JP2009051905A - Aqueous solution having property for forming clathrate hydrate, clathrate hydrate containing quaternary ammonium salt as guest compound, slurry of the clathrate hydrate, method for producing clathrate hydrate, method for increasing rate of generating or growing clathrate hydrate, and method for preventing or reducing supercooling phenomenon caused when generating or growing clathrate hydrate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technique for increasing a heat-reserving rate of a clathrate hydrate and a technique of preventing or reducing supercooling by adding a specific additive to a raw material aqueous solution. <P>SOLUTION: The aqueous solution having properties for generating a clathrate hydrate by being cooled, and containing a tetra(iso-pentyl)ammonium salt added thereto contains a quaternary ammonium salt except the tetra(iso-pentyl)ammonium salt being a guest compound of the clathrate hydrate. The clathrate hydrate using the quaternary ammonium salt as the guest compound is generated by cooling the aqueous solution containing the quaternary ammonium salt except the tetra(iso-pentyl)ammonium salt and the tetra(iso-pentyl)ammonium salt. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a technique capable of increasing the heat storage rate of a clathrate hydrate that can be used as a latent heat storage agent or a component thereof, and more specifically, an aqueous solution having a property of generating a clathrate hydrate based on the technique. , Inclusion clathrate hydrate containing quaternary ammonium salt as guest compound, slurry of clathrate hydrate, method of clathrate hydrate formation, and rate of clathrate hydrate formation or growth The present invention relates to a method and a method for preventing or suppressing a supercooling phenomenon that occurs when clathrate hydrate is generated or grows.

In the present invention, the following terms shall be interpreted as follows unless otherwise explained.
(1) The “clathrate hydrate” includes quasi clathrate hydrate.
(2) “Clusion clathrate hydrate” is sometimes abbreviated as “hydrate”.
(3) “Guest compound” may be abbreviated as “guest”.
(4) “Slurry” refers to a substance in which solid particles are dispersed or suspended in a liquid or in that state. A surfactant may be added or mechanically stirred to make solid particles that tend to settle, but as long as the solid particles are dispersed or suspended in the liquid, That's it. As long as the solid particles are dispersed or suspended in the liquid, even if the dispersion or suspension is not uniform, it is referred to as “slurry”.

(5) “Raw material aqueous solution” refers to an aqueous solution containing a clathrate hydrate guest compound. Even if a trace substance different from the guest compound is added, it is referred to as “raw aqueous solution”. Moreover, even if the clathrate hydrate is dispersed or suspended, the clathrate hydrate is referred to as a “raw material aqueous solution” if it is an aqueous solution containing a guest compound of clathrate hydrate.
(6) “Hydrate formation temperature” refers to an equilibrium temperature at which clathrate hydrate should be generated when the raw aqueous solution is cooled. Even when the temperature at which the clathrate compound is generated varies depending on the concentration of the guest compound 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”.
(7) “The clathrate hydrate containing a quaternary ammonium salt as a guest compound” may be abbreviated as “a hydrate of a quaternary ammonium salt”. A clathrate hydrate containing a specific quaternary ammonium salt as a guest compound may also be abbreviated as the specific quaternary ammonium salt hydrate. The “clathrate hydrate containing a salt as a guest compound” may be abbreviated as “tetra n-butylammonium salt hydrate”.
(8) “Cold heat” refers to thermal energy that gives a temperature in a range higher than 0 ° C. and lower than 30 ° C. or corresponding to the temperature. The “cold range” refers to a temperature range higher than 0 ° C. and lower than 30 ° C. “Cool storage” refers to the accumulation of thermal energy by clathrate hydrate having a hydrate formation temperature in the cold range.

(9) “Heat storage” refers to the property of storing heat energy. The property of accumulating cold energy is sometimes referred to as “cold storage”.
(10) “Heat storage agent” refers to a substance having a heat storage property, regardless of the purpose or mode of storage, transportation or other use of heat energy, or the field of use. 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”.
(11) “Heat storage material” refers to a member having heat storage properties. The heat storage agent can be a component of the “heat storage material”. “Cool storage material” refers to a member having cold storage properties. A cold storage agent can be a component of a “cold storage material”.
(12) “Heat storage rate” refers to the amount of heat energy that a heat storage agent of unit volume or unit weight can store within a unit time by a heat exchange operation under a certain condition, or a parameter having a positive correlation with this. A similar speed in the case where the cold storage agent accumulates cold heat may be referred to as “cold storage speed”.
(13) “Harmonic melting point” means that when the clathrate hydrate is generated from the liquid phase of the raw material aqueous solution, the concentration of the guest compound in the raw material aqueous solution is equal to the concentration of the guest compound in the clathrate hydrate, The temperature at which the composition of the liquid phase does not change before and after the clathrate hydrate is formed.
In the state diagram in which the vertical axis represents the hydrate formation temperature and the horizontal axis represents the concentration of the guest compound in the liquid phase of the raw material aqueous solution, the maximum point is the “harmonic melting point”. The concentration of the guest compound in the raw material aqueous solution that gives the harmonic melting point is called “harmonic melting point concentration”. When clathrate hydrate is produced from a raw material aqueous solution having a concentration lower than the harmonic melting point concentration, the concentration of the guest compound in the raw material aqueous solution decreases as the clathrate hydrate is produced, and the hydrate formation temperature relative to that concentration is reduced. descend.

The clathrate hydrate is produced by cooling the raw material aqueous solution to a hydrate formation temperature or lower, and heat energy equivalent to latent heat is accumulated in the clathrate hydrate crystals thus produced. Used as a heat storage agent or its component.
A non-gas clathrate hydrate is known as an example of the above clathrate hydrate, that is, a non-gas clathrate hydrate (Non-Patent Document 1). In addition, those using a quaternary ammonium salt as a guest are known (Patent Document 1).

