June 14, 1960 A. H. REDIES ETAL 2,940,823 PRODUCTION OF Filed Oct. i0, 1956

MnO2 AC. KO

blo VAPOR KMNO-KOH Son

Aq KOH Fitrate

INVENTORS: ARNO H. REDIES MLTON B. CARUS >27--ee,BY 9-1-1-1 4-e (2-4 ATT'YS 2,940,823 United States Patent Office Patiented June 14, 1960 1. 2 mercial scale. This is very likely due to the fact that during the process, the mixture gets very thick or viscous, so that it is extremely difficult to disperse the oxygen suf 2,940,823 ficiently for the reaction and a very large provision of PRODUCTION OF POTASSUMMANGANATES 5 power is required in order to agitate the reaction mass at Arno H. Reidies and Milton B. Carus, La Salle, Ill., as all. This thickening occurs within a period of several signors to Carus Chemical Company, La Sale, Ill., a hours, even with a much reduced quantity of corporation of Illinois dioxide in the melt. We have now provided a process which overcomes Filed Oct. 10, 1956, Ser. No. 615,033 O the foregoing difficulty of the prior melt oxidation proc ess, and in doing so, have discovered the reasons for the 14 Claims. (C. 23-58) difficulty and have provided a solution to the problems. We have found that, apparently, the principal source of trouble is that the swells up to The invention relates to the production of potassium 5 many times its original volume after a short period of manganates by oxidation of manganese compounds in an time. Even a small excess of manganese dioxide will aqueous melt. More particularly, swell up to convert the already somewhat viscous liquid the invention relates to the production of potassium into a thick paste. (V) KMnO, and to the production of po We have discovered that the key to the solution of the tassium manganate (VI) K2MnO, by oxidation com 20 problem is to add a manganese oxide to an aqueous mencing with an oxidic manganese compound. The in potassium hydroxide melt at a rate of addition which is vention provides a process which renders production in not substantially greater than its rate of oxidation to a such manner commercially practicable. valence above 4. In the new process, an oxidic man Prior to the invention, potassium manganate KMnO, ganese compound having a manganese valence of less has been produced for many years, and several methods 25 than 5 is oxidized to KMnO, wherein manganese has of production have been devised. A large part of the a valence of 5, the oxidic manganese compound being potassium manganate produced is subsequently converted added at a rate not substantially greater than its rate of to potassium . Fundamentally, the reac oxidation to KMnO4. tions involved in the prior production of potassium man We have further discovered that oxidation of an oxidic ganate and are represented by 30 manganese compound having a manganese valence of the following equations: less than 5, to KMnO4 is very desirably effected by reaction with a potassium manganate having a manganese (1) MnO2--2KO-2O-KMnO-H2O valence of greater than 5, i.e., potassium manganate (VI) (2) electr. or potassium permanganate. The latter decomposes to KMnO-H-I-O-KMnO-KO-36H 35 potassium manganate (VI) very quickly under the re The present invention is concerned with the production action conditions, according to the equation of K2MnO, according to different equations, which also involve the production of KMnO. The latter com pound may be recovered for use as such or for produc In this manner, the oxidation of the manganese oxide is tion of KMnO4 therefrom. 40 not dependent upon oxidation with a gas, such as air, Of the several methods proposed for manufacturing and a favorable relatively low temperature may be em K2MnO4, the primary commercial method apparently is ployed for optimum results. the roasting method. This involves mixing hot concen The KaMnO4 produced is further oxidized to KMnO. trated potassium hydroxide and manganese dioxide, cool The further oxidation may take place in the same re ing and grinding the mixture. The concentrated potas s action zone or vessel, concomitantly with or subsequent sium hydroxide starting material is produced by evaporat to the oxidation of the manganese compound having a ing water from aqueous potassium hydroxide up to 385 valence below 5. Preferably, the oxidation of KMnO, C. Alternatively, a slurry of 50% KOH and manganese to K2MnO4 is carried out in a separate reaction zone or dioxide is sprayed into a hot oven, and the product is vessel, after removing the KMnO, from the first reaction cooled and ground. The ground product is then roasted SO Zone, preferably at a rate comparable to its production. at about 225 C. with air, while intermittently spray In prior chemical studies, KaMnO4 had been produced ing water on the mixture. The