Patentamt Europaisches ||| || 1 1| || || || || || || || || ||| || (19) J European Patent Office

Office europeen des brevets (1 1 ) EP 0 517 782 B1

(12) EUROPEAN PATENT SPECIFICATION

(45) Date of publicationation and mention (51) |nt. CI.6: C01 B 1 1/06 of the grant of the patent: 30.10.1996 Bulletin 1996/44 (86) International application number: PCT/US91/01300 (21) Application number: 91905450.2 (87) International publication number: (22) Date of filing: 28.02.1991 WO 91/13025 (05.09.1991 Gazette 1991/21)

(54) PROCESS FOR THE PRODUCTION OF VERFAHREN ZUR HERSTELLUNG VON LITHIUMHYPOCHLORIT PROCEDE POUR LA PRODUCTION D'HYPOCHLORITE DE LITHIUM

(84) Designated Contracting States: • WOODEN, William, T. ES FR GB IT Cleveland, TN 37311 (US)

(30) Priority: 02.03.1990 US 489316 (74) Representative: Baker, Colin John et al 25.02.1991 US 6581 11 Withers & Rogers, 4 Dyer's Buildings, (43) Date of publication of application: Holborn 16.12.1992 Bulletin 1992/51 London EC1N2JT(GB)

(73) Proprietor: OLIN CORPORATION (56) References cited: Cheshire, CT 06410-0586 (US) EP-A- 0 099 152 BE-A- 628 396 SU-A- 349 262 US-A- 1 481 039 (72) Inventors: US-A- 1 481 040 US-A- 3 171 814 • DUNCAN, Budd, L. US-A- 3 498 924 US-A- 4 146 578 Athens, TN 37303 (US) • CARPENTER, Larry, D. Remarks: Cleveland, TN 37311 (US) The file contains technical information submitted • OSBORNE, Leslie R. after the application was filed and not included in Chattanooga, TN 37421 (US) this specification

CO CM CO

Note: Within nine months from the publication of the mention of the grant of the European patent, give 10 any person may notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in o a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. Q_ 99(1) European Patent Convention). LU Printed by Rank Xerox (UK) Business Services 2.13.8/3.4 EP 0 517 782 B1

