U.S. patent number RE34,595 [Application Number 07/847,968] was granted by the patent office on 1994-05-03 for process for removing oxygen and nitrogen from crude argon.
This patent grant is currently assigned to Air Products and Chemicals, Inc.. Invention is credited to Michael S. K. Chen, Philip J. Cook.
United States Patent |
RE34,595 |
Chen , et al. |
May 3, 1994 |
**Please see images for:
( Certificate of Correction ) ** |
Process for removing oxygen and nitrogen from crude argon
Abstract
.[.A process is provided for purifying argon gas, especially an
argon gas stream obtained by cryogenically separating air, wherein
the argon gas is heated and compressed, and then permeated through
a solid electrolyte membrane selective to the permeation of oxygen
over other components of the gas, and removing oxygen from the
argon by selective permeation of oxygen through the membrane. The
purified argon can then be distilled to remove other components
such as nitrogen..]..Iadd.A process is provided for producing a
purified argon stream wherein oxygen and nitrogen are removed from
crude bulk argon streams, particularly those produced by cryogenic,
adsorptive or membrane separation of air. The process comprises
separating a heated, compressed crude argon stream containing
nitrogen and oxygen into an oxygen permeate stream and an
oxygen-depleted argon stream by passing the compressed heated argon
stream through a solid electrolyte membrane selective to the
permeation of oxygen. The oxygen-depleted argon stream is then fed
to a distillation column to separate nitrogen from the
oxygen-depleted argon stream to form the purified argon stream and
a nitrogen waste stream. .Iaddend.
Inventors: |
Chen; Michael S. K.
(Zionsville, PA), Cook; Philip J. (Schnecksville, PA) |
Assignee: |
Air Products and Chemicals,
Inc. (Allentown, PA)
|
Family
ID: |
24108074 |
Appl.
No.: |
07/847,968 |
Filed: |
March 6, 1992 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
Reissue of: |
528997 |
May 24, 1990 |
05035726 |
Jul 30, 1991 |
|
|
Current U.S.
Class: |
95/54; 95/47 |
Current CPC
Class: |
B01D
53/326 (20130101); F25J 3/08 (20130101); B01D
53/22 (20130101); C01B 13/0251 (20130101); C01B
23/00 (20130101); F25J 3/04739 (20130101); F25J
3/04969 (20130101); F25J 2205/82 (20130101); F25J
2230/58 (20130101); F25J 2205/80 (20130101); F25J
2215/58 (20130101); C01B 2210/0078 (20130101); F25J
2245/02 (20130101) |
Current International
Class: |
B01D
53/22 (20060101); B01D 53/32 (20060101); C01B
13/02 (20060101); C01B 23/00 (20060101); F25J
3/08 (20060101); B01D 053/22 (); B01D 071/02 () |
Field of
Search: |
;55/16,68,158 ;62/18
;204/129 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
R E. Latimer, "Distillation of Air", Chemical Engineering Progress,
pp. 35-59, Feb. 1967 (vol. 63, No. 2). .
Jennings et al. "Conceptual Processes For Recovery of Argon with
Membranes in an Air Separation Process", American Institute of
Chemical Engineers, 1987 Summer Nat'l Meeting, 40 pages. .
Agrawal et al., "Membrane/Cryogenic Hybrid Scheme for Argon
Production from Air", American Institute of Chemical Engineers,
1988 Summer Meeting. .
Yuan and Krogu, Stabilized Zirconia as an Oxygen Pump, J.
Electrochem. Soc., pp. 594-600, May 1969. .
Takahashi and Iwahara, Oxide Ion Conductors Based on
Bismusthsequioxide, Mat. Res. Bull., vol. 13, No. 12 pp. 1447-1453,
1978. .
Gur and Huggins, "Decomposition of Nitric Oxide Using Solid State
Electrolyte", Fast Ion Transporting Solids, pp. 109-112, 1979.
.
Fukatsu et al., "On the Control of Oxygen Potential In Gas
Atmosphere Using the Stabilized Zirconia Galvanic Cell as an Oxygen
Pump" (1976). .
Rincon-Rubio et al., "Mathematical Modeling of a Solid Electrolyte
Tubular Flow Electrochemical Reactor"; International Society of
Electrochemistry, 35th Meeting; Aug. 5-Aug. 10 (1984), pp. 686-687.
.
Nguyen et al., "Mechanisms of Catalytic Oxidation of Hydrocarbons
In A Solid-Electrolyte Fuel Cell", pp. 331-347. .
