JP2018111086A - Temperature responsive hygroscopic material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a temperature responsive hygroscopic material that improves hygroscopic property at a low humidity and has a wide temperature change width.SOLUTION: In a temperature responsive hygroscopic material, only a hydrophilic functional group is chemically bonded inside a pore of a mesoporous body of which average pore diameter is 2 nm or more and 4 nm or less.SELECTED DRAWING: Figure 1

Description

  The present application discloses a temperature-responsive hygroscopic material.

  Conventionally, in a desiccant-type dehumidifier or air conditioner, a temperature-responsive hygroscopic material having a characteristic of absorbing and releasing water vapor in the air according to a temperature change is used. The temperature-responsive moisture-absorbing material is repeatedly used as a recyclable dehumidifying material because it can recover moisture absorption by releasing water vapor under a predetermined condition even when the moisture absorption is reduced by absorbing water vapor.

  As such a temperature-responsive hygroscopic material, for example, Patent Document 1 discloses a temperature-responsive hygroscopic material in which a thermosensitive molecule is chemically bonded inside the pores of a mesoporous body having an average pore diameter of 2 nm or more and less than 50 nm. Disclosed is a temperature-responsive moisture-absorbing material, wherein the number-average molecular weight of the temperature-sensitive molecule is 2000 or more and 5000 or less, and the introduction amount of the temperature-sensitive molecule is 5.2 mass% or more and 21.4 mass% or less. Has been.

Japanese Patent Laid-Open No. 2006-97359

  In the temperature-responsive hygroscopic material described in Patent Document 1, when a mesoporous material having a small average pore diameter of 2 to 4 nm is used in order to improve the hygroscopic property at low humidity, the temperature sensitivity having a small molecular weight is used. Only molecules could be introduced into the pores. If the molecular weight of the temperature-sensitive molecule introduced is reduced, the number of water molecules to be hydrated / dehydrated decreases, so the temperature-responsive moisture-absorbing material that changes with temperature changes the width of the change in relative humidity that exhibits hygroscopic properties. (Hereinafter, referred to as “temperature change width”) becomes small.

  Therefore, an object of the present disclosure is to provide a temperature-responsive hygroscopic material having improved hygroscopicity at low humidity and a large temperature change range.

In order to solve the above problems, the present disclosure takes the following means.
The present disclosure is a temperature-responsive hygroscopic material in which only hydrophilic functional groups are chemically bonded inside the pores of a mesoporous material having an average pore diameter of 2 nm or more and 4 nm or less.

  According to the present disclosure, it is possible to provide a temperature-responsive hygroscopic material with improved hygroscopicity at low humidity and a large temperature change range.

FIG. 1A schematically shows the behavior of temperature-sensitive molecules and water vapor molecules at a low temperature (20 ° C.) and a high temperature (40 ° C.) estimated on the pore surface of the conventional material, and FIG. FIG. 3 is a diagram schematically showing the behavior of water vapor molecules at the same temperature estimated on the pore surface of the temperature-responsive hygroscopic material of the present disclosure. It is a figure which shows the measurement result of the water vapor | steam adsorption isotherm of Examples 1-3 and the comparative example 1. FIG. FIG. 3A is a diagram showing the pore distribution before moisture absorption and after repeated moisture absorption / drying of the temperature-responsive moisture-absorbing material according to Example 1, and FIG. 3B is the temperature-responsive moisture-absorbing material according to Comparative Example 2. It is a figure which shows the pore distribution before moisture absorption, after moisture absorption, and after repeated moisture absorption and drying. 4A is a diagram showing the same measurement results as FIG. 2A, and FIG. 4B is a diagram showing the measurement results of the water vapor adsorption isotherm of Comparative Example 2. FIG. It is a figure which shows the result of the solid ²⁹ Si-NMR measurement of Example 1 and Comparative Example 2. FIG. 6A is a diagram schematically showing the state of the pore surface of the material (mesoporous body) according to Comparative Example 2, and FIG. 6B is the pore of the temperature-responsive moisture-absorbing material according to Example 1. It is a figure which shows the mode of the surface roughly.