Description

This invention is related to the production of concentrated lithium hypochlorite. More particularly, this invention is related to the production of concentrated lithium hypochlorite from pure concentrated solutions of . 5 Lithium hypochlorite has found application as a swimming pool sanitization agent. Current commercial processes for the manufacture of lithium hypochlorite produce a low assay product of approximately 29% by weight of LiOCI by the chlorination of . The impurities in the commercial product include chlorates, carbonates, sulfates, and chlorides of potassium, sodium, or lithium. The process is in addition complex and costly. Various other processes for the manufacture of hyprochlorites of higher purity have been described. For example, 10 US-A-1,481,039 describes a method of producing , in particular calcium hypochlorites by extracting hypochlorous acid from aqueous solutions with a reagent which will not extract chlorides, and causing the extracted hypochlorous acid to react with an alkaline substance to form the corresponding hypochlorite. US-A-1 ,148,040 likewise describes improvements in hypochlorite manufacture, in particular calcium hypochlorites, this time by causing an extract of hypochlorous acid in an organic solvent to react with a metal hydroxide, with the amount of available 15 being in excess of that theoretically required to react with the hydroxide. US-A-3,498,924, issued March 3, 1970 to Walsh et al. describes the reaction of dilute hypochlorous acid solutions with sodium hydroxide. According to the patent, anhydrous , sodium hypochlorite hydrate, and basic sodium hypochlorites can be produced. The authors contemplate the formation of solid products of , lithium hypochlorite, and alkaline earth metal hypochlorites by this reaction. 20 Surprisingly, now it has been discovered that solid lithium hypochlorite can be produced directly and with ease for use in sanitizing and bleaching applications. It is an object of the present invention to provide a process for producing lithium hypochlorite which substantially reduces the presence of impurities such as chlorates, carbonates, sulfates, and chlorides. Another object of the present invention is to provide a process for producing lithium hypochlorite which eliminates 25 the need for extraction with an organic solvent. An additional object of the present invention is to provide a process for producing lithium hypochlorite which reduces the amount of expensive lithium hydroxide required. A further object of the present invention is to provide a process for producing lithium hypochlorite which readily dries the lithium hypochlorite product to desired moisture contents at reduced energy requirements and with a minimum 30 of product loss. A still further object of the present invention is to provide a process for producing lithium hypochlorite which reduces the number of processing steps required. The novel process for producing lithium hypochlorite comprises admixing a hypochlorous acid solution having a concentration of 35 percent or greater by weight of HOCI with an aqueous slurry of lithium hydroxide at a temperature 35 in the range of from about 0° to about 20° to produce a solution of lithium hypochlorite, and subsequently extracting the lithium hypochlorite by use of a low temperature crystallisation and separation step. The novel process of the present invention employs as the starting material a concentrated solution of hypochlo- rous acid, HOCI. A process for producing the concentrated solution of hypochlorous acid is carried out in a suitable reactor such as one provided with means for spraying discrete droplets of an aqueous solution of an alkali metal hydrox- 40 ide into the reactor; means for feeding gaseous chlorine into the reactor; means for withdrawing solid alkali metal chlo- ride product from the reactor; and means for withdrawing a gaseous mixture comprised of hypochlorous acid, chlorine monoxide, unreacted chlorine and water vapor from the reactor. The reactor, reactant feed lines, or both are provided with suitable heating means for maintaining the reaction at a temperature sufficiently high to vaporize the hypochlorous acid product and water and to dry the alkali metal chloride 45 particles. Any alkali metal hydroxide capable of reacting with gaseous chlorine to form hypochlorous acid may be employed as a reactant in the process of this invention. Typical examples of suitable alkali metal hydroxides include sodium hydroxide, potassium hydroxide, lithium hydroxide and mixtures thereof. Sodium hydroxide is the preferred reactant since the resulting sodium chloride by-product is more easily disposed of than the other alkali metal chlorides. As gas- so eous mixtures having high concentrations of hypochlorous acid and chlorine monoxide are desired, highly concentrated aqueous solutions of the alkali metal hydroxide are used. Suitable concentrations include those in the range of from about 40 to about 80, and preferably from about 45 to about 60 percent by weight of alkali metal hydroxide. The alkali metal hydroxide solution is sprayed from at least one atomizer preferably positioned at or near the top of the reactor. The atomizer is preferably positioned along the central axis of a cylindrical reactor, to provide minimum con- 55 tact between the atomized droplets and the walls. The atomizer may be directed up, down, sideways or any other ori- entation that meets the above conditions. Droplet sizes are selected which permit a substantially complete reaction of the droplets of alkali metal hydroxide with chlorine, the vaporization of hypochlorous acid and water produced and the production of substantially dry alkali metal chloride particles having low concentrations of chlorate.

2 EP 0 517 782 B1

The dry alkali metal chloride particles produced, while smaller than the original droplets, are preferably sufficiently large enough to prevent a significant portion of the particles from being entrained in the gaseous mixture of hypochlo- rous acid produced. Typical atomizing techniques of the pneumatic, hydraulic, and spinning disc type, among others, which are suitable 5 for use in the process of this invention, are described in the monograph entitled "Atomization and Spray Graining" by W. R. Marshall, Jr., Chemical Engineering Progress Monograph Series, No. 2, Volume 50, 1954. A gas, such as chlorine gas, under pressure may be used to atomize droplets of aqueous alkali metal hydroxide by premixing before discharge from the nozzle, or the liquid droplets and chlorine gas are mixed after discharge from their respective nozzles. The chlorine gas which reacts with the alkali metal hydroxide is fed directly to the reactor. 10 The process of for producing concentrated hypochlorous acid employs a large excess of chlorine gas above the stoichiometric amount of alkali metal hydroxide as illustrated by the following equation:

C\2 + NaOH -> HOCI + NaCI (1).

