Semi-clathrate hydrate and method for producing the same

Abstract

To provide a semi-clathrate hydrate capable of lowering the energy needed for recrystallization, or to provide a semi-clathrate hydrate that is free from components with high environmental load such as halogen-containing compounds.SOLUTION: A semi-clathrate hydrate according to one embodiment of the present invention includes component A: water; component B: a tetraalkylammonium cation and / or a tetraalkylphosphonium cation; and component C: a tricarboxylic acid anion.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to semi-clathrate hydrates and a method for producing the same.

Background Art

[0002] It is known that when certain guest substances are mixed with water molecules and cooled, crystals called clathrate hydrates are formed. In clathrate hydrates, multiple water molecules form a cage-like crystal structure, and the guest substance is included in this cage. Among clathrate hydrates, those in which guest substance molecules participate in the formation of the cage-like crystal structure are called semi-clathrate hydrates.

[0003] Since semi-clathrate hydrates have a large latent heat when the crystals decompose, their application as heat storage materials has been studied. For example, Patent Document 1 discloses a semi-clathrate hydrate using tetrabutylammonium bromide as a guest substance. However, this semi-clathrate hydrate has problems of high environmental impact and high corrosivity because the guest substance contains halogen atoms.

[0004] On the other hand, semi-clathrate hydrates using guest molecules that do not contain halogen atoms have also been studied. Patent Document 2 discloses a semi-clathrate hydrate using a tetrabutylammonium cation and a monocarboxylic acid anion represented by R-COO as guest substances. Patent Document 3 discloses a semi-clathrate hydrate using a tetrabutylammonium cation and - O2C-R1-CO2 - a dicarboxylic acid anion represented by as guest substances.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0006] The semi-class rate hydrates disclosed in Patent Documents 2 and 3 have problems that the memory effect described later is small, and the energy required to recrystallize the semi-class rate hydrate that has once changed its state to a liquid is large.

[0007] One aspect of the present invention is to provide a semi-class rate hydrate capable of reducing the energy required for recrystallization. Another aspect of the present invention is to provide a semi-class rate hydrate that does not contain a halogen-containing compound having high corrosiveness and a large environmental load.

Means for Solving the Problems

[0008] The present invention includes the following aspects. <1> A semi-class rate hydrate containing the following components A to C: Component A: water; Component B: a tetraalkylammonium cation and / or a tetraalkylphosphonium cation; Component C: a tricarboxylic acid anion. <2> In the above component B, the central nitrogen atom or phosphorus atom is bonded to four alkyl groups, among which, the carbon numbers of three of the above alkyl groups are all 3 to 5, the carbon number of one of the above alkyl groups is 1 to 6, The semi-class rate hydrate according to <1>. <3> The carbon number of the above component C is 5 to 7, The semi-class rate hydrate according to <1> or <2>. <4> In the recrystallization test carried out by the following procedure, it recrystallizes into a semi-class rate hydrate. The semi-class rate hydrate according to any one of <1> to <3>: 1. Hold 1 g of the semi-class rate hydrate at a temperature 5 °C higher than the decomposition temperature of the semi-class rate hydrate for 30 minutes to change its state to a liquid. 2. Cool the above liquid at 0.1 °C / min until the temperature reaches 10 °C lower than the above decomposition temperature. <5> Substantially free of halogen compounds. The semi-class rate hydrate according to any one of <1> to <4>. <6> Containing the semi-class rate hydrate according to any one of <1> to <5>. Heat storage material. <7> A method for producing a semi-class rate hydrate, comprising a step of cooling a mixture containing the following components A to C: Component A: water; Component B: tetraalkylammonium cation and / or tetraalkylphosphonium cation; Component C: tricarboxylic acid anion. <8> When the cooling temperature in the above cooling is T A (°C) and the decomposition temperature of the semi-class rate hydrate is T (°C), the following relationship holds. The production method according to <7>. T - T A ≦10 °C

Advantages of the Invention

[0009] According to one aspect of the present invention, a semi-class rate hydrate capable of reducing the energy required for recrystallization is provided. According to another aspect of the present invention, a semi-class rate hydrate containing no components with a large environmental load such as halogen-containing compounds is provided.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Modes for Carrying Out the Invention

[0011] Hereinafter, an example of an embodiment of the present invention will be described in detail. However, the present invention is not limited to the following embodiments, and various modifications may be made within the scope shown in the claims. Embodiments combining technical means described in different embodiments are also included in the technical scope of the present invention.

