EPA-R2-73-197
March 1973 Environmental Protection Technology Series
Optimum Production
of Atomic Oxygen
for Use in Analytical Technology
Office of Research and Monitoring
U.S. Environmental Protection Agency
Washington. D.C. 20460
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EPA-R2-73-197
Optimum Production
of Atomic Oxygen
for Use in
Analytical Technology
by
Dale J. Milnes and Joseph D. Henry
Ozone Research and Equipment Corporation
3840 North 40th Avenue
Phoenix, Arizona 85019
Contract No. 68-02-0558
Program Element No. 1A1010
EPA Project Officer: Frank Black
Chemistry and Physics Laboratory
National Environmental Research Center
Research Triangle Park, North Carolina 27711
Prepared for
OFFICE OF RESEARCH AND MONITORING
U. S. ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, D.C. 20460
March 1973
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This report has been reviewed by the Environmental Protection Agency
and approved for publication. Approval does not signify that the
contents necessarily reflect the views and policies of the Agency,
nor does mention of trade names or commercial products constitute
endorsement or recommendation for use.
11
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Page 1
SECTION I. PURPOSE AND SCOPE
The purpose of this contract has been to investigate
the feasibility of generating atomic oxygen by chemically
induced catalytic decomposition of ozone at near ambient
temperatures. The scope has been to perform a complete
literature survey to discover chemicals known to decompose
ozone and then to introduce these into a linear analytical
set up in which operating parameters could be varied to
establish optimum production of atomic oxygen as a function
of ozone decomposition.
SECTION II. BACKGROUND
It is well known that at high temperatures, 1832°F,
ozone decomposes to atomic oxygen and, at very low pressures
of less than 10 torr, atomic oxygen exists for a sufficient
time interval to be measured by the reaction NOo + 0—* NO + 02;
NO + 0 —*• N0£ + hv. This reaction is accompanied by measur-
able light emission, the magnitude of which is a function of
gas concentrations. The reaction has been exploited in ex-
perimental techniques for the determination of NO concentra-
X
tions by back titration of 0 to determine NO. However, the
technique is debilitated in two respects by dependence upon
high temperature: first, precision apparatus is required to
achieve and reasonably stabilize the required high temperature
in a reaction chamber. Second, light emission must be measured
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Page 2
significantly downstream of the high temperature reaction
chamber due to interfering radiation from the chamber itself;
thus, the light intensity measurement is at a locale where
the magnitude of the reaction light intensity is below maxi-
mum.
It is known that at ambient temperatures a stream of
0-j + 02 can be passed through beds of certain materials or
chemicals, that downstream measurements establish no ozone
is present in the effluent gas, and that there is no chemical
change in the bed material. These materials can be categorized
as catalysts, adsorbents, and catalyst-adsorbents of ozone.
Ozone is an unstable chemical that decomposes to oxygen
at ambient temperatures, the rate being a function of tempera-
ture, pressure and what might be called the container effect.
When a certain activation energy is supplied, the ozone mole-
cule decomposes. A change in temperature or pressure increases
the collision rate of molecules with each other and with the
container walls and collisions provide the activation energy
for decomposition. Various materials sensitize to varying
degrees the decomposition rate and those which do so to a very
high degree are in effect decomposition catalysts. Catalysts
such as Hopcalite and Iron Oxide probably involve an even ex-
change of oxygen atoms between ozone and the catalyst but,
upon reformation of the oxygen atoms, molecular oxygen (02)
rather than triatomlc oxygen (03) is formed.
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Page 3
Decomposition of ozone is accompanied by the liberation
of the heat of ozone formation. At high ozone concentrations
(30%-40% by weight) the liberated heat of formation is suf-
ficient to provide activation energy for the decomposition of
surrounding molecules resulting in a self-sustaining decom-
position of ozone. The liberated heat of adsorption of ozone
provides sufficient activation energy for decomposition of
ozone as an attendant to adsorption, e.g., adsorption in
active carbon is accompanied by decomposition.
