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Патент USA US3085389

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April 16, 1963
KAzUO KlYoNAGA ET AL
3,085,379
PURIFICATION oF LIGHT GASES WITH MOLECULAR sIEvEs
Filed March 9, 1960
KAZUO KIYONAGA
MARVIN L. SUVAL
llnited States Patent O
3,085,379
ICC
Patented Apr. 16, 1963
2
l
PURIFICATIÜN 0F LIGHT GASES
3,085,379
r e”
vention will be apparent from the ensuing description and
accompanying drawing.
H
The novel ‘process employs fixed beds of adsorbent in
MOLECULAR SIEVES
two chambers so that the temperature and/ or pressure is
changed as a particular chamber is switched ¿from an ad~
poration, a corporation of New York
sorption stroke to a desorption stroke.
An important feature of the present process is the re
cycling of at least a por-tion of the desorbate gas stream
Kazuo Kiyonaga, Buffalo, NX., and Marvin L. Suval,
North Bergen, NJ., assignors to Union Carbide Cor
Filed Mar. 9, 1960, Ser. No. 13,859
18 Claims. (Cl. 55-23)
to an incoming fresh gas stream containing low concen
of impurities. In this manner, `an impurities
This invention relates to an irn‘proved process for sepa# 1 0 trations
containing feed gas stream is formed which is passed
rating a minor amount of impurities from a gas stream
and more particularly to an improved process for adsorb
ing impurities from a gas stream as, for example, remov
ing air traces from a helium feed gas.
The use of selective adsorbents to separate mixtures of
ñuids is known.
'Zeolitic molecular sieves have more `
recently been used for this type of separation. These
zeolitic molecular sieves are especially useful when purify
ing gas streams containing impurities which are more
strongly adsorbed than the desired gas components.
According to the prior art using zeolitic molecular sieves
as the selective adsorbent, the incoming gas stream con
taining low concentrations of impurities is ’passed through
a bed of zeolitic molecular sieves thereby adsorbing the
and obtaining a purified product gas. These 2
impurities
prior art methods provide for the zeolitic molecular sieve
bed to be desorbed in a manner such that the desorbate
-through the selective »adsorbent during the adsorption
stroke. The recycled desorbate gas stream «contains a
greater concentration of impurities than the incoming
fresh gas stream and therefor increases the percentage of
impurities entering the selective adsorbent bed as the
impurities-containing feed gas stream. This results in a
higher loading of the impurity on the adsorbent. Con
sequently, the desorption stream, a part of which is vented
off as the impurity stream, has a higher concentration of
the impure components and a lower concentration of the
product gas. Any product gas contained in the recycled
portion of the desorbate stream is available for further
recovery in the adsorption stroke. Product gas in the
desorbate stream is primarily due to entrapment in the
-voids during the adsorption stroke. By thus raising Ilthe
concentration of the impurity in the vented gas, the ‘pro
portion of product gas thus vented can be controlled to
gas stream is completely discarded. Although the puri
low levels. This results in a higher percentage recovery
fied product gas can be obtained by these prior art sys 30
of purified product gas.
tems with little or no impurities remaining after the ad
Certain adsorbents which selectivity adsorb molecules
sorption stroke, the discarded desorbate gas stream will
on the basis of size and shape of the adsorbate molecule
Äalways contain a quantity of the product gas as well as
the impurities.
Depending upon the nature and concentration of the
impure component involved, the temperature and pres
are referred to as molecular sieves.
Zeolites are metal
alumino-silicates which exist in crystalline form. -Only
the Zeolites having the basic formula:
M2 OzAliOazXSiOztYHzO
sure at which adsorption is conducted, and the volume of
free spaces provided in the adsorbent, the amount of
11
desired gas entrapped with the impurity during adsorption
can vary from a negligible to a considerable fraction of
where M represents a metal cation and n its valence, are
the total quantity being processed. When removing low
concentrations of impurities that are only slightly ad
termed zeolitic molecular sieves. In general, la partic
ular crystalline zeolite will have values for X and Y that
sorbable on zeolitic molecular sieve materials at normal
temperatures and pressures, it often becomes necessary to
operate at high pressures and/ or low temperatures to eñect
fall within a definite range.
The fundamental “building block” of any zeolite crys
the desi-red puriiications with satisfactory yields of prod
tal is a tetrahedron of Áfour oxygen ions surrounding a
smaller silicon or aluminum ion. Each of the oxygen
uct gas. The loss of. Vthe gas being puriñed in the desor
bate gas stream may be considerable under such operating
positive charges', each aluminum ion, three. A silicon
ions has two negative charges; each silicon ion has four
thus takes on a “half-interest” in the eight charges of the
One method of reducing the loss of the gas being puri 50 four oxygens which surround it. Each oxygen retains
one negative charge which enables it to combine with an
fied. is to carry out additional selective -adsorption separa
other silicon or aluminum ion and extend the crystal lat
tions on the impurity or desorbate gas stream. Each
tice in all directions. The aluminum ion, with one less
additional separation, of course, requires a complete
positive charge than the silicon, can only satisfy .three
adsorption-desorption system with all the necessary com 55 negative charges of the four oxygens which surround it.
ponents such as adsorbent-filled chambers, valves, pumps,
To produce a stable crystal structure it must have the
controls, and the like. It will be apparent that such a
help of another positively charged ion. This is the func
system would be excessively expensive to construct and
tion of the metal cation “M.”
The structure of] most crystals extends uniformly in
operate.
‘
IOne object of the present invention is to provide an
all directions without leaving empty spaces. In zeolitic
improved process for removing low concentrations of
molecular sieves, however, the framework of silicon
conditions and can make such a process uneconomical.
impurities from »a gas stream which will yield a high re
oxygen and aluminum-oxygen tetrahedra forms a struc
covery of purified gas.
Another object of this invention is to provide an im
ture which is honeycombed with relatively large cavities
which are normally filled wtih Water molecules. The
proved ‘process for removing low concentrations of im~ 65 size and shape of these cavities depends on the variety of
the zeolite.
The zeolitic molecular sieves as described above may be
activated by heating to effect the loss of the water of hy
purities from a gas stream under economical pressure and
temperature opera-ting conditions.
