EP0238728B1 - Corrosion inhibiting - Google Patents

Corrosion inhibiting Download PDF

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EP0238728B1
EP0238728B1 EP86118127A EP86118127A EP0238728B1 EP 0238728 B1 EP0238728 B1 EP 0238728B1 EP 86118127 A EP86118127 A EP 86118127A EP 86118127 A EP86118127 A EP 86118127A EP 0238728 B1 EP0238728 B1 EP 0238728B1
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acid
weight
corrosion
polymer
composition according
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EP0238728A1 (en
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John E. Hoots
Donald A. Johnson
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ChampionX LLC
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Nalco Chemical Co
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    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23F—NON-MECHANICAL REMOVAL OF METALLIC MATERIAL FROM SURFACE; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL; MULTI-STEP PROCESSES FOR SURFACE TREATMENT OF METALLIC MATERIAL INVOLVING AT LEAST ONE PROCESS PROVIDED FOR IN CLASS C23 AND AT LEAST ONE PROCESS COVERED BY SUBCLASS C21D OR C22F OR CLASS C25
    • C23F11/00—Inhibiting corrosion of metallic material by applying inhibitors to the surface in danger of corrosion or adding them to the corrosive agent
    • C23F11/08—Inhibiting corrosion of metallic material by applying inhibitors to the surface in danger of corrosion or adding them to the corrosive agent in other liquids
    • C23F11/10—Inhibiting corrosion of metallic material by applying inhibitors to the surface in danger of corrosion or adding them to the corrosive agent in other liquids using organic inhibitors

Definitions

  • the invention concerns the use of a composition for inhibiting 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 t-butyl acrylamide.
  • Phosphonates refers to organic materials containing one or more -POsH 2 groups and salts thereof.
  • Phosphonates particularly useful in this invention include i-hydroxy-i, i-ethane diphosphonic acid (HEDP), 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTC), amino-tris-methylenephosphonic acid (AMP), and their salts.
  • HEDP i-hydroxy-i, i-ethane diphosphonic acid
  • PBTC 2-phosphonobutane-1,2,4-tricarboxylic acid
  • AMP amino-tris-methylenephosphonic acid
  • Corrosion occurs when metals are oxidized to their respective ions and/or insoluble salts.
  • corrosion of metallic iron can involve conversion to soluble iron in a 2+ or 3+ oxidation state or insoluble iron oxides and hydroxides.
  • corrosion has a dual nature in that a portion of the metal surface is removed, while the formation of insoluble salts contributes to the buildup of deposits. Losses of metal cause deterioration of the structural integrity of the system. Eventually leakage between the water system and process streams can occur.
  • Inhibition of metal corrosion by oxygenated waters typically involves the formation of protective barriers on the metal surface. These barriers prevent oxygen from reaching the metal surface and causing metal oxidation.
  • a chemical additive In order to function as a corrosion inhibitor, a chemical additive must facilitate this process such that an oxygen-impermeable barrier is formed and maintained. This can be done by interaction with either the cathodic or anodic half-cell reaction.
  • Inhibitors can interact with the anodic reaction 1 by causing the resultant Fe 2 + to form an impermeable barrier, stifling further corrosion. This can be accomplished by including ingredients in the inhibitor compound which: react directly with Fe 2+ causing it to precipitate; facilitate the oxidation of Fe 2+ to Fe 3 +, compounds of which are typically less soluble; or promote the formation of insoluble Fe 3+ compounds.
  • Reaction (2) represents the half-cell in which oxygen is reduced during the corrosion process.
  • the product of this reaction is the hydroxyl (OH-) ion. Because of hydroxyl production, the pH at the surface of metals undergoing oxygen-mediated corrosion is generally much higher than that of the surrounding medium. Many compounds are less soluble at elevated pH's. These compounds can precipitate at corrosion cathodes and act as effective inhibitors of corrosion if their precipitated form is impervious to oxygen and is electrically nonconductive.
  • Corrosion inhibitors function by creating an environment in which the corrosion process induces inhibitive reactions on the metal surface.
  • the components of the composition must not precipitate under the conditions in the bulk medium.
  • Inhibitors which effectively inhibit this precipitation by kinetic inhibition have been extensively described in the literature.
  • An example of this art is US-A 3 880 765 which teaches the use of polymers for prevention of calcium carbonate prepitation.
  • Corrosion inhibition can be achieved by a combination of the use of inhibitors and modification of the chemistry of the medium.
  • US-A 4 547 740 teaches a method of corrosion inhibition relying on operation under conditions of high pH and alkalinity. This method does not rely on the use of inorganic phosphates, giving a more desirable product from an environmental impact point of view.
  • Said copolymers in connection with threshold inhibition of salt-forming scales and dispersion of particulate matter find usage as scale inhibitors - but not as corrosion inhibitors.
  • FR-A 1 598 419 The subject matter of FR-A 1 598 419 is the inhibition of scale formation and corrosion by using a water-soluble polymer and a phsophonate, with a considerable amount of homopolymers and copolymers being stated for the water soluble polymer. Despite that enormous number of polymer classes the copolymers of acrylic acid with the specifically substituted acrylamide according to the invention cannot be seen from this cited reference.
