WO2023136284A1 - Heat storage material and method for using heat energy - Google Patents

Abstract

The purpose of the present invention is to provide a heat storage material and a method for using heat energy that make it possible to further increase the amount of stored heat. Another purpose of the present invention is to provide a heat storage material and a method for using heat energy that offer fast heat dissipation and can be used repeatedly. The heat storage material of the present invention is a layered manganese oxide that is represented by formula (I) and has a delta-type crystal structure.　Formula (I): A_xMnO₂·nH₂O (in formula (I), A represents an element that makes it possible to maintain the delta-type crystal structure, x is a number between 0.00-0.50 inclusive, and n is a number between 0.00-1.00 inclusive).

Description

Thermal storage material and method of using thermal energy

The present invention relates to a heat storage material and a method for utilizing thermal energy.
This application claims priority based on Japanese Patent Application No. 2022-003139 filed in Japan on January 12, 2022, the contents of which are incorporated herein.

In recent years, the effective use of sustainable energy has attracted attention from the viewpoint of protecting the global environment.
For example, heat recovery systems such as chemical heat pumps that effectively utilize heat sources such as surplus waste heat are known. A chemical heat pump is a system that supplies heat (dissipates heat) and stores heat by utilizing heat generation and heat absorption phenomena associated with reversible chemical reactions (hydration reaction and dehydration reaction) between a reaction medium and a heat storage material. .

As a heat storage material used in chemical heat pumps, for example, Patent Document 1 proposes a heat storage material containing magnesium sulfate. Since magnesium sulfate can absorb a large amount of water, it has a high energy density and can increase the amount of heat stored.

However, when magnesium sulfate absorbs water, the surface of magnesium sulfate deliquesces, the crystal structure changes, the reaction rate decreases, and the reversible reaction becomes difficult to proceed. That is, the invention of Patent Document 1 has a problem that the speed of heat dissipation is slow and it is difficult to use repeatedly.

In response to such problems, for example, Non-Patent Document 1 proposes a heat storage material containing lanthanum sulfate monohydrate. According to the invention of Non-Patent Document 1, since the change in the crystal structure is small, it is possible to increase the reaction rate and promote the progress of the reversible reaction.

Japanese Patent Application Laid-Open No. 2014-177619

However, in the invention of Non-Patent Document 1, the amount of water that can be absorbed by lanthanum sulfate is small, so the energy density is low and the heat storage amount cannot be increased.

Accordingly, an object of the present invention is to provide a heat storage material and a method of utilizing thermal energy that can increase the amount of heat stored.
Another object of the present invention is to provide a heat storage material that can be used repeatedly with a high rate of heat release, and a method for utilizing thermal energy.

In order to solve the above problems, the present invention has the following aspects.
[1] A heat storage material represented by the following formula (I) and being a layered manganese oxide having a delta-type crystal structure.
_{AxMnO2.nH2O (} I ₎
[In formula (I), A represents an element capable of maintaining the delta crystal structure, x is a number of 0.00 or more and 0.50 or less, and n is 0.00 or more and 1.00 or less. is the number of ]
[2] In [1], wherein A in the formula (I) is one or more selected from metal elements capable of forming cations, preferably metal elements capable of forming monovalent or divalent cations. The heat storage material described.

[3] A method for utilizing thermal energy, comprising a heat storage step of heating the heat storage material according to [1] or [2] to desorb water from the heat storage material.
[4] The method for utilizing thermal energy according to [3], wherein the temperature for heating the heat storage material in the heat storage step is 50 to 300°C.
[5] The method for utilizing thermal energy according to [3] or [4], further comprising a heat release step of adsorbing water to the heated heat storage material to release heat.
[6] The method of utilizing thermal energy according to [5], wherein the heat storage step and the heat dissipation step are defined as one cycle, and two or more of the cycles are provided.

According to the heat storage material and the method of utilizing thermal energy of the present invention, the heat storage amount can be further increased.
Moreover, according to the heat storage material and the method of utilizing thermal energy of the present invention, the speed of heat dissipation is high and the material can be used repeatedly.

1 is a schematic diagram showing a crystal structure of a heat storage material according to one embodiment of the present invention; FIG. FIG. 4 is a photograph showing the results of X-ray crystal structure analysis when the heat storage material according to one embodiment of the present invention adsorbs and desorbs water. FIG. 4 is a photograph showing the results of X-ray crystal structure analysis of a heat storage material when heating and cooling are repeated in dry nitrogen gas. 4 is a graph showing TG/DTA results for a heat storage material according to an embodiment of the present invention; 4 is a graph showing TG/DTA results of heat storage materials according to other embodiments of the present invention. 4 is a graph showing DSC results of a heat storage material according to an embodiment of the present invention; 4 is a graph showing DSC results of a heat storage material according to another embodiment of the present invention; 4 is a graph showing DSC results of heat storage materials according to other embodiments of the present invention and one form other than the present invention. BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic diagram which shows the outline|summary of this invention. 4 is a graph showing DSC results of a heat storage material (Sample A) according to one embodiment of the present invention. 4 is a graph showing DSC results of a heat storage material (sample B) according to one embodiment of the present invention. 4 is a graph showing DSC results of a heat storage material (Sample C) according to one embodiment of the present invention. 4 is a graph showing DSC results of a heat storage material (Sample D) according to one embodiment of the present invention. 4 is a graph showing DSC results of a heat storage material (Sample E) according to one embodiment of the present invention. 4 is a graph showing DSC results of a heat storage material (Sample F) according to one embodiment of the present invention. 4 is a graph showing DSC results of a heat storage material (Sample G) according to one embodiment of the present invention. 4 is a graph showing DSC results of a heat storage material (Sample H) according to one embodiment of the present invention. FIG. 4 is a graph showing DSC results of a heat storage material (Sample I) according to one embodiment of the present invention. FIG. 4 is a graph showing DSC results of a heat storage material (Sample J) according to one embodiment of the present invention. 4 is a graph showing DSC results of a heat storage material (Sample K) according to one embodiment of the present invention. 4 is a graph showing the amount of water inserted/desorbed in a heat storage material according to one embodiment of the present invention. 4 is a graph showing TG change of a heat storage material according to one embodiment of the present invention; 4 is a graph showing TG changes (converted to the number of moles of water molecules per mole of Mn atoms) of the heat storage material according to one embodiment of the present invention.