[0012] Unless otherwise specified in this specification, "A~B" representing a numerical range means "A or more and B or less".

[0013] 〔1. Memory Effect〕 Semiclassrate hydrate is produced by supercooling an aqueous solution in which a guest substance is dissolved to a temperature lower than the decomposition temperature of the semiclassrate hydrate. The degree of supercooling required at this time is usually about 15 to 20 °C lower than the decomposition temperature. However, when the semiclassrate hydrate is changed to a liquid state at a temperature slightly higher than the decomposition temperature and then cooled again for recrystallization, the required degree of supercooling may be about 5 to 10 °C lower than the decomposition temperature. This phenomenon is referred to as the "memory effect" in this specification.

[0014] The cause of the memory effect is considered to be the partial structure of the semiclassrate hydrate remaining in the liquid. In the prior art, the stability of this partial structure was low, and when the semiclassrate hydrate was changed to a liquid state at a temperature higher than about the decomposition temperature + 1 °C, the memory effect was not exhibited. However, as a result of the studies by the present inventors, it was found that the semiclassrate hydrate using component B and component C as guest substances exhibited the memory effect even when it was changed to a liquid state at about the decomposition temperature + 5 °C.

[0015] That is, the semiclassrate hydrate according to one aspect of the present invention has a wide temperature range in which the memory effect is maintained, so it can be recrystallized with a smaller degree of supercooling than the conventional semiclassrate hydrate. Therefore, for example, when used as a heat storage material in a refrigeration device, the energy required for recrystallization can be reduced.

[0016] The semiclassrate hydrate according to one embodiment of the present invention is characterized by the memory effect described above. The semiclassrate hydrate according to one embodiment of the present invention has a large memory effect, so even after being changed to a liquid state at a temperature relatively higher than the decomposition temperature, the degree of supercooling required for recrystallization is small. Therefore, the semiclassrate hydrate according to one embodiment of the present invention recrystallizes into a semiclassrate hydrate in the recrystallization test performed by the following procedure. 1. Hold 1 g of the semi-class rate hydrate at a temperature 5 °C higher than the decomposition temperature of the semi-class rate hydrate for 30 minutes to effect a state change to a liquid. 2. Cool the liquid obtained in Step 1 at 0.1 °C / min until the temperature reaches 10 °C (preferably 9 °C or 8 °C) lower than the decomposition temperature.

[0017] [2. Components Contained in the Semi-Class Rate Hydrate] The semi-class rate hydrate according to one aspect of the present invention contains Component A: water, Component B: a tetraalkylammonium cation and / or a tetraalkylphosphonium cation, and Component C: a tricarboxylic acid anion. The semi-class rate hydrate may contain components other than these components. Each component contained in the semi-class rate hydrate may be only one type or two or more types may be used in combination.

[0018] [2.1. Component A: Water] Component A is water. Component A is not particularly limited as long as it is industrially used water. Preferably, Component A is deionized water and / or distilled water.

[0019] [2.2. Component B: Tetraalkylammonium Cation and / or Tetraalkylphosphonium Cation] Component B is a tetraalkylammonium cation and / or a tetraalkylphosphonium cation. The structure of the tetraalkylammonium cation is represented by the following Formula I. The structure of the tetraalkylphosphonium cation is represented by the following Formula II. [Chemical Formula]

[0020] In the formula, R 1 ~R 4 are all alkyl groups. R 1 ~R 4Among them, the alkyl groups having the same structure may be two, three, or four. R 1 ~R 4 The structures of may all be different from each other. R 1 ~R 4 may have a double bond, a triple bond, or a ring.

