Chemical heat storage material, its manufacturing method, and chemical heat pump

Abstract

A chemical heat storage material comprising a sulfuric acid salt of an alkaline earth metal and a compound of an alkali metal.

Description

[Technical field]

[0001] The present invention relates to a chemical heat storage material, a manufacturing method thereof, and a chemical heat pump. [Background technology]

[0002] In recent years, carbon dioxide emission regulations have required a reduction in the use of fossil fuels, and in addition to energy conservation in each manufacturing process, it is necessary to promote the use of waste heat. Hot water thermal storage of water at temperatures below 100°C is known as a means of utilizing waste heat. However, there are problems with hot water thermal storage, such as (1) the impossibility of long-term heat storage due to heat dissipation losses, (2) the difficulty of compacting the thermal storage equipment due to the small amount of sensible heat required, and (3) the output temperature is non-steady and gradually drops depending on the amount of use. Therefore, in order to promote the use of waste heat, it is necessary to develop a more efficient thermal storage technology.

[0003] Heat storage methods other than hot water heat storage include heat storage methods that utilize phase transitions and chemical heat storage methods. Heat storage methods that utilize phase transitions utilize the inflow and outflow of latent heat and sensible heat that occurs due to the phase transition (phase change) of a substance. This method has the advantage that it can operate in low temperature ranges and the phase transition point can be designed to a certain degree.

[0004] Among the heat storage materials used in the heat storage method utilizing phase transition, sodium acetate-based materials and polyhydric sugar alcohol-based materials such as erythritol are known as solid-liquid phase change materials (Patent Document 1). For example, sodium acetate trihydrate has a melting point of approximately 58°C, and this phase transition between solid and liquid is utilized. Furthermore, sodium acetate itself is also excellent in safety and stability.

[0005] Chemical heat storage is a more efficient heat storage technology. Because it involves chemical changes such as the adsorption and hydration of substances, it has the advantage of being able to store more heat per unit weight than heat storage methods that utilize the latent and sensible heat of the materials themselves (such as water and molten salts), such as heat storage methods that utilize phase transitions.

[0006] As chemical heat storage methods, the following methods have been proposed: the water vapor adsorption / desorption method, which utilizes the adsorption / desorption of water vapor in the atmosphere; a method that utilizes ammonia absorption (ammine complex formation reaction) and desorption reaction for metal salts; and a method that utilizes the reaction due to the adsorption / desorption of organic substances such as alcohol. Considering the burden on the environment and the simplicity of the equipment, the water vapor adsorption / desorption method is the most advantageous.

[0007] The water vapor adsorption / desorption method utilizes the reversible reaction of a chemical heat storage material. As a chemical heat storage material used in the water vapor adsorption / desorption method, oxides and hydroxides of alkaline earth metals such as calcium or magnesium are known (Patent Document 2). The reaction formula when calcium or magnesium is used as the alkaline earth metal is shown below.

[0008] CaO+H 2 O⇔Ca(OH) 2 : ΔH = -109.2 kJ / mol MgO+H 2 O⇔Mg(OH) 2 : ΔH = -81.0 kJ / mol

[0009] In each formula, the reaction to the right is an exothermic hydration reaction of calcium oxide or magnesium oxide. Conversely, the reaction to the left is an endothermic dehydration reaction of calcium hydroxide or magnesium hydroxide. Heat can be stored by the progress of the dehydration reaction of calcium hydroxide or magnesium hydroxide, and the stored thermal energy can be dissipated or supplied to the outside by the progress of the hydration reaction of calcium oxide or magnesium oxide.

[0010] However, the heat storage method utilizing phase transition as described in Patent Document 1 has problems such as a low amount of heat storage per unit weight (heat storage density), which results in a large weight and volume of the entire device, is relatively expensive, and the heat storage and release temperature is limited to near the melting point.

[0011] In addition, chemical heat storage methods (e.g., Patent Document 2) that use oxides and hydroxides of alkaline earth metals (such as magnesium hydroxide) have excellent heat storage density, but have the problem that the temperature range in which heat can be stored is generally 250°C or higher, and therefore low-temperature heat sources of 150°C or lower cannot be used.

