CA2085167C - Disinfectant for use in aqueous systems - Google Patents
Disinfectant for use in aqueous systemsInfo
- Publication number
- CA2085167C CA2085167C CA 2085167 CA2085167A CA2085167C CA 2085167 C CA2085167 C CA 2085167C CA 2085167 CA2085167 CA 2085167 CA 2085167 A CA2085167 A CA 2085167A CA 2085167 C CA2085167 C CA 2085167C
- Authority
- CA
- Canada
- Prior art keywords
- hypochlorite
- solution
- inorganic
- hypobromite
- mole
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Fee Related
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Classifications
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B11/00—Oxides or oxyacids of halogens; Salts thereof
- C01B11/20—Oxygen compounds of bromine
Abstract
The preparation of an inexpensive disinfecting solution containing hypobromite as active ingredient is described. The solution having stable biocidal activity is made up by mixing hypochloride and bromide dissolved in water in specific mole equivalent ratios. The disinfecting solution containing all the ingredients has a relatively long shelf life and is ready to be added to swimming pools, industrial cooling waters or similar bodies of water, as required.
Description
20~al67 BP File No. 5628-006 Title: Disinfectant For Use in Aqueous Systems FIELD OF THE lNv~ ON
This invention is related to treating bodies of water with a composition having biocidal properties.
Water which is circulated in swimming pools, industrial cooling water, effluents which may be fed into rivers and lakes, need to-~e treated to prevent bacterial proliferation and growth, development of fungus colonies, mildew, slime, and generally to eliminate the growth of harmful micro-organisms. It is essential that such treatment of the water be harmless to higher organisms, especially to humans. It is also important that the by-products of the treatment of swimming pools, industrial waters and similar systems be non-toxic.
Another important requirement of such treatment is that the reagents utilized are relatively inexpensive, readily available and have a long shelf life.
Hypochlorite bearing solutions have been used for their notable oxidizing properties. It is known that hypochlorous acid is ~ormed when chlorine gas is dissolved and reacts with water. The reaction product contains hydrochloric (HCl) and hypochlorous (EIOCl) acids, which are strong irritants to humans in notable concentrations.
It has also been known that a composition containing hypochlorite (OCl-) is an effective biocide and germicide. However hypochlorite utilized by itself and in the absence of other chemical additives, may be too powerful as oxidizing agent, especially when human beings are exposed to the hypochlorite treated water for prolonged periods.
" .. , , ~
:, ,, ,:' , ' ' " ', . , ' ~
; , , :. ; :
: , : , 2~85~7 It is known that the hypobromite ion (OBr~) and dissolved bromine, while still strong oxidizing agents, have lower oxidizing powers (oxygen potential) than hypochlorite. It is also known that bromAmi n~ which may be the by-product of treating swimming pool waters by hypobromite, is less irritant to h ~n~ than the chloramine resulting in a similar reaction with hypochlorite.
Thus hypobromite and blo i ne are more desirable disinfectants in swimming pools than hypochlorite. A
solution of hypobromike, in the absence o~ other reagents, however is unstable, and the biocidal properties are easily lost due to the reaction of hypobromite with the environment. In the course of this reaction hypobromite is reduced to bromide. Moreover, the biocidal properties of the hypobromite solution are also ~irinished by sunlight and high temperature.
Hypobromite solutions may be obtained by dissolution of a solid hypobromite compound in water, or 2~ adding bromine gas to water, however, the rate of dissolution is slow. Furthermore, these reagents are relatively expensi~e.
It is known to utilize hypochlorite and hypobromite in combination to achieve a desired biocidal effect. It is ~nown to add a hypochlorite cont~ining solution and crystalline bromine or a bromide cont~in;ng solution, as separate reagents to the water to be treated.
British patents 1,327,531 and 1,475,570 describe a process and an apparatus to be utilized in a swimming pool to attain a desired bromine content in circulating water.
; The bLo ine generation is maintained by adding an inorganic bromide compound and an inorganic hypochlorite compound separately and reacti.ng these reagents in the circulating water. The separate reagent additions are , ., , ,,,, -. . ". , , ~ 3 - 2~ 67 continuously metered and adjusted to provide the desired bromine level. Maintenance of such apparatus may be costly, and any breakdown in either the analysing function or in the metering function of the system of GB 1,327,531 S and 1,475,570 may have prolonged deleterious effect.
