US20070289720A1

US20070289720A1 - Self-Heating Chemical System for Sustained Modulation of Temperature

Info

Publication number: US20070289720A1
Application number: US11/610,192
Authority: US
Inventors: Aydin Sunol; Brandon Smeltzer; Sermin Sunol; Raquel Carvallo
Original assignee: University of South Florida
Current assignee: University of South Florida
Priority date: 2005-12-13
Filing date: 2006-12-13
Publication date: 2007-12-20
Also published as: WO2007087039A2; WO2007087039A3; CA2633250A1; EP1969295A2; EP1969295A4

Abstract

A self-heating chemical system using one or more primary components for exothermic reactions (such as calcium oxide), one or more porous components that can serve as a heat sink and conductor of heat as well as under going chemical transformations that release heat (zeolite), a weak acid (citric acid) for sustained modulation of temperature and pH. Exothermic reactions, mixing of some chemicals, sorption of certain chemicals, phase changes in chemicals, and dissolution of some chemicals in solvents release heat during these operations. The rate of heat generation coupled with mass and energy transfer rates to or from system(s) allows modulation of the temperature of systems. The modulation can be further enhanced by controlled release and availability of some of the components. This method provides with a class of self-heating product applications and focuses on the modulation of temperature through sequestering of reactions with different rates, heat release through dissolution, heat release through mixing, heat release through sorption, heat release through phase change as well as controlling mass and heat transfer rates.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to currently pending U.S. Provisional Patent Application 60/597,605, entitled, “Self Heating Chemical Systems for Sustained Modulation of Temperature”, filed Dec. 13, 2005, the contents of which are herein incorporated by reference.

FIELD OF INVENTION

This invention relates to a self-heating system where the heat is provided by chemical reactions, mixing, sorption, phase change, and dissolution.

BACKGROUND OF THE INVENTION

Many self-heating products are emerging in the marketplace. The applications include products for food, beverages, and hand warmers. There are many areas such as disposable wipes where an unmet need exists is in the application of the technology. These applications, as well as others, require self-heating through the reaction of chemicals. The initiation and control of these reactions, retention and distribution of heat, and handling of materials are key issues. These issues are only partially handled for various products in the market. One key area not addressed in the market is a sustained modulation of heat.

