JP6765198B2 - Latent heat storage material and heat storage system using it - Google Patents

Description

The present disclosure comprises a mixture of a first compound composed of a first cation and an anion composed of hydrogen and a Group 13 or 15 element, and a second compound composed of a second cation and an anion, 400. It relates to a latent heat storage material that can store heat in a temperature range of ℃ or less and has a high heat storage density.

In recent years, there has been a demand to reduce the use of fossil fuels, and in addition to saving energy in each process, it is necessary to promote the use of unused heat. About 70% of primary energy is not effectively used and is discharged into the environment as unused heat. For example, only 20% of automobile gasoline engines and 40% of electricity generation can effectively utilize the energy of fuel. If there is a technology that can store such unused heat and use it at a temperature close to the original temperature, it is very effective in terms of energy recovery and energy reuse. Unused heat sources include gasoline engines for automobiles, gas engines for power generation, diesel engines, and the like. In addition, a lot of heat energy is discharged unused from factories, waste incinerators, etc.

The means for storing unused heat can be broadly divided into sensible heat storage, latent heat storage, and chemical heat storage. Of these, as sensible heat storage, hot water heat storage at 100 ° C. or lower using water is known. However, hot water heat storage cannot be stored for a long time due to (1) heat dissipation loss, and (2) a large amount of water is required because the amount of apparent heat in water is small, making it difficult to make the heat storage facility compact. (3) There are problems such as the output temperature is unsteady according to the amount of utilization and gradually decreases. Therefore, in order to promote such unused heat utilization, it is necessary to develop a more efficient heat storage technology.

In addition, since chemical heat storage involves chemical changes such as adsorption and hydration of substances, it is per unit mass compared to heat storage methods that utilize the sensible heat or latent heat of the material itself (water, hydrated salt, paraffin, etc.). The amount of heat storage increases. As chemical heat storage, a method by adsorption / desorption of water vapor, absorption of ammonia into a metal salt (ammine complex formation reaction), adsorption / desorption reaction of organic substances such as alcohol, etc. have been proposed, but in consideration of environmental load and convenience of the device. Then, the water vapor absorption / desorption method is the most advantageous.

In addition, latent heat storage utilizes phase changes such as melting of substances. Latent heat storage has the advantages that the heat storage density is higher and the phase change temperature is constant, so that the heat extraction temperature is stable, as compared with sensible heat storage. For this reason, the practical use of latent heat storage is progressing. When heat storage is performed using latent heat storage, the latent heat storage material is heated to a liquid state during heat storage. After that, the latent heat storage material is kept warm so that the liquid state is maintained. The heat stored in the retained latent heat storage material can be taken out by crystallizing (solidifying) the latent heat storage material when necessary.

Among these latent heat storage materials, lithium hydride (LiH) is known as a material having a heat storage density (heat storage amount per unit mass) higher than that of chemical heat storage (Patent Documents 1 and 2).

Patent No. 2746943 Patent No. 5498191

However, the heat storage device described in Patent Document 1, the hydrogen power storage system described in Patent Document 2, and the lithium hydride of the hydrogen power storage method are covalently bonded molecules with strong ionicity and have a low molecular weight. Although it has a high heat storage density per weight, it has a high melting point of 672 ° C., and there is a problem that exhaust heat recovery and heat storage cannot be performed from a temperature range of 400 ° C. or lower downstream of an exhaust gas purification catalyst such as an automobile or a gas engine heat pump.

An object of the present disclosure is to provide a latent heat storage material capable of storing heat in a temperature range of 400 ° C. or lower and having a high heat storage density, and a heat storage system using the latent heat storage material. That is, the present disclosure provides a latent heat storage material and a heat storage system using the latent heat storage material, which can be used for warming up at the time of starting by recovering and storing exhaust heat from the downstream of an exhaust gas purification catalyst of an automobile, a gas engine heat pump, or the like. The purpose is. Another object of the present disclosure is to provide a latent heat storage material capable of storing heat even in a low temperature range of 150 ° C. or lower and having a high heat storage density, and a heat storage system using the latent heat storage material.

