JP2014159497A - Chemical heat storage material, method of producing the same and chemical heat storage structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a new chemical heat storage material whose consistency with a heat medium storage material can be more improved and which enables efficiency of a chemical heat storage system to be more improved.SOLUTION: The chemical heat storage material is provided which is a chemical heat storage material generating or absorbing heat by occluding or releasing a heat medium. The chemical heat storage material contains a composite metal salt (MX, n:an average valency of M) being a metal halide which is composed of a metal element (M) and a halogen element (X), at least one of the elements consisting of two or more elements. The composite metal salt has an average electronegativity difference (ΔEa=EXa-EMa) of 0.3 to 2.16 or 2.21 to 3.2, the electronegativity difference being obtained by subtracting the average electronegativity of the metal element (EMa) from the average electronegativity of the halogen element (EXa). An example of the chemical heat storage material is Ca(ClBr)which is an alkali earth metal composite halide. A method of producing the chemical heat storage material and a chemical heat storage structure using the same are also provided.

Description

  The present invention relates to a chemical heat storage material comprising a double metal salt, a production method thereof, and a chemical heat storage structure using the same.

  With the heightened awareness of the environment, research and development aimed at saving energy and improving energy efficiency are being actively pursued. As one of them, a chemical heat storage system using a chemical heat storage material that has a large heat storage density and can store heat for a long period of time without keeping heat is attracting attention. According to this, relatively low-temperature waste heat (or exhaust heat) generated from various devices and plants can be effectively utilized.

  The chemical heat storage system performs heat storage (heat absorption) and heat dissipation (heat generation) by moving a heat medium (such as ammonia or water) between the chemical heat storage material and the heat medium storage material. In order to increase the efficiency and compactness of this system, it is important to match the operating temperature and the operating pressure between the chemical heat storage material and the heat medium storage material. For this reason, chemical heat storage materials are required not only to have a high heat storage density, but also to be able to efficiently occlude or release the heat medium at an operating temperature and pressure consistent with the heat medium storage material. It is done.

Conventionally, calcium oxide (quick lime) that forms hydroxide by reaction with water has been generally used for this chemical heat storage material, but recently, an ammonia complex (ammine) that can operate at lower temperatures. Metal chlorides forming a complex) are being used. However, in a chemical heat storage material composed only of a single metal salt such as calcium chloride (CaCl ₂ ), its operating temperature and pressure are fixed and not necessarily consistent with the heat medium storage material. There was a limit to the efficient operation of the system. Therefore, chemical heat storage materials using a plurality of types of single metal salts have been proposed. For example, the following patent document describes the related description.

Japanese Patent No. 311667 Japanese Patent Publication No.59-25159 JP-A-1-302077 Special Table 2007-531209 US Pat. No. 5,289,690

Patent Document 1 describes that a calcium salt mixture obtained by dissolving, concentrating and drying CaCl ₂ and CaBr ₂ has a higher ammonia (NH ₃ ) release temperature than a simple mixture thereof. However, in this patent document, the crystal structure and action of the calcium salt mixture are not clear. Calcium salt mixture thereof, coordination number changes when release ammonia is less than CaCl ₂ alone _{(CaCl 2 · 4NH 3 + 4NH} 3 ⇔ CaCl 2 · 8NH 3), also the heat storage density can be reversibly used small.

In Patent Document 2, sodium vapor (NaCl) and potassium chloride (KCl) are mixed in an appropriate amount of molten zinc chloride (ZnCl ₂ ) to lower the vapor pressure and melting temperature of ZnCl ₂ that reacts with NH _3. There is a description that can be made. However, NaCl or KCl in this case merely serves to stabilize molten ZnCl ₂ that absorbs and releases NH ₃ . That is, Patent Document 2 does not provide a new chemical heat storage material having different characteristics.

  Patent Documents 3 to 5 disclose a chemical heat storage system and the like, and metal halides are cited as an example of a chemical heat storage material used therefor. However, there is no specific description regarding the chemical heat storage material itself.

  The present invention has been made in view of such circumstances, and differs from a conventional chemical heat storage material made of a single metal salt in a pressure / temperature region in which a heat-medium absorption / release reaction occurs and a change in coordination number. An object of the present invention is to provide a new chemical heat storage material that is more consistent with the storage material and can efficiently operate the chemical heat storage system, and a method for manufacturing the same. Moreover, it aims at providing the chemical thermal storage structure using the chemical thermal storage material.

As a result of extensive research and trial and error, the present inventor is different from mixed metal salts of calcium chloride (CaCl ₂ ) and calcium bromide (CaBr ₂ ), which are single metal salts. We have successfully synthesized Ca (Cl _0.5 Br _0.5 ) ₂ (or CaClBr), which is a double metal salt. This double metal salt caused a heat medium absorption / release reaction under conditions different from those of conventional single metal salts, and showed a large change in coordination number. By developing this result, the present invention described below has been completed.

