U.S. patent application number 09/810797 was filed with the patent office on 2002-03-07 for ammonium biacetate as a heat storage material.
Invention is credited to Anderson, Albert Gordon.
Application Number | 20020027216 09/810797 |
Document ID | / |
Family ID | 22704687 |
Filed Date | 2002-03-07 |
United States Patent
Application |
20020027216 |
Kind Code |
A1 |
Anderson, Albert Gordon |
March 7, 2002 |
Ammonium biacetate as a heat storage material
Abstract
Ammonium biacetate is a useful material for heat storage
applications such as culinary implements, medicinal uses, and solar
energy storage.
Inventors: |
Anderson, Albert Gordon;
(Wilmington, DE) |
Correspondence
Address: |
E I DU PONT DE NEMOURS AND COMPANY
LEGAL DEPARTMENT - PATENTS
1007 MARKET STREET
WILMINGTON
DE
19898
US
|
Family ID: |
22704687 |
Appl. No.: |
09/810797 |
Filed: |
March 16, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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60191243 |
Mar 22, 2000 |
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Current U.S.
Class: |
252/70 ; 165/10;
165/104.17; 562/607 |
Current CPC
Class: |
C09K 5/063 20130101 |
Class at
Publication: |
252/70 ; 165/10;
165/104.17; 562/607 |
International
Class: |
C09K 005/00; C09K
005/14 |
Claims
What is claimed is:
1. A process of storing heat comprising using ammonium biacetate to
store heat energy.
2. The process of claim 1 wherein ammonium biacetate is in a
container.
3. The process of claim 2 wherein said container is rigid.
4. The process of claim 2 wherein said container is flexible.
5. A heat storage device comprising ammonium biacetate and a
container for housing said ammonium biacetate.
6. The device of claim 5 further comprising a material that is
substantially inert in the presence of ammonium biacetate and
acetates.
7. The device of claim 5 wherein said container is rigid.
8. The device of claim 5 wherein said container is flexible.
9. A method for holding food or other matter at a constant
temperature comprising the steps of: (a) heating a heat storage
device comprising ammonium biacetate and a container for housing
said ammonium biacetate; and (b) placing the food or other matter
to be temperature-controlled in proximity to the heat storage
device thereby maintaining the temperature of the food or other
matter.
10. The method of claim 9 further comprising moving said heat
storage device and said food or other matter from one location to
another.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to the use of ammonium
biacetate as a heat storage material.
TECHNICAL BACKGROUND
[0002] The potential of objects for heat storage is based on a
variety of thermodynamic properties. Heat storage potential can be
based on the sensible heat of a fluid such as water or the sensible
heat of a solid such as stone. Sensible heat is the amount of
energy needed to change the temperature of a substance without
changing the phase of that substance. Heat storage potential of a
material can also be based on the heat of transition of a material
as it changes from one physical state to another, e.g., the heat of
fusion or heat of vaporization. Additionally, heat storage
potential can be determined by a combination of sensible heat and
heat of a transition, particularly the latent heat of fusion, using
materials such as inorganic salt hydrates, paraffin or organic
polymers.
[0003] The heat of fusion is a particularly effective indicator for
determining the heat storage potential of materials. Energy is
absorbed by the transition of a material from solid to liquid and
released by the transition of a material from liquid to solid.
During uptake or release of energy during phase change, the
temperature of a material is a constant value that is referred to
as "phase transition temperature". The amount of energy that
changes the state of matter of a substance, e.g., from solid state
to liquid state, but does not change the temperature of that
substance, is the heat of fusion (.DELTA.H.sub.f). A higher heat of
fusion of a material indicates a greater heat storage potential of
such materials at the phase transition temperature.
[0004] To add heat energy to a heat storage material, the phase
transition temperature of a heat storage material must be below the
temperature of the material from which heat is to be transferred.
To retrieve heat from a heat storage material, the phase transition
temperature of the heat storage material must be equal to or
greater than the temperature to be maintained by the stored heat in
the heat storage material.
