NOTICE

NASA CASE NO.

PRINT FIG. 1

LAR 14398-1

The invention disclosed in this document resulted from research in aeronautical and

space activities performed under programs of the National Aeronautics and Space

Administration. The invention is owned by NASA and is, therefore, available for licensing

in accordance with the NASA Patent Licensing Regulation (14 Code of Federal

Regulations 1245.2).

To encourage commercial utilization of NASA-owned inventions, it is NASA policy to grant

licenses to commercial concerns. Although NASA encourages nonexclusive licensing to

promote competition and achieve the widest possible utilization, NASA will provide the

necessary incentive to the licensee to achieve early practical application of the invention.

Address inquiries and all applications for license for this invention to NASA Patent

Counsel, Langley Research Center, Code 143, Hampton, Virginia 23665-5225.

Serial No.: 07/736,985

Filed: 07-29-91 LaRC

(NASA-C_se-LAR-14398-1) C_NVERTING A

ATMQSPH=RP TO A HIGH-PURITY 02 SUPPLY

Appl icJtion (NASA) 9 p

CO2 N92-30098

Patent

Unclas

G3/Z5 0111096
NASA Cme NO. UR 14398-1 

AWARDS ABSTRACT 

CONVERTING A CO, ATMOSPHERE TO A HIGH-PURITY 0, SUPPLY 

Planned exploration of Mars by human extravehicular activity in the early part of 

the next century (2007, 2009, 201 1) may require techniques to produce oxygen for 

human consumption (and/or other applications) from the existing Martian environment. 

Mission outlines presently indicate a 220-day round trip with 30-day sojourn times, 20 

days of which will be on the Mars surface. Clearly, it is desirable to provide a method of 

extracting environmental oxygen from existing sources, such as the oxide surface, the 

CO, ice, or the atmosphere itself, in order to alleviate the extensivg requirement of 

sufficient oxygen necessary for such a long-term mission. Perhaps the most energy 

efficient approach would be the continual utilization of the six millibar CO, atmospheric 

surface pressure that exists on Mars. . 

The present invention provides a technique for conversion of an oxygen bearing 

gas such as a CO, atmosphere to that of a high-purity 0, supply by the use of glow 

discharge dissociation that produces atomic oxygen and some molecular oxygen in the 

near vicinity of a hot silver or silver alloy membrane. The oxygen then adsorbs, dissolves 

and permeates the membrane to a downstream region where it thermally recombines to 

0, at the membrane surface and is pumped away and compressed in a storage volume. 

The pure oxygen can then be used for human consumption or other applications requiring 

0,. An application of the invention is the conversion of the Martian atmosphere of CO, 

to a useful and breathable 0, supply for astronaut consumption. There are also other 

applications, such as cabin atmosphere purification for the space shuttle or the Space 

Station Freedom. Also, there may be public interest where CO, is an unwanted 

byproduct that can be converted to useful 0,. 

The novelty of the present invention resides in the conversion of an oxygen bearing 

gas, such as CO, atmosphere, to a high-purity 0, supply by means of glow discharge 

dissociation of the oxygen bearing gas to produce atomic or molecular oxygen in 

proximity to a hot silver or silver alloy membrane, which serves to separate and direct the 

oxygen to a collection volume. 

Inventor: Ronald A. Outlaw 

Address: 98 Cove Road 

New ort News VA 23602 

ss: P 

Employer: NASA LaRC 

lntial Evaluator: Billy T. Upchurch 

serial NO.: 07/ 23 1, YpaFiled: 07- A 7- ?/ 
LAR 14398-1 -1- PATENT APPLICATION

CONVERTING A CO2 ATMOSPHERE TO A HIGH-PURITY 02 SUPPLY

Origin of the Invention

5 The invention described herein was made by a Government employee

and may be manufactured and used by or forthe Government for governmental

purposes without the payment of any royalties thereon or therefor.