roasting is carried out by the following reaction carried out with powdered ma in large rotary drums or tubes. This operation requires terials in the dry state at about 800° C. a very large amount of equipment, with accompanying dry high capital investment, power, heat, labor and main SS (3) 2MnO2-6R. OH+40- a 2K Mino-3H,o tenance requirements. Furthermore, the process is slow, inconsistent and difficult to supervise. The reaction can The compound had also been produced by a high tem not be carried to completion. This is apparently because perature decomposition of K2MnO, as follows: of the difficulty in supplying sufficient water to the re actants and because sufficient potassium hydroxide can 60 not be supplied. As regards the former condition, the Both of these methods are technically impractical and presence of water is necessary for the reaction although result in an anhydrous product. it does not appear on the left of the equation. The The present invention is based upon the following re potassium hydroxide quantity is limited, because over a actions: certain ratio to manganese dioxide, the product ag 65 (5) KO-HO son glomerates seriously and prevents further oxidation. MnO--4KOH--KMnO------>2KsMnO2HO A number of years ago, a process was devised wherein 170-81.0° C. (6) KOB-IO son manganese dioxide was oxidized to KMnO, with air in 2Ks MnO4-3-3O2--HO- -->2KMnO-2KOH a concentrated aqueous potassium hydroxide melt. De 70 40-310° C. spite the potential attractiveness of such a process, it has So far as known, this represents the first time a process apparently never been successfully employed on a com has been based upon Equation 5, which is especially sig 2,940,823 - 4. nificant as employed in the production of KMnO4. The droxide melt at a temperature of about 170 C. to 310 C., equation represents reaction in an aqueous melt at a preferably about 220° C. to 260° C. The reaction rate relatively low temperature, which provides a practical is greater at the higher temperatures, while corrosion is commercial process producing an aqueous product which reduced at the lower temperatures. Further increase in is readily further processed, and the operating conditions, 5 temperature is preferably avoided, to avoid possible de such as temperature, pressure and concentration are com composition of K2MnO4. The potassium hydroxide con mercially attractive. Reaction 6 represents a very use : centration is preferably about 65% to 90%, by weight. ful and economic process of manufacturing K2MnO4; - However, the concentration and reaction temperature may starting with KMnO, advantageously the product of be varied. - Equation 5...... O It is also preferred: that the melt contain an excess of Each reaction may be carried out at a favorable rela potassium hydroxide over the 'theoretical molar ratio to tively low temperature, which is especially advantageous manganese dioxide of 4:1. A considerable molar excess in materially reducing corrosion. Also, the solids and of potassium hydroxide, is-preferably employed, on the solutions are handled and processed with less difficulty, order of 30 to 60:1 or greater, which provides a melt and construction, maintenance and operation of the ves 15 of suitable viscosity. In this connection, it will be ap sels, filters, pumps and other equipment are facilitated. parent that Equation 5 will be appropriately varied when Reaction 6 may take place in the same reaction zone the manganese oxide is other than manganese dioxide, and with Reaction 5, furnishing an adequate supply of oxygen ... the potassium hydroxide and potassium manganate re for that purpose and removing the KMnO, which crys quirements will be adjusted accordingly. - tallizes, as it is produced. Reaction 6 may take place 20 The reaction proceeds with vigorous agitation while pro while Reaction 5 occurs with the continued addition of viding a potassium manganate having a manganese valence the manganese oxide. Alternatively, Reaction 5 may be of greater than 5 in the melt. A quantity of the manganate completed without substantial production of KMnO ac is added initially, and further manganate is added con cording to Reaction-6, and thereafter, the KaMnO may tinuously or intermittently as the reaction proceeds. The 25 potassium manganate is very advantageously supplied by t be oxidized to KMnO, according to Reaction 6. cycling part of the KMnO, produced by oxidation of i A It is preferred in the invention to withdraw the KMnO, KMnO. While a slight excess of the manganese oxide produced in Reaction 5. at a rate comparable to or ap maybe tolerated, it is preferred to continually maintain proximately the same as its rate of production, and oxidize the average