CA2161919A1 - Use of ethylenically unsaturated compound/polyalkylene oxide copolymers for scale and corrosion inhibition - Google Patents

Abstract

A method of inhibiting corrosion and scale formation and the deposition of phosphates and phosphonates in aqueous systems is dis-closed. The method comprises treatment of aqueous systems with a copolymer of an ethylenically unsaturated compound and an unsatu-rated polyalkylene oxide compound.

Description

21 61~1~

USE OF ETHYLENICALLY UNSATURATED
COMPOUND/POLYALKYLENE OXIDE COPOLYMERS
FOR SCALE AND CORROSION INHIBITION

FIELD OF THE INVENTION

The present invention relates to methods for inhibiting corrosion and controlling the formation and deposition of scale imparting com-pounds in water systems such as cooling, boiler, and gas scrubbing systems.

BACKGROUND OF THE INVENTION

The problems of corrosion and scale formation and attendant ef-fects have troubled water systems for years. For instance, scale tends to 10 accumulate on internal walls of various water systems, such as boiler and cooling systems and thereby materially lessen the operational efficiency of the system.

216191~

Deposits in lines, heat exchange equipment, etc., may originate from several causes. For example, precipitation of calcium carbonate, calcium sulfate and calcium phosphate in a water system leads to an accumulation of these scale imparting compounds along or around the 5 metal surfaces which contact the flowing water circulating through the system. In this manner, heat transfer functions of the particular system are severely impeded.

Corrosion, on the other hand, is a degrative electrochemical reac-10 tion of a metal with its environment. Simply stated, it is the reversion ofrefined metals to their natural state. For example, iron ore is iron oxide.
Iron oxide is refined into steel. When steel corrodes, it forms iron oxide, which if unattended, may result in failure or destruction of the metal.
Scale can also cause rapid localized corrosion and subsequent penetra-15 tion of metallic surfaces through the formation of differential oxygen con-centration cells. The localized corrosion resulting from differential oxy-gen cells originating from deposits is commonly referred to as "under deposit corrosion".

In cooling water systems, the formation of calcium sulfate, calcium phosphate, and calcium carbonate among others, has proven deleterious to the overall efficiency of a cooling water system. Recently, the use of high levels of orthophosphate to promote passivation of metal surfaces in contact with aqueous systems has grown in popularity. In such systems, it is critically important to control calcium phosphate crystallization so that the desired relatively high levels of orthophosphate may be maintained in the system. Such high levels of orthophosphate are desired, however, it is also necessary to avoid fouling or impeding heat transfer functions which can result upon the formation and deposition of a calcium phos-phate scale.

Although steam generating systems are somewhat different from cooling water systems, they share a common problem in regard to de-posit formation.

Scale forming compounds can be prevented from precipitating by inactivating their cations with chelating or sequestering agents, so that the solubility of their reaction products is not exceeded. Since chelation is a stoichiometric reaction, it necessitates adding as much chelating or sequestering agent as cation. Such amounts are not always desirable or 1 0 economical.

Certain materials, such as inorganic polyphosphates, will prevent such precipitation when added in amounts far less than the concentration needed for sequestering or chelating. The use of an inhibitor at markedly lower concentrations than that required for stoichiometric binding of scale forming cations is typically referred to as "threshold" treatment.

U.S. Patent No. 4,485,223 discloses copolymers of itaconic acid and (meth)acrylic acid and their use to prevent alkaline calcium and magnesium scale formation in aqueous systems. U.S. Patent No.
4,618,448 discloses a process for inhibiting corrosion and the formation and deposition of scale and iron oxide in aqueous systems comprising adding to the system a threshold amount of a water soluble terpolymer prepared from (a) an unsaturated carboxylic acid; (b) an unsaturated sulfonic acid; and (c) an unsaturated polyalkylene oxide compound.

` ' 216I919 SUMMARY OF THE INVENTION

The present inventors have discovered a method of inhibiting cor-rosion and scale formation and the deposition of phosphates and phos-5 phonates in aqueous systems. The method comprises the thresholdtreatment of aqueous systems with a copolymer of an ethylenically un-saturated compound and an unsaturated polyalkylene oxide compound.
The method of the present invention is effective in systems susceptible to phosphate and/or phosphonate scale formation and deposition.
The use of phosphates and phosphonates as corrosion inhibitors is growing. In such systems the formation of scales such as calcium phosphate and calcium phosphonate can be a problem. The problem can be compounded because as the corrosion inhibitor levels fall due to 15 scale formation, more is added to control corrosion which, in turn, creates more scaling. Furthermore, for water conservation reasons, industrial processes are reusing water to a greater extent which tends to concen-trate the ions that occur naturally in the water. This increased cycles of concentration, can create even greater problems in the control of scale.
20 The copolymers of the present invention have shown efficacy in control-ling the scaling tendencies of phosphate/phosphonate ions in industrial waters at threshold treatment levels.
The water soluble copolymers of the invention have the structure:

-Formula I

[E]c [CH2-- lC]d C=O
o10 lR2 15 wherein E is the repeat unit remaining after polymerization of an alpha, beta ethylenically unsaturated compound, R1 is H or lower (C1-C4) alkyl, R2 is (CH2--CH2--)n, (CH2--Cl H--)n, or a mixture of both, n is an integer of from about 1 to about 40, R3 is hydrogen, lower (C1-C4) alkyl, or an acetate formed as a cap on the polyethyleneglycol methacrylate by reacting an acetylating agent with 25 polyethyleneglycol methacrylate to produce an acetate capped poly-ethyleneglycol methacrylate which is then reacted with the alpha, beta ethylenically unsaturated compound E to form the copolymer of Formula 1, c is the molar percentage being between 0-95 molar %, d is the molar percentage being between 100-5 molar %, c and d should add up to 1 00%.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In accordance with the present invention, it has been discovered that certain water soluble copolymers are effective in controlling the for-5 mation of phosphate/phosphonate deposits as scale and in inhibitingunder deposit corrosion on metallic surfaces in various water systems.
The method of the present invention comprises adding to the system to be treated a water soluble copolymer of an ethylenically unsaturated compound and an unsaturated polyalkylene oxide compound. The co-10 polymer of the present invention is substantially free of sulfonic acidbased materials.

The water soluble copolymers of the invention have the structure:
15 Formula I

[E]c [CH2--C]d C=O
o I

I

wherein E of Formula I comprises the repeat unit obtained after polymeri-30 zation of an alpha, beta ethylenically unsaturated monomer, preferably a ~ 2161919 carboxylic acid, amide form thereof, or lower alkyl (C1-C4) ester or hy-droxylated lower alkyl (C1-C4) ester of such carboxylic acids. Exemplary compounds encompassed by E include, but are not restricted to, the repeat unit formed by polymerization of acrylic acid, methacrylic acid, 5 acrylamide, maleic acid or anhydride, fumaric acid, itaconic acid, and 2-acrylamido-2-methylpropanesulfonic acid and the like. Water soluble salt forms of these acids are also within the purview of the invention.

R1 in Formula I is H or lower (C1-C4) alkyl, R2 is (CH2--CH2~)n, (CH~CI H~)n~

or a mixture of both, n is an integer of from about 1 to about 40, R3 is 15 hydrogen, lower (C1-C4) alkyl, or an acetate formed as a cap on the poly-ethyleneglycol moiety by reacting an acetylating agent with a (meth) acrylate of polyethyleneglycol to produce an acetate capped polyethyl-eneglycol (meth)acrylate which is then reacted with the alpha, beta ethylenically unsaturated compound E to form the copolymer of Formula 20 I. Suitable acetylating agents include acetic acid, acetic anhydride, acetyl chloride, and the like as described in U.S. Patent Nos. 4,959,156 and 4,847,410 fully incorporated herein by reference, c is the molar per-centage being between 0-95 molar %, d is the molar percentage being between 100-5 molar %, c and d should add up to 100%.
A preferred copolymer of the present invention includes acrylic acid, methacrylic acid or itaconic acid/polyethyleneglycol monometh-acrylate copolymers of the general formula:

~ 2161919 Formula ll H Rs R
5[ f -- f]c [CH2 -- Ic~d R4 f=o f=o OM O

lR2 5 wherein R1 is H or lower (C1-C4) alkyl, R2 is (CH2~H2--)n, (CH2--I H--)n~

20 or a mixture of both, n is an integer of from about 1 to about 40, R3 is H, lower (C1-C4) alkyl or an acetale, R4 is H or COOM, R5 is H, (C1-C4) alkyl or CH2COOM and M is H or a water soluble cation, c is the molar percentage being between 0-95 molar %, d is the molar percentage being between 100-5 molar %, c and d should add up to 100%. Acrylic acid 25 (R4=H, R5=H) or methacrylic acid (R4=H, Rs=CH3) may be replaced with itaconic acid (R4=H, Rs=CH2COOH) in Formula ll.

~ 2161919 A homopolymer of polyethyleneglycol monomethacrylate is within the scope of the present invention.

