Two systems, one for helium and one for argon, are used for purifying inert atmospheres. The helium system uses an activated charcoal bed at liquid nitrogen temperature to remove oxygen and nitrogen. The argon system uses heated titanium sponge to remove nitrogen and copper wool beds to remove oxygen. Both use molecular sieves to remove water vapor

Foster, M. S.

Johnson, C. E.

Kyle, M. L.

English

NASA Technical Reports Server

February 1969
	
Brief 69-10026 
•ICY C
 AEC-NASA TECH BRIEF 
AEC-NASA Tech Briefs describe innovations resulting from the research and development program 
of the U.S. AEC or from AEC-NASA interagency efforts. They are issued to encourage commercial 
application. Tech Briefs are published by NASA and may be purchased, at 15 cents each, from 
the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia 22151. 
Two Systems Developed for Purifying Inert Atmospheres 
Catalyst Bed 
Liquid Nitrogen	 Carbon Bed 
The problem: 
To maintain a pure inert gas atmosphere when 
handling reactive materials. The principal contami-
nants of such a system are oxygen, nitrogen, and 
water vapor, and less frequently, hydrogen, organic 
vapors, or acid vapors. Two methods of maintaining 
high purity in an inert atmosphere in a working en-
closure are (I) continually flushing with a pure gas 
and (2) recycling the inert gas through a purification 
unit. As the volume of the enclosure and rate of con-
tamination increase, economic considerations may 
favor the installation of a gas purification system. 
The problem then is to maintain the purity of the 
atmosphere in spite of continuing recontamination. 
The solution: 
Two systems which achieve and maintain a high 
level of gas purity have been developed for purifying 
inert atmospheres. One system, for helium, uses an 
activated charcoal bed at liquid nitrogen temperature 
to remove oxygen and nitrogen and uses molecular 
sieves to remove water vapor. The other system, for 
argon, uses heated (900, C) titanium sponge to remove
LJ Filter P	 I 
Argon Atmosphere
Working Enclosure
CopperTitanium 
Bed	 Bed 
6OO C	 9OO C 
Water-cooled 
Heat 
Eochanger I bat 
1 Catalyst Bed
Molecular	
I	
Bypass 
Sieve Bed
	
