JP2007302844A - Heat-absorbing and emitting material, method for producing heat-absorbing and emitting material, and chemical heat pump system using the heat-absorbing and emitting material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a heat-absorbing and emitting material hardly deteriorated with age when used for a chemical heat pump. <P>SOLUTION: The heat-absorbing and emitting material is aggregate of fine particles. Each heat-absorbing and emitting material particle 1 comprises a first compound particle 2 emitting the heat by hydration reaction, and a second compound 3 having pores allowing the permeation of water molecules used for the hydration reaction of the first compound particle, and not forming solid solution with the first compound particle, and the first compound particle 2 is covered with the second compound 3. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a heat absorbing / dissipating material, a method for producing the heat absorbing / dissipating material, and a chemical heat pump system using the heat absorbing / dissipating material.

  A material that generates heat and generates a solvate by a solvation reaction such as a hydration reaction, and changes to the original material by an endothermic reaction of this solvate has attracted attention for use as a chemical heat pump as an endothermic material. . Examples of the heat absorbing / dissipating material usable for the chemical heat pump using the hydration reaction include alkaline earth metals and alkali metal oxides such as magnesium oxide (MgO). This oxide-based chemical heat pump material such as magnesium oxide has an advantage that the energy density per unit weight) is higher than that of other chemical heat pump materials, for example, alcohol-based liquid chemical heat pump materials.

A chemical heat pump using magnesium oxide is described in Patent Document 1, for example.
JP 2004-243305 A

  When conventional oxide-based chemical heat pump materials are applied to a chemical heat pump and repeat an exothermic reaction and an endothermic reaction, the amount of heat generation gradually decreases and the performance as a heat pump decreases, resulting in the recovery of thermal energy. The efficiency was decreasing.

  Such deterioration over time of the chemical heat pump could not be solved even with the heat absorbing / dissipating material described in Patent Document 1 having a high-purity starting material and a uniform average particle diameter.

  The heat-absorbing and heat-dissipating material of the present invention that can advantageously solve the above-described deterioration of the chemical heat pump with time includes the first compound particles that generate heat due to the hydration reaction, and the water molecules used in the hydration reaction of the first compound particles. It is made of a second compound that has permeable pores and is insoluble in the first compound particle, and the first compound particle is covered with the second compound. The gist.

  In the method for producing a heat absorbing / dissipating material of the present invention, after preparing a colloidal solution in which a precursor of first compound particles that generates heat by a hydration reaction is dispersed, the precursor of the first compound in the colloidal solution is prepared. The gist of the present invention is to provide a step of forming a second compound around the particles and then firing.

Furthermore, the chemical heat pump system of the present invention contains a heat-absorbing and heat-dissipating material that generates heat by a hydration reaction, and can be heated.
A storage container containing water supplied to the reaction container;
A gas flow path connecting the reaction vessel and the storage vessel,
The heat-absorbing and heat-dissipating material has first compound particles that generate heat due to a hydration reaction, pores that can permeate water molecules used for the hydration reaction of the first compound particles, and the first It is composed of a second compound that is insoluble in the compound particles, and the first compound particles are covered with the second compound.

  According to the heat absorbing / dissipating material of the present invention, even if it is used for a long time using a chemical heat pump, there is an excellent effect that there is little deterioration in performance.

  Embodiments of the heat absorbing / dissipating material of the present invention will be described with reference to the drawings.

  FIG. 1 is a cross-sectional view schematically showing the configuration of one particle in one embodiment of the heat absorbing / dissipating material according to the present invention. The heat absorbing / dissipating material according to the present invention is an aggregate of fine particles, and the heat absorbing / dissipating material particle 1 generates heat during a solvation reaction, more specifically, a hydration reaction that generates a hydrate, and The first compound particle 2 that reversibly changes to the original substance by an endothermic reaction that heats the hydrate, and the first compound particle 2 formed around the first compound particle 2 And the second compound 3 covering the surface. The second compound 3 is a compound insoluble in the first compound, and has a plurality of pores 4 leading from the surface of the second compound 3 to the first compound particles 2 inside. ing. The pores 4 have a size that allows permeation of water molecules (water vapor molecules) used for the hydration reaction of the first compound particles. Note that the heat absorbing / dissipating material particles 1 shown in FIG. 1 are schematically illustrated in order to facilitate understanding of the heat absorbing / dissipating material according to the present invention, and the actual particles include the number of pores 4. The thickness of the second compound 3 and the like are not limited to those shown in FIG.

