USRE34595E - Process for removing oxygen and nitrogen from crude argon - Google Patents

Process for removing oxygen and nitrogen from crude argon Download PDF

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USRE34595E
USRE34595E US07/847,968 US84796892A USRE34595E US RE34595 E USRE34595 E US RE34595E US 84796892 A US84796892 A US 84796892A US RE34595 E USRE34595 E US RE34595E
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oxygen
argon
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argon stream
iaddend
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Michael S. K. Chen
Philip J. Cook
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Air Products and Chemicals Inc
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    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01DSEPARATION
    • B01D53/00Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/22Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by diffusion
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01DSEPARATION
    • B01D53/00Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/32Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by electrical effects other than those provided for in group B01D61/00
    • B01D53/326Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by electrical effects other than those provided for in group B01D61/00 in electrochemical cells
    • CCHEMISTRY; METALLURGY
    • C01INORGANIC CHEMISTRY
    • C01BNON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B13/00Oxygen; Ozone; Oxides or hydroxides in general
    • C01B13/02Preparation of oxygen
    • C01B13/0229Purification or separation processes
    • C01B13/0248Physical processing only
    • C01B13/0251Physical processing only by making use of membranes
    • CCHEMISTRY; METALLURGY
    • C01INORGANIC CHEMISTRY
    • C01BNON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B23/00Noble gases; Compounds thereof
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25JLIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J3/00Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/02Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
    • F25J3/04Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream for air
    • F25J3/04642Recovering noble gases from air
    • F25J3/04648Recovering noble gases from air argon
    • F25J3/04721Producing pure argon, e.g. recovered from a crude argon column
    • F25J3/04733Producing pure argon, e.g. recovered from a crude argon column using a hybrid system, e.g. using adsorption, permeation or catalytic reaction
    • F25J3/04739Producing pure argon, e.g. recovered from a crude argon column using a hybrid system, e.g. using adsorption, permeation or catalytic reaction in combination with an auxiliary pure argon column
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25JLIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J3/00Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/02Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
    • F25J3/04Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream for air
    • F25J3/04763Start-up or control of the process; Details of the apparatus used
    • F25J3/04866Construction and layout of air fractionation equipments, e.g. valves, machines
    • F25J3/04969Retrofitting or revamping of an existing air fractionation unit
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25JLIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J3/00Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/08Separating gaseous impurities from gases or gaseous mixtures or from liquefied gases or liquefied gaseous mixtures
    • CCHEMISTRY; METALLURGY
    • C01INORGANIC CHEMISTRY
    • C01BNON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B2210/00Purification or separation of specific gases
    • C01B2210/0043Impurity removed
    • C01B2210/0078Noble gases
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25JLIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2205/00Processes or apparatus using other separation and/or other processing means
    • F25J2205/80Processes or apparatus using other separation and/or other processing means using membrane, i.e. including a permeation step
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25JLIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2205/00Processes or apparatus using other separation and/or other processing means
    • F25J2205/82Processes or apparatus using other separation and/or other processing means using a reactor with combustion or catalytic reaction
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25JLIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2215/00Processes characterised by the type or other details of the product stream
    • F25J2215/58Argon
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25JLIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2230/00Processes or apparatus involving steps for increasing the pressure of gaseous process streams
    • F25J2230/58Processes or apparatus involving steps for increasing the pressure of gaseous process streams the fluid being argon or crude argon
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25JLIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2245/00Processes or apparatus involving steps for recycling of process streams
    • F25J2245/02Recycle of a stream in general, e.g. a by-pass stream

