JP2011111496A - Heat-storing agent - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a heat-storing agent having a high heat-storing speed and hardly causing bilayer separation, and a heat-storing material by using such heat-storing agent. <P>SOLUTION: This heat-storing agent containing a quaternary ammonium salt, water, an alkali metal phosphate and water soluble polysaccharides is characterized in that the water soluble polysaccharides have at least one of carboxyl group and carboxymethyl group. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a latent heat storage agent, and more particularly to a technique for increasing the heat storage rate and suppressing layer separation.

  As the heat storage agent used as the main component of the heat storage material, a material having a higher heat storage amount per unit time (hereinafter referred to as “heat storage speed”) is more practically preferable. This is because if the heat storage speed is higher, more heat energy can be stored in a shorter time.

  The quaternary ammonium salt clathrate hydrate (including quasi clathrate hydrate; the same shall apply hereinafter) produced by cooling an aqueous solution of a quaternary ammonium salt (hereinafter referred to as “raw aqueous solution”) is a heat storage type. It is well known as the main agent of heat storage materials used for building air conditioning equipment and cold storage materials for preservation of fresh fish (for example, see Patent Documents 1 and 2), and is also known to be difficult to cause phase separation (for example, (See Patent Document 3). And the amount of heat storage per unit time when the clathrate hydrate of the quaternary ammonium salt is produced from the raw material aqueous solution (this is when the clathrate hydrate of the quaternary ammonium salt returns to the raw material aqueous solution. Development of technology for increasing the heat storage speed is proceeding, which is substantially equal to the amount of heat released per unit time. As such a technique, there is a technique for improving the heat storage rate by adding an alkali metal phosphate to a raw material aqueous solution (see, for example, Patent Document 4).

JP 2001-280875 A JP 2007-161894 A Japanese Patent Laying-Open No. 2005-126728 JP 2008-214527 A JP 2006-131856 A Japanese Patent No. 3774530

  Here, it is certain that clathrate hydrate of quaternary ammonium salt produced from the raw material aqueous solution is unlikely to cause phase separation in the raw material aqueous solution, but if left standing for a long time, it will eventually be separated into two phases. become. When heating and cooling are repeated for the raw material aqueous solution in which such clathrate hydrate is in a phase-separated state, unless the phase separation state is eliminated in advance by stirring or the like, the heat storage rate is reduced. The improvement effect does not last long. It has also been confirmed that when more alkali metal phosphate is added to the raw material aqueous solution in order to maintain the effect of improving the heat storage rate, two-phase separation occurs more remarkably.

  On the other hand, the following example is known as a technique for preventing or suppressing phase separation caused by the heat storage agent.

  (1) A method of using a polysaccharide such as starch to suppress phase separation of a heat storage agent mainly composed of sodium sulfate decahydrate (Patent Document 5). According to this method, phase separation can be prevented or suppressed by the physical effect of gelation of the heat storage agent using polysaccharides such as starch.

  (2) A technique in which a thickener is added in order to suppress sedimentation of the supporting crystals for preventing overcooling contained in the heat storage agent mainly composed of sodium acetate trihydrate (Patent Document 6). According to this technique, due to the physical effect of viscosity increase by the thickener, sedimentation of the supercooling-preventing supported crystals is suppressed, and phase separation caused by the sedimentation can be prevented or suppressed.

  However, in order to maintain the physical effects in the above methods (1) and (2), the viscosity of the heat storage agent must be significantly increased. When the viscosity of the heat storage agent increases significantly, the heat transfer in the heat storage agent slows down, causing a performance problem that the heat exchange rate between the heat storage agent and the outside (and hence the heat storage rate) decreases, Handling problems such as difficulty in filling the heat storage container with the heat storage agent occur.

  The present invention has been made in view of the above circumstances, and is a heat storage agent containing a quaternary ammonium salt, water and an alkali metal phosphate, which has a high heat storage rate and is unlikely to cause two-layer separation. And it aims at providing the thermal storage material using such a thermal storage agent.