15 Suitable excess amounts of chlorine gas include those in which the molar ratio of chlorine to alkali metal hydroxide is equal or greater than about 20:1 . For example, excess amounts of chlorine may include molar ratios from 20:1 to about 200:1 , preferably from about 25:1 to about 100:1 , and more preferably from about 30:1 to about 50:1 . These large excesses of chlorine gas result in increased yields of hypochlorous acid as the formation of chlorate is minimized and its concentration in the alkali metal chloride particles is less than about 10 percent by weight, and pref- 20 erably less than about 6 percent by weight. In addition, the use of large excesses of chlorine gas provide an improved method of maintaining the reaction temperature. In a continuous process, the gaseous mixture of hypochlorous acid vapor, water vapor, chlorine gas, and chlorine monoxide gas produced in the reactor is removed from the reactor and passed through a solids separator to remove any fine particles of alkali metal chloride which may be present. The sol- ids-free gaseous mixture is then liquified to produce an aqueous solution of hypochlorous acid having, for example, 25 from about 40 to about 60, and preferably from about 45 to about 50 percent by weight of HOCI. The liquefaction may be carried out, for example, by condensing the gaseous mixture at temperatures in the range of from about -5° to about +10°C. The concentrated hypochlorous acid solution is substantially free of ionic impurities such as alkali metal, chloride, and chlorate ions. For example, concentrations of the chloride ion are less than about 50 parts per million; the alkali 30 metal ion concentration is less than about 50 parts per million; and the chlorate ion concentration is no higher than about 100 parts per million. The second reactant in the novel process of the present invention is lithium hydroxide in the anhydrous or monohy- drated form. The lithium hydroxide employed is, for example, a commercially available industrial grade, preferably hav- ing low concentrations of impurities such as . In the process, lithium hydroxide is employed as an 35 aqueous slurry containing from about 10 to about 40, preferably from about 15 to about 35, and more preferably from about 25 to about 35 percent by weight of LiOH. While lower concentrations of LiOH may be used, their use results in excessive amounts of filtrate for recycle or disposal. In the novel process of the present invention, the hypochlorous acid solution, having a concentration of 35 percent or greater by weight of HOCI, is admixed with a lithium hydroxide slurry to form a reaction mixture. The reaction mixture 40 is preferably stirred or agitated to provide a homogeneous reaction mixture. During the process, the temperature of the reaction mixture is maintained for example, in the range of from about 0°C. to about 20°C, and preferably from about 5°C to about 10°C. Additional lithium hydroxide is added until the desired lithium hypochlorite concentration is attained. The reaction mixture is monitored for excess alkalinity and when this decreases to about 1 percent or less, addition of HOCI is discontinued, and the product solution is recovered. 45 The process of the invention is represented by the following equation:

LiOH + HOCI -> LiOCI + H20 (2)

As shown in the above equation, only one mole of lithium hydroxide is required per mole of lithium hypochlorite. The so lithium hypochlorite solution produced has a concentration of from about 15 to about 40, and preferably from about 25 to about 40 percent by weight of LiOCI. The product solutions contain small amounts of impurities such as lithium chlo- rate and lithium chloride which are formed during the reaction. The lithium hypochlorite solutions produced are highly pure and could be used directly in the sanitizing of water. However it is preferred to use solid forms of lithium hypochlorite. 55 In a further stage of the process according to the invention, the solutions of lithium hypochlorite are concentrated by cooling the solutions at subzero temperatures, for example, at a temperature in the range of from about 0 to about - 20°C, and preferably in the range of from about -5 to about -15°C. Crystals of lithium hypochlorite are separated from excess solution by any suitable solid-liquid separation method such as filtration. The crystals recovered may be dried in any suitable manner.