In view, therefore, of the fact that ozone does decompose
to 62, there is the reasonable expectation that 0 exists for
an interval of time. The decomposition reaction would appear
limited to (a) 203-v20 + 202~^302 or (b) 203 —• 60 —" 302.
In either case 0 exists for an interval. If, in the case of
catalytic decomposition to molecular oxygen, an even inter-
change of oxygen atoms occurs between ozone and the catalyst,
then the reactions would appear similarly limited and again
atomic oxygen would exist for an interval of time.
A. 03 + RO —>RO + 0 + 02
B. 03 + R02 —*-R02 + 0 + 02
C. 03 + R03—» R03 + 0 + 02
The contract effort, therefore, has been directed toward
discovering materials which significantly accelerate the de-
composition of ozone at ambient temperatures and ascertain
if the time interval during which atomic oxygen persists in
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Page 4
the presence of such a material is sufficient for the reaction
NOX + 0 to be favorable over 0+0, or at least to be suffi-
ciently competitive to provide a measurable NOX + 0 reaction
within reasonable instrumentation standards. It has been so
established that attendant to high temperature decomposition
the time interval that 0 persists is adequate and the NGX + 0
reaction is competitive. The contract effort further intended
to optimize the reaction by investigating the consequence of
changing experimental parameters: temperature and pressure
over a moderate span, system geometry, flow rates, etc.
SECTION III. LITERATURE RESEARCH
An extensive literature survey was proceeded upon to
discover candidate chemicals for the decomposition of ozone.
Subsidiary research was performed to achieve familiarity
with the experiences, instrumentation, and circumstances
attendant to prior investigations into atomic oxygen pro-
duction and atomic oxygen-NOx reactions.
The following selected references were studied and would
be recommended as a bibliography for researchers in this area:
Bartz, J. A. and J. J. Vidal, "Catalytic Oxygen Atom
Probe for Determining Concentration in High Temper-
ature High Velocity," U. S. Clearinghouse Federal
Scientific Technical Information. AD 1970, No. 704814
1970.
or,, S. W. and A. E. Axworthy, "Mechanism of Gas
Phase, Thermal Decomposition of Ozone," Journal of
Chemical Physics. Vol. 26, p. 1718, 1957.
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Page 5
Benson, S. W. and A. E. Axworthy, "Reconsideration
of the Rate Constants from the Thermal Decomposition
of Ozone," Journal of Chemical Physics, Vol. 42,
No. 7, pp. 2614-2615, 1965.
Boberg, J. E. and M. Levine, "Catalytic Filtration
of Ozone in Airborne Application," Journal of the
Engineering Industry. Vol. 84, pp. 42-48, 1962.
Curran, R. K., "Negative Ion Formation of Ozone,"
Journal of Chemical Physics, Vol. 35, No. 5, pp.
1849-1851, 1961.
Emelyanova, G. I., V. P. Lebedev, and H. I. Kobozev,
Abstract from "Catalytic Decomposition of Liquid Ozone
at Low Temperatures. Activation Energy of the Low
Temperature Decomposition of Ozone and the Activity
of Palladium Black," Vestnik Moskov Univ.. Ser. 11,
Khim., Vol. 16, Nos. 2 and 6, pp. 31-34, 1961.
Emelyanova, G. I., V. P. Lebedev, and U. I. Kobozev,
"Physical Chemistry of Concentrated Ozone. XII. The
Low Temperature Heterogeneous Catalytic Decomposition
of Concentrated Liquid Ozone," Zhurnal Fizicheskoi
Khimii. Vol. 38, No. 1, pp. 170-175, 1964.
Harteck, P., S. Dondes, and B. Thompson, "Ozone:
Decomposition by Ionizing Radiation," Science. Vol.
147, No. 3656, pp. 393-394, 1965.
