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3,352,642 United States Patent Office Patented Nov. 14, 1967 2 stabilized during storage for long periods of time with 3,352,642 out degradation of its oxidizing properties. STABLZATION OF Lawrence J. Heidt, Arlington, and Vincent R. Landi, In accordance with these and other objects, the present rookine, Mass., assignors to Massachusetts in invention involves the stabilization of ozone through the stitute of Technology, Cambridge, Mass., a corpo use of , and in particular, and ration of Massachusetts other sources of hydroxyl-. This is a wholly new and No Drawing. Fied June 29, 1964, Ser. No. 378,990 Surprising approach to the problem of stabilizing ozone. 15 Clains. (Cl. 23-222) In fact, it has heretofore been generally believed that sodium hydroxide would have the opposite effect upon This invention relates to a method for the stabilization O oZone. For example, the Encyclopedia of Chemical Tech of ozone and in particular to a method whereby ozone nology, vol. 9, p. 735, reports that the ozone decomposi can be stored and transported with a much slower rate tion reaction is greatly accelerated by increasing the of decomposition than was heretofore thought possible. hydroxyl-ion concentration. Other references are made Ozone (O3) is an unstable blue gas which is formed in the same volume and article on ozone to the supposedly photochemically in nature in the earth's stratosphere but 5 detrimental effect of sodium hydroxide on the stability which exists only in great dilution with air or at of ozone. It is also reported in the article that the de ground levels. At -112 C. ozone condenses to a dark composition of ozone is more rapid in aqueous blue liquid which is easily exploded, as are concentrated than in the gaseous state, and that the decomposition is ozone-oxygen mixtures (above about 30% ozone) in powerfully catalyzed by hydroxyl-ion. In an article by either the liquid or the vapor state. Explosions are initi 20 M. L. Kilpatrick, Claude C. Herrick and M. Kilpatrick, ated by small amounts of organic matter, shocks, electric Journal of the American Chemical Society, vol. 78, at p. sparks, and sudden changes in and pressure. 1788, the authors reported that the rate of decomposi The very explosive nature of ozone has suggested its use tion of ozone increases as the hydroxyl-ion increases. It as a component in rocket fuels. OZone is a potent germi is important to note that they employed concentrations cide, a powerful oxidant in organic and inorganic reac 25 of NaOH in the range from 10-6 N to 10-4 N in making tions, and has also been found useful in the treatment their decomposition study, since, by way of contrast, it of supplies and industrial wastes as well as in the has been found that the use of NaOH at much higher deodorization of air and sewage gases. concentrations results in a startling increase in the sta Ozone is commercially produced from air or oxygen bility of the ozone. The work of Kilpatrick et al. has by means of an apparatus known as an ozonizer which 30 been cited by Clark E. Thorp, of the Armour Research utilizes an electrical discharge known as the ozonator Foundation, Chicago, Illinois in his Bibliography of discharge, to produce the O . The ozone pro Ozone Technology, vol. 2, p. 44, in which the statement duced thereby contains those impurities which are present is made that “with few exceptions, the decomposition of in ordinary air plus small quantities of pentoxide ozone increases with increasing ion concentration.” Thus, (NOs) and nitrous (N2O). The mole ratio of 35 the consensus of workers in the field of ozone technology nitrogen pentoxide to ozone under typical conditions is has been that the stability of ozone is decreased as the in the range of 1-2%. However, with moist air the pro concentration of hydroxyl-ion is increased. This inven portion of nitrogen pentoxide rises and it combines with tion, which is based on the stabilization of ozone by the the water vapor present to form nitric (HNO3) addition of hydroxyl-ion, is, therefore, all the more novel which causes severe corrosion of the metal surfaces which 40 and unexpected in view of the foregoing. it contacts. Ozone relatively free of impurities can be pre It has been found that oZone is increasingly stable with pared by the ozonization of pure dry oxygen. One of the increasing base concentration above 104 N NaOH, and major problems which has been encountered in the pro greatly stabilized in the range from 1 N to 20 N NaOH. duction of ozone has been the preparation and utilization Ozone and Ozonide (O3), the anion of the strong