Cooler 
Filter	 '—' Pump 
nitrogen, copper wool beds to remove oxygen, and 
molecular sieves to remove water vapor. Impurity 
levels of <5 ppm each for 02 and N 2 and <I ppm 
H 2O vapor in the helium system and <20 ppm N2, 
5-15 ppm 02, and 5-25 ppm 1-120 vapor in the argon 
system are routinely obtained. These impurity levels 
are, however, dependent upon other variables such as 
enclosure volume, leak rate, diffusion rate through 
gloves, size and flow rate of the purification system, 
etc., but values such as these are considered typical for 
a well designed system. 
How it's done: 
In the helium purification unit shown in the left 
figure, the contaminated gas from the work enclosure 
first passes through a palladium catalyst. This unit 
reduces the hydrogen to I ppm by catalytic combina-
tion with oxygen to form water. 
The molecular sieve bed absorbs water vapor to 
minimize ice or snow formation in the cold sections. 
The heat exchanger, two concentric tubes formed 
into a single compact coil, is suspended in the vapor 
space above the boiling liquid nitrogen. The incoming 
(continued Irverlcil( 
Helium 
Workin 
Enclost 
This document was prepared under the sponsorship of the Atomic 
Energy Commission and/or the National Aeronautics and Space 
Administration. Neither the United States Government nor any per-
son acting on behalf of the United States Government assumes any
liability resulting from the use of the information contained in this 
document, or warrants that the use of any information, apparatus, 
method, or process disclosed in this document may not infringe pri-
vately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19690000026 2020-03-16T17:28:13+00:00Z
gas flows in the annular section where it is cooled 
by the nitrogen vapor outside and the cold helium gas 
exciting from the inner tube. 
The activated charcoal adsorber bed uses 8-14 mesh 
coconut charcoal in a copper vessel. This bed removes 
oxygen, nitrogen, and remaining traces of water 
vapor. To be most effective, the activated charcoal 
and the incoming gas stream should be at liquid nitro-
gen temperatures. 
A "canned" blower returns the gas to the working 
enclosure. An eight-stage centrifugal blower, com-
pletely enclosed in a steel container, has operated 
satisfactorily for over 12,000 hr. 
During dryer and adsorber regeneration, the boxes 
and blower are isolated. The carbon bed is regener-
ated by heating to —150°C and then evacuating. The 
dryer is regenerated by heating to 300°C and passing 
Ito 2 cfm of hot, dry nitrogen in reverse flow. 
Operation of the purification unit at a total recir-
culation rate of -'-10 cfm gave oxygen and nitrogen 
levels of <5 ppm and a moisture level of <I ppm 
routinely to two 30-ft volume work enclosures con-
nected in parallel. 
Argon Svsteni 
Chemical "getters" such asTi, Ca, V, and Ti—Zr 
alloy are generally used to remove nitrogen from 
argon. Titanium costs the least per mole of nitrogen 
removed and is readily available in sponge form. 
Oxygen is removed by passing the gas over a heated 
bed of copper wool. 
In the argon purification system shown at the right 
a palladium catalyst bed removes the hydrogen as in 
the helium system. The water vapor also is adsorbed 
from the gas stream on a bed of molecular sieves. A 
filter removes any dust arising from the molecular 
sieve bed. 
A critical component is the gas circulating pump 
which produces a discharge pressure sufficient' to 
overcome the resistance of' the titanium bed. Leak-
tightness of the pump is required to avoid air and 
water-vapor contamination of the circulating gas. A 
rotary-vane pump is used to circulate the gas stream. 
Remaining oxygen and water are removed by cop-
per wool at 600°C. This step is particularly impor-
tant because oxygen and water vapor passivate the 
titanium sponge with oxide, which inhibits the ti-
tanium—nitrogen reaction. 
Nitrogen is removed by the titanium sponge at 900'C. 
For maximum conversion of the titanium sponge, the
gas now through the bed is periodically reversed to 
cause a more uniform conversion to titanium nitride. 
The filter removes entrained particles. In opera-
tion, the circulation rate through the system is —4 
box-volumes/hr (2 cfm for 30-11 . enclosure). 
Oxygen levels of 5 to 15 ppm and water levels of 
5 to 25 ppm are routinely obtained. Low nitrogen 
levels in the working enclosure are more difficult 
to obtain because titanium is an effective getter for 
nitrogen only in the absence of oxygen and water 
vapor. In the absence of oxygen contamination in the 
inlet gas, nitrogen levels of <20 ppm can be main-
tained. 
In both systems, the oxygen and moisture impurity 
levels are observed by electrolytic cells, in-line de-
vices attached directly to the work enclosure. Nitrogen 
and hydrogen impurities are determined by standard 
chromatographic techniques. All methods have excel-
lent accuracy in the 0 to 5 ppm range. 
Notes: 
1. The innovation is significant in that many chemi-
cal systems, i.e., metals, hygroscopic materials, and 
reactive materials, must be handled in a working 
enclosure. 
2. Reference: Additional details may be found in 
Nuclear Applications, vol. 3, September 1967, p. 
563-567. 
3. Inquiries concerning this innovation may be di-
rected to:
Office of Industrial Cooperation 
Argonne National Laboratory 
9700 South Cass Avenue 
Argonne, Illinois 60439 
Reference: B69-10026 
Source: C. E. Johnson, M. S. Foster,

and M. L. Kyle
Chemical Engineering Division

Argonne National Laboratory
(ARG- 10234) 
Patent status: 
Inquiries about obtaining rights for commercial use 
of this innovation may be made to: 
Mr. George H. Lee, Chief 
Chicago Patent Group 
U.S. Atomic Energy Commission 
Chicago Operations Office 
9800 South Cass Avenue 
Argonne, Illinois 60439
. 
is 
S. 
Brief 69-10026	 Category 03


Two systems developed for purifying inert atmospheres

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server