  When the alkali metal phosphate was added to a heat storage agent containing a quaternary ammonium salt and water at a specific concentration or more, a phenomenon that the liquid phase separated into two layers was observed. For example, to a heat storage agent obtained by dissolving 40 parts by weight of tetra n-butylammonium bromide (TBAB) in 60 parts by weight of water, 1.5 parts by weight of disodium hydrogen phosphate is added and heated and stirred. When dissolved and allowed to stand, it was already separated into two layers in the solution state.

  At this time, the upper layer liquid part was 90% or more by volume ratio, and the lower layer liquid part was 10% or less by volume ratio. When each layer was analyzed, the upper layer liquid part was mainly composed of TBAB and water, and the lower layer liquid part was mainly composed of disodium hydrogen phosphate and water.

  Here, the phenomenon that the liquid separates into two layers immediately after the solution is prepared is the solid-liquid phase separation phenomenon in which the solid phase part gradually precipitates by repeated solidification and melting and separates into a solid phase and a liquid phase. It is fundamentally different. In order to suppress solid-liquid phase separation, attempts have been made to prevent sedimentation of the solid part by increasing the viscosity of the solution. The possibility of suppressing the layer is low.

  Even when the inventors actually increased the viscosity of the solution by adding known thickeners (starch, gelatin, sodium polyacrylate, polyvinyl alcohol, etc.), the two-layer separation could not be suppressed. . That is, it is difficult to suppress two-layer separation due to physical action such as increase in viscosity.

  Therefore, as a result of intensive studies by the present inventors, a water-soluble polysaccharide having at least one of a carboxyl group and a carboxymethyl group is added to a heat storage agent containing a quaternary ammonium salt, water, and an alkali metal phosphate. It was also found that the two-layer separation can be suppressed by adding a water-soluble polysaccharide having at least one of a carboxyl group and a carboxymethyl group and having an alkali metal.

  This is not simply a physical action such as an increase in viscosity, but a chemical action of an alkali metal phosphate and a water-soluble polysaccharide having at least one of a carboxyl group and a carboxymethyl group, or a carboxyl group. It is considered that the two-layer separation can be suppressed by a chemical action with a water-soluble polysaccharide having at least one of carboxymethyl groups and an alkali metal.

  In the present invention, typical examples of water-soluble polysaccharides having at least one of a carboxyl group and a carboxymethyl group are carrageenan and carboxymethylcellulose. Typical examples of the water-soluble polysaccharide having at least one of a carboxyl group and a carboxymethyl group and having an alkali metal are sodium alginate and sodium carboxymethylcellulose.

  In the present invention, typical examples of the alkali metal phosphate are sodium phosphate and potassium phosphate. Specifically, sodium dihydrogen phosphate, disodium hydrogen phosphate, trisodium phosphate, phosphorus Potassium dihydrogen acid, dipotassium hydrogen phosphate, and tripotassium phosphate, or a mixture thereof.

  In the present invention, a typical example of a quaternary ammonium salt is a tetraalkylammonium salt. A typical example of a tetraalkylammonium salt is tetra nbutylammonium bromide.

  Further, the present inventor has found that even when these water-soluble polysaccharides are added, the performance of the heat storage agent, that is, the supercooling release performance and the heat storage speed are not impaired to a problem.

  Furthermore, the present inventor suppresses the two-layer separation, although the viscosity of the solution varies depending on the molecular weight and the amount of these water-soluble polysaccharides added to the aqueous solution containing a quaternary ammonium salt and an alkali metal phosphate. We found that the effect has little to do with its viscosity. Therefore, since two-layer separation can be suppressed without increasing the viscosity of an aqueous solution containing a quaternary ammonium salt and an alkali metal phosphate, heat transfer in the heat storage agent becomes slow due to the increase in viscosity, and the heat storage agent. It is possible to avoid problems in performance in which the rate of heat exchange with the outside decreases and problems in handling such as difficulty in filling the heat storage container with the heat storage container due to high viscosity.

  A first aspect of the present invention is a heat storage agent comprising a quaternary ammonium salt, water, an alkali metal phosphate and a water-soluble polysaccharide, wherein the water-soluble polysaccharide is a carboxyl group or a carboxymethyl group. There is provided a heat storage agent characterized by being a water-soluble polysaccharide having at least one.