In order to solve the conventional problems, the present disclosure is made.
A first compound composed of a first cation and an anion consisting of hydrogen and a Group 13 or 15 element,
Contains a mixture of a second cation and a second compound composed of said anion.
The first cation and the second cation are alkali metal ions.
Provide a latent heat storage material.

According to the present disclosure, it is possible to provide a latent heat storage material capable of storing heat in a temperature range of 400 ° C. or lower and having a high heat storage density, and a heat storage system using the latent heat storage material. That is, the present disclosure provides a latent heat storage material and a heat storage system using the latent heat storage material, which can be used for warming up at the time of starting by recovering and storing exhaust heat from the downstream of an exhaust gas purification catalyst of an automobile, a gas engine heat pump, or the like. be able to. Further, the present disclosure can provide a latent heat storage material capable of storing heat even in a low temperature range of 150 ° C. or lower and having a high heat storage density, and a heat storage system using the latent heat storage material.

It is a figure which shows an example of the heat storage system using the latent heat storage material of this disclosure. This is the differential scanning calorimetry evaluation result for calculating the device constant when a stainless steel sealed pan is used. It is a differential scanning calorimetry evaluation result of lithium hydride of Comparative Example 1. It is an analysis result by an X-ray diffractometer before the differential scanning calorimetry evaluation of lithium hydride of Comparative Example 1. It is an analysis result by an X-ray diffractometer after the differential scanning calorimetry of lithium hydride of Comparative Example 1. This is the differential scanning calorimetry evaluation result for calculating the device constant when using an aluminum pan. Is a differential scanning calorimetry results of evaluation of lithium borohydride high dry de of Reference Example 1 (LiBH _4). It is an analysis result of differential scanning calorimetry evaluation prior to X-ray diffraction apparatus lithium borohydride high dry de of Reference Example 1 (LiBH _4). Is an analysis result by X-ray diffraction apparatus after differential scanning calorimetry assessment of lithium borohydride high dry de of Reference Example 1 (LiBH _4). Is a differential scanning calorimetry results of evaluation of potassium borohydride high dry de of Comparative Example 2 (KBH _4). Potassium borohydride high dry de of Comparative Example 2 is a result of analysis by X-ray diffraction apparatus of differential scanning calorimetry evaluated before and after (KBH _4). This is a differential scanning calorimetry result of a latent heat storage material composed of a mixture of LiBH ₄ : KBH ₄ = 0.92: 0.08 (molar ratio) of Example 1. This is a differential scanning calorimetry result of a latent heat storage material composed of a mixture of LiBH ₄ : KBH ₄ = 0.87: 0.13 (molar ratio) of Example 1. This is a differential scanning calorimetry result of a latent heat storage material composed of a mixture of LiBH ₄ : KBH ₄ = 0.80: 0.20 (molar ratio) of Example 1. It is an analysis result by an X-ray diffractometer after differential scanning calorimetry evaluation of a latent heat storage material composed of a mixture of LiBH ₄ and KBH ₄ of Example 1. It is a phase diagram of the mixture of LiBH ₄ and KBH ₄ of Example 1.

The first aspect of the present disclosure is
A first compound composed of a first cation and an anion consisting of hydrogen and a Group 13 or 15 element,
Contains a mixture of a second cation and a second compound composed of said anion.
The first cation and the second cation are alkali metal ions.
Provide a latent heat storage material.

According to the latent heat storage material of the first aspect, heat can be stored at a high heat storage density and in a temperature range of 400 ° C. or lower.

Further, according to the first aspect, the pre-mixing compound (the first compound and the second compound) has high instability of the crystal structure of the compound due to being an ion-bonded molecule having a large anion size. At the same time, mixing of the compounds causes a freezing point drop. Therefore, the phase transition or phase change temperature of the compound before mixing can be lowered, and the temperature can be further lowered by lowering the freezing point of the mixture.