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In a preferred embodiment, the crystals are allowed to melt to form a substantially pure solution of lithium hypochlo- rite. Melting of the pure lithium hypochlorite crystals takes place at ambient temperatures, however, gentle heating con- ditions may be employed if desired. The concentrated solution or slurry of LiOCI is dried using any suitable gentle drying method to produce solid lith- 5 ium hypochlorite having the desired moisture content. For example, the concentrated LiOCI may be dried in a f luidized bed dryer, a spray dryer, a vacuum pan dryer, etc. where the drying temperature is in the range of from about 50°C. to about 200°C. The low concentrations of impurities in the lithium hypochlorite solutions or crystals minimizes the hygro- scopicity of the product permitting ease of drying at reduced energy requirements. Concentrated solutions or slurries of LiOCI are preferably dried in a spray dryer employing inlet temperatures in the range of from about 1 20° to about 200°C. 10 The solid lithium hypochlorite product produced is a highly pure source of available chlorine having a concentration of at least 55 percent by weight of LiOCI, and preferably, in the range of from about 75 to about 100 percent by weight of LiOCI. These solid products contain at least 65% of available chlorine, and preferably from about 90 to 120% of avail- able chlorine. As the process of the invention does not employ extraction with an organic solvent, the product is free of organic 15 impurities. Further, the process employs a molar ratio of the costly lithium hydroxide to hypochlorous acid of about 1 :1 in comparison to the processes commercially employed up to the present which require a molar ratio of at least 2:1 . The addition of a potassium compound, such as solid KOH or a solution of KOCI to any LiOCI filtrate recovered results in the precipitation of solid KCI03 which is readily removed from the solution. The remaining filtrate may be uti- lized to suspend lithium hydroxide for further hypochlorination. 20 Small amounts of this filtrate may be discarded depending upon the level of the chloride impurities present. It is envisioned that this same technique would be useful in the removal of deleterious Ca(CI03)2 from solutions generated in the manufacture of calcium hypochlorite. To further illustrate the invention the following examples are provided without any intention of being limited thereby. All parts and percentages are by weight unless otherwise specified. 25 EXAMPLE 1

Deionized water (8537g) and 4737g of LiOH.H20 were mixed in a 68.2 litre (15 gallon) reactor. The slurry was cooled to 3°C and 48% HOCI was added at a rate to maintain the temperature between 0°C and 15°C. As the alkalinity 30 decreased, solid LiOH.H20 was added to the reactor. A total of 18,948g of LiOH.H20 was added to the reactor. The HOCI flow was shut off when the residual alkalinity of the LiOCI solution, as measured by a "drop test", was less than about 1%. The LiOCI solution was poured into a container and refrigerated at a temperature of 2-5°C. After 6 days the solution was fed directly to a spray dryer operated at an inlet temperature of 1 75°C and an outlet temperature of 98°C. During the drying operation, a collection chamber filled with dry product. After one hour dried LiOCI crystals were 35 removed from the collection chamber and analyzed. The analysis is reported as Example 1a below. Dried LiOCI crys- tals were removed from the collection chamber after 2 hours of drying and again after 3 hours of drying. The analyses are reported below as Examples 1 b and 1 c respectively.

Solution* LiOCI 31.4 LiCI03 1 .3 LiCI 0.8 45 LiOH 0.5 H20 66.0 wt%. 50

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Spray Dried LiOCI Crystals*: Example 1a Example 1b Example 1c LiOCI 75.13 76.43 74.84 LiCI03 5.39 5.32 5.70 LiCI 6.15 6.58 6.64 LiOH 0.00 2.02 1.73 H20 13.33 9.65 11.09 wt%.

EXAMPLE 2 20 Deionized water (8537g) and 4737g of LiOH.H20 were mixed in a 68.2 litre (15 gallon) reactor. The slurry was cooled to 3°C and 48% HOCI was added at a rate to maintain the temperature between 0°C and 15°C. As the alkalinity decreased, solid LiOH.H20 was added to the reactor. A total of 18,948g of LiOH.H20 was added to the reactor. The HOCI flow was shut off when the residual alkalinity of the LiOCI solution, as measured by a "drop test", was reduced to 25 less than 1%. A container of the LiOCI solution was refrigerated at a temperature of 2-5°C. After 23 days the solution was stored in a freezer at -6°C. After 6 days the frozen LiOCI crystal agglomerates were removed and exposed to ambi- ent conditions for 24 hours. The crystal agglomerates, having sizes in the range of about 1 .2 to 3.6 centimeters, were then readily separated by filtration from the mother liquor and both the crystals and the mother liquor were analyzed. The crystals were allowed to melt at room temperature and the concentrated solution formed was fed directly to the 30 spray dryer. The spray dryer was operated at an inlet temperature of 145-160°C and an outlet temperature of 90-1 20°C. During the drying operation, a collection chamber filled with dry product. After 70 minutes dried LiOCI crystals were removed from the collection chamber and analyzed. The analysis is reported as Example 2a) below. Dried LiOCI crys- tals were removed from the collection chamber after 2.5 hours of drying and analyzed (Example 2b). At this time the dryer was shutdown, cleaned and restarted. After 2 additional hours of drying the dried LiOCI crystals in the collection 35 chamber were removed and analyzed (Example 2c).