[Heat storage material]
The heat storage material of the present invention is a layered manganese oxide represented by the following formula (I) and having a delta-type crystal structure.
_{AxMnO2.nH2O (} I ₎
In formula (I), A represents an element capable of maintaining a delta crystal structure, x is a number of 0.00 or more and 0.50 or less, and n is a number of 0.00 or more and 1.00 or less. is.
In this specification, "layered manganese oxide having a delta-type crystal structure" is expressed as, for example, delta-type manganese dioxide, delta-type manganese dioxide, delta-type MnO ₂ and delta-MnO ₂ , all of which are the same. shall mean.

As shown in FIG. 1, δ-type manganese dioxide is a hexagonal crystal with a layered structure in which oxygen octahedral units of MnO ₆ are arranged in layers.
The δ-type manganese dioxide shown in FIG. 1 has a layer _L1 , a layer _L2 , and a layer _L3 . The layer _L2 is positioned above the layer _L1 in the c-axis direction, and the layer _L3 is positioned above the layer _L2 in the c-axis direction.
An interlayer region _S1 is formed between the layer _L1 and the layer _L2 . An interlayer region _S2 is formed between the layer _L2 and the layer _L3 .
δ-type manganese dioxide can contain elements and water molecules capable of maintaining a delta-type crystal structure in the interlayer regions S ₁ and S ₂ .
δ-type manganese dioxide generates heat by adsorbing (absorbing) water molecules (water, water vapor) in the interlayer regions S ₁ and S ₂ , and the water molecules in the interlayer regions S ₁ and S ₂ desorb (desorb). By doing so, it absorbs heat. δ-type manganese dioxide serves as a host molecule, and water molecules serve as guest molecules.
In this way, δ-type manganese dioxide is a heat storage material that repeats heat generation (radiation) and heat absorption (heat storage) by a reversible reaction in which water molecules enter and leave the regions S ₁ and S ₂ between the layers. Function. The reversible reaction described above is also called an intercalation reaction of water.
In addition, since δ-type manganese dioxide can accommodate a large number of water molecules with a small structural change, it is possible to increase the reaction rate and increase the heat storage amount.

In formula (I), n represents the number of moles of water molecules per mole of Mn atoms in δ-type manganese dioxide, and is 0.00 or more and 1.00 or less. When n in formula (I) is 0.00, it means that δ-type manganese dioxide does not have water molecules in the region between the layers, and the larger n is, the higher the heat storage capacity is. Further, when n is equal to or less than the above upper limit, the heat storage material can be used repeatedly.

The structural change of δ-type manganese dioxide can be expressed by the change rate of the interlayer distance according to the inflow and outflow of water (adsorption and desorption). The change rate of the interlayer distance is preferably 15% or less, more preferably 10% or less. When the rate of change of the interlayer distance is equal to or less than the upper limit, the structural change is small and the heat dissipation rate can be increased. In addition, when the rate of change in interlayer distance is equal to or less than the above upper limit, the structural change is small and the heat storage material can be used repeatedly. Although the lower limit of the rate of change in the interlayer distance is not particularly limited, it is substantially 1%. The change rate of the interlayer distance is preferably 1 to 15%, preferably 1 to 10%, for example.

The change rate of the interlayer distance is represented by the following formula (II).
Rate of change in interlayer distance (%) = {(interlayer distance at expansion (Å)) - (interlayer distance at contraction (Å))/(interlayer distance at contraction (Å))} × 100 (II )
Here, the interlayer distance of δ-type manganese dioxide is the length in the c-axis direction represented by _d1 or _d2 in FIG. d ₁ is approximately 7 Å (Angstroms)=0.7 nm. _d2 is the same as _d1 .
The interlayer distance during expansion represents the interlayer distance when water molecules are absorbed to the maximum extent, and the interlayer distance during contraction represents the interlayer distance when water molecules are desorbed.

The interlayer distance of δ-type manganese dioxide is determined by X-ray crystal structure analysis based on the following formulas (III) and (IV).
2d sin θ=λ (III)
c=2d (IV)
In formula (III), d is the interlayer distance, θ is the diffraction angle, and λ is the X-ray wavelength.
In formula (IV), c represents a lattice constant.