[0012] Low-temperature waste heat below 150°C faces the issue that most of it is discharged unused due to limited uses at the site of generation, and there is a demand for its effective use.

[0013] A survey of factory waste heat by industry also reported that there is a large amount of waste heat in the temperature range of around 100 to 150°C (Non-Patent Document 1). In fact, a survey of unused heat by temperature range also showed that there is a very high need for utilizing waste heat below 150°C (Non-Patent Document 2). Therefore, efforts are being made to develop heat storage technology that can be applied in low temperature ranges.

[0014] Sulfate compounds of alkaline earth metals are being considered as promising chemical heat storage materials that can utilize low-temperature waste heat (Patent Document 3). When used in the water vapor adsorption / desorption method, magnesium sulfate, which is one of the sulfate compounds of alkaline earth metals, has a theoretical capacity of 2.8 GJ / m 3 It has a high energy density.

[0015] An example of a reaction formula when magnesium sulfate is used as a chemical heat storage material in the water vapor adsorption / desorption method is shown below. MgSO 4 mH 2 O(s)⇔MgSO 4 nH 2 O(s)+(mn)H 2 O(g) Here, m and n are the average values ​​of the hydration numbers of magnesium sulfate, and satisfy the relationship m>n≧1.

[0016] In each equation, the reaction to the right is the endothermic dehydration reaction of magnesium sulfate, while the reaction to the left is the exothermic hydration reaction of magnesium sulfate.

[0017] However, the chemical heat storage material using sulfates of alkaline earth metals does not have sufficient characteristics (reaction temperature, reaction efficiency, reactivity, etc.), and there is room for improvement. In particular, magnesium sulfate has a high energy density in theory, but in reality, the reactivity of the chemical reaction in the low temperature range (for example, 60 to 150 ° C) is insufficient, so the energy cannot be used efficiently. In the case of magnesium sulfate, there is a problem with low hydration reactivity, and it has been reported that there is a problem that the rehydration process after dehydration takes a long time (Non-Patent Document 3). [Prior art documents] [Patent documents]

[0018] [Patent Document 1] Japanese Patent Publication No. 52-149659 [Patent Document 2] Japanese Patent Publication No. 6-213529 [Patent Document 3] Japanese Patent Application Publication No. 2018-040554 [Non-patent literature]

[0019] [Non-Patent Document 1] Japan Science and Technology Agency, Research and Development Strategy Center, Environment and Energy Unit, Technical Survey Report on Advanced Medium- and Low-Temperature Heat Utilization (2015) [Non-Patent Document 2] Research Association for Innovative Thermal Energy Utilization Technology Development Center, Report on the Actual State of Waste Heat in the Industrial Sector (2019) [Non-Patent Document 3] K.Porsern et al., Thermochimica Acta, Volume 611, 10 July 2015, Pages 1-9 Summary of the Invention [Problem to be solved by the invention]

[0020] Thus, it remains an important task to further improve the properties of the chemical heat storage material, such as its reactivity. In particular, it is necessary to develop a chemical heat storage material that is highly reactive in the low temperature range in terms of improving the heat storage and release efficiency and expanding the applicable temperature range of the heat storage and release system.

[0021] An object of the present invention is to provide a chemical heat storage material that utilizes the dehydration and hydration reactions of alkaline earth metal sulfates and has excellent reactivity in a low temperature range. [Means for solving the problem]

[0022] In order to solve the above problems, the inventors conducted intensive research while taking into consideration the conventional technology, and discovered that a chemical heat storage material containing an alkaline earth metal sulfate and an alkali metal compound exhibits excellent reactivity in the low temperature range, thereby completing the present invention.

[0023] The first aspect of the present disclosure relates to a chemical heat storage material that includes an alkaline earth metal sulfate and an alkali metal compound.

[0024] In the chemical heat storage material, the content of the alkali metal compound is preferably 0.1 to 50 mol % relative to the alkaline earth metal sulfate.

[0025] In the chemical heat storage material, the alkaline earth metal constituting the alkaline earth metal sulfate is preferably at least one selected from the group consisting of magnesium and calcium.