In the second aspect of the present disclosure, for example, in addition to the first aspect, a latent heat storage material having an ionic radius difference between the first cation and the second cation of 39 pm (picometer) or more and 87 pm or less is used. provide. In the present disclosure, "pm" means picometer, unless otherwise stated.

According to the second aspect, the optimum ionic radius difference between the cations of the premixed compound forms a eutectic as a mixture (if the ionic radius difference is too small, a solid solution is formed, if it is too large, phase separation. Therefore, the degree of freezing point depression of the mixture can be increased.

In the third aspect of the present disclosure, for example, in addition to the first or second aspect, a latent heat storage material in which the first cation is lithium ion (Li ⁺ ) and the second cation is potassium ion (K ⁺ ). I will provide a.

According to the third aspect, heat can be stored at a high heat storage density and in a temperature range of 400 ° C. or lower.

The fourth aspect of the present disclosure, for example, in addition to any of the embodiments of the first to third aspect, wherein the anion is Borohaidorai de ion (BH ₄ ^-) a, to provide a latent heat storage material.

According to the fourth aspect, by including the low atomic weight elements hydrogen and boron in the first compound and the second compound, the anion size is obtained as the pre-mixing compound (the first compound and the second compound). By constructing an ion-bonded molecule having a large and low molecular weight, the instability of the crystal structure of the compound can be enhanced, the heat storage density per weight of the compound before mixing is improved, and the phase transition or phase change temperature is lowered. Can be compatible with.

A fifth aspect of the present disclosure, for example, in addition to the first or second aspect, wherein the first compound is lithium borohydride high dry de (LiBH _4), wherein said second compound potassium borohydride high dry de ( Provide a latent heat storage material, which is KBH ₄ ).

According to the fifth aspect, the combination of the elements having the smallest sum of atomic weights of the two cations is selected from the combination of the two alkali metal ions having the ionic radius difference between the cations of 39 pm or more and 87 pm or less. As a result, low molecular weight eutectic crystals are formed, so that it is possible to both improve the heat storage density per weight of the mixture of the first compound and the second compound and increase the degree of freezing point depression.

A sixth aspect of the present disclosure, for example, in addition to the fifth aspect, a lithium borohydride high dry de of the first compound (LiBH _4), wherein the potassium second compound Greensboro high dry de and (KBH ₄₎ Provided is a latent heat storage material having a molar ratio of LiBH ₄ : KBH ₄ = 17: 3 to 7: 3.

According to the sixth aspect, since the eutectic point is generated by the appropriate composition ratio of the first compound and the second compound before mixing, the degree of freezing point depression of the mixture can be maximized and a single phase transition can be achieved. Alternatively, a phase change temperature can be obtained, which facilitates heat utilization in a specific temperature range.

A seventh aspect of the present disclosure provides, for example, a heat storage system including the latent heat storage material according to any one of the first to sixth aspects. According to the seventh aspect, exhaust heat can be recovered and stored in a temperature range of 400 ° C. or lower from the downstream of the exhaust gas purification catalyst of an automobile, a gas engine heat pump, or the like, and can be used for warming up at the time of starting.

Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. The following description relates to an example of the present disclosure, and the present disclosure is not limited thereto.

(Embodiment)
First, an example of a heat storage system using the latent heat storage material of the present embodiment will be described with reference to FIG. The heat storage system 100 includes a heat storage device 10, a heat source device 20, a heat output device 22, and a heat medium flow path 14 for circulating a heat medium between them. The heat storage device 10 includes a container 12 for accommodating a latent heat storage material. A pump 16 and a three-way valve 18 are provided in the heat medium flow path 14. The heat medium flow path 14 is configured so that the heat medium can exchange heat with the latent heat storage material via the container 12.

When storing heat, the heat medium is circulated in the direction of arrow 26. The heat medium circulates between the heat storage device 10 and the heat source device 20 to heat the latent heat storage material in the heat storage device 10. As a result, the latent heat storage material is melted. The heating temperature is not particularly limited as long as the latent heat storage material can be melted.

