NZ226331A - Method of inhibiting corrosion of metallic surfaces in aqueous systems using acrylic polymers and zinc ions; compositions therefor - Google Patents

Abstract

Compositions containing a low molecular weight polymer of acrylic acid, a zinc source and a carboxylic/sulfonic acid polymer effectively inhibit the corrosion of metals by oxygen bearing waters at high pH.

Description

New Zealand Paient Spedficaiion for Paient Number £26331 22 1 Priority Date(s): Complete Specification Filed: ...Xfe.n.^.T.S.'SL Class: (5).. x .FT. 11.. /. 1.73 . /.& <. olb. , * i >o>o ^ 4»" j ^ ii f > ra. ilft Publication Date: . P.O. Journal, No: 2 7 AUb'{y9t • •••• j<f..

No.: Date.

NO DRAWINGS NEW ZEALAND PATENTS ACT, 1953 method of COMPLETE SPECIFICATION CONTROLLING CORROSION AT HIGH pH I_/We. CALGON CORPORATION, a corporation duly organized and existing under the laws of the State of Delaware, United States of America of Route 60-Campbell's Run Road, Robinson Township, State of Pennsylvania, United States of America, hereby declare the invention for which i~/ we pray that a patent may be granted to meYus, and the method by which it is to be performed, to be particularly described in and by the following statement: - - I - (followed by page la) -)c\ - 22 C-1455 TITLE OF THE INVENTION "METHOD OF CONTROLLING CORROSION AT HIGH pH" BACKGROUND OF THE INVENTION U.S. Patent 3,885,914 discloses the use of zinc/polyacrylate compositions to control the corrosion of metals by oxygen bearing waters.

However, such compositions are ineffective at high pH. The inventors have surprisingly discovered that the addition of a carboxylic/sulfonic acid polymer to the compositions of the '914 patent synergistically inhibits corrosion in alkaline systems. 221 - 2 - C-1455 U.S. Patent 4,640,793 discloses the use of zinc and carboxylic acid/sulfonic acid polymers to control the corrosion of steel in contact with aqueous systems. This reference does not, however, disclose a 5 method of controlling corrosion at high pH.

U.S. Patent 4,663,053 discloses a method of inhibiting the corrosion of metallic parts in contact with aqueous systems using a water soluble zinc 10 compound in combination with a water soluble sulfonated styrene/maleic anhydride copolymer and an organophosphorus acid compound or water soluble salt thereof.

The instant invention relates to the inhibition of corrosion in alkaline water systems in which oxygen bearing waters contact metallic surfaces.

More particularly, this invention relates to the 20 use of compositions comprising a water-soluble, low molecular weight polycarboxylic acid, a water-soluble zinc salt and a water-soluble carboxylic acid/sulfonic acid polymer to inhibit the corrosion of metals in water systems which contain high pH, oxygen bearing 25 waters.

Oxygen corrosion is a serious problem in any metal-containing water system. The corrosion of iron and steel is a primary concern because they are 30 extensively used in water systems. Copper and its alloys, aluminum and its alloys, and galvanized steel are also used in water systems and are subject to 22633 - 3 - C-1455 corrosion. The inventors have discovered novel corrosion inhibiting compositions which inhibit oxygen corrosion in high pH water systems containing such metals.

SUMMARY OF THE INVENTION The inventors have found that compositions comprising low molecular weight, water soluble polycarboxylates, water soluble zinc salts and water 10 soluble carboxylic/sulfonic polymers are effective corrosion inhibitors at high pH. Suitable carboxylic polymers include low molecular weight acrylic acid polymers, low molecular weight methacrylic acid polymers and hydrolyzed polyacrylamides. These 15 polymers may be homo-, co-, or ter- polymers of any of the aforementioned types and may have molecular weights ranging from about 500 to about 25,000.

Suitable water soluble zinc sources include, but 20 are not limited to, salts such as zinc chloride, zinc acetate, zinc nitrate and zinc sulfate. Of course, the zinc ion may also be supplied by adding zinc to the system being treated.

The carboxylic/sulfonic polymer is an acrylic acid/2-acrylamido-2-methylpropyl sulfonic acid-type polymer having a molecular weight of less than about 25,000, wherein the weight ratio of the carboxylic moiety to the sulfonic moiety is from about 1:20 to 30 about 20:1. The addition of the carboxylic/sulfonic acid polymer to the polyacrylic acid-type polymer and the zinc source enables control of carbon steel 226^31 - 4 - C-1455 corrosion at alkaline pH's. Polyacrylate/zinc products alone are only effective to neutral pH.

Thus, the addition of the carboxylic/sulfonic polymer extends the pH range to alkaline conditions while 5 improving corrosion control. This polymer also stabilizes zinc above pH 7.5.