It is known, that an inorganic hypobromite ion is more stable in an alkaline medium. For obvious reasons, however, high alkalinity is not tolerated in swimming pools. ~igh alkalinity in industrial waters may lead to unwanted precipitation of metallic compounds or other deleterious side effects. Japanese patent 1-164,701 issued to Maeda et al. and published on June 20, 1989, describes the stabilization of hypobromite in the presences of bromide, and in the additional presence of sodium hydroxide and sodium chloride. Maeda et al. teach concentration ranges and industrial applications which are different from those of the present invention. Moreover, it is to be noted that the addition and maintenance of the concentration of the additional reagents may further increase the cost of disinfection. It is also questionable that the sodium hydroxide concentration may be maintained in a swimming pool for a prolonged period at a level which is low enough to avoid irritation and unpleasant side effects, and still be capable of stabilizing the hypobromite level in the aqueous medium.
Japanese Patent 64-15200, published on January 19, 1989, by Yoshihiko Kunimitsu, describes the reacting of hypochlorite with bromide for eliminating slim and industrial waters. The Kl~nim;tsu publication does not teach storage of the reagent solution, and refers to uses and concentration ranges which are different from the invention described herein below.
rn other conventional processes organic reagents are added, or incorporated with the oxy-halogen radical . .
', , ; . :
' ~ .
.
~, , ,; .
2~851~7 for the stabilization of the hypobromite concentration in the aqueous medium.
It may thus be concluded that conventional processes for the stabilization of hypobromite generated in an aqueous medium requires either costly organic reagent additions or the maintenance of costly apparatus.
It has now been found that hypobromite ions may be generated in the presence of hypochlorite and stabilized in a more concentrated aqueous solution without other additives for stabilization of the hypobromite, and that such solution may have a prolonged shelf life.
STA~ .l QF iNV~ ON
Accordingly, the present invention provides a method of stabilizing hypobromite in the presence of hypochlorite, without the addition of organic stabilizing agents, the implov~~ -nt essentially comprises:
adding to an aqueous solution containing 5-18 wt.% sodium hypochlorite (0.67-2.43 mole hypochlorite ion per litre) an inorganic bromide compound selected from the group consisting of alkali metal bromides, and alkaline earth metal bromides, in an amount ranging between 31-98 mole equivalent percent relative to the hypochlorite content of said solution.
In another aspect of the in~ention a process is described for disinfecting an aqueous medium by the addition o~ a hypobromite containing solution to the aqueous medium.
The preferred embodiment of the invention will now be described and illustrated by way of examples and graphs.
Figures 1-5 show the biocidal oxidizing , ,, : , :, ,:
20~167 stability of sodium hypochlorite (NaOCl) solutions of various strength, as the ~unction of the concentration of the added bromide solution, at room temperature and at elevated temperature.
5 DETAILI:D Dl~:SCRIPTION
Disinfection of recirculated waters is a requirement o~ swimming pools operated as a public undertaking or by private pool owners. Usually larger volumes of water are required to be treated by a disinfectant added at regular intervals. It is thus of importance to have a relatively concentrated and readily available solution, which can be added to the pool in a prere~uisite amount. It is of added benefit, if the solution already contains all the necessary ingredients~
and such a solution has a shelf life which extends to several months without substantial loss of its biocidal activity.
The present process may also be used for the prevention of growth of micro-organisms and befouling of recirculated cooling waters or mild industrial effluents which are to be discharged to the environment without further treatment.
The first ingredient of the present process is sodium hypochlorite. Any other water soluble hypochlorite, such as potassium, calcium, or other readily available inorganic hypochlorite or a mixture of these, may be substituted for NaOCl.
In Table I hereinbelow the concentration of the NaOC]. is shown in weight percent, as well as in mole per litre to permit easy conversion to other hypochlorite compounds.
The second ingredient utilized is an inorganic .
~' , , - 6 - 2 0 ~ 7 bromide. Sodium bromide was used in the tests illustrating the present invention, however, any other alkali or alkaline earth metal bromide may be used. The biocidal activity of the solution obtained is related by a simple molecular relationship to the molar concentration of hypochlorite reacting with the added bromide. The relationship is conveniently represented as mole equivalent percent. Thus the concentration of the bromide added to the sodium hypochlorita solution is expressed in the Table and in the Figures hereinbelow as mole equivalent percent based on the initial hypochlorite mole per litre concentration.
It is to be noted that reacting hypochlorite with a bromide to yield a biocidal compound has been known before. Surprisingly, the bromide concentration range found to be the most effective in the present invention has been outside the bromide concentration range practiced by conventional processes.
~he loss of activity of the hypochlorite solution has been expressed in weight percent, based on the initial concentration oE the hypochlorite solution.
For sake of clarity, the weight percent figures reEer to one litre of solution.
The activity of the hypochlorite solution was ~5 assessed by dete ;ning the available oxidizing power of the solution by means of conventional iodometric titration.
The reaction of bromine gas with water yields bromic acid and hypobromous acid according to the equation:
Br2 + H20 ~ HBr + HOBr (1) .
:;.
