WO2001042149A1

WO2001042149A1 - Method of inhibiting corrosion of yellow metal surfaces in aqueous systems

Info

Publication number: WO2001042149A1
Application number: PCT/US2000/031625
Authority: WO
Inventors: Jennifer C. Horne; Larry E. Brammer, Jr.; Frank F.-Y. Lu; John E. Hoots
Original assignee: Nalco Chemical Company
Priority date: 1999-12-13
Filing date: 2000-11-17
Publication date: 2001-06-14
Also published as: AU1619101A; AR026736A1

Abstract

Corrosion inhibition of yellow metals in aqueous systems containing oxidizing halogens is achieved through the addition of at least one nitrated triazole to the aqueous system.

Description

METHOD OF INHIBITING CORROSION OF

YELLOW METAL SURFACES IN AQUEOUS SYSTEMS

FIELD OF THE INVENTION

This invention relates generally to corrosion inhibition and, more particularly, to a method of inhibiting corrosion of yellow metal surfaces in aqueous systems .

BACKGROUND OF THE INVENTION

Aromatic triazoles, namely tolyltriazole and benzotriazole, have been used for corrosion protection of yellow metals (e.g., copper and copper alloys) for several decades. However, tolyltriazole is generally preferred because of its lower cost. More recently, butylbenzotriazole and chlorotolyltriazole have also been used in industrial cooling water systems as disclosed, for example, in U.S. Patent Nos. 4,744,950; 5,772,919 and 5,773,627.

Triazoles function as corrosion inhibitors by adsorbing to copper surfaces, thus providing a protective film that prevents both metal loss and oxygen reduction reactions. However, despite the fact that tolyltriazole and benzotriazole are among the most useful inhibitors for controlling yellow metal corrosion, the performance and cost-effectiveness of triazoles is limited by their consumption in aqueous systems .

The adsorption of triazoles to form protective films results in one form of triazole consumption, but with normal feed rates and metal surface area-to-system volume, this type of triazole loss is typically minimal. Biodegradation is another known mechanism for the consumption of certain triazoles, such as the 5-methyl isomer of tolyltriazole. Triazoles can also be consumed by precipitation from solution with dissolved copper. This is not considered a major contributing factor to triazole demand in typical applications, however, where copper is rarely in high enough concentrations to deplete the residual. Another major source of triazole consumption is due to reaction of triazoles with oxidizing halogens .

Many cooling water systems are treated with oxidizing halogens, such as chlorine gas, hypochlorite bleach, iodine/hypoiodous acid, chlorine dioxide, hypobromous acid, bromochloridimethylhydantoin, or stabilized versions of hypochlorous or hypobromous acids, to control microbiological growth. When yellow metals that have previously been protected with triazoles are exposed to an oxidizing halogen, corrosion protection breaks down. Many triazoles, including benzotriazole and tolyltriazole, are vulnerable to halogen attack. Very high dosages of triazoles are frequently added to cooling water systems in an attempt to form new protective films and improve performance .

Not only are triazoles consumed in cooling water systems treated with oxidizing halogens, but the halogens themselves are consumed as well. As the oxidizing halogen attacks the triazole, the halogen is consumed, thereby reducing its biocidal efficiency and reducing cost-performance of the biocide.

Other triazole consumption-related problems associated with combining triazoles and oxidizing halogens in aqueous systems include the formation of (1) volatile by-products which have an objectionable odor and can be released into the environment, (2) by-products that are less effective corrosion inhibitors and (3) toxic halogenated organics . The halogenated organics are particularly undesirable when waters from the aqueous systems are released into the environment, especially into a receiving body of water where toxicity to fish is a concern. Another problem is the inherent aggressiveness of the halogens towards the base metal.

Different triazoles provide different levels of protection to the metal from direct halogen attack based on factors such as the film hydrophobicity, triazole packing density and film thickness.