In formula (I), A represents an element that allows the layered manganese oxide to maintain the delta-type crystal structure. A is not particularly limited as long as it is an element that allows the layered manganese oxide to maintain the delta-type crystal structure. A is, for example, a metalloid element or a metal element, and among these, a metal element is preferable, and a metal element capable of forming a cation is preferable because it easily enters between the layers of δ-type manganese dioxide and has excellent stability. A metal element capable of forming a monovalent or divalent cation is more preferred.
Examples of metal elements capable of forming cations include potassium (K), sodium (Na), lithium (Li), cesium (Cs), calcium (Ca), zinc (Zn), copper (Cu), aluminum ( Al) is preferable, among which elements selected from alkali metals and alkaline earth metals are more preferable, sodium, potassium and zinc are more preferable, sodium and potassium are particularly preferable, and potassium is particularly preferable.
A may be composed of one type of element, or may be composed of two or more types of elements. When it is composed of two or more elements, it is preferable that one element is potassium and the other one or more elements are selected from the group consisting of sodium, lithium, cesium, calcium, zinc, copper, and aluminum. More preferably, the type is potassium and at least one other type is selected from the group consisting of calcium and zinc. Further, when it is composed of two or more elements, it is preferable that one element is sodium and the other one or more elements are selected from the group consisting of potassium, lithium, cesium, calcium, zinc, copper, and aluminum. .
Metalloid elements include, for example, boron (B), silicon (Si), germanium (Ge), antimony (Sb), and tellurium (Te).
Examples of metal elements include alkali metals, alkaline earth metals, base metals, and transition metals.
Examples of metal elements capable of forming cations or metal elements capable of forming monovalent or divalent cations include alkali metals, alkaline earth metals, and transition metals.
Examples of alkali metals include lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and francium (Fr).
Examples of alkaline earth metals include beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra).
Examples of base metals include aluminum (Al), gallium (Ga), indium (In), thallium (Tl), tin (Sn), lead (Pb), and bismuth (Bi).
Examples of transition metals include scandium (Sc), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn ), zirconium (Zr), molybdenum (Mo), palladium (Pd), silver (Ag), cadmium (Cd), tungsten (W), platinum (Pt), and gold (Au).

In formula (I), x represents the number of moles of element A per 1 mole of Mn atom, and is 0.00 or more and 0.50 or less, preferably 0.01 or more and 0.40 or less, and 0.06 or more and 0.06 or less. 40 or less is more preferable, 0.10 or more and 0.35 or less is still more preferable, and 0.10 or more and 0.33 or less is particularly preferable. When x is at least the above lower limit, the layered structure of δ-manganese dioxide can be stabilized and the water absorption can be increased. Therefore, the energy density can be increased, and the heat storage amount can be further increased. In addition, when x is equal to or greater than the above lower limit, resistance to repeated use can be further enhanced. When x is equal to or less than the above upper limit, it is possible to secure a gap between the layers of the δ-type manganese dioxide and increase the water absorption amount. Therefore, the heat dissipation amount can be further increased.
In formula (I), when x is 0.00, it means that the δ-type manganese dioxide does not have the element A in the region between the layers. Moreover, in the formula (I), when x exceeds 0.00, it means that the δ-type manganese dioxide has the element A in the region between the layers. x is preferably 0.01 or more because the layered structure of δ-type manganese dioxide can be stabilized.
x can be determined, for example, by X-ray crystal structure analysis.
x can be adjusted by chemical treatment using an acid such as hydrochloric acid, electrochemical treatment, or a combination thereof.

The shape of the heat storage material of the present invention is not particularly limited, and any shape can be selected according to the embodiment of the consumer as long as the properties of the heat storage material are not impaired. Examples of the shape of the heat storage material include the shape of powder, granules, and compacts.

Known techniques can be applied to manufacture the heat storage material in the form of powder, granules, or molded bodies.
When producing the powdered heat storage material, for example, sieving, pulverizing, and pulverizing processes can be applied.
Granulation processes such as extrusion granulation, tumbling granulation, fluidized bed granulation, and spray drying can be used to produce the heat storage material in granules.
When manufacturing the heat storage material of the molded body, for example, molding processes such as press molding, injection molding, blow molding, vacuum molding, and extrusion molding can be applied.

[How to use thermal energy]
Next, a method for utilizing thermal energy (a method for storing heat and a method for releasing heat) using the heat storage material of the present invention will be described.
The method of utilizing thermal energy of the present invention has a heat storage step.

<Heat storage process>
The heat storage step is a step of heating the heat storage material of the present invention and desorbing water from the heated heat storage material.
The method of heating the heat storage material is not particularly limited, and examples include a method of exposing the material to direct sunlight, a method of using exhaust heat from a factory, a method of using exhaust heat from an engine such as an automobile, and a method of heating with an oven, heater, or the like. is mentioned.
From the viewpoint of effective use of energy, the method of heating the heat storage material is preferably a method of exposing it to direct sunlight, a method of using exhaust heat from a factory, or a method of using exhaust heat from an automobile engine.

The temperature when heating the heat storage material (hereinafter also referred to as "heating temperature") is preferably 50 to 300°C, more preferably 80 to 250°C, and even more preferably 100 to 200°C. When the heating temperature is equal to or higher than the above lower limit, water molecules can be sufficiently desorbed from the heat storage material. When the heating temperature is equal to or lower than the upper limit, structural change of the heat storage material can be suppressed.

The time for heating the heat storage material (hereinafter also referred to as "heating time") is preferably 10 minutes or more and 6 hours or less, more preferably 30 minutes or more and 4 hours or less, and even more preferably 1 hour or more and 3 hours or less. When the heating time is equal to or longer than the above lower limit, a sufficient heat storage amount can be secured. When the heating time is equal to or less than the above upper limit, the ease of use (usability) of the heat storage material can be further enhanced.

The heat storage amount in the heat storage step is preferably 500 MJ/m ³ or more, more preferably 600 MJ/m ³ or more, and even more preferably 700 MJ/m ^{3 or} more in terms of volumetric energy density. When the amount of heat stored in the heat storage step is equal to or greater than the lower limit value, a sufficient amount of thermal energy can be dissipated. The upper limit of the amount of heat stored in the heat storage step is considered to be 2000 MJ/m ³ , which is the limit value in the intercalation reaction of water at 100-200°C. The heat storage amount in the heat storage step is, for example, preferably 500 to 2000 MJ/m ³ , more preferably 600 to 2000 MJ/m ³ and even more preferably 700 to 2000 MJ/m ³ .
The amount of heat stored in the heat storage step is determined by, for example, differential scanning calorimetry (DSC).

