CA1329474C - Cooling water corrosion control method and composition - Google Patents

Abstract

ABSTRACT

A composition and method 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

Il 1 329474 FIELD OF INVENTION
This inVention is related to a composition and method ~or 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 aci5 and certain substituted acrylamides such as t-butyl acrylamide.
The term "phosphonate" refers to organic materials containing one or more -PO3H2 groups and salts thereof.
Phosphonates particularly useful in this invention include l-hydroxy-l,l-ethane diphosphonic acid (HEDP), 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTC), amino-tris-methylenephosphonic acid (AMP), and their salts. The concentrations and dosage levels and/or ranges of polymers, phosphonates and compositions are listed as actives.
INTRûDUCTION
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 hydroxi~es. 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 can occur, through areas subject to corrosive deterioration, for example between a water system and a process stre . . ~ . ~
- 2 - ~
:~
: ~ :

Corrosion of iron in oxygenated waters is known to occur ¦
by the following coupled electrochemical processes:
(1) ~e -~~ Fe+2 2e~ (Anodic Reaction) (2) 2 ~ 2e --~ 2ûH (Cathodic Reaction) Inhibition of metal corrosion by oxygenated waters typically involves the formation of protective barriers on the metal surface. These barriers prevent oxygen from reaohing 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 Fe+2 to form an impermeable barrier, stifling further corrosion. This can be accomplished by including in~redients in the inhibitor compound which: react directly wlth Fe+2 causing it to precipitate; facilitate the oxidation of Fe+