Method for Producing Sodium Persulfate

Home , Potassium persulfate, Sodium persulfate

Patentamt J JEuropâischesEuropean Patent Office (§) Publication number: 0 081 063 Office européen des brevets B 1

® Dateof publication of patent spécification: 10.07.85 @ ht. Cl.4: C 01 B 15/08

® Application number: 82109350.7 (22) Date offiling: 08.10.82

@) Method for producing sodium persulfate.

(§) Priority: 10.11.81 US 320145 (7jj) Proprietor: FMC Corporation 2000 Market Street Philadelphia Pennsylvania 19103 (US) (§) Date of publication of application: 15.06.83 Bulletin 83/24 (7?) Inventor: McCarthy, MichaelJoseph 14 Lannigan Drive (§) Publication of the grant of the patent: Lawrenceville New Jersey 08648 (US) 10.07.85 Bulletin 85/28 Inventor: Schillaci, Phillip Vincent 226 Kaymar Drive Tonawanda New York (US) (§) Designated Contracting States: AT BE CH DE FR GB IT LI LU NL SE @) Representative: Barz, Peter, Dr. et al Patentanwalte Dr. V. Schmied-Kowarzik Dipl.- (68) References cited: Ing. G. Dannenberg Dr. P. Weinhold Dr. D. Gudel FR-A-1 493 723 Dipl.-lng. S. Schubert Dr. P. Barz US-A-2 899 272 Siegfriedstrasse 8 US-A-3 71 6 629 D-8000 Miinchen 40 (DE) US-A-3 954952 The file contains technical information submitted after the application was filed and not included in this specification

Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European patent convention). Courier Press, Leamington Spa, England. reaction solution. This patent also discloses that sodium sulfate builds up in the recirculated This invention relates to a method for mother liquor and after 24-30 cycles can be separately crystallizing sodium persulfate and removed by cooling to precipitate sodium sulfate sodium sulfate decahydrate from a mother liquor decahydrate plus some sodium persulfate. If regenerated with ammonium persulfate and excess water builds up in the system, it is also sodium hydroxide or sodium carbonate. removed at this time by adding anhydrous Sodium peroxydisulfate (commonly called sodium sulfate to the system prior to cooling thus sodium persulfate) is a commercial chemical removing the water as the water of crystallization. particularly useful for etching printed circuits, for Zumbrunn partially controls the loss of active cleaning copper before plating or soldering, and oxygen due to hydrolysis by maintaining reaction for initiating polymerization reactions. Other com- temperatures at 15°C to 25°C. mercially available persulfate salts are Nevertheless, active oxygen is lost by crystal- ammonium persulfate and potassium persulfate; lizing with sodium sulfate and by reacting with however, ammonium persulfate introduces ammonia to produce sulfate and nitrogen gas. objectionable ammonium ions into solution, This loss of active oxygen and the periodic while the solubility of potassium persulfate is purification of the mother liquor add to the cost of much less than ammonium or sodium persulfate. the product by this process. Consequently, sodium persulfate is the preferred Hall et al in U.S. Patent No. 3,954,952 disclose a compound for some applications. process for the production of sodium or Sodium persulfate can be prepared by elec- potassium persulfate by continuously reacting a trolysis of a solution containing sodium and solution of the corresponding sodium or sulfate ions according to U.S. Patent No. potassium hydroxide with a solution of slurry of 4,127,456 and U.S. Patent No. 4,144,144, as well ammonium persulfate. The reaction conditions as by the reaction of sodium hydroxide with are maintained at 15°C to 45°C, at atmospheric ammonium persulfate as taught by U.S. Patent pressure and in the pH range of 11-13; the No. 2,899,272 and U.S. Patent No. 3,954,952. The ammonia concentration in the reaction medium is electrolytic processes yield a high quality product, kept below 6 weight percent at 25°C by air or inert but do not permit the flexibility of producing gas stripping to avoid the formation of explosive ammonium, sodium, and potassium persulfates mixtures with air. The product is recovered by utilizing the same electrolyte; processes based on spray drying or other conventional means. While the electrolytic production of ammonium per- the potassium