<Heat dissipation process>
The method of using thermal energy according to the present embodiment may have processes other than the heat storage process. A heat radiation process is mentioned as processes other than a heat storage process.
The heat radiation step is a step of causing the heated heat storage material to adsorb water and release heat.
The relative humidity of the atmosphere in the heat radiation step is preferably 20-80% RH, more preferably 30-70% RH, and even more preferably 40-60% RH. When the relative humidity of the air is equal to or higher than the above lower limit, the contact efficiency between the heat storage material and water can be enhanced, and more water molecules can be adsorbed. Structural change of the heat storage material can be suppressed when the atmospheric relative humidity is equal to or lower than the upper limit.

The temperature of the atmosphere in the heat radiation step is preferably 0 to 40°C, more preferably 5 to 35°C, and even more preferably 10 to 30°C. When the temperature of the atmosphere is equal to or higher than the above lower limit, more water molecules can be adsorbed by the heat storage material. When the atmospheric temperature is equal to or lower than the upper limit value, the heat dissipation effect can be further enhanced.

The heat release amount in the heat release step is preferably 50 J/g or more, more preferably 100 J/g or more, and even more preferably 150 J/g or more per unit mass of the heat storage material. A sufficient amount of thermal energy can be radiated when the heat release amount in the heat release step is equal to or higher than the lower limit. The upper limit of the heat release amount in the heat release step is not particularly limited, but is set to 1400 J/g, for example. The heat release amount in the heat release step is preferably 50 to 1400 J/g, more preferably 100 to 1400 J/g, and even more preferably 150 to 1400 J/g per unit mass of the heat storage material.
The heat release amount in the heat release process is determined by, for example, DSC.

In the method of using thermal energy according to the present embodiment, it is preferable to repeatedly perform the heat storage process and the heat radiation process. That is, it is preferable that the thermal energy utilization method of this embodiment has two or more cycles, with the heat storage step and the heat dissipation step being one cycle.
By repeatedly performing the heat storage process and the heat dissipation process, thermal energy can be reused, contributing to effective utilization of sustainable energy.
The number of cycles between the heat storage process and the heat dissipation process (hereinafter also referred to as "cycle number") is preferably 2 or more, more preferably 5 or more, still more preferably 10 or more, and particularly preferably 15 or more. Heat energy can be effectively utilized as the number of cycles is more than the said lower limit. Although the upper limit of the number of cycles is not particularly limited, it is set to 50, for example. The number of cycles is, for example, preferably 2-50, more preferably 5-50, still more preferably 10-50, and particularly preferably 15-50.

When the cycle of the heat storage process and the heat radiation process is provided, the heat storage process may be performed first, or the heat radiation process may be performed first.

Since the heat energy utilization method of the present embodiment uses the heat storage material of the present invention, the heat storage amount can be further increased.
Since the heat energy utilization method of the present embodiment uses the heat storage material of the present invention, the speed of heat dissipation can be increased.
Since the heating temperature is 50 to 300° C., the heat energy utilization method of this embodiment can utilize low-grade waste heat.
Since the heat energy utilization method of the present embodiment repeats the heat storage process and the heat dissipation process, it has reversibility and contributes to the effective utilization of sustainable energy.

The present invention will be described in more detail below using examples, but the present invention is not limited to these examples.

Using powder K _0.33 MnO ₂ ·nH ₂ O (n is a number from 0 to 0.83, hereinafter also referred to as “sample 1”) as a heat storage material, each experiment described later was performed. The results of each experiment are discussed below with reference to the drawings.
For sample 1, potassium permanganate (KMnO ₄ ) was heat-treated at 700° C. for 10 hours, washed with water and filtered until the water became colorless and transparent in order to remove water-soluble by-products. It was obtained by drying in a vacuum drying oven at 80° C. for 12 hours.

<Confirmation of Desorption and Absorption of Water Molecules>
Sample 1 was placed in an atmosphere of 25° C. and a relative humidity of 60% RH, and the temperature was raised from 40° C. to 240° C. and lowered from 240° C. to 40° C. twice. Sample 1 at this time was subjected to X-ray crystal structure analysis to observe changes in interlayer distance (c-axis lattice constant). The results are shown in FIG.
As shown in FIG. 2, in the 002 diffraction line, it was confirmed that the c-axis lattice constant changed in four regions A ₁ to A ₄ . The change rate of the interlayer distance at this time is
{1−sin (6.30°)/sin (5.75°)}×100≈−9.5%
Met. It was found that in the regions A ₁ and A ₃ , desorption of water occurred between 120° C. and 160° C., and the interlayer distance was reduced. In regions A ₂ and A ₄ , it was found that water adsorption occurred between 160° C. and 120° C. and the interlayer distance expanded.

Next, sample 1 was placed in dry nitrogen gas, and the temperature was raised from 40°C to 240°C and lowered from 240°C to 40°C twice. Sample 1 at this time was subjected to X-ray crystal structure analysis to observe changes in the interlayer distance. The results are shown in FIG.
As shown in FIG. 3, when the temperature of sample 1 was increased _, desorption of water occurred between 80.degree. C. and 120.degree. However, it was found that the interlayer distance did not change even after the sample 1 was subsequently cooled and the temperature was lowered. This means that water cannot be adsorbed in dry gas and the interlayer distance cannot be restored.
It was confirmed that the interlayer distance was restored (widened) as shown in region _A6 by exposing Sample 1 with a reduced interlayer distance to the atmosphere at 24° C. and a relative humidity of 80% RH.

