U.S. patent application number 10/112731 was filed with the patent office on 2002-10-03 for method for rapidly carrying out hydrogenation of a hydrogen storage material.
This patent application is currently assigned to HYDRO-QUEBEC. Invention is credited to Bouaricha, Salim, Guay, Daniel, Huot, Jacques, Schulz, Robert.
Application Number | 20020141939 10/112731 |
Document ID | / |
Family ID | 24839132 |
Filed Date | 2002-10-03 |
United States Patent
Application |
20020141939 |
Kind Code |
A1 |
Schulz, Robert ; et
al. |
October 3, 2002 |
Method for rapidly carrying out hydrogenation of a hydrogen storage
material
Abstract
Disclosed is a method for rapidly carrying out a hydrogenation
of a material capable of absorbing hydrogen. It was discovered that
when a powder of a material capable of absorbing hydrogen is ground
under a hydrogen pressure, not at room temperature but at a higher
temperature (about 300.degree. C. in the case of magnesium) and in
the presence of a hydrogenation activator such as graphite and
optionally a catalyst, it is possible to transform completely the
powder of this material into a hydride. Such a transformation is
achieved in a period of time less than 1 hour whereas the known
methods call for periods of time as much as 10 times longer. This
is an unexpected result which gives rise to a considerable
reduction in the cost of manufacture of an hydride, particularly
MgH.sub.2.
Inventors: |
Schulz, Robert; (Ste-Julie,
CA) ; Bouaricha, Salim; (Longueuil, CA) ;
Huot, Jacques; (Boucherville, CA) ; Guay, Daniel;
(St-Lambert, CA) |
Correspondence
Address: |
FOLEY AND LARDNER
SUITE 500
3000 K STREET NW
WASHINGTON
DC
20007
US
|
Assignee: |
HYDRO-QUEBEC
|
Family ID: |
24839132 |
Appl. No.: |
10/112731 |
Filed: |
April 2, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10112731 |
Apr 2, 2002 |
|
|
|
09706809 |
Nov 7, 2000 |
|
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|
Current U.S.
Class: |
423/658.2 |
Current CPC
Class: |
Y02E 60/32 20130101;
Y02E 60/327 20130101; Y02E 60/325 20130101; C01B 6/04 20130101;
C01B 3/0005 20130101 |
Class at
Publication: |
423/658.2 |
International
Class: |
C01B 003/04 |
Claims
1. A method for rapidly carry out a hydrogenation of a hydrogen
storage material, comprising the step of subjecting said material
to a mechanical grinding in the presence of a hydrogenation
activator and under hydrogen pressure and a temperature higher than
the room temperature.
2. The method according to claim 1, wherein the hydrogen pressure
is equal to or higher than 1 bar.
3. The method according to claim 2, wherein the temperature is
equal to or higher than 50.degree. C.
4. The method according to claim 3, wherein the mechanical grinding
is carried out within an enclosure with a mechanical energy equal
to or higher than 0.05 kW/liter.
5. The method according to claim 4, wherein the hydrogenation
activator is graphite.
6. The method according to claim 5, wherein the graphite is used in
an amount equal to or higher than 1% by weight.
7. The method according to claim 6, wherein the graphite is used in
an amount equal to or higher than 3% by weight.
8. The method according to claim 4, wherein the hydrogenation
activator is a hydrocarbon.
9. The method according to claim 4, wherein the hydrogenation
activator is selected from the group consisting of naphthalene,
perylene, pentacene, adamantane, fullerene and vulcan.
10. The method according to claim 4, wherein the material is
magnesium.
11. The method according to claim 10, wherein in that the hydrogen
pressure is equal to about 4 bars and the temperature is equal to
about 300.degree. C.
12. The method according to claim 11, wherein the hydrogenation
activator is graphite and is used in an amount equal to or higher
than 1% by weight.
13. The method according to claim 12, wherein the mechanical
grinding is carried out in the presence of vanadium as a
catalyst.
14. The method according to claim 4, wherein the mechanical
grinding is carried out in the presence of a catalyst.
15. The method according to claim 14, wherein the catalyst consists
of vanadium and is present in an amount equal to or higher than 1%
at.