A further object of this invention is to provide a process
for removing low concentrations of impurities from a gas
stream which will yield a high recovery of, purified gas
without the use of multiple contacting stages.
Still further objects and advantages of the present in
0
dration. The dehydration results in crystals interlaced
with channels of molecular dimensions that offer very high
surface areas for the adsorption of foreign particles.
Adsorption is limited to molecules having size and
3,085,379
4
shape such as to permit entrance through the pores which
connect to the inner sorption areas or cavities, =all other
Erionite, a naturally occurring zeolite which has a pore
size of about 5 A.
Synthetic zeolite R which has a pore size of about 4 A.,
is described and claimed in U.S. Patent No. 3,030,181,
molecules being excluded. _ The pore size can be varied
within limits, by replacement, in part or entirely, of the
metal cations “M” with smaller` or larger cations. Such 5 issued April 17, 196,2.
ion-exchange is accomplished by conventional ion
Synthetic zeolite D which is described -in U.S. patent
exchange techniques.
The zeolitie molecular sieves contemplated herein ex
hibit adsorptive properties that are unique among known
adsorbents which make them a preferred selective adsorb
ent for` this invention. The common adsorbents, as for
application Serial No. 680,383 filed August 26, 1957, in
the names of D. W. Breek and N. A. Acara which has a
pore size of about 4 A.
10
Synthetic zeolite L which is described in U.S. patent
application Serial No. 711,5 65 tiled January 28, 1958,
example, charcoal and silica gel, exhibit adsorption selec
now abandoned, in the names of D. W. Breek and N. A.
Acara which has a pore -size of about 10i A.
Synthetic zeolite Y which is described in U.S. patent
tivities -based primarily on the boiling point or critical tem
perature of the adsorbate. Activated zeolitic molecular
sieves on the other hand exhibit a selectivity based on the 15
application Serial No. 109,487, filed May 19, 1961, in the
name of D. W. Breek, which has a pore size of about 10 A.
adsorbate molecules whose size and shape are such as to
Y Synthetic zeolite T which has a pore size of about 5 A.,
permit adsorption by zeolitic molecular sieves, a very
size and shape of the adsorbate molecule. Among those
strong preference is exhibited toward those that are polar,
polarizable, or unsaturated.
Another property of zeo
litic molecular sieves that contributes to its novel position
among adsorbents `is that of adsorbing large quantities of
adsorbate either at very low pressures, at very low partial
pressures, or at very low concentrations.
One or a corn
ZU
is described and claimed in U.S. Patent No. 2,950,952,
issued August 30, 1960.
»Synthetic zeolite X which is described in U.S. Patent
No. 2,882,244 issued April 14, 1959, which has a pore
size of about 10 A.
Referring now more specifically to the drawing, the irn
bination'of one or more of these three particular adsorp 25 purities-containing feed gas stream is directed through con
duit 11 to the compressor 5t). After being compressed, the
tion characteristics or others make zeolitic molecular
impurities-containing feed gas stream is preferably di
sieves useful for numerous gas or liquid separation proc
rected through conduit 12 to the passageway 40 of heat
esses where adsorbents are not now employed. The use
exchanger 51 and thence through conduit 13 to cooler 52
of zeolitic molecular sieves permits more efiicient and
more economical operation of numerous processes now 30 where it is further cooled. Switching valve 81 in conduit
15 i-s open allowing the compressed and cooled impurities
employing other adsorbents.
containing feed gas stream coming from conduit 14 to be
. Z-eolite A, a zeolitic molecular sieve, is described in U.S‘.
directed through conduit 15 into the first selective adsorb
ent bed S3'. In passing through the first selective adsorb
from helium or methane from hydrogen. The general 35 ent bed 53, the feed gas stream has adsorbed within the
adsorbent its impurities as well `as a quantity of entrapped
formula for zeolite A is written as follows:
product gas. The gas stream ílowing out of the adsorbent
1.0:I:0.2M 2 O : A1203: 1.85:!:0.5SiOn:YH20
bed 53 into conduit y22. is a substantially purified product
11
gas stream. Switching valve 82 in conduit 23` is open
In this formula M is a metal cation, n is its valence, and 40 allowing the purified product gas stream to pass from con
Patent No. 2,882,243, _issued April 14, 1959, and `is the
preferred selective adsorbent for the separation of air
Y may be any value up to 6 depending on the identity of
duit 22 through conduit 23 and thence to conduit 24.
the metal and lthe degree of dehydration of the crystals.
ÄAs already discussed, the pore `size of a particular
crystalline zeolite is determined by the metal cation M
that it contains. Both the air from helium and methane
from hydrogen separations require a zeolitic molecular
Conduit 24 directs the purified product gas stream through
passageways 41 and 42 of heat-exchanger 51 where its
refrigeration is recovered. The purified product gas is
then directed through conduit `25 to product storage.
After the adsorption stroke, valve 85 located in conduit
17 is opened with switching valves 83, 84, 88 and valves
89 and 90* located respectively in conduits ‘16, 23, 21 and
»sieve >having a pore size of at least 4 angstrom units. It
has been discovered, however, that in the air from helium
30 and 29 closed. This equalizes the pressure in the two
separation a zeolitic molecular sieve having a pore size
of at least 5 angstrom units is the preferred adsorbent 50 selective adsorbent beds 53 and 5‘4. After the pressure is
equalized in the two beds, valve 85- in conduit 17 is closed
because of the greater rate of adsorptionV of air by sieves
and switching valves 81 and 82 located in conduits 15 and
having pore sizes of at least 5 angstrom units from those
23, respectively, are closed. Switching valve 83- in con
of about 4 angstrom units. Sodium zeolite A (zeolite A
duit 16 is simultaneously opened thereby directing the
having sodium as the metal cation) is the preferred selec
tive adsorbent for the methane from hydrogen separation 55 feed gas stream in conduit 14 through conduit 16 into
the second selective adsorbent bed 54. Switching Valve 84
because of its pore size of about 4 angstrom units. Ion
in conduit is open allowing the product gas stream to
exchanging at least 40' percent of the sodium of zeolite A
pass through conduits 21, 23 and 24 and thence through
passageway/s 41 and 42 of heat-exchange 51 and conduit
25 to product storage.
about 5 angstrom units.
