U.S. patent application number 10/659306 was filed with the patent office on 2004-04-08 for solid compositions which generate hydrogen by combustion, comprising an alkali metal borohydride or alkaline earth metal borohydride and strontium nitrate sr(no3)2.
This patent application is currently assigned to SNPE. Invention is credited to Desgardin, Nancy, Perut, Christian, Renouard, Joel.
Application Number | 20040065395 10/659306 |
Document ID | / |
Family ID | 31985439 |
Filed Date | 2004-04-08 |
United States Patent
Application |
20040065395 |
Kind Code |
A1 |
Desgardin, Nancy ; et
al. |
April 8, 2004 |
Solid compositions which generate hydrogen by combustion,
comprising an alkali metal borohydride or alkaline earth metal
borohydride and strontium nitrate Sr(NO3)2
Abstract
The invention relates to a solid composition which can decompose
with the generation of hydrogen according to a self-sustaining
combustion reaction after initiation of this reaction by an
appropriate heat source, this composition being characterized in
that it comprises an alkali metal borohydride or alkaline earth
metal borohydride and strontium nitrate Sr(NO.sub.3).sub.2.
Inventors: |
Desgardin, Nancy; (Arpajon,
FR) ; Perut, Christian; (St. Fargeau, FR) ;
Renouard, Joel; (St. Martin en Biere, FR) |
Correspondence
Address: |
OLIFF & BERRIDGE, PLC
P.O. BOX 19928
ALEXANDRIA
VA
22320
US
|
Assignee: |
SNPE
12 Quai Henri IV
Paris
FR
75004
|
Family ID: |
31985439 |
Appl. No.: |
10/659306 |
Filed: |
September 11, 2003 |
Current U.S.
Class: |
149/22 |
Current CPC
Class: |
Y02E 60/36 20130101;
C01B 3/065 20130101; C06B 47/10 20130101; C06D 5/06 20130101; H01M
8/065 20130101; Y02E 60/50 20130101 |
Class at
Publication: |
149/022 |
International
Class: |
C06B 043/00; C06B
047/10 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 4, 2002 |
FR |
02 12313 |
Claims
1. Solid composition which can decompose with the generation of
hydrogen according to a self-sustaining combustion reaction after
initiation of this reaction by an appropriate heat source,
characterized in that the said composition comprises an alkali
metal borohydride or alkaline earth metal borohydride and strontium
nitrate Sr(NO.sub.3).sub.2.
2. Solid composition according to claim 1, characterized in that it
is provided in the form of a compact material.
3. Solid composition according to claim 2, characterized in that
the compact material is a pellet or a grain.
4. Solid composition according to claim 1, characterized in that it
is devoid of organic matter.
5. Solid composition according to claim 1, characterized in that it
is composed essentially of alkali metal borohydride or alkaline
earth metal borohydride and of strontium nitrate
Sr(NO.sub.3).sub.2.
6. Solid composition according to claim 1, characterized in that
the sum of the contents by weight of alkali metal borohydride or
alkaline earth metal borohydride and of strontium nitrate
Sr(NO.sub.3).sub.2 is greater than or equal to 90% with respect to
the total weight of the composition.
7. 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 their mixtures.
8. Solid composition according to claim 1, characterized in that
the alkaline earth metal borohydride is magnesium borohydride.
9. Solid composition according to claim 1, characterized in that
the ratio of content by weight of alkali metal borohydride or
alkaline earth metal borohydride to content by weight of strontium
nitrate Sr(NO.sub.3).sub.2 is between 1 and 10.
10. Process for the generation of hydrogen by self-sustaining
combustion of a solid composition comprising an alkali metal
borohydride or alkaline earth metal borohydride and strontium
nitrate Sr(NO.sub.3).sub.2, characterized in that: a pulverulent or
granular homogeneous solid composition comprising an alkali metal
borohydride or alkaline earth metal borohydride and strontium
nitrate Sr(NO.sub.3).sub.2 is prepared, this composition is
subsequently agglomerated using appropriate means, so as to form a
compact material, the compact material is placed in a combustion
chamber, the combustion of the compact material is initiated using
an appropriate heat source, which brings about the self-sustaining
combustion of the material with generation of hydrogen up to the
end of the combustion.
11. Hydrogen generator intended to supply hydrogen to a proton
exchange membrane fuel cell, characterized in that this generator
is a pyrotechnic generator comprising a solid composition according
to claim 1.
