DK169709B1 - Corrosion Inhibition Method - Google Patents

Abstract

A composition and the use of the composition for inhibiting corrosion in industrial cooling waters which contain hardness and have a pH of at least 8, which composition comprises a water-soluble organic phosphonate capable of inhibiting corrosion in an aqueous alkaline environment and a co- or terpolymer of acrylic acid and certain substituted acrylamides such as t-butyl acrylamide.

Description

X

DK 169709 B1

The invention relates to a method for inhibiting corrosion in industrial cooling water having a relatively high hardness and a pH of at least 8.

The term "phosphonate" refers to organic matter containing 1 or more -PO 2 groups and salts thereof.

Phosphonates particularly useful in the invention include 1-hydroxy-1,1-ethane diphosphonic acid (HEDP), 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTC), amino-tris-methylene phosphonic acid (AMP) and their salts. The concentrations and dosage levels and / or ranges of polymers, phophonates and agents are listed in their active states.

Corrosion occurs when metals are oxidized to their corresponding ions and / or insoluble salts. For example.

For example, corrosion of metallic iron may involve conversion 20 to soluble iron in an oxygenation step of +2 or +3 or to insoluble iron oxides and hydroxides. Corrosion also has a two-sided nature in the sense that part of the metal surface is removed, while the formation of insoluble salts contributes to the formation of precipitates. Metal loss produces degradation of the structural integrity of the system. Finally, leakage may occur between the water system and the process streams.

It is known that corrosion of iron in oxidizing water masses occurs according to the following interconnected electrochemical processes: (1) Fe ° ---> Fe + 2e ~ (anodic reaction) ( 2) ° 2 + + e ~ -> 20H_ (cathodic reaction)

Inhibition of metal corrosion by oxidizing water masses typically involves the formation of protective barriers on the metal surface. These barriers prevent oxygen from reaching the metal surface and produce metal oxidation. In order to act as a corrosion inhibitor, a chemical additive must promote this process in such a way as to create and maintain an oxygen-impermeable barrier. This can be done by interacting with either the cathodic or anodic half-cell reaction.

Inhibitors can affect the anodic reaction 1 by causing 2+ 15 of the resulting Fe to form an impermeable barrier, thereby preventing further corrosion. This can be done by incorporating constituents into the inhibitor compound, which: reacts directly with Fe, thereby precipitating 2+ 3+ precipitates, facilitating the oxidation of Fe to Fe, whose 20 compounds are typically less soluble, or promoting 3+ formation of insoluble compounds of Fe.

The reduction of oxygen by corrosion cathodes provides another means by which inhibitors can function. Reaction 2 represents the half-cell in which oxygen is reduced during the corrosion process. The product of this reaction is the hydroxyl ion (OH). Due to hydroxyl production, the pH of the surface of metals subjected to corrosion from oxygen is generally much higher than that of the surrounding medium. Many compounds are less soluble at higher pH values. These compounds can precipitate by corrosion cathodes and act as effective inhibitors of corrosion if their precipitated form is impermeable to oxygen and is electrically nonconductive.

Corrosion inhibitors function by creating an environment in which the corrosion process induces inhibitory reactions to the metal surface. In order for an inhibitory agent to function effectively, the components of the agent must not settle under the conditions prevailing for most of the medium. Inhibitors that effectively inhibit this precipitation by kinetic inhibition have been extensively described in the literature. An example of this type is U.S. Patent No. 3,880,765, which describes the use of polymers to prevent calcium carbonate precipitation.

The use of inorganic phosphates and phosphonates in conjunction with a threshold inhibitor to control corrosion resulting from oxidizing water masses is described in U.S. Patent No. 4,303,568. This method is further described in U.S. Patent No. 4,443,340, which describes , that a mixture comprising exclusively inorganic phosphates and a polymeric inhibitor has good properties in the presence of dissolved iron.

20

Corrosion inhibition can be achieved by a combination of the use of inhibitors and modification of the chemistry of the medium. U.S. Patent No. 4,547,540 discloses a method of corrosion inhibition comprising operating under conditions comprising high pH and alkalinity. This method does not depend on the use of inorganic phosphates, since it provides a product which is more desirable from an environmental point of view.

30 In FR patent specification No. 1 598 419, a process for preventing scaling and corrosion in cooling water systems is described, which consists in supplying such systems with an agent containing a water-soluble organic polymer and an organic phosphonic acid derivative. An example of a water-soluble polymer is mentioned, among others. a. acrylamide / acrylic acid copolymers.

