MX2008009539A - Corrosion inhibitor treatment for closed loop systems - Google Patents

Abstract

The present invention provides an effective method of inhibiting corrosion on metallic surfaces in contact with a fluid contained in a closed loop industrial fluid system, which comprises adding to such fluid an effective corrosion controlling amount of a combination of an organic diacid, a triamine and a phosphonate compound.

Description

TREATMENT OF CORROSION IN HIBI DOR FOR CLOSED CIRCUIT SYSTEMS FIELD OF THE INVENTION The present invention relates generally to a corrosion inhibitor treatment for closed circuit systems. More specifically, the present invention relates to a non-nitrite, non-molybdenum corrosion inhibitor treatment, and environmentally friendly, for closed loop systems.

BACKGROUND OF THE I NVENTION The corrosion of metallic components in industrial plants can cause system failures and sometimes the closure of the plant. In addition, the corrosion products accumulated on the metal surface will decrease the rate of heat transfer between the metal surface and the water or other fluid medium, and therefore, corrosion will reduce the efficiency of the system operation. In this way, corrosion can increase maintenance and production costs and decrease the life expectancy of metal components. The most common way to combat corrosion is to add corrosion inhibiting additives to the fluid of such systems. However, the currently available corrosion inhibiting additives are either non-biodegradable, toxic, or both, which limits the applicability of such additives.

Regulatory pressures have been steadily increasing to eliminate the release of molybdate and / or nitrite into the environment. Additionally, nitrite treatments can develop serious microbiological growth in the closed circuit. Currently, the most reliable treatments to eliminate corrosion in closed circuit systems are based on molybdate, nitrite or a combination of the two. Existing all-organic treatments do not perform well in systems where corrosion has occurred, and iron and / or iron oxide levels are high, or water in the closed system has aggressive ions. The composition of water as found in closed circuits can vary significantly. In this way, environmental concerns are being directed to the use of corrosion inhibitors away from heavy metals, molybdenum and nitrite. Purely organic treatments existnes, although desirable, are not reliable when applied in systems loaded with iron or iron oxide or aggressive waters. By their nature, closed circuits are prone to having high iron. Therefore, there is a strong need for a non-nitrite, non-molybdenum, environmentally friendly corrosion inhibitor treatment for closed circuit systems. In the present invention, a combination of an organic acid, a triamine and a phosphonate compound surprisingly provides enhanced protection of metal surfaces from corrosion in closed loop systems. The organic treatments of the present invention can provide good corrosion protection in aggressive water, since be with or without hardness, and even in corroded systems.

BRIEF DESCRIPTION OF THE INVENTION The present invention provides an effective method to inhibit corrosion on metal surfaces in contact with a fluid contained in a closed loop industrial fluid system, which comprises adding to said fluid an effective corrosion controlling amount of an combination of an organic diacid, a triamine and a phosphonate compound. The diacid can be, for example, sebacic acid. The triamine may be, for example, triethanolamine, although the phosphonate may be, for example, a polyisopropenyl phosphonic material of different molecular weights, or for example, 1,6-hexamethylenediamine-N, N, N ', N'-tetra (methylene phosphonic), or for example,?,? - dihydroxyethyl N'.N'-diphosphonomethyl-1,3-propanediamine, N-oxide. The compositions of the present invention should be added to the fluid system for which the corrosion inhibiting activity of the metal parts in contact with the fluid system is desired., in an amount effective for the purpose. This amount will vary depending on the particular system for which the treatment is desired, and will be influenced by factors such as the area subject to corrosion, pH, temperature, amount of water and respective concentrations in the water of corrosive species. For the most part, the present invention will be effective when used at levels of up to about 10,000 parts per million (ppm) of fluid, and preferably from about 2,000-1,000 ppm of the formulation in the fluid contained in the system to be treated. The present invention can be added directly to the desired fluid system in a fixed amount and in a state of an aqueous solution, continuously or intermittently. The fluid system can be, for example, cooling water or kettle water system. Other examples of fluid systems which may benefit from the treatment of the present invention include aqueous heat exchanger, gas scrubber, air scrubber, air conditioning and refrigeration systems, as well as those employed in, for example, fire protection of construction and water heaters.

