real world of
edited by
W. C. FERNELIUS Kent State University Kent. OH 44242 HAROLD
WITTCOFF
Koor Chemicals Ltd. Beer-Sheva, Israel P.O.B. 60
Industrial Uses of Ozone Gerhard A. Cook State University of New York at Buffalo, Buffalo, NY 14214 Almost evervone is familiar with ozone (.0 2-.) .. the allotronic form of oxygen, and recognizes its characteristic odor in the vicinity of electrical equipment. Yet few persons are accustomed to thinking of ozone as an industrial chemical. Its uses, although now relatively small, are expected to increase significantly. A t present, they are (1)in water treatment, (2) in the preparation of intermediates for the manufacture of plasticizers and synthetic lubricants, and (3) in the production of important pharmaceuticals. Water Treatment ( 1) The earliest commercial use for ozone was in the treatment of domestic water. The ozone served two purposes: disinfection and the oxidation of traces of undesirable oreanic compounds dissolved in the water. These uses never h & n e very extensive in the United States because Federal health regulations compelled every city to treat its drinking water with chlorine before the water was distributed to consumers. Ozone for the treatment of water was and is, more widely used in Europe. In the U.S.. denendence unon chlorine for the treatment of water is todav rhnllenged by a branch of the Federal governmen1 itself. In 1971 the Knvirunrnental I'rotection Aeencv (EPA) examined ( 2 )the New Orleans water supply an; di;. covered the Dresence of small amounts of 66 different chlorinated organic nmpounds. 'l'hese apparently resulted from the reactlam of chlorine with matrriali dissolved in the water. Evidence has accumulated to show that some of these chlorinated organic compounds are carcinogenic. In addition, chlorine often introduces unpleasant tastes and odors; and, if the water contains dissolved ammonia, chlorine produces chloramines which are toxic to fish and other aquatic life. Thus, ozone has advantages in treating wastewater, both in
392
Journal of Chemical Education
oxidizing organic imnurities and in disinfecting the water. Ozonikili$ bacteria faster, and viruses mu& faster, than does chlorine. Ozone has a very high oxidation potential, exceeded only by that of fluorine, atomic oxygen, hydroxyl radicals, and a few other s ~ e c i e (3): s and the oxidation products of such pollutants as phenols, cyanides, surfactants, sulfites, and chloramines are tasteless, odorless, and harmless. In earlier years, before the emphasis upon avoidance of oollution. manv chemical and other factories were freelv discharging toxic wastes into nearby rivers. One such river was the Schuylkill, from which the city of Philadelphia was ohtaining about a fifth of its water supply. The drinking water obtained from this river smelled and tasted so had that the city decided, at the suggestion of the Welshach Corporation, to try ozone treatment. Although this was successful, the water still had to be chlorinated to meet federal government regulations. Since ozone had already removed the organic impurities, no bad odors or tastes were produced by the chlorine. When industrial discharges into the river were finally stopped under government pressure, the ozone plant was shut down. Today, according to the EPA ( 4 ) , "ozone appears to be the most promising alternative to chlorine. . . . Its popularity in the U.S. is on the upswing." The treatment of water with ozone, although now one of the smaller uses for ozone in the U.S., may, within the next few years, he the largest. In some parts of the U.S., drinking water is becoming scarce; and often the best wav of imnrovine the situation is to recvcle the available water. After purification of the wastewater for recvclina. it would be given an ozone treatment to oxidize org k i c impurities andto disinfect the water before distribution to homes.
Ozonization of Oleic Acid
The ability of ozone to sever organic double bonds is employed by Emery Industries, Inc., of Cincinnati in what is now by far the largest single use of ozone in the world (5). This plant consumes many tons of ozone per day to react with oleic acid 0
II
CH~~~~~H=CFI(CHJ+.-OH
+
O,
-
0
(c,H,,)+GH,,)c-oH
II
00'
molozonide
(A molozonide is the initial addition product of ozone to a double hond.)