60
While the impurities-containing feed gas stream is pass
Zeolitic molecular sieves having pore sizes which make
ing through the second selective adsorbent bed 54, switch
them suitable for use in the process of this invention in
clude the following:
ing valve 86 in conduit 22. and control valves 89 and 90
in conduits 30 and 29’, respectively are opened to regulate
`Monovalent cation forms of zeolite A, excepting the
potassium form which has a pore size of about 3 A., »which 65 the desorption of the loaded or adsorbed impurities and
have a pore size of about 4 A.
entrapped product gas contained in the ñrst selective ad
sorbent bed 53. The vacuum pump `5S now operates so as
Zeolite A, in which at least about 40 percent of the
to depressurize the adsorbent bed 53 and desorb the im
monovalent cation sites are satisfied with di or trivalent
purities and entrap-ped gas molecules by drawing a de
metal cations, which has a pore size of about 5 A.
Both the natural and the synthetic forms of mordenite 70 sorbate gas stream through the adsorbent bed 53 and
conduits 22, 27 28 and 29. Valve 89 is open to allow a
which have a pore size of about 4 A. and the hydrogen
portion of the desorbate gas stream to be discarded
ion-exchanged form of mordenite which has a pore size of
through conduit 38. The remaining desorbate gas stream
about 5 A.
-is ydirected through conduit 29 and control valve 90 there
Chabazite, a naturally occurring zeolite, which has a
pore size of about 4 A.
75 in for mixing Iwith the incoming fresh gas stream contain
ing low concentrations of impurities from conduit 10 so
with calcium provides the preferred selective adsorbent
for the air from helium separation since its pore size is
3,085,379
as to lform the impurities-containing :feed gas stream ñow
ing through conduit 11.
6
economics of producing the desired puriiication tempera
ture, with the gain in adsorptive capacity.
p
Z1 are substituted for switching valves 81, 82 and 86 and
The selection of the desorption -stroke pressure is more
critical as `it determines the purity of the gaseous product
produced. The requirement is that at the end of the
conduitsl 15, and 22, respectively.
left on the adsorbent must be such that upon switching
'I'he cycle is repeated for the second selective adsorbent
but switching valves 83, 84, and S8 and conduits 16, and
desorption stroke, the partial pressure of the impurities
Instead of continually discarding a portion of the de
sorbate gas stream through conduit 30 and valve S9 dur
ing the entire desorption stroke, a portion of the desorbate
back to the adsorption stroke the partial pressure of the
impurity divided by the total pressure of adsorption
equals the tolerable impurities mole fraction in the prod
10
gas stream may be discarded at a particular time. rI'he
uct. For example, if a 99.9 percent pure product is re
product gas molecules entrapped in the adsorbent bed
quired and the adsorption stroke pressure is 300 p.s.i.a,
after the adsorption stroke are more easily removed than
then the desorption stroke pressure should be about
the impurities and consequently the initial or first de
sorbate gas stream is somewhat richer in product gas.
During the initial .part of desorption, valve 89 may be 15 (l.00~.999 )(-ïlQ(-)1%-;-60-)=15.5 mm. Hg (absolute)
closed and valve 9i) opened thereby allowing the richer
Thus, desorption is conducted until a residual impurity
product gas íirst desorbate gas stream to be recycled
loading is obtained which corresponds to a partial pres
through conduit 29. During the latter part of the desorp
sure of about 15.5 mm. Hg at the adsorption tempera
tion stroke, valve 59 is opened and valve 90 'closed there
by passing the impurities rich tail-end desorbate gas 20 ture.
The effects of different adsorption pressures were de
stream through conduit 30 to `be discarded.
termined using the present process `for »the removal of air
In another embodiment, the desorption stroke may be
from helium. The adsorbent used was zeolite A having
accomplished by applying heat to the selective adsorbent
a pore size of 5 angstrom units as described in United
beds `53 and 54 by heat-exchange means through conduits
States Patent No. 2,882,243 issued April 14, 1959. The
31 and 32 embedded in the first and second adsorbent 25 specifications for the helium puriñer require an iniiuent
beds, respectively, at the same time as the pressure is being
or incoming fresh helium gas stream of 600 lb./hr. of
reduced within the adsorbent bed. lIn some instances,
which 1 percent by Volume was air and an efliuent or
heat alone may be used to effect the desorption.
product gas stream of 99.9 percent pure helium. Listed
Heat may also be introduced to the adsorbent bed by
in Table A are the required -operating conditions of the
passing a heated purge `gas stream therethrough. During 30 present process for three different pressures.
the desorption stroke, valves 92 or 93 located in conduits
TABLE A
18 and 19, respectively, can be opened, depending on
which adsorbent bed is to be desorbed, thereby allowing
Helium Purifier
a heated purge gas stream to pass consecutively through
conduits 20, 18 or 19 and 15 or 16 and then the adsorbent 35
bed. The heated purge gas stream may be a portion of
Gase
I
the pure product gas stream by opening valve 91 which
directs the gas stream through con-duit 26 to conduit Zd.
Number of Adsorber Beds_____
Adsorption Pressure, p.s.i
A combination of the above embodiments of the inven
Adsorption Temp., ° F
tion is found particularly advantageous in some instances. 40 Desorption Pres., mm. Hg a
Desorption Temperature ___________________ _.
As before, during the desorption stroke, valve 89 is closed
Zeolite A(5 A.) Molecular Sieve required, per
and valve 90 is yopened thereby recycling the richer prod
desor‘bate gas stream through conduit 30 to be discarded.
Simultaneously, valve 92 or 93, depending on which ad
sorbent is being desorbed, is opened `allowing a heated
purge gas stream to pass through the adsorbent bed. This
Helium
45
sorable impurities are present. Traces of moisture or
high boiling or polyinerizable hydrocarbons which'tend
to be accumulated in a zeolitic molecular sieve adsorbent
bed may be efîiciently removed in this manner.
The pressure and temperature of the adsorption and 55
purification problem which is involved and to a certain
extent on the other factors which control the economics
of the operation.
-40
bed, lbs ___________________________________ -_
embodiment is particularly useful when diñicultly de
desorption strokes must be selected on the basis of the
-40
Impurities-containing feed:
uct gas desorbate gas stream. Valve 89 `is then opened
and valve 10 closed allowing the impurities rich tail-end
-40
.
