Process for the Production of Highly Pure Concentrated Solutions of Potassium Hypochlorite

Europaisches Patentamt European Patent Office © Publication number: 0 513 167 B1 Office europeen des brevets

@ Date of filing: 23.01.91

The file contains technical information submitted after the application was filed and not included in this specification

© Publication of the grant of the patent: @ Inventor: DUNCAN, Budd, L. 08.03.95 Bulletin 95/10 1207 Towanda Trail Athens, TN 37303 (US) © Designated Contracting States: Inventor: FLOWERS, William, O. AT BE CH DE DK ES FR GB GR IT LI LU NL P.O. Box 127 Englewood, TN 37329 (US) © References cited: EP-A- 0 054 996 DE-A- 2 940 708 FR-A- 574 988 GB-A- 0 581 945 © Representative: Badcock, Michele et al US-A- 3 498 924 US-A- 4 146 578 Withers & Rogers US-A- 4 428 918 4 Dyer's Buildings 00 Holborn London EC1N 2JT (GB) CO

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). Rank Xerox (UK) Business Services (3. 10/3.09/3.3.3) EP 0 513 167 B1

Description

This invention is related to the production of pure concentrated solutions of potassium hypochlorite. More particularly, this invention is related to the production of pure concentrated solutions of potassium 5 hypochlorite from pure concentrated solutions of hypochlorous acid. Potassium hypochlorite has found application as a component of detergent products, a sanitizing agent and as an industrial ozidizer. Known methods for the manufacture of potassium hypochlorite include the chlorination of potash as represented by equation (1): w 2KOH + Cl2- KOCI + KCI + H20 (1)

or by the reaction of a salt of potash with a hypochlorite salt as illustrated by equation (2):

KzSO* + Ca(OCI)2- 2KOCI + CaSO+ (2) 75 Both of these methods produce a solution which is contaminated by impurities which limit the concentration of the potassium hypochlorite solution or which inhibit the stability of the potassium hypochlorite solution. Potassium hypochlorite is available commercially as an aqueous solution containing up to about 15% by weight of potassium hypochlorite. The attempted concentration of these solutions of potassium 20 hypochlorite having high concentrations of potassium chloride or other salts results in substantial de- composition. The concentration of sodium hypochlorite, lithium hypochlorite, and alkaline earth hypochlorites such as calcium hypochlorite, results in the formation of solid products which can be dried to provide solid hypochlorites having high concentrations of available chlorine. 25 P. Pierron attempted to prepare solid potassium hypochlorite by reacting potassium hydroxide with a solution of chlorine monoxide in carbon tetrachloride. The reaction mixture was evaporated under vacuum at 40 to 45 °C. During concentration, the potassium hypochlorite decomposed and an orange residue was recovered which was identified as a mixture of chlorate, hypochlorite and peroxide. Thus, up to the present time, it has not been possible to prepare concentrated solutions of potassium 30 hypochlorite directly by the concentration of more dilute hypochlorite solutions. Further, in the case of potassium hypochlorite, solutions above about 20 percent by weight of KOCI have not been available. Surprisingly, now it has been discovered that concentrated solutions of highly pure potassium hypochlorite can be produced for use in the production of the detergent products, as well as sanitizing and bleaching applications. 35 It is an object of the present invention to provide a process which substantially reduces the formation of salts such as potassium chloride and thereby increasing the solubility of potassium hypochlorite. Another object of the present invention is to provide a process for producing concentrated potassium hypochlorite solutions having improved stability. An additional object of the present invention is to provide a process for producing concentrated 40 potassium hypochlorite solutions which reduces the amount of expensive potassium hydroxide required. A further object of the present invention is to provide a process for producing concentrated potassium hypochlorite solutions which reduces the number of processing steps required These and other advantages are accomplished in a process for producing an aqueous solution of potassium hypochlorite which comprises admixing at a temperature below 45 °C a hypochlorous acid 45 solution having a concentration of 35 percent by weight or greater of HOCI, with an aqueous solution or slurry of potassium hydroxide containing 35 percent by weight or greater of KOH to produce a potassium hypochlorite solution containing 30 percent or greater by weight of KOCI. The novel process of the present invention employs as the starting material a concentrated solution of hypochlorous acid, HOCI. One method of producing high purity concentrated HOCI solutions is that in which 50 gaseous mixtures, having high concentrations of hypochlorous acid vapors and chlorine monoxide gas and controlled amounts of water vapor are produced, for example, by the process described by J. P. Brennan et al in U.S. Patent No. 4,147,761, which is incorporated in its entirety by reference. The gaseous mixture is then converted to a concentrated hypochlorous acid solution. The concentrated hypochlorous acid solutions employed as one reactant have a concentration in the 55 range of from 35 to 60, and preferably from 40 to 55 percent by weight of HOCI. The solution is substantially free of ionic impurities such as chloride ions and alkali metal ions and has low concentrations of dissolved chlorine. For example, concentrations of the chloride ion are less than about 50 parts per million and the alkali metal ion concentration is less than about 50 parts per million.

