U.S. patent application number 08/609255 was filed with the patent office on 2003-03-06 for process for removing carbon monoxide from a gas stream.
Invention is credited to DUCHATEAU, ERIC L., GIACOBBE, FREDERICK W., MCKEAN, KEVIN P..
Application Number | 20030044338 08/609255 |
Document ID | / |
Family ID | 24439984 |
Filed Date | 2003-03-06 |
United States Patent
Application |
20030044338 |
Kind Code |
A1 |
GIACOBBE, FREDERICK W. ; et
al. |
March 6, 2003 |
PROCESS FOR REMOVING CARBON MONOXIDE FROM A GAS STREAM
Abstract
Apparatus and process for removing carbon monoxide from a gas
stream comprising a major portion of an inert gas and a minor
portion of carbon monoxide are provided. The process involves
contacting a feed gas stream with at least a primary metal oxide in
a reaction zone of a reactor vessel at conditions effective to
convert substantially all of the carbon monoxide to carbon dioxide,
thus producing a purified gas stream consisting essentially of the
inert gas and carbon dioxide and substantially free of carbon
monoxide. This process has (inter alia) a particular application as
a tertiary purification process for producing a more highly
purified source of gaseous nitrogen from a source of nitrogen
originally produced from a conventional membrane air separation
system, wherein the oxygen concentration in the nitrogen stream my
vary around a setpoint value, and then further (or secondarily)
purified by converting excess oxygen in the nitrogen to carbon
monoxide and carbon dioxide using a fuel gas/combustion process,
wherein the carbon monoxide concentration varies due to varying
oxygen concentration in the feed stream to the combustion
process.
Inventors: |
GIACOBBE, FREDERICK W.;
(NAPERVILLE, IL) ; DUCHATEAU, ERIC L.; (CLARENDON
HILLS, IL) ; MCKEAN, KEVIN P.; (FLOWER MOUND,
TX) |
Correspondence
Address: |
BURNS DOANE SWECKER & MATHIS L L P
POST OFFICE BOX 1404
ALEXANDRIA
VA
22313-1404
US
|
Family ID: |
24439984 |
Appl. No.: |
08/609255 |
Filed: |
February 29, 1996 |
Current U.S.
Class: |
423/247 |
Current CPC
Class: |
C01B 2210/0009 20130101;
C01B 21/0416 20130101; C01B 23/0021 20130101; Y02C 20/40 20200801;
Y02A 50/2341 20180101; B01D 53/864 20130101; Y02C 10/04 20130101;
B01D 53/229 20130101; B01D 53/62 20130101; C01B 23/0094 20130101;
C01B 2210/005 20130101; C01B 2210/0004 20130101; C01B 21/0494
20130101; Y02A 50/20 20180101 |
Class at
Publication: |
423/247 |
International
Class: |
B01D 053/62 |
Claims
What is claimed is:
1. A process for removing carbon monoxide from a feed gas stream
comprising a major portion of an inert gas and a minor portion of
carbon monoxide, said process comprising contacting said feed gas
stream with a metal oxide in a reaction zone of a reactor vessel at
conditions effective to convert substantially all of said carbon
monoxide to carbon dioxide and produce a purified gas stream
comprising said inert gas and carbon dioxide and substantially no
carbon monoxide.
2. The process according to claim 1, wherein said feed gas stream
comprises not less than about 50 ppm carbon monoxide.
3. The process according to claim 2, wherein said feed gas stream
comprises from about 50 to 30,000 ppm carbon monoxide.
4. The process according to claim 1, wherein said feed gas stream
comprises carbon monoxide varying in concentration.
5. The process according to claim 1, wherein said purified gas
stream comprises less than about 1.0 ppm carbon monoxide.
6. The process according to claim 1, wherein substantially all of
said metal oxide is reduced during contacting with said feed gas
stream to form a reduced metal, and wherein said reduced metal is
regenerated by contacting said reduced metal with an
oxygen-containing regeneration gas stream at conditions effective
to oxidize substantially all of said reduced metal to form said
metal oxide.
7. The process according to claim 1, wherein said feed gas stream
is split to form a plurality of feed gas streams, each of said feed
gas streams passing through a corresponding plurality of reaction
zones of a corresponding plurality of reactor vessels.
8. The process according to claim 1, wherein at least one reactor
bed comprises said metal oxide and is contacted with said feed gas
stream to convert said carbon monoxide to said carbon dioxide, and
at least one other reactor bed comprises said reduced metal and is
contacted with an oxygen-containing regeneration gas stream to
regenerate substantially all of said reduced metal to form oxidized
metal.
9. The process according to claim 1, wherein said inert gas is
nitrogen.
10. The process according to claim 6, wherein said
oxygen-containing regeneration gas stream is passed through said
reaction zone along with said feed gas stream to regenerate said
reduced metal in situ.
11. The process according to claim 1, wherein said reaction zone is
operated at a temperature ranging from ambient to about 350.degree.
C.
12. The process according to claim 11, wherein said reaction zone
is operated at a temperature of about 100 to about 300.degree.
C.
13. The process according to claim 1, wherein said metal oxide
comprises a major portion of a primary metal oxide selected from
the group consisting of palladium oxides, platinum oxides, nickel
oxides, and mixtures thereof, and a minor portion of a promoter
metal oxide selected from the group consisting of copper oxides,
silver oxides, cadmium oxides or any suitable mixture thereof.
14. The process according to claim 13, wherein said primary metal
oxide is a palladium oxide.
15. The process according to claim 14, wherein said palladium oxide
is supported on alumina or on another suitable inert support
material.
16. The process according to claim 15, wherein said palladium (in a
reduced condition) comprises between about 0.01 and 10.0 percent by
weight of a total weight of said palladium plus alumina or other
inert support material.
17. The process according to claim 16, wherein said palladium
(reduced) comprises about 0.1 to about 1.0 percent by weight of the
total weight of said palladium plus alumina or other inert support
material.
18. The process according to claim 1 wherein said inert gas is
selected from the group consisting of nitrogen, helium, neon,
argon, xenon, krypton, and mixtures thereof.
19. A process for removing carbon monoxide from a feed gas stream
comprising a major portion of nitrogen and a minor portion of
carbon monoxide, said process comprising the steps of: (a)
contacting said feed gas stream with a metal oxide by passing the
feed gas stream through a reaction zone of a reactor vessel at
conditions effective to react said carbon monoxide with said metal
oxide to convert substantially all of said carbon monoxide to
carbon dioxide and produce a reduced metal and a purified gas
stream, the purified gas stream comprising nitrogen and carbon
dioxide but substantially devoid of carbon monoxide, with said
conditions including a temperature ranging from ambient to about
350.degree. C.; and (b) regenerating said reduced metal by
contacting said reduced metal with an oxygen-containing
regeneration gas stream at conditions effective to oxidize said
reduced metal to form said oxidized metal.