DETAILED DESCRIPTION OF THE INVENTION The instant invention is directed to a method of inhibiting the corrosion of metallic surfaces in contact with an aqueous system comprising adding to said system an effective amount of a composition compr ising: (A) a water-soluble polycarboxylate, or salt thereof, having a molecular weight of less than substantially 25,000, preferably substantially 500 to substantially 10,000, (B) a source of zinc ions; and (C) a water soluble polymer having an intrinsic viscosity of 0.05 to 2.5 dl/g prepared from: (i) an unsaturated carboxylic acid, or salt thereof; and (ii) an unsaturated sulfonic acid, or salt thereof, having a (i):(ii) weight ratio of from substantially 1:20 to substantially 20:1, preferably substantially 1:10 to substantially 10:1 and most prefe||£bi^j3ub- stantially 1:4 to substantially 4:1; H2633I wherein the weight ratio of (A):(B) ranges from substantially 1:1 to substantially 10:1, preferably substantially 2:1 to substantially 5:1, and the weight ratio of (B):(C) ranges from substantially 1:10 to substantially 10:1, preferably substantially 1:5 to substantially 5:1, and most preferably substantially 2:1 to substantially 1:2. In more preferred compositions, the weight ratio of (A): (B): (C) is substantially 3.5-4.5:1:0.5-2. The most preferred compositions contain (A):(B):(C) weight ratios of about 4:1:1.

The above described compositions are also claimed.

An effective amount of one of the instant compositions should be added to the aqueous system being treated. As used herein, the term "effective amount" is that amount of an instant composition necessary to inhibit the corrosion of metallic surfaces in contact with the alkaline aqueous system being treated. Generally, the effective amount will range from about 1 to about 1,000 ppm of the total composition, on an active basis, based on the total weight of the aqueous system being treated.

The term "aqueous system" as used herein, is meant to include any type of system containing water, including but not limited to, cooling water systems, boiler water systems, desalination systems, gas scrubber water systems, blast furnace water systems, reverse osmosis systems, evaporator water systems, paper manufacturing systems, mining systims and-the like JSH2S3r SE6S3.1 The essential aspect of this invention is that the instant compositions are effective at controlling corrosion in alkaline systems. Thus, the instant compositions are effective when the pH of the aqueous system being treated is greater than 7.0, preferably from substantially 7.0 to substantially 10.0, more preferably from substantially 7.0 to substantially 9.0, and most preferably substantially 7.0 to substantially 8.5.

Component (A) of the instant compositions may be any water-soluble polycarboxylate selected from the group consisting of polymers prepared from acrylic acid, methacrylic acid, vinyl acetic acid, allyl acetic acid, fumaric acid, maleic acid or anhydride, itaconic acid, o-halo acrylic acid and 0-carboxyethylacrylate. Preferably, component A is selected from the group consisting of water soluble homopolymers of acrylic acid, water soluble homopolymers of methacrylic acid, water soluble copolymers of acrylic acid and methacrylic acid and water soluble hydrolyzed polyacrylamides, wherein the molecular weight is less than substantially 25,000, preferably substantially 1,000 to substantially 10,000, and salts of these polymers.

Any zinc ion source may be used as component B. For example, the zinc ion may be added by utilizing a water-soluble zinc salt, such as zinc chloride, zinc acetate, zinc nitrate or zinc sulfate. Also, the zinc ion may be.added by supplying zinc to the aqueous system being treated.

For component C, any unsaturated carboxylic acid or salt thereof may be used as (i). Examples include, but are not limited to, acrylic acid, methacrylic acid, a-halo acrylic acid, maleic acid, itaconic acid, vinyl acetic acid, allyl acetic acid, fumaric acid, /3-carboxyethyl acrylate, their salts and admixtures thereof. The most preferred carboxylic monomers are acrylic acid, methacrylic and their salts.

Any unsaturated sulfonic acid or salt thereof may be used as (ii) in component C. Examples include, but are not limited to, 2-acrylamido-2-methylpropyl sulfonic acid, 2-methacrylamido-2-methylpropyl sulfonic acid, styrene sulfonic acid, vinyl sulfonic acid, sulfo alkyl acrylate or methacrylate, allyl sulfonic acid, methallyl sulfonic acid, 3-methacrylamido-2-hydroxy propyl sulfonic acid acrylate, their salts and mixtures thereof. The most preferred sulfonic monomers are 2-acrylamido-2-methylpropylsulfonic acid, 2-methacrylamido-2-methylpropylsulfonic acid and their salts.

Mixtures of the various monomers may be used, and nonionic monomers (such as acrylamide, methacrylamide and acrylonitrile) may also be present in the polymers. However, copolymers are preferred.

These polymers are prepared using an (i):(ii) monomer weight ratio of substantially 1:20 to substantially 20:1, preferably substantially 1:10 to substantially 10:1, and most preferably substantially 1:4 to substantially 4:1. 226 - 8 - C-1455 Thus, the preferred polymers for component C are water soluble polymers having an intrinsic viscosity of 0.05 to 2.5 dl/g, prepared from: (i) an unsaturated carboxylic compound selected 5 from the group consisting of acrylic acid, methacrylic acid, their salts and mixtures thereof; and (ii) an unsaturated sulfonic compound selected 10 from the group consisting of 2-acrylamido- 2-methylpropyl sulfonic acid, 2-methacrylamido-2-methylpropylsulfonic acid, their salts and mixtures thereof.