When recovering heat, the latent heat storage material is cooled and solidified, and heat is released from the latent heat storage material. At this time, the heat medium is circulated in the direction of arrow 28. The heat medium circulates between the heat storage device 10 and the heat output device 22, whereby the heat released from the latent heat storage material can be recovered to the heat output device 22. The recovered heat is used from the heat output device 22 depending on the application such as warming up at the time of starting. The cooling temperature is not particularly limited as long as it is equal to or lower than the melting point of the latent heat storage material.

As described above, in order to recover and store exhaust heat from the downstream of the exhaust gas purification catalyst of automobiles, gas engine heat pumps, etc. and use it for warming up at start-up, etc., heat can be stored in the temperature range of 400 ° C. or less, and A material with a high heat storage density is required. LiH has a high heat storage density (2170 kJ / kg) because it is a covalently bonded molecule with strong ionicity and a low molecular weight, but it also has a solid-liquid phase change temperature. It is as high as 672 ° C.

On the other hand, the heat storage system of the present embodiment includes the latent heat storage material of the present disclosure, and by cooling and / or heating the latent heat storage material, it is discharged in a temperature range of 400 ° C. or lower from the downstream of the exhaust gas purification catalyst. Heat recovery and heat storage can be performed. The lower limit of the temperature range in which the latent heat storage material of the present disclosure can be used is not particularly limited, but may be about 60 ° C. or higher from the viewpoint of being usable as a heat source.

It is desirable that the latent heat storage material (heat storage material composition) of the present embodiment is substantially composed of only the first compound and the second compound. When the latent heat storage material is substantially composed of only the first compound and the second compound, the content of the components other than the first compound and the second compound contained in the latent heat storage material is less than 5.0 wt%. It is preferably less than 3.0 wt%, more preferably less than 1.0 wt%, and even more preferably less than 0.5 wt%.

The alkali metal ions of the first cation and the second cation used in the latent heat storage material of the present embodiment are not particularly limited, and examples thereof include lithium ion, sodium ion, potassium ion, and rubidium ion.

The group 13 element contained in the first compound and the second compound used in the latent heat storage material of the present embodiment is not particularly limited, and examples thereof include boron and aluminum, and boron is preferable. Nitrogen is desirable as the Group 15 element contained in the first compound and the second compound used in the latent heat storage material of the present embodiment.

The group 15 element contained in the first compound and the second compound used in the latent heat storage material of the present embodiment is not particularly limited, and examples thereof include nitrogen and phosphorus. Nitrogen is desirable as the Group 15 element contained in the first compound and the second compound used in the latent heat storage material of the present embodiment.

As the cation used for the first cation and the second cation, an alkali metal ion is desirable.

Lithium amide (LiNH ₂ ) is desirable as the compound composed of the first cation, hydrogen and Group 13 elements.

The compound composed of a first cation, hydrogen and Group 15 elements, lithium borohydride high dry de (LiBH ₄₎ is desirable.

Potassium amide (KNH ₂ ) is desirable as the compound composed of the second cation, hydrogen and the Group 13 element.

As the compound including a second cation, hydrogen and Group 15 elements, potassium borohydride high dry de (KBH ₄₎ it is desirable.

The difference in ionic radius between the first cation and the second cation in the mixture may be 40 pm or more and 86 pm or less, and 42 pm or more, from the viewpoint of forming eutectics and increasing the degree of freezing point depression of the mixture. It may be 84 pm or less.

Compounding ratio of LiBH ₄ and KBH ₄ as (molar ratio), while reducing phase transition or phase change temperature 200 ° C. or less, from the viewpoint of 310kJ / kg or more thermal storage density is obtained, LiBH _4: KBH ₄ = It may be 17: 3 to 7: 3, 21: 4 to 3: 1, 41; 9 to 39:11, or 4: 1.