12. Proton exchange membrane fuel cell using hydrogen as fuel,
comprising at least one electrochemical cell (1) and one hydrogen
generator connected to the anode compartment of the cell (1),
characterized in that this hydrogen generator is a pyrotechnic
generator according to claim 11.
Description
[0001] The present invention relates to the field of generators of
hydrogen, a gas widely used as fuel or reducing agent in numerous
devices or industrial processes.
[0002] A more specific subject-matter of the invention is novel
solid compositions which can decompose with the generation of
hydrogen according to a self-sustaining combustion reaction, and
the use of these compositions for supplying hydrogen to proton
exchange membrane fuel cells.
[0003] Numerous solid compositions which generate hydrogen by
combustion are known, in particular for producing hydrogen intended
to act as fuel in chemical lasers.
[0004] Patent U.S. Pat. No. 3,948,699 discloses solid compositions
which generate hydrogen by combustion composed of a mixture of
alkali metal borohydride, for example sodium borohydride
NaBH.sub.4, with a metal oxide, for example iron oxide
Fe.sub.2O.sub.3.
[0005] However, the yields by mass of hydrogen produced are low,
less than 5%, expressed by weight of hydrogen obtained with respect
to the total weight of the composition.
[0006] Patent U.S. Pat. No. 4,064,225 discloses other solid
compositions which generate hydrogen by combustion composed of a
mixture of alkali 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 yields by mass are slightly higher, of the order of
6%.
[0008] Such hydrogen yields, less than or in the vicinity of 5%,
prove in practice to be inadequate, in particular when
miniaturization of systems is desired, for example when it is
desired to replace the batteries of portable electronic systems,
such as telephones and computers, with miniature hydrogen fuel
cells.
[0009] Patent U.S. Pat. No. 4,673,528 discloses a solid
hydrogen-generating composition which can be in the form of pellets
which can be used as fuels in chemical lasers. The
hydrogen-generating compositions disclosed in this patent are
thermally stable and comprise, as percentage by mass, between 5 and
15% of an oxidizing agent chosen from lithium nitrate LiNO.sub.3
and potassium nitrate KNO.sub.3, from 80 to 90% of magnesium
borohydride diammoniate Mg(BH.sub.4).sub.2. 2NH.sub.3 and
optionally from 2 to 15% of a binder, such as
polytetrafluoroethylene- . The hydrogen yields obtained with this
type of composition can reach 12.5%.
[0010] A person skilled in the art who wishes to replace the
batteries of portable electronic systems, such as telephones and
computers, with miniature hydrogen fuel cells is continually
preoccupied with trying to find novel solid compositions which
generate hydrogen by combustion which are completely stable and
which provide better yields by mass of hydrogen.
[0011] The present invention provides a solution to this
problem.
[0012] A more specific subject-matter of the invention is novel
solid compositions which can decompose with the generation of
hydrogen according to a self-sustaining combustion reaction after
initiation of this reaction by an appropriate heat source, the said
composition comprising an alkali metal borohydride or alkaline
earth metal borohydride and, as oxidizing salt, strontium nitrate
Sr(NO.sub.3).sub.2.
[0013] It has been found, unexpectedly, that such compositions make
it possible to provide a yield by mass of hydrogen which can reach
12% depending on the nature and the relative proportions of the
constituents, which constitutes a particularly advantageous
technical and economic advance for the abovementioned reasons.
[0014] According to a preferred alternative form, the compositions
according to the invention are devoid of organic matter, that is to
say that they are composed solely of inorganic compounds.
[0015] In a particularly preferred way, they are composed
essentially of an alkali metal borohydride or alkaline earth metal
borohydride and of strontium nitrate Sr(NO.sub.3).sub.2, that is to
say that these constituents are the predominant ones by weight. It
will be appreciated that the sum of the contents by weight of
alkali metal borohydride or alkaline earth metal borohydride and of
strontium nitrate Sr(NO.sub.3).sub.2 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.
[0016] Compositions composed solely of alkali metal borohydride or
alkaline earth metal borohydride and of strontium nitrate
Sr(NO.sub.3).sub.2, that is to say for which the sum of the
contents by weight of the two constituents reaches 100%, are
particularly preferred. The term "composed solely" should be
understood as meaning that the compositions can nevertheless
include the impurities present in the crude or purified alkali
metal borohydride or alkaline earth metal borohydride and in the
crude or purified Sr(NO.sub.3).sub.2 salt used, or alternatively
additives, such as stabilizers, whether these products are
commercially available or are synthesized according to conventional
methods.