  Hereinafter, the present disclosure will be described. In addition, the form shown below is an illustration of this indication and this indication is not limited to the form shown below.

<Temperature responsive hygroscopic material>
The present disclosure is a temperature-responsive hygroscopic material in which only hydrophilic functional groups are chemically bonded inside the pores of a mesoporous material having an average pore diameter of 2 nm or more and 4 nm or less.
The temperature-responsive hygroscopic material of the present disclosure can be produced, for example, by performing a coupling reaction described later using a mesoporous material and a silane coupling agent described below as materials.

(Mesoporous material)
The mesoporous material used in the present disclosure is a porous material having pores (mesopores) having an average pore diameter of 2 nm or more and 4 nm or less. The mesoporous material that can be used in the present disclosure is not particularly limited as long as it has such pores (mesopores) and has a hydroxyl group (silanol group) on the surface of the particle skeleton. The mesoporous material described in JP-A-11-114410 can be used.

(Silane coupling agent)
A silane coupling agent is an organosilicon compound having both an organic functional group that reacts with an organic material and a hydrolyzable group that reacts with an inorganic material in one molecule. The silane coupling agent used in the present disclosure has only a hydrophilic functional group as an organic functional group. By using a silane coupling agent having only a hydrophilic functional group as an organic functional group, only the hydrophilic functional group can be chemically bonded inside the pores of the mesoporous material by a coupling reaction described later. Examples of the hydrophilic functional group that the silane coupling agent has as an organic functional group include an amino group, a carboxyl group, a thiol group, an amide group, or an alkyl group having at least one group selected from these. . The hydrolyzable group possessed by the silane coupling agent is not particularly limited, and examples thereof include alkoxy groups such as methoxy group and ethoxy group.

(Coupling reaction)
In the temperature-responsive hygroscopic material of the present disclosure, only hydrophilic functional groups are chemically bonded inside the pores of the mesoporous material. The chemical bond is formed by performing a coupling reaction described below using the mesoporous material and the silane coupling agent.

  When performing the coupling reaction, first, the silane coupling agent is introduced into the pores of the mesoporous material. The method for introducing the silane coupling agent is not particularly limited. For example, a silane in which the mesoporous material and the silane coupling agent are dispersed or dissolved in an appropriate solvent and dispersed or dissolved in the solvent in the pores of the mesoporous material. The method of impregnating a coupling agent is mentioned. At this time, in order to promote introduction of the silane coupling agent into the pores of the mesoporous material, decompression, stirring, or the like may be performed.

  The coupling reaction proceeds by the following hydrolysis reaction and dehydration condensation reaction.

  The hydrolysis reaction is a reaction in which the hydrolyzable group of the silane coupling agent undergoes hydrolysis to generate a silanol group. The hydrolysis reaction can proceed by contacting the silane coupling agent with water. Therefore, the hydrolysis reaction can be advanced by including water in the solvent for introducing the silane coupling agent into the pores of the mesoporous material.

  In the dehydration condensation reaction, the silanol groups on the pore surface of the mesoporous material and the silanol groups of the siloxane oligomer generated by the self-condensation of silanol groups of the silane coupling agent or silanol groups of the silane coupling agent are dehydrated and condensed. It is a reaction. Due to the dehydration condensation reaction, only the hydrophilic functional group of the silane coupling agent is chemically bonded (covalently bonded) inside the pores of the mesoporous material via the siloxane skeleton formed by self-condensation of the silane coupling agents. . Thus, the hydrophilic functional group is chemically bonded to the mesoporous material via the siloxane skeleton derived from the silane coupling agent. In the present disclosure, the siloxane skeleton derived from the silane coupling agent is mesoporous. As part of the particle skeleton.

  The dehydration condensation reaction can proceed by a known method used for dehydration condensation of silanol groups, such as heating or addition of a catalyst. For example, in the form in which the solvent of the silane coupling agent contains water, the silane coupling agent can be advanced by heating after introducing the silane coupling agent into the pores of the mesoporous material.

