Liquid purification or separation – Processes – Chemical treatment
Reexamination Certificate
1999-06-01
2001-10-16
Hoey, Betsey Morrison (Department: 1724)
Liquid purification or separation
Processes
Chemical treatment
C210S758000, C210S764000, C252S175000, C252S180000, C252S181000
Reexamination Certificate
active
06303038
ABSTRACT:
TECHNICAL FIELD
This invention relates to water sanitzation methods which utilize dialkylhydantoins, bromide ions, and oxidants for bromide ions.
BACKGROUND
There is a need for disinfection and sanitization of a large number of types of bodies of water, including, for example, cooling water systems, pasteurizing systems, waste water effluents, pulp and paper mills, swimming pools, hot tubs, spas, fountains, water attractions, oil fields, air washers, fire reservoirs, and evaporative condensers. In these bodies of water, the growth of bacteria, fungi, algae, slime, and mollusks are undesirable and/or detrimental. Unfortunately, these systems often have ideal conditions for growth of these organisms. Many methods for preventing and killing such growths have been devised.
Many of these methods for sanitizing bodies of water have a drawback. For example, the use of trichloroisocyanuric acid by itself as a sanitizing chemical poses problems because trichloroisocyanuric acid reverts to chloride ion and cyanuric acid upon performing biocidal chemistry; cyanuric acid can build up to levels where the hypochlorite is rendered less effective, causing the phenomenon known as “chlorine lock.” Halogenated hydantoins, which are common water-sanitizing chemicals, are notorious for their dusts, which are irritating to human mucous membranes. Hypobromous acid is a desirable biocide because it is known to be more effective than hypochlorous acid at the conditions of most bodies of water needing sanitization. Hypobromous acid is usually produced in situ due to its instability in water. Methods to produce hypobromous acid in situ have included the use of a bromide ion source and an oxidant, such as hypochlorous acid or hypochlorite ion. Further, it is known that the hypobromous acid (or whatever biocidal bromine species is formed) may be stabilized in the presence of a suitable chemical. For example, Mines de Potasse, in GB 1,358,617, use dimethylhydantoin to prolong the life of the biocidal bromine species; the biocidal bromine species only remained for several hours.
Thus, it is clear that there are several unmet needs in known water sanitization methods. A method which either prevents or circumvents chlorine lock is needed. A need exists for a method of dosing halogenated hydantoins to a body of water which minimizes the exposure of the human handler to the halogenated hydantoins. Additionally, a method for stabilizing biocidal bromine species for longer periods of time is also desirable.
SUMMARY OF THE INVENTION
This invention is deemed to satisfy all of these needs in a highly efficient and novel way. The sanitization methods described herein function in bodies of water with conditions corresponding to chlorine lock, do not expose human handlers to halogenated hydantoins, and stabilize biocidal bromine species for periods of weeks.
In one embodiment, this invention provides a method for sanitizing a body of water which comprises introducing into the body of water in the range of from about 0.15 to about 0.70 millimole per liter of a water soluble dialkylhydantoin wherein the alkyl groups are the same or different and each alkyl group contains 1 to about 6 carbon atoms, and in the range of about 0.090 to about 0.39 millimole per liter of a water soluble source of bromide ion. An amount of an oxidizing agent capable of oxidizing the bromide ion in situ is also provided to the body of water.
Another embodiment of this invention entails a method for sanitizing a body of water. The method comprises introducing into the body of water ingredients comprising (i) a composition which itself comprises a solid mixture of a water soluble dialkylhydantoin wherein the alkyl groups are the same or different and each alkyl group contains 1 to about 6 carbon atoms, and a water soluble source of bromide ion, wherein the molar ratio of water soluble dialkylhydantoin to source of bromide ion in the mixture ranges from about 1.2:1 to about 7.2:1, and (ii) an oxidizing agent.
Still another embodiment of this invention provides a method for sanitizing a body of water, the method comprising introducing into the body of water (i) a composition which comprises a solid mixture of a water soluble dialkylhydantoin wherein the alkyl groups are the same or different and each alkyl group contains from 1 to about 6 carbon atoms, and a source of bromide ion, wherein the molar ratio of water soluble dialkylhydantoin to source of bromide ion in the mixture ranges from about 1.2:1 to about 7.2:1, and (ii) an oxidizing agent This method further comprises periodically introducing additional oxidizing agent into the body of water to replenish the content therein of biocidal species.
Yet another embodiment of this invention provides a composition which comprises a solid mixture of (i) a water soluble dialkylhydantoin wherein the alkyl groups are the same or different and each alkyl group contains 1 to about 6 carbon atoms, and (ii) a source of bromide ion, wherein the molar ratio of water soluble dialkylhydantoin to source of bromide ion in the mixture is in the range of about 1.2:1 to about 7.2:1.
A non-exhaustive list of bodies of water that may be sanitized using this invention includes cooling water systems, pasteurizing systems, waste water effluents, pulp and paper mills, swimming pools, hot tubs, spas, fountains, water atttactions, oil fields, air washers, fire reservoirs, and evaporative condensers. Organisms which are destroyed by the practice of this invention include, for example, bacteria, fungi, algae, slime, and mollusks.
Further embodiments of this invention will become apparent from the following detailed description and appended claims.
DETAILED DESCRIPTION OF THE INVENTION
It will now be appreciated that this invention provides, among other things, for the in situ generation of biocidal species for water sanitization. This is accomplished by the addition of a dialkylhydantoin and a source of bromide ion, both at low concentration, to the body of water, in which at least a portion of the body of water is contacted with an oxidizing agent; this system is stable for weeks. It has been found that using lower concentrations of bromide ion than are taught in the prior art yields desirable levels of biocidal activity. Further, it has been observed that the presence of a dialkylhydantoin inhibits the irreversible formation of bromate ion, a possible carcinogen.
In the present invention, the alkyl groups of the dialkylhydantoin may be the same or different, and are both bound to the carbon atom at the 5-position of the hydantoin ring. Suitable alkyl groups include methyl, ethyl, isopropyl, tert-butyl, methylcyclopentyl, cyclohexyl, and the like. Preferred alkyl groups are ethyl and methyl; preferred dialkylhydantoins are 5-ethyl-5-methyl-hydantoin and 5,5-dimethylhydantoin; 5,5-dimethylhydantoin is highly preferred as the dialkylhydantoin moiety. It is desired that the concentration of the added dialkylhydantoin is in the range of from about 0.15 to about 0.70 millimole per liter; the concentration of dialkylhydantoin preferably is in the range of from about 0.50 millimole per liter to about 0.62 millimole per liter.
Bromide ions may be obtained from any convenient source; the source is preferably a solid, and nonhazardous to humans. It is preferred to use water soluble metal bromide salts or water soluble ammonium bromide salts. Examples of water soluble metal bromide salts that may be used include sodium bromide, potassium bromide, magnesium bromide, calcium bromide, and zinc bromide. Tetraethylammonium bromide, tetramethylammonium bromide, and ammonium bromide are examples of water soluble ammonium bromide salts that may be used in the practice of this invention. Sodium bromide is the most highly preferred source of bromide ion. The desired concentration of the source of bromide ion is in the range of from about 0.090 to about 0.39 millimole per liter, with the preferred concentration in the range of from about 0.20 millimole per liter to about 0.35 millimole per liter. Although the source of bromide ion concentration is
Nalepa Christopher J.
Sanders Michael J.
Albemarle Corporation
Hoey Betsey Morrison
Spielman, Jr. E. E.
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