  A second aspect of the present invention is a heat storage agent comprising a quaternary ammonium salt, water, an alkali metal phosphate and a water-soluble polysaccharide, wherein the water-soluble polysaccharide is a carboxyl group or a carboxymethyl group. There is provided a heat storage agent characterized by being a water-soluble polysaccharide having at least one and an alkali metal.

  In the above heat storage agent, disodium hydrogen phosphate can be used as the alkali metal phosphate.

  In the present specification, the following terms are interpreted as follows unless otherwise explained.

  (1) The “clathrate hydrate” includes quasi clathrate hydrate.

  (2) The “clathrate hydrate” is sometimes abbreviated as “hydrate”.

  (3) “Raw material aqueous solution” refers to an aqueous solution of a quaternary ammonium salt. Even if a trace substance other than the quaternary ammonium salt is added, it is referred to as “raw aqueous solution”. Moreover, even if the clathrate hydrate containing a quaternary ammonium salt as a guest compound is dispersed or suspended, an aqueous solution containing a quaternary ammonium salt is referred to as a “raw material aqueous solution”.

  (4) “Hydrate formation temperature” refers to an equilibrium temperature at which clathrate hydrate having a quaternary ammonium salt as a guest compound is generated when an aqueous raw material solution is cooled. Even when the temperature at which the clathrate compound is generated varies depending on the concentration of the quaternary ammonium salt in the raw material aqueous solution, this is referred to as “hydrate formation temperature”. For convenience, the “hydrate formation temperature” may be referred to as “melting point”.

  (5) “The clathrate hydrate containing a quaternary ammonium salt as a guest compound” may be abbreviated as “a hydrate of a quaternary ammonium salt”.

  (6) “Heat storage agent” refers to a substance having a heat storage property regardless of the purpose and mode of use, storage, and other uses of thermal energy. Substances having cold storage properties are sometimes referred to as “cold storage agents”. The clathrate hydrate having heat storage properties can be a constituent of “heat storage agent” or “cold storage agent”.

  (7) “Heat storage rate” refers to the amount of heat energy that a heat storage agent of unit volume or unit weight can store in a unit time by a heat exchange operation under a certain condition, or a parameter having a positive correlation with this.

  According to the heat storage agent of the present invention, it is possible to have a high heat storage rate due to the action of the alkali metal phosphate, and it is possible to effectively suppress separation into two layers, and a high heat storage rate even after repeated solidification and melting. Can be maintained.

  In addition, since the viscosity of the heat storage agent does not increase, the heat transfer in the heat storage agent becomes slow due to the increase in viscosity and the heat exchange rate between the heat storage agent and the outside decreases, and the heat storage due to high viscosity There are no handling problems such as difficulty in filling the container with the heat storage agent.

  Hereinafter, embodiments of the present invention will be described in detail by showing examples and comparative examples of the present invention.

<Hydrate generation experiment>
To an aqueous solution of tetra-n-butylammonium bromide (TBAB) as a typical example of a quaternary ammonium salt, disodium hydrogen phosphate as a typical example of an alkali metal phosphate is added, and further a water-soluble polysaccharide is added. The formation behavior of the clathrate hydrate and the amount of heat storage were investigated.

  A 33% by weight aqueous solution of TBAB is used as a blank raw material aqueous solution, and its hydrate formation temperature is about 10 ° C.

[experimental method]
A glass container containing 30 g of the raw material aqueous solution was inserted into a 4 ° C. cooling liquid and cooled, and the formation behavior of hydrate crystals was observed.

  Next, the glass container containing the raw material aqueous solution that was cooled to 4 ° C. and produced hydrate crystals was inserted into 12 ° C. water contained in a heat insulating container equipped with a heater inside. Then, an electric current was passed through the heater so as to keep the water temperature at 12 ° C., and the solution was left until the aqueous solution temperature in the glass container reached 12 ° C. while heating. The TBAB hydrate crystals generated during this time melt.

  The amount of heat until the glass container containing the raw material aqueous solution in which the hydrate crystals at 4 ° C are formed reaches 12 ° C is obtained from the measured value of the cumulative amount of heat applied to the heater. By subtracting the amount of heat from 4 ° C. to 12 ° C., the amount of heat until the raw material aqueous solution became 4 ° C. to 12 ° C. was obtained, and the amount of heat stored was determined based on 12 ° C. of the heat storage agent.