[0017] When the compositions are not composed solely of alkali
metal borohydride or alkaline earth metal borohydride and of
strontium nitrate Sr(NO.sub.3).sub.2, they can, for example, also
comprise other metal, alkali metal or alkaline earth metal
borohydrides and/or a metal hydride and/or other oxidizing
inorganic salts, such as alkali metal nitrates, ammonium sulphate,
ammonium dichromate and iron oxides.
[0018] According to another preferred alternative form of the
invention, the alkali metal borohydride is chosen from the group
consisting of lithium borohydride, sodium borohydride and their
mixtures.
[0019] According to another preferred alternative form of the
invention, the alkaline earth metal borohydride used can be
magnesium borohydride Mg(BH.sub.4).sub.2, which has available a
high level of hydrogen.
[0020] Generally and preferably, according to the invention, the
ratio of content by weight of alkali metal borohydride or alkaline
earth metal borohydride to content by weight of strontium nitrate
is between 1 and 10, better still between 2 and 10 and preferably
between 4 and 10.
[0021] One aim of the invention is to obtain hydrogen-generating
compositions having a good yield by mass of hydrogen per gram of
solid composition and which are combusted at a temperature which is
sufficiently high for the reaction to be self sustaining and to
prevent the solid composition from being extinguished and thus from
being entirely consumed. The relative proportions by weight between
the oxidizing agent and the reducing agent should be established so
as to achieve this aim.
[0022] According to another preferred alternative form, the solid
compositions according to the invention are provided in the form of
a compact material having a specific form, for example and
preferably in the form of pellets or grains. The grains can have
any shape, preferably spherical, ovoid or cylindrical.
[0023] The pellets can also have any thickness and any peripheral
geometry, for example circular, elliptical, square or
rectangular.
[0024] The thickness of the pellets may not be constant.
[0025] The solid compositions according to the invention can be
obtained by analogy with the described methods used to produce the
abovementioned solid compositions of the state of the art, for
example by simple mixing of the constituents, milling and then
mechanical homogenization. It is also possible to mill the
constituents before the mixing or alternatively to use constituents
already in pulverulent form.
[0026] The compositions can also be obtained by granulation.
[0027] When, preferably, it is desired to obtain a solid
composition which is provided in the form of a compact material,
the granular or pulverulent homogeneous mixture of the various
constituents can, for example, be agglomerated by compacting in a
pressing container having the shape and the dimensions which are
desired for the compact material.
[0028] It is also possible to obtain a compact material by
dissolving and/or suspending the constituents in a liquid medium.
After homogenizing and placing in a mould with the appropriate
dimensions desired for the compact material, the liquid is removed,
for example by evaporation, which makes it possible to obtain a
compact material.
[0029] Another subject-matter of the present invention is a process
for the generation of hydrogen by self-sustaining combustion of a
solid composition comprising an alkali metal borohydride or
alkaline earth metal borohydride and, as oxidizing salt, strontium
nitrate Sr(NO.sub.3).sub.2.
[0030] According to this process, a pulverulent or granular
homogeneous solid composition comprising an alkali metal
borohydride or alkaline earth metal borohydride and strontium
nitrate Sr(NO.sub.3).sub.2 is first of all prepared.
[0031] This composition is subsequently 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 under an inert gas or placed
under vacuum.
[0032] 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.
[0033] The combustion of the compact material is then initiated
using an appropriate heat source, which brings about the
self-sustaining combustion of the material with generation of
hydrogen up to the end of the combustion.
[0034] The appropriate heat sources which make possible the
initiation of the combustion by the "Joule" effect are well known
to a person skilled in the art, in particular electrical
initiators. The use of a nickel-chromium ignition filament placed
in contact or coated with the composition to be initiated, on which
a sufficient voltage and a sufficient current intensity (and
therefore a sufficient power) are imposed, is entirely suitable. It
is possible, for example, for a given voltage, to increase the
intensity of the current until the combustion is initiated.
[0035] In some cases, to promote the ignition, a conventional
relay-ignition powder well known to a person skilled in the art can
be positioned between the filament and the compact material. In
this case, use will preferably be made of a relay-ignition powder
of the same nature as the compact material according to the
invention, that is to say having the same constituents but with a
markedly lower ratio of content by weight of alkali metal
borohydride or alkaline earth metal borohydride to content by
weight of strontium nitrate Sr(NO.sub.3).sub.2, for example between
0.1 and 1.
[0036] Another subject-matter of the present invention is a
pyrotechnic hydrogen generator, intended to supply hydrogen to a
proton exchange membrane fuel cell, comprising an abovementioned
solid composition according to the invention.