DESCRIPTION OF THE PREFERRED MODALITIES The invention will now be further described with reference to a variety of specific examples, which will be considered only as illustrative and not as restricting the scope of the present invention. Water was used from the local key for testing, with 60 ppm Ca (as CaCO3), 20 ppm Mg (as CaCO3), 4 ppm Si02, and 35 ppm M-Alk (as CaCO3): This water is identified as TRV . Aggressive water was tested, with 60 ppm of Ca (with CaC03), 20 ppm of Mg (as CaC03), 200 ppm of S04, 4 ppm of Si02 and 35 M-Alk ppm (as CaC03): This water is identified as AGG . Aggressive water was also tested, but without calcium (similar to AGG in composition but without calcium), containing 20 ppm Mg (as CaCO3), 200 ppm S04 and 51 ppm chloride as Cl ", 4 ppm of Si02, and 35 M-Alk ppm as CaC03: This water is identified as AGG *. In order to simulate the presence of corrosion products, 3 ppm of initially soluble Fe + 2 was added to a sample of the aggressive water, AGG: This water is identified as A / Fe. Because the closed system is made of iron pipes, there is no constant elimination of naturally occurring iron oxides that are present, a fifth water that would represent those characteristics was also designed. The tension of a highly corroded system was simulated when adding to the water of the local key (TRV) a section of corroded pipe, an iron oxide in one piece (3 g), 1050 ppm of ground oxide and 4 pp of Fe + 2 initially soluble: This water is identified as CR or "intensive iron test". The iron oxides were taken from real corroded pipes in the field. In order to test corrosion, the corrosion laboratory vessel test apparatus (BCTA) was used. The tests were run in a general manner for 18 hours at 48.89 ° C (120 ° F); the laboratory vessels were shaken at 400 rpm and opened into the air. The metallurgy was probes and samples of low carbon steel. The test was based on measuring corrosion through the established linear polarization electrochemical technique. The BCTA made consecutive measurements by automatically multiplexing 1 2 laboratory vessels. The trademark product of comparison was a combination of molybdate, nitrite. In the synthetic water pool, the corrosion inhibitor was challenged in different ways according to the Water composition changed, in order to stop corrosion. Note that a good corrosion inhibitor should be able to stop corrosion in all waters. As shown in Table I below, such is the case for the comparison trademark molybdate / nitrite combination. The conventional organic treatment is ineffective in CR water and in AGG *, aggressive water without calcium. It is also a weak inhibitor in water A / Fe, or water with dissolved iron.

Table I Corrosion rates measured in different waters, units of mils per year (mpy) for low carbon steel metallurgy without treatment and with conventional treatments. they tested four phosphonates. Two were phosphonate Experimental (A = (?,? - dihydroxyethyl? ',?' - diphosphonomethyl) 1,3-propanediamine, N-oxide and B = 1,6-hexamethylene-diamino-N, N, N ', N'-tetra ( methylene phosphonic)), the other two were (poly) isopropenyl phosphonic acid (C is higher molecular weight and made in organic solution, while D is made in aqueous medium and has lower molecular weight.) Polymers C and D were made as described in U.S. Patent Nos. 4,446,064 and 5,519,102.

Table II Corrosion rates measured in water as defined in text, units of mils per year (mpy) for low carbon steel metallurgy for phosphonates and diacid amine mixture.

As shown in Table I I, in order to obtain corrosion inhibition in the CR water, the preferred diacid is sebacic acid, a a concentration of at least 500 ppm. The preferred amine is triethanol amine (TEA). The preferred mass ratio of diacid (for example, sebacic) to amine is at least 1: 1. An increase in sebacic acid / TEA concentrations does not provide corrosion inhibition in all synthetic waters. The worst protection is in synthetic waters AGG, AGG * and A / Fe. As shown in Table I I, in TRV and CR waters, sebacic acid / TEA at 500 ppm / 500 ppm provides good corrosion protection, ie, less than 0.05 mpy, in such waters. This is in contrast to its performance in waters AGG, AGG * and A / Fe; in these waters, corrosion protection is in the order of more than 38 mpy. Phosphonates are known to be useful corrosion inhibitors. However, as shown in Table I I, none of the phosphonates tested offered effective corrosion protection for the CR water. The performance in the other synthetic waters was less effective than the commercial brand of comparison; Increasing their concentration did not radically change performance, especially in CR water.

