Chemical apparatus and process disinfecting – deodorizing – preser – Chemical reactor – Including solid – extended surface – fluid contact reaction...
Reexamination Certificate
2000-09-18
2001-08-14
Tran, Hien (Department: 1764)
Chemical apparatus and process disinfecting, deodorizing, preser
Chemical reactor
Including solid, extended surface, fluid contact reaction...
C422S198000, C422S198000, C422S198000
Reexamination Certificate
active
06274102
ABSTRACT:
TECHNICAL FIELD
This invention relates to the production of an oxygen-free stream of nitrogen, optionally containing hydrogen, such as may be used in a heat treating furnace.
BACKGROUND ART
Nitrogen or nitrogen/hydrogen atmospheres are used in many heat treating systems. It is important that oxygen not be present in the heat treating atmosphere as this will have a deleterious effect on the articles being treated. One way of providing a nitrogen or nitrogen/hydrogen stream into a heat treating furnace which is free of oxygen is to provide pure nitrogen, or mix pure hydrogen with pure nitrogen, produced by the cryogenic separation of air, and pass this stream to the heat treating system. While this method is effective, it is also quite expensive.
Nitrogen having a modest oxygen concentration can be produced at somewhat lower cost using non-cryogenic air separation methods such as adsorption or membrane separation systems. The oxygen is removed by reacting it with hydrogen in a catalytic reactor to form water. Excess hydrogen is used to establish a nitrogen/hydrogen stream if such is desired. However, such systems operate efficiently only at flowrates exceeding about 10,000 standard cubic feet per hour (SCFH) because for small systems having capacities less than about 10,000 SCFH, the advantages of using relatively inexpensive impure nitrogen are nullified by the expense of the deoxo system. Typical heat treating systems have atmosphere flowrate requirements within the range of from 1,000 to 8,000 SCFH.
Accordingly, it is an object of this invention to provide a system for economically producing an oxygen-free nitrogen stream, which can optionally contain hydrogen, and which can operate efficiently at flowrates less than 10,000 SCFH.
SUMMARY OF THE INVENTION
The above and other objects, which will become apparent to one skilled in the art upon a reading of this disclosure, are attained by the present invention, one aspect of which is:
A method for producing an oxygen-free nitrogen product stream comprising:
(A) providing an initial stream comprising nitrogen in a concentration of at least 98 mole percent and oxygen in a concentration within the range of from 0.1 to 2.0 mole percent, and passing hydrogen into said initial stream to form a reactor feed stream having a hydrogen concentration within the range of from 2 to 20 times that of the oxygen concentration but not more than twice the oxygen concentration plus 4 mole percent;
(B) passing the reactor feed stream into a catalytic reactor containing a catalyst bed comprising noble metal having a specific surface area exceeding 1 m
2
/gram on a ceramic carrier having a specific surface area exceeding 100 m
2
/gram;
(C) reacting hydrogen with essentially all of the oxygen in the reactor feed stream within the catalytic reactor to form water; and
(D) withdrawing a water-containing, oxygen-free nitrogen product stream from the catalytic reactor at a space velocity of at least 50,000/hr.
Another aspect of the invention is:
Apparatus for producing an oxygen-free nitrogen product stream comprising:
(A) means for providing an initial stream comprising nitrogen and oxygen;
(B) means for passing hydrogen into said initial stream to form a reactor feed stream;
(C) a catalytic reactor containing a catalyst bed comprising noble metal having a specific surface area exceeding 1 m
2
/gram on a ceramic carrier having a specific surface area exceeding 100 m
2
/gram; and
(D) means for passing the reactor feed stream into the catalytic reactor, and means for withdrawing a product stream from the catalytic reactor at a space velocity of at least 50,000/hr.
As used herein the term “specific surface area” means (a) for the carrier, the surface area in m
2
per gram of catalyst; the surface area being measured by the physical adsorption of nitrogen gas on the catalyst surface using the conventional BET analysis as described in “Characterization of Catalysts” by J. M. Thomas and R. M. Lambert published by John Wiley, 1980 see p. 17 ff; and (b) for the noble metal, the surface area in m
2
per gram of catalyst; the noble metal surface area being measured by the chemisorption of hydrogen on the metal surface as described in “Characterization of Heterogeneous Catalysts” by Francis Delannay published by Marcel Dekker, 1984 see p. 310 ff.
As used herein the term “noble metal” means one or more of platinum, rhodium, ruthenium, iridium, osmium and palladium. Platinum and rhodium are preferred.
As used herein the term “ceramic” means one or more of alumina, zirconia, titania, magnesia and silica. Gamma-alumina is preferred.
As used herein the term “oxygen-free” means having an oxygen concentration less than 10 parts per million (ppm).
As used herein the term “space velocity” means the flowrate in SCFH of gas exiting a catalytic reactor per cubic foot of catalyst bed in the catalytic reactor.
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Babor, J., Basic College Chemistry, pp. 255-261 (1953).
Black Donald T.
Praxair Technology Inc.
Tran Hien
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