《Chemical heat storage material》
(1) The chemical heat storage material of the present invention is a chemical heat storage material that generates heat or absorbs heat by occlusion or release of a heat medium, and is composed of a metal element (M) and a halogen element (X), at least one of which is two types A double metal salt (MX _n , n: average valence of M), which is a metal halide composed of the above elements, and the double metal salt is obtained from the average electronegativity (EXa) of the halogen element. An average electronegativity difference (ΔEa = EXa−EMa) obtained by subtracting the average electronegativity (EMa) is 0.3 to 2.16 or 2.21 to 3.2.

(2) The chemical heat storage material of the present invention is not a mere mixture of a single metal salt (a compound in which a kind of metal ion (cation) and a kind of anion is ion-bonded), but a plurality of metal elements and / or a plurality of halogen elements. It consists of a double metal salt compounded (ion bonded) at the atomic level.

  This double metal salt can exhibit various characteristics different from those of single metal salts and mixtures thereof (mixed metal salts) that have been used as chemical heat storage materials. For example, the crystal structure, the equilibrium pressure that causes the heat medium absorption / release reaction, the change in coordination number, and the like are different from those of the conventional single metal salt. Further, the equilibrium pressure, the coordination number change, and the like can be changed by adjusting the ratio (composite ratio) of the elements constituting the double metal salt. Therefore, according to the present invention, it is possible to provide a chemical heat storage material having a high heat storage density, which is suitable for improving the operating characteristics of the heat medium storage material and thus the efficiency of the chemical heat storage system.

(3) The reason why the double metal salt according to the present invention exhibits characteristics different from those of the conventional single metal salt is not necessarily clear, but at present, it is considered as follows. That is, it is considered that the average ionic radius ratio and the electronegativity ratio of the cation and the anion have appropriate values, and the crystal structure and lattice volume have a large change in coordination number.

(4) The chemical heat storage material of the present invention only needs to contain the above-described double metal salt, and may be composed of two or more double metal salts, or a mixture of double metal salts and single metal salts. By adjusting the components of the chemical heat storage material by mixing other metal salts with the double metal salt, consistency with the heat medium storage material, the equilibrium region of the heat medium absorption and release reaction, changes in the coordination number of the heat medium, etc. Can be further optimized.

《Method for producing chemical heat storage material》
The above-described chemical heat storage material of the present invention is obtained, for example, by the following production method of the present invention. That is, the above-described chemical heat storage material can be obtained by a firing step of firing a mixed metal salt obtained by mixing two or more kinds of metal salts. Through the firing process, metal ions (for example, Ca ²⁺ , Sr ²⁺ ) and halogen ions (for example, Cl ⁻ , Br ⁻ , I ^−, etc.) contained in the metal salt are diffused, so that thermodynamics is more than a simple mixed metal salt. Stable metal salt (for example, Ca (Cl _1-y Br _y ) ₂ , y is a composite ratio, and 0 <y <1) is considered to be generated.

  Moreover, the manufacturing method of this invention is further equipped with the shaping | molding process which obtains the molded object which pressure-molded the mixed metal salt before the said baking process, and the said baking process is good also as a process of obtaining the sintered body which baked the molded object. Thereby, a more uniform chemical heat storage material can be obtained. In addition, you may use the obtained sintered body as a chemical heat storage material as it is, and you may use what was crushed and grind | pulverized as a chemical heat storage material.

《Chemical heat storage structure》
(1) The present invention can be grasped not only as the above-described chemical heat storage material and its manufacturing method, but also as a chemical heat storage structure comprising the chemical heat storage material. That is, this invention can be grasped | ascertained also as a chemical heat storage structure characterized by consisting of the chemical heat storage material mentioned above and the binder holding this chemical heat storage material. As a result, a chemical heat storage structure having a form according to the specifications of the reactor and the like and excellent in mechanical strength is obtained.

(2) It is preferable that the chemical heat storage structure further includes a high heat conductive material that is more excellent in thermal conductivity than the chemical heat storage material and the binder. By including the high heat conductive material, the heat exchange rate between the chemical heat storage structure and the outside is increased, and the heat medium absorption / release reaction is promoted, so that the chemical heat storage system is highly efficient. Note that the binder and the high thermal conductive material do not need to be separate materials, and may be the same material. For example, carbon fiber which is a high thermal conductive material can be used as a binder.

<Others>
Unless otherwise specified, “x to y” in this specification includes a lower limit value x and an upper limit value y. However, the average electronegativity (EMa, EXa) or the average electronegativity difference (ΔEa) does not include an upper limit value and a lower limit value. Arbitrary numerical values included in various numerical values and numerical ranges described in this specification are appropriately selected or extracted, and a numerical range such as “ab” is arbitrarily set as a new lower limit or upper limit. Can do.

3 is a graph showing an X-ray diffraction pattern of Sample 1.

  The present invention will be described in more detail with reference to embodiments of the invention. One or more contents arbitrarily selected from the present specification may be added as the above-described configuration of the present invention. The contents described in the present specification are appropriately applied not only to the chemical heat storage material but also to the manufacturing method and the chemical heat storage structure. A configuration related to a manufacturing method can be a configuration related to an object if understood as a product-by-process. Which embodiment is the best depends on the target, required performance, and the like.

