JPH0726251A - Heat storage microcapsule and method for producing the same - Google Patents

Abstract

PURPOSE:To prepare the subject microcapsule which is difficultly broken underwater and can transport heat without fail. CONSTITUTION:This microcapsule for heat storage, composed of a core substance comprising a paraffin and a capsule wall comprising calcium silicate and surrounding the core substance, is produced by dispersing a paraffin in an aqueous sodium silicate solution to form an O/W dispersion, dispersing the O/W dispersion in an organic solvent to form an (O/W)/O dispersion and pouring an aqueous calcium chloride solution into the (O/W)/O dispersion to form an ((O/W)/O)/W dispersion, whereupon the calcium chloride dissolved in the outermost aqueous phase diffuses into the innermost aqueous phase and reacts with sodium silicate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat storage microcapsule and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, heat energy such as subway waste heat and waste incineration waste heat has not been used so much. In recent years, there has been a demand for energy saving by effectively utilizing these heat energies to centrally supply hot water for heating and hot water supply. For this purpose, it is necessary to transport heat from the heat source to the destination. At present, there is no suitable technique other than transporting the fluid itself by utilizing the sensible heat of a fluid such as water for this heat transport. However, in such a method, the heat is dissipated during the transportation of the fluid to lower the temperature, so that the utilization efficiency of the heat energy is not sufficient.

[0003]

Therefore, in order to stably carry out heat transfer over a long distance without causing a temperature drop due to heat dissipation, it is necessary to use a large heat storage medium rather than sensible heat of water. It is effective to utilize latent heat to transport the heat storage medium while the heat storage medium stores the heat. Specifically, a new method of heat transport has been considered in which the latent heat storage material is microencapsulated and suspended in water.

Paraffin, which is an organic substance, is suitable as the latent heat storage material in consideration of safety and corrosiveness when the capsule is broken. When encapsulating such an organic substance, it is general to employ a water-soluble polymer as a material forming the capsule wall. However, when a heat storage capsule having a capsule wall made of a water-soluble polymer is put into water, it is expected that water will invade the capsule wall to swell and destroy the capsule.

The object of the present invention is to prevent destruction in water,
It is an object of the present invention to provide a heat storage microcapsule capable of reliably transporting heat and a method for easily producing such a heat storage microcapsule.

[0006]

The heat storage microcapsules of the present invention are characterized in that a capsule wall made of calcium silicate is formed around a core substance made of paraffin. The method for producing microcapsules for heat storage of the present invention is carried out by dissolving an anionic surfactant in an aqueous solution of sodium silicate and heating, dissolving paraffin in this solution and stirring, and further stirring under cooling to perform O / W.
Step of preparing dispersion system, dissolving oil-soluble surfactant in organic solvent that does not dissolve water and paraffin, and mixing the O / W dispersion system with this solution to prepare (O / W) / O dispersion system And a calcium chloride aqueous solution is injected into the obtained (O / W) / O dispersion system to prepare a ((O / W) / O) / W dispersion system, which is dissolved in the outermost aqueous phase. And diffusing calcium chloride to the inner aqueous phase to react with sodium silicate to form a capsule wall made of calcium silicate around a core substance made of paraffin.

Here, O represents a water-insoluble phase and W represents a water-soluble phase. Therefore, an O / W dispersion system is a system in which paraffin is dispersed in an aqueous sodium silicate solution, and an (O / W) / O dispersion system is a system in which a (paraffin / sodium silicate aqueous solution) dispersion system is dispersed in an organic solvent, ( The (O / W) / O) / W dispersion system means a system in which the ((paraffin / sodium silicate solution) / organic solvent) dispersion system is dispersed in a calcium chloride solution.

The present invention will be described in more detail below. In the method of the present invention, first, an anionic surfactant is dissolved in an aqueous solution of sodium silicate and heated, paraffin is dissolved in this solution and stirred, and further stirred under cooling so that the paraffin is an aqueous solution of sodium silicate. To prepare an O / W dispersion system. In the present invention, as the paraffin, one having a melting point of 5 to 70 ° C. is used.

In this step, the concentration of the aqueous sodium silicate solution is adjusted so that the capsule wall of the finally manufactured microcapsules has an appropriate thickness and O / O during manufacturing.
It is appropriately set so that the W dispersion system does not become unstable and sodium silicate does not precipitate. Examples of the anionic surfactant include sodium dodecyl sulfate and sodium benzenesulfonate. The concentration of the anionic surfactant is set appropriately. This solution is heated to a temperature at which paraffin can be sufficiently dissolved. The temperature is preferably {melting point of paraffin + 5 ° C.} or higher. Paraffin is added to this solution and dissolved.

This paraffin / sodium silicate aqueous solution is stirred in a heated state and further stirred under cooling to prepare an O / W dispersion system in which paraffin is dispersed in the sodium silicate aqueous solution.