16. The method according to claim 4, wherein said material contains
sodium and aluminum.
17. A material for the storage, transportation and/or production of
hydrogen said material containing a hydrogenation activator and
having been subjected to a hydrogenation carried out by the method
according to claim 4, with the proviso that when the activator is
graphite, cyclohexane, tetrahydrofuran or anthracene, then the
material is not selected from the group consisting of Mg, Mg--Ni,
Mg--Ru, Mg--Pt, Mg--Pd, NaAlH.sub.4 and Na.sub.3AlH.sub.6.
18. The material according to claim 16, wherein the hydrogenation
activator is a solid, liquid or gaseous hydrocarbon.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a method for rapidly
carrying out a hydrogenation of a hydrogen storage material.
BRIEF DESCRIPTION OF THE PRIOR ART
[0002] It is known that the hydrogenation of a material capable of
absorbing hydrogen and more specifically the first hydrogenation
thereof, can be very difficult to carry out, since there is usually
a natural oxide at the surface of a material, which acts as a
barrier to the penetration of hydrogen. Therefore, one must break
down this barrier to hydrogenate the material for a first time.
Thereafter, the second and subsequent hydrogenations are carried
out much more easily.
[0003] The first hydrogenation that is carried out to break the
oxide coating at the surface of the material is called
"activation". Such activation is usually achieved by exposing the
hydrogen storage material to a high temperature, typically several
hundred degrees Celsius under a high hydrogen pressure, typically
from 15 to 50 bars. The lower are the temperature and the pressure
required for the hydrogenation, the easier is the activation and
the shorter is the hydrogenation time.
[0004] One of the hydrogen storage materials that is particularly
difficult to activate, is magnesium. Many researchers have tried
for years to rapidly produce magnesium hydride at low cost,
starting from metallic magnesium, but without great success.
[0005] The most conventional method of hydrogenation of a magnesium
powder is described as follows in the article of E. BARTMANN et al,
Chem. Ber. 123 (1990) 1517, at page 1523:
[0006] <<(Mg powder was placed into a steel autoclave fitted
with a glass vessel. The autoclave was evacuated twice and
pressurized with 3 bars H.sub.2. The hydrogen pressure was
increased to 5 bars, and the autoclave heated to 345.degree. C. and
at that temperature the H.sub.2 pressure was then increased to 15
bars and maintained constant until completion of hydrogenation
(.gtoreq.24 h). >>
[0007] The extreme conditions used in this conventional method have
led researchers to experiment the use of catalysts to facilitate a
first hydrogenation of magnesium.
[0008] In U.S. Pat. No. 5,198,207 of 1993 in the name of TH.
GOLDSCHMIDT AG, column 1, lines 38-45, it is described that the
doping of magnesium with other metals such as aluminium, indium,
iron, etc has been already used to catalyze the hydrogenation of
magnesium, but without great success. As an alternative, U.S. Pat.
No. 5,198,207 suggests to add to the magnesium a small amount of
magnesium hydride, typically higher than 1.2% by weight, in order
to catalyze the hydrogenation of magnesium at temperatures above
250.degree. C. under a pressure ranging between 5 and 50 bars.
According to what is disclosed in the patent, this technique called
"autocatalysis" permits to complete the hydrogenation in a period
of time longer than 7 hours (see column 3).
[0009] All the known methods described hereinabove consist in
subjecting the magnesium to a high hydrogen pressure at a high
temperature to produce magnesium hydride. However, it has been
discovered that it is possible to produce a magnesium hydride at
room temperature by carrying out a mechanical alloying consisting
in subjecting a magnesium powder to an intense mechanical grinding
in presence of hydrogen under pressure. In an article entitled
"Formation of metal hydrides by mechanical alloying" and published
in J. of Alloys and Compounds, 217 (1994), 181, Y. CHEN et al. have
demonstrated that after 471/2 hours of intensive grinding of a
magnesium powder under a hydrogen pressure of 240 kPa (about 2.4
bars), a large amount of magnesium is converted to magnesium
hydride. However, the time period required to complete the
hydrogenation is very long. In an article entitled "Synthesis of
Magnesium and Titanium Hydride via Reactive Mechanical Alloying"
and published in the Journal of Alloys and Compounds, 298 (2000)
279, J. L. BOBET et al. have conducted the same type of experiments
with a mechanical alloying except they added to the magnesium in
the crucible of the grinder, a catalyst made of a 3d transition
metal, such as cobalt. These authors have discovered that only 35%
of magnesium hydride is formed after 5 hours when magnesium is
ground alone in the presence of hydrogen, but this percentage is
increased up to 47% within the same period of time when cobalt is
added as a catalyst. However, even when cobalt is used as a
catalyst, only 71% of hydride is formed after 10 hours of
grinding.