[0037] Fuel cells operating with hydrogen, also known as proton
exchange membrane fuel cells, are well known to a person skilled in
the art.
[0038] Such a fuel cell is composed essentially of 2 parts:
[0039] the core of the fuel cell, composed of one or more
electrochemical cells mounted in series, which produces the
electrical energy;
[0040] the fuel, namely hydrogen, reservoir.
[0041] Attached to these two main parts are auxiliary systems
relating in particular to supplying hydrogen to the core of the
fuel cell, to discharging the water produced or to cooling.
[0042] An electrochemical cell of the core of the fuel cell is
represented diagrammatically in FIG. 1.
[0043] It is observed, in this FIG. 1, that an electro-chemical
cell 1 of the core of the fuel cell supplies electrical energy from
two electrochemical reactions carried out on two electrodes 2 and 3
generally composed of carbon and separated by a proton exchange
membrane 4 acting as electrolyte and generally composed of
fluoropolymers impregnated with water. Hydrogen H.sub.2 is oxidized
on the anode 2 in the presence of a generally platinum-based
catalyst, the hydrogen being separated into protons H.sup.+and
electrons e.sup.-. The stream of protons H.sup.+passes through the
membrane 4, while the electrons e.sup.-, which are not able to pass
through the membrane 4, are captured by a current collector 5
connected to an external electrical circuit 6 to rejoin the cathode
3. On the other side of the membrane 4, at the cathode 3, the
protons H.sup.+and the electrons e.sup.-recombine with oxygen
O.sub.2, generally originating from the surrounding air, to produce
water H.sub.2O.
[0044] The pyrotechnic hydrogen generators according to the
invention are essentially composed 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 released in the chambers to the anode of
a cell of the core of the fuel cell are placed.
[0045] Preferably, the overall amount of hydrogen capable of being
supplied by the generator is released dis-continuously by a
separate initiation of the solid compositions present in the
various chambers. The mass of solid composition in each chamber can
be identical or different from one chamber to another. The last
alternative form makes possible release of hydrogen in an amount
suited to a specific need.
[0046] The various chambers can emerge in a chamber for the
expansion of the hydrogen released, this chamber being connected to
the anode compartment of a cell or having one of its walls at least
partially formed by the anode.
[0047] Another subject-matter of the present invention is a proton
exchange membrane fuel cell using hydrogen as fuel, comprising at
least one electrochemical cell and one abovementioned pyrotechnic
hydrogen generator according to the invention connected to the
anode compartment of the cell.
[0048] The following nonlimiting examples illustrate the invention
and the advantages which it provides.
Example 1
[0049] Solid composition composed of a mixture of NaBH.sub.4 and of
Sr(NO.sub.3).sub.2 in the relative proportions by weight 60/40
respectively
[0050] A mixture of 90 g of NaBH.sub.4 and 60 g of
Sr(NO.sub.3).sub.2 is milled and then homogenized.
[0051] A fraction of the pulverulent and homogeneous mixture thus
obtained is subsequently introduced 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).
[0052] The circular pellet thus obtained, with a diameter of 5 mm
and a mass of 80 mg, is subsequently introduced into a combustion
chamber with a volume of 10 cm.sup.3 and equipped with a pressure
gauge, a temperature probe and a conventional ignition device
comprising a nickel (80 weight%)-chromium (20 weight%) filament.
The pellet is brought into contact with the filament and then the
chamber is purged with an inert gas (nitrogen) under an absolute
pressure of 10.sup.5 Pa (1 bar).
[0053] The filament is subsequently heated by the Joule effect
until initiation of the combustion.
[0054] Once initiated, the combustion of the composition is
self-sustaining and lasts approximately 3 s.
[0055] The combustion temperature, measured experimentally from the
maximum pressure, varies between 480 and 600.degree. K.
approximately following the firings.
[0056] On completion of the combustion, the chamber is allowed to
cool to ambient temperature and then the pressure in the chamber is
recorded.
[0057] The measured increase in pressure and the analysis of the
gases present after combustion by chromatography coupled to a mass
spectrometer makes it possible to calculate a yield by mass of
hydrogen of 5.32 to 5.88%, expressed as grams of hydrogen released
per gram of solid composition.
[0058] DTA analyses were carried out on this composition formed of
60/40 sodium borohydride NaBH.sub.4 and Sr(NO.sub.3).sub.2 to
determine whether it was stable.