2~85~67 The hypobromite ion is also a powerful oxidizing agent, and is capable of killing microorganisms, but at the same time is less of an irritant to humans. BLU ; ne gas, however, is much less soluble in water than chlorine gas, and hence, it is easily lost to the surrounding atmosphere.
Increasing the pH of the bLo ;ne water to above 7.0 will increase bromine solubility, but pH values higher than 9.0 have unpleasant effects on humans.
It is also known that the hypochlorite ion generally replaces the hypobromite ion in its compounds.
It has been found that in th~ presence of bromide ions the hypobromite ion may coexist with hypochlorite ion, such as is described by equilibrium equation (2).
OCl- + Br~ ~ OBr~ + Cl- (2) This reaction will proceed in the right hand side direction of the equation under certain circumstances. In other words, the oxidi~ing species will be predu ;n~ntly hypobromite ions. Moreover, it has been surprisingly found that the hypobromite ion can be ret~ine~ in solution for several months, provided the bromide is added in certain specific ratios to the hypochlorite ion present in the solution, and also provided that the pH of the solution is kept above the value of 7Ø
The biocidal activity of an alkali metal or alkaline earth metal hypobromite-hypochlorite mixture, having an initial hypochlorite concentration ranging between 0.65-2.45 mole per litre, may be maintained in storage for several months, if the activity of the solution is stabilized by the addition of an alkali metal ,' .
,: . , : , ''' ,,', "
, 2~8~167 and/or alkaline earth metal bromide. It has been found that in the preferred embodiment of the invention the bromide concentration is present in amounts between 31 to 98 mole equivalent percent relative to the hypochlorite concentration of the solution. The most advantageous concentration of the bromide added is between 31-40 mole equivalent percent.
It is of further advantage if the solution cont~;n;ng hypochlorite and bromide is kept at room temperature or below, but above the freezing point of water.
~ n increase in temperature and/or strong light will d-minish the stability of the hypochlorite-bromide solution, but to a substantially lesser degree than the stability of either hypochlorite solution or hypobromite solution without additives would be.
The unexpected advantage of a solution contAin;ng predomin~ntly hypobromite ions as the active species in a hypochlorite-hypobromite solution, is that it may be stored for several months without substantial loss of activity.
The solution is prepared, stored in a relatively concentrated form and added to the swimming pool, industrial cooling water, water tower, etc. in amounts and at time intervals, as required.
The hypochlorite solution, usually in the form of sodium hypochlorite, may be prepared by dissolving the solid substance or may be obtained as a commercially available solution. The sodium hypochlorite solution available commercially usually has a concentration range between 10-12%. ~t is found that the most useful concentration range of NaOCl from the point of view of a ;
,, .: ~
, ;: , , : :
.. .:,:
:, ,. , ~:
.:, :.: ~.
.
~0851B'7 g stable disinfecting solution concentrate with the required biocidal activity, is between 5 and 18 weight percent expressed in ~rams per litre of solution. This range translates to 0.67-2.~3 mole of hypochlorite ion per litre of solution. The most readily available and hence least expensive hypochlorite is sodium hypochlorite, but other alkali metal or/and alkali earth metal salts and mixtures of these ma~ also be used. It should be noted, however, that alkaline earth metal hypochlorites may partially decompose and/or have side reactions leading to some precipitate formation.
The water soluble bromide may be added to the aqueous hypochlorite solution as a solid, i.e. crystalline bromide, or as a solution. The bromide which is most often utilized is sodium bromide (NaBr), but other alkali metal and/or alkaline earth metal bromides may be used depending on availability and cost. The amount of bromide to be added, as has already been mentioned hereinabove, is calculated as the mole equivalent percent based on the 2~ concentration of the hypochlorite in solution. It has been found that to obtain a solution which is stable for several months, the preferred bromide concentration range was 30-100 mole equivalent percent, and the optimum concentration with respect to stability was ranging between 31-40 mole equivalent percent.
The solution obtained should preferably be stored in a dark bottle at room temperature or below.
Sodium hypochlorite solutions in water were prepared having concentrations: 6, 9, 12 and 15 weight percent, calculated in g/litre; and their respective activity was determined iodometrically.
,, :, , 2~galS7 Each of the different hypochlorite solutions were divided and to each portion, except one, sodium bromide was added in the following amounts: 10 mole equivalent percent, 33 mole equivalent percent, 66 mole equivalent percent and 100 mole equivalent percent.
The above solutions cont~i n i ng both hypochlorite and bromide were kept in a continuous strong fluorescent light simulating daylight, at room temperature for a prolonged period. At regular intervals aliquot samples were taken from each solution and the activity of the sample solution was determined by iodometric titration.
The activity of the hypochlorite solutions of different concentrations and without bromide addition, has also been determined as a function of time.