[0021] In one embodiment, R 1 ~R 3 The lower limit of the carbon number of is each 3 or more or 4 or more. In one embodiment, R 1 ~R 3 The upper limit of the carbon number of is 5 or less or 4 or less. Examples of such alkyl groups include propyl group, isopropyl group, butyl group, isobutyl group, s-butyl group, t-butyl group, pentyl group, isopentyl group, s-pentyl group, t-pentyl group, neopentyl group. These alkyl groups may have a double bond and / or a triple bond inside. Preferably, R 1 ~R 3 is independently selected from the group consisting of propyl group, isopropyl group, butyl group, isobutyl group, pentyl group, isopentyl group, 2-propenyl, 3-butenyl group, and 4-pentenyl group.

[0022] In one embodiment, R 4 The lower limit of the carbon number of is 1 or more, 2 or more, or 3 or more. In one embodiment, R 4 The upper limit of the carbon number of is 6 or less, 5 or less, or 4 or less. Examples of such alkyl groups include methyl group, ethyl group, propyl group, isopropyl group, butyl group, isobutyl group, s-butyl group, t-butyl group, pentyl group, isopentyl group, s-pentyl group, t-pentyl group, neopentyl group, hexyl group, isohexyl group, neohexyl group. These alkyl groups may have a double bond and / or a triple bond inside. Preferably, R 4is independently selected from the group consisting of a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a pentyl group, an isopentyl group, a hexyl group, an isohexyl group, ethenyl, 2-propenyl, 3-butenyl group, and 4-pentenyl group.

[0023] In one embodiment, R 1 ~R 4 are all alkyl groups having 4 carbon atoms. In one embodiment, R 1 ~R 3 are all butyl groups, and R 4 is an alkyl group having 3 to 5 carbon atoms. In one embodiment, R 1 ~R 4 are all butyl groups.

[0024] When component B is an ammonium cation and when it is a phosphonium cation, there are different advantages respectively. When an ammonium cation is adopted as component B, the decomposition temperature of the semi-clathrate hydrate becomes relatively high. Therefore, it can be suitably used for heat storage materials for refrigeration devices and the like. When a phosphonium cation is adopted as component B, since it does not contain ammonium, the environmental load becomes smaller, and the stability of the guest substance is also improved.

[0025] [2.3. Component C: Tricarboxylic Acid Anion] Component C is a tricarboxylic acid anion. A tricarboxylic acid anion is an anion having three carboxy groups (-COOH or -COO - ). Each of the three carboxy groups contained in component C may be in a state where a hydrogen ion is ionized or in a non-ionized state.

[0026] In one embodiment, the lower limit of the carbon number of component C is 5 or more, or 6 or more. In one embodiment, the upper limit of the carbon number of component C is 7 or less, or 6 or less. Since one carbon atom is included in the carboxy group, in this embodiment, the carbon number of component C excluding the carboxy group is 2 or more, or 3 or more, and 4 or less, or 3 or less. Examples of such component C include citric acid, 1,2,3-propanetricarboxylic acid, cis-propen-1,2,3-tricarboxylic acid, and trans-propen-1,2,3-tricarboxylic acid. From the viewpoint of low toxicity to the human body, citric acid is preferred among these.

[0027] [2.4. Other Components] The semi-clathrate hydrate may contain components other than components A to C (such as additives). Examples of additives include preservatives, rust preventives, viscosity modifiers, foam stabilizers, antioxidants, defoamers, abrasive grains, fillers, pigments, dyes, colorants, thickeners, surfactants, flame retardants, plasticizers, lubricants, antistatic agents, heat stabilizers, tackifiers, curing catalysts, stabilizers, silane coupling agents, and waxes.

[0028] In one embodiment, the semi-clathrate hydrate substantially does not contain components other than components A to C. In one embodiment, the content of components other than components A to C is 1% by weight or less, or 0.1% by weight or less, based on 100% by weight of the semi-clathrate hydrate. In one embodiment, the semi-clathrate hydrate does not contain components other than components A to C. The semi-clathrate hydrate according to one embodiment of the present invention can exhibit a greater memory effect than the prior art even if it substantially does not contain additives other than components A to C (for details, refer to the examples). However, in this specification, "components other than components A to C" does not include counterions of component B and component C.

