TWI868355B - Chemical heat storage material and manufacturing method thereof - Google Patents

Abstract

A chemical thermal storage material contains hydroxide and/or oxide of an alkali earth metal, wherein the total content of boron and fluorine is 10 ppm or more and less than 1200 ppm relative to the content of the hydroxide of the alkali earth metal. The chemical thermal storage material further contains an alkali metal compound, and the amount of the alkali metal compound relative to the hydroxide and/or oxide of the alkali earth metal is preferably 0.1 to 50 mol%.

Description

Chemical heat storage material and manufacturing method thereof

The present invention relates to a chemical heat storage material and a manufacturing method thereof.

In recent years, in accordance with the regulations on carbon dioxide emissions, the use of fossil fuels has been required to be reduced. In addition to saving energy in various processes, it is also necessary to promote the use of waste heat. As a means of utilizing waste heat, it is known to use warm water below 100°C for heat storage. However, warm water heat storage has the following problems: (1) It cannot store heat for a long time due to the existence of heat loss; (2) The sensible heat is small, so a large amount of water is required, and the heat storage equipment is difficult to miniaturize; and (3) The output temperature is unstable and gradually decreases depending on the amount of utilization. Therefore, in order to promote the civilian use of this kind of waste heat, it is necessary to develop more efficient heat storage technology.

As a heat storage technology with high efficiency, the following can be cited: chemical heat storage method. Chemical heat storage method is accompanied by chemical changes such as adsorption and hydration of substances. Therefore, compared with the heat storage method that utilizes the latent heat or sensible heat of the material itself (water, molten salt, etc.), the heat storage per unit mass is higher. As a chemical heat storage method, there are: water vapor adsorption and desorption method that utilizes the adsorption and desorption of water vapor in the atmosphere, ammonia absorption of metal salts (ammonia complex formation reaction), and adsorption and desorption reactions of organic substances such as alcohols. If the load on the environment or the simplicity of the device is taken into consideration, the water vapor adsorption and desorption method is the most advantageous. As a chemical heat storage material used in the water vapor adsorption desorption method, calcium hydroxide or magnesium hydroxide, which is a hydroxide of an alkali earth metal, is known.

However, these calcium hydroxides and magnesium hydroxides do not cause effective dehydration reactions in the low temperature range of 100 to 400° C., and therefore, there is a problem that they cannot function as practical heat storage materials.

To solve this problem, Patent Document 1 proposes the following chemical heat storage material: it is a material that can store heat at about 100 to 300°C by utilizing a composite hydroxide with at least one metal component selected from the group consisting of magnesium, nickel, cobalt, copper and aluminum.

Furthermore, Patent Document 2 proposes the following chemical heat storage material: it is formed by adding a hygroscopic metal salt such as lithium chloride to magnesium or calcium hydroxide for the purpose of improving the heat storage capacity of the chemical heat storage material described in Patent Document 1. Prior Art Document Patent Document

Patent document 1: Japanese Patent Publication No. 2007-309561 Patent document 2: Japanese Patent Publication No. 2009-186119

[The problem that the invention wants to solve]

According to the technology disclosed in Patent Documents 1 and 2, although the heat storage operating temperature can be lowered to a certain extent, for example, when the factory waste heat is to be stored, the temperature range of the factory waste heat is 200-250°C or lower, so the heat storage operating temperature is not low enough, and it is difficult to use the factory waste heat efficiently, and it is required to pursue a further lowering of the operating temperature. Furthermore, lowering the heat storage operating temperature is also to improve the heat storage density and reaction efficiency. Expanding the applicable scope of factory waste heat recovery and improving the economic efficiency of renewable energy utilization are still important issues.

In view of the above-mentioned current situation, the purpose of the present invention is to provide a chemical heat storage material and a manufacturing method thereof, wherein the chemical heat storage material is a heat storage material that utilizes the dehydration reaction of the hydroxide of an alkali earth metal, exhibits a higher reaction rate, and can achieve heat storage at a lower temperature. [Technical means to solve the problem]

In order to solve the above-mentioned problems, the inventors of the present invention have repeatedly conducted various studies and found that: in a chemical thermal storage material utilizing the dehydration reaction of an alkali earth metal hydroxide, by setting the content of boron and fluorine to 10 ppm or more and less than 1200 ppm relative to the content of the alkali earth metal hydroxide, a chemical thermal storage material showing a higher reaction rate and capable of achieving thermal storage at a lower temperature can be manufactured, thereby completing the present invention.

