JP7275689B2 - Cold storage material - Google Patents

Description

The present invention relates to a cold storage material.

Patent Literature 1 discloses a heat storage device and a heat storage method. More specifically, in the heat storage device disclosed in Patent Document 1, supercooling of the heat storage material that forms clathrate hydrate by cooling can be canceled with less energy.

Japanese Patent Application Laid-Open No. 2017-003182

An object of the present invention is to provide a new cold storage material that crystallizes by an unprecedented mechanism.

The cold storage material according to the present invention is an aqueous cold storage material,
at least one ammonium cation selected from the group consisting of tetra-n-butylammonium cations and tetra-isopentylammonium cations;
carboxylate anion,
oxygen-containing anions, and silver ions,
contains
here,
The oxygen-containing anion has a molecular structure different from that of the carboxylate anion,
the oxygen-containing anion is capable of combining with the at least one ammonium cation to form a first guest molecule during cooling of the cold storage material;
the first guest molecule is capable of forming a first clathrate hydrate crystal using a water molecule as a first host molecule;
The first clathrate hydrate crystal has a melting point of 0 degrees Celsius or more and 30 degrees Celsius or less,
the carboxylate anion is capable of combining with the at least one ammonium cation to form a second guest molecule during cooling of the cold storage material;
the second guest molecules are capable of forming second clathrate hydrate crystals using water molecules as second host molecules;
The second clathrate hydrate crystal has a melting point of 0 degrees Celsius or more and 30 degrees Celsius or less,
The melting point of the second clathrate hydrate crystals is lower than the melting point of the first clathrate hydrate crystals,
the molar ratio of the oxygen-containing anion to the carboxylate anion is less than 0.5;
The first clathrate hydrate crystal has a crystal structure similar to the second clathrate hydrate crystal,
The cold storage material has a melting point of 3 degrees Celsius or more, and the cold storage material has a degree of supercooling ΔT of 8 Kelvin or less.

The present invention provides a new cold storage material that crystallizes by an unprecedented mechanism.

FIG. 1 is a graph showing characteristics of a cold storage material during cooling. FIG. 2 is a graph showing the characteristics of the cold storage material during heating. FIG. 3A shows a schematic diagram of step (a). FIG. 3B shows a schematic diagram of step (b) following step (a). FIG. 3C shows a schematic diagram of step (c) following step (b). FIG. 3D shows a schematic diagram of step (d) following step (c). FIG. 4A shows a schematic diagram of a first clathrate hydrate crystal 88 . FIG. 4B shows a schematic diagram of a second clathrate hydrate crystal 91 .

Hereinafter, this embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a graph showing characteristics of a cold storage material during cooling. In FIG. 1, the horizontal and vertical axes indicate time and temperature, respectively.

The cold storage material according to this embodiment is cooled. See section A included in FIG. Unlike the case of general liquids, as is well known in the technical field of cold storage materials, even if the temperature of the cold storage material reaches its melting point due to the cooling of the cold storage material, the cold storage material does not solidify. Cool down. See interval B included in FIG. In the supercooled state, the cold storage material is liquid.

The cold storage material then begins to crystallize spontaneously. As it crystallizes, the cold storage material releases heat of crystallization which is almost equal to latent heat. As a result, the temperature of the cold storage material begins to rise. See interval C included in FIG. In this specification, the temperature at which the cold storage material starts to spontaneously crystallize is referred to as "crystallization temperature".

ΔT represents the difference between the melting point and the crystallization temperature of the cold storage material. ΔT may also be referred to as the “degree of subcooling”. Crystallization of the cold storage material in a supercooled state causes the cold storage material to become class hydrate crystals (see, for example, Patent Document 1). Here, clathrate hydrate crystals refer to crystals formed by water molecules forming cage-like crystals through hydrogen bonding, and substances other than water being wrapped in the basket-like crystals. As used herein, unless otherwise specified, the term "clathrate hydrate crystals" includes not only clathrate hydrate crystals, but also semi-clathrate hydrate crystals. A semi-clathrate hydrate crystal is a crystal formed by guest molecules participating in a hydrogen bonding network of water molecules. The concentration at which water molecules and guest molecules form hydrate crystals in just the right amount is called the harmonic concentration. Generally, hydrate crystals are often used near the harmonic concentration. Here, the melting point of clathrate hydrate crystals is defined as the "harmonic concentration melting point (harmonic melting point)". If the number of water molecules per guest molecule is plotted on the horizontal axis and the melting point of the clathrate hydrate crystal is plotted on the vertical axis, an upwardly convex curve is obtained and the harmonic melting point takes the maximum value. That is, the harmonic melting point is the maximum melting point that can be taken by the clathrate hydrate crystal.

After the crystallization is completed and the heat of crystallization of the cold storage material is released, the temperature of the cold storage material gradually decreases to become equal to the ambient temperature. See section D included in FIG.

The crystallization temperature is lower than the melting point of the cold storage material. The melting point of the cold storage material can be measured using a differential scanning calorimeter (which may also be referred to as "DSC"), as is well known in the cold storage material art.

FIG. 2 is a graph showing the characteristics of the cold storage material during heating. In FIG. 2, the horizontal and vertical axes indicate time and temperature, respectively. During section E, the temperature of the cold storage material is maintained at a temperature equal to or lower than the crystallization temperature. For example, the temperature inside the refrigerator is set below the crystallization temperature so that the temperature of the cold storage material placed in the refrigerator is maintained below the crystallization temperature while the door of the refrigerator is closed.

Next, the cold storage material is gradually warmed. See section F included in FIG. For example, when the refrigerator door is opened at the end of interval E (that is, the beginning of interval F) (or when the door is opened and food is put in), the temperature inside the refrigerator gradually increases.

When the temperature of the cold storage material reaches the melting point of the cold storage material, the temperature of the cold storage material is maintained near the melting point of the cold storage material. See section G included in FIG. In the unlikely event that there is no cold storage material, the temperature inside the refrigerator rises continuously as shown in section Z included in FIG. On the other hand, when there is a cold storage material, the temperature inside the refrigerator is maintained near the melting point of the cold storage material during the certain period of section G. In this way, the cold storage material exhibits a cold storage effect. At the end of section G, the crystals of the cold storage material melt and disappear. As a result, the cold storage material is liquefied.

