JP2018168224A - Chemical thermal storage medium and method for producing the same - Google Patents

Abstract

To provide a chemical thermal storage medium that performs thermal storage using the dehydration reaction of hydroxides of alkaline earth metals, wherein, the thermal storage can be realized at lower temperature.SOLUTION: A chemical thermal storage medium has a composite compound of alkaline earth metals and alkali metals; the content of alkali metals in the composite compound is 0.1-50 mol% relative to the content of alkaline earth metals. The composite compound is a compound containing hydroxide chlorides of alkaline earth metals. The alkaline earth metal is calcium, and preferably, the intensity of a peak appearing in a range of 38.0°-38.5° in X-ray incidence angle, has a value of 20% or more of the intensity of a peak appearing in a range of 28.4°-29.0° in X-ray incidence angle.SELECTED DRAWING: None

Description

  The present invention relates to a chemical heat storage material and a method for producing the same.

  In recent years, the use of fossil fuels has been demanded by carbon dioxide emission regulations, and it is necessary to promote the use of exhaust heat in addition to energy saving in each process. As means for using exhaust heat, warm water storage at 100 ° C. or less using water is known. However, in hot water heat storage, (1) long-term heat storage is impossible due to heat dissipation loss, and (2) a large amount of water is required because the amount of sensible heat is small, making it difficult to make the heat storage equipment compact. (3) There is a problem that the output temperature is unsteady according to the usage amount and gradually drops. Therefore, it is necessary to develop a more efficient heat storage technology in order to promote consumer use of such waste heat.

  A chemical heat storage method is an example of a highly efficient heat storage technology. Since the chemical heat storage method involves chemical changes such as adsorption and hydration of substances, the amount of heat stored per unit mass is higher than the heat storage method using 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 to a metal salt (ammine complex formation reaction), a reaction by adsorption / desorption of an organic substance such as alcohol, and the like have been proposed. The water vapor adsorption / desorption method is most advantageous in view of environmental load and simplicity of the apparatus. As chemical heat storage materials used in the water vapor adsorption and desorption method, calcium hydroxide and magnesium hydroxide, which are alkaline earth metal hydroxides, are known.

  However, since these calcium hydroxide and magnesium hydroxide do not cause an effective dehydration reaction in a low temperature range of 100 to 300 ° C., there is a problem that they do not function as a practical heat storage material.

  In order to solve this problem, Patent Document 1 discloses that a composite hydroxide of magnesium and at least one metal component selected from the group consisting of Ni, Co, Cu, and Al is used. A chemical heat storage material capable of storing heat at about ~ 300 ° C has been proposed.

  Furthermore, in Patent Document 2, for the purpose of improving the heat storage amount of the chemical heat storage material described in Patent Document 1, by adding a hygroscopic metal salt such as lithium chloride to a hydroxide of magnesium or calcium, A chemical heat storage material that has a high heat storage amount per unit mass or unit volume and can store heat at about 100 to 350 ° C. has been proposed.

  However, depending on the technique disclosed in Patent Document 2, it may be difficult to store heat at a target temperature. In Patent Document 3, alkaline earth metal hydroxide and alkali metal chloride are chemically synthesized. A composite heat storage material including a structurally coupled structure is disclosed.

JP 2007-309561 A JP 2009-186119 A JP 2013-216863 A

  According to the technique disclosed in Patent Document 3, it is possible to achieve an improvement in the heat storage density, but the inventors of the present application have examined, the starting temperature of heat storage by dehydration has not been sufficiently reduced, There was a problem that waste heat could not be used.

  In view of the above situation, the present invention aims to provide a chemical heat storage material that realizes heat storage at a lower temperature in a chemical heat storage material that performs heat storage using a dehydration reaction of a hydroxide of an alkaline earth metal. .