Many quaternary ammonium salt hydrates are produced at normal pressure, have a large latent heat when producing hydrates, have a relatively large amount of heat storage, and are not flammable like paraffin and are easy to handle. It is.
Also, many quaternary ammonium salt hydrates have a harmonic melting point or hydrate formation temperature higher than the melting point of ice (0 ° C under normal pressure), so the heat storage agent is cooled to produce a hydrate. The temperature of the refrigerant at the time of heating may be high, and the coefficient of performance (COP) of the refrigerator that cools the refrigerant is increased.
In addition, quaternary ammonium salt hydrates are easy to disperse or suspend in water or aqueous solutions, and are generally produced in a slurry because they are uniformly dispersed, have low agglomeration properties, have no significant phase separation, and have a very low flow resistance. If it carries out (patent document 2, patent document 3), a thermal storage material or a thermal storage agent, and a heat transport medium can be comprised as a slurry, and can be handled (patent document 4, patent document 5).
Therefore, it can be said that the hydrate of a quaternary ammonium salt is promising as a heat storage material or a heat storage agent, or its component or component.

Specific examples of quaternary ammonium salt hydrates are clathrate hydrates using tetra-n-butyl ammonium salt or tri-n-butyl-n-pentyl ammonium salt as a guest compound, particularly tetra-n-butyl ammonium bromide ( Regarding clathrate hydrates using TBAB) as guests, it is known that there are first and second hydrates having different hydration numbers (Patent Document 6).
Further, it is known that tetrabutylammonium nitrate hydrate is impregnated into a porous solid substance to tetrabutylammonium nitrate, which is a heat storage main agent, and this is used as a supercooling inhibitor (Patent Document 7).
Narutake Kawasaki et al., “Application of Gas Hydrate to Cold Heat Storage Material”, Chemical Engineering, Chemical Industry Co., Ltd., August 1, 1982, Vol. 27, No. 8, p. 603, Table 1 Japanese Patent Publication No.57-35224 Japanese Patent Laid-Open No. 2004-3718 JP 2002-263470 A Japanese Patent Laid-Open No. 10-259978 Japanese Patent Application Laid-Open No. 2001-301884 JP 2001-280875 A Japanese Patent No. 3324392

  Now, in using a thermal storage agent, it may be said that the higher the thermal storage rate, the better. If the heat storage rate of the heat storage agent is high, more heat energy can be stored in a shorter time.For example, there is a time margin or a margin in technical specifications for the operation of a heat storage air conditioner or facility that uses a heat storage agent. This is because the design of the device or equipment becomes easy, and the configuration, mechanism, operation, etc. of the device or equipment can be avoided in many cases, leading to cost reduction. Therefore, a technique for further increasing the heat storage rate of the heat storage agent is required.

On the other hand, in the case of latent heat storage using clathrate hydrate as a heat storage agent, the heat storage rate of clathrate hydrate is closely related to the formation and growth of crystals of clathrate hydrate. This is because the latent heat storage by clathrate hydrate is based on the phenomenon that when the raw material aqueous solution is cooled to the hydrate formation temperature, crystals of clathrate hydrate having heat storage properties are formed and grow. .
In addition, since the clathrate hydrate crystals have a complicated structure, the formation and growth of crystals is slower than, for example, ice. This means that the formation and growth of clathrate hydrate crystals can be the rate-determining heat storage by clathrate hydrate. Therefore, when building a technology to increase the heat storage rate of clathrate hydrate in latent heat storage by clathrate hydrate, the behavior of crystal formation and growth of clathrate hydrate is improved more favorably. A technique to do this is required.

  In addition, when an aqueous raw material solution is cooled to produce a quaternary ammonium salt hydrate, if it is cooled at a certain cooling rate, a hydrate will not be produced even if the temperature falls below the hydrate production temperature. However, a phenomenon in which the solution state is maintained at least temporarily, that is, a supercooling phenomenon occurs. This phenomenon delays the formation and growth of hydrate crystals, and generally reduces the heat storage rate of the heat storage agent. Therefore, in order to avoid the decrease in the heat storage rate or increase the heat storage rate, a technique for preventing or suppressing the supercooling of the raw material aqueous solution is required.

  However, the adverse effect of the supercooling phenomenon is not limited to a decrease in the heat storage rate. For example, when the supercooled state of the raw material aqueous solution is unexpectedly canceled, a large amount of clathrate hydrate crystals are formed and grow, which may hinder the normal operation of the apparatus and equipment. Therefore, the purpose of preventing or suppressing the supercooling of the raw material aqueous solution is not only to avoid a decrease in the heat storage rate of the clathrate hydrate.

From such a background, when using clathrate hydrate as a latent heat storage agent or a component thereof, a fine particle which is a nucleus of hydrate formation is added to the raw material aqueous solution, and the heat transfer surface of the heat exchanger is machined. Ingenuity is made to prevent or suppress the supercooling phenomenon or promote the release of supercooling by applying a means such as applying mechanical vibration or stirring the raw material aqueous solution (see, for example, Patent Document 3).
However, adding these means to equipment and facilities that use clathrate hydrate as a latent heat storage agent or component thereof leads to complications in the structure, mechanism, operation, etc. of the equipment and equipment, thereby reducing costs. It will be against the request. Therefore, if the supercooling phenomenon is to be suppressed or prevented, it is preferable to devise an additive to the raw material aqueous solution to meet the above cost reduction request.
Further, the supercooling release method in Patent Document 7 requires that a porous solid substance such as alumina particles be mixed with the heat storage material, and thus there is a problem that installation and handling of the heat storage material become complicated. In addition, in this supercooling release method, tetranbutylammonium fluoride hydrate, which is a supercooling preventive agent, is impregnated or encapsulated in the porous solid material, but is not in physical contact with the external heat storage material. Since there is a contradiction that it should not be, there is a problem that the effect of the supercooling preventive agent will be dissolved and the effect will not last long. Furthermore, in applications where the heat storage material is used as a cold transport medium or distributed inside pipes, containers, etc., when this supercooling release method is applied, the supercooling inhibitor is impregnated or encapsulated, such as alumina particles. Although the porous solid material is mixed with the heat storage material and distributed together, it is difficult in principle to realize that the effect of releasing the supercooling by the porous solid material lasts for a long time, and no realization example is known.

