crease in yield of combined HMX and R D X products resulting from inclusion of (CHzO), could be accounted for on this basis. With nitrogen-15 it became possible to indicate that this actually can take place by the condensation of the increased concentration of equilibrated methylene fragments with the ammonium radical. The extent of this participation with ammonium nitrate is approximately 8% for the formation of H M X and 407, for RDX: which is indeed equivalent to the 10% over-all increase in H M X i R D X yields observed Xvhen (CHIO), is included in the reaction mixture. The evidence given for the existence of a common precursor to H M X / R D X of the type --CH?,SHSOZ justifies any effort to prepare H M X from monomerhylene-containing compounds. .4 more direct approach to the formation of HMX free of R D X contamination in a simple reaction medium \vould greatly reduce the current cost of production.
Conclusions
The conclusions drawn from earlier work with carbon-14 are substantiated by these tracer studies with nitrogen-1 5. In addition, a mdre complete understanding of the chemistry of amino groups and the processes involved in the formation of the nitramino structure has been obtained through the use of nitrogen-1 5 rt'ith carbon-14 indirect evidence had indicated that ammonium nitrate does not condense independently with (CHzO), to yield H M X and R D X . With nitrogen-15 this was shown directly to be the case. The equilibration of methylene groups was found to be independent of ammonium nitrate concentration; and with nitrogen-1 5 the equilibration of amino nitrogens was shown to be independent of the (CH20), concentration. The two processes are mutually independent of each other, because their respective modes of equilibration are different. The equilibration of amino nitrogens, being ionic in character, takes place by means of exchange and, therefore, precedes the equilibration of methylene groups, which is attributed solely to a reaction process. It was concluded in the previous study with carbon-14 that hexamine and D P T degrade nonselectively to low molecular weight species, which then recombine to form products. The possibility of selective cleavage has been discounted by data obtained u i t h nitrogen-1 5 and carbon-14 The complementary nature of the data obtained from the two studies makes possible the narrowing down of the common fragmentary precursor to H M X and R D X as being of the type H O C H JYHSO 2. In the earlier work it was postulated that (CHZO), increases the concentration of methylene groups which exist in precursors to H M X and R D X . I t was suggested that the in-
Acknowledgment
The authors express appreciation to 51'. S. McKee for his assistance in conducting the extensive series of nitrolyses. They are grateful to F. S. Holahan, S. Helf, and J. M. VanderVeen for their critical evaluation of this study and helpful comments. literature Cited
(1) Bachmann, LV. E., unpublished work, University of Michigan, OSKD Kept. 1981. (2) Bachmann, LV. E., Horton, LV. J., Jenner, E. L., MacNaughton, N. LV., Scott, L. B., J . rlrri. Cheni. Sot. 73, 2769 (1951). 13) Castorina. T. C.. H o l a h m . F. S . Gravbush. l i . J.. Knufnian. J. V. K., Helf, S., Ibid., 82, 1617 (1460). (4) Gordy, LV., J . Chern. Phys. 14, 305-20 (1946). (5) Schiessler, R.LY,- Ross. I . F i . (to McGill University), U. S. 'Patent 2,434,230 (Jan. 6, 1948). RECEIVED for review Xovember 20, I964 ACCEPTEDMay 6, 1965 \
I
I
,
STORAGE OF OZONE IN DICHLORODIFLUOROMETHANE C H A R L E S S. S T O K E S , W I L L I A M J .
M U R P H Y , A N D T H E O D O R E R.
F L I N T '
Research Institute of Temple Uniuersity, Philadelphia, Pa. A ND R EW
E
.
P0TT E R
,
J R
.,
Lewis Research Center, N A S A , Cleueland, Ohio
Ozone is readily soluble in Freon-1 2 at temperatures as low as - 150" C.
Freon-1 2-ozone solutions of
7 0
up to 1 3 weight Os are stable when kept a t - 7 8 " C. and under a helium overpressure of at least 1000 p.s.i.g. These solutions are not sensitive to mechanical, electrical, or high brisance shock.