~, The results of the above tests are shown in Figures 1, 2 and 3. In these figures the loss of activity is plotted against storage time, and separate curves are shown for different bromide additions to the original hypochlorite solutions.
Figure 4 shows the loss of activity as a function of the mole equivalent percent bxomide added to a 15 weight percent sodium hypochlorite solution in a test period of 89 days.
Figure 5 shows the same type of curve as Figure 4, however in Figure 5 the tests have been conducted on 12 weight percent sodium hypochlorite solution at 34+1~C
temperature and in a time period of 76 days.
Selective results ohtained on room temperature tests have also been tabulated and are shown in ~able 1 below.
. ~
- . . , - ~
' . ' :::
~ ~ ;. : :
20~167 It may be seen that for all the sodium hypochlorite concentrations tes~ed for a period of 4 months, the most stable activity is obtained when the mole equivalent percent of bromide is added in the range of 31-40 mole equivalent percent.
The solutions made up according to the present invention are ready to be added to a body of water to be treated in order to ~iminish, preferably eliminate growth of microorganisms and bacteria therein. The solution may be stored ~or a period lasting several months without significant loss in biocidal activity. The solutions are made up of relatively inexpensive ingredients which are readily available and are not harmful to humans in the amount used.
Although the present invention has been described with reference to the preferred embodiment, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention as those skilled in the art will readily understand. Such modifications and variations are considered within the purview and scope of the invention and the invention as claimed.
.. ' ' ' .
': Test NaBr 6 wt.% NaOCl 9 wt.% NaOCl 12 wt.% NaCCl 15 wt. % NaOCl 18 wt. %
No. mole soln. soln. soln. soln. NaOCl soln.
- equiv %
added Elapsed Loss Elapsed Loss Elapsed Loss Elapsed Loss Elapsed Loss time, wt.% time, Wt.~ time, wt. % time, wt. time~ wt.
days days days days % days %
'- 1 10 48 4 _____ _______ _____ _______ _____ _______ _____ ____ _ _ _ _______ ____ ~8*) 89 30 89 43 ; 2 (16*) 89 lg 89 28 _____ _______ _____ ____ _ _______ _____ _ _ ______ ____ I
~ (26~) 39 6 89 24 -- -- -- ------------ -- ---- 'S' " - ---- 48 2 -~ 33 122 4 125 3.5 125 3 ~ .
: ' 3 (54*) 89 12 85 38 _____ _____ _____ __ _ _______ _____ _______ ____ -~ ' - 66 48 2 1.5 122 2 125 125 2.5 ' 4 (80*) 89 ~0 85 ~2 _____ _____ _ _____ ____ _______ ____ 10048 Q.8 2 2 None 48 7.5 Blank 89 45 89 59 e~
Test 122 18 125 30 125 45 co ~Tests a~ditionally condu~ted with solutions containing ind_cated ~aBr mole ~quivalent ~ ~
This invention is related to treating bodies of water with a composition having biocidal properties.
Water which is circulated in swimming pools, industrial cooling water, effluents which may be fed into rivers and lakes, need to-~e treated to prevent bacterial proliferation and growth, development of fungus colonies, mildew, slime, and generally to eliminate the growth of harmful micro-organisms. It is essential that such treatment of the water be harmless to higher organisms, especially to humans. It is also important that the by-products of the treatment of swimming pools, industrial waters and similar systems be non-toxic.
Another important requirement of such treatment is that the reagents utilized are relatively inexpensive, readily available and have a long shelf life.
Hypochlorite bearing solutions have been used for their notable oxidizing properties. It is known that hypochlorous acid is ~ormed when chlorine gas is dissolved and reacts with water. The reaction product contains hydrochloric (HCl) and hypochlorous (EIOCl) acids, which are strong irritants to humans in notable concentrations.
It has also been known that a composition containing hypochlorite (OCl-) is an effective biocide and germicide. However hypochlorite utilized by itself and in the absence of other chemical additives, may be too powerful as oxidizing agent, especially when human beings are exposed to the hypochlorite treated water for prolonged periods.
" .. , , ~
:, ,, ,:' , ' ' " ', . , ' ~
; , , :. ; :
: , : , 2~85~7 It is known that the hypobromite ion (OBr~) and dissolved bromine, while still strong oxidizing agents, have lower oxidizing powers (oxygen potential) than hypochlorite. It is also known that bromAmi n~ which may be the by-product of treating swimming pool waters by hypobromite, is less irritant to h ~n~ than the chloramine resulting in a similar reaction with hypochlorite.
