WO2015176184A1

WO2015176184A1 - Phase change material composition and uses thereof

Info

Publication number: WO2015176184A1
Application number: PCT/CA2015/050456
Authority: WO
Inventors: Dominic Tessier; Louis Bibeau
Original assignee: Logistik Unicorp Inc.
Priority date: 2014-05-20
Filing date: 2015-05-20
Publication date: 2015-11-26

Abstract

A phase change material (PCM) composition is disclosed. The composition comprises an aqueous solution of nitrate (LiNO₃) and nitric acid (HNO₃). Preferably, the composition may further comprise a nucleation additive such as carbon black, graphite, clay, green clay or mixture thereof. The PCM composition has lessened efficiency reduction due to supercooling effect, has improved chemical stability, and has a complete reversible freeze/melt cycle without appreciable degradation of the composition after a large number of freeze/melt cycles. The PCM composition can be encapsulated into non-flammable or fire-resistant packets and placed in uniforms, vests, under-garments, etc. for thermoregulation purposes (e.g. reduction of heat-stress, cooling effect, etc.).

Description

PHASE CHANGE MATERIAL COMPOSITION AND USES THEREOF

Cross-Reference to Related Applications [0001] The present patent application claims the benefits of priority of commonly assigned United States of America Patent Application No. US 62/000,752, entitled "Phase Change Material Composition And Uses Thereof and filed at the United States Patent And Trademark Office on May 20, 2014, the content of which is incorporated herein by reference. Field of the Invention

[0002] The present invention generally relates to phase change material (PCM) compositions and more particularly to PCM compositions comprising lithium salts. Background of the Invention

[0003] Phase Change Material (PCM) compositions are chemical substances or compounds capable of reversible storage and release of thermal energy through fusion/crystallization processes. Heat is absorbed when the material changes from solid state to liquid state and heat is released when the material changes from liquid state to solid state.

[0004] Several materials with adequate phase change capabilities have been previously described. For example, paraffin has been used for applications where there is no requirement for fire or flame-like resistance, such as in sportswear.

[0005] However, it has been disclosed in the prior art that, for PCM applications requiring flame resistant or inherently flame resistant materials, salt hydrates are preferred because they are non-flammable, and because they possess, in addition, high latent heat storage capacity, sharp melting point and high thermal conductivity. [0006] For example, U.S. Patent No. 4,303,541 discloses a process for preparing a salt hydrate composition having a phase transition heat greater than the heat capacity of water at a corresponding temperature, for charging a latent heat storage device. [0007] However, due to supercooling effect, the crystallization of the salt hydrates often occurs well below zero degree Celsius, therefore requiring a freezer to "recharge" the PCM composition, that is to convert the composition to its solid state. The "recharge" of the salt hydrate is necessary in order to allow back the renewal of the maximum heat storage capacity after the complete fusion.

[0008] Several attempts have been made in the past to overcome these limitations. For example, patent nos. US 4,689, 164, US 5,827,915 and US 4,231,885, and patent application nos. US 2011/0121246, US 2012/0048768, WO 96/23848 and CN 101235272 describe formulations of different salt hydrates with a variety of additives such as salts, dispersing agents and nucleating agents, for the intended effect to reduce or prevent the supercooling effect of the PCM compositions.

[0009] In addition, it has been found that PCM compositions based on salt hydrates often suffer from instability after repeated solidification/fusion cycles. As a result, the latent heat storage capacity of the related salt hydrates PCM compositions tend to decrease, which often ends with a significant loss of performance.

[0010] To improve the thermal conductivity of the PCM composition, the addition of carbon black has also been proposed, for instance, in Intemational patent application published under no. WO 2010/092393. However, the addition of carbon black may present flammability issues.

[0011] In any event, despite ongoing developments in the field of PCM compositions, there is still a need for novel salt hydrate based PCM compositions that can at least mitigate some of the shortcomings of the prior art. Summary of the Invention

[0012] At least some of the shortcomings of the prior art are generally mitigated by a PCM composition comprising an aqueous solution of lithium nitrate (L1NO₃) and nitric acid

[0013] Such a PCM composition has been found to exhibit a lessened reduction of efficiency reduction due to supercooling effect, and an improved chemical stability. A PCM composition comprising an aqueous solution of lithium nitrate and nitric acid also has a complete reversible freeze/melt cycle without appreciable degradation of the composition after a large number of freeze/melt cycles.