  The reaction temperature, reaction time, and pH of the dehydration condensation reaction are appropriately set depending on the type of silane coupling agent and the like. For example, after the reaction in the temperature range of 4 to 12 and the reaction temperature of 10 ° C. to 100 ° C. for about 10 minutes to 12 hours, the reaction solution has a temperature of 100 ° C. to 150 ° C. for 30 minutes to 120 minutes. By drying for about a minute, the dehydration condensation reaction can be completed.

  In the temperature-responsive hygroscopic material of the present disclosure, the introduction amount of the hydrophilic functional group introduced into the mesoporous material ensures a pore space where a temperature change width of 5% or more can be obtained without blocking the pores. From the viewpoint of facilitating, it is preferably 3% by mass or more and 45% by mass or less. In addition, the hydrophilic functional group may be held in a surface region other than the pores of the mesoporous material.

According to the present disclosure, even when a mesoporous material having a small pore diameter is used in order to improve hygroscopicity at low humidity, the temperature change width can be increased.
FIG. 1 is a diagram for explaining the presumed mechanism, and FIG. 1 (a) is a temperature-sensitive molecule and a water vapor molecule at a low temperature (20 ° C.) and a high temperature (40 ° C.) estimated on the pore surface of a conventional material. FIG. 1B is a diagram schematically showing the behavior of water vapor molecules at the same temperature estimated on the pore surface of the temperature-responsive hygroscopic material of the present disclosure.

As shown in FIG. 1A, in the conventional material, water molecules cooperatively hydrate between the hydrophilic groups of the temperature-sensitive molecules at a low temperature (20 ° C.), and hydrophilic groups at a high temperature (40 ° C.). Moisture absorption characteristics change by dehydration of water molecules that had been hydrated together. In conventional materials whose hygroscopic properties change due to such a mechanism, the number of hydrophilic groups decreases when the molecular weight of the thermosensitive molecule is decreased in accordance with the mesoporous material having a small pore diameter, and water is cooperatively provided between the hydrophilic groups. Since the number of water molecules to be summed and dehydrated decreases, the temperature change width is considered to be small.
On the other hand, according to the temperature-responsive hygroscopic material of the present disclosure, as shown in FIG. 1 (b), water molecules are cooperatively hydrated on the surface of the hydrophilic functional group at low temperatures, and molecular activities are activated at high temperatures, Water molecules on the surface of the hydrophilic functional group are dehydrated at once. Therefore, even when a mesoporous material having a small pore diameter is used, the temperature change width is considered to be larger than that of a conventional material using a temperature-sensitive molecule.

<Examples 1-3>
[Main ingredients]
The temperature-responsive hygroscopic materials according to Examples 1 to 3 were synthesized using the main raw materials shown below.
-Mesoporous material: mesoporous silica TMPS-4R (manufactured by Taiyo Chemical Co., Ltd.)
Average particle size: 11 μm
Specific surface area: 891 m ² / g
Average pore diameter: 3.6 nm
・ Silane coupling agent: 3-aminopropyltrimethoxysilane (manufactured by Tokyo Chemical Industry Co., Ltd.)
Hydrophilic functional group: aminopropyl group

[Synthesis of temperature-responsive hygroscopic material]
Example 1
The temperature-responsive hygroscopic material according to Example 1 was synthesized by the following introduction steps (1) to (8).
(1) A 500 ml two-necked flask was charged with 5 g of mesoporous material and 250 ml of a mixed solvent prepared by mixing 2-propanol and distilled water at a weight ratio of 1: 1.
(2) While stirring with a stirrer, 2.5 g of 3-aminopropyltrimethoxysilane was added, and then a vacuum was drawn for 5 minutes with a diaphragm pump to infiltrate the mixed solvent into the pores of the mesoporous material.
(3) The cock was opened and the inside of the flask was returned to atmospheric pressure, then sealed, and kept in a water bath at 30 ° C. for 5 hours while stirring with a stirrer at about 300 rpm.
(4) The contents of the flask were subjected to suction filtration, the obtained filtrate was transferred to a 200 ml beaker, 50 ml of ion-exchanged water was added, and the mixture was stirred for 5 minutes with a stirrer and then suction filtered.
(5) The obtained filtrate was transferred to a 200 ml beaker, 50 ml of ion-exchanged water was added, and the mixture was stirred with a stirrer for 5 minutes, followed by suction filtration.
(6) The obtained filtrate was transferred to a 200 ml beaker, 50 ml of ion exchange water was added, and the mixture was stirred with a stirrer for 5 minutes, and then filtered with suction.
(7) The obtained residue was dried under reduced pressure at 120 ° C. for 2 hours and subjected to dehydration condensation.
(8) The obtained powder was dried under reduced pressure at 30 ° C. for 12 hours to obtain a temperature-responsive hygroscopic material according to Example 1 in which only aminopropyl groups were modified inside the pores of the mesoporous material.