__________ __
Air, iis/ar ..... __
Air, lb. hr
Desorbate Recycle:
Helium, 1b.]hr __________________________ __
Air, 1b. hr ____________ __
Desorbate Vent:
Helium 1b./hr._-__
Air, 110./hr _______ __
__
26. 4
23. 8
22. 4
327. 5
192.0
110. 0
3. 6
5. 4
8. 8
4s. 5
4s. 5
43. 5
Helium recovery, percent
99.4
99. 1
98. 5
Unit length,
17. 0
15. 5
14. 5
Unit diameter, ft. ___
10. 5
9. 5
Unit height, it _____ __
Electric Power, kw _____________________ __
____________ __
9.0
35
9.0
35
8. 5
9. 0
35
1 After reaching this desorption pressure, a small amount'ot puriñed
roduct gas was passed to the bed to sweep out the air remaining in the
ed While maintaining the desorption pressure of 200 mm. Hg abs.
It is at once noticed that as the adsorption pressure in»
The best operation, in the embodiment wherein the de GO creases, the efficiency of recovery decreases. However,
counteracting the increase of eñìciency ¿for lower pres
sorption stroke is carried out in its entirety Without the
sures is the decrease in amount of zeolitic molecular sieve
introduction of heat, is achieved when the adsorption
needed and the decrease in the amount of impurities-con
stroke is conducted at a temperature at least as high as
taining feed gas i.e., incoming fresh gas plus desorbate
the critical temperature of the impurity being adsorbed.
When the desorption is conducted with the addition of 65 recycle, as the «adsorption pressure is increased. As the
amount of impurities-containing feed gas required in
heat, either by indirect means or by the use of a heated
creases, there must be a corresponding «increase in the
purge iiuid, the desorption temperature should be at least
size of the compressor and cooling units of the process.
as high as the critical temperature of the impurity being
The requirements for each individual «application as well
desorbed. ’The reason for the above preference for con
duct of the process above certain critical temperatures 70 as the adsorbent used must dictate the correct pressure for
adsorption to effect the greatest economies. l
is based on the fastest rates of ydesorption attained there
The process is adaptable to «many situations in which
by.
low concentrations of impurities are lto be removed from
The selection of the adsorption stroke temperature and
gases. As Ilong as the impurity is more strongly adsorbed
pressure is ldetermined by comparing the adsorptivity of
than the desired gas constituents, the present invention
75
the adsorbent -for the impurities involved, as well as the
3,085,379
'î
may 4be advantageously employed. The following list of
impurities and gases is typical of the uses to which this`
process can be applied.
ì
(1) Removal of oxygen, nitrogen, argon, krypton, arn-~
monia, water, carbon dioxide, carbon monoxide and hy-~
drogen sulfide from helium and hydrogen.
(2) Removal of hydrocarbon impurities such as meth
8
.
gas stream formed, 94.68 moles/hr. of H2, 39.32 moles/
hr. of CH4, which was now 29 percent by volume CH4
Was compresed to 50 p.s.i.a., then heat-exchanged and
-cooled to 0° C. It was then passed through an adsorbent
'.bed packed with Zeolite A molecular sieve pellets, having
‘a bore size of .about 4 angstrom units. The eñiuent gas
stream of the adsorbent, consisting of 93.3 percent of the
ane, ethane, propane, Ibutane, ethylene, propylene, butyl
ene, yand higher hydrocarbons from hydrogen, helium,
“entering hydrogen, contained 88.40' moles/hr. of pure
hydrogen. This purified hydrogen was heat-exchanged
argon, neon, krypton, oxygen, and nitrogen.
»'With the `en-tering feed gas stream to recover the refrigera
(3) lRemoval of carbon dioxide, hydrogen sulfide, tam
monia, water, sulfur dioxide, from hydrogen, helium,
tion and passed to product storage. IDuring the desorp
tion stroke, the remaining entrapped 6.28 moles/hr. of
tion for removing ílow concentration of impurities from
fdesorbed by depressurizing «the «adsorption lbed using a
nitrogen, argon, neon, krypton, oxygen.
`In the following examples, the advantages of this inven
¿hydrogen :and adsorbed 39.32 moles/ hr. of methane were
`vacuum until a final presure of -about 2.6 mm. -Hg (a-b
helium and hydrogen are shown.
solute) was reached. Alternatively, desorption may be
EXAMPLE 2
»conduted at more moderate vacuums or pressures. How
ever, in this case, when the more moderate desorption
>pressure is reached, a small amount of «purified product gas
air (99 moles/hr. of helium, 1 mole/hr. of air) was com 20 is added to the bed to sweep out the methane remaining in
-the .bed while maintaining .the more moderate desorption
bined with a recycled desorbate gas stream containing
pressure. This is done until a residual yloading of methane
3.93 moles/hr. of helium and 4.42 moles/hr. of air.
`corresponding to a partial pressure of y2.6 mm. Hg at the
This `feed gas stream formed, which was now 5 per
Iadsorption temperature is obtained. The direction of
cent «by volume of lair (102.93 moles/hr. of helium and
5.42 moles/hr. of air), was compressed -to 300l p.s.i.a.„ 25 gas iiow during the desorption -stroke was preferably op
_posite to the flow direction during .the adsorption stroke
then heat-exchanged and cooled to y-40° C. It was
in order to take advantage of the chromatographic ef
then passed through an adsorbent bed packed with zeo
' fect ywhich would occur. A portion of the desorbate gas
lite A molecular sieve pellets having a pore size of about
stream, l0 moles/hr. of CH4, 1.6 moles/hr. of hydrogen
5 angstrom units. The eiiiuent gas stream of the ad
sorbent, consisting of 95.4 percent' of the entering 30 Acontaining the same total quantity of air as was entering
the system in the incoming »fresh hydrogen gas stream was
helium, entering the adsorbentl bed during the adsorp
ven-ted as waste gas and the remaining (4.68 moles/hr. H2
tion stroke contained 98.11 moles/hr. of pure he
29.32 moles/hr. CHQ desorbate gas stream was recycled
lium. This pure helium was heat-exchanged with
to combine with the incoming fresh hydrogen gas stream
the entering feed gas stream to rec-over its refrigera-V
An incoming fresh heliu-rn gas stream flow at the rate
of 100 moles/hr. and containing 1 percent by volume of
- :and the cycle was repeated.