  In determining the amount of heat storage, 12 ° C. is used as a reference because the temperature at which the refrigerant sent to the load in the general central cooling air conditioning system returns is 12 ° C., and the heat storage agent is a general central cooling air conditioning system. This is because the upper limit temperature of the temperature range when used in the above is 12 ° C., and the amount of heat held in the temperature range up to 12 ° C. is evaluated as the amount of stored heat. On the other hand, the reason why the temperature for cooling is based on 4 ° C. is that the cooling temperature of a general cooling refrigerator is 4 ° C.

  Next, the glass container containing the raw material aqueous solution at 12 ° C. was placed in a thermostatic bath and heated to 50 ° C. The heating temperature was set to 50 ° C because the heat storage material used in the heat storage building air-conditioning equipment and the heat storage agent as the main ingredient of the cold storage material for preserving fresh fish often reached the summer, Based on empirical knowledge that the temperature is about 40-50 ° C.

  The above 4 ° C. cooling, 12 ° C. heating, and 50 ° C. heating were taken as one cycle, and the formation behavior of hydrate crystals was observed and the amount of heat stored in the heat storage agent was measured.

[Comparative Example 1]
A TBAB 33 wt% aqueous solution was prepared as a blank raw material aqueous solution at about 40 ° C. and used as the raw material aqueous solution of Comparative Example 1.

  The glass container containing the raw material aqueous solution of Comparative Example 1 was inserted into a 4 ° C. cooling liquid and cooled in a state where the aqueous solution was allowed to stand. After about 10 minutes, the temperature of the aqueous solution reached 4 ° C. When 60 minutes had passed since the start of cooling, no hydrate crystals were observed, and the product was still in a supercooled state.

  Next, when the heater heating amount until the aqueous solution temperature reached 4 ° C. to 12 ° C. was obtained, and the heat storage amount at 4 ° C. to 12 ° C. was obtained, it was about 7 calories per 1 g of aqueous solution. There was no change in the state of the aqueous solution. Next, when the aqueous solution was heated to 50 ° C., the state of the aqueous solution was not changed. Furthermore, the cycle of 4 ° C. cooling, 12 ° C. heating, and 50 ° C. heating was repeated 10 times, but formation of hydrate crystals was not observed.

  As described above, in the case of an aqueous solution containing only TBAB, hydrate crystals are not generated, so that latent heat cannot be stored.

[Comparative Example 2]
A raw material aqueous solution was prepared at a concentration of 33% by weight of TBAB and 2% by weight of disodium hydrogen phosphate at about 40 ° C. to obtain a raw material aqueous solution of Comparative Example 2. The aqueous solution was somewhat turbid, and the liquid phase separated into two layers upon standing. The proportion of the lower layer was less than 1% by volume of the whole.

  The glass container containing the raw material aqueous solution of Comparative Example 2 was inserted into a 4 ° C. cooling liquid and cooled in a state where the aqueous solution was allowed to stand. Hydrate crystal formation was confirmed after a while after the aqueous solution temperature reached about 4 ° C. When 60 minutes passed, it was confirmed that many parts of the raw material aqueous solution were crystallized.

  Next, when the heater heating amount until the aqueous solution temperature reached 4 ° C. to 12 ° C. was obtained, and the heat storage amount at 4 ° C. to 12 ° C. was obtained, it was about 30 calories per 1 g of the aqueous solution. It was confirmed that a small amount of crystals remained in the aqueous solution that reached 12 ° C. Next, when the aqueous solution was heated to 50 ° C., a small amount of crystals remaining in the aqueous solution disappeared, and the aqueous solution was separated into two layers. The proportion of the lower layer was less than 1% by volume of the whole.