That is, the first invention of this case is related to a chemical thermal storage material, which contains hydroxide and/or oxide of alkali earth metal, and the content of boron and fluorine is 10 ppm or more and less than 1200 ppm relative to the content of hydroxide of alkali earth metal. Preferably, the alkali earth metal is at least one selected from the group consisting of calcium, magnesium, strontium and barium. The chemical thermal storage material may further contain an alkali metal compound, and the amount of the alkali metal compound may be 0.1-50 mol% relative to the hydroxide and/or oxide of alkali earth metal. Preferably, the alkali metal is at least one selected from the group consisting of lithium, potassium and sodium. The chemical thermal storage material may further contain a compound of at least one metal selected from the group consisting of nickel, cobalt, copper and aluminum, and the amount of the metal may be 0.1 to 40 mol% relative to the hydroxide and/or oxide of the alkali earth metal. The chemical thermal storage material may further contain an acid salt of a metal, and the amount of the acid salt of the metal may be 0.05 to 30 mol% relative to the hydroxide and/or oxide of the alkali earth metal. Preferably, the acid salt of the metal is an acid salt of at least one metal selected from the group consisting of alkali metals and alkali earth metals. More preferably, the acid salt of at least one metal selected from the group consisting of alkali metals and alkali earth metals is an acid salt of at least one metal selected from the group consisting of lithium, sodium, potassium, calcium, magnesium, strontium and barium. Furthermore, more preferably, the acid salt of the metal is an acid salt of at least one metal selected from the group consisting of aluminum, iron, cobalt, nickel, copper and zinc.

The second invention of this case is related to a method for manufacturing a chemical heat storage material, which includes the steps of preparing the following chemical heat storage material, wherein the chemical heat storage material contains hydroxide and/or oxide of alkali earth metal, and the total content of boron and fluorine relative to the content of hydroxide of alkali earth metal is more than 10 ppm and less than 1200 ppm. The above method may further include the step of mixing hydroxide and/or oxide of alkali earth metal with a compound of alkali metal, and the amount of the above compound of alkali metal may be 0.1 to 50 mol% relative to the above hydroxide and/or oxide of alkali earth metal. The above method may further include the step of mixing the hydroxide and/or oxide of the alkali earth metal with a compound of at least one metal selected from the group consisting of nickel, cobalt, copper and aluminum, wherein the amount of the above metal may be 0.1 to 40 mol% relative to the hydroxide and/or oxide of the alkali earth metal. The above method may further include the step of mixing the hydroxide and/or oxide of the alkali earth metal with an acid salt of the metal, wherein the amount of the above metal acid salt may be 0.05 to 30 mol% relative to the hydroxide and/or oxide of the alkali earth metal. [Effect of the invention]

According to the present invention, a chemical thermal storage material and a method for manufacturing the same can be provided. The chemical thermal storage material is a thermal storage material that utilizes a dehydration reaction of an alkali earth metal hydroxide, exhibits a higher reaction rate, and can achieve thermal storage at a lower temperature.

The following is a detailed description of the embodiments of the present invention. The chemical thermal storage material of the present invention utilizes the following reversible reaction with hydroxide and oxide of alkali earth metal. In the following reaction formula, calcium or magnesium is used as the alkali earth metal. CaO + H ₂ O Ca(OH) ₂ ΔH＝-109.2 kJ/mol MgO＋H ₂ O Mg(OH) ₂ ΔH＝-81.0 kJ/mol

In each formula, the reaction to the right is the exothermic hydration reaction of calcium oxide or magnesium oxide. Conversely, the reaction to the left is the endothermic dehydration reaction of calcium hydroxide or magnesium hydroxide. That is, the chemical heat storage material of the present invention can store heat by performing the dehydration reaction of calcium hydroxide or magnesium hydroxide, and can also supply the stored heat energy by performing the hydration reaction of calcium oxide or magnesium oxide.

The chemical heat storage material in the present invention may contain either hydroxide of alkali earth metal or oxide of alkali earth metal, or both. Examples of the above-mentioned alkali earth metal include calcium, magnesium, strontium, and barium. It may contain only one of these or a combination of two or more of these. Among them, calcium and/or magnesium are preferred, and magnesium is more preferred. Examples of hydroxide of alkali earth metal and oxide of alkali earth metal include magnesium hydroxide, calcium hydroxide, composite hydroxide of magnesium and calcium, magnesium oxide, calcium oxide, and composite oxide of magnesium and calcium. These may be used alone or in combination of two or more.

In the chemical thermal storage material of the present invention, the total content of boron and fluorine is 10 ppm or more and 1200 ppm or less relative to the content of hydroxide of alkali earth metal. The content relative to the hydroxide of alkali earth metal means: when the chemical thermal storage material contains an oxide of alkali earth metal, the weight of the oxide is converted into the weight of hydroxide, and the content is relative to the weight of the converted hydroxide. If the total content of boron and fluorine is more or less than the above range, it is difficult to obtain the following effects: showing a higher reaction rate and achieving lower temperature heat storage. The lower limit of the above total content is preferably 20 ppm or more, more preferably 50 ppm or more, and further preferably 100 ppm or more. The upper limit of the above-mentioned total content is preferably 1000 ppm or less, and further preferably 700 ppm or less.

