Note: Descriptions are shown in the official language in which they were submitted.
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.
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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
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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
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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
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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
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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)
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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
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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
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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.
EXAMPLES 1-5
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.
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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.
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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.
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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.
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TABLE 1
': 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
122 10 125 17O6 125 27
_____ _______ _____ _______ _____ _______ _____ ____ _ _ _ _______ ____
~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
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: ' 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
122 2 125 - 125
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 ~ ~
