CA2045060A1

CA2045060A1 - Method for purifying an inert gas stream

Info

Publication number: CA2045060A1
Application number: CA002045060A
Authority: CA
Inventors: Satish S. Tamhankar; Alberto I. Lacava
Original assignee: BOC Group Inc
Current assignee: Messer LLC
Priority date: 1990-07-10
Filing date: 1991-06-20
Publication date: 1992-01-11
Also published as: AU8018991A; KR920002205A; JPH04256418A; KR930012038B1

Abstract

ABSTRACT OF THE DISCLOSURE

A process for the removal of impurities selected from carbon monoxide, carbon dioxide, oxygen, hydrogen and water vapor to part per million levels in which an inert gas stream containing said impurities is passed through catalyst and/or adsorbents adapted to remove the impurities at temperatures as low as -30°C.

Description

CA~ r~-L~

~ he present invention relates generally to a process for re~oving impuri~ies ~ro~ an inert gas ~ream at low temperatures ~nd particularly to a process ~or removing combinations of carbon ~onoxide, carbon Aioxide, ~ater vapor, hydrogen and oxygen from nn inert gas stream at te~peratures of as low as 30C.

13AC~GRO~IND OF q~l3 PRIOR ART

~ ethods are known in the art for removing minute amounts of impurities from an inert gas stream inc~uding carbon ~onoxide, carbon dioxide, oxygen, hydrogen and wa~er vapor. These ~ethods are primarily directed to the purification of nitrogen produced from the cryogenic distillation of air and are intended to remove the impurities to the level of less than one part per million at ambient temperatures.
For example~ ~etal ~getters~ typi~ally composed of mixtures of zirconia, aluminum, iron and vanadium, are used to remove impurities by oxidation I and/or adsorption.
: Platinum group metal catalysts including platinum and palladium catalyze the reaction of oxygen pre ent in the inert gas and hydrogen to ~orm water : vapor, as describe~, for example, in U.~. Patent No.
3,535,074. Oxygen has also been removed from inert gas streams by the use of reduced copper or nickel containing beds.
Platinum group metal catalysts have been used in combination with hydrotalcite to catalyze the oxidation of carbon monoxide with oxygen as described in Delzer et al., U.S. Patent No. 4,911,904.
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2 ~ 0 o A~ the semiconductor industry is developing inte~rated circuits ~ith ever inereasing line densities, the manu~acturin~ processes employed require that ~aterials utilized are 3S frce of impurities 8S i~
S possible. Inert gases such ~s nitrogen ~nd argon, etc., are frequently utilized in ~emicondue~or manufacturing processes and while co~mercially available nitrogen and ~rgon are relatively pure, it is necessary to insure that even greater purities are maintained ~o as to avoid contamination of semiconductor materials. This has led tQ the employment of integra~ed processes for the removal of the combined impurities of carbon monoxide, carbon dioxide, oxygen, hydrogen and water vapor.
One such method is disclosed in Weltmer et al., U.S. Patent No. 4,579,723 in which a commerical catalytic ~aterial (e~g. Engelhard Deoxo A), containing rhodium and platinum, converts carbon monoxide and hydrogen at ambient temperatures to carbon di~xide and water vapor, respectively. Residual oxygen, carbon dioxide and water vapor are removed in a second bed containing a getter material ~uch as Dow Ql.
Another procedure is di closed in Tamhankar et al., U.S. P~tent No. 4,713,224. ~n inert stream is passed throu~h a bed of a particulate material comprised of nickel having a large ~urface ~rea at ~mbient temperatures to remove varying quantities of all five impurities ~rom the inert gas stream.
~ horogood et al., U.S. Patent No. 4,B69,883 disclose a three step process for the purifi~a~ion of an inert gas stream. Carbon monoxide and hydrogen are reacted with oxygen in the presence of reduced copper at elevated temperatures of from 150 to 250C ~o form carbon dioxide and water. Unreacted carbon monoxide and oxygen react with a copper oxide Gatalyst at the ~ame elevated temperatures to form carbon dioxide and water.