SUMMARY OF INVENTION

BRIEF DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the invention, reference should be made to the following detailed description, taken in connection with the accompanying drawings, in which:
FIG. 1 is an illustration depicting a procedure for a chemical mixture for a self-heating chemical system for sustained heat modulation. The mix includes 17 g. of CaO (uncalcined), 8.5 g. HZeo, 1 g. citric acid, 4 g. PE and 36 ml. water.
FIG. 2 is a graph illustrating the temperature profile of the activated system depicted in FIG. 1. T1 through T4 refer to the temperature at various distances from the chemical pouch containing the reactants with distance increasing from T1 to T4.
FIG. 3 is an illustration depicting a procedure for a calcined CaO chemical mixture of a self-heating chemical system for sustained heat modulation. The mix included 17 g. of CaO (calcined), 8.5 g. HZeo, 1 g. citric acid, 4 g. PE and 36 ml. water.
FIG. 4 is a graph illustrating the temperature profile of the activated system depicted in FIG. 3. T1 through T4 refer to the temperature at various distances from the chemical pouch containing the reactants.
FIG. 5 is a graph depicting the moisture absorbed by the CaO as a function of time.
FIG. 6 is a graph illustrating the center temperature profile using the chemical mix composed of a primary heater (CaO), a porous component that also generates heat (Zeolite), and a weak acid (citric acid).
FIG. 7 is a graph illustrating the use of a slight vacuum to mix the chemicals with the water.
FIG. 8 is graph illustrating temperature profiles for a system using 5 towels and having a composition including 17.5 g. of CaO, 4.5 g. Chabazite, 3 g. citric acid, and 35 ml. water. The graph illustrates the temperature at various points within the pouch system.
FIG. 9 is a pair of illustration. (A) is a graph depicting a desirable time-temperature band, and modulation thereof, for the heating system. (B) is an illustration depicting a coated chemical component/substrate for the system.
FIG. 10 is an illustration depicting a five towel application of the chemical pouch system utilizing a self-heating chemical system for sustained heat modulation.
FIG. 11 is an illustration depicting the chemical pouch system of the five towel application depicted in FIG. 10.
FIG. 12 is an illustration depicting a generalized scheme for a chemical pouch.
FIG. 13 is a series of illustrations depicting the activation of the generalized scheme of the chemical pouch depicted in FIG. 12. (A) depicts the pouch in an unactivated state with water filling the inner pouch exerting pressure on the pouch walls as indicated by the “p”. (B) depicts the activation of the chemical pouch by applying pressure/force, denoted “F” externally to the pouch resulting in rupture of the inner pouch and release of water contained therein. (C) depicts the activated chemical pouch releasing heat denoted “Q”.
FIG. 14 is a series of illustrations depicting a chemical pouch, based upon the generalized scheme of FIG. 12, surrounded by a towel. (A) depicts the pouch in the unactivated state where the pouch is completely surrounded by a towel. (B) depicts the pouch and towel system upon activation with the release of heat (Q).
FIG. 15 is a series of illustrations depicting a self-heating chemical system with the system seal in a in a pouch. (A) depicts the system in the unactivated state. (B) depicts the activated system in the pouch.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The disclosed invention is a self-heating chemical system for sustained modulation of temperature. A self-heating chemical system using one or more primary components for exothermic reactions (such as calcium oxide), one or more porous components that can serve as a heat sink and conductor of heat as well as under going chemical transformations that release heat (zeolite), a weak acid (citric acid) for sustained modulation of temperature and pH. Exothermic reactions, mixing of some chemicals, sorption of certain chemicals, phase changes in chemicals, and dissolution of some chemicals in solvents release heat during these operations. The rate of heat generation coupled with mass and energy transfer rates to or from system(s) allows modulation of the temperature of systems. This invention relates to a mixture that allows sequencing. The key reactions/transformation are as follows:
CaO+H₂O→Ca(OH)₂
calcium oxide+water→calcium hydroxide
Zeolite+Water→Hydrated zeolite+Water
CaO.MgO+H₂O→Ca(OH)₂+MgO
MgO+H₂O→Mg(OH)₂
2Ca(OH)₂+3C₆H₈O₇(aq.)→Ca₂(C₆H₅O₇)₃.4H₂O+2H₂O
calcium hydroxide+citric acid→calcium citrate
Referring to FIG. 6 there is a graph illustrating the heat generated as a function of time of a chemical mix composed of a primary heater (CaO), a porous component that also generates heat (Zeolite), and a weak acid (citric acid). The amount of chemical used is this illustration is about 42 gr. The mix is 77% CaO, 14% Zeolite and 9% Citric Acid by weight for full recipe; and 84% CaO and 16% Zeolite for the recipe without citric acid. The total amount of chemicals and water used is the same in all three cases. As shown, the system can heat fast and maintain a uniform and high temperature.
Referring to FIG. 7 there is shown a graph illustrating the temperature profile comparing a vacuum to non-vacuum. The results illustrate the advantages of using slight vacuum. As depicted, the vacuum provides an avenue for rapid and thorough mixing of water (solvent) with the chemicals. The resulting reaction avoids hot spots due to improper mixing that happens during the initial period. Furthermore, vacuumed containment results in more uniform and higher temperatures, at latter periods, upon mixing. The porous component allows intra-particle void space. The inter-particle void space is not pertinent and is reduced during vacuuming.