  The effect of the heat absorbing / dissipating material particles 1 of the present embodiment having the configuration shown in FIG. 1 will be described. As a result of intensive studies to investigate the cause of deterioration over time of the heat absorbing / dissipating material used in the chemical heat pump using the hydration reaction, the inventors have determined that the deterioration of the heat absorbing / dissipating material is caused by the reaction surface (absorption of water). It has been found that the surface of the heat-dissipating compound particles is significantly lost due to aggregation of the compound particles themselves. More specifically, when an ordinary heat absorbing / dissipating material such as MgO (magnesium oxide) generates heat due to its hydration reaction, the surface energy of each particle is reduced, that is, the surface area of the particle is reduced. Mass transfer occurs in the direction. Thereby, adjacent MgO particles are bonded to each other and the MgO particles themselves are aggregated. When the MgO particles themselves aggregate, the surface area of the MgO particles decreases, so the contact area that reacts with water molecules as the heat absorbing / dissipating material decreases. It has been found that the decrease in the contact area with water molecules due to the aggregation of the heat absorbing / dissipating material particles is a cause of deterioration with time when used in a chemical heat pump. This agglomeration of the heat absorbing / dissipating material particles cannot be solved even if the heat absorbing / dissipating material particles are simply of high purity or have a uniform particle diameter.

  In the present embodiment, the second compound 3 is formed around the first compound particles 2 that absorb and dissipate heat in order to suppress the aggregation of the heat absorbing / dissipating material particles. The particles 2 are covered with the second compound 3. Accordingly, the contact between the first compound particles 2 is suppressed by the second compound 3, and aggregation is suppressed. In addition, since the second compound 3 has a large number of pores 4 that can penetrate water molecules, the water molecules can contact the first compound particles 2 through the pores 4. The decrease in the contact area between the water molecules and the first compound particles 2 due to the formation of the second compound 3 is suppressed. From the above, the heat absorbing / dissipating material of the present embodiment includes the first compound particles 2 which are finely absorbing / dissipating particles by inclusion and fixation of the first compound particles 2 with the second compound. It is possible to obtain an absorption / release material having a high energy density while suppressing aggregation degradation.

  The particle diameter of the first compound particles 2 is preferably 10 nm or less. When the particle diameter of the first compound particles 2 having a function of absorbing and releasing heat is 10 nm or less, the surface area is dramatically increased as compared with the case of exceeding 10 nm, and excellent heat absorbing and releasing characteristics are exhibited. By reducing the particle size of the first compound particles 2, the reaction area with water molecules increases, and as a result, a remarkable temperature increase effect can be obtained during an exothermic reaction. Furthermore, by controlling the particle diameter to a predetermined particle diameter of 10 nm or less, it becomes possible to control the amount of heat generation (temperature increase) or the heat generation rate.

  The size of the pores 4 of the second compound 3 is preferably smaller than the particle diameter of the first compound particles 2. Since the pores of the second compound 3 are smaller than the first compound particles 2, the first compound particles 2 move through the pores 4 of the second compound 3 and the first compound particles 2. It is possible to maintain the water molecule permeation function of the second compound 3 while suppressing the aggregation of each other. Since the diameter of the water molecule is very small, less than 0.3 nm, the lower limit of the size of the pores 4 of the second compound 3 is less than 0.3 nm, but the size of the pores 4 of the second compound 3 In a normal material that can be used as the second compound 3 if the particle diameter is smaller than the particle diameter of the first compound particles 2, the size of the pores 4 has a function of penetrating water molecules. There is no hindrance.