<Confirmation of the amount of water molecules that can be adsorbed and desorbed, the desorption temperature, and the reaction rate>
Next, sample 1 was placed in nitrogen gas with a relative humidity of 70% RH (nitrogen gas with a moisture content of 2.2% by mass) under a thermogravimetric differential thermal analyzer (TG/DTA, differential thermal analysis in a high-concentration steam atmosphere). Thermal analysis was performed using a balance (manufactured by Rigaku Corporation: Thermo plus EVO2 TG-DTA8122/HUM-1)).
Sample 1 was heated to 250°C at a temperature increase rate of 10°C/min and then cooled to 30°C at a temperature decrease rate of 5°C/min (first cycle). For the second time, sample 1 was heated to 250°C at a temperature increase rate of 20°C/min, and then cooled to 30°C at a temperature decrease rate of 5°C/min. For the third to fifth times, the sample 1 was heated to 250°C at a temperature increase rate of 40°C/min, and then cooled to 30°C at a temperature decrease rate of 5°C/min. Finally, for the sixth time, sample 1 was heated to 250°C at a temperature increase rate of 100°C/min, and then cooled to 30°C at a temperature decrease rate of 5°C/min. FIG. 4 shows the result of performing such a temperature rising/falling cycle six times.
In FIG. 4, the graph of area _P1 represents the TG of sample 1. In FIG. The graph in region _P2 represents the DTA for sample 1.

Looking at the TG data, the mass of sample 1 decreases after heating, and the rate of mass decrease decreases when the temperature exceeds 160°C. After that, a mass loss of approximately 13% was observed up to 250°C. When the sample 1 is cooled, the mass begins to increase, and the mass of the sample 1 rapidly increases when the temperature drops below 130°C. The mass of Sample 1 was observed to recover to a 5% loss. After the second cycle, the mass of Sample 1 was observed to range from a 5% decrease to a 13% decrease. During this time, it is considered that the water molecules between the layers of δ-type manganese dioxide are repeatedly adsorbed and desorbed. Thus, it was confirmed that the amount of water molecules capable of repeating adsorption and desorption was 0.5 mol per 1 mol of Mn atoms. This is a value calculated by the following formula (V).
moles of water molecules/moles of K _0.33 MnO ₂ =
{(mass of sample 1 (mg))×(reversible mass change rate)÷(molecular weight of H ₂ O)}/{(mass of sample 1 (mg))×(1−(maximum mass change rate)) ÷ (K _0.33 molecular weight of MnO ₂ )}=
{0.07767/18.0152}/{(1-0.1306)/99.839}=0.495≈0.5 (V)

In the 6th cycle, the rate of mass reduction decreased when the temperature exceeded 200 ° C., so when heating at a temperature increase rate of 100 ° C./min, water is desorbed (charged) within 3 minutes. was confirmed to be complete. This is probably because the structural change of δ-type manganese dioxide is small and the reaction rate of the water elimination reaction is fast.

Looking at the DTA data, after the first heating, an endothermic peak was observed at a temperature of around 60°C, and then an endothermic peak was observed again at a temperature of around 140°C. This is considered to be due to desorption of water molecules between the layers of δ-type manganese dioxide. It was observed that the temperature at which the endothermic peak was observed shifted to higher temperatures as the heating rate increased. When sample 1 was cooled, exothermic peaks were observed at temperatures around 110°C and around 80°C. This is considered to be due to the adsorption of water molecules between the layers of δ-type manganese dioxide.

<Confirmation of reversibility and reaction mechanism of water molecule adsorption/desorption reaction>
A thermal analysis was performed using the same thermogravimetric differential thermal analysis apparatus as above, with the rate of temperature increase during heating of sample 1 being fixed at 20° C./min. FIG. 5 shows the results of 16 cycles of heating and cooling.
In FIG. 5, the lower graph represents the TG of sample 1. The upper graph represents the DTA for sample 1.
Looking at the TG data, the mass of sample 1 decreases after heating, and the rate of mass decrease decreases when the temperature exceeds 160°C. After that, a mass loss of approximately 13% was observed up to 250°C. When the sample 1 is cooled, the mass begins to increase, and the mass of the sample 1 rapidly increases when the temperature drops below 130°C. The mass of Sample 1 was observed to recover to a loss of 5.5%. From the shape of the TG graph, it was confirmed that the adsorption-desorption reaction of water molecules between layers of δ-manganese dioxide maintained reversibility up to the 16th cycle. Also, from the shape of the TG graph, it was found that the equilibrium temperature of the adsorption/desorption reaction of water molecules is around 120°C. Furthermore, from the shape of the TG graph, it is considered that the adsorption-desorption reaction of water molecules between layers of δ-manganese dioxide is a single-phase reaction in which the amount of water molecules changes continuously with temperature.

Looking at the DTA data, after heating, an endothermic peak was observed in the temperature range of 130°C to 160°C. This is considered to be due to desorption of water molecules between the layers of δ-type manganese dioxide. When sample 1 was cooled, exothermic peaks were observed at temperatures around 120°C and around 80°C. This is considered to be due to the adsorption of water molecules between the layers of δ-type manganese dioxide. From the shape of the DTA graph, it was confirmed that the adsorption-desorption reaction of water molecules between layers of δ-manganese dioxide maintained reversibility up to the 16th cycle.

