Patent Description:
Biocidal solutions of haloamines, particularly monochloramine (MCA), have generated a great deal of interest for control of microbiological growth in a number of industries, including the dairy industry, the food and beverage industry, the pulp and paper industries, the oil and gas industries, the fruit and vegetable processing industries, various canning plants, the poultry industry, the beef processing industry, and miscellaneous other food processing applications.

Haloamines can be formed by reacting a dilute ammonia solution or at least one ammonium salt or other nitrogen source with at least one halogen-containing oxidant. The required parent reagents are commonly available as concentrated solutions. The parent solutions are commonly stored near a haloamine generator in which they are combined in defined proportions to form the biocide treatment. Unfortunately, storage results in a degradation of actives in the parent solutions. In addition to creating difficulties for maintaining the proper ratio of reactants, the degradation of halogen-containing oxidants results in the accumulation of harmful halogen polyoxyanions such as chlorite, chlorate, perchlorate, and/or analogous bromine ions including bromate.

Halogen oxyanions can be generally presented by the formula:.

where X is a halogen atom such as fluorine, chlorine, bromine, iodine, and astatine bonded with up to n oxygen atoms. The halogen oxyanions of interest to the present invention can be listed in the order of increasing number of oxygen atoms as follows:.

The halogen oxyanions containing more than one oxygen atom, or halogen polyoxyanions, have been found to be particularly harmful to human health. For example, the perchlorate and chlorate ions have been found to inhibit thyroid iodine uptake and thus are a potential health concern for children, especially those with mild or moderate iodine deficiency. Bromate has been found mutagenic in vitro and in vivo and classified as a probable human carcinogen under the <NUM> EPA Guidelines for Carcinogen Risk Assessment.

For this reason, various regulatory agencies are restricting or banning the presence of halogen polyoxyanions in certain applications. Since commercially-available halogen-containing oxidant solutions will contain significant amounts of halogen polyoxyanions formed during storage that will end up in produced haloamine solutions, other methods of producing halogen-containing precursors of haloamines are needed.

Thus, there is a need in the art for methods of preparing haloamine solutions with reduced amounts of halogen polyoxyanions. There is also need in the art for haloamine solutions with reduced amounts of harmful compounds, such as halogen polyoxyanions.

The current invention provides a solution to these needs.

<CIT> discloses a process for substantially reducing the corrosiveness of a composition containing in situ generated sodium hypochlorite in which the sodium hypochlorite is converted to a haloamine.

<CIT> discloses a method for preparing a solution comprising monochloramine which includes the steps of: a) in an electrolyser including an anode area and a cathode area separated by a membrane limiting the migration of hypochlorite ions, forming hypochlorite ions in the anode area by means of the oxidation of chloride ions in an aqueous solution, and forming ammonium ions in the cathode area by means of the reduction of nitrate and/or nitrite ions in an aqueous solution; and b) reacting the ammonium ions with at least one portion of the hypochlorite ions, with a molar ratio of hypochlorite ions to ammonium ions no lower than <NUM>, resulting in the formation of monochloramine.

<CIT> discloses production of a biocidal solution in situ, including a reaction between an ammonium salt and an electrolytically generated bromine oxidative species.

In a paper presented at the 68th Annual Water Industry Engineers and Operators' Conference on <NUM>-<NUM> September <NUM> (XP055116316), John Hooper discussed basic operating principles and design considerations for the on-site generation of sodium hypochlorite.

The present invention provides methods of producing a haloamine solution comprising less than <NUM>% by weight of halogen polyoxyanions comprising (a) the on-site generation of a halogen-containing oxidant solution and (b) reacting on-site the halogen-containing oxidant with a nitrogen source, to thereby produce the haloamine solution, wherein the halogen is chlorine, the on-site generation comprises reacting chlorine gas with an alkaline solution and wherein the haloamine comprises monochloramine (MCA). Both reactions may be combined into a single step.

Further objects, features, and advantages of the present invention will become apparent from a review of the detailed description that follows.

The present invention is directed to online production of biocidal haloamines solutions with reduced amounts of halogen polyoxyanions, preferably that are substantially free of halogen polyoxyanions. The formed solutions contain less than <NUM>% by weight, or less than <NUM>% by weight, or less than <NUM>% by weight, or less than <NUM> percent, or less than <NUM> percent by weight of halogen polyoxyanions, such as chlorates, or no measurable amount of any halogen polyoxyanions or chlorates. The present methods provide a haloamine product for which the risks to human health related to the presence of halogen polyoxyanions such as chlorate are effectively reduced or eliminated.