  • composition for inhibiting corrosion in industrial cooling waters which contain hardness and have a pH of at least 8 which composition comprises:
  • any water-soluble phosphonate may be used that is capable of providing corrosion inhibition in alkaline systems. See US-A 4 303 568 which lists a number of representative phosphonates.
  • the organo-phosphonic acid compounds are those having a c-P bond, i.e.,
  • R is lower alkyl having from 1 to 6 carbon atoms, e.g., methyl, ethyl, butyl, propyl, isopropyl, pentyl, isopentyl and hexyl; substituted lower alkyl of from 1 to 6 carbon atoms, e.g., hydroxyl and amino- substituted alkyls; a mononuclear aromatic (aryl) radical, e.g., phenyl, benzene, as a substituted mononuclear aromatic compound, e.g., hydroxyl, amino, lower alkyl substituted aromatic, e.g., benzyl phosphonic acid; and M is a water-soluble cation, e.g., sodium, potassium, ammonium, lithium, or hydrogen.
  • R 1 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 substituted alkylenes, and M is as earlier defined above.
  • R 2 is a lower alkylene having from 1 to 4 carbon atoms, or an amine or hydroxy substituted lower alkylene
  • R 3 is [R 2 -P0 3 M 2] H, OH, amino, substiuted amino, an alkyl having from 1 to 6 carbon atoms, a substituted alkyl of from 1 to 6 carbon atoms (e.g., OH, NH 2 substituted) a mononuclear aromatic radical and a substituted) a mononuclear aromatic radical (e.g., OH, NH 2 substituted);
  • R 4 is R 3 or the group represented by the formula
  • R 5 and R 6 ar each hydrogen, lower alkyl of from 1 to 6 carbon atoms, a substituted lower alkyl (e.g., CH, 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 Rs, Rs, or the group R 2 -PO 3 M 2 (R 2 is as defined above); n is 1 to 15; y is 1 to 14; and M is as earlier defined.
  • Preferred phosphonates are the two compounds:
  • additives such as tolytriazole may be utilized.
  • Tolytriazole is effective in the reduction of copper substrate corrosion.
  • Suitable acrylic acids for purposes herein are generally defined as monounsaturated monocarboxylic acids containing 3 or 4 carbon atoms. Specific examples of such acids include acrylic and methacrylic acids, with acrylic acid being preferred.
  • comonomers can be used with an acrylic acid and tert.butyl acrylamide provided that such additional comonomers do not deleteriously affect the desired properties.
  • additional comonomers examples include acrylic acid and tert.butyl acrylamide, acrylamide and methacrylamide, acrylonitrile, vinyl esters.
  • the acrylic acid units in the copolymer can be in the acid form or in a neutralized form where the hydrogen of the carboxyl group is replaced with an alkali metal, alkaline earth metal, or an ammonium cation, depending on the neutralizing medium.
  • the copolymers can be neutralized with a strong alkali, such as sodium hydroxide, in which instance, the hydrogen or the carboxyl group of the acrylic acid units will be replaced with sodium. With the use of an amine neutralizing agent, the hydrogen will be replaced with an ammonium group.
  • Useful copolymers include copolymers that are unneutralized, partially neutralized, and completely neutralized.
  • the copolymer is preferably formed in a high yield ranging from 50% to 99% by weight of the comonomers.
  • polymers of the type described above may be modified by incorporating into their structure up to 30% by weight of a termonomer which contains: a non-ionic or anionic polar group from the group selected perferably consisting of amido, lower alkyl ester, and maleic acid salt groups.
  • a termonomer which contains: a non-ionic or anionic polar group from the group selected perferably consisting of amido, lower alkyl ester, and maleic acid salt groups.
  • Examples of preferred monomers that may be polymerized to form terpolymers are acrylamide, methyl, or ethyl acrylate, maleic anhydride.
  • Other polar monomers that may be used are, for example, vinyl acetate, acrylonitrile, the various vinyl ketones, and vinyl ethers.
  • Illustrative of these monomers are the compounds: vinyl pyrrolidone, methyl vinyl ether, methacrylonitrile, allyl alcohol, methyl methacrylate, beta-diethylaminoethyl methacrylate, vinyl trimethylacetate, methyl isobutyrate, cyclohexyl methacrylate, vinyl laurate, vinyl stearate, N-vinyl imides, N-vinyl lactams, diethylene glycol dimethacrylate, diallylmaleate, allyl methacrylate, diallyl phthalate, and diallyl adipate.
  • the polymers formed may have weight average molecular weight in the range of 1,000 to 50,000, and preferably 2,000 to 30,000, as determined of known gel permeation chromatography using polystyrene of known molecular weight as a reference material.
  • the acid numbers of the copolymers formed may range from 310 to 740, corresponding to a weight fraction of from 40% to 95% by weight of monomer units having COOH groups.
  • the preferred polymers have more than 50% by weight of free carboxyl groups and an acid number in the range from 390 to 700.
  • Polymer Composition Nos. 1-12 are unneutralized copolymers of acrylic acid and t-butylacrylamide (t-BAm).