Hereinafter, the latent heat storage material of the present disclosure will be described in more detail by way of examples. However, the present disclosure is not limited to the following examples.

In the following examples and comparative examples, a differential scanning calorimetry (DSC Q10 manufactured by TA Instruments) was used for the differential scanning calorimetry (DSC) used for evaluating the heat storage density. An X-ray diffractometer (RINT2000 manufactured by Rigaku) was used for the structural analysis of the sample before and after the differential scanning calorimetry. The weight of the sample is a value measured using an electronic balance (AD-6 manufactured by PERKIN ELMER). Indium (molar heat of fusion: 3.281 kJ / mol, atomic weight: 114.82), which has a known amount of heat of fusion due to solid-liquid phase change, is used to measure the correction data used for correction by the measuring container in the calculation of heat storage density. There was.

<Comparative example 1>
The phase change temperature and heat storage density of LiH as a compound composed of lithium and hydrogen were evaluated.

The measurement conditions for the differential scanning calorimetry were an argon atmosphere (flow rate: 50 sccm), pressure: 0.1 MPa, temperature rise rate: 10 deg / min, and temperature range: room temperature to 715 ° C. Further, as a sample, 1.56 mg of LiH (41596 manufactured by Alfa Aesar) was placed in a stainless steel sealed pan for evaluation.

In the evaluation, the device constants when a differential scanning calorimeter and a stainless steel sealed pan were used were calculated. As a result of evaluation using indium as a sample, as shown in FIG. 2, the measured value of the heat storage density was 33 kJ / kg. Based on this result, it was calculated that the device constant for correcting the heat storage density to 28.575 kJ / kg, which was calculated using the heat of fusion and the atomic weight of indium, was 0.866.

FIG. 3 shows the evaluation results of the phase change temperature and the heat storage density of the sample using LiH. From this result, the phase change temperature was 672 ° C., and the heat storage density was 2170 kJ / kg, which was obtained by multiplying the measured value of 2506 kJ / kg by the device constant 0.866.

Further, FIGS. 4 and 5 show the analysis results of the samples before and after the differential scanning calorimetry evaluation by the X-ray diffractometer. From this result, the samples before and after the differential scanning calorimetry were both lithium hydride (LiH), and the endothermic peak in the differential scanning calorimetry was not a chemical change but a physical change (solid-liquid phase change). It was confirmed that it was caused.

As described above, in order to recover and store exhaust heat from the downstream of the exhaust gas purification catalyst of automobiles, gas engine heat pumps, etc. and use it for warming up at start-up, etc., heat can be stored in the temperature range of 400 ° C. or less, and While a material with a high heat storage density is required, LiH has a high heat storage density (2170 kJ / kg) because it is a covalent bond type molecule with strong ionicity and a low molecular weight, but it is a solid-liquid phase. The change temperature was as high as 672 ° C.

<Reference example 1>
A lithium ion (Li ⁺⁾ as the cation, Borohaidorai de ions as an anion (BH ₄ ^-) as from the compounds consisting of, for LiBH _4, the phase change temperature and evaluated for heat storage density.

The measurement conditions for differential scanning calorimetry were an argon atmosphere (flow rate: 50 sccm), pressure: 0.1 MPa, temperature rise rate: 5 deg / min, and temperature range: room temperature to 450 ° C. Further, as a sample, 6.32 mg of LiBH ₄ (686026 manufactured by Alfa Aesar) was placed in an aluminum pan and evaluated.

In the evaluation, the device constants when using a differential scanning calorimeter and an aluminum pan were calculated. As a result of evaluation using indium as a sample, as shown in FIG. 6, the measured value of the heat storage density was 24.85 kJ / kg. Based on this result, it was calculated that the device constant for correcting the heat storage density to 28.575 kJ / kg, which was calculated using the heat of fusion and atomic weight of indium, was 1.150.