manganese valence in the melt at a value of it in a separate second zone according to reaction 6. In 30 at least 5, which requires that a stoichiometric amount complicatedthis manner, byReaction the presence 6 and the of KMnO,significant product quantities are notof or greater of potassium manganate (VI) or potassium manganese oxide, the starting material in Reaction 5. permanganate be present at all times, throughout the When carrying out both reactions in one zone at the same - process. It is preferred to maintain the molar ratio of time, unreacted manganese oxide is found in the KMnO KMnO, or KMnO, to manganese dioxide at about 14:1 crystalline product, and such is not the case when the 35 or greater, and further preferably, at 2:1 or greater. reactions are carried out in separate zones. Since KMnO is relatively insoluble, it is preferable not Further advantages accrue from carrying out Reactions to provide a great excess, such as will interfere with agita 5 and 6 in separate zones. KaMnO, is rapidly produced. tion and mixing. : separately and in high yield, and it may be used for other : The manganese oxide is added at a rate not substan purposes, for example, as an oxidizing agent. Each reac 40 tially greater than the rate of oxidation to KMnO4 or tion is individually controlled, so that the manganese oxide oxidation of the manganese to a valence of 5. The oxide is converted to K2MnO4 in high-yield and in a successful may be added intermittently or continuously, care being continuous commercial process. - taken that at no time is a considerable quantity of un In certain of its broader aspects, the invention involves, reacted MnO present. The rate at which the manganese then, an improvement in the production of KMnO, by 45 oxide should be added is best determined empirically, for oxidizing-amanganese oxide in an aqueous potassium hy each set of conditions. The examples which follow are. droxide melt. The improvement comprises adding man- ; illustrative of substantially maximum rates of addition. ganese oxide to the melt containing a potassium manga The reaction mixture also can be analyzed from time to nate having a manganese valence of greater than 5, and time for KMnO content and for MnO, content, to deter izing the manganese oxide to KMnO, by reaction mine the rate of oxidation, for adjusting the rate of with the potassium manganate. The preferred process manganese-oxide addition...... also includes providing a rate of manganese oxide addi While Reaction 5 advantageously does not require an tion which is not substantially greater than its rate of oxygen-containing gas, such may be provided in intimate oxidation to KaMnO4. The KMnO4 is advantageously dispersion through the mixture for concomitant reaction oxidized to KMnO, preferably in a separate reaction 55 according to the following equation: - zone. The invention thus provides commercially impor tant advantages in the production of KMnO, and pro (7), 2MnO,--6KOH--20-2KMnO,--3HO vides a practical process for the production of KMnO, Reaction 5 is apparently more rapid, so that The prior problems are overcome, so that it is no longer under the defined conditions including maintaining at least necessary to carry out the much more cumbersome and -80 a stoichiometric amount of potassium manganate having a expensive production of K2MnO, by roasting. Also, the manganese valence of greater than 5, in the melt, the rate of production per unit volume is many times greater. production of KMnO, according to Reaction 7 would The invention contemplates the oxidation of an oxidic apparently not be so great as to render the modification manganese compound wherein the manganese has a important. valence of less than 5. Various manganese oxides having 65 The reactions can be carried out-in batch, semi-continu cus or continuous operation. For continuous type opera ... bination,a manganese pure valenceor impure, of mayfrom be 2 employed. to 4, alone For or example,in com tion, it is of course necessary to replace the potassium pyrolusite containing on the order of 87% of MnO, hydroxide consumed in Reaction 5, and this may be done calcined rhodochrosite, which is approximately. MnO, at least in part by cycling the potassium hydroxide pro manganese oxides from permanganate reactions, e.g., duced in the second zone by Reaction 6 and potassiini 5MnO, K2O3-5H2O, electrolytically and chemically pro hydroxide added to the secondzone and subsequently with duced manganese oxides, manganese oxide hydrates, and drawn in more concentrated form, where the reactions are carried out in-separate zones. The balance of the potassi: manganesemetals may oxidesbe employed. or oxide hydrates combined with alkali um hydroxide