Accordingly, it would be desirable to provide an improved method of inhibiting corrosion of yellow metals in aqueous systems containing oxidizing halogens. It would also be desirable to utilize a triazole which is resistant to halogen attack and which does not interfere with the biocidal efficacy of the halogen. Furthermore, it would be desirable if the combination of the triazole and oxidizing halogen reduced the formation of volatile by-products having objectionable odors, by-products which are less effective corrosion inhibitors and toxic byproducts .

SUMMARY OF THE INVENTION

The method of the invention calls for adding at least one nitrated triazole to an aqueous system being treated with an oxidizing halogen to inhibit the corrosion of yellow metal surfaces in the aqueous system. The inventive method is not only effective, but economically appealing as well because the use of nitrated triazoles is minimized due to the fact that they are resistant to halogen attack and thus not consumed. Likewise, the oxidizing halogens are not consumed, so their biocidal efficacy remains intact. The present method is also environmentally acceptable because it reduces the formation of undesirable by-products, in particular those which are volatile, foul-smelling, less effective corrosion inhibitors and toxic.

DETAILED DESCRIPTION OF THE INVENTION The present invention is directed to a method of inhibiting corrosion of yellow metal surfaces in an aqueous system. In accordance with the invention, one or more nitrated triazoles are added to the aqueous system.

The nitrated triazoles which may be used in the practice of this invention include compounds having the formula :

wherein A is one or more aromatic or heteroaromatic rings; R is one or more substituents selected from the group consisting of -H, -alkyl, -aryl, -CN, -carboxylic acid, -amide,

-carbamoyl, -sulfate, -phosphate, -hydroxy, -alkoxy, - thiol, -thioalkyl, -thioaryl, -halo and substituted triazoles; and X is one or more nitro (-N0₂) groups. Preferred nitrated triazoles include nitrotolyltriazole, nitrobenzotriazole, nitrobutylbenzotriazole, nitronaphthotriazole and dinitronaphthotriazole . Nitrotolyltriazole is the most preferred nitrated triazole .

It is preferred that the amount of nitrated triazole which is added to the aqueous system be in the range of about 0.01 ppm to 100 ppm. More preferably, the amount of the nitrated triazole is from about 0.01 ppm to about 20 ppm, with about 0.01 ppm to about 5 ppm being most preferred. The nitrated triazole can be introduced into the aqueous system by any conventional method and may be fed on either an intermittent or a continuous basis. The nitrated triazole can also be fed alone or with other treatment chemicals such as biocides, scale inhibitors, dispersants, defoamers, inert fluorescent tracers and/or other corrosion inhibitors.

The nitrated triazoles can be used in any aqueous system which is in contact with a yellow metal surface, particularly surfaces containing copper and/or copper alloys. Representative aqueous systems include, but are not limited to cooling towers, once-through cooling systems, closed-loop systems and gas scrubber systems.

The present inventors have discovered that nitrated triazoles are surprisingly effective yellow metal corrosion inhibitors, especially in the presence of oxidizing halogens. In contrast to other commonly used triazoles, such as tolyltriazole, chlorotolyltriazole and benzotriazole, the consumption of nitrated triazoles in the presence of halogens is minimized due to their strong resistance to halogen attack. Because nitrated triazoles are not as reactive as other triazoles with oxidizing halogens, the biocidal efficacy of the halogens remain intact and the formation of undesirable by-products is reduced, especially those which are volatile, foul- smelling, less effective corrosion inhibitors and toxic.

EXAMPLES

The following examples are intended to be illustrative of the present invention and to teach one of ordinary skill how to make and use the invention. These examples are not intended to limit the invention or its protection in any way.

Example 1

Benchtop tests were performed to investigate the effects of the combination of triazoles with bromine- based biocides. Hypobromite (ACTI-BROM^®, available from Nalco Chemical Company, 1:1 HOCl to Br) or stabilized bromine (STABREX^®, available from Nalco Chemical Company) was added at various amounts (1 ppm is a "normal" level, 5 ppm is an "upset" level) to 3 ppm triazole solutions in synthetic cooling water, and allowed to react at a temperature of 100 °F and a pH of approximately 8.5 for 3 hours. Residual biocide was reduced with erythorbic acid at the end of the experiment to terminate further reaction. Concentrations of the triazole control and the reacted solutions were determined by high performance liquid chromatography (HPLC) and used to compute the percent loss of triazole. The halogenated biocide concentration was measured and maintained as a total residual chlorine (TRC as Cl₂) level.