The first compound particles 2 are preferably a compound of at least one metal selected from alkali metals, alkaline earth metals, and rare earth metals. A material that generates heat from the hydration reaction and reversibly changes to the original compound by the endothermic reaction can be applied to the first compound particles 2. These compounds can be arbitrarily selected depending on the operating temperature range of the chemical heat pump. For example, in the endothermic process, the temperature range at which the first compound particles 2 as the heat absorbing / dissipating material can be obtained is 150 ° C CaO, 300 ° C MgO, and 650 ° C Pr ₂ O. ₃ and Li ₂ O can be selected and applied at 1000 ° C. In the chemical heat pump, the endothermic process normally uses unnecessary waste heat, and therefore, any compound described above can be selected and used in the chemical heat pump depending on the waste heat temperature range.

Among the various first compound particles 2 listed above, MgO has an excellent heat absorption / exotherm per unit weight. Furthermore, MgO also has the property that the Mg (OH) ₂ → MgO + H ₂ O reaction proceeds (can absorb heat) even in a temperature range of about 300 ° C., which is relatively difficult to use waste heat. Therefore, although it depends on the operating temperature of the chemical heat pump, it is preferable to employ a magnesium compound, especially MgO, as the first compound particles 2.

The second compound 3 is preferably at least one compound selected from CeO ₂ , ZrO ₂ , TiO ₂ and SiO ₂ . The material of the second compound 3 covers the first compound particles 2 and exhibits a function of suppressing the aggregation of the first compound particles 2 with the first compound particles 2 (so-called “so-called”). A compound that does not generate a solid solution can be selected, and CeO ₂ , ZrO ₂ , TiO _2, and SiO ₂ listed above satisfy the requirement. Further, CeO ₂ , ZrO ₂ , TiO ₂ and SiO ₂ can all be formed around the first compound particles 2 in the form of fine particles or fibers, thereby forming the aforementioned predetermined pores. Is a material that can be. For example, if the first compound particle 2 is MgO, by arranging CeO ₂ as the second compound 3 around the MgO, the MgO particles can be prevented from coarsening and stabilized without reacting with the MgO particles. Can be maintained.

  Next, an embodiment according to the method of manufacturing the heat absorbing / dissipating material of the present invention will be described. In one embodiment of the manufacturing method, after preparing a colloidal solution in which a precursor of the first compound particles that generates heat due to a hydration reaction is dispersed, around the first compound precursor particles in the colloidal solution The method may further include a step of forming a second compound and then baking. First compound particles 2 or a precursor thereof having a size of 10 nm or less are formed in a colloidal state finely dispersed in a liquid. By dispersing the minute first compound particles 2 or the precursor thereof in the colloidal solution, the first compound particles 2 or the precursor thereof are prevented from contacting and aggregating with each other during the manufacturing process, and as a result The surface area of the first compound particle 2 can be remarkably increased in the heat absorbing / dissipating material after manufacture. As the first compound particle 2 or a precursor thereof, a conventionally known material can be used, and a known material such as PVP (polyvinylpyrrolidone) can be used as the colloid material. Moreover, the particle diameter of the 1st compound particle 2 can be adjusted by adjusting the quantity ratio of the 1st compound particle 2 or its precursor, and a colloid material.

  Next, a second compound is formed around the first compound particle 2 or its precursor in the colloidal solution. By mixing the colloidal solution in which the first compound particle 2 or its precursor is dispersed and the separately prepared second compound or its precursor solution, around the first compound particle 2 or its precursor. A second compound can be formed. In order to form the second compound, for example, a sol-gel method can be used. Therefore, it is preferable to mix a colloidal solution and a solution containing the metal alkoxide of the second compound. The pore size of the second compound can be adjusted by adjusting the concentration of the solution of the second compound or a precursor thereof (for example, a metal alkoxide solution). The adjustment of the pore size is not limited to the adjustment of the concentration of the second compound or its precursor in the solution of the second compound or its precursor. For example, the firing conditions at the time of firing described below are adjusted. It can also be adjusted by doing.