tion and passed to product storage. During the desorp~
tion stroke, the remaining entrapped 4.82 moles/hr. of
To illustrate the advantages of this novel process, as~
sume the same temperature and pressure conditions for
helium `and adsorbed 5.42 moles/ hr. of air were descr-bed
by depressurizing the adsorption bed using a vacuum
treating the incoming fresh hydrogen gas stream of 90
until a final pressure of about 15 mm. Hg (absolute) was
moles/hr. H2 and 10 moles/hr. of methane without a
recycle desonb‘ate gas stream. According to the prior
reached. The direction of gas liow during the desorption
stroke was preferably opposite to the liow direction dur
ing yadsorption in order to take advantage of the chro
-art all the desorbate was discarded. When adsorption is
stopped, the adsorbent bed will contain not only adsorbed
methane, but also hydrogen in the void spaces. For the
conditions given, if complete desorption was achieved by
matographic effect which..would occur.. As an alterna
tive, a higher desorption> stroke pressure'may 'be used, as
for example, 200 mm. Hg. However, in ths case, when 45 total vacuum, every mole of methane desorbed will be
accompanied by approximately 0.6 mole of hydrogen to
the desorption pressure> of'200 mm. Hg is reached a.v
give a 93 percent recovery of purified hydrogen whereas
small amount of purified product 4gas »is added to the bed
the proposed process has a 98+ percent recovery of hy
to sweep lout the air remainingY in .the tbed while main
drogen.
taining the desorption-stroke pressure of 200i mm1. Hg
The process of this ínvetnion may also be employed
(absolute). This is done until a residual loading of air 50
corresponding to -a partialV pressure of 15 mm. Hg at the
to recover, when desired, the adsorbable but low con
adsorption temperature is obtained. This is necessary to
centrations of impurities in higher concentrations than
maintain the desired purity yofthe helium product during
obtainable from conventional adsorption recovery proc
the adsorption strok .
esses.
A portion of the desorbate gasv
stream,- l mole/hr. air, 0.89 mole/hr. helium, containing
55
Although preferred embodiments of this invention
the same total quantity off air as was entering the system
in the incoming fresh helium gas stream was vented as
modifications of the process may be made and that some
waste gas and the remaining (3.83 mole/hr. of helium,
features may be employed Without others, all within the
have been described in detail, it is contemplated that
4.42 moles/ hr. of air) desorbate gas stream was recycled
spirit and scope of the invention.
What is claimed is:
to combine with the incoming fresh helium gas stream 60
and .the cycle was repeated.
’
1. A process for removing low concentrations of im
This process yielded «a helium recovery of at least 99
purities from a gas stream comprising the steps of pro
percent with a purity of practically 100 percent while .the
viding at least two separate zones, each containing a
operation of a single-stroke purification system of the
zeolitic molecular sieve adsorbent bed which has a selec
same incoming fresh gas stream at the same tempera 65 tivity for the impurities over the product component of
ture 4and pressure and using the same molecular sieve ad
said gas stream; providing an impurities-containing feed
sorbent yielded 90 percent of 99 moles/hr. or 89 moles/
gas stream; passing said feed gas stream through a first
hr.of helium which is approximately 90 percent recovery.
EXAMPLE 2
selective adsorbent bed as an adsorption stroke thereby
removing at least most of the impurities from said feed
70 gas stream; discharging a substantially impurities-free
An incoming fresh hydrogen gas stream flow at the rate
product gas stream from said first selective adsorbent
of 100 moles/hrs. and containing 10‘ percent methane (90
bed; simultaneously depressurizing a second selective ad~
moles/hr. of H2, 10 m-oles/hr. of CH4) was combined
sorbent bed as a desorption stroke thereby removing
with ia recycled desorbate gas stream containing 4.68
mole/hr. 'of H2 and 29.32 moles/hr. of CH4. The feed 75. previously deposited impurities and entrapped product
gas in a desorbate gas stream; recycling a suiiicient part
3,085,379.
9
of the desorbate gas stream directly to an incoming fresh
gas stream to form said impurities-containing feed gas
stream having a higher concentration of impurities than
said fresh gas stream; periodically switching the flows
between the two selective adsorbent beds so that said
impurities-containing feed gas stream flows through the
second selective adsorbent bed and said desorbate gas
stream is removed from the first selective adsorbent bed.
2. A process for removing low concentrations of im
purities from a gas stream comprising the steps of pro
viding at least two separate zones, each containing zeolitic
molecular sieve adsorbent bed which has a selectivity for
the impurities over the product component of said gas
stream; providing an impurities-containing feed gas
stream and compressing such feed gas stream; passing
said compressed feed gas stream through a first selective
adsorbent bed as an adsorption stroke thereby removing
at least most of the impurities from said feed gas stream;
discharging a substantially impurities-free compressed
10
the compressed impurities-containing feed gas stream as
said first colder fluid; simultaneously depressurizing a
second selective adsorbent bed as a desorption stroke until
a residual impurities loading is obtained which corre
sponds to a partial pressure at adsorption temperature
equal to about the adsorption stroke pressure multiplied
by the tolerable impurities mole fraction in the product
gas stream thereby removing previously deposited impuri
ties and entrapped product gas in a desorbate gas stream;
recycling a sufficient part of the desorbate gas stream di
rectly to an incoming fresh gas stream to form said
impurities-containing feed gas stream having a higher
concentration of impurities than said fresh gas stream;
periodically switching the flows between the two selec
ti-ve adsorbent beds so that said impurities-containing feed
gas stream flows through the second selective adsorbent
bed and said desorbate gas stream is removed from the
ñrst selective adsorbent bed.
5. A process as set forth in claim 1 wherein at least
part of said desorbate gas stream is recycled to said
product gas stream from said first selective adsorbent bed; 20 incoming fresh gas stream containing low concentrations
simultaneously depressurizing a second selecitve ad
of impurities during the first part of said desorption stroke
sorbent bed as a desorption stroke thereby removing pre
and .discarded during the last part of such stroke.
viously deposited impurities and entrapped product gas
6. A process as set forth in claim l wherein heat is
in a desorbate gas stream; recycling a suñîcient part of
the desorbate gas stream directly to an incoming fresh
gas stream to form said impurities-containing feed gas
introduced to each adsorbent bed during its desorption
stroke.
having a higher concentration of impurities than said fresh
gas stream; periodically switching the flows between the
purge gas is passed through each adsorbent bed during
the last part of its desorption stroke.