The triazoles utilized in this example were obtained as follows:

The synthesis of naphtho [2 , 3-d] triazole (NT) was according to the published procedure of Wheeler, G.L.;

Andrejack, J.; Wiersma, J. H.; Loft, P. J.; Anal. Chim .

Acta (1969) 46, 239, from the diazotization of 2,3- diaminonaphthalene (Aldrich Chemical Co.; Milwaukee, WI) .

The synthesis of 5-nitrobenzotriazole (NBT) was according to the published procedure of Hofmann, A. W.; Annalen

115, 251, from the diazotization of 4-nitro-l,2- phenylenediamine. Chlorotolyltriazole (Cl-TT) was synthesized according to the procedure described in U.S.

Patent No. 5,773,627. Benzotriazole (BZT) and carboxybenzotriazole (CBT) were obtained commercially from PMC Specialties Group, Inc. of Cincinnati, Ohio.

Nitrotolyltriazole (NTT) and 4-nitro-5-butyl-lH- benzotriazole (nitrobutylbenzotriazole, NBBT) were synthesized as follows. A 100 mL flask, equipped with a stirrer, thermometer, and a nitrogen inlet was charged with 20 mL of nitric acid (70%) . After cooling the acid to 0 °C, 20 mL of sulfuric acid was added at a rate slow enough to maintain the temperature below 5 °C. Once the addition was complete, the acid mixture was chilled to 0 °C, and 2 g of either tolyltriazole (TT) (mixture of 4- and 5-methyl-lH-benzotriazole, obtained from PMC

Specialties Group, Inc.) or 5-butyl-lH-benzotriazole

(BBT) (available from Bayer AG of Krefeld-Uerdingen,

Germany) was added in portions such that the reaction temperature could be maintained below 5 °C. After the addition was complete, the reaction mixture was allowed to warm to room temperature and then stirred for 2 hours.

After this time, the reaction mixture was carefully mixed with 100 g of ice. The solid that formed was collected by filtration and washed with water until the pH of the aqueous washings was neutral . The crude products were isolated in 60-80% yields and used without further purification. Analytical samples were obtained by recrystallizing the crude products in a 70/30 mixture of ethanol and water. NMR spectra were consistent with the structure of aromatic ring-nitrated products.

5 -Nitro- IH-naphtho [2 , 3 -d] triazole

(nitronaphthotriazole, NNT) was synthesized as follows.

A 50 mL flask, equipped with a stirrer, thermometer, and a nitrogen inlet was charged with 25 mL of nitric acid

(70%) . After cooling the acid to -15 °C, 10 mL of sulfuric acid was added at a rate slow enough to maintain the temperature below -5 °C. Once the addition was complete, the acid mixture was chilled to -15 °C, and 0.5 g of IH-naphtho [2, 3-d] triazole was added in portions such that the reaction temperature could be maintained below -

10 °C. After the addition of the triazole was complete, the reaction was stirred for an additional 1 hour at or below -10 °C. After this time, the reaction mixture was carefully mixed with 100 g of ice. The solid that formed was collected by filtration and washed with water until the pH of the aqueous washings was neutral . The crude product was isolated in a 57% yield and used without further purification. Analytical samples were obtained by recrystallizing the crude product in a 70/30 mixture of ethanol and water. NMR spectra were consistent with the structure of aromatic ring-nitrated products.

