300 m ² / g, wherein the inner surface of the nanopore structure is hydrophilized. 2. The nanoporous material exhibits a small hysteresis absorption / desorption characteristic, and controls the pore diameter to set the relative vapor pressure in the range of 5 to 50% in water adsorption. 20% for the percent vapor pressure range
The hydrophilic nanoporous material according to claim 1, wherein the hydrophilic nanoporous material has an adsorption characteristic having an adsorption amount change of ６０60% by weight. 3. The hydrophilic nanoporous material according to claim 1, wherein the heat of adsorption of water of the hydrophilic nanoporous material is 1.2 times or less of the heat of condensation of water. 4. Use of a silica source and a surfactant in a molar ratio of silica: surfactant: H ₂ O = 1: 0.1 to
A step of preparing a uniform solution obtained by adding an acid to an aqueous solution or an aqueous alcohol solution of 0.5: 1 to 100; a step of applying a shape as a material by casting, coating, or spraying the solution; A step of removing a surfactant from the applied body to form a porous body having regular nanopores; and a step of hydrophilizing the inner surface of the porous body. Manufacturing method. 5. The surfactant according to claim 1, wherein one or more linear alkyl groups having 8 to 22 carbon atoms are selected.
The method for producing a hydrophilic nanoporous material according to claim 4, wherein the diameter of the pore is controlled.