Jenkins, A. C., A. H. Malik, and R. L. Pruett, "De-
composition of Ozone," Canadian Patent, No. 688,560,
Issued June 9, 1964, U. S. Patent No. 2,980,494,
Issued April 18, 1961.
Kaufman, F. and J. R. Kelso, "Rate Constant of the
Reaction 0 + 202—^03 + 02," Discussions of the Fara-
day Society. No, 37, pp. 26-37, 1964.
Kaufman, F., Proceeds of the Royal Society, A247,
pp. 123-139, 1958.
Kelso, J. R. , "The Productio/n of Atomic Oxygen by
the Thermal Decomposition of Ozone," paper available
through National Technical Information Service, 1966.
Mahieux, F., Abstract from "Some Tests on the Catalysis
of Ozone Decomposition," Genie Chimique, Vol. 87, No.
1, pp. 15-17, 1962.
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Page 6
McKenney, D. J. and K. J. Laidler, "Elementary Pro-
cesses in the Decomposition of Ozone," Canadian Journal
of Chemistry. Vol. 40, pp. 539-544, 1962.
Means, A. M. and A. J. Morris, "Use of the N02 Titration
Technique for 0 Atom Determination at Pressures Above
2 Torr," Journal of Physical Chemistry. Vol. 74, No. 22
pp. 3999-4001, 1970.
Reeves, R. R., P. Harteck, and W. H. Chace, "Chenilumin-
escent Nitric Oxide-Oxygen Atom Reaction at Low Pressures,"
Journal of Chemical Physics. Vol. 41, p. 764, 1964.
Reeves, R. R., P. Harteck, and Mannella, "Rate of Re-
combination of Oxygen Atoms," Journal of Chemical
Physics. Vol. 32, p. 632, 1960.
Reeves, R. R., P. Harteck, and Mannella, "Rate of Re-
combination of Nitrogen Atoms," Journal of Chemical
Physics. Vol. 29, p. 608, 1958.
Reeves, R. R., P. Harteck, and Mannella, "Reaction of
Oxygen Atoms with Nitric Oxide," Journal of Chemical
Physics. Vol. 29, p. 1333, 1958.
Rolfes, T. R., R. R. Reeves, Jr., and P. Harteck, "The
Chemiluminescent Reaction of Oxygen Atoms with Sulfur
Monoxide at Low Pressures," Journal of Physical Chem-
istry. Vol. 69, No. 3, pp. 849-853, 1965.
Trusk, B. A., "The Recombination of Oxygen Atoms in
a Discharge Flow System," Journal of Chemical Educ-
ation. Vol. 41, No. 8, pp. 429-431, 1964.
SECTION IV. RESULTS OF LITERATURE RESEARCH
As a consequence of a survey of the literature plus
in-house (Ozone Research & Equipment Corporation) experience
with ozone decomposition, the following chemicals were se-
lected as candidates for the decomposition of ozone:
A. Molecular Sieve: Na12[(A102)i2(Si02>12J * H2°
B. Hopcalite: Mn02, CuO, CoO, and Ag20
C. Silica Gel: Si02
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Page 7
D. Activated Charcoal: C
E. Soda Lime: NaOH and CaO
F. Nickel: Ni
G. Iron Oxide: Ye2°^
H. Manganese Dioxide: Mn02
I. Sodium Hydroxide: NaOH
J. Calcium Metasilicate: CaSi03
K. Sodium Metasilicate: Na2Si03
L. Vanadium Pentoxide: ^2®$
The literature survey established and/or confirmed the
following significant data:
A. The substances which catalytically decompose ozone
are mainly oxides of metal.
B. There has been no determination of the intermediate
product, atomic oxygen, attendant to the decomposition
of ozone to oxygen.
C. There has been no study on the feasibility of gener-
ating atomic oxygen from the catalytic decomposition
of ozone by substances at or near ambient temperatures.
