Note: Descriptions are shown in the official language in which they were submitted.
~300346
S~PERPURIFIER ~OR NITROGrN AND PROC2SS
FOR P~R~FYING SAME
[~rlor Art3
Nltrogen ls a useful gas enJoylng steadlly grawing demand
ln many sectors o~ lndustry lncluding the flelds of electronlcs,
chemicals, lron and steel making, and shlpbùildlng.
It has been a common lndustrlal process for the productlon
of nitrogen to repeat compression of air by a compressor and
adiabatic expansion of the compressed air untll llquid alr is
obtained and then sub~ect it to fractional distillatlon under
high pressure to produce liquld nitrogen of high purity. The
product is fllled elther in liquid or gaseous form i~to cyl-
inders and put on the marXet.
A typical inert gas, nltrogen is widely used in the afore=
mentioned fields to provide atmospheres for heat treatments
of metals, for the manufacture of semiconductors and the like.
When lt is to be employed ln superfine microprocesslng such
as in electronics industry, it must be further purlfieq by
removlng impuritles to a higher purity immediately before use.
For large-volume conswnptlon in industrial-operatlons it is
customary to vaporize liquid nitrogen and supply the resultlng
gas through plpelines. Here the pt.oblem is how to meet the
~, '.
.
1300346
requirement of rapid and posltlve removal of the lmpurlties,
such as oxygen, hydrogen, carbon monoxlde, carbon dloxide,
h~drogen, hydrocarbons, and water, from the gasified nitrogen.
In order to remove these impurltles and purify nitrogen
to hi8h purity, various nitrogen gas purlfiers have heretofore
been marketed and used. For instance, one of the applicants,
Taiyo Sanso Co., has since 1974 sold gas purifiers (~lodels
TI~-lO, -~0, -60, -100, -200, -300, -400, and -500). These
and other co~mercially available gas puriflers use oxidation
catalysts of metal oxides suc~. as of nic~el, chromlum, and
copper to oxidize carbon mor.oxide, hydrocarbons, hydrogen and
the ll~e into carbon dioxide and water and then re.~ove lmpurl-
ties by adsor~lion from ~he resultants by the use of a zeolite
molecular sieve, ac~ive charcoal or the like for the ~as purifi-
catior.. Where high-purity nitrogen is to be simply obtained,
these gas purifiers are convenient and are therefor_ in wide
use.
The impurlties in tha gas purified by these existing equip-
ment, according to the manufacturers' brochures, are generally
as follo~s:
Constituent Oxygen Hydrocarbon Carbon dioxide Moisture
ppm <O.l <O.l <0.4 <0,5 (dew point -80aC)
.
'
~300346
'rO this end, the USQ`O~ hydrogen-occluding alloys, namely,
T'i-r~n, Ti-~e, and rare-earth-rli alloys, have been proposed in
Japanese Patenc Application Pub~lic Disclosure No. 156~08/1982.
They have, however, failed to purlfy nitrogen beyond the level
tabulated above.
,Problem the Invention is to Solve]
The commercially available gas purifiers as mentioned above
are simple, convenient, and efficient for obtainlng high-purity
nitrogen gas. However, the recent progress of the semiconductor
industry sug~ests that more ~nd more precise microprocessing
and hence nitrog2n gas of even higher purity will be required
for future production of highly inte2rated circuits. In fact,
there is already strong dem~nd for high-purity gas for testing
purposes. The technical problem the present inventlon ls
lntended ~o solve is lowering the current levels of impurities
according to the prior art technology to much lower levels,
by one figure in parts per million.
~ r~leans for ~olving the Problem~
'~le have intensively s.udled on the rneans for purifying
ni~rogen ~as to decrease its i,~lpu.ity concentrations by oneorder of
m~itude in ppm each frorn the usual levels as stated above. As
a result, we have arrlved at an apparatus and a process capable
of purifying the conventionally purified gas of hlgh purity
to an even higher purity. The present invention has now been
perfected on this basls.