DK 169709 B1 4 FR patent specification No. 2,235,205 discloses a method of preventing scaling and corrosion in water supply pipes, which method involves introducing at least one phosphonecarboxylic acid into such pipes and another compound, such as a polyacrylamidde derivative.

DE Patent No. 3,001,500 discloses a corrosion inhibiting composition based on a water-soluble phosphonic acid, a water-soluble polymer of acrylic acid, methacrylic acid, maleic or maleic anhydride, and tolyl triazole. An example of a water-soluble polymer is mentioned copolymers of acrylic acid and acrylamide.

The use of polymers with tert-butyl acrylamide groups is not known from any of these publications.

The present invention relates to the use of phosphonate-containing corrosion inhibiting agents containing a unique combination of polymers, phosphonates and the optional use of aromatic azoles. The use of these polymers results in significantly improved properties of corrosion inhibitors.

The use of the copolymers as inhibitors of scales is discussed in U.S. Patent No. 4,566,973. The use of copolymers containing tert.-butyl-acrylamide units is known, but in connection with other comonomers. It has now been found that copolymers containing tert-butalacrylamide units in combination with calcium phosphonate inhibitors are effective and that they function effectively as components of a phosphonate-containing corrosion inhibitor.

The method according to the invention, which is of the kind set forth in the preamble of claim 1, is characterized by a feature as defined in the characterizing part of claim 1.

DK 169709 B1 5

In general, any water-soluble phosphonate capable of providing corrosion inhibition in alkaline systems can be used. In U.S. Pat.

5 4 303 568 there is a list of a number of representative phosphonates.

The organophosphonic acid compounds are those having a carbon-to-phosphorus bond, ie.

10 0

II

-C-P-OM

15 OM

Compounds which are within the scope of the foregoing description are generally comprised of one of perhaps three categories represented by the following general formulas: 0

II

R-P-OM

25 I

ABOUT

wherein R is lower alkyl having from 1 to 6 carbon atoms, for example methyl, ethyl, butyl, propyl, isopropyl, pentyl, isopentyl and hexyl; substituted lower alkyl having from 1 to 6 carbon atoms, for example hydroxyl and amino substituted alkyls; a mononuclear aromatic (aryl) radical, e.g., phenyl, benzene, etc., such as a substituted mononuclear aromatic compound, e.g., hydroxyl, amino, (lower alkyl) -substituted aromatics, e.g. eg benzyl phosphonic acid; and M is a water-soluble cation, e.g., sodium, potassium, ammonium, lithium, etc., or hydrogen.

DK 169709 B1 6

Specific examples of compounds encompassed by this formula include: methylphophonic acid CHgPOgl ^ ethylphophonic acid CH3CH2PO3H2 2 -hydroxyethylphosphonic acid CH2 -CH2-PO3H2

10 I

OH

2-amino-ethylphosphonic acid CH2-CH2 ~ PO3H2 NH2 isopropylphosphonic acid CH3 CH3-CH-CH2-PO3H2 benzene-phosphonic acid CgHg-PO3H2 benzylphophonic acid CgHgCH2PO3H2 25 0 0

II II

M0-P - R 1 - P-0M

I I

OM OM

Wherein is an alkylene having from 1 to 12 carbon atoms or a substituted alkylene having from 1 to 12 carbon atoms, e.g. hydroxyl, amino, etc. substituted alkylenes, and M is as previously defined.

Specific exemplifying compounds and their respective formulas encompassed by the above formula are as follows: methylene-diphosphonic acid 5 ethylidene-diphosphonic acid H2O3P-CH (CH2) POg ^ isopropylidene-diphosphonic acid (CHg) 2C (PO t 2) 2 1-hydroxy, ethylidene-diphosphonic acid (HEDP) 10

OH

H203P-C (CH3) -PO3H2 hexamethylene diphosphonic acid H2 ° 3P-CH2 ^ CH2 ^ 4CH2 ** PO3H2 trimethylene diphosphonic acid H2 ° 3P_ (CH2) 3 "PO3H2 decamethylene diphosphonic acid H2 ° 3P" (CH2) iq ~ p0H 1-hydroxy, propylidene diphosphonic acid h2o3pc (oh) ch2 (ch3) po3h2 1,6-dihydroxy, 1,6-dimethyl, hexamethylene diphosphonic acid h2o3pc (ch3) (oh) (ch2) 4c (ch3) (oh) po3h2 dihydroxy, diethyl-ethylene diphosphonic acid 30 H 2 O 3 PC (0Η) (C 2 H 5) C (0Η) (C 2 H 5) PO 2 35 DK 169709 B1 8 0 R "R3

