BROMIDE REMOVAL

EXTRACTION DU BROMURE

English Abstract

A chlorination system in which brine is converted to sodium hypochlorite by an
electrolyser. Brine (1) fed to the electrolyser (3) is
passed through a filter (2) which is capable of adsorbing bromine or
hypobromous acid. Some of the sodium hypochlorite produced in an
electrolyser (3) is fed back to a point in the brine feed upstream of the
filter (2) such that any bromide in the brine is oxidized to bromine
or hypobromous acid and therefore adsorbed by the filter (2).

French Abstract

Poste de chloration dans lequel la saumure est transformée en hypochlorite de sodium par un électrolyseur. La saumure (1) envoyée dans l'électrolyseur (3) passe dans un filtre (2) capable d'adsorber le brome ou l'acide hypobromeux. Une partie de l'hypochlorite de sodium produit dans un électrolyseur (3) est renvoyée vers un point de l'alimentation en saumure situé en amont du filtre (2) de sorte que tout le bromure contenu dans la saumure soit oxydé et transformé en brome ou acide hypobromeux et adsorbé ensuite par le filtre (2).

Claims

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CLAIMS:
1. An electrolytic method of obtaining hypochlorite from a
brine solution containing bromide, comprising the steps of:
providing a brine solution containing bromide;
oxidizing the bromide in the brine solution to produce
bromine-containing species;
filtering the brine solution through an adsorption medium
to produce a substantially bromine-free solution; and
passing the substantially bromine-free solution through an
electrolyzer to produce bromate-free hypochlorite.
2. The method of claim 1, wherein the bromine-containing
species is selected from the group consisting of bromine and
hypobromous acid.
3. The method of claim 1, wherein the bromide is oxidized using
a source of hypochlorite.
4. The method of claim 3, wherein the source of hypochlorite
is the bromate-free hypochlorite.
5. The method of claim 1, further comprising reducing the pH
of the brine solution.
6. The method of claim 5, wherein the pH of the brine solution
is reduced by adding hydrochloric acid.
7. The method of claim 1, wherein the adsorption medium is
selected from the group consisting of activated carbon, zeolites
and insoluble reducing agents.
8. An electrolytic system for producing hypochlorite from a
brine solution containing bromide, comprising:
an inlet for receiving a brine solution containing bromide;

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a source of oxidizing agent fluidly connected to the inlet
for oxidizing the bromide to produce bromine or hypobromous acid;
a filter positioned downstream of the source of oxidizing
agent, adapted to adsorb bromine or hypobromous acid;
an electrolyzer positioned downstream of the filter, for
producing hypochlorite from the filtered brine solution; and
an outlet for discharging a bromate-free hypochlorite
solution.
9. The system of claim 8, wherein said oxidizing agent includes
hypochlorite.
10. The system of claim 9, wherein the source of hypochlorite
is connected to the outlet.
11. The system of claim 8, further comprising a source of acid
fluidly connected to the system upstream of the filter.
12. The system of claim 11, wherein the acid is hydrochloric
acid.
13. The system of claim 8, wherein the filter comprises a
sorbing media selected from the group consisting of activated
carbon, zeolites, and insoluble reducing agents.