  In order to solve the above-mentioned problems, the present inventors have made various studies. In a chemical heat storage material based on an alkaline earth metal hydroxide, a predetermined amount of alkali is added to the alkaline earth metal hydroxide. A new composite compound is formed by mixing the metal salt under predetermined conditions, and using such a composite compound enables heat storage at a lower temperature than the chemical heat storage material disclosed in Patent Document 3. As a result, the present invention has been achieved.

  That is, the present invention is a chemical heat storage material, wherein the chemical heat storage material is composed of a composite compound of an alkaline earth metal and an alkali metal, and the content of the alkali metal in the composite compound is the same as that of the alkaline earth metal. It is 0.1-50 mol% with respect to this, and the said complex compound is a chemical heat storage material which is a compound containing the chloride hydroxide of an alkaline-earth metal.

  The alkaline earth metal is preferably at least one selected from the group consisting of calcium, magnesium, and barium.

  In the composite compound, the alkaline earth metal is calcium, and the intensity of a peak appearing in an X-ray incident angle range of 38.0 ° to 38.5 ° is X-ray incident angle of 28.4 ° to 29.0 °. It is preferable to have a value of 20% or more of the peak intensity appearing in the range.

  In the composite compound, the alkaline earth metal is magnesium, and an intensity of a peak appearing in an X-ray incident angle range of 15.0 ° to 15.5 ° is X-ray incident angle of 18.3 ° to 18.8 °. It is preferable to have a value of 20% or more of the peak intensity appearing in the range.

  The alkali metal is preferably at least one selected from the group consisting of lithium, potassium, and sodium.

  The present invention also relates to a method for producing the chemical heat storage material, comprising mixing alkaline earth metal hydroxide and alkali metal salt under hydration conditions for 120 minutes or more to obtain alkaline earth metal water. It also relates to a method comprising the step of forming a complex compound of an oxide and an alkali metal salt.

  ADVANTAGE OF THE INVENTION According to this invention, in the chemical heat storage material which performs heat storage using the dehydration reaction of the alkaline-earth metal hydroxide, the chemical heat storage material which implement | achieves heat storage at lower temperature can be provided.

Chart obtained by X-ray diffraction analysis of the composite compound produced in Example 1 Chart obtained by X-ray diffraction analysis of the composite compound produced in Example 2 Chart obtained by X-ray diffraction analysis of composite compound produced in Comparative Example 1 Chart obtained by X-ray diffraction analysis of composite compound produced in Comparative Example 2

  Hereinafter, embodiments of the present invention will be described in detail.

The chemical heat storage material of the present invention is composed of a complex compound of an alkaline earth metal and an alkali metal. The chemical heat storage material of the present invention utilizes the following reversible reaction with alkaline earth metal hydroxides and oxides. In the following reaction formula, the case where calcium or magnesium is used as the alkaline earth metal is shown.
CaO + H ₂ O⇔Ca (OH) ₂ ΔH = −109.2 kJ / mol MgO + H ₂ O⇔Mg (OH) ₂ ΔH = −81.2 kJ / mol In each formula, the reaction in the right direction is calcium oxide or oxidation. It is a hydration exothermic reaction of magnesium. Conversely, the reaction in the left direction is a dehydration endothermic reaction of calcium hydroxide or magnesium hydroxide. That is, the chemical heat storage material of the present invention can store heat by the dehydration reaction of calcium hydroxide or magnesium hydroxide, and the hydrated reaction of calcium oxide or magnesium oxide proceeds to the stored thermal energy. Can be supplied by doing.

  As described above, the chemical heat storage material of the present invention stores and dissipates heat by a reversible reaction with an alkaline earth metal hydroxide and an alkaline earth metal oxide. The alkali metal is contained in the form of an alkaline earth metal hydroxide, in the form of an alkaline earth metal oxide, or in both forms. That is, the alkaline earth metal and alkali metal complex compound may be a complex compound of an alkaline earth metal oxide and an alkali metal salt.