FIG. 7 shows the evaluation results of the phase change temperature and the heat storage density of the sample using LiBH ₄ . From this result, when the first and second measured values are averaged, the first phase change temperature is 114 ° C., the heat storage density is 192 kJ / kg, the second phase change temperature is 286 ° C., and the heat storage density. Was 361 kJ / kg, which was obtained by multiplying the measured value of 314.1 kJ / kg by the device constant 1.150.

Further, FIGS. 8 and 9 show the analysis results of the samples before and after the differential scanning calorimetry evaluation by the X-ray diffractometer. From this result, the samples before and after the differential scanning calorimetry are both LiBH ₄ and aluminum (Al) caused by the aluminum pan, and the endothermic peak in the differential scanning calorimetry is not a chemical change but a physical change (phase). It was confirmed that it was caused by (change).

Further, Table 1 shows the molecular weight, anion size, phase change temperature, and heat storage density for each compound containing lithium ion (Li ⁺ ) as a cation and various monovalent ions as anions. From this result, the instability of the crystal structure of the compound can be enhanced by forming a low molecular weight ion-bonded molecule having a large anion size with an anion composed of hydrogen and a group 13 element, and as a result, halogen as an anion. It can be seen that the phase change temperature can be lowered as compared with the lithium compound containing ions. Moreover, BH ₄ is an anion consisting of hydrogen and boron is a low atomic weight elements ^- by including a compound containing the components of the latent heat storage material, it is possible to improve the thermal storage density per weight. As a result, the phase change temperature: 114 ° C. (first), 286 ° C. (second), the heat storage density (sum of the first and second phase change temperatures): 553 kJ / kg, and the phase change temperature: 613 ° C. Compared with lithium (LiCl), lithium bromide (LiBr) at 505 ° C, and lithium iodide (LiI) at 469 ° C, the phase change temperature can be lowered and the heat storage density per weight can be improved. it can.

<Comparative example 2>
Then, potassium as cation (K ^+), Borohaidorai de ions as an anion (BH ₄ ^-) as a compound composed of, for KBH _4, the phase change temperature and evaluated for heat storage density.

The measurement conditions for differential scanning calorimetry were an argon atmosphere (flow rate: 50 sccm), pressure: 0.1 MPa, temperature rise rate: 10 deg / min, and temperature range: room temperature to 700 ° C. In addition, as a sample, 3.5 mg of KBH ₄ (455571-100G manufactured by Aldrich) was placed in an aluminum pan and evaluated.

FIG. 10 shows the evaluation results of the phase change temperature and the heat storage density of the sample using KBH ₄ . From this result, when the first and second measured values were averaged, the phase change temperature was 628 ° C. and the heat storage density was 409 kJ / kg.

In addition, FIG. 11 shows the analysis results of the samples before and after the differential scanning calorimetry by the X-ray diffractometer. From this result, it was confirmed that the samples before and after the differential scanning calorimetry were both KBH ₄ , and the endothermic peak in the differential scanning calorimetry was caused not by the chemical change but by the physical change (phase change). ..

Table 2 shows the molecular weight, anion size, and phase change temperature of each compound containing potassium ion (K ⁺ ) as a cation and various monovalent ions as an anion. From this result, the instability of the crystal structure of the compound can be enhanced by forming a low molecular weight ion-bonded molecule having a large anion size with an anion composed of hydrogen and a group 13 element, and as a result, halogen as an anion. It can be seen that the phase change temperature can be lowered as compared with the potassium compound containing ions. Moreover, BH ₄ is an anion composed of hydrogen and boron is a low atomic weight elements ^- by including a compound containing the components of the latent heat storage material, it is possible to improve the thermal storage density per weight. However, for potassium compounds, the phase change temperature was as high as 600 ° C. or higher.

<Example 1>
Next, lithium-ion (Li ⁺⁾ as the first cation, Borohaidorai de ions as an anion (BH ₄ ^-) and LiBH ₄ is a compound composed of potassium as the second cation (K ^+), as an anion Borohaidorai de ion (BH ₄ ^-) for mixtures of KBH ₄ is a compound composed of a phase change temperature and evaluated for heat storage density. Here, the ionic radius of lithium ion (Li ⁺ ) as the first cation is 60 pm, the ionic radius of potassium ion (K ⁺ ) as the second cation is 133 pm, and the first cation and the second cation are The ionic radius difference of is 73 pm.