20. The process in accordance with claim 19 wherein the carbon
monoxide concentration in said feed gas stream varies from about 30
to about 50,000 ppm.
21. An apparatus for removing carbon monoxide from a gas stream
comprising a major amount of an inert gas and a minor amount of
carbon monoxide, the apparatus comprising a reactor vessel, a
reactor vessel gas inlet and a reactor vessel gas outlet, the
reactor vessel having an internal reaction zone space at least
partially filled with a metal oxide, the metal oxide present in
sufficient volume for contacting the gas stream with the metal
oxide at conditions effective to convert substantially all of the
carbon monoxide to carbon dioxide and thus produce a purified gas
stream substantially free of carbon monoxide.
22. Apparatus in accordance with claim 21 wherein the reactor
vessel includes an oxidizing gas inlet and an oxidizing gas outlet,
allowing the reduced metal which was formerly oxidized to be
regenerated and form anew the metal oxide.
23. Apparatus in accordance with claim 21 which further includes a
plurality of reactor vessels have a corresponding plurality of
reaction zones, the reactor vessels arranged in parallel flow
relationship with respect to the feed gas stream from which carbon
monoxide is to be removed.
24. Apparatus in accordance with claim 23 wherein at least one of
said plurality of reactor vessels is adapted to function in a
carbon monoxide removal mode, while one or more reactor vessels are
adapted to operate simultaneously in a regeneration mode.
25. Apparatus in accordance with claim 23 wherein all of said
plurality of reactor vessels are adapted to function simultaneously
in a carbon monoxide removal mode, and then simultaneously in a
regeneration mode.
26. The apparatus according to claim 21 wherein said metal oxide
comprises a major portion of a primary metal oxide selected from
the group consisting of palladium oxides, platinum oxides, nickel
oxides, and mixtures thereof, and a minor portion of a promoter
metal oxide selected from the group consisting of copper oxides,
silver oxides, cadmium oxides or any suitable mixture thereof.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a process for the removal
of carbon monoxide from a gas comprising a minor portion of carbon
monoxide and a major portion of an inert gas, such as nitrogen.
[0003] 2. Description of Related Art
[0004] Conventional membrane systems employed to produce gaseous
nitrogen from air typically produce high purity nitrogen gas. The
nitrogen purity level can be greater than 99 volume percent. The
flow rate at high purity levels, however, tends to be too low to be
useful because energy requirements escalate significantly with
increasing purity levels of nitrogen. Therefore, this method of
producing high purity nitrogen gas is not very efficient.
[0005] Alternatively, the membrane system can be operated more
economically by increasing the outlet flow rate of the purified
nitrogen. The effect of a higher nitrogen outlet flow rate is that
higher concentrations of oxygen, as well as other impurities, are
entrained in the "purified" nitrogen gas stream, thus producing a
nitrogen gas stream of lower purity. If the membrane system is
operated at a high outlet nitrogen flow rate, the most
objectionable impurity in the nitrogen gas stream is oxygen. Oxygen
is harmful in most uses of the nitrogen as an inert gas because
oxygen is an oxidizer. Therefore, the presence of oxygen is not
desirable in an inert gas environment or in a gas to be used to
produce a reducing atmosphere, which is required in many
applications such as in heat treating metal parts.
[0006] Another problem with membrane separators is that the
concentration of oxygen in the nitrogen product stream is not
constant from moment to the next moment, that is, if the setpoint
or target oxygen concentration in the nitrogen stream is 2 volume
percent, the concentration of oxygen may actually vary over time
from 1.8 volume percent or lower and up to 2.2 volume percent or
higher.
[0007] The residual oxygen in a nitrogen gas stream outlet from a
membrane generator may be removed by combustion with methane or
some other hydrocarbon within a chemical reactor containing a hot
active catalyst which is capable of facilitating the reaction of
oxygen with the hydrocarbon, thus "burning out" or combusting the
residual oxygen. However, even when using the best operating
parameters, burning the residual oxygen with a hydrocarbon may
produce other impurities such as carbon dioxide, carbon monoxide,
and water vapor. This process is well known and is described in
U.S. Pat. No. 5,242,509 to Rancon et al.
[0008] The carbon dioxide and water vapor impurities are relatively
inert and, thus, are not objectionable in many subsequent uses of
this purified nitrogen gas mixture. The carbon monoxide impurity,
however, is a reducing agent and, potentially, a poisonous
contaminant. This problem may be a severe impediment to the use of
purified nitrogen produced by burning residual oxygen impurities
out of a contaminated source of nitrogen. Moreover, if the feed to
the chemical reactor is the nitrogen product stream from a membrane
purifier, as stated previously the oxygen content of the nitrogen
stream varies from moment to moment, and thus the carbon monoxide
impurity will vary from zero to some positive value.
[0009] Consequently, several processes have been developed to
remove carbon monoxide from a gas such as air, argon, or nitrogen.
For example, U.S. Pat. No. 3,758,666 to Frevel et al. discloses a
process for removing carbon monoxide from air by initial adsorption
and subsequent oxidation to carbon dioxide on the surface of a
catalyst. The catalyst comprises metallic palladium on an alumina
support.
[0010] Another example of such a process is described in U.S. Pat.
No. 4,808,394 to Kolts et al. This patent discloses the use of a
catalyst which facilitates the oxidation of carbon monoxide with
free oxygen to carbon dioxide. The disclosed catalyst is reduced
platinum and/or palladium on an alumina support.
[0011] Other patents describe a process of reacting carbon monoxide
with oxygen gas to produce carbon dioxide using different types of
catalysts. For example, U.S. Pat. No. 4,991,181 to Upchurch et al.
discloses a catalyst containing a platinum group metal (in a
reduced condition) and a reducible metal oxide. The metallic
element in these reducible metal oxides may be tin, titanium,
manganese, copper, or cesium.
[0012] In all of the above processes, the noble metal catalytic
component was in a reduced or metallic state. Therefore, it was
necessary to add oxygen gas to the feed gas stream in order to
promote the conversion of carbon monoxide to carbon dioxide. The
oxygen source was either in the starting gas stream itself or, more
typically, from an outside gas stream. In addition to oxygen gas,
these processes require hydrogen to regenerate (or reduce) the
platinum or palladium component of the catalyst. Obviously, the
addition of oxygen and hydrogen gases increases the cost of such
processes.
