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.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.

Description

TECHNICAL FIELD

This invention relates to a method for removing oxygen DRAWING). 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

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.} 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. 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. 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.} 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. 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. 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

(h) recovering the purified argon stream. 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). 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). 29. The process according to claim 28 wherein the at least one high temperature solid electrolyte membrane consists of a mixed conductor. 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.} 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. 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. 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.} 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. 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.

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

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. 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. 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). 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. 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). 19. The process according to claim 18 wherein the solid electrolyte membrane consists of a mixed conductor. PAR