Referring to FIG. 8 there is shown the time-temperature profile of a 5 towel system employing 7.5 g. of CaO, 4.5 g. Chabazite, 3 g. citric acid, and 35 ml. water. The figure illustrates temperature profiles of five disposable wash clothes heated using the aforementioned chemical system composed of chemicals containment (chemical pouch) and containment comprised of water (water pouch). All but water is in one pouch while water is in another pouch. When the chemicals are mixed the reaction is initiated to heat the adjacent wash clothes. The time-temperature profiles of five wash clothes are given in FIG. 8 along with the chemical recipe.
FIG. 9(A) illustrates a desirable time-temperature band the heating system should be modulated within as well as one of the ways it can be achieved. The coated material, as shown in FIG. 9(B), can be any of the chemical (zeolite, calcium oxide and citric acid) components. All or fraction of the compounds can be encapsulated. The particle size of the chemicals, chemicals coated, coating thickness, coating material, porosity of the porous compounds, the amount of chemicals used, the composition of the chemical mix, and the amount of water used all enable modulating and sustained performance within the desirable time-temperature band.
FIG. 10 illustrates a self-heating system for sustained modulation providing a contained packet system (16) with five towels (60). A vacuum is used to create a gradient for the water to move into the chemical pouch (10). Referring to FIG. 11, the vacuum allows the chemical mix (20) to wet faster and therefore heat faster and more evenly when the water pouch (42) containing the water (40) is broken. As the water pouch (42) is broken, the water is contained within the sealant film (22) of the chemical pouch (10). The porous material allows more reaction area and enables pulling vacuum better. The pull vacuum helps to empty void space. Since the pouch material is flexible and takes the shape of material (i.e. the chemical particles) you are vacuuming, the available space for the water to go through is very limited if you do not have porous particles. In the absence of porous particles, the volume you would have is limited to void space between neighboring particles. Instead, in the present instance, the porous matrix in the particles allows space for water without the chemical pouch expanding significantly.
Referring to FIG. 12, there is shown a generalized schema of the chemical pouch (10) of the self-heating chemical system for sustained modulation of heat. The pouch is a dual layer system with water (40) contained in the inner water pouch (42) and the chemical mix (20) contained in the outer pouch, the limit of which is defined by the outer sealant film (22). By sequestering the water in the inner pouch, the system can be stored and transported in an unactivated/unreacted state. Heat generation begins upon rupture of the water pouch (40).
Referring to FIG. 13 there is shown the procedure for activation of an exemplary system. In the unactivated state the water (40) is maintained in the water pouch (42), filling the pouch and applying a pressure (p) on the inner walls of the water pouch (42). Referring to FIG. 13 (B), a user exerts a force (F) on the external walls of the sealant film (22) chemical pouch (10), causing the water pouch (22) to rupture. The rupture of the water pouch (42) allows the water (40) contained therein the escape the water pouch (42) and mix with the chemical mix (20) contained within the sealant film (22). Referring to FIG. 13(C), it is illustrated that the mixture of the water (40) with the chemical mix (20) within the chemical pouch system (10) produces an exothermic reaction that liberates heat (Q).
Referring to FIG. 14(A) there is shown a generalized schema of a towel system (12) employing the self-heating chemical system for sustained modulation of heat. The towel system utilizes one or more towels (60) chemical surrounding a chemical pouch system (10). FIG. 14(B) illustrates the towel system upon rupture of the water pouch (42), thus allowing the mixture of the water (40) with the chemical mixture (20) resulting in the liberation of heat (Q) from the system.
Referring to FIG. 15 there is shown a generalized schema of a towel-pouch system (16) wherein a towel system (12) employing the self-heating chemical system (10) for sustained modulation of heat is contained. The towel-pouch system (16) includes an outer film (82) to store and contain the towel system (12) employing the chemical pouch (10) of the self-heating chemical system for sustained modulation of heat. Where applicable, an insulator can be localized to the area (80) immediately adjacent to the outer film (82) to insulate the chemical system and the heat (Q) produced by the reaction of the system. The outer film (82) further includes a seal (84) to facilitate entry into the towel-pouch system (16) and removal of the towels system (12) contained therein.
The present invention facilitates the time-temperature modulation of heating. Furthermore, components, principally the water which initiates the reaction is sequestered, while upon the rupture of the water pouch the chemical component system enables the effective missing of the water with the chemicals. In certain aspect, the two pouch system utilizes heating components such as CaO/Zeolite/Citric acid in an outer pouch that is vacuumed. The inner pouch contains the water. When you break the inner pouch by squeezing pouches, the inner pouch breaks and water rapidly permeates and diffuses into the chemicals.
Citric acid is used in the reaction to neutralize the reaction mix. The citric acid goes through an exothermic reaction producing calcium citrate to further generate heat. It also has an endothermic dissolution step in water that cools the system in a regulated fashion to keep the temperatures within acceptable limits. Also, Calcium citrate is environmentally friendly compound. MgO as shown in the previous formulas above is quick lime raw material mix. The mixture enables the following:

- The CaO reactions are fast and generate more heat while Zeolite generates less heat and more slowly. A mix avoids hot spots and enables sustained heating.
- The zeolite is highly porous and enable pulling vacuum. Thus, we can mix both zeolite and CaO rapidly and uniformly.
- The zeolite stores heat and conducts uniformly.
- Zeolites are environmentally friendly.

The system can be further tailored by encapsulating the chemical mixture in a coating. The coating chemicals can then dissolve and disintegrate with temperature, pH change and mixing with water. It is further envisioned that the thickness of the coating can be tailored to achieve desired rates of reaction, such as delaying the initiation of reaction by the contact with the water. It is further envisioned that particles of various depths of coating may be used in an individual application to further tailor the modulation of response by having particles with thinner coatings initiate reaction more quickly, while thicker coatings producing a delayed response. The coating chemicals can be water soluble polymers or sugars or any other chemical that disintegrates with heating
The system provides economy, sustainment and modulation of heat release, storage of energy. The towels used in such a system can be wet towels or dry towels, The towel system is meant to be exemplary of the types of uses that can be provided in a chemical system for sustained modulation of heat, but should not be interpreted as limiting to that particular application.
The disclosures of all publications cited above are expressly incorporated herein by reference, each in its entirety, to the same extent as if each were incorporated by reference individually.
It will be seen that the advantages set forth above, and those made apparent from the foregoing description, are efficiently attained and since certain changes may be made in the above construction without departing from the scope of the invention, it is intended that all matters contained in the foregoing description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.
It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention which, as a matter of language, might be said to fall there between. Now that the invention has been described,

Claims

1. A heat-producing composition comprising calcium oxide, zeolite and one or more weak acids.

2. The composition according to claim 1 wherein the one or more weak acids is citric acid.

3. The composition according to claim 2 wherein the weight ratio of the calcium oxide:zeolite:citric acid is about 8:1:1.

4. The composition according to claim 1 wherein the composition is encapsulated in a coating.

5. The composition according to claim 4 wherein the coating is water-soluble.

6. The composition according to claim 4 wherein the coating is selected from the group consisting of water-soluble polymers and sugars.

7. A heating element to provide extended heat transmission comprising:

a containment member comprising water; and

a reaction mixture comprising calcium oxide and zeolite, wherein release of the water in the containment member allows contact with the reaction mixture thereby producing an exothermic reaction.

8. The heating element according to claim 7 wherein the reaction mixture further comprises one or more one or more weak acids to neutralize the calcium hydroxide produced by the reaction of the water with the calcium oxide and further regulate temperature.

9. The heating element according to claim 8 wherein the one or more weak acids is citric acid.

10. The heating element according to claim 9 wherein the weight ratio of the reaction mixture of calcium oxide:zeolite:citric acid is about 8:1:1.

11. The heating element according to claim 7 wherein the reaction mixture is encapsulated in a coating.

12. The heating element according to claim 11 wherein the coating is water-soluble.

13. The heating element according to claim 11 wherein the coating is selected from the group consisting of water-soluble polymers and sugars.

14. A heating element to provide extended heat transmission comprising:

an inner containment member comprising water; and

an outer containment member comprising a reaction mixture comprising calcium oxide, zeolite and a weak acid, wherein release of the water in the inner containment member allows contact with the reaction mixture thereby producing an exothermic reaction.

15. The heating element according to claim 14 wherein the one or more weak acids is citric acid.

16. The heating element according to claim 14 wherein the contents of the outer containment member are under vacuum.

17. The heating element according to claim 14 wherein the inner containment member is at a pressure higher that the outer containment member.

18. The heating element according to claim 16 wherein the outer containment member is vacuum-sealed to the inner containment member.

19. The heating element according to claim 14 wherein the reaction mixture is encapsulated in a coating.

20. The heating element according to claim 19 wherein the coating is water-soluble.

21. The heating element according to claim 19 wherein the coating is selected from the group consisting of water-soluble polymers and sugars.

22. The heating element according to claim 15 wherein the reaction mixture is encapsulated in a coating.

23. A self-heating chemical system for the production of warm towels comprising a pouch system containing one or more towels and a heating element, the heating element comprising an inner containment member comprising water and an outer containment member comprising a reaction mixture comprising calcium oxide, zeolite and a weak acid, wherein release of the water in the inner containment member allows contact with the reaction mixture thereby producing an exothermic reaction.

24. The self-heating chemical system according to claim 23 wherein the one or more weak acids is citric acid.

25. The self-heating chemical system according to claim 23 wherein the contents of the outer containment member are under vacuum.

26. The self-heating chemical system according to claim 23 wherein the reaction mixture is encapsulated in a coating.