Incidentally, as in the ion radius difference 38pm between sodium ions (ionic radius 95Pm) and potassium ions (ionic radius 133Pm), if the ion radius difference is too small, the anion size 181Pm (chloride ion (Cl ^-)) above A solid solution is formed. On the other hand, if the ionic radius difference is too large, such as the ionic radius difference of 88 pm between lithium ions (ionic radius 60 pm) and rubidium ions (ionic radius 148 pm), phase separation occurs.

The measurement conditions for differential scanning calorimetry were an argon atmosphere (flow rate: 50 sccm), pressure: 0.1 MPa, temperature rise rate: 5 deg / min, and temperature range: room temperature to 400 ° C. Further, as a sample, LiBH ₄ (Aldrich Ltd. 686026-10G), using KBH ₄ the (Aldrich Ltd. 455571-100G), LiBH _4: the molar mixing ratio of KBH _4, the condition (1) 0.92: 0.08, (2) 0.87: 0.13, (3) 0.80: 0.20, put in a mortar in a glove box, mix with a pestle for 3 minutes, and then 3.5 mg. Was put in an aluminum pan and evaluated.

FIGS. 12 to 14 show the evaluation results of the phase change temperature and the heat storage density of the sample using the latent heat storage material composed of a mixture of LiBH ₄ and KBH ₄ . From this result, the average of the first and second measurements was as follows:
Conditions (1) Under LiBH ₄ : KBH ₄ = 0.92: 0.08, the first phase change temperature is 113 ° C., the heat storage density is 301 kJ / kg, and the second phase change temperature is 238 ° C., and the heat storage density is 208kJ / kg;
Condition (2) Under LiBH ₄ : KBH ₄ = 0.87: 0.13, the first phase change temperature is 113 ° C., the heat storage density is 286 kJ / kg, and the second phase change temperature is 203 ° C., and the heat storage density is 86kJ / kg;
Conditions (3) At LiBH ₄ : KBH ₄ = 0.80: 0.20, the phase change temperature is 112 ° C. and the heat storage density is 339 kJ / kg.

As shown in FIG. 14, when a mixture of LiBH ₄ and KBH ₄ blended in a specific ratio is used as an active ingredient of a latent heat storage material, it is 300 kJ / kg or more even in a low temperature range of 150 ° C. or less. It was confirmed that a high heat storage density can be obtained.

Further, FIG. 15 shows the analysis result of the sample after the differential scanning calorimetry by the X-ray diffractometer. From this result, the samples after differential scanning calorimetry are generally LiBH ₄ and KBH ₄ , and the endothermic peak in differential scanning calorimetry is not due to chemical change but due to physical change (phase change), and LiBH ₄ It was confirmed that a eutectic with KBH ₄ was formed.

Further, a mixture of LiBH ₄ and KBH ₄ prepared based on the evaluation results of the phase change temperature and heat storage density in FIGS. 7, 10, 12 to 14 and the analysis results by the X-ray diffractometer in FIGS. 8, 9, 11 and 15. The phase diagram of is shown in FIG. From this result, the LiBH ₄ of the first compound, the molar ratio of KBH ₄ the second compound 4: becomes eutectic point in the first composition, the freezing point depression relative to LiBH ₄ of the first compound before mixing 174K The freezing point depression of the second compound with respect to KBH ₄ was 516K.