Dinitronaphtho [2, 3-d] triazole (DNNT) was synthesized as follows. A 25 mL flask, equipped with a stirrer, thermometer, and a nitrogen inlet was charged with 5 mL of nitric acid (70%) . After cooling the acid to 5 °C, 5 mL of sulfuric acid was added at a rate slow enough to maintain the temperature below 10 °C. Once the addition was complete, the acid mixture was chilled to 0 °C, and 0.5 g of IH-naphtho [2 , 3-d] triazole was added in portions such that the reaction temperature could be maintained below 10 °C. After the addition was complete, the reaction was stirred for an additional 2 hours. After this time, the reaction mixture was carefully mixed with 100 g of ice. The solid that formed was collected by filtration and washed with water until the pH of the aqueous washings was neutral . The crude products were isolated in a 57% yield and used without further purification. Analytical samples of the crude products were obtained through preparatory thin layer chromatography (TLC) analysis on silica gel with 95/5 mixtures of chloroform and ethanol . NMR spectra were consistent with the structure of aromatic ring-nitrated products .

As shown below in Table 1, this example demonstrates the stability of nitrated triazoles to the STABREX and ACTI-BROM biocides under benchtop conditions. Other substituents, such as chloro- or carboxy- have stabilizing effects, but not to the degree of the nitro- group. Also, because the nitrated triazoles are not consumed, they do not form any brominated derivatives, so toxicity of by-products is not an issue when using these triazoles .

Table 1

'TT = tolyltriazole; ²NTT = nitrotolyltriazole; ³BZT = benzotriazole; ⁴NBT = nitrobenzotriazole; ^BNT = naphthotriazole; ⁶NNT = nitronaphthotriazole; ⁷DNNT = dinitronaphthotriazole; ⁸BBT = 5-butylbenzotriazole; ⁹NBBT = nitrobutylnitrobenzotriazole; ^,0CI-TT = chlorotolyltriazole; ⁿCBT = carboxybenzotriazole

Example 2

Pilot cooling tower (PCT) tests were conducted to compare the consumption of triazoles in the presence of oxidizing biocides, namely bleach (HOCl) and STABREX. Triazoles obtained in accordance with Example 1 were slug fed into the basin to have initial concentrations of 5 ppm in synthetic cooling water. The tower was operated at pH 7 and 100 °F, with stainless steel metallurgy, and no blowdown. Deionized water was used for makeup water to keep the cycles of concentration constant. An inert fluorescent tracer was also added, to compensate for any hydrodynamic losses due to tower dynamics or mechanical losses. Bleach levels were controlled at 0.5 ppm free residual chlorine (FRC) , and STABREX biocide levels were controlled at 0.5 ppm total residual chlorine (TRC), using a Nova chlorine analyzer calibrated to the Hach N,N-diethyl-p-phenylenediamine (DPD) method (Standard Methods for the Examination of Water and Wastewater, 19^th Ed., 1995; Method 4500-C1 F) . Concentrations of the triazoles were determined by HPLC of intermittent grab samples. The error of the measurements was ± 2%. Table 2 lists the results from these experiments, from a 24- hour period. As shown in the Table, NTT experiences the least amount of consumption in the presence of either oxidizing biocide.

Table 2

This example illustrates the superior stability of NTT relative to other triazoles in the presence of oxidizing biocides. This means that NTT is resistant to stripping, as well as to other derivatization or degradation reactions. This example also illustrates that, because very little NTT is consumed, significant amounts of toxic halogenated by-products are not formed.

Example 3

The corrosion inhibition of NTT was tested in a pilot cooling tower. The test synthetic cooling water contained 600 ppm Ca (as CaC0₃) , 300 ppm Mg (as CaC0₃) , and 440 ppm NaHC0₃ (as CaC0₃) . The system was run at 100 °F by heating rods inserted into heat exchanger tubes, ΔT = 10 °F, pH 7 controlled with sulfuric acid, with heat exchanger metallurgy including: admiralty brass (ADM) , copper (Cu) , 90/10 copper/nickel alloy (Cu/Ni) , mild steel (MS) and stainless steel. Corrosion rates were monitored by Corraters^® (Rohrback Cosaco Systems of Santa Fe Springs, CA) (linear polarization resistance device) and were also determined by gravimetric analysis of the heat exchanger tubes at the conclusion of the test in mils per year (mpy) . Triazole was fed at 2.9 ppm as TT actives (equimolar amounts) as part of a stabilized phosphate treatment program. Intermittent grab samples were measured for triazole residual throughout the duration of the test. After approximately a 16-hour initial passivation time, hypochlorite bleach was fed and controlled at a residual of 0.3 ppm FRC, using a chlorine analyzer calibrated to the Hach DPD test for chlorine.