  The present invention has been made in view of the above circumstances, and a technique for increasing the heat storage rate when a clathrate hydrate is used as a heat storage agent by introducing a specific additive into an aqueous raw material solution, and supercooling. It aims at providing the technique which suppresses or prevents.

As a result of diligent research, the inventors added tetraisopentylammonium salt to a raw material aqueous solution having a property of forming a clathrate hydrate having a quaternary ammonium salt other than tetraisopentylammonium salt as a guest compound. It has been found that when the raw material aqueous solution is cooled to produce clathrate hydrate, the heat storage rate increases.
Further, the inventors added a tetraisopentylammonium salt to a raw material aqueous solution having a property of forming a clathrate hydrate having a quaternary ammonium salt other than the tetraisopentylammonium salt as a guest compound. It was found that supercooling is prevented or suppressed when clathrate hydrate is formed upon cooling.
This invention is made | formed based on these new knowledge, and has the following structures.

  The aqueous solution (raw material aqueous solution) according to the first embodiment of the present invention contains a quaternary ammonium salt other than tetraisopentylammonium salt, and is cooled to include the quaternary ammonium salt as a guest compound. An aqueous solution having a property of generating tetraisopentylammonium salt.

  The clathrate hydrate according to the second aspect of the present invention includes a quaternary ammonium salt other than the tetraisopentylammonium salt and is produced by cooling an aqueous solution to which the tetraisopentylammonium salt is added. The quaternary ammonium salt is a guest compound.

  The clathrate hydrate slurry according to the third aspect of the present invention is obtained by dispersing or suspending the clathrate hydrate according to the second aspect in the raw material aqueous solution.

  The method for producing a clathrate hydrate according to the fourth aspect of the present invention includes a step of preparing an aqueous solution containing a quaternary ammonium salt other than a tetraisopentylammonium salt and to which a tetraisopentylammonium salt is added. And a step of producing an clathrate hydrate containing the quaternary ammonium salt as a guest compound by cooling the aqueous solution.

  A method for increasing the rate of formation or growth of clathrate hydrate according to the fifth aspect of the present invention is to guest the quaternary ammonium in an aqueous solution containing a quaternary ammonium salt other than tetraisopentylammonium salt. A method for increasing the rate of formation or growth of clathrate hydrate as a compound, the step of preparing the aqueous solution to which tetraisopentylammonium salt is added, and the aqueous solution to which tetraisopentylammonium salt is added And a step of cooling.

  The method for preventing or suppressing the supercooling phenomenon that occurs when the clathrate hydrate according to the sixth aspect of the present invention is produced is to cool an aqueous solution containing a quaternary ammonium salt other than the tetraisopentylammonium salt. A method for preventing or suppressing a supercooling phenomenon that occurs when an clathrate hydrate having a quaternary ammonium salt as a guest compound is formed or grown, wherein the aqueous solution to which a tetraisopentylammonium salt is added. What prevents or suppresses the supercooling phenomenon that occurs when the clathrate hydrate is produced or grows, characterized by having a step of preparing and a step of cooling the aqueous solution to which tetraisopentylammonium salt is added It is.

The harmonic melting point of clathrate hydrate using tetraisopentylammonium salt as a guest compound is about 30 ° C., and clathrate hydrates containing many quaternary ammonium salts other than tetraisopentylammonium salt as guest compounds. Higher than the harmonic melting point. For this reason, when the aqueous solution containing a quaternary ammonium salt other than the tetraisopentylammonium salt is cooled to produce an inclusion hydrate of the quaternary ammonium salt, the tetraisopentylammonium salt is added in advance. In this way, the clathrate hydrate of tetraisopentylammonium salt is first produced in the cooling process, and the effect of preventing or suppressing the supercooling phenomenon by promoting the production of clathrate hydrate of the quaternary ammonium salt. It is thought to give birth.
Further, it has been found that even when a tetraisopentylammonium salt is added at a very low concentration (for example, 1 wt% or less), the supercooling phenomenon is prevented or suppressed.
Examples of such a tetraisopentylammonium salt include tetraisopentylammonium bromide, tetraisopentylammonium fluoride, and tetraisopentylammonium chloride. Further, tetraisopentylammonium salts having an anion moiety such as phosphoric acid, nitric acid and sulfuric acid can be mentioned.
In the present invention, a typical example of a quaternary ammonium salt other than the tetraisopentylammonium salt is a tetra-n-butylammonium salt.

  According to the present invention, since the tetraisopentylammonium salt is added to the raw material aqueous solution having the property of producing a hydrate of a quaternary ammonium salt other than the tetraisopentylammonium salt, the raw aqueous solution is hydrated. When the hydrate is produced by cooling below the product formation temperature, the heat storage rate increases (hereinafter referred to as “heat storage rate increase effect”).

Further, according to the present invention, since the tetraisopentylammonium salt is added to the raw material aqueous solution having the property of forming a quaternary ammonium salt hydrate other than the tetraisopentylammonium salt, When the clathrate hydrate is produced by being cooled below the hydrate formation temperature, supercooling can be prevented or suppressed (hereinafter referred to as “supercooling suppression effect”). Generally speaking, the present invention exhibits at least one of a heat storage speed increase effect and a supercooling suppression effect.
The effect which each form of this invention has is as follows.