[0013] In view of the above prior art processes, a need exists in
the art for an efficient and economical membrane purification
process to produce a high purity inert gas stream which is free of
undesirable impurities such as oxygen and carbon monoxide. More
particularly, a need exists in the art for a process that
effectively removes carbon monoxide from an inert gas stream
without the need for using hydrogen or an added oxygen gas, and
without regard to the flow rate of the inert gas.
SUMMARY OF THE INVENTION
[0014] In accordance with the present invention, apparatus and
process are provided for purifying a stream of nitrogen or another
inert gas contaminated with carbon monoxide so as to minimize the
reducing effect of carbon monoxide and its potential threat of
toxicity.
[0015] In one aspect of the present invention, a process is
presented for removing substantially all carbon monoxide from a gas
stream comprising a major amount of an inert gas (preferably
nitrogen) and a minor amount of carbon monoxide, which amount of
carbon monoxide may be varying from substantially zero to a
positive amount. In one embodiment, the process comprises
contacting the gas stream with a metal oxide in a reaction zone at
conditions effective to convert substantially all of the carbon
monoxide to carbon dioxide and thus produce a purified gas stream
substantially free of carbon monoxide. Preferably, the metal oxide
is selected from the group consisting of palladium oxides, platinum
oxides, and nickel oxides.
[0016] A second aspect of the present invention is an apparatus for
removing carbon monoxide from a gas stream comprising a major
amount of an inert gas and a minor amount of carbon monoxide. The
apparatus comprises a reactor vessel, a reactor vessel gas inlet
and a reactor vessel gas outlet, the reactor vessel having an
internal reaction zone space at least partially filled with a metal
oxide, the metal oxide present in sufficient volume for contacting
the gas stream with the metal oxide at conditions effective to
convert substantially all of the carbon monoxide to carbon dioxide
and thus produce a purified gas stream substantially free of carbon
monoxide.
[0017] Preferably the reactor vessel includes an oxidizing gas
inlet and an oxidizing gas outlet, allowing the residual metal
which was formerly oxidized to be regenerated and form anew the
metal oxide. Particularly preferred are methods and apparatus of
the invention wherein two or more reactor vessels are arranged in
parallel flow relationship with respect to the gas stream from
which carbon monoxide is to be removed. In the case where there are
two reactor vessels in parallel, a first reactor vessel can be
functioning in the carbon monoxide removal mode, while a second
reactor vessel is being regenerated, as is further described
herein.
[0018] The apparatus and process of the present invention provide a
more efficient and economical means for removing carbon monoxide
from nitrogen or another inert gas by using one or more metal oxide
reactors. One advantage of the inventive apparatus and process is
that means are provided for removing carbon monoxide from a feed
stream of nitrogen or another inert gas without the addition of
hydrogen or oxygen gas to the feed gas stream, and without regard
to the flow rate of the feed gas stream. Also, it does not matter
if the feed gas stream to the reactor vessel of the inventive
apparatus varies in carbon monoxide concentration, thus solving a
major problem with previous methods.
[0019] The product gas stream from the process and apparatus of the
present invention has a variety of uses, including heat treatment
atmospheres, electronics packaging atmospheres for processes such
as wave soldering and reflow soldering, as well as others which may
be envisioned by those skilled in the art.
[0020] These and other objects of the present invention will become
apparent after reviewing the following description of preferred
embodiments and the appended drawing.
BRIEF DESCRIPTION OF THE DRAWING
[0021] FIG. 1 is a schematic flow diagram (reduced in scale) for
the removal of carbon monoxide from a feed gas stream with an
apparatus in accordance with the present invention;
[0022] FIG. 2 illustrates many of the same features described in
FIG. 1, however, FIG. 2 has two reactor beds instead of one to
convert the carbon monoxide in a feed gas stream to carbon dioxide;
and
[0023] FIG. 3 illustrates in graphical form the consequence of a
varying oxygen concentration in the impure nitrogen feed to a prior
art catalytic reactor.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0024] The process of the present invention comprises the use of a
gas processing step that can be employed to remove objectionable
amounts of carbon monoxide from any inert gas contaminated by
carbon monoxide. However, one preferred use for this process is in
removing carbon monoxide from a nitrogen gas stream which has been
produced by membrane separation of air (wherein the oxygen
concentration in the nitrogen stream may vary) and then treated in
a hydrocarbon processing (i.e., combustion) step to remove residual
oxygen to produce a stream containing essentially nitrogen, carbon
monoxide, and carbon dioxide.
[0025] Specifically, the present invention relates to a process for
removing carbon monoxide from a feed gas stream comprising a major
amount of an inert gas and a minor amount of carbon monoxide. The
inert gas is preferably nitrogen. The maximum amount of carbon
monoxide in the feed gas stream that may be removed by the process
and apparatus of the present invention may be greater than 5000
ppmv (i.e., parts per million, by volume and hereinafter referred
to simply as ppm), for example from 50 to 30,000 ppm, but
preferably it is 500 ppm or lower. The carbon monoxide
concentration in the feed stream may vary if the feed stream is the
product nitrogen gas stream from a hydrocarbon processing step.
[0026] The inventive process comprises contacting the feed gas
stream with a metal oxide in a reaction zone at conditions
effective to convert substantially all of the carbon monoxide
present in the feed gas stream to carbon dioxide, thus producing a
purified gas stream consisting essentially of the inert gas and
some carbon dioxide. The purified gas stream is substantially free
of carbon monoxide. As used herein the phrase "substantially free
of carbon monoxide" depends on the end use of the purified gas;
however, the term "substantially free" means that the amount of
carbon monoxide in the purified gas stream is less than 5 ppm, or
more preferably less than 1 ppm. This is true even if the carbon
monoxide concentration in the feed gas stream varies. To decrease
the amount of carbon monoxide in the purified gas stream, one would
either use more metal oxide, increase the residence time of the
feed gas in the reactor vessel, or both. Increasing temperature
and/or pressure, while kinetically favoring the reaction between
carbon monoxide and oxygen to produce carbon dioxide, must be
carefully monitored in practice. Among other problems that might be
created, increasing temperature too much might be detrimental to
the conversion process due to possible sintering of the ceramic
support material, and increasing pressure too much would require
more costly pressure vessels.
[0027] I. Metal Oxides
[0028] The metal oxide is preferably selected from noble metal
oxides such as palladium oxides (e.g., PdO, PdO.sub.2) and platinum
oxides (e.g., PtO and PtO.sub.2), with palladium oxides being the
most preferred. Nickel oxides (e.g., NiO, NiO.sub.2) may also be
used. (The palladium, platinum, and nickel oxides are also referred
to herein as "primary" metal oxides to distinguish them from
promoter metal oxides, discussed herein.) Mixtures of metal oxides
can also be employed, meaning that mixtures of oxides of a single
metal atom may be used. Binary mixtures such as PtO/PdO,
PtO.sub.2/PdO.sub.2, PtO/PdO.sub.2, NiO/PtO, and the like, as well
as ternary mixtures such as PtO/PdO/NiO,
PtO.sub.2/PdO.sub.2/NiO.sub- .2, PtO/PdO.sub.2/NiO,
NiO/PtO/NiO.sub.2, and the like may be employed. The metal oxide
may generally be denoted MO.sub.x, wherein M designates a metal
atom, O designates an oxygen atom, and x designates the number of
oxygen atoms bonded to each metal atom.