Thus hypobromite and blo i ne are more desirable disinfectants in swimming pools than hypochlorite. A
solution of hypobromike, in the absence o~ other reagents, however is unstable, and the biocidal properties are easily lost due to the reaction of hypobromite with the environment. In the course of this reaction hypobromite is reduced to bromide. Moreover, the biocidal properties of the hypobromite solution are also ~irinished by sunlight and high temperature.
Hypobromite solutions may be obtained by dissolution of a solid hypobromite compound in water, or 2~ adding bromine gas to water, however, the rate of dissolution is slow. Furthermore, these reagents are relatively expensi~e.
It is known to utilize hypochlorite and hypobromite in combination to achieve a desired biocidal effect. It is ~nown to add a hypochlorite cont~ining solution and crystalline bromine or a bromide cont~in;ng solution, as separate reagents to the water to be treated.
British patents 1,327,531 and 1,475,570 describe a process and an apparatus to be utilized in a swimming pool to attain a desired bromine content in circulating water.
; The bLo ine generation is maintained by adding an inorganic bromide compound and an inorganic hypochlorite compound separately and reacti.ng these reagents in the circulating water. The separate reagent additions are , ., , ,,,, -. . ". , , ~ 3 - 2~ 67 continuously metered and adjusted to provide the desired bromine level. Maintenance of such apparatus may be costly, and any breakdown in either the analysing function or in the metering function of the system of GB 1,327,531 S and 1,475,570 may have prolonged deleterious effect.
It is known, that an inorganic hypobromite ion is more stable in an alkaline medium. For obvious reasons, however, high alkalinity is not tolerated in swimming pools. ~igh alkalinity in industrial waters may lead to unwanted precipitation of metallic compounds or other deleterious side effects. Japanese patent 1-164,701 issued to Maeda et al. and published on June 20, 1989, describes the stabilization of hypobromite in the presences of bromide, and in the additional presence of sodium hydroxide and sodium chloride. Maeda et al. teach concentration ranges and industrial applications which are different from those of the present invention. Moreover, it is to be noted that the addition and maintenance of the concentration of the additional reagents may further increase the cost of disinfection. It is also questionable that the sodium hydroxide concentration may be maintained in a swimming pool for a prolonged period at a level which is low enough to avoid irritation and unpleasant side effects, and still be capable of stabilizing the hypobromite level in the aqueous medium.
Japanese Patent 64-15200, published on January 19, 1989, by Yoshihiko Kunimitsu, describes the reacting of hypochlorite with bromide for eliminating slim and industrial waters. The Kl~nim;tsu publication does not teach storage of the reagent solution, and refers to uses and concentration ranges which are different from the invention described herein below.
rn other conventional processes organic reagents are added, or incorporated with the oxy-halogen radical . .
', , ; . :
' ~ .
.
~, , ,; .
2~851~7 for the stabilization of the hypobromite concentration in the aqueous medium.
It may thus be concluded that conventional processes for the stabilization of hypobromite generated in an aqueous medium requires either costly organic reagent additions or the maintenance of costly apparatus.
It has now been found that hypobromite ions may be generated in the presence of hypochlorite and stabilized in a more concentrated aqueous solution without other additives for stabilization of the hypobromite, and that such solution may have a prolonged shelf life.
STA~ .l QF iNV~ ON
Accordingly, the present invention provides a method of stabilizing hypobromite in the presence of hypochlorite, without the addition of organic stabilizing agents, the implov~~ -nt essentially comprises:
adding to an aqueous solution containing 5-18 wt.% sodium hypochlorite (0.67-2.43 mole hypochlorite ion per litre) an inorganic bromide compound selected from the group consisting of alkali metal bromides, and alkaline earth metal bromides, in an amount ranging between 31-98 mole equivalent percent relative to the hypochlorite content of said solution.
In another aspect of the in~ention a process is described for disinfecting an aqueous medium by the addition o~ a hypobromite containing solution to the aqueous medium.
The preferred embodiment of the invention will now be described and illustrated by way of examples and graphs.
Figures 1-5 show the biocidal oxidizing , ,, : , :, ,:
20~167 stability of sodium hypochlorite (NaOCl) solutions of various strength, as the ~unction of the concentration of the added bromide solution, at room temperature and at elevated temperature.
5 DETAILI:D Dl~:SCRIPTION
Disinfection of recirculated waters is a requirement o~ swimming pools operated as a public undertaking or by private pool owners. Usually larger volumes of water are required to be treated by a disinfectant added at regular intervals. It is thus of importance to have a relatively concentrated and readily available solution, which can be added to the pool in a prere~uisite amount. It is of added benefit, if the solution already contains all the necessary ingredients~
and such a solution has a shelf life which extends to several months without substantial loss of its biocidal activity.
The present process may also be used for the prevention of growth of micro-organisms and befouling of recirculated cooling waters or mild industrial effluents which are to be discharged to the environment without further treatment.