acid of high purity oxygen to produce a high purity ozone. HO, were produced as a result of the absorption of light This is extremely important in view of the fact that ozone 45 by peroxide and in aqueous is highly unstable in the presence of even the slightest sodium hydroxide. Flash photolysis was used as a light amount of impurity such as nitrogen pentoxide. source in initiating the reaction. The optical Ozone, being quite unstable, decomposes to biatomic (O.D.) of the system was measured by means of a oxygen. The decomposition is slow at room temperature 50 spectrophotometer at the light absorption peaks of ozone and low concentrations, but is greatly accelerated by heat, and ozonide at 2600 A. and 4300 A. respectively. The being almost instantaneous at of several stability of ozone as measured by its thermal half hundred degrees centigrade. The decomposition has been (T/2) (the time required for the ozone concentration reported to be catalyzed by moisture, silver, platinum, to decrease by one-half from its initial concentration) and some other metals as well as some metallic , 55 was greatly increased with an increase in base concen , bromine, , and nitrogen pentoxide. tration. The ozonide also was stabilized, although to a Thus, it can be seen that the purity of the product is a lesser degree than the ozone. The effect of NaOH con highly important factor in its stability. Much work has centration on the stability of ozone in a sodium hy done to improve the methods of producing ozone in order droxide- solution is shown in Table I. to obtain a high purity stable product. This has been a very expensive and largely unsuccessful venture thus far. 60 Table I The importance of stabilizing ozone cannot be over NaOH (concentration): O-T/2 (seconds) emphasized in view of the many possible uses to which 10' N ------0.02 it could be put were it not for its instability and difficulty 10°N ------0.07 10' N.------4.76 in handling. 65 It is, therefore, an object of this invention to provide 2.5X10' N ------9.04 a means for the stabilization of ozone. 5X10' N ------24.8 More specifically, it is an object of the present inven 10 N ------110. tion to provide a method for the reduction of the rate of 70 N ------2000. decomposition of OZone. 70 It can be seen from Table I that as the NaOH concentra It is likewise an object of the invention to provide a tion is increased from 104 to 7.0 N the thermal half life of means for the storage of ozone whereby the ozone is the OZone in solution, as calculated from optical density 3,352,642 3 4. measurements, is increased from 0.02 second to 2000 sec tacts this highly oxidized layer should not react with it onds. This is in marked contrast to the results of work and should not decompose. done by others in the field (Kilpatricket al.) which shows It is contemplated that the ozone stabilized and stored a decrease in ozone stability as the NaOH concentra according to this invention can be made available for tion is increased from 10-6 N to 10 4 N. The ozone in 5 use in the pure form by various means. For example, the strongly basic solution (7 N NaOH) decomposed the alkaline ozone solution can be distilled at low tem smoothly with no untoward effects even when the solu peratures to separate the ozone from the NaOH solu tion was rapidly heated, shaken and boiled. Similar ex tion. Ozone may be run through alkaline dehydrating periments carried out with concentrations of agents such as sodium hydroxide pellets, potassium hy hydroxide up to 14 N gave results similar to those ob 10 droxide pellets, barium oxide, oxide, and cal tained with sodium hydroxide. cium oxide to remove any water present in applications Table II shows the effect of base concentration on the where pure ozone is required. Pipes and other vessels stability of ozone in a sodium hydroxide-sodium per used in the transportation of flowing ozone can be made sulfate solution. Optical density measurements at 2600 A. of alkaline materials such as alkaline or alkaline were made and from these were calculated the thermal 15 glass-lined materials. In other words, the ozone may be safely handled and stored provided it is in an alkaline half presented in Table II. medium or alkaline surroundings until used. It may be Table II used in the pure form by presently available separation NaOH (concentration): O-T2 (seconds) techniques provided that it is kept in a strongly alkaline 10 N ------0.001 20 environment until use. 10°N ------0.01 The preferred embodiments of the invention described 7 N------2500 in this specification are illustrative only. Various modifi In the experiments which resulted