[0029] When speaking of the total metal oxide present in the
reaction zone of the reactor vessel, one may represent the metal
oxide present at any given time as MO.sub.x, wherein x may range
from zero when the oxygen has been completely depleted, up to 2
when the metal oxide is fully regenerated. At any given time
between these two extremes, the metal oxide may be present as, for
example, MO.sub.0.5, MO.sub.1.1, MO.sub.1.7, and the like.
[0030] If mixtures of metal oxides of two different metal atoms are
employed, the weight percentage of the first metal atom to the
total weight of metal atoms present may range from 1 to 99 weight
percent, more preferably ranging from about 30 to 70 weight
percent.
[0031] Metal oxides commonly referred to as "promoters", such as
disclosed in U.S. Pat. No. 5,182,088 (incorporated herein by
reference), which discloses use of CuO promoted with AgO, HgO, or
CdO, may be present in conjunction with the above-mentioned metal
oxides. If such promoter metal oxides are present, the weight
percentage of promoter metal oxide to "primary" metal oxide (i.e.
oxides of Pt, Pd and Ni) is at least about 0.01 weight percent,
more preferably at least about 0.1 weight percent. Generally, it is
unnecessary to use more than about 10 weight percent of the
promoter. Most preferably, the promoter is present at a weight
ranging from about 0.2 to about 5 weight percent of the total
weight of promoter and primary metal oxide.
[0032] When promoter metal oxides are employed, the primary metal
oxide of choice and the promoter metal oxide of choice are
preferably prepared by coprecipitating both in the desired amounts,
drying the material to a powdered form and then pressing the
composition into tablets. A binder may be used for the pressing
step, if necessary. Each of these steps are, individually, known to
those skilled in the art and pose no unusual manufacturing
problems.
[0033] The amount of fully reduced noble metal on the support
material preferably ranges from about 0.01 to about 10.0 percent by
weight of the support material, more preferably ranging from about
0.1 to 1.0 percent by weight based on weight of fully reduced noble
metal on the support material, and most preferably the fully
reduced noble metal is present in an amount of about 0.5 percent by
weight based on the weight of the support material.
[0034] While not wishing to be bound by any particular theory, it
is believed that the reaction of carbon monoxide with the metal
oxide to produce carbon dioxide occurs because the carbon monoxide
actually removes oxygen that had previously combined with the metal
to create the metal oxide. The metal oxide, therefore, is a source
of oxygen for the carbon monoxide and does not act as a catalyst.
The metal oxide is considered a chemical reactant and not a
catalyst because it is consumed during the reaction. During the
reaction, the metal oxide changes from an oxide to a reduced
metal.
[0035] Noble metal oxides are preferred over other types of metal
oxides for two primary reasons. First, oxygen reacts with certain
noble metals to produce noble metal oxides. Second, noble metal
oxides are relatively unstable compared to other metal oxides, such
as iron oxide or chromium oxide. The instability of noble metal
oxides means that the conversion of carbon monoxide to carbon
dioxide can be carried out at lower temperatures because the noble
metal oxide gives up its combined oxygen to form carbon dioxide
from carbon monoxide more readily than other kinds of metal
oxides.
[0036] II. Metal Oxide Support Materials
[0037] The noble metal oxide can be supported on any material well
known in the art. A non-limiting list of examples of suitable
support materials include those selected from the group of
aluminas, aluminosilicates, silicas, silica-alumina mixtures,
kieselguhr, titania extrudate, and mixtures of these. Alumina
(aluminum oxide) is the most preferred support material. Aluminum
oxide is commercially available in many forms, including brown,
blue, ceramic, heat-treated, and fused aluminum oxide. All of these
may be used as the catalyst support, or any combination
thereof.
[0038] In the practice of the present invention, the metal oxide
plus support is typically placed in a contactor of any shape,
preferably a tubular shape, and the feed gas stream passed
therethrough, entering one end of the tube and exiting out the
other end of the tube. The metal oxide and support is typically
available as a particulate material, and the size of the
particulate material generally and preferably ranges from about 1.0
micrometer to about 10.0 micrometers, and preferably does not
exceed 1/5 of the effective diameter of the contactor. It is more
preferred that the support size be no more than about {fraction
(1/10)} of the effective diameter of the contactor.
[0039] In some apparatus and process embodiments, it may be
preferred to position support material (without "catalyst" thereon)
upstream of, or downstream of, or both upstream and downstream of
the metal oxide/catalyst bed. One advantage for upstream placement:
the plain support is less expensive than the metal oxide-loaded
material, and in the upstream position it can act as a high area
preheat zone to preheat the gases before they come in contact with
the metal oxide-loaded support. Using the metal oxide-loaded
material for this preheating process is uneconomical. Of course,
there are other ways to preheat the gases but this method allows
all preheating and "reacting" to occur within one vessel. An
advantage for downstream placement: downstream placement of the
plain support material creates another preheat section for incoming
gases if the flow direction must be reversed for any reason during
the process or during any periodic "cleaning" steps that must be
performed within the system. For example "carbon fouling" sometimes
occurs within reactive systems employing hydrocarbons or carbon
monoxide and this carbon must be "burned out" in a separate step
using heat and very low concentrations of oxygen in an inert
gas.
[0040] III. Process Conditions
[0041] A. Conversion of Carbon Monoxide to Carbon Dioxide
[0042] The conversion of carbon monoxide in the feed gas stream to
carbon dioxide proceeds at elevated temperatures in the reaction
zone of the reactor vessel (in other words, in the presence of the
metal oxide), preferably at temperatures ranging from about ambient
(about 25.degree. C.) to about 350.degree. C., more preferably
ranging from about 100 to about 300.degree. C. The pressure in the
reaction zone of the reactor vessel preferably ranges from about 1
atm to about 15 atm (approx. 101 kPa to about 1520 kPa), with
higher pressures tending to be more favorable than lower pressures.
However, a more preferred pressure range (if the original source of
impure gas is a membrane system) ranges from about 3 atm to about
10 atm (approx. 304 kPa to about 1013 kPa).