The first ingredient of the present process is sodium hypochlorite. Any other water soluble hypochlorite, such as potassium, calcium, or other readily available inorganic hypochlorite or a mixture of these, may be substituted for NaOCl.
In Table I hereinbelow the concentration of the NaOC]. is shown in weight percent, as well as in mole per litre to permit easy conversion to other hypochlorite compounds.
The second ingredient utilized is an inorganic .
~' , , - 6 - 2 0 ~ 7 bromide. Sodium bromide was used in the tests illustrating the present invention, however, any other alkali or alkaline earth metal bromide may be used. The biocidal activity of the solution obtained is related by a simple molecular relationship to the molar concentration of hypochlorite reacting with the added bromide. The relationship is conveniently represented as mole equivalent percent. Thus the concentration of the bromide added to the sodium hypochlorita solution is expressed in the Table and in the Figures hereinbelow as mole equivalent percent based on the initial hypochlorite mole per litre concentration.
It is to be noted that reacting hypochlorite with a bromide to yield a biocidal compound has been known before. Surprisingly, the bromide concentration range found to be the most effective in the present invention has been outside the bromide concentration range practiced by conventional processes.
~he loss of activity of the hypochlorite solution has been expressed in weight percent, based on the initial concentration oE the hypochlorite solution.
For sake of clarity, the weight percent figures reEer to one litre of solution.
The activity of the hypochlorite solution was ~5 assessed by dete ;ning the available oxidizing power of the solution by means of conventional iodometric titration.
The reaction of bromine gas with water yields bromic acid and hypobromous acid according to the equation:
Br2 + H20 ~ HBr + HOBr (1) .
:;.
2~85~67 The hypobromite ion is also a powerful oxidizing agent, and is capable of killing microorganisms, but at the same time is less of an irritant to humans. BLU ; ne gas, however, is much less soluble in water than chlorine gas, and hence, it is easily lost to the surrounding atmosphere.
Increasing the pH of the bLo ;ne water to above 7.0 will increase bromine solubility, but pH values higher than 9.0 have unpleasant effects on humans.
It is also known that the hypochlorite ion generally replaces the hypobromite ion in its compounds.
It has been found that in th~ presence of bromide ions the hypobromite ion may coexist with hypochlorite ion, such as is described by equilibrium equation (2).
OCl- + Br~ ~ OBr~ + Cl- (2) This reaction will proceed in the right hand side direction of the equation under certain circumstances. In other words, the oxidi~ing species will be predu ;n~ntly hypobromite ions. Moreover, it has been surprisingly found that the hypobromite ion can be ret~ine~ in solution for several months, provided the bromide is added in certain specific ratios to the hypochlorite ion present in the solution, and also provided that the pH of the solution is kept above the value of 7Ø
The biocidal activity of an alkali metal or alkaline earth metal hypobromite-hypochlorite mixture, having an initial hypochlorite concentration ranging between 0.65-2.45 mole per litre, may be maintained in storage for several months, if the activity of the solution is stabilized by the addition of an alkali metal ,' .
,: . , : , ''' ,,', "
, 2~8~167 and/or alkaline earth metal bromide. It has been found that in the preferred embodiment of the invention the bromide concentration is present in amounts between 31 to 98 mole equivalent percent relative to the hypochlorite concentration of the solution. The most advantageous concentration of the bromide added is between 31-40 mole equivalent percent.
It is of further advantage if the solution cont~;n;ng hypochlorite and bromide is kept at room temperature or below, but above the freezing point of water.
~ n increase in temperature and/or strong light will d-minish the stability of the hypochlorite-bromide solution, but to a substantially lesser degree than the stability of either hypochlorite solution or hypobromite solution without additives would be.
The unexpected advantage of a solution contAin;ng predomin~ntly hypobromite ions as the active species in a hypochlorite-hypobromite solution, is that it may be stored for several months without substantial loss of activity.
The solution is prepared, stored in a relatively concentrated form and added to the swimming pool, industrial cooling water, water tower, etc. in amounts and at time intervals, as required.
The hypochlorite solution, usually in the form of sodium hypochlorite, may be prepared by dissolving the solid substance or may be obtained as a commercially available solution. The sodium hypochlorite solution available commercially usually has a concentration range between 10-12%. ~t is found that the most useful concentration range of NaOCl from the point of view of a ;
,, .: ~
, ;: , , : :
.. .:,:
:, ,. , ~:
.:, :.: ~.
.
~0851B'7 g stable disinfecting solution concentrate with the required biocidal activity, is between 5 and 18 weight percent expressed in ~rams per litre of solution. This range translates to 0.67-2.~3 mole of hypochlorite ion per litre of solution. The most readily available and hence least expensive hypochlorite is sodium hypochlorite, but other alkali metal or/and alkali earth metal salts and mixtures of these ma~ also be used. It should be noted, however, that alkaline earth metal hypochlorites may partially decompose and/or have side reactions leading to some precipitate formation.