  In the present invention, examples of the alkaline earth metal include calcium, magnesium, and barium. One of these may be included, or a combination of two or more may be included. Among these, calcium and / or magnesium are preferable, and calcium is more preferable. Preferred alkaline earth metal compounds include magnesium hydroxide, calcium hydroxide, magnesium-calcium composite hydroxide, magnesium oxide, calcium oxide, magnesium-calcium composite oxide, and these can be used alone. Alternatively, two or more kinds may be mixed and used.

  As said alkali metal, lithium, potassium, and sodium are mentioned, These may contain only 1 type and may contain 2 or more types in combination. Among these, lithium and sodium are preferable, and lithium is more preferable. The alkali metal salt is not particularly limited as long as it can be combined with an alkaline earth metal compound and exhibits the effects of the present invention, but is a hygroscopic salt that adsorbs moisture in the atmosphere. Or a salt capable of producing the corresponding hydrate. Examples of such salts include halides such as chlorides and bromides, hydroxides, carbonates, acetates, nitrates, and sulfates that can be easily handled. 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, more preferably lithium chloride, lithium bromide, and / or lithium hydroxide. The potassium salt is preferably potassium halide and / or potassium hydroxide, more preferably potassium chloride, potassium bromide and / or potassium hydroxide. As a salt of sodium, sodium halide and / or sodium hydroxide are preferable, and sodium chloride, sodium bromide, and / or sodium hydroxide are more preferable. Of these, lithium salts are preferred, with lithium chloride being most preferred.

  In the present invention, the alkaline earth metal and alkali metal composite compound means a compound having a structure in which an alkaline earth metal hydroxide and an alkali metal salt are chemically bonded. For example, an alkali metal salt that is physically attached to the surface of a particle made of an alkaline earth metal hydroxide and that is not chemically bonded to each other is a composite compound referred to in the present invention. Not applicable.

  In the composite compound, an alkaline earth metal compound is a major component. Therefore, when the content of the alkaline earth metal contained in the composite compound is 100 mol%, the content of the alkali metal contained in the composite compound is 0.1 to 50 mol%. If the content of the alkali metal is too small, it is impossible to achieve a decrease in the heat storage temperature due to the combination with the alkali metal salt. Moreover, when there is too much content of an alkali metal, there exists a possibility that the thermal storage amount by a chemical thermal storage material may fall. Preferably it is 0.5-30 mol%, More preferably, it is 1.0-20 mol%, More preferably, it is 2.0-10 mol%.

  The composite compound in the present invention is a composite compound having a diffraction peak in the range of an X-ray incident angle of 38.0 ° to 38.5 ° in the X-ray diffraction analysis using CuKα rays when the alkaline earth metal is calcium. There is a feature in a certain point. In contrast, the composite compound disclosed in Patent Document 3 has a peak with a predetermined intensity in the range of an X-ray incident angle of 28.0 ° or more and 28.4 ° or less. The peak appearing in the X-ray incident angle range of 38.0 ° to 38.5 ° means that the composite compound in the present invention contains a specific compound called “alkaline earth metal (calcium) chloride hydroxide”. ing. The inventors of the present invention have said that an alkaline earth metal (calcium) and a complex compound of an alkaline earth metal (calcium) are identified by a peak appearing in an X-ray incident angle range of 38.0 ° to 38.5 °. As a result, it was found that heat storage can be realized at a lower temperature as compared with conventional composite compounds.

  In the present invention, the intensity of the peak appearing in the X-ray incident angle range of 38.0 ° to 38.5 ° is 20% of the peak intensity appearing in the X-ray incident angle range of 28.4 ° to 29.0 °. It is preferable to have a value of% or more. By showing such intensity | strength, the thermal storage temperature in a chemical thermal storage material can be reliably made low. The peak appearing in the range of the X-ray incident angle of 28.4 ° to 29.0 ° is a peak that means the presence of an alkaline earth metal (calcium) hydroxide.