[0043] The process and apparatus of the invention can be operated
at almost any gaseous feed gas flow rate, so long as a sufficient
quantity of hot metal oxide remains in the reaction zone. Feed gas
flow rates as low as 1.0 standard cubic foot per hour (scfh--1.0
atm and 70.degree. F.) (0.02628 meters.sup.3/hour--1.0 atm and
0.0.degree. C.) at 0.9 pounds per square inch gauge (psig) (108
kPa) and at 250.degree. C. (using 46.8 g of 0.5 weight percent
palladium deposited on an alumina support) and as high as 56.9 scfh
(1.50 meters.sup.3/hour) at 75.5 psig (622 kPa) and at 250.degree.
C. (using 15.6 g of 0.5 weight percent palladium deposited on
alumina support) have been tested, with no significant differences
in performance. Highest flow rates and pressures are preferred
because these conditions maximize the efficiency of the processing
system.
[0044] As previously mentioned, the apparatus of the invention may
have one or more reactors or reactor vessels, at least one of which
contains the oxidized metal. The reactor vessels can be operated
continuously or batchwise.
[0045] The feed gas stream may have a constant carbon monoxide
concentration, or a varying carbon monoxide concentration. One
advantage of the process and apparatus of the invention is that if
this carbon monoxide concentration varies (for example because the
oxygen concentration in the nitrogen stream from a membrane
separator is varying between .+-.1 volume percent of setpoint or
target) the process and apparatus of the invention will remove
substantially all of the carbon monoxide to form a stream of
nitrogen and carbon dioxide.
[0046] Purified gas streams produced according to the present
invention preferably comprise less than about 1.0 ppm of carbon
monoxide, more preferably less than 0.5 ppm of carbon monoxide.
[0047] B. Regeneration of Reduced Metal Oxide
[0048] Unless a continuous supply of oxygen is mixed with the
carbon monoxide containing feed gas stream, the conversion of
carbon monoxide to carbon dioxide ceases when the metal oxide has
been completely reduced. Therefore, after the conversion of carbon
monoxide has progressed so that a major portion of the metal oxide
becomes reduced, the carbon monoxide to carbon dioxide conversion
process should be stopped.
[0049] An oxygen-containing regeneration gas, preferably an
oxygen-rich regeneration gas, is then introduced into the reaction
zone to regenerate the reduced metal. The regeneration gas passing
through the partially or completely reduced bed of the metal oxide
and re-oxidizes it. After regeneration is complete, the oxidation
of carbon monoxide may resume.
[0050] The regeneration gas preferably contains a sufficient
concentration of oxygen to allow a reasonably rapid conversion (or
reconversion) of the reduced (or partially reduced) metal oxide
back to the metal oxide form. However, pure oxygen is preferably
avoided during this re-oxidation process because a rapid (and
generally uncontrollable) oxidation reaction, accompanied by a
significant system temperature increase, may decrease the effective
surface area of the metal oxide deposited on the inert support
(e.g., on the alumina) by sintering or partially melting some of
this composite material. This decrease in effective surface area
may permanently damage the efficiency of the reactant bed.
[0051] Generally, the regeneration gas comprising inert gases (such
as nitrogen, argon, helium, and the like) containing up to about
2.0 percent oxygen (by volume) can safely be used to oxidize (or
re-oxidize) fully reduced active metals dispersed (in relatively
low weight percentages) upon inert support materials. Of course, it
will be readily understood by those skilled in the art that system
operating temperatures and pressures must also be considered when
employing this type of process. In other words, there are many
possible conditions that may be safely employed during the
oxidation process. These conditions will depend upon the particular
system dimensions, active and inert material and containment vessel
properties, as well as on convenient and desirable operating
parameters. In any case, one may easily estimate maximum possible
temperature increases that can be expected due to this type of
oxidation reaction by properly employing standard thermodynamic
property information as well as oxygen concentrations, gas flow
rates, system pressures, and relevant system heat capacity
data.
[0052] In several actual experimental regeneration test trials, a
gaseous mixture of nitrogen containing oxygen (in concentrations
ranging from about 50 to about 100 ppm) was employed to re-oxidize
a bed of fully reduced palladium (0.5 percent by weight) supported
on an alumina substrate. This material was enclosed within a
stainless steel reactor vessel and was heated to about 250.degree.
C. prior to the introduction of the oxidizing gas at a flow rate of
about 2.0 scfh (0.0526 meters.sup.3/hour) and at a pressure
slightly greater than 1.0 atm (about 101.3 kPa). A thermocouple,
within the center of the bed of the reduced metal, exhibited no
significant temperature increases during the entire regeneration
process. Of course, at higher oxygen concentrations, a hot zone
(the site of the oxidation process which actually moves through the
system bed in the same direction as the regeneration gas flow), and
more significant bed temperature increases can be expected.
However, one can control this temperature increase very precisely
by controlling all regeneration parameters.
[0053] A preferred regeneration condition is to use nitrogen (or
any other inert gas) containing about 0.5 to 2.0 percent oxygen as
the regeneration gas and to pass this gas mixture at about 1.0 to
3.0 atm (about 101.3 to 304 kPa) through the bed of reduced metal
oxide that has been allowed to cool to about 200.degree. C. A rapid
re-oxidation process without a damaging increase in system
temperature will occur.
[0054] Alternatively, instead of permitting a major portion of the
metal oxide to become reduced, an oxygen-containing gas stream may
be introduced into the reaction zone along with the feed gas stream
to regenerate the metal oxide in situ. In this embodiment, the
amount of metal oxide that has been reduced does not reach an
unacceptable level. Thus, the purification process can be carried
out continuously. And, in this case, the metal oxide acts as a true
catalyst.
[0055] IV. Discussion of the Drawing
[0056] Turning now to the drawing figures, FIG. 1 illustrates a
mode of removing residual oxygen from a stream of nitrogen
initially separated from a source of compressed air using a
membrane purification system. A feedstream 100 of compressed air is
fed to a membrane purifier 101. The compressed air contains
approximately 78 percent nitrogen, 21 percent oxygen, and 1.0
percent argon. Membrane purifier 101 produces a permeate stream
102A rich in nitrogen and containing about 0.5 to 5.0 percent
oxygen and negligible amounts of other impurities or inert gases
such as argon. The permeate stream 102A preferably contains less
than 2.0 percent oxygen. However, the concentration of oxygen in
stream 102A may vary from .+-.1 volume percent of setpoint or
target.