(Example 2)
The mesoporous material was finely treated in the same manner as in Example 1, except that the amount of the mixed solvent in step (1) was 150 ml and the amount of 3-aminopropyltrimethoxysilane in step (2) was 1.5 g. A temperature-responsive hygroscopic material according to Example 2 in which only the aminopropyl group was modified inside the pores was synthesized.

(Example 3)
The pores of the mesoporous material were the same as in Example 1 except that the amount of the mixed solvent in step (1) was 50 ml and the amount of 3-aminopropyltrimethoxysilane in step (2) was 0.5 g. A temperature-responsive hygroscopic material according to Example 3 in which only the aminopropyl group was modified inside was synthesized.

[Organization / characteristic evaluation method]
(Amount of hydrophilic functional group introduced)
The mesoporous material before the introduction of the hydrophilic functional group and the temperature-responsive hygroscopic material after the introduction of the hydrophilic functional group were heated at 10 ° C. with a thermogravimetric apparatus (Pyris 1 TGA manufactured by PerkinElmer) in a dry air flow. The amount of hydrophilic functional groups introduced was calculated by heating to 1,000 ° C./min, measuring the weight reduction rate, and subtracting the weight reduction rate of the mesoporous material from the weight reduction rate of the temperature-responsive hygroscopic material. . The results are shown in Table 1.

(Pore properties)
By measuring the nitrogen adsorption isotherm of the temperature-responsive hygroscopic material with BELSORP-max (manufactured by Nippon Bell Co., Ltd.), and analyzing the obtained results by the BJH method, the total pore volume, average pore diameter, ratio Surface area values were obtained. The results are shown in Table 2.

(Water vapor adsorption isotherm)
A water vapor adsorption isotherm of a temperature-responsive hygroscopic material hydrophilized under saturated water vapor at 80 ° C. for 3 hours was measured at a high temperature (40 ° C.) with BELSORP-max (manufactured by Nippon Bell Co., Ltd.) and then at a low temperature ( 20 ° C.). Prior to measurement at each temperature, the sample was vacuum dried at 60 ° C. for 6 hours. The results are shown in FIG. Table 3 shows the temperature change width [Rh ₅₀ (H) −Rh ₅₀ (L)] of the relative humidity (Rh ₅₀ ) when adsorbing 50% of the maximum adsorption amount.

<Comparative Example 1>
[Main ingredients]
A temperature-responsive hygroscopic material according to Comparative Example 1 was synthesized using the main raw materials shown below.
-Mesoporous material: mesoporous silica TMPS-4R (manufactured by Taiyo Kagaku Co., Ltd .; the same as that used in Examples 1 to 3)
-Temperature sensitive molecule: Carboxyl-terminated N-isopropylamide (NIPAM) oligomer (manufactured by Nard Laboratories)
Number average molecular weight: 2238

