Aug. 8, 1939 G. L. CUNNINGHAM 2,169,066 PREPARATION OF SODIUM CHLORATE AND SODIUM CHLORITE AND THE SEPARATION THEREOF Filed July l, l938 277. M% (2/7 CZ(2.

M% (Zoe Cezarz/9e A 30 °C. -----i------(Arzyze: ; 38-45°C. A/ozzer ----- Z727

/0% (Z(23/40 A6 (70-MézCZ(2, Zezvor

/Wa (70, M% (7(2.3/20

M% (23/20

NVENOR

ATTORNEYS Patented Aug. 8, 1939 2,169,066 UNITED STATES PATENT office 2,169,066 PREPARATION OF soloIUM CHLoRATE AND SODUM CHILORITE AND THE SEPARATION THEREOF George Lewis Cunilinghania, Niagara Falls, N. Y., assignor to The Mathieson Alkali Works, Inc., New York, N. Y., a corporation of Virginia Application July 1, i938, Serial No. 216,890 11 Claims. (Cl. 23-85) This invention relates to improvements in the chlorine dioxide and sodium hydroxide. In ac separation and recovery of sodium chlorate, Cordance With my invention chlorine dioxide is NaClO3, sodium chlorite, NaClO3, and sodium absorbed in an aqueous solution Containing chlorite trihydrate, NaClO2.3H2O from aqueous Sodium hydroxide in Suitable amount until the Solutions containing sodium chlorate and sodium Solution is substantially neutral. It will be ap chlorite, and particularly from Solutions pro parent from the above equation that the amount duced by reacting chlorine dioxide with aqueous of ClO2 added should be equal, or substantially caustic soda. equal to the molar quantity of the NaOH present When chlorine dioxide is absorbed by an in the solution to accomplish this result. The 0. acqueous caustic soda solution, sodium chlorate aqueous solution to which the sodium hydroxide O and Sodium chlorite are formed in equal molecul is added is advantageously a solution already lar proportions as follows: containing Sodium chlorate and Sodium chlorite, for example, the mother liquor resulting from the 2ClO2-2NaOH->NaClO3--NaClO2-H2O final separation step of the process. I have found 15. A satisfactory method for the separation and that by a suitable procedure the formed Sodium 5 separate recovery directly from the solution of chlorate, sodium chlorite and also sodium chlorite the Sodium chlorate and sodium chlorite So trihydrate may be separated from Such Solutions formed has not, so far as I am aware, been pro in a pure state. These and other aspects of the posed. The application and use of the above re separation will be more fully understood in the action in the preparation of sodium chlorite has, light of the accompanying drawings which are 20 in consequence, been limited. flow sheets showing the sequence of steps in three I have discovered that an aqueous Solution, alternative methods of carrying out the process having dissolved therein suitable proportions of of the invention. Sodium chlorate and sodium chlorite, will pre In accordance with one embodiment, as illus cipitate sodium chlorate substantially free from trated in Fig. 1, the temperature of an aqueous 25 Sodium chlorite when adjusted to a tempera solution containing sodium chlorate and Sodium. ture of about 30° C. and that, when the tempera chlorite is adjusted to about 30° C. at which point ture of such a solution is lowered substantially the sodium chlorate in excess of the limit of Solu below 30° C., there is a tendency to simultaneously bility in the particular Solution used Will sepa precipitate Sodium chlorate and sodium chlorite rate from the Solution and may be removed by a 30 trihydrate. When the temperature of such a centrifuge or by filtration. A minor proportion of solution is held for a time at about 30° C. to per water is added to the mother liquor resulting mit sodium chlorate to precipitate in a relatively from the separation in order to produce a solution pure condition, and subsequently the tempera having a sodium chlorate concentration less than ture is increased substantially above 30° C. the maximum solubility of sodium chlorate in 35 35 have found that anhydrous sodium chlorite pre the presence of sodium chlorite in water at a tem cipitates from the Solution free from chlorate. perature of about 5° C. By this procedure con I have found moreover, that the transition tem tamination of subsequently crystallized chlorite perature between the chlorite trihydrate and the trihydrate by Small quantities of chlorate is anhydrous chlorite is 38 C., and that, if sub avoided. The solution is cooled to about 5 C. 40 stantial proportions of sodium chlorate are pres and the precipitated chlorite in the form of the ent, the transition temperature may be lowered trihydrate is removed by centrifugation. The to 3.8 C. when the Solution is Saturated with mother liquor which will contain approximately respect to chlorate. I have further found that equimolar quantities of chlorate and chlorite 45 45 when the temperature of Such a solution is may then be returned to the absorber vessel and lowered substantially below 