As illustrated below in Table 3, this example shows the efficacy of NTT as a corrosion inhibitor for a variety of yellow metals with and without the presence of bleach. Although the gravimetric analysis shows higher corrosion rates, these are consistent with the harsh experimental conditions. In addition, this example shows that a higher triazole residual can be maintained for NTT in the presence of bleach, without increasing chemical feed. Table 3

While the present invention is described above in connection with preferred or

illustrative embodiments, these embodiments are not intended to be exhaustive or

limiting of the invention. Rather, the invention is intended to cover all alternatives, modifications and equivalents included within its spirit and scope, as defined by the appended claims.

Claims

1. A method of inhibiting corrosion of yellow metal surfaces in an aqueous system, wherein the aqueous system is treated with an oxidizing halogen, comprising the step of adding an effective corrosion inhibiting amount of at least one nitrated triazole to the aqueous system.

2. The method of claim 1 wherein the nitrated triazole has the formula:

wherein A is at least one aromatic or heteroaromatic ring; R is at least one substituent selected from the group consisting of -H, -alkyl, -aryl, -CN, -carboxylic acid, -amide,

-carbamoyl, -sulfate, -phosphate, -hydroxy, -alkoxy, - thiol, -thioalkyl, -thioaryl, -halo and substituted triazoles; and X is one or more nitro groups.

3. The method of claim 2 wherein the nitrated triazole is selected from the group consisting of nitrotolyltriazole, nitrobenzotriazole, nitrobutylbenzotriazole, nitronaphthotriazole and dinitronaphthotriazole .

4. The method of claim 2 wherein the nitrated triazole is nitrotolyltriazole.

5. The method of claim 1 wherein the nitrated triazole is added to the aqueous system in an amount of from about 0.01 ppm to about 100 ppm.

6. The method of claim 1 wherein the nitrated triazole is added to the aqueous system in an amount of from about 0.01 ppm to about 20 ppm.

7. The method of claim 1 wherein the nitrated triazole is added to the aqueous system in an amount of from about 0.01 ppm to about 5 ppm.

8. The method of claim 1 wherein the nitrated triazole is added to the aqueous system on an intermittent basis.

9. The method of claim 1 wherein the nitrated triazole is added to the aqueous system on a continuous basis .

10. The method of claim 1 wherein the nitrated triazole is added to the aqueous system with at least one other treatment chemical selected from group consisting of biocides, scale inhibitors, dispersants, defoamers, inert fluorescent tracers and corrosion inhibitors.

11. A method of inhibiting corrosion of yellow metal surfaces in an aqueous system, wherein the aqueous system is treated with an oxidizing halogen, comprising the step of adding nitrotolyltriazole to the aqueous system in an amount of from about 0.01 ppm to about 100 ppm.

12. The method of claim 11 wherein nitrotolyltriazole is added to the aqueous system in an amount of from about 0.01 ppm to about 20 ppm.

13. The method of claim 11 wherein nitrotolyltriazole is added to the aqueous system in an amount of from about 0.01 ppm to about 5 ppm.

14. The method of claim 11 wherein nitrotolyltriazole is added to the aqueous system on an intermittent basis.

15. The method of claim 11 wherein nitrotolyltriazole is added to the aqueous system on a continuous basis.

16. The method of claim 11 wherein nitrotolyltriazole is added to the aqueous system with at least one other treatment chemical selected from group consisting of biocides, scale inhibitors, dispersants, defoamers, inert fluorescent tracers and corrosion inhibitors.