U.S. patent application number 10/117915 was filed with the patent office on 2003-03-20 for solid compositions generating hydrogen by combustion, comprising an alkali metal borohydride and an ammonium salt.
Invention is credited to Gauthier, Corinne, Perut, Christian, Roller, Denis.
Application Number | 20030051785 10/117915 |
Document ID | / |
Family ID | 8862140 |
Filed Date | 2003-03-20 |
United States Patent
Application |
20030051785 |
Kind Code |
A1 |
Gauthier, Corinne ; et
al. |
March 20, 2003 |
Solid compositions generating hydrogen by combustion, comprising an
alkali metal borohydride and an ammonium salt
Abstract
The invention relates to solid compositions that can decompose
generating hydrogen in a self-sustaining combustion reaction after
this reaction has been initiated by an appropriate heat source.
These compositions comprise an alkali metal borohydride and an
oxidizing mineral ammonium salt of formula NH.sub.4Y, in which Y
represents a group consisting only of nitrogen and oxygen. The
ratio of the weight content of alkali metal borohydride to the
weight content of the salt of general formula NH.sub.4Y is between
1 and 4. Thus, high hydrogen mass yields are obtained, of around 8
to 14%, thereby making it possible to reduce the size and the
weight of the hydrogen generators used in certain systems,
especially in proton exchange membrane fuel cells.
Inventors: |
Gauthier, Corinne; (Vert Le
Petit, FR) ; Perut, Christian; (St. Fargeau
Ponthierry, FR) ; Roller, Denis; (La Ferte Alais,
FR) |
Correspondence
Address: |
BUCKNAM AND ARCHER
600 Old Country Road
Garden City
NY
11530
US
|
Family ID: |
8862140 |
Appl. No.: |
10/117915 |
Filed: |
April 8, 2002 |
Current U.S.
Class: |
149/22 |
Current CPC
Class: |
C06B 47/10 20130101;
Y02E 60/36 20130101; C06B 43/00 20130101; H01M 8/065 20130101; C01B
3/065 20130101; Y02E 60/50 20130101 |
Class at
Publication: |
149/22 |
International
Class: |
C06B 043/00; C06B
047/10 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 10, 2001 |
FR |
FR 01 04839 |
Claims
1. Solid composition that can decompose generating hydrogen in a
self-sustaining combustion reaction after this reaction has been
initiated by an appropriate heat source, the said composition
comprising an alkali metal borohydride and an oxidizing mineral
ammonium salt, characterized in that the said salt satisfies the
general formula NH.sub.4Y in which Y represents a group consisting
only of nitrogen and oxygen, and in that the ratio of the weight
content of alkali metal borohydride to the weight content of the
salt of general formula NH.sub.4Y is between 1 and 4.
2. Solid composition according to claim 1, characterized in that Y
represents the nitrate or dinitramide group.
3. Solid composition according to claim 1, characterized in that it
is in the form of a compact material
4. Solid composition according to claim 3, characterized in that
the compact material is a pellet or a particle.
5. Solid composition according to claim 1, characterized in that it
contains no organic matter.
6. Solid composition according to claim 1, characterized in that it
essentially consists of an alkali metal borohydride and a salt of
general formula NH.sub.4Y.
7. Solid composition according to claim 1, characterized in that
the sum of the weight contents of alkali metal borohydride and of
the salt of general formula NH.sub.4Y is greater than or equal to
90% compared with the total weight of the composition.
8. Solid composition according to claim 1, characterized in that
the alkali metal borohydride is chosen from the group consisting of
lithium borohydride, sodium borohydride and mixtures thereof.
9. Process for generating hydrogen by self-sustaining combustion of
a solid composition comprising an alkali metal borohydride and an
oxidizing mineral ammonium salt, characterized in that: a
homogenous, pulverulent or granular, solid composition comprising
an alkali metal borohydride and an ammonium salt of general formula
NH.sub.4Y, in which Y represents a group consisting only of
nitrogen and oxygen, the ratio of the weight content of alkali
metal borohydride to the weight content of the salt of general
formula NH.sub.4Y being between 1 and 4, is produced; next, this
composition is agglomerated using appropriate means so as to form a
compact material; the compact material is placed in a combustion
chamber; and the combustion of the compact material is initiated
using an appropriate heat source, which causes the self-sustaining
combustion of the material with generation of hydrogen until the
end of combustion.
10. Hydrogen generator intended to supply a proton exchange
membrane fuel cell with hydrogen, characterized in that this
generator is a pyrotechnic generator comprising a solid composition
according to claim 1.
