JPS6356919B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a latent heat type heat storage material, and particularly to a heat storage material composition with excellent durability. In recent years, energy problems have become widely recognized, and various alternative energies to oil are being considered, one of which is the use of solar energy as a heat source. However, since this solar energy can only be used during the daytime, especially when the weather is clear, it cannot be used as a stable heat source unless some kind of heat storage device is used. Most conventional heat storage devices have been of the so-called sensible heat type, in which hot water or high-temperature rocks are filled in an insulated container.
Recently, heat storage using latent heat has been attracting attention. Various types of latent heat storage materials can be considered, such as Na ₂ SO ₄ 10H ₂ O,
Inorganic hydrated salts such as Na ₂ S ₂ O ₃ ·5H ₂ O, AlK(SO ₄ ) ₂ ·12H ₂ O, n-paraffin, stearic acid, polyethylene, naphthalene, etc. have been investigated. Among these, inorganic hydrated salts are considered to be the most promising and have been extensively studied because of their excellent economic efficiency and safety. In particular, Na ₂ SO ₄・10H ₂ O is easy to obtain,
It is attracting attention because of its low price and safety. However, in order to utilize this Na ₂ SO ₄ .10H ₂ O as a heat storage material, two problems had to be solved: supercooling and phase separation. The present inventors have conducted extensive studies on methods for solving the two problems of supercooling and phase separation of inorganic hydrated salts, such as Na ₂ SO ₄ 10H ₂ O, and making them function as heat storage materials. As a result, the invention of the prior application (Japanese Patent Application No. 158224-1982) was completed. That is, it is a latent heat type heat storage material in which a seed crystal and a water-insoluble resin are added to an inorganic hydrated salt to form a uniform gel-like dispersion system in the molten state as a whole. The seed crystals in this heat storage material are gel-like even when the system is in a molten state, so they do not fall to the bottom and can be uniformly dispersed throughout. Generation and growth can occur uniformly throughout the system. As described above, the prior invention of the present inventors has solved the biggest problem when using an inorganic hydrated salt as a heat storage material. Based on this prior invention, the present inventors have
Further studies were carried out to put Na ₂ SO ₄ 10H ₂ O-based heat storage materials into practical use. That is, Na ₂ B ₄ O ₇・10H ₂ O is added as a seed crystal to Na ₂ SO ₄・10H ₂ O, and a water-insoluble super absorbent resin is added to this to create a material in which the entire system is gelled. , we discussed its practical application. The function required of a heat storage material is, of course, to stably radiate and absorb a certain amount of heat at a constant temperature during repeated cycles of melting and solidification over a long period of time. In general, the durability of heat storage materials is at least
It is said that 1000 cycles are required. The present inventors conducted a melting/solidification cycle test on the earlier Na ₂ SO ₄ 10H ₂ O based heat storage material based on the earlier invention, and as a result, as is clear from Comparative Example 1 below. Up to 100 cycles, it releases a certain amount of heat for a certain period of time with a melting point of 30℃, maintaining good storage and heat dissipation functions, but after 200 cycles, deterioration occurs and the melting point drops to 28-26℃. And it became impossible to maintain a constant temperature. In addition, the amount of latent heat storage is originally 50 cal/g.
This decreased by 28% to 36 cal/g. When this deteriorated material was removed from the melt and examined, many large-diameter anhydrous Na ₂ SO ₄ crystals were observed. The cause of the deterioration of this material is complex and has many factors, and is not clear, but one of the causes is:
The phase equilibrium of the Na ₂ SO ₄ /H ₂ O system is not simple, and the hydrated salt is not only Na ₂ SO ₄・10H ₂ O but also metastable.
