Chemical heat storage material

Abstract

A chemical heat storage material containing magnesium hydroxide and / or magnesium oxide, wherein the ratio of the half width of a diffraction peak at a Bragg angle of 2θ=38° in the (101) plane of magnesium hydroxide in X-ray diffraction measurement using CuKα rays after a hydration reaction of the chemical heat storage material to the half width of a diffraction peak at a Bragg angle of 2θ=43° in the (200) plane of magnesium oxide in X-ray diffraction measurement using CuKα rays after a dehydration reaction of the chemical heat storage material is 0.5-2 (inclusive).

Description

Technical Field

[0001] The present invention relates to a chemical heat storage material.

Background Art

[0002] In recent years, due to carbon dioxide emission regulations, reduction of the use of fossil fuels has been demanded. In addition to energy conservation in each process, it is necessary to promote the utilization of waste heat. As a means of utilizing waste heat, hot water heat storage at 100°C or lower using water is known. However, hot water heat storage has the following problems: (1) Heat dissipation loss makes long-term heat storage impossible; (2) Since the sensible heat amount is small, a large amount of water is required, making it difficult to compact the heat storage equipment; (3) The output temperature is unsteady according to the usage amount and gradually decreases. Therefore, in order to promote such civilian use of waste heat, it is necessary to develop a more efficient heat storage technology.

[0003] As a highly efficient heat storage technology, the chemical heat storage method can be mentioned. Since the chemical heat storage method involves chemical changes such as adsorption and hydration of substances, the heat storage amount per unit mass is higher than that of heat storage methods using the latent heat or sensible heat of the material itself (water, molten salt, etc.). As the chemical heat storage method, a water vapor adsorption / desorption method by adsorption / desorption of water vapor in the atmosphere, ammonia absorption into metal salts (ammine complex formation reaction), a reaction by adsorption / desorption of organic substances such as alcohol, etc. have been proposed. Considering the environmental load and the simplicity of the device, the water vapor adsorption / desorption method is the most advantageous. As the chemical heat storage material used in the water vapor adsorption / desorption method, calcium hydroxide and magnesium hydroxide, which are hydroxides of alkaline earth metals, are known.

[0004] However, these calcium hydroxide and magnesium hydroxide do not cause an effective dehydration reaction in the low temperature range of 100 to 400°C, and thus have the problem of not functioning as a practical heat storage material.

[0005] In order to solve this problem, Patent Document 1 proposes a chemical heat storage material capable of storing heat at about 100 to 300°C by using a composite hydroxide of magnesium and at least one metal component selected from the group consisting of nickel, cobalt, copper, and aluminum.

[0006] Furthermore, Patent Document 2 proposes a chemical heat storage material obtained by adding a hygroscopic metal salt such as lithium chloride to a hydroxide of magnesium or calcium for the purpose of improving the heat storage amount of the chemical heat storage material described in Patent Document 1.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0008] According to the technologies disclosed in Patent Documents 1 and 2, although the heat storage operation temperature can be lowered to a certain extent, for example, when attempting to store factory waste heat, since the temperature range of factory waste heat is 200 to 250°C or a lower temperature range, the heat storage operation temperature is not sufficiently low, it is difficult to efficiently utilize factory waste heat, and further lowering of the operation temperature is required. Furthermore, lowering the heat storage operation temperature also means improving the heat storage density and reaction efficiency. Expanding the applicable range for recovering factory exhaust heat and improving the economic efficiency of utilizing renewable energy still remain important issues.

[0009] In view of the above situation, an object of the present invention is to provide a chemical heat storage material that performs heat storage using the dehydration reaction of magnesium hydroxide and can start heat storage at a lower temperature and achieve a higher reaction rate.