130034~
The apparatus according to this invention is a superpurifier
for nitrogen comprising an outer shell provided with an inlet for
nitrogen gas to be purified, an outlet for purified nitrogen gas,
a gas flow passage connecting the gas inlet and outlet, at least
one getter chamber packed with a getter of an alloy consisting
of from 15 to 30% by weight of iron and from 85 to 70% by weight
of zirconium and disposed midway in the gas flow passage, and
neater means to maintain the getter at the temperatare at which
it functions.
The process according to the invention is based on a process
for purifying nitrogen characterized by the steps of first
conventionally purifying impure nitrogen gas by passing it
through a bed of metal oxide catalyst for oxidation at an
oxidation reaction temperature and then through an adsorbent bed
of zeolite molecular sieve or the like, and thereafter removing
the remaining impurities by adsorption from the nitrogen gas of
low impurity contents by further passing it through a getter bed
packed with a getter of an alloy consisting of from lS to 30% by
weight of iroh and from 35 to 70~ by weight of zirconium and
maintained at a temperature of 20 to 500C.
As the getter for use in the invention which is an alloy
¢onsisting of from 15 to 30% by weight of iron and from 85 to 70%
by weight of zirconium, the one described in U.S. Patent
5pecification No. 4,306,887 may be employed.
In view of the characteristic of the getter of iron-zirco-
1300346
nlum alloy that does not a~sol~bnitro~enbuta ~ rbsot~er lmpurltiesselectively, particularly deslrable ls a getter of an alloy
consisting of from 22 to 25h by~weight of lron and from 75 to
78% by weight of zirconlum.
The getter o~ such an iron-zlrcon~um alloy ls substantlally
a non-adsorbent for nitrogen but practically completely adsorb
and remove impurities such as carbon dioxide, moisture, and
hydrogen at a temperature between 20 and 500C.
The iron-zirconium composition is deslred to range from
15 to 30% by weight of iron and 85 to 70% by weight of zirco-
nium. At higher percentage zirconlum contents the alloy starts
to sorb significant amounts of nitrogen! the gas which is
re~uired to be purified and not sorbed, whereas at lower per-
centage zirconium contents the efficiency of removal (sorption)
of active gases from the nitrogen is considerably reduced.
It is desirable that the getter alloy be used in the form
of an intermetallic compound7 which is readily pulverized and
can be handled with ease. ~loreover, the increased surface area
renders the powdered material more active.
The process for the preparation of such an alloy may gene-
rally conform to the procedure described in U.S. Patent Specifi-
cation No. 4,312,669 that teaches the manufacture of a ternary
iron-zirconium-vanadium alloy. Following practically the same
procedure but omitting the addition of vanadium, a desired alloy
can be made. Commercially available products, made and sold
13003~6
by SA~S Getters S.p.A. of ~llan, Italy, are approprlate for
this use.
The bLnary alloy getter is packed in at least one bed zone
provided midwzy ln a gas flow passage connecting an inlet for
iMpure nitrogen gas and an oulet for purlfied nitrogen gas of
an outer shell. The 8etter bed comblnes with a heater rneans
associated with the outer shell for maintaining tha getter at
its adsorption reaction temperature to constitute the essential
parts of the nltrogen superpurifler accordlng to the invention.
Mi~rogen to be purified is passed through thls superpurifier
so that its impure contents are brought into contact w~th the
getter and are removed by adsorption.
The getter to be packed ln the chæmber ta~es ~he form o~
pelle~s in preference to fine ~articles since the former are
easier to provlde sufficient interstices therebetween for the
gas flow. Also, the getter as pellets of uniform size rather
than small lumps irregular in size renders it easy to maintain
a constant void ratio in the getter ~ed, to design the appara-
tus, and to reproduce the good performance. Thus, whlle the
getter in the forrn of fine particles or small lumps ls noC
obJectionaole, the use of pelle~lzed gectar, compression molded
of the alloy powder, is preferred as it better meets the re-
qui~ements for industrial designlng and manuracture of the
nitrogen gas superpurlfier.
The heater means ~o be incorporated in the apparatus of
~300346
the invention to keep the getter hot enough for the adsorption
reaction may take varied forms as will be explained later in
connection with preferred embodiments of the invention. The
heating method may be electric heating or indirect heating by the
use of a heating medium circulated through a double-wall
structure or the like. Also, the heating zone may be suitably
chosen, for example, in the gas preheating region upstream of the
getter bed or chamber, or around or inside the getter mass.
