Chemistry of inorganic compounds – Hydrogen or compound thereof
Reexamination Certificate
2000-11-07
2004-01-20
Langel, Wayne A. (Department: 1754)
Chemistry of inorganic compounds
Hydrogen or compound thereof
C423S645000, C423S646000, C423S647000, C423S658200
Reexamination Certificate
active
06680042
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for rapidly carrying out a hydrogenation of a hydrogen storage material.
BRIEF DESCRIPTION OF THE PRIOR ART
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.
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.
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.
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:
<<Mg powder was placed into a steel autoclave fitted with a glass vessel. The autoclave was evacuated twice and pressurized with 3 bars H
2
. The hydrogen pressure was increased to 5 bars, and the autoclave heated to 345° C. and at that temperature the H
2
pressure was then increased to 15 bars and maintained constant until completion of hydrogenation (≡24 h).>>
The extreme conditions used in this conventional method have led researchers to experiment the use of catalysts to facilitate a first hydrogenation of magnesium.
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° 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).
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 47½ 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.
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° 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.
Table 1 summarizes all the experiments disclosed in the prior art for use to produce magnesium hydride starting from a powder of metallic Mg.
TABLE 1
Percentage
of hydride
Hydrogen-
formed
Hydrogen
Tem-
ation
during the
Method
Pressure
perature
time
reaction
(1) Hydrogenation at
15
bars
345° C.
24
h
≅100%
high temperature and
high pressure
(2) Hydrogenation at
5
bars
350° C.
>7
h
≅100%
high temperature and
high pressure with a
catalyst (MgH
2
autocatalysis)
(3) Grinding under
2.4
bars
Room
47.5
h
≅100%
hydrogen atmosphere
tem-
without catalyst
perature
(4) Grinding under
10
bars
Room
10
h
≅70%
hydrogen atmosphere
tem-
with catalyst (Co)
perature
(5) Grinding with
≅1
bar
180° C.
20
h
5%
graphite followed
by an hydrogenation
at high temperature
(5) Grinding with
≅1
bar
180° 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
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.
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.
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
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 hydroge
Bouaricha Salim
Guay Daniel
Huot Jacques
Schulz Robert
Foley & Lardner
Hydro-Quebec
Langel Wayne A.
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