Although it is not completely clear how boron and fluorine act on the hydration or dehydration reaction of the chemical thermal storage material, it is believed that boron and fluorine are adsorbed on the hydroxide and/or oxide of the alkali earth metal near the surface of the chemical thermal storage material or form insoluble salts. It is speculated that by controlling this situation, it is helpful to improve or stabilize the cycle characteristics of the hydroxide and/or oxide of the alkali earth metal (that is, the reactivity during the heating dehydration reaction and the hydration reaction introduced by water vapor).

The boron and/or fluorine contained in the chemical thermal storage material may be "contained as impurities in the hydroxide and/or oxide of the alkali earth metal which is the raw material of the chemical thermal storage material", or "added to the hydroxide and/or oxide of the alkali earth metal". The form of the boron and/or fluorine when added may be the following alkali metal compound, specific metal compound or metal acid salt, and may also be an inorganic acid.

The chemical thermal storage material of the present invention may contain not only hydroxides and/or oxides of alkali earth metals, but also alkali metal compounds. By further mixing alkali metal compounds, the reaction rate of the chemical thermal storage material may be further increased.

Alkaline metals constituting the alkali metal compound include lithium, potassium, and sodium. The alkali metal compound may contain only one of these or a combination of two or more of these. Among them, lithium and sodium are preferred, and lithium is more preferred. The alkali metal compound is not particularly limited as long as it can exert the effect of the present invention. However, it is preferably a hygroscopic salt that can absorb moisture in the environment or generate a corresponding hydrate. Such salts include, for example, halides such as fluoride, chloride, and bromide, hydroxides, borates, carbonates, acetates, nitrates, or sulfates that are easy to handle. These may be used alone or in combination of two or more.

More specifically, the lithium salt is preferably lithium halide and/or lithium hydroxide, and more preferably lithium chloride, lithium bromide and/or lithium hydroxide. The potassium salt is preferably potassium halide and/or potassium hydroxide, and more preferably potassium chloride, potassium bromide and/or potassium hydroxide. The sodium salt is preferably sodium halide and/or sodium hydroxide, and more preferably sodium chloride, sodium bromide and/or sodium hydroxide.

As the usage amount of the above-mentioned alkali metal compound, when the amount of the above-mentioned hydroxide and/or oxide of the alkali earth metal is set to 100 mol%, the amount of the alkali metal compound is preferably 0.1-50 mol%. If the amount of the alkali metal compound is less than the above range, it is difficult to achieve the increase in reaction rate or the lowering of heat storage temperature obtained by the use of the alkali metal compound. In addition, if the amount of the alkali metal compound is more than the above range, there is a concern that the heat storage capacity per unit volume or per unit mass provided by the chemical heat storage material will decrease. The amount of the above-mentioned alkali metal compound is preferably 0.5-30 mol%, more preferably 1.0-20 mol%, and further preferably 2.0-10 mol%. By adjusting the amount of the alkali metal compound, the dehydration endothermic temperature of the chemical thermal storage material can be controlled. Wherein, when the alkali metal compound contains boron or fluorine, the alkali metal compound can be used within the range that satisfies the total content of boron and fluorine in the chemical thermal storage material.

The chemical thermal storage material of the present invention may further contain a specific metal compound in addition to the above-mentioned hydroxide and/or oxide of the alkali earth metal and the above-mentioned alkali metal compound of any component. By further containing the above-mentioned specific metal compound, the reaction rate of the chemical thermal storage material can be further improved. In this case, the above-mentioned specific metal compound is preferably chemically compounded with the hydroxide and/or oxide of the alkali earth metal.

The specific metal is selected from the group consisting of nickel, cobalt, copper and aluminum, and may contain only one of them or a combination of two or more thereof. Among them, at least one selected from the group consisting of nickel, cobalt and aluminum is preferred, and nickel and/or cobalt is more preferred.

The compound of the above-mentioned specific metal is not particularly limited, and preferably is a compound with a hydroxide and/or oxide of an alkali earth metal, and examples thereof include halides such as fluorides, chlorides, and bromides, hydroxides, oxides, borates, carbonates, acetates, nitrates, or sulfates. These may be used alone or in combination of two or more. More specifically, nickel hydroxide, cobalt hydroxide, a composite hydroxide of nickel and cobalt, nickel oxide, cobalt oxide, and/or a composite oxide of nickel and cobalt are preferred.