[0029] In one embodiment, the semi-clathrate hydrate substantially does not contain a halogen compound. When the total weight of the semi-clathrate hydrate is 100% by weight, the content of the halogen compound can be 5% by weight or less, 1% by weight or less, 0.5% by weight or less, or 0.1% by weight or less. In one embodiment, the semi-clathrate hydrate does not contain any halogen compound at all. Such a semi-clathrate hydrate is preferable in that it has a small environmental load and reduced corrosivity.

[0030] [3. Method for producing semi-clathrate hydrate] The method for producing a semi-clathrate hydrate according to one aspect of the present invention includes a step of cooling a mixture containing components A to C. Regarding components A to C, it is as described in section [2]. Since component A is water, this mixture can be said to be an aqueous solution of component B and component C.

[0031] The production method may include a step of preparing an aqueous solution containing component B and component C. In this step, a precursor of component B and / or component C may be added to water (component A). The precursor of component B is a substance that changes into component B in water. Examples include salts of tetraalkylammonium and salts of tetraalkylphosphonium. The precursor of component C is a substance that changes into component C in water. Examples include salts of tricarboxylic acids and anhydrides of tricarboxylic acids (the number of carboxy groups involved in the formation of the salt or anhydride is not particularly limited).

[0032] In one embodiment, when the cooling temperature in cooling is T A (°C) and the decomposition temperature of the semi-clathrate hydrate is T (°C), then T - T AThe relationship of ≦10 °C (preferably 9 °C, 8 °C, 7 °C, 6 °C or 5 °C) holds. As shown in the examples of the present application, the semi-class rate hydrate according to one embodiment of the present invention has a large memory effect. Therefore, the degree of supercooling required for recrystallization after once changing to the liquid state can be small. In this embodiment, the manufacturing method of the semi-class rate hydrate may have the following steps (T is the decomposition temperature of the semi-class rate hydrate, and T A is the cooling temperature of the liquid). 1. A step of cooling a mixture containing components A to C to prepare a semi-class rate hydrate. T A in this step (°C) is not particularly limited. 2. A step of changing the state of the semi-class rate hydrate to a liquid at T + 5 °C or lower (preferably T + 4 °C or lower, T + 3 °C or lower, T + 2 °C or lower, or T + 1 °C or lower). 3. A step of cooling the liquid again to recrystallize the semi-class rate hydrate. The cooling temperature at this time satisfies T - T A ≦10 °C (preferably 9 °C, 8 °C, 7 °C, 6 °C or 5 °C).

[0033] The above manufacturing method is a manufacturing method that utilizes the large memory effect of the semi-class rate hydrate according to one embodiment of the present invention. Such a melting-recrystallization process involves endothermic heat absorption during melting or exothermic heat generation during recrystallization, and is therefore suitable for use as a heat storage material.

[0034] [4. Use of semi-class rate hydrate] The semi-class rate hydrate according to one aspect of the present invention can be used in various conventionally known applications. For example, since the semi-class rate hydrate has a large latent heat, it can be used as a heat storage material (including a cold storage material). Alternatively, since the semi-class rate hydrate can take in gas into the cage-like crystal, it can be used as a gas absorbent. [Examples]

[0035] [Production Example 1] Using tetrabutylammonium cation as Component B and citric acid as Component C, a semi-clathrate hydrate was prepared. The specific procedure is as follows. 1. Tetrabutylammonium hydroxide (41 wt% aqueous solution, Tokyo Chemical Industry Co., Ltd.) was prepared. 2. Citric anhydride (Tokyo Chemical Industry Co., Ltd.) was added to the aqueous solution, mixed, and neutralized. The amount of citric anhydride added was such that the molar ratio of tetrabutylammonium cation:citrate anion was 3:1. In this way, a tetrabutylammonium-citric acid aqueous solution was obtained. 3. The aqueous solution was cooled to -6°C. The rate of temperature decrease was 0.5°C / min. 4. The aqueous solution was heated again to 9°C. The rate of temperature increase was 0.5°C / min. This decomposed the metastable phase that might have been formed. 5. The aqueous solution was cooled again to -6°C. The rate of temperature decrease was 0.5°C / min. In this way, a semi-clathrate hydrate was formed.