  • Polymer Composition No. 5 Polymer Composition No. 6, and Polymer Composition Nos. 7-12 are terpolymers which respectively contain the additional mer units of ethyl acrylate (EA), acrylamide (Am), and methacrylic acid (MAA).
  • EA ethyl acrylate
  • Am acrylamide
  • MAA methacrylic acid
  • the copolymers composed of acrylic acid and t-butyl acrylamide contains between 50 to 90% by weight of acrylic acid and from 50-10% by weight of t-butyl acrylamide.
  • the acrylic acid is present in a weight percent amount ranging between 70-90 with the t-butyl acrylamide being present at between 30-10.
  • the acrylic acid is present in a weight percent amount ranging between 80-90 with the t-butyl acrylamide being present at between 20-10.
  • the terpolymers are within the following weight percent composition ranges:
  • the aqueous system is dosed based on active ingredients to provide thereto on a weight basis from between 5-50 ppm, preferably 8 to 40 ppm and most preferably 15-30 ppm of Compositions 1 and 2 previously described.
  • compositions When the compositions are first added it is beneficial if they are dosed on the side to control the corrosion and to begin forming protective films. After a week or so the dosages can be diminished until an optimum maintenance dosage is established.
  • the systems treated are industrial recirculating and once through cooling waters that either due to their natural make-up or by pH adjustment have a pH of at least 8.
  • the pH of the systems are within the range of 8-9.5 and are most often within the range of 8.5-9.2.
  • These systems are characterized as containing at least 10 ppm of calcium ion and are considered to be corrosive to ferrous metals as well as non-ferrous with which they come in contact.
  • the mixture was cooled in an ice-bath and then basified by slow addition of approximately 22 grams of aqueous sodium hydroxide (50 wt%) to the vigorously stirred solution. During the addition of base, the solution's temperature was maintained below (130 ° F) 55 ° C. The pH was adjusted to 13 with 4.7 grams of a 50 weight percent of a sodium tolyltriazole solution. Finally, sufficient softened water to produce 100 grams of product were added. The cooling bath was removed and the solution stirred until ambient temperature was reached.
  • aqueous sodium hydroxide 50 wt%
  • the stock solutions were added to attain 360 ppm Ca2+, 10 ppm inhibitor, 5.6 ppm Dequest and 8 ppm PBS-AM in the final 500 ml test volume.
  • the pH was adjusted to 9.2 using aqueous sodium hydroxide.
  • test samples The pH of the test samples was manually adjusted at 15 minute intervals during the first hour and at 1 hour intervals, subsequently. A 4 hour test durating was sufficient for these precipitation reactions to stabilize. Finally, a portion of each test solution was passed through cellulose acetate/nitrate Millipore filter (type HA, 0.45 ⁇ m). Both filtered and unfiltered aliquots were spectrophotometrically analyzed for total phosphate content. To study particle size effects, an additional sample was passed through a 0.10 Il m Millipore filter (type VC). The % inhibition was determined by a following formula: In calcium phosphonate inhibition tests, polymer performance versus precipitated particle size was examined and the results are presented in Table B.
  • the calcium phosphonate "inhibition" process involves minimizing particle growth. Maintaining scale particles at an extremely small size and mass may ultimately prove to be a pivotal factor in determining polymer performance.
  • filters with mean pore sizes of 0.10 and 0.45 ⁇ m differences in polymer performance were readily observed.
  • Versa TL-4 the low molecular weight copolymer of sulfonated styrene and maleic acid
  • Polymer Composition Nos. 1 and 5 exhibited very good inhibition (0.45 ⁇ m filter), but performance decreased rapidly when the filter pore size was reduced to 0.10 ⁇ m.
  • Polymer Composition No. 11 exhibited the best overall performance in both bench-top and PCT tests.
  • the pilot cooling tower test is a dynamic test which simulates many features present in an industrial recirculating cooling water system.
  • the general test method is described in the article "Smail-Scale Short-Term Methods of Evaluating Cooling Water Treatments ... Are They Worthwhile?", by D.T. Reed and R. Nass, Minutes of the 36th Annual Meeting of the INTERNATIONAL WATER CONFERENCE, Pitts- burgh, Pennsylvania, November 4-6, 1975.
  • Tolytriazole is explained inhackh's Chemical Dictionary, Fourth Edition, page 91 (CF. benzotriazole) and is employed as a corrosion inhibitor for copper and copper alloy surfaces in contact with water when it is used it is applied to the system at a dosage ranging between 1-20 ppm by weight.

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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

  • The invention concerns the use of a composition for inhibiting 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 t-butyl acrylamide.
  • The term "phosphonate" refers to organic materials containing one or more -POsH2 groups and salts thereof. Phosphonates particularly useful in this invention include i-hydroxy-i, i-ethane diphosphonic acid (HEDP), 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTC), amino-tris-methylenephosphonic acid (AMP), and their salts.
    • Introduction
  • Corrosion occurs when metals are oxidized to their respective ions and/or insoluble salts. For example, corrosion of metallic iron can involve conversion to soluble iron in a 2+ or 3+ oxidation state or insoluble iron oxides and hydroxides. Also, corrosion has a dual nature in that a portion of the metal surface is removed, while the formation of insoluble salts contributes to the buildup of deposits. Losses of metal cause deterioration of the structural integrity of the system. Eventually leakage between the water system and process streams can occur.