Agrawal et al., "The Control of Oxygen Activities In Argon-Oxygen
Mixtures By Coulometric Titration"; Journal of Electrochemical
Society; Electrochemical Service and Technology; (Mar. 1974); pp.
354-359, vol. 121, No. 3. .
Wakihara; "A Method For Removing Impurity Oxygen From Gases By
Means of Air Oxygen Pump", Dec. 24, 1982, pp. 1-10..
|
Primary Examiner: Spitzer; Robert
Attorney, Agent or Firm: Gourley; Keith D. Simmons; James C.
Marsh; William F.
Claims
What is claimed is: .[.1. A process for purifying bulk argon which
comprises recovering a crude bulk argon gas containing oxygen from
a cryogenic, adsorptive or membrane separation of air, heating the
crude argon gas to a temperature of from about 450.degree. to
800.degree. C. and comprising the crude argon gas to a pressure of
about 30 to 80 psig, feeding the heated, compressed gas to a high
temperature solid electrolyte membrane selective to the permeation
of oxygen over other components of the gas, and separating oxygen
from the argon gas by selective permeation of oxygen through the
membrane..]. .[.2. The process of claim 1 wherein the oxygen in the
argon gas stream is reduced to less than about 1 ppm..]. .[.3. The
process of claim 2 wherein the oxygen gas is permeated through two
or more membranes..]. .[.4. The process of claim 1 wherein the
membrane is made of mixed conductors with mixed conductivity for
oxygen ions and electrons..]. .[.5. The process of claim 4 wherein
the oxygen is permeated through a doped zirconia membrane..]. .[.6.
The process of claim
5 wherein the membrane is doped with yttrium oxide..]. .[.7. The
process of claim 4 wherein the oxygen is permeated through a doped
bismuth oxide membrane..]. .[.8. The process of claim 7 wherein the
membrane is doped with yttrium oxide..]. .[.9. The process of claim
1 wherein a sweep gas is used to lower permeate oxygen pressure..].
.[.10. The process of claim 1 which comprises feeding the argon gas
from the membrane to a distillation column to separate argon from
any other components of the gas..]. .[.11. The process of claim 10
wherein nitrogen is separated from argon in the distillation
column..]. .[.12. The process of claim 1 which comprises subjecting
the argon gas from the membrane to hydrogen deoxidation..]. .[.13.
The process of claim 12 which comprises feeding the argon gas from
the hydrogen deoxidation to a distillation column to separate argon
from any other components of the gas..]. .[.14. The process of
claim 13 wherein nitrogen is separated from argon in the
distillation column..]. .Iadd.15. A process for removing oxygen and
nitrogen from a crude argon stream comprising the steps of:
(a) compressing the crude argon stream to about 30 to 90 psig to
form a compressed crude argon stream;
(b) heating the compressed crude argon stream to a temperature of
about 450.degree. to about 800.degree. C. to form a compressed
heated crude argon stream;
(c) separating the compressed heated argon stream into an oxygen
permeate stream and an oxygen-depleted argon stream by contacting
the compressed heated argon stream with a solid electrolyte
membrane selective to the permeation of oxygen;
(d) cooling the oxygen-depleted argon stream by indirect heat
exchange with the compressed crude argon stream to form a cooled
oxygen-depleted argon stream;
(e) distilling nitrogen from the cooled oxygen-depleted argon
stream to form a purified argon stream and a nitrogen-rich waste
stream; and
(f) recovering the purified argon stream. .Iaddend. .Iadd.16. The
process according to claim 15 further comprising warming the crude
argon stream by indirect heat exchange with the oxygen-depleted
argon stream prior to compressing the crude argon according to step
(a). .Iaddend. .Iadd.17. The process according to claim 16 further
comprising countercurrently sweeping the solid electrolyte membrane
with a sweep gas to facilitate removal of the oxygen permeate
stream. .Iaddend. .Iadd.18. The process according to claim 17
further comprising warming the nitrogen-rich waste stream by
indirect heat exchange with the cooled oxygen-depleted argon stream
prior to distilling the cooled oxygen-depleted argon stream
according to step (e). .Iaddend. .Iadd.19. The process according to
claim 18 wherein the solid electrolyte membrane consists of a mixed
conductor. .Iaddend.
