US3085854.Pdf

3,085,854 United States Patent Office Patented Apr. 16, 1963 2 3,085,854 the production of alkali bromite solutions of higher con PRODUCTION OF BROMINE OXYGEN centrations is a practical possibility, and they have suc COMPOUNDS ceeded in preparing, from such solutions, crystallized al Jean Meybeck, Mulhouse, René Kircher, Argenteuil, and kali bromite which was never previously produced. Jacqueline Leclerc, Paris, France, assignors to Societe We have further discovered that alkali-earth bromites d’Etudes Chimiques Pour Industrie Agriculture, could be prepared in a similar way. The existence of Paris, France these compounds has never been mentioned in the litera Filed Apr. 19, 1957, Ser. No. 654,041. ture of which the applicants are aware, whether in solu Claims priority, application France Apr. 24, 1956 tion or in solid form. 20 (Caims. (C. 23-85) 0 Since the general conditions for preparing concentrated This invention relates to a method for producing con solutions both of alkali and alkali-earth bromites are ceiltrated solutions of metal bromites and to alkali metal broadly the same, the said general conditions will be and alkaline earth metal salts of bromous acid produced disclosed hereinafter without the particular cation con by this method. templated being specifically pointed out. To clarify the Various authorities have shown that solutions of alkali 5 description however, some typical numerical data will be hypobromites when subjected to suitable conditions evolve given by way of illustration, which relates to sodium, it gradually to a condition wherein the hypobromite is par being understood that the sodium cation is selected for tially converted to the corresponding bromite. The bro purposes of example only. mites thus detected, however, have only been obtained The hypobromite solution stock subjected to the con heretofore in highly dilute solution together with the 20 version conditions can be prepared in any suitable way, bromide, bromate and hydroxide of the alkali metal, as as by reacting bromine with an alkali, reacting a hypo well as extraneous salts utilized as buffer compounds. chlorite with a bromide, or by electrolysis, etc. The feas Solid bromites have never been heretofore separated, and ibility of preparing concentrated bromite solutions is pred hence no descriptions of their properties is to be found icated on the following properties which have been dis in the literature on the subject. 25 covered by us. The reason is, that even in those cases where conditions First, the bromite concentration in the resulting solu are most favourable for the conversion process, the in tion is increasingly high as the concentration in the vestigators have never succeeded in obtaining bromite initial solutions is high. In other words, when concentrations higher than 20 grams active bromine per operating under certain predetermined conditions to be liter (active bromine being defined as the weight of bro 30 specified below, the use of initially concentrated hypobro mine releasable from one liter solution). Attempts to mite solutions does not cause the decomposition of the concentrate the dilute solutions obtained or separate bro bromite. mite in the solid state failed, and it was believed that Secondly, the conversion ratio or yield of the hypo bromite salts could only exist in highly diluted solutions bromite-to-bromite conversion depends on a number of up to the aforesaid concentration. There was, incidental 35 physico-chemical factors control of which makes it pos ly, no way of telling in advance that concentrated Solu sible to improve greatly on the yields obtained by earlier tions and/or solid bromite would be stable enough to investigators. make it possible to separate them. A basis discovery of ours has been that, in contrast with Due to the lack of a method for concentrating bromite what could be anticipated concerning the stability of solutions or producing solid bromites, use of bromite so 40 bromites, it is feasible to start from hypobromite solu lutions was restricted in the past. It was, indeed, known tions of higher concentration than what was heretofore that bromites, the same as hypobromites, selectively oxi used. It has further been found that the conversion yield dize, for instance, arsenites in the cold while this oxida of hypobromite to bromite could be increased by observ tion of arsenites could not be achieved with bromates. ing certain predetermined pH and temperature ranges. (Supplement to Mellor's Comprehensive Treatise of In 45 The hypobromite conversion reaction can be repre organic and Theoretical Chemistry, Suppl. II, Part I, page sented by the following two equations: 753, published by Longmans, Green & Co. in 1956.) (1) 2MeBrO->MeBrO--MeBr However, it is obvious to a skilled chemist that full use (2) MeBrO--MebrO->MeBrO--Mebr of the selective oxidizing power of bromites such as so 50 wherein Me represents an