[0010] In an article entitled "Hydriding-dehydriding behaviour of
magnesium composites obtained by mechanical grinding with graphite
carbon" and published in the International Journal of Hydrogen
Energy, 25 (2000) 837-843, H. IMAMURA et al. have also shown that
if magnesium powder is ground with graphite in presence of
cyclohexane (CH) or tetrahydrofuran (THF) with or without a
catalyst (Pd), the obtained composite (Mg/C or Mg/C/Pd) CF or THF
is hydrogenated more rapidly than magnesium alone when, after
grinding, the mixture is exposed to a hydrogen pressure of 66.7 kPa
(about 0.7 bars) at 180.degree. C. The Mg ground with graphite
alone, that is, without the presence of CH of THF, results in a
composite that is not very reactive and only absorbs 5% of hydrogen
in 20 hours. However, when the grinding of Mg is carried out with
graphite in presence of cyclohexane, 80% of Mg is converted into
hydride after 20 hours of grinding.
[0011] Table 1 summarizes all the experiments disclosed in the
prior art for use to produce magnesium hydride starting from a
powder of metallic Mg.
1TABLE 1 Percentage of Hydro- hydride formed Hydrogen genation
during the Method Pressure Temperature time reaction (1) Hydrogena-
15 bars 345.degree. C. 24 h .congruent.100% tion at high
temperature and high pressure (2) Hydrogena- 5 bars 350.degree. C.
>7 h .congruent.100% tion at high temperature and high pressure
with a catalyst (MgH.sub.2 autocatalysis) (3) Grinding 2.4 bars
Room 47.5 h .congruent.100% under hydrogen temperature atmosphere
without catalyst (4) Grinding 10 bars Room 10 h .congruent.70%
under hydrogen temperature atmosphere with catalyst (Co) (5)
Grinding with .congruent.1 bar 180.degree. C. 20 h 5% graphite
followed by an hydrogenation at high temperature (5) Grinding with
.congruent.1 bar 180.degree. C. 20 h 80% graphite in the presence
of cyclohexane followed by an hydrogenation at high temperature (1)
Conventional method with no catalyst (2) U.S. Pat. No. 5.198.207
(3) Article of Y. CHEN et al (4) Article of J. L. BOBET et al (5)
Article of H. IMAMURA et al
[0012] In view of what is summarized in Table 1, one can see that
to completely convert a powder of magnesium into magnesium hydride,
at least 10 hours are typically required whatever be the method
that is used. In view of the strategic importance of magnesium as a
hydrogen storage material, it would be very interesting, from a
technical standpoint, to provide a method that would significantly
reduce the time of manufacture of magnesium hydride.
[0013] This is particularly important especially in view of the
content of Applicant's international patent application WO 99/2422
published in Apr. 29, 1999, which discloses a process for the
preparation of a nanocomposite for the storage of hydrogen
comprising the step of subjecting to an intensive mechanical
grinding a magnesium hydride or an hydride of a Mg-based compound
and one or more elements or compounds that are known to absorb
hydrogen and to be not miscible with magnesium during grinding.
Indeed, this process requires the use of magnesium hydride as
starting material.
[0014] Of course, one may easily understand the importance of a
method that would facilitate the hydrogenation of a material
capable of absorbing hydrogen, and would apply not only to
magnesium but to any other material currently used for hydrogen
storage.