.Iadd. 0. The process according to claim 19 wherein the mixed
conductor demonstrates an oxygen ionic conductivity ranging from
0.01 to 1 ohm.sup.-1 cm.sup.-1 and an electronic conductivity
ranging from about 1 to 30 ohm.sup.-1 cm.sup.-1. .Iaddend.
.Iadd.21. The process according to claim 20 wherein the mixed
conductor is an oxide selected from the group consisting of the
oxides of Co-Sr-Bi, Co-La-Bi, Co-Sr-Ce and Co-La-Ce. .Iaddend.
.Iadd.22. The process according to claim 18 wherein the solid
electrolyte membrane comprises a solid electrolyte material which
demonstrates ionic conductivity and has electrodes attached thereto
to facilitate the transport of oxygen. .Iaddend. .Iadd.23. The
process according to claim 22 wherein the solid electrolyte
material demonstrates an ionic conductivity ranging from 0.01 to 2
ohm.sup.-1 cm.sup.-1. .Iaddend. .Iadd.24. The process of claim 23
wherein the solid electrolyte material is selected from the group
consisting of doped zirconium oxide and doped bismuth oxide.
.Iaddend. 25. The process of claim 24 wherein the solid electrolyte
material is doped with an oxide selected from the group consisting
of the oxides of yttria, calcia and baria. .Iadd.26. A process for
removing oxygen and nitrogen from a crude argon stream comprising
the steps of:
(a) compressing the crude argon stream to about 30 to 80 psig to
form a compressed argon stream;
(b) heating the compressed argon stream to a temperature ranging
from about 500.degree. to about 750.degree. C. to form a compressed
heated argon stream;
(c) separating the compressed heated argon stream into an oxygen
permeate stream and an oxygen-depleted argon stream by contacting
the compressed heated argon stream with at least one high
temperature solid electrolyte membrane selective to the permeation
of oxygen;
(d) cooling the oxygen-depleted argon stream by indirect heat
exchange with the compressed argon stream to form a cooled
oxygen-depleted argon stream;
(e) catalytically reacting the cooled oxygen-depleted argon stream
with hydrogen to form an argon stream containing water
condensate;
(f) separating the argon stream containing water condensate into a
water condensate stream and a dehydrated argon stream;
(g) distilling nitrogen from the dehydrated argon stream to form a
purified argon stream and a nitrogen-containing waste stream;
and
(h) recovering the purified argon stream. .Iaddend. .Iadd.27. The
process according to claim 26 further comprising contacting the
dehydrated argon stream with a drying agent prior to distilling the
dehydrated argon stream according to step (g). .Iaddend. .Iadd.28.
The process according to claim 27 further comprising warming the
crude argon stream by indirect heat exchange with the
oxygen-depleted argon stream prior to compressing the crude argon
stream according to step (a). .Iaddend. .Iadd.29. The process
according to claim 28 wherein the at least one high temperature
solid electrolyte membrane consists of a mixed conductor. .Iaddend.
.Iadd.30. The process according to claim 29 wherein the mixed
conductor demonstrates an oxygen ionic conductivity ranging from
0.01 to 1 ohm.sup.-1 cm.sup.-1 and an electronic conductivity
ranging from about 1 to 30 ohm.sup.-1 cm.sup.-1. .Iaddend.
.Iadd.31. The process according to claim 30 wherein the mixed
conductor is an oxide selected from the group consisting of the
oxides of Co-Sr-Br, Co-La-Bi, Co-Sr-Ce and Co-La-Ce. .Iaddend.
.Iadd.32. The process according to claim 28 wherein the at least
one high temperature solid electrolyte membrane comprises a solid
electrolyte material demonstrating ionic conductivity and having
electrodes attached thereto to facilitate the transport of oxygen.
.Iaddend. .Iadd.33. The process according to claim 32 wherein the
solid electrolyte material demonstrates an ionic conductivity
ranging from 0.01 to 2 ohm.sup.-1 cm.sup.-1. .Iaddend. .Iadd.34.
The process of claim 33 wherein the solid electrolyte material is
selected from the group consisting of doped zirconium oxide and
doped bismuth oxide. .Iaddend. .Iadd.35. The process of claim 34
wherein the solid electrolyte material is doped with an oxide
selected from the group consisting of the oxides of yttria, calcia
and baria. .Iaddend.
Description
TECHNICAL FIELD
This invention relates to a method for removing oxygen .Iadd.and
nitrogen .Iaddend.from crude argon, and particularly for the
removal of oxygen .Iadd.and nitrogen .Iaddend.from a crude argon
stream produced by cryogenically separating argon from air.