persulfate produced by this sulfate optionally followed by metathesis to method is satisfactory, the sodium persulfate sodium and potassium persulfate and ammonia tends to cake badly because of the greater provide the desired flexibility of operation. solubility of sodium persulfate, which permits a However, none of these processes are completely greater buildup of by-product sodium sulfate satisfactory for the production of sodium from the side reaction with ammonia. The persulfate. process results in a fine product which must be The process disclosed by Flach et al in U.S. compacted and granulated to reduce its tendency Patent No. 2,899,272 reacts aqueous solutions of to cake which is caused by the sodium sulfate in ammonium persulfate and an alkali metal or the product. alkaline earth hydroxide or carbonate at tem- The present invention is a process for con- peratures between 0°C and 45°C. Ammonia is tinuously making sodium persulfate from an removed from the reaction zone by vacuum aqueous mother liquor which is recycled and stripping. The reaction solutions are held for over replenished by reacting solutions of ammonium 24 hours in a crystallizer to provide time for the persulfate and either sodium hydroxide or crystals to grow and the water and ammonia to be sodium carbonate. A slurry of sodium persulfate removed. This long residence time is a disadvan- crystals is formed by cooling the mother liquor. tage because it allows the persulfate to react with Sodium persulfate crystals are extracted from a ammonia to produce the corresponding alkali first part of the slurry while a second part is fed to sulfate. The sulfate levels build up in the a combined fines destruction loop and gas crystallizer mother liquor. Eventually, the alkali stripper which removes ammonia, as well as sulfate will precipitate with the persulfate or the water vapor from the mother liquor. A third part alkali sulfate must be removed from the mother of the mother liquor is diluted so that pure liquor, or if permitted, the liquor must be sodium sulfate decahydrate crystals are formed discarded. on further cooling and are removed to prevent a Zumbrunn, in French Patent No. 1,493,723, buildup of sodium sulfate in solution and teaches the isothermal reaction of solid sodium coprecipitation with the product sodium hydroxide or sodium carbonate with ammonium persulfate. persulfate in a saturated sodium persulfate In the drawing, Figure 1 is a ternary phase solution to produce crystalline sodium persulfate. diagram of the system: water, sodium persulfate, Preferably, the reaction is maintained without and sodium sulfate illustrating the phase relation- cooling at temperatures of 15°C to 25°C with the ships during the process of the present invention. ammonia and water formed by the process partially removed by passing air through the Figures 2A and 28 are flow diagrams of alter- native embodiments of the process of the present crystallization loop which is physically shown invention. operating as a subloop between lines 23 and 27 in Figure 1 includes two superimpsoed ternary Figure 2A or between line 21 and 24 in Figure 2B phase diagrams of the system sodium persulfate which comprises line 25 delivering mother liquor (point S), sodium sulfate (point R), and water and line 39 delivering dilution water to a cooling (point O). The compositions represented by crystallizer 6 operated at temperature T' thereby letters without primes and solid lines are for the crystallizing a slurry of sodium sulfate deca- system at 25°C and represents in the general hydrate crystals. The slurry is conducted by line discussions, the temperature of the sodium 30 to a filter or centrifuge 7 separating the slurry persulfate crystallizer, T; the compositions repre- into a low sulfate mother liquor which is returned sented by letters with primes and dashed lines are to the system by line 31 and the sodium sulfate for the system at 15°C and represents in the decahydrate crystals for disposal through line 38. general discussions, the temperature of the It is obvious that the source of mother liquor for sodium sulfate crystallizer T'. The compositions many of these loops could be wholly, or in