Patent Number: 062623281
Section: description

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT In accordance with the present invention, it has been found that a hydrogen absorbing composition may be used in a container or any other environment in which hydrogen gas is produced or is present. The hydrogen-absorbing composition disclosed in U.S. patent application Ser. No. 09/094,293 and incorporated herein by reference, is prepared by a method generally as follows. A first solution (solution A) is prepared by mixing an alcohol such as ethanol and water at a ratio of 1 part ethanol to 2.7 parts water by volume. Drops of hydrochloric acid are added to the solution to reach a pH value of 1.6. A second solution (solution B) is prepared by mixing alcohol (ethanol) and tetraethyl orthosilicate (TEOS) at a ratio of 1 part ethanol to 2 parts TEOS by volume. Solution A is slowly added to solution B with continuous mixing. The combined solutions are continuously mixed for about 30 minutes until a sol is achieved. To the sol solution, metal particles are added which have been prepared as follows. A metal alloy, such a LaNi0.25Al0.75 or other metal hydride is repeatedly reacted with hydrogen in a cyclic process which results in the production of a metal hydride fines. The desired alloy fines have a particle size of less than 45 microns. The fines/particles are slowly exposed to air and surface oxidized until a thin layer of metal oxide has slowly formed on the surfaces of the metal fines. The surface oxidation prevents further oxidation of the inner portions of the metal particles. The oxidation is done at a slow, controlled rate to prevent the entire particle from becoming oxidized which renders the material useless for hydrogen absorption. Once the controlled oxidation has occurred, the metal particles are stable in the presence of air and can be easily handled for use in the composition of the present invention. The metal hydride particles described and prepared above, are added to the sol at a ratio of about 20 grams of metal to 240 cc of sol. The mixture is placed on a rotating mixer which maintains the metal particles in a suspension within the sol. The mixing continues for about 24 hours until the sol has solidified. The solidified sol-gel with the dispersed metal hydride particles is removed from the mixer and placed in a sealed container for about 10 days. During the 10 day seasoning time, a liquid phase gradually appears. Following seasoning, the seal is removed and the liquid is allowed to evaporate at room temperature. Following evaporation of the liquid phase, the remaining solid product is vacuum dried at ambient temperature to remove any residual volatile compounds. While under vacuum, the temperature is increased to 300.degree. C. over a 30 minute time interval (curing) which is maintained along with the negative pressure for two hours. The heat treated material, hereinafter "composite", is allowed to cool to room temperature. Following cooling, the composite is mechanically broken to a useful size range of final product which is between 20 to 8 mesh (0.5 to 1 mm particle size). The final product can then be used in a conventional gas separation column or apparatus to remove hydrogen gas from a gas stream. The composite provided above is particularly useful for absorbing hydrogen from gas streams which contain known metal hydride gaseous poisons. These metal hydride poisons have no effect on the composition's ability to absorb hydrogen. With regard to the present invention, as seen in FIG. 1, a closed container 1, seen here as a waste drum, is provided containing a material 5 which produces hydrogen gas emissions 7. In a first embodiment, the container 1 is used to store waste comprising Pu-238 and high activity fraction of Pu-239. As a result of a radiolysis reaction, hydrogen gas is produced, creating an over pressurization and explosion concern during the transportation and long-term storage of the waste. In a first embodiment of the invention, the container 1 comprises various layers for protection, including a primary containment vessel 2 which holds the stored waste. At the upper portion of the primary containment vessel 2 is a vent structure 11 which allows the hydrogen gas 7 to escape from the primary containment vessel 2 to the secondary containment vessel 3. The secondary containment vessel 3 also comprises a secondary vent system 9 which vents to an outer containment area 4. The secondary vent system 9, however, is in communication with a hydrogen absorbing composition 13. The hydrogen absorbing composition 13 removes the hydrogen gas 7 from the container 1 environment, thus, eliminating the danger of over-pressurization and the build-up of dangerous hydrogen gas concentrations. The hydrogen absorbing composition 13 continues to remove hydrogen gas 7 from the container 1 even in the presence of gases that are poisonous to the hydrogen absorber. The present invention is not limited to a sealed or vented container, however. In a second embodiment of the invention, the hydrogen absorber is used in conjunction with a chamber housing a battery or battery systems which emit hydrogen gas. Battery systems generate hydrogen gas emissions such that the danger of a build up of hydrogen gas emissions is a concern. If the system is a vented system, then the concentration of hydrogen gas in the environment to which the system is vented must be controlled. If the system is a closed system, H.sub.2 build-up or over-pressurization of the system must be avoided. As seen in FIG. 2, a housing 21 for a battery system is provided. The housing 21 comprises a vent system 23 having at least one venting route. In the second embodiment, two venting routes are provided 27 and 29. The presence of the two venting routes allows sufficient quantities of hydrogen gas to be carried out of the housing 21 and also allows outside air to be brought in. The vent system 23 is in communication with a hydrogen absorber 25 which removes the hydrogen gas from the housing environment prior to releasing the air to the outside environment. Hydrogen absorber 25 may be placed within the actual exhaust vent 27. Alternatively, hydrogen absorber 25 may be placed anywhere within the interior of housing 21 where it would be operative to remove hydrogen gas and thereby maintain a hydrogen gas concentration below a critical threshold value. In instances where the exhausting of hydrogen gas build-up from the battery housing 21 into the surrounding environment is not feasible, the venting routes 27 and 29 may be removed or sealed to provide a sealed container environment. The hydrogen storage composition can be molded to any desired shape or size. The composition is useful within any sealed environment where released hydrogen gas may create pressurization problems or accumulate to explosive concentrations. As discussed above, specific embodiments of the present invention are discussed in terms of a shipping and storage container for radioactive waste and an external housing for a battery. However, any sealed container, broadly defined herein to include a room, compartment, container, package, sealed vessel, or similar environment, may be useful in the present invention. The present hydrogen storage composition is also useful for providing a system for preventing dangerous concentrations of hydrogen gas from accumulating in poorly ventilated environments as well. For instance, battery compartments associated with electric vehicles or electrical generation and storage may benefit from the inclusion of the hydrogen storage composition. Such compartments have an inherent risk associated with hydrogen gas generation and release. The use of a hydrogen storage composition in the compartments will provide an additional safeguard against excessive hydrogen gas accumulation. It is also envisioned that the present hydrogen storage composition may be useful in some situations where hydrogen getters are used. For instance, inside a sealed incandescent lamp bulb, the hydrogen absorber composition may be provided within the bulb interior to remove evolved hydrogen and thereby prolong the useful life of the lamp. Additional applications of the present invention include providing a sealed protective enclosure around possible ignition sources of hydrogen prone environments. For instance, traditional ventilation techniques for battery rooms or other environments where hydrogen gas accumulations may occur, can be supplemented with enclosures, the enclosures having hydrogen absorbing materials therein. The enclosures are used to provide a sealed housing for light switches, electrical equipment, lighting sources and other spark or ignition sources. In this manner, possible ignition sources are sealed against hydrogen infiltration and accumulation. Upon reading the above detailed description, it will be apparent to those skilled in the art that many changes and substitutions can be made to the preferred embodiment herein described without departing from the spirit and scope of the present invention as defined by the appended claims.