JP2002030280A - Method for producing granule of agent for preventing supercooling of salt hydrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an economical, safe and simple method suitable for mass- production for producing an agent for preventing supercooling, comprising a salt hydrate. SOLUTION: This method for producing the granule of the agent for preventing supercooling, comprising the salt hydrate is characterized in that a mixture of a molten liquid of the salt hydrate kept at a temperature not less than the melting point with a supporting crystal for preventing the supercooling is kept at the temperature not less than the melting point to form droplets on a water-repellent material, and cooling and solidifying the resultant mixture. The heat storage material or the heat storage device is obtained by using the granules of the agent for preventing the supercooling of the salt hydrate, produced by the production method.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for producing a supercooling inhibitor for salt hydrate. More specifically, the present invention relates to a method for producing a salt hydrate supercooling inhibitor granule suitably used for a latent heat storage material.

[0002]

2. Description of the Related Art Many proposals have been made to use a salt hydrate having a property of solid-liquid phase change as a heat storage material, and it has already been put to practical use in the field of floor heating and the like.
Representative salt hydrates include sodium sulfate decahydrate,
Calcium chloride hexahydrate, disodium hydrogen phosphate dodecahydrate, sodium acetate trihydrate and the like. Each of these salt hydrates alone exhibited a supercooling phenomenon, which was a great barrier to use as a heat storage material. Many proposals have been made for a supercooling inhibitor or a method for preventing supercooling in order to overcome this barrier.

It was found in 1952 that sodium tetraborate decahydrate was effective as a supercooling inhibitor for sodium sulfate decahydrate. Since this combination belongs to the same crystal system and the lattice constant of the crystal is close, it is known that nucleation is based on heteroepitaxial growth. After this discovery, the search for other salt hydrates was continued with a crystallographic approach, but similar combinations have not yet been found.

On the other hand, a method using a specific supported crystal for sodium acetate trihydrate has been proposed. As the supported crystals, sodium salts such as disodium hydrogen phosphate and trisodium phosphate (JP-B-61-42957,
JP-B-2-15598) and the like are disclosed.
In these methods, a supported crystal or a press-formed supported crystal is placed in a melt of sodium acetate trihydrate, and the melt is solidified by forced cooling. In these methods, the supercooling prevention effect cannot be obtained unless the melt is solidified once to solidify sodium acetate trihydrate on the surface of the supported crystal, so that the supercooled state is broken after filling the container. Therefore, forced cooling-solidification operation is essential,
This is an inconvenient method for mass production. In addition, it is necessary to use a large amount of supported crystals. When adopting a method of solidifying the melt by introducing a seed crystal instead of forced cooling, it is necessary to pre-cool the melt in advance so that the seed crystal does not melt. Is an inconvenient method.

As a method for solving this, Japanese Patent Publication No. 1-5
No. 1515 and Japanese Patent Publication No. 58-27301,
There is disclosed a method of separately adding a supercooling inhibitor by adding sodium pyrophosphate as a supporting crystal (base material) to a melt and solidifying it by cooling as it is or by taking out the sodium pyrophosphate.
Japanese Patent Application Laid-Open No. 64-75583 discloses a method in which a supported crystal is put into a melt, solidified once, heated and melted again, and then the crystal filtered from the melt is used to prevent supercooling. I have. In these methods, operability is improved because a supercooling inhibitor may be added to the filling melt, but it is necessary to prepare the melt to produce the supercooling inhibitor. Further, since it is solidified after being filtered off from the melt, it needs to be crushed to be used as a supercooling inhibitor, and thus has problems in energy consumption, operation safety, operability and the like. Furthermore, the present inventors have disclosed in JP-A-10-298543 a method for producing a salt hydrate supercooling inhibitor by mixing and grinding a salt hydrate and a supercooling-preventing supporting crystal. This method has the advantage that it is not necessary to prepare a melt.However, in the case of mixing and milling, a large number of batches are required because the throughput per batch is small. In order to use it as a supercooling inhibitor, there is a problem in that it is necessary to take measures such as packaging or molding a small amount at a time, or adding the powder as it is in a powder feeder.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a more economical, safer and simpler method for producing supercooling inhibitors for salt hydrates, which is convenient for mass production. .

[0007]

Means for Solving the Problems The present inventors have conducted intensive studies in such a situation, and as a result, formed droplets of a mixture of a melt of a salt hydrate and a supporting crystal for preventing supercooling, and then cooled the mixture. It has been found that the above-mentioned problems can be solved by making the particles into a granular form, and the present invention has been completed.

Namely, the present invention is, after forming the droplet on the揆水material mixture is held above the melting point of the melt and the supercooling-preventing supported crystalline salt hydrates held above its melting point, A method for producing a superhydrate inhibitor granule of a salt hydrate characterized by cooling and solidifying the mixture, and a heat storage material or a heat storage device using the supercool inhibitor granule of a salt hydrate produced by the method. It is.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, these inventions will be described in detail. In the present invention, the salt hydrate is a salt hydrate having a property of solid-liquid phase change, and is used, for example, as a heat storage material. Representative salt hydrates include sodium sulfate decahydrate, calcium chloride hexahydrate, disodium hydrogen phosphate decahydrate, disodium hydrogen phosphate decahydrate, calcium nitrate tetrahydrate, sodium acetate trihydrate And strontium chloride hexahydrate. These are used alone or as a composition with a eutectic salt or a melting point modifier. In some cases, it is preferable to add a small excess of water in addition to the water of crystallization.