[0036] [Production Example 2] Using tetrabutylammonium cation as Component B and 1,2,3-propanetricarboxylic acid as Component C, a semi-clathrate hydrate was prepared. The specific procedure is as follows. 1. Tetrabutylammonium hydroxide (41 wt% aqueous solution, Tokyo Chemical Industry Co., Ltd.) was prepared. 2. 1,2,3-Propanetricarboxylic anhydride (Tokyo Chemical Industry Co., Ltd.) was added to the aqueous solution, mixed, and neutralized. The amount of 1,2,3-propanetricarboxylic anhydride added was such that the molar ratio of tetrabutylammonium cation:1,2,3-propanetricarboxylate anion was 3:1. In this way, a tetrabutylammonium-1,2,3-propanetricarboxylic acid aqueous solution was obtained. 3. The aqueous solution was cooled to -6°C. The rate of temperature decrease was 0.5°C / min. 4. The aqueous solution was heated again to 9°C. The rate of temperature increase was 0.5°C / min. This decomposed the metastable phase that might have been formed. 5. The aqueous solution was cooled again to -6°C. The rate of temperature decrease was 0.5°C / min. In this way, semi-class rate hydrates were formed.

[0037] [Example 1] The decomposition temperature and decomposition heat of the semi-class rate hydrates prepared in Production Examples 1 and 2 were measured. For the decomposition temperature, while heating 1 g of the semi-class rate hydrate at 0.1°C / min, the time point when the whole amount decomposed was visually confirmed. For the decomposition heat, using 20 mg of the semi-class hydrate as a sample, it was measured by differential scanning calorimetry while heating at 0.1°C / min. Also, the decomposition temperature and decomposition heat when the molar fraction of the guest substance with respect to water was changed were examined.

[0038] The results are shown in Figures 1 and 2. The semi-class rate hydrate with tetrabutylammonium-citric acid as the guest substance reached a maximum decomposition temperature of 12.8°C, and the decomposition heat at this time was 190 kJ / kg. The molar fraction of tetrabutylammonium-citric acid with respect to water at the maximum decomposition temperature was 0.011.

[0039] The semi-class rate hydrate with tetrabutylammonium-1,2,3-propanetricarboxylic acid as the guest substance reached a maximum decomposition temperature of 13.2°C, and the decomposition heat at this time was 195 kJ / kg. The molar fraction of tetrabutylammonium-1,2,3-propanetricarboxylic acid with respect to water at the maximum decomposition temperature was 0.011.

[0040] As shown by these results, the semi-class rate hydrates prepared in Production Examples 1 and 2 have a high decomposition heat and can be used as heat storage materials. Since the maximum decomposition temperature of these semi-class rate hydrates is about 13°C, they can be suitably used especially as heat storage materials for refrigeration devices.

[0041] [Example 2] The memory effect of the semi-class rate hydrates prepared in Production Examples 1 and 2 was examined. The specific procedure is as follows. 1. The semi-classrate hydrate was prepared as described in Production Examples 1 and 2. The molar fraction of the guest substance in water was set to the concentration that achieves the maximum decomposition temperature. 2. 1 g of the semi-classrate hydrate was maintained at a temperature equal to or higher than the decomposition temperature and allowed to stand for 30 minutes. 3. The temperature of the liquid obtained in Step 2 was decreased at a rate of 0.1 °C / min. The temperature at which recrystallization occurred in the semi-classrate hydrate was measured, and the difference between this temperature and the decomposition temperature (degree of supercooling) was recorded.

[0042] The results are shown in Figure 3. In the semi-classrate hydrate with tetrabutylammonium-citric acid as the guest substance, the degree of supercooling required for recrystallization of the semi-classrate hydrate was significantly different when the holding temperature was 18 °C or lower and when the holding temperature was 19 °C or higher. That is, it can be said that the memory effect of this semi-classrate hydrate was maintained up to 18 °C (decomposition temperature + about 5 °C).