11. Proton exchange membrane fuel cell using hydrogen as fuel,
comprising at least one electrochemical cell and a hydrogen
generator connected to the anode compartment of the electrochemical
cell, characterized in that this hydrogen generator is a
pyrotechnic generator according to claim 10.
Description
[0001] The present invention relates to the field of hydrogen
generators, hydrogen being a gas widely used as fuel or as reducing
agent in many industrial processes or devices.
[0002] More specifically, the subject of the invention is novel
solid compositions that can decompose generating hydrogen in a
self-sustaining combustion reaction, and the use of these
compositions to supply proton exchange membrane fuel cells with
hydrogen.
[0003] Many solid compositions generating hydrogen by combustion
are known, especially for producing hydrogen intended to serve as
fuel in chemical lasers.
[0004] U.S. Pat. No. 3,948,699 describes solid compositions
generating hydrogen by combustion, these consisting of a mixture of
a metal borohydride, for example sodium borohydride NaBH.sub.4,
with a metal oxide, for example iron oxide FE.sub.2O.sub.3 or
aluminium oxide Al.sub.2O.sub.3.
[0005] However, the mass yields of hydrogen produced are low, less
than 5% expressed as weight of hydrogen obtained with respect to
the total weight of the composition.
[0006] U.S. Pat. No. 4,064,225 describes other solid compositions
generating hydrogen by combustion, these consisting of a mixture of
a metal borohydride, for example sodium borohydride, with ammonium
sulphate (NH.sub.4).sub.2SO.sub.4 or ammonium dichromate
(NH.sub.4).sub.2Cr.sub.2O- .sub.7.
[0007] The mass yields are slightly higher, around 6%.
[0008] Such hydrogen yields, less than or about 5%, prove in
practice to be insufficient, especially when miniaturization of
systems is desired, for example when it is wished to replace the
batteries of portable electronic systems, such as telephones and
computers, with miniature hydrogen fuel cells.
[0009] A person skilled in the art therefore is permanently trying
to find novel solid compositions generating hydrogen by combustion
which provide better hydrogen mass yields so as to reduce as far as
possible the size and the weight of generators in these portable
miniaturized systems.
[0010] The present invention provides a solution to this
problem.
[0011] More specifically, the subject of the invention is a novel
solid composition that can decompose generating hydrogen in a
self-sustaining combustion reaction after this reaction has been
initiated by an appropriate heat source, the said composition
comprising an alkali metal borohydride and an oxidizing mineral
ammonium salt satisfying the general formula NH.sub.4Y in which Y
represents a group consisting only of nitrogen and oxygen, the
ratio of the weight content of alkali metal borohydride to the
weight content of the salt of general formula NH.sub.4Y being
between 1 and 4.
[0012] Unexpectedly, it has been found that such compositions
result in a hydrogen mass yield of around 8% to 14% depending on
the nature and the relative proportions of the constituents, this
constituting a particularly advantageous technical and economic
advance for the reasons mentioned above.
[0013] Preferably, Y represents the nitrate group (--NO.sub.3) or
the dinitramide group 1
[0014] Ammonium nitrate is particularly preferred.
[0015] According to a preferred embodiment, the compositions
according to the invention contain no organic matter, that is to
say they only consist of mineral compounds.
[0016] Particularly preferably, they essentially consist of the
alkali metal borohydride and the mineral ammonium salt of formula
NH.sub.4Y, that is to say these constituents are the predominant
ones by weight. It should be understood that the sum of the weight
contents of the alkali metal borohydride and of the ammonium salt
of formula NH.sub.4Y is greater than or equal to 75%, better still
greater than or equal to 90% and even greater than or equal to 95%,
with respect to the total weight of the composition.
[0017] Compositions consisting only of an alkali metal borohydride
and a salt of formula NH.sub.4Y are particularly preferred. The
expression "consisting only" should be understood to mean that the
compositions may, however, include the impurities present in the
as-received or purified alkali metal borohydride and in the
as-received or purified salt of formula NH.sub.4Y which are used,
or else additives such as stabilizers, whether these products are
commercial products or are synthesized using standard methods.
[0018] When the compositions do not consist only of the alkali
metal borohydride and the ammonium salt of formula NH.sub.4Y, they
may, for example, also include other metal, especially
alkaline-earth metal, borohydrides and/or a metal hydride and/or
other oxidizing mineral salts such as alkali metal nitrates,
ammonium sulphate, ammonium dichromate, iron oxides and aluminium
oxide.