As for the usage amount of the above-mentioned specific metal compound, it is preferred that when the amount of the above-mentioned hydroxide and/or oxide of the above-mentioned alkali earth metal is set to 100 mol%, the amount of the above-mentioned specific metal is 0.1-40 mol%. If the amount of the above-mentioned specific metal is less than the above-mentioned range, it is difficult to achieve an increase in reaction rate or a lowering of heat storage temperature by using the above-mentioned specific metal compound. Moreover, if the amount of the above-mentioned specific metal is more than the above-mentioned range, there is a concern that the heat storage capacity per unit volume or per unit mass provided by the chemical heat storage material will decrease. The amount of the above-mentioned specific metal is preferably 3-40 mol%, more preferably 5-30 mol%, and further preferably 10-25 mol%. By adjusting the usage amount of the specific metal compound, the dehydration heat absorption temperature of the chemical thermal storage material can be controlled. Wherein, when the specific metal compound contains boron or fluorine, the specific metal compound can be used within the range satisfying the total content of boron and fluorine in the chemical thermal storage material.

The chemical thermal storage material of the present invention may be a mixture or dispersion of hydroxide and/or oxide of alkali earth metal, a compound of alkali metal as appropriate, or a compound of specific metal as appropriate, but is not limited thereto. It may be a compound of some or all of the constituents chemically combined with each other, or it may be a compound of some or all of the constituents chemically reacting with each other to generate a third component.

The chemical thermal storage material of the present invention may further contain metal acid salts in addition to the above-mentioned hydroxides and/or oxides of alkali earth metals, the above-mentioned compounds of alkali metals as arbitrary components, and the above-mentioned compounds of specific metals as arbitrary components. Metal acid salts refer to salts formed by the reaction of metal compounds and acids, and in particular, preferably salts formed by neutralizing metal hydroxides with acids. Specifically, for example, magnesium nitrate, magnesium acetate, magnesium benzoate, magnesium citrate, calcium nitrate, calcium acetate, calcium benzoate, calcium citrate, lithium nitrate, lithium acetate, lithium benzoate, lithium citrate, etc. can be listed, but it is not limited to them.

Examples of metals constituting the acid salts of the metals mentioned above include: alkali earth metals such as calcium, magnesium, strontium, and barium; alkali metals such as lithium, sodium, and potassium; aluminum, iron, cobalt, nickel, copper, and zinc. It may contain only one of these or a combination of two or more of these. Among them, calcium, lithium, and/or magnesium are preferred, and calcium and/or magnesium are more preferred. The alkali earth metals constituting the acid salts of the metals mentioned above may be the same as or different from the alkali earth metals constituting the hydroxides and/or oxides of the alkali earth metals mentioned above. However, from the viewpoint of increasing the reaction rate of the chemical thermal storage material, it is preferred that they are the same. Among them, when the metal acid salt used in the present invention is an alkaline earth metal acid salt, it is preferred not to use carbonates and chlorides of alkaline earth metals as the alkaline earth metal acid salt.

The acid constituting the acid salt of the metal is not particularly limited, and a known acid may be used appropriately, and may be any of an inorganic acid and an organic acid. In addition, it may be a water-soluble acid, or an acid that is poorly soluble or insoluble in water. In addition, only one type may be used, or two or more types may be used in combination appropriately.

Examples of the inorganic acid include hydrofluoric acid, hydrochloric acid, hydrobromic acid, hydroiodic acid, boric acid, sulfuric acid, nitric acid, phosphoric acid, phosphonic acid, sulfonic acid, and hydrocyanic acid.

Examples of organic acids include organic sulfonic acids, organic phosphonic acids, aliphatic hydroxy acids (including dihydroxy acids and trihydroxy acids), aromatic hydroxy acids (including dihydroxy acids and trihydroxy acids), aliphatic carboxylic acids (including dicarboxylic acids and tricarboxylic acids), aliphatic unsaturated carboxylic acids (including dicarboxylic acids and tricarboxylic acids), aromatic carboxylic acids (including dicarboxylic acids and tricarboxylic acids), aromatic unsaturated carboxylic acids (including dicarboxylic acids and tricarboxylic acids), other oxygen-containing acids, other pendant carboxylic acids, amino acids, and acids of their derivatives.