Analysis: Original LiOCI LiOCI Solution* Crystals* Filtrate* LiOCI 32.43 38.99 15.76 LiCI03 0.48 0.59 3.30 LiCI 0.88 0.53 4.66 LiOH 0.26 0.00 1.00 H20 65.95 59.89 75.23 wt%.

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Spray Dried LiOCI Crystals*: Example 2a Example 2b Example 2c LiOCI 78.19 77.07 81.51 LiCI03 3.47 4.92 5.40 LiCI 4.07 5.36 6.47 LiOH 0.94 1.34 1.55 H20 13.33 11.31 5.07 wt%.

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Claims

20 1 . A process for producing a dried solid lithium hypochlorite characterized by the steps:

(a) admixing an aqueous hypochlorous acid solution having a concentration of 35% or greater by weight of HOCI with an aqueous slurry of lithium hydroxide having a concentration of 15 to 40% by weight of LiOH; (b) allowing said admixture to react to form an aqueous lithium hypochlorite solution having a concentration of 25 about 1 5 to 40% at a reaction temperature in the range from 0°C to 20°C and at a mole ratio of one mole HOCI to one mole LiOH; characterised in that the process additionally comprises the steps of: (c) cooling said aqueous lithium hypochlorite solution at a temperature of -20°C to 0°C to form lithium hypochlorite crystals in said aqueous solution; (d) separating said lithium hypochlorite crystals from said solution; and 30 (e) drying said lithium hypochlorite crystals to form a dried solid lithium hypochlorite product having a concen- tration of at least 55% by weight of LiOCI.

2. The process of claim 1 wherein said aqueous hypochlorous acid solution has a concentration of from 40 to 60% by weight of HOCI. 35 3. The process of Claim 2 wherein said aqueous hypochlorous acid solution has a concentration of from 45 to 50% by weight of HOCI.

4. The process of claim 1 wherein said aqueous lithium hydroxide solution has a concentration from 15 to 35% by 40 weight of LiOH.

5. The process of claim 1 wherein said aqueous lithium hydroxide solution has a concentration from 25 to 35% by weight of LiOH.

45 6. The process of claim 1 wherein said reaction temperature in step (b) is 5°C to 10°C.

7. The process of claim 1 wherein said aqueous lithium hypochlorite solution formed in step (b) has a concentration of 25 to 40% by weight of LiOCI. so 8. The process of claim 1 wherein said cooling step (c) is carried out at -15°C to -5°C.

9. The process of claim 1 wherein said drying step is carried out at a drying temperature from 50°C to 200°C.

10. The process of claim 1 wherein said dried solid lithium hypochlorite product has a concentration from 75 to 100% 55 by weight LiOCI.

Patentanspruche

1. Ein Verfahren zur Herstellung eines getrockneten, festen Lithiumhypochlorits, gekennzeichnet durch die Schritte:

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(a) Beimischen einer wassrigen Hypochlorsaurelosung mit einer Konzentration von 35 Gew.-% oder hoher an HOCI mit einem Wassrigen Schlamm von Lithiumhydroxid mit einer Konzentration von 15 bis 40 Gew.-% an LiOH; (b) Reagierenlassen der Beimischung zum Bilden einer Wassrigen Lithiumhypochloritlosung mit einer Konzen- tration von etwa 15 bis 40% bei einer Reaktionstemperatur im Bereich von 0°C bis 20°C und bei einem Mol- verhaltnis von einem Mol HOCI zu einem Mol LiOH; dadurch gekennzeichnet, daB das Verfahren zusatzlich die Schritte umfaBt: (c) Kiihlen der Wassrigen Lithiumhypochloritlosung bei einer Temperatur von -20°C bis 0°C zum Bilden von Lithiumhypochloritkristallen in der Wassrigen Losung; (d) Separieren der Lithiumhypochloritkristalle von der Losung und (e) Trocknen der Lithiumhypochloritkristalle zum Bilden eines getrockneten, festen Lithiumhypochloritprodukts mit einer Konzentration von zumindest 55 Gew.-% an LiOCI.