BACKGROUND OF THE INVENTION
Argon is a useful inert gas which has many applications such as in
light bulbs, in the welding of metals, as inert atmosphere for
steel production as well as in various electronic industries, and
the like. A major source of argon is atmospheric air, about 1% of
which is argon.
Commercially, argon is produced as a valuable by-product in
cryogenic air separation plants for producing oxygen and nitrogen.
Crude argon produced cryogenically usually contains trace amounts
of nitrogen (0.02 to 1%) and appreciable quantities of oxygen (2 to
7%). This crude argon stream must be purified to reduce nitrogen
and oxygen before it is suitable for use, particularly as an inert
gas. Because of the proximity of the boiling point of argon
(87.28.degree. K) and oxygen (90.19.degree. K), distillative
separation of argon and oxygen in particular is very difficult and
energy intensive.
Heretofore, oxygen has been removed from crude argon streams by
catalytic reduction to water with excess hydrogen over platinum
catalyst beds, referred to herein as the deoxo process, followed by
drying to remove the water and then by dual pressure distillation
to remove nitrogen and excess hydrogen. See, for example, R. E.
Latimer, Distillation of Air, Chemical Engineering Process, pp.
35-59, February, 1967, which illustrates a typical scheme.
Although argon streams purified by this method usually contain only
ppm levels of nitrogen, oxygen, and hydrogen, the process does have
significant drawbacks. First, the hydrogen used in conventional
cryo/deoxo processes is expensive. For example, for a crude argon
stream containing only about 2.8% oxygen, about 3 mols of hydrogen
are consumed for each ton of argon processed. At eight dollars per
thousand standard cubic feet of hydrogen cost, the oxygen removal
cost is $9.20 per ton of argon for hydrogen consumption alone.
Further, hydrogen is not always conveniently available in many
parts of the world.
Another shortcoming of the cryo/deoxo process for purifying argon
is that the water produced from the deoxo reaction must be removed
completely before the argon is fed to the final cryogenic
distillation column. This requires feeding the argon stream through
a dryer preliminary to the cryogenic distillation. Capital and
operating costs associated with this additional step add
significantly to overall cost.
Further, the excess hydrogen introduced to remove the oxygen in the
first place must itself be removed and recovered before a pure
argon stream can be produced. This adds further to the complexity
and cost of the overall design and operation of the process.
Other techniques for purifying argon gas streams have also been
suggested. For example, U.S. Pat. Nos. 4,144,038 and 4,477,265
suggest separating argon from oxygen using aluminosilicate zeolites
and molecular sieves. Such processes trade argon recovery for
purity.
U.S. Pat. No. 4,230,463 suggests using polymeric membranes such as
polysulfones, polysiloxanes, polyaryleneoxides, polystyrenes,
polycarbonate, cellulose acetate and the like for separating pairs
of gases such as hydrogen and argon and polymeric membranes such as
polysulfones have been suggested for the removal of oxygen from
argon. Studies of hybrid processes involving cryogenic distillation
and membrane separation have been reported as, see, for example,
Jennings. et al., Conceptual Processes for Recovery of Argon with
Membranes in an Air Separation Process, American Institute of
Chemical Engineers, 1987 Summer National Meeting, and Agrawal, et
al., Membrane/Cryogenic Hybrid Scheme for Argon Production from
Air. American Institute of Chemical Engineers, 1988 Summer Meeting
in Denver, Colo. Selectivity and recovery in such hybrid schemes
has been rather poor. Much of the argon permeates with oxygen
through membranes and must be recycled to crude argon distillation
columns.
Therefore, there is a need in the industry for an improved process
for purifying crude argon produced by cryogenic air separation.
SUMMARY OF THE INVENTION
A new process is provided for the removal of oxygen .Iadd.and
nitrogen .Iaddend.from crude bulk argon streams, particularly those
produced by the cryogenic, adsorptive or membrane separation of
air, which comprises feeding crude bulk argon gas .Iadd.containing
oxygen and nitrogen .Iaddend.over the feed side of a high
temperature solid electrolyte membrane (SEM) selective to the
permeation of oxygen over the other components of the gas,
separating oxygen from the gas by selective permeation through the
membrane to its permeate side, and recovering oxygen-depleted argon
gas from the feed side of the membrane. The oxygen-depleted argon
stream can then be fed to a final distillation column for the
separation of argon from any other components in the gas such as
nitrogen.