Means for Solving the Problems

[0010] In order to solve the above problems, the inventors have conducted various studies. As a result, in a chemical heat storage material using the dehydration reaction of magnesium hydroxide and the hydration reaction of magnesium oxide, the ratio of the half-value width of the diffraction peak at 2θ = 38° on the (101) plane of magnesium hydroxide in the X-ray diffraction measurement using CuKα rays after the hydration reaction to the half-value width of the diffraction peak at 2θ = 43° on the (200) plane of magnesium oxide in the X-ray diffraction measurement using CuKα rays after the dehydration reaction is 0.5 or more and 2 or less. It has been found that such a chemical heat storage material can start heat storage at a lower temperature and achieve a higher reaction rate, leading to the present invention.

[0011] That is, the first aspect of the present invention is a chemical heat storage material containing magnesium hydroxide and / or magnesium oxide, wherein the ratio of the half-value width of the diffraction peak at the Bragg angle 2θ = 38° on the (101) plane of magnesium hydroxide in the X-ray diffraction measurement using CuKα rays after the hydration reaction of the chemical heat storage material to the half-value width of the diffraction peak at the Bragg angle 2θ = 43° on the (200) plane of magnesium oxide in the X-ray diffraction measurement using CuKα rays after the dehydration reaction of the chemical heat storage material is 0.5 or more and 2 or less.

[0012] Preferably, the half-value width of the diffraction peak at 2θ = 43° on the (200) plane of magnesium oxide in the X-ray diffraction measurement using CuKα rays after the dehydration reaction of the chemical heat storage material is 0.2 or more and 0.45 or less, and the half-value width of the diffraction peak at 2θ = 38° on the (101) plane of magnesium hydroxide in the X-ray diffraction measurement using CuKα rays after the hydration reaction of the chemical heat storage material is 0.2 or more and 0.45 or less. The chemical heat storage material may further contain an alkali metal compound, and the amount of the alkali metal compound may be 0.1 to 50 mol% based on the magnesium hydroxide and / or magnesium oxide. Preferably, the dehydration temperature of the chemical heat storage material is 350°C or lower.

Advantages of the Invention

[0013] According to the present invention, in a chemical heat storage material that performs heat storage using the dehydration reaction of magnesium hydroxide, a chemical heat storage material that can start heat storage at a lower temperature and achieve a higher reaction rate can be provided.

Embodiments for Carrying Out the Invention

[0014] Hereinafter, embodiments of the present invention will be described in detail. The chemical heat storage material of the present invention utilizes a reversible reaction between magnesium hydroxide and magnesium oxide represented by the following reaction formula. MgO + H2O ⇔ Mg(OH)2 △H = -81.0 kJ / mol

[0015] In each formula, the reaction in the right direction is the hydration exothermic reaction of magnesium oxide. Conversely, the reaction in the left direction is the dehydration endothermic reaction of magnesium hydroxide. That is, the chemical heat storage material of the present invention can store heat by the progress of the dehydration reaction of magnesium hydroxide, and can supply the stored thermal energy by the progress of the hydration reaction of magnesium oxide.

[0016] The chemical heat storage material of the present invention shows a ratio of the half-width of the diffraction peak at a Bragg angle 2θ = 38° of the (101) plane of magnesium hydroxide in the X-ray diffraction measurement (XRD) using CuKα rays after the hydration reaction of the chemical heat storage material to the half-width of the diffraction peak at a Bragg angle 2θ = 43° of the (200) plane of magnesium oxide in the X-ray diffraction measurement using CuKα rays after the dehydration reaction of the chemical heat storage material, which is 0.5 or more and 2 or less. Within this range, the chemical heat storage material can start heat storage at a lower temperature and achieve a higher reaction rate. The ratio of the half-width is preferably 0.52 or more and 1.9 or less, and more preferably 0.55 or more and 1.8 or less.

[0017] Although the mechanism by which the heat storage start temperature of the chemical heat storage material decreases when the chemical heat storage material satisfies the ratio of the half-widths is not necessarily clear, it is presumed that the reactivity of the dehydration reaction of magnesium hydroxide is improved by controlling the change in the crystallite size of the primary particles of magnesium hydroxide or magnesium oxide due to the dehydration reaction near the surface of the chemical heat storage material.