The stirring conditions in the heated state are appropriately set so that paraffin droplets having an appropriate particle size are formed and stably dispersed. By cooling this, the paraffin having the target particle size is solidified and stably dispersed in the aqueous solution. The temperature during cooling is preferably {melting point of paraffin-5 ° C} or less. However, {melting point of paraffin-
5 ° C.} is 0 ° C. or lower, it is cooled to 0 ° C. The stirring conditions under cooling are appropriately set so that the formed paraffin grains are stably maintained.

Next, the oil-soluble surfactant is dissolved in an organic solvent which does not dissolve water and paraffin, and the O / W dispersion system obtained in the previous step is mixed with this solution to obtain (paraffin /
An (O / W) / O dispersion system in which the sodium silicate aqueous solution) dispersion system is dispersed in an organic solvent is prepared.

Examples of the organic solvent which does not dissolve water and paraffin used in this step include octyl alcohol. Further, examples of the oil-soluble surfactant include sorbitan fatty acid ester. The concentration of the oil-soluble surfactant in the organic solvent is, for example, 1 to 4 wt%
Is set to.

The ratio of O / W dispersion to organic solvent is
It is appropriately set in consideration of the final yield of microcapsules and the stability of the dispersion system during production. The stirring conditions in this step are also set as appropriate in consideration of the stability of the dispersion system.

Further, an aqueous calcium chloride solution is injected into the obtained (O / W) / O dispersion system to obtain ((O / W) / O) /
A W dispersion is prepared, and calcium chloride dissolved in the outermost aqueous phase is diffused to the inner aqueous phase and reacted with sodium silicate to form a capsule wall made of calcium silicate around a paraffin core substance. Let

In this step, the injection amount of the calcium chloride aqueous solution is appropriately set in consideration of the thickness of the capsule wall made of calcium silicate, which is produced by the reaction between calcium chloride and sodium silicate.

By the method as described above, microcapsules having a structure in which a core material made of paraffin is wrapped with a capsule wall made of calcium silicate can be manufactured. When the heat storage microcapsules produced by the method of the present invention are purified and isolated, ((O / W) /
A polar solvent is added to the O) / W dispersion to dissolve the unencapsulated paraffin, the residue is collected by filtration, and the residue is washed with a polar solvent and dried. Examples of polar solvents used at this time include ethanol, methanol, and acetone.

The heat storage microcapsule of the present invention has a structure in which a core substance made of paraffin is wrapped in a capsule wall made of calcium silicate, and the calcium silicate constituting the capsule wall is not easily broken in water. Since it is an inorganic substance, it can reliably transport heat without destruction in water.

[0019]

Embodiments of the present invention will be described below with reference to the flow chart shown in FIG. (1) Preparation of O / W Dispersion System 6 ± 1 mol% sodium silicate aqueous solution 1 was added with anionic surfactant sodium dodecyl sulfate 2 0.0
It was dissolved so as to have a concentration of 1 to 0.2 mol / l.
After heating the solution to 70 ° C., 2 to 4 g of paraffin (melting point 45 ° C.) 3 was added and dissolved.

By heating to 70 ° C. in this way,
The paraffin can be sufficiently melted, the interfacial tension and the viscosity can be lowered, and the paraffin can be made into microdroplets.

The concentration of the aqueous sodium silicate solution is set to 6 ± 1 mol% in consideration of the stability of the dispersion system at the time of production and the thickness of the finally prepared capsule wall. Here, if the concentration of the sodium silicate aqueous solution is too low, the finally prepared capsule wall becomes thin and becomes brittle. On the other hand, if the concentration is too high, the O / W dispersion system becomes unstable or sodium silicate is precipitated.

Next, while maintaining the paraffin / sodium silicate aqueous solution at 70 ° C., 50
High-speed stirring was performed at 0 rpm for 10 minutes (high-speed stirring operation 4).
Furthermore, in a constant temperature bath maintained at 10 ° C, 400r
Low speed stirring was performed for 5 minutes at pm (low speed stirring operation 5). The O / W dispersion system 6 was prepared as described above.

By the high speed stirring operation of 500 rpm for 10 minutes, necessary and sufficient stirring energy can be obtained so that the paraffin droplets in the O / W dispersion system have a target particle size. Here, if the stirring speed is too fast and the stirring time is too long, the air bubbles are entrapped and the paraffin droplets are destroyed. On the other hand, if the stirring speed is too slow and the stirring time is too short, the paraffin droplets will not have the target particle size.

By lowering the temperature from 70 ° C. to 10 ° C., the paraffin having the desired particle size can be solidified and can be stably dispersed in the aqueous solution. Further, by lowering the stirring speed from 500 rpm to 400 rpm, paraffin can be formed into a spherical shape with individual separation. This is because the paraffin droplets coalesce when the mixture is stirred for a long time while keeping the stirring speed high.

(2) Preparation of (O / W) / O dispersion system In 115 g of octyl alcohol 7, 1 to 4 wt% of sorbitan fatty acid ester 8 as an oil-soluble surfactant was dissolved. This solution and 70 g of the O / W dispersion system 6 obtained in the previous step were kept at 10 ° C. and kept at 400 rpm for 5 times.
Stir for minutes (stir operation 9), (O / W) / O dispersion system 10
Was prepared.