Na ₂ SO ₄・7H ₂ O may also exist, and the melting point is the peritectic reaction point, and when melted, about 15% anhydride
Na ₂ SO ₄ is produced, but as a result of the peritectic reaction not being fully completed during solidification, it gradually enlarges as the cycle is repeated, and the heat storage capacity decreases. Examples include changes in the composition of the wall and center of the material due to penetration through the wall of the container. It is thought that the deterioration of the material is caused by a complex combination of these factors. The present inventors have made extensive studies in order to overcome the limitations of the technology disclosed in the prior invention and find a Na ₂ SO ₄ .10H ₂ O-based heat storage material that can withstand repeated cycles over a long period of time. As a result, the present invention was discovered. That is, the present invention is a heat storage material composition comprising sodium sulfate decahydrate, sodium tetraborate decahydrate, a water-insoluble superabsorbent resin, and an organic sulfonic acid or a salt thereof, or a sulfuric ester or a salt thereof. The present inventors thought that in order to improve the durability of heat storage materials, it would be effective to add a substance that has some influence on the solidification and melting process of heat storage materials, and as a result of their investigation, they found that organic sulfonic acid or sulfuric acid The present invention was completed based on the discovery that the addition of ester or its salt significantly improves the durability of the heat storage material. According to the present invention, for example, as is clear from Example 1, a heat storage material containing 0.5% sodium dodecylbenzenesulfonate to Na ₂ SO ₄ 10H ₂ O can be used not only for 200 cycles but also for 1000 cycles. The melting point remains unchanged even after repeated solidification and melting processes.
The temperature was maintained at 30°C, and the amount of heat storage was 48.5 cal/g, with little loss of performance. As is clear from each example, this surprising effect occurs specifically when an organic sulfonic acid or its salt is added, and when this is a compound having a carboxy group or an inorganic compound, For example, sodium oleate, benzoic acid, sulfamic acid, ammonium sulfate, etc. are ineffective. As described above, the present inventors succeeded in obtaining a practical composition with excellent durability as a heat storage material by adding the above three types of additives to Na ₂ SO ₄ .10H ₂ O. . In other words, sodium tetraborate decahydrate as a seed crystal, a water-insoluble super absorbent resin to cause solidification and melting to occur uniformly and stably throughout the system, and an organic sulfonic acid or its salt as a durability improver. This is a heat storage material composition containing three types of additives. Even if any of these is lacking, the function as a heat storage material cannot be fulfilled satisfactorily. On the other hand, the melting point of Na ₂ SO ₄ 10H ₂ O is approximately around 30°C, but by mixing a salt such as NaCl with it, it is possible to lower the melting point from 30°C to around 10°C. has been known for a long time, and attempts have been made to use such a mixed salt system as a cold storage material, but in this case, the durability is even worse, and after repeated solidification and melting cycles of several dozen times, It has been difficult to put it into practical use because the phase change does not occur smoothly and the functionality deteriorates. The present invention is also effective when applied to this mixed system, and can greatly improve durability, opening the way to practical use of heat storage materials. Next, the present invention will be explained in more detail. As the organic sulfonic acid or its salt or sulfuric ester or its salt referred to in the present invention, a wide variety of compounds can be used, but preferred examples include firstly anionic surfactants. Specific compounds include sodium laurate, sodium cetyl sulfate, sodium dodecylbenzene sulfonate, sodium alkylnaphthalene sulfonate, sodium dialkyl sulfosuccinate, sodium polyoxyethylene alkyl ether sulfate, sodium polyoxyethylene alkyl phenol ether sulfate, and higher alcohols. Sodium sulfate, etc. may be mentioned.
Secondly, so-called acid dyes also have a sulfone group in their molecules and are effective and preferred.
For example, silk scarlet, solar orange,
There are many such as Amaranth, Aminil Brown, Kayanol Red BL, etc. As other compounds, vinyl monomers such as sodium styrene sulfonate and sodium acrylamide propane sulfonate are also effective and preferred. The organic sulfonic acid or salt thereof, sulfuric acid ester, or salt thereof of the present invention is not limited to the above. Further, it is not necessarily necessary to take the form of a sodium salt, but a potassium salt, an ammonium salt, or an acid form may be used. The water-insoluble superabsorbent resin referred to in the present invention absorbs a large amount of liquid in a short time when it comes into contact with water or an aqueous liquid, and has the ability to maintain the liquid absorption state even under some pressure. It is increasingly being used in water-retaining agents for gardening, sanitary products, disposable diapers, and other liquid-absorbing products. The present invention exploits the characteristic properties of this resin by converting it into Na ₂ SO ₄ in the molten state.