[0018] In the chemical heat storage material of the present invention, it is preferable that the half-width of the diffraction peak at 2θ = 43° on the (200) plane of magnesium oxide in the X-ray diffraction measurement using the CuKα line after the dehydration reaction of the chemical heat storage material is 0.2 or more and 0.45 or less, and more preferably 0.25 or more and 0.45 or less. Further, in the chemical heat storage material of the present invention, it is preferable that the half-width of the diffraction peak at 2θ = 38° on the (101) plane of magnesium hydroxide in the X-ray diffraction measurement using the CuKα line after the hydration reaction of the chemical heat storage material is 0.2 or more and 0.45 or less, and more preferably 0.2 or more and 0.4 or less. If the crystallinity of magnesium hydroxide or magnesium oxide is too high with each half-width being small, the reactivity of the dehydration reaction of magnesium hydroxide or the hydration reaction of magnesium oxide may decrease. Also, if each half-width is too large and the crystallinity is too low, pulverization of the chemical heat storage material and solidification blockage near the surface may be promoted, resulting in a decrease in reactivity.

[0019] The chemical heat storage material of the present invention may further contain a compound of an alkali metal in addition to magnesium hydroxide and / or magnesium oxide. By further blending a compound of an alkali metal, the reaction rate of the chemical heat storage material can be further increased.

[0020] Examples of the alkali metal that constitutes the alkali metal compound include lithium, potassium, and sodium. It may contain only one of these, or it may contain a combination of two or more. Among these, lithium and sodium are preferred, and lithium is more preferred. The alkali metal compound is not particularly limited as long as it exhibits the effects of the present invention, but a salt having hygroscopicity and capable of adsorbing moisture in the atmosphere or forming a corresponding hydrate is preferred. Examples of such salts include halides such as chlorides and bromides, hydroxides, carbonates, acetates, nitrates, or sulfates, etc., which are easy to handle. These may be used alone or in combination of two or more.

[0021] More specifically, as the lithium salt, lithium halide and / or lithium hydroxide are preferred, and lithium chloride, lithium bromide, and / or lithium hydroxide are more preferred. As the potassium salt, potassium halide and / or potassium hydroxide are preferred, and potassium chloride, potassium bromide, and / or potassium hydroxide are more preferred. As the sodium salt, sodium halide and / or sodium hydroxide are preferred, and sodium chloride, sodium bromide, and / or sodium hydroxide are more preferred.

[0022] When the amount of the magnesium hydroxide and / or magnesium oxide is 100 mol%, the amount of the alkali metal compound is preferably in the range of 0.1 to 50 mol%. If the amount of the alkali metal compound is less than the above range, it becomes difficult to achieve an improvement in the reaction rate or a decrease in the heat storage temperature by using the alkali metal compound. Also, if the amount of the alkali metal compound exceeds the above range, the heat storage amount per unit volume or unit mass of the chemical heat storage material may decrease. The amount of the alkali metal compound is preferably 0.5 to 30 mol%, more preferably 1.0 to 20 mol%, and even more preferably 2.0 to 10 mol%. By adjusting the amount of the alkali metal compound, the dehydration endothermic temperature of the chemical heat storage material can be controlled.

[0023] The chemical heat storage material of the present invention may further contain a compound of a specific metal in addition to magnesium hydroxide and / or magnesium oxide and the compound of the alkali metal which is an optional component. By further including the compound of the specific metal, the reaction rate of the chemical heat storage material can be further increased. At this time, it is preferable that the compound of the specific metal is chemically complexed with magnesium hydroxide and / or magnesium oxide.

[0024] The specific metal is selected from the group consisting of nickel, cobalt, copper, and aluminum, and may contain only one of these, or may contain a combination of two or more. Among these, at least one selected from the group consisting of nickel, cobalt, and aluminum is preferable, and nickel and / or cobalt is more preferable.