N-R 2 ~ P-ON

R 4 is wherein R 2 is a lower alkylene having from 1 to 4 carbon atoms, or an amine or hydroxy substituted lower alkylene; R 1 is [R2-P0 M 2] H, OH, amino, substituted amino, an alkyl of from 1-6 carbon atoms, a substituted alkyl of from 1-6 carbon atoms (e.g. OH, NH2 substituted) a mononuclear aromatic radical and a substituted mononuclear aromatic radical (e.g., OH, NH 2 substituted); R 2 is R 2 or the group represented by the formula rL) ° 1 3

C-N --- R-P-OM

I I I

20 R6 "RVy 0M

wherein Rg and Rg are each hydrogen, lower alkyl having from ca. 1-6 carbon atoms, a substituted lower alkyl (e.g. OH, NH 2 substituted), hydrogen, hydroxyl, amino group, substituted amino group, a mononuclear aromatic radical, and a substituted mononuclear aromatic radical (e.g. OH and amine substituted); R is Rg, Rg or the group R2 ~ PO2M2 (R2 is as defined hereinbefore); n is a number from 1 to approx. 15; Y is a number from approx. 1 to approx. 14, and M is as previously defined.

Compounds or formulas which may be considered exemplary of the previously mentioned formulas are therefore as follows: nitrilo-tri (methylene-phosphonic acid) N (CH2 PO3H2) DK 169709 B1 9 imino-di (methylene-phosphonic acid) NH (CH2PO3H2) 2 n-Butyl-amino-di (methyl-phosphonic acid) C ^HgN (CH₂PO3H₂) decyl-amino-di (methyl-phosphonic acid) cioH₂NN₂CH₂PO0H₂₂-2-triina-pentadecyl-amino-dimethyl-phosphate C15HH31NN (CH2PO3HNa) (CH2PO3Na2) n-butyl amino-di (ethyl phosphonic acid) c4h9n (ch2CH2PO3h2) 2 tetrasodium-n-butyl amino-di (methyl phosphate) C4H9N (CH2 PO3Na2) 2 triammonium amino tetradecyl di (methyl phosphate) C 14 H 29 N (CH 2 PO 3 (^ 45 2) CH 2 PO 3 HNH 4 phenylamino-di (methylphosphonic acid) CgH 2 -N (Cl 2 POgH 2) 2 4-hydroxy-phenylamino-di (methyl-phosphonic acid) hoc6h4n (ch2po3h2) 2 phenyl-propylamino-di (methyl-phosphonic acid) C6H5 (CH2) 3N <CH2PO3H2) 2 tetrasodium-phenyl-ethyl-amino-di (methyl-phosphonic acid) C6H5 ^ CH22N ^ CH2PO3Na2 ^ 2 DK 169709 B1 10 ethylenediamine tetra (methylphosphonic acid) (h2o3pch2 ) 2n (ch2) 2n (ch2po3h2) 2 trimethylenediamine tetra (methylphosphonic acid) (H2O3PCH2) 2N (CH2) 3N (CH2PO3H2) 2 heptamethylenediamine tetra (methylphosphonic acid) 10 (H2O3PCH2) 2N (CH2)? N ( CH2PO3H2) 2 decamethylenediamine tetra (methylphosphonic acid) (H2O3PCH2) 2N (CH2) 10N (CH2PO3H2) 2 tetradecamethylenediamine tetra (methylphosphonic acid) (H2 ° 3PCH2) 2N (CH2> 14N (CH2PO3H2) 2 (methylphosphonic acid) (h2o3pch2) 2n (ch2) 2nhch2po3h2 ethylenediamine di (methylphosphonic acid) (h2o3pch2) 2nh (ch2) 2nhch2po3h2 n-hexylamine di (methylphosphonic acid) C6H13N2 CH2 penta (methyl-phosphonic acid) (H 2 O 3 PO 2) 2N (CH 2) 2N (CH 2 PO 3 H 2) - (CH 2) 2 N (.CH 2 PO 3 H 2) 2 ethanolamine-di (methyl-phosphonic acid) DK 169709 B1 11 HO (CH 2) 2 N (CH 2 PO 3 H 2) 2 n -hexylamino (isopropylidene-phosphonic acid) methylphosphonic acid C6H13N (c (ch3) 2po3h2) (ch2po3h2) trihydroxymethyl, methylamine-di (methylphosphonic acid) 10 (hoch2) 3cn (ch2po3h2) 2 triethylene-tetraamine-hexa -phosphonic acid) 3.5 (h2o3pch2) 2n (ch2) 2n (ch2po 3h2) (ch2) 2n- (CH2PO3H2) (CH2) 2N (CH2PO3H2) 2 monoethanol, diethylene triamine tri (methylphosphonic acid) HOCH2CH2N (CH2PO3H2) (CH2) 2NH (CH2) 2N- (C 2 chloroethylenamine-di (methylphosphonic acid) cich2ch2n ((ch2po (OH) 2) 2

