JPS6356276B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to materials for thermal energy storage. More specifically, the present invention relates to a thermal energy storage material suitable for use in devices for utilizing solar thermal energy as energy for hot water supply, space heating, and in particular cooling. In recent years, there has been much talk of an energy crisis, and various systems that effectively utilize solar energy are being developed. Hot water is obtained from solar heat, and the hot water can be used as is or after being adjusted to an appropriate temperature for heating, bathing, etc.
So-called solar water heaters, which are used directly for cooking, washing, etc., have already been put into practical use. In addition, the hot water obtained by collecting solar heat with a collector is not only used for heating and kitchen purposes, but also for cooling by using so-called solar-powered refrigerators, which use this water as a heat source to drive refrigerators. The development of a system for this purpose is currently being strongly advanced. The mainstream of solar-powered refrigerators for air conditioning are compression refrigerators driven by organic crankine cycle steam engines that use fluorocarbons as the operating medium, and aqueous solutions such as lithium bromide, lithium chloride, or glycol that use water as the refrigerant. These include hot water absorption type refrigerators. By the way, in the above-mentioned system that uses solar thermal energy as a heat source, solar heat is It is necessary to temporarily store energy in a heat storage tank so that it can be extracted as needed. Therefore, in such a system as described above, a heat storage tank is indispensable, and the selection of the material for thermal energy storage used in the heat storage tank is an extremely important issue. The properties generally required for thermal energy storage materials are high specific heat and/or latent heat of fusion, good thermal stability, non-corrosion, low vapor pressure and non-flammability, and non-toxicity. It is a characteristic of things. In particular, when using a material that stores thermal energy as latent heat, the amount of heat storage can be increased, so the volume occupied by the energy storage material can be reduced, which is convenient in practice. Materials useful for storing thermal energy as latent heat have the property of reversibly transitioning from one form to another upon heating to a specific transition temperature. Examples of thermal energy storage materials that involve such a transition include hydrated calcium chloride hexahydrate, magnesium iodide hexahydrate, sodium sulfate decahydrate, barium hydroxide octahydrate, and ammonium alum dodecahydrate. Inorganic salts, organic substances such as tetradecane, pentadecane, decanol, sodium acetate/sodium chloride mixtures, and low molecular weight organic acid salts have been proposed. However, when these inorganic salts and low molecular weight organic acid salts are used, there is a problem in that the equipment is severely corroded. For this reason, the containers used are often corrosion-resistant metal containers, but these containers are generally heavy and have high thermal conductivity. Additionally, such containers are also generally expensive, adding to the cost of the thermal energy storage device. Furthermore, damage and leakage of containers and pipelines is a constant concern;
Seepage of these solutions or molten salts occurs.
Further, when an inorganic organic hydrate is used as a thermal energy storage material, there is a drawback that insoluble substances increase when thermal cycles of melting and solidification are repeated, resulting in a decrease in performance. A composition with a desired melting point can be obtained by mixing inorganic salts with different inorganic salts, but if a mixture of salts that does not match the eutectic composition is selected, a separation phenomenon may occur when the molten liquid solidifies. It happens. For this purpose, only mixtures of eutectic composition are used as materials for thermal energy storage. However, eutectic compositions of these inorganic salts have the problem of supercooling and require the addition of seed crystals, in which case the above-mentioned separation phenomenon occurs. Of course, there is also the drawback that it is difficult to add seed crystals into the normally sealed heat storage tank after each melting-solidification thermal cycle. On the other hand, when paraffin is used as a thermal energy storage material,
It has a wide range of melting points and is not practical due to its high manufacturing cost. Furthermore, as mentioned above, materials that store thermal energy as latent heat generally have a drawback of slow response speed in heat exchange with a heating medium. In other words, thermal energy storage materials, especially solar thermal energy storage materials, have various required characteristics as described above, and these required characteristics cannot be determined unless they are actually tested as storage materials. There are many factors. Therefore, it is impossible to select a material for thermal energy storage, especially a material for solar thermal energy storage, based only on some physical property values, and it has been difficult to search for such a material. However, as a result of intensive search for substances suitable as thermal energy storage materials, the present inventors discovered that acid amide represented by the following general formula () has excellent performance as a thermal energy storage material. This completes the present invention. C _o H _2o+1 −CO−NH−C _p H _2p+1 …() In the above formula, n is an integer from 15 to 18, and p is an integer from 1 to 18. In the above general formula, if the value of n is less than 15, the heat of fusion will generally be small and it is not suitable for thermal energy storage materials of the type that utilize latent heat.
Moreover, those in which the value of n exceeds 18 are not preferred because the acid amide cannot be obtained easily and inexpensively. This is because, as described below, acid amides are produced from fatty acids and alkylamines, but it is difficult to obtain fatty acids with more than 18 carbon atoms. As mentioned above, in fluorocarbon turbine-driven compression refrigerators and hot water absorption refrigerators, which are suitable for solar-powered refrigerators that are driven using thermal energy, especially solar thermal energy, There is an optimal heat source temperature to operate the refrigerator efficiently. The temperature of this heat source is usually 90 to 100°C.