According to the first aspect of the present invention, it has the property of producing a hydrate of a quaternary ammonium salt other than the tetraisopentylammonium salt when cooled to a hydrate production temperature or lower. A raw material aqueous solution capable of increasing the heat storage rate of the hydrate can be realized.
In addition, according to the first aspect of the present invention, it has a property of producing a hydrate of a quaternary ammonium salt other than a tetraisopentylammonium salt when cooled to a hydrate formation temperature or lower, and the cooling thereof. In this case, a raw material solution in which overcooling is prevented or suppressed can be realized. These are suitable as a raw material aqueous solution for producing a clathrate hydrate used as a latent heat storage agent or a component thereof.

  According to the 2nd form of this invention, the clathrate hydrate with a higher heat storage rate is realizable. In addition, when the raw material aqueous solution having the property of generating a hydrate of a quaternary ammonium salt other than the tetraisopentylammonium salt is cooled to a hydrate formation temperature or lower, overcooling of the raw material aqueous solution is prevented or suppressed. The clathrate hydrate produced can be realized. These are suitable as clathrate hydrates used as latent heat storage agents or components thereof.

  According to the 3rd form of this invention, the slurry of the clathrate hydrate which concerns on a 2nd form is realizable. This slurry can be produced by cooling the aqueous raw material solution according to the first embodiment to a hydrate formation temperature or lower, and with this, a heat storage material, a heat storage agent, or a heat transport medium can be configured and handled.

  According to the fourth aspect of the present invention, the quaternary ammonium salt is contained by cooling an aqueous solution containing a quaternary ammonium salt other than the tetraisopentylammonium salt and added with the tetraisopentylammonium salt. Since clathrate hydrate as a guest compound is generated, at least one of the effect of increasing the heat storage rate and the effect of suppressing supercooling is exhibited. As a result, the clathrate hydrate according to the second embodiment can be realized.

  According to the fifth aspect of the present invention, the quaternary ammonium salt is added to the guest by cooling an aqueous solution containing a quaternary ammonium salt other than the tetraisopentylammonium salt and added with the tetraisopentylammonium salt. Since the clathrate hydrate as a compound is generated, it is possible to realize a technique capable of increasing the rate at which the quaternary ammonium hydrate is generated or grown, and the overall heat storage rate.

  The increase in the hydrate formation rate and the increase in the growth rate both contribute to the increase in the heat storage rate. From the viewpoint that hydrate growth is premised on its formation, it can be said that the increase in the generation rate contributes more to the increase in the heat storage rate than the increase in the growth rate. From the viewpoint that the crystals of the hydrate become the nucleus when other crystals are formed, it can be said that the increase in the growth rate also contributes to the increase in the heat storage rate.

  According to the sixth aspect of the present invention, a quaternary ammonium salt other than the tetraisopentylammonium salt is contained, and the aqueous solution to which the tetraisopentylammonium salt is added is cooled to bring the quaternary ammonium salt into a guest. Since the clathrate hydrate as a compound is generated, it is possible to realize a technique capable of preventing or suppressing the supercooling of the aqueous solution that occurs during the generation.

Hereinafter, the present invention will be described in detail by way of examples.
[Hydrate generation beaker experiment]
An aqueous solution of tetra-n-butylammonium bromide (TBAB) as a typical example of a quaternary ammonium salt other than the tetraisopentylammonium salt is added to an aqueous solution of tetraisopentylammonium bromide (hereinafter referred to as TiPAB) as a typical example of a tetraisopentylammonium salt. ) Was added, and the formation behavior of the clathrate hydrate and the cold storage amount were investigated.

  In the following comparative examples and examples, the generated clathrate hydrate is heated by an electric heater provided in a glass beaker and melted to measure the amount of heat from the amount of electricity until the aqueous solution temperature reaches 12 ° C. It was calculated as the amount of cold storage based on. 12 ° C. is the standard because the temperature at which the refrigerant sent to the load side returns to 12 ° C. in a general central cooling air-conditioning system is used, and a cold storage agent or a cold transport medium is used in the general central cooling air-conditioning system. It is because the upper limit temperature of the temperature range at the time of being carried out 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.

  In addition, TBAB hydrate includes a first hydrate having a hydration number of 26 and a second hydrate having a hydration number of 36. Depending on cooling conditions such as TBAB concentration and temperature in the aqueous solution, Different hydrates are produced. In this experiment, it was performed under the conditions for producing a second hydrate having a larger latent heat.

[Comparative Example 1]
<Only TBAB aqueous solution without stirring>
90 g of a room temperature aqueous solution having a concentration of 40.5 wt%, which is the harmonic melting point concentration of TBAB, was placed in a glass beaker, and the glass beaker was inserted into a 1 ° C cooling liquid, and the aqueous solution was cooled without being stirred.
When the temperature of the aqueous solution reached about 1 ° C. and 10 hours had passed, the formation of clathrate hydrate was not recognized and the supercooled state remained. Therefore, latent heat could not be stored.

<Addition of TiPAB to TBAB aqueous solution without stirring>
90 g of an aqueous solution obtained by adding 1 wt% of TiPAB to an aqueous solution of 40.5 wt% concentration, which is the harmonic melting point concentration of TBAB, is placed in a glass beaker, and the glass beaker is inserted into a 1 ° C. cooling solution. Cooled in place.
When the temperature of the aqueous solution reached about 1 ° C. and 5 hours passed, the formation of clathrate hydrate was observed. Further cooling is continued, and when 10 hours have elapsed from the start of cooling, the glass beaker is taken out of the cooling liquid and heated by an electric heater provided in the glass beaker to melt the clathrate hydrate and the aqueous solution temperature becomes 12 ° C. The amount of heat was measured from the amount of electricity up to and calculated as the amount of heat stored based on 12 ° C., and it was 28 cal per gram of the aqueous solution.
It has been found that by adding TiPAB, the supercooling of the TBAB aqueous solution is released, and clathrate hydrate is generated and latent heat can be stored.
In addition, a series of solidification and melting operations of heating this aqueous solution to 40 ° C. and then cooling it were repeated 60 times, but no decrease in the effect of releasing the supercooling was observed. In the process of solidification and melting, the composition of the aqueous solution does not change, so the decrease in the effect of releasing the supercooling does not occur in principle, but it has been experimentally verified.

