Chemistry of inorganic compounds – Hydrogen or compound thereof – Elemental hydrogen
Reexamination Certificate
2000-04-10
2003-06-03
Langel, Wayne A. (Department: 1754)
Chemistry of inorganic compounds
Hydrogen or compound thereof
Elemental hydrogen
C423S657000, C423S658200
Reexamination Certificate
active
06572836
ABSTRACT:
BACKGROUND OF THE INVENTION
a) Field of the Invention
The present invention relates to a method for producing gaseous hydrogen by chemical reaction of a metal or a metal hydride that is or has been subjected to intense mechanical deformations.
The invention also relates to an apparatus for producing gaseous hydrogen, which is specially desired to carry out the above method.
The invention further relates to a method for producing gaseous hydrogen by chemical reaction of a nanocrystalline metal hydride.
In the following description and appended claims, the term “nanocrystalline” is used to identify products whose particles have nanocrystalline grains with an average size of 3 to 300 nm. The term <<chemical hydride>> as used hereinafter means a metal hydride that can be used in a chemical reaction to produce hydrogen or other secondary products.
b) Brief Description of the Prior Art
It is known that CaH
2
, NaH and LiH can be used as chemical reactants together with water to produce hydroxides and hydrogen by a reaction that is called <<hydrolysis>>:
CaH
2
+2H
2
O→Ca(OH)
2
+2H
2
1)
NaH+H
2
O→NaOH+H
2
2)
LiH+H
2
O→LiOH+H
2
3)
It is also known that hydrogen can be released by reacting pure metals with water, as in the following reaction:
Mg+2H
2
O→Mg(OH)
2
+H
2
4)
The above reactions and industrial processes using them to produce gaseous hydrogen have been known for a long time.
For instance, U.S. Pat. No. 3,787,186 (1974) entitled “calcium hydride gas generator>> discloses a gas generator in which CaH
2
is reacted with water to generate hydrogen gas to activate a gas operated pump.
U.S. Pat. No. 5,372,617 (1994) entitled <<Hydrogen generation by hydrolysis of hydrides for undersea vehicle fuel cell energy systems>> discloses a hydrogen generator for hydrolyzing hydrides to provide hydrogen on demand to a fuel cell, the water for the reaction being provided as the by-product of the fuel cell.
U.S. Pat. No. 5,833,934 (1998) entitled <<Demand responsive hydrogen generator based on hydride water reaction>> discloses a novel generator configuration for reacting an alkali or alkali-earth metal hydride with water to generate hydrogen.
U.S. Pat. No. 5,593,640 and U.S. Pat. No. 5,702,491 (1997) entitled <<Portable hydrogen generator>> disclose a hydrogen generator and a method for generating hydrogen by hydrolysis. This method requires that the chemical hydride be heated prior to hydrolyzing.
In two papers entitled a Hydrogen transmission/storage with a metal hydride/organic slurry” and a <<Hydrogen for a PEM fuel cell vehicle using a chemical-hydride slurry>> published in the proceedings of the 1999 US DOE Hydrogen Program Review, Ronald W. Breault et al. disclose a process wherein a chemical hydride is mixed with an organic compound such as a mineral oil in a 50/50 mixture to stabilize the product and the so prepared chemical hydride/organic slurry is reacted with water to release hydrogen.
The main problems with these existing processes to produce hydrogen, are that the hydrolysis reaction is often incomplete or proceeds either at an insufficient rate or, in other cases, at a too high or uncontrollable rate (explosive reaction like in the case of LiH). With conventional metal hydrides, the hydroxide film which is formed on the surface of the material during hydrolysis may passivate this surface and stop the reaction. The following are examples of problems described by some authors:
<<sodium hydride has a base-limited hydrolysis reaction. When the pH of the system reaches approximately 13.6 the hydrolysis reaction stalls>>;
<<the calcium hydride was observed to be considerably slower than the sodium hydride and the lithium hydride>>;
<<one of the essential considerations of the metal hydride is its hydrogen generation efficiency, which includes reaction chemistry between metal hydride and water to complete hydrolysis reactions in a safe and controlled manner>>;
<<calcium hydride (CaH
2
) reacts with water to form the hydroxide Ca(OH)
2
at room temperature. Any hydroxide formed below 400° C. decomposes endothermically above 580° C., liberating water. If there is any unreacted hydride present when the water is released, it will react instantaneously producing H
2
and CaO. The hydride itself decomposes thermally only above 600° C.>> (this means that if the temperature increases too much due to the exothermic reaction between CaH
2
and water, a self-sustain or explosive reaction can occur); and, finally,
<<regeneration of the end products is potentially problematic>>.
In all the above mentioned patents and articles, MgH
2
has never been used in practice in spite of its low cost, probably because the reaction of MgH
2
with H
2
O proceeds at a rate too low for practical applications and is incomplete because of the formation of passivating Mg(OH)
2
layers.
On the other hand, U.S. Pat. No. 5,882,623 (1999) naming one of the present coinventors, Mr. SCHULZ, also as coinventor, discloses inter alia a method for chemically inducing hydrogen desorption from a metal hydride. In accordance with this method, a powder of a Mg-based hydride is mixed with a small amount of a powder capable of reacting with water such as LiAlH
4
(see example 2). Addition of an appropriate amount of water causes a rapid and exothermic reaction (LiAlH
4
+4H
2
O→Li(OH)+Al(OH)
3
+4H
2
) which releases a large amount of heat and causes desorption of hydrogen from the Mg-based hydride.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a method for producing gaseous hydrogen by chemical reaction of a metal or a metal hydride, which method is an improvement to the technologies disclosed in the above mentioned patent U.S. Pat. No. 5,882,623 and solves the above listed problems.
The present invention is based on a discovery made by the present inventors that when instead of using conventional metal hydrides (Mg-based or others), use is made of a metal or metal hydride that is or has been subjected to intensive mechanical deformations, such as a metastable nanocrystalline metal hydride, the chemical reaction (especially hydrolysis) will then take place much more readily, at a much higher rate and, most of the time, up to completion (100% conversion).
This is a very important discovery for practical applications. Indeed, because of the particular microstructure and the very large number of grain boundaries and crystalline defects, nanocrystalline metal or metal hydrides especially those made by high energy ball milling, are much more reactive than conventional metal hydride. Thus, the chemical reactions (hydrolysis is a particular case) take place much more rapidly and up to completion.
Thus, the present invention provides an improved method for producing gaseous hydrogen by subjecting a metal or a metal hydride to a chemical reaction, wherein the metal or metal hydride subjected to the chemical reaction is nanocrystalline.
The invention also provides an improved method for producing gaseous hydrogen by subjecting a metal or metal hydride to a chemical reaction, wherein the metal or metal hydride is subjected before or during the reaction to intense mechanical deformations to activate said reaction.
The invention further provides an apparatus for producing gaseous hydrogen, which comprises a reactor in which a metal or metal hydride is subjected to a chemical reaction. In accordance with the invention, this apparatus also comprises means within the reactor for subjecting the metal or metal hydride to intense mechanical deformations in order to activate the chemical reaction.
REFERENCES:
patent: 3787186 (1974-01-01), Geres
patent: 5372617 (1994-12-01), Kerrebrock et al.
patent: 5593640 (1997-01-01), Long et al.
patent: 5702491 (1997-12-01), Long et al.
patent: 5833934 (1998-11-01), Adlhart et al.
patent: 5882623 (1999-03-01), Zaluska et a
Boily Sabin
Huot Jacques
Liang Guoxian
Schulz Robert
Hydro-Quebec
Langel Wayne A.
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