The aforementioned compounds are given for illustrative reasons and it is not intended that they constitute a complete list of the compounds which may be used within the scope of the invention.

30

The preferred phosphonates are the two compounds: A. 2-Phosphonbutane-1,2,4-tricarboxylic acid and B. 1-Hydroxyethane-1,1-diphosphonic acid.

Although individual phosphonates can be used, in combination with polymer (s), far better results have been obtained by using a mixture of phosphonates such as A and B. When combined, it is in a weight ratio A: B from 0.5 / 1-4 / 1 and preferably from 0.5 / 1-2 / 1, in particular approx. 0.67 / 1st

In addition to phosphonates, such additives as tolytriazole can be used. Tolytriazole can effectively reduce copper substrate corrosion.

The water-soluble, non-crosslinked, randomized copolymers are described in detail in U.S. Pat.

No. 4,566,973, and specifically, those described by the patent holder are as follows:

The copolymers suitable for the invention are randomized polymers containing polymerized units of an acrylic acid and substituted acrylamide, represented by the following structural formula 1: * R1 4CHr_C) -m ^ h 2 -_; L> ert._butyl

0 = C "QX 0 = C - N

t-butyl 25 where m and n are numbers between 0.1 and 700, where m is in the range of 10 to 700 and n is in the range of 0.1 - 350, where there are also molecular weight constraints; R and R "are individually selected from hydrogen 30 and methyl; X is hydrogen, potassium, calcium, ammonium and magnesium.

Suitable acrylic acids for the purposes of this invention are generally defined as monounsaturated monocarboxylic acids containing from 3 to 4 carbon atoms. Specific examples of such acids include acrylic and methacrylic acids, with acrylic acid being particularly preferred.

DK 169709 B1 13

Other comonomers may be used with an acrylic acid and a substituted acrylamide, provided that such additional comonomers do not adversely affect the desired properties. Examples of such comonomers include acrylate and methacrylate esters, acrylamide and methacrylamide, acrylonitrile, vinyl esters, etc.

The acrylic acid moieties of the copolymer may be present on sieve reform or in a neutralized form, wherein the hydrogen atom in the carboxyl group is replaced by an alkali metal, an alkaline earth metal or an ammonium cation, depending on the neutralizing medium. Generally, the copolymers can be neutralized with a highly alkaline material such as sodium hydroxide, in which case the hydrogen or carboxyl group of the acrylic acid units will be replaced with sodium. Using an amine neutralizing agent, the hydrogen atom will be replaced by an ammonium group. Applicable copolymers include copolymers that are unneutralized, partially neutralized and completely neutralized.

Polymerization of the monomers results in a substantially non-crosslinked, randomized copolymer whose molecular weight can be adjusted by a less routine experimental work. The copolymer is preferably prepared in a high yield which is between about 50 and approx. 99% by weight of the comonomers.

The polymers of the type described above can be modified by incorporating in their structure up to 30% by weight of thermonomers containing a nonionic or anionic polar group preferably selected from amido, lower alkyl ester and maleinsyresaltgrupper.