[0026] In the chemical heat storage material, the alkali metal compound is preferably at least one selected from the group consisting of alkali metal halides and hydroxides.

[0027] In the chemical heat storage material, the alkali metal constituting the alkali metal compound is preferably at least one selected from the group consisting of lithium, sodium, and potassium.

[0028] In the chemical heat storage material, the alkali metal compound is preferably a lithium halide.

[0029] In the chemical heat storage material, the alkali metal compound is preferably at least one selected from the group consisting of lithium chloride, lithium bromide, and lithium hydroxide.

[0030] A second aspect of the present disclosure relates to a method for producing a chemical heat storage material, the method including a step of mixing the alkaline earth metal sulfate and the alkali metal compound.

[0031] A third aspect of the present disclosure relates to a chemical heat pump that has the chemical heat storage material and utilizes the dehydration endothermic reaction and the hydration exothermic reaction of the chemical heat storage material. Effect of the Invention

[0032] According to the present invention, it is possible to provide a chemical heat storage material that is excellent in reactivity in a low temperature range by utilizing the dehydration and hydration reactions of an alkaline earth metal sulfate. [Brief description of the drawings]

[0033] [Figure 1] 1 is a graph showing the weight change (%) in an isothermal reaction test in the chemical thermal storage materials of the examples and comparative examples. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0034] Hereinafter, an embodiment of the present invention will be described in detail. [Chemical heat storage material] The chemical heat storage material of the present disclosure includes an alkaline earth metal sulfate and an alkali metal compound. Chemical heat storage refers to heat storage that utilizes heat generation and endothermic heat associated with a reversible chemical reaction of a substance. Chemical heat storage material refers to a material capable of chemical heat storage.

[0035] The chemical heat storage material of the present disclosure is a heat storage material that utilizes the endothermic dehydration reaction and the exothermic hydration reaction caused by an alkaline earth metal sulfate. The reaction formulas of the endothermic dehydration reaction and the exothermic hydration reaction caused by an alkaline earth metal sulfate are shown below. MSO 4 mH 2 O⇔MSO 4 nH 2 O+(mn)H 2 O Here, M is an alkaline earth metal, m and n are average values ​​of the hydration numbers of sulfates of the alkaline earth metal, and the relationship m>n≧1 is satisfied.

[0036] In the formula, the reaction to the right is the endothermic dehydration reaction of the alkaline earth metal sulfate. Conversely, the reaction to the left is the exothermic hydration reaction of the alkaline earth metal sulfate. The chemical heat storage material of the present disclosure can store heat by the progress of the dehydration reaction of the alkaline earth metal sulfate, and can dissipate the stored heat energy or supply it to the outside by the progress of the hydration reaction of the alkaline earth metal sulfate.

[0037] The sulfate of an alkaline earth metal of the present disclosure is MSO, where M is an alkaline earth metal. 4 This refers to normal salt, which is expressed as:

[0038] The sulfate of an alkaline earth metal is preferably at least one selected from the group consisting of magnesium sulfate and calcium sulfate, and more preferably magnesium sulfate.

[0039] The alkaline earth metal constituting the alkaline earth metal sulfate is preferably at least one selected from the group consisting of magnesium and calcium, and more preferably magnesium.

[0040] An example of the reaction formula when magnesium or calcium is used as the alkaline earth metal is shown below.

[0041] MgSO 4 7H 2 O(s)⇔MgSO 4 H2 O(s)+6H 2 O(g) CaSO 4 2H 2 O(s)⇔CaSO 4 1 / 2H 2 O(s)+3 / 2H 2 O(g)

[0042] In each formula, the reaction to the right is an endothermic dehydration reaction of magnesium sulfate or calcium sulfate. Conversely, the reaction to the left is an exothermic hydration reaction of magnesium sulfate or calcium sulfate. The chemical heat storage material of the present disclosure can store heat by the progress of the dehydration reaction of magnesium sulfate or calcium sulfate, and can dissipate the stored heat energy or supply it to the outside by the progress of the hydration reaction of magnesium sulfate or calcium sulfate.