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~he carbon dioxide and water thus formed are removed by ~olec~lar ~ie~e adsorbent.
None of the processes developed to date appear capable o removing a ~ide ranqe of impurities from inert gas s~reams at temperatures below those employed by Thorogood et al. And especially below ambient temperatures to as low as about -30C.
Further~ore, there are no known prior ar~ processes which ale effective in removing parts-per-million level~
of carbon monoxide, particularly at low temperatures.
The ability to remove parts-per-million levels of impurities from an inert gas stream at well below ambient temperatures allows the operation of purification plants in environments previously considered unsuitable for such purposes~ Thus, if inert gas streams can be treated successfully at temperatures as low as -30C, facilities can be built outdoors in climates of fluctuating temperature such as the ~ortheast United States as well as frigid climates, as for exampleJ in ; 20 the Northwest United States where low temperatures and high levels of carbon monoxide are commonplace.
It is also desirable to have a process which can be tailored according to the content of impurities present in the feedstream to provide a purified gaseous product in an efficient, cost effective manner.
S~MAR~ OF T~E INV~NTION

The present invention iz generally directed to a process for puriying an inert gas stream containing the impurities carbon monoxide, carbon dioxide, oxygen, hydrogen and water vapor and, particularly to the ~ treatment of feed streams containing minute quantities ; of the impurities at less than ambient temperatures.
The process employs up to three beds of material which , .

, 20~060 _ 4 _ are particularly ~uited to convert and/or adsorb one or more of ~he impuri~ies even at temperatures as low a8 bel~w 0C to about -30C, ~ypically in ~he range of 3bout -30C to ~0C and under fluctuating temperatur~
conditions arising from ~hanging ~easons~ The process can be tailored to the parti~ular composition and concentration of impurities.
In its broadest 3spects, the present process comprises passing an inert gas stream through a bed containing a ~aterial adapted to convert carbon monoxide to carbon dioxide and to remove ~t least carbon dioxide from the inert gas stream. The resulting gaseous product is substantially free of these impurities to levels ~f no more than about 0.1 ppm of each impurity.
If the inert gas ~tream contains at least 3 ppm of hydrogen then a second bed of material may be - used to convert the hydrogen present in the stream to water vapor. The second bed of material is a catalyst capable of catalyzing the reaction of hydrogen to water vapor at temperatures as low as about -30~C. The preferred catalyst for this purpose is ~elected from noble metals on an alumina support, most preferably palladium on activated alumina. Thus, in one aspect of the invention, excessive Amounts of carbon monoxide and hydrogen are removed from an inert gas tream down to about 0.1 ppm levels.
If t~e inert gas ~tream contains high levels of carbon monoxide on tbe order of at least about 3 ppm, 30 then it is preferred to reduce the quantity of carbon monoxide down to no more than about 1.0 ppm~ This can be ~ccomplished by first passing the inert gas stream through a bed of at least one transition metal oxide which converts relatively large quantities of carbon monoxide to carbon dioxide, particularly at temperatures .: ,. ^
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belQw O~C to as ~ow ~s about -30C.
In accord~nce ~ith the present invention~ the beds are Iegenerated in a conventional manner to remove the impurites ~d~orbed therein. The process of the present invention can be conducted batchwise or continuously in single or multiple vessels and regeneration can be conducted ~eparately or simultaneously with the purification process.

_RIEF DESCRIPTION OF T~E D~AWI~GS

The following drawings in which like reference characters indicate like pacts are illustrative of embodi~ents of the invention and are not intended ~o limit the invention as encompassed by the claims forming part of the application.
FIGURES lA and lB are schematic views of one embodiment of the invention showing a batchwise process using three beds for purifying an inert gas stream and regeneration of the beds;
FIGURES 2A and 2B are schematic views of another embodiment of the invention showing a batchwise process using two beds for puri~yin~ an inert gas stream and regenerstion of the beds;
~IGURE 3 is a ~chematic view of another e~bodi~ent of the invention ~howing a continuous process for purifying ~n i~ert gas stream usin~ three beds;
FIG~RES 4A and 4B are schematic views of another embodiment of the invention ~howing a batchwise 3~ process using a single bed for purifying an inert yas stream and regeneration of the bed; and FIGURES 5A and 5B are schematic views of another embodiment of the invention showing a batchwise process using two beds and regeneration of the beds.