After that, the temperature of the liquefied cold storage material rises to become equal to the ambient temperature. See interval H included in FIG.

The cold storage material can be cooled and reused. For example, after the refrigerator door is closed, the cold storage material is cooled and reused again as shown in section A included in FIG.

The following two conditions (I) and (II) must be satisfied for a cold storage material to be suitably used for a refrigerator.
- Condition (I) The cold storage material must have a melting point of 3 degrees Celsius or higher.
- Condition (II) The cold storage material should have a small degree of supercooling ΔT of 8 Kelvin or less (preferably 6 Kelvin K or less).
Desirably, the cold storage material has a melting point of 25 degrees Celsius or less (ie, room temperature or less).

The reason for condition (I) is that the temperature inside the refrigerator should be maintained at a temperature of approximately 3 degrees Celsius or higher (and preferably 25 degrees Celsius or lower, i.e., preferably room temperature or lower). . In other words, if the temperature inside the cooler is maintained below 0 degrees Celsius, such a cooler is a "freezer" rather than a "refrigerator". On the other hand, from a food preservation point of view, such a cooler would be of little practical use as a refrigerator if the temperature inside the cooler is maintained above 25 degrees Celsius.

The reason for condition (II) is explained below. As the degree of supercooling ΔT increases, the crystallization temperature decreases. Therefore, excessive cooling is required to crystallize the cold storage material in the supercooled state. As an example, the crystallization temperature of ice (that is, pure water) used as a cold storage material is about minus 12 degrees Celsius. That is, the melting point of ice used as a cold storage material is 0 degrees Celsius, and its degree of supercooling ΔT is equal to 12 Kelvin. Therefore, when ice is used as a cold storage material, the cooler needs the ability to cool the inside to minus 12 degrees Celsius or less (for example, minus 18 degrees Celsius). This increases the power consumed by the cooler. Needless to say, low power consumption is desirable. Therefore, the degree of supercooling ΔT of the cold storage material is required to be small. The cold storage material according to this embodiment has a small degree of supercooling of 8 Kelvin or less. Desirably, the regenerator material according to this embodiment has a small degree of supercooling of 6 Kelvin or less.

The cold storage material according to this embodiment can be used not only for refrigerators but also for cold storage. Refrigerator means a building whose interior is cooled.

To avoid confusion, "Kelvin" is used herein for the degree of supercooling ΔT. For example, the inventor of the present invention expresses that "the degree of supercooling ΔT is n Kelvin or less." Needless to say, n is a real number. The description "degree of supercooling ΔT≦5 Kelvin" means that the difference between the crystallization temperature and the melting point of the cold storage material is 5 Kelvin or less. On the other hand, in this specification, "Celsius" is used for temperature. For example, the inventors write that "the crystallization temperature is 5 degrees Celsius" (that is, 5 degrees Celsius).

The cold storage material according to the present embodiment includes (I) at least one ammonium cation selected from the group consisting of tetra-n-butylammonium cations and tetra-isopentylammonium cations, (II) carboxylate anions, and (III) oxygen. containing anions, and (IV) silver ions. The cold storage material according to this embodiment is water-based. Therefore, the cold storage material according to the present embodiment contains (V) water molecules.

(I: ammonium cation)
The at least one ammonium cation is selected from the group consisting of tetra-n-butylammonium cations and tetra-isopentylammonium cations. The tetra-n-butylammonium cation is represented by the chemical formula ((CH ₃ (CH ₂ ) ₃ ) ₄ N ⁺ ). As is well known in the technical field of cold storage materials, these ammonium cations are used as the main component of the cold storage material, that is, as the main cold storage component. Desirably, the molar ratio between the at least one ammonium cation and the water molecule is between 1:20 and 1:40. In other words, the molar ratio of at least one ammonium cation to water molecules is preferably 1/40 or more and 1/20 or less.

Instead of or in addition to the tetra-n-butylammonium cation, the tetra-isopentylammonium cation represented by the chemical formula ((CH ₃ CH(CH ₃ )CH ₂ CH ₂ ) ₄ N ⁺ ) can also be used. At least one ammonium cation can be derived from at least one ammonium cation carboxylate, as will be apparent from the method for producing a cold storage material described later.

(II: Carboxylate anion)
Each carboxylate anion is represented by the following chemical formula (II).
R- ^COO- (II)
where R is a hydrocarbon group.
Desirably, the carboxylate anion is a monocarboxylate anion.

Desirably, each carboxylate anion has from 1 to 10 carbon atoms. More desirably, each carboxylate anion has from 1 to 7 carbon atoms. The carboxylate anion may have 2 or more carbon atoms.

R may be a straight chain hydrocarbon group. For example, the carboxylate anion is the 1-pentanoate anion represented by the chemical formula ^--OCO (CH ₂ ) ₃ CH ₃ or the 1-heptanoate anion represented by the chemical formula ^--OCO (CH ₂ ) ₅ CH ₃ .

Alternatively, R may be a branched hydrocarbon group. For example, the carboxylate anion _{can be} 2-methylbutanoate, represented by the chemical formula ^--OCOCH ( _CH3 ) _CH2CH3 , or 2- _{ethylbutanoate} , represented by the chemical formula ^--OCOCH ( _CH2CH3 ) _CH2CH3 . is an anion. Other examples of carboxylate anions are methylpentanoate, ethylpentanoate, propylpentanoate, methylhexanoate, ethylhexanoate, propylhexanoate, and butylhexanoate.

The cold storage material according to this embodiment may contain two or more types of carboxylate anions.

Desirably, the molar ratio between carboxylate anions and water molecules is between 1:20 and 1:40. In other words, the molar ratio of carboxylate anions to water molecules is preferably 1/40 or more and 1/20 or less.

As is clear from the method for producing a cold storage material described later, the carboxylate anion can be derived from at least one kind of carboxylate of ammonium cation.