Examples of organic sulfonic acids include methanesulfonic acid, benzenesulfonic acid, p-toluenesulfonic acid, etc. Examples of organic phosphonic acids include dimethyl phosphate, benzenephosphonic acid, etc. Examples of aliphatic hydroxy acids or aromatic hydroxy acids include lactic acid, apple acid, citric acid, tartaric acid, etc. Examples of aliphatic carboxylic acids or aliphatic unsaturated carboxylic acids include fusic acid, acetic acid, propionic acid, butyric acid, acrylic acid, sorbic acid, pyruvic acid, oxalacetic acid, squaric acid, oxalic acid, malonic acid, succinic acid, glutaric acid, citric acid, acetic acid, etc. Examples of aromatic carboxylic acids or aromatic unsaturated carboxylic acids include benzoic acid, phthalic acid, salicylic acid, shikimic acid, gallic acid, pyromelitic acid, etc. Examples of amino acids include aspartic acid and glutamic acid.

As the usage amount of the above-mentioned metal acid salt, when the amount of the above-mentioned alkali earth metal hydroxide and/or oxide is set to 100 mol%, the amount of the above-mentioned metal acid salt is preferably 0.05 to 30 mol%. If the usage amount of the metal acid salt is less than the above-mentioned range, it is difficult to achieve an increase in reaction rate or a decrease in heat storage temperature by adding the acid salt. In addition, if the usage amount of the metal acid salt is more than the above-mentioned range, the influence on the above-mentioned alkali earth metal hydroxide and/or oxide that becomes the parent material is greater, and there is a concern that the heat storage capacity per unit volume or per unit mass provided by the chemical heat storage material is reduced. The usage amount of the above metal acid salt is preferably 0.1-20 mol%, more preferably 0.3-15 mol%, further preferably 0.5-10 mol%, further more preferably 0.8-8 mol%, and particularly preferably 1-6 mol%. Wherein, in the case where the above metal acid salt contains boron or fluorine, the metal acid salt can be used within the range satisfying the total content of boron and fluorine in the above chemical thermal storage material.

The chemical thermal storage material of the present invention utilizes the endothermic dehydration reaction and the hydration exothermic reaction caused by the hydroxide of alkali earth metal and the oxide of alkali earth metal. Within this range, the chemical thermal storage material of the present invention may contain other components, and may also contain chemical thermal storage components other than the components described above, and components that do not show chemical thermal storage effects (e.g., adhesives). Among them, when these other components contain boron or fluorine, the other components can be used within the range that satisfies the total content of boron and fluorine in the above-mentioned chemical thermal storage material.

The shape of the chemical thermal storage material of the present invention is not particularly limited, for example, it can be in the shape of powder, granules, molded bodies, etc. When manufacturing chemical thermal storage materials in the shape of powder, granules, and molded bodies, known techniques can be applied. For example: when manufacturing chemical thermal storage materials in the form of powder, screening, cracking, and crushing steps can be applied. In addition, when manufacturing chemical thermal storage materials in the form of granules, granulation steps such as extrusion granulation, rotary granulation, fluidized bed granulation, and spray drying can be applied. When manufacturing chemical thermal storage materials in the form of molded bodies, molding steps such as stamping, injection molding, blow molding, vacuum molding, and extrusion molding can be applied. That is, as long as there is no damage and the properties of the chemical thermal storage material can be implemented, any shape can be selected according to the implementation form required.

Next, the method for producing the chemical thermal storage material in the present invention is described. The method for producing the chemical thermal storage material in the present invention is not particularly limited, but at least the total content of boron and fluorine relative to the content of hydroxide of alkali earth metal is 10 ppm or more and less than 1200 ppm, and preferably includes the step of preparing a chemical thermal storage material containing hydroxide and/or oxide of alkali earth metal.

The alkali metal hydroxide and/or oxide used as the raw material for preparing the chemical thermal storage material may be a high purity product with a purity of 99.9% by weight or more, or a relatively low purity product with a purity of 95% by weight or more but less than 99.9% by weight. As the raw material, magnesium oxide obtained by seawater method, which is a source of magnesium for industrial use, magnesium oxide calcined from natural ore, fused magnesium oxide, etc. may be used.

When the raw material alkali earth metal hydroxide and/or oxide contains more boron and fluorine than the above-mentioned total content range, it is preferred to perform an operation to reduce the boron and/or fluorine by appropriate refining treatment. In addition, the chemical thermal storage material of the present invention can also be manufactured by adding components containing boron and/or fluorine to the raw material alkali earth metal hydroxide and/or oxide to meet the above-mentioned total content range.

An example of a method for producing a chemical thermal storage material containing the above-mentioned alkali metal compound, the above-mentioned specific metal compound, and/or the above-mentioned metal acid salt is described. First, the alkali metal compound is dissolved in ion exchange water to prepare an aqueous solution of the alkali metal compound, and the powder of the hydroxide of the alkali earth metal is added to the aqueous solution and stirred and mixed. At this time, the specific metal compound or the metal acid salt can be added at the same time. The obtained slurry can be dried to produce a chemical thermal storage material as a dry powder. The method of stirring and mixing is not particularly limited, as long as the ion exchange water of the solvent and the powder of the hydroxide of the alkali earth metal are fully mixed.