part, within the areas OMKJ and O'M'K'J' are not in supplied by other mother liquor sources. For equilibrium with solid sodium persulfate or example, line 24 feeding the ammonium per- sodium sulfate phase at the temperature T or T' sulfate make-up tank 8 could be fed from line 27, respectively. Compositions on the lines MK and from the ammonia stripper 5. The particular M'K' are in equilibrium with sodium persulfate at arrangement of lines and tanks would, in practice, temperatures T and T' respectively. Similarly, the be dictated by the equipment and selected compositions KJ and K'J' are in equilibrium with operating conditions. For example, an a sodium sulfate crystal at the temperatures T and evaporation crystallizer with a fines destruction T', and the sodium sulfate crystal will be sodium loop would combine the functions of the primary sulfate decahydrate at the temperature T'. crystallizer loop and the combined fines Figures 2A and 2B represent two of many destruction and stripper loop. possible embodiments of the apparatus of the In operation, the persulfate values are replaced invention. Both show a cooling crystallizer 1 with in the recirculating mother liquor by adding a stirrer 10, although an evaporation crystallizer ammonium persulfate, preferably as a solid; the would be satisfactory. The primary crystallizer corresponding sodium values are provided by loop involves line 36 carrying solution from the adding a solution sodium hydroxide or sodium crystallizer to cooler 3 and back to the crystallizer carbonate, preferably 50% sodium hydroxide. At 1 through line 37. Persulfate values are added to the temperature T, a slurry of sodium persulfate is this loop by dissolving ammonium persulfate formed; the composition of the slurry may be from line 32 in mother liquor from line 24 and represented as a point D in the area SMK of Figure feeding such enriched mother liquor to the 1. The mother liquor will then have the com- primary crystallizer loop through line 33. position represented by the point A on the line Similarly, a base such as a solution sodium MK. hydroxide or sodium carbonate is fed by line 34 If no sulfate were present in the system, the into tank 9 and thence by line 35 into the primary points D and A would be on the line SO. However, crystallizer loop. Part of the slurry is fed from the the sulfate values will continuously increase primary crystallizer loop through line 20 to a either by being introduced as impurities in the centrifuge orfilter2 and returns the mother liquor raw materials orthrough the reaction of ammonia directly or indirectly to the primary crystallizer and persulfate to form nitrogen and sulfate. This loop through line 21 and conducts product results in a continued shifting of the points A and sodium persulfate out of the system through line D towards the point K, and if uncorrected point A 22 to a conventional dryer or for subsequent use. would fall on point K and crystals of sodium Preferably, a separator or classifier should be sulfate would be found in the product. used to divide the slurry into a coarse fraction to To avoid the formation of sodium sulfate be used as feed to the centrifuge or filter 2 and a crystals in the product, advantage is taken of the fine crystal fraction to be used as feed to the fines greater temperature coefficient of solubility of destruction and ammonia stripper and other sodium sulfate decahydrate (0.66%/°C) compared loops, a combined fines destruction and to sodium persulfate (0.15%/°C). Water is added ammonia stripper loop is shown as lines 23, 26, to part of the mother liquor or slurry to change the and 27 connecting a source of mother liquor, such composition to that represented by point B which as the crystallizer, a heater 4, and a gas stripper 5. will be within the area J'K'L' when the solution is The heat necessary to evaporate the ammonia cooled to temperature T'. The solution will then from the solution also dissolves any crystals in comprise a slurry of sodium sulfate decahydrate warming the solution in heater 4 and air or any crystals without any solid sodium persulfate and other gas introduced through line 28 strips a mother liquor with the composition