Catalyst – solid sorbent – or support therefor: product or process – Solid sorbent – Free carbon containing
Reexamination Certificate
1999-01-29
2001-12-11
Hendrickson, Stuart L. (Department: 1754)
Catalyst, solid sorbent, or support therefor: product or process
Solid sorbent
Free carbon containing
C502S432000
Reexamination Certificate
active
06329316
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a granular active carbon for natural-gas occlusion and a process for producing the same.
BACKGROUND OF THE INVENTION
In motor vehicles in which natural gas (main component: methane) is used as a fuel, the techniques employed for storing natural gas include a method of filling a vessel with compressed natural gas and a method of filling a vessel with liquefied natural gas.
However, the former technique has problems that the equipment cost is high because vessels are required to withstand a high pressure (about 20 MPa) and that poor suitability of the vessels in mounting on vehicles results in the reduction in the capacity, e.g., that of the trunk. On the other hand, the latter technique has problems that a vacuum double-wall vessel is necessary since liquefied natural gas should be kept at a very low temperature (−162° C.), and that an apparatus for vaporizing the liquefied natural gas is also necessary. As a result, the equipment cost in the latter technique is as high as in the former.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a granular active carbon for natural-gas occlusion which can occlude natural gas at a relatively low pressure, has a high natural-gas occlusion capacity, and can bring about satisfactory suitability for mounting on vehicles, etc.
In order to accomplish the above object, the present invention provides a granular active carbon for natural-gas occlusion which has first and second pores for the occlusion of constituent gas molecules of natural gas, the first pores each having a diameter d
1
, satisfying 2d<d
1
≦2.5d and the second pores each having a diameter d
2
satisfying 5d<d
2
≦6d, wherein d is the diameter of the constituent gas molecules.
In the granular active carbon, many first pores are interconnected and are further connected to second pores.
The process of natural-gas occlusion under pressure proceeds by the following mechanisms. The first pores each function to rapidly adsorb constituent gas molecules of natural gas in such a manner that each adsorption site on the pore wall adsorbs two constituent gas molecules stacked up in a pore radius direction because of the above-described relationship between the two diameters dand d
1
, i.e., a two-layer adsorption state appears. This is because the van der Waals force base on which a constituent gas molecule is adsorbed onto the pore wall extends through the adsorbed constituent gas molecule to another constituent gas molecule present nearby.
In the second pores, the two-layer adsorption state appears on the pore wall along the circumferential direction because of the above-described relationship between the two diameters d and d
2
and, simultaneously therewith, a passageway for transporting constituent gas molecules is formed at the center of each pore. Constituent gas molecules are led through these passageways to first pores and occluded therein.
The above-described occlusion of constituent gas molecules is conducted at a relatively low pressure, and the occlusion capacity is high. In addition, the granular active carbon can be packed into a vessel of any desired shape.
However, if the relationship between the two diameters d and d
1
, is d
1
≦2d, the two-layer adsorption state described above cannot occur. On the other hand, if d
1
>2.5d, the ability to adsorb constituent gas molecules onto pore walls is reduced. Furthermore, if the relationship between the two diameters d and d
2
is d
2
≦5d, the passageways described above cannot be formed. On the other hand, if d
2
>6d, the ability to adsorb constituent gas molecules on pore walls is reduced.
Another object of the present invention is to provide a process by which the above-described granular active carbon for natural-gas occlusion can be mass-produced.
In order to accomplish the above object, the present invention provides a process for producing a granular active carbon for natural-gas occlusion which comprises subjecting a granular carbonized material to a gas activation treatment under the conditions that the holding temperature (T) is in the range of 900° C.≦T≦1,000° C. and the holding time (t) is in the range of 4.7 h≦t≦7.5 h. when a granular carbonized material is subjected to a gas activation treatment under those conditions, then first pores are formed by collisions of the gas against the granular carbonized material and second pores are formed as a result of diameter enlargement in part of the first pores. Thus, the granular active carbon for natural-gas occlusion can be mass-produced. Examples of the gas which can be used in the gas activation treatment include carbon dioxide, steam, and oxygen.
However, if the holding temperature is lower than 900° C. or if the holding time is shorter than 4.7 hours, a granular active carbon having the constitution described above cannot be obtained. On the other hand, if the holding temperature is elevated beyond 1,000° C. or if the holding time is prolonged beyond 7.5 hours, then the pore structure retention strength of the resultant granular active carbon drastically decreases and its adsorbing ability is considerably impaired.
REFERENCES:
patent: 4957897 (1990-09-01), Maroldo et al.
patent: 5710092 (1998-01-01), Baker
Muto Akinori
Ogasa Hiroshi
Sakata Yusaku
Hendrickson Stuart L.
Honda Giken Kogyo Kabushiki Kaisha
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