《Chemical heat storage material》
(1) MX _n
The double metal salt according to the present invention is represented by MX _n (M: metal element, X: halogen element, n: average valence of M), and at least one of M or X is composed of two or more elements. Salt. Here, the average valence (n) of M is an average value of ionic valences when a plurality of metal elements respectively become metal ions. For example, it consists of two kinds of metal elements (M1, M2) and one kind of halogen element (X), and the M1 ion valence: m1, the M2 ion valence: m2, and the M1 atom relative to the total number of atoms of the metal element Number ratio (composite ratio): In the case of a double metal salt (M1 _x M2 _1-x X _n ) where x (0 <x <1), n = m1 × x + m2 × (1-x).

Further, the double metal salt may be composed of a plurality of halogen elements. Since the ionic valence of a halogen element is usually -1, for example, a double metal salt composed of two types of halogen elements (X1, X2) has a ratio of the number of X1 atoms to the total number of atoms of the halogen element (composite). The ratio is expressed as M (X1 _y X2 _1-y ) _{n where} y (0 <y <1). Further, a double metal salt composed of two kinds of metal elements and two kinds of halogen elements is represented as M1 _x M2 _1-x (X1 _y X2 _1-y ) _n . In any case, the average valence (n) of M is the sum Σmi · pi (i = 1, 2, 3) of the product of the valence (mi) of each metal element and the existence ratio (pi), as described above. ..., Σpi = 1).

(2) Electronegativity Electronegativity is the strength with which each atom attracts electrons, and is determined for each element. The reason for focusing on the electronegativity regarding the double metal salt constituting the chemical heat storage material is as follows. Since the heat transfer medium (ammonia or water) molecules enter between the metal ion (cation) and the halogen ion (anion) in the double metal salt, the binding force between the two due to the difference in electronegativity between the cation and the anion (Coulomb) This is because there is a relationship between the force) and the ease of entry of the heat transfer molecule (stability).

The average electronegativity (EXa) of the halogen element referred to in this specification is the average value of the electronegativity of each halogen element constituting the double metal salt, and the average electronegativity (EMa) of the metal element is the double metal salt. It is the average value of the electronegativity of each metal element which comprises. For example, the double metal salt of the present invention comprises two kinds of metal elements (M1, M2) and one kind of halogen element (X), and the ratio (composite ratio) of the number of M1 atoms to the total number of atoms of the metal element is x. (0 <x <1) (M1 _x M2 _1-x X _n ), M1 electronegativity: EM1, M2 electronegativity: EM2, X electronegativity: EX, EXa = EX , EMa = EM1 × x + EM2 × (1-x), ΔEa = EX− {EM1 × x + EM2 × (1-x)}.

The double metal salt of the present invention comprises a kind of metal element (M) and a plurality of halogen elements (X1, X2), and the ratio (composite ratio) of the number of X1 atoms to the total number of halogen element atoms is y ( When 0 <y <1) (M (X1 _y X2 _1-y ) _n ), when M electronegativity: EM, X1 electronegativity: EX1, X2 electronegativity: EX2, EMa = EM, EXa = EX1 * y + EX2 * (1-y), [Delta] Ea = {EX1 * y + EX2 * (1-y)}-EM.

Further, when the double metal salt of the present invention comprises two kinds of metal elements (M1, M2) and two kinds of halogen elements (X1, X2) (M1 _x M2 _1-x (X1 _y X2 _1-y ) _n ), Similarly, EMa = EM1 * x + EM2 * (1-x), EXa = EX1 * y + EX2 * (1-y), [Delta] Ea = {EX1 * y + EX2 * (1-y)}-{EM1 * x + EM2 * (1-x) }.

  By the way, the reason why the average electronegativity difference (ΔEa) according to the double metal salt of the present invention is 0.3 to 2.16 or 2.21 to 3.2 is as follows. When ΔEa deviates from these ranges, the stability of the intruding heat medium (ammonia or water) decreases. ΔEa is more preferably 1.0 to 2.16 or 2.21 to 2.6.

In addition, the average electronegativity and the average electronegativity difference as used in this specification were calculated | required based on the electronegativity calculated along the calculation formula defined by Pauling (Pauling). According to this definition, for example, F: 3.98, Cl: 3.16, Br: 2.96, I: 2.66, Be: 1.57, Mg: 1.31, Ca: 1. 00, Sr: 0.95, Ba: 0.89. Examples of calculating the double metal salt ΔEa based on these electronegativity are, for example, Ca (Cl _0.5 Br _0.5 ) ₂ : ΔEa = 2.06, Ca _0.5 Sr _0.5 Cl ₂ : ΔEa = 2.18, Ca _0.3 Sr _0.7 Cl ₂ : ΔEa = 2.195.