[0043] The chemical heat storage material of the present disclosure preferably contains an alkaline earth metal sulfate as its main component. The content of the alkaline earth metal sulfate is preferably 60% by weight or more, more preferably 70% by weight or more, and even more preferably 85% by weight or more, relative to the chemical heat storage material. Also, it is preferably 99.99% by weight or less. If the content of the alkaline earth metal sulfate is less than the above range, the heat storage density may decrease and the heat storage efficiency may be insufficient. If the content of the alkaline earth metal sulfate is more than the above range, it becomes difficult to achieve the improvement in responsiveness by using an alkali metal compound.

[0044] The alkali metal compound of the present disclosure is not particularly limited as long as it is a compound containing an alkali metal and exhibits the effects of the present invention. The alkali metal compound is preferably a salt having hygroscopic properties.

[0045] Examples of salts capable of forming the corresponding hydrates include, as they are easy to handle, alkali metal halides (chlorides, bromides, etc.), hydroxides, carbonates, acetates, nitrates, and sulfates, etc. These may be used alone or in combination of two or more.

[0046] The alkali metal compound is preferably at least one selected from the group consisting of alkali metal halides and hydroxides, and more preferably an alkali metal halide.

[0047] The alkali metal constituting the alkali metal compound is not particularly limited, but is preferably at least one selected from the group consisting of lithium, sodium, and potassium, more preferably at least one selected from the group consisting of lithium and sodium, and even more preferably lithium.

[0048] More specifically, the lithium compound is preferably at least one selected from the group consisting of lithium halides and lithium hydroxide, and more preferably lithium halide, because it has superior reactivity in the low temperature range.

[0049] The lithium compound is preferably at least one selected from the group consisting of lithium chloride, lithium bromide, and lithium hydroxide, more preferably at least one selected from the group consisting of lithium chloride and lithium bromide, and even more preferably lithium chloride or lithium bromide, because it has superior reactivity in the low temperature range.

[0050] The sodium compound is preferably at least one selected from the group consisting of sodium halide and sodium hydroxide, and more preferably at least one selected from the group consisting of sodium chloride, sodium bromide and sodium hydroxide.

[0051] Furthermore, the potassium compound is preferably at least one selected from the group consisting of potassium halide and potassium hydroxide, and more preferably at least one selected from the group consisting of potassium chloride, potassium bromide and potassium hydroxide.

[0052] The content of the alkali metal compound in the chemical heat storage material of the present disclosure is preferably 0.1 to 50 mol% relative to the sulfate of the alkaline earth metal. If the content of the alkali metal compound is less than the above range, it becomes difficult to achieve the improvement in reactivity by using the alkali metal compound. In addition, if the content of the alkali metal compound is more than the above range, the amount of heat stored per unit volume or unit weight by the chemical heat storage material may decrease. The content of the alkali metal compound is preferably 0.5 to 40 mol%, more preferably 1.0 to 30 mol%, further preferably 2.0 to 25 mol%, particularly preferably 5.0 to 20 mol%, and most preferably 10 to 20 mol%, relative to the sulfate of the alkaline earth metal. By adjusting the content of the alkali metal compound, the dehydration endothermic temperature of the chemical heat storage material can be controlled.

[0053] The chemical heat storage material of the present disclosure may contain other components (components other than alkaline earth metal sulfates and alkali metal compounds) within the scope of the effects of the present invention. Such optional components include chemical heat storage components other than alkaline earth metal sulfates; and components that do not exhibit chemical heat storage properties (for example, binders, reinforcing materials, additives, etc.).

[0054] The shape of the chemical heat storage material of the present disclosure is not particularly limited. For example, the shapes include powder, granules, and molded bodies. As long as the properties as a chemical heat storage material are not impaired to an extent that they can be implemented, any shape can be selected according to the embodiment of the consumer.

[0055] [Method of manufacturing chemical heat storage material] The method for producing the chemical heat storage material of the present disclosure is not particularly limited, but may be a method for producing a chemical heat storage material that includes a step of mixing the sulfate of the alkaline earth metal and the compound of the alkali metal.