<Confirmation of heat storage amount>
Next, Sample 1 was subjected to thermal analysis in a dry argon gas atmosphere using a differential scanning calorimeter (DSC) device.
Sample 1 was heated from 30°C to 240°C at a heating rate of 5°C/min. After that, it was cooled from 240° C. to 30° C. at a cooling rate of 5° C./min, and this was taken as the initial cycle (curve A). Sample 1 was then exposed to air (room temperature) for 30 minutes and heated under the same conditions as the initial cycle (second cycle, curve B).
Separately, sample 1 was heated at 250° C. and then exposed to the atmosphere (room temperature) for 12 hours and heated under the same conditions as the initial cycle (curve C).
Also, after heating sample 1 at 250° C., it was immersed in water at room temperature and then heated under the same conditions as the initial cycle (curve D).
After each temperature rise, Sample 1 was cooled without being exposed to the air (curve E). These results are shown in FIG. The vertical axis on the left side of the graph represents the DSC of Sample 1, and the vertical axis on the right side of the graph represents the amount of heat per unit mass of Sample 1.

It was confirmed that the above four curves A to D (temperature rise curves) have endothermic peaks in the temperature range of 120 to 150°C. The area surrounded by the curve E (temperature drop curve) and the temperature rise curve is the heat absorption amount (heat storage amount) in each temperature rise test.
In the case of curve A, the amount of water molecules that can exist between the layers of δ-type manganese dioxide is 0.83 mol with respect to 1 mol of Mn atoms, so in the case of the other three curves (curves B to D) It was confirmed that the amount of heat stored was larger than that of the
In the tests after the second cycle, the amount of water molecules that can be reversibly adsorbed and desorbed is 0.50 mol with respect to 1 mol of Mn atoms. I was able to confirm that there is.
When the heat storage amount in curve B was obtained from the DSC device, it was 30.5 kJ/mol. By dividing this by the molar volume (30.3 cm ³ /mol) of δ-type manganese dioxide, the volume energy density ((30.5 kJ/mol)/(30.3 cm ³ /mol) = 1007 MJ/m ³ ) is obtained. asked. That is, the heat storage amount of sample 1 converted by volumetric energy density was 1007 MJ/m ³ . This value is on the same order as 2000 MJ/m ³ , which is considered to be the limit value for the intercalation reaction of water at 100 to 200° C., and can be said to be comparable to the limit value for the intercalation reaction of water.

<Confirmation of calorific value>
Sample 1 of the initial cycle in the above <Confirmation of heat storage amount> was placed in an air atmosphere at a temperature of 28° C., and thermal analysis was performed using a DSC device (curve F). The results are shown in FIG.
As shown in FIG. 7, in the case of curve F, heat generation starts immediately after the sample 1 is exposed to the atmosphere, reaches a heat generation peak around 200 seconds after the start of exposure, and then the amount of heat released decreases. Approximately 900 seconds after the start of exposure, the slope of the curve F becomes gentle, and it was confirmed that the amount of heat released becomes 0 after 1000 seconds from the start of exposure.
Sample 1 after repeating the cycle of heating and cooling twice was similarly placed in an air atmosphere at a temperature of 28° C. and subjected to thermal analysis using a DSC apparatus (curve G, third cycle).
In the case of curve G, the height of the peak top of the exothermic peak is lower than that of curve F. This is probably because the amount of water molecules that can be adsorbed and desorbed between the layers of δ-manganese dioxide is smaller in the third cycle than in the initial cycle.
In the case of the curve F and the curve G, the area of the portion surrounded by the baseline H means the calorific value of the heat storage material. For curve G, the calorific value determined by the DSC apparatus was 190 J/g.
In addition, in the case of curve F and curve G, the slope of the curve becomes gentle around 900 seconds after the start of exposure, so heat generation is completed 15 minutes after the start of exposure. was confirmed. It was found that the reaction rate of the adsorption and desorption reaction of water molecules in the heat storage material of the present embodiment is remarkably fast, compared to the fact that when magnesium sulfate is used as the heat storage material, it takes 2 to 3 hours to absorb water.

<Confirmation of difference in number of moles of element A>
FIG. 8 shows the case of using sample 1 as the heat storage material, the case of using K _0.06 MnO ₂ ·nH ₂ O (n is a number from 0 to 0.83, sample 2), and the case of beta type. 3 shows the results of DSC measurement when manganese dioxide (β-MnO ₂ , sample 3) having a crystal structure is used.
Sample 2 was obtained by subjecting sample 1 to leaching treatment in nitric acid. Sample 3 was obtained by sealing an aqueous solution of 1 mol/L of MnSO ₄ and 1 mol/L of (NH ₄ ) ₂ S ₂ O ₈ ) in an autoclave (Teflon-lined stainless-steel autoclave) and heating at 180°C. was heat treated for 6 hours at The obtained sample was washed with water until the water became colorless and transparent, and then dried in a vacuum drying oven at 40° C. for 12 hours.
As shown in FIG. 8, an endothermic peak due to desorption of water was observed in the temperature range of 100 to 200° C. in both the case of using sample 1 and the case of using sample 2. It was confirmed from the depth of the endothermic peak that the amount of endotherm was greater when sample 1 was used. From this, it was found that in the layered manganese oxide represented by the formula (I), the larger the number of moles of potassium atoms per 1 mole of Mn atoms, the higher the endothermic value. It is believed that this is because more water molecules can be taken into the interlayers of δ-type manganese dioxide as the number of moles of potassium atoms per mole of Mn atoms increases.
Also, when sample 2 was used, endothermic peaks were observed in the temperature range of 400 to 500° C. and in the temperature range of 550 to 600° C., respectively. This is presumably because δ-type manganese dioxide changed to trimanganese tetraoxide (Mn ₃ O ₄ ) and then to manganese oxide (MnO). Moreover, it is considered that this is because when the number of moles of potassium atoms to 1 mole of Mn atoms is small, it becomes difficult for the δ-type manganese dioxide to maintain a layered structure, and structural changes are likely to occur.
In contrast, when sample 3 was used, no endothermic peak was observed in the temperature range of 100 to 200°C. Note that the endothermic peak in the temperature range of 550 to 600° C. is considered to occur when beta manganese dioxide changes to manganese oxide.