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The dissolved chlorine concentration in the hypochlorous acid solution is less than about 2 percent, and preferably less than about 1 percent by weight. The highly concentrated hypochlorous acid solution has a density, for example, in the range of from about 1.15 to about 1.26, preferably from about 1.17 to about 1.24, and more preferably of from 1.19 to 5 about 1 .23 grams per milliliter (gm/ml) at a temperature in the range of from 10 ° C to 15 ° C. The second reactant in the novel process of the present invention is potassium hydroxide. The potassium hydroxide is employed as an aqueous solution or slurry The potassium hydroxide employed is, for example, an industrial grade having low concentrations of impurities such as potassium chloride. In the novel process of the present invention, the hypochlorous acid solution is admixed with the io potassium hydroxide to form a reaction mixture which is stirred or agitated to provide a homogeneous reaction mixture. During the process, the temperature of the reaction mixture is maintained at up to about 45 ° C, for example, those in the range of from about 0 ° to about 45 ° , and preferably from about 0 ° C to about about 25 ° C. The reaction mixture is monitored for excess alkalinity and when this decreases to about 1 percent, the reaction is terminated. is In a single step process the initial slurry of KOH contains at least 35 percent by weight of KOH, and preferably from 40 to 60 percent by weight of KOH. The potassium hypochlorite solution produced has a concentration of at least 30 percent by weight of KOCI. A concentration of KOCI up to about 40 percent by weight of KOCI can be achieved by this direct hypochlorination of pumpable slurries of KOH. Solutions having higher concentrations of KOCI, for example, up to about 50 percent by weight of KOCI, 20 can be produced in an embodiment in which the KOH concentration is initially in the range of from about 35 to about 50 percent by weight of KOH. During the hypochlorination reaction solid KOH is fed to the reaction mixture. Where a concentration of potassium hypochlorite above about 50 percent by weight is desired, the solutions may be concentrated, for example, by evaporation at sub-atmospheric pressures at temperatures of up to 45° - 50 °C. Preferably in the range of from about 0 to about 45 °C. Suitable pressures are those 25 below the vapor pressure of water in the solution at the evaporation temperature. Thus the novel process of the invention is able to produce potassium hypochlorite solutions having KOCI concentrations in the range of from about 30 to about 60 percent by weight The product solutions may contain small amounts of solid impurities which are formed during the reaction. These impurities can be removed by any suitable solid-liquid separation method such as filtration. 30 The clear potassium hypochlorite solutions produced are highly pure. These solutions may be used directly in the production of detergent products or the sanitizing of water, etc. The concentrated solutions produced by the novel process of the present invention are surprisingly stable, undergoing only slight losses of available chlorine concentration when stored, for example, at 0°C . Storage temperatures below that of 0 ° C. may be preferred as it has been discovered that solutions of KOCI with a concentration in excess of 35 58% by weight may be cooled to temperatures below -20 ° C. without formation of a solid phase. Thus low temperatures may facilitate the storage and shipment of these very highly concentrated and pure solutions of KOCI. Thus the novel process of the present invention produces clear aqueous solutions of potassium hypochlorite having available chlorine concentrations which have not been previously attained by the 40 processes available. Further, these highly concentrated solutions are novel sanitizing and bleaching agents which have not previously been available. 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. 45 EXAMPLE 1

To an aqueous slurry containing 49% by weight of KOH was continuously added a hypochlorous acid solution containing 43% by weight of HOCI in a stirred cooled reactor. During the addition of the 50 hypochlorous acid, the temperature of the reaction mixture was maintained below about 25 °C. by cooling. Addition of the hypochlorous acid was continued until an excess of less than 1.5% KOH remained in the solution. The clear solution obtained as the reaction product contained 34.4% KOCI and 1.3% KCI. To this solution solid KOH was added periodically while the hypochlorination was continued to produce a solution containing 47% by weight of KOCI.