In the present invention, a crystal capable of supporting a salt hydrate is used as a supported crystal for a supercooling inhibitor. For example, when the salt hydrate is sodium acetate trihydrate, the supported crystals are disodium hydrogen phosphate, monosodium dihydrogen phosphate, trisodium phosphate, sodium tetraborate, sodium bromide, sodium sulfate, and salts thereof. Hydrates are exemplified. When strontium chloride hexahydrate is used as the salt hydrate, strontium hydroxide octahydrate is used as the supported crystal, and when the salt hydrate is disodium hydrogen phosphate dodecahydrate, the supported crystal is tetraborate. In the case where sodium acid and hydrates thereof are disodium hydrogen phosphate heptahydrate as a salt hydrate, examples of the supported crystals include disodium hydrogen phosphate dihydrate.

Preferably, the salt hydrate is sodium acetate trihydrate, and the supported crystals are disodium hydrogen phosphate, monosodium dihydrogen phosphate, trisodium phosphate, sodium tetraborate, sodium bromide, sodium sulfate or a salt thereof. And a combination of disodium hydrogen phosphate heptahydrate as a salt hydrate and disodium hydrogen phosphate dihydrate as a supported crystal, more preferably sodium acetate trihydrate as a salt hydrate In particular, disodium hydrogen phosphate or trisodium phosphate is used as the supported crystal, particularly preferably sodium acetate trihydrate as the salt hydrate, and disodium hydrogen phosphate as the supported crystal.

In the present invention, the melt of the salt hydrate used for producing a mixture of the melt of the salt hydrate and the supporting crystals for preventing supercooling comprises a salt hydrate and water optionally added. Is heated above the melting point of the salt hydrate. The amount of water added as required is limited to a range such that the concentration in terms of salt anhydride in the melt after adding water is equal to or higher than the saturated solubility at room temperature (about 25 ° C.). If a large amount of water is added so as to have a saturation solubility at room temperature or less, it is not preferable because the dripping liquid does not solidify at all or the strength is low even after solidification. When the salt hydrate is sodium acetate trihydrate, the saturated solution at 20 ° C. in terms of sodium acetate anhydrate is 31% by mass, and water is added so as to have a higher concentration. When water is not added at all, the anhydrous equivalent of trihydrate is 60.0% by mass. Therefore, in the case of sodium acetate, a range of 32% by mass to 60.0% by mass, preferably 40% by mass to 58% by mass is suitable as a melt concentration.
The concentration of the supporting crystals for preventing supercooling in the mixture is not less than the concentration exceeding the solubility in the mixture and not more than 90% by mass. When the solubility is lower than the solubility, the compound is dissolved and disappears, and thus does not serve as a supported crystal. If it exceeds 90% by mass, the fluidity of the mixture becomes poor, making it unsuitable for dropping. When the salt hydrate is sodium acetate trihydrate, and when the supported crystal for preventing supercooling is disodium hydrogen phosphate, 3
To 90% by mass, 20 to 90% by mass for sodium bromide, and 10 to 90% by mass for sodium sulfate. A more preferable range is that, from the viewpoint of the fluidity of the mixture, the amount of the supported crystals is 20 to 50% by mass based on the mixture.

[0013] A thickener may be added in order to prevent sedimentation of the supported crystals in the mixture of the melt of the salt hydrate and the supported crystals for preventing supercooling. Thereby, the homogeneity of the dripping liquid can be improved. As a thickener to be used, a polymer thickener such as carboxymethylcellulose, sodium polyacrylate, etc., a superabsorbent resin, finely divided silica, etc., which has a thickening effect on salt hydrate can be selected. Good. When the salt hydrate is sodium acetate trihydrate, carboxymethylcellulose, partially hydrolyzed polyacrylamide and the like are preferably used.

The temperature range in which the mixture of the melt of the salt hydrate and the supporting crystals for preventing supercooling is maintained is not lower than the melting point of the salt hydrate in the mixture of the salt hydrate and water added as required. is there. In the case of an aqueous solution of sodium acetate trihydrate, it depends on the amount of water, but is preferably from 50 to 70C, more preferably from 55 to 6O <0> C.
5 ° C. is exemplified. Although there is no inconvenience even if it exceeds 70 ° C,
If the temperature is too high, there is evaporation of water, so it is not preferable to heat more than necessary.

In the present invention, as the water-repellent material, many commonly used materials such as resin, metal and ceramics can be used without any trouble. The shape can be selected as needed, such as a film, a sheet, a plate, and a tray.