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li~ILE:D DlESCRIPTION OF q~lal~ I~VBN~ION

The process o the p~esent invention produces a highly purified gase~s produc~ ~ubstantially free of the impurities; carbon ~onoxide, earbon ~io~ide, hydrogen, oxygen and water vapor. The feed ~tream is an inert yas 8UCh ~S argon. It should be understood, ~owever, that alt~ough nitrogen ~ill react with certain elements unde~ ~articular conditions, the term ~inert gas~ as used herein includes nitrogen. In particular, the present process can be utilized ~o purify a nitrogen stream obtained from the cryogenic distillation of air.
It should also be understood that the gaseous ; prod~cts produced in accordance with the present invention are suitable for use in the semiconductor industry. ~he development of integrated circuits with ~` eve~ increasing line densities reguires gases that are .~ as free of impurities as is possible. Commercially available nitrogen and argon containing parts per million levels of impurites are insufficient for the manufacture of integrated ci~cuits. Accordingly, the present process while capable of removing impurities in amounts of up to about 10,000 ppm~ is particularly intended to purify inert gas s~reams ~ontaining up to about 5.0 ppm ` 25 of each of o~y~en, car~on ~ono~ide and hydrogen, and up to ~out 2.0 ppm of each of car~on dioxide and water . vapor to produce a highly purified gaseous product, preferably con~aining no more than 0.1 ppm of any of the :~
impurities.
Referring to FIGURE lA there is ~hown a bulk or discontinuous process for the production of a purified gas using three beds in which the feed stream is terminated during regeneration of the beds.
A feed gas stream, as for example, nitrogen gas obtained from the cryogenic distillation of air - - ) . : :....................... :: : : , . ~ ,.",., ,;,.,:.

-_ 7 -containing no more than 5.0 ppm of each of oxygen, ~arbon ~onoxide and hydrogen ~nd up to 2.0 ppm of each of car~on dioxide and water vapor i~ fed via a line 2 to a column 4. The ~olumn 4 contains a first bed 6 containing a ~o~position of transition ~etal oxides ~uch as ~opcalite ~a ~omposition c~ntaining copper and ~anganese oxides in an amount of about 10.8% copper, 52.4~ ~ang~nese and the balance o~ygen, ~anufactured by Mine Safety Appliances). An alternative catalyst is nickel oxide such as oxidized ~arshaw nickel catalyst.
Another tranqitional metal oxide composition is Carulite (made by the Carus Chemical Co.) which is a mixture o~
copper and cobalt oxides. The foregoing transition ~etal oxides are particularly effective at converting large quantities of sarbon monoxide to carbon dioxide at temperatures below 0C to as low as about -30C even in the presence of less than stoichiometric amounts of oxygen.
The first bed 6 converts the carbon monoxide present in the feed stream into carbon dioxide with or without the presence of oxygen in the feed stream. The carbon dioxide is passed along in the feed stream to a second bed 8 containing a catalyst capable of converting hydrogen to water vapor.
The particular hydrogen catalyst chosen depends on the quan~ity of oxygen present in the feed stream for converting hydroqen to water vapor and the temperature of t~e ~eed ~tream. In general, noble ~etal catalysts on an activated ~upport such ~s alumina are particularly ~uited for this purpose. For example, pla~inum, rhodium or combinations thereof on activated alumina convert hydrogen to water vapor when oxygen is present in greater than a stoichiometric amount and, preferably, the temperature of the reaction is around ambient temperatures.

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Palladium on a~u~ina is particularly preferred because it catalyzes the reactio~ of hydrogen to water vapor ~nd ~imu~taneously converts carbon ~onoxide to carbon dioxide in ~e presence of ~toichiometric amounts o~ 02ygen, particularly at temperatures below 0C to about -30C. Thus, in accordance with the present invention an inert gas ~tream can be purified ~ith~ut adding o~ygen ~o the systen and at less than ambient te~peratures, particularly less than 0C. Most 1~ preferably, the amount of palladium is about 0.5% by weight based on the weight of the catalyst present in the outer shell of the alumina pellets.
Alternatively, a catalyst containing palladium and copper on alumina can be used at low temperatures.
In particular~ a catalyst containing about 0.5-1.0 weight ~ of palladium and about 8-12% of copper on activated alumina is advantageous because it also adsorbs carbon dioxide, oxygen and water vapor from the feed stream.
The feed ~tream leaving the bed 8 contains water vapor and carbon dioxide and perhaps minute amounts of unconverted hydrogen, oxygen and carbon dioxide. ~he feed stream is then sent to a bed 10 containing an adsorbent particularly adapted to chemically adsorb carb~n dioxide, water vapor and oxygen from the feed ~tream.
~ he adsorbent particularly preferred for this purpose i~ copper on a~umina as, ~or example, DOW Q-5 ~anufactured by the DOW Chemical Company. This material can also convert relatively low levels of carbon monoxide to carbon dioxide. O~her examples include reduced nickel on a suitable suppor~ such as silica or alumina ~hich is particularly effective at temperatures below about O~C to -30C.