Most preferably component C is 20 to 80%, by weight, acrylic acid or its salt and 80 to 20%, by weight, 2-acrylamido-2-methylpropylsulfonic acid, or its salt, wherein the intrinsic viscosity is about 0.05 to about 0.5 dl/g.

An additional advantage of the instant compositions is that the component C polymer stabilizes the aqueous system being treated against zinc deposition, especially at pH's above 7.5.

The use of components A, B, and C is critical to the instant method in that compositions comprising these components effectively control corrosion of metallic surfaces in contact with aqueous systems 30 having alkaline pH's. 2 - 9 - C-1455 Optionally, additional components, such as an azole compound, can be added. Preferred azole compounds are tolyltriazole and mercapto-benzotriazole.

The components of the instant invention may be added to the aqueous system being treated by any technique known in the art of water treatment. The components may be added as a mixture or separately. However, if added separately, the zinc source should 10 be added last to prevent deposition of zinc salts in highly alkaline waters.

EXAMPLES In the examples, an 8L cell equipped with a pH stat and heater was used to measure the corrosion of mild steel coupons. The water composition was as follows: 100 mg/1 18 mg/1 120 mg/1 36 mg/1 3.1 mg/1 Each test was run for one (1) week. After this time, the corrosion rate in mils per year (mpy) for a 1" X 2" mild steel coupon was determined. The results are 15 shown in Table I.

HCO- 01 SO Ca Mg -2 %2 +2 TABLE I Active Inhibitor Mild Steel Corrosion Rates (mpy) Example Number Inhibitor Weight Ratio Dosage (mq/L) 6.5 § pH 7.3 8.0 1* PAA/Zn /3.8 23.5 33 2 PAA/Zn/AA-AMPS1* 7.5/3/7.5 22.5 3 37 3 PAA/Zn/AA-AMPS 12/3/3 22.5 2 4* None _ — 89 1. AMPS is a registered trademark of The Lubrizol Corporation.

Comparison Example. n i i—* Ln Ln Po o> CM 22^33(

Claims (7)

WHAT WE CLAIM IS:

1. A method of inhibiting corrosion of metallic sur faces in contact with an aqueous system comprising adding to said system an effective amount of a composition comprising : (A) a water-soluble polycarboxylate, having a molecular weight of less than substantially 25,000, wherein said polycarboxylate is selected from the group consisting of homopolymers of acrylic acid, homopolymers of methacrylic acid, copolymers of acrylic acid and methacrylic acid, hydrolyzed polyacrylamides and salts thereof; (B) a source of zinc ions; and (C) a water soluble polymer having an intrinsic viscosity of 0.05 to 2.5 dl/g prepared from: (i) an unsaturated carboxylic acid selected from the group consisting of acrylic acid, methacrylic acid and salts thereof; and (ii) an unsaturated sulfonic acid selected from the group consisting of 2-acrylamido-2-methyl propyl sulfonic acid, 2-methacryl-amido-2-methyl propyl sulfonic acid and salts thereof, having a (i) : (ii) weight ratio of from substantially 1:20 to substantially 20:1; wherein said aqueous system has an alkaline pH, wherein the weight ratio of (A):(B) is from substantially 1:1 to substantially 10:1, and wherein the weight ratio of (B):(C) is from substantially 1:10 to substantially 10:1. ^

2. The method of Claim 1, wherein (i):(ii) stantially 1:10 to substantially 10:1. EE633I

3. The method of Claim 2, wherein (a):(B), by weight, is substantially (2):(1) to substantially (5):(1) and wherein (B):(C), by weight, is substantially (2):(1) to substantially (1):(2).

4. The method of Claim 3, wherein said alkaline pH is from substantially 7.0 to substantially 10.0.

5. The method of Claim 4, wherein said alkaline pH is from substantially 7.0 to substantially 9.0.

6. The method of Claim 5, wherein the weight ratio of (A):(B):(C) is about 4:1:1.

7. A composition comprising: (A) a water-soluble polycarboxylate, having a molecular weight of less than substantially 25,000, wherein said polycarboxylate is selected from the group consisting of homopolymers of acrylic acid, homopolymers of methacrylic acid, copolymers of acrylic acid and methacrylic acid, hydrolyzed poly-acrylamides and salts thereof; (B) a source of zinc ions; and (C) a water-soluble polymer having an intrinsic viscosity of 0.05 to 2.5 dl/g, prepared from: (i) an unsaturated carboxylic acid selected from the group consisting of acrylic acid, T_ methacrylic acid and salts thereof; and (ii) an unsaturated sulfonic acid selectj! from the group consisting of 2-acrylamido-^-® JUt methyl propyl sulfonic acid and 2-methacr} amido-2-methyl propyl sulfonic acid and salt?J thereof; wherein the weight ratio o'£--X.i4,; (ii) ranges from substantially 1:20 to substantially 20:1; and wherein the weight ratio of (A):(B):(C) is substantially 3.5-4.5:1:0.5-2. DATED THIS l&X. DAY OF (j j 19-? / A. J. per agent£b% the applicant? t v ^3/