The water soluble bromide may be added to the aqueous hypochlorite solution as a solid, i.e. crystalline bromide, or as a solution. The bromide which is most often utilized is sodium bromide (NaBr), but other alkali metal and/or alkaline earth metal bromides may be used depending on availability and cost. The amount of bromide to be added, as has already been mentioned hereinabove, is calculated as the mole equivalent percent based on the 2~ concentration of the hypochlorite in solution. It has been found that to obtain a solution which is stable for several months, the preferred bromide concentration range was 30-100 mole equivalent percent, and the optimum concentration with respect to stability was ranging between 31-40 mole equivalent percent.
The solution obtained should preferably be stored in a dark bottle at room temperature or below.
Sodium hypochlorite solutions in water were prepared having concentrations: 6, 9, 12 and 15 weight percent, calculated in g/litre; and their respective activity was determined iodometrically.
,, :, , 2~galS7 Each of the different hypochlorite solutions were divided and to each portion, except one, sodium bromide was added in the following amounts: 10 mole equivalent percent, 33 mole equivalent percent, 66 mole equivalent percent and 100 mole equivalent percent.
The above solutions cont~i n i ng both hypochlorite and bromide were kept in a continuous strong fluorescent light simulating daylight, at room temperature for a prolonged period. At regular intervals aliquot samples were taken from each solution and the activity of the sample solution was determined by iodometric titration.
The activity of the hypochlorite solutions of different concentrations and without bromide addition, has also been determined as a function of time.
~, The results of the above tests are shown in Figures 1, 2 and 3. In these figures the loss of activity is plotted against storage time, and separate curves are shown for different bromide additions to the original hypochlorite solutions.
Figure 4 shows the loss of activity as a function of the mole equivalent percent bxomide added to a 15 weight percent sodium hypochlorite solution in a test period of 89 days.
Figure 5 shows the same type of curve as Figure 4, however in Figure 5 the tests have been conducted on 12 weight percent sodium hypochlorite solution at 34+1~C
temperature and in a time period of 76 days.
Selective results ohtained on room temperature tests have also been tabulated and are shown in ~able 1 below.
. ~
- . . , - ~
' . ' :::
~ ~ ;. : :
20~167 It may be seen that for all the sodium hypochlorite concentrations tes~ed for a period of 4 months, the most stable activity is obtained when the mole equivalent percent of bromide is added in the range of 31-40 mole equivalent percent.
The solutions made up according to the present invention are ready to be added to a body of water to be treated in order to ~iminish, preferably eliminate growth of microorganisms and bacteria therein. The solution may be stored ~or a period lasting several months without significant loss in biocidal activity. The solutions are made up of relatively inexpensive ingredients which are readily available and are not harmful to humans in the amount used.
Although the present invention has been described with reference to the preferred embodiment, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention as those skilled in the art will readily understand. Such modifications and variations are considered within the purview and scope of the invention and the invention as claimed.
.. ' ' ' .
': Test NaBr 6 wt.% NaOCl 9 wt.% NaOCl 12 wt.% NaCCl 15 wt. % NaOCl 18 wt. %
No. mole soln. soln. soln. soln. NaOCl soln.
- equiv %
added Elapsed Loss Elapsed Loss Elapsed Loss Elapsed Loss Elapsed Loss time, wt.% time, Wt.~ time, wt. % time, wt. time~ wt.
days days days days % days %
'- 1 10 48 4 _____ _______ _____ _______ _____ _______ _____ ____ _ _ _ _______ ____ ~8*) 89 30 89 43 ; 2 (16*) 89 lg 89 28 _____ _______ _____ ____ _ _______ _____ _ _ ______ ____ I
~ (26~) 39 6 89 24 -- -- -- ------------ -- ---- 'S' " - ---- 48 2 -~ 33 122 4 125 3.5 125 3 ~ .