" :, ~ 9 -Th~ re~ulting feed ~tream, substantially free c~f C:21 r bon ~i~xi,~ er ~ bc~ IÆonoxide, oxyg en, hydrogen and Ya~e~ ~ap~r. eYits ~he~ r~lm~n 4 via a valve 11 and a line 1~ where it i6 sen~ to a stora~e facility or to a S parallel plant in which the purified gaseous product is employed.
In the discontinuous process of FIGURE lA~ the beds 6, 8 and 10 ~ust be periodically r2generated. This is accomplished as ~hown in FIGURE lB by terminating entry of the feed stream throu~h the line 2 by a ~alve 14 or other customary mean~. A regenerating gas stream containing a predominant amount o an inert gas such as nitroqen and/or argon and a minor amount ~f hydrogen, preferably about 1-10% by volume of hydrogen, most preferably about 3~ by volume is sent via the line 12 and the valve 11 through the beds 10 and 8 to remove accumulations of the impurities contained therein. The regeneration gas containing the previously ~dsorbed impurities is vented ~rom the column 4 via the line 18.
The regeneration process is typically conducted at temperatures of up to abo~t 200C.
The bed 6 containing the transition metal oxides is sensitive to the presence of hydrogen at the regeneration tem~erature. Accordingly, the catalyst in the bed 6 is regenerated by opening the valve 14 and passing the nitrogen gas ~tream through ~he bed 6 and discharging the impurity containing gas out of the column 4 via the line 1~.
Another embodiment of the process of the present invention is shown in FIGURES 2A ~nd 2~. In this embodiment, the bed 6 has been eliminated because the feed stream contains low levels of carbon monoxide o~ less than about 3 ppm.
Referring to FIGURE 2A~ the feed stream p~oceeds through the valve 14 via the line 2 directly .