requirement may be added intermittently of Reaction 5 is carried out in an aqueous potassium hy 5 continuously in the form of aqueous-potassium hydroxide 2,940,823 S solution, which advantageously contains about 50% KOH, Reactions 5 and 6 may be carried out in conventional by weight, or greater. An equilibrium is reached in the apparatus, such as a vat or vats equipped with suitable melt by removal of water by evaporation, so that the KOH means of agitation and means for dispersing air through concentration is readily maintained between 65% and out the batch. Provision is made for introducing the 90%. reagents and for withdrawing the products. In the pre The KMnO, is very soluble and remains in solution. ferred process, KMnO4 and K2MnO, are produced con It may be further oxidized to KMnO4 in the same ves tinuously or semi-continuously, in the manner illustrated sel, the latter being withdrawn from time to time as it schematically in the attached drawing. crystallizes out of solution. When operating in this man An aqueous potassium hydroxide melt is provided in ner, an oxygen-containing gas must be supplied to the 0. a vessel 1, and initial quantities of manganese oxide melt to furnish the requirements of the further oxida and K2MnO4 or KMnO4 are added to the melt. Agita tion. The conditions are comparable to those subsequent tion is provided, and the manganese oxide and potassium ly described for the further oxidation. It is preferred, manganate are added from time to time or continuous however, to intermittently or continuously withdraw the ly. Makeup aqueous potassium hydroxide is also added, KaMnO, about as fast as it is produced, in its solution, 5 according to its consumption. Baffle means schematical and pass it to a second reaction zone. The reaction in ly illustrated by a baffle 2 is provided in the vessel 1, be the second zone may take place at about the same tem tween the inlets and outlet for the materials entering and perature. leaving the vessel. '. - In the second reaction zone, it is again preferred that As the production of KMnO4 proceeds, the solution the melt contain about 65% to 90% of potassium hy 20 may be allowed to overflow through a conduit 3 into a droxide, by weight. The reaction may be carried out second reaction vessel 4, thus favorably affecting the above the solidification point of the mixture, and is pref reaction equilibrium in vessel 1, and supplying the initial erably carried out at about 140 C. to 310 C. It is fur material for the oxidation in the second vessel 4. ther preferred that the melt be maintained at a tempera aqueous potassium hydroxide melt is provided in Anthe ture of about 210 C. to 230 C. The melt is vigorous 25. Second vessel 4, and the vessel is supplied with means for ly agitated, and air or other oxygen-containing gas is introduction of air and heat, and for agitation. Aqueous intimately mixed therewith, to provide about 4 or more potassium hydroxide solution of 50% concentration or times the theoretical amount of oxygen. greater is supplied to the second vessel 4 from time to Air is the preferred oxygen-containing gas, for eco time, to replace material withdrawn, and it becomes con nomic reasons, but oxygen, air enriched with oxygen, or 30 centrated by evaporation. K2MnO4 crystallizes in the a mixture of oxygen and an inert gas might be employed. Second vessel and may be withdrawn in the form of a The oxygen-containing gas is preferably under substan slurry and filtered by a filter 5. The filtrate is recycled tially atmospheric pressure plus any differential required to the second vessel through a conduit 6, to return to overcome the resistance to gas flow, but subatmospheric K3MnO4 and KOH to the process. Filter cake washes or Superatmospheric pressures can be provided with 35 preferably are used as makeup KOH solution supplied appropriate adjustment of the conditions of temperature to the second vessel. - and potassium hydroxide concentration. When air is Part of the K2MnO4 slurry removed from the second employed, it is preferred to contact the melt with a vessel 4 is preferably cycled directly to the first vessel 1, quantity equivalent to 4 or more times the theoretically through a conduit 7, without filtering. This material required quantity of oxygen. 