represented ammonia and water vapor from solution. The by the point C. By selecting the temperatures T ammonia is conducted by line 29 to a conven- and T' and the fraction of the mother liquor tional ammonia recovery system while the through the sodium sulfate decahydrate loop, it is deammoniated mother liquor is returned to the possible to control the composition of the mother system through line 27. liquor A so that crystals of sodium sulfate never The final loop is the sodium sulfate decahydrate form in the sodium persulfate crystallizer. To minimize the sodium sulfate in the system, it Example 1 is necessary to have T' be almost at the freezing A laboratory scaie sodium sulfate decahydrate point of the solution (slightly below 0°C) and to crystallizer was run for 6 hours at 11°C with a feed maximize the fraction of the mother liquor of synthetic mother liquor averaging 29.5% passing through the sodium sulfate decahydrate sodium persulfate and 8.37% sodium sulfate. The loop. The maximum temperature for T' is 32°C, operating data are presented as Table I. approximately the melting point of sodium sulfate decahydrate. The maximum operating temperature for the sodium persulfate crystallizer Example 2 is about 35°C to minimize the decomposition of Pilot production of sodium persulfate was run persulfate although temperatures of 45°C or even for 2 days producing 5 drums of sodium per- higher would be possible. A temperature dif- sulfate, over 360 kg, using a feed liquor con- ference of at least 5°C is the minimum practical taining 8.0% sodium sulfate and 32% sodium temperature difference for the two crystallizers. persulfate. The mother liquor was warmed to Therefore, the temperature T' may range from 0°C 40°C and enough ammonium persulfate dissolved to 32°C, while the temperature T may range from to form a 20% ammonium persulfate solution. 5°C to 37°C. Preferably, for economy, temperature The mother liquor was reacted with 50% sodium T'should be 10°C to 25°C, while the temperature T hydroxide to adjust the pH to about 10-11 should be 20°C to 30°C varying according to the forming a 20% slurry of sodium persulfate. The specific plant conditions available. sodium persulfate crystallizer was operated at The operating conditions of the stripper loop 25°C. The assay and particle size distribution of are not critical except that it is undesirable for the individual drums are presented as Table II. crystals of any solid phase to form in the stripper because of the potential for plugging. Crystal- Example 3 lization could occur if too much water is A pilot sodium sulfate decahydrate crystallizer evaporated from the solution, either because of was run for 44 hours at 15°C. The feed to the too great a quantity of stripper gas or too high an crystallizer was 6.3 cm3/s water plus 61.2 cm3/s of inlet temperature of feed to the stripper; either a solution at 25°C containing 32.09% sodium cause would result in an excessive evaporation of persulfate, 8.40% sodium sulfate, and 56.95% water and crystal formation. The calculation of water. This was equivalent to 67.5 cm3/s of a the optimum stripper gas flow and feed solution solution containing 32.09% sodium persulfate, temperature of the stripper would be obvious to 7.79% sodium sulfate, and 60.12% water. The one skilled in the art and would depend on the total sodium sulfate decahydrate production was specific plant conditions. 1361 kg equivalent to 8.6 g/s average production The water losses in the system are determined (3.8 g/s Na2S04 and 4.8 g/s water of crystal- by the water removed from the system as water lization). Only traces of sodium persulfate could of crystallization of sodium sulfate decahydrate be detected, which were attributed to the mother and the water evaporated by the stripper. The liquor wetting the crystals. water balance is completed by the water of The feed solution without dilution would have reaction and solution added by the sodium produced 12.7 g/s crystals including 3.0 g/s hydroxide or sodium carbonate, plus the water sodium persulfate and 9.7 g/s sodium sulfate added in the sodium sulfate decahydrate loop. decahydrate.