Definitions

  • 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.
  • 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.
  • 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° K) and oxygen (90.19° K), distillative separation of argon and oxygen in particular is very difficult and energy intensive.
  • 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.
  • the deoxo process catalytic reduction to water with excess hydrogen over platinum catalyst beds
  • dual pressure distillation to remove nitrogen and excess hydrogen.
  • argon streams purified by this method usually contain only ppm levels of nitrogen, oxygen, and hydrogen, the process does have significant drawbacks.
  • 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.
  • 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.
  • polymeric membranes such as polysulfones, polysiloxanes, polyaryleneoxides, polystyrenes, polycarbonate, cellulose acetate and the like
  • 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.
  • a new process 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.
  • 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°-800° 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.
  • 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.
  • 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.
  • 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 2 or Bi 2 O 3 doped with Y 2 O 3 or other oxides or mixtures thereof.
  • SEM solid electrolyte membrane
  • 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.
  • 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.
  • 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° to 800° 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 2 or Bi 2 O 3 doped materials, which conducts the ionized oxygen and transports it across the membrane having virtually an infinite selectivity to oxygen.
  • appropriate oxygen-ion conducting solid electrolyte materials such as ZrO 2 or Bi 2 O 3 doped materials, which conducts the ionized oxygen and transports it across the membrane having virtually an infinite selectivity to oxygen.
  • 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.
  • 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°-750° 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.
  • SEM solid electrolyte membrane
  • 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 2 -Y 2 O 3 at 750° C. with pure oxygen in the permeate.
  • Design 2 uses Bi 2 O 3 -Y 2 O 3 at 560° 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.
  • 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.
  • 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°-2000° F. .[.[535°-1100° C.].].).
  • high temperatures e.g. 1000°-2000° F. .[.[535°-1100° C.].].
  • 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.
  • solid electrolyte materials examples include bismuth oxide, zirconia, and the like doped with various oxides such as yttria, calcia, barium oxides, and the like.
  • bismuth oxide doped with calcia is used.
  • 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.
  • SLM lanthanum-strontium-magnesium oxide
  • LSC lanthanum-strontium-cobalt oxide
  • 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 -1 cm -1 , preferably 0.5 to 1 ohm -1 cm -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 2 , most preferably 0.5 to 1 ampere/cm 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 -1 cm -1 and electronic conductivities in the range of about 1 to 30 ohm -1 cm -1 , most preferably with ionic conductivities in the range of about 0.5 to 1 ohm -1 cm -1 and electronic conductivities in the range of about 10 to 25 ohm -1 cm -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.
  • 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.
  • 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.

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.

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° K) and oxygen (90.19° 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°-800° 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 ZrO2 or Bi2 O3 doped with Y2 O3 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° to 800° 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 ZrO2 or Bi2 O3 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:
O.sub.2 +4e.sup.- →20.sup.= (cathode)
20.sup.50 →O.sub.2 +4e.sup.- (anode)
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°-750° 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 ZrO2 -Y2 O3 at 750° C. with pure oxygen in the permeate. Design 2 uses Bi2 O3 -Y2 O3 at 560° 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° 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° 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° 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:                                                  
                     ˜145° 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° 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                                       
__________________________________________________________________________
    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                                
__________________________________________________________________________
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                                  
__________________________________________________________________________
Other:                                                                    
Temp. Rise Across SEM's: ˜80°  F.                            
Area for High Temperature H-X:                                            
                         500 Ft.sup.2                                     
Total Power: (SEM & Sweep Comp.):                                         
                         6.93 + 7 = ˜14 KW                          
SEM Total Area:          259.1 Ft.sup.2 (<1 ppm O.sub.2)                  
__________________________________________________________________________
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°-2000° F. .[.[535°-1100° 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-1 cm-1, preferably 0.5 to 1 ohm-1 cm-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/cm2, most preferably 0.5 to 1 ampere/cm2.
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-1 cm-1 and electronic conductivities in the range of about 1 to 30 ohm-1 cm-1, most preferably with ionic conductivities in the range of about 0.5 to 1 ohm-1 cm-1 and electronic conductivities in the range of about 10 to 25 ohm-1 cm-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.

Claims (3)

    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° to 800° 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
  1. 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° to about 800° 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.
  2. .Iadd. 0. The process according to claim 19 wherein the mixed conductor demonstrates an oxygen ionic conductivity ranging from 0.01 to 1 ohm-1 cm-1 and an electronic conductivity ranging from about 1 to 30 ohm-1 cm-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-1 cm-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° to about 750° 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
  3. (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-1 cm-1 and an electronic conductivity ranging from about 1 to 30 ohm-1 cm-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-1 cm-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.
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EP0663230A2 (en) * 1994-01-12 1995-07-19 Air Products And Chemicals, Inc. Oxygen production by staged mixed conductor membranes
US5557951A (en) * 1995-03-24 1996-09-24 Praxair Technology, Inc. Process and apparatus for recovery and purification of argon from a cryogenic air separation unit
US5562754A (en) * 1995-06-07 1996-10-08 Air Products And Chemicals, Inc. Production of oxygen by ion transport membranes with steam utilization
US5730003A (en) * 1997-03-26 1998-03-24 Praxair Technology, Inc. Cryogenic hybrid system for producing high purity argon
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