Description

CA 02220112 1997-11-04
WO 96134999 PCT/US9~5/OSIi03
BROMIDE REMOVAL
The present invention relates to a method and
apparatus for removing bromide from an electrolytic
c:hlorination system.
It is well known to produce sodium hypochlor.ite
i:rom sodium chloride brine by converting the brim= to
sodium hypochlorite in an electrolyser. Sodium
hypochlorite is used to treat potable water.
Ilnfortunately, if the brine includes traces of br~~mide,
t:he electrolyser causes the conversion of the bromide
by oxidation to bromate. It is desirable to produce
bromate-free sodium hypochlorite for the treatment of
potable water as experiments have indicated that
bromate may be carcinogenic.
It is an object of t-.he present invention to
provide a method and apparatus for removing bromide
from an electrolytic chlorination system so as to
obviate or mitigate the problem outlined above.
According to the present invention, there is
provided a method for removing bromide from an
electrolytic chlorination system in which brine is
converted to sodium hypochlorite in an electrolysE~r,
wherein the brine is fed to the electrolyser through a
i:ilter containing a medium capable of adsorbing b~rom.ine
or hypobromous acid, and sodium hypochlorite is fEad
back from the electrolyser and mixsd with the brine
i:eed upstream of the filter to oxidize any bromidE~ in
t:he brine to bromine or hypobromous acid.
The present invention also provides an
e:lectrolyser for converting brine to sodium
hypochlorite, means for feeding brine to the
e:lectrolyser, a filter through which the brine is fed
t:o the electrolyser, the filter being capable of
adsorbing bromine or hypobromous acid, and means :Eor
mixing sodium hypochlorite from the electrolyser with
t:he brine upstream of the filter such that bromids~ in
t:he brine is oxidized to bromine or hypobromous ac: id.

CA 02220112 1997-11-04
WO 96/34999 PCT/US95105603
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Preferably hydrochloric acid is mixed with the
brine upstream of the filter to maintain a low pH and
thereby ensure effective oxidation of the bromide.
An embodiment of the present invention will now be
described, by way of example, with reference to the ,,
accompanying drawing which illustrates a bromide
removal system incorporated into a conventional on-site
electrolytic chlorination system.
The illustrated electrolytic chlorination system
comprises a salt saturator 1 in which brine is
prepared. The saturator 1 may have a capacity of, for
example, l5 cubic meters. Brine flows from the
saturator 1 through a filter 2 to an electrolyser 3,
the brine flow being maintained by a brine transfer
pump 4. A flow rate through the pump 4 of 51.5 liters
per hour may be established. The electrolyser 3 is of
conventional form and is effective to oxidize the brine
to sodium hypochlorite. The contents of the
electrolyser are mixed with dilution water supplied
through line 5 at a rate of 540 liters per hour, the
resultant sodium hypochlorite being transferred to a
product tank 6 with a capacity of 13 cubic meters.
With the exception of the filter 2, the components
shown in the drawing and described above are entirely
conventional. With the operation of such a
conventional system, however, traces of bromide in the
brine flow are converted to bromate and reach the
product tank 6. This is undesirable as the content of
the product tank 6 is delivered via line 7 to a
treatment plant (not shown) in which the contents of
the product's tank is mixed with a supply of potable
water. '
In accordance with the present invention, sodium
hypochlorite from the product tank 6 is fed back '
through line 8 to a point upstream of the filter 2.
The flow of hypochlorite is maintained by a
hypochlorite transfer pump 9. Hydrochloric acid is
also delivered to the brine flow upstream of the

CA 02220112 2006-04-06
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filter 2 via line 10, the flow of hydrochloric acid being
maintained by a pump 11. In the illustrated system the flow of
sodium hypochlorite was 1 liter per hour and the flow of
hydrochloric acid was 1 liter per hour. The supply of
hydrochloric acid is controlled to maintain a low pH in the
brine flow upstream of the filter 2. Typically the acidity
will be controlled to approximately 4 pH. At such a low pH,
bromide in the brine flow is rapidly converted into bromine and
hypobromous acid which is adsorbed by the filter 2. By
appropriate selection of the stoichiometry and reaction time
the further oxidation of the hypobromous acid to bromate can be
minimized or substantially eliminated. Accordingly, providing
the filter is capable of adsorbing bromine or bromine released
by the reduction of hypobromous acid, substantially no bromine
compounds reach the electrolyser and accordingly substantially
no bromate reaches the product tank 6.
Appropriate materials for the filter 2 are activated
carbon zeolites and insoluble reducing agents, for example
calcium sulphite.

Representative Drawing