10

Back.qround of the Invention

.

m

Field of the Invention

15

This invention relates generally to a process for preparing oxygen from

an oxygen bearing gas. More particularly, it relates to a process for converting

an oxygen bearing gas, such as CO 2 atmosphere, to a high-purity 02 supply

by means of glow discharge dissociation of the oxygen bearing gas to produce

atomic or molecular oxygen in proximity to a hot silver or silver alloy membrane,

which serves to separate and direct the oxygen to a collection volume.

20 , Description of the Background Art

25

3O

Planned exploration of Mars by human extravehicular activity in the early

part of the next century (2007, 2009, 2011 ) may require techniques to produce

oxygen for human consumption (and/or other applications) from the existing

Martian environment. Mission outlines presently indicate a 220-day round trip

with 30-day sojourn times, 20 days of which will be on the Mars surface.

Clearly, it is desirable to provide a method of extracting environmental oxygen

from existing sources, such as the oxide surface, the CO 2 ice, or the

atmosphere itself, in order to alleviate the extensive requirement of sufficient

oxygen necessary for such a long-term mission. Perhaps the most energy
5

10

LAR 14398-1 -2- PATENT APPLICATION

efficient approach would be the continual utilization of the six millibar CO2

atmospheric surface pressure that exists on Mars.

Accordingly, a primary object of the present invention is to provide a high

purity supply of oxygen from an oxygen bearing gas such as a carbon dioxide

atmosphere.

Another object of this invention is to use glow discharge to dissociate the

moleculesof an oxygen bearing gas such as carbon dioxide into atomic oxygen

in conjunction with a hot permeable silver or silver alloy membrane within the

glow discharge, which dissolves and separates the atomic oxygen, followed by

recombining the atomic oxygen into oxygen molecules and subsequent

compression and storage thereof.

Other objects and benefits of the present invention will become apparent

to those of skill in the art, upon consideration of the following disclosure.

15 Summary of the Invention

20

25

3O

The present invention provides a technique for conversion of an oxygen

bearing gas such as a CO2 atmosphere to that of a high-purity 02 supply by the

use of glow discharge dissociation that produces atomic oxygen and some

molecular oxygen in the near vicinity of a hot silver or silver alloy membrane.

The oxygen then adsorbs, dissolves and permeates the membrane to a

downstream region where it thermally recombines to 02 at the membrane

surface and is pumped away and compressed in a storage volume. The pure

oxygen can then be used for human consumption or other applications requiring

02. An application of the invention is the conversion of the Martian atmosphere

of CO2 to a useful and breathable 02 supply for astronaut consumption. There

are also other applications, such as cabin atmosphere purification for the space

shuttle or the Space Station Freedom. Also, there may be public interest where

CO2 is an unwanted byproduct that can be converted to useful 02.
LAR 14398-1

Brief Description of the Drawin,qs

-3- PATENT APPLICATION

10

For a more complete understanding of the present invention, including

its objects and attending benefits, reference should be made to the Description

of the Preferred Embodiments, which is set forth in detail below. This

description should be read together with the accompanying drawing, wherein:

FIG. 1 is a schematic showing the process of the present invention as

carried out in a suitable apparatus; and

FIG. 2 is a plot of downstream oxygen pressure vs. time for an actual

experiment employing the process of the present invention.

Description of the Preferred Embodiments

15

20

Referring now to FIG. 1, a schematic of the process of the present

invention is shown. As an example of an oxygen bearing gas, a flow of CO 2

10 from a carbon dioxide atmosphere is inlet into chamber 11 with the aid of

pump 12 at a rate to maintain an optimum pressure thereof at about 0.5 to 1

Torr for facilitating glow discharge. A voltage of about 380 volts DC in this

geometry is applied at electrode 13 to create glow discharge 14 which

dissociates the CO2 by electron impact as follows to form a partial pressure of

atomic oxygen:

25

or

CO2+ e _ CO + O + eCO + e --) C + O + e.