[0043] In the semi-classrate hydrate with tetrabutylammonium-1,2,3-propanetricarboxylic acid as the guest substance, the degree of supercooling required for recrystallization of the semi-classrate hydrate was significantly different when the holding temperature was 19 °C or lower and when the holding temperature was 20 °C or higher. That is, it can be said that the memory effect of this semi-classrate hydrate was maintained up to 19 °C (decomposition temperature + about 6 °C). Therefore, less energy is required for recrystallization of the semi-classrate hydrate.

[0044] Here, it is known that the size and charge of guest molecules are one of the factors determining the properties of semi-classrate hydrates. R 1 ~R 4 When the structures are the same, tetraalkylammonium cations and tetraalkylphosphonium cations have almost the same molecular size and similar charge distributions among the constituent atoms. Therefore, it is considered that similar results can be obtained even when tetraalkylammonium cations are changed to tetraalkylphosphonium cations.

[0045] 〔Comparative Example〕 Component C: Instead of the tricarboxylic acid anion, a monocarboxylic acid anion or a dicarboxylic acid anion was employed to prepare a semi-clathrate hydrate. The memory effect of the obtained semi-clathrate hydrate was examined in the same manner as in Example 2.

[0046] The results are shown in Figs. 4 and 5. The results are also summarized below. ● Tetrabutylammonium - propionate · Mole fraction of guest substance with respect to water: 0.036 · Decomposition temperature: 18.1 °C · Temperature range in which the memory effect is maintained: None ● Tetrabutylammonium - acetate · Mole fraction of guest substance with respect to water: 0.032 · Decomposition temperature: 14.8 °C · Temperature range in which the memory effect is maintained: Decomposition temperature + about 1 °C ● Tetrabutylammonium - oxalate · Mole fraction of guest substance with respect to water: 0.017 · Decomposition temperature: 16.6 °C · Temperature range in which the memory effect is maintained: None ● Tetrabutylammonium - glutarate · Mole fraction of guest substance with respect to water: 0.018 · Decomposition temperature: 19.7 °C · Temperature range in which the memory effect is maintained: Decomposition temperature + about 1 °C

[0047] Thus, in the semi-clathrate hydrate in which a monocarboxylic acid anion or a dicarboxylic acid anion was employed instead of the component C: tricarboxylic acid anion, the memory effect was small. Therefore, it was shown that when recrystallizing the semi-clathrate hydrate according to the comparative example, more energy is required than in the case of the semi-clathrate hydrate according to the example.

Industrial Applicability

[0048] The present invention can be used for cold storage materials, gas absorbents, etc.

Claims

1. Semi-class rate hydrate containing the following components A to C: Component A: water; Component B: tetraalkylammonium cation and / or tetraalkylphosphonium cation; Component C: tricarboxylic acid anion.

2. In the above component B, the central nitrogen atom or phosphorus atom is bonded to four alkyl groups, among which, The carbon number of three of the above alkyl groups is all 3 to 5, The carbon number of one of the above alkyl groups is 1 to 6, The semi-class rate hydrate according to Claim 1.

3. The carbon number of the above component C is 5 to 7, The semi-class rate hydrate according to Claim 1.

4. In the recrystallization test performed by the following procedure, it recrystallizes into semi-class rate hydrate, The semi-class rate hydrate according to Claim 1:

1. Hold 1 g of the semi-class rate hydrate at a temperature 5 °C higher than the decomposition temperature of the semi-class rate hydrate for 30 minutes to cause a state change to a liquid.

2. Cool the above liquid at 0.1 °C / min until the temperature reaches 10 °C lower than the above decomposition temperature.

5. Substantially free of halogen compounds, The semi-class rate hydrate according to Claim 1.

6. A heat storage material containing the semi-class rate hydrate according to any one of Claims 1 to 5. Heat storage material.

7. A method for producing semi-class rate hydrate having a step of cooling a mixture containing the following components A to C: Component A: water; Component B: tetraalkylammonium cation and / or tetraalkylphosphonium cation; Component C: tricarboxylic acid anion.

8. Let the cooling temperature in the above cooling be T Ａ (°C), and let the decomposition temperature of the above semi-class rate hydrate be T (°C). Then, the following relationship holds: The manufacturing method according to Claim 7. T - T Ａ ≦ 10 °C

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