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~ 10_ into the bed B c)f the column 4. The bed 8 contains the same type of hyar~en ~a~alyst de6cribed above an connection with FIGU~ES lA and lB ~uch as palladium on alumina or pa~ladiu~ and coppe~ on alumina ~nd the like.
S The hydrogen catalyst in t~e bed 8 ~onverts hydrogen to water vapor. If palladium on alumina is employed the carbon ~onoxide present will also be converted to carbon a io~i~e.
The feed stream is then sent to the bed 10 containing an adsorbent for chemically adsorbing carbon dioxide, water vapor and oxygen from the feed stream.
Copper on alumina, such ~s DOW Q-5 is particularly preferred for the bed 10. Substantially pure nitrogen gas is withdrawn from the column 4 through the valve 11 and line 12.
Regeneration of the column 4 is performed as shown in ~IGURE 2B by providing an inert gas such a5 nitrogen or argon and containing about 1-10% of hydrogen through the column 4 via the line 12 and venting the impurity containing gas out ~he line 2.
The present process may also be conducted in a continuous manner employing at lea~t two columns with at least one of the columns undergoing production of the purified gaseous product ~hile at least one of the : 25 columns undergoes regeneration. Referring to FIGVRE 3, there is ~hown a system containing two columns 30, 3~.
It çhould be understood, however, that more than two columns ca~ be u~ed within the ~pirit and scope of the invention, ~ach colu~n 30, 32 contains three beds 34, 36, 38 containing a transition metal oxide catalyst such as Hopcalite, palladium on alumina, ~nd DOW Q-5 as described previously in connection with FIGURE 1. It ~hould also be understood that the continuous process described herein with reference to FIGURE 3 can be run using one or two beds as well depending on the content ,, . , ~
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of the fee~ stream as p~eviously described.
A feed stream of the ame type described in connecti~n with FIGURES lA ~nd lB is ~ent via a line 40 to a line ~2 having a pair of valves 44, 46. Valve 46 is turned o~ to permit tbe feed to pass through the open valve 44 into the CQlUmn 30. The feed strea~
undergoes the same reactions as dessribea above in ~ connection with the three bed column of FIG~RES lA and : lB. ~ure product gas exi~s the column 30 through a line 48 and an open valve 50 where it is collected from a line 52, The column 30 can be re~enerated to remove impurities from the beds 36 and 38 by closing the valve ~ to ~event the flow of the feed stream via the line 42. P~oduct gas exiting the column 32 via the line 80 proceeds through the valve 82 and a portion of the ~r~duct ~tre~m pr~ceeds via a line S3 through a valve 55 to combine with hydrogen gas supplied via a line 70 through a valve 72. The resulting regeneration or purge gas most preferably containing abou~ 97% by volume nitrogen and about 3~ by volume hydrogen is fed via a line 56 through a valve 58 into the beds 38 and 36 to collect impurities adsvrbed therein. The impurity containing vent gas is evacuated from the column 30 via a line 6a through a valve 64.
The bed 34 containing a transition ~etal oxide catalyst such as ~op~alite 1s not purged wi~h the hydrogen containing gas because transition ~etal oxides can deactivate in t~e presence of hydrogen~ Accordingly, pure nitrogen product gas obtained from the column 32 is fed via the line 80 to line 53 and is recycled via a line 74 through a control valve 76 and a s~op valve 78 into the bed 34 of the column 30 containing the Bopcalite. The pure nitrogen purge gas removes impurities from the ~opcalite bed 34 and is vented out of ~he column 30 via the line . .:
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:., o ~ o n ~2 ~nd ~e Ya~ve ~4~
As shown in FIG~RE 3 a continuous process is provided by feeding the feea stream to one of the ~olumns 30, 3~ while regenerating the other of the 5 columns. ~hus, ~hen the valve ~4 is open the feed gas proceeds via the lines 40, 42 into the column 30. At the ~ame time the valve 46 is turned off. The product stream ~oming f~om the ~olu~n 30 passes via a line 48 t~rough a YalYe 50 to the lines 52, 53. A ~ajor portion 10 of the product gas is collected from the line 52 while . the remainder flows through the line 53 to combine with ? hydrogen rom the line 70 via the valves 72 and 55. The resulting regeneration gas flows via a line 77 throuyh a valve 60 into ~he beds 38 and 36. The impurity laden 15 gas is vented from the column 32 via the line 79 and the valve 81.
As previously indicated transition ~etal oxides can not be regenerated in the presence of hydrogen.
Accordingly, a portion of the gaseous product obtained 20 from the line 53, operating at a higher pressure than the gas in line 54, prsceeds in the absence of added hydrogen via a line 84 through a flow control valve 86 and a 6top valve 88 to the bed 34. The regeneration gas removes impurities in the bed 34 which is vented from 25 the ~ystem via the line 79 through the valve 81.
The system can proceed continuously by closing the ~alve 44 to regenerate the bed 30 and opening the valve 46 to pur~y product gas passing through the col~mn 32. When the column 32 can no longer effectively 30 adsorb the impurities, regenera~ion i6 co~menced by closing the valve 46 and passing the feed stream to the column 30 via the open valve 44.
Thus, the present process can be conducted batchwise and continuously while tailoring the number of beds and the type of catalysts and/or adsorbents to the ... . ,................................. :
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_13_ co~position of the feedstream and the desired puriication level of the final product.
In o~ygen poo~ feed ~treams ~uch as those containing less than abo~t S ppm, the trznsitional metal oxides whicb conYert ~ar~on ~onoxide to carbon dioxide may suffer a loss of o~ygen thereby dimi~ishing catalytic capacity. In this event, it ~ay be desirable to add ~inor amounts of oxygen tv the purge ~tream to replenish the olcygen lost fr~m the transitional metal 10 Oxides.
As shown in FIGURE 3, ~eplacement oxygen is supplied from a line 90 into ~ line 92 and a valve 94 to combine with the purge ~tream flowing in line 74. A
similar pathway is provided for the column 32 ~o that 15 one column may receive replenishing oxygen during the purge cycle while the other column is in the production cycle. ~o~e specifically, replenishing oxygen is supplied to the bed 34 of the column 32 by closing the valve 94 and forwarding the oxygen from the line 90 to a line 96 and through a valve 98. The amount of oxygen added to the purge gas is typically in the range of about 200 to l,000 ppm, preferably about 200 to 400 ppm.
For gases containing low levels of hydrogen, and especially less than about 0.1 ppm and no more than about 3 ppm of carbon ~onoxide, a single bed system can be used in accordance with the present invention.
Referring to FIGURES 4A and 4B, the feed ~tream i8 ~ent via the line 2 through the valve 14 to the co~umn 4 which contains a ~ingle bed lO of a material adapted to convert carbon ~onoxide to carbon dioxide and to adsorb carbon dioxide, oxygen and water vapor. The preferred materials are DOW Q-5 or ~arshaw nickel catalyst previously described.
Regeneration of the single bed system shown in FIGURE 4B is conducted in a manner ~imilar to that of ' .