[Comparative Example 2]
<Only TBAB aqueous solution with stirring>
90 g of a normal temperature aqueous solution having a TBAB concentration of 14.5 wt% was placed in a glass beaker, the glass beaker was inserted into a 1 ° C. cooling liquid, and the aqueous solution was cooled while stirring. When the temperature of the aqueous solution reached about 1 ° C. and 30 minutes had passed, no hydrate formation was observed, and the solution remained in a supercooled state. Therefore, latent heat could not be stored.
When 30 minutes have elapsed, the glass beaker is taken out of the coolant, heated by an electric heater provided in the glass beaker while stirring, and the amount of heat is measured from the amount of electricity until the aqueous solution temperature reaches 12 ° C. The amount of heat stored as a standard was 9.9 cal per 1 g of aqueous solution. This corresponds to sensible heat when the temperature of the aqueous solution rises from 1 ° C to 12 ° C.

<Addition of TiPAB to TBAB aqueous solution with stirring>
90 g of an aqueous solution obtained by adding 0.025 wt% of TiPAB to a 14.5 wt% aqueous solution of TBAB was placed in a glass beaker, the glass beaker was inserted into a 1 ° C. cooling liquid, and the aqueous solution was cooled while stirring. When the temperature of the aqueous solution reached about 1 ° C. and 16 minutes had passed, formation of clathrate hydrate was observed, and eventually a slurry was formed.

  Further cooling was continued, and after 30 minutes from the start of cooling, the glass beaker was taken out of the cooling liquid and heated by the electric heater provided in the glass beaker while continuing to stir. The calorific value was measured from the amount of electricity up to 12 ° C., and the calorific value was determined as 12 ° C., and the calorific value was 16 cal per 1 g of the aqueous solution.

  The amount of stored heat is greatly increased as compared with Comparative Example 2. Even if all the added TiPAB becomes a hydrate, it is estimated that only 0.03 to 0.05 cal of latent heat is generated per 1 g of the aqueous solution. Moreover, when the specific heat of the aqueous solution state was measured, the specific heat change by addition of 0.025 wt% TiPAB was not able to be confirmed. Therefore, it can be said that the effect on the heat storage amount by TiPAB itself is very small, and it is recognized that the heat storage amount of the TBAB clathrate hydrate increased in Example 2.

It was confirmed that the addition of TiPAB promotes the release of supercooling of the TBAB aqueous solution, promotes the formation of clathrate hydrate and promotes the accumulation of latent heat.
That is, an improvement in the cold storage rate was recognized.

[Comparative Example 3]
<Only TBAB aqueous solution, with stirring, add nucleation core>
A glass beaker containing 90 g of a normal TBAB 14.5 wt% aqueous solution was inserted into a 4 ° C. cooling liquid, and the aqueous solution was cooled while stirring. When the aqueous solution temperature reached 5.4 ° C., 0.05 g of TBAB dihydrate was added as a hydrate-forming nucleus. The TBAB dihydrate was prepared separately based on a TBAB 14.5 wt% aqueous solution.

  Simultaneously with the introduction of the core, the glass beaker was taken out of the cooling liquid, and the cooling was temporarily stopped, and the stirring was continued for 2.5 minutes. During this time, the aqueous solution showed a slurry state and a temperature increase of about 1 to 2 ° C. was observed. Since the reaction capable of forming TBAB hydrate is an exothermic reaction, the formation of TBAB hydrate was confirmed from the temperature increase and the visual confirmation that a slurry state was exhibited. The TBAB hydrate produced here is a second hydrate.

After holding for 2.5 minutes, the glass beaker was again inserted into the 4 ° C. coolant and cooled with stirring for 3 minutes. As the temperature of the slurry gradually decreased, the concentration of the slurry was visually increased.
After cooling for 3 minutes, the glass beaker was taken out of the coolant, and the cooling was stopped while stirring was continued. After holding for 1 minute, the glass beaker was heated at a constant power by an electric heater inserted into the glass beaker while stirring. The hydrate was melted by heating, and the slurry gradually became thin and eventually became a transparent aqueous solution.
Heating with an electric heater was continued until the temperature of the aqueous solution further increased and reached 12 ° C.
The amount of heating until the temperature of the aqueous solution reached 12 ° C. was determined, and the amount of heat stored based on 12 ° C. was determined to be 8.4 cal per gram of the aqueous solution.

<0.01 wt% of TiPAB is added to the TBAB aqueous solution, with stirring, and a nucleus for hydrate formation>
A glass beaker in which 90 g of an aqueous solution containing 0.01 wt% of TiPAB was added to a 14.5 wt% aqueous solution of TBAB at room temperature was inserted into a 4 ° C. cooling liquid, and the aqueous solution was cooled while stirring. When the aqueous solution temperature reached 5.4 ° C., 0.05 g of TBAB dihydrate was added as a nucleus for hydrate formation. The TBAB dihydrate charged as a core was prepared separately based on a TBAB 14.5 wt% aqueous solution.