(III: oxygen-containing anion)
Each oxygen-containing anion contains an oxygen atom in its molecule.
・Examples of oxygen-containing anions are
(I) a sulfonate anion represented by the chemical formula R ₁ —SO ₃ ^— ;
(II) a disulfonate anion represented by the chemical formula ^—O ₃ S—R ₁ —SO ₃ ^— ;
(III) a carboxylate anion represented by the chemical formula R ₁ —CO ₂ ^— ;
(IV) an amino acid anion represented by the chemical formula H ₂ N—CHR ₁ —CO ₂ ^— ;
(V) a dicarboxylic acid anion represented by the chemical formula ^—O ₂ C—R ₁ —CO ₂ ^— ;
(VI) Nonmetallic acid anions represented by the chemical formulas NO ₂ ⁻ , NO ₃ ⁻ , ClO ⁻ , ClO ₂ ⁻ , ClO ₃ ⁻ , ClO ₄ ⁻ , CO ₃ ²⁻ , SO ₄ ²⁻ , or PO ₄ ³⁻ ,
(VII) a hydroxide anion represented by the formula ^OH- ,
(VIII) a metal acid anion represented by the chemical formula CrO ₄ ^2- or WO ₄ ^2- , and (IX) an organic sulfate ester represented by the chemical formula R ₁ -O-SO ₃ ^- ,
is.

here,
R ₁ represents a substituted or unsubstituted linear or branched organic residue.

When the oxygen-containing anion is a carboxylate anion or a dicarboxylate anion, each oxygen-containing anion has a different molecular structure from the carboxylate anions described in the section "(II) Carboxylate anions". For example, when the oxygen-containing anion is an acetate anion represented by the chemical formula CH _COO ^- , the carboxylate anion described in the section "(II) Carboxylate anion" is a carboxylate anion other than the acetate anion. . As an example, when the oxygen-containing anion is an acetate anion represented by the chemical formula CH ₃ COO ^— , examples of carboxylate anions described in the section “(II) Carboxylate anions” are represented by the chemical formula ^—OCOCH (CH ₃ ) is the 2-ethylbutanoate anion represented by CH ₂ CH ₃ .

An example of a counter cation for an oxygen-containing anion is the sodium ion. That is, the oxygen-containing anion can be derived from its metal salt (eg, sodium, potassium, or calcium salt).

(IV: silver ion)
The cold storage material according to this embodiment contains silver ions. Silver ions can be derived from silver carboxylate, as is clear from the manufacturing method of the cold storage material described later.

(V: water molecule)
The cold storage material according to this embodiment contains water molecules. The cold storage material according to this embodiment is water-based. In other words, the cold storage material according to the present embodiment is an aqueous solution containing the four components described in items (I) to (IV) above.

(Mechanism of crystallization)
The crystallization mechanism of the cold storage material containing the five components described in the above items (I) to (V) will be described below.
- The mechanism includes the following four steps (a) to (d).
- A series of steps (a) to (d) are performed by cooling the cold storage material according to the present embodiment. Step (a) and step (b) are performed in at least one section of section A and section B. Step (c) and step (d) are performed in section B.

(Step a)
In step (a), the cold storage material according to the present embodiment is cooled. As shown in FIG. 3A, in step (a), a first composite 81 in which silver carboxylate is incorporated into metallic silver core particles 80 is formed. As is well known, when silver ions are irradiated with ultraviolet rays, the silver ions are reduced and changed into metallic silver particles. Due to Brownian motion or intermolecular interaction in the aqueous solution, a plurality of metallic silver particles aggregate to form a metallic silver core particle 80 composed of a plurality of metallic silver particles. Since the cold storage material according to the present embodiment is often irradiated with ultraviolet rays contained in light emitted from the sun or ceiling lights, part of the silver ions contained in the cold storage material according to the present embodiment changes to metallic silver particles. and then metallic silver core particles 80 are formed. Thus, in the cold storage material according to the present embodiment, metallic silver core particles 80 derived from silver ions are formed. The charge of the metallic silver core particles 80 is neutral.

Next, silver carboxylate is incorporated into metallic silver core particle 80 to form first composite 81 . Note that equilibrium is formed in the cold storage material according to this embodiment. Examples of such equilibria are equilibria between carboxylate anions, silver ions, and silver carboxylates. In other words, the cold storage material according to the present embodiment contains not only many carboxylate anions and many silver ions, but also little silver carboxylate. Needless to say, silver carboxylate is composed of silver ions and carboxylate anions.

As shown in FIG. 3A, first complex 81 is composed of macrocation 82 and carboxylate anion 83 . Macrocations 82 are cations of metallic silver core particles 80 . Macrocations 82 include not only silver atoms derived from metallic silver particles, but also silver ions derived from silver carboxylate. Therefore, the charge of macrocation 82 is positive. A carboxylate anion 83 derived from silver carboxylate is located near the macrocation 82 . The charge of the first complex 81 is neutral.

(Step b)
Next, in step (b), the cold storage material according to the present embodiment is further cooled after step (a). In step (b), oxygen-containing anions 84 are attracted to macrocations 82 to form a second complex 85, as shown in Figure 3B. As noted above, macrocations 82 include not only silver atoms derived from metallic silver particles, but also silver ions derived from silver carboxylates, although the silver atoms and silver ions are indistinguishable from each other. Therefore, as long as a positive charge is maintained within the macrocation 82, the silver ions derived from the silver carboxylate are converted to silver atoms, and some of the silver atoms derived from the metallic silver particles are converted to silver ions.

Oxygen-containing anions 84 are attracted to macrocations 82 by electrostatic attraction (ie, Coulomb force). Thus, the second composite 85 is formed. A second complex 85 is composed of macrocations 82 , carboxylate ions 83 , and oxygen-containing anions 84 . Oxygen-containing anions 84 contained in the second complex 85 are located near the macrocations 82 . The charge of the second complex 85 is negative.

(Step c)
Next, in step (c), as shown in FIG. 3C, in the supercooled state of the cold storage material, at the first temperature, the oxygen-containing anions 84 contained in the second complexes 85 are added with at least one kind of ammonium Cations 86 are attracted to form primary clathrate hydrate crystals 88 with water molecules 87 .