  Further, the cycle of 4 ° C. cooling, 12 ° C. heating, and 50 ° C. heating was repeated nine times. During the 9th repeated cooling at 4 ° C., it was confirmed that a part of the lower part of the raw material aqueous solution was crystallized when 60 minutes passed. The amount of heat stored at 4 ° C. to 12 ° C. was about 18 calories per 1 g of the aqueous solution. When the aqueous solution was heated to 50 ° C., a small amount of crystals in the aqueous solution disappeared, the aqueous solution was separated into two layers, and the proportion of the lower layer was about 3% by volume of the whole.

  As described above, in the case of an aqueous solution in which disodium hydrogen phosphate is added to TBAB, the aqueous solution is separated into two layers, and hydrate crystals are formed, but the latent heat amount that is stored as the number of cycles of cooling and heating is accumulated. Decreased.

[Examples 1 to 4]
A raw material aqueous solution was prepared at a concentration of 33% by weight of TBAB, 2% by weight of disodium hydrogen phosphate, and 1% by weight of sodium carboxymethylcellulose at about 40 ° C. to obtain a raw material aqueous solution of Example 1. The aqueous solution was colorless and transparent. Sodium carboxymethylcellulose is one of typical examples of water-soluble polysaccharides having a carboxymethyl group and having an alkali metal.

  The glass container containing the raw material aqueous solution of Example 1 was inserted into a 4 ° C. cooling liquid and cooled in a state where the aqueous solution was allowed to stand. Crystal formation was confirmed after a while after the aqueous solution temperature reached about 4 ° C. When 60 minutes passed, it was confirmed that many parts of the raw material aqueous solution were crystallized.

  Next, when the heater heating amount until the aqueous solution temperature reached 4 ° C. to 12 ° C. was obtained, and the heat storage amount at 4 ° C. to 12 ° C. was obtained, it was about 35 calories per 1 g of the aqueous solution. It was confirmed that a small amount of crystals remained in the aqueous solution that reached 12 ° C. The aqueous solution was then heated to 50 ° C. A small amount of crystals remaining in the aqueous solution disappeared, and the solution became colorless and transparent, and the aqueous solution was not separated into two layers.

  Further, the cycle of 4 ° C. cooling, 12 ° C. heating, and 50 ° C. heating was repeated nine times. During the 9th repeated cooling at 4 ° C., it was confirmed that many parts of the raw material aqueous solution were crystallized after 60 minutes had passed. The amount of heat stored at 4 ° C. to 12 ° C. was about 35 calories per 1 g of the aqueous solution. When the aqueous solution was heated to 50 ° C., a small amount of crystals in the aqueous solution disappeared and became colorless and transparent.

  As described above, in the case of an aqueous solution in which disodium hydrogen phosphate is added to TBAB and sodium carboxymethylcellulose is added, the aqueous solution is not separated into two layers, and hydrate crystals are smoothly generated and stored by cooling. The amount of latent heat was larger than that of Comparative Example 2, and the amount of latent heat stored was maintained without lowering even when the cooling and heating cycle was repeated.

  Furthermore, the raw material aqueous solution was prepared by changing the concentration of sodium carboxymethylcellulose in the range of 0.5 to 2% by weight to obtain the raw material aqueous solutions of Examples 2 to 4. When the same experiments as in Example 1 were performed on the raw material aqueous solutions of Examples 2 to 4, as shown in Table 1 below, the aqueous solution was not separated into two layers, and hydrate crystals were generated smoothly by cooling. However, the amount of latent heat stored does not change even when the concentration of sodium carboxymethylcellulose is changed, and is about 35 calories per gram of the aqueous solution. Also, the amount of stored latent heat is maintained without decreasing even if the cooling and heating cycle is repeated. It was done.

  The viscosity of the raw material aqueous solution to which the water-soluble polysaccharides of Examples 1 to 4 were added was measured at room temperature. The results are shown in Table 1 below. As shown in Table 1 below, the higher the addition rate, the higher the viscosity. On the other hand, it was confirmed that the effect of suppressing the two-layer separation by adding the water-soluble polysaccharide and the amount of latent heat stored were almost unrelated to the viscosity of the aqueous raw material solution.

Therefore, since the two-layer separation can be suppressed without increasing the viscosity of the aqueous solution containing the quaternary ammonium salt and the alkali metal phosphate, the heat transfer in the heat storage agent becomes slow due to the viscosity increase, and the heat storage It was possible to avoid problems in performance such as a decrease in the rate of heat exchange between the agent and the outside, and problems in handling such as difficulty in filling the heat storage container into the heat storage container due to high viscosity.