2. Das Verfahren nach Anspruch 1 , worin die wassrige Hypochlorsaurelosung eine Konzentration von 40 bis 60 Gew.- % an HOCI aufweist.

3. Das Verfahren nach Anspruch 2, worin die Wassrige Hypochlorsaurelosung eine Konzentration von 45 bis 50 Gew.-% an HOCI aufweist.

4. Das Verfahren nach Anspruch 1, Worin die Wassrige Lithiumhydroxidlosung eine Konzentration von 15 bis 35 Gew.-% an LiOH aufweist.

5. Das Verfahren nach Anspruch 1 , worin die Wassrige Lithiumhydroxidlosung eine Konzentration von 25 bis 35 Gew.-% an LiOH aufweist.

6. Das Verfahren nach Anspruch 1 , Worin die Reaktionstemperatur in Schritt (b) 5°C bis 10°C ist.

7. Das Verfahren nach Anspruch 1 , worin die Wassrige, in Schritt (b) gebildete Lithiumhypochloritlosung eine Konzen- tration von 25 bis 40 Gew.-% an LiOCI aufweist.

8. Das Verfahren nach Anspruch 1 , worin der Kuhlschritt (c) bei -15°C bis -5°C ausgefiihrt ist.

9. Das Verfahren nach Anspruch 1 , worin der Trocknungsschritt bei einer Trocknungstemperatur von 50°C bis 200°C ausgefiihrt ist.

1 0. Das Verfahren nach Anspruch 1 , worin das getrocknete, teste Lithiumhypochloritprodukt eine Konzentration von 75 bis 100 Gew.-% an LiOCI aufweist.

Revendications

1 . Procede de production d'hypochlorite de lithium solide seche caracterise par les etapes consistant a :

(a) melanger une solution aqueuse d'acide hypochloreux ayant une concentration de 35 % ou plus en poids de HOCI avec une suspension aqueuse d'hydroxyde de lithium ayant une concentration de 1 5 a 40 % en poids de LiOH ; (b) laisser ledit melange reagir pour former une solution aqueuse d'hypochlorite de lithium ayant une concen- tration d'environ 15 a 40 % a une temperature de reaction comprise entre 0°C et 20°C et a un rapport molaire d'une mole de HOCI pour une mole de LiOH ; caracterise en ce que le procede comprend en outre les etapes consistant a : (c) refroidir ladite solution aqueuse d'hypochlorite de lithium a une temperature de -20°C a 0°C pour former des cristaux d'hypochlorite de lithium dans ladite solution aqueuse ; (d) separer lesdits cristaux d'hypochlorite de lithium de ladite solution ; et (e) secher lesdits cristaux d'hypochlorite de lithium pour former un produit d'hypochlorite de lithium solide seche ayant une concentration d'au moins 55 % en poids de LiOCI.

2. Procede selon la revendication 1 , dans lequel ladite solution aqueuse d'acide hypochloreux a une concentration comprise entre 40 et 60 % en poids de HOCI. EP 0 517 782 B1

3. Procede selon la revendication 2, dans lequel ladite solution aqueuse d'acide hypochloreux a une concentration comprise entre 45 et 50 % en poids de HOCI.

4. Procede selon la revendication 1 , dans lequel ladite solution aqueuse d'hydroxyde de lithium a une concentration comprise entre 15 et 35 % en poids de LiOH.

5. Procede selon la revendication 1 , dans lequel ladite solution aqueuse d'hydroxyde de lithium a une concentration comprise entre 25 et 35 % en poids de LiOH.

6. Procede selon la revendication 1 , dans lequel ladite temperature de reaction a I'etape (b) est de 5°C a 1 0°C.

7. Procede selon la revendication 1 , dans lequel ladite solution aqueuse d'hypochlorite de lithium formee a I'etape (b) a une concentration de 25 a 40 % en poids de LiOCI.

8. Procede selon la revendication 1 , dans lequel ladite etape de ref roidissement (c) est realisee a une temperature de -15°Ca-5°C.

9. Procede selon la revendication 1 , dans lequel ladite etape de sechage est realisee a une temperature de sechage de 50°C a 200°C.

10. Procede selon la revendication 1 , dans lequel ledit produit hypochlorite de lithium solide seche a une concentration de 75 a 100 % en poids de LiOCI.

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