A convenient oxidizing agent
pelargonie acid
azelaio acid
In carrying out these reactions, oleic acid is first dissolved in pelargonic acid and then treated with ozone to form the molozonide, which is then oxidized by a convenient oxidizing acids, which are separated and agent to azelaic and -pelargonic The oleic acid comes mostly in an impure form called "red oil," made from beef tallow in meat packing plants. Another source of crude oleic acid is the distillation of "tall oil." a by-product of paper making ( 6 ) . Pelargonic acid is now in such demand that Celanese Corporation has recently introduced a product made from a Ca-alpha olefin obtained during petroleum refining. This hydrocarbon is first converted to pelargonyl aldehyde by a variant of the 0x0 reaction, in which hydrogen and carbon monoxide are used under pressure in the presence of a catalyst, to react with the double hond of the Cs olefin. The pelargonyl aldehyde is then oxidized to pelargonic acid. The n-hexyl, cyclohexyl, isooctyl, and 2-ethylhexyl esters of azelaic acid are use extensively as plasticizers (to soften and to impact flexibility to organic resins) and as synthetic lubricants (7).Esters of pelargonic acid with polyhydric alcohols such as pentaerythritol are used primarily as high-grade plasticizers in alkyd resins ( 8 )to impart good color and gloss retention. Aluminum and lithium salts of azelaic acid are used as lubricating greases.
'
Manufacture of Pharmaceuticals
Severance at the double bond by Ozone is employed by the pharmaceutical companies to give a number of valuable products, although the volume of production is small cornoared with that of azelaic and pelargonic acids. However, the Galue per gram of the drugs and sex hormones made by the pharmaceutical factories is very large compared with the unit value of azelaic and pelargonic acids. The pharmaceutical companies start with naturally occurring polycyclic compounds called steroids, which come from either plants or animals. All steroid? have a fused 17carbon-atom ring system, the cyclopentenophenanthrene nucleus (9,101:
Steroid alcohols, called sterols, also have the 17-carbonatom nucleus and are therefore steroids. An important example of such alcohols is stigmasterol, readily available from soybean oil and one of our most important sterol raw materials (10). Stigmasterol has an OH group on Ca, a double bond hetween carbon atoms 5 and 6, and aside chain (R) attached to It C17 where R = -CH(CH~)CH=CHCH(C~H~)CH(CH~)Z. is the double bond in the side chain which is ozonized. Methods other than ozonization to break this double bond have been tried over the years, hut the yield of the desired nroduct was noor. Bv suitable treatment of the molozonide Hnd hy modikcationbf the stigmasterol unit, a good yield of .roee..ester one is oroduced. This is a molecule which not onlv has uses of its own. hut also it ser\,esas an i n t e r m d a t e in the hiosynthes~sof all other steruid hurmmei, including cortisone and-the male and female sex hormones (11). Cortisone, a powerful drug for relieving pain (but toxic if used in too large doses), has the usual steroid nucleus with R = -COCH20H, a double hond between C4and Cg, and =O at Ca and Cn. The Cll keto group does not occur in more than traces in nature; the interesting story of how it was chemically introduced in quantity (e.g., to make cortisone) has been told by Hazen (9). Industrial Manufacture of Ozone
The only process known to he feasible for the industrial manufacture of ozone is as follows: a stream of either air or oxygen is passed through a space or gap between two parallel-plates or concentric metal tube electrodes while an alternating electric potential between 3000 and 20,000 volts, ranging from 50 to 10,000 Hz (cycles per second) is supplied, producing a "silent electric discharge" which fills the gap. A dielectric material (usually glass) must he present between the two electrodes, one of which is at the high potential while the other is grounded. The dielectric serves the purpose of spreading the electric discharge evenly throughout the space between the electrodes and of preventing arcing or the formation of sizable sparks. Collisions of electrons with gas molecules produce many ions and some ozone molecules. Since the ozone is unstable in the presence of an electric discharge, and increasingly so as the temperature rises, it is necessary to cool one (rarely both) of the electrodes with cooling water or a gas, such as air. In practice, only the grounded electrode is cool~a -- - - - -.