40 serves for the reaction in the first vessel , supplying The KMnO4 solution from the first reaction is in both the KMnO4 and KOH requirements. In continu termittently or continuously introduced into the melt. It ous type operation, it preferably corresponds to about is preferred to maintain a high concentration of KMnO4 two-thirds of the K2MnO4 withdrawn from the second in the melt, on the order of about 200 to 400 grams per vessel 4. Of the K2MnO cycled to the first vessel, about liter, for example. The KMnO, is very solubie, and is 45 one-half takes part in the reaction, and the remainder therefore readily oxidized to K2MnO, in the homogene constitutes an excess and is continuously cycled between ous Solution, more readily than in the case of a hetero the first and second vessels. geneous mixture, as is the case when the further oxida The manganese oxide in the first vessel is substantially tion is carried out concomitantly and in the same zone prevented from entering the second vessel 4 by the baffle with Reaction 5. w 50 2 and also owing to a relatively small flow rate. The The K2MnO4 is relatively insoluble and precipitates out rate of flow is such that the average residence or reten of the reaction mixture. It can be separated by con tion time for each particle is greater than the reaction ventional methods, such as settling and decantation, cen time for the manganese oxide. The average residence trifugation, or filtration. The reaction can be carried out time may be, for example, from 1 to 3 hours, while the in batch, semi-continuous or continuous operation. It is 55 oxidation of the manganese oxide may require about 15 preferably carried out in a continuous manner, supplying to 20 minutes or less, as subsequently exemplified. Con KaMnO4 solution to the reaction zone and withdrawing sequently, at most a very small amount of the oxide K2MnO4 crystals continuously or periodically as they are reaches the second vessel 4. In the second vessel, the produced. Aqueous potassium hydroxide solution of at average residence time may be about 1 to 2 hours, dur least 50% KOH is added to the second zone to replace 80 ing which the small quantity of manganese oxide may be the KOH withdrawn with the KMnO, oxidized. The result is that very little if any unreacted Carrying out the process in successive steps in the fore manganese oxide will appear in the KMnO product. going manner, conversion to KMnO, and to KMnO, An advantage of the process is that the heat require approaches the quantitative. The product of the first ments may be supplied entirely to one vessel, the second reaction may be, for example, an aqueous potassium hy 85 vessel 4. With the relatively low temperatures involved, droxide solution containing about 300-350 grams of the thermal efficiency can be very high. The initial po KaMnO4 per liter. The product of Reaction 6 initially tassium hydroxide melt for both vessels may be prepared contains adherent mother liquor, containing KMnO, in the Second vessel by evaporating water from 50% potassium hydroxide and water. After washing, the KOH solution. crystals contain about 80% to 90% of KMnO, potas O As the reactions proceed, heat is supplied to the sec sium hydroxide, water, and minor impurities. The ond vessel, concentrating the additional 50% potassium KaMnO4 is removed by washing and returned to the proc hydroxide solution subsequently added and furnishing ess, so that the yield of K2MnO4 is practically quantita the heat required to maintain the reaction temperature. ve. The hot K2MnO4 slurry cycled from the second vessel 4 s to the first vessel 1 supplies the heat necessary to main

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2,940,828 tain the reaction temperature in the latter vessel, the first someto remove, potassium the liquor hydroxide, contains water, 82%. and to 90%minor of impurities. KMnO. ...vessel A number then operating of: additional at a slightlyadvantages lower flow temperature. from the new- . . . The yield based on KaMnO4 is: practically... a ' '... quantitative.. . process; which is now-eminently suited for commercial ... . ; :... Example: ...... operation.continuous typeThe operation,process-can in be either carried one outor twoin batch vats, orto 5. . The. . procedure-of-Example. . . - - - 1- is repeated,. except. . . that. . . produce large quantities of KMnO, and KMnO, The an 85%. KOH met is maintained at a temperature of simple and inexpensive equipment is substituted for an: - about 300 C. The reaction periods are reduced from . entire series of roasters; having the aforementioned-dis 15. I inutes-to about 2 minutes. The KMnO. product advantages. The products are obtained in a state of highs 10: solution is substantially the same...... purity. The dust problem of roasting is eliminated. Op- . . Example 4 - . erational time is greatly reduced- and a much more ef. The procedure. . of. Example. - 1- - -is - - . . . ficient process-is provided. The requirements of air-or: 100 grams: of calcined rhodochrositerepeated, are employed except that. for otherand an oxygen-containing accompanying advantage gas- are isconsiderably, that