The haloamine comprises monochoramine. The invention reduces the amount of chlorate anion, depending on the halogen-containing precursors used and depending if sodium salts or another starting compound is used. The methods can reduce all halogen polyoxyanions, and preferably produce haloamines solutions free of halogen polyoxyanions of any type.

The most common of biocidal haloamines, chloramine solutions, can be produced by combining bleach (a solution of sodium hypochlorite, NaOCl) with an ammonia-containing solution. Formation of monochloramine, the most efficacious of biocidal chloramines, proceeds according to the following overall reaction:.

The ammonia-containing solution may vary between an ammonium carbamate solution, an ammonium bromide solution, and an ammonium sulfate solution and others. For example, any desired source of nitrogen can be used, including ammonium salts. Commercial bleach is intended to deliver a certain concentration of hypochlorite ion. However, during storage, hypochlorite (OCl-) decomposes with formation of chlorine polyoxyanions such as chlorite (ClO<NUM>-) and further into chlorate (ClO<NUM>-) via the following disproportionation reaction:.

Perchlorate ion forms as a result of interaction between hypochlorite and chlorate:.

At room temperature (<NUM> ° C), about <NUM>% of hypochlorite in commercial bleach (<NUM>-<NUM> weight %) decomposes within <NUM> - <NUM> days. Chlorate is the most abundant decomposition product present in commercial bleach at as high as <NUM>%. In solutions, any halogen oxyanions are balanced by available metal cations, with cations of transition metals such as iron or manganese, if present, accelerating increasing hypohalite decomposition by more than <NUM> times.

The present invention provides methods of producing haloamines comprising MCA which result in a significantly reduced content of halogen polyoxyanions. In particular, the present method uses hypochlorite produced in-situ, which contains less of the undesired by-product chlorate anions. The produced hypochlorite can be used directly and immediately such that undesired chlorate anions are not formed.

The hypochlorite used in the invention can be produced in-situ by reacting chlorine gas with caustic soda. In certain embodiments, electrolysis or passing an electric current through a solution is not used in any stage of the method, for example, not used to produce chlorine or the hypochlorite. The ammonia-containing component then reacts with, and converts, the sodium hypochlorite to monochloramine having biocidal properties.

The reaction of the ammonia-containing component and the in-situ generated sodium hypochlorite can be controlled to achieve a quantitative conversion of sodium hypochlorite to monochloramine (i.e., a reaction yield of at least about <NUM> percent, preferably at least about <NUM> percent). Control of the reaction can avoid production of unwanted byproducts, such as dichloramine and nitrogen trichloride.

For example, (a) an excess of ammonia, or at least no excess hypochlorite can be used; and/or (b) an alkaline pH, preferably at least about <NUM> to about <NUM> can be used. With these reaction controls, the conversion of sodium hypochlorite to monochloramine can be about <NUM> percent, or <NUM>% or higher. The produced monochloramine solution can contain, for example, <NUM> to <NUM>% or <NUM> to <NUM>% or <NUM> to <NUM>% by weight of MCA.

In one embodiment of the present invention, shown in <FIG>, the hypochlorite solution is produced by reacting chlorine gas with an alkaline solution. Any desired alkaline solution can be used. The chlorine gas can be provided in a compressed form. The reaction of chlorine gas can be conducted using a continuous or intermittent process with the resulting hypochlorite solution accumulated, for example, in a storage tank downstream from the gas source and/or by mixing chlorine gas with alkaline water in such an intermediate tank. Preparing concentrated solutions of hypochlorite is not necessary. In fact, only a dilute solution, with hypochlorite concentration in the range <NUM>-<NUM>/L, or <NUM>-<NUM>/L or <NUM>-<NUM>/L or <NUM>-<NUM>/L is advantageously needed. Such a concentration is more than <NUM> times lower than that of the most common commercial <NUM>/L hypochlorite solution. The hypochlorite tank volume and residence time should be selected to ensure the proper retention time of hypochlorite solution to avoid chlorate formation.