D. The principle of atomic oxygen measurement using NC>2
is well established. The reaction NO + 0 —>-N02 + hi/-
provides a measurable yellow-green glow, the intensity
of which varies as a function of concentration.
E. In the cited reaction, maximum light intensity occurs
when the concentration of N02 is equal to one-half
the concentration of atomic oxygen.
F. In the cited reaction, the light is extinguished when
the NC>2 concentration equals the atomic oxygen concen-
tration.
G. The measurement instrumentation is critical and the
work of Kaufman* provides the best data for model
construction.
^Reference Cited.
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Page 8
H. The Kaufman technique provides the following prin-
ciples and parameters:
1. Vacuum in the one torr range is required.
2. A photometer sensitive in the 5500A region is
required.
3. Precision measurement of gas flows are required.
4. Because of the extremely low gas flows, a mano-
meter measured pressure drop across precision
bore capillaries is essential to gas flow mea-
surement .
5. Determination of capillary size may be established
using Poiseuille's Law of Gases which is expressed:
F = 7Tr4(Pi2-P22)
16I?LRT
Where F • molar flow rate, gmole/sec
r ° radius of capillary, cm
P! • pressure at inlet of capillary, dynes/cm2
?2 ° pressure at outlet of capillary, dynes/cm
t^ = viscosity of gas, g/cm-sec
L = length of capillary, cm
R « gas law constant, cm^-dynes/cm2
gmole-°K
T « temperature of gas, °K
SECTION V. INITIAL EXPERIMENTATION
Initial experimentation was conducted using an analytical
set up as illustrated in Figure I. A total of 72 tests were
conducted upon the above cited candidate chemicals and the
results were entirely negative, that is, the photometric equip-
ment provided a zero light signal indication in every test.
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Page 9
A number of parameters were varied during these tests:
A. Tests were conducted at both 75° and 200°F.
B. Three different reaction vessels were employed
having the following dimensions:
1. 8 mm ID x 6 mm long
2. 3 mm ID x 20 mm long
3. 8 mm ID x 25 mm long
C. The oxygen-ozone stream of 20-60 cc/min at 1 torr
and the N02 stream of .12-. 36 cc/min at 1 torr were
presented in alternative manners.
1. The oxygen-ozone stream was passed through the
catalytic chemical bed and immediately upon
exiting the N0£ stream was impinged upon it.
2. The oxygen-ozone stream and the N02 stream
were joined before entering the catalytic
chemical bed.
SECTION VI. ANALYSIS OF INITIAL EXPERIMENTATION
It was concluded, upon analysis, that the negative results
of initial experimentation could be attributed to one or more
of the following:
A. An atomic oxygen yield does not occur as an at-
tendant to the catalytic decomposition of ozone
at near ambient temperatures.
B. The existance interval of atomic oxygen generated
by catalytic decomposition of ozone at or near am-
bient temperatures is not adequate for the NOX 4- 0
reactions to occur.
C. At near ambient temperatures the reaction 0 + 0-»02
is preponderantly more favorable than the reactions
NOX + 0.
D. The photometric instrumentation employed was not
adequately sensitive to respond to the emitted
reaction light signal.
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A meeting was held at the facility of the Contractor
between project personnel and representatives of the Environ-
mental Protection Agency: Mr. John E. Sigsby, Project Officer,
and Mr. Frank Black, subsequent Project Officer. An in depth
analysis of instrumentation and the experimental set up pro-
vided the following conclusions and recommendations:
A. A more sensitive photometric circuit and components
would be required to establish the certainty of the
negative results.
B. Recommended improvements in high vacuum system
techniques would enhance the possibility of
positive results.
C. High flows of low concentrations NC>2 (100 ppm)
rather than low flows of high concentrations N0£
(100%) as had been employed in the initial ex-
periments would both enhance the possibility of
positive results and be more equatable with
existing data on thermal decomposition of ozone.