Examples of preferred monomers which can be polymerized to form terpolymers are acrylamide, methyl, or ethyl acrylate, maleic anhydride. Other polar monomers which may be used are, for example, vinyl acetate, acrylonitrile, the various vinyl ketones, vinyl ethers and the like. Illustrative examples of these monomers are the compounds: vinyl pyrrolidone, methyl vinyl ether, methacrylonitrile, alkyl alcohol, methyl methacrylate, beta-diethylaminoethyl methacrylate, vinyl trimethyl acetate, methyl isobutyrate, cyclohexyl methacrylate, vinyl laurate, vinyl laurate, vinyl laurate, vinyl laurate, vinyl laurate vinyl lactamer, diethylene glycol dimethacrylate, di-allyl maleate, allyl methacrylate, diallyl phthalate, diallyl adipate, etc.

The polymers formed must have an average molecular weight by weight in the range of 1000 to 50,000, and preferably 2000 to 30000, determined by aqueous gel permeation chromatography using polystyrene of known molecular weight as a reference material.

The acid numbers of the copolymers formed, determined by conventional titration with KOH, are from 310 to 740, corresponding to a weight fraction of from 40 to 95% by weight of monomer units having C00H groups. The preferred polymers have more than 50 wt% free carboxyl groups and an acid number between 390 and 700.

25

Preferred materials are described in Table A below as polymer blends Nos. 1-12.

30 35 DK 169709 B1 15

Table A

Polymeric Materials 5 Polymer

Material No. M.W. Material, mole% 1 9300 AA / t-BAm 88:12 2 12000 3 17700 10 4 25900 5 8900 AA / EA / t-BAm 86: 8: 6 6 9400 AA / Am / t-BAm 84: 11: 6 15 ------------------------------------------------- ------- 7 8200 AA / MAA / t-BAm 68:19:13 8 13300 * 9 14300 * "10 15700 * 20 11 15600 12 23000

Average molecular weight by weight, ie. W., or Mw · 25 * Aqueous M evaluated based on the value of GPC below

W

using THF as eluent.

Polymer blends # 1-4 are unneutralized copolymers 30 of acrylic acid and t-butyl acrylamide (t-BAm). Polymer Blend # 5, Polymer Blend # 6 and Polymer Blend #

7 are terpolymers containing the additional mer units ethyl acetate (EA), acrylamide (Am) and methacrylic acid (MAA), respectively.

A distinguishing feature of all these polymers is the t-butyl acrylamide moiety. This sterically hindered hydrophobic alkylamide group exhibits excellent resistance to hydrolysis and the unit appears to confer exceptional properties.

The copolymers consisting of acrylic acid and t-butyl acrylamide contain between 50 and 90 wt% acrylic acid and from 10-50 wt% t-butyl acrylamide. Preferably, the acrylic acid is present in a weight percent ranging from 70-90, whereby the t-butyl acrylamide is present in an amount between 10-30.

In the most preferred case, the acrylic acid is present in a weight% ranging from 80-90, with the t-butyl acrylamide present in an amount between 10-20.

The terpolymers are within the following ranges of 15% by weight: a) acrylic acid 40-90, especially 40-80 and especially 60-80 b) methacrylic acid 5-30, especially 10-30 and in particular 10-20 20 c t-butyl acrylamide 5-50, in particular 10-30 and in particular 10-20

The aqueous system is dosed on the basis of active ingredients so that on the weight basis the substrate is obtained from between 5-50 ppm, preferably 8-40 ppm, especially 15-30 ppm of mixtures I and II, as previously described.

When the mixtures are first added, it is advantageous if dosed on the high side to control the corrosion and to begin the formation of protective films. After about a week, the doses can be reduced until an optimal maintenance dose is established.

The systems being treated are once-through-flow industrial recycled water or cooling water which, either due to their natural composition or at pH adjustment, has a pH of at least 8. Preferably, the pH of systems within the range of 8-9.5, and most often within the range of 8.5-9.2. These systems are characterized as containing at least 10 ppm calcium ion 5 and are believed to be corrosive to ferrous metals as well as non-ferrous metals with which they come into contact.

The following example is a representative wording used in this program.

10

Example 1

To a glass or stainless steel container is added 14 g of soft water. With stirring, 15 aqueous solutions of the following materials are consecutively added: 7 g of 1-hydroxyethane-1,1-diphosphonic acid (60% by weight) 12 g of 2-phosphonobutane-1,2,4-tricarboxylic acid (50% by weight) , 3 g of acrylic acid / t-butyl acrylamide copolymer (49% by weight).