HE
use of liquid Freon-ozone solutions has been postulated
T as a method for stabilizing and storing ozone in concentra-
tions up to 1570 ( 7 ) . After a careful survey of the Freons, it \vas decided that dichlorodifluoromethane (Freon-1 2), would be the best choice for use with ozone since its liquid range is long, -138' to -30" C . , and the boiling point of ozone, -112" C., fell within this range. This work was performed in conjunction with an investigation of the mechanism of the Present address, Penn Valley Polymers Co., Gladwyne, Pa. 176
l & E C PRODUCT RESEARCH A N D DEVELOPMENT
hydroxyl air glow by the use of liquid ozone release a t 75-km. altitude ( 3 ) . Miscibility of liquid Ozone with Freon-1 2 at Cryogenic Conditions
The miscibility was determined in a vacuum system by mixing and observing the measured volumes of liquid ozone and liquid Freon-12 in a graduated borosilicate glass tube at various temperatures. The density of liquid ozone was considered to be 1.571 grams per cc. at 90" K.; the density of Freon-12 was 1.6 grams per cc. at its melting point. The
FREON-I2 COOLANT -
- STEEL
CONTAINER
-
OZONE
-
FREON-I2 SWTION
OZONE
CONCENTRATION-
MOLE %
Figure 1. Relation of vapor pressure to mole per cent ozone
results obtained are presented in Table I. The ozone used in the miscibility studies was prepared from a Welsbach Model T-23 ozonator ( 7 ) . Freon-12 (dichlorodifluoromethane, CC12F2) was obtained from the Freon Products Division, E. I. du Pont de Xemours 8r Co., Inc., Wilmington 98, Del. Liquid ozone can be mixed homogeneously with liquid Freon-12 in all proportions a t temperatures down to 123' K. ( - 150' C.). Figure 1 shows the effect of vapor pressure us. mole per cent ozone.
Figure 2.
Table 1.
Spark gap apparatus
Vapor Pressure of Homogeneous Mixtures of Freon12 and Ozone
-4bst.
v. P., ~
T h e ozone-Freon-12 solution was made by distilling pure liquid ozone over into the spark gap apparatus containing Freon-12 cooled to -150' C., with liquid nitrogen (Figure 2). The resulting solution at -150' C. was overpressured to 1 atm. with helium. The apparatus was then sealed off and placed behind a barricade with the electrode wires attached. A copper constantan thermocouple \vas placed in the cooling bath containing Freon-1 2. \\-hen the thermocouple indicated that the apparatus had warmed to -120' C., the first electrical discharge was sent through the liquid or the vapor as desired. A true liquid phase detonation was never experienced. Two low-level vapor phase detonations were observed. Vapor phase detonations were distinguished from liquid phase detonations by the low-level brisance and the intense ozone odor remaining. The results of these tests are given in Tables I1 and 111.
~~~~
Of;.
10.0
90.0
21.85
78.15
liquid-Vapor Sensitivity Tests of Ozone-Freon-12 Solution
Electrical Discharge. Low PRESSURE TESTS.The first series of sensitivity tests was performed with a 10% solution of ozone in Freon-12, to test the sensitivity of the vapor and liquid phases to a high voltage electrical discharge which was calculated to be far in excess of necessary activation energy required to detonate ozone gas or liquid. T h e experiments were conducted for a series of temperatures usually starting a t -120' C .
7'criiper cilia e
19.75
28.4
51.2
80.25
71.6
48.8
38.27
50.0
72.6
61.73
50.0
27.4
123 133 143 153 163 173 195 123 133 143 153 1'3 195 123 133 143 153 163 123 133 143
I53 163
~
"c'. 150 140 130 120 110 100 78 150 140 130 120 100 78 150 140 130 120 110 150 140 130 120 110
03,
.iIm. Hi! ... 15 32 61
...
...
... ... 26
__
33
110
... ... ...
34 75 150
...
... 50 110 223
...
HIGHPRESSURE TESTS. High pressure sensitivity tests Lvere designed to test detonability of a 10Tc ozone-Freon-1 2 solution. A special high pressure bomb designed and fabricated for this experiment (Figure 3). was made from 316 stainless steel with an inside volume of 19.6 cc. Exploding \\ires were used to test the sensitivity of the mixture. A spark discharge could not be used because of the high pressure (1500 p.s.i.g.) of helium. VOL. 4
NO. 3
SEPTEMBER
1965
177
Vapor Phase Sensitivity Tests of Freon-12-Ozone Solution b y Electrical Discharge Liquid 03 Discharge Val. yG Charge. Concn.. Temp., Pressure, 0 3 in Detona'M1. Cc "C. M m . Hg Vapor tion 1115 32 Yes 10 0 - 65 1.5 7 N0 -120 821 1.5 10 0 -100 882 14 NO - 80 1012 25 No 1.5 10.0 -120 821 7 S O - 74 1048 27.2 No - 70 1076 29.5 NO 1.5 10.0 - 81 1016 25 Yes
Table II.
Sam-
wt.