(3) Crystal Structure The double metal salt according to the present invention can have various crystal structures depending on the constituent elements. For example, it has a crystal structure such as CaF ₂ type, SrI ₂ type, CaCl ₂ type, SrBr ₂ type, PbCl ₂ type, CdCl ₂ type, CdI ₂ type. The crystal structure of the double metal salt is not limited, and the crystal structure may be different from or the same as the crystal structure of the basic single metal salt. However, even when the crystal structures are the same, the lattice volume of the double metal salt is different from that of the single metal salt. Thereby, a double metal salt can express the characteristics (equilibrium pressure, a coordination number change, etc.) different from a single metal salt. Specific examples of the crystal structure of the double metal salt are Ca (Cl _0.5 Br _0.5 ) ₂ : CaCl ₂ type, Ca _0.5 Sr _0.5 Cl ₂ : SrI ₂ type, Ca _0.3 Sr. _0.7 Cl ₂ : SrBr ₂ type.

  The double metal salt is preferable because the heat storage density consistent with the heat medium storage material becomes higher as the change in the coordination number of the heat medium changes more rapidly in a specific operating range. Therefore, in the double metal salt, the coordination number of the heat medium changes at least 4 or more, 5 or more, or 6 or more in the vicinity (before and after) of the equilibrium region in which the heat medium absorption / release reaction for occluding or releasing the heat medium is in an equilibrium state. It is preferable to have a crystal structure.

(4) Affinity When the double metal salt according to the present invention comprises two or more metal elements (M1, M2...) Or two or more halogen elements (X1, X2. It is preferable that the element has a high affinity for. Thereby, a stable double metal salt is easily synthesized. In addition, double metal salts made from two or more kinds of single metal salts composed of affinity elements depend on the composition and composite ratio, but the operating range of the heat medium absorption / release reaction is in the middle of those single metal salts. easy. Therefore, if a double metal salt in which the types of single metal salts and their blending ratios (composite ratios) are appropriately selected is used, it is possible to compensate for the blank area in the working range that has occurred when the single metal salt is used. As a result, it is possible to improve the consistency with the heat medium storage material, and thus improve the efficiency of the chemical heat storage system. In addition, the affinity referred to in this specification is not only that two or more elements have similar characteristics as a simple substance, but also approximates the amount of heat generated as a halide (single metal salt) during a heat medium absorption / release reaction. Including. For example, the amount of heat generated when the halide forms a hydrate with water as a heat medium and the amount of heat generated when an ammine complex with ammonia as a heat medium are approximated between two or more elements. In the present specification, there is an affinity between elements.

  Examples of cases where a plurality of elements are affinity include cases where each element is a homogenous element, cases where it can be an ion with the same valence number, cases where the electron configuration is close, and cases where solid solutions are generated. In addition, as a single metal salt (halide), there may be a case where an operating range causing a heat medium absorption / release reaction, a coordination number, or a coordination number change is close.

In the case where the double metal salt is composed of two or more kinds of halogen elements, the halogen element is any one of chlorine (Cl), bromine (Br), and iodine (I) having affinity among the elements of the same group (Group 17 element). It is preferable that it is a seed or more. Moreover, when a double metal salt consists of 2 or more types of metal elements, it is preferable that these metal elements are affinity alkaline-earth metal elements (Mg, Ca, Sr, Ba, etc.). As a preferable example of the double metal salt in such a case, an alkaline earth metal double halide (M (X1 _y X2 _1-y ) ₂ : 0 <y <1) composed of an alkaline earth metal element and two or more halogen elements. Etc.) and double alkaline earth metal halides (M1 _x M2 _1-x X ₂ : 0 <x <1 etc.) composed of two or more kinds of alkaline earth metal elements and halogen elements.

Such a double metal salt (MX _n ) has a crystal index value (V / Z) obtained by dividing the unit cell volume (V) by the number of chemical units (Z) contained in the crystal unit cell, 50 to 130 Å ³ , 75 to 90 cm ^{3 or} 77 to 85 cm ³ . Incidentally, the double metal salt can have different crystal structures as described above depending on the composite ratio (the above x, y, etc.).

In addition, double metal salts of the present _{invention, Sr α Ba 1-α Cl} 2 (0 <α <1), Sr (Cl 1-β Br β) 2 (0.25 <β <1), K 2 SrCl ₄ or KSr ₂ Cl ₅ may be used. Α and β are compound ratios.

(5) Others The chemical heat storage material of the present invention may be a double metal salt alone or a mixture of a double metal salt and a single metal salt. Further, these double metal salts and single metal salts may be hydrates or ammine complexes.

《Method for producing chemical heat storage material》
(1) Raw material The metal salt used as a raw material may be a single metal salt or a double metal salt regardless of the type. Examples of the single metal salt used as the raw material include alkali metal chlorides such as LiCl, NaCl and KCl, alkali metal bromides such as LiBr, NaBr and KBr, alkali metal iodides such as LiI, NaI and KI, MgCl ₂ and CaCl. _2, alkaline earth metal chlorides such as SrCl _2, MgBr _2, CaBr 2, alkaline earth metal bromides such as SrBr _2, MgI _2, CaI 2, alkaline earth metal iodides such as SrI _2, MnCl 2, FeCl ₂ , transition metal chlorides such as CoCl ₂ , NiCl ₂ , transition metal bromides such as MnBr ₂ , FeBr ₂ , CoBr ₂ , NiBr ₂ , transition metal iodides such as MnI ₂ , FeI ₂ , CoI ₂ , NiI ₂ , etc. There is. Although the combination of these metal salts is free, the combination of affinity metal salts is preferable as described above.