The mixture was cooled in an ice bath and then basified by the slow addition of ca. 22 g aqueous sodium hydroxide (50 wt%) to the solution with vigorous stirring. During the addition of the base, the temperature of the solution was kept below 54 ° C. The pH was adjusted to 13 with 4.7 g of a 50 wt% of a solution of sodium tolyl triazole. Finally, softened water was added in a quantity sufficient to produce 100 g of product. The cooling bath was removed and the solution kept under stirring until the temperature was equal to ambient temperature.

Changes to the formulation are easily made by simple modification of the method described above. For example, a reduction in the amount of polymer and sodium hydroxide, followed by increasing the final amount of added water, will produce a formulation containing lower active polymeric constituents. Alternatively, the polymeric and corrosion inhibitors may be added separately, 5

In laboratory experiments, hardness-forming cations M and alkalinity are expressed as CaCO 3 or cycles of concentration.

Fe + n is listed as Fe, and inhibitors (monomers and polymers) are listed as active substances. In analyzes of precipitates of heat exchangers, all components are listed as weight percent of the chemical element or of the acid form of the compound.

A standard "beaker" sample 15 was used to evaluate the properties of phosphonate inhibitors.

(Table B). Calcium and inhibitor stock solutions from the calcium phosphate inhibition sample were used. In addition, stock solutions (1000 ppm of active substances) were prepared by Bayer PBS-AM and Dequest 2010 Dequest-2010, manufactured by Monsanto Company, St. Louis, Missouri, is described as hydroxyethylidene-1,1-diphosphonic acid (HEDP) (cf. U.S. Patent No. 3,959,168). PBS-AM is a trademark of Bayer for 2-phosphonobutane-1,2,4-tricarboxylic acid. When starting the sample, add distilled water (400 ml) 25 to the sheathed cups held at 60 τ 2 ° C. The stock solutions were added to obtain 360 ppm • 2

Ca ', 10 ppm inhibitor, 5.6 ppm Dequest and 8 ppm PBS-AM in the final 500 ml test volume. Next, the pH was adjusted to 9.2 using aqueous sodium hydroxide.

The pH values in the test samples were manually set at 15 minute intervals during the first hour and then at 1 hour intervals. A duration of the sample of four 35 hours was sufficient to stabilize these precipitation reactions. Finally, part of each sample solution was passed through a Millipore filter of type DK 169709 B1 19 cellulose acetate / nitrate (type HA, 0.45 µm). Both filtered and non-filtered aliquots were spectrophotometrically analyzed for total phosphate content. To study the side effects of the particles, a further sample was passed through a 0.10 µm Millipore filter (type VC). The percent inhibition was determined using the following formula: [filtered - control] 10% inhibition --------------------------- X 100 [unfiltered - control] 15 20 25 30 35 DK 169709 B1 20

Table 8

Calcium phosphonate inhibition 5 10 ppm polymer active substances 5.6 ppm Dequest 2010 and 8 ppm Bayer PBS-AM (as active substances) 360 pm Ca (as CaCOg) 60 ° C / pH 9.2 / 4 h.

10% inhibition

Polymer ... filter size (thawed) ...

Compound No. (M.W. H 2 O) 0.45_0.10_ 1 (9300) 82% 26 15 5 (8900) 74 24 6 (9400) 8 13 11 (15600) 98 58

Versa TL-4 (19000) 95 26 20

In the calcium phosphonate inhibition tests, the properties of the polymer versus particle size of the precipitate were investigated and the results are represented in Table B.

The "calcium phosphonate" inhibition "process involves minimizing particle growth. Retention of scale particles at a very small particle size and mass may ultimately prove to be a critical factor in determining polymer properties. By using filters with average pore sizes of 0.10 and 0.45 µm, differences in polymer properties could be easily observed. Polymer blend # 11 (molecular weight = 15,600), as a whole, considered the best properties and was the only polymer to exhibit good inhibition when using a 0.10 wm filter. Versa TL-4 (the low molecular weight copolymer of sulfonated styrene and maleic acid) DK 169709 B1 21 and polymer blend Nos. 1 and 5 showed excellent inhibition (0.45 µm filter), but the properties deteriorated rapidly when the size of the filter pores was reduced to 0. 10 pm In particular, polymer blend # 11 as a whole showed the best properties, both in the "bench-top" and PCT samples.