alkali or alkali-earth metal dium bromite, could not be made, unless solutions of de atom. The bromite MeBrO2 which forms according to termined bromite concentration could be obtained, which Reaction 1 tends to react with the hypobromite MeBrO required the availability of crystalline, pure bromite salts. according to Reaction 2. However, in order that the It is, therefore, an object of our invention to produce over-all yield of the hypobromite-to-bromite conversion new oxidizing agents in the form of certain solid, crystal 55 Reaction 1 be high in the initial solution having a given line salts of bromous acid which are easy to transport, and hypobromite concentration, certain definite prescriptions from which aqueous solutions can be prepared that have as to pH and temperature must be observed. In partic new and specific oxidizing properties. ular, the solutions should be maintained at a temperature It is another object of our invention to provide a process not higher than 0° C., it being understood that if higher for producing alkali metal and alkaline earth metal salts 60 temperatures are used, while some bromite may still be of bromous acid, in solid crystallized form for use as a obtained, the yield will be substantially less. source for the afore-said oxidizing as well as brominating The pH value in the initial solutions should preferably agents. be also held within predetermined limits. Thus, for so Our research on this subject has now established that lutions initially containing 200 to 300 grams per liter 3,085,854 3 6. active bromine in the form of sodium hypobromite, the rate depends; thus a decrease in temperature slows down pH should preferably be within a range of from 10.5 to the conversion process and an increase in the initial pH 11. The pH adjustment should preferably be performed has a similar effect. by directly adding an excess of one or the other of the In accordance with the above, conversion yields of reagents used in preparing the hypobromites, i.e. without 50% to 55% have been obtained for example, by using using buffer ions of foreign character. The absence of sodium hypobromite solutions containing about 500 foreign ions in the solution appreciably simplifies the final grams per liter active bromine maintained at an operat separation step of the solid bromite. ing temperature of about 0° C., with the initial pH of the Investigation of the spontaneous conversion of dilute solutions in the range 11-12. The maximum bromite hypobromite solutions with time, as performed by earlier O concentration is attained after a time that increases from workers, has shown that the bromite concentration passes a few minutes to two hours as the pH value is increased through a peak value and then drops off. Our work has from 11 to 12. shown, in addition to this, that the lower the initial Con In addition to their high bromite concentrations, the centration, the slower the rate of change in the Solutions solutions thus obtained have yet another advantage over at a given temperature. The curves 1, 2, 3 and 4 of the the solutions prepared from less concentrated initial solu graph indicated as FIG. 1 in the accompanying drawings tions. This is the fact that they contain relatively less illustrate, against time, the changes in bromite content (in hypobromite thereby facilitating the ultimate separation terms of grams active bromine per liter) in Solutions of the solid bromite. It should be understood that after having respectively increasing initial hypobromite concer the conversion process the active bromine is present in trations, the four curves all being plotted for an initial 20 the solutions in the forms of bromite, hypobromite and temperature of substantially 20 C. bromate, with the relative proportions between the three Moreover, a decrease in temperature reduces the rate compounds being approximately as follows when using of conversion of the solutions and makes it possible, there initial Sodium hypobromite solutions at 500 grams active fore, to use initial solutions of higher concentration. This bromine per liter. Per 100 parts active bromine, 50 parts is illustrated by curve 5 in F.G. 2, which is plotted for occur as bromite, 25 as hypobromite and 25 as bromate. a solution having the same initial concentration as that When using solutions initially containing from 200 to of curve 4 in FIG. 1, but at an operating temperature 300 grams per liter active bromine, the corresponding within the range -20° C. to -10° C. instead of --20 figures are 40, 40 and 20 parts respectively. C. for F.G. 1. In order to stop the conversion process at the point It is seen that at --20° C. the peak concentration value 30 where the bromite concentration is at its peak value, the cannot practically be attained since deconopsition Sets solutions are stabilized by suddenly raising their pH value in and proceeds too rapidly.

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