Ne 1 2 3
4
liquid Phase Sensitivity Tests of Freon-1 2-Ozone Solutions b y Electrical Discharge
Table 111.
Liquid Chalce. Sample 1
.111.
1 5
0 3
Concri 119. c c 10 0
2
1 5
10 0
3
1 5
10 0
Uischaige
Tfmp "C -120 -100 - 80 - -0 - 81
Detonation i n in Liquid 40 S O
so NO NO (Yes in vapor)
-119 - 79 - 69
N O
KO KO
Tivo exploding \\-ires \vere used, each a 3i',-inch length of stainless steel \\.ire, one in the liquid phase and one in the gaseous phase of the mixture. S o detonation or rapid decomposition in either the liquid o r gas phase resulted when the t\vo \vires \\-ere exploded in a 10-cc. solution of 12.5% ozone in Freon-12. at -78' C. and under 1500-p.s.i.g. helium. Low O r d e r Shock. .% simple qualitative drop-weight test was conducted on t\vo samplcs which were used to test vapor and liquid phase sensirivit).. but byliich had not detonated. A 12.5-poL1nd lead Jveight \vas dropped on the glass tube containing the 10 iveighi $; ozone liquid mixture from a height of 14.25 inchcs. l ' h e samples had been allo\ved to lvarm up to -60' C. As expected! a low order gaseous detonation occurred a1 this relatively \\-arm temperature level in each sample. l h i s test indicated a sensitivity to lo\\. order shock at temperatures above -70' C. for the vapor phase only. High Brisance Shock. For these tests a glass cartridge
KO.30
FITTING
FOR AUTOCLAVE
VAPOR
LIQUID
ENG.
PHASE
9 6 STAINLESS STEEL BODY
PHASE
PACKING
(22-mm. diameter) was filled with the ozone-Freon-12 solution. A piece of PETN Primacord approximately 1.5 inches long was inserted into a sealed dip tube which extended 1 inch into the mixture. The ozone-Freon-12 solution was cooled continuously by a surrounding bath of Freon-12 coolant in a tin can 3 inches in diameter. The whole apparatus was set on an aluminum plate inch thick, which in turn was supported by a short section of iron pipe 4 inches in diameter. The data for the tests are shown in Table IV; no ozone detonations were detected. Any such ozone detonation would have shown u p as a ruptured aluminum plate and an absence of strong ozone odor. It can be concluded from the liquid phase sensitivity tests that Freon-12-ozone solutions of up to 13 weight yo ozone are stable and insensitive to mechanical, electrical, and high brisance shock in the temperature range -120' to -69' C. Although no consistent vapor phase detonations occurred, the detonation limit for gaseous 0 8 - 0 2 mixtures is 9.2 volume 7c0 3 (2). The fact that vapor phase mixtures of Freon-12, ozone, and helium did not detonate 100% of the time at ozone concentrations about 10 volume % may be due to the low initial temperature and the small diameter of the tube. The detonation limit for liquid Os-liquid 0 2 mixtures is 18.3 mole% 0 3 (27.8 weight Yo) a t -183' C. ( 2 ) . Although that is about double the weight per cent ozone used in the Freon-12 solutions, the temperature is approximately 2l/2 times lower (-183' us. -78' C.) than that used for the liquid phase sensitivity tests. From the sensitivity test data it was determined that 10 weight Yo for ozone-Freon-12 solutions at -78' C. is safe. Preparation of Ozone-Freon-12 Solutions
The following experiments were carried out using a Welsbach Model C-9 ozonator with oxygen supplied either by bottles or a liquid oxygen cylinder. Small Scale Preparations. T h e ozonator was turned on and allowed to come to full operating ozone concentration. When stability of concentration (3% ozone) and pressure (10 p.s.i.g.) was reached, the entire 0 3 / 0 2 flow was diverted into a Freon-12 cooling coil (-30°C.) and from there into the cooled (-150' C.) bubbler cylinder. The Freon-12 (50 ml.) in the bubbler turned blue, indicating the absorption of ozone. For analysis of the spent gas from the bubbler cylinder, part of the flow was diverted from the hood vent to a bubbler flask containing 500 ml. of 27, potassium iodide solution. Total flow of gas was measured by water displacement. Samples of 1000 ml. of gas were used, taken every 10 minutes. Titration of the potassium iodide solutions with 0.1 .V sodium thiosulfate and starch indicator provided the data for calculation of the time necessary to produce a 10% solution of ozone in Freon-12. The final solution was analyzed by bubbling pure oxygen through the bubbler cylinder containing the ozone-Freon-12 mixture and making the absorbed ozone react in a pair of 4% potassium iodide solution bubbler flasks in series. When the second bubbler flask started turning amber, the saturated flask was removed and a fresh one was installed. T h e ozoneFreon-12 solution was allowed to warm slowly by remogin: heat from the oxygen, but was still cooled with Freon-12 to prevent too fast a warmup.