(2) Molding step The molding step is a step of obtaining a molded body obtained by press-molding a mixed metal salt obtained by mixing two or more kinds of metal salts, and is arbitrarily performed. The molding pressure at this time is preferably, for example, 40 MPa or more, further 60 MPa or more. If the molding pressure is too low, the contact between two or more metal salts becomes insufficient, and the diffusion in the firing process cannot be sufficiently promoted. The upper limit of the molding pressure is not limited, but productivity is good when it is 300 MPa or less, further 150 MPa or less. In order to avoid deliquescence, the molding step is preferably performed in a low humidity environment where the water concentration is 0.3% or less, 100 ppm or less, 10 ppm or less, or 1 ppm or less.

(3) Firing step The firing step is a step for firing the mixed metal salt, and is an essential step for diffusing the constituent elements of the double metal salt to form a composite at the atomic level. When performing a shaping | molding process before this process, a baking process becomes a process of obtaining the baked body which baked said molded object. The firing temperature is preferably 300 to 800 ° C, 500 to 700 ° C, and more preferably 550 to 650 ° C. If the firing temperature is too low, the diffusion of each element becomes insufficient, and if the firing temperature is too high, the productivity may be lowered. The firing step is preferably performed at a vacuum degree of 1000 Pa or less, 100 Pa or less, and further 10 Pa or less in order to prevent deterioration of the chemical heat storage material due to reaction with atmospheric components.

(4) Others When a fired body is obtained in the firing step, it may be used as it is as a chemical heat storage material, but may be used as a chemical heat storage material by crushing, pulverizing, or the like as appropriate. Furthermore, what granulated the powder particle of double metal salt is good also as a chemical heat storage material.

《Chemical heat storage structure》
The chemical heat storage structure of the present invention basically comprises a chemical heat storage material composed of the above-described double metal salt and a binder that holds the chemical heat storage material, and appropriately includes a high heat conductive material.

(1) Chemical heat storage material The chemical heat storage material (heat storage particle) used as a raw material may be the double metal salt hydrate or ammine complex described above. The chemical heat storage material is in the form of powder or granules, but the particle shape, particle size, etc. are not limited. However, the particle size is preferably 1 μm to 1 mm when observed with an electron microscope in consideration of the miscibility with the binder and the moldability.

(2) Binder The type of binder is not limited, but an inorganic material is preferable. Further, it is preferable to use silicate or low melting point glass. The silicate is preferably an alkali silicate, for example, sodium metasilicate (Na ₂ SiO ₃ ), lithium metasilicate (Li ₂ SiO ₃ ), potassium metasilicate (K ₂ SiO ₃ ), sodium orthosilicate (Na ₄ SiO ₄ ), sodium metasilicate (Na ₂ Si ₂ O ₅ ) or the like. Examples of the low melting point glass include borosilicate (lead) glass, lead oxide glass, bismuth oxide glass, and vanadium oxide glass. Furthermore, it is also possible to use carbon fiber as a binder. The carbon fiber at this time also functions as a high heat conductive material, and forms a skeleton structure of a chemical heat storage structure to improve its mechanical strength.

(3) High thermal conductivity material By mixing the high thermal conductivity material, a thermal conduction path is formed in the chemical heat storage structure, and the thermal conductivity is improved. The type of the high thermal conductive material is not limited, and examples thereof include carbon fiber and ceramics having high thermal conductivity. The carbon fiber may be a PAN-based carbon fiber made from acrylic fiber or a PITCH-based carbon fiber made from pitch. Examples of the ceramic include silicon carbide (SiC) and aluminum nitride (AlN). In any case, a stable one in a heat medium such as ammonia is preferable.

  Incidentally, the reason why the higher thermal conductivity of the chemical heat storage structure is preferable is as follows. The performance of the chemical heat storage system depends on the reaction rate between the chemical heat storage structure and the heat medium (such as water or ammonia). This reaction rate is as follows: (i) Penetration rate (absorption rate, release rate) of heat medium to chemical heat storage structure, (ii) Formation rate of hydrate or ammine complex, etc. (iii) Chemical heat storage structure and external It is affected by the heat exchange rate. Among these, the heat exchange rate is rate-limiting and greatly affects the performance of the chemical heat storage system. Accordingly, when an appropriate amount of a high heat conductive material (carbon fiber or the like) excellent in heat conductivity and heat transfer exists in the chemical heat storage structure, the heat exchange rate can be improved, and consequently the performance of the chemical heat storage system can be improved.