[Synthesis of temperature-responsive hygroscopic material]
A temperature-responsive hygroscopic material according to Comparative Example 1 was synthesized by modifying the mesoporous material with a NIPAM oligomer as a temperature-sensitive molecule by the following introduction steps (1) to (10).
(1) 0.5 g of mesoporous material was put into a 300 ml three-necked flask, held in a water bath at 60 ° C. for 3 hours while evacuating with a rotary pump, and the mesoporous material was dried and then evacuated. The product was taken out of the water bath as it was and cooled to room temperature.
(2) In an inert gas atmosphere, thermosensitive molecule 0.0723 g, dimethylformamide (DMF) 6.2699 g, hydroxysuccinimide (NHS) 0.0416 g, 1-ethyl-3- (3-dimethylaminopropyl) carbodiimide 0.1206 g of hydrochloride (EDC) was sequentially added, stirred and dissolved, and then introduced into a 15 ml syringe.
(3) The solution of (2) was injected through a rubber septum attached to the three-necked flask of (1).
(4) The pressure was reduced for 5 minutes while stirring with a stirrer, and then argon was allowed to flow at a flow rate of 50 ml / min for 5 minutes. This operation was repeated a total of 3 times, and the mixed solution was infiltrated into the pores of the mesoporous material.
(5) Argon gas was introduced into the flask to near atmospheric pressure, and the mixture was kept at room temperature for 24 hours while stirring at about 300 rpm with a stirrer.
(6) 50 ml of ion exchange water was put into a flask, dispensed into a centrifuge tube having a capacity of 60 ml, and centrifuged at 5000 rpm for 2 minutes.
(7) The supernatant was discarded, 50 ml of distilled water was added to each centrifuge tube, and the mixture was centrifuged at 15000 rpm for 5 minutes.
(8) The supernatant was discarded, and 50 ml of distilled water was added to each centrifuge tube and centrifuged at 15000 rpm for 7 minutes.
(9) The supernatant was discarded, 50 ml of distilled water was added to each centrifuge tube, and centrifuged at 15000 rpm for 10 minutes.
(10) The obtained precipitate was dried under reduced pressure at 70 ° C. for 4 hours to obtain a temperature-responsive hygroscopic material according to Comparative Example 1 in which the mesoporous material was modified with the NIPAM oligomer.

[Organization / characteristic evaluation method]
(Introduction amount of thermosensitive molecule)
The mesoporous material before the introduction of the temperature-sensitive molecule and the temperature-responsive hygroscopic material after the introduction of the temperature-sensitive molecule were heated at 10 ° C. with a thermogravimetric apparatus (Pyris 1 TGA manufactured by PerkinElmer) in a dry air flow. The amount of temperature-sensitive molecules introduced was calculated by heating to 1,000 ° C./min, measuring the weight reduction rate, and subtracting the weight reduction rate of the mesoporous material from the weight reduction rate of the temperature-responsive hygroscopic material. . The results are shown in Table 1.

(Pore properties)
Similar to Examples 1 to 3, the total pore volume, average pore diameter, and specific surface area of the temperature-responsive hygroscopic material according to Comparative Example 1 were measured. The results are shown in Table 2.

(Water vapor adsorption isotherm)
In the same manner as in Examples 1 to 3, the water vapor adsorption isotherm at the high temperature (40 ° C.) and the low temperature (20 ° C.) of the temperature-responsive hygroscopic material according to Comparative Example 1 was measured. The results are shown in FIG. Table 3 shows the temperature change width [Rh ₅₀ (H) −Rh ₅₀ (L)] of the relative humidity (Rh ₅₀ ) when adsorbing 50% of the maximum adsorption amount.

[result]
2 and Table 3, the temperature-responsive hygroscopic material according to Example 1 having the largest temperature change width showed a temperature change width of 6.5%, and the temperature according to Example 3 with the smallest temperature change width. Also in the responsive hygroscopic material, the temperature change width was about 2.3 times that of the temperature responsive hygroscopic material according to Comparative Example 1 which is a conventional material.

<Ancillary experiments on water resistance>
Example 1
About the temperature-responsive hygroscopic material which concerns on Example 1, the physical property after repeating moisture absorption and drying (after the said water vapor | steam adsorption isotherm measurement) was measured.

[Organization / characteristic evaluation method]
(Pore properties)
Nitrogen adsorption isotherm of temperature-responsive hygroscopic material after repeated moisture absorption and drying (after measurement of water vapor adsorption isotherm) was measured with BELSORP-max (manufactured by Nippon Bell Co., Ltd.), and the obtained results were obtained by BJH method. By analysis, values of pore size distribution, total pore volume, average pore size, and specific surface area were obtained. FIG. 3A shows the pore distribution, and Table 4 shows the measured values of total pore volume, average pore diameter, and specific surface area.