[0025] The compound of the specific metal is not particularly limited, but is preferably one that complexes with magnesium hydroxide and / or magnesium oxide, and examples thereof include halides such as chlorides and bromides, hydroxides, oxides, 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 preferable.

[0026] The amount of the specific metal compound used is preferably such that when the amount of magnesium hydroxide and / or magnesium oxide is 100 mol%, the amount of the specific metal is 0.1 to 40 mol%. When the amount of the specific metal is less than the above range, it becomes difficult to achieve an improvement in the reaction rate or a decrease in the heat storage temperature by using the specific metal compound. Further, when the amount of the specific metal exceeds the above range, the heat storage amount per unit volume or unit mass of the chemical heat storage material may decrease. The amount of the specific metal is preferably 3 to 40 mol%, more preferably 5 to 30 mol%, and even more preferably 10 to 25 mol%. By adjusting the amount of the specific metal compound used, the dehydration endothermic temperature of the chemical heat storage material can be controlled.

[0027] The chemical heat storage material in the present invention may be one in which magnesium hydroxide and / or magnesium oxide, optionally the alkali metal compound, and optionally the specific metal compound are simply physically mixed or dispersed, but is not limited thereto. A part or all of each constituent component may be chemically compounded with each other, or a part or all of each constituent component may chemically react with each other to form a third component.

[0028] The chemical heat storage material of the present invention may further contain a metal acid salt in addition to magnesium hydroxide and / or magnesium oxide, the alkali metal compound which is an optional component, and the specific metal compound which is an optional component. The metal acid salt refers to a salt formed by the reaction of a metal compound with an acid, and particularly preferably a salt formed by neutralizing a metal hydroxide with an acid. 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 mentioned, but are not limited thereto.

[0029] Examples of the metal constituting the metal oxyacid salt include alkaline earth metals such as calcium, magnesium, strontium, and barium; alkali metals such as lithium, sodium, and potassium; and aluminum, iron, cobalt, nickel, copper, and zinc. These may contain only one of them, or may contain a combination of two or more. Among these, calcium, lithium, and / or magnesium are preferred, and calcium and / or magnesium are more preferred. The alkaline earth metal constituting the metal oxyacid salt may be magnesium or an element other than magnesium, but from the viewpoint of improving the reaction rate of the chemical heat storage material, it is preferably magnesium. However, when the metal oxyacid salt used in the present invention is an alkaline earth metal oxyacid salt, it is preferable not to use carbonates and chlorides of alkaline earth metals as the alkaline earth metal oxyacid salt.

[0030] The acid constituting the metal oxyacid salt is not particularly limited, and known acids can be appropriately used, and it may be either an inorganic acid or an organic acid. Further, it may be a water-soluble acid or an acid hardly soluble or insoluble in water. Further, only one type may be used, or two or more types may be appropriately combined and used.

[0031] Examples of the inorganic acid include hydrochloric acid, hydrobromic acid, hydroiodic acid, hydrofluoric acid, halogen oxo acid, sulfuric acid, nitric acid, phosphoric acid, phosphonic acid, sulfonic acid, boric acid, hydrocyanic acid, hexafluorophosphoric acid, and the like.

[0032] Examples of the organic acid include organic sulfonic acid, organic phosphonic acid, aliphatic hydroxy acid (including dihydroxy acid and trihydroxy acid), aromatic hydroxy acid (including dihydroxy acid and trihydroxy acid), aliphatic carboxylic acid (including dicarboxylic acid and tricarboxylic acid), aliphatic unsaturated carboxylic acid (including dicarboxylic acid and tricarboxylic acid), aromatic carboxylic acid (including dicarboxylic acid and tricarboxylic acid), aromatic unsaturated carboxylic acid (including dicarboxylic acid and tricarboxylic acid), other oxy acids, other oxocarboxylic acids, amino acids, and acids of their derivatives.