As described above, by setting the ionic radius difference between the lithium ion (Li ⁺ ), which is the first cation, and the potassium ion (K ⁺ ), which is the second cation, in the mixture to be 39 pm or more and 87 pm or less, the compound before mixing can be used. Eutectic formation is formed as a mixture based on the optimum ionic radius difference between cations (if the ionic radius difference is too small, a solid solution is formed, and if it is too large, phase separation occurs), so that the freezing point of the mixture drops. The degree can be increased. Further, among the combinations of two kinds of alkali metal ions in which the difference in ionic radius between cations is 39 pm or more and 87 pm or less, the combination of elements that minimizes the sum of atomic weights of the two kinds of cations (that is, lithium ion (Li ⁺ )). And potassium ion (K ⁺ )) to form low molecular weight eutectic, which makes it possible to improve the heat storage density per weight of the mixture and increase the degree of freezing point drop. Further, a particularly appropriate composition is obtained at a molar ratio of 4: 1 between the first compound LiBH ₄ and the second compound KBH _4, and eutectic points are generated, so that the degree of freezing point depression of the mixture can be maximized. At the same time, a single phase transition or phase change temperature is obtained, which facilitates heat utilization in a specific temperature range (for example, 150 ° C. or lower). As a result, the phase change temperature can be lowered (phase change temperature: 112 ° C.), and the heat storage is higher than that of the conventional material: erythritol (phase change temperature: 120 ° C., heat storage density: 320 kJ / kg) in the same temperature range. A density (339 kJ / kg) could be achieved.

From the above, the first compound composed of the first cation, the anion composed of hydrogen and the group 13 or 15 element, the second cation, and the second compound composed of the anion By using a latent heat storage material in which the first cation and the second cation are alkali metal ions, the instability of the crystal structure of the compound is enhanced by the ion-bonded molecule having a large anion size. Since the mixing causes a freezing point drop, the phase transition or phase change temperature can be lowered.

According to the latent heat storage material according to the present disclosure, a first compound composed of a first cation, an anion composed of hydrogen and a group 13 or 15 element, and a second compound composed of a second cation and an anion. By using a latent heat storage material containing a mixture with the compound in which the first cation and the second cation are alkali metal ions, the instability of the crystal structure of the compound is enhanced by the ion-bonded molecule having a large anion size. At the same time, the mixing causes a freezing point drop, and the phase transition or phase change temperature can be lowered. Therefore, exhaust heat is recovered and stored from the downstream of the exhaust gas purification catalyst of automobiles, gas engine heat pumps, etc., which can store heat in the temperature range of 400 ° C or less and requires a material with high heat storage density, and warms up at start-up. Can be used for.

Claims (7)

A first compound composed of a first cation and an anion composed of hydrogen and a Group 13 or 15 element,
Contains a mixture of a second cation and a second compound composed of said anion.
The first cation and the second cation Ri alkali metal ions der,
The anion is, borohydride ion ^- is, (BH ₄₎
Latent heat storage material. The latent heat storage material according to claim 1, wherein the difference in ionic radius between the first cation and the second cation is 39 pm or more and 87 pm or less. The latent heat storage material according to claim 1 or 2, wherein the first cation is lithium ion (Li ⁺ ) and the second cation is potassium ion (K ⁺ ). Wherein said first compound is lithium borohydride high dry de (LiBH _4), wherein said second compound is potassium borohydride high dry de (KBH _4), latent heat storage material according to claim 1 or 2. Molar ratio of KBH ₄ the first LiBH ₄ and the second compound _{compound, LiBH 4: KBH 4 = 17} : 3~7: a 3, latent heat storage material according to claim 4. A heat storage system comprising the latent heat storage material according to any one of claims 1 to 5 . A first compound composed of a first cation and an anion composed of hydrogen and a Group 13 or 15 element,
Contains a mixture of a second cation and a second compound composed of said anion.
The first cation and the second cation Ri alkali metal ions der,
The anion is, borohydride ion ^- is, (BH ₄₎
It is a method of storing heat in a latent heat storage material.
A heat medium flowing out of the heat source is circulated along the container containing the latent heat storage material.
The latent heat storage material and the heat medium are exchanged for heat through the container to heat the latent heat storage material.
By melting the latent heat storage material, heat is stored in the latent heat storage material.
Method.

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