The time required for the aqueous solution temperature to reach 5.4 ° C. (cooling rate) was the same as in Comparative Example 3.
Simultaneously with the introduction of the nuclei, the glass beaker was taken out of the cooling liquid, the cooling was temporarily stopped, and the mixture was kept for 2.5 minutes while continuing to stir. During this time, the aqueous solution showed a slurry state, and the temperature rise was measured. From the visual confirmation that the temperature rise and the slurry state were exhibited, the formation of TBAB hydrate could be confirmed.
In addition, the temperature increase width after introducing the nucleus and releasing the supercooling was about 2 to 3 ° C., which was larger than that of Comparative Example 3. Also, the rate of temperature increase was larger than that of Comparative Example 3.

After holding for 2.5 minutes, the glass beaker was again inserted into the 4 ° C. cooling liquid and cooled with stirring for 3 minutes. While the temperature of the slurry gradually decreased, the concentration of the slurry was visually increased.
After cooling for 3 minutes, the glass beaker was taken out of the coolant, and the cooling was stopped while stirring was continued. After holding for 1 minute, the glass beaker was heated at a constant power by an electric heater inserted into the glass beaker while stirring. The hydrate was melted by heating, and the slurry gradually became thin and eventually became a transparent aqueous solution. Heating with an electric heater was continued until the temperature of the aqueous solution further increased and reached 12 ° C.

  The amount of heating until the temperature of the aqueous solution reached 12 ° C. was determined, and the amount of heat stored based on 12 ° C. was determined to be 9.8 cal per gram of the aqueous solution. Compared with the comparative example 3, it is increased by 1.4 cal per gram of the aqueous solution, which corresponds to an increase of about 20%.

Here, the heat storage amount of Example 3 increased as compared with Comparative Example 3 will be considered.
TiPAB is added only about 7/10000 of TBAB. Even if all of the added TiPAB becomes a hydrate, it is estimated that only 0.01 to 0.02 cal of latent heat per 1 g of the aqueous solution is generated.
Moreover, when the specific heat of the aqueous solution state was measured, the specific heat change by addition of 0.01 wt% TiPAB was not able to be confirmed. Therefore, it can be said that the effect of heat on the amount of heat stored by TiPAB itself is very small. In Example 3, it is recognized that the amount of heat stored in the second hydrate of TBAB has increased.
Thus, by adding TiPAB, the amount of heating until the temperature of the aqueous solution reaches 12 ° C., that is, the amount of heat stored in the second hydrate of TBAB in a series of cooling processes can be increased, that is, the heat storage rate can be increased. I was able to improve.
In addition, the increase in the temperature rise after releasing the supercooling (that is, the increase in the amount of hydrate formation) and the increase in the temperature increase rate are due to the addition of TiPAB to increase the production rate of TBAB hydrate. It is shown that.

[Comparative Example 4]
In Comparative Example 3, the aqueous solution after being heated to 12 ° C. was cooled again. That is, a glass beaker containing a 12 ° C. aqueous solution was inserted into a 4 ° C. cooling liquid, and the aqueous solution was cooled while stirring.
When the temperature of the aqueous solution reached about 4 ° C. and 10 minutes had passed, no hydrate formation was observed.
In Comparative Example 3, TBAB dihydrate was added as a nucleus for hydrate formation, but it was heated to 12 ° C. and melted, and it was confirmed that it did not function as a nucleus for hydrate formation during the second cooling. did it.

The experiment was performed in the same manner as in Example 3 except that the addition concentration of TiPAB was 0.025 wt%.
The amount of heating until the temperature of the aqueous solution reached 12 ° C., that is, the amount of heat storage, was higher than that of Comparative Example 3 and was similar to Example 3.
The aqueous solution after heating to 12 ° C. was cooled again.
That is, a glass beaker containing a 12 ° C. aqueous solution was inserted into a 4 ° C. cooling liquid, and the aqueous solution was cooled while stirring.
As a result, even if TBAB dihydrate was not used as the nucleus for hydrate formation, when the aqueous solution reached about 7 ° C, the supercooling was released and the formation of hydrate was confirmed as the temperature rose. It was done.

Thereafter, the same aqueous solution was heated to 12 ° C. and then repeatedly cooled, but similarly, the supercooling release was observed at about 7 ° C.
When the temperature at which the aqueous solution was heated was 35 ° C., no overcooling cancellation during cooling was observed.
The harmonic melting point of TiPAB hydrate is 30 ° C, but when heated to 35 ° C, TiPAB hydrate melts and TiPAB hydrate particles do not remain in the aqueous solution, so cooling and heating to 12 ° C are repeated. In this case, it is presumed that TiPAB hydrate particles remain and express the effect of releasing the supercooling when TBAB hydrate is produced.
Even if the cooling and heating as described above are repeated, the effect of releasing the supercooling appears when the concentration of TiPAB to be added is 0.025 wt% or more. I understood by repeating.
Once TiPAB hydrate is generated, it is possible to release the supercooling only by cooling, without performing a special supercooling release operation, such as adding TBAB dihydrate as the nucleus for hydrate generation. It turns out that it can be achieved.

[Experiment with heat exchanger]
Using a plate-type heat exchanger (height 1.6m, width 0.6m, depth 0.9m, retained water volume 0.2m ³ on one side, counter-flow system), the TBAB aqueous solution that has been supercooled to a predetermined temperature is further cooled. An experiment to release the cooling was performed.
The aqueous solution has a TBAB concentration of 14.5 wt%, and the TBAB clathrate hydrate formation temperature at this concentration is 8.1 ° C.
Cold water is introduced into the heat exchanger, and an aqueous TBAB solution that is supercooled to a predetermined temperature is introduced into the heat exchanger to exchange heat and further cool. The aqueous TBAB solution that has flowed into the heat exchanger is further cooled by cold water and flows out of the heat exchanger, and then heated by another heat exchanger downstream, and then returned to the supercooled state at the initial predetermined temperature before the heat exchanger. Will be re-entered.