As a method for forming droplets of a mixture of a melt of a salt hydrate and a supporting crystal for preventing supercooling, a method of intermittently flowing a liquid flow of the mixture, a method of passing through a perforated plate or a net, etc. and so on. In addition, there are methods of generating a liquid flow such as a natural flow type and a pump pressure type. In order to form droplets on the repellent material, either the liquid supply side or the repellent material needs to move, which may be selected by ordinary engineering judgment.

In order to form the droplets and solidify them later, the droplets are cooled or forcedly cooled. If there are droplets that do not solidify even after cooling, they solidify immediately upon addition of a minute amount of fine crystals of the salt hydrate. If these fine crystals are sprayed on a water-based material in advance, the uncured rate can be significantly reduced.

When the droplets are solidified, granules are obtained. The size of the granule is determined by the size of the droplet, and a desired size may be selected. Usually, it is required to be smaller than the size of the injection hole of the filling container. The size of the granules is 3 to 15 in diameter
The range of mm is preferred. The shape of the granules is determined by the shape of the droplets, but in the case of highly viscous droplets, they are close to spherical,
In the case of a liquid droplet having a low viscosity, the liquid droplet becomes almost flat. In any case, there is no difference in the effect of preventing supercooling.

The supercooling inhibitor granules of the present invention are used to reliably solidify in the container after the heat storage material melt is filled. The granules can be added to the container before the heat storage material melt is filled. Granules can also be added after the heat storage material melt is filled in a container. One granule to be added is sufficient, but a plurality of granules does not matter depending on the size of the container.

The heat storage material using the supercooling inhibitor granules of the present invention includes salt hydrate, which is a main material of the heat storage material, a melting point regulator, a supercooling inhibitor, and a solid-liquid separation inhibitor added as needed. By adding the granules to a melt of a composition comprising At this time, the salt hydrate, which is the main material of the heat storage material, and the salt hydrate of the granules need to be the same. The heat storage material is used after being filled and sealed in a panel-like or tubular container. The heat storage device using the supercooling inhibitor granules of the present invention is composed of a heat storage material prepared as described above and filled in a container, a heating element such as an electric heater, a heat insulating material, and the like. All or some of them are integrated or individual ones are sequentially installed and used at the construction site. Taking the case of floor heating as an example, it is common to have a structure of floor structural material / heat insulating material / heating element / heat storage material / floor material / floor finishing material in order from the bottom.

[0021]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, but it should not be construed that the invention is limited thereto.

Example 1 9.72 sodium acetate (anhydrous) in a 50 ml beaker
g and 8.28 g of water, and heated in a 60 ° C. water bath to prepare a 54% by mass sodium acetate melt. To this, 12.00 g of disodium hydrogen phosphate (anhydrous) was added and stirred for 30 minutes. The operation of sucking up the slurry with a dropper while continuing stirring and dropping the slurry on a polyethylene film previously laid in a tray was repeated several times, and as a result, 122 droplets were formed. After 30 minutes from the dropping, 98% of the droplets were cured (curing rate). Leave this in the tray 7
When placed in a constant temperature oven and taken out after 2 hours, the curing rate is 10
It was 0%. The granules thus obtained were subjected to the following melt stability test. 30 g of a melt (62 ° C.) composed of 56% by mass of sodium acetate, 2% by mass of disodium hydrogen phosphate and the balance of water was placed in a glass screw tube,
It was immersed in a 2 ° C. water bath. One granule was added thereto and kept at 62 ° C. for 6 hours. There was no change in the shape of the granules. Thereafter, the heating of the water bath was stopped while being kept in the water bath, and the solution was allowed to cool. After 30 minutes, the water temperature reached 37 ° C., and the melt in the glass screw tube had solidified. The effect of the granules as a supercooling inhibitor was confirmed.

Examples 2 to 11 and Comparative Examples 1 to 3 In the same manner as in Example 1, a mixture having a different concentration of sodium acetate melt and a different concentration of disodium hydrogen phosphate was prepared, and the mixture was dropped on a polyethylene film. The drop cure rate and the stability of the resulting granules in the melt were tested. Table 1 shows the above results.

[0024]

[Table 1]

[0025]

According to the present invention, there is disclosed a method for producing a supercooling inhibitor for salt hydrate which is excellent in economy, safety and simplicity. It greatly contributes to the production of heat storage materials.

Claims (5)

[Claims] The present invention is characterized in that a mixture of a melt of a salt hydrate and a supporting crystal for preventing supercooling is maintained at a melting point or higher to form droplets on an aqueous material, and the mixture is cooled and solidified. For producing supercooling inhibitor granules of salt hydrate. 2. The method for producing a superhydrate inhibitor granule of a salt hydrate according to claim 1, wherein the mixture further comprises a thickener. 3. The method of claim 1, wherein the salt hydrate crystals are pre-existing on the water-repellent material, and the mixture is dropped thereon to form droplets. Production method. 4. The supercooling inhibitor granules for salt hydrate according to claim 1, wherein the droplets are dropped on the repellent material to form droplets, and then the salt hydrate crystals are added to the droplets to solidify by cooling. Manufacturing method. 5. A heat storage material or a heat storage device using supercooling inhibitor granules of a salt hydrate produced by the production method according to any one of claims 1 to 4.