[0057] Permeate stream 102A is then mixed with a fuel gas 104,
preferably methane, within a heated catalyst bed (I) in order to
burn substantially all of the residual oxygen. The catalyst in
catalyst bed (I) may be a noble metal catalyst, such as platinum or
palladium, as described in U.S. Pat. No. 5,242,509, incorporated by
reference herein, operated at a temperature ranging from about 400
to about 900.degree. C. The resulting gas stream 105 exiting the
heated catalyst bed (I) contains nitrogen and impurities such as
carbon monoxide, carbon dioxide, water vapor, and small quantities
of methane and argon. The concentration of carbon monoxide in the
resulting gas stream 105 may range from about 50 to 500 ppm, or
higher.
[0058] The resulting gas stream 105 is then passed to a reactor bed
(II) comprising a metal oxide that is capable of converting
substantially all of the carbon monoxide to carbon dioxide. After
the conversion, a product gas stream 106 leaves reactor bed (II)
and consists essentially of nitrogen, carbon dioxide, and water
vapor. The carbon dioxide and water vapor can be removed easily in
a subsequent adsorption step or process (not illustrated) to
produce a more purified nitrogen gas stream.
[0059] Preferably the methane added to catalyst bed I (through gas
stream 104) is only slightly in excess of the exact stoichiometric
quantity needed to completely react with the excess oxygen in
stream 102, and if stream 102A contains about 98 percent nitrogen
and 2.0 percent oxygen, the gas mixture leaving catalyst bed I
(105) will consist essentially of approximately 97 percent
nitrogen, 1.0 percent carbon dioxide, 2.0 percent water vapor,
small quantities of carbon monoxide (about 50 to 5,000 ppm), and
very small quantities of other impurities such as argon and traces
of methane.
[0060] The stoichiometric reaction between methane and oxygen, at
elevated temperatures, is:
CH.sub.4(g)+2O.sub.2(g)=CO.sub.2(g)+2H.sub.2O(g)
[0061] However, carbon monoxide tends to form during the combustion
of any hydrocarbon when there is an excess (more than
stoichiometric) quantity of the hydrocarbon over the amount needed
to react completely with all of the oxygen actually present. This
is illustrated graphically in FIG. 3. In FIG. 3, the concentration
of oxygen in the feedstream 102A to the catalytic reactor is
plotted against time. Also, the concentration of carbon monoxide in
stream 105 is plotted against time. It can be appreciated that as
the concentration of oxygen varies, for example cyclicly around a
setpoint concentration of 2 volume percent in the product stream of
nitrogen from a membrane air separator, the amount of carbon
monoxide in feed stream 105 will vary between zero and a positive
value. Advantageously, the process and apparatus of the present
invention may be operated to remove carbon monoxide from the feed
stream 105 even if the concentration of carbon monoxide varies, as
illustrated.
[0062] While reactor bed (II) can be operated without an added gas
stream containing oxygen, a portion 103 of the permeate stream 102A
can be bypassed around the heated catalyst bed (I) by opening valve
114 and combining it with the carbon monoxide-containing gas stream
105 exiting the heated catalyst bed (I) to regenerate the reduced
metal, which is formed during the conversion of carbon monoxide to
carbon dioxide, in situ. Thus, if a portion of stream 103 is passed
to reactor bed (II) simultaneously with stream 105, the conversion
of carbon monoxide to carbon dioxide in reactor bed (II) can be
carried out continuously and without the need to take reactor bed
(II) off-line to regenerate the reduced metal.
[0063] In an alternative embodiment, the flow of stream 105 could
be stopped by closing valve 111 when the metal oxide in reactor bed
(II) becomes reduced to an unacceptable level, and a portion 103 of
the permeate stream 102A can then be introduced directly into
reactor bed (II) to regenerate the reduced metal, again by opening
valve 114. During regeneration, all or substantially all of the
oxygen in stream 103 reacts with the reduced metal to form the
metal oxide. It should be noted that the reduced metal is also a
very good reactant with the oxygen. As a result, the regeneration
effluent from reactor bed (II) comprises substantially pure
nitrogen, which can be combined with the product gas stream 106.
Further, rather than stream 103, stream 102B could be used to
regenerate the reactor bed (II) if temperature is controlled so as
to avoid overheating the support material.
[0064] Special Comments Regarding FIG. 1:
1 Gas Bed I Bed II Approximate Moles of Specific Gas Leaving:
Nitrogen A A Carbon Dioxide B B + C Carbon Monoxide C Zero (less
than 0.5 ppm) Water Vapor D D Total Moles N = A + B + C + D N = A +
(B + C) + D Approximate Volume (or Mole) Percentages of Gases
Leaving: Nitrogen 100 (A/N) 100 (A/N) Carbon Dioxide 100 (B/N) 100
(B + C)/N Carbon Monoxide 100 (C/N) Zero (less than 0.5 ppm) Water
Vapor 100 (D/N) 100 (D/N) Note: Volume and Mole Percentages are the
Same:
[0065] Changes in the specific gas concentrations leaving beds I
and II mainly involve carbon dioxide and carbon monoxide. In fact,
the carbon dioxide concentration leaving bed II is only slightly
higher than its concentration in the gas stream leaving bed I, but
changes in the carbon monoxide concentration are preferably much
greater. For example, if the initial carbon dioxide and carbon
monoxide concentrations leaving bed I are about 20,000 and 500 ppm
(respectively), then the final carbon dioxide and carbon monoxide
concentrations leaving bed II will be approximately 20,500 and less
than 0.5 ppm (respectively). This change in the carbon dioxide
concentration ratio may be designated by the factor of
20,500/20,000 or about 1.025 (i.e., there is only a slight increase
in the carbon dioxide concentration). The corresponding change in
the carbon monoxide concentration ratio is approximately 0.5/500 or
0.001 (i.e., there is a one thousand fold decrease in the carbon
monoxide concentration).
[0066] FIG. 2 illustrates many of the same features described in
FIG. 1. However, FIG. 2 has two reactor beds instead of one to
convert the carbon monoxide in stream 105 to carbon dioxide.
Reactor bed (III), which also contains an oxidized metal, allows
for cyclical switching between reactor bed (II) and reactor bed
(III) using valves 112, 114, 116 and 118. Each of these beds may be
alternatively oxidized with an oxygen-containing gas stream 103
while the other bed is converting the nitrogen-rich gas stream 105
to produce a purified nitrogen gas stream 108. The purified gas
stream 108 contains almost pure nitrogen and very small quantities
of carbon dioxide and water vapor, and practically no carbon
monoxide. However, other gaseous impurities that are either inert
or at very low concentration levels may also be present. Lines 107
and 109 are purge gas streams for reactor beds (II) and (III),
respectively. These purge gas streams may be useful for
initializing, testing, evaluation, and monitoring of individual bed
performance, and are normally closed off by closing valves 120 and
121.
