Chemistry of inorganic compounds – Hydrogen or compound thereof – Elemental hydrogen
Patent
1998-01-14
2000-08-22
Langel, Wayne
Chemistry of inorganic compounds
Hydrogen or compound thereof
Elemental hydrogen
25218235, 423644, 4236582, C01B 304, C01B 624, C09K 300
Patent
active
061068012
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process for the reversible storage of hydrogen in the form of complex alkali metal aluminium hydrides (alkali metal alanates).
2. Description of Related Art
The methods for the storage of hydrogen used today in the art are predominantly the storage as a compressed gas in pressure tanks, at normal pressure in gasometers, and at low temperatures (.ltoreq.20 K) as liquid hydrogen.
SUMMARY OF THE INVENTION
A more recent method for hydrogen storage (H.sub.2 storage) which is currently being developed, especially for the use of hydrogen as a fuel (combustible), is based on the reversible thermal dissociation of metal hydrides (MH.sub.n, Equation 1; H. Buchner, "Energie-speicherung in Metallhydriden", Springer-Verlag 1982; G. Sandrock et al., in "Hydrogen in Intermetallic Compounds II", page 197 (Ed. L. Schlapbach), Springer-Verlag 1992). In addition to H.sub.2 storage for stationary or mobile use, reversible metal hydride/metal systems (Equation 1) can be used technically for a number of other, potential or already realized, applications, such as hydrogen separation, purification and compression, heat storage, heat conversion and refrigeration (heat pumps), and as electrodes for electric batteries. ##EQU2## M=metal, metal alloy, intermetallic compound
The reversible H.sub.2 storage in the form of metal hydrides has several advantages over conventional storage methods. Over compressed H.sub.2 gas, metal hydrides have considerable advantages with respect to the achievable volumetric storage density. In addition, metal hydrides have the advantage, with respect to safety, that their hydrogen dissociation pressure is lower by powers of ten as compared to the same concentration of pressurized hydrogen. The volumetric H.sub.2 densities achievable with hydride containers reach those of liquid hydrogen containers without the necessity of using cryotechnology, which is expensive and cumbersome. The disadvantages of the latter can be seen, inter alia, from the fact that the recovery of one unit of energy of liquid hydrogen requires 2.5 to 5 times as high an expense of primary energy.
The main drawback of the currently known reversible metal hydrides as H.sub.2 storage materials, as compared to liquid hydrogen, is their relatively low storage density per weight of storage material (expressed in % by weight of H.sub.2 in the metal hydride) Magnesium hydride (MgH.sub.2, 7.6% by weight of H.sub.2) and hydrides of magnesium alloys (Mg.sub.2 NiH.sub.4, 3.7% by weight of H.sub.2) can compete technically with liquid hydrogen in this respect, provided that enough heat above 300.degree. C. is available for desorption of the hydrogen from the hydride.
The most serious disadvantage of the so-called low and medium temperature hydrides known today (H. Buchner, 1982, pages 26-29) is the high costs of the intermetallic compounds and alloys used for H.sub.2 storage while their H.sub.2 storage capacity is lower by a factor of 4-5 than that of MgH.sub.2 (LaNi.sub.5 : 1.4%; TiFe: 1.9% by weight of H.sub.2). From this point of view, it appears highly desirable and technically necessary to develop novel reversible low and/or medium temperature metal hydrides with higher H.sub.2 storage capacities than are known to date (Sandrock 1992, page 220; S. Suda, G. Sandrock, Ztschr. Physikal. Chem., Neue Folge 1994, 183, 149).
It has now been surprisingly found that the complex sodium and potassium alanates and the mixed sodium-lithium, sodium-potassium and potassium-lithium alanates of general formula 1 are suitable as reversible H.sub.2 storage materials under certain conditions. In addition, it has been found that the properties of compounds 1 as reversible H.sub.2 storage materials can be still improved considerably by doping with foreign metals, intermetals and their hydrides according to the invention. 1.ltoreq.p.ltoreq.3
Sodium alanate, NaAlH.sub.4, is produced on a technical scale. Na.sub.3 AlH.sub.6 can be prepared from NaAlH.sub.4 and NaH in the presen
REFERENCES:
patent: 3313598 (1967-04-01), Gluckstein
patent: 3931395 (1976-01-01), Beckert et al.
patent: 4563343 (1986-01-01), Nelson
Bogdanovic Borislav
Schwickardi Manfred
Langel Wayne
Studiengesellschaft
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