SUMMARY OF THE INVENTION
[0015] It has now been discovered that by suitably coupling three
of the methods of hydrogenation previously mentioned, one may
obtain a completely unexpected synergistic effect which permits to
considerably reduce the time required for the preparation of an
hydride. More precisely, it has been discovered that when a powder
of a material capable of absorbing hydrogen is subjecting to
intense mechanical grinding under hydrogen pressure not at room
temperature but at a higher temperature (of about 300.degree. C. in
the case of Mg) in the presence of an hydrogenation activator such
as graphite, and optionally a catalyst, it is possible to
completely transform the powder of said material into the
corresponding hydride in less than one hour, whereas the above
prior art methods are 10 times longer. This is of course an
unexpected result, which is extraordinary and results in a
considerable reduction in the cost of manufacture of a hydride, in
particular MgH.sub.2.
[0016] Thus, the present invention is directed to a method for
carrying out rapidly a hydrogenation of a hydrogen storage
material, which combines three of the above methods previously used
separately for hydrogenating a hydrogen storage material,
namely:
[0017] 1) the conventional method wherein the hydrogenation is
carried out at high temperature and high pressure;
[0018] 2) the method wherein the hydrogenation is carried out by
grinding under a hydrogen atmosphere with or without additives;
and
[0019] 3) the method wherein the material is ground with a
hydrogenation activator such as graphite and thereafter
hydrogenated at high temperature.
[0020] More precisely, the invention as claimed hereinafter is
directed to a method for rapidly carrying out the hydrogenation of
a hydrogen storage material wherein the material is subjected to an
intense mechanical grinding in the presence of an hydrogenation
activator under a hydrogen pressure and at a temperature higher
than the room temperature.
[0021] In the present description and the appended claims, the
expression "hydrogenation activator" means any solid, liquid or
gaseous material which, when it is applied to the surface of the
hydrogen storage material to be hydrogenated by mechanical
grinding, permits to protect the surface of said hydrogen storage
material against contamination and thus avoids the risks of
unwanted oxidation or reaction other than hydrogenation and which,
at the same time, permits infiltration of hydrogen and thus
acceleration of the hydrogenation at high temperature. The
activator may also reduce agglomeration and cold welding of
particles during milling and it may facilitate powder compaction
after manufacture. As an example of a particularly efficient
hydrogenation activator, reference can be made to graphite. As
other examples of hydrogenation activators, reference can be made
to hydrocarbons such as naphthalene (C.sub.10H.sub.8), perylene
(C.sub.20H.sub.12), pentacene (C.sub.22H.sub.14), adamantane
(C.sub.10H.sub.16) and anthracene (C.sub.14H.sub.10). Reference can
also be made to fullerene (C60); vulcan; organic liquids; polymeric
solids . . . .
[0022] A non-restrictive, more detailed description of the
invention will now be given.
DETAILED DESCRIPTION OF THE INVENTION
[0023] As indicated hereinabove, the method according to the
invention for rapidly carrying out a hydrogenation of a hydrogen
storage material, consists in subjecting the material to a
mechanical grinding in the presence of a hydrogenation activator
under a hydrogen pressure and at a temperature higher than the room
temperature.
[0024] By "hydrogen storage material", there is meant any element,
alloy, solid solution, liquid solution or complex hydride known to
be capable of absorbing hydrogen in order to store it, transport it
and/or produce it. This material can belong to any one of the
following non-limitative groups.
[0025] 1) Elements selected from the group consisting of Li, Be, B,
Na, Mg, Al, Si, K, Ca, Sc, Ti, V, Cr, Mn, Ni, Cu, Zn, Ga, Rb, Sr,
Y, Zr, Nb, Pd, Cs, Ba, La, Hf, Ta, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho,
Er, Tm, Yb, Lu, Ac, Th and U.
[0026] 2) Alloys of the AB.sub.5 type, in which:
[0027] A is at least one element selected from the group consisting
of La, Ca, Y, Ce, Mm, Pr, Nd, Sm, Eu, Gd, Yb and Th
[0028] B is at least one element selected from the group consisting
of Ni, Al, Co, Cr, Cu, Fe, Mn, Si, Ti, V, Zn, Zr, Nb, Mo and Pd
[0029] 3) Alloys of the AB.sub.2 type in which:
[0030] A is at least one element selected from the group consisting
of Ca, Ce, Dy, Er, Gd, Ho, Hf, La, Li, Pr, Sc, Sm, Th, Ti, U, Y and
Zr; and
[0031] B is at least one element selected from the group consisting
of Ni, Fe, Mn, Co, Al, Rh, Ru, Pd, Cr, Zr, Be, Ti, Mo, V, Nb, Cu
and Zn.