Since it is desirable that sufficient heating be done to effect
a smooth adsorption reaction of the getter with the gas and
produce as uniform a temperature distribution as feasible, the
combination of the heating method and zone may be varied,
according to the necessity, to best attain the end.
While it is possible that the getter chamber in the
apparatus of the invention be provided inside the outer shell,
as directly packed in the latter, a preferred arrangement is such
that the getter bed consists of at least one cartridge packed
with the getter material and which is adapted to be fitted in the
outer shell detachably for ease of replacement. The getter
components according to this invention adsorb and remove
impurities from impure nitrogen by chemical adsorption that
involves chemical changes. They therefore are consumed
stoichiometrically and have a limited life. After service for
a predetermined period the getter must be replaced by fresh one;
otherwise the purpose of superpurifying nitrogen will no longer
~ .
13~34~
be achleved. To this end the superpurlfier lncludlng the outer
shell packed wlth the 8etter may be handled as a slngle unlt
and replaced as such from time to tlme~ It is also possible
to fill up the getter in a cartrldge lnstead and dlsmount the
cartridge from the outer shell for replacement at proper lnter-
vals of time.
The cartridge desirably employs a metal case so perforated
as to facilitate the gas flow.
Because the superpurifier of the inventlon is intended to
purify nitrogen until the concentrations of its ingredients
as impurities zre reduced to about 0.01 ppm or less each, it
is advisable that the inner wall portion of the apparatus with
which nitrogen gas ccmes in contact be made of a metal polished
on the surface to be close-grained and smooth enough to minimize
gas adsorption and which does not form powder due to corrosion.
Such metzls include, for ex~ple, but are not limited to,
stalnless steels, ~lastelloy, ~ncoloy, and l~onel metal. Any
other metal material which satisfies the above requiremen~s
may be su1tably chosen and used.
~ .~ sta~ed above, the inner wall material o~ the apparatus
that contacts the nitrogen gas is desired to have a densely
and smoothly polished surface to minimize gas adsorption. The
desirable degree of s,noothness of the polished surface is
numerically defined to be such that the roughness of the inner
wall surface to contact nitrogen gas is 0.5 ~m or less, polyme~
.
:
130034~i
0.25/lm or less in terms o~ the centerline average height
tRa) ~Japanese Indu~trial Standard (JIS) B 0601-1970]. This
numerical range i9 not alwayq critical but i3 recommended as
a dependable, safe range.
Although the polished inner wall material is advantageously
used in the zone whe-e the gas flowing out of the cartridge
ch?mber comes in contact, it is, of course, possible to use
it also in the zone where the $as passing throug~ the cartridge
contacts. In many cases it is rather inconvenient to use
the polished material only in the zone where the gas that
has flowed past the cartridge contacts. The surface polishing
and baking will marlfiedly shorten the time period required
before h~ghly-purified gas begins to be obtained at a constant
rate, even from a new apparatus.
In the appa-atus of the present invention the means for
solving the technical problem before iS can be ~ariously
embodied as suggested above. Thus it is to be understood
that the invention is not limited to the specific embodiments
thereof BO far described but various modifications may be
ma~e without departing from the spirit and scope af the
invention.
In the process of the invention it is essential that the
nitrogen gas to be purified be passed through the bed of
a metal-oxide oxidation catalyst at its oxidation reaction
temperature. This is because the lack of adsorbability of
;.
g
,
- 13003~;
the getter used in the in~ention with re~pect to methane
and other hydrocarbon~ by converting the hydrocarbons and
carbon monoxide contained in the nitrogen gas into ~ater
and carbon dioxide and removing most of them by adsorption
by passage through 2n adsorbent bed of zeolite molecular
sieve or the like.
~ he nitrogen gas puri-ied to low impurity contents by
the ~nown purification process is passed through a getter
bed pacXed with a getter of an alloy consisting of from 15
to 30~ by weight of iron and from 8~ to 70~ by weight of
zirconiu~ and maintained at a temperature in the range of
to ~00 C, so that the impurities contained in the nitrogen
are ad30rbed away. If the re~ction temperature at which
the impurities are removed
-- 1.0
.