Subsequently to this meeting, the Contractor was pro-
vided on loan from the Environmental Protection Agency the
following more sensitive photometric equipment:
A. RCA Type 7265 Photomultiplier tube
B. Keithley Model 414S Plcoammeter
C. Keithley Model 245 High Voltage Supply
SECTION VII. FINAL EXPERIMENTATION
A. Instrumentation and Set Up
Figure II is a perspective drawing of the experimental
\
set up for the determination and measurement of atomic oxygen.
Figure III is a block diagram of this set up. Figure IV is
a drawing of the reaction vessel.
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Page 11
In operation, the motive force for the flow of gases is
the vacuum pump, providing a vacuum of .5 to 3 torr in the
reaction vessel. Candidate chemicals were charged into one
or the other of the two catalytic chambers illustrated in
Figure IV. A 2%/wt. concentration of ozone in an 11 cc/min
(SIP) oxygen stream passed from the ozonator through the
catalytic chamber and impinged upon the glass window in the
immediate view of the photomultiplier tube. Simultaneously
a 100 ppm/volume N02 concentration in a 0-28 cc/min (SIP)
argon stream impinged adjacently upon the window. The gener-
ation of atomic oxygen by the catalytic decomposition of ozone
is sensed and measured by the photometer responding to the
ultimate reaction of N02 + 0 -*NO + 02; NO + 0 -»-N02 + h^.
To establish the facility and accuracy of the experimental set
up, a signal was deliberately generated by introducing NO + 03
to produce the reaction NO + 0^ —»N02 + 02 + hv. This photo-
metry responded quite sensitively to this reaction.
b, Final Experimental Results and Data
A total of 24 test schedules were conducted as set forth
in Figure V. Each candidate chemical was charged into the
teflon catalytic chamber (Figure IV Detail B) and the experi-
ment conducted at 75°F. Each candidate chemical was then
charged successively into the ceramic catalytic chamber (Figure
IV Detail A) and the experiment conducted over the temperature
span of 75°F to 380°F proceeding over a 15 minute interval.
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Page 12
The light signal was zero in the instance of every
candidate chemical under every test condition.
SECTION VIII. CONCLUSIONS
Ozone can be catalytlcally decomposed to molecular
oxygen at ambient temperatures by certain selected chemicals,
predominantly oxides of metals. The existence of the inter-
mediate product, atomic oxygen, is a persuasive deduction that
has neither been proved nor controverted by this contract
effort.
It is concluded that any atomic oxygen generated as an
intermediate product in the catalytic decomposition of ozone
does not at ambient temperatures provide the following reaction:
N02 •+ 0 -*• NO + 02 5 NO + 0 -* N02 + hv.
It is theorized that the reaction of oxygen atoms to
combine as oxygen molecules proceeds to the exclusion of
atomic oxygen reactions with oxides of nitrogen at ambient
temperatures.
It is recognized that the extensive surface area of the
catalysts may enhance the molecular oxygen reaction.