[Comparative Examples 3 to 6]
A raw material aqueous solution was prepared at a concentration of 33% by weight of TBAB, 2% by weight of disodium hydrogen phosphate, and 2% by weight of polyvinyl alcohol at about 40 ° C. to obtain a raw material aqueous solution of Comparative Example 3. Furthermore, what added polyethylene oxide, methylcellulose, and sodium polyacrylate at the density | concentration of 2 weight% or 1 weight%, respectively instead of polyvinyl alcohol was used as raw material aqueous solution of Comparative Examples 4, 5, and 6.

  The raw material aqueous solutions of Comparative Examples 3, 4, 5, and 6 were somewhat turbid, and the liquid phase separated into two layers when allowed to stand. The proportion of the lower layer was less than 1% by volume of the whole.

  The glass containers containing the raw material aqueous solutions of Comparative Examples 3, 4, 5, and 6 were inserted into a 4 ° C. cooling liquid, and the aqueous solution was allowed to cool in a stationary state. Hydrate crystal formation was confirmed after a while after the aqueous solution temperature reached about 4 ° C. When 60 minutes passed, it was confirmed that many parts of the raw material aqueous solution were crystallized.

  Next, when the heater heating amount until the aqueous solution temperature reached 4 ° C. to 12 ° C. was obtained, and the heat storage amount at 4 ° C. to 12 ° C. was obtained, all were about 30 calories per gram of the aqueous solution. It was confirmed that a small amount of crystals remained in the aqueous solution that reached 12 ° C. The aqueous solution was then heated to 50 ° C. The small amount of crystals remaining in the aqueous solution disappeared, and the aqueous solution was separated into two layers. The proportion of the lower layer was less than 1% by volume of the whole.

  Further, the cycle of 4 ° C. cooling, 12 ° C. heating, and 50 ° C. heating was repeated nine times. During the 9th repeated cooling at 4 ° C., it was confirmed that a part of the lower part of the raw material aqueous solution was crystallized when 60 minutes passed. As shown in Table 2 below, the amount of heat stored at 4 ° C. to 12 ° C. is about 18 calories in 1 g of aqueous solution, about 19 calories in Comparative Example 4, about 16 calories in Comparative Example 5, and Comparative Example 6 There were about 18 calories. When the aqueous solution was heated to 50 ° C., a small amount of crystals in the aqueous solution disappeared, the aqueous solution was separated into two layers, and the proportion of the lower layer was about 3% by volume of the whole.

The viscosity measured at room temperature is shown in Table 2 below, and it was a result that the two-layer separation could not be prevented even when the viscosity was equal to or larger than that of Example 1.

As shown in Table 2 above, in the case of an aqueous solution obtained by adding disodium hydrogen phosphate to TBAB and adding any of polyvinyl alcohol, polyethylene oxide, methylcellulose, and sodium polyacrylate, the aqueous solution is separated into two layers. However, although hydrate crystals were formed, the amount of latent heat stored was decreased as the number of cycles of cooling and heating was repeated.
The technical scope of the present invention is not limited by the above embodiments, and can be implemented in various forms without changing the gist of the invention. Further, the technical scope of the present invention extends to an equivalent range. The meaning or interpretation of each term in this specification does not preclude the technical scope of the present invention from reaching an equivalent range.

Claims (3)

  A heat storage agent comprising a quaternary ammonium salt, water, an alkali metal phosphate and a water-soluble polysaccharide, wherein the water-soluble polysaccharide has at least one of a carboxyl group and a carboxymethyl group A heat storage agent characterized by   A heat storage agent comprising a quaternary ammonium salt, water, an alkali metal phosphate and a water-soluble polysaccharide, wherein the water-soluble polysaccharide has at least one of a carboxyl group and a carboxymethyl group, and an alkali metal A heat storage agent characterized by being a water-soluble polysaccharide.   The heat storage agent according to claim 1 or 2, wherein the alkali metal phosphate is disodium hydrogen phosphate.