The order of adding the components may also be changed. In this case, for example, the chemical thermal storage material may be manufactured as follows: first, an alkali metal compound or an alkali metal compound and a specific metal compound are dissolved in ion exchange water, a metal acid salt is added to the aqueous solution, and then a powder of an alkali earth metal hydroxide is added to prepare a slurry, which is then dried to manufacture the chemical thermal storage material.

The chemical thermal storage material of the present invention can store heat by absorbing heat from a heat source of about 100 to 400°C (for example, unused heat from factory exhaust heat, etc.) and dehydrating it. The dehydrated chemical thermal storage material can easily maintain the thermal storage state by keeping it dry, and can be transported to the required location while maintaining the thermal storage state. In the case of heat release, the hydration reaction heat (depending on the situation, the water vapor adsorption heat) can be taken out as heat energy by contacting water, preferably contacting water vapor. In addition, water vapor can be adsorbed on one side of the airtight closed space, and water can be evaporated on the other side to generate cold and heat energy.

In addition, the chemical heat storage material of the present invention is also suitable for effectively utilizing the heat of exhaust gas discharged from engines or fuel cells. For example, the heat of exhaust gas can be used to shorten the operation of the thermal engine of the car, improve the environmental comfort of passengers, improve fuel costs, and reduce the harmfulness of exhaust gas by increasing the activity of exhaust catalysts. In particular, the load caused by the operation of the engine is uncertain, and the exhaust gas output is also unstable. Therefore, the direct use of the exhaust heat from the engine is inevitably inefficient and accompanied by inconvenience. If the chemical heat storage material of the present invention is used, the exhaust heat from the engine is temporarily chemically stored and the heat is output according to the heat demand, thereby achieving a more ideal exhaust heat utilization. [Example]

The present invention is further described in detail with reference to the following embodiments, but the present invention is not limited to these embodiments.

(Evaluation method) The chemical thermal storage materials obtained by each embodiment and comparative example were thermally evaluated using a differential thermal and thermogravimetric simultaneous measuring device (DTG-60, manufactured by Shimadzu Corporation). Specifically, the sample of the chemical thermal storage material to which the alkali metal compound was added was heated to 300°C, and the sample of the chemical thermal storage material to which the alkali metal compound was not added was heated to 350°C at a heating rate of 10°C/min, under atmospheric conditions, and under normal pressure conditions. Thereafter, the temperature was kept constant and the weight loss was measured over time. Based on the obtained weight loss value, the reaction rate, which is the ratio of magnesium hydroxide in each chemical thermal storage material to magnesium oxide, was calculated.

The reaction rate is calculated as follows: In order to exclude the influence of volatile components, the weight of the chemical thermal storage material at the time when the temperature is raised to 200°C is set as the starting weight and the reaction rate is set to 0%, and the weight loss value assuming that all magnesium hydroxide is converted into magnesium oxide is set as the reaction rate of 100%.

The performance evaluation of chemical thermal storage materials is based on the following reaction rate: the time point when the sample temperature reaches 200°C is set as 0 seconds, and then the reaction rate is calculated from the weight loss value after 2000 seconds. The results show that the higher the reaction rate, the faster the endothermic dehydration reaction proceeds, the greater the heat storage capacity, and heat storage can be performed by lower temperature heat. In addition, the relative reaction rate numbers in the table are not absolute values, but relative values when the reaction rate of each comparative example is set to the benchmark of 100.

The magnesium hydroxide used in this embodiment and comparative example is produced by the inventors of the present invention. The purity of magnesium hydroxide is determined by measuring the contents of various impurities using a multi-element simultaneous fluorescent X-ray analyzer (Simultix12, manufactured by Rigaku Corporation), and the contents of the oxides of Ca, Si, Al, Fe, P, and S, which are the main impurities, are converted and calculated together with the Cl content from 100%. The boron content is measured by using an ICP emission spectrometer (trade name "PS3520 VDD" manufactured by Hitachi High-Tech Corporation) after the sample is completely dissolved. The fluorine content was measured by the ion electrode method (device name: ion meter D-53S, manufactured by Horiba, Ltd.) to determine the amount of fluorine in a solution prepared by dissolving a sample in hydrochloric acid. The BET specific surface area was measured by a specific surface area measuring device (Macsorb, manufactured by Mountech Co. Ltd.) using a gas adsorption method (BET method) using nitrogen. The volume average particle size was measured by a laser diffraction scattering particle size distribution measuring device (MT3300, manufactured by Nikkiso Co., Ltd.).