[0033] Examples of the organic sulfonic acid include methanesulfonic acid, trifluoromethanesulfonic acid, benzenesulfonic acid, p-toluenesulfonic acid, and the like. Examples of the organic phosphonic acid include dimethyl phosphate, phenylphosphonic acid, and the like. Examples of the aliphatic hydroxy acid or aromatic hydroxy acid include lactic acid, malic acid, citric acid, tartaric acid, and the like. Examples of the aliphatic carboxylic acid or aliphatic unsaturated carboxylic acid include formic acid, acetic acid, propionic acid, butyric acid, acrylic acid, sorbic acid, pyruvic acid, oxaloacetic acid, squaric acid, oxalic acid, malonic acid, succinic acid, glutaric acid, maleic acid, aconitic acid, and the like. Examples of the aromatic carboxylic acid or aromatic unsaturated carboxylic acid include benzoic acid, phthalic acid, salicylic acid, shikimic acid, gallic acid, pyromellitic acid, and the like. Examples of the amino acid include aspartic acid, glutamic acid, and the like.

[0034] As for the usage amount of the metal acid salt, when the amount of magnesium hydroxide and / or magnesium oxide is 100 mol%, it is preferably an amount such that the amount of the metal acid salt is 0.05 to 30 mol%. When the usage amount of the metal acid salt is less than the above range, it becomes difficult to achieve an improvement in the reaction rate or a decrease in the heat storage temperature due to the addition of the acid salt. Further, when the usage amount of the metal acid salt exceeds the above range, the influence on magnesium hydroxide and / or magnesium oxide as the base material is large, and there is a risk that the heat storage amount per unit volume or unit mass of the chemical heat storage material may decrease. The usage amount of the metal acid salt is preferably 0.1 to 20 mol%, more preferably 0.3 to 15 mol%, still more preferably 0.5 to 10 mol%, even more preferably 0.8 to 8 mol%, and particularly preferably 1 to 6%.

[0035] The chemical heat storage material of the present invention is a chemical heat storage material that utilizes the endothermic dehydration reaction and the hydration exothermic reaction of magnesium hydroxide and magnesium oxide. In that range, the chemical heat storage material of the present invention may contain other components, and may contain chemical heat storage components other than the constituent components described above, or components that do not exhibit a chemical heat storage effect (for example, a binder).

[0036] The shape of the chemical heat storage material of the present invention is not particularly limited, and may be, for example, in the form of powder, granulated body, molded body, etc. When manufacturing a chemical heat storage material having a shape of powder, granulated body, or molded body, known methods can be applied. For example, when manufacturing a powder chemical heat storage material, screening, crushing, and pulverizing processes can be applied. Further, when manufacturing a granulated chemical heat storage material, granulation processes such as extrusion granulation, rolling granulation, fluidized bed granulation, spray drying, etc. can be applied. When manufacturing a molded chemical heat storage material, molding processes such as press molding, injection molding, blow molding, vacuum molding, and extrusion molding can be applied. That is, as long as the properties as a chemical heat storage material are not impaired to an extent that can be implemented, any shape according to the implementation form of the consumer can be selected.

[0037] Next, a method for manufacturing the chemical heat storage material in the present invention will be described. A method for manufacturing a chemical heat storage material according to an embodiment includes: (A) a step of preparing magnesium hydroxide as a base material; (B) a step of mixing, if necessary, the prepared magnesium hydroxide with the compound of the alkali metal, the compound of the specific metal, or the metal acid salt; (C) a step of crushing and pulverizing magnesium hydroxide.

[0038] In step (A), for example, an aqueous magnesium chloride solution and an aqueous alkali solution are reacted to obtain a magnesium hydroxide slurry, which is then filtered, washed with water, and dried to obtain magnesium hydroxide. As the aqueous magnesium chloride solution, for example, magnesium chloride hexahydrate, magnesium chloride dihydrate, anhydrous magnesium chloride, bittern, kansui, seawater, etc. can be used, and these can also be used in appropriate combinations. As the above aqueous alkali solution, for example, aqueous solutions of sodium hydroxide, calcium hydroxide, ammonia, etc. can be used, and these can also be used in appropriate combinations.