1300346
by adsorption from the nltrogen gas in the getter bed ls below
20C, t~e impurities are adsorbed by the getter surface but
cannot be expected to dlffuse lnto the getter mass, Thus the
adsorptlon practlcally comes to an end ln the state of satura-
tion on the surface, wlthout fully making use of the getter
capacity. In the specifled range of 20 to 500C the getter
performs adsorption to the full, allowing the impuritles to
diffuse thorou~hly therein. The apparent life of the getter
is accordlngly extended.
On the other har.d, in the temperature region above 500C,
nitrogen g~s is easily adsorbed by the getter. Setting a reac-
tion temperature in excess of S00C is therefore undeslrable.
Within the specified tempe-ature r~nge o.' 20 to 500C,
a narrower range of 350 lo 450C is most pre~^rred. A tempera-
tu-e in the latter range is the most recommendable reaction
temperature in that it assures a hi8h adsorption rate and
thorougn diffusion of the impurities in~o the bed of getter
wlth no possibillty of hydrogen desorption.
tEmbodlments,
The present invention will no-~ be described in more detail
be~ow in connection with embodiments thereof.
Nitrogen super,ourlflers embodying the lnvention are lllus-
trated in Figs. 1 through 9. Fig. 1 shows a nitrogen super-
purifier comprising: an outer shell 3 made of a stainless steel
tube (grade SUS 304 TP conforming to Japanese Industrial Stan~-
1300346
ard JIS G 3448) which has a nitrogen inlet 1 formed near the topand a nitrogen outlet 2 near the bottom, the shell being covered
with a heat insulator 12 all over the surface; a top cover 14
fitted to the top of the outer shell 3; a heater 6 inserted
through the top cover 14 into the space 25 inside the shell; a
bed of getter 4 packed in the space defined below the heater 6
between upper and lower buffers 16, 15; and a perforated plate
7 held by a support 13 which in turn is secured to the inner wall
of the outer shell and is supporting the bed as well as the
perforated plate. The getter used was an iron (22-25 wt%)-
zirconium (75-78%) alloy getter manùfactured and marketed by SAES
Getters S.p.A., in the form of columnar pellets having a diameter
of 3 mm and height of 4 mm.
The buffers, indicated at 15, 16, consist of a layer each
of small alumina spheres 4 mm in diameter packed up to a height
of about 5 cm. They correct any ununiform flow af the gas
through the getter bed, keep the fine particles of the getter
from scattering, and uniformalize the temperature distribution.
While the embodiment being described uses small alumina
spheres in forming the buffers, small stainless steel balls or
a stack of fine-mesh stainless steel screens may be employed
instead. Also, the buffers are not always used, and a buffer-
less embodiment will be described later.
In the upper portions of the buffers 15, 16 are embedded
sheathes 20, 19 accommodating thermometers 18, 17, respectively.
~300346
Chromel* and Alumel* thermocouples are used as the thermometers.
Nitrogen gas g to be purifled is introduced into the vessel
at the inlet 1, heated by the heater 6, passes through the upper
buffer 16 and thence, as a uniform flow, through the bed of
getter 4 where it is freed from impure gas contents by
adsorption. The purified gas is led through the perforated plate
7 and taken out of the vessel at the outlet 2.
Fig. 2 and following figures show other embodiments of the
invention. Throughout these figures like parts are designated
by like numerals and the description is omitted or minimized
each.
Fig. 2 shows a superpurifier of the same construction as the
embodiment in Fig. 1 excepting that an electric heater 21 is
coiled round the outer shell 3 and a thermocouple 22 is installed
to measure the heater temperature. This modification facilitates
the temperature control of the getter bed.
Although Figs. 1 and 2 illustrate the embodiments in which
the bed of getter 4 is directly packed in the outer shell 3, the
getter bed may be separately provided as well. Fig. 3 shows an
arrangement of cartridge 5 where the getter 4 and buffers 15, 16
ars accommodated in a cylinder equipped with perforated plates
7 at both ends. After service for a given period, the cartridge
S may be taken out by removing the top cover 14 and replaced by
a new one. This permits more efficient operation than with the
arrangements of Figs. 1 and 2.