liquid-Vapor Sensitivity Tests b y High Brisance Shock Sample 1 Sample 2 T u b e diameter. Inm. 22 20 Sample size. 5 . 40.15 50 0 Liqu-id phase-ozone concn.. 11.20 12.75 \vt. ( c - 7 8 " C. Temperature. C. -130
Table IV.
Results
Figure 3. 178
I&EC
High pressure bomb
PRODUCT RESEARCH AND DEVELOPMENT
No
detonation
So
detonation
As seen from Table V, the temperature, inlet ozone concentration (controlled by 0 2 flow and pressure into ozonator), and absorption time all contribute to efficient preparation of ozone-Freon-12 solutions. I n the fast preparation the temperature was too high and inlet 0 3 concentration was too low. I n the second, the inlet O 3concentration and the flow was too low. I n the third all parameters were met and the preparation of a 13.4 weight yo 0 8 solution was accomplished.
FREON EXIT SAMRER
Large Scale Preparations, A stainless steel tank of approximately 450 cu. inches with appropriate stainless steel inlet and outlet valves was used for the large scale preparations. The inlet valve had a dip tube attached to it which went to the bottom of the tank. A series of holes was drilled in the side of the dip tube, and the end was sealed off. This provided a system for bubbling ozone-oxygen through the Freon-1 2. Figure 4 shows a flow diagram of the method used for preparation of the ozone-Freon-12 solution. The tank and accessories were pacified for the ozone-Freon mixture by passing 3 to 47, ozonated oxygen through for 5 hours. T h e ozone tank was filled with 24.6 pounds of Freon-1 2 and immersed in a liquid nitrogen-cooled Freon-1 2 bath. The inlet and outlet valves were closed, and the Freon bath was cooled down to - 150' =t2' C. in 6 hours. At this point the ozonator was turned on and allowed to stabilize for 1 hour under the flow conditions which were to be used in the ozonization of the Freon-12. During this time temperature of the tank was checked by means of thermo couples to ensure a constant temperature in the bath. When the bath temperature had no variation of more than 2' C., the ozonated oxygen from the ozonator was allowed to flow into the ozone tank. The ozone inlet concentration varied from 3.04 to 3.807,: and the outlet ozone concentration varied from 0.05 to 1.lYc. After several initial disturbances the oxygen flow steadied out to 10.6 liters per minute. By integration of the inlet and outlet ozone concentrations from the ozone tank, an accurate determination of the concentration of the dissolved ozone in the Freon-12 was made every 15 minutes during the ozonization. The ozonization was stopped after 27"4 hours with a final ozone concentration of 8.0 weight 70in Freon-12. The Freon-12 also contained approximately 2 7 , dissolved oxygen. At this point the ozonator was turned off and the ozone tank was disconnected from the ozonator. The tank was then connected to a helium pressurization system which included a dry ice-cooled trap. The pressure was built up in the tank by a series of line entrapments to a pressure of 950 pounds. 'The tank was then removed from the Freon bath and placed in dry ice in the storage box. Dry ice was placed completely around the tank, and the box was closed and carried out to the test area: approximately 150 yards from the preparation site. A pressure test was made on the tank after 2 l / 2 hours; the final pressure was 1700 p.s.i.g. This procedure \vas repeated many times with no problems encountered.
COOLING H 2 0
IN
I
PRES. RELIEF
0-15
I/MIN.
Y PRES. REG.
HIGH
Figure 4. tion
PRES.
PRES. REG.
OXYGEN
Flow diagram of Freon-12 ozoniza-
Determination of O3 i n Vapor i n Helium Overpressure. A determination of percentage of ozone in the helium overpressuring gas us. temperature was made starting at -130' C. T h e results of these experiments are shown i n Figure 5. Extrapolation of the data 10 -78' C. shows thaL the expected percentage (l.OYG)is present in the space over the liquid, shobving that the helium gas-ozone vapor mixtures above the liquid is Table V.
Small
Scale
Freon-12, ml. Coolant, ' C. Ozonator Ozone concentration, wt.