correspondingly, reduced, 15- each addition instead-of 100 grams of pyrolusite. The less carbonate is:formed by absorption of carbon dioxide remaining.conditions are the same, except that the reac from the air. The air-dispersion is much more intimate, tion time... is about 20-minutes instead of 15 minutes. and the reactions are improved correspondingly. Each. The product is substantially the same. - - - of the melts stirs very well, so that the power require- - - - - ... Example 5 . mentThe is following low, as is examples the wear are on furnishedthe stirring to apparatus.assist in pro-. -20 - 50 .gallons . . . . of. 80%. aqueous. . . . potassium. - - hydroxide- - -are: - ... viding a complete understanding of the invention, but it maintained at 220. C. In the manner of Example, 1,... is to be understood that the invention is not limited. 60 pounds of KMnO, or 50 pounds of KMnO4 are -thereto-nor to the quantities, materials, conditions and added. 10-pounds of pyrolusites are added and allowed procedures illustrated-therein, which are merely illus-- 25 to react for about 15 minutes. Thereafter, three succes-s trative...... sive additions of 20 pounds of KMnO, and 10 pounds. .Aqueous . . . . v:potassium -- ... Example:hydroxide 1 is evaporated... - to pro-. ofutes. pyrolusite The product are made, and with yield reaction-intervals are substantially of the 15, same mini. duce: 80% KOH having a yolume of 4-liters. The solu- as in Example 1. "...... -...... - tionfirin is maintainedmaintaina?. at 220 o. C, and 500gramsarranger of KMnO,Maf . ing. The KMnO, invention and thus for providesproducing a newKaMnO, process, which for produc-. consti or 400 m grams s of KMnOA. are i.e.added , infallyinitially... . . 100 grams:of .. tutes-RYassyli a substantial sa. improvement- - overa st the y. prior methods. Tien260E.E.E.E.E. fans of kMnO, and 106 grams of pyrolusite andis very overconthstage. advantageously oxidized by reactionAgiosite with a Po are added and allow - reactors. . minutes" ' three". . . . tassiumgreater thanmanganate 5. A major having characteristic a manganese of the valence process ofis successive times...... that the manganese:oxide is added at a rate which is not About 15 minutes after the last addition; K3MnO is substantially greater than its rate of oxidation to. produced in a yield of about 98%, based on MnO: The KMnO4. When this important condition, is not ob product of the oxidation reaction is an aqueous potas: served, and the manganese oxide is added substantially. sium hydroxide solution containing about 15% of more rapidly than it is, oxidized, the excess oxide in the KMnO4, by weight. - . . . . suspension swells up, prevents adequate agitation and ...... Example 2. proper mixing, so that it is very difficult to carry out the . 150 liters of an 80% potassium hydroxide solution reaction. The addition of the manganese oxide accord containing 300 grams of KaMnO, per liter are placed in 45. ing to the invention also takes advantage of the reaction. a reaction vessel equipped with an efficient agitator and rate and provides a successful continuous process. The: provided with means for introducing air. The solution manganese dioxide is substantially consumed, so that the. may be prepared according to Example 1 or according. K3MnO, solution conveyed to the second reaction zone. to the succeeding examples. The solution or melt is for production of K2MnO, contains an insubstantial maintained at a temperature of 225 C. 50 quantity of manganese dioxide, avoiding contamination. The mixture is agitated vigorously, and in excess of of the KMnO, product...... , four times the theoretical quantity of oxygen in the form The process of the invention is rapid and reliable, and. of air is intimately mixed-therewith. Intimate mixture. produces high quality products in high yields. The con is obtained by violent agitation while-introducing air over, sumption of materials is a minimum, and the operation -- - is carried out in but a small equipment installation with: the mixture, so as to intimately disperse fine bubbles of 55 slow investment, power, heat, labor and maintenance.