When oxygen (instead of air) is used as the feed gas to the ozone generator, approximately twice the weight of ozone is produced per kilowatt hour of electrical energy. Since the most ozone is the expensive non-capital item employed in electrical energy, it pays to use oxygen if it is available at
,.,,,.
Because the concentration of the element oxygen in relatively pure industrial oxygen is about five times that in air, one would think that five times, rather than twice as much ozone should he oroduced from oxvaen as from air. In this case, however, the law of mass act& does not apply, because the ozone is produced in a complicated series of reactions (13)and hocanae there is an unfortunate comnetitive reaction. namelv - - - - - --~~~ the decomposition of ozone by electrdnic homhardmedt, which reduces the net vield, -~~~~~~~~ When oxygen is used as the feed gas, it must he recycled, since onlv 1-3% of the oxveen is converted to ozone oer Dass through the ozone generator. The recycling i n v o l v e ~ t h ~ f o l lowing steps: purification of the oxygen, drying, and then passing the purified oxygen through the ozone generator again. In recent years, the cost of ozone bas been reduced hy improvements in ozone generation and by other minor advances. One example of these improvements is the use of porcelainenameled steel as electrodes in which the enamel serves as a built-in dielectric material. A special porcelain enamel has been developed which is not punctured by the high-voltage ~
~
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~~
~
~
~
~~~
~
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Volume 59
Number 5
May 1982
393
electric discharge (14). Such coated steel shapes, bent as desired before enameling, hecome the chief material of construction of ozone The cost advantage of using enameled steel instead of glass is significant.
Acknowledgment The author wishes to thank Dr. Charles Matsch (now retired) and Dr. Maurice Lynch of the Linde Division of Union Carbide Corporation; E m d y Industries, Inc.; and Mr. Victor Hann (formerly of the Ozone Processes Division of the Welshach Corporation) for supplying some of the information used in this article. Llterature Cited
Attempted Shipping of Ozone At present, ozone is always manufactured on site, i.e., at the location a t which it is used. Efforts (15) have been made to develow safe means of transwortine" ozone. but none of them has yet been put into commercial practice. In the most promising method, ozone is adsorhed on Silica Gel@a t the temperature of Dry
[email protected] other methods, ozone is dissolved either in liquid oxygen, or in a mixture of liquid oxygen with argon or with trifluorochloromethane. The concentration of the ozone is kept below the limit at which an explosion will take place if H spark is passed through the mixture. In the case of ozone adsorhed on Silica Gel, the solid mixture did not explode when a dynamite charge buried in the material was set off. One reason that none of these methods has yet been implemented commercially is that in case of the wreck of a truck or railroad tank car containing the ozone mixture, ozone gas or liquid would escape; ozone vapor is extremely toxic, and either the vapor or the liquid might explode.
394
Journal of Chemical Education
(1) Evans, FranelsL., (Editor),"Omne in Water and Wasteuate.Treatment:AnnArbor
Science Publishers. Ine.. P.O. Box 1425. Ann Arbor, Michigan, 1972. (2) Pavani, J. L., ef al.. ''Progress in Wastewater Disinfection Technoioki. Proeeedinga of the National Sympmium. Cincinnati, Ohio, Sept. 1978." U S Environmental P r o w i o n Agency, June 1979, p. 261. (3) cotton, F. A.,and WiUriuri", GGGGGAd~codI"0'ganiiChhmiat~:~ 1st Ed.,J,,terrrrrrrrr Publlahers, a Division of John Wiley & Sons, New York,1962, p. 278. (4) Hair,Alsn B.snd Albert D. Vanma,"EPAOveruiewof Municipd Wastewater Oisinrection,"J o f t h e WaterPollufion Control Federation. 50.2474 (No?.1978). (5) Emery Industries. h e . , brahure "Emerzone Ozone Systems," 1979. (61 Cwk, Gerhard A,, "Survey of Modern Industrial Chemistry? Ann Arbor Science Publishers, Ine., P.O. Box 1425, Ann Arbor, Michigan, p. 283. (7) risnny. M. W., "Smthetic Lub.iranta." Noyes Data corporation,Park Ridge. New _Isrssu 1111