6. The process of any of claims 1-5 characterized by: 1. A process for continuously recovering (a) removing heat by means of a stirred sodium persulfate from an aqueous mother liquor crystallizer from mother liquor to maintain a which is recycled and replenished by introducing temperature of 20°C to 30°C at which said mother ammonium persulfate and a compound selected liquor is in equilibrium with sodium persulfate from the group consisting of sodium hydroxide crystals forming a slurry of sodium persulfate in and sodium carbonate which react to produce said mother liquor, sodium persulfate and ammonia, the persulfate (b) separating the slurry into a fraction con- being in part reduced by the ammonia to form taining coarse crystals and a fraction containing sodium sulfate, characterized by: fine crystals, (a) removing heat from said mother liquor to (c) extracting the sodium persulfate crystals maintain a temperature T at which the mother from the mother liquor fraction from step (b) liquor is in equilibrium with sodium persulfate containing coarse crystals, crystals forming a slurry of sodium persulfate (d) evaporating ammonia from the fraction crystals in said mother liquor, from step (b) containing fine crystals by: (b) extracting sodium persulfate crystals from said mother liquor slurry from step (a), optionally (1) heating said mother liquor fraction to the slurry of step (a) is separated into a fraction provide the energy to evaporate said containing large crystals which fraction is fed to ammonia whereby any crystals are dis- step (b) and a fraction containing fine crystals solved, and which fraction is fed to step (c), (2) stripping said heated mother liquor with an (c) evaporating ammonia from a part of said inert gas whereby water vapor is also mother liquor or slurry from step (a) or step (b) evaporated from the solution and the tem- by: perature of the solution drops, and

(1) heating said mother liquor or slurry to (e) removing sodium sulfate from the system provide the energy to evaporate said by: ammonia whereby any crystals are dissolved, and (1) diluting a part of said mother liquor from (b) (2) stripping said heated mother liquor to containing fine crystals to a composition evaporate said ammonia whereby water which will correspond in Figure 1 to a point vapor is also evaporated from the solution B within the area J'K'L' after cooling step and the temperature of the solution drops, (e)(2), (2) cooling the diluted mother liquor from step (d) removing sodium sulfate from the system (d)(1) to a temperature of 15°C to 20°C at by: which sodium sulfate decahydrate crystals are formed, and (1) diluting a part of said mother liquor to a (3) extracting said sodium sulfate decahydrate composition which will correspond in Figure crystals from said mother liquor. 1 to a point B within the area J'K'L' after cooling step (d) (2), 7. The process of any of claims 1-6 charac- (2) cooling the diluted mother liquor from step terized in that the ammonium persulfate is added (d) (1) to the temperature T' at which sodium as a solid. sulfate decahydrate crystals are formed, and (3) extracting said sodium sulfate decahydrate crystals from said mother liquor.

2. The process of Claim 1 characterized by 1. Verfahren zur kontinuierlichen Gewinnung separating said slurry (a) into a fraction con- von Natriumpersulfat aus einer wässrigen Mutter- taining large crystals which fraction is fed to step lauge, die im Kreislauf geführt und ergänzt wird (b) and a fraction containing fine crystals which durch Einbringen von Ammoniumpersulfat und fraction is fed to step (c). einer Verbindung, die ausgewählt ist aus der aus 3. The process of Claim 1 or 2 characterized in Natriumhydroxid und Natriumcarbonat that the temperature T is in the range of 15°C to bestehenden Gruppe, welche unter Bildung von 35°C and the temperature T' is in the range of 0°C Natriumpersulfat und Ammoniak reagieren, to 30°C. wobei das Persulfat teilweise durch das 4. The process of Claim 3 characterized in that Ammoniak unter Bildung von Natriumsulfat the temperature T is in the range of 20°C to 30°C reduziert wird, gekennzeichnet durch: and the temperature T' is in the range of 15°C to (a) Ableiten von Wärme aus der Mutterlauge, 20°C. um eine Temperatur