-- - air in the suspension. Alternatively, air is introduced - - requirements. The invention provides a very advanta through a tube directly into the mixture. geous solution to the problem of oxidizing a manganese Oxidation proceeds: at the rate of about 2 grams of oxide in an aqueous. melt, rendering the process suitable i KMnO, per liter per minute. The KMnO, consumed for large scale commercial operation. . . . . is continuously replaced, as with the solution from Ex-60 The invention is hereby claimed as follows: ample 1... KaMnO, crystallizes out of the reaction mix 1. In a process for producing KMnO, by oxidizing ture, is withdrawn from time to time in the form of a a manganese oxide having a manganese valence of less. slurry in potassium hydroxide solution, and is separated than 5 in a hot aqueous potassium hydroxide solution, from the mother liquor by filtration. Part of the slurry the improvement which comprises adding said manga may be used in the method of Example 1, for the produc-- 65 nese oxide to said solution containing a potassium man tion of additional KaMnO, Makeup potassium hy ganate having a manganese valence of greater than 5, droxide solution of 50%. strength or greater is added to oxidizing said manganese oxide to KMnO, by reaction theThe vessel. fifter cake of- K.MnO, is washed with 60%. with said potassium manganate, the rate of said man .. aqueous potassium hydroxide solution at 100 C., and 70. ganese oxide addition being not substantially greater the liquid is removed from the cake by suction. The than its rate of oxidation to KMnO, and oxidizing the filtrate is recycled to the reaction vessel wherein the KaMnO42. in aproduced process tofor KMnO. producing KMnO,. . . by oxidizing. KMnO4 is produced, and the washes are employed as a manganese oxide. having a manganese valence of less, theThe above-makeup product after solution. washing and application of suction is: than 5 in a hot aqueous potassium hydroxide solution,

2,940,828 g 10 the improvement which comprises adding said manga manganese valence of greater than 5 in said solution, nese oxide to said solution containing a potassium man oxidizing said manganese oxide to KaMnO, by reaction ganate having a manganese valence of greater than 5, with said potassium manganate, the rate of said man oxidizing said manganese oxide to KMnO, by reaction ganese oxide addition being not substantially greater with said potassium manganate, maintaining the average than its rate of oxidation to KMnO, removing the manganese valence in said solution at a value of at least KMnO produced, and oxidizing the KMnO, removed 5, the rate of said manganese oxide addition being not to KMnO, in a separate reaction zone by intimately substantially greater than its rate of oxidation to mixing an oxygen-containing gas with an aqueous about KaMnO4, and oxidizing the KMnO, produced to 65% to 90% potassium hydroxide solution of the for KMnOa. mer at a temperature of about 140 C. to about 310 C. 3. In a process for producing KMnO by oxidizing 8. The process which comprises adding a manganese a manganese oxide having a manganese valence of less oxide having a manganese valence of less than 5 to a than 5 in a hot aqueous potassium hydroxide solution, hot aqueous potassium hydroxide solution containing a the improvement which comprises adding said manga potassium manganate having a manganese valence of nese oxide to said solution containing a potassium man 15 greater than 5, and oxidizing said manganese oxide to ganate having a manganese valence of greater than 5, KMnO, by reaction with said potassium manganate, the oxidizing said manganese oxide to KMnO, by reaction rate of said manganese oxide addition being not substan with said potassium manganate, the rate of said manga tially greater than its rate of oxidation to KaMnO. nese oxide addition being not substantially greater than 9. The process which comprises adding a manganese its rate of oxidation to KMnO, removing the KMnO4 20 oxide having a manganese valence of less than 5 to a produced, and oxidizing the KMnO, removed to hot aqueous potassium hydroxide solution containing a K2MnO4 in a separate reaction zone. potassium manganate having a manganese valence of 4. In a process for producing KMnO4 by oxidizing greater than 5, oxidizing said manganese oxide to a manganese oxide having a manganese valence of less KMnO4 by reaction with said potassium manganate, the than 5 in a hot aqueous potassium hydroxide solution, 25 rate of said manganese oxide addition being not substan the improvement which comprises providing an aqueous tially greater than its rate of oxidation to KMnO, and about 65% to 90% potassium hydroxide solution and removing the KMnO4 produced. maintaining it at a temperature of about 220 C. to 260 10. The process which comprises adding a manganese C., adding said manganese oxide to said solution contain oxide having a manganese valence of less than 5 to a hot ing a potassium manganate having a manganese valence 30 aqueous about 65% to 90% potassium hydroxide solution of greater than 5, oxidizing said manganese oxide to containing a potassium manganate having a manganese KaMnO4 by reaction with said potassium manganate, valence of greater than 5, maintaining said solution at a the rate of