The ammonium ion containing solution can be prepared in a separate tank using any suitable ammonium source including, for example, ammonia, aqueous ammonia, ammonium sulfate, ammonium phosphate, ammonium chloride, and ammonium fluoride. The source of ammonia can be provided by many different ammonia-containing components. For example, the ammonia source may be the Busan® <NUM> product, which is commercially available from Buckman Laboratories (Memphis, Tennessee) and is a blend of ammonia-containing compounds containing a total of <NUM>% ammonia.

In another embodiment of the present invention, shown in <FIG>, a suitable chloramine solution is produced using a dilute hypochlorite solution obtained from a mixture of caustic, water, and chlorine gas, wherein the latter is generated electrolytically. The hypochlorite solution is accumulated at a minimal volume in an intermediate tank and/or fed directly into a chloramines generator.

In another process (not claimed), shown in <FIG>, a chloramines solution is produced using a dilute hypochlorite solution instantly delivered by an electrolytic generator / electrolyzer. Suitable electrolyzers are available commercially from such suppliers as Electrolytic Technologies Systems LLC, North Miami Beach, FL, MIOX Corporation, Albuquerque, NM, or VDH Products, Roden, Drenthe, Netherlands. The electrolyzers produce hypochlorite solutions using salt brines or sea water. The electrolyzer output can optionally be adjusted to proper pH such as <NUM>-<NUM> or <NUM>-<NUM>, with caustic and water and accumulated in an intermediate tank or fed directly into a chloramines generator. Alternatively, the hypochlorite solution can be fed directly into a chloramines generator without any time in an intermediate tank.

In another process (not claimed), the chloramine producing reactions are combined into a single step as shown in <FIG>. In such a method, electrolysis or passing an electric current through a solution is not used to produce chlorine gas or hypochlorite solution in an intermediate upstream stage.

In yet another embodiment, the present invention can be realized using a system comprising one or more or all the above configurations as shown in <FIG>. Thus, the dilute hypochlorite solution can be obtained simultaneously or intermittently from a number of sources selected but not limited to a group of those using chlorine gas, an electrolytic chlorine gas generator, or an electrolytic hypochlorite generator (not claimed).

The present invention provides on-site generation of halogen-containing oxidant solutions such as hypochlorite solutions by reacting chlorine gas with an alkaline solution, which then can be used immediately to produce biocidal haloamines. Such immediate conversion with no storage period of the hypochlorite solutions eliminates formation of harmful halogen polyoxyanions, such as chlorates. In some embodiments, there is no storage period, and in others, a short storage period (for example, less than an hour), in an intermediate tank can be used. Such a short residence time, especially with the lower concentration hypochlorite solutions that can be used in the invention, reduces or eliminates the formation of harmful chlorates.

The haloamines, such as chloramines, and solutions thereof produced in the present invention can be used anywhere such biocides are used. For example, biocidal haloamine applications in food processing and sanitation industry are known. The invention can be used in all current haloamine applications, especially including those regulated for the presence of chlorate or other halogen polyoxyanions, such as at starch and sugar mills, in brewing industry, bioethanol plants, the oil and gas industry, and swimming pools.

The present invention is especially useful in the food processing industry. The flexible methods of the present invention produce the lowest possible chlorate level in the chloramine solutions produced.

Advantageously, many different on-site methods of producing the hypochlorite can be used, including use of a gaseous chlorine as a source of hypochlorite instead of or in combination with an electrolytic generator. Also, a stand-alone electrolytic generator of chlorine gas can be usedinstead of or in addition to electrolytic generation of hypochlorite solutions.

The present invention is flexible in that an optional intermediate hypochlorite tank having a low residence time (for example, less than <NUM> hours, or less than <NUM> hours, or less than one hour, or less than half an hour, or less than <NUM> minutes, or less than <NUM> minute, such as one minute to <NUM> hours or <NUM> minutes to <NUM> hours) can be used. Furthermore, commercial hypochlorite generators can be used without regard to the actual method utilized to generate hypochlorite.

Claim 1:
A method for producing a haloamine solution comprising less than <NUM>% by weight of halogen polyoxyanions comprising (a) on-site generation of a halogen-containing oxidant solution and (b) reacting on-site the on-site generated halogen-containing oxidant with a nitrogen source, to thereby produce the haloamine solution comprising less than <NUM>% by weight of halogen polyoxyanions,
wherein the halogen is chlorine, the on-site generation comprises reacting chlorine gas with an alkaline solution and wherein the haloamine comprises monochloramine (MCA).