Preferably, crude argon obtained by cryogenic separation of air is
compressed and heated, preferably to a pressure of about 30 to 80
psig and a temperature ranging from about 450.degree.-800.degree.
C. The compressed, heated argon gas stream is then fed to a solid
electrolyte membrane unit to remove oxygen either with or without
the use of a sweep gas on the permeate side of the membrane to
lower the permeate oxygen pressure. The oxygen-depleted effluent
from the SEM is then cooled. It can be fed to a distillation column
to remove any other components of the gas such as nitrogen to make
a high purity argon product.
Although the SEM of the invention can be used alone to remove
oxygen substantially completely from an argon gas stream, the SEM
of the invention can also be used in conjunction with
hydrogen-deoxidation, if desired.
BRIEF DESCRIPTION OF THE .[.DRAWING.]. .Iadd.DRAWINGS .Iaddend.
FIG. 1 is a schematic representation of a process of the
invention.
FIG. 2 is a schematic representation of an embodiment of the
invention incorporating the deoxo process.
DETAILED DESCRIPTION OF THE INVENTION
Although the invention will be described in further detail with
reference to the accompanying drawings which illustrate preferred
embodiments in which like numerals indicate like elements, it is to
be understood that the invention is not limited to those
embodiments.
FIG. 1 illustrates a scheme by which substantially all oxygen can
be removed from an argon gas stream using a high temperature solid
electrolyte membrane (SEM) such as ZrO.sub.2 or Bi.sub.2 O.sub.3
doped with Y.sub.2 O.sub.3 or other oxides or mixtures thereof. The
purified argon stream contains less than 1 ppm oxygen. It can then
be fed to a final purification column for nitrogen removal. This
embodiment is preferred because it requires no hydrogen and is
therefore well-suited for a grass-roots crude argon purification
plant. Not only are the deoxo unit and dryer eliminated in this
embodiment but final distillation column pressure is reduced from
90 psig to about 45 psig because only nitrogen need be separated
from the argon. This reduces compression power and requires a
simpler single-pressure column instead of the dual-pressure column
required for final argon purification by conventional
processes.
In FIG. 1, low pressure crude argon stream 10 is warmed in argon
heat exchanger 11. Warmed stream 12 is fed to compressor 13 and
compressed to a pressure in the range of 30-80 psig, preferably 45
psig. Effluent stream 14 is heated in heat exchanger 15 from which
exit stream 16 is further heated to from about 450.degree. to
800.degree. C. by passing it through startup heater 17. Heated
stream 18 is fed to the feed side of SEM unit 19 in which the
oxygen level is reduced to less than about 1 ppm by the selective
permeation of oxygen through the SEM to permeate side 20.
The membrane stage comprises two electrodes and appropriate
oxygen-ion conducting solid electrolyte materials, such as
ZrO.sub.2 or Bi.sub.2 O.sub.3 doped materials, which conducts the
ionized oxygen and transports it across the membrane having
virtually an infinite selectivity to oxygen. The mechanism for
oxygen transport is as follows:
The pure oxygen emerges from the permeate side and is removed from
the SEM unit either by its own pressure at about 20 psig or by
using any suitable sweep gas, such as nitrogen, which comes from
the upstream air separation plant as waste or gaseous nitrogen 25.
Nitrogen stream 25 is warmed in heat exchanger 15 to produce
effluent stream 24 which is further heated in start-up heater 17 to
produce hot stream 26 which is used to sweep 27 the oxygen from SEM
permeate side 20 countercurrently. This sweep gas effectively
lowers the oxygen partial pressure to enable a high degree of
oxygen removal from the argon stream and hence reduce the power
required to pump the oxygen across the membrane. Exiting permeate
stream 28 is cooled in heat exchange 15 and returned to an upstream
cryogenic unit for further separation of oxygen and nitrogen.
Argon stream 22 exiting SEM membrane unit 19 is cooled in heat
exchanger 15, the effluent stream 32 from which is further cooled
by cooler 33 and passed 34 on to argon heat exchanger 11.
Cooled substantially oxygen-free argon stream 36 is then further
cooled to a cryogenic temperature in heat exchanger 37 preparatory
to removal of nitrogen therefrom. Cryogenic stream 38 is fed to
single-pressure distillation column 39 which is refluxed at the top
by the vaporization 42 of liquid nitrogen 40 and reboiled at the
bottom by cooling gaseous nitrogen stream 44. Purified argon 48 is
withdrawn from the bottom of column 39 and warmed in heat exchanger
41 to produce product argon stream 50.