At least one ammonium cation 86 is attracted to the oxygen-containing anion 84 contained in the second complex 85 by electrostatic attraction (ie, Coulomb force). Under the unstable conditions of supercooling, when the at least one ammonium cation 86 is attracted to the oxygen-containing anion 84 in the aqueous solution, the thus-attracted at least one ammonium cation 86 and the oxygen-containing anion 84 transforms into first clathrate hydrate crystals 88 together with water molecules 87 . In other words, the first clathrate hydrate crystals 88 are formed from at least one ammonium cation (reference number: 86), an oxygen-containing anion (reference number: 84), and water molecules (reference number: 87).

The first clathrate hydrate crystals 88 are described in detail below. As shown in FIG. 4A, first clathrate hydrate crystals 88 are composed of oxygen-containing anions 84, at least one ammonium cation 86, and a plurality of water molecules (reference number: 87). As is well known in the art of clathrate hydrate crystals, clathrate hydrate crystals are composed of a guest material and a host material. A host material is positioned so as to surround the guest material. As shown in FIG. 4A, first clathrate hydrate crystals 88 are composed of first guest material 89 and first host material 90 .

A first guest material 89 is located in the center of the first clathrate hydrate crystal 88 . First guest material 89 is composed of at least one ammonium cation 86 and an oxygen-containing anion 84 . A first host material 90 is located in the vicinity of the first guest material 89 . The first host material 90 is formed from a plurality of water molecules (reference number: 87). The ratio of the number of water molecules (reference numeral: 87) to one first host substance 90 is about 25 or more and 100 or less.

(Step d)
Finally, in step (d), as shown in FIG. 3D, in the supercooled state of the cold storage material, the second clathrate hydrate is produced at the second temperature using the first clathrate hydrate crystals 88 as seed crystals. Rate crystals 91 are formed.

The first clathrate hydrate crystals 88 have a similar structure to the second clathrate hydrate crystals 91 . As shown in FIG. 4B, second clathrate hydrate crystals 91 are composed of second guest material 92 and second host material 93 .

A second guest material 92 is located in the center of the second clathrate hydrate crystal 91 . Like first guest material 89 , second guest material 92 is composed of at least one ammonium cation 86 and carboxylate anion 83 . A second host material 93 is positioned in the vicinity of the second guest material 92 . The second host material 93 is made up of a plurality of water molecules (reference number: 87). The ratio of the number of water molecules (reference numeral: 87) to one second host substance 93 is about 25 or more and 100 or less. Thus, the second clathrate hydrate crystals 91 are composed of carboxylate anions 83, at least one kind of ammonium cations 86, and a plurality of water molecules (reference number: 87). Needless to say, the water molecules contained in the second clathrate hydrate crystals 91 are different from the water molecules contained in the first clathrate hydrate crystals 88 . In other words, the water molecules contained in the second clathrate hydrate crystals 91 are not contained in the first clathrate hydrate crystals 88, and the water molecules contained in the first clathrate hydrate crystals 88 are not contained in the second clathrate hydrate crystals 88. It is not included in the hydrate crystals 91.

When the first clathrate hydrate crystals 88 are formed under the unstable condition of supercooling, the first clathrate hydrate crystals 88 function as seed crystals, and the first clathrate hydrate crystals 88 A second clathrate hydrate crystal 91 having a similar crystal structure is formed. That is, in the vicinity of a first clathrate hydrate crystal 88 functioning as a seed crystal, at least one kind of ammonium cation 86, a carboxylate anion 83, and a plurality of water molecules (reference numeral: 87) form a first clathrate hydrate. It transforms into second clathrate hydrate crystals 91 having a crystal structure similar to the rate crystals 88 .

As described above, the first clathrate hydrate crystals 88 function as seed crystals for the formation of the second clathrate hydrate crystals 91, so that the formation of the first clathrate hydrate crystals 88 is followed by the formation of the second clathrate hydrate crystals 88. It must precede the formation of hydrate crystals 91 . In other words, the first clathrate hydrate crystals 88 must be formed before the second clathrate hydrate crystals 91 are formed. These series of steps (a) to (d) are performed by cooling the cold storage material. Therefore, the melting point (ie, freezing point) of the first clathrate hydrate crystals 88 is required to be higher than the melting point (ie, freezing point) of the second clathrate hydrate crystals 91 . This will be explained in detail later.

Since the first clathrate hydrate crystals 88 sufficiently function as seed crystals even in a small amount, in the cooling agent, the molar ratio of the oxygen-containing anion (reference symbol: 84) to the carboxylate anion (reference symbol: 83) is The ratio is less than 0.5. Desirably, the molar ratio is less than 0.1. More desirably, the molar ratio is less than 0.01. An excessive amount of oxygen-containing anions (reference numeral: 84) raises the melting point of the cold storage material according to the present embodiment and causes the cold storage material to lose its function.

As described above, in the supercooled state of the regenerator material according to this embodiment, the oxygen-containing anions 84 are used in combination with at least one ammonium cation 86 to form the first guest substance 89 . A first guest material 89 forms a first clathrate hydrate crystal 88 using a plurality of water molecules (reference number: 87 ) as a first host material 90 .

Carboxylate anion 83 is used in combination with at least one ammonium cation 86 to form second guest material 92 . The second guest material 92 forms a second clathrate hydrate crystal 91 using a plurality of water molecules (reference number: 87 ) as a second host material 93 . Needless to say, the first clathrate hydrate crystals 88 contain a plurality of first guest substances (reference number: 89). Similarly, the second clathrate hydrate crystal 91 contains a plurality of second guest substances (reference number: 92).

(First temperature, second temperature, melting point of clathrate hydrate crystal)
The first temperature, the second temperature, the melting point of the first clathrate hydrate crystals 88, and the melting point of the second clathrate hydrate crystals 91 are described below.

The first temperature is the temperature at which the first clathrate hydrate crystals 88 are formed in step (c).

The first clathrate hydrate crystals 88 have a melting point of 0 degrees Celsius or higher and 30 degrees Celsius or lower. Therefore, the first temperature is 0 degrees Celsius or higher and 30 degrees Celsius or lower. As shown in Tables 1 to 4 below, almost all clathrate hydrate crystals have a melting point of 30 degrees Celsius or less. In other words, clathrate hydrate crystals with melting points above 30 degrees Celsius are extremely difficult to obtain.