[0019] According to another preferred embodiment of the invention,
the alkali metal borohydride is chosen from the group consisting of
lithium borohydride, sodium borohydride and mixtures thereof.
[0020] According to another preferred embodiment, the solid
compositions according to the invention are in the form of a
compact material, having an intrinsic shape, for example, and as a
preference, in the form of pellets or particles. The particles may
have any, preferably spherical, ovoid or cylindrical, shape.
[0021] The pellets may also have any thickness and any peripheral
geometry, for example circular, elliptical, square or rectangular
geometry.
[0022] The thickness of the pellets may not be constant.
[0023] The solid compositions according to the invention may be
obtained by analogy with the methods described, used to obtain the
aforementioned solid compositions of the prior art, for example by
simple mixing of the constituents, grinding and then mechanical
homogenization. It is also possible to grind the constituents
before mixing them, or else to use constituents already in a
pulverulent form.
[0024] The compositions may also be obtained by granulation.
[0025] When, preferably, it is desired to obtain a solid
composition in the form of a compact material, the homogeneous,
granular or pulverulent, mixture of the various constituents may,
for example, be agglomerated by compacting them in a pressing
container having the desired shape and dimensions of the compact
material.
[0026] It is also possible to obtain a compact material by putting
the constituents into solution and/or suspension in a liquid
medium. After homogenization and injection into a mould having the
appropriate dimensions desired for the compact material, the liquid
is removed, for example by evaporation, thereby producing a compact
material.
[0027] The subject of the present invention is also a process for
generating hydrogen by self-sustaining combustion of a solid
composition comprising an alkali metal borohydride and an oxidizing
mineral ammonium salt.
[0028] According to this process, a homogeneous pulverulent or
granular, solid composition, comprising an alkali metal borohydride
and an ammonium salt of general formula NH.sub.4Y, Y having the
aforementioned meaning and the ratio of the weight content of
alkali metal borohydride to the weight content of the salt of
general formula NH.sub.4Y being between 1 and 4, is firstly
produced.
[0029] Next, this composition is agglomerated using appropriate
means, for example those mentioned above, so as to form a compact
material, and then the compact material is placed in a combustion
chamber which is purged with an inert gas or in which a vacuum is
created.
[0030] When the dead volume (the volume remaining in the chamber
after the compact material has been placed therein) is low, such a
purge may in practice be unnecessary.
[0031] Combustion of the compact material is then initiated using
an appropriate heat source, which causes the self-sustaining
combustion of the material with generation of hydrogen until the
end of combustion.
[0032] Appropriate heat sources for initiating the combustion by
the "Joule" effect are well known to those skilled in the art,
especially electrical initiators. It is perfectly suitable to use a
nickel-chromium ignition filament placed in contact with or
encapsulated in the composition to be initiated, on which filament
a sufficient voltage and a current of sufficient intensity (and
therefore a sufficient power) are imposed. It is possible, for
example, for a given voltage to increase the intensity of the
current until the combustion is initiated.
[0033] In certain cases, in order to promote ignition, a
conventional relay-ignition powder, well known to those skilled in
the art, may be placed between the filament and the compact
material.
[0034] The subject of the present invention is also a pyrotechnic
hydrogen generator intended to supply a proton exchange membrane
fuel cell with hydrogen, comprising an aforementioned solid
composition according to the invention.
[0035] Fuel cells operating with hydrogen, also called proton
exchange membrane fuel cells, are well known to those skilled in
the art.
[0036] Such a fuel cell essentially consists of two parts:
[0037] the core of the fuel cell, consisting of one or more
electrochemical cells mounted in series, which produces the
electrical energy;
[0038] the fuel, namely hydrogen, reservoir.
[0039] Attached to these two main parts are auxiliary systems,
especially those for supplying the core of the fuel cell with
hydrogen, for removing the water produced or for cooling.
[0040] Each cell of the core of the fuel cell delivers the
electrical energy as a result of the two electrochemical reactions
taking place at the two electrodes which are immersed in an
electrolyte and separated by a proton exchange membrane. In the
presence of a catalyst, the hydrogen at the anode is oxidized,
separating into protons and electrons. The flux of protons passes
through the membrane, while the electrons are captured by an
external electrical circuit. The protons and the electrons
recombine with oxygen on the other side of the membrane, at the
cathode, in order to produce water.