[0039] In the production of magnesium hydroxide in Process (A), it is desirable to suppress grain growth and agglomeration. This is because during the subsequent grinding in Process (C), the grinding conditions can be relaxed, the grinding can proceed without distorting the crystals, and an increase in the ratio of the full width at half maximum can be suppressed. To suppress grain growth and agglomeration, it is preferable to carry out the production reaction of magnesium hydroxide at a low to normal temperature for a short time while stirring well, and immediately after the reaction is completed, perform filtration and water washing.

[0040] In Process (B), optionally, additives are mixed. As an example, a compound of an alkali metal is dissolved in ion-exchanged water to prepare an aqueous solution of the alkali metal compound, and powdered magnesium hydroxide is added thereto and stirred and mixed. Here, a compound of a specific metal or a metal acid salt may also be added together. The resulting slurry is dried. The method of stirring and mixing is not particularly limited as long as the ion-exchanged water as the solvent and the powdered magnesium hydroxide are sufficiently mixed.

[0041] The order of adding each component may be changed. In this case, for example, first dissolve the alkali metal compound, or a compound of an alkali metal and a compound of a specific metal in ion-exchanged water, add the metal acid salt thereto, then add the powdered magnesium hydroxide to prepare a slurry, and subsequently dry it.

[0042] In Process (C), in order to adjust the range of the ratio of the full width at half maximum of the obtained chemical heat storage material, it is desirable to appropriately adjust the crushing and grinding conditions of magnesium hydroxide. If the energy applied to the powder is excessive, as the grinding proceeds, the distortion of the crystals increases (the ratio of the full width at half maximum becomes larger), and the reactivity as a heat storage material tends to decrease. On the other hand, if the energy applied to the powder is too small, the grinding does not proceed and it becomes difficult to use as a heat storage material. The grinding can be appropriately adjusted by selecting the grinding time, the material and size of the media, etc.

[0043] The pulverization can be carried out using known devices. Also, dry pulverization or wet pulverization can be utilized. For example, a roll crusher, cutter mill, stamp mill, ring mill, hammer mill, pin mill, ball mill, power mill, vibration mill, etc. can be used.

[0044] The chemical heat storage material of the present invention can store heat by absorbing heat from a heat source of about 100 to 400 °C, such as unused heat from factory exhaust heat, etc., and dehydrating. The dehydrated chemical heat storage material can be easily maintained in a heat storage state by keeping it in a dry state, and can be carried to a desired location while maintaining its heat storage state. When releasing heat, heat can be taken out as heat energy by bringing it into contact with water, preferably steam. Also, heat and cold energy can be generated by causing water vapor sorption on one side in a hermetically sealed space and evaporating water on the other side.

[0045] The chemical heat storage material of the present invention preferably has a dehydration operation temperature of 350 °C or lower, more preferably 330 °C or lower, and even more preferably 320 °C or lower. Also, the hydration operation temperature is preferably 70 °C or higher, more preferably 80 °C or higher, and even more preferably 90 °C or higher. The chemical heat storage material of the present invention is preferably subjected to a heat storage operation at the above dehydration operation temperature, and is preferably subjected to a heat release operation by bringing it into contact with water at the above hydration operation temperature. Thereby, the change in the crystallite size of magnesium hydroxide or magnesium oxide due to the dehydration reaction or hydration reaction is suppressed, and the range of the ratio of the half-value widths described above can be stably maintained.

[0046] 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, fuel cells, etc. For example, the heat of exhaust gas can be utilized for shortening the warm-up operation of automobiles, improving the amenity of passengers, improving fuel efficiency, and reducing the harmfulness of exhaust gas by improving the activity of exhaust gas catalysts. In particular, in an engine, since the load due to operation is not constant and the exhaust output is also unstable, the direct utilization of exhaust heat from the engine is inevitably inefficient and inconvenient. By using the chemical heat storage material of the present invention, the exhaust heat from the engine can be chemically stored once, and heat output can be performed according to the heat demand, enabling more ideal utilization of exhaust heat.