There is no point in using clathrate hydrate crystals with melting points below 0 degrees Celsius. Clathrate hydrates are characterized by crystallization that occurs at temperatures above 0 degrees Celsius. That is, the clathrate hydrate is characterized by having a melting point of 0 degrees Celsius or higher. Clathrate hydrate crystals with melting points below 0 degrees Celsius do not exhibit such characteristics. Clathrate hydrate crystals with melting points below 0 degrees Celsius are rarely used. Rather, ice is used when a crystal with a melting point below 0 degrees Celsius is required as a cold storage material. That is, crystallized water is used.

The second temperature is the temperature at which the second clathrate hydrate crystals 91 are formed in step (d).

For the same reason as above, the second clathrate hydrate crystal 91 also has a melting point of 0 degrees Celsius or more and 30 degrees Celsius or less. The second temperature is also between 0 degrees Celsius and 30 degrees Celsius.

The melting point of the second clathrate hydrate crystals 91 is lower than the melting point of the first clathrate hydrate crystals 88 . In other words, the melting point of the first clathrate hydrate crystals 88 is higher than the melting point of the second clathrate hydrate crystals 91 .

As described above, the series of steps (a) to (d) are performed by cooling the cold storage material according to this embodiment. The first clathrate hydrate crystals 88 are seed crystals for the formation of the second clathrate hydrate crystals 91 . Therefore, the first temperature (ie, the melting point of the first clathrate hydrate crystals 88) is higher than the second temperature (ie, the melting point of the second clathrate hydrate crystals 91). In other words, the second temperature is lower than the first temperature. If the first temperature is lower than the second temperature, the second clathrate hydrate crystals 91 are formed before the first clathrate hydrate crystals 88 functioning as seed crystals. It makes no sense to form hydrate crystals 88 (ie, seed crystals).

(Melting point of clathrate hydrate crystal)
As described above, in the cold storage agent according to the present embodiment, the melting point (ie, freezing point) of the first clathrate hydrate crystals 88 is higher than the melting point (ie, freezing point) of the second clathrate hydrate crystals 91 . Tables 1-4 below show the melting points of the major clathrate hydrate crystals.

Based on Tables 1 to 4 below, the melting point (ie, freezing point) of the first clathrate hydrate crystals 88 is higher than the melting point (ie, freezing point) of the second clathrate hydrate crystals 91. The selection of the oxygen-containing anion 84 used to form the first clathrate hydrate crystals 88 and the carboxylate anion 83 used to form the second clathrate hydrate crystals 91 is readily available to those skilled in the art. be.

As described above, the carboxylate anion (reference: 84) of the oxygen-containing anion (reference: 84)
83) is less than 0.5. This means that the amount of the carboxylate anion (reference code: 83) is greater than the amount of the oxygen-containing anion (reference code: 84) in the cooling storage agent according to the present embodiment. Therefore, it is desirable to select the carboxylate anion (reference number: 83) first.

As a first example, as at least one ammonium cation (reference sign: 86) and ^a carboxylate anion ₍ reference sign: _{83 )} , _tetra When the -n-butylammonium cation and the 2-ethylbutanoate anion represented by the chemical formula ^-OCOCH (CH ₂ CH ₃ )CH ₂ CH ₃ are selected, the tetra - Clathrate hydrate crystals containing the n-butylammonium cation and the 2-ethylbutanoate anion have a melting point of 10.0 degrees Celsius. That is, at least one kind of ammonium cation (reference code: 86) and carboxylate anion (reference code: 83) contained in the second clathrate hydrate crystal 91 are tetra-n-butylammonium cation and 2-ethylbutanoate anion, respectively. is selected, the second clathrate hydrate crystals 91 have a melting point of 10.0 degrees Celsius.

Since the melting point (ie, freezing point) of the first clathrate hydrate crystals 88 is higher than the melting point (ie, freezing point) of the second clathrate hydrate crystals 91, the first clathrate hydrate crystals 88 have a temperature of 10°C. Clathrate hydrate crystals with melting points greater than 0 degrees are selected from Tables 1-4. For example, as shown in Table 1, row 20, a tetra-n-butylammonium cation represented by the chemical formula ((CH ₃ (CH ₂ ) ₃ ) ₄ N ⁺ ) and a tetra-n-butylammonium cation represented by the chemical formula CH _COO ^- Clathrate hydrate crystals containing the acetate anion have a melting point of approximately 14.8 degrees Celsius. Therefore, clathrate hydrate crystals containing tetra-n-butylammonium cations and acetate anions are suitably selected as first clathrate hydrate crystals 88 . Thus, the 2-ethylbutanoate anion and the acetate anion are readily selected from Tables 1 to 4 as the carboxylate anion (reference sign: 83) and the oxygen-containing anion (reference sign: 84), respectively. See Examples 1 and 3 below. As is clear from Tables 1 to 4, the melting point of clathrate hydrate crystals slightly depends on the number of water molecules contained in the clathrate hydrate crystals (that is, hydration number).

As a modification of the first example (that is, an example in which 2-ethylbutanoate anion is selected as the carboxylate anion (reference code: 83)), as shown in rows 53-54 of Table 2: , clathrate hydrate crystals containing the tetra-n-butylammonium cation represented by the chemical formula ((CH ₃ (CH ₂ ) ₃ ) ₄ N ⁺ ) and the tungstate anion represented by the chemical formula WO4 ^2- It has a melting point of 15.0°C to 15.1°C. Therefore, clathrate hydrate crystals containing tetra-n-butylammonium cations and tungstate anions are suitably selected as first clathrate hydrate crystals 88 . Thus, 2-ethylbutanoate anion and tungstate anion are readily selected from Tables 1 to 4 as carboxylate anion 83 and oxygen-containing anion 84, respectively. See Example 2 below.

As a second example, if the n-pentanoate anion is chosen as the carboxylate anion (reference sign: 83), as shown in Table 1, line 24, the tetra-n-butylammonium cation and the n - Clathrate hydrate crystals containing the pentanoate anion have a melting point of approximately 10.6 degrees Celsius. As shown on line 20 of Table 1, the clathrate hydrate crystals containing the tetra-n-butylammonium cation and the acetate anion have a melting point of approximately 14.8 degrees Celsius, so the first clathrate hydrate A clathrate hydrate crystal containing a tetra-n-butylammonium cation and an acetate anion is suitably selected as the rate crystal 88 . See Example 4 below.