[0032] 4) Alloys of the AB type in which:
[0033] A is at least one element selected from the group consisting
of Ti, Er, Hf, Li, Th, U and Zr; and
[0034] B is at least one element selected from the group consisting
of Fe, Al, Be, Co, Cr, Mn, Mo, Nb and V.
[0035] 5) Alloys of the A.sub.2B type in which:
[0036] A is at least one element selected from the group consisting
of Hf, Mg, Th, Ce, Al, Ti and Zr; and
[0037] B is a combination of Ni, Co, Fe, Al, Be, Cu, Cr, V, Zn and
Pd.
[0038] 6) Alloys of the AB.sub.3 type in which:
[0039] A is at least one element selected from the group consisting
of Ce, Dy, Er, Gd, Ho, Lu, Nd, Sm, Tb, Th, Ti, U and Y; and
[0040] B is at least one element selected from the group consisting
of Co, Ni, Fe, Mn, Cr and Al.
[0041] 7) Alloys of the A.sub.2B7 type in which:
[0042] A is at least one element selected from the group consisting
of Ce, Dy, Er, Gd, La, Nd, Pr, Tb, Th and Y; and
[0043] B is at least one element selected from the group consisting
of Co, Ni, Fe and Mn.
[0044] 8) Solid solutions where the solvent is an element selected
from the group consisting of Pd, Ti, Zr, Nb and V.
[0045] 9) Complex hydride of transition metals selected among those
comprising at least one of the following complex structures:
[ReH.sub.9].sup.2-, [ReH.sub.6].sup.5-, [FeH.sub.6].sup.4-,
[RuH.sub.6].sup.4-, [Ru.sub.2H.sub.6].sup.12-, [RuH.sub.4].sub.n,
[CoH.sub.5].sup.4-, [CoH.sub.4].sup.5-, [NiH.sub.4].sup.4-,
[PdH.sub.3].sup.3- et [ZnH.sub.4].sup.2-.
[0046] 10) Complex hydride selected from the family of hydrides of
the general formula A(BH.sub.4).sub.n in which A is a metal
(typically of group IA or IIA) with a valence n and B is a metal of
group IIIB (typically B, Al or Ga).
[0047] 11) Alloys of the BCC type as described in U.S. Pat. No.
5,968,291.
[0048] By "hydrogen pressure", there is meant an hydrogenated
atmosphere preferably maintained under a pressure higher than or
equal to 1 bar.
[0049] By "temperature higher than the room temperature", there is
meant a temperature that is preferably equal to or higher than
50.degree. C. Of course, this temperature can vary within a broad
range depending on the nature of the selected material. In the case
of magnesium known to be difficult to hydrogenate, this temperature
will preferably be of about 300.degree. C.
[0050] Preferably, the mechanical grinding is carried out in a
closed enclosure with a mechanical energy superior or equal to 0.05
kW/liter. This grinding can be carried out with any type of
conventional grinders, such as a SPEX 8000, FRITCH or ZOZ
grinder.
[0051] In practice, the hydrogenation activator must be used in a
sufficient amount to obtain the desired effect. In the particular
case of magnesium, a minimal amount of 1% by weight of graphite
seems to be required. Excellent results are obtained with 3% by
weight of graphite (see the following examples). The determination
of the optimal amount of hydrogenation activator to be used can
easily be carried out and is obvious for anyone skilled in the art,
as a function of the selected material to be hydrogenated.
[0052] According to a preferred embodiment of the invention, the
mechanical grinding can be carried out in the presence of a
catalyst. In this connection, one may refer to the contents of the
numerous patents obtained by the Applicant in this field (see in
particular international applications numbers WO 96/23906, WO
97/26214; WO 99/20422 and WO 00/18530). As examples of catalysts,
reference can be made by Pd, Ni, Pt, Ir, Rh, V, etc. Preferably,
use will be made of vanadium for the hydrogenation of Mg.