  • Corrosion of iron in oxygenated waters is known to occur by the following coupled electrochemical processes:
  • Figure imgb0001
    Figure imgb0002
    Inhibition of metal corrosion by oxygenated waters typically involves the formation of protective barriers on the metal surface. These barriers prevent oxygen from reaching the metal surface and causing metal oxidation. In order to function as a corrosion inhibitor, a chemical additive must facilitate this process such that an oxygen-impermeable barrier is formed and maintained. This can be done by interaction with either the cathodic or anodic half-cell reaction.
  • Inhibitors can interact with the anodic reaction 1 by causing the resultant Fe2+ to form an impermeable barrier, stifling further corrosion. This can be accomplished by including ingredients in the inhibitor compound which: react directly with Fe2+ causing it to precipitate; facilitate the oxidation of Fe2+ to Fe3+, compounds of which are typically less soluble; or promote the formation of insoluble Fe3+ compounds.
  • The reduction of oxygen at corrosion cathodes provides another means by which inhibitors can act. Reaction (2) represents the half-cell in which oxygen is reduced during the corrosion process. The product of this reaction is the hydroxyl (OH-) ion. Because of hydroxyl production, the pH at the surface of metals undergoing oxygen-mediated corrosion is generally much higher than that of the surrounding medium. Many compounds are less soluble at elevated pH's. These compounds can precipitate at corrosion cathodes and act as effective inhibitors of corrosion if their precipitated form is impervious to oxygen and is electrically nonconductive.
  • Corrosion inhibitors function by creating an environment in which the corrosion process induces inhibitive reactions on the metal surface. In order for an inhibitor composition to function effectively, the components of the composition must not precipitate under the conditions in the bulk medium. Inhibitors which effectively inhibit this precipitation by kinetic inhibition have been extensively described in the literature. An example of this art is US-A 3 880 765 which teaches the use of polymers for prevention of calcium carbonate prepitation.
  • The use of inorganic phosphates and phosphonates in conjunction with a threshold inhibitor in order to control corrosion by oxygenated waters is described by US-A 4 303 568. This method is further elaborated by US-A 4 443 340 which teaches that a composition comprised of only inorganic phosphates and a polymeric inhibitor performs well in the presence of dissolved iron.
  • Corrosion inhibition can be achieved by a combination of the use of inhibitors and modification of the chemistry of the medium. US-A 4 547 740 teaches a method of corrosion inhibition relying on operation under conditions of high pH and alkalinity. This method does not rely on the use of inorganic phosphates, giving a more desirable product from an environmental impact point of view.
  • The use of the copolymers containing t-butyl acrylamide units in conjunction with other comonomers as scale inhibitors is discussed in US-A 4 566 973 (EP 0 171 048).
  • Said copolymers in connection with threshold inhibition of salt-forming scales and dispersion of particulate matter find usage as scale inhibitors - but not as corrosion inhibitors.
  • The subject matter of FR-A 1 598 419 is the inhibition of scale formation and corrosion by using a water-soluble polymer and a phsophonate, with a considerable amount of homopolymers and copolymers being stated for the water soluble polymer. Despite that enormous number of polymer classes the copolymers of acrylic acid with the specifically substituted acrylamide according to the invention cannot be seen from this cited reference.
    • Invention
  • According to the invention a composition is used for inhibiting corrosion in industrial cooling waters which contain hardness and have a pH of at least 8 which composition comprises:
    • A. a water-soluble organic phosphonate capable of inhibiting corrosion in an aqueous alkaline environment, and
    • B. a water-soluble non-crosslinked random copolymer of 50 to 90 wieght parts of acrylic acid units and 50 to 10 weight parts of substituted acrylamide units on the basis of a total of 100 weight parts of polymerized monomers, the polymer having a weight average molecular weight in the range of 1,000 to 50,000 and an acid number from 310 to 740, and the polymerized units of the acrylic acid and the substituted acrylamide are defined by the following formula:
      Figure imgb0003
      where m is 10 to 700 and n is 0.1 to 350, subject to the molecular weight limitations, R and R1 are hydrogen or methyl; X is selected from hydrogen, sodium, potassium, calcium, ammonium, and magnesium; with the weight ratio of polymer:phophonate being within the range of 0.2:1 to 2:1.
  • Surprisingly, it could be noticed that the polymers stated as being present in the composition used according to the present invention, have an unpredictable effect.
    • The Phosphonates
  • Generally any water-soluble phosphonate may be used that is capable of providing corrosion inhibition in alkaline systems. See US-A 4 303 568 which lists a number of representative phosphonates.
    • The Organo-Phosphonic Acid Derivatives
  • The organo-phosphonic acid compounds are those having a c-P bond, i.e.,
  • Figure imgb0004
  • Compounds within the scope of the above description generally are included in one of perhaps 3 categories which are respectively expressed by the following general formulas:
    Figure imgb0005
    where R is lower alkyl having from 1 to 6 carbon atoms, e.g., methyl, ethyl, butyl, propyl, isopropyl, pentyl, isopentyl and hexyl; substituted lower alkyl of from 1 to 6 carbon atoms, e.g., hydroxyl and amino- substituted alkyls; a mononuclear aromatic (aryl) radical, e.g., phenyl, benzene, as a substituted mononuclear aromatic compound, e.g., hydroxyl, amino, lower alkyl substituted aromatic, e.g., benzyl phosphonic acid; and M is a water-soluble cation, e.g., sodium, potassium, ammonium, lithium, or hydrogen.