(Water resistance evaluation)
A solid ²⁹ Si-NMR was measured for the temperature-responsive hygroscopic material after repeated moisture absorption and drying (after measurement of water vapor adsorption isotherm) with INOVA300 (manufactured by Agilent). The results are shown in FIG.

(Comparative Example 2)
The mesoporous material used in Examples 1 to 3 and Comparative Example 1 (the mesoporous material itself not modified with a hydrophilic functional group or a temperature-sensitive molecule) is a material according to Comparative Example 2, and before moisture absorption, after moisture absorption ( Physical properties were measured after moisture absorption under saturated water vapor at 80 ° C. for 3 hours and after repeated moisture absorption and drying (after measuring water vapor adsorption isotherms in the same manner as in Examples 1 to 3 and Comparative Example 1).

[Organization / characteristic evaluation method]
(Pore properties)
BELSORP-max (made by Nippon Bell Co., Ltd.) Before moisture absorption, after moisture absorption (after absorbing moisture for 3 hours under saturated steam at 80 ° C.), and after repeated moisture absorption and drying (after measurement of water vapor adsorption isotherm below) The nitrogen adsorption isotherm of the mesoporous material was measured, and the obtained results were analyzed by the BJH method to obtain values of pore size distribution, total pore volume, average pore size, and specific surface area. FIG. 3B shows the pore distribution, and Table 4 shows the measured values of total pore volume, average pore diameter, and specific surface area.

(Water vapor adsorption isotherm)
In the same manner as in Examples 1 to 3 and Comparative Example 1, the water vapor adsorption isotherm at high temperature (40 ° C.) and low temperature (20 ° C.) of the mesoporous material was measured. The results are shown in FIG. For comparison, FIG. 4 (a) also shows the same diagram as FIG. 2 (a).

(Water resistance evaluation)
With INOVA300 (manufactured by Agilent), solid ²⁹ Si-NMR was measured for the temperature-responsive hygroscopic material before moisture absorption and after repeated moisture absorption and drying (after water vapor adsorption isotherm measurement). The results are shown in FIG.

[result]
From Table 4, in the material according to Comparative Example 2 (untreated mesoporous material), the total pore volume decreased by 33.1% after repeated moisture absorption and drying compared to before moisture absorption, whereas the temperature according to Example 1 In the responsive hygroscopic material, the decrease in the total pore volume was suppressed to 9.6% after repeated moisture absorption and drying.
In addition, as shown in FIG. 4B, when the material according to Comparative Example 2 repeats moisture absorption and drying, the shape of the water vapor adsorption isotherm changes from V type to IV type, and the water vapor adsorption amount is greatly increased. On the other hand, the temperature-responsive moisture-absorbing material according to Example 1 did not change the shape of the water vapor adsorption isotherm even after repeated moisture absorption and drying, and the water vapor adsorption amount was maintained.
Further, as shown in FIG. 5, in the material according to Comparative Example 2, after repeating moisture absorption and drying, a clear peak of Q2 indicating that the Si—O—Si bond, which is the porous skeleton, was broken appeared. In the temperature-responsive hygroscopic material according to Example 1, no clear peak of Q2 appeared even after repeated moisture absorption and drying. From this result, in the material according to Comparative Example 2, when moisture absorption and drying were repeated, the Si—O—Si bond of the skeleton was cut (see FIG. 6A), and the water vapor adsorption property was deteriorated. In the temperature-responsive hygroscopic material according to the present invention, it is considered that the skeleton is reinforced by organic modification, and the Si—O—Si bond is hardly broken even after repeated moisture absorption and drying (see FIG. 6B).
From the above results, it is considered that the temperature-responsive hygroscopic material of the present disclosure modified with a hydrophilic functional group has improved water resistance as compared to an untreated mesoporous material.

Claims (1)

  A temperature-responsive hygroscopic material in which only hydrophilic functional groups are chemically bonded inside the pores of a mesoporous material having an average pore diameter of 2 nm or more and 4 nm or less.