Trade-marks
- 13 -
1300~46
Fi8. 4 shcws another embodiment 11, ln whlch the outer shell
3 is of a double-wall construction, conslsting of an inner wall
24 and an outer wall 23. The space between the walls provides
a passage through which a heating medium such as steam flows
from a heating medlum inlet 30 to an outlet 31. In the space
d-fined ~y the inner wall is accommodated a cartrid~e 5 contain-
ing a getter 4, with a coil of electric heater 6 embedded ln
the gette~. The heater 6 is connected to an exte,rnal power
source not shown throug~ lea~s 8 (only one OL them being shown)
and a terminal assembly 10. The cartridge 5 has inner and outer
porous w~lls 26 concen~rically held in spaced relatlon by a
support 13. The inner wall 24 of the outer shell is abutted
at its lower end against a bottom pla'e with a flange 27,
through which a gas inlet pipe 1 and an outlet pipe 2 extend.
The pipe 2 serves also to support the ca~tri ~é 5. Nitrogen
gas 9 to be purified is fed through the inlet 1 into the outer
space 25, heated there to a proper temperature, and thence
forced through the porous wall 26 into the getter layer 4 for
purlrlcation. The purified gas flows out into the inner space
25' and 1s taken out via the outlet 2.
Fig. S shows still another embodiment of superpurifier 11.
The oute- shell 3 is again of double-wall construction, with
a space rormed therein to circulate a heating medium lntroduced
at an inlet 30 and d~scharged at an outlet 31 to perform tem-
perature control. Inslde the inner wall is disposed a cartridge
.
.
1300346
5 packed with a getter 4 between porous walls. On both sldes
o~ the cartridge are arran8ed heaters 6 whlch are connected
to external pcwer sources through leads 8. Impure nltrogen
gas 9 is fed at an inlet 1, preheated by the heating med~um,
puri~ied by passage through the getter mass 4 kept at a given
temperature by the heaters 6, and then taken out at an outlet 2.
Yet another embodiment of superpurifier 11 is shown in Flg.
6. A cylindrical outer shell 3 supports a cartridge 5 by means
of upper and lower plates (not shown). ~he cartridge S com-
prises a built-in electric heater 6 with leads 8 and a mass
of getter 4 filled in the space between upper and lower per-
forated plates or bu~fer layers, with the heater embedded there-
in.
Fig. 7 shows another apparatus 11 embodying the invention.
An inner cylinder is provided inside an outer shell 3 which
consists of inne- and outer walls and a heat insulator 12
fllling up the sp-ace between the walls. A getter 4 is packed
in ~he space bet~een the inner cyllnder and the outer shell,
and an electrLc heater 6 coiled round a ceramic rod 36 is
inserted into the central space in the inner cylinder. Nitrogen
gas 9 to be purified enters ~he vessel at an inlet 1, passes
through the getter 4, and the purified gas leaves the vessel
at an outlet 2.
Fig. 8 shows another embodiment, which is a modification
of the superpurifier illustrated in Fig. 3 and is characterized
-- 15 --
1300~46
by means for recoverlng the heac of purlfled nltrogen. Nltrogen
9 ~o be purified enters a heat exchanger 28 lnstalled under
the purifier body, undergoes heat exchange with the outgolng
gas, and the gas so preheated moves through a plpe 29 surrounded
by a heat insulator 12 and through an upper inlet 1 lnto a bed
of getter 4. The purified gas is cooled in the h~at exchanger
and leaves tne purifier at an outlet 2.
FLg. 9 shows a further embodiment. The outer shell ~ is
a double-wall cylinder, and a heatlng medium is introduced into
the space between the walls a~ an inlet 33 and is discharged
at an outlet 34. Inside the outer shell 3 is disposed a gas-
tight cartridge 35. The space in the cartridge case ls partl-
tioned horizontally with a plurality of perforated plates 7,
and a plurality of getter beds 4 are formed, each filling up
the space formed by every other pair of the perforated plates.
The getter beds have electrlc heaters 6 embedded therein, one
for eacn, and supplied with electricity through leads 37, 38.
Nltrogen gas 9 to be purlf~ed flows in at an inlet 1 and the
purlfled gas flows out at an outlet 2.
Examples of the invention whlch used a specific getter
composltlon w111 now be explalned.