30° C., for example sodium hydroxide and chlorine dioxide added to to 5° C., sodium chlorite trihydrate may be re render the process cyclic. As shown in Fig. 1, covered from the solution by crystallization. NaOH and ClO2 are introduced into an ab These discoveries are applied in the process of sorber to produce additional quantities of chlorite the present invention which comprehends a pro and chlorate in the mother liquor which has been SO 50 cedure suitable to accomplish the Separation of recycled from the chlorite trihydrate separation. Sodium chlorate and sodium chlorite from aqueous The following experimental example will serve solutions and more specifically provides a method to illustrate the invention in accordance with whereby these two salts may be recovered from this embodiment. 55 solutions resulting from the reaction between Eacample No. 1.- To a mother liquor contain 2 2,169,066 ing 36 gm. NaClO3, 32.0 gm. NaClO2 and 69.7 gm. chlorite is precipitated and is removed from the H2O, 31.1 gm. NaOH and 52.5gm. ClO2 are added. Solution. Following this separation the mother The solution is brought to 30° C. and 41.4 gm. liquor may be cooled to about 5° C. to precipitate NaClO3 are removed by using a filter or cen Sodium chlorite trihydrate which is separated trifuge. 14.4 gm. H2O are added to the mother from the solution by centrifugation, for example. liquor and it is cooled at 5° C. 56.2 gn. The Sodium chlorite trihydrate separated by this NaClO2.3H2O are removed. The nother liquor step, or at least a part thereof, may with advan now contains 36 gm. NaClO3, 32 gm. NaClO2 and tage be returned to the mixer containing the 69.7 gn. H2O and the cycle is repeated. mother liquor from the chlorate separation which U A Second embodiment of my invention involves is regulated to a temperature of 45° C. In this O certain variations in the just described procedure embodiment, as in the previous Ones, the chlo which are indicated in dotted lines in Fig. 1, and rate-chlorite liquor resulting from the trihydrate which permit the separate recovery from the separation may be returned to an absorber vessel process of anhydrous sodium chlorite in additlon where sodium hydroxide is added followed by to quantities of sodium chlorite trihydrate. In absorption therein of chlorine dioxide. The foll this method of procedure sodium chlorate is lowing experimental example illustrates an Oper Separated from a solution adjusted to a tempera ation in accordance with this embodiment. ture of about 30° C. which contains sodium chlo Eacample No. III-To a mother liquor contain rite and chlorate. At this point additional so ing 36.0 gm. NaClO3, 32.0 gm. NaCO2 and 69.7 gm. 20 dium chlorite and water are added to the Solu H2O, 31.1 gm. NaOH and 52.5gm. ClO2 are added. 20 tion. This is accomplished with particular ad The Solution is brought to 30° C. and 41.4 gm. Vantage by separately heating Sodium chlorite NaClO3 are removed. To this Solution 224.0 gm. trihydrate crystals to a temperature in excess NaClO2.3H2O are added and the solution brought of about 38° C., and preferably between 38 C. to 45° C. 31.39 gm. anhydrous NaClO2 can be 25 and 45 C., whereby the crystals are transformed removed by using a filter or centrifuge. The into a solution of chlorite in which is suspended mother liquor is brought to 5° C. 230.0 gm. precipitated anhydrous sodium chlorite which is NaClO2.3H2O are removed. This Sodium chlorite then separated by appropriate means such as by trihydrate is used to add back in the above, centrifuging, and the mother liquor from the 6.0 gm. NaClO2.3H2O being in excess. To the separation added to the solution remaining from mother liquor from the above 5 C. Step, 31.1 gm. 30 the above-mentioned chlorate separation. The NaOH and 52.5 gm. CO2 are added and the cycle mixed solution is cooled to a temperature of is repeated. about 5° C. Without addition of water other than What I claim is: that added with the Sodium chlorite which was ... A process for the preparation and separate derived from the trihydrate crystals, and a fur recovery of sodium chlorate and sodium chlorite 35 ther quantity of precipitated trihydrate is sepa which comprises introducing chlorine dioxide in rated from the solution. The separated trihy an amount, sufficient to produce a Substantially drate or at least, a portion thereof may advan neutral solution into an aqueous solution con tageously be heated to produce anhydrous chlo taining sodium hydroxide, adjusting the tem 40 rite and at the same time yield a solution of perature of the solution to about 30° C., Sepa chlorite which may be returned to the process rating the resulting precipitated Sodium chlorate, subsequent to the chlorate separation as above diluting the remaining solution until the concern described. In this method of operation