[0005] Materials that melt incongruently, i.e., the composition of
the melt differs from the composition of the solid, and materials
that supercool upon solidification, i.e., exist as liquids at
temperatures below their freezing points, do not exhibit reliable
transition properties, and thus are not as useful as heat storage
materials. For example, salt hydrates generally melt at
temperatures in a range to make them potentially useful as heat
storage materials. Unfortunately, salt hydrates undergo significant
supercooling which decreases their usefulness as heat storage
materials. Methods employed to prevent the supercooling of salt
hydrates include the addition of seed crystals to salt hydrates.
However, seed crystals often separate due to gravity and thereby
become unavailable to seed salt hydrate crystals. Salt hydrates can
also produce gels which make them undesirable as heat storage
materials. Examples of salt hydrates include sodium sulfate
decahydrate (Na.sub.2SO.sub.4.10 H.sub.2O) which melts
incongruently, and sodium acetate trihydrate (CH.sub.3CO.sub.2Na.3
H.sub.2O), which, although melting congruently at a sharp melting
point, 58.degree. C., supercools and is thereby undesirable as a
heat storage material. Salts themselves do not generally make good
heat storage materials because the melting point of most salts is
too high for most heat storage applications.
[0006] End uses for heat storage materials, such as culinary
implements (i.e., steam table inserts and other food containers
that must hold food at an optimum temperature), require that the
materials perform well at elevated temperatures. Many heat storage
materials do not perform well at desired temperatures. A good heat
storage material for a specific end use would have (1) a transition
temperature that is close to the desired temperature of the
substance for which the heat storage material is being used, and
(2) resistance to supercooling, and (3) exhibit congruent melting
at the melting point of the heat storage material. Other
considerations for determining a good heat storage material can
include cost of production and relative toxicity.
[0007] In view of the foregoing, applicants have developed a heat
storage material that has a high heat of fusion, melting range
about 65.degree. C., low toxicity, low production expense, and can
be used in containers of any shape and size.
SUMMARY OF THE INVENTION
[0008] The present invention relates to a process of storing heat
comprising using ammonium biacetate to store heat energy.
[0009] This invention also relates to a heat storage device
comprising ammonium biacetate and a container for containing the
ammonium biacetate. It further relates to a method for holding food
or other matter at a constant temperature comprising the steps
of:
[0010] (a) heating a heat storage device comprising ammonium
biacetate and a container for housing said ammonium biacetate;
and
[0011] (b) placing the food to be temperature-controlled in
proximity to the heat storage device thereby maintaining the
temperature of the food until the heat from the heat storage device
dissipates; and
[0012] (c) optionally moving said food in proximity to said heat
storage device from one location to another.
DETAILS OF THE INVENTION
[0013] Ammonium biacetate (NH.sub.4.H.(OAc).sub.2), wherein OAc
represents an acetate group (CH.sub.3COO.sup.-), is unique as far
as its use as a heat storage medium is concerned, as it does not
supercool, melts congruently, and does not require seeding, e.g.,
by using a nucleating agent. The melting point/freezing point of
ammonium biacetate is 65.degree. C.-66.degree. C. As this invention
teaches, the heat of fusion (.DELTA.H.sub.f) of ammonium biacetate
is 35 cal/g-38 cal/g. Ammonium biacetate cycles well, meaning that
it can melt and resolidify indefinitely without decomposition. Upon
melting, ammonium biacetate expands only slightly making it useful
for packaging in closed containers.
[0014] Ammonium biacetate can be made by combining ammonium acetate
and acetic acid, heating to dissolve any ammonium acetate formed,
followed by distilling off any unreacted acetic acid (see Example 1
below). The method of Example 1 is derived from that disclosed in
A. W. Davidson, H. H. Sisler and R. Stoenner, J. Amer. Chem. Soc.,
66 (1944) 779-782.