[0041] The pyrotechnic hydrogen generators according to the
invention essentially consist of one or more chambers in which a
solid composition according to the invention, separate means for
initiating the combustion of the composition in each of the
chambers, means for actuating this initiation and means for
transferring the hydrogen liberated in the chambers to the anode of
a cell of the core of the fuel cell are placed.
[0042] Preferably, the overall amount of hydrogen capable of being
delivered by the generator is liberated discontinuously by a
separate initiation of the combustion of the solid compositions
contained in the various chambers. The mass of solid composition in
each chamber may be identical or different from one chamber to
another. This latter variant makes it possible to liberate hydrogen
in an amount tailored to a particular need.
[0043] The various chambers may run into a chamber in which the
liberated hydrogen expands, this expansion chamber being connected
to the anode compartment of a cell, or one of the walls of which is
at least partly formed by the anode.
[0044] The subject of the present invention is also a proton
exchange membrane fuel cell using hydrogen as fuel, comprising at
least one electrochemical cell and at least one aforementioned
pyrotechnic hydrogen generator according to the invention,
connected to the anode compartment of the cell.
[0045] The following non-limiting examples illustrate the invention
and the advantages that it affords.
EXAMPLE 1
[0046] Solid composition consisting of a mixture of NaBH.sub.4 and
NH.sub.4NO.sub.3 in relative weight proportions of 60/40
respectively.
[0047] A mixture of 90 g of NaBH.sub.4 and 60 g of NH.sub.4NO.sub.3
containing 7% by weight of KNO.sub.3 as phase-stabilizing additive
were ground and then homogenized.
[0048] Next, one portion of the homogeneous, pulverulent mixture
thus obtained was put into and then compacted in the compression
die of a pelletizer having the desired pellet geometry, under a
pressure of 10.sup.7 Pa (100 bar).
[0049] Next, the circular pellet thus obtained, having a diameter
of 5 mm and a mass of 80 mg, was put into a combustion chamber
having a volume of 10 cm.sup.3, the said chamber being fitted with
a pressure gauge, a temperature probe and a standard ignition
device comprising a nickel (80 wt %)-chromium (20 wt %) filament.
The pellet was brought into contact with the filament and the
chamber then purged with an inert gas (nitrogen) at an absolute
pressure of 10.sup.5 Pa (1 bar) The filament was then heated by the
Joule effect until initiation of the combustion of the
composition.
[0050] Once initiated, the combustion of the composition was
self-sustaining and lasted about 3 s.
[0051] The measured combustion temperature was 1044 K.
[0052] After combustion, the chamber was cooled to room temperature
and the pressure in the chamber then noted.
[0053] The measured increase in pressure and the analysis of the
gases present after combustion, using chromatography coupled to a
mass spectrometer, were used to calculate a hydrogen mass yield of
8.2%, expressed as g of hydrogen liberated per g of solid
composition.
EXAMPLES 2 to 5
[0054] Solid compositions consisting of NaBH.sub.4/NH.sub.4NO.sub.3
mixtures in other weight proportions.
[0055] For these examples, the same procedure as in Example 1 was
strictly carried out, with the same two constituents (NaBH.sub.4
and NH.sub.4NO.sub.3), with a pellet of the same mass being
obtained, but with different weight proportions of these two
constituents.
[0056] Table 1 below specifies, for each example, the
NaBH.sub.4/NH.sub.4NO.sub.3 weight proportions of the composition,
the measured combustion temperature and the hydrogen mass yield
obtained.
1 TABLE 1 Combustion Hydrogen NaBH.sub.4/NH.sub.4NO.sub.3
temperature yield mass ratio (K) (%) Example 2 65/35 958 8.7
Example 3 70/30 865 9.0 Example 4 75/25 515 9.3 Example 5 78/22 265
9.4
EXAMPLES 6 to 10
[0057] Solid compositions consisting of LiBH.sub.4/NH.sub.4NO.sub.3
mixtures in various weight proportions.
[0058] For these examples, the same procedure as in Examples 1 to 5
was strictly carried out, but the sodium borohydride was replaced
with lithium borohydride.
[0059] Table 2 below specifies, for each example, the
LiBH.sub.4/NH.sub.4NO.sub.3 weight proportions of the composition,
the measured combustion temperature and the hydrogen mass yield
obtained.
2 Combustion Hydrogen LiBH.sub.4/NH.sub.4NO.sub- .3 temperature
yield mass ratio (K) (%) Example 6 50/50 1500 11.8 Example 7 55/45
1435 12.4 Example 8 60/40 1320 13.1 Example 9 65/35 1060 13.4
Example 10 70/30 805 13.5
* * * * *