  The composite compound according to the present invention is a composite having a diffraction peak in the X-ray incident angle range of 15.0 ° to 15.5 ° in the X-ray diffraction analysis using CuKα rays when the alkaline earth metal is magnesium. It is characterized by being a compound. The peak appearing in the X-ray incident angle range of 15.0 ° to 15.5 ° means that the composite compound in the present invention contains a specific compound called “alkaline earth metal (magnesium) chloride hydroxide”. ing. The inventors of the present invention have found that an alkaline earth metal (magnesium) and an alkaline earth metal complex compound are identified by a peak appearing in an X-ray incident angle range of 15.0 ° to 15.5 °. As a result, it was found that heat storage can be realized at a lower temperature as compared with conventional composite compounds.

  In the present invention, the intensity of the peak appearing in the X-ray incident angle range of 15.0 ° to 15.5 ° is 20% of the peak intensity appearing in the X-ray incident angle range of 18.3 ° to 18.8 °. It is preferable to have a value of% or more. By showing such intensity | strength, the thermal storage temperature in a chemical thermal storage material can be reliably made low. Note that the peak appearing in the range of the X-ray incident angle of 18.3 ° to 18.8 ° is a peak that means the presence of an alkaline earth metal (magnesium) hydroxide.

  In the X-ray diffraction analysis by the CuKα ray, the numerical value of the diffraction intensity obtained by performing the X-ray diffraction analysis of the composite compound is two-dimensional with the X-ray incident angle (2θ) as the horizontal axis and the diffraction intensity as the vertical axis. It is possible to confirm the peak of the diffraction intensity by plotting the coordinates.

  Note that the chemical heat storage material of the present invention is composed of the composite compound means that the chemical heat storage material contains the composite compound to such an extent that the heat storage effect exhibited by the chemical heat storage material is mainly realized by the composite compound. Means that. Therefore, the chemical heat storage material of the present invention may contain a chemical heat storage component other than the composite compound or a component that does not exhibit a chemical heat storage action (for example, a binder).

  Although the shape of the chemical heat storage material of this invention is not specifically limited, For example, it may be shapes, such as powder, a granulated body, a molded object.

  Next, a method for producing the composite compound in the present invention will be described.

  The method for producing the composite compound in the present invention is not particularly limited, but the composite compound in the present invention is obtained by mixing an alkaline earth metal hydroxide powder and an alkali metal salt powder under specific conditions. Can do. The mixing operation is an operation of mixing two or more kinds of raw material compounds using a known mixing means such as a stirrer or a ball mill, and may be wet mixing or dry mixing. However, in any mixing operation, by continuing the mixing operation for 120 minutes or more under hydration conditions, an alkaline earth metal chloride hydroxide is efficiently produced, and a composite compound containing this is produced. be able to. Although the upper limit of mixing time is not specifically limited, For example, 720 minutes or less is preferable.

  When performing dry mixing, when mixing two or more raw material compounds in a stirrer such as a ball mill, the humidity of the atmosphere in the stirrer is set to 80 Rh%, and the temperature of the atmosphere is set to 35 ° C. or higher. By performing mixing for 120 minutes or more, the composite compound of the present invention can be obtained.

  When performing wet mixing, prepare a dispersion of two or more raw material compounds using pure water or the like, mix the dispersion for 120 minutes or more, then dry, and crush as necessary. Thus, the composite compound of the present invention can be obtained.

  The chemical heat storage material of the present invention can store heat by heating and dehydrating the heat storage material with a heat source of about 100 to 300 ° C., for example, unused heat such as factory exhaust heat. The dehydrated heat storage material can be easily maintained in a dry state by keeping it in a dry state, and can be carried to a desired place while maintaining the heat storage state. In the case of radiating heat, the heat of hydration reaction (water vapor sorption heat) can be taken out as thermal energy by contacting with water vapor at a predetermined pressure. It is also possible to generate cold by causing water vapor sorption on the one hand in the hermetic chain space and evaporating water on the other.