[0056] As a specific example of a method for producing a chemical heat storage material, a method of stirring and mixing an alkaline earth metal sulfate, an alkali metal compound, and an optional component contained in the chemical heat storage material as necessary can be mentioned. At this time, all components may be mixed and stirred at once, or after stirring and mixing any two or more components, other components may be further mixed and stirred in the mixture.

[0057] The order of blending and adding each component may be appropriately selected. An alkali metal compound may be added to an alkaline earth metal sulfate and mixed; an alkaline earth metal sulfate may be added to an alkali metal compound and mixed. The order of adding each optional component such as a binder, a reinforcing material, and an additive may also be appropriately selected.

[0058] The alkaline earth metal sulfate and the alkali metal compound used in the production are preferably in powder form. In this case, the chemical heat storage material can be obtained in the form of powder.

[0059] The stirring and mixing method is not limited as long as each component, particularly the alkaline earth metal sulfate and the alkali metal compound, is uniformly mixed. The alkaline earth metal sulfate and the alkali metal compound may form a composite compound. The stirring and mixing may be performed by at least one method selected from the group consisting of sieving, crushing, and pulverization. For example, a ball mill may be used as the device.

[0060] When manufacturing a chemical thermal storage material having a powder, granule, or molded shape, it is possible to apply a known method. For example, when manufacturing a powdered chemical thermal storage material, a sieving, crushing, and / or pulverization process can be applied.

[0061] When manufacturing a granulated chemical heat storage material, a granulation process such as extrusion granulation, rolling granulation, fluidized bed granulation, or spray drying can be applied. Depending on the granulation process and the type of sulfate, dry granulation or wet granulation can be used. When wet granulation is used, a suitable granulated molded body can be obtained by drying and sieving after granulation.

[0062] When producing a molded chemical thermal storage medium, a molding process such as press molding, injection molding, blow molding, vacuum molding, or extrusion molding can be applied.

[0063] (Application) When the chemical heat storage material of the present disclosure is applied to a chemical heat pump, the dehydration endothermic reaction and the hydration exothermic reaction of the chemical heat storage material of the present disclosure are utilized, so that heat in a low temperature range (for example, 60 to 150°C) can be efficiently utilized. Here, the chemical heat pump refers to a heat storage and release system using a chemical heat storage material.

[0064] By using the dehydration endothermic reaction of the chemical heat storage material of the present disclosure, it is possible to absorb and store heat from a heat source such as factory exhaust heat in a low temperature range (for example, 60 to 150 ° C), which has been difficult to use in the past. The dehydrated chemical heat storage material can be easily maintained in a heat storage state by keeping it in a dry state, and can be carried to a desired location while maintaining the heat storage state. When dissipating heat, a hydration exothermic reaction occurs by contacting it with water, preferably water vapor, and the generated hydration reaction heat (in some cases, water vapor sorption heat) can be taken out as thermal energy. In addition, cold can be generated by performing water vapor sorption on one side of the airtight chain space and evaporating water on the other side.

[0065] In addition, the chemical heat storage material of the present disclosure is also suitable for effectively utilizing the heat of exhaust gas discharged from engines, fuel cells, etc. For example, the heat of exhaust gas can be utilized to shorten the warm-up operation of a car, improve the amenity of passengers, improve fuel efficiency, and reduce the harmfulness of exhaust gas by improving the activity of exhaust gas catalysts. In particular, since the load due to operation of an engine is not constant and the exhaust output is unstable, direct utilization of the exhaust heat from the engine is inevitably inefficient and inconvenient. By utilizing the chemical heat storage material of the present disclosure, the exhaust heat from the engine is chemically stored once and heat is output according to the heat demand, making it possible to utilize the exhaust heat more ideally. EXAMPLES

[0066] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0067] (Evaluation method) The chemical heat storage materials obtained in each of the examples and comparative examples were subjected to thermal evaluation using a differential thermobalance (TGD9600, Advance Riko Co., Ltd.). Specifically, a 25 mg sample was used, and a platinum cell was used. Under argon gas flow (100 mL / min.), the temperature was raised from room temperature to 60°C at 10°C / min., and then the temperature was kept constant while measurements were taken for 4200 seconds, and the weight change was measured over time (isothermal reaction test). "Weight change (%)" is expressed as a relative value of the weight of the sample at each time point when the weight of the sample at the start of the reaction was taken as 100 (%).