The ratio of the O / W dispersion to octyl alcohol is set in consideration of the yield of the final microcapsules and the stability of the dispersion during the production. That is, if the proportion of the O / W dispersion system is small, the yield will decrease,
On the contrary, when the amount is large, the dispersion system becomes unstable and the emulsion droplets aggregate.

The stirring conditions in this step are set in consideration of the stability of the dispersion system. That is, if the stirring speed is too fast and the stirring time is too long, the walls of the (O / W) / O dispersion system will be broken and paraffin will leak. Conversely, if the stirring speed is too slow and the stirring time will be too short, the dispersion system will Becomes unstable.

(3) Preparation of Microcapsules The (O / W) / O dispersion system 10 obtained in the previous step was treated at 10 ° C.
10m while stirring at 400 rpm while maintaining
1 (2 mol% calcium chloride aqueous solution 11) was injected all at once to prepare ((O / W) / O) / W dispersion system 12, and the following reaction was started.

2CaCl ₂ + Na ₄ SiO ₄ → Ca ₂ S
iO ₄ + 4NaCl As shown in this formula, in the ((O / W) / O) / W dispersion system, calcium chloride dissolved in the outermost water phase diffuses in the oil phase, Reacts with sodium silicate to produce calcium silicate. In this way, microcapsules having a structure in which a core substance made of paraffin was wrapped with a capsule wall made of calcium silicate were prepared.

At this time, the injection amount of the aqueous solution of calcium chloride is determined in consideration of the thickness of the capsule wall made of calcium silicate, which is produced by the reaction between calcium chloride and sodium silicate.

(4) Purification of microcapsules After reacting for 2 hours, ethanol (13), which is a polar solvent, was added to ((O / W) / O) / W dispersion system 12, and the mixture was heated to 70 ° C.
The temperature was raised to 400 rpm and the mixture was stirred at 400 rpm for 5 minutes (stirring operation 14).

As described above, ethanol, which is a polar solvent, is added to dissolve unencapsulated paraffin. Also, by raising the temperature from 10 ° C to 70 ° C,
It facilitates the separation of the microcapsules from the ((O / W) / O) / W dispersion.

Then, the residue was collected by filtration (filtering operation 15). The residue is washed with ethanol (washing operation 1
6) The microcapsules 18 were isolated by drying (drying operation 17).

The microcapsules of the obtained microcapsules were photographed to determine the particle size. As a result, the sodium dodecyl sulfate concentration was 0.01 to 0.0 as in this example.
2 mol / l, particle size 1 to 100 μ under the condition of initial emulsion (O / W dispersion system) volume fraction of 0.05 to 0.2
m microcapsules could be produced. Although the paraffin having a melting point of 45 ° C. has been described above, similar results can be obtained when paraffin having a melting point of 5 to 70 ° C. is used.

[0035]

As described in detail above, according to the present invention, it is possible to provide a heat storage microcapsule which is less likely to be broken in water and can reliably transfer heat, and a method for easily manufacturing such a heat storage microcapsule. .

[Brief description of drawings]

FIG. 1 is a flowchart showing a method of manufacturing a heat storage microcapsule according to an embodiment of the present invention.

[Explanation of symbols]

1 ... Sodium silicate aqueous solution, 2 ... Sodium dodecyl sulfate, 3 ... Paraffin, 4 ... High speed stirring operation, 5 ... Low speed stirring operation, 6 ... O / W dispersion system, 7 ... Octyl alcohol,
8 ... Sorbitan fatty acid ester, 9 ... stirring operation, 10 ...
(O / W) / O dispersion system, 11 ... Calcium chloride aqueous solution,
12 ... ((O / W) / O) / W dispersion system, 13 ... Ethanol, 14 ... Stirring operation, 15 ... Filtration operation, 16 ... Ethanol washing operation, 17 ... Drying operation, 18 ... Microcapsule.

Claims (3)

[Claims] 1. A microcapsule for heat storage, wherein a capsule wall made of calcium silicate is formed around a core substance made of paraffin. 2. A step of preparing an O / W dispersion system by dissolving an anionic surfactant in an aqueous solution of sodium silicate and heating it, dissolving paraffin in this solution, stirring and further stirring under cooling. A step of dissolving an oil-soluble surfactant in an organic solvent that does not dissolve water and paraffin, and mixing the O / W dispersion system with the solution to prepare an (O / W) / O dispersion system. A calcium chloride aqueous solution is injected into the (O / W) / O dispersion system to prepare a ((O / W) / O) / W dispersion system, and calcium chloride dissolved in the outermost aqueous phase is transferred to the inner aqueous phase. And diffusing and reacting with sodium silicate to form a capsule wall made of calcium silicate around a core substance made of paraffin, the method for producing microcapsules for heat storage. 3. A polar solvent is added to the ((O / W) / O) / W dispersion after completion of the reaction to dissolve unencapsulated paraffin, and the residue is recovered by filtration. The method for producing microcapsules for heat storage according to claim 2, wherein the microcapsules are isolated by washing with a polar solvent and drying.