Table I I I Corrosion rates measured in waters as defined in the text, units of mils per year (mpy) for low carbon steel metallurgy for the synergistic mixtures of phosphonates and diacids / amine.

As shown in Table I I, it was found that the combination of organic diacid / triamine with any of the four phosphonates tested provided excellent corrosion protection in all synthetic waters, when sebacic acid / triethanolamine are at least 500 ppm each and the phosphonates are at least 50 ppm as active. The performance achieved at the aforementioned concentrations in synthetic waters AGG, AGG * and A / Fe is unexpected can be explained by a synergistic effect of the mixtures. Please note that none of the individual components can provide more than 90% protection in that pool of waters, and the combination provides protection equal to or greater than 99.9%. Table IV further demonstrates the unexpected results of the diacid / amine / phosphonate combination, where a comparison of the corrosion rates in mpy is presented as measured and predicted. The predicted corrosion rate is: a) the calculated average of the corrosion rates of the individual phosphonate and diacid / amine inhibitors, b) the corrosion rate com obtained with the one that performs better of the two, and c) the Assumption calculated from a decrease in the corrosion rate of the one that performs best as the reduction in the corrosion rate between the control water and the same treated by the other inhibitor.

Table IV Phosphonate A 50 ppm, sebacic acid 500 ppm triethanol amine 500 ppm Phosphonate B 50 ppm, sebacic acid 500 ppm, triethanol amine 500 ppm Phosphonate C 50 ppm, sebacic acid 500 ppm, triethanol amine 500 ppm Phosphonate D 50 ppm, sebacic acid 500 ppm, triethanol amine 500 ppm As shown in Table IV, none of the predictions can answer for the measured results. The closest one is the prediction by method c), but even by this prediction, the corrosion rate is still at least 30 times greater than any of the measurements. In a preferred embodiment, from about 200-1,000 ppm of sebacic acid, about 200-1,000 ppm of triethanolamine and about 25-100 ppm of polyisopropenyl phosphonic material can be added to the system in need of treatment. The polyisopropenyl phosphonic material can be made in organic solution or aqueous medium. Although this invention has been described with respect to the particular embodiments thereof, it is evident that numerous other forms and modifications of this invention will be obvious to those skilled in the art. The appended claims in this invention should generally be construed to cover such obvious forms and modifications, which are within the true spirit and scope of the present invention.

Claims (9)

REIVI N DICACIONES

1 . A method for inhibiting corrosion on metal surfaces in contact with a fluid contained in a closed circuit industrial fl uid system, which comprises adding to said fluid an effective corrosion controlling amount of a combination of an organic diacid, a triamine and a phosphonate.

2. The method as recited in claim 1, wherein said diacid is sebacidic acid.

3. The method as recited in claim 1, wherein said triamine is triethanolamine.

4. The method as set forth in claim 1, wherein the phosphonate is? ,? -dihydroxyethyl? ' ,? '- diphosphonomethyl 1,3-propanediamine, N-oxide or 1,6-hexamethylenediamine-N, N, N', N'-tetra (methylene phosphonic acid). The method as set forth in claim 1, wherein the phosphonate is a polyisopropenyl phosphonic material. 6. The method as set forth in claim 1, wherein said fluid system is a closed circuit, aqueous heat exchanger system. The method as set forth in claim 1, wherein said fluid system is a low pressure boiler system. 8. The method as recited in claim 1, wherein said fl uid system is a gas scrubber or air scrubber system. 9. The method as claimed in claim 1, wherein said Fluid system is a cooling and air conditioning system. The method as set forth in claim 1, wherein said fluid system is employed in fire protection of construction and water heating systems. eleven . The method as set forth in claim 1, wherein said combination is added to said fluid in an amount from about 2,000-10,000 ppm of fluid. The method as set forth in claim 2, wherein from about 200-1,000 ppm of sebacic acid is added to the fluid. The method as set forth in claim 3, wherein from about 200-1,000 ppm of triethanolamine is added to the fluid. 14. The method as set forth in claim 5, wherein from about 200-1,000 ppm of polyisopropenyl phosphonic material is added to the fluid. The method as set forth in claim 5, wherein the polyisopropenyl phosphonic material can be made in organic solution or aqueous medium.