While circulating this TBAB aqueous solution, the temperature of the fluid flowing out of the heat exchanger was measured and observed. Here, the fluid refers to a supercooled aqueous solution or a slurry that is released from supercooling to form clathrate hydrate and floats in the aqueous solution.
When the supercooled aqueous solution is released from the supercooling and clathrate hydrate is generated, the temperature rises and the temperature of the fluid flowing out of the heat exchanger increases. The time from the start of heat exchange in the heat exchanger until the temperature of the fluid flowing out of the heat exchanger rises after the supercooling is released and clathrate hydrate is generated is taken as the time until the supercooling is released. Measurement was made to compare the case of only the TBAB aqueous solution with the case of adding TiPAB to the TBAB aqueous solution.
The results are shown in Table 1. When the degree of supercooling relative to the clathrate hydrate formation temperature of the supercooled aqueous solution is 1.7 degrees and 1.4 degrees, the time until the temperature rise of the fluid flowing out from the heat exchanger occurs is excessive. Shown as time to cool down.

It has been found that by adding TiPAB to the TBAB aqueous solution, the time to release the supercooling is significantly shortened compared to the case where it is not added, and the supercooling release is promoted. Moreover, it turned out that the effect which shortens the time to supercooling cancellation | release is so high that the addition density | concentration of TiPAB is high.
It has been found that by adding TiPAB to the TBAB aqueous solution, the supercooling release is promoted and the production rate of the TBAB clathrate hydrate is increased, so that the cold storage rate can be improved.

[Experiment with tank]
An experiment was conducted in which a supercooled TBAB aqueous solution was passed through the tank to release supercooling.
A supercooled TBAB aqueous solution is introduced from the upper side of a cylindrical tank (volume 0.4 m ³ ) that does not have a heat exchange function, and the supercooling is released while passing through the tank to produce clathrate hydrate. A hydrate slurry is generated and the hydrate slurry is withdrawn from just below the tank.
A small amount of hydrate slurry is added to the inflowing supercooled TBAB aqueous solution as a nucleus for clathrate hydrate formation. The temperature of the supercooled aqueous solution flowing in and the temperature of the hydrate slurry flowing out were measured, and the temperature rise in the tank was measured. When the aqueous solution is released from the supercooling in the tank, the temperature rises, and the larger the value of the temperature rise, the larger the ratio of the supercooling release.

The supercooling release ratio is set to 0 when the temperature does not rise at all in the tank and the supercooling release does not proceed at all. The supercooling is completely released in the tank, and the hydrate slurry has reached the temperature that should originally be reached. The case was defined as 100% and evaluated.
The subcooling release ratio was determined.
The flow rate of the supercooled aqueous solution flowing into the tank is about 0.1 m ³ / min, and the tank is completely sealed. The concentration of the TBAB aqueous solution was 14.5 wt%.
Compared with the case where only the TBAB aqueous solution is added to the case where TiPAB is added to the TBAB aqueous solution, the tank in the case where the supercooling degree with respect to the clathrate hydrate formation temperature of the supercooled aqueous solution is 1.7 degrees and 1.5 degrees The subcooling release ratio was calculated.
The results are shown in Table 2.

It was found that by adding TiPAB to the TBAB aqueous solution, the supercooling release ratio increases compared to the case where it is not added, and the supercooling release is promoted. Moreover, it turned out that the effect which enlarges a supercooling cancellation | release ratio is so high that the addition density | concentration of TiPAB is high.
By adding TiPAB to the TBAB aqueous solution, the release of supercooling is promoted and the production rate of TBAB clathrate hydrate is increased, so that the cold storage rate can be improved.

[Experiments with a two-stage heat exchanger]
As an apparatus for producing hydrate slurry for storing heat with a hydrate slurry, there is an apparatus described in Japanese Patent Application Laid-Open No. 2004-3718, and an aqueous solution supercooling heat exchange for supercooling an aqueous solution of a hydrate guest compound. And a hydrate slurry heat exchanger that cools the hydrate slurry, and as a means of releasing supercooling in the middle of the piping between the two heat exchangers, the hydrate slurry is used as the nucleus of hydrate crystal formation. Some are provided with means for injecting into the supercooled aqueous solution.

This manufacturing apparatus has a problem that the hydrate slurry cannot be sufficiently cooled by the hydrate slurry heat exchanger in the subsequent stage because the supercooling is not sufficiently released in the middle of the piping between the two heat exchangers. .
Therefore, a buffer tank is provided between the two heat exchangers as a means to release the supercooling of the aqueous solution, and a hydrate slurry is injected into the supercooled aqueous solution flowing into the buffer tank as a nucleus for hydrate crystal formation. A hydrate slurry production device has been devised that facilitates cooling release.

However, the supercooled aqueous solution may not be sufficiently released while circulating in the buffer tank, and the hydrate slurry cooling in the hydrate slurry heat exchanger cannot be sufficiently performed, resulting in insufficient heat storage. In order to solve this problem, in order to lengthen the residence time in the buffer tank, it is necessary to enlarge the buffer tank, which causes an increase in cost and securing the installation location.
Therefore, an experiment to investigate the effect of adding TiPAB to an aqueous TBAB solution to promote the release of supercooling and promote the generation of clathrate hydrates to improve the amount of heat storage was conducted using an aqueous supercooling heat exchanger and hydrate slurry heat. The experiment was carried out using an experimental apparatus in which a buffer tank was provided between the two heat exchangers of the exchanger, and a hydrate slurry was added to the supercooled aqueous solution flowing into the buffer tank as a nucleus for hydrate crystal formation. The concentration of the TBAB aqueous solution is 14.5 wt%. The experiment was conducted with the temperature condition of the aqueous solution cooled by the aqueous supercooling heat exchanger in the previous stage and the flow rate flowing into the hydrate slurry heat exchanger being constant.