2~4~0~0 _14 _ the t~ be~ ~ystem described in connection with FIGURES
2~ a~d 2~ ~ F~ge~e~ion gas containing an inert gas 6uch as nitrogen or a~gon ~nd hydrogen in an amount of abo~t 1-10~ by volu~e is ~ent via the line 12 through the bed 10 and the ~mpurity laden gas is then discharged from the system through the feed line 2.
If the feed stream contains amounts of carbon ~ono~ide exceeding about 3 ppm then the ~ingle bed ~ystem of ~IGURES 4A and 4a can be altered to a two bed system of the type ~hown in FIGURES 5A and SB. In this embodiment, the uppermost bed 6 is packed with a composition of transition metal o~ides, ~u~h as Hopcalite, which converts carbon monoxide to carbon dioxide. The lower bed 10 preferably contains DOW Q-5 for adsorbi~g carbon dioxide, oxygen and water vapor.
The path of the feed stream and the manner in which the beds 6, 10 are regenerated are ~imilar to that of the three bed system described in connection with FIGURES lA
and lB.

~AMPL~ 1 A feed stream containing about 1 ppm of each carbon monoxide and hydrogen, about 6 ppm of oxygen and the balance nitrogen gas obtained from the cryogenic distillation of air was fed at the rate of 10 standard liters per minute (SLP~) to a column of the type shown in FIGURE 4 containing DOW Q-5 at a temperature of 38C
and a pressure ~f 30 psig.
The column was operated for 12 hours during which ti~e the product gas contained virtually pure ~itrogen gas, with no detectable carbon monoxide, hydrogen, oxygen, water vapor or carbon dioxide. After 12 hours, hydrogen gas was detected in the product gas in an amount of less than about 0.1 ppm.

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: 15_ The process was continued for seven days ~ith~ut ~ignificant change in the composition of the product gasO After eight days, the fir~t detectable ~mount~ of oxygen ~ere ~bserved in the product gas to S the e~tent of ess than ~bout 0O2 ppmO The process was continued for an additional 2 days at which time the first detectable amounts of ~arbon dioxide were observed. Carbon ~onoxide remained absent from the product gas during the entire course of the test run.
~AMPL~ 2 A nitrogen feed ~tream ~ontaining about 2 ppm of each of carbon monoxide and hydrogen, about 12 ppm of oxygen and the balance nitrogen ~as fed under the same conditions to the ~ame column described above in connection with FIGURE 1 except that temperature of the bed was set at ~20C. ~he resultin~ product stream had no detectable hydroyen after 12 hours while the first detectable oxygen was not observed until the eighth day.
Carbon dioxode was not detected until the 10th day while carbon monoxide remained,absent during the 10 day test run.

~A~PLE ~

A feed stream containing about 1 ppm carbon ~noxi~e and ~out 2 ppm oxygen and the balance nitrogen ,125 fed to the 6ame type of column and under the same 30 conditions as in Example 1 except that the temperature of the bed was set at -10C. The reaction was carried out for 30 days. The resulting gaseous product contained no detectable amounts of carbon monoxide or oxygen.

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_16 _ o ~A~P~ 4 A eed ~tream ~Dntaininy about 2~5 ppm carbon ~on~ider a~out 2 pp~ hydrogen ~nd a~ut 15.6 ppm oxygen 5 and the balance nitrogen was fed a~ t~e rate of 15 SLPM
to a column of the type ~hown in FIGl~E 5 packed wi~h 340g (230 cc. ~ of oxidized ~arshaw nickel catalyst.
The feed stream was ~ubjecte~ to a temperature o~ 2~C and a pressure of 40 psig. The process was conducted in excess of 10 days. The gaseous product obtained from the column had no detectable amounts of carbon monoxide~and only a~out 1 ppm of hydrogen, about 15 ppm of ~xygen, about 0.1 ppm of carbon dioxide and }ess than about 0.1 ppm of water vapor.
E~A~PLE S

A feed stream identical to the feed tream described in Example 1 except that it contained about 3 ppm of carbon monoxide was 6ent to a two bed column of the type sh~wn in FIGURE 5. The top bed contained ~opcalite. The catalyst had a ~urface area of about 192m2/9 and an average grannul~r size of 2 4 mm. The - bottom bed contained DOW Q-S.
The process was ~onducted for four days at a temperature of 20C. The gaseous product contained no detec a~le car~on ~onoxide and less than about 1 ppm of ~ydrogen.
~he process was continued for four edditional 30 days at a temperature of 10C. ~idway through the second four day period the carbon monoxide content of the feed ~tream was raised to about 5 ppm. After the ;
eight days of operation, the prod~ct contained no detectable amount~ of carbon monoxide and no more than about 1 ppm of hydrogen.