(Example)
The present invention will now be described in more detail with reference to examples.

(Example 1)
(Synthesis of TBA-2-EB)
Tetra-n-butylammonium-2-ethylbutanoic acid (hereinafter referred to as “TBA-2-EB”) represented by the following chemical formula (I) was synthesized as follows.

First, in a tetra-n-butylammonium hydroxide aqueous solution (0.1 mol, obtained from Tokyo Chemical Industry Co., Ltd., 40% aqueous solution, hereinafter referred to as "TBA-OH") represented by the following chemical formula (II), 2-Ethylbutanoic acid (chemical formula: HOOC-CH(CH ₂ CH ₃ )CH ₂ CH ₃ , 0.1 mol, obtained from Tokyo Chemical Industry Co., Ltd.) was added. Thus, an aqueous solution was obtained.

The resulting aqueous solution was dried at a temperature of 40 degrees Celsius under reduced pressure using an evaporator. Water was thus removed from the resulting aqueous solution to obtain TBA-2-EB. TBA-2-EB (0.1 mol) was thus obtained.

The resulting TBA-2-EB (9785 micromoles) was then dissolved in pure water (361100 micromoles). Thus, an aqueous TBA-2-EB solution (35% by weight) was obtained.

(purchase of silver acetate)
Silver acetate represented by the chemical formula CH ₃ CO ₂ Ag was purchased from Fujifilm Wako Pure Chemical.

(purchase of sodium acetate)
Silver acetate represented by the chemical formula CH ₃ CO ₂ Na was purchased from Fujifilm Wako Pure Chemical.

(Preparation of cold storage material)
A cold storage material according to Example 1 was prepared as follows. First, silver acetate (40 micromoles) and sodium acetate (400 micromoles) were added to a TBA-2-EB aqueous solution containing 9785 micromoles of TBA-2-EB to obtain a mixture. Note that silver carboxylates such as silver acetate are insoluble in both hydrophilic solvents (e.g. water) and hydrophobic solvents (e.g. oils), but are soluble in aqueous quaternary ammonium salts. do it.

Immediately after the addition, the aqueous solution became cloudy, but after several hours, the aqueous solution became clear. A slight precipitate was observed in the aqueous solution. The aqueous solution was left at room temperature for over 24 hours. Thus, a cold storage material according to Example 1 was prepared. As is clear from the above, the cold storage material according to Example 1 has the composition shown in Table 5 below.

(Measurement of melting point and latent heat)
Using a differential scanning calorimeter, the melting point and latent heat amount of the cold storage material according to Example 1 were measured as follows. First, the cold storage material (10 mg) according to Example 1 was put into an aluminum container. The container was then sealed with a lid.

The container was incorporated into a differential scanning calorimeter (obtained from PerkinElmer, trade name: DSC-8500). The cold storage material charged into the container was cooled from room temperature to minus 20 degrees Celsius at a rate of 2 degrees Celsius/minute. Next, the cold storage material was allowed to stand at minus 20 degrees Celsius for 5 minutes. The present inventor considered that the cold storage material crystallized to become a semi-class hydrate. Finally, the cold storage material was heated from minus 20 degrees Celsius to room temperature at a rate of 2 degrees Celsius/minute. Thus, the crystallized cold storage material was melted.

Based on the endothermic peak output from the DSC while the cold storage material (that is, the semi-class hydrate cold storage material) is melting, the melting point of the cold storage material according to Example 1 is determined, and the latent heat amount of the cold storage material according to Example 1 is determined. was calculated. As a result, the melting point of the cold storage material according to Example 1 was 10.0 degrees Celsius. The latent heat quantity of the cold storage material according to Example 1 was 170 Joules/gram.

(Measurement of degree of supercooling ΔT)
The degree of supercooling ΔT of the cold storage material according to Example 1 was measured as follows. First, the cold storage material (10 g) according to Example 1 was introduced into a glass bottle having a capacity of 60 ml. The vial was then sealed using a lid.

The glass bottle was placed in a constant temperature bath (obtained from Espec Co., Ltd., product name: SU-241). The temperature inside the constant temperature bath was 20 degrees Celsius.

After the temperature inside the constant temperature bath was decreased to 4 degrees Celsius at a rate of minus 1 degree Celsius/min, the temperature inside the constant temperature bath was maintained at 4 degrees Celsius.

After 20 minutes from the start of maintaining the temperature inside the constant temperature bath at 4 degrees Celsius, the cold storage material according to Example 1 self-crystallized. Along with the crystallization, the cold storage material according to Example 1 released heat of crystallization. The release of heat of crystallization caused the temperature of the cold storage material according to Example 1 to rise. Finally, the inventor visually confirmed the completion of crystallization of the cold storage material according to Example 1. The time between the start of crystallization and the end of crystallization was 5 hours.

As described above, the cold storage material according to Example 1 crystallized by itself at a temperature of 4 degrees Celsius. It had a crystallization temperature)) of 4 degrees Celsius.

(Example 2)
In Example 2, the same experiment as in Example 1 was conducted, except that sodium tungstate represented by the chemical formula Na ₂ WO ₄ (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was used instead of sodium acetate. was broken

(Example 3)
In Example 3, an experiment similar to Example 1 was performed, except that the amount of sodium acetate added was 800 micromoles.

(Example 4)
In Example 4, tetra-n-butylammonium-pentanoic acid (hereinafter referred to as "TBA-P", 11662 micromoles) was used instead of TBA-2-EB, and the number of moles of water was 333300. An experiment similar to Example 1 was performed, except that it was micromolar. TBA-P was synthesized as follows.

(Synthesis of TBA-P)
Tetra-n-butylammonium-pentanoic acid (ie, TBA-P) represented by formula (III) below was synthesized as follows.

First, a TBA-OH aqueous solution (0.1 mol, obtained from Tokyo Chemical Industry Co., Ltd., 40% aqueous solution) was added with pentanoic acid (chemical formula: HOOC(CH ₂ ) ₃ CH ₃ , 0.1 mol, Tokyo Chemical Industry Co., Ltd. ) was added. Thus, an aqueous solution was obtained.