[0053] As is shown in Table 1 hereinabove, one of the shortest
times that has ever been obtained for the hydrogenation of
magnesium as a hydrogen storage material is of about 7 hours (see
the U.S. patent of TH. GOLDSMITH). Moreover, all the articles
mentioned hereinabove that describe the step of grinding magnesium
prior to subjecting it to hydrogenation at a high temperature,
mention an hydrogenation time of 20 hours. In accordance with the
present invention, it has been discovered that when the
hydrogenation of magnesium at high temperature is carried out
simultaneously with a grinding thereof with graphite under a
hydrogen pressure as low as 4 bars, this hydrogenation time,
formerly of 20 hours, is significantly reduced to less than 1 hour.
Such was a priori not obvious and demonstrates the existence of a
synergistic effect.
EXAMPLE 1
[0054] Using the method according to the invention, three tests
were carried out in order to obtain a first hydrogenation of
magnesium using 5% at. of V as a catalyst. These three tests were
respectively carried out with 3%, 1% and 0.3% by weight of
graphite, as an hydrogenation activator. All the grindings were
carried out for 1 hour at 300.degree. C. under 4 bars of
hydrogen.
[0055] With 3% by weight of graphite, the transformation of Mg into
MgH.sub.2 was almost complete.
[0056] With 1% by weight of graphite, the transformation of Mg into
MgH.sub.2 was achieved but the amount was much lower.
[0057] With 0.3% by weight of graphite, the powder of magnesium
agglomerated in little balls and there was no formation of
hydride.
[0058] Thus, in the case of magnesium, the lower limit of the
amount of hydrogenation activator to be used seems to be 1% by
weight in the case of graphite.
COMPARATIVE EXAMPLE 1
[0059] In order to verify the importance of using graphite in the
method according to the invention, a comparative test was carried
out with the same material as in example 1 (Mg+V at. %) under the
same conditions (1 hour at 300.degree. C. under 4 bars of
hydrogen), but without graphite.
[0060] During this test, only a very small amount of hydride was
produced. In fact, the powder agglomerated and formed little balls
of magnesium like in the case of example 1 with 0.3% of
graphite.
[0061] Therefore, the use of a minimum of at least 1% by weight of
graphite seems to be essential to obtain good results with
magnesium.
COMPARATIVE EXAMPLE 2
[0062] In order to verify the importance of carrying out the
grinding at a temperature higher than the room temperature, another
comparative test was carried out with the same material as in
example 1 (Mg+V 5% at) in the presence of 3% by weight of graphite.
The grinding was carried out under a pressure of 4 bars of
hydrogen, but at room temperature rather than at 300.degree. C.
[0063] Even after 2 hours, no transformation of magnesium into
hydride was detected. This confirms that it is necessary to grind
the material under hot conditions.
EXAMPLE 2
[0064] By using the method according to the invention, three tests
were carried out to obtain a first hydrogenation of magnesium with
5% at. of vanadium as a catalyst.
[0065] These tests were carried out with 3% by weight of graphite
at 300.degree. C. under 4 bars of hydrogen, for periods of time of
30 min., 1 hour and 2 hours, respectively.
[0066] The determination of the amount of hydride formed during the
grinding was made by X-ray diffraction. After 1/2 hour, more than
50% of the magnesium was transformed into Mg hydride
.beta.-MgH.sub.2. After 1 hour, more than 95% of the magnesium was
transformed into .beta.-MgH.sub.2. We also detected that in either
one of the cases, traces of metastable Mg hydride
.gamma.-MgH.sub.2. After 2 hours, the obtained result was similar
to the one obtained after 1 hour. However, there was a larger
amount of metastable MgH.sub.2 (.gamma.-MgH.sub.2) due to the
intensive mechanical grinding of the .gamma.-MgH.sub.2 phase.
[0067] The amounts of hydrides thus obtained are reported in Table
2 below.