Nitrogen stream 42 exits the top of column 39 and passes through
argon heat exchanger 11. Nitrogen exit stream 54 can then be
disposed of as desired; for example, it can be dumped into a waste
stream or vented or used with pure gaseous nitrogen as a sweep gas
for the SEM unit or the like.
Warmed nitrogen 49 from the column bottom reboiler is mixed with
the vaporized overhead nitrogen stream 42 and warmed in heat
exchangers 37 and 41. Effluent 46 is returned for use in the
upstream air separation plant.
FIG. 2 illustrates a hybrid SEM/deoxo process for near complete
removal of oxygen from crude argon. In this embodiment, the
objective is to use the SEM for bulk removal of oxygen (about
90-95%) and to use the hydrogen deoxo unit to remove the remaining
oxygen from the argon. This embodiment is well adapted to retrofit
an exiting deoxo unit thereby increasing the capacity of the
existing plant facility and reducing the hydrogen consumption.
Low pressure crude argon stream 10 containing about 2.8% oxygen is
warmed in argon heat exchanger 11. Exit stream 12 is fed to
compressor 13 to about 90 psig. Discharge stream 14 is heated in
the range of about 560.degree.-750.degree. C. in heat exchanger 15.
Hot argon stream 16 is passed through startup heater 17 to the feed
sides of the two-stage solid electrolyte membrane units 19 and 21
in which oxygen is removed from argon stream 18 by selective
permeation thereof through SEM units 19 and 21 to produce
intermediate purified argon stream 23 and exit purified argon
stream 22. The permeate stream emerges on the permeate side as pure
oxygen at about 20 psig, either by its own pressure or mixed with
any suitable sweep gas such as nitrogen 124 fed countercurrently
through the units to produce intermediate stream 126 and exit
stream 128. The oxygen contained in stream 22 from the SEM units is
reduced to about 0.15%. This stream is then cooled in heat
exchanger 15 and mixed with hydrogen 132 and recycled
hydrogen/argon stream 134. The mixture of the three streams is fed
to catalytic deoxo unit 135 in which the oxygen is reduced to about
1 ppm by reaction with hydrogen to produce water. Effluent stream
136 is cooled in heat exchanger 15 and exit stream 138 is cooled in
cooler 139. Exit stream 140 is further cooled in glycol cooler 141.
Resulting stream 142 is fed to separator 143 from which water is
removed as stream 144 and overhead dehydrated argon stream 146 is
passed to molecular sieve unit 147 for final drying. Dehydrated
stream argon stream 148, still containing unremoved nitrogen and
excess hydrogen is cooled in argon heat exchanger 11. Effluent
stream 150 is then fed to a final distillation column (not shown)
from which pure argon is obtained. Excess hydrogen containing some
argon is returned as stream 154 from the final distillation column
and warmed in argon heat exchanger 11 to be used as hydrogen source
stream 134.
Any suitable high temperature solid electrolyte membrane (SEM) unit
design can be employed in the invention. For example, a
shell-and-tube configuration with the crude argon on the shell side
can be used. The tubes, made of solid electrolyte materials, are
coated with electron conducting electrodes and connected to an
external DC power source. Other configurations include
plate-and-frame and honeycomb (monolithic layer) geometric
configurations. Power input, current density, applied voltage and
membrane area can all be properly designed and calculated based on
electrolyte electrode materials, thickness, and ionic
conductivity.
Tables 1, 2, and 3 illustrate three different SEM unit designs.
Design 1 uses ZrO.sub.2 -Y.sub.2 O.sub.3 at 750.degree. C. with
pure oxygen in the permeate. Design 2 uses Bi.sub.2 O.sub.3
-Y.sub.2 O.sub.3 at 560.degree. C. with pure oxygen in the
permeate. Design 3 is the same as Design 1 except that a nitrogen
sweep gas is used to lower the oxygen permeate pressure and, hence,
to reduce the electrical power consumption. All of the above
designs are more cost-effective than the conventional
cryogenic/hydrogen deoxo process for removing oxygen from crude
argon gas streams. For example. Design 1 when used to retrofit an
existing deoxo unit is estimated to save about 70% of the hydrogen
cost. When Designs 1 and 3 are used in a grass-roots plant, capital
cost savings as high as 10% on top of no cost at all for hydrogen
consumption are easily realized.