[0014] In addition, since the PCM composition is based on a salt hydrate, the PCM composition is essentially non-flammable and can thus be used in environments where flames can be present.

[0015] The PCM composition in accordance with the principles of the present invention can be encapsulated into non-flammable or fire-resistant packets and placed in uniforms, vests, under-garments, etc. for thermoregulation purposes (e.g. reduction of heat-stress, cooling effect, etc.).

[0016] In typical yet non-limitative embodiments of the PCM composition in accordance with the principles of the present invention, the composition comprises an aqueous solution of lithium nitrate and nitric acid.

[0017] In some other non-limitative embodiments of the PCM composition in accordance with the principles of the present invention, the composition further comprises clay (e.g. green clay) to reduce, for instance, the corrosiveness of the aqueous solution. [0018] In some other non-limitative embodiments of the PCM composition in accordance with the principles of the present invention, the composition further comprises graphite to reduce, for instance, supercooling. In such embodiments, the dark color of the composition caused by the presence of graphite can also further contribute to the absorption of heat. [0019] The invention is also directed to a thermoregulating assembly for thermoregulation purposes, the assembly comprising the phase change material composition as disclosed herein encapsulated into a non-flammable or fire-resistant packet. The thermoregulating assembly may be adapted to be inserted into a protective garment, such as but not limited to uniform (such firemen gear), a vest or an under-garment.

[0020] The invention is also directed to the use of the phase change material composition as disclosed herein, for thermoregulation of a non-flammable or fire-resistant protective garment.

[0021] The invention is also directed to the use of the phase change material composition as disclosed herein, for the making of a thermoregulated protective, non-flammable and/or fire- resistant garment.

[0022] The invention is also directed to a method of use of the thermoregulating assembly disclosed herein, wherein when the phase change composition is free of nucleation additive, the assembly may be placed in a freezer having a temperature up to 0 °C for solidifying the composition prior to use.

[0023] The invention is also directed to a method of use of the thermoregulating assembly disclosed herein, wherein when the phase change composition comprises nucleation additives, the composition may be placed in a refrigerator having a temperature above 0 °C for solidifying the composition prior to use. [0024] The invention is also directed to a protective garment being non-flammable and/or fire-resistant, the garment comprising the phase change material composition as disclosed herein or a thermogulating assembly as disclosed herein. The garment can be a uniform, such as a firemen gear, a vest or an under-garment.

[0025] Other and further aspects and advantages of the present invention will be obvious upon an understanding of the illustrative embodiments about to be described or will be indicated in the appended claims, and various advantages not referred to herein will occur to one skilled in the art upon employment of the invention in practice. Detailed Description Preferred Embodiments

[0026] A novel phase change material (PCM) composition and uses thereof will be described hereinafter. Although the invention is described in terms of specific illustrative embodiments, it is to be understood that the embodiments described herein are by way of example only and that the scope of the invention is not intended to be limited thereby.

[0027] A PCM composition in accordance with the principles of the present invention generally comprises an aqueous solution of lithium nitrate (L1NO₃) and nitric acid (HNO₃). It has been found that such a composition improves the latent heat absorption performance of the composition.

[0028] It is generally known that a given salt, having a negative ion (A^"), can be combined, as a conjugate base, with its corresponding acid HA in an aqueous solution to form a salt hydrate. Thus, it has been found that the negative ion (NO₃ ^") of the lithium nitrate (L1NO₃), when combined, as its conjugate base, to an aqueous solution of nitric acid (HNO₃), allows for the formation of salt hydrates that possess thermoregulation properties and behaves as a PCM. [0029] In the case of the present PCM composition, it was found that the thermal energy absorption capacity of the composition could be modified, and possibly preferably optimized, by varying certain parameters of the composition.

[0030] Firstly, it was found that the thermal energy absorption capacity of the present PCM composition could be modified by varying the pH of the acidic solution. In the present embodiment, to obtain satisfactory results, it was found that the pH of the nitric acid solution can be varied from a pH of 7 down to a pH of 2, preferably from a pH of 5 down to a pH of 2.5. [0031] Secondly, it was found that the thermal energy absorption capacity of the present PCM composition could be modified by varying the salt/hydration solution ratio (weight ratio). In the present embodiment, to obtain satisfactory results, the weight ratio of lithium nitrate/nitric acid solution (LN/NAS) can be varied between 1.0 and 3.0, and preferably between 1.20 and 1.75.