[0015] Equation 1 represents a potential synthesis used in this
invention: 1
[0016] The product of equation (1) is ammonium biacetate which
forms a crystalline structure when solidified as described in I.
Nahringbauer, Acta. Chem. Scand. (1968), 22(4), 1141-58 and (1969),
23(5), 1653-66. The crystal structure reveals hydrogen bonding that
increases the amount of attraction between the molecules. The
increased attraction between molecules may be responsible for the
unexpectedly high heat of fusion which makes possible the use of
ammonium biacetate as a heat storage material.
[0017] The product is hygroscopic, so it is preferred that ammonium
biacetate be manufactured and used in a sealed system.
[0018] Ammonium biacetate can be used neat or combined with other
substances that do not react with ammonium biacetate. Examples of
these substances include, but are not limited to, clays, metal such
as stainless steel (powder, shot, beads, etc.), cementitious
materials, and other materials which are substantially inert with
respect to ammonium biacetate and acetates in general. By
substantially inert is meant that the substantially inert substance
may not react with ammonium biacetate so as to change the heat of
fusion (.DELTA.H.sub.f) of the original mass of ammonium biacetate
more than 2.degree. C. Any ratio of ammonium biacetate may be used
in any amount in combination with the substantially inert
substances. containers can comprise any material that is
substantially inert in the presence of ammonium biacetate, e.g.,
stainless steel, plastics and glass. Containers may be rigid (i.e.,
stainless steel or rigid plastic containers) or flexible enough to
conform to the shape of another object. Other materials that could
be used to hold ammonium biacetate would be known to those skilled
in the art. Ammonium biacetate could be used in any end-use
requiring the storage of heat. Such uses include culinary utensils,
such as food service trays, steam table inserts and the like;
medicinal uses such as heating pads and hot-water bottles; and
storage of solar energy for heating purposes. A further example of
the use of this invention is that of a method for holding food or
other material at a constant temperature by heating a heat storage
device comprising ammonium biacetate and a container for containing
the ammonium biacetate; and placing the food or other matter (e.g.,
water) to be temperature-controlled in proximity to the heat
storage device thereby maintaining the temperature of the food.
These devices could be stationary or mobile.
EXAMPLES
Example 1
Synthesis of Ammonium Biacetate, NH.sub.4.H.(OAc).sub.2
[0019] Into a 500 ml round bottom flask 38.5 grams (0.5 mole)
ammonium acetate and 30 grams (0.5 mole) acetic acid were admixed.
The flask was subsequently heated under nitrogen until all solids
were melted. The reaction mixture was then distilled in a
distillation column from 80.degree.-151.degree. C. at 20 mm Hg
pressure, using steam in the distillation condenser. The first
fraction was discarded, and the second fraction was collected at 15
mm Hg pressure and 70.degree. C. The melting point of the distilled
product was found to be 67.86.degree..+-.1.08.degr- ee. C.
(literature value 69.degree. C.), and the delta heat of fusion of
the distilled product was found to be 37.44.+-.1.97 cal/g.
[0020] The melting point and delta heat of fusion were determined
by differential scanning calorimetry (DSC), an analytical technique
that measures heat flow and temperature associated with transitions
between states of matter. In this method, the sample and a
reference material are subjected to a closely controlled
temperature. In the event that a phase change occurs in the sample,
thermal energy is added to or subtracted from the sample or
reference materials in order to maintain both sample and reference
at the same temperature. Because this energy input is precisely
equivalent in magnitude to the energy absorbed or evolved in the
transition between solid and liquid, quantification of the
balancing energy yields a direct calorimetric measurement of the
transition energy, i.e., .DELTA.H.sub.f.
[0021] Specifically, during differential scanning calorimetry the
sample was analyzed under a nitrogen atmosphere at 50 ml/min flow,
heating rate of 10.degree. C./min, and a temperature scan of
0.degree. C. to 90.degree. C. The data were obtained on a TA 2910
DSC coupled to a TA 5000 controller (TA Instruments, New Castle,
Del.).
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