  • Specific examples of compounds which are encompassed by this formula include:
    • methylphosphonic acid
    • CH3P03H2
    • ethylphosphonic acid
    • CH3CH2PO3H2
    • 2-hydroxyethylphosphonic acid
      Figure imgb0006
    • 2-amino-ethylphosphonic acid
      Figure imgb0007
    • isopropylphosphonic acid
      Figure imgb0008
    • benzene phosphonic acid
    • C6H5-PO3H2
    • benzylphosphonic acid
    • C6H5CH2PO3H2
      Figure imgb0009
  • wherein R1 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 substituted alkylenes, and M is as earlier defined above.
  • Specific examplary compounds an their respective formulas which are encompassed by the above formula are as follows:
    • methylene diphosphonic acid
    • H2O3P-CH2-PO3H2
    • ethylidene diphosphonic acid
    • H203P-CH(CH3)P03H2
    • isopropylidene diphosphonic acid
    • (CH3)2C(PO3H2)2
    • 1-hydroxy, ethylidene diphosphonic acid (HEDP)
      Figure imgb0010
    • hexamethylene diphosphonic acid
    • H2O3P-CH2(CH2)4CH2-PO3H2
    • trimethylene diphosphonic acid
    • H2O3P-(CH2)3-PO3H2
    • decamethylene diphosphonic acid
    • H2O3P-(CH2)10-PO3H2
    • 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
    • H2O3PC(OH)(C2H5)C(OH)(C2H5)PO3H2
      Figure imgb0011
  • where R2 is a lower alkylene having from 1 to 4 carbon atoms, or an amine or hydroxy substituted lower alkylene; R3 is [R2-P03M2] H, OH, amino, substiuted amino, an alkyl having from 1 to 6 carbon atoms, a substituted alkyl of from 1 to 6 carbon atoms (e.g., OH, NH2 substituted) a mononuclear aromatic radical and a substituted) a mononuclear aromatic radical (e.g., OH, NH2 substituted); R4 is R3 or the group represented by the formula
    Figure imgb0012
  • where R5 and R6 ar each hydrogen, lower alkyl of from 1 to 6 carbon atoms, a substituted lower alkyl (e.g., CH, NH2 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 Rs, Rs, or the group R2-PO3M2 (R2 is as defined above); n is 1 to 15; y is 1 to 14; and M is as earlier defined.
  • Compounds or formulas therefore which can be considered exemplary for the above formulas are as follows:
    • nitrilo-tri(methylene phosphonic acid)
    • N(CH2PO3H2)3
    • imino-di(methylene phosphonic acid)
    • NH(CH2PO3H2)2
    • n-butyl-amino-di(methyl phosphonic acid)
    • n-butyl-amino-di(methyl phosphonic acid)
    • C4H9N(CH2PO3H2)2
    • decyl-amino-di(methyl phosphonic acid)
    • C10H21N(CH2PO3H2)2
    • trisodium-pentadecyl-amino-di-methyl phosphate
    • C15H31N(CH2PO3HNa)(CH2PO3Na2)
    • n-butyl-amino-di(ethyl phosphonic acid)
    • C4H9N(CH2CH2PO3H2)2
    • tetrasodium-n-butyl-amino-di(methyl phosphate)
    • C4H9N(CH2P03Na2)2
    • triammonium tetradecyl-amino-di(methyl phosphate)
    • C14H29N(CH2PO3(NH4)2)CH2PO3HNH4
    • phenyl-amino-di(methyl phosphonic acid)
    • C6H5N(CH2PO3H2)2
    • 4-hydroxy-phenyl-amino-di(methyl phosphonic acid)
    • HOC6H4N(CH2PO3H2)2
    • phenyl propyl amino-di(methyl phosphonic acid)
    • C6H5(CH2)3N(CH2PO3H2)2
    • tetrasodium phenyl ethyl amino-di(methyl phosphonic acid)
    • C6H5(CH2)2N(CH2PO3Na2)2 ethylene diamine tetra(methyl phosphonic acid)
    • (H2O3PCH2)2N(CH2)2N(CH2PO3H2)2
    • trimethylene diamine tetra(methyl phosphonic acid)
    • (H2O3PCH2)2N(CH2)3N(CH2PO3H2)2
    • hepta methylene diamine tetra(methyl phosphonic acid)
    • (H2O3PCH2)N(CH2)7N(CH2PO3H2)2
    • decamethylene diamine tetra(methyl phosphonic acid)
    • (H2O3PCH2)2N(CH2)10N(CH2PO3H2)2
    • tetradecamethylene diamine tetra(methyl phosphonic acid)
    • (H203PCH2)2N(CH2)14N(CH2P03H2)2
    • ethylene diamine tri(methyl phosphonic acid)
    • (H2O3PCH2)2N(CH2)2NHCH2PO3H2
    • ethylene diamine di(methyl phosphonic acid)
    • H203PCH2)2NH(CH2)2NHCH2P03H2
    • n-hexyl amine di(methyl phosphonic acid)
    • C6H13N(CH2PO3H2)2
    • diethylamine triamine penta(methyl phosphonic acid)
    • (H203PCH2)2N(CH2)2N(CH2P03H2)-(CH2)2N(CH2PO3H2)2
    • ethanol amine di(methyl phosphonic acid)
    • HO(CH2)2N(CH2PO3H2)2
    • n-hexyl-amino(isopropylidene phosphonic acid)methylphosphonic acid
    • C6H13N(C(CH3)2PO3H2)(CH2PO3H2)
    • trihydroxy methyl, methyl amine di(methyl phosphonic acid
    • HOCH2)3CN(CH2P03H2)2
    • triethylene tetra amine hexa(methyl phosphonic acid)