3 EP 0 513 167 B1

EXAMPLE 2

The potassium hypochlorite solution prepared in example 1 was poured into a distillation vessel and distilled at 25 °C under a pressure less than the vapor pressure of water in the solution. When the 5 distillation was stopped, the solution was filtered to remove small amounts of solid materials which had formed during the evaporation. Upon analysis, the solution contained 57.4% by weight of KOCI and 0.62% by weight of KCI. This solution was cooled to a temperature of -20 °C. without the formation of a solid hypochlorite compound. w EXAMPLES 3 and 4

Aliquots of the potassium hypochlorite solution prepared in Example 2, were diluted with deionized water to concentrations of 49.2% KOCI and 39.8% KOCI. These solutions were each placed in a sealed container and stored at zero degrees for a period of eight days. Upon analysis, the stored solutions were 75 found to contain 47.5% KOCI and 39.2% KOCI, respectively.

EXAMPLES 5-8

A KOCI solution containing 22.3% by weight of KOCI and 1 .8% by weight of KCI was divided into four 20 aliquot portions. Two aliquot portions were diluted with deionized water to give two solutions of potassium hypochlorite each containing 14.8% by weight of KOCI and 1.2% by weight of KCI. The remaining two aliquot portions were diluted with deionized water to give two solutions of potassium hypochlorite each containing and 9.9% by weight of KOCI and 0.9% KCI. The four vessels containing these solutions were sealed. One vessel for each solution concentration was stored for 66 days at 32 °C. After storage, the 25 potassium hypochlorite solutions contained 10.36 and 8.40% by weight of KOCI respectively. The second pair of vessels containing each solution was stored for 66 days at 40 °C. After storage, the potassium hypochlorite solutions contained 5.37 and 5.49% by weight of KOCI respectively.

Comparative Examples A-D 30 A slurry containing 19.25% potassium hydroxide was chlorinated with gaseous chlorine until the excess KOH was less than 1.5%. The chlorinated solution contained 14.9% by weight of KOCI and 12.3% KCI. This solution was divided into four equal portions. Two of these portions were diluted with deionised water to a KOCI concentration of 9.9%. After sealing the vessels, the storage procedure of Examples 5-8 was followed 35 exactly. The two solutions containing 14.9% and 9.9% by weight of KOCI stored for 66 days at 30 °C. were analyzed and found to contain 7.75 % by weight of KOCI and 7.42% by weight of KOCI respectively. The two solutions containing 14.9% and 9.9% by weight of KOCI stored for 66 days at 40 °C. were found to contain 3.05 % by weight of KOCI and 1 .72% by weight of KOCI respectively. The loss of KOCI during storage at 30 ° C. for 66 days in the solutions produced by the process of the 40 invention was 30% and 15% respectively. In contrast, the loss of KOCI during storage of the solutions of Comparative Examples A and B at 30 ° C for 66 days was 48% and 25% respectively. Thus the stability of the solutions produced by the process of the invention is nearly twice that of the solutions prepared by the process of the prior art.

45 Comparative Example E

A slurry containing 38% by weight of KOH in water was reacted with gaseous chlorine, while maintaining the temperature below 25 °C. immediately upon the addition of chlorine, solids appeared; after approximately one half of the KOH had been reacted with chlorine, the slurry viscosity increased to where 50 no more chlorine could be adsorbed. Sufficient water had to be added such that the effective initial concentration of the KOH was reduced to 28%. The chlorination was then continued until the remaining KOH was less than 2% by weight. The concentration of the slurry obtained was 17.9% by weight of KOCI and 14.4% by weight of KCI. Excess crystals were removed by filtration and found to represent about 5% of the total weight. The final filtrate 55 analyzed 18% KOCI and 12.9% KCI. This solution represents the maximum concentration of potassium hypochlorite which can be attained by the reaction with gaseous chlorine.