[0032] Depending on the final proportion of lithium nitrate and nitric acid, the present PCM composition will generally exhibit a melting temperature ranging between 25 and 40 degrees Celsius, and preferably ranging from 28 to 35 degrees Celsius. These melting temperature ranges make the present PCM composition particularly suited for applications in human body thermoregulation. Indeed, it is around these temperatures that the human body starts to experience discomfort. Being able to absorb heat in these temperature ranges is thus particularly advantageous in such applications.

[0033] The following exemplary compositions provide thermoregulation capabilities that can be used where flame-resistant characteristics are required. Such flame-resistant characteristics are generally required in applications such as transportation, construction and protective clothing (e.g. firefighter protective uniforms).

[0034] Example 1

A salt hydrate composition was prepared as follows:

Lithium nitrate : 3.0 mg

Nitric acid solution (pH 5) : 2.0 mg

[0035] The resulting composition showed high stability to repeated melting/crystallisation cycles and high latent heat absorption capacity. The melting occurred at temperatures ranging from 28 up to 35 degrees Celsius while the crystallisation occurred at temperatures ranging approximately from -15 up to 0 degree Celsius.

[0036] Example 2

A salt hydrate composition was prepared as follows:

Lithium nitrate : 3.0 mg

Nitric acid solution (pH 3) : 2.0 mg

[0037] The resulting composition showed high stability to repeated melting/crystallisation cycles and high latent heat absorption capacity. The melting occurred at temperatures ranging from 28 up to 35 degrees Celsius while the crystallisation occurred at temperatures ranging approximately from -25 up to -5 degrees Celsius.

[0038] In the above two examples, the PCM compositions comprise only lithium nitrate in a nitric acid solution. In the following example, the PCM composition further comprises graphite. The addition of graphite has been found to reduce supercooling of the liquid phase, which is commonly observed with salt hydrate systems. The addition of graphite thereby preferably allows the composition to crystallize at higher temperatures. [0039] Example 3

A salt hydrate composition was prepared as follows:

Lithium nitrate : 3.0 mg

Nitric acid solution (pH 3): 2.0 mg

Graphite: 0.25 mg

[0040] In addition to exhibiting high stability to repeated melting/crystallisation cycles and high latent heat absorption capacity, the resulting composition also showed reduced supercooling. The melting occurred at temperatures ranging from 28 up to 35 degrees Celsius while the crystallisation occurred at temperatures ranging approximately from 0 up to 20 degrees C.

[0041] Interestingly, the composition of Example 3 crystallizes at temperatures generally above the freezing point (i.e. 0 degree Celsius). This allows the third composition to be recharged in a regular refrigerator instead of in a freezer.

[0042] Example 4 :

An example of a composition is detailed in the following table:

[0043] The order of preparation for the above composition is preferably as follows: - adding component 5 in component 2 and stir for 5 min at 50 degrees Celsius; adding component 4 and stir;

adding component 3 and stir;

adding component 1; and

shaking or stirring at about 50 degrees Celsius for 10 minutes with cover to prevent evaporation.

[0044] The present PCM composition shows a high latent heat of fusion per unit volume with relatively high thermal conductivity (compared to paraffin). [0045] Also, as prepared, the PCM composition shows an improved chemical stability, a complete reversibility of freeze/melt cycle, and no appreciable degradation of the composition after a large number of freeze/melt cycles (e.g. more than ten cycles).

[0046] Understandably, various additives can be added to the PCM composition. For instance, nucleation additives such as carbon black, graphite and clay can be added to the composition in relative quantity ranging between 0.1% up to 20%, preferably between 0.5% and 10%, most preferably between 0.5 to 5%. Without limitation, other metals or non-metals, oxides and insoluble salts could be used as well. [0047] Also, the propensity for corrosion of the present PCM composition can be adequately mitigated with the addition of inorganic clay (e.g. green clay).

[0048] As mentioned above, since the present PCM composition has a melting temperature between 28 and 35 degrees Celsius, it can be advantageously used in thermoregulation applications for personnel working in hot environments.