The number average molecular weight of the water soluble or 5 water dispersible copolymers of Formulas I or ll is not critical and may fall within the Mn range of about 1,000 to 100,000 desirably, 1,000 to 30,000 and more desirably 1,500 to 10,000. The key criteria is that the copoly-mer be water soluble or water dispersible. Water soluble or water dis-persible terpolymers comprising monomer c and d of Formula I may also 10 be effective for use in the present invention. Also, minor amounts of additional monomers may be added to the polymers.

Polyethyleneglycol monomethacrylate (HEM) is prepared by ethoxylation of methacrylate esters. These compounds are commercially 15 available from Rhone-Poulenc under the SIPOMER(~' Trademark. The monomers are then copolymerized with methacrylic acid or maleic acid to obtain the copolymers of the invention. Polyethyleneglycol monometh-acrylate may also be polymerized to form a homopolymer. The polymeri-zation may proceed in accordance with conventional solution, precipita-20 tion or emulsion polymerization techniques. Conventional polymerizationinitiators such as azo compounds, persulfates, peroxides, UV light, etc., may be used. Chain transfer agents such as alcohols (preferably isopro-panol), amine or mercapto compounds may be used to regulate the molecular weight of the polymer. The resulting polymer may be isolated 25 by well known techniques including precipitation, etc. If polymerized in water, the polymer may simply e used in its aqueous solution.

2l6l9l~

The polymerization may be conducted by any of a variety of pro-cedures, for example, in solution, suspension, bulk, and emulsion.

The copolymers of the present invention are used in treatment 5 dosages of from .1 to 1,000 ppm, preferably from about 5 to 25 ppm. In practice, the required treatment dosage will be dependent upon factors such as phosphate/phosphonate concentration, pH, temperature, etc.

Examples The present invention will now be described with reference to a number of specific examples which are to be regarded solely as illustra-tive and not as restricting the scope of the present invention.

15 Coolin~ Studies Example 1 Preparation of Itaconic acid/Polyethyleneglycol monometh-20 acrylate(HEM-10) Copolymer Molar Ratio 3/2.

A suitable flask was equipped with a condenser, mechanical stir-rer, thermometer, inlet for monomer and initiator feeds and nitrogen sparger. 100.0 9 of deionized water and 13.1 9 (0.1 mol) of itaconic acid 25 were charged to the flask. 41.2 9 (0.7 mol ~ 90%) of HEM-10 was placed in a 60 cc syringe. 10.0 9 of a 16.7% aqueous sodium persulfate solution (SPS) was charged to a 10 cc syringe. The solution was heated to 85C under a nitrogen sparge which was maintained throughout the reaction. The monomer and SPS solutions were added to the reaction 30 flask over three hours. One hour after the addition was complete, 0.5 cc ~ ~ 1 2161919 of a 70% t-butyl hydrogen peroxide solution was added to the reaction mixture. The resulting mixture was held at 85C for one more hour then cooled to room temperature. Caustic (50%) was then added to the solu-tion to adjust the pH to 5Ø

The polymer solution had a final solids of 30.2% and a Brookfield viscosity of 60.1 cps at 25C. The structure of the copolymer was veri-fied by 1 3C NMR. The spectrum was characterized by a broad poly (meth)acrylic acid-type backbone, strong resonances at 60, 69, and 71 10 ppm corresponding to the polyethyleneglycol moiety and a broad car-bonyl region (177-183 ppm). Copolymer 1 in the Tables.

Similar procedures were used to prepare the copolymers 2 and 3 (itaconic acid/HEM with different mole ratios and degree of ethoxylation, 15 n). The results are shown in Table 1.

Example 2 Preparation of Acrylic Acid/HEM-10 Copolymer Molar Ratio 1/1.
Utilizing the apparatus as described in Example 1, 75 g of de-ionized water and 25 g of isopropanol were charged to the flask. 6.36 g (0.088 mole) of acrylic acid, 51.5 g (0.088 mol~90%) of HEM-10 and 10.0 g of a 25% aqueous sodium persulfate solution were each weighed 25 into separate syringes of appropriate size added to the flask over 150 minutes at 85C. The reaction product was heated for one more hour followed by azeotropic removal of isopropanol/water. The reaction ~ I 2161919 mixture was then cooled to room temperature and adjusted to a pH=4.4 with 50% sodium hydroxide. The copolymer, after being diluted to 25%
solids had a Brookfield viscosity of 10.6 cps at 25C. The polymer was characterized by 13C NMR. Copolymer 4 in the Tables.