The pilot-type cooling tower test is a dynamic test that simulates many features of an industrial system with recirculating cooling water. The general test method is described in the article "Small-Scale Short-Term Methods of Evaluating Cooling Water Treatments ... Are They Worthwhile?", By DT Reed and R. Nass, Minutes of the 36th Annual Meeting of the INTERNATIONAL WATER CONFERENCE, 15 Pittsburgh, Pennsylvania, November 4-6, 1975.

The general operating conditions are summarized in Table C.

20 25 30 35 DK 169709 B1 22

Table C

Operating conditions in pilot plant cooling tower size 5 Pipes # Metal * / Heat load (Btu / ft2-h) 8 MS / 15,000 (top) 7 SS / 15,000 6 MS / 12,400 5 Adm / 5,000 10 4 MS / 5,000 3 SS / 12,400 2 Adm / 12,400 1 SS / 12,400 (bottom) 15 Supply water: Synthetic # 31 Desired Cycles: 4

Basin volume / temp.2 '50 1/52 ° C

Hold time index 24 h

Flow rate 7.56 l / min pH 9.2

Product - high level 200 ppm

Product maintenance 100 ppm

Duration of sample 14 days 25 * MS = soft steel

Adm = Special brass SS = 306 stainless steel

Synthetic # 3 contains a total ion content of 90 + 2 + 2 - 30 ppm Ca, 50 ppm Mg, 90 ppm Cl, 50 ppm sulfate, 110 ppm Na + and 110-120 ppm "M" alkalinity (as CaCO 2) · 2

Return water is 5.6 eC higher. Polymer blends Nos. 1, 3, 5, 6, 7 and 11, as described in Table D, were prepared according to Example 1 and were used to directly replace VTL-4 in the standard high formulation formulation. pH. Prolonged stability testing (49 ° C / pH 13) for these formulations carried out in DK 169709 B1 23 according to the method of Example 1, but containing polymer blends # 1, 6 or 11, revealed that no hydrolysis of the polymer over a 3 month period. The PCT precipitation / corrosion rates are summarized in the following Table D.

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In some cases it has been recommended to add small amounts of tolytriazole.

Tolytriazole is explained in Hackh's Chemical Dictionary, 5th Edition, page 91 (cf. benzotriazole) and is used as a corrosion inhibitor for copper and copper alloy surfaces in contact with water; when used, it is used in the system at a dose between 1 and 20 ppm by weight.

10 15 20 25 30 35

Claims (7)

A method of inhibiting corrosion in aqueous systems having a degree of hardness and a pH of at least 8, characterized in that a mixture is dosed into this system comprising: 1. a water-soluble organic phosphonate capable of to inhibit corrosion in an aqueous, alkaline environment, and II. a water-soluble, non-crosslinked randomized polymer of 50-90 parts by weight of an acrylic acid and 10-50 parts by weight of a substituted acrylamide, based on a total of 100 parts by weight of polymerized monomers, which polymer has an average molecular weight in the range of 1000-50000 and an acid number of 310-740, whereby the polymerized units of an acrylic acid and a substituted acrylamide are defined by the following formula: P1 ii - "tert -butyl I 1/25 0 = C - OX 0 = C - N -butyl where m is a number from 10-700 and n is a number from 0.1-350, 30 limited by the specified molecular weights, R and R 1 are individually selected from hydrogen and methyl, X is selected from hydrogen, sodium, potassium, calcium, ammonium and magnesium, whereby the weight ratio of polymer: phosphonate is in the range of 0.2 / 1 to 35 2/1. Process according to claim 1, characterized in that the phosphonate is a mixture of 2-phosphonobutane-1,2,4-tricarboxylic acid and 1-hydroxyethane-1,1-diphosphonic acid. The method according to claim 1 or 2, characterized in that the randomized polymer further contains up to 30% by weight of a thermonomer containing either an anionic or a non-anionic group. Process according to claim 3, characterized in that the polymer is a terpolymer of acrylic acid, methacrylic acid and tert-butyl acrylamide and the phosphonate is selected from 1-hydroxyethane-1,1-diphosphonic acid and 2-phosphonbutane-1. , 2,4-tricarboxylic acid. 15 Process according to claim 3, characterized in that the terpolymer has an average molecular weight of 9000-30000. Process according to claims 1-5, characterized in that the mixture further comprises tolyltriazole in an amount which acts as a corrosion inhibitor. Process according to claims 1-6, characterized in that the aqueous system is dosed 5-50 ppm, preferably 8-30 ppm, of the mixture. 30 35