[0049] In that sense, the PCM composition can be (macro)encapsulated into non-flammable or fire resistant packets and these packets can be placed in uniforms, vests, under-garments, and other forms of clothing. When used, the pieces of clothing can produce a cooling effect on the skin or even prevent heat-stress.

[0050] In addition, when the PCM composition comprises graphite (or any other additive(s) reducing supercooling), the packets can be recharged using widely available typical refrigerators.

[0051] While illustrative and presently preferred embodiments of the invention have been described in detail hereinabove, it is to be understood that the inventive concepts may be otherwise variously embodied and employed and that the appended claims are intended to be construed to include such variations except insofar as limited by the prior art.

Claims

WHAT WE CLAIM IS:

1) A phase change material composition comprising an aqueous solution of lithium nitrate (L1NO3) and nitric acid (HN0₃).

2) The composition of claim 1, wherein the aqueous solution has a pH from 2 to 7.

3) The composition of claim 1 or 2, wherein the aqueous solution has a pH from 2.5 to 5.

4) The composition of any one of claims 1 to 3, wherein the aqueous solution is prepared by mixing lithium nitrate with a solution of nitric acid with a weight ratio of lithium nitrate to nitric acid solution of from 1.0 to 3.

5) The composition of claim 4, wherein the weight ratio of lithium nitrate to nitric acid solution is from 1.2 to 1.75.

6) The composition of claim 4 or 5, wherein the nitric acid solution has a pH of between 3 and 5.

7) The composition of any one of claims 1 to 6, wherein the composition has a melting point from 25 to 40 °C.

8) The composition of claim 7, wherein the melting point is from 28 to 35 °C.

9) The composition of any one of claims 1 to 8, further comprising a nucleation additive.

10) The composition of claim 9, wherein the nucleation additive comprises carbon black, graphite, clay, green clay or mixture thereof.

11) The composition of claim 9 or 10, wherein the nucleation additive is present in the composition with an amount ranging from 0.1 wt.% up to 20 wt.%.

12) The composition of any one of claims 9 to 11, wherein the nucleation additive is present in the composition with an amount ranging from 0.5 wt.% and 10 wt.%.

13) The composition of any one of claims 9 to 12, wherein the nucleation additive is present in the composition with an amount ranging from 0.5 wt.% to 5 wt.%. 14) The composition of any one of claims 1 to 8, wherein the composition has a crystallisation temperature ranging from -25 to 0 °C.

15) The composition of claim 13, wherein the crystallisation temperature is ranging from -25 to -5 °C. 16) The composition of any one of claims 9 to 13, having a crystallisation temperature ranging from 0 to 20 °C.

17) The composition of any one of claims 1 to 16, further comprising a dispersant.

18) The composition of any one of claims 1 to 17, wherein the composition is encapsulated into a non-flammable or fire-resistant packet used for thermoregulation purposes.

19) A thermoregulating assembly for thermoregulation purposes, the assembly comprising the phase change material composition as claimed in any one of claims 1 to 18 encapsulated into a non-flammable or fire-resistant packet.

20) The thermoregulating assembly of claim 19, wherein the assembly is adapted to be inserted into a protective garment.

21) The thermoregulating assembly of claim 20, wherein the protective garment is a uniform, a vest or an under-garment.

22) Use of the phase change material composition as claimed in any one of claims 1 to 18, for thermoregulation of a non-flammable or fire-resistant protective garment. 23) Use of the phase change material composition as claimed in any one of claims 1 to 18, for the making of a thermoregulated protective, non-flammable and/or fire-resistant garment.

24) Method of use of the thermoregulating assembly of claims 19 to 21, wherein the phase change composition is free of nucleation additive, the assembly being placed in a freezer having a temperature up to 0 °C for solidifying the composition prior to use. 25) Method of use of the thermoregulating assembly of claims 19 to 21, wherein the phase change composition comprises nucleation additives, the composition being placed in a refrigerator having a temperature above 0 °C for solidifying the composition prior to use.

26) A protective garment being non-flammable and/or fire-resistant, the garment comprising the phase change material composition as claimed in any one of claims 1 to 18 or a thermogulating assembly as claimed in any one of claims 19 to 21.

27) The protective garment of claim 26, wherein the garment is a uniform, a vest or an under-garment.

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