Copolymers 5-7 were prepared similarly to Copolymer 4 using different mole ratios and degree of ethoxylation, n.
TABLE I
10Copolymer Polymer Copolymer % Brookfield # ComPosition Ratio Solids Visc.tcps) IA/HEM 10 3/2 30.2 60.1 2 IA/HEM 5 1t1 28.6 406.5 3 IA/HEM 5 1/1 29.3 78.8 4 AAJHEM 10 1/1 25.7 10.6 A~VHEM 5 1/1 25.2 10.7 6 A~VHEM 5 3/1 25.0 15.6 7 A~VHEM 10 3/1 25.5 21.7 IA = itaconic acid HEM 10 = polyethyleneglycol monomethacrylate, having an average of 10 moles of ethylene oxide.
HEM 5 = polyethyleneglycol monomethacrylate, having an average of 5 25 moles of ethylene oxide.
AA = acrylic acid HEM 5& 10 are sold by Rhone Poulenc under the tradename Sipomer R

~ ~ 2161919 Static calcium phosphate scale inhibition tests were conducted by adding a treatment to an aqueous solution containing calcium and mag-nesium. A second solution contairiing phosphate and carbonate was added and the mixture incubated for 18 hours at 49C and pH 8.2. The 5 treatment was preadjusted to pH 8.2 prior to addition to the test solution.
After 18 hours, a measured portion of the hot solution was filtered through a 0.2 micron filter and analyzed for phosphorous by inductively coupled plasma atomic emission. The percent inhibition was calculated with the formula:
% Inhibition = ppm PO4(treated) - ppm Po4(control) ppm PO4(stock) - ppm PO4(control) The test solution contained: 1,820 ppm Ca, 840 ppm Mg, 20.77 ppm CO3 (all as CaC03), 1,303 ppm Na, 807 ppm SO4, and 15 ppm PO4.
The test results are summarized in Table ll.

TABLE ll % Inhibition at ppm Active*
Treatment 15 PPm 20 ppm Copolymer 1 91.0 100 Copolymer 2 78.1 86.1 (Low Molecular Weight) Copolymer 3 74.8 87.8 (High Molecular Weight) Copolymer 4 85.2 84.7 Copolymer 5 85.2 84.2 Copolymer 6 88.9 97.7 Copolymer 7 82.4 87.5 30 ~Average of two tests The data in Table I shows the efficacy of the copolymer employed in the method of the present invention at controlling phosphate scale formation and deposition in aqueous systems.

While the present invention has been described with respect to particular embodiments thereof, it is apparent that numerous other forms and modifications of the invention will be obvious to those skilled in the art. The appended claims and this invention generally should be con-strued to cover all such obvious forms and modifications which are within the true scope and spirit of the present invention.

Claims (9)

1. A method of inhibiting corrosion and the formation and deposition of phosphate and/or phosphonate scale in aqueous systems comprising adding to said systems an effective inhibiting amount of a copolymer having the structure:

wherein R1 is H or lower (C1-C4) alkyl, R2 is (CH2-CH2-O)n, or a mixture of both, n is an integer of from about 1 to about 40, R3 is H, lower (C1-C4) alkyl or an acetate, R4 is H or COOM, R5 is H, (C1-C4) alkyl or CH2COOM and M is H or a water soluble cation, c is the molar percentage being between 0-95 molar %, d is the molar percentage being between 100-5 molar %, c and d should add up to 100%.

2. The method of claim 1 wherein the copolymer has a molecular weight (Mn) of between about 1,000 and 100,000.

3. The method of claim 2 wherein the copolymer has a molecular weight (Mn) of between about 1,000 and 30,000.

4. The method of claim 3 wherein the copolymer has a molecular weight (Mn) of between about 1,500 and 10,000.

5. The method of claim 1 wherein the copolymer is added to the water in the cooling water system in an amount of 0.1 to 1,000 parts polymer based upon 1 million parts of the water.

6. The method of claim 1 further comprising adding to the cooling water system an effective amount for the purpose of a topping agent selected from the group consisting of phosphoric acids and water soluble salts thereof and phosphonic acids and water soluble salts thereof.

7. The method of claim 6 wherein the phosphoric acid is a member selected from the group consisting of orthophosphoric acid, pyrophosphoric acid, tripolyphosphoric acid, trimetaphosphoric acid, tetrametaphosphoric acid and water soluble salts thereof.

8. The method of claim 6 wherein the phosphonic acid is a member selected from the group consisting of ethylene diaminetetra-methylene phosphonic acid, methylene diphosphonic acid, hydroxy-ethylidene diphosphonic acid, 2-phosphonobutane 1,2,4-tricarboxylic acid and hydroxy phosphonoacetic acid.

9. The method of claim 6 wherein the topping agent is added to said system in an amount of 1 to about 500 parts per million parts of the water.