7. A process as set forth in claim 1 wherein a heated
two selective adsorbent beds so that said impurities-con
8. A process as set forth in claim 4 wherein a portion
taining feed gas stream flows through the second selective 30 of the product gas stream after being heated-exchanged
adsorbent bed and said desorbate gas stream is removed
as the first colder fluid is passed through each adsorbent
from the first selective adsorbent bed.
bed during the last part of the desorption stroke.
3. A process for removing low concentrations of im
9. A process as set forth in claim 4 wherein the im
purities from a gas stream comprising the steps of pro
35 purities containing feed gas stream is cooled to a tempera
viding at least two separate Zones, each containing a
ture at most as low as the critical temperature of the
zeolitic molecular sieve adsorbent bed which has a selec
impurities being adsorbed.
tivity for the impurities over the product component of
10. A process for removing low concentrations of air
said gas stream; providing an impurities-containing feed
from helium comprising the steps of providing at least
gas stream and compressing such feed gas stream; passing 40 two separate zones, each containing a zeolitic molecular
said compressed feed gas stream through a first selective
sieve adsorbent bed which has a selectivity for air over
adsorbent bed as an adsorption stroke thereby removing
helium; providing an air containing helium feed gas
at least most of the impurities from said feed gas stream;
stream and compressing said air-containing helium feed
discharging a substantially impurities-free compressed
gas stream; cooling the compressed air-containing helium
product gas stream from said first selective adsorbent bed;
feed gas stream to at most as low as the critical tempera
45
simultaneously depressurizing a second selective adsorbent
ture of air by heat-exchange with a ñrst colder ñuid;
bed as a desorption stroke until a residual impurity load
passing the cooled and compressed air-containing helium
ing is obtained which corresponds to a partial pressure
feed gas stream through the first zeolitic molecular sieve
at adsorption temperature equal to about the adsorption
adsorbent bed as an adsorption stroke thereby removing
stroke pressure multiplied by the tolerable impurities 50 at least most of the air from said air-containing helium
mole fraction in the product, thereby removing previously
feed gas stream; discharging a substantially air-free com
deposited impurities and entrapped product gas in a de
pressed helium gas stream from said first zeolitic molec
sorbate gas stream; recycling a sufficient part of the
ular sieve adsorbent bed for heat-exchange with said
desorbate gas stream directly to an incoming fresh gas
compressed air containing helium feed gas stream as said
stream to form said impurities-containing feed gas stream 55 first Colder fluid; simultaneously depressurizing and draw
ing a vacuum on the second zeolitic molecular sieve ad
sorbent bed as a desorption stroke until a residual air
the two selective adsorbent beds so that said impurities
loading is obtained which corresponds to a partial pres
having a higher concentration of impurities than said
fresh gas stream; periodically switching the ñows between
containing feed gas stream liows through the second selec
sure at adsorption temperature equal to about the adsorp
tive adsorbent bed and said desorbate gas stream is re 60 tion stroke pressure multiplied by the tolerable air mole
moved from the first selective adsonbent bed.
fraction in the product helium gas stream, thereby remov
4. A process for removing low concentrations of im
ing previously deposited air and entrapped helium gas
purities from a gas stream comprising the steps of pro
in a desorbate gas stream; recycling one portion of the
viding at least two separate zones, each containing a
desorbate gas stream to an incoming fresh helium gas
zeolitic molecular sieve adsorbent ‘bed which has a selec 65
stream containing low concentrations of air thereby form
tivity for the impurities over the product component of
ing said air containing helium feed gas stream for pas
a gas stream; providing an impurities-containing feed
sage to said first zeolitic molecular sieve adsorbent bed
gas stream and compressing such feed gas stream; cool
for said adsorption stroke and discarding the other Portion
ing said compressed feed gas stream by heat-exchange
with a first colder fluid; passing the cooled gas stream 70 of the desorbate gas stream containing the same total
quantity of air as is entering the system in said incoming
through a first selective adsorbent bed as an adsorption
fresh helium gas stream during said adsorption stroke;
stroke thereby removing at least most of the impurities
periodically switching the flows between the two zeolitic
from said gas stream; discharging a substantially impuri
molecular sieve adsorbent beds so that said air containing
ties-free compressed and cooled product gas stream from
said first selective adsorbent bed for heat-exchange with 75 helium feed gas stream fiows through the second zeolitic
ll
3,085,379
molecular sieve adsorbent bed and said desorbate gas
stream is removed from the first zeolitic molecular sieve
adsorbent bed.
l1. A process for removing low >concentrations of air
from helium comprising the steps of providing at least
.
.
i2
as the first colder fluid through the adsorbent bed until
a residual loading of air corresponding to a partial pres
sure of 15 mm. Hg at the adsorption temperature is ob
tained thereby completing the desorption stroke and re
moving previously deposited air and entrapped helium
two separate zones, each containing a zeolitic molecular
gas in a desorbate gas stream; recycling one portion of
sieve adsorbent bed wherein the zeolitic molecular sieve
the desorbate gas stream to an incoming fresh helium
adsorbent is chosen from the group consisting of zeolite
gas stream containing low concentrations of air thereby
A in which at least 40 percent of the monovalent cation
sitesl are satisfied with trivalent metal cations, zeolite A 10 forming said air containing helium feed gas stream for
passage to said first -zeolitic molecular sieve adsorbent
in which at least 40 percent of the monovalent cation
sites are satisfied with divalent metal cations, hydrogen .
ion-exchanged form of mordenite, erionite, zeolite L,
zeolite T, zeolite Y and zeolite X; providing an air con
bed for said adsorption stroke and discarding the other
portion of the desorbate gas stream containing the same
total quantity of air as is entering the system in said in
taining helium feed gas stream and compressing said air 15 coming fresh helium gas stream during said adsorption
stroke; periodically switching the flows between the two
containing helium feed gas stream; cooling the com
zeolitic molecular sieve adsorbent beds so that said air
pressed air-containing helium feed gas stream to at most
containing helium feed gas stream flows through the sec
as low as the critical temperature of air by heat-exchange
ond zeolitic molecular sieve adsorbent bed and said
with a first colder fluid; passing the cooled and corn
pressed air-containing helium feed gas stream through 20 desorbate gas stream is removed from the first zeolitic
molecular sieve adsorbent bed.