[0059] DTA (Differential Thermal Analysis) is a calorimetric
measurement test. It consists in heating the composition from 15 to
200.degree. C., the temperature being increased by 8.degree. C. per
minute. During this rise in temperature, this test consists in
plotting the temperatures of the endothermic or exothermic peaks
and in measuring the energy released or absorbed. If no energy is
released or absorbed, this means that the composition is stable and
thus that the constituents of the composition analysed are entirely
compatible.
[0060] The tests carried out on the composition of Example 1, 60/40
NaBH.sub.4/Sr(NO.sub.3).sub.2, show that this composition is
stable. This is because, during the DTA test, no energy was
released or absorbed during the rise in temperature.
[0061] Examples 2 to 8 are carried out in exactly the same way,
only the relative proportions by weight between the two
constituents being modified.
[0062] For each of Examples 1 to 7, the results obtained
experimentally, on the one hand, and the results obtained by
calculations, on the other hand, are shown in Table 1 below. Two or
three tests were carried out for each of the examples but only the
mean result appears. For some of the examples, no experiment has
yet been carried out and therefore only the results obtained
theoretically appear.
1 TABLE 1 NaBH.sub.4/ Theoretical Experimental Sr(NO.sub.3).sub.2
yield of yield of ratio by hydrogen hydrogen mass (%) (%) Example 1
65/35 6.93 4.55 Example 2 60/40 6.39 5.90 Example 3 55/45 5.86 5.75
Example 4 50/50 5.33 -- Example 5 40/60 4.2 -- Example 6 30/70 3.0
-- Example 7 20/80 0.47 --
[0063] The theoretical yield of hydrogen decreases, of course, when
the proportion of hydrogen-carrying reducing agent decreases.
However, the measured yield only corresponds to the theoretical
yield for sufficiently high values of combustion temperatures.
Examples 8 to 14
[0064] Solid compositions composed of a mixture of LiBH.sub.4 and
Sr(NO.sub.3).sub.2 in different relative proportions by weight.
[0065] In this example, sodium borohydride NaBH.sub.4 is replaced
by lithium borohydride LiBH.sub.4. The preparation is carried out
in exactly the same way as in Example 1 described above, that is to
say with the production of a pellet with the same mass. As in
Examples 1 to 7 above, the relative proportions by weight between
the two constituents are varied.
[0066] The theoretical results calculated for the various
compositions are displayed in Table 2 below:
2 TABLE 2 LiBH.sub.4/ Sr(NO.sub.3).sub.2 Combustion Yield of ratio
by temperature hydrogen mass (.degree. K) (%) Example 8 70/30 265
11.20 Example 9 60/40 743 10.20 Example 10 50/50 1251 9.26 Example
11 40/60 1491 7.40 Example 12 30/70 1680 5.53 Example 13 20/80 2048
3.58 Example 14 10/90 2392 0.02
[0067] The tests carried out on the composition of Example 9, 60/40
LiBH.sub.4/Sr(NO.sub.3).sub.2, show that this composition is not
completely stable. This is because, during the DTA test, an energy
absorption of 112 J/gram was observed between 113 and 124.degree.
C.
Examples 15 to 22
[0068] In these examples, an alkali metal borohydride, such as
NaBH.sub.4 or LiBH.sub.4, is no longer used but rather an alkaline
earth metal borohydride, Mg(BH.sub.4).sub.2, and strontium nitrate
Sr(NO.sub.3).sub.2 is still used as oxidizing agent. The
preparation is carried out in the same way as in the preceding
examples with different relative proportions by weight between the
two constituents. The theoretical results obtained by calculations
are displayed in Table 3 below.
3 TABLE 3 Mg(BH.sub.4).sub.2/ Sr(NO.sub.3).sub.2 Combustion Yield
of ratio by temperature hydrogen mass (.degree. K) (%) Example 15
80/20 571 11.95 Example 16 70/30 1079 10.45 Example 17 60/40 1789
8.93 Example 18 50/50 1947 7.16 Example 19 40/60 2049 5.51 Example
20 30/70 2145 4.04 Example 21 20/80 2673 1.74 Example 22 10/90 2477
0.01
[0069] Measurements were carried out with a pellet having the two
constituents with relative proportions by weight of the
Mg(BH.sub.4).sub.2 to the strontium nitrate Sr(NO.sub.3).sub.2 of
70/30 respectively. A yield by mass of H.sub.2, expressed as grams
of hydrogen released per gram of solid composition, of 9.55% was
obtained as results.
* * * * *