  Thereafter, the colloidal solution is filtered, and the gel is dried and baked to obtain a heat absorbing / dissipating material. The heat absorbing / dissipating material can be pulverized to adjust the particle size as necessary.

  Next, a chemical heat pump system using the heat absorbing / dissipating material according to the present invention will be described. FIG. 2 is a configuration diagram of an example of a chemical heat pump system according to the present invention. The chemical heat pump system 10 shown in the figure includes a reaction vessel 11 that contains the heat absorbing and radiating material according to the present invention, a storage vessel 12 that contains water for water vapor supplied to the reaction vessel 11, and the reaction vessel 11 A steam channel 13 serving as a gas channel connecting the storage container 12 and a valve 14 provided in the middle of the steam channel 13 are provided. The reaction vessel 11 is a vessel that generates an exothermic or endothermic reaction of the heat-absorbing / dissipating material accommodated therein, and can recover heat generated by the exothermic reaction. It is configured to be able to supply inside the container. The storage container 12 is configured to generate water vapor by heating and to condense the water vapor. The water vapor channel 13 is for moving the water vapor from the reaction vessel 11 to the storage vessel 12, and conversely from the storage vessel 12 to the reaction vessel 11, and a valve 14 provided in the middle of the water vapor channel 13. The movement of water vapor is regulated, and the movement amount (water vapor pressure) can be adjusted.

  When supplying heat to the outside, the chemical heat pump system 10 shown in FIG. 2 heats the water stored in the storage container 12 into steam, and guides the steam to the reaction container 11 through the steam channel 14. Then, in the reaction vessel 11, the heat absorbing / dissipating material accommodated in the reaction vessel 11 reacts with water vapor to produce a hydrate. Since this reaction is an exothermic reaction and heat is released, heat can be recovered by recovering this heat.

  In the chemical heat pump system 10, when storing waste heat or the like, the reaction vessel 11 is placed in a waste heat environment, and the hydrate of the heat-absorbing / dissipating material housed in the reaction vessel 11 is heated from the outside. . Then, in a predetermined temperature range corresponding to the type of the heat absorbing / dissipating material accommodated in the reaction vessel 11, the hydrate of the heat absorbing / dissipating material returns to the original compound as the heat absorbing / dissipating material by the endothermic reaction, and water vapor appear. This water vapor is guided to the storage container 12 through the water vapor flow path 14 and condensed.

In this way, in the reaction vessel 11, the heat of ΔH ₁ is released or absorbed by the heat absorption / release reaction of the heat absorbing / dissipating material, and in the storage vessel 12, the heat of ΔH ₂ is generated with the phase change during water evaporation and condensate. Endothermic or released. The chemical heat pump system according to the present invention utilizes these heat dissipation and endothermic changes.

  Since the chemical heat pump system uses the heat absorbing / dissipating material according to the present invention as the heat absorbing / dissipating material, aggregation due to the repetition of the exothermic-endothermic reaction of this absorbing / releasing material is suppressed, and thus a high-performance chemical over a long period of time. A heat pump system can be maintained.

[Example 1]
An aqueous solution of Mg acetate, polyvinylpyrrolidone (PVP), and ion-exchanged water are put into a container in an amount such that the PVP / Mg molar ratio is 8, stirred for 1 hour, and then heated to 100 ° C at a rate of 5 ° C / min. The temperature was raised to prepare a 5 wt% -PVP-Mg colloidal solution (average particle size 4 nm).

  On the other hand, cerium isopropoxide was added to another container in an amount adjusted to 10 wt% in the solvent (hexylene glycol), stirred at 100 ° C. for 1 hour, and then the PVP-Mg colloidal solution described above in this container. Was introduced.

Thereafter, the gel obtained was dried and fired to obtain the heat absorbing / dissipating material of Example 1. The composition of the obtained heat absorbing / dissipating material powder was MgO (65%) / CeO ₂ (residue). The particle diameter of MgO in this powder was 4 nm, and the pore diameter of CeO ₂ was measured to be 3 nm.