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~ he proce~s was continued for a third four dayperiod during which time the ~e~perature was lowered to about 25C~ Tbe resulting product ~till had no detectable carbon ~ono~ ide and less than about 1 ppm of S hydrogen.

I~XAMPI.~ ~

A feed ~tream containing about 1.5 ppm of each of carbon monoxide and hydrogen, about 6 ppm of oxygen, and the balance nitrogen was sent to a three bed column of the type shown in FIG~RE 3O The middle bed contained about 0.5 weight percent of palladium on an activated alumina support manufactured by ~ngelhard, Inc.
The process was conducted under the same process conditions and for the Qame leng h of time as in Example 5. The resulting product had no detectable amounts of carbon monoxide or hydrogen.
; Regeneration of the two column system shown in FIGURE 3 was conducted as ~ollows. The beds 36 and 38 containing palladium on alumina and DOW Q-5, respectively are purged with a gas ~tream containing about 974 DitrOgen and a~out 3% hydrogen. The pure nitrogen is removed from the column 30 through the lines 50 and 53.
Yalve 55 is opened so that the nitrogen can be mixed ~ith ~he appropriate amount of ~ydrogen from the line 70 through the valve 72~
The purge stream containing nitrogen and hydrogen gas proceeds via the lines 54, 56 ~hrough ~he valve 58 into the bed~ 38~ 36 of the column~ The purge ~tream and impurities contained therein are vented out of the column 30 via the line 62 and the valve 64~
The transition metal oxides and particularly ~opcalite contained within the bed 34 are sensitive to hydrogen and therefore purging should be accomplished ~. :
,:
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~4~
_18 _ with purified nitrogen in the ~bsence of hydrogen.
~c~sd~gly, purified ni~rog~n is sent via the lines 53, ~n~ ~4 ~ ~a~e ~6~ 78 to the bed 3~ of the column 30.
T~e puri~ied nitrogen strea~ containing the ~dsorbed impuritie~ is ~entea ~i~ the line 62 and the valve 64.

~I~nPL~ 7 The process was conducted using a three bed column as in Example 6 except that the catalyst in the second bed was replaced with 1~ by weight of palladium on an activated alumina support. The feed ~tream was altered to double the concentration of carbon monoxide to about 3 ppm. The process was conducted in the same manner as in E~a~ple ~. A reduction gas analyzer made by Trade Analytical, Inc. ~as employed to de~ermine the presence of hydrogen and carbon monoxide in the product gas. An analysis of the product gas showed that 100% of the hydrogen was converted to water vapor and 93% of the carbon monoxide was converted to carbon dioxide.

æ~MPL~ 8 , The process of Example 7 is repeated except that the second bed was provided with a catalyst containing 0.5-1.0 wt% of palladium and 8-12 weight ~ of copper toget~er ~eposited in the outer ~hell of alumina having a surface area of 100-200 m2/g.
The process i~ conducted in the ~ame manner as in ~xample 7 to obtain a gaseous product containing less than one ppm of all impurities.
The foregoing examples are illustrative of embodiments of the invention when modification of said examples can be made within the pirit and scope of the invention. For example, the columns have been described ,: '''' , ': "

2~0~

o as ~ontaining discrete beds of the catalysts and or adsorbent~ It should ~e under~itood, however, that each bed may contai~ a plurality of laye~ of different catalysts and/or ~dsorbenta. Sv, ~or example, the bed S 36 ~ihown in FIGURE 3 may contain o~e or more layers of ~OW Q-~ ~nd/or ~opcalite. It i6 preferred, however, that the Hopcalite be separate fxom the other materials because of its sensitivity to tbe presence of hydrogen in t~e purge stream.
As shown in the Examples, the process of the present invention can be run under fluctuating temperature conditions associated with many regions of the United States and elsewhere throughout the world.
This provides a ~ignificant advankage over systems which must operate in warm climates or must be fitted with costly heating systems to operate in colder environments.

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Claims

1. A process for the removal of impurities selected from the group consisting of carbon monoxide, carbon dioxide, oxygen, hydrogen and water vapor from an inert gas stream, comprising passing the inert gas stream through at least one bed containing a material adapted to catalyze the conversion of carbon monoxide to carbon dioxide and to remove carbon dioxide from the inert gas stream at a temperature as low as about -30°C
and withdrawing a purified gas from the bed.

2. The process of Claim 1 wherein the process is conducted outdoors under fluctuating temperatures.

3. The process of Claim 1 wherein the process is carried out at a temperature in the range of from about -30°C to +40°C.

4. The process of Claim 1 wherein the process is carried out at a temperature in the range of from below 0°C to about -30°C.