said manganese oxide addition being not sub temperature of about 170° C. to 310 C., and oxidizing stantially greater than its rate of oxidation to KMnO, said manganese oxide to KaMnO4 by reaction with said removing the KMnO produced, and oxidizing the 35 potassium manganate, the rate of said manganese oxide KMnO, removed to K2MnO, in an aqueous about 65% addition being not substantially greated than its rate of to 90% potassium hydroxide solution maintained at a oxidation to KMnO4. temperature of about 210° C. to 230° C. in a separate 11. The process which comprises adding manganese reaction zone. dioxide to a hot aqueous potassium hydroxide solution 5. In a process for producing KMnO, by oxidizing 40 containing a potassium manganate having a manganese manganese dioxide in a hot aqueous potassium hydroxide valence of greater than 5, maintaining an excess of said solution, the improvement which comprises adding said potassium manganate in said solution, and oxidizing said manganese oxide to said solution containing an excess manganese dioxide to KMnO4 by reaction with said of a potassium manganate having a manganese valence potassium manganate, the rate of said manganese dioxide of greater than 5, oxidizing said manganese dioxide to 45 addition being not substantially greater than its rate of KMnO, by reaction with said potassium manganate, oxidation to KMnO. the rate of said manganese dioxide addition being not 12. The process which comprises adding manganese substantially greater than its rate of oxidation to dioxide to a hot aqueous about 65% to 90% potassium KMnO, removing the KMnO produced, and oxidizing hydroxide solution containing a potassium manganate the KMnO, removed to KMnO, in a separate reaction 50 2Ole. - having a manganese valence of greater than 5, maintain 6. In a process for producing K2MnO4 by oxidizing ing said solution at a temperature of about 220 C. to manganese dioxide in a hot aqueous potassium hydroxide 260 C., maintaining the molar ratio of said potassium solution, the improvement which comprises providing manganate to manganese dioxide in said solution at a an aqueous about 65% to 90% potassium hydroxide value of at least about 1.4:1, and oxidizing said manga solution and maintaining it at a temperature of about 55 nese dioxide to KMnO4 by reaction with said potassium 220 C. to 260 C., adding said manganese dioxide to manganate, the rate of said manganese dioxide addition said solution containing a potassium manganate having being not substantially greater than its rate of oxidation a manganese valence of greater than 5, oxidizing said to KMnO4. manganese dioxide to KMnO4 by reaction with said 13. In a process for producing a potassium manganate potassium manganate, maintaining the molar ratio of by oxidizing a manganese oxide having a valence of less said potassium manganate to manganese dioxide in said than 5 in a hot aqueous potassium hydroxide solution, the solution at a value of at least about 1.4:1, the rate of improvement which comprises continually maintaining said manganese dioxide addition being not substantially in the solution a quantity of potassium manganate having greater than its rate of oxidation to KaMnO4, removing a manganese valence of greater than 5 which is at least the KMnO produced, and oxidizing the KaMnO4 re 65 about stoichiometrically equivalent to the quantity of moved to KMnO, in an aqueous about 65% to 90% said manganese oxide in the solution. potassium hydroxide solution maintained at a tempera 14. In a process for producing a potassium manganate ture of about 210 C. to 230 C. in a separate reaction by oxidizing a manganese oxide having a valence of less . ZOile. than 5 in a hot aqueous potassium hydroxide solution, 7. The process for producing KMnO, which com 70 the improvement which comprises initially providing in prises adding a manganese oxide having a valence of less the solution a quantity of potassium manganate having a than 5 to a hot aqueous about 65% to 90% potassium manganese valence of greater than 5, adding said manga hydroxide solution at a temperature of about 170 C. nese oxide to the solution, and continually maintaining to 310 C., providing a potassium manganate having a 75 in the solution a quantity of said potassium manganate 2,940,823. -- . . . . 11 12. which is at least about stoichiometrically equivalent to OTHER REFERENCES . . . . the quantity. of said manganese oxide in the solution: Scholder et al.: "Zeitschrift für anorganische -und: all - References Cited- in- - the file of this patent gemeine: Chemie,” Band: 277 (1954), pages: 243-245, UNITED STATES. PATENTS 5 1826,594. Bellone ------Oct. 6, 1931

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