(Example 1) Weigh 5 g of magnesium hydroxide (purity of about 99%, BET specific surface area of 40 ^m2 /g, volume average particle size of 4.2 μm), and further weigh boric acid (Kanto Chemical Reagents, special grade) in an amount to make the boron content of the magnesium hydroxide 440 ppm, and further weigh magnesium fluoride (Kanto Chemical Reagents, special grade) in an amount to make the fluorine content of the magnesium hydroxide 10 ppm. The weighed boric acid and magnesium fluoride are completely dissolved in 50 ml of ion exchange water to obtain an aqueous solution. The weighed magnesium hydroxide is added to the aqueous solution, and stirred with a magnetic stirrer for 300 seconds at 200 rpm to prepare a slurry. The slurry was dried in a dryer (Advantech Co., Ltd., DRA430DA) at 110°C for more than 12 hours to remove moisture, thereby manufacturing a chemical thermal storage material. The thermal behavior of the obtained chemical thermal storage material was confirmed by the above-mentioned evaluation method and the reaction rate was calculated.

(Example 2) Except that boric acid was used so that the boron content was 660 ppm, the chemical thermal storage material was manufactured in the same manner as in Example 1, and the reaction rate was calculated in the same manner.

(Example 3) Except that boric acid and magnesium fluoride were used so that the boron content was 440 ppm and the fluorine content was 220 ppm, a chemical thermal storage material was manufactured in the same manner as in Example 1, and the reaction rate was calculated in the same manner.

(Comparative Example 1) Except that boric acid and magnesium fluoride were used so that the boron content was 1030 ppm and the fluorine content was 800 ppm, a chemical thermal storage material was produced in the same manner as in Example 1, and the reaction rate was calculated in the same manner.

(Example 4) Weigh 5 g of magnesium hydroxide (same as in Example 1), and further weigh lithium chloride monohydrate (Kanto Chemical Reagents, special grade, purity 98.0%) in an amount of 10 mol% relative to the magnesium hydroxide, and further weigh boric acid (Kanto Chemical Reagents, special grade) in an amount of 400 ppm relative to the boron content of the magnesium hydroxide, and further weigh magnesium fluoride (Kanto Chemical Reagents, special grade) in an amount of 10 ppm relative to the fluorine content of the magnesium hydroxide. The weighed lithium chloride monohydrate is completely dissolved in 50 ml of ion exchange water to obtain an aqueous solution. The above-weighed magnesium hydroxide, boric acid and magnesium fluoride were added to the aqueous solution, and stirred with a magnetic stirrer at 200 rpm for 300 seconds to prepare a slurry. The slurry was dried in a dryer (manufactured by Advantech Co., Ltd., DRA430DA) at 110°C for more than 12 hours to remove moisture, thereby preparing a chemical thermal storage material. The thermal behavior of the obtained chemical thermal storage material was confirmed by the above-mentioned evaluation method and the reaction rate was calculated.

(Example 5) Except that boric acid was used so that the boron content was 600 ppm, the chemical thermal storage material was manufactured in the same manner as in Example 4, and the reaction rate was calculated in the same manner.

(Example 6) Except that boric acid and magnesium fluoride were used so that the boron content was 440 ppm and the fluorine content was 200 ppm, a chemical thermal storage material was manufactured in the same manner as in Example 4, and the reaction rate was calculated in the same manner.

(Example 7) Except that boric acid and magnesium fluoride were used in such a way that the boron content was 1030 ppm and the fluorine content was 10 ppm, a chemical thermal storage material was manufactured in the same manner as in Example 4, and the reaction rate was calculated in the same manner.

(Comparative Example 2) Except that boric acid and magnesium fluoride were used so that the boron content was 1060 ppm and the fluorine content was 800 ppm, a chemical thermal storage material was produced in the same manner as in Example 4, and the reaction rate was calculated in the same manner.

The results are shown in Tables 1 and 2. In Table 1, the reaction rate of the chemical thermal storage material obtained in Comparative Example 1 is set as 100 as the standard, and the reaction rates obtained in each embodiment are converted into relative reaction rates. In Table 2, the reaction rate of the chemical thermal storage material obtained in Comparative Example 2 is set as 100 as the standard, and the reaction rates obtained in each embodiment are converted into relative reaction rates.