Examples

[0047] The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

[0048] (Evaluation method) For the chemical heat storage materials obtained in each example and comparative example, thermal evaluation was performed using a thermogravimetric / differential thermal analysis measuring device (TG / DTA6300, manufactured by Seiko Instruments Inc.). Specifically, the temperature was raised at a rate of 10 °C / min. under atmospheric conditions and normal pressure up to 300 °C, and then the temperature was kept constant, and the weight loss amount was measured over time. Based on the obtained weight loss value, the reaction rate was calculated as the ratio of the change of magnesium hydroxide in each chemical heat storage material to magnesium oxide.

[0049] To calculate the reaction rate, in order to exclude the influence of volatile components, etc., the weight of the chemical heat storage material at the time when the temperature was raised to 200 °C was set as the starting weight and the reaction rate was set to 0%, and the weight loss value assuming that all magnesium hydroxide had changed to magnesium oxide was defined as the reaction rate of 100% and the calculation was performed.

[0050] The performance evaluation of the chemical heat storage material was carried out based on defining the temperature at which the weight loss rate reached 1% during the heating process at the above heating rate as the reaction start temperature. At the same time, the temperature at which the reaction rate reached 5% was also evaluated. The lower these temperatures are, the faster the endothermic dehydration reaction proceeds, indicating a larger heat storage capacity and the ability to store heat with lower-temperature heat.

[0051] The purity of magnesium hydroxide was calculated by measuring the content of each impurity with a multi-element simultaneous fluorescence X-ray analyzer (Simultix12, manufactured by Rigaku Corporation) and subtracting the content of oxides of Ca, Si, Al, Fe, P, S, and Na, which are the main impurities, from 100%. The BET specific surface area was measured by the gas adsorption method (BET method) using nitrogen gas with a specific surface area measuring device (Macsorb, manufactured by Mountech Co., Ltd.). The volume average particle size was measured using a laser diffraction scattering particle size distribution measuring device (MT3300, manufactured by Nikkiso Co., Ltd.). The half-value width by powder X-ray diffraction analysis using CuKα radiation was measured using MiniFlex600 (manufactured by Rigaku Corporation). The measured diffraction intensities were plotted on a graph with the X-ray incident angle 2θ (unit: °) on the horizontal axis and the diffraction intensity (unit: cps) on the vertical axis, and the specific incident angle and the peak height of its diffraction intensity were read. The measurement was carried out under the conditions of X-ray source CuKα radiation (0.154 nm), scanning speed 2° / min, scanning range 2θ = 3 - 90°, sampling interval 0.02°, voltage = 40 kV, current = 40 mA, divergence slit = 2 / 3°, divergence vertical slit 10 mm, scattering slit = 2 / 3°, and receiving slit = 0.45 mm. Using analysis software (product name: Jade6, manufactured by Rigaku), the peak near 2θ = 38° of magnesium hydroxide was taken as the (111) plane, and the peak near 2θ = 43° of magnesium oxide was taken as the (200) plane, and the half-value width of each peak was calculated.