T aufrechtzuerhalten, bei der 5. The process of any of claims 1-4 charac- die Mutterlauge im Gleichgewicht mit terized in that step (a) is accomplished in a stirred Natriumpersulfatkristallen ist, die eine Auf- crystallizer and step (d)(2) is accomplished in a schlämmung von Natriumpersulfatkristallen in cooled crystallizer. der Muttterlauge bilden, (b) Extrahieren von Natriumpersulfatkristallen (c) Extrahieren der Natriumpersulfatkristalle aus der Mutterlaugenaufschlämmung von Stufe aus der Mutterlaugenfraktion von Stufe (b), die (a), wobei gegebenenfalls die Aufschlämmung grobe Kristalle enthält, von Stufe (a) aufgetrennt wird in eine Fraktion, die (d) Abdampfen von Ammoniak aus der Fraktion grosse Kristalle enthält und zur Stufe (b) geführt von Stufe (b), die feine Kristalle enthält, durch: wird, und eine Fraktion, die feine Kristalle enthält und zur Stufe (c) geführt wird, (1) Erhitzen der Mutterlaugenfraktion zum (c) Abdampfen von Ammoniak aus einem Teil Zwecke der Energiezufuhr, um das der Mutterlauge oder Aufschlämmung von Stufe Ammoniak abzudampfen, wobei etwaige (a) oder Stufe (b) durch: Kristalle gelöst werden, und (2) Strippen der erhitzten Mutterlauge mit (1) Erhitzen der Mutterlauge oder Auf- einem Inertgas, wobei auch Wasserdampf schlämmung zum Zwecke der Energie- aus der Lösung abdampft und die zufuhr, um das Ammoniak zu verdampfen, Temperatur der Lösung sinkt, und wodurch etwaige Kristalle gelöst werden, und (e) Entfernen von Natriumsulfat aus dem (2) Strippen der erhitzten Mutterlauge, um das System durch: Ammoniak abzudampfen, wobei auch Wasserdampf aus der Lösung abdampft und (1) Verdünnen eines Teils der Mutterlauge von die Temperatur der Lösung sinkt, (b), die feine Kristalle enthält, auf eine Zusammensetzung, die in Fig. 1 einem Punkt (d) Entfernen von Natriumsulfat aus dem B innerhalb des Bereiches J'K'L' nach der System durch: Kühlstufe (e)(2) entspricht, (2) Abkühlen der verdünnten Mutterlauge von (1) Verdünnen eines Teils der Mutterlauge auf Stufe (d)(1) auf eine Temperatur von 15°C eine Zusammensetzung, die in Fig. 1 einem bis 20°C, bei der Natriumsulfat-deka- Punkt B innerhalb des Bereiches J'K'L' nach hydrat-Kristalle gebildet werden, und der Kühlstufe (d)(2) entspricht, (3) Extrahieren der Natriumsulfat-deka- (2) Abkühlen der verdünnten Mutterlauge aus hydrat-Kristalle aus der Mutterlauge. Stufe (d)(1) auf eine Temperatur T', bei der Natriumsulfat-dekahydrat-Kristalle gebildet 7. Verfahren nach irgendeinem der Ansprüche 1 werden, und bis 6, dadurch gekennzeichnet, dass das (3) Extrahieren der Natriumsulfat-deka- Ammoniumpersulfat als Feststoff zugesetzt wird. hydrat-Kristalle aus der Mutterlauge.

2. Verfahren nach Anspruch 1, gekennzeichnet durch Auftrennen der Aufschlämmung (a) in eine Fraktion, die grosse Kristalle enthält und zur Stufe (b) geführt wird, und eine Fraktion, die feine 1. Un procédé pour la récupération en continu Kristalle enthält und zur Stufe (c) geführt wird. du persulfate de sodium à partir d'une liqueur 3. Verfahren nach Anspruch 1 oder 2, dadurch mère aqueuse qui est recyclée et remplie par d'un gekennzeichnet, dass die Temperatur T im introduction de persulfate d'ammonium et Bereich von 15°C bis 35°C und die Temperatur T' composé choisi dans le groupe composé im Bereich von 0°C bis 30°C liegt. d'hydroxyde de sodium et de carbonate de 4. Verfahren nach Anspruch 3, dadurch gekenn- sodium qui réagit pour produire le persulfate de zeichnet, dass die Temperatur T im Bereich von sodium et l'ammoniaque, le persulfate étant en du 20°C bis 30°C und die Temperatur T' im Bereich partie réduit par l'ammoniaque pour former von 15°C bis 20°C liegt. sulfate de sodium, caractérisé par: 5. Verfahren nach irgendeinem der Ansprüche 1 (a) l'élimination de chaleur de ladite liqueur bis 4, dadurch gekennzeichnet, dass die Stufe (a) mère pour maintenir une température T à laquelle in einem gerührten Kristallisator und die Stufe la liqueur mère est en équilibre avec les cristaux (d)(2) in einem gekühlten Kristallisator durch- de persulfate de sodium formant une boue de geführt wird. cristaux de persulfate de sodium dans ladite 6. Verfahren nach irgendeinem der Ansprüche 1 liqueur mère, bis 5, gekennzeichnet