TABLE 1 ______________________________________ SEM DESIGN #1
______________________________________ Description: ZrO.sub.2
--Y.sub.2 O.sub.3 @ 750.degree. C. Shell: Crude Argon @ 90 psia
Total Flow Inlet: 30.32 moles/hr O.sub.2 (inlet): 2.8% Tube: Pure
O.sub.2 @ 20 psia ______________________________________ Crude
O.sub.2 Argon O.sub.2 Re- O.sub.2 Conc. Removed Applied moved
In/Out (moles/ Power Area Voltage % Stage (ppm) hr) (KW) (ft.sup.2)
(volts) Feed ______________________________________ 1 28000/9190
.5755 6.16 39.3 0.22 68.8 2 9190/1470 .230 2.46 41.7 0.22 27.1 3
1470/216 .0371 0.40 42.9 0.22 4.37 4 216/43 .0051 0.06 40.2 0.22
0.60 5 43/7.5 .00105 0.01 39.8 0.28 0.12 6 7.5/1.0 1.91E-4 0.003
50.0 0.30 0.01 ______________________________________ Other: Temp.
Rise Across SEM: 200.degree. F. Area for High Temperature H-X: 110
Ft.sup.2 SEM Total Power: 9.02 KW SEM Total Area: 254 Ft.sup.2 (1
ppm O.sub.2) <100 Ft.sup.2 (0.15% O.sub.2)
______________________________________
TABLE 2 ______________________________________ SEM DESIGN #2
______________________________________ Description: Bi.sub.2
O.sub.3 --Y.sub.2 O.sub.3 @ 750.degree. C. Shell: Crude Argon @ 90
psia Total Flow Inlet: 30.32 moles/hr O.sub.2 (inlet): 2.8% Tube:
Pure O.sub.2 @ 20 psia ______________________________________ Crude
O.sub.2 Argon O.sub.2 Re- O.sub.2 Conc. Removed Applied moved
In/Out (moles/ Power Area Voltage % Stage (ppm) hr) (KW) (ft.sup.2)
(volts) Feed ______________________________________ 1 28000/9190
.5755 4.48 39.70 0.16 67.8 2 9190/1470 .230 1.79 42.76 0.16 27.1 3
1470/216 .0371 0.29 45.17 0.16 4.37 4 216/43 .0051 0.47 39.9 0.18
0.60 5 43/7.5 .00105 0.11 40.8 0.22 0.12 6 7.5/1.0 1.91E-4 0.002
46.3 0.26 0.02 ______________________________________ Other: Temp.
Rise Across SEM's: .about.145.degree. F. Area for High Temperature
H-X: 110 Ft.sup.2 SEM Total Power: 6.6 KW SEM Total Area: 255
Ft.sup.2 (<1 ppm O.sub.2) <100 Ft.sup.2 (0.15% O.sub.2)
______________________________________
TABLE 3
__________________________________________________________________________
SEM DESIGN #3
__________________________________________________________________________
Description: ZrO.sub.2 --Y.sub.2 O.sub.3 @ 750.degree. C. Shell:
Crude Argon @ 90 psia Total Flow Inlet: 30.32 moles/hr O.sub.2
(inlet): 2.8% Tube: Total Flow Inlet: 20 moles/hr N.sub.2 (sweep
gas) O.sub.2 Conc. Inlet: 2 ppm Pressure: 20-25 psia
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Crude Argon Sweep Gas O.sub.2 Conc. O.sub.2 Conc. O.sub.2 Applied
O.sub.2 In/Out In/Out Removed Power Area Voltage Removed Stage
(ppm) (ppm) (moles/hr) (KW) (ft.sup.2) (volts) % Feed
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1 28000/9190 13490/40720 .5755 5.04 40.6 0.18 67.8 2 9190/1470
2170/13490 .230 1.68 43.2 0.15 27.1 3 1470/216 319/2170 .0371 0.18
44.8 0.10 4.37 4 216/43 64/319 .0051 0.02 40.6 0.075 0.60 5 43/7.5
11.5/64 .00105 0.004 43.8 0.075 0.12 6 7.5/1.0 2/11.5 .60019 0.001
46.1 0.10 0.02
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Other: Temp. Rise Across SEM's: .about.80.degree. F. Area for High
Temperature H-X: 500 Ft.sup.2 Total Power: (SEM & Sweep Comp.):
6.93 + 7 = .about.14 KW SEM Total Area: 259.1 Ft.sup.2 (<1 ppm
O.sub.2)
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The SEM units or cells can be constructed of any suitable solid
electrolyte materials, or mixtures thereof, which are capable of
transporting oxygen ions at high temperatures (e.g.