%
0
Preparation Solutions
50 - 123
of
Ozone-Freon-12
50 -150
40 -148
3
Start End Pressure, p.s.i.g. Absorption time, min. 0 8 / 0 2 flow, min. Final solution, wt. yc 0
0.456 3,66 9
45 8
4.2 0.88
0.616 3.22 10 107 2.80 4.0
3.15 10 130 3.1 13.4
-I40
-130
-120
-110
-100
TEMPERATURE,
-90
-00
-70
*C.
Figure 5. Relation of temperature to per cent ozone in helium overpressure VOL. 4
NO. 3
SEPTEMBER
1965
179
Warmup Test 2400
f\
To determine the ozone built up in the helium pressure and whether autoignition would occur, the storage tank was allowed to warm up to -19.5' C. T h e pressure rose to 2050 p.s.i.g., 390 p.s.i.g. of which was due to ozone coming out of solution. This represents 19% ozone in the vapor phase. This tank was equipped with an explosive valve, and it was blown open after 2 hours and 5 minutes. Various pieces of protective clothing were placed under the discharge port. No fire or oxidation was evidenced on explosion. Curves of temperature and pressure us. time are presented in Figure 6.
Conclusions
\ 0
I 20
I
I
40 TIM
I
I
I
60
BO
100
120
-
MINUTES
Figure 6.
140
Warmup test
completely safe when the tank is pressurized above 1000 p.s.i.g. a t -78' C.
T h e use of Freon-12 as a solvent for ozone in concentrations up to 13 weight % ' is a convenient and safe way to store large quantities of ozone (1 to 10 pounds), provided the solution is kept a t -78' C. and overpressured with helium to at least 1000 p.s.i.g. Sensitivity tests show that the solutions are insensitive to mechanical, electrical, and high brisance shock. However, the solutions must be handled with precaution, since ozone is innately unstable.
Storage Test
Acknowledgment
A heavy-walled storage tank similar to the one used in the previous tests was used. T h e tank was instrumented with a stainless steel-sheathed thermocouple and a Statham pressure transducer. The storage tank volume was 448 inches. After the usual pressure checks, calibrations, and passivation procedures, 11.5 pounds of double-distilled Freon-12 were put into the tank, the system was cooled to -152' C., and the ozonation process was accomplished. The final weight of ozone was 1.042 pounds and the final weight of Freon-12 was 11.50 pounds, giving an 8.31y0 solution and an ullage of approximately 50%. The test tank was pressurized a t 800 p.s.i.g. a t - 145' C. and then stored i n dry ice in a closed shed. Tank conditions were checked a t least once a day for a week. The pressure and temperature held steady a t the aforementioned values for the entire time.
The authors thank A. V. Grosse for his helpful suggestions A. G. Streng for carrying out the solubility studies, and L. A. Streng, R. W. Segletes, and W. J. Liddell for assisting in carrying out much of the experimental work.
I t can be concluded from this test that no ozone decomposed during the storage period, and solutions of 10% ozone-Freon-12 can be stored for long periods of time.
literature Cited
(1) Grosse, A. V., Streng, A. G . , Research Institute of Temple University, Tech. Note 4 (Aug. 1, 1957). (2) Harper, S. A., Gordon, W. E., Aduan. Chem. Ser., No. 21, 28 (1959). ( 3 ) Potter, A. E., Jr., Stokes, C. S., National Aeronautics and Space Administration, Tech. Note, in press. RECEIVED for review February 25, 1965 ACCEPTED June 18, 1965 Work sponsored by the National Aeronautics and Space Administration, Lewis Research Center, under Contract No. NAS-3-1918.
ANTIOXIDANT INHIBITION B Y SUBSTITUTED PHENOLS Concentration and Temperature Efects in Cumene W . G.
L L O Y D ' AND
R . G. Z I M M E R M A N
Polymer Research Laboratory, The Dow Chemical Co., Midland, Mich.
major practical problem in antioxidant stabilization is that of selecting the best antioxidant (or, often, finding a reasonably good antioxidant) for a given substrate material under given conditions of exposure to an oxidizing environment. L'arious factors, such as color, compatibility, and cost, enter into actual selection processes. \Ye are here concerned, 1 Present address. The Lummus Co., Newark, N. J.
THE
180
I&EC PRODUCT RESEARCH A N D DEVELOPMENT
however, only with the most basic factor, the actual chemical efficacy of a n antioxidant in protecting an oxidation-susceptible system from oxidative degradation. While countless specific stabilization problems have been solved by screening programs, the amount of generalized information of broad predictive value is surprisingly small. A recent review by Ingold ( 7 7 ) encompasses a good portion of