the first zeolitic molecular sieve adsorbent bed as an
14. A process for removing low concentrations of air
adsorption stroke thereby removing at least most of the
from helium comprising the steps of providing at least
air from said air-containing helium feed gas stream; dis
two separate Zones, each containing an adsorbent bed
charging a substantially air-free compressed helium gas
stream from said first zeolitic molecular sieve adsorbent 25 composed of zeolite A having a pore size of about 5 A.;
providing an air-containing helium feed gas stream and
bed for heat-exchange with said compressed air contain
compressing said air-containing helium gas stream to
ing helium feed gas stream as said first colder fluid;
about 300 p.s.i.a.; cooling the compressed air-containing
simultaneously depressurizing and drawing a vacuum on
helium feed gas stream by heat-exchange with a first
the second zeolitic molecular sieve adsorbent bed as a
desorption stroke until a residual air loading is obtained 30 colder iiuid to about _40° C.; passing the cooled and
compressed air-containing helium feed gas stream
which corresponds to a partial pressure at adsorption
through the first lzeoliteY A adsorbent bed as an adsorp
temperature equal to about the adsorption stroke pres
tion stroke thereby removing at least most of the air from
sure multipliedV by the tolerable air mole fraction in the
said air-containing helium feed gas stream; discharging a
product helium gas stream thereby removing previously
deposited air and entrapped helium gas in a desorbate 35 substantially air-free compressed helium gas stream from
said first zeolite A adsorbent bed for heat-exchange with
gas stream; recycling one portion of the desorbate gas
said compressed air containing helium feed gas stream as
stream to an incoming fresh helium gas stream contain
said first colder fluid; simultaneously depressurizing the
ing low concentrations' of air thereby forming said air
second zeolite A adsorbent bed to about 200 mm. Hg and
containing helium feed gas stream for passage to said
first zeolitic molecular sieve adsorbent bed for said ad 40 then passing a portion of the product gas stream after
beingV heat-exchanged as the first colder iiuid through the
sorption stroke and discarding the other portion of the
adsorbent bed until a residual loading of air correspond
desorbate gas stream containing the same total quantity
ing to a partial pressure of 15 mm. Hg at the adsorption
of air as is entering the system in said incoming fresh
helium gas stream during said adsorption stroke; period
temperature is obtained thereby completing the desorp
ically switching the flows between the two zeolitic molec 45 tion stroke and removing previously deposited air and
entrapped helium gas in a desorbate gas stream; recycling
ular sieve adsorbent beds so that said air containing heli
one portion of the desorbate gas stream to an incoming
um feed gas stream flows through the second zeolitic
fresh helium gas stream containing low concentrations of
molecular sieve adsorbent bed and said desorbate gas
air thereby forming said air containing helium feed gas
stream is removed from the first zeolitic molecular sieve
stream
for passage to said first zeolitic molecular sieve
adsorbent bed.
50
adsorbent bed for said adsorption stroke and discarding
12. A process as set forth in claim 10 wherein the
the other portion of the desorbate gas stream containing
zeolitic molecular adsorbent beds are composed of zeolite
the same total quantity of air as is entering the system
A having a pore size of about 5 angstrom units; said
in said incoming fresh helium gas stream during said ad
helium feed gas stream is compressed to about 300 p.s.i.a.
and cooled to about _40° C.; and the vacuum for the 55 sorption stroke; periodically switching the iiows between
the two zeolitic molecular sieve adsorbent beds so that
desorption stroke is about 15 mm. Hg.
said air containing helium feed gas stream flows through
13. A process for removing low concentrations of air
the second zeolitic molecular sieve adsorbent bed and
from helium comprising the steps of providing at least
said desorbate gas stream is removed from the first zeo
two separate zones, each containing an adsorbent bed
composed of zeolite A having a pore size of about 5 A.; 60 litic molecular sieve adsorbent bed.
15. A process for removing low concentrations of
providing an air-containing helium feed gas stream and
compressing said air-containing helium gas stream to
methane from hydrogen comprising the steps of provid
about 300 p.s.i.a.; cooling the compressed air-containing
ing at least two separate zones, each containing a zeolitic
molecular sieve adsorbent bed having a selectivity for
helium feed gas stream by heat-exchange with a first
colder fluid to about _40° C.; passing the cooled and 65 methane over hydrogen; providing a methane-containing
hydrogen feed gas stream and compressing said methane
compressed air-containing helium feed gas stream
containing hydrogen feed gas stream; cooling the com
through the first zeolite A adsorbent bed as an adsorption
stroke thereby removing at least most of the air from
pressed methane-containing hydrogen feed gas stream to
said air-containing helium feed gas stream; discharging a
at most as low as the critical temperature of methane by
substantially air-free compressed helium gas stream from 70 heat-exchange with a first colder'fluid; passing the cooled
said first zeolite A adsorbent bed for heat-exchange with
methane-containing hydrogen feed gas stream through
said compressed air containing helium feed gas stream as
the first zeolitic molecular sieve adsorbent bed as an ad
said first colder fluid; simultaneously depressurizing the
sorption stroke thereby removing at least most of the
second zeolite A adsorbent bed and then passing a por
methane from said methane-containing hydrogen feed
tion of the product gas stream after being heat-exchanged 75 gas stream; discharging a substantially methane-free
13
compressed hydrogen gas stream from said ñrst zeolitìc
molecular sieve adsorbent bed for heat-exchange with the
14
ane-containing hydrogen feed gas stream ñows through
the second zeolitìc molecular sieve adsorbent bed and
stream as said first colder fluid; simultaneously depres
said desorbate gas stream is removed from the first zeo
litìc molecular sieve adsorbent bed.