1000.degree.-2000.degree. F. .[.[535.degree.-1100.degree. C.].].).
By applying an external power input through electrodes and an
electric circuit, the ionic nature of the membrane allows it to
transport or "pump" oxygen from a region of low partial pressure to
a region of higher pressure. The selectivity of such membranes for
oxygen is very high because the ionic transport mechanism would not
be operative for other combustion gas components.
Examples of some such solid electrolyte materials which may be used
include bismuth oxide, zirconia, and the like doped with various
oxides such as yttria, calcia, barium oxides, and the like.
Preferably bismuth oxide doped with calcia is used. Most
preferably, bismuth sesquioxide-based materials are used because
they have very high ionic conductivities.
Any suitable electrode materials having high electronic
conductivity as well as high oxygen transport properties can be
used such as, for example, silver, platinum,
lanthanum-strontium-magnesium oxide (SLM),
lanthanum-strontium-cobalt oxide (LSC), and the like. Preferably,
LSM oxides are used for their high conductivities and thermal
compatibility with the solid electrolyte materials.
The electrolyte membrane can have any suitable thickness,
preferably in the range of from about 10 to 1000 micrometers, most
preferably 20 to 100 microns, and can have any suitable oxygen
conductivity such as, for example, conductivities in the range of
about 0.01 to 2 ohm.sup.-1 cm.sup.-1, preferably 0.5 to 1
ohm.sup.-1 cm.sup.-1. The electrodes can have any suitable
thickness and can be situated on either side of the electrolyte
membrane. The electrodes are preferably porous and operated at any
suitable current density, preferably ranging from about 0.05 to 2
amperes/cm.sup.2, most preferably 0.5 to 1 ampere/cm.sup.2.
Electrodeless SEM cells composed of a thin solid electrolyte film
without electrodes can also be used. Suitable solid electrolyte
materials can be any mixed conductors having high oxygen ionic and
electronic conductivities such as Co-Sr-Bi, Co-La-Bi, Co-Sr-Ce.
Co-La-Ce oxides, and the like, with oxygen ionic conductivities in
the range of about 0.01 to 1 ohm.sup.-1 cm.sup.-1 and electronic
conductivities in the range of about 1 to 30 ohm.sup.-1 cm.sup.-1,
most preferably with ionic conductivities in the range of about 0.5
to 1 ohm.sup.-1 cm.sup.-1 and electronic conductivities in the
range of about 10 to 25 ohm.sup.-1 cm.sup.-1. The electrodeless SEM
cells are preferably operated by maintaining an oxygen pressure on
the feed side such that a positive driving force for oxygen ion
transport can be achieved in the absence of an externally applied
voltage and power source. The electrons released at the anode would
flow back to the cathode side through the mixed conductor film
itself without going through electrodes and an external electrical
circuit. One particular advantage of such a cell is a significant
reduction in overpotential loss associated with electrode SEM cell
systems.
Solid electrolytes as disclosed in U.S. Pat. Nos. 3,400,054;
4,131,514; 4,725,346, the disclosures of which are hereby
incorporated herein by reference, and the like can also be
employed.
The use of high temperature solid electrolyte membranes to remove
oxygen from a crude bulk argon stream from cryogenic, adsorptive or
membrane air separation plants by the processes of the invention
provides considerable advantage over the conventional hydrogen
deoxo process for the same purpose. For example, the invention
eliminates or reduces the need for hydrogen and hydrogen storage
capacity which are expensive. The need for a deoxo catalytic system
and dryer is eliminated or reduced. A simpler final purification
distillation column can be used (single pressure versus dual
pressure) for argon/nitrogen separation and hydrogen/argon recovery
and recycle are obviated. The crude argon compression requirement
is lowered to 45 versus 90 psig and overall capital and operating
costs are lowered significantly. Bulk argon is deemed to be that
volume of argon that is usually handled commercially as opposed to
bench-scale, experimental or laboratory quantities. For such bulk
quantities of argon the process of the present invention has been
shown to be unexpectedly and advantageously efficient and
economical.
Although the invention has been described in considerable detail in
the foregoing, it is to be understood that such detail is solely
for the purpose of illustration and that variations may be made by
those skilled in the art without departing from the spirit and
scope of the invention except as set forth in the claims.
* * * * *