<Confirmation of difference in type of element A>
Following the operation of "<Confirmation of heat storage amount>" described above, the various samples shown below (Sample A to Sample K) were heated using a differential scanning calorimetry (DSC) device in a dry argon gas atmosphere. Analysis was carried out. That is, each sample was heated from 30° C. to 240° C. at a temperature increase rate of 5° C./min, and then cooled from 240° C. to 30° C. at a temperature decrease rate of 5° C./min, and this was taken as the initial cycle (curve A). , then the various samples were exposed to air (room temperature) for 30 minutes and heated under the same conditions as the initial cycle (second cycle, curve B). The results are shown in FIGS. 10 to 20, respectively.

_{[ Sample} A ( _{K0.27MnO2.nH2O} )]
Potassium permanganate (KMnO ₄ ) was heat-treated at 700° C. for 10 hours, washed with water and filtered until the water became colorless and transparent in order to remove water-soluble by-products. After that, it was dried in a vacuum drying oven at 40° C. for 12 hours to obtain a sample A.
FIG. 10 shows the test results using sample A. FIG.

_{[ Sample B} ( _{K0.05Zn0.125MnO2.nH2O} )]
Sample A2 was added to a mixture (aqueous solution) of 89.24 g (0.3 mol) of zinc nitrate hexahydrate (Zn(NO ₃ ) _{2.6H 2} O) and 200 g of water at room temperature for 2 weeks without stirring. .30 g (0.02 mol) was immersed and the sample obtained by filtration was vacuum-dried at 40° C. for 12 hours to obtain sample B.
FIG. 11 shows the test results using sample B. FIG.

_{[ Sample} C ( _{Cs0.28MnO2.nH2O} )]
2.30 g (0.02 mol) of sample A was immersed in a mixture (aqueous solution) of 50.51 g (0.3 mol) of cesium chloride (CsCl) and 200 g of water at room temperature for 2 weeks without stirring, and filtered. The obtained sample was vacuum-dried at 40° C. for 12 hours to obtain Sample C.
FIG. 12 shows the results of the above test using sample C. As shown in FIG.

[ _{Sample D ( K0.075Ca0.1MnO2.nH2O} )]
Sample A2 was added to a mixture (aqueous solution) of 70.85 g (0.3 mol) of calcium nitrate tetrahydrate (Ca(NO ₃ ) ₂ 4H ₂ O) and 200 g of water without stirring at room temperature for 2 weeks. A sample obtained by immersing .30 g (0.02 mol) and filtering was vacuum-dried at 40° C. for 12 hours to obtain sample D.
FIG. 13 shows the test results using sample D. FIG.

_{[ Sample} E ( _{Cu0.11MnO2.nH2O} )]
A mixture (aqueous solution) of 72.48 g (0.3 mol) of copper nitrate trihydrate (Cu(NO ₃ ) _{2.3H 2} O) and 200 g of water (aqueous solution) was added without stirring at room temperature for 2 weeks. .30 g (0.02 mol) was immersed and the sample obtained by filtration was vacuum-dried at 40° C. for 12 hours to obtain sample E.
FIG. 14 shows the results of the above test using sample E. FIG.

_[ Sample F _{( Li0.34MnO2.nH2O} )]
2.30 g (0.02 mol) of sample A was immersed in a mixture (aqueous solution) of 20.68 g (0.3 mol) of lithium nitrate (LiNO ₃ ) and 200 g of water at room temperature for 2 weeks without stirring, and filtered. The sample thus obtained was vacuum-dried at 40° C. for 12 hours to obtain Sample F.
FIG. 15 shows the results of the above test using sample F.

[Sample G (Al _0.015 MnO ₂ ·nH ₂ O)]
Sample A2 was added to a mixture (aqueous solution) of 112.5 g ( _0.3 mol) of aluminum nitrate nonahydrate (Al( _NO3 ) _3.9H2O ) and 200 g of water at room temperature for 2 weeks without stirring. A sample obtained by soaking .30 g (0.02 mol) and filtering was vacuum-dried at 40° C. for 12 hours to obtain sample G.
FIG. 16 shows the test results using sample G. FIG.

_{[ Sample} H ( _{Na0.25MnO2.nH2O} )]
11.5 g (0.1 mol) of sample A was immersed in a mixture (aqueous solution) of 25.5 g (1.5 mol) of sodium nitrate (NaNO ₃ ) and 200 g of water at room temperature for 2 weeks without stirring, and filtered. The sample thus obtained was vacuum-dried at 40° C. for 12 hours to obtain Sample H.
FIG. 17 shows the results of the above test using sample H.

_{[ Sample} I ( _{K0.29MnO2.nH2O} )]
20.54 g (0.13 mol) of potassium permanganate (KMnO ₄ ), 100 g of water, 6.027 g (0.025 mol) of manganese sulfate pentahydrate (MnSO _{4.5H 2} O), and manganese oxide (MnO ₂ ) 3.622 g (0.042 mol) of the mixture (aqueous solution) were sealed in an autoclave (Teflon-lined stainless-steel autoclave) and heat treated at 120° C. for 12 hours. The obtained sample was washed with water and collected by filtration until the water became colorless and transparent. After that, it was dried in a vacuum drying oven at 40° C. for 12 hours to obtain a sample A.
FIG. 18 shows the results of the above test using sample I.