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FIGURE V
Test Schedule
Test No.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
Chemical
Molecular Sieve
Eopcalite
Silica Gel
Charcoal
Soda Lime
Nickel
Iron Oxide
Manganese Dioxide
Sodium Metasilicate
Calcium Metasilicate
Sodium Hydroxide
Vanadium Pentoxide
Molecular Sieve
Hopcalite
Silica Gel
Charcoal
Temp °F
75°F
75?F
75°F
75°F
75°F
75°F
75°F
75°F
75°F
75°F
75°F
75°F
75°F-380°F
75°F-380°F
75°F-380°F
75°F-380°F
Ozone Flow
2% 0^/wt (STP)
11 cc/min
11 cc/min
11 cc/min
11 cc/min
11 cc/min
11 cc/min
11 cc/min
11 cc/min
11 cc/min
11 cc/min
11 cc/min
11 cc/min
11 cc/min
11 cc/min
11 cc/min
11 cc/min
Nitrogen Dioxide Flow
100 ppm' NO 2 in Argon (STP)
0-28 cc/min
0-28 cc/min
0-28 cc/min
0-28 cc/min
0-28 cc/min
0-28 cc/min
0-28 cc/min
0-28 cc/min
0-28 cc/min
0-28 cc/min
0-28 cc/min
0-28 cc/min
0-28 cc/miri
0-28 cc/min
0-2,8 cc/min
0-28 cc/min
Signal
Zero
Zero
Zero
Zero
Zero
Zero
Zero
Zero
Zero
Zero
Zero
Zero
Zero
Zero
Zero
Zero
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Test Schedule
Page 2
Test No*
17
18
19
20
21
22
23
24
Chemical
Soda Lime
Nickel
Iron Oxide
Manganese Dioxide
Sodium Metasilicate
Calcium Metasilicate
Sodium Hydroxide
Vanadium Pentoxide
Temp °F
75°F-380°F
75°F-380°F
75°F-380°F
75°F-380°F
75°F-380°F
75°F-380°F
75°F-380°F
75°F-380°F
Ozone Flow
2% 03/wt (STP)
11 cc/min
11 cc/min
11 cc/min
11 cc/min
11 cc/min
11 cc/min
11 cc/min
11 cc/min
Nitrogen Dioxide Flow
100 ppm N02 in Argon (STP)
0-28 cc/min
0-28 cc/min
0-28 cc/min
0-28 cc/min
0-28 cc/min
0-28 cc/min
0-28 cc/min
0-28 cc/min
Signal
Zero
Zero
Zero
Zero
Zero
Zero
Zero
Zero
Molecular Sieves Na12[(A102)12(Si°2)121 x H2°
Silica Gels Si02
Charcoals C
Soda Lime: NaOH and CaO
Iron Oxides Fe203
Manganese Dioxides
Nickels Ni
Sodium Metasilicate:
Calcium Metasilicate: CaS103
Sodium Hydroxides NaOH
Hopcalite: Mixture of Mn02, CuO, CoO, and Ag20
Vanadium Pentoxides V205
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A.
B.
C.
D.
E.
F.
G.
H.
I»
J.
Oxygen tank
0*yg«n flow control valve
Ozonator
Ozone flow control valve
Ozone concentration sample
outlet
Capillary tube ozone flowmeter
Catalyst
Nitrogen Dioxide tank
Nitrogen Dioxide flow control
valve
Capillary tube Nitrogen Dioxide
f lowrator
Reaction vessel
Vacuum bypass control valve
Vacuum pump
Exhaust
Photomultiplier tube Ji-G
Photometer
Thermocouple vacuum gauge
Thermocouple gauge control
Thermometer
Heating Coil
FIGURE I
INITIAL EXPERIMENTAL APPARATUS
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COW/bTXWT. VOLUME
UITROQEy_HlOXIDE
SHUT-OFF VALVE
I) TTH.ERMDCOU
y X oc? «?:>•-/» i i frtz.- T
VACUUM
PICOAMMETEK
UWE"
OZQhiATOR
QH.
TAQE
POWER eUPPL
PRESSURE METER
FIQUR.E
EXPER-IMEMTA.L APPARATUS
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PIOOA.MMETER.
DYMODE
CIRCUITRY
- PMOTOMUUTIPLIER.
THERMOCOUPLE
PRESSURE.
METER
WINDOW
THERMOCOUPLE
PRESSURE
1MLET
/.
SHUT-OFF
VKLVE
SUPPL
OE
LY
LIQHT SHIELD
REACTOR
HJ
OZOMATOR.
^NEEDLE
VALVE
SHUT-OFF
VALVE
VACUUM
PUMP
FIGURE
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T
T
DIA
*±
DIA
S.S.TUBE
I J
SEE DETAIL
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