impor tration of sodium chlorate therein is less than tant economies are also achieved by cyclically the maximum solubility of sodium chlorate in returning the Sodium chlorite-sodium chlorate the presence of the sodium chlorite and water liquor from the trihydrate separation to the ab in the Solution at a temperature of about 5 C., SOrber vessel to serve as the absorption medium cooling said solution to about 5 C. and Sepa for chlorine dioxide after an additional quantity rating the resulting precipitated Sodium chlorite of NaOH has been added thereto. The following in the form of the trihydrate. experinental example illustrates this method of 2. A process for the preparation and Separate Operation. - recovery of sodium chlorate and Sodium chlorite Eacample No. II.--To a mother liquor contain Which comprises adding Sodium hydroxide to an ing 36.0gm. NaClO3, 32.0 gm. NaClO2 and 69.7 gm, aqueous Solution containing sodium chlorate and H2O, 31.1 gm. NaOH and 52.5 gm, ClO2 are added. sodium chlorite and thereafter introducing into 5 5 The Solution is brought to 30° C. and 41.4 gm. said solution chloride dioxide in an amount Suffi NaClO3 are removed. 119.6 gm. NaClO2.3H2O are cient to produce a Substantially neutral Solution, 55 heated to 45° C., the crystals will melt and 24.4 adjusting the temperature of the solution to about parts anhydrous NaClO2 is filtered off. The 30° C., separating the resulting precipitated so mother liquor from this operation is added to the dium chlorate, diluting the remaining solution 60 mother liquor from the sodium chlorate crystals. until the concentration of Sodium chlorate there The combined mother liquor is cooled to 5° C., in is less than the maximum Solubility of Sodium 80 136.75 gm. NaClO2.3H2O will be precipitated. chlorate in the presence of the Sodium chlorite The mother liquor now contains 36 gm. NaClO3, and water in the solution at a temperature of 32.0 gn. NaClO2 and 69.7 gm. H2O and is used about 5 C., cooling said solution to about 5° C., 65 to repeat the cycle. Separating the resulting precipitated Sodium chlo In accordance With a third embodiment of my rite in the form of the trihydrate, and returning 65 invention as illustrated in Fig. 2 of the drawing, the mother liquor containing Sodium chlorate and a Solution containing sodium chlorite and sodium Sodium chlorite to further addition of Sodium chlorate is adjusted to a temperature of about hydroxide and chlorine dioxide as first recited, 30° C., and the precipitated sodium chlorate sep 3. A process for the preparation and separate al'ated by suitable means, the mother liquor from recovery of sodium chlorate and sodium chlorite 70 the Separation is transferred to a mixing vessel which comprises introducing chlorine dioxide in to which is added a proportion of sodium chlorite an amount sufficient to produce a substantially trihydrate and the temperature of the mixture 75 adjusted to about 45° C. Anhydrous sodium neutral Solution into an aqueous solution con taining Sodium hydroxide, adjusting the tem 75 2,169,066 3 perature of the solution to about 30° C., separat rite trihydrate to the resulting solution, heating ing the precipitated Sodium chlorate, adding Wa the solution to a temperature of about 45° C., ter and Sodium chlorite to the remaining solution, Separating the precipitated anhydrous sodium cooling the resulting Solution to a temperature chlorite, cooling the resulting solution to about of about 5 C. and separating the precipitated 5 C., and separating the precipitated sodium sodium chlorite trihydrate. chlorite trihydrate. 4. A process for the preparation and separate 8. A process for the preparation and separate recovery of sodium chlorate and Sodium chlorite recovery of sodium chlorate and Sodium chlorite which comprises introducing chlorine dioxide in Which comprises adding SOdium hydroxide to an ) an amount sufficient to produce a substantially aqueous solution containing SOdium chlorate and O neutral solution into an aqueous solution con Sodium chlorite and thereafter introducing into taining SOdium hydroxide, adjusting the ten Said Solution chlorine dioxide in an amount suf perature of the solution to about 30° C., separat ficient to produce a substantially neutral solu ing the precipitated sodium chlorate, separately tion, adjusting the temperature of the Solution heating sodium chlorite trihydrate to a tempera to about 30° C., separating the precipitated so 5 ture upwards of about 38° C. and separating an dium chlorate, adding sodium chlorite trihydrate hydrous sodium chlorite therefroin, adding the to the resulting Solution, heating the solution to mother liquor from said separation and contain a temperature of about 45° C., separating the ing sodium chlorite to the Solution from the so precipitated anhydrous Sodium chlorite, cooling