Liquid purification or separation – Processes – Chemical treatment
Reexamination Certificate
2000-03-03
2001-09-11
Hoey, Betsey Morrison (Department: 1724)
Liquid purification or separation
Processes
Chemical treatment
C210S752000, C210S759000, C210S760000, C210S764000, C162S161000, C422S037000, C423S472000, C424S613000, C424S723000
Reexamination Certificate
active
06287473
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to formulations used in biofouling control in industrial water systems. More specifically, the present invention relates to methods of preparing stable oxidizing bromine formulations and their use in biofouling control in industrial water systems.
BACKGROUND OF THE INVENTION
While elemental liquid bromine, is an effective biocide, its low solubility (<4 g/100 g water), low boiling point (54.3° C.), high vapor pressure (214 mm Hg at 25° C.) and extreme corrosivity limit its use as a biocide in industrial applications. Another oxidizing bromine compound, bromine chloride, has slightly higher water solubility but is more volatile than elemental bromine. One other oxidizing bromine compound, bromate, is very toxic to mammals and is a suspected carcinogen. Nonoxidizing inorganic bromine compounds, such as bromide, have little or no antimicrobial activity.
A mixture of an aqueous bromine solution and a bromine stabilizer has been used to generate, stable oxidizing bromine compounds for use as a biocide. An unstabilized aqueous bromine solution is very acidic, unstable and emits very pungent bromine fumes. The concentration of stabilized hypobromite solution that can be made from liquid bromine, however, has been limited due to the low solubility of bromine in water.
It has also been suggested that, in addition to a bromine stabilizer, an oxidizer, such as hypochlorite, be added to activate the bromide to hypobromite. After the completion of the conversion of bromide to hypobromite, the hypobromite is stabilized by the addition of a halogen stabilizer, such as sulfamate. While this is an improved process with a higher level of oxidizing halogen content (around 14% as Br
2
), this process still requires the separate step of synthesizing sodium hypobromite (NaOBr) as a bromine source. NaOBr is known to be very unstable and will rapidly disproportionate to bromide and bromate, both of which have little or no antimicrobial activity. In addition, because sodium hypochlorite (NaOCl) is used as an activation agent, the concentration of stabilized product is limited by the available concentration of NaOCl.
Also known are methods of generating bromine for on-site use. Such processes involve electrolytically converting bromate into active bromine compounds such as bromine, hypobromous acid, hypobromite ion and hydrogen tribromide under acidic conditions. However, because the above process generates bromine for on-site use, methods or measures for optimizing bromine stabilization are not addressed.
Therefore, methods of generating higher concentrations of stable oxidizing bromine formulations in a safer manner are needed.
SUMMARY OF THE INVENTION
The present invention satisfies the aforementioned needs by providing a method of generating a stable oxidizing bromine compound which includes the steps of preparing a caustic solution comprising a halogen stabilizer, water and an alkali or alkaline earth metal hydroxide, the halogen stabilizer being selected from the group consisting of R—NH
2
, R—NH—R
1
, R—SO
2
—NH
2
, R—SO
2
—NHR
1
, R—CO—NH
2
, R—CO—NH—R
1
and R—CO—NH—CO—R
1
wherein R is a hydroxy group, an alkyl group or an aromatic group and R
1
is an alkyl group or an aromatic group, adding bromine chloride to the solution while mixing the solution, and cooling the solution.
DETAILED DESCRIPTION OF THE INVENTION
The method of the present invention calls for generating a stable oxidizing bromine compound which includes the steps of preparing a caustic solution comprising a halogen stabilizer, water and an alkali or alkaline earth metal hydroxide, adding bromine or bromine chloride to the solution while agitating the solution and cooling the solution.
In an embodiment, the halogen stabilizer is selected from the group consisting of R—NH
2
, R—NH—R
1
, R—SO
2
—NH
2
, R—SO
2
—NHR
1
, R—CO—NH
2
, R—CO—NH—R
1
and R—CO—NH—CO—R
1
wherein R is a hydroxy group, an alkyl group or an aromatic group and R
1
is an alkyl group or an aromatic group. Preferred halogen stabilizers include saccharin, benzenesulfonamide, urea, thiourea, creatinine, cyanuric acids, alkyl hydantoins, mono or di ethanolamine, organic sulfonamides, biuret, sulfamic acid, organic sulfamates and melamine.
In an embodiment, the caustic solution has a pH greater than 13 after the addition of bromine or bromine chloride.
In an embodiment, the step of adding bromine or bromine chloride is further characterized as adding bromine or bromine chloride in a molar amount approximately equal to the molar amount of halogen stabilizer and approximately equal to one-half of the molar amount of alkali or alkaline earth metal hydroxide.
In an embodiment, the solution is cooled to a temperature of less than 25° C.
In an embodiment, the step of adding bromine or bromine chloride is performed without exposing the bromine or bromine chloride to air.
In an embodiment, an alkali or alkaline earth metal hydroxide is added to the solution after the addition of bromine or bromine chloride to increase the pH of the solution above 13.
In an embodiment, the present invention provides an aqueous biocide solution containing a stable oxidizing bromine formulation. The solution comprises at least one oxidizing bromine compound selected from the group consisting of SO
3
NHBr and SO
3
NBr
2
when sulfamate is used as the bromine stabilizer and a base in an amount sufficient to raise the pH of the solution to a level greater than 13.
In an embodiment, the base in the solution is an alkali or alkaline earth metal hydroxide.
It is therefore an advantage of the present invention to generate a stable oxidizing bromine solution using liquid elemental bromine or bromine chloride in a safe and efficient manner whereby no bromine or bromine chloride fumes are generated.
It is another advantage of the present invention to generate a higher concentration of stabilized hypobromite without the need for a separate step for hypobromite generation.
Another advantage of the present invention is that it provides a method for generating water soluble solid stable oxidizing bromine compounds.
Still another advantage of the present invention is that it provides a method for generating stable oxidizing bromine compounds without unwanted by-products such as high levels of bromate.
Yet another advantage of the present invention is that it provides stable oxidizing bromine compounds that are safer to transport and that are non-acidic.
Yet another advantage of the present invention is that it generates stable oxidizing bromine compounds for biofouling control in industrial water systems that are more compatible with other water treatment chemicals than unstabilized oxidizing bromine compounds.
The industrial water systems include cooling water systems, cooling ponds, reservoirs, sweetwater applications, decorative fountains, pasteurizers, evaporative condensers, hydrostatic sterilizers and retorts, gas scrubber systems and air washer systems.
Another advantage of the present invention is that it provides an improved method of biofouling control in pulp and paper processing systems.
Another advantage of the present invention is that it provides an improved method of biofouling control occurring on the surfaces of equipment in contact with produced oil field waters.
Another advantage of the present invention is that it provides an improved method of biofouling control in a food processing system.
Yet another advantage of the present invention is that it provides improved biofouling control in a beverage processing system.
Still another advantage of the present invention is that it provides improved biofouling control in a recreational water system.
Another advantage of the present invention is that it provides an improved method of disinfecting a hard surface.
Another advantage of the present invention is that it provides an improved bleaching method for the laundering of soiled garments and for the manufacture of cellulosic materials.
And, another advantage of the present invention is that it provides an improved method of washing
Dallmier Anthony W.
McCoy William F.
Yang Shunong
Breininger Thomas M.
Cummings Kelly L.
Hoey Betsey Morrison
Nalco Chemical Company
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