  The chemical heat storage material of the present invention is also suitable for effectively utilizing the heat of exhaust gas discharged from an engine, a fuel cell, or the like. For example, the heat of exhaust gas can be used for shortening the warm-up operation of an automobile, improving passenger amenity, improving fuel consumption, reducing exhaust gas damage by improving the activity of an exhaust gas catalyst, and the like. In particular, in the case of an engine, since the load due to operation is not constant and the exhaust output is also unstable, the direct use of exhaust heat is necessarily inefficient and inconvenient. According to the chemical heat storage material of the present invention, exhaust heat is temporarily stored once, and more ideal exhaust heat can be used by outputting heat according to the heat demand.

  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.

(Measurement method of dehydration start temperature)
About the composite compound obtained by each Example and the comparative example, thermal evaluation was performed using the thermogravimetric / differential thermal analysis measuring device (TG / DTA6300, Seiko Instruments Inc. make). The measurement was performed at a rate of temperature increase of 10 ° C./min. , It was carried out in the range from room temperature to 500 ° C. under atmospheric conditions and normal pressure. The temperature at which calcium hydroxide in each composite compound starts changing to calcium oxide was measured from the endothermic behavior, and this was used as the dehydration start temperature.

(Measurement method of X-ray diffraction analysis)
The structure of the chemical heat storage material was subjected to structural analysis using an X-ray diffractometer (MiniFlex 600, manufactured by Rigaku Corporation). Using CuKα rays, the horizontal axis represents the X-ray incident angle 2θ (unit: °) and the vertical axis represents the diffraction intensity (unit: cps). The specific incident angle and the peak height of the diffraction intensity are read to confirm the structure. did.

Example 1
10 g of powdered calcium hydroxide (Kanto Chemical Reagent, special grade) was weighed. Next, powdered lithium chloride (Kanto Chemical Reagent, special grade) is weighed so as to be 10 mol% with respect to calcium hydroxide, and this is added to an appropriate amount of ion-exchanged water at room temperature and dissolved by stirring. An aqueous solution was created. The powdered calcium hydroxide was added to the aqueous solution and stirred for 120 minutes to obtain a dispersion. The dispersion was dried at 110 ° C. for 18 hours in a dryer. The lump obtained by drying was crushed with a commercially available handy mill to obtain a composite compound of calcium hydroxide and lithium chloride. When the diffraction peak by a CuK alpha ray was measured about the obtained complex compound, the diffraction peak existed in the range of X-ray incident angles 38.0 degrees-38.5 degrees. The intensity of the peak was approximately 23% with respect to the intensity of the peak appearing in the range of the X-ray incident angle of 28.4 ° to 29.0 °. Further, the dehydration start temperature of the obtained composite compound was measured by the above method.

(Example 2)
Weigh 10 g of powdered calcium hydroxide (Kanto Chemical Reagent, Special Grade), and weigh the powdered lithium chloride (Kanto Chemical Reagent, Special Grade) to 10 mol% with respect to calcium hydroxide. Mixing was performed. Mixing was performed dry, and was performed for 180 minutes in an atmosphere of 40 ° C. and 80 Rh%. Thereby, a complex compound of calcium hydroxide and lithium chloride was obtained. When the diffraction peak by CuKα ray was measured for the obtained composite compound, a diffraction peak was present in the range of X-ray incident angle of 38.0 ° to 38.5 °. The intensity of the peak was approximately 55% with respect to the intensity of the peak appearing in the X-ray incident angle range of 28.4 ° to 29.0 °. Further, the dehydration start temperature of the obtained composite compound was measured by the above method.