<< Method for producing chemical heat storage structure >>
The method for producing a chemical heat storage structure of the present invention basically includes a structure mixing step of mixing the above-described chemical heat storage material (heat storage particles), a binder, and an arbitrary high heat conductive material, and pressurizing the obtained mixture. It is preferable to include a structure body forming step for forming, and further comprising a structure body firing step in which the formed body is heated to form a fired body.

(1) Structure mixing step The structure mixing step is a step of obtaining a mixture obtained by mixing (or dispersing) a chemical heat storage material, a binder, and a high thermal conductivity material, for example. The mixing method is not limited, but when carbon fiber or the like that is easily damaged is included, the dispersion medium may be removed from the dispersion liquid in which the raw material is dispersed in the dispersion medium to obtain a mixture. In addition, the metal halide which comprises a chemical heat storage material reacts with water, and is easy to deliquesce. For this reason, the dispersion medium is preferably one that does not contain water like the organic dispersion medium, for example, acetone, heptane, hexane, toluene, and the like. In any case, this step is preferably performed in a low humidity environment. In this “low humidity environment”, the moisture concentration in the atmosphere is preferably 0.7% or less, 0.3% or less, and more preferably 0.1% or less.

(2) Structure forming process In the structure forming process, a mixture of a chemical heat storage material and a binder or the like may be put into a cavity of a forming mold and may be pressure-molded, or may be compressed with a roller or the like without using a forming mold. You may shape | mold. A method corresponding to the desired shape of the chemical heat storage structure may be employed. The molding pressure at this time is preferably 40 to 300 MPa or 60 to 250 MPa, for example. If the molding pressure is too low, the heat output per volume of the chemical heat storage structure and the mechanical strength will be reduced, and if it is too high, it will be difficult to ensure the porosity necessary for adsorption / desorption of the heat medium. This step is also preferably performed in a low humidity environment.

(3) Structure firing step The structure firing step is not essential, but by performing this step, a chemical heat storage structure in which a chemical heat storage material and a binder or the like are firmly bonded is obtained. The firing temperature is preferably 100 to 300 ° C, more preferably 150 to 250 ° C. If the firing temperature is too low, a strong fired body (chemical heat storage structure) cannot be obtained. If the firing temperature is too high, sintering of the chemical heat storage materials proceeds excessively, impeding the penetration of the heat medium into the chemical heat storage structure. It is not preferable. The firing step is preferably performed at a degree of vacuum of 1000 Pa or less, further 100 Pa or less. This is to prevent deterioration of the chemical heat storage material due to reaction with atmospheric components.

  The present invention will be described more specifically with reference to examples.

<Production of sample>
<First Example: Sample 1>
(1) Mixing step As raw materials, calcium chloride hydrate (CaCl ₂ .2H ₂ O) powder (Aldrich C5080), which is a metal halide (alkaline earth metal chloride), and hydration of calcium bromide (CaBr ₂ · 2H ₂ O) powder (Kanto Chemical Co., Ltd. deer special grade) was prepared. These powders were weighed so that the molar ratio was 1: 1 and mixed in an agate bowl to obtain a mixed powder. This mixing step was performed in a low humidity environment with a moisture concentration of 1 ppm or less using a glove box manufactured by Miwa Seisakusho.

(2) Molding step The mixed powder was pressurized with 0.7 tonf / cm ² (68.6 MPa) to obtain a 15 × 15 × 3 mm sheet-like molded body. This forming step was performed in a low humidity environment with a moisture concentration of 1 ppm or less using the above-described glove box.

(3) Firing step A fired body obtained by firing the compact at 450 ° C. was obtained. This firing step was performed in a vacuum processing furnace of 10 Pa or less. The fired body thus obtained was used as sample 1 for various measurements described below. In addition, what grind | pulverized this sintered body was used for the sample for X-ray diffraction measurement.

<Comparative example: Samples C1 to C3>
(1) Sample C1
CaCl ₂ powder (C4901 made by Aldrich) and CaBr ₂ · 2H ₂ O powder (Kanto Chemical Co., Ltd. deer special grade) were heated to 200 ° C. in a vacuum processing furnace of 10 Pa or less and dehydrated CaBr ₂ powder in a molar ratio. Was weighed to 1: 1 and mixed using a spoon. The mixed powder thus obtained was designated as Sample C1. In addition, mixing of the raw material powder was performed in a low humidity environment with a moisture concentration of 1 ppm or less using the above-described glove box.

(2) Sample C2 and Sample C3
The CaCl ₂ powder itself was used as Sample C2, and the CaBr ₂ powder itself was used as Sample C3. Samples C1 to C3 were also subjected to the same measurement as Sample 1.

<Measurement>
(1) X-ray diffraction The chemical heat storage material (powder) of Sample 1 was subjected to X-ray diffraction measurement. The X-ray diffraction pattern thus obtained is shown in FIG. In addition, the measurement was performed by 450 degreeC and the vacuum (10 Pa or less) using the CuK alpha ray source by Bruker D8ADVANCE. In order to prevent the sample from falling off, the sample was covered with an Al sheet, and Si powder was mixed with the sample as a reference material for calculating the lattice constant of the sample.