2 TABLE 2 Percentage of Hydro- hydride formed Hydrogen genation
during the Pressure Temperature time grinding Grinding under 4 bars
300.degree. C. 30 min .congruent.64% hydrogen at high temperature
with graphite and a catalyst Grinding under 4 bars 30.degree. C. 1
h .congruent.100% hydrogen at high temperature with graphite and a
catalyst Grinding under 4 bars 300.degree. C. 2 h .congruent.100%
hydrogen at high temperature with graphite and a catalyst
EXAMPLE 3
[0068] By using the method according to the invention, a test was
carried out to obtain a first hydrogenation of pure Mg without a
catalyst. This test was carried out with 3% by weight by graphite
at a temperature of 300.degree. C. under a hydrogen pressure of 4
bars.
[0069] After 2 hours of grinding, the hydrogenation was not
complete. There was still some metallic magnesium that was not
hydrogenated. However, in the presence of vanadium, all the
magnesium was hydrogenated after 1 hour.
[0070] Thus, the use of a catalyst seems to help hydrogenation.
However, even without vanadium, the reaction of hydrogenation at
high temperature under hydrogen atmosphere in the presence of
graphite under mechanical action is much more rapid than the
reaction that was ever tested so far in the prior art.
EXAMPLE 4
[0071] To prove the applicability of the method according to the
invention on other types of materials, tests were carried out to
obtain a first hydrogenation of a mixture of sodium hydride and
aluminium.
[0072] By carrying out the grinding of a NaH+Al system with 3% by
weight of graphite at 140.degree. C. for 9 hours under 12 bars of
hydrogen, .beta.-Na.sub.3AlH.sub.6 was formed. Thus, the method
according to the invention also applies to systems other than
magnesium.
[0073] By carrying out the grinding of a 3 NaH+Al system with 3% by
weight of graphite during 14 hours under 12 bars of hydrogen at
140.degree. C., the transformation of the starting system into
.beta.-Na.sub.3AlH.sub.6wa- s not complete. In fact, the reaction
turned out to be slower than for the system NaH+Al.
[0074] By carrying out the same type of grinding as previously
described (that is, with a 3 NaH+Al system during 14 hours under 12
bars of hydrogen at 140.degree. C.) but with 6% by weight of
graphite as compared to 3%, the transformation turned out to be
almost complete. This is exceptional inasmuch as it is known that
this first hydrogenation of a mixture of NaH and Al is known to be
extremely difficult to carry out (see for example A. Zaleska et
al., J. of Alloys and Compounds, 298(2000) 125.)
[0075] The above results confirm that the presence of graphite is
essential but the percentage of graphite to be used can be
optimised as a function of the nature of the material or system to
be hydrogenated. As previously described, this optimization is easy
and obvious for any one skilled in the art.
EXAMPLE 5
[0076] To prove that there are materials other than graphite that
have a beneficial effect similar to graphite for favorising the
hydrogenation reaction and thus can be used as hydrogenation
activators, a test was carried out in order to obtain a first
hydrogenation of Mg+V5% at. with perylene.
[0077] A mixture containing 1.002 g of Mg, 0.099 g of V and 0.031 g
of perylene was ground for 2 hours at 250.degree. C. under a
pressure of hydrogen of 10 bars. The X-ray diffraction spectrum
obtained after the grinding has shown that a complete hydrogenation
was achieved.
[0078] This clearly demonstrates that the present invention can be
broadened to encompass other hydrogenation activators, such as
naphtalene, fullerene, vulcan, pentacene and/or adamantane.
EXAMPLE 6
[0079] To prove that the hydrogenation activator may be in a form
other than solid, a test was carried out to obtain a hydrogenation
of Mg with anthracene. A mixture containing 0,900 g of Mg and 0,100
g of anthracene was ground for 1 hour at 300.degree. C. (a
temperature at which anthracene is liquid) under a pressure of
hydrogen of 4 bars. The X-ray diffraction spectrum obtained after
grinding has shown that 40% of the material has been transformed
into magnesium hydride.
[0080] This demonstrates that the present invention can be
broadened to encompass hydrogenation activators which are not in a
solid form, for instance liquid hydrocarbons such as anthracene at
elevated temperatures.
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