    • (H203PCH2)2N(CH2)2N(CH2P03H2)(CH2)2-(CH2PO3H2)(CH2)2N(CH2PO3H2)2
    • monoethanol, diethylene triamine tri(methyl phosphonic acid
    • HOCH2CH2N(CH2PO3H2)(CH2)2NH(CH2)2N-(CH2PO3H2)2
    • chloroethylene amine di(methyl phosphonic acid)
    • CICH2CH2N((CH2PO(OH)2)2
  • The above compounds are included for illustration purposes and are not intended to be a complete listing of the compounds which are operable within the confines of the invention.
  • Preferred phosphonates are the two compounds:
    • A. 2-phosponobutane-1 , 2, 4-tricarboxylic acid and
  • B. 1-hydroxyethane-1, 1-diphosphonicacid.
  • While individual phosphonates may be used in combination with polymer(s) much better results have been obtained by using a blend of phosphonates such as A and B. When they are combined it is in a weight ratio of A:B of from 0.5/1-4/1 and preferably from 0.5/1-2/1 and most preferably about 0.67/1.
  • In addition to phosphonates, additives such as tolytriazole may be utilized. Tolytriazole is effective in the reduction of copper substrate corrosion.
    • The Water-Soluble Noncross Linked Random Copolymers
  • These polymers are described in detail in US-A 4 566 973.
  • Suitable acrylic acids for purposes herein are generally defined as monounsaturated monocarboxylic acids containing 3 or 4 carbon atoms. Specific examples of such acids include acrylic and methacrylic acids, with acrylic acid being preferred.
  • Other comonomers can be used with an acrylic acid and tert.butyl acrylamide provided that such additional comonomers do not deleteriously affect the desired properties. Examples of such comonomers in- dude acrylate and methacrylate esters, acrylamide and methacrylamide, acrylonitrile, vinyl esters.
  • The acrylic acid units in the copolymer can be in the acid form or in a neutralized form where the hydrogen of the carboxyl group is replaced with an alkali metal, alkaline earth metal, or an ammonium cation, depending on the neutralizing medium. Generally, the copolymers can be neutralized with a strong alkali, such as sodium hydroxide, in which instance, the hydrogen or the carboxyl group of the acrylic acid units will be replaced with sodium. With the use of an amine neutralizing agent, the hydrogen will be replaced with an ammonium group. Useful copolymers include copolymers that are unneutralized, partially neutralized, and completely neutralized.
  • Polymerization of the monomers results in an essentially non-crosslinked random copolymer, the molecular weight of which can be adjusted with a little trial and error. The copolymer is preferably formed in a high yield ranging from 50% to 99% by weight of the comonomers.
  • The polymers of the type described above may be modified by incorporating into their structure up to 30% by weight of a termonomer which contains: a non-ionic or anionic polar group from the group selected perferably consisting of amido, lower alkyl ester, and maleic acid salt groups.
  • Examples of preferred monomers that may be polymerized to form terpolymers are acrylamide, methyl, or ethyl acrylate, maleic anhydride. Other polar monomers that may be used are, for example, vinyl acetate, acrylonitrile, the various vinyl ketones, and vinyl ethers. Illustrative of these monomers are the compounds: vinyl pyrrolidone, methyl vinyl ether, methacrylonitrile, allyl alcohol, methyl methacrylate, beta-diethylaminoethyl methacrylate, vinyl trimethylacetate, methyl isobutyrate, cyclohexyl methacrylate, vinyl laurate, vinyl stearate, N-vinyl imides, N-vinyl lactams, diethylene glycol dimethacrylate, diallylmaleate, allyl methacrylate, diallyl phthalate, and diallyl adipate.
  • The polymers formed may have weight average molecular weight in the range of 1,000 to 50,000, and preferably 2,000 to 30,000, as determined of known gel permeation chromatography using polystyrene of known molecular weight as a reference material.
  • The acid numbers of the copolymers formed, as determined by a conventional titration with KOH, may range from 310 to 740, corresponding to a weight fraction of from 40% to 95% by weight of monomer units having COOH groups. The preferred polymers have more than 50% by weight of free carboxyl groups and an acid number in the range from 390 to 700.