The amount of heat exchanged in the hydrate slurry heat exchanger was determined by measuring the cold water temperature flowing into the heat exchanger, the cold water temperature flowing out from the heat exchanger, and the cold water flow rate.
Change the temperature of the cold water flowing into the hydrate slurry heat exchanger to 3.7 ° C, 4.6 ° C, 5.6 ° C, and hydrate the case of only the TBAB aqueous solution and the case of adding TiPAB to the TBAB aqueous solution The amount of heat exchanged in the slurry heat exchanger was determined, and the results are shown in Table 3.

By adding TiPAB to the TBAB aqueous solution, the amount of heat exchanged in the hydrate slurry heat exchanger is larger than in the case where it is not added. It has been found that the amount of heat storage has been improved. It was also found that the higher the concentration of TiPAB added, the greater the amount of exchange heat and the greater the effect of increasing the amount of stored heat.
By adding TiPAB to the TBAB aqueous solution, the release of supercooling is promoted and the production rate of TBAB clathrate hydrate is increased, so that the heat storage rate can be improved.
By adding TiPAB to the TBAB aqueous solution, it is possible to sufficiently release the supercooling, so there is no need to increase the buffer tank so as to lengthen the residence time in the buffer tank. It can solve problems such as securing the location.
Moreover, although this experiment was continuously carried out over about 40 days, the effect of increasing the heat storage rate by promoting the release of supercooling of the additive and increasing the production rate of TBAB clathrate hydrate was reduced. It was never seen. During this period, the aqueous solution was repeatedly solidified and melted 1400 times, but no decrease in the above effect of the additive was observed during that time.

  In the above embodiment, tetra-n-butylammonium bromide (TBAB) is given as a typical example of the quaternary ammonium salt other than the tetraisopentylammonium salt, and tetraisopentylammonium bromide (TiPAB) is given as a typical example of the tetraisopentylammonium salt. However, by adding tetraisopentylammonium phosphate as a tetraisopentylammonium salt to an aqueous solution of tetranbutylammonium phosphate as a quaternary ammonium salt, supercooling release is promoted and clathrate hydration It is also possible to increase the heat storage rate by advancing the generation of objects.

[Comparative Example 5]
<Mixing the TBAB aqueous solution with porous particles impregnated with TBAF (tetra-n-butylammonium fluoride) aqueous solution without stirring>
Experiments were conducted by mixing porous particles impregnated with TBAF into a 40.5 wt% aqueous solution having a harmonic melting point concentration of TBAB.
Activated carbon particles are used as the porous fluid, and the TBAF harmonic melting point aqueous solution is mixed with the activated carbon heated to 40 ° C., and the vacuum / normal pressure change is repeated to expel the gas inside the activated carbon and impregnate with the TBAF aqueous solution. I let you.
The prepared activated carbon was mixed with 90 g of the TBAB aqueous solution and subjected to the test. The amount of the TBAF harmonic melting point aqueous solution contained in the mixed activated carbon corresponded to about 0.1% of the TBAB aqueous solution.
These mixtures were put into a glass beaker, the glass beaker was inserted into a 1 ° C. cooling liquid, and the aqueous solution was cooled without being stirred.
When the temperature of the aqueous solution reached about 1 ° C., clathrate hydrate was formed around the activated carbon. When the solidification and melting operation in which this was heated to 40 ° C. for melting and cooling was repeated, hydrate crystals were not formed at the fifth repetition of solidification and melting.
As shown in Comparative Example 5, it was found that the method of impregnating the activated carbon particles, which are porous bodies, with the harmonic melting point concentration aqueous solution of TBAF has a significant problem of deterioration of the supercooling prevention performance due to repeated solidification and melting operations. did.

[Comparative Example 6]
The activated carbon particles of the porous body of Comparative Example 5 were replaced with an alumina porous body, and the supercooling prevention performance was similarly evaluated. Hydrate crystals no longer formed after the 20th repetition of the solidification and melting operation.
Also in this case, it has been found that there is a significant problem that the overcooling prevention performance is lowered due to repeated solidification and melting operations.

Claims (6)

An aqueous solution containing a quaternary ammonium salt other than tetraisopentylammonium salt and having the property of being cooled to produce an clathrate hydrate having the quaternary ammonium salt as a guest compound, the tetraisopentylammonium salt An aqueous solution characterized in that is added. A quaternary ammonium salt other than the tetraisopentylammonium salt is included, and the quaternary ammonium salt generated by cooling an aqueous solution to which the tetraisopentylammonium salt is added is used as a guest compound. Clathrate hydrate. A clathrate hydrate slurry comprising the clathrate hydrate according to claim 2 dispersed or suspended in the aqueous solution. A step of preparing an aqueous solution containing a quaternary ammonium salt other than the tetraisopentylammonium salt and added with the tetraisopentylammonium salt, and cooling the aqueous solution to make the quaternary ammonium salt a guest compound A method of producing an clathrate hydrate, comprising the step of producing an clathrate hydrate. A method for increasing the rate of formation or growth of clathrate hydrate containing quaternary ammonium as a guest compound in an aqueous solution containing a quaternary ammonium salt other than tetraisopentylammonium salt, comprising tetraisopentylammonium A step of preparing the aqueous solution to which the salt has been added and a step of cooling the aqueous solution to which the tetraisopentylammonium salt has been added. Method. By cooling an aqueous solution containing a quaternary ammonium salt other than the tetraisopentylammonium salt, a supercooling phenomenon that occurs when an clathrate hydrate containing the quaternary ammonium salt as a guest compound is formed or grown is prevented or A method for inhibiting inclusion water comprising: preparing the aqueous solution to which tetraisopentylammonium salt is added; and cooling the aqueous solution to which tetraisopentylammonium salt is added. A method for preventing or suppressing a supercooling phenomenon that occurs when a Japanese product is produced or grown.