The resulting aqueous solution was dried at a temperature of 40 degrees Celsius under reduced pressure using an evaporator. Thus, water was removed from the resulting aqueous solution to obtain TBA-P. TBA-P (0.1 mol) was thus obtained.

The resulting TBA-P (9407 micromoles) was then dissolved in pure water (376294 micromoles). Thus, an aqueous TBA-P solution (32.3% by weight) was obtained.

Tables 6-7 below show the results of Examples 1-4.

(Comparative example 1)
In Comparative Example 1, an experiment similar to Example 1 was performed, except that no silver acetate was used.

(Comparative example 2)
In Comparative Example 2, the same experiment as in Example 1 was performed, except that n-heptanoic acid was used instead of sodium acetate.

Clathrate hydrate crystals containing the tetra-n-butylammonium cation represented by the chemical formula ((CH ₃ (CH ₂ ) ₃ ) ₄ N ⁺ ) and the acetate anion represented by the chemical formula CH ₃ ^COO- have a temperature of approximately 14 degrees Celsius. (see Example 1, and Table 1, line 20), while the chemical formula ((CH ₃ (CH ₂ ) ₃ ) ₄ , as listed in Table 2, line 33, has a melting point of 0.8 degrees C. N ⁺ ) and a heptanoate anion represented by the chemical formula CH ₃ (CH ₂ ) ₅ COO ⁻ have a melting point as low as approximately 2.3 degrees Celsius. have The low melting point of 2.3 degrees Celsius is attributed to the tetra-n-butylammonium cation represented by the chemical formula ((CH ₃ (CH ₂ ) ₃ ) ₄ N ⁺ ) and the chemical formula ^-OCOCH (CH ₂ CH ₃ )CH ₂ CH ₃ Note that it is lower than the melting point of clathrate hydrate crystals containing the 2-ethylbutanoate anion represented by (10.0 degrees Celsius, see Table 1, line 32).

(Comparative Example 3)
In Comparative Example 3, an experiment similar to Example 1 was performed, except that the number of moles of sodium acetate was 107635 micromoles instead of 400 micromoles.

(Comparative Example 4)
In Comparative Example 4, instead of TBA-2-EB, tetra-n-butylammonium-n-octanoic acid (hereinafter referred to as "TBA-n-O", 10909 micromoles) was used. An experiment similar to Example 1 was performed.

(Synthesis of TBA-nO)
Tetra-n-butylammonium-octanoic acid (ie, TBA-n-O) represented by formula (IV) below was synthesized as follows.

First, octanoic acid (chemical formula: HOOC(CH ₂ ) ₆ CH ₃ , 0.1 mol, Tokyo Chemical Industry Co., Ltd.) was added to an aqueous TBA-OH solution (0.1 mol, obtained from Tokyo Chemical Industry Co., Ltd., 40% aqueous solution). ) was added. Thus, an aqueous solution was obtained.

The resulting aqueous solution was dried at a temperature of 40 degrees Celsius under reduced pressure using an evaporator. Thus, water was removed from the resulting aqueous solution to obtain TBA-n-O. Thus TBA-nO (0.1 mol) was obtained.

The resulting TBA-nO (11025 micromoles) was then dissolved in pure water (319735 micromoles). An aqueous solution of TBA-n-O (approximately 42.4% by weight) was thus obtained.

Tables 8 to 9 below show the results of Comparative Examples 1 to 4.

As is clear from a comparison of Examples 1 to 4 with Comparative Example 1, a composition containing no silver does not function as a cold storage material.

As is clear from a comparison of Examples 1 to 4 with Comparative Example 2, the first temperature (ie, the melting point of the first clathrate hydrate crystal) is the second temperature (ie, the second clathrate hydrate crystal). melting point), the regenerative material does not spontaneously crystallize.

In Comparative Example 3, since the acetate anion is excessive, the cold storage material has a melting point exceeding 10 degrees Celsius. In Comparative Example 3, the cold storage material was crystallized, but the thermophysical properties of TBA-2-EB, which functions as a main agent for cold storage, were not obtained.

In Comparative Example 4, tetra-n-butylammonium-n-octanoic acid was used instead of tetra-n-butylammonium-2-ethylbutanoic acid, so the cold storage material has a melting point of less than 3 degrees Celsius. Therefore, at 4 degrees Celsius, clathrate hydrate crystals of tetra-n-butylammonium cation and acetate anion (i.e., first clathrate hydrate crystals) would have been produced as seed crystals, but second clathrate hydrate crystals would have formed. No rate crystals (ie clathrate hydrate crystals of tetra-n-butylammonium cation and n-octanoate ion, note that the melting point is 1.3 degrees Celsius) were formed. In other words, the cold storage material according to Comparative Example 4 did not crystallize at a temperature of 4 degrees Celsius.

The cold storage material according to the present invention may be included in a refrigerator or cold storage that maintains an internal temperature of 0°C to 30°C.

80 metallic silver core particles 81 first complex 82 macrocations 82
83 carboxylate anion 84 oxygen-containing anion 85 second complex 86 at least one ammonium cation 87 water molecule 88 first clathrate hydrate crystal 89 first guest substance 90 first host substance 91 second clathrate hydrate crystal 92 Second guest substance 93 Second host substance

Claims (12)

