Patented Apr. 29, 1941 2,240,344 UNITED STATES PATENT OFFICE Irving E. Muskat, Akron, and George H. Cady, Wadsworth, Ohio, assignors to Pittsburgh Plate Glass Company, Allegheny County, Pa., a cor poration of Pennsylvania No Drawing. Application July 23, 1938, Serial No. 221,018 16 Claims. (CI. 23-152) This invention relates to the manufacture of the presence of a small amount of Water. These hypochlorous acid and is particularly directed processes have been more fully described in to the manufacture of a highly concentrated copending applications of George H. Cady, product which is substantially free from chlo Serial No. 190,618, filed February 15, 1938, and rides, chlorates and other impurities. Prior to: 5 Serial No. 216,475, filed June 29, 1938. While this invention, it has been considered that hypo these processes produce chlorine monoxide in chlorous acid, particularly in high concentra good yield, the percentage conversion may be tions, could not be commercially produced. relatively low and in consequence, it is generally While it has long been recognized that chlorine found that the amount of chlorine monoxide monoxide produced hypochlorous acid when O a does not exceed 5 percent by volume and in dissolved in water, the preparation of this ma many cases is less than 2-3 percent by volume. terial has been considered to be too expensive Similarly, chlorine monoxide in low concentra for a commercial process. In addition, chlorine tions may be secured by contact of chlorine With monoxide in its pure state not only has been barium hydroxide or strontium hydroxide. Somewhat difficult to produce economically but 15 Such low concentrations are found to be par aiso is extremely unstable, often decomposing ticularly desirable in the present process. While With explosive violence. For these and other the process is particularly adapted for use With reaSOIS, the production of hypochlorous acid those methods of preparation in which a major has not been considered commercially feasible portion of the chlorine remains unconverted, it prior to this invention. 20 may also be applied to those methods wherein In accordance with our invention, we have conversion is ordinarily high. Thus, chlorine found that these objections may be avoided and monoxide may be produced by contact With hypochlorous acid produced in a simple and oxygen carriers such as mercuric oxide or silver economical manner. We have found that, in oxide. In such cases, however, it is found pref the production of hypochlorous acid in large erable to avoid a possible complete conversion quantities, it is desirable to convert only a por of the chlorine in order to carry out the process tion of a body of chlorine, preferably a minor efficiently and economically. portion thereof, into chlorine monoxide whereby Other methods of converting chlorine into a mixture of these gases in which the chlorine chlorine monoxide may also be used. However, monoxide concentration is not excessive, is it is generally considered essential that the obtained. The chlorine monoxide in this mix chlorine-chlorine monoxide mixture be free ture may be separated therefrom by passage from gases which would tend to decompose hypo of the gas through a controlled quantity of chlorous acid or to form undesirable compounds Water in which this compound dissolves without in the solution. Thus, it is found desirable substantial solution of chlorine. The chlorine to avoid the presence of Other oxides of chlorine, may then be recycled to produce further such as chlorine dioxide or of acidic gases such amounts of chlorine monoxide. In order to avoid as HCl and methods which tend to produce such formation of chlorates in accordance with our materials in objectionable amounts are prefer invention, it has been found desirable to remove ably avoided, salts or alkaline materials which may be sus 40 The treatment is preferably carried out in pended or otherwise present in the chlorine the presence of a diluent in order to insure max chlorine monoxide mixtures and to use water imum yield and efficiency in the production of which is Substantially free from these materials. chlorine monoxide and to prevent substantial This process is particularly adapted to the consumption of chlorine by formation of chlo preparation of hypochlorous acid using processes rates or other compounds during the treatment. wherein the percent of conversion of chlorine Gaseous diluents, . Such as carbon dioxide, air into chlorine monoxide and the chlorine mon or nitrogen, have been found suitable in many oxide concentration in the mixture to be treated cases. In addition, liquid diluents, such as carbon with water are relatively low. For example, it tetrachloride may also be used. When gaseous has been found that chlorine monoxide in con diluents are used, it is found desirable to use a centrations up to 5 percent by volume may be