durch: (b) l'extraction de cristaux de persulfate de (a) Ableiten von Wärme aus der Mutterlauge sodium de ladite boue de liqueur mère de la mit Hilfe eines eine gerührten Kristallisators, um phase (a) éventuellement la boue de la phase (a) 30°C Temperatur von 20°C bis aufrechtzuerhalten, est séparé en une fraction contenant des cristaux bei im mit der die Mutterlauge Gleichgewicht plus dont la fraction est envoyée à la phase die eine Auf- gros Natriumpersulfatkristallen ist, (b) et une fraction contenant les cristaux fins qui in der Mutter- schlämmung von Natriumpersulfat est une fraction envoyée à la phase (c), lauge bilden, (b) Auftrennen der Aufschlämmung in eine (c) l'évaporation de l'ammoniaque d'une partie Fraktion, die grobe Kristalle enthält, und eine de ladite liqueur mère ou de la boue de la phase Fraktion, die feine Kristalle enthält, (a) ou de la phase (b) par: (1) chauffage de ladite liqueur mère ou de la (a) l'élimination de la chaleur au moyen d'un boue pour fournir l'énergie pour évaporer cristalliseur à agitation de ladite liqueur mère ladite ammoniaque pour dissoudre tous les pour maintenir une température de 20°C à 30°C à cristaux, et laquelle ladite liqueur mère est en équilibre avec (2) décapage de ladite liqueur mère réchauffée les cristaux de persulfate de sodium formant une pour évaporer ladite ammoniaque ce qui fait boue de persulfate de sodium dans ladite liqueur que la vapeur d'eau est également évaporée mère, de la solution et la température de la (b) la séparation de la boue dans une fraction solution baisse, contenant des cristaux grossiers et une fraction de cristaux fins, (d) élimination du sulfate de sodium du (c) l'extraction de cristaux de persulfate de système par: sodium d'une fraction de liqueur mère de la phase (b) contenant des cristaux grossiers, (1) dilution d'une partie de ladite liqueur mère (d) l'évaporation de l'ammoniaque d'une en une composition qui correspond dans la fraction de la phase (b) contenant des cristaux fins figure 1 à un point B dans la zone J'K'L' en effectuant après l'étape de refroidissement (2) refroidissement de la liqueur mère diluée de (1) le chauffage de ladite fraction de liqueur la phase (d)(1) à la température T' à laquelle mère pour fournir l'énergie pour évaporer les cristaux de décahydrate de sulfate de ladite ammoniaque de sorte que tous les sodium sont formés, cristaux soient dissous, et (3) extraction desdits cristaux de décahydrate (2) le strippage de ladite liqueur mère chauffée de sulfate de sodium de ladite liqueur mère. avec un gaz inerte de sorte que la vapeur d'eau est également évaporée de la solution 2. Procédé de la revendication 1, caractérisé par et la température de la solution baisse, et la séparation de ladite boue (a) en une fraction contenant des gros cristaux, cette fraction est (e) l'élimination du sulfate de sodium du envoyée à la phase (b) et une fraction contenant système en effectuant: des cristaux fins envoyée à la phase (c). 3. Le procédé de la revendication 1 ou 2, (1) la dilution d'une partie de ladite liqueur caractérisé par le fait que la température T est mère de (b) contenant les cristaux fins à une dans la gamme de 15°C à 35°C et la température composition qui correspond sur la figure 1 à T' dans la gamme de 0°C à 30°C. un point P dans la zone J'K'L' après la phase 4. Le procédé de la revendication 3, caractérisé (e) de refroidissement, par le fait que la température T est dans la gamme (2) le refroidissement de la liqueur diluée de la de 20°C à 30°C et la température T' est dans la phase (d)(1) à une température de 15°C à gamme de 15°C à 20°C. 20°C à laquelle les cristaux de décahydrate 5. Le procédé de l'une ou l'autre des revendi- de sodium sont formés, et cations 1-4, caractérisé par le fait que la phase (3) l'extraction desdits cristaux de décahydrate (a) est accomplie dans un cristalliseur à agitation de sulfate de sodium de la liqueur mère. et la phase (d)(2) est accomplie dans un cristalliseur refroidi. 7. Le procédé de l'une ou l'autre des revendi- 6. Le procédé de l'une ou l'autre des revendi- cations 1-6, caractérisé dans le fait que le cations 1-5 est caractérisé par: persulfate d'ammonium est ajouté à l'état solide.