It is skillfully used as an absorbing and gelling agent for saturated aqueous solutions, and is extremely effective in preventing supercooling and phase separation that occur during solidification of inorganic hydrated salts. Water-insoluble superabsorbent resins are known to have various structures, such as crosslinked polyacrylates, starch graft polymers, cellulose graft polymers, and vinyl acetate-acrylic acid ester copolymer parts. Examples include saponified products, crosslinked polyvinyl alcohol, and crosslinked polyethylene oxide. In the present invention, any of these can be used, but among them, crosslinked polyacrylates are preferred because they can withstand repeated solidification and melting cycles at relatively high temperatures, have little deterioration, and can be used in small amounts. Particularly preferred is crosslinked polyvinyl alcohol. Next, sodium tetraborate added as a seed crystal is also called borax or borax, and is effective as a crystallization accelerator for Na ₂ SO ₄ .10H ₂ O. The blending ratio of Na ₂ SO ₄・10H ₂ O and these three additives varies depending on the organic sulfonic acid used and the type of super absorbent resin, but in general, the amount of super absorbent resin is Na ₂ SO 0.1~ for ₄・_10H2O
20wt%, preferably 2 to 10wt%. The optimum amount to be added is preferably determined so that the gel-like dispersion in the molten state has a slight fluidity near the limit. The amount of organic sulfonic acid or its salt added is approximately 0.1 to 10wt to Na ₂ SO ₄・10H ₂ O
%, preferably 0.5 _to 5 wt%, and the amount of sodium tetraborate added is approximately 1 to 30 wt%, preferably 5 to 10 _wt %, based on _Na2SO4.10H2O . The heat storage material composition obtained with the above blending ratio solidifies and dissolves at a melting point of approximately 30°C, and exhibits endothermic and
Heat dissipation is repeated, but as mentioned earlier,
By further adding a halogenated alkali metal salt or a halogenated ammonium salt to this, the melting point can be arbitrarily lowered to some extent. As the amount added increases, it is possible to lower the melting point to a minimum of 7°C. Examples of this additive include sodium chloride, potassium chloride, lithium chloride, ammonium chloride, and the like. Addition amount is 1wt for Na ₂ SO ₄・10H ₂ O
% or more is required, and the upper limit is 40wt%. Adding more than this does not lower the melting point and only lowers the amount of heat storage per unit heat storage material, which is meaningless. When preparing the heat storage material composition of the present invention, it is possible to simply mix each component in a solid state (powder), but by heating it above its melting point and mixing each component other than the super absorbent resin in a molten state, By gradually adding superabsorbent resin in a dissolved and dispersed state and gelling the entire system, a more uniform dispersion system can be obtained, which results in a more durable material with a larger amount of heat storage. It is preferable because it can be obtained. Of course, Na ₂ SO ₄・10H ₂ O can be used by itself, but anhydrous Na ₂ SO ₄ and
It may be used in combination with H ₂ O, and the latter is rather more practical. The amount of H ₂ O in this case does not need to be strictly the chemically theoretical amount, and some excess or deficiency is allowed. As explained in detail above, the heat storage material composition according to the present invention overcomes various technical difficulties when using Na ₂ SO ₄ .10H ₂ O as a heat storage material.
It has the ability to withstand repeated solidification and melting cycles, and can be used not only when using solar energy, but also when using various types of energy such as nighttime electricity and factory waste heat. It can be used for the purpose of adjusting and is extremely useful industrially. Hereinafter, the present invention will be explained in more detail with reference to Reference Examples, Examples, and Comparative Examples. Reference example 1 36wt% of sodium acrylate, aqueous solution 836
g, 100 g of acrylic acid, 0.4 g of methylenebisacrylamide, and 208 g of distilled water were charged into a separable flask (No. 2). After adjusting the temperature to 20°C, nitrogen was blown into the system to remove oxygen from the system. To this were added 0.2 g of ammonium persulfate and 0.2 g of sodium sulfite. Polymerization started after 40 minutes, and after another 3 hours, the peak temperature reached 95°C and the polymerization was completed. The resulting gel was taken out and formed into a string with a diameter of 5 mm using an extruder, and then dried with hot air at 120°C. Grind the obtained polymer to 60-100mesh
A white powder was obtained. Distilled water of this powder, 1N
The water absorption of NaCl solution was measured and was 580 times and
It was 40 times hotter. Example 1 176 g of Na ₂ SO ₄ , 14 g of Na ₂ B ₄ O ₇ 10H ₂ O, 224 g of distilled water and 2.0 Na dodecylbenzenesulfonate
g were mixed at a temperature of 40°C. While keeping this at 40℃ and stirring rapidly, 12g of 60-100mesh powder of cross-linked sodium polyacrylate synthesized in Reference Example 1 was prepared.
was added little by little. The mixture gradually thickened and finally converted to a mushy hydrogel dispersion.