[0068] The "weight loss rate (%)" was calculated by subtracting the weight (%) of the sample at the start of the reaction from the weight (%) of the sample after 3600 seconds had elapsed. The weight loss rate (%) indicates the weight loss caused by the dehydration of magnesium sulfate. The higher the weight loss rate (%), the faster the endothermic dehydration reaction proceeds, i.e., the higher the reactivity.

[0069] Example 1 As the sulfate of alkaline earth metal, magnesium sulfate heptahydrate (MgSO 4 7H 2 O, Fujifilm Wako Pure Chemical Industries, Ltd., special grade, purity 99.5%), 100 mol parts, and lithium chloride monohydrate (LiCl H 2 O (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., special grade, purity 99.9%) was thoroughly mixed in an agate mortar until homogeneous, to obtain a chemical heat storage material. The obtained chemical heat storage material was evaluated by the above evaluation method. The results are shown in Table 1 and Figure 1.

[0070] (Example 2-3) A chemical heat storage material was obtained in the same manner as in Example 1, except that the blending amount of each component was changed as shown in Table 1. The obtained chemical heat storage material was evaluated by the above-mentioned evaluation method. The results are shown in Table 1 and FIG.

[0071] (Examples 4-6) Instead of lithium chloride monohydrate, lithium bromide monohydrate (LiBr H 2 A chemical heat storage material was obtained in the same manner as in Example 1, except that the amount of each component was changed as shown in Table 1, using 1,000g of ...

[0072] Comparative Example 1 As an alkaline earth metal sulfate, magnesium sulfate heptahydrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., special grade, purity 99.5%) was evaluated using the above evaluation method. The results are shown in Table 1 and Figure 1.

[0073] [Table 1]

[0074] From Table 1 and Figure 1, it was confirmed that the chemical heat storage materials of Examples 1 to 6 containing an alkali metal compound such as lithium chloride or lithium bromide have a large weight loss rate and excellent reactivity compared to the chemical heat storage materials of the comparative examples that do not contain an alkali metal compound. From this, it can be seen that the chemical heat storage materials of Examples 1 to 6 have high reactivity even in a low temperature range and can efficiently utilize heat in a low temperature range.

Claims

1. Contains sulfates of alkaline earth metals and compounds of alkali metals, The chemical heat storage material, wherein the alkali metal compound is at least one alkali metal compound selected from the group consisting of alkali metal halides, acetates, nitrates, sodium hydroxide, and potassium hydroxide.

2. The chemical heat storage material according to claim 1, wherein the content of the alkali metal compound is 0.1 to 50 mol% relative to the alkaline earth metal sulfate.

3. The chemical heat storage material according to claim 1 or 2, wherein the alkaline earth metal constituting the alkaline earth metal sulfate is at least one selected from the group consisting of magnesium and calcium.

4. The chemical heat storage material according to any one of claims 1 to 3, wherein the alkali metal compound is at least one selected from the group consisting of alkali metal halides, sodium hydroxide, and potassium hydroxide.

5. The chemical heat storage material according to any one of claims 1 to 4, wherein the alkali metal constituting the alkali metal compound is at least one selected from the group consisting of lithium, sodium and potassium.

6. The chemical heat storage material according to any one of claims 1 to 5, wherein the alkali metal compound is a lithium halide.

7. The chemical heat storage material according to any one of claims 1 to 5, wherein the alkali metal compound is at least one selected from the group consisting of lithium chloride and lithium bromide.

8. A method for producing a chemical heat storage material according to any one of claims 1 to 7, A method for producing a chemical heat storage material, comprising: mixing the alkaline earth metal sulfate and the alkali metal compound.

9. The chemical heat storage material according to any one of claims 1 to 7 is provided. A chemical heat pump that utilizes the dehydration endothermic reaction and the hydration exothermic reaction of the chemical heat storage material.

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