5. The process of Claim 3 wherein said material is copper supported on aluminum.

6. The process of Claim 4 wherein said material is nickel supported on alumina or silica.

7. The process of Claim 1 further comprising regenerating said material with a purge gas.

8. The process of Claim 7 wherein the purge gas contains a predominant amount of an inert gas and a minor amount of hydrogen.

9. The process of Claim 7 comprising terminating the flow of said inert gas stream to be purified through said bed, heating said bed to a temperature of up to about 200°C, and passing an inert purge gas flow through said bed to remove impurities adsorbed therein and thereby regenerate said bed.

10. The process of Claim 1 wherein the total amount of impurities in the feed stream is no more than about 10,000 ppm.

11. The process of Claim 10 wherein the feed stream contains up to about 5.0 ppm of each of oxygen, carbon monoxide and hydrogen and up to about 2.0 ppm of each of carbon dioxide and water vapor.

12. The process of Claim 11 wherein the feed stream contains less than 3.0 ppm of hydrogen.

13. The process of Claim 1 further comprising prior to passing the inert gas stream through the bed containing the material adapted to convert carbon monoxide to carbon dioxide, passing the inert gas stream through a second bed containing a catalyst adapted to convert hydrogen to water vapor.

14. The process of Claim 13 wherein the catalyst is selected from noble metals on an activated support.

15. The process of Claim 14 wherein the process is conducted in the presence of greater than a stoichiometric amount of oxygen and the catalyst is selected from platinum, rhodium and combinations thereof on activated alumina.

16. The process of Claim 14 wherein the process is conducted in the presence of about a stoichiometric amount of oxygen and the catalyst is palladium on alumina.

17. The process of Claim 16 wherein the catalyst in the second bed also converts carbon monoxide to carbon dioxide.

18. The process of Claim 14 wherein the catalyst contains palladium and copper on activated alumina.

19. The process of Claim 18 wherein the catalyst contains about 0.5-1.0 weight % of palladium and about 8-12 weight % of copper.

20. The process of Claim 13 wherein the inert gas stream contains at least 3.0 ppm of hydrogen.

21. The process of Claim 13 further comprising terminating the flow of said inert gas stream to be purified through said beds; heating said beds to a temperature of up to about 200°C; and passing an inert purge gas flow through said beds to remove impurities adsorbed therein and thereby regenerate said beds.

22. The process of Claim 1 or 13 further comprising prior to passing the inert gas stream through the bed containing the material adapted to convert carbon monoxide to carbon dioxide, passing the inert gas stream through another bed containing a catalyst adapted to convert carbon monoxide to carbon dioxide.

23. The process of Claim 22 wherein the catalyst in said another bed is at least one transition metal oxide.

24. The process of Claim 23 comprising conducting the reaction in the presence of less than a stoichiometric amount of oxygen.

25. The process of Claim 23 wherein the catalyst in said another bed is a composition containing copper and manganese oxides.

26. The process of Claim 22 wherein the inert gas stream contains at least 3.0 ppm of each of hydrogen and carbon monoxide.

27. The process of Claim 22 further comprising terminating the flow of said inert gas stream to be purified through said beds; heating said beds to a temperature of up to about 200°C; and passing an inert purge gas flow through said beds to remove impurities adsorbed therein and thereby regenerate said beds.

28. A process for the removal of impurities selected from the group consisting of carbon monoxide, carbon dioxide, oxygen, hydrogen and water vapor from an inert gas stream comprising:
(a) passing the inert gas stream through a first bed containing a transition metal oxide to thereby convert carbon monoxide to carbon dioxide;
(b) passing the inert gas stream from step (a) through a second bed containing palladium on alumina to thereby convert hydrogen to water vapor; and (c) passing the inert gas stream from step (b) through a third bed containing a material adapted to convert carbon monoxide to carbon dioxide and to adsorb carbon dioxide, oxygen and water vapor at a temperature of from about -30°C to +40°C to thereby obtain a product gas containing less than 1 ppm of each impurity.

29. The process of Claim 28 wherein the material in the third bed is selected from nickel or copper supported on alumina.

30. The process of Claim 28 further comprising regenerating said material with a purge gas.

31. The process of Claim 29 further comprising terminating the flow of said inert gas stream to be purified through said beds; heating said beds to a temperature of up to about 200°C; and passing an inert purge gas flow through said beds to remove impurities adsorbed therein and thereby regenerate said beds.

32. The process of claim 28 wherein the process is conducted outdoors under fluctuating temperatures.