Therefore, in systems where the heat medium from the heat storage tank is used as a direct heat source for the refrigerator, such as cooling systems using solar heat, 90% is used as a thermal energy storage material in the heat storage tank.
It is preferable to use a latent heat of ~100°C. However, since the melting point of an acid amide changes depending on the number of carbon atoms in the alkyl group, the relationship between the melting point of an acid amide and the number of carbon atoms in the alkyl group is shown in FIG. 1. From this figure, it was found that the melting point of N-ethylstearic acid amide was outside the range of 90 to 100°C. Therefore, acid amides that have a melting point in the range of 90 to 100°C and a sufficiently high heat of fusion and are particularly preferable as thermal energy storage materials include N-methylstearamide, N-octadecylpalmitic acid amide, and N-octadecyl Stearic acid amide or N-hexadecyl stearic acid amide. As described later, these compounds are also used as one of the raw materials for producing stearic acid and palmitic acid, and are preferred acid amides because stearic acid and palmitic acid are inexpensive and abundant raw materials. The acid amide of the invention can be prepared, for example, from a fatty acid corresponding to the acid amide of the invention and a corresponding alkyl primary amine. That is, the present invention can be easily carried out in a high yield by heating and mixing stearic acid, palmitic acid, etc. with methylamine, octadecylamine, etc. in the presence of an appropriate solvent such as toluene or xylene, and distilling off the produced water. acid amide can be produced. The thermal energy storage material of the present invention is suitable for use in devices that utilize solar energy for air conditioning and hot water supply, as well as for heat storage materials inside pocket warmers, hair curling rollers, and other heat storage applications. It is possible. Next, the present invention will be explained in detail with reference to Examples. Example 1 [Synthesis of N-octadecyl stearic acid amide] 10 kg of stearic acid, 9.4 kg of octadecylamine (Furmin 80 manufactured by Kao Soap Co., Ltd.), xylene 10,
Stainless steel 40 with stirrer, cooling tube and thermometer
The mixture was charged into a reactor, kept at about 140°C, and reacted for about 5 hours under xylene reflux. After the reaction was completed, xylene as a solvent and water as a by-product were removed by distillation. The obtained reaction product was heated and dried at 100° C. for 24 hours under reduced pressure of 4 to 5 mmHg. Yield is 18.5Kg
It was hot. The acid value of this product was 5.0. The melting point and heat of fusion of this product were measured using a differential scanning calorimeter DS-2 manufactured by PerkinElmer.
They were 93.8°C and 50.4 cal/g, respectively. Example 2 [Synthesis of N-hexadecylstearamide] Stearic acid 7.5Kg, hexadecylamine 6.4Kg
and xylene 10 in a stainless steel 40 reactor equipped with a stirrer, cooling tube, and thermometer, and approx.
The reaction was carried out at 200°C for 5 hours. After the reaction was completed, the reactor was cooled to 100°C, 15% of benzene was added, and by-product water was removed by azeotropy while the benzene was refluxed. The reaction solution was further transferred to a container containing 60% hot benzene, cooled slowly, and the acid amide compound was recovered by recrystallization. The yield was 12.3Kg. The melting point and heat of fusion of this product were measured in the same manner as in Example 1, and were found to be 90°C and 45.4 cal/g, respectively. Example 3 [Synthesis of N-octadecylpalmitic acid amide] Palmitic acid 10Kg, octadecylamine 10.5Kg
were reacted in the same manner as in Example 1. Yield is 18.0
It was Kg. The melting point and heat of fusion of the product are each 92
℃, 37 cal/g. Example 4 [Synthesis of N-methylstearic acid amide] 20 kg of stearic acid was maintained at 190°C in a stainless steel 40 reactor equipped with a stirrer, a cooling tube, and a thermometer. 6 kg of methylamine was gradually blown into the reaction solution in gaseous form, and the reaction was allowed to proceed for 6.5 hours. After the reaction was completed, the product was recrystallized from 250 kg of benzene to obtain purified N-methylstearamide. The melting point and heat of fusion were 92°C and 56 cal/g, respectively. Example 5 [Performance evaluation as a heat storage material] 9.0 kg of each of the acid amide compounds obtained in Examples 1, 2, 3, and 4 was taken, and a diameter of 5 cm was taken.
They were each sealed in 10 stainless steel cylindrical tubes with a length of 50 cm, and these were placed in a closed container. in this container
The sample was heated and melted from the outside of the cylindrical tube by flowing hot water at 100°C. After melting, instead of hot water, 80°C hot water was flowed at a rate of 100 ml/min to exchange heat with the cylindrical tube, and the temperature of the hot water at the outlet was measured. The results are shown in the table below.

[Table] In the performance evaluation of these four types of acid amides, almost no supercooling phenomenon was observed. Furthermore, no insoluble matters such as precipitates were particularly observed, and the responsiveness of heat exchange was also good. The results of these Examples show that the acid amide compound of the present invention exhibits excellent heat storage properties.

[Brief explanation of drawings]

FIG. 1 is a graph showing the melting point of N-alkylstearamide.

Claims (1)

[Claims] 1. A thermal energy storage material comprising an acid amide represented by the following general formula (). C _o H _2o+1 −CO−NH−C _p H _2p+1 …() In the above formula, n is an integer from 15 to 18, and p is an integer from 1 to 18. 2 The acid amide represented by the general formula () is
The thermal energy storage material according to claim 1, which is N-methylstearamide, N-octadecylpalmitate amide, N-octadecylstearamide or N-hexadecylstearamide.