(2) Lattice constant In order to specify the unit cell volume (V) related to V / Z of each sample, the crystal yarn of the sample and the diffraction index of each diffraction line are identified from the profile obtained from the X-ray diffraction measurement. The lattice constant of the crystal of each sample was calculated using the square method.

(3) Pressure-composition isotherm measurement The chemical heat storage materials of Samples 1 to C3 were charged into a reactor, and the pressure (10 to 650 kPa) and composition (ammonia coordination number) under isothermal (60 ° C.) based on the capacity method. ) Was investigated. The results for each sample are shown in FIG. Specifically, this measurement was performed as follows. The sample was filled in a reactor (internal volume of about 5 cc) in a low humidity environment with a moisture concentration of 1 ppm or less and sealed. The reactor was connected to a handmade Siebels type apparatus, and the inside of the reactor was evacuated. Using a water bath, the sample filling portion of the reactor was heated to 60 ° C., NH ₃ was pressurized to 650 kPa, and measurement was started from this state. Incidentally, the reactor used here is made of stainless steel and includes a valve and a pressure gauge for supplying and degassing ammonia gas.

<Evaluation>
(1) As it is clear from the X-ray diffraction pattern shown in crystal structure diagram 1, only the compound phase having the same CaCl ₂ type crystal structure and CaCl ₂ and CaBr ₂ Sample 1 was observed. A lattice volume 186.8A ³ calculated from the pattern of Figure _1, CaCl _2, CaBr 2 of cell volume (respectively 167.8Å ^3, 196.3Å ³⁾ was a value between. From the above, unlike the mixed powder of CaCl ₂ and CaBr ₂ , sample 1 is a new metal double halide (Ca (Cl _0.5 Br _0.5 ) ₂ ) in which constituent elements are bonded at the atomic level. It can be said that there is. The average electronegativity difference of this metal double halide is ΔEa = 2.06 as described above. Incidentally, although it is not a double metal salt, CaCl ₂ which is a single metal salt has ΔEa = 2.16, and CaBr ₂ has ΔEa = 1.96.

(2) V / Z
The crystal index value (V / Z) was obtained by dividing the unit cell volume (V) obtained from the lattice constant for each sample by the number of chemical units (Z) of each sample. The V / Z of sample 1 was 93.4 cm ³ (V: 186.8 cm ³ / Z: 2). On the other hand, V / Z of sample C2 (CaCl ₂ ) is 83.9 Å ³ (V: 167.8 ／ ³ / Z: 2), and V / Z of sample C3 (CaBr ₂ ) is 98.2 Å ³ (V: 196.3Å ³ / Z: 2). From these, it can be seen that V / Z of sample 1 is between sample C2 and sample C3.

From the above, the diffusion of calcium ions (Ca ²⁺ ), chlorine ions (Cl ⁻ ), and bromine ions (Br ⁻ ) can be achieved by molding and firing a mixture of CaCl ₂ .2H ₂ O and CaBr ₂ .2H ₂ O. Thus, it can be said that a metal double halide (Ca (Cl _0.5 Br _0.5 ) ₂ ) having a crystal structure which is thermodynamically more stable than a simple mixture of CaCl ₂ and CaBr ₂ was generated.

On the other hand, in the case of Sample C1, the following four-step reaction was performed according to the equilibrium ammonia pressure at which the ammonia absorption / release reaction reached an equilibrium state.
(Reaction C1-1 / Ammonia pressure: 30 kPa)
_{0.5CaBr 2 · 2NH 3 + 2NH 3} ⇔ 0.5CaBr 2 · 6NH 3
(Reaction C1-2 / Ammonia pressure: 260 kPa)
0.5CaCl ₂ · 2NH ₃ + NH ₃ ０．５ 0.5CaCl ₂ · 4NH ₃
(Reaction C1-3 / Ammonia pressure: 470 kPa)
_{0.5CaCl 2 · 4NH 3 + 2NH 3} ⇔ 0.5CaCl 2 · 8NH 3
(Reaction C1-4 / Ammonia pressure: 600 kPa)
0.5CaBr ₂ · 6NH ₃ + NH ₃ ０．５ 0.5CaBr ₂ · 8NH ₃

  When the chemical heat storage material of the sample C1 is used, the coordination number change accompanying the ammonia absorption / release reaction occurring under one equilibrium pressure is only 1 to 2. That is, the heat absorption or heat release per ammonia absorption / release reaction is small, and the heat storage density is also small. Moreover, in order to obtain a large coordination number change (6), the ammonia pressure is changed over a wide range (pressure difference 570 kPa) of at least 30 to 600 kPa, and the reactions C1-1 to C1-4 are continuously advanced. Needed and not efficient.