[Example 2]
The heat absorbing / dissipating material of Example 2 was obtained in the same manner except that the PVP / Mg molar ratio of Example 1 was 2.4 and the solution concentration of cerium isopropoxide was 26 wt%. The composition of the obtained heat absorbing / dissipating material powder was MgO (65%) / CeO ₂ (residue). The particle diameter of MgO in this powder was 6 nm, and the pore diameter of CeO ₂ was measured to be 5 nm.

[Example 3]
The heat absorbing / dissipating material of Example 3 was obtained in the same manner except that the PVP / Mg molar ratio of Example 1 was 1.2 and the solution concentration of cerium isopropoxide was 40 wt%. The composition of the obtained heat absorbing / dissipating material powder was MgO (65%) / CeO ₂ (residue). The particle diameter of MgO in this powder was 10 nm, and the pore diameter of CeO ₂ was measured to be 9 nm.

[Example 4]
An aqueous solution of Pr acetate, polyvinylpyrrolidone (PVP)) and ion-exchanged water are put into a container in an amount such that the molar ratio of PVP / Pr is 8, and after stirring for 1 hour, the rate of temperature increase to 100 ° C is 5 ° C / min. The temperature was raised to 5 wt% -PVP-Pr colloidal solution (average particle size 6 nm).

  On the other hand, zirconium isopropoxide was put into another container in an amount adjusted to 30 wt% in a solvent (hexylene glycol), stirred at 100 ° C. for 1 hour, and then the PVP-Pr colloidal solution described above in this container Was introduced.

Thereafter, the gel obtained was dried and fired to obtain the heat absorbing / dissipating material of Example 4. The composition of the obtained heat absorbing / dissipating material powder was PrO ₂ (65%) / ZrO ₂ powder (residue). The powder had a PrO ₂ particle diameter of 6 nm and ZrO ₂ pore diameter of 10 nm.

[Example 5]
An aqueous solution of La acetate, polyvinylpyrrolidone (PVP), and ion-exchanged water were put into a container in an amount such that the PVP / La molar ratio was 6, stirred for 1 hour, and then heated to 100 ° C at 5 ° C / min. A 5 wt% -PVP-La colloidal solution (average particle size 6 nm) was prepared.

  On the other hand, cerium isopropoxide was added to a solvent (hexylene glycol) in an amount adjusted to 30 wt%, and stirred at 100 ° C. for 1 hour, and then the PVP / La colloid solution described above was added to this container. Was introduced.

Thereafter, the gel obtained was dried and fired to obtain the heat absorbing / dissipating material of Example 5. The composition of the obtained heat absorbing / dissipating material powder was La ₂ O ₃ (65%) / CeO ₂ powder (residue). The particle diameter of La ₂ O ₃ in this powder was 6 nm, and the pore diameter of CeO ₂ was 10 nm.

[Comparative Example 1]
In Example 3, a heat absorbing / dissipating material of Comparative Example 1 was obtained in the same manner except that the step of including the PVP-Mg colloid solution with cerium isopropoxide was not performed. The composition of the obtained heat absorbing / dissipating material powder was MgO. The particle diameter of MgO in this powder was 10 nm.

[Comparative Example 2]
An aqueous solution of Mg acetate, polyvinylpyrrolidone (PVP), and ion-exchanged water are put into a container in an amount such that the PVP / Mg molar ratio is 8, stirred for 1 hour, and then heated to 100 ° C at a rate of 5 ° C / min. The temperature was raised to prepare a 5 wt% -PVP-Mg colloidal solution (average particle size 4 nm).

  On the other hand, cerium isopropoxide was put into another container in an amount adjusted to 40 wt% in the solvent (hexylene glycol), stirred for 1 hour at 100 ° C., and then the PVP-Mg colloidal solution described above in this container Was introduced.