4 EP 0 513 167 B1

EXAMPLES 9 and 10

The viscosity (centipoise, CP) and density (g/ml) of KOCI solutions prepared by the process of the invention containing 30% by wt. of KOCI and 40% by wt. of KOCI were determined at 0° and about 20° C. 5 The results are given in Table I below;

TABLE I

VISCOSITIES AND DENSITIES OF CONCENTRATED HYPOCHLORITE SOLUTIONS Compound Cone. (Wt.%) Temp. Viscosity (CP) Density (g/ml) KOCI 40 0 4.39 1.376 18 2.05 30 0 3 1.277 22 1 .41 1 .273

Claims

1. A process for producing potassium hypochlorite solutions which comprises admixing at a temperature below 45 ° C a hypochlorous acid solution having a concentration of 35 percent or greater by weight of HOCI with an aqueous solution or slurry of potassium hydroxide containing 35 percent by weight or greater of KOH selected to produce a potassium hypochlorite solution containing 30 percent or greater by weight of KOCI.

2. The process of claim 1 in which the potassium hypochlorite solution produced contains from 40 to 60 percent by weight of KOCI.

3. The process of claim 1 in which the potassium hydroxide contains from 40 to 60 percent by weight of KOH.

4. The process of claim 1 in which the potassium hypochlorite solutions are further concentrated by evaporation at sub-atmospheric pressures and temperatures below 40 ° C.

5. The process of any one of the preceding claims in which the hypochlorous acid solution is added to the aqueous solution or slurry of potassium hydroxide; the solutions are thereafter admixed while maintaining the temperature of the reaction mixture in the range of from 0° to 45 °C; and solid potassium hydroxide is added to form the potassium hypochlorite solution.

6. The process of claim 5 in which the aqueous solution or slurry of potassium hydroxide contains from 35 to 50 percent by weight of KOH.

7. The process of claim 5 in which the reaction mixture is maintained at a temperature of from 0° to 25 °C.

8. The process of claim 5 in which the aqueous slurry of potassium hydroxide contains from 35 to 50 percent by weight of KOH.

9. The process of claim 5 in which the potassium hypochlorite solutions are further concentrated by evaporation at sub-atmospheric pressures and temperatures below 40 ° C.

10. The process of claim 9 in which the potassium hypochlorite solutions contain from 40 to 60 percent by weight of KOCI.

11. A potassium hypochlorite solution containing from 30 to 60 percent by weight of KOCI and having a density in the range of from 1 .27 to 1 .6 g/ml at a temperature of 0 ° C.

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12. The potassium hypochlorite solution of claim 11 containing from 40 to 60 percent by weight of KOCI and having a density in the range of from 1 .37 to 1 .6 g/ml at a temperature of 0 ° C.

13. The potassium hypochlorite solution of claim 11 having a viscosity of at least 3«10-3 Pa«s (3 5 centipoises) at 0 ° C.

Patentanspruche

I. Verfahren zur Herstellung von Kaliumhypochloritlosungen, bei dem bei einer Temperatur unterhalb von io 45 °C eine hypochlorige Saurenlosung mit einer Konzentration von 35 Gew.-% HOCI oder mehr mit einer wasserigen Losung oder einem Brei von Kaliumhydroxid mit 35 Gew.-% KOH oder mehr vermischt wird und dazu ausersehen ist, urn eine Kaliumhypochloritlosung mit 30 Gew.-% KOCI oder mehr zu erzeugen. is 2. Verfahren nach Anspruch 1 , bei dem die erzeugte Kaliumhypochloritlosung zwischen 40 und 60 Gew.- % KOCI enthalt.

3. Verfahren nach Anspruch 1 , bei dem das Kaliumhydroxid zwischen 40 und 60 Gew.-% KOH enthalt.

20 4. Verfahren nach Anspruch 1 , bei dem die Kaliumhypochloritlosungen durch Verdampfung bei Tempera- turen unterhalb von 40 °C und bei einem Druck unter Atmospharendruck weiter konzentriert werden.

5. Verfahren nach einem der vorhergehenden Anspruche, bei dem die hypochlorige Saurenlosung der wasserigen Losung oder dem Brei von Kaliumhydroxid zugefugt wird und bei dem die Losungen 25 danach zusammengemischt werden, wahrend die Temperatur der Reaktionsmischung im Bereich vom 0° bis 45° C gehalten und testes Kaliumhydroxid zur Bildung der Kaliumhypochloritlosung zugefugt wird.

6. Verfahren nach Anspruch 5, bei dem die wasserige Losung oder der Brei des Kaliumhydroxids 30 zwischen 35 und 50 Gew.-% KOH enthalt.