The lnstrumen~s used for gas analyses in the examples were
as follows:
Gas analysis instrument:
Gas chromatograph-mass spectrometer, Model TE-360B
16
1300346
(mf~. by Anelva Corp.)
Gas chromatograph-F.I.D., Model GC-9A
(m~d. by Shimadzu Selsakusho, Ltd.)
Moisture mecer:
Hygrometer, Model 700
- (mfd. by Panametric Co.)
Sur~ace roughness meter:
Surfcorder, Model CE-3Y.
(mfc. by Xos~ka Laboratory Co., Ltd.)
Examole l
A powder-d non-evaporable getter alloy having a weight com-
position o~ 70.6% zirconium and 2~.4h iron and a particle si3e
of between 50 and 250 ~m were placed in the superpurifier for
nitrogen shown in Fig. l. The stalnless steel (trade designa-
tion, CUS 304) cylinder had an outside diameter of 21.7 mm and
an inside diameter of 17.5 mm, its length belng 350 mm. The
length of cyllnder occupied by the getter material was 200 mm,
and the heights of the upper and lower buffers of alumina
spheres were 5 cm each. Impure nltrogen gas was introduced
into the superpurifier at a temperature Or 26c and a pressure
of 6 kg/cm2 ~gauge) at a flow rate of 0.17 ~/min. The nitrogen
flowed through the getter bed held at 375C and issued at a
pressure of 4 kg/cm2 (gauge) from the outlet. Its impurlty
level was measured for various gases 40 minutes after the start
of the flow of the gas. The results of Table I were obtalned.
.
~ ~7 ~
,
.
.
.
1300346
~able
Im- Inlet impurity Outlet lmpurlty
purity level (ppm) level (ppm)
2 0'4 0.006
CH4 O.Ol 0.01
CO 0.0~ 0.008
C2 0 04 0.007
H20 3.0 no trace
The level cf impurities in the outlet g-s remained cons~ant
for 1030 hours.
~xamDle 2
Pellets were produced having a diame~er of 3 mm and height
of 4 mm by compressing and pelletizing a non-evaporable getter
alloy having a composition and particle size identical to those
of the getter alloy of Example 1. The pellets were loaded into
the superpurifier sAown in Fig. 2. The stainless steel ~SUS
304) cylinder had an outer diameter of 89.1 mm and an inner
diameter of 83.1 mm. Its length was 660 mm. The length of
the cylinder occupied b~ the pellets of getter material,
including the thicknesses of the upper and lower buffers (of
alumina spheres) each having a bed height of S cm, was 18S mm.
Impure nitrogen was inlroduced into the superpurifier at a
temperature of 25C and a pressure of 4 kg/cm2 (gauge) at a
flow rate of 12 l/min.
, ~ 18 ~
i300~46
The lmpure nltrogen flowed through the non-evaporable 8etter
bed held at a temperature of 375~C by means o~ a spiral resist-
ance heater and lssued at a pressure of 3.95 kg/cm2 (gauge) ,
from the outlet. Its lmpurity level was measured for various
gases 40 minutes after the start of the flow of nitrogen. The
results obtained were as shown in Table II.
Table II
..... _
Im- Inlet impurity Outlet impurity
purit-~ level (pDm) lQvel (ppm)
2 11.29 0.006
CH4 0.01 0.01
CO 8.8 0.008
C2 8.3 0.007
H20 5.0 no trace
.
The level of the impurities in the outlet gas remaine8
constant for ~60 hours.
Exam~le 3
Pellets were produced exactly as ln Example 2 and place8
in the cartridge shown in Fig. 3. The cartridge had an outside
dlameter of 80 mm, an inside diameter of 78 mm, and length of
244 mm. The same mass of pellets was used as in Example 2.
The cartridge was then placed in a cylinder identical to that
of Example 2 (except that its iength was 719 mm). Impure
nitrogen was caused to flow through the superpurifier at the
1300346
same inlet pressure, temperature, and flow rate as descrlbed
in Example 2. The cartrLdge was maintalned at 375~C. The
outlet gas pressure and composition were found to be ldentical
to those found in Ex~nple 2 at the point 40 minutes after the
start of the flow of nitrogen. The level of the lmpurltles
ln the outlet gas aga~n remained constant for 760 hours.
