Gas separation: processes – Solid sorption – Inorganic gas or liquid particle sorbed
Reexamination Certificate
1999-09-22
2001-09-18
Simmons, David A. (Department: 1724)
Gas separation: processes
Solid sorption
Inorganic gas or liquid particle sorbed
C095S903000, C206S000700, C502S416000, C502S526000
Reexamination Certificate
active
06290753
ABSTRACT:
TECHNICAL FIELD
The present invention concerns a method for storing hydrogen in a carbon material comprising turbostratic microstructures of elemental carbon, wherein said microstructures are including cones, the cone angles of which being multiples of 60°.
Finally, the invention concerns the use of a carbon material of this kind.
BACKGROUND ART
Environmental considerations have lead to a comprehensive research with the aim of developing new technologies which may replace gasoline as the primary fuel for powering vehicles and vessels of different kinds. Pollutants produced by today's transport means include carbon monoxide and carbon dioxide, nitrogen oxides and sulphur oxides, hydrocarbons and particulates, and increasingly stricter rules and regulations in order to reduce or eliminate pollutants of this kind have for instance forced the car producers to consider the use of cleaner fuels or alternative methods for powering the vehicles. Hydrogen is the ultimate clean fuel, as the only combustion product is water. Hydrogen may with minor modifications be used in a conventional internal combustion engine. Hydrogen may also be used in a fuel cell powering vehicles and this seems in fact to be the best solution currently available. Another currently used technology is vehicles powered by electrical batteries. Both hydrogen-powered and battery-powered vehicles have zero pollutant emission.
A major obstacle which has prevented hydrogen from being the primary choice as clean fuel for use in vehicles, is the problem of storing hydrogen in the vehicles. Extensive research activity has in the past 30 years been centered on storing hydrogen in the form of solid metal hydrides. Metal hydrides are generated exothermally when metals and alloys are exposed to hydrogen. The hydrogen decomposes to atomic hydrogen in an exothermal reaction and subsequently enters interstices in the metal lattice. The hydrogen is recovered for use by heating, which in the present context may take place by means of the heat of combustion. The advantage of using metal hydrides for hydrogen storage is based on the fact that their volume density is very large. In reality the volume density of many hydrides is larger than that of solid hydrogen, for instance there are 4.3×10
22
H atoms/cm
3
in solid hydrogen at 4.2 K while there are almost twice as many in TiH
2
, i.e. 9.2×10
22
H atoms/cm
3
. The major disadvantage is among others caused by low values for the hydrogen content based on weight or unacceptable high temperatures for the hydrogen recovery. The well-known hydrogen storage systems FeTiH
2
and LaN
2
and LaNi
5
H
6
contains for instance 1.9 and 1.5% by weight hydrogen and even though they have acceptable recovery temperatures, their hydrogen content is too low for use in vehicles. MgH
2
and TiH
2
have in contrast thereto higher hydrogen content, respectively 7.6 and 4.0% by weight, but must be heated to high temperatures in order to recover the hydrogen. Disproportionation, poisoning and accompanying loss of capacity and the need for regeneration of some of the storage alloys are also serious drawbacks.
Onboard storage of hydrogen in the form of gas or liquid is also a possibility. Compressed hydrogen is a relatively inexpensive alternative in onboard storage, However, weight and volume considerations make this alternative little attractive. Even if liquid hydrogen is acceptable with regard to weight and volume, it is very expensive due to the need for cooling the gas to 21 K and maintaining a low temperature in order to prevent hydrogen loss due to evaporation. Safety requirements also appear as potential drawbacks.
Hydrogen adsorption on activated carbon is another possible method for hydrogen storage. Hydrogen is in this case physisorbed at low temperatures on an active carbon material with high surface area. An advantage of this method is that only low energy is required to recover the hydrogen. However, the method requires the system all the time to be maintained at a low temperature in order to prevent a build up of the hydrogen gas pressure to dangerously high levels.
U.S. Pat. No. 5,614,460 (Schwartz & al.) discloses a method for producing microporous carbon materials which may be used as storage media for light fuel gases such as methane or hydrogen or as catalyst supports. U.S. Pat. No. 5,653,951 (Rodriguez & al.) generally concerns storage of hydrogen in layered nanostructures in form of carbon nanotubes, carbon nanofibrils, carbon nanoshells and carbon nanofibres. Hydrogen is chemisorbed in the interstices in the nanostructures. The method for storing hydrogen according to this patent specification discloses the use of nanostructures with a surface area of 50 800 m
2
/g, a crystallinity of at least 50% and interstices in the crystalline areas with a size from 0.335 to 0.67 nanometers, the surfaces in the nanostructures defining the interstices being stated as having to posses chemisorption properties with regard to hydrogen. The method comprises introduction of hydrogen in a vessel at a pressure of at least 300 torr. However, the production of the stated materials in large volumes is difficult and reproducible absorption results have also turned out to be difficult to achieve.
DISCLOSURE OF INVENTION
The object of the present invention is to provide a method for storing hydrogen in a material which has low weight and is compact, easy in use, safe and which does not need to be subjected to a regeneration process after use.
The above object and advantages are achieved according to the invention with a method which is characterized by comprising steps for introducing said carbon material in a reaction vessel, evacuating said reaction vessel to a pressure less than 10
−6
torr by keeping the carbon material at a temperature in the range of 295 K to 800 K, introducing pure hydrogen gas in the evacuated reaction vessel to expose said carbon material to said pure hydrogen gas at a pressure in the range of 300 torr to 7600 torr, allowing said pure hydrogen gas to absorbed into said microstructures of said carbon material, and leaving said reaction vessel at ambient temperature, typically 295 K or slightly below, the material contained therein being under a fixed hydrogen gas pressure within said pressure range, the hydrogen as required being released as a gas from said carbon material at said ambient temperature or by heating said carbon material in said reaction vessel, and a method which is characterized by comprising the step of adding a catalyst means to a reaction chamber wherein said carbon material is being produced, in order to adjust a cone angle distribution of microstructures of elemental carbon, thereby increasing the hydrogen storage capacity of said carbon material.
According to the invention the carbon material used in the method according to the invention is applied for hydrogen storage.
Advantageously the carbon material is heated in step b) of the method to a temperature in the range of 400 to 700 K, preferably by heating the carbon material to a temperature in the range of 400 to 600 K.
Advantageously the carbon material in step c) of the method is exposed to pure hydrogen gas at a pressure corresponding to the saturation pressure of the carbon material in order to obtain a hydrogen storage capacity of at least 5 percent by weight of the carbon material.
Advantageously the absorption of pure hydrogen gas into the microstructures of the carbon material is accomplished in step d) of the method for storage by means of a chemisorption process.
Advantageously a carbon material whose crystallinity is at least 10 percent and which has a surface area in the range of 1 m
2
/g to 2000 m
2
/g is used in the method for storing. According to the invention, the carbon material is used for storing hydrogen.
REFERENCES:
patent: 5614460 (1997-03-01), Schwarz et al.
patent: 5626650 (1997-05-01), Rodriguez et al.
patent: 5653951 (1997-08-01), Rodriguez et al.
patent: 6113673 (2000-09-01), Loutfy et al.
patent: 6159538 (2000-12-01), Rodriguez et al.
patent: WO 94/07794 (1
Maeland Arnulf Julius
Skjeltorp Arne Torbjørn
Institutt for Energiteknikk
Lawrence Frank M.
Senterfitt Akerman
Simmons David A.
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