  • Preferred species are described in Table A below as Polymer Composition Nos. 1-12.
    Figure imgb0013
    Polymer Composition Nos. 1-4 are unneutralized copolymers of acrylic acid and t-butylacrylamide (t-BAm). Polymer Composition No. 5, Polymer Composition No. 6, and Polymer Composition Nos. 7-12 are terpolymers which respectively contain the additional mer units of ethyl acrylate (EA), acrylamide (Am), and methacrylic acid (MAA).
  • A distinctive feature of all these polymers is the t-butylacrylamide unit. That sterically-hindered, hydrophobic alkylamide group exhibits excellent resistance to hydrolysis and the unit appear to confer exceptional performance characteristics upon polymers.
  • The copolymers composed of acrylic acid and t-butyl acrylamide contains between 50 to 90% by weight of acrylic acid and from 50-10% by weight of t-butyl acrylamide. Preferably the acrylic acid is present in a weight percent amount ranging between 70-90 with the t-butyl acrylamide being present at between 30-10. Most preferably the acrylic acid is present in a weight percent amount ranging between 80-90 with the t-butyl acrylamide being present at between 20-10.
  • The terpolymers are within the following weight percent composition ranges:
    • a) acrylic acid 40-90 more preferably 40-80 and most preferably 60-80
    • b) methacrylic acid 5-30 more preferably 10-30 and most preferably 10-20
    • c) t-butyl acrylamide 5-50 more preferably 10-30 and most preferably 10-20
    Dosage
  • The aqueous system is dosed based on active ingredients to provide thereto on a weight basis from between 5-50 ppm, preferably 8 to 40 ppm and most preferably 15-30 ppm of Compositions 1 and 2 previously described.
  • When the compositions are first added it is beneficial if they are dosed on the side to control the corrosion and to begin forming protective films. After a week or so the dosages can be diminished until an optimum maintenance dosage is established.
    • Systems Treated and DH
  • The systems treated are industrial recirculating and once through cooling waters that either due to their natural make-up or by pH adjustment have a pH of at least 8. Preferably the pH of the systems are within the range of 8-9.5 and are most often within the range of 8.5-9.2. These systems are characterized as containing at least 10 ppm of calcium ion and are considered to be corrosive to ferrous metals as well as non-ferrous with which they come in contact.
    • Example
  • To a glass or stainless steel container is added 14 grams of softened water. With stirring, aqueous solutions of the following materials were added consecutively:
    • 7 grams of 1-hydroxyethane-1,1-diphosphonic acid (60 wt%)
    • 12 grams of 2-phosphonobutane-1,2,4-tricarboxylic acid (50 wt%)
    • 15.3 grams of acrylic acid/t-butylacrylamide copolymer (49 wt%).
  • The mixture was cooled in an ice-bath and then basified by slow addition of approximately 22 grams of aqueous sodium hydroxide (50 wt%) to the vigorously stirred solution. During the addition of base, the solution's temperature was maintained below (130°F) 55°C. The pH was adjusted to 13 with 4.7 grams of a 50 weight percent of a sodium tolyltriazole solution. Finally, sufficient softened water to produce 100 grams of product were added. The cooling bath was removed and the solution stirred until ambient temperature was reached.
  • Changes in the formulation are easily accommodated by simple modification of the previously listed procedure. For example, decreasing the amount of polymer and sodium hydroxide, followed by increasing the final amount of water added, will produce a formulation containing lower polymer actives. Alternatively, the polymer and corrosion inhibitors may be fed separately.
  • In laboratory tests, hardness cations and M alkalinity are expressed as CaC03 or cycles of concentration. Fen+ is listed as Fe, and inhibitors (monomeric and polymeric) are listed as actives. In analyses of heat-exchanger deposits, all components are listed as wt% of the chemical element or acid-form of the compound.
  • A standard heated "beaker" test was employed for evaluating performance of phosphonate inhibitors (Table B). Calcium and inhibitor stock solutions from the calcium phosphate inhibition test were used. In addition, stock solutions (1000 ppm actives) of Bayer PBS-AM and Dequest 2010 were prepared. Dequest-2010, made by the Monsanto Company, St. Louis, Missouri is described as hydroxy ethylidene 1,1-diphosphonic acid (HEDP) (cf. US-A 3 959 168). PBS-AM is a trademark of Bayer for 2-phosphonobutane-1,2,4-tricarboxylic acid. To begin the test, distilled water, (400 ml) was added to the jacketed-beakers maintained at 60 ± 2°C. The stock solutions were added to attain 360 ppm Ca2+, 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 of the test samples was manually adjusted at 15 minute intervals during the first hour and at 1 hour intervals, subsequently. A 4 hour test durating was sufficient for these precipitation reactions to stabilize. Finally, a portion of each test solution was passed through cellulose acetate/nitrate Millipore filter (type HA, 0.45 µm). Both filtered and unfiltered aliquots were spectrophotometrically analyzed for total phosphate content. To study particle size effects, an additional sample was passed through a 0.10 Ilm Millipore filter (type VC). The % inhibition was determined by a following formula:
    Figure imgb0014
    Figure imgb0015
    In calcium phosphonate inhibition tests, polymer performance versus precipitated particle size was examined and the results are presented in Table B.