In the case of the sample C2, the ammonia absorption / release reaction is the following two-step reaction according to the equilibrium ammonia pressure.
(Reaction C2-1 / Ammonia pressure: 260 kPa)
CaCl ₂ · 2NH ₃ + 2NH ₃ Ｃａ CaCl ₂ · 4NH ₃
(Reaction C2-2 / Ammonia pressure: 470 kPa)
CaCl ₂ · 4NH ₃ + 4NH ₃ Ｃａ CaCl ₂ · 8NH ₃

  In this case as well, the coordination number change associated with the ammonia absorption / release reaction that occurs under one equilibrium pressure is 2 or 4, and the heat absorption or heat release per ammonia absorption / release reaction is small. Also, in order to obtain a large coordination number change (6), the ammonia pressure is changed over a wide range of at least 260 to 470 kPa (pressure difference 210 kPa), and the reactions C2-1 and C2-2 are continuously advanced. It is necessary and still not efficient.

Further, in the case of the sample C3, as can be seen from FIG. 2, the ammonia absorption / release reaction is a two-step reaction according to the equilibrium ammonia pressure as follows.
(Reaction C3-1 / Ammonia pressure: 30 kPa)
_{CaBr 2 · 2NH 3 + 4NH 3} ⇔ CaBr 2 · 6NH 3
(Reaction C3-2 / Ammonia pressure: 600 kPa)
_{CaBr 2 · 6NH 3 + 2NH 3} ⇔ CaBr 2 · 8NH 3

  In this case, the coordination number change due to the ammonia adsorption / release reaction occurring under one equilibrium pressure is 2 or 4, but in order to obtain a larger coordination number change (6), the ammonia pressure is at least 30 to 600 kPa. It is necessary to make reaction C3-1 and reaction C3-2 proceed continuously by changing over a wide range (pressure difference 570 kPa).

  Thus, unlike a conventional single metal salt or a mixed metal salt thereof, a chemical heat storage material made of a double metal salt such as Sample 1 causes a large change in coordination number near the equilibrium ammonia pressure. Therefore, by using the chemical heat storage material of the present invention, the efficiency of the chemical heat storage system can be improved. In addition, since the equilibrium ammonia pressure is different from that of the single metal salt, the consistency with the heat medium storage material, which has a low consistency with the conventional single metal salt, is improved.

Claims (14)

A chemical heat storage material that generates heat or absorbs heat by occlusion or release of a heat medium,
A double metal salt (MX _n , n: average valence of M) which is a metal halide composed of a metal element (M) and a halogen element (X), at least one of which is composed of two or more elements,
The double metal salt has an average electronegativity difference (ΔEa = EXa−EMa) obtained by subtracting the average electronegativity (EMa) of the metal element from the average electronegativity (EXa) of the halogen element from 0.3 to 2. Chemical heat storage material characterized by being .16 or 2.21-3.2. The heating medium is ammonia or water,
By storing the ammonia, an ammine complex (MX _n · aNH ₃ , a: coordination number of ammonia) or hydrated by storing the water (MX _n · bH ₂ O, b: coordination number of water) The chemical heat storage material according to claim 1.   3. The chemical heat storage material according to claim 1, wherein the double metal salt has a crystal structure in which the coordination number of the heat medium changes by at least 4 by occlusion or release of the heat medium. The double metal salt has a crystal structure in which the crystal index value (V / Z) obtained by dividing the unit cell volume (V) by the number of chemical units (Z) of MX _n contained in the crystal unit cell is 50 to 130 ^3. The chemical heat storage material according to any one of claims 1 to 3. The double metal salt has a crystal structure of any one of CaF ₂ type, SrI ₂ type, CaCl ₂ type, SrBr ₂ type, PbCl ₂ type, CdCl ₂ type, or CdI ₂ type. The chemical heat storage material described.   The chemical heat storage material according to claim 1, wherein the metal element is an alkaline earth metal element.   The chemical heat storage material according to any one of claims 1 to 6, wherein the double metal salt is an alkaline earth metal double halide composed of an alkaline earth metal element and two or more halogen elements. The chemical heat storage material according to claim 7, wherein the alkaline earth metal double halide is Ca (Cl _1-y Br _y ) ₂ (0 <y <1). The chemical heat storage material according to claim 7, wherein the alkaline earth metal double halide is Sr (Cl _1-y Br _y ) ₂ (0 <y <1). Comprising a firing step of firing a mixed metal salt obtained by mixing two or more metal salts;
A method for producing a chemical heat storage material, wherein the chemical heat storage material according to claim 1 is obtained. Furthermore, a molding step for obtaining a molded body obtained by pressure molding the mixed metal salt before the firing step is provided,
The method for producing a chemical heat storage material according to claim 10, wherein the firing step is a step of obtaining a fired body obtained by firing the molded body.   It consists of the chemical heat storage material in any one of Claims 1-9, and the binder holding this chemical heat storage material, The chemical heat storage structure characterized by the above-mentioned.   The chemical heat storage structure according to claim 12, wherein the binder is made of carbon fiber, which is a high heat conductive material that is more excellent in thermal conductivity than a chemical heat storage material.   Furthermore, the chemical heat storage structure of Claim 12 or 13 containing the high heat conductive material which is more excellent in heat conductivity than the said chemical heat storage material and the said binder.

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