30

However, as in understood by those of skill in the art, a glow discharge may be

effected by other suitable means, such as radio frequency, microwave energy

or laser energy, among others, and atomic oxygen may be produced from the

CO2 by a mechanism other than electron impact dissociation. The atomic
LAR 14398-1 -4- PATENT APPLICATION

oxygen formed can recombine to form CO2, 02 and other oxygen bearing

gases, but can also adsorb and dissolve in silver membrane 15, which is

located in proximity to the glow discharge and kept at a temperature between

about 400 and 800°C by means of heater 16, ultimately permeating to a

5 vacuum interface in downstream region 17, where the atomic oxygen thermally

recombines on the surface of membrane 15 to form 02 and subsequently

desorbs. As is also understood by those of skill in the art, other oxygen

bearing gases may be employed, such as N20 or NO2, among others.

Permeable silver membrane 15 may be silver metal or advantageously a silver

10 alloy having a thickness of less than about 10.2cm, which thickness is capable

of supporting a pressure differential across the membrane. By means of

transfer pump 18 the desorbed 02 is pumped away from downstream region 17

to maintain as low a concentration of 02 therein as possible in order to provide

the necessary concentration gradient, as is understood by those of skill in the

15 art. The pumped away 02 is compressed into storage tank 19 to provide an

adequate pressure of oxygen for functional utilization. Following adsorption and

dissolution of atomic oxygen into silver membrane 15, the concentration

gradient across the membrane serves as the driving force to transport the

atomic oxygen to the downstream side, where the oxygen atoms recombine

20 and desorb into the low pressure region. At this point they are removed to

storage tank 19 by transfer pump or compressor 18. The downstream side 17

is at a significantly lower pressure than the upstream side, thus maintaining the

oxygen concentration gradient.

FIG. 2 shows the results of an actual experiment employing the process

25 of the present invention in which the temperature of a permeable Ago._Zro.os

membrane was kept at 650°C, and the CO2 atmosphere was maintained at 0.5

Torr. As shown in FIG. 2, application of the DC field as detailed above creates

a glow discharge, which supplies oxygen to the permeable silver membrane,

whereupon a mass spectrometer detected 02 signal goes up by several orders

30 of magnitude and reaches a steady-state level.
5

10

LAR 14398-1 -5- PATENT APPLICATION

A primary consideration of the process of the present invention is how

rapidly the atomic oxygen can permeate the heated silver membrane. This is

controlled primarily by the temperature, the upstream oxygen pressure, the

thickness of the membrane and the silver microstructure. As is understood by

those of skill in the art, the thickness should be as small as possible for most

efficient transfer; however, it must be large enough so that the membrane is

capable of maintaining a pressure differential across it. If the membrane is a

thin film of silver covering a porous plug, the thickness can be reduced

significantly. Another possibility is the employment of nanocrystals, which have

a large grain boundary diffusivity resulting in an increase of permeability.

What is claimed is:
LAR 14398-1 _ PATENT APPLICATION

CONVERTING A CO2ATMOSPHERE TO A HIGH-PURITY 02 SUPPLY

Abstract of the Disclosure

5 A CO2 atmosphere or any other oxygen bearing gas is converted to a

high-purity 02 supply by in-letting a flow of CO2 from the atmosphere into a

closed container, which is equipped with a means for creating a glow discharge

or other method for dissociation in proximity to a permeable silver membrane

kept at a temperature between about 400 and 800°C. A glow discharge is

10 created to dissociate the CO2 to form a partial pressure of atomic and

molecular oxygen. The oxygen produced is allowed to adsorb, dissolve as

atoms, permeate the silver membrane to a vacuum interface in a downstream

region thereof, where the atomic oxygen thermally recombines on the surface

of the membrane to 02 and desorbs: O + O _ 02 . The desorbed 02 is

15 pumped away from the downstream region to maintain as low a concentration

of 02 in the downstream region as possible. The pumped away 02 is then

compressed into a storage volume to provide an adequate pressure of oxygen

for functional utilization.
I0

CO

02 02

12

II

C02,C0 , 02

FIG. 1
o

rv.

D

(I)

(f)

i,i

N

0

10-5

10-6 _

I,I

iv"

p-

(/)

I0 -7-

0

a

I0-8

,THERMAL DISSOCIATION

AND PERMEATION

_L

0

i

GLOW DISCHARGE DISSOCIATION

AND PERMEATION

CO2/O 2

I I

2 3

TIME, MIN

I

4

I

5

FIG 2