  • The calcium phosphonate "inhibition" process involves minimizing particle growth. Maintaining scale particles at an extremely small size and mass may ultimately prove to be a pivotal factor in determining polymer performance. By using filters with mean pore sizes of 0.10 and 0.45 µm, differences in polymer performance were readily observed. Polymer Composition No. 11 (MW = 15,600) produced the best overall performance, and was the only polymer which exhibited good inhibition when a 0.10 µm filter was used. Versa TL-4 (the low molecular weight copolymer of sulfonated styrene and maleic acid) and Polymer Composition Nos. 1 and 5 exhibited very good inhibition (0.45 µm filter), but performance decreased rapidly when the filter pore size was reduced to 0.10 µm. In particular, Polymer Composition No. 11 exhibited the best overall performance in both bench-top and PCT tests.
  • The pilot cooling tower test is a dynamic test which simulates many features present in an industrial recirculating cooling water system. The general test method is described in the article "Smail-Scale Short-Term Methods of Evaluating Cooling Water Treatments ... Are They Worthwhile?", by D.T. Reed and R. Nass, Minutes of the 36th Annual Meeting of the INTERNATIONAL WATER CONFERENCE, Pitts- burgh, Pennsylvania, November 4-6, 1975.
  • The general operating conditions are provided in Table C.
    Figure imgb0016
    Polymer Composition Nos. 1, 3, 5, 6, 7 and 11, as described in Table D, were prepared pursuant to Example 1 and were used to directly replace VTL-4 in the high pH, standard formulation. Long-term stability testing (120°F) 49°C/pH 13 of those formulations made pursuant to the procedure of Example 1 but containing polymer Composition Nos. 1, 6 or 11 revealed no hydrolysis of the polymer occurred over a 3 month period. PCT deposit/corrosion rates are summarized in Table D below:
    Figure imgb0017
  • It has been found advisable in some cases to add small quantities of tolytriazole.
  • Tolytriazole is explained in Hackh's Chemical Dictionary, Fourth Edition, page 91 (CF. benzotriazole) and is employed as a corrosion inhibitor for copper and copper alloy surfaces in contact with water when it is used it is applied to the system at a dosage ranging between 1-20 ppm by weight.

Claims (7)

1. The use of a composition for inhibiting corrosion in industrial cooling waters which contain hardness and have a pH of at least 8 which composition comprises:
A. a water-soluble organic phosphonate capable of inhibiting corrosion in an aqueous alkaline environment, and
B. a water-soluble non-crosslinked random copolymer of 50 to 90 weight parts of acrylic acid units and 50 to 10 weight parts of substituted acrylamide units on the basis of a total of 100 weight parts of polymerized monomers, the polymer having a weight average molecular weight in the range of 1,000 to 50,000 and an acid number from 310 to 740, and the polymerized units of the acrylic acid and the substituted acrylamide are defined by the following formula:
Figure imgb0018
where m is 10 to 700 and n is 0.1 to 350, subject to the molecular weight limitations,
R and R1 are hydrogen or methyl; -
X is selected from hydrogen, sodium, potassium, calcium, ammonium, and magnesium;
with the weight ratio of polymer:phosphonate being within the range of 0.2:1 to 2:1.
2. The use of a composition according to claim 1, wherein the phosphonate is a blend of 2-phosphonobutane-1,2,4-tricarboxylic acid and 1-hydroxyethane-1,1-diphosphonic acid.
3. The use of a composition according to claim 1 or 2, wherein the random polymer is further characterized of containing up to 30% by weight of a termonomer with contains either an anionic or non-anionic group.
4. The use of a composition according to claim 3, wherein the polymer is a terpolymer of acrylic acid, methacrylic acid and t-butyl acrylamide; and the phosphonate is selected from 1-hydroxyethane-1,1-diphosphonic acid and 2-phosphonobutane-1,2,4-tricarboxylic acid.
5. The use of a composition according to claim 3, wherein the terpolymer has a weight average molecular weight of 9,000 to 30,000.
6. The use of a composition according to claims 1 to 5 further including a corrosion inhibiting amount of tolyltriazole.
7. The use of a composition according to claims 1 to 6 for improving the performance of phosphonate corrosion inhibitors in aqueous systems having hardness and a pH of at least 8 by dosing the system with from 5 to 50 ppm, preferably 8 to 30 ppm of the composition.
EP86118127A 1986-03-26 1986-12-30 Corrosion inhibiting Expired - Lifetime EP0238728B1 (en)

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WO1989007633A1 (en) * 1988-02-18 1989-08-24 John Kenneth Bethune Absorbent polymer compositions
CN1034738C (en) * 1993-03-27 1997-04-30 云浮硫铁矿企业集团公司 A protectant composition
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EP1853690A1 (en) * 2005-03-04 2007-11-14 The Procter and Gamble Company Automatic dishwashing composition with corrosion inhibitors
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US10351453B2 (en) 2016-04-14 2019-07-16 Nch Corporation Composition and method for inhibiting corrosion
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US4317744A (en) * 1979-04-25 1982-03-02 Drew Chemical Corporation Corrosion inhibitor
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