[Table 1] (Magnesium hydroxide system) Total content Boron content Fluoride content Response rate Relative value (ppm) (ppm) (ppm) (%) Embodiment 1 450 440 10 81.5 109.0 Embodiment 2 670 660 10 79.7 106.6 Embodiment 3 640 440 220 82.1 109.8 Comparison Example 1 1830 1030 800 74.8 100

[Table 2] (Lithium chloride added system) LiCl・H ₂ O Addition Amount Total content Boron content Fluoride content Response rate Relative value (mol%) (ppm) (ppm) (ppm) (%) Embodiment 4 10 410 400 10 81.3 113.5 Embodiment 5 10 610 600 10 77.4 108.1 Embodiment 6 10 650 440 200 81.6 114.0 Embodiment 7 10 1040 1030 10 77.5 108.2 Comparison Example 2 10 1860 1060 800 71.6 100

According to Table 1, it can be confirmed that the chemical thermal storage materials of Examples 1 to 3, whose total content of boron and fluorine is within the range of 10 ppm or more and less than 1200 ppm, and Comparative Example 1, under the same evaluation conditions, have a faster endothermic dehydration reaction than Comparative Example 1. It can be seen that the chemical thermal storage materials of Examples 1 to 3 have a larger heat storage capacity than the chemical thermal storage material of Comparative Example 1, and can store heat at a lower temperature.

According to Table 2, it can be confirmed that the chemical thermal storage materials of Examples 4 to 7 in which 10 mol% of lithium chloride is added to magnesium hydroxide and the total content of boron and fluorine is within the range of 10 ppm or more and less than 1200 ppm and Comparative Example 2, under the same evaluation conditions, the endothermic dehydration reaction proceeds more rapidly than that of Comparative Example 2. It can be seen that the chemical thermal storage materials of Examples 4 to 7 have a larger heat storage capacity than the chemical thermal storage material of Comparative Example 2, and can store heat at a lower temperature.

without

without

Claims (13)

A chemical thermal storage material containing hydroxide and/or oxide of an alkali earth metal, wherein the total content of boron and fluorine relative to the content of hydroxide of the alkali earth metal is 100 ppm or more and less than 1200 ppm, and the chemical thermal storage material contains boron and fluorine. As in the chemical thermal storage material of claim 1, the alkaline earth metal is at least one selected from the group consisting of calcium, magnesium, strontium and barium. The chemical thermal storage material of claim 1 or 2 further contains an alkali metal compound, and the amount of the alkali metal compound is 0.1~50mol% relative to the hydroxide and/or oxide of the alkali earth metal. As in the chemical thermal storage material of claim 3, the alkali metal is at least one selected from the group consisting of lithium, potassium and sodium. The chemical thermal storage material of claim 1 or 2 further contains a compound of at least one metal selected from the group consisting of nickel, cobalt, copper and aluminum, and the amount of the above metal is 0.1~40mol% relative to the hydroxide and/or oxide of the above alkali earth metal. The chemical thermal storage material of claim 1 or 2 further contains a metal acid salt, and the amount of the metal acid salt is 0.05~30mol% relative to the hydroxide and/or oxide of the above-mentioned alkali earth metal. As in the chemical thermal storage material of claim 6, the above-mentioned metal acid salt is an acid salt of at least one metal selected from the group consisting of alkali metals and alkaline earth metals. The chemical thermal storage material of claim 7, wherein the acid salt of at least one metal selected from the group consisting of alkali metals and alkaline earth metals is an acid salt of at least one metal selected from the group consisting of lithium, sodium, potassium, calcium, magnesium, strontium and barium. As in the chemical thermal storage material of claim 6, the metal acid salt is an acid salt of at least one metal selected from the group consisting of aluminum, iron, cobalt, nickel, copper and zinc. A method for manufacturing a chemical thermal storage material, which is a method for manufacturing a chemical thermal storage material according to any one of claims 1 to 9, comprising the step of preparing the following chemical thermal storage material, wherein the chemical thermal storage material contains hydroxide and/or oxide of an alkali earth metal, and the total content of boron and fluorine relative to the content of hydroxide of the alkali earth metal is 100 ppm or more and less than 1200 ppm, and the chemical thermal storage material contains boron and fluorine. The manufacturing method of the chemical thermal storage material as claimed in claim 10 further includes the step of mixing the hydroxide and/or oxide of alkali earth metal and the compound of alkali metal, wherein the amount of the compound of alkali metal is 0.1~50mol% relative to the hydroxide and/or oxide of alkali earth metal. The method for manufacturing a chemical thermal storage material as claimed in claim 10 or 11 further comprises the step of mixing a hydroxide and/or oxide of an alkali earth metal with a compound of at least one metal selected from the group consisting of nickel, cobalt, copper and aluminum, wherein the amount of the metal is 0.1 to 40 mol% relative to the hydroxide and/or oxide of the alkali earth metal. The manufacturing method of the chemical heat storage material of claim 10 or 11 further includes the step of mixing the hydroxide and/or oxide of the alkali earth metal and the acid salt of the metal, and the amount of the acid salt of the metal is 0.05~30mol% relative to the hydroxide and/or oxide of the alkali earth metal.