Examole 4 ~
In this e.Yo^mple the procedure of Example 2 was followed
in all respects except that the inner surface roughness of the
cylinder was Ra = 0 5 ~m (normally ~a = ~ m) and the stain-
less st-el outlet piping had an outslde diameter 9.5 mm, inside
diameter 7.5 mm, and an inner surface roughness of Ra = 0.2 ~m.
The results shown in Table III were obtained 40 minutes after
the start of the flow of nitrogen.
Table III
Im- Inlet impurity Outlet impurity
purity level (pom) level (pom)
2 11.29 0.003
CH4 0.01 0.01
CO 8.~ 0.008
C2 8.3 0.003
H20 5.0 no trace
The level of the impurlties ln the outlet gas remained
constant for 160 hours.
_ 20 -
~300346
Example 5
In this example nitrogen gas to be purifled was flrst paSsed
through a stainless steel (SUS 304) cyllnder having an outside
diameter of 89;1 mm, inside diameter of 83.1 mm, and length
of 660 mm fllled to a bed height of 185 mm wlth pelletq ~3 mm
in diameter and 4 mm in length) and maintained at a temperature
of 450C. Then, the water vapor content of the nitrogen gas
to be purified was reduced by passing it through a dryer con-
sisting of a stainless steel (SUS 301) cylinder having an out-
side diameter of 89.1 mm, inside diameter of~83.1 mm, and }ength
of 660 mm filled to a bed height of 200 mm with a molecular
sieve typé 5-A, the pellet size being 3.2 mm across and 24 mm
long. This gas was treated by the procedure of Example 2.
The outlet pressure from the dryer bed and therefore the inlet
pressure to the superpurl~ier was 4 kg/cm2 (gauge); The temper-
ature was varied to see the effects of dlfferent getter temper-
atures. The results are given in Table IV.
- .
.
- .21 -
'
.
1300346
Table IV
Outlet impurity level tppm)
Inlet impurity at temperature
level (~pm~ 20C 250C 375C500C
2 11 . 29 0.006 0.006 0.006 0.004
CH~ 3.7 o.oos o.oo9 0.009 o.009
CO 8.8 0.008 0.008 0.008 0.004
Co2 8.3 0.007 0.007 0.007 0.004
H2O 5.0 no trace no trace no trace no trace
Outlet gas
remained 21 hr 1050 hr 2330 hr 2390 hr
constant for
Power 0 0.61 kW/h 1.1 kW/h1.7 kW/h
consumption
of getter cyl.
The table indicates that the getter of the invention
exhibits excellent purification capability in the temperature
range of 20~500C.
ples 6 and 7
Pellets were produced having a diameter of 3 mm and a length
of 4 mm by compre~sion of non-evaporable getter powders
conBisting of an alloy of Zr 84% and 16% by weight (Example 6~
and an alloy of Zr 71% and Fe 29% by weight (Example 7) and
having particle ~izes of 50 - 250 ~m (150 ~m in average). These
pellete were loaded into a superpurifier having the same
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. : ,
. .
.,.
1300346
constructlon in the samc manner as Example 2. Nltrogen ~a~
containlng impurities was 1ntroduced lnto the superpurifler
at a temperature Or 25 C, pre~sure of 4 Xg/cm2 (gau~) and
a flow rate of 12 }/mln.
The impurity-consisting nitrogen gas wa~ passed through
the bed of the non-evaporable getter kept at a temperature
of 375 C by means of a spiral re istance heater and emerged
from the outlet at a pressure of 3.95 Xg/cm2 (gzuge).. The
lmpurity level waq mea~ured 40 min after the start of the
flow of the nitrogen gas and the results in Tab}e Y were
obtained. . c
Table V
.
GasInlet impurity Outlet impurity
(ppm) Ex. 6 E~. 7
(ppm) (ppm)
2 11.~9 0.003 0.01
CH4 0.01 0.01 O.Ql
CO 8.8 0.005 o.oog
C2 8.3 0.005 0.01
~2 5.0 no trace no trace
The outlet impurity levels were con~tant for 960 hr3 and 690
hrs, respectively.
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