_{[ Sample} J ( _{Zn0.179MnO2.nH2O} )]
_{Sample I 2} A sample obtained by soaking .30 g (0.02 mol) and filtering was vacuum-dried at 40° C. for 12 hours to obtain sample J.
FIG. 19 shows the test results using sample J. FIG.

[ _Sample K _{( Na0.28MnO2.nH2O} )]
11.5 g (0.1 mol) of sample I was immersed in a mixture (aqueous solution) of 25.5 g (1.5 mol) of sodium nitrate (NaNO ₃ ) and 200 g of water at room temperature for 2 weeks without stirring, and filtered. The sample thus obtained was vacuum-dried at 40° C. for 12 hours to obtain Sample K.
FIG. 20 shows the test results using sample K. FIG.

As shown in FIGS. 10 to 20, in any sample, heat absorption was confirmed during temperature rise, and it was confirmed that, like sample 1 and sample 2, it could be used as a heat storage material.

<Humidity Dependence of Isothermal Water Insertion and Desorption>
For sample 1, in order to investigate the humidity dependence of the amount of water deinsertion under isothermal conditions, a thermogravimetric differential thermal analyzer (TG/DTA, high-concentration steam atmosphere differential thermal balance (manufactured by Rigaku Corporation: Thermo plus EVO2 TG- Thermal analysis was performed using DTA8122/HUM-1)).
As shown in FIG. 21, the thermal The relative humidity (25° C. standard) at the gas inlet of the gravimetric differential thermal analyzer main body was reciprocally swept from 0% to 90% (water vapor partial pressure 28.5 hPa) (0.5% RH/min). The humidity of the introduced gas was adjusted by mixing wet nitrogen passed through a water bath with high-purity dry nitrogen at an appropriate ratio, and feedback-controlling the relative humidity at the gas inlet. The flow rate of the introduced gas was approximately 500 sccm regardless of the relative humidity.
As described above, the relative humidity in FIG. 21 represents the 25° C. reference humidity at the gas inlet. .9% RH. However, the water vapor partial pressure does not change with temperature. TG: 0% in FIG. 21 corresponds to the completely dehydrated state in sample 1.
22 and 23 show the humidity dependence of TG at corresponding temperatures and the humidity dependence of the number of moles of water molecules per mole of Mn atoms corresponding to n in formula (I) for the above thermal analysis results. Each is represented.

By reading the water content at each temperature and humidity, the heat storage temperature, heat radiation temperature, and water desorption/insertion amount at the ambient humidity can be determined.
As shown in FIGS. 21 to 23, in the case of heat dissipation at 28° C. (room temperature level) in sample 1, even if the environmental humidity changes such as summer humidity/winter dryness, the It can be seen that the amount does not change significantly. In other words, it can be seen that Sample 1 can provide a stable amount of heat dissipation without being significantly affected by the environmental humidity in heat dissipation at the room temperature level.
Moreover, as shown in FIGS. 21 to 23, if the heat storage temperature is 135° C. or higher, water in the sample can be almost completely desorbed regardless of the environmental humidity.

<Summary>
As a summary, FIG. 9 shows a schematic diagram showing the outline of the present invention.
As shown in FIG. 9, it was found that the layered manganese oxide of the present embodiment can adsorb and desorb water molecules in the region between the layers due to the intercalation reaction of water.
It was found that the layered manganese oxide of this embodiment can reversibly intercalate 0.5 mol of water molecules per 1 mol of Mn atoms. It was found that the desorption reaction (dehydration reaction) of water was completed within 3 minutes at a rate of 100°C/min. It is considered that such a fast reaction rate is realized by utilizing the intercalation reaction of water.
It was found that in the layered manganese oxide of this embodiment, the intercalation reaction of water proceeds mainly by a single-phase reaction.
The heat storage capacity of the heat storage material of this embodiment was 1007 MJ/m ³ in terms of volume energy density. This value was close to the limit value (2000 MJ/m ³ ) of heat storage for the intercalation reaction of water at 100 to 200°C.
The present invention is the first application of the intercalation reaction of water to a heat storage material. It was found that the heat storage material of the present invention is an excellent material among existing heat storage materials in terms of energy density, reaction rate, and reversibility.

As described above, it was found that the heat storage material of the present invention can further increase the amount of heat stored.
In addition, it has been found that the heat storage material of the present invention has a high heat release rate and can be used repeatedly.

Claims (8)

1. A heat storage material represented by the following formula (I) and being a layered manganese oxide having a delta-type crystal structure.
   _{AxMnO2.nH2O (} I ₎
   [In formula (I), A represents an element capable of maintaining the delta crystal structure, x is a number of 0.00 or more and 0.50 or less, and n is 0.00 or more and 1.00 or less. is the number of ]
2. The heat storage material according to claim 1, wherein A in the formula (I) is one or more selected from metal elements capable of forming cations.
3. A method for utilizing thermal energy, comprising a heat storage step of heating the heat storage material according to claim 1 or 2 to desorb water from the heat storage material.
4. The method of utilizing thermal energy according to claim 3, wherein the temperature for heating the heat storage material in the heat storage step is 50 to 300°C.
5. The method of utilizing thermal energy according to claim 3, further comprising a heat dissipation step of causing the heated heat storage material to adsorb water to release heat.
6. The method of utilizing thermal energy according to claim 4, further comprising a heat release step of causing water to be adsorbed on the heated heat storage material to release heat.
7. With the heat storage step and the heat dissipation step as one cycle,
   6. The method of utilizing thermal energy according to claim 5, comprising two or more of said cycles.
8. With the heat storage step and the heat dissipation step as one cycle,
   7. The method of utilizing thermal energy according to claim 6, comprising two or more of said cycles.

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