in the data shown cations may be made without departing from the spirit in Tables I and II, ozone was produced from hydrogen and scope of the invention as set forth in the appended 25 claims. peroxide and sodium persulfate respectively, by means of What is claimed is: flash photolysis. There is in experiments of this type the 1. The process of stabilizing ozone comprising the step inherent, although doubtful, possibility that the hydrogen of storing said ozone in a container, the walls of said peroxide and sodium persulfate exercised a protective ef container being lined with a highly alkaline material. fect upon the ozone and thus were responsible for its 30 2. The process of stabilizing ozone comprising the step greatly increased stability rather than the NaOH. To con of storing said ozone in a container, the walls of said firm the theory that NaOH was responsible for the sta container being lined with a highly alkaline glass. bilization of ozone an experiment was performed in which 3. The process of stabilizing ozone comprising the step both the hydrogen peroxide and sodium persulfate were of storing said ozone in a container, the walls of said eliminated. Ozone produced by an ozonizer, was bub 35 container being rendered inert by reacting them with bled through distilled water containing various concen strong . trations of NaOH. The thermal half lives of ozone in 4. The process of stabilizing ozone comprising the step various concentrations of NaOH were calculated, as be of storing said ozone in a container, the walls of said fore, with startling results. Concentrations of NaOH up container being rendered inert by reacting them with to 20 N were employed and the half lives were measured 40 concentrated NaOH. in minutes rather than seconds. Table III shows the very 5. The process of stabilizing ozone comprising the step great stabilizing effect of NaOH in high concentrations of storing said ozone in a container, the walls of said upon ozone in water at 23° C. container being rendered inert by reacting them with con Table III centrated KOH. NaOH (concentration): O-T/2 (minutes) 45 6. A process of stabilizing ozone which comprises dis N ------3 solving it in an containing a hydroxyl 5 N ------40 ion-yielding base in a concentration of at least 102 N. 10 N ------2000 7. The process of claim 6 wherein the hydroxyl ion 20 N ------5000 yielding base is a member selected from the group con 50 sisting of NaOH, KOH, RbCH, LiOH, CsCH, and In accordance with this inventon liquid ozone or ozone Ba(OH)2. dissolved in other can be stabilized by the ad 8. The process of claim 7 wherein the concentration of dition thereto of sodium hydroxide or other sources of hydroxyl ion-yielding base is from 1 N to 20 N. hydroxyl-ion such as , 9. The process of claim 8 wherein the hydroxyl ion such as , cesium hydrox 55 yielding base is NaOH. ide, and hydroxide, and alkaline earth hydrox 10. The process of claim 8 wherein the hydroxyl ion ides Such as . Methods of stabilizing yielding base is KOH. ozone for storage and transportation other than by the 11. A composition for storing ozone under stabilized addition of Solutions of strongly basic compounds should conditions comprising water, ozone and a hydroxyl ion be effective provided that hydroxyl-ion is present to con 60 yielding base in a concentration of at least 102 N. tact the ozone. For example, containers coated with a 12. A composition of claim 11 wherein the concen highly alkaline material such as an alkaline glass should tration of hydroxyl ion-yielding base is from 1 N to Serve as a stabilizing influence on the ozone. con 20 N. tainers could be treated with strong base and rendered 13. A composition of claim 12 wherein the hydroxyl inactive to prevent any reaction between the ozone and 65 ion-yielding base is a member selected from the group the iron. In other words, surface concentrations of a consisting of NaOH, KOH, RbCH, LiOH, CsCH and two dimensional or molecular-depth type exercise a pro Ba(OH)2. tective effect upon the ozone. Any non-readily oxidizable 14. A composition of claim 12 wherein the member basic groups such as (OH) or O-2 on the surface of is NaOH. the metal walls of a container would not readily react 70 15. A composition of claim 12 wherein the member with the ozone and, thus, in effect, would stabilize it. is KOH. An iron container, for example, if treated with NaOH No references cited. Would produce a surface layer of , the iron being in the completely oxidized oxide form with oxygen JOSEPH SCOVRONEK, Primary Examiner. in the -2 oxidation state. Thus, the ozone which con- 75 B. S. RICHMAN, Assistant Examiner.