This molten material was filled into vinyl chloride pipes with an inner diameter of 3 cm and a length of 8 cm, and both ends were sealed to produce five filled heat storage materials. Take 4 of these
The samples were alternately immersed in a 50°C hot water tank and a 10°C cold water tank for 30 minutes each to repeat the cycle of melting and solidification. Perform a long repeated cycle 100,
After each cycle of 200, 500, and 1000 cycles, one piece of wood was taken out, and the heat storage capacity of the wood was measured in the following manner and compared with the wood before the test. <Measurement of phase change duration and temperature> Insert a thermocouple into the center of the heat storage material to be tested and
Immerse in a constant temperature water bath. When the internal temperature reaches 50℃,
The material is immersed in a separate 20°C constant temperature water bath, the temperature at the center of the material is measured over time, and the phase change temperature and time are recorded. <Measurement of heat storage capacity> After completing the phase change temperature and time measurements, remove the material from the container, place a portion of it in a sealed aluminum sample pan, and place it in a Perkin-Elmer DSC.
-Measure the latent heat storage capacity using a type IB differential scanning calorimeter. The results obtained are shown in Table 1. As can be seen from Table 1, there is almost no change in performance even after 1000 cycles.

[Table] Comparative Example 1 In Example 1, a similar durability test was conducted on a material to which Na dodecylbenzenesulfonate was not added. Material sampling is 100, 200,
This was done after 1000 cycles. The results are shown in Table 2.

[Table] As can be seen from Table 2, it was stable after 100 cycles, but deteriorated significantly after 200 cycles. Examples 2 to 6 In Example 1, lauryl sulfate and lauryl sulfate were used instead of sodium dodecylbenzenesulfonate.
We created materials to which 2.0g each of Na, sodium dialkyl sulfosuccinate (product name Perex CS, manufactured by Kao Atlas Co., Ltd.), Solar Orange (acid dye manufactured by Sumitomo Chemical Co., Ltd.), and sodium styrene sulfonate were added to achieve similar durability. A sex test was conducted. The results are shown in Table 3. Comparative Examples 2 to 5 In Example 1, materials were prepared in which 2.0 g each of sodium oleate, benzoic acid, sodium sulfamine, and ammonium sulfate were added instead of sodium dodecylbenzenesulfonate, and the same durability test was conducted. Ta. The results are shown in Table 3.

[Table] This is a summary of the amount of heat storage.
Example 7 In Example 1, cross-linked polyvinyl alcohol-based super absorbent resin was used instead of cross-linked polyacrylic Na.
KI Gel-201 (manufactured by Clarei Soprene Chemical Co., Ltd.)
20 Metsuyupas powder, distilled water absorption capacity approximately 200 times) 14
g was added. A porridge-like hydrogel dispersion system similar to that in Example 1 was obtained. Durability tests were conducted in the same manner below. The amount of heat storage after 1000 cycles is 47.0 cal/g,
In addition, the phase change temperature was 30°C, which was almost unchanged compared to before the test, indicating excellent durability. Example 8 Na ₂ SO ₄ 176g, Na ₂ B ₄ O ₇・10H ₂ O 14g,
62 g of NaCl, 224 g of distilled water and 2.0 g of Na dodecylbenzenesulfonate were mixed at a temperature of 40°C. Thereafter, 12 g of crosslinked polyacrylic acid Na was added in the same manner as in Example 1 to obtain a porridge-like hydrogel dispersion system, and a material filled in a vinyl chloride pipe was obtained. When the phase change temperature and latent heat storage amount of this material were measured, they were 11°C and 38 cal/g, respectively, and it was found that it is effective as a cold storage material. Next, in order to examine the durability of this material, it was alternately immersed in a 30°C constant temperature water bath and a cold water bath controlled at 2 to 3°C for 60 minutes each to repeat the cycle of melting and solidification. After 200 cycles, it was taken out and the phase change temperature and amount of latent heat storage were measured, and they were 11°C and 34 cal/g, respectively, which were almost the same as before the test, indicating excellent durability. Comparative Example 6 In Example 8, a similar durability test was conducted on a material to which Na dodecylbenzenesulfonate was not added. After 50 cycles, the material was taken out and the phase change temperature was measured, but no phase change occurred and measurement was impossible.

Claims (1)

[Claims] 1 Sodium sulfate decahydrate, sodium tetraborate
A heat storage material composition comprising a 10-hydrate salt, a water-insoluble superabsorbent resin, and an organic sulfonic acid or its salt or a sulfuric acid ester or its salt.