7. Verfahren nach Anspruch 5, bei dem die Reaktionsmischung auf einer Temperatur zwischen 0° und 25 ° C gehalten wird.

35 8. Verfahren nach Anspruch 5, bei dem der wasserige Brei von Kaliumhydroxid zwischen 35 und 50 Gew.-% KOH enthalt.

9. Verfahren nach Anspruch 5, bei dem die Kaliumhypochloritlosungen durch Verdampfung bei Tempera- turen unterhalb 40 °C und bei Drucken unterhalb des Atmospharendruckes weiter konzentriert werden. 40 10. Verfahren nach Anspruch 9, bei dem die Kaliumhypochloritlosungen zwischen 40 und 60 Gew.-% KOCI enthalten.

II. Kaliumhypochloritlosung, die zwischen 30 und 60 Gew.-% KOCI enhalt und eine Dichte im Bereich 45 zwischen 1 ,27 und 1 ,6 g/ml bei einer Temperatur von 0 ° C aufweist.

12. Kaliumhypochloritlosung nach Anspruch 11, die zwischen 40 und 60 Gew.-% KOCI enthalt und eine Dichte im Bereich zwischen 1 ,37 bis 1 ,6 g/ml bei einer Temperatur von 0 ° C aufweist.

50 13. Kaliumhypochloritlosung nach Anspruch 11, die eine Viskositat von mindestens 3 • 10-3 Pa.s (3 Centipoise) bei 0 ° C aufweist.

Revendicatlons

55 1. Procede pour la production de solutions d'hypochlorite de potassium comprenant les etapes consistant a admettre en melange a une temperature inferieure a 45 °C une solution d'acide hypochloreux presentant une concentration de 35 % ou superieure en poids de HOCI avec une solution aqueuse ou une bouillie d'hydrate de potassium contenant 35 % en poids ou davantage de KOH choisie de

6 EP 0 513 167 B1

maniere a produire une solution d'hypochlorite de potassium contenant 30 % ou davantage en poids de KOCI.

2. Procede selon la revendication 1 , dans lequel la solution d'hypochlorite de potassium produite contient 5 entre 40 et 60 % en poids de KOCI.

3. Procede selon la revendication 1 , dans lequel I'hydrate de potassium contient de 40 a 60 % en poids de KOH. io 4. Procede selon la revendication 1, dans lequel les solutions d'hypochlorite de potassium sont ensuite concentrees par evaporation a des pressions inferieures a la pression atmospherique et a des temperatures inferieures a 40 ° C.

5. Procede selon I'une quelconque des revendications precedentes, dans lequel la solution d'acide is hypochloreux est ajoutee a la solution aqueuse ou a la bouillie d'hydrate de potassium ; les solutions sont ensuite admises en melange tout en maintenant la temperature du melange reactionnel dans I'intervalle compris entre 0° et 45 °C ; et de I'hydrate de potassium sous forme solide est ajoute de fagon a constituer la solution d'hypochlorite de potassium.

20 6. Procede selon la revendication 5, dans lequel la solution aqueuse ou bouillie d'hydrate de potassium contient de 35 a 50 % en poids de KOH.

7. Procede selon la revendication 5, dans lequel le melange reactionnel est maintenu a une temperature comprise entre 0 ° et 25 ° C. 25 8. Procede selon la revendication 5, dans lequel la bouillie aqueuse d'hydrate de potassium contient de 35 a 50 % en poids de KOH.

9. Procede selon la revendication 5, dans lequel les solutions d'hypochlorite de potassium sont ensuite 30 concentrees par evaporation a des pressions inferieures a la pression atmospherique et a des temperatures inferieures a 40 ° C.

10. Procede selon la revendication 9, dans lequel les solutions d'hypochlorite de potassium contiennent de 40 a 60 % en poids de KOCI. 35 11. Solution d'hypochlorite de potassium contenant de 30 a 60 % en poids de KOCI et presentant une densite comprise dans I'intervalle de 1 ,27 a 1 ,6 g/ml a une temperature de 0 ° C.

12. Solution d'hypochlorite de potassium selon la revendication 11, contenant de 40 a 60 % en poids de 40 KOCI et presentant une densite situee dans I'intervalle de 1 ,37 a 1 ,6 g/ml a une temperature de 0 ° C.

13. Solution d'hypochlorite de potassium de la revendication 11, presentant une viscosite d'au moins 3.1 0-3 Pa.s (3 centipoises) a 0°C.