(Comparative Example 1)
10 g of powdered calcium hydroxide (Kanto Chemical Reagent, Special Grade) is weighed, and further, the powdered lithium chloride (Kanto Chemical Reagent, special grade) is weighed so as to be 10 mol% with respect to calcium hydroxide. Both compounds were mixed at 45 Rh%. Mixing was performed by a dry method, and a commercially available handy mill was used as the mixing method. Thereby, a mixture of calcium hydroxide and lithium chloride was obtained. When the diffraction peak by CuKα ray was measured for the obtained mixture, the intensity of the diffraction peak in the range of X-ray incident angle 38.0 ° to 38.5 ° was X-ray incident angle 28.4 ° to 29.0. It was approximately 7% with respect to the intensity of the peak appearing in the range of °. Further, the dehydration start temperature of the obtained mixture was measured by the above method.

(Comparative Example 2)
10 g of powdered calcium hydroxide (Kanto Chemical Reagent, Special Grade) is weighed, and further, the powdered lithium chloride (Kanto Chemical Reagent, special grade) is weighed so as to be 10 mol% with respect to calcium hydroxide. Both compounds were mixed at 45 Rh%. Mixing was performed by a dry method, and a commercially available handy mill was used as the mixing method. The obtained mixture was baked in an electric furnace at 300 ° C. to 1 hr (heating rate 6 ° C./min.) To obtain a baked product. When the diffraction peak by CuKα ray was measured for the obtained fired product, the intensity of the diffraction peak in the range of X-ray incident angle 38.0 ° to 38.5 ° was X-ray incident angle 28.4 ° to 29.29. It was approximately 15% with respect to the intensity of the peak appearing in the range of 0 °. Moreover, the dehydration start temperature was measured by the said method about the obtained baked product.

  The above results are summarized in Table 1. In Table 1, the dehydration start temperature in Examples 1 and 2 and Comparative Example 2 is shown as a relative value with the dehydration start temperature in Comparative Example 1 being 100.

  From Table 1, in the composite compounds of Examples 1 and 2, the intensity of the peak appearing in the range of the X-ray incident angle of 38.0 ° to 38.5 ° is X-ray incident angle of 28.4 ° to 29.0 °. It was 20% or more of the intensity of the peak appearing in the range, and the dehydration start temperature was lower than the mixture or fired product of Comparative Example 1 or 2 in which the intensity of the peak was less than 20%. Therefore, the composite compounds of Examples 1 and 2 can be used as a material constituting a chemical heat storage material that realizes heat storage at a relatively low temperature.

Claims (6)

A chemical heat storage material,
The chemical heat storage material is composed of a complex compound of alkaline earth metal and alkali metal,
The content of the alkali metal in the composite compound is 0.1 to 50 mol% with respect to the alkaline earth metal, and the composite compound is a compound containing a chloride hydroxide of an alkaline earth metal. Chemical heat storage material.   The chemical heat storage material according to claim 1, wherein the alkaline earth metal is at least one selected from the group consisting of calcium, magnesium, and barium.   In the composite compound, the alkaline earth metal is calcium, and the intensity of a peak appearing in an X-ray incident angle range of 38.0 ° to 38.5 ° is X-ray incident angle of 28.4 ° to 29.0 °. The chemical heat storage material according to claim 1 or 2, wherein the chemical heat storage material has a value of 20% or more of the intensity of the peak appearing in the range.   In the composite compound, the alkaline earth metal is magnesium, and an intensity of a peak appearing in an X-ray incident angle range of 15.0 ° to 15.5 ° is X-ray incident angle of 18.3 ° to 18.8 °. The chemical heat storage material according to claim 1 or 2, wherein the chemical heat storage material has a value of 20% or more of the intensity of the peak appearing in the range.   The chemical heat storage material according to any one of claims 1 to 4, wherein the alkali metal is at least one selected from the group consisting of lithium, potassium, and sodium. A method for producing the chemical heat storage material according to any one of claims 1 to 4,
Forming a complex compound of an alkaline earth metal hydroxide and an alkali metal salt by mixing the alkaline earth metal hydroxide and the alkali metal salt for 120 minutes or more under hydration conditions. .

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