dium chlorate separation, cooling the mixed So the resulting solution to about 5 C., separating lution to about 5° C., separating the precipitated the precipitated sodium chlorite trihydrate, re Sodium chlorite trihydrate, and subjecting at turning at least a portion of the separated tri least a part of the separated trihydrate salt to hydrate to the solution from the chlorate sep the said heating treatment at a temperature up aration, and returning the mother liquor from Wards of about 38 C. to recover further quan the trihydrate separation containing sodium chlo 25 tities of anhydrous sodium chlorite. rate and sodium chlorite to further addition of 5. A process for the preparation and separate Sodium hydroxide and chlorine dioxide as first recovery of sodium chlorate and sodium chlorite recited. which comprises adding sodium hydroxide to an 9. The method of separately recovering sodium 30 aqueous solution containing sodium chlorate and chlorate and sodium chlorite from an aqueous 30 Sodium chlorite and thereafter introducing into solution containing said salts which comprises said solution chlorine dioxide in an amount suf adjusting the temperature of the solution to about ficient to produce a substantially neutral solu 30° C., separating the precipitated Sodium chlo tion, adjusting the temperature of the solution rate, diluting the remaining solution until the to about 30° C., separating the precipitated sodi concentration of sodium chlorate therein is less 35 um chlorate, separately heating sodium chlorite than the maximum solubility of Sodium chlorate trihydrate to a temperature upwards of about in the presence of the Sodium chlorite and water 38 C. and separating anhydrous sodium chlorite in the Solution at a temperature of about 5° C., therefrom, adding the mother liquor from said cooling said solution to about 5 C., and separat 40 Separation and containing Sodium chlorite to the ing the precipitated sodium chlorite in the form 40 solution from the sodium chlorate separation, of the trihydrate. cooling the mixed solution to about 5 C. separat 10. The method of separately recovering so ing the precipitated sodium chlorite trihydrate, dium chlorate and sodium chlorite from an aque Subjecting at least a part of the separated tri ous solution containing said salts which comprises hydrate salt to the said heating treatinent at a adjusting the temperature of the solution to 45 temperature upwards of about 38° C. to recover about 30° C., separating the precipitated sodium further quantities of anhydrous sodium chlorite, chlorate, separately heating sodium chlorite tri and returning the mother liquor from the trihy hydrate to a temperature upwards of about 38°C., drate Separation containing sodium chlorate and and separating anhydrous sodium chlorite there 50 Sodium chlorite to further addition of sodium hy from, adding the mother liquor from said separa 50 droxide and chlorine dioxide as first recited. tion and containing sodium chlorite to the solu 6. A process for the preparation and separate tion from the sodium chlorate separation, cool recoVery of Sodium chlorate and Sodium chlorite ing the mixed solution to about 5° C., separating which comprises introducing chlorine dioxide in the precipitated sodium chlorite trihydrate, and s an amount Sufficient to produce a Substantially subjecting at least a part of the separated tri 55 neutral solution into an aqueous solution of so hydrate salt to the said heating treatment at a dium hydroxide, adjusting the temperature of temperature upwards of about 38° C. to recover the solution to about 30° C., separating the pre further quantities of anhydrous Sodium chlorite. cipitated sodium chlorate, adding sodium chlo 11. The method of separately recovering sodi 60 rite trihydrate to the resulting solution, heating um chlorate and Sodium chlorite from an aqueous 60 the Solution to a temperature of about 45 C., and solution containing said salts which comprises separating the precipitated anhydrous Sodium adjusting the temperature of the solution to about chlorite. 30° C., separating the precipitated sodium chlo 7. A process for the preparation and separate rate, adding sodium chlorite trihydrate to the re recovery of Sodium chlorate and sodium chlorite sulting solution, heating the solution to a tem 65 65 which comprises introducing chlorine dioxide in perature of about 45° C., separating the pre an amount Sufficient to produce a Substantially cipitated anhydrous sodium chlorite, cooling the neutral solution into an aqueous solution of so resulting solution to about 5 C., and separating dium hydroxide, adjusting the temperature of the precipitated sodium chlorite trihydrate. the solution to about 30° C., separating the pre 70 70 cipitated sodium chlorate, adding sodium chlo GEORGE LEWIS CUNNINGHAMI.