A water-based cold storage material,
tetra-n-butylammonium cation,
2-ethylbutanoate anion ,
acetate or tungstate anion ,
silver ions, and
water
contains
The cold storage material has a melting point of 3 degrees Celsius or more, and the cold storage material has a degree of supercooling ΔT of 8 Kelvin or less.
Cold storage material.
A water-based cold storage material,
tetra-n-butylammonium cation,
pentanoate anion,
acetate anion,
silver ions, and
water
contains
The cold storage material has a melting point of 3 degrees Celsius or higher, and
The cold storage material has a degree of supercooling ΔT of 8 Kelvin or less,
Cold storage material.
The cold storage material according to claim 1 or 2 ,
The cold storage material has a melting point of 25 degrees Celsius or less,
Cold storage material.
The cold storage material according to claim 1 or 2 ,
wherein the molar ratio is less than 0.1;
Cold storage material.
The cold storage material according to claim 4 ,
wherein the molar ratio is less than 0.01;
Cold storage material.
A refrigerator comprising the cold storage material according to claim 1 or 2 .
A cold-storage box comprising the cold storage material according to claim 1 or 2 .
tetra-n-butylammonium cation,
2-ethylbutanoate anion,
acetate or tungstate anion ,
silver ions, and
water
A method for crystallizing a cold storage material containing
(a) cooling the cold storage material to form a first composite in which silver acetate is incorporated into metallic silver core particles;
here,
The metallic silver core particles are derived from a plurality of the silver ions,
The first complex is composed of a macrocation and the 2-ethylbutanoate anion, and the macrocation is composed of the metallic silver core particles and the silver ions contained in the silver acetate,
(b) further cooling the cold storage material after step (a) to attract the acetate anion or the tungstate anion to the macrocation to form a second complex;
here,
The second complex is composed of the macrocation, the 2-ethylbutanoate anion, and the acetate anion or the tungstate anion ,
(c) continuing to cool the cold storage material after step (b), and in the supercooled state of the cold storage material, the at least one acetate anion or the tungstate anion contained in the second composite, attracting said tetra-n- butylammonium cations to form first clathrate hydrate crystals at a first temperature;
here,
The first clathrate hydrate crystal is composed of the acetate anion or the tungstate anion , the tetra-n- butylammonium cation, and the water molecule,
In the first clathrate hydrate crystal, a first guest substance is formed from the acetate anion or the tungstate anion and the tetra-n- butylammonium cation,
In the first clathrate hydrate crystal, the water molecules are arranged as a first host substance around the first guest substance,
The first clathrate hydrate crystal has a melting point of 0 degrees Celsius or more and 30 degrees Celsius or less, and a first temperature of 0 degrees Celsius or more and 30 degrees Celsius or less,
(d) continuing to cool the cold storage material after step (c), using the first clathrate hydrate crystals as seed crystals in the supercooled state of the cold storage material to produce a second clathrate at a second temperature; forming hydrate crystals;
here,
The second clathrate hydrate crystal is composed of the 2-ethylbutanoate anion, the tetra-n- butylammonium cation, and the water molecule,
In the second clathrate hydrate crystal, a second guest substance is formed from the 2-ethylbutanoate anion and the tetra-n- butylammonium cation,
In the second clathrate hydrate crystal, the water molecules are arranged as a second host around the second guest substance,
The structure of the first clathrate hydrate crystal is similar to the structure of the second clathrate hydrate crystal,
The second clathrate hydrate crystal has a melting point of 0 degrees Celsius or more and 30 degrees Celsius or less,
The second temperature is 0 degrees Celsius or higher and 30 degrees Celsius or lower,
The melting point of the second clathrate hydrate crystals is lower than that of the first clathrate hydrate crystals,
the second temperature is lower than the first temperature,
In the cold storage agent, the molar ratio of the acetate anion or the tungstate anion to the 2-ethylbutanoate anion is less than 0.5,
The first clathrate hydrate crystal has a crystal structure similar to the second clathrate hydrate crystal,
The cold storage material has a melting point of 3 degrees Celsius or more, and a degree of supercooling ΔT of the cold storage material is 8 Kelvin or less.
Method.
tetra-n-butylammonium cation,
pentanoate anion,
acetate anion,
silver ions, and
water
A method for crystallizing a cold storage material containing
(a) cooling the cold storage material to form a first composite in which silver acetate is incorporated into metallic silver core particles;
here,
The metallic silver core particles are derived from a plurality of the silver ions,
The first complex is composed of a macrocation and the pentanoate anion, and
The macrocation is composed of the metallic silver core particles and the silver ions contained in the silver acetate,
(b) further cooling the cold storage material after step (a) to attract the acetate anion to the macrocation to form a second complex;
here,
the second complex is composed of the macrocation, the pentanoate anion, and the acetate anion;
(c) continuing to cool the cold storage material after step (b), and in the supercooled state of the cold storage material, the at least one acetate anion contained in the second complex is converted to the tetra-n-butyl attracting ammonium cations to form first clathrate hydrate crystals at a first temperature;
here,
The first clathrate hydrate crystal is composed of the acetate anion, the tetra-n-butylammonium cation, and the water molecule,
In the first clathrate hydrate crystal, a first guest substance is formed from the acetate anion and the tetra-n-butylammonium cation,
In the first clathrate hydrate crystal, the water molecules are arranged as a first host substance around the first guest substance,
The first clathrate hydrate crystal has a melting point of 0 degrees Celsius or more and 30 degrees Celsius or less, and
the first temperature is 0 degrees Celsius or higher and 30 degrees Celsius or lower;
(d) continuing the cooling of the cold storage material after step (c), using the first clathrate hydrate crystals as seed crystals in the supercooled state of the cold storage material to produce a second clathrate at a second temperature; forming hydrate crystals;
here,
The second clathrate hydrate crystal is composed of the pentanoate anion, the tetra-n-butylammonium cation, and water molecules,
In the second clathrate hydrate crystal, a second guest substance is formed from the pentanoate anion and the tetra-n-butylammonium cation,
In the second clathrate hydrate crystal, the water molecules are arranged as a second host around the second guest substance,
The structure of the first clathrate hydrate crystal is similar to the structure of the second clathrate hydrate crystal,
The second clathrate hydrate crystal has a melting point of 0 degrees Celsius or more and 30 degrees Celsius or less,
The second temperature is 0 degrees Celsius or higher and 30 degrees Celsius or lower,
The melting point of the second clathrate hydrate crystals is lower than that of the first clathrate hydrate crystals,
the second temperature is lower than the first temperature,
In the cold storage agent, the molar ratio to the pentanoate anion is less than 0.5,
The first clathrate hydrate crystal has a crystal structure similar to the second clathrate hydrate crystal,
The cold storage material has a melting point of 3 degrees Celsius or higher, and
The degree of supercooling ΔT of the cold storage material is 8 Kelvin or less,
Method.
10. A method according to claim 8 or 9 ,
The cold storage material has a melting point of 25 degrees Celsius or less,
Method.
10. A method according to claim 8 or 9 ,
wherein the molar ratio is less than 0.1;
Method.
12. The method of claim 11 , wherein
wherein the molar ratio is less than 0.01;
Method.

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