surizing and drawing a vacuum on the second zeolitìc
molecular sieve adsorbent bed as a desorption stroke
litic molecular adsorbent beds are composed of zeolite A
having a pore size of about 4 angstrom units, said meth
compressed methane-containing hydrogen feed gas
until a residual methane loading is obtained which cor
responds to a partial pressure at adsorption temperature
equal to about the adsorption stroke pressure multiplied
by the tolerable methane mole fraction in the product
hydrogen gas stream thereby removing previously de
posited methane and entrapped hydrogen gas in a desorb
ate gas stream; recycling one portion of the desorbate
gas stream to an incoming fresh hydrogen gas stream con
taining low concentrations of methane-containing hydro
gen feed gas stream for passage to said ñrst zeolitìc
molecular sieve adsorbent bed for said adsorption stroke
and discarding the other portion of the desorbate gas
stream containing the same total quantity of methane as
17. A process as set forth in claim 15 wherein the zeo
ane-containing hydrogen feed gas stream is compressed
to about 50 p.s.i.a. and cooled to about 0° C., and the
vacuum for the desorption stroke is about 2.6 mm. Hg.
`18. A process for removing low concentrations of
methane from hydrogen comprising the steps of provid
ing at least two separate zones, each containing and ad
sorbent bed composed of zeolite A having a pore size of
about 4 A.; providing a methane-containing hydrogen
feed gas stream and compressing said methane-contain
ing hydrogen feed gas stream to about 50 p.s.i.a.; cool
ing the compressed methane-containing hydrogen feed
gas stream by heat-exchange with a ñrst colder fluid to
about 0° C.; passing the cooled and compressed meth
is entering the system in said incoming fresh hydrogen
ane-containing hydrogen feed gas stream through the
gas stream during said adsorption stroke; periodically
ñrst zeolite A adsorbent bed as an adsorption stroke
switching the ñows between the two zeolitìc molecular
thereby removing at least most of the methane from said
sieve adsorbent beds so that said methane-containing hy
methane-containing hydrogen feed gas stream; discharg
drogen feed gas stream flows through the second zeolitìc
ing a substantially methane-free compressed hydrogen
25
molecular sieve adsorbent bed and said desorbate gas
gas stream from said ñrst zeolite A adsorbent bed for
stream is removed from the first zeolitìc molecular sieve
heat-exchange with said compressed methane-containing
adsorbent bed.
hydrogen feed gas stream as said first colder ñuid; simul
16. A process for removing low concentrations of
taneously depressurizing the second zeolite A adsorbent
methane from hydrogen comprising the steps of provid
bed and then passing a portion of the product gas stream
30
ing at least two separate zones, each containing a zeolitìc
after being 'heat-exchanged as the first colder ñuid
molecular sieve adsorbent bed wherein the zeolitìc
through the adsorbed bed until a residual loading of
molecular sieve adsorbent is chosen from the group con
methane corresponding to a partial pressure of about 2.6
sisting of zeolite A, mordenite, chabazite, erionite, zeo
mm. Hg at the adsorption temperature is obtained there
lite R, zeolite D, zeolite L, zeolite Y, zeolite T and zeolite
completing the desorption stroke and removing previ
X; providing a methane-containing hydrogen feed gas 35 by
ously deposited methane and entrapped hydrogen gas in
stream and compressing said methane-containing hydro
a desorbate gas stream; recycling one portion of the de
sorbate gas stream to an incoming fresh hydrogen gas
gen feed gas stream; cooling the compressed methane
containing hydrogen feed gas stream to at most as low
stream containing low concentrations of methane-con
as the critical temperature of methane by heat-exchange 40 taining
hydrogen feed gas stream for passage to said first
with a first colder ñuid; passing the cooled methane-con
zeolitìc molecular sieve absorbent bed for said adsorp
taining hydrogen feed gas stream through the ñrst zeolitìc
tion stroke and discarding the other portion of lthe de
molecular sieve adsorbent bed as an adsorption stroke
sorbate gas stream containing the same total quantity
thereby removing at least most of the methane from said
of methane as is entering the system in said incoming
methane-containing hydrogen feed gas stream; discharg 45 fresh hydrogen gas stream during said adsorption stroke;
ing a substantially methane free compressed hydrogen gas
periodically switching the iiows between the two zeolitìc
stream from said ñrst zeolitìc molecular sieve adsorbent
molecular sieve adsorbent beds so that said methane-con
bed for heat-exchange with the compressed methane-con
taining hydrogen feed gas stream ñows through the sec
taining hydrogen feed gas stream as said íirst colder
zeolitìc molecular sieve adsorbent bed and said de
fluid; simultaneously depressurizing and drawing a 50 ond
sorbate gas stream is removed from the first zeolitìc
vacuum on the second zeolitìc molecular sieve adsorbent
molecular sieve adsorbent bed.
bed as a desorption stroke until a residual methane load
ing is obtained which corresponds to a partial pressure at
References Cited in the file of this patent
adsorption temperature equal to about the adsorption
stroke pressure multiplied by the tolerable methane mole
fraction in the product hydrogen gas stream thereby re
55
moving previously deposited methane and entrapped hy
drogen gas in a desorbate gas stream; recycling one por
tion of the desorbate gas stream to an incoming fresh
hydrogen gas stream containing low concentrations of 60
methane-containing hydrogen feedk gas stream for passage
to said ñrst zeolitìc molecular sieve adsorbent bed for
said adsorption stroke and discarding the other portion
of the desorbate gas stream containing the same total
UNITED STATES PATENTS
2,519,874
2,747,681
2,793,507
2,861,651
2,882,243
zeolitìc molecular sieve adsorbent beds so that said meth
1950
1956
1957
1958
1959
` 2,886,123
` 2,893,512
2,918,140
Miller et a1. _________ __ May 12, 1959
Armond ______________ __ July 7, I1959
Brooks _____________ __ Dec. 22, 1959
2,944,627
Skarstrom ________ _'____ July 12, 1960
555,482
Canada ______________ _.. Apr; 1, 1958
quantity of methane as is entering the system in said in 65
coming fresh hydrogen gas stream during said adsorption
stroke; periodically switching the flows between the two
Berg _______________ _- Aug. 22,
Schuftan et al _________ __ May 29,
Hnilicka ____________ __ May 28,
Miller _____________ __ Nov. 25,
Milton ______________ __ Apr. 14,
FOREIGN PATENTS
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