Thereafter, the gel obtained was dried and fired to obtain the heat absorbing / dissipating material of Comparative Example 2. The composition of the obtained heat absorbing / dissipating material powder was MgO (65%) / CeO ₂ (residue). The particle diameter of MgO in this powder was 4 nm, and the pore diameter of CeO ₂ was measured to be 9 nm.

  The heat absorbing / dissipating materials of Examples and Comparative Examples thus obtained were evaluated as described below.

1) The calorific value when the gas composition was switched was measured with TG / DTA so that the water vapor was 50% / He from the He air flow at a constant temperature.

2) From the start of steam introduction, the heat generation for 30 minutes was converted per hour to calculate the work rate.

3) Immediately after the preparation of each of the above examples and comparative examples, the initial state was set, and after the cycle endurance test shown in FIG. The maintenance ratio of the work rate was obtained by comparing the work rate in the initial state and the work rate in the state after cycle endurance.

  In the cycle endurance test shown in FIG. 3, each sample powder was held for 30 minutes at 200 ° C. in an atmosphere of 10% water vapor / remainder He and a predetermined temperature (water of the first compound) in the He atmosphere. This is a test in which the time of holding for 20 minutes at a temperature equal to or higher than the decomposition temperature of the oxide is 1 cycle with a temperature rising time of 5 minutes and a temperature falling time of 2 minutes. Corresponding model test.

The evaluation results of each example and comparative example are shown in Table 1.

  As is clear from Table 1, Examples 1 to 5 according to the present invention have high work rate maintenance ratios after the cycle endurance test, regardless of the difference in the material of the first compound particles as the heat absorbing / dissipating material. It was possible to maintain excellent characteristics over a long period of time. On the other hand, in Comparative Example 1, the second compound was not formed so as to cover the heat-absorbing / dissipating material, and thus the power reduction after the cycle durability test was remarkable. In Comparative Example 2, the pore diameter of the second compound was remarkably larger than the particle diameter of the first compound particles as the heat absorbing / dissipating material. After that, the degree of deterioration was large.

It is typical sectional drawing of the heat absorbing / dissipating material used as one Embodiment of this invention. It is a block diagram of an example of the chemical heat pump system which concerns on this invention. It is explanatory drawing of a cycle durability test.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Absorbing / radiating material particle 2 1st compound particle 3 2nd compound 4 Pore

Claims (8)

First compound particles that generate heat by a hydration reaction;
The first compound particles have a pore that can permeate water molecules used for the hydration reaction, and the second compound is insoluble in the first compound particles.
The first compound particle is covered with the second compound.   2. The heat absorbing / dissipating material according to claim 1, wherein a particle diameter of the first compound particles is 10 nm or less.   3. The heat absorbing / dissipating material according to claim 1, wherein the pore size of the second compound is smaller than the particle diameter of the first compound particle.   2. The heat absorbing / dissipating material according to claim 1, wherein the first compound particles are a compound of at least one metal selected from alkali metals, alkaline earth metals, and rare earth metals. 2. The heat absorbing / dissipating material according to claim 1, wherein the second compound is at least one compound selected from CeO ₂ , ZrO ₂ , TiO _2, and SiO ₂ .   The heat absorbing / dissipating material according to claim 4, wherein the first compound particles are made of a magnesium compound.   After preparing the colloidal solution in which the precursor of the first compound particle that generates heat due to the hydration reaction is dispersed, the second compound is formed around the particle of the precursor of the first compound in the colloidal solution. And the manufacturing method of the heat absorbing / dissipating material characterized by including the process of baking after that. Contains a heat-absorbing and heat-dissipating material that generates heat by a hydration reaction and can be heated;
A storage container containing water supplied to the reaction container;
A gas flow path connecting the reaction vessel and the storage vessel,
The heat-absorbing and heat-dissipating material has first compound particles that generate heat due to a hydration reaction, pores that can permeate water molecules used for the hydration reaction of the first compound particles, and the first A chemical heat pump system comprising: a second compound insoluble in compound particles, wherein the first compound particles are covered with the second compound.

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