Laboratory Generlator for Batch Synthesis of Pure Ozone B. F. Myers, E. R. Bertle, P. R. Erickson, and E. A. Meckstroth Space Science Laboratory, General DynamicsiConuair, San Diego, Calg. 92112 A LABORATORY OZONE GENERATOR is described in which quantities of pure ozone are synthesized in batch, The advantages of the prestnt apparatus over the conventional flow system (1) for synthesizing ozone result from the complete conversion to ozone of the initial oxygen charge to the generator. These advantages are circumvention of the need to separate mixtures ( 2 ) of liquid ozone-oxygen with the attendant explosion hazards; the elimination of the problem of ozone disposal throu,gh the synthesis of only the required amount of ozone; the absence of gas flow and the regulation required in maintaining flow as well as a reduction in the possible introduction of contaminants along the route of gas flow; and reduction in operating expenses when using high purity oxygen as the starting material. In the design of the present apparatus, use was made of previous observations (3, 4 ) that ozonization at low temperatures significantly increased the product yield. A diagram of the ozone generator is shown in Figure 1 . The generator volume, excluding the inlet and outlet tube volumes, consists of an annulus formed from borosilicate glass having a wall thickness of 2.5 mm. The mean diameter of the annulus is 7.7 cm, the length is 16.5 cm as measured to the center of the inlet and exit tubing and the spacing between the walls of the annulus i:; 2.0 mm. The electrodes with which a discharge is maintained in the generator during ozonization are formed from thin cDpper alloy sheets which are spring loaded and snapped ontc the inner and outer perimeters of the ozonizer annulus. During ozonization the generator is immersed in liquid nitrogen and by spring loading the electrodes, the different thermal contractions of the glass annulus and the metal electrodes are accommodated upon immersion. In the present apparatus, the electrodes were 6.7 cm in length resulting in a discharge volume of the order of 30 cc. Valves A and B are stainless steel, bellows-sealed, angle valves (Vacuum Electronic Corp., No. R5OPSS) with O-rings of Teflon. A stainless steel fitting (Crawford Fitting Co., No, 1210-2-12-316) is welded to one of the pipe nipples of each valve; these fittings haire Teflon ferrules which provide an inert, vacuum seal c o n n d n g valves A and B with the glass inlet and exit tubing. With this arrangement, the attained vacuum corresponded to a pressure less than m m H g and mm Hg/min for pressures between a leak rate of 3 X and m m H g as measured o n the inlet side of valve B . In operating the genera tor, valve A (Figure 1) is closed after evacuation and oxygen is admitted to the ozonizer. The oxygen supply was Liquid Carbonic O2(electrolytic laboratory grade) containing less than 10 ppm of contaminants which were mainly HzO, H2, and NP. With the Dewar raised, liquid nitrogen is added to a level above the electrodes as indicated in Figure 1 and the oxygen pressure in the ozonizer falls to 162
and B. G. Gowenlock, “Experimental Methods in Gas Reactions,” p. 187, Fdacrnillan, New York, 1964. (2) A . C. Jenkins, ‘‘Ozonl: Chemistry and Technology,” p. 13, Adcan. Chem. Ser. 21, A nerican Chemical Society, Washington, (1) H. Melville
D. C., 1959. (3) E. Briner and M. Ricca, Helc. Chim. Acta, 39, 340 (1955). (4) C. M. Bridsall, A. C. Jenkins, and E. Spadinger, ANAL. CHEM. 24, 662 (1952).
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A
Figure 1. Laboratory ozone generator (cross sectional view)
m m H g (the vapor pressure of oxygen at 77” K) as oxygen condenses. The quantity of oxygen ultimately transferred to the ozonizer was determined by regulating the pressure change in an adjacent oxygen reservoir of known volume. When the amount of oxygen desired to be converted to ozone has been condensed in the ozonizer, valve B is closed and the high voltage turned on. Discharge voltages from 15 to 19 K V are applied to the electrodes with a conventional gaseous tube transformer (France Mfg. Co., 15060P). During the synthesis, practically all of the ozone condenses (the vapor pressure of 03 is 3.5 X mrn H g at 77” K ) while liquid oxygen vaporizes to maintain its vapor plessure at the effective temperature of the ozonizer. The vapor pressure of oxygen could be measured during reaction with a sulfuric acid manometer connected to the ozonizer through valve A . The ozone production rate is essentially constant until the liquid oxygen is completely vaporized and then decreases in direct proportion as the oxygen vapor pressure decreases until all of the oxygen is converted to ozone. The liquid nitrogen Dewar is lowered, using the pneumatically operated piston, and the ozone slowly warms, vaporizes, and expands through valve A into the storage system. This is the most hazardous part of the operation and if the vaporization appears to be occurring too rapidly, a safety button may be depressed which activates the pneumatic cylinder and as a result the liquid nitrogen Dewar is rapidly raised to the position shown in Figure 1 . Furthermore, the entire ozone generation system is enclosed o n five sides by a ‘i4-inch Plexiglas shield and by a fine mesh screen on the remaining side behind the ozonizer to prevent injury to the operator in the event of an explosion. No explosions have occurred using this ozonizing system in over VOL 39, NO. 3, MARCH 1967
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100 experiments in which quantities of ozone up to 3 grams have been produced. However, one should remember that ozone is potentially an explosive and toxic chemical and while employing ozone, suitable precautions should always be taken. The Mylar curtain attached to the Plexiglas cover serves three purposes. After the air has been displaced by addition of liquid nitrogen to the Dewar, it maintains the atmosphere of nitrogen around the electrodes and prevents the formation of ozone which would occur if atmospheric oxygen were not excluded; it also prevents water vapor from being condensed in the Dewar and on the ozonizer and electrodes. Finally, it serves as a heat shield and decreases the rate at which the ozonizer warms during the vaporization of condensed ozone. Three methods were employed for the quantitative analysis of ozone: a measurement of the pressure in a calibrated volume ( 5 ) ,a standard titration procedure (6),and a chromatographic
method (5). The latter analytical method consisted of adding a gas sample directly to the charcoal column of a Perkin Elmer Model 154D Vapor Fractometer. The ozone readily decomposed in the presence of the column material to form oxygen; from the chromatographic analysis of the quantity of oxygen eluted, the original ozone concentration of the gas mixture sample was computed. The analyses of ozone samples by these three methods were in agreement with an error of _< = t 2 X . With these analyses it was demonstrated that pure ozone can be synthesized in the present apparatus. The ozone production rate is strongly dependent upon the voltage and varies from 1.1 grams 0 3 / h r at 19 KV to 0.6 gram Oa/hr at 15 KV for the particular ozonizer geometry employed. A larger ozonizer volume and higher applied voltages could increase the ozone production rate in the present apparatus.
( 5 ) General Dynamics/Convair Report GD/C-DBE-66-008, July
RECEIVED November 21, 1966. Accepted January 9, 1967.
1966. (6) D. H. Byers and B. E. Saltzmann, “Ozone Chemistry and . Ser. 21, American Chemical Technology,” p. 93, A d ~ a n Chem. Society, Washington, D. C., 1959.
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Work supported by the Advanced Research Projects Agency and monitored by the U. S. Army Missile Command under Contract No. DA-01-021 -AMC-l2050(Z).