: ' 3 (54*) 89 12 85 38 _____ _____ _____ __ _ _______ _____ _______ ____ -~ ' - 66 48 2 1.5 122 2 125 125 2.5 ' 4 (80*) 89 ~0 85 ~2 _____ _____ _ _____ ____ _______ ____ 10048 Q.8 2 2 None 48 7.5 Blank 89 45 89 59 e~
Test 122 18 125 30 125 45 co ~Tests a~ditionally condu~ted with solutions containing ind_cated ~aBr mole ~quivalent ~ ~
Claims (7)
1. In a method of stabilizing hypobromite in the presence of hypochlorite, without the addition of organic stabilizing reagents, the improvements to enable the hypohalite containing solution to be stored for at least one month, essentially comprising:
adding to an aqueous solution containing an alkali metal hypochlorite (0.67-2.43 mole hypochlorite ion per litre) an inorganic bromide compound selected from the group consisting of alkali metal bromides and alkaline earth metal bromides, in an amount ranging between 31 to 98 mole equivalent percent relative to the hypochlorite content of said solution.
adding to an aqueous solution containing an alkali metal hypochlorite (0.67-2.43 mole hypochlorite ion per litre) an inorganic bromide compound selected from the group consisting of alkali metal bromides and alkaline earth metal bromides, in an amount ranging between 31 to 98 mole equivalent percent relative to the hypochlorite content of said solution.
2. A method of preparing an inorganic hypochlorite and hypobromite containing solution having stable composition on prolonged storage, comprising the steps of:
(a) preparing an aqueous inorganic alkali metal hypochlorite first solution containing 3.5 to 12.5% by weight hypochlorite (OCl-) ions (0.67-2.43 mole hypochlorite ion per litre);
(b) dissolving in said first hypochlorite solution an inorganic bromide compound selected from the group consisting of alkali metal bromides and alkaline earth metal bromides, in an amount ranging between 31 and 98 mole equivalent percent relative to the hypochlorite content of said first solution, with agitation, to form an inorganic hypochlorite and hypobromite; and (c) placing the hypochlorite and hypobromite solution so obtained in a closed container, whereby the solution so obtained is capable of retaining a stable composition for a period of at least one month.
(a) preparing an aqueous inorganic alkali metal hypochlorite first solution containing 3.5 to 12.5% by weight hypochlorite (OCl-) ions (0.67-2.43 mole hypochlorite ion per litre);
(b) dissolving in said first hypochlorite solution an inorganic bromide compound selected from the group consisting of alkali metal bromides and alkaline earth metal bromides, in an amount ranging between 31 and 98 mole equivalent percent relative to the hypochlorite content of said first solution, with agitation, to form an inorganic hypochlorite and hypobromite; and (c) placing the hypochlorite and hypobromite solution so obtained in a closed container, whereby the solution so obtained is capable of retaining a stable composition for a period of at least one month.
3. A method of claim 2, wherein said aqueous inorganic alkali metal hypochlorite first solution is sodium hypochlorite solution containing 5-18 wt.%sodium hypochlorite.
4. A method of claim 2, wherein said aqueous inorganic alkali metal hypochlorite first solution is sodium hypochlorite solution containing 6-15 wt.% sodium hypochlorite.
5. A method of claim 4, wherein said inorganic bromide compound is dissolved in said sodium hypochlorite solution in an amount between 31-40 mole equivalent percent.
6. A method of claim 5, wherein said inorganic bromide compound is sodium bromide.
7. An aqueous inorganic disinfecting solution capable of retaining stable composition on prolonged storage, comprising:
a) inorganic hypohalite ions in a concentration of 0.67-2.43 mole hypohalite per litre, said hypohalite consisting of hypochlorite (OCl-) and hypobromite (OBr-), and b) at least one inorganic cation selected from the group consisting of alkali metals and alkaline earth metals, and c) wherein the total bromine atom (1/2 Br2) content of the solution is between 31 and 98 atom equivalent percent relative to the inorganic hypohalite content of the solution.
a) inorganic hypohalite ions in a concentration of 0.67-2.43 mole hypohalite per litre, said hypohalite consisting of hypochlorite (OCl-) and hypobromite (OBr-), and b) at least one inorganic cation selected from the group consisting of alkali metals and alkaline earth metals, and c) wherein the total bromine atom (1/2 Br2) content of the solution is between 31 and 98 atom equivalent percent relative to the inorganic hypohalite content of the solution.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US80577391A | 1991-12-12 | 1991-12-12 | |
| US07/805,773 | 1991-12-12 |
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| Publication Number | Publication Date |
|---|---|
| CA2085167A1 CA2085167A1 (en) | 1993-06-13 |
| CA2085167C true CA2085167C (en) | 1999-07-06 |
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| Application Number | Title | Priority Date | Filing Date |
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| CA 2085167 Expired - Fee Related CA2085167C (en) | 1991-12-12 | 1992-12-11 | Disinfectant for use in aqueous systems |
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| US20110200685A1 (en) * | 2010-02-16 | 2011-08-18 | Harvey Michael S | Methods and compositions for the reduction of pathogenic microorganisms from meat and poultry carcasses, trim and offal |
| CN113880204A (en) * | 2021-10-29 | 2022-01-04 | 昆山市供排水水质检测中心有限公司 | Control method of bromate content in water and detection method of bromate content in sodium hypochlorite |
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