chlorine-diluent mixture wherein the diluent produced in gaseous form by contacting chlorine concentration is 40-95 percent by volume of the gas and a suitable diluent, such as air, carbon total gas in the conversion chamber. Gaseous dioxide with sodium or potassium carbonate, diluents appear to have the property of decreas sodium bicarbonate, hydroxide, silicate, etc., in ing the amount of chlorine which is absorbed 2 2,240,844 by the water without exerting any substantial weight is considered undesirable. In order to influence upon the amount of chlorine monoxide obtain efficient absorption, it is preferred to use absorbed. At all events, it is found that When cool or cold water. In general, the temperature gaseous diluents are used substantially less chlo of absorption is maintained below 25 C. Ab rine is absorbed in the HOCl solution than When Sorption may be carried out with some Success they are not present. at higher temperatures however. Thus, when the diluent concentration is 40-95 The absorption of the chlorine monoxide may percent by volume of the total amount of gas be carried out in any convenient manner but is being treated, it is found that the chlorine Con generally effected in a suitable extraction tower. tent in the hypochlorous acid is only about one .0 In such a case, Water is introduced in an upper tenth to one-half of the chlorine concentration portion of the tower while the gaseous mixture in hypochlorous acid of the same concentration is introduced in a lower portion thereof, the two which is produced without use of these diluents. contacting each other in countercurrent flow. In cases where carbon tetrachloride is used as By regulation of the rate of flow of Water and/or the diluent, the chlorine concentration may be 5 of the gas, the concentration of the resulting of any convenient value up to saturation. The Solution may be regulated in a simple manner. chlorine monoxide may be extracted from the Where a solution of chlorine and chlorine mon carbon tetrachloride solution by contact with oxide is formed, for example a carbon tetra water, without substantial extraction of chlorine chloride solution, similar countercurrent ex and the remaining solution of chlorine in Carbon traction methods may be provided or the solution tetrachloride recycled for further treatment. may be agitated with a controlled body of water. In order to secure hypochlorous acid which After contact of the chlorine-chlorine mon is substantially free of chlorate, it is found pref oxide mixture with water in accordance with our erable to remove suspended impurities, such as invention, the major portion of the chlorine chlorides, chlorites, alkaline materials, or other monoxide is removed while substantially all of materials which may be taken up during the con the chlorine remains. This chlorine may then be version step, from the chlorine-chlorine mon recycled for the production of further quantities oxide mixture prior to contacting it with water. of chlorine monoxide. When chlorine is contacted with sodium car The hypochlorous acid prepared in accordance bonate, bicarbonate, mercuric oxide or other 30 with the present invention is found to be ex agent for the production of chlorine monoxide, tremely pure. In general, it contains not in ex the resulting mixture is often found to contain cess of about 0.3-0.4 percent of chlorine or chlo residual amounts of these materials or their rides, generally not more than 0.05 percent of reaction products. If the mixture is directly these materials, and up to 10-30 percent of introduced into the Water, undesirable quantities: HOCl. Due to its purity, it is exceptionally stable of chlorate and other inpurities will be formed and retains its active chlorine content for a long in the hypochlorous acid. The suspended period of time. impurities may be removed from the gas in The following examples illustrate the inven suitable manner as by filtration, settling, or tion: other separation processes, such as by contacting (40 Eacample I the gas with hypochlorous acid. In order to separate the chlorine and chlorine A. mixture of 648 parts by volume of carbon monoxide, the mixture thus secured is intro dioxide and 82 parts by volume of chlorine was duced into a body of water. Some control of humidified by bubbling through water at 16° C. the ratio of the amount of water to the amount 45 This mixture was then countercurrently con of chlorine-chlorine monoxide mixture to be tacted with powdered, dry sodium carbonate in treated is required since the presence of a sub the proportion of 15 liters of gas per gram of soda, stantial excess of water results in the solution of ash at a temperature of 30° C. at atmospheric an undesirable amount of chlorine. It has been pressure. The gas, after treatment, contained determined that the presence of chlorine mon- : 1.25 percent by volume of chlorine monoxide.