BROMOSULFAMATE AS BIOCIDE IN NITRITE-CONTAINING CORROSION INHIBITION

Abstract: Bromosulfamate is stable with respect to a nitrite corrosion inhibitor in for example cooling systems and provides an effective biocide, bactericide and fungicide. The bromosulfamate is utilized at about 0.1 to 10 ppm (residual) with an optimum of about 0.2 ppm of bromosulfamate. The bromosulfamate is made by reacting together sodium bromide (NaBr), sodium hypochlorite (NaOCl) or chlorine, and sodium sulfamate (NaSO₃NH₂) or sulfamic acid, and using the product within about 5 hours in treating the nitrite solution.

Description: The term nitrite corrosion inhibitor applies to a wide group of inhibitors useful in industry, in metals such as steel and in closed and open recirculating systems of many types such as, especially, cooling systems. These inhibitors, which contain nitrite, usually contain as an active ingredient a water-soluble nitrite salt, such as sodium nitrite. These nitrites may be converted to molecular nitrogen or ammonia by denitrifying bacteria and fungi. Therefore, bactericides and fungicides have also been present. However, chlorine bromine and iodine compounds, known as bactericides and fungicides, have in many cases deleterious effects on the effective strength of the nitrite-containing corrosion inhibitor composition. The invention is based on the discovery that bromosulfamate is inert to or does not oxidize the nitrite corrosion inhibitor composition and yet is an effective biocide. Bromosulfamate utilized as a liquid is preferably used in a range of about 0.1 to 10 ppm (residual) with an optimum of about 0.2 ppm. The residual is that product which is left of the bromosulfamate after mixing with the nitrite composition. The feed amount of the bromosulfamate, namely the input of the compound to the nitrite composition, is preferably about 5 ppm. The bromosulfamate composition is prepared from sodium bromide, sodium hypochlorite (or chlorine), and sodium sulfamate (or sulfamic acid) mixed together at ambient temperature or higher. The product bromosulfamate is utilized "fresh", where "fresh" is defined as up to five hours after preparation, as a biocide in the nitrite solution. The prior art includes a few distantly related patents as follows: "Method for Prevention of Phosphonate Decomposition by Chlorine," U.S. Patents 4,642,194 and 4,711,724; also "Use of Sulfamic Acid to Inhibit Phosphonate Decomposition by Chlorine-Bromine Mixtures", U.S. Patent 4,759,852. The sulfamate form noted in the ′852 patent halts decomposition of phosphonates, whereas the bromide does not, but the disclosure there is concerned with the decomposition of phosphonates, which is not the object of the present invention. Example I This method has been tested on a small scale to discover that by the use of bromosulfamate bromine residuals could be maintained without destroying nitrite. Tests showed that without sulfamic acid, nitrite was destroyed when bromine or chlorine was added to the system, and that chlorosulfamate did not destroy nitrite. However, chlorosulfamate is not as strong a microbiocidal agent as bromosulfamate, and the bromosulfamate compound is preferred. Two pilot cooling tower tests have further confirmed these results. Test results: In these tests, when chlorine was used as the biocide, fed at approximately 50 ppm, 0.2 ppm of chlorine residual was maintained, but >90% of the nitrite was oxidized. A similar result occurred when bromine was used, fed at approximately 50 ppm. 0.2 ppm of bromine residual was maintained, but >90% of the nitrite was also oxidized. When chlorosulfamate was used, fed at approximately 5 ppm, only a trace, or about .05 ppm, of chlorine residual was maintained, but less than 10% of the nitrite was oxidized. Bromosulfamate, fed at approximately 5 ppm, maintained 0.2 ppm of bromosulfamate residual, and less than 10% of the nitrite was oxidized. The tests showed that the feed concentration for chlorosulfamate and bromosulfamate was much less than that for chlorine and bromine and that bromosulfamate is at least equal to chlorine and bromine in oxidant residual recovery, but chlorine and bromine are not useful biocides in the system because they destroy nitrite. On the other hand, chlorosulfamate does not destroy nitrite but is not as effective a biocide as bromosulfamate. Example II Preparation of the Bromosulfamate Treatment Composition 50-200 grams of sodium bromide, NaBr, was added to 75 grams of sodium hypochlorite, NaOCl. After mixing the solution for 15-60 seconds, 50-200 grams of sodium sulfamate, NaSO₃NH₂, was added to the solution. The resulting composition was usable as a biocide. This procedure is all prepared in solution. Additionally, it has been found that "fresh" treatment composition is of great importance since the oxidizing biocide system is not stable to be transported or preserved. The composition should be used within about 5 hours of preparation.

Claims: The use of bromosulfamate as a bactericide and fungicide in a system having a nitrite-containing corrosion inhibitor. A method of suppressing microbial attack on a nitrite-containing corrosion inhibitor in a cooling system which consists of adding bromosulfamate to the system. The method of claim 2 wherein the effective amount of bromosulfamate is about 0.1 to 10 ppm (residual). A nitrite-containing corrosion inhibitor composition containing an effective amount of a bromosulfamate as a bactericide and fungicide. The composition according to claim 4 wherein the effective amount of bromosulfamate is 0.1 to 10 ppm (residual). The composition according to claim 5 wherein the effective amount is about 0.2 ppm. A composition according to any one of claims 4 to 6 which is a solution. A method of preparation and utilization of bromosulfamate biocidal composition which comprises reacting together sodium bromide (NaBr), sodium hypochlorite (NaOCl) or chlorine, and sodium sulfamate (NaSO₃NH₂) or sulfamic acid, and utilizing said product within about 5 hours of preparation as a biocidal additive to a solution of nitrite-containing corrosion inhibitor.

Inventors: SMYK, EUGENE B., SMYRNIOTIS, CHRIS R., WIATR, CHRISTOPHER L.
Applicants: NALCO CHEMICAL COMPANY
Application year: 1990
Main classification: C02F1
IPC codes: C23F11, C02F1