[0052] (Example 1) Magnesium chloride anhydride with a purity of 98% by mass was dissolved in pure water, and the magnesium chloride aqueous solution was adjusted so that the Mg ion concentration became 2.0 mol / L. To this magnesium chloride aqueous solution, pure water was added to a reagent-grade sodium hydroxide solution to adjust the concentration to 2.0 mol / L. The solution was stirred at 20 °C and 300 rpm, and using a roller pump, it was dropped at 10 mL / min so that the reaction rate of sodium hydroxide with respect to magnesium chloride became 90% to obtain a magnesium hydroxide slurry. Immediately after the dropping was completed, the magnesium hydroxide slurry was filtered and washed with water, and then dried at 110 °C for 6 hours to obtain magnesium hydroxide. 5 g of the obtained magnesium hydroxide (purity approximately 99%) was weighed, and further, lithium hydroxide monohydrate (Kanto Chemical reagent, special grade, purity 98.0%) in an amount of 10 mol% with respect to the magnesium hydroxide was weighed. The weighed lithium hydroxide monohydrate was completely dissolved in 50 mL of ion-exchanged water to obtain an aqueous solution. The magnesium hydroxide weighed above was added to the aqueous solution, and the mixture was stirred at 200 (rpm) for 300 seconds with a magnetic stirrer to prepare a slurry. The slurry was dried at 110 °C for 12 hours or more in a dryer (DRA430DA manufactured by Advantec Co., Ltd.) to remove moisture, thereby obtaining magnesium hydroxide powder. This magnesium hydroxide powder was pulverized in a wet pot mill for 0.5 hours with an iron-core nylon ball (about φ15 mm) to produce a chemical heat storage material. For the obtained chemical heat storage material, the full width at half maximum was measured and the thermal behavior was confirmed by the above evaluation method, and the reaction rate was calculated.

[0053] (Example 2) A chemical heat storage material was produced in the same manner as in Example 1 except that it was wet pulverized in an alcohol solvent in a pot mill for 1 hour with an iron-core nylon ball (about φ15 mm), and the full width at half maximum was measured and the reaction rate was calculated in the same manner.

[0054] (Comparative Example 1) The chemical heat storage material was produced in the same manner as in Example 1, except that the dropping rate of the sodium hydroxide solution was set at 5 mL / min and the mixture was pulverized for 3 hours using a dry pot mill with a nylon ball (approx. φ15 mm) with an iron core. The full width at half maximum was measured and the reaction rate was calculated in the same manner.

[0055] The results are shown in Table 1.

[0056]

Table 1

[0057] From Table 1, it can be confirmed that the chemical heat storage materials of Examples 1 and 2, where the ratio of the full width at half maximum is 0.5 or more and 2 or less, have a lower dehydration reaction start temperature and a faster dehydration reaction compared to Comparative Example 1 under the same evaluation conditions. From this, it can be seen that the chemical heat storage materials of Examples 1 and 2 can store heat with low-temperature heat compared to the chemical heat storage material of Comparative Example 1.

Claims

1. A chemical heat storage material containing magnesium hydroxide and / or magnesium oxide, in an X-ray diffraction measurement using CuKα rays after the dehydration reaction of the chemical heat storage material, with respect to the full width at half maximum of the diffraction peak at a Bragg angle 2θ = 43° on the (200) plane of magnesium oxide, the ratio of the full width at half maximum of the diffraction peak at a Bragg angle 2θ = 38° on the (101) plane of magnesium hydroxide in an X-ray diffraction measurement using CuKα rays after the hydration reaction of the chemical heat storage material is 0.89 or more and 2 or less. The chemical heat storage material.

2. In an X-ray diffraction measurement using CuKα rays after the dehydration reaction of the chemical heat storage material, the full width at half maximum of the diffraction peak at 2θ = 43° on the (200) plane of magnesium oxide is 0.2 or more and 0.45 or less, In an X-ray diffraction measurement using CuKα rays after the hydration reaction of the chemical heat storage material, the full width at half maximum of the diffraction peak at 2θ = 38° on the (101) plane of magnesium hydroxide is 0.2 or more and 0.45 or less. The chemical heat storage material according to claim 1.

3. Furthermore, it contains a compound of an alkali metal, The amount of the compound of the alkali metal is 0.1 to 50 mol% with respect to the magnesium hydroxide and / or magnesium oxide. The chemical heat storage material according to claim 1 or 2.

4. The dehydration temperature is 350°C or lower. The chemical heat storage material according to any one of claims 1 to 3.

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