[0067] Alternatively, the process and apparatus of the invention
may employ a parallel scheme wherein feed gas stream 105 is split
to form a plurality of feed gas streams 105a, 105b . . . 105n, each
of the feed gas streams passing through a corresponding plurality
of reaction zones of corresponding reactor vessels, to produce a
corresponding plurality of purified nitrogen streams 108a, 108b, .
. . 108n, which may or may not be joined to form a final purified
stream 108.
[0068] An additional and very important aspect of the present
invention is that this gas purification process can be performed
with very little regard to the overall flow rate of the inert gas.
As long as there is a sufficient supply of metal oxide in one of
the reactor beds, the flow rate of stream 105 may vary over a very
wide range. The main advantage of the present invention is that
relatively complicated analysis and control systems needed to
continuously adjust inlet oxygen flow rates to match changes in the
downstream nitrogen demand flow rates and, thus, upstream feed gas
flow rates are not necessary.
EXAMPLES
[0069] The following examples are presented in further illustration
of the present invention and should not be construed as unduly
limiting the scope of the appended claims. All parts and
percentages are by weight unless otherwise noted.
Example I
Formation of Palladium Oxide and Its Use in Converting CO to
CO.sub.2
[0070] Several separate experiments were performed in order to
prove that palladium oxide is capable of: 1) forming at 250.degree.
C. and 2) converting carbon monoxide to carbon dioxide at
250.degree. C. In one of these experiments, a test reactor filled
with 207.1 g of 0.5 percent palladium on alumina, available from
DeGussa under the trade designation E252 P/D, was pretreated with
hydrogen to fully reduce the (as received) material. This material
was then fully oxidized at 250.degree. C. using a flowing mixture
of nitrogen and oxygen, with the mixture flowing at about 2.3 scfh
(0.060 meters.sup.3/hour) wherein the initial oxygen concentration
in the nitrogen was about 85 ppm. After this oxidation reaction was
completed (in approximately 7.5 hr as determined by measuring
oxygen concentrations in the gas streams entering and exiting the
"catalytic" reactor), another nitrogen gas stream (also flowing at
about 2.3 scfh (0.060 meters.sup.3/hour)) containing only carbon
monoxide as the primary impurity (at approximately 200 ppm) was
directed into the same bed of fully oxidized material maintained at
250.degree. C. A time period of about 12.5 hr elapsed before the
carbon monoxide concentration in the outlet gas stream exceeded 0.5
ppm. Carbon dioxide concentrations were also monitored in the
outlet gases at the same time, and it was found that the carbon
dioxide concentrations did not increase significantly in the outlet
gas stream until approximately 6.5 hr after the start of this
purification process step. This delay in the onset of carbon
dioxide breakthrough is thought to be due to adsorption of carbon
dioxide, within the "catalyst" bed, during the carbon
monoxide-carbon dioxide conversion process. The concentrations,
flow rates, and reaction times indicated in this example also
signify a transfer of oxygen from the gas phase to form palladium
oxide and then (in a subsequent step) a nearly quantitative
transfer of oxygen between the palladium oxide and the carbon
monoxide to form carbon dioxide.
[0071] In a separate experiment, the same test reactor (at
250.degree. C.) was treated with a different mixture of flowing
nitrogen and oxygen flowing at about 2.3 scfh
[0072] (0.060 meters.sup.3/hour) wherein the initial oxygen
concentration in the nitrogen was about 76 ppm. After this
oxidation reaction was completed (in approximately 9.0 hr), another
flowing nitrogen gas stream (also flowing at about 2.3 scfh)
containing only carbon monoxide as the primary impurity (at
approximately 200 ppm) was directed into the same bed of fully
oxidized material maintained at 250.degree. C. In this case, a time
period of about 13.5 hr elapsed before the carbon monoxide
concentration in the outlet gas stream exceeded 0.5 ppm. Carbon
dioxide concentrations were also monitored in the outlet gases at
the same time, and it was found that the carbon dioxide
concentrations did not increase significantly in this outlet gas
stream until approximately 7.0 hr after the start of this
purification process step.
[0073] These experimental results indicated that palladium oxide is
capable of 1) forming at 250.degree. C. and 2) quantitatively (or
nearly quantitatively) oxidizing carbon monoxide to carbon dioxide
at 250.degree. C.
Example II
Carbon Monoxide Oxidation Using 0.5 Percent Palladium Oxide
[0074] In this example, another batch of the same "catalyst" that
was used in Example I was used with the following parameters:
2TABLE 3 indicates the data collected using these parameters. Mass
of "catalyst" loaded to form reaction zone = 46.8 g Length of
Reaction Zone = 7.62 cm (3.0 in) Mass of Ceramic Pre-Heat (Inlet)
Zone = 275.9 g Length of Ceramic Pre-Heat (Inlet) Zone = 16.4 cm
(6.5 in) Mass of Ceramic Exit (Outlet) Zone = 128.4 g Length of
Ceramic Exit (Outlet) Zone = 7.6 cm (3.0 in) Total Mass of Ceramic
= 404.3 g Total Length of Ceramic = 24.1 cm (9.5 in) Overall Length
of Reactor = 39.9 cm (15.7 in) Internal Thermocouple (From Gas
Outlet End) = 11.4 cm (4.5 in) Reaction Zone Temperature =
250.degree. C.
[0075]
3TABLE 3 Carbon Monoxide Oxidation Using 0.5 Percent Palladium
Oxide.sup.a) Sys- Sys- Outlet Gas tem tem Inlet Concentrations
Concentrations Flow Pres- Gas Pres- (ppm) (ppm) (m.sup.3/ sur Flow
sur [CO] [CO.sub.2] [CO] [CO.sub.2] hr) (kPa) (scfh) (psig)
[O.sub.2] [O.sub.2] 0.026 108 1.00 0.9 155 <0.5 140 <0.5 124
93 0.056 114 2.13 1.9 151 <0.5 145 <0.5 134 80 0.300 208
11.41 15.5 151 <0.5 144 <0.5 182 99 0.206 166 7.84 9.4 197
<0.5 99 <0.5 193 9 0.318 216 12.1 16.7 178 <0.5 117
<0.5 203 60 0.629 329 23.9 33.0 182 <0.5 114 <0.5 155
.sup. 38.sup.b) .sup.a)Inlet concentrations were estimated; outlet
concentrations were measured; initial CO in reactor cylinder: [CO]
= 295 ppm; initial O.sub.2 in reactor cylinder: [0.sub.2] = 296
ppm; N.sub.2 corrected for air calibration FM = 1.021; Press. corr.
(psig) = P + 0.3; gas flow rates corrected for N.sub.2 and
pressure; charged reactor pre-conditioned at 250.degree. C. with
2.0 scfh (0.053 m.sup.3/hr) of flowing N.sub.2 containing about 80
ppm 0.sub.2 for 24 hr. .sup.b)P inlet was 33.0 psig (329 kPa), P
outlet was 23.4 psig (263 kPa).
Example III
Carbon Monoxide Oxidation Using a 0.5 Percent Palladium
Catalyst
[0076] In this example, another batch of the same "catalyst" that
was used in Examples I and II was used with the following
parameters:
4TABLE 4 The results using these parameters are reported in. Mass
of "Catalyst" loaded into reactor = 15.6 g Length of Reaction Zone
= 2.54 cm (1.0 in) Mass of Ceramic Pre-Heat (Inlet) Zone = 247.9 g
Length of Ceramic Pre-Heat (Inlet) Zone = 15.1 cm (5.96 in) Mass of
Ceramic Exit (Outlet) Zone = 157.5 g Length of Ceramic Exit
(Outlet) Zone = 9.63 cm (3.79 in) Total Mass of Ceramic = 405.4 g
Total Length of Ceramic = 24.8 cm (9.75 in) Overall Length of
Reactor = 39.1 cm (15.4 in) Reactor OD/ID = 3.81/3.20 cm (1.50/1.26
in) Internal Thermocouple (From Gas Outlet End) = 11.2 cm (4.4 in)
Reaction Zone Temperature = 250.degree. C.
[0077]
5TABLE 4 Carbon Monoxide Oxidation Using a 0.5 Percent Palladium
Catalyst.sup.a) Sys- Outlet Gas tem Inlet Concentrations
Concentration Flow Pres- Gas System (ppm) (ppm) (m.sup.3/ sur Flow
Pressur [CO] [CO.sub.2] [CO] [CO.sub.2] hr) (kPa) (scfh) (psig)
[O.sub.2] [O.sub.2] 0.203 140 7.7 5.6 180 <0.5 115 <0.5 161
82.sup.b) 0.784 347 29.8 35.6 183 <0.5 112 <0.5 165 30.sup.c)
1.496 622 56.9 75.5 190 <0.5 105 <0.5 170 30.sup.d)
.sup.a)Initial CO reactor cylinder: [CO] = 295 ppm; initial O.sub.2
reactor cylinder: [O.sub.2] = 294 ppm; N.sub.2 corrected for air
calibration FM = 1.021; gas flow rates corrected for N.sub.2 and
pressure; charged reactor pre-conditioned at 250.degree. C. with
2.0 scfh (0.053 m.sup.3/hr) of flowing N.sub.2 containing about 80
ppm O.sub.2 for 60 hr.; internal thermocouple: ca. 0.32 cm (1/8 in)
below top of catalyst bed. .sup.b)P inlet was 5.6 psig (140 kPa), P
outlet was 5.0 psig (136 kPa). .sup.c)P inlet was 35.6 psig (347
kPa), P outlet was 31.0 psig (315 kPa). .sup.d)P inlet was 75.5
psig (622 kPa), P outlet was 66.0 psig (556 kPa).
Example IV
Carbon Monoxide Oxidation Using Ceramic Bed Only
[0078] In this example, no "catalyst" was used on the support
material, and the following parameters were employed:
6TABLE 5 The results are collected in. Mass of "Catalyst" loaded
into reactor = 0.0 g Length of Catalyst Zone = 0.0 cm (0.0 in)
Total Mass of Ceramic = 405.5 g Length of Ceramic Zone = 24.8 cm
(9.75 in) Overall Length of Reactor = 39.9 cm (15.7 in) Internal
Thermocouple (From Gas Outlet End) = 11.4 cm (4.5 in) System
Temperature = 250.degree. C.
[0079]
7TABLE 5 Carbon Monoxide Oxidation Using Ceramic Bed Only.sup.a)
Sys- Sys- tem tem Inlet Concentrations Outlet Concentrations Gas
Pres- Gas Pres- (ppm) (ppm) Flow sur Flow sure [CO] [CO.sub.2] [CO]
[CO.sub.2] (m.sup.3/hr) (kPa) (scfh) (psig) [O.sub.2] [O.sub.2]
0.0418 111 1.59 1.42 196 <0.5 99 135 50 94 0.0510 113 1.94 1.75
164 <0.5 132 103 56 >100 0.2062 166 7.84 9.35 197 <0.5 99
200 8 >100 .sup.a)Inlet concentrations were estimated; outlet
concentrations were measured; initial CO in reactor cylinder: [CO]
= 295 ppm; initial O2 in reactor cylinder: [O2] = 296 ppm; N.sub.2
corr. for air calib. FM = 1.021; Press. corr. (psig) = P + 0.3; gas
flow rates corrected for N2 and pressure; charged reactor
precon-ditioned at 250.degree. C. with 2.0 scfh (0.0526 m.sup.3/hr)
of flowing nitrogen containing about 80 ppm O2 for 24 hr.;
[0080] This data illustrated that the ceramic packing was
ineffective in converting carbon monoxide to carbon dioxide at
250.degree. C. and at flow rates greater than ca. 7.8 scfh (0.206
m.sup.3/hr) at P=9.4 psig (166 kPa) [i.e., the "catalyst" must be
present to cause the changes that were measured and documented as
illustrated by the previous two examples].
[0081] Summary of Results for Examples I-IV
[0082] Example I (above) illustrated, using experimental data, that
palladium oxide was capable of forming at 250.degree. C. and was
also capable of converting carbon monoxide to carbon dioxide at
250.degree. C. Example II (above) illustrated the catalytic carbon
monoxide to carbon dioxide conversion results that were obtained
using a small scale laboratory reactor containing a 3.0 inch
catalyst bed depth and operated at 250.degree. C. Gas flow rates up
to about 24 scfh (0.63 m.sup.3/hr) and internal pressures of about
33 psig (329 kPa) were employed during this study. Example III
(above) illustrated the catalytic carbon monoxide to carbon dioxide
conversion results that were obtained using a small scale
laboratory reactor containing only a 1.0 inch (2.54 cm) catalyst
bed depth and also operated at 250.degree. C. Gas flow rates up to
about 57 scfh (1.5 m.sup.3/hr) and internal pressures of about 75
psig (622 kPa) were employed during this study. Example IV (above)
illustrated the fact that the catalytic support material alone (an
alumina type of ceramic material) was almost completely ineffective
in converting carbon monoxide to carbon dioxide under the same
conditions that were effective in this conversion process when the
metal oxide was present. This data (in Table 5) illustrated that
the "catalyst" actually selected for this process is indeed
responsible for the reactions that actually occur.
[0083] The present invention has been described in detail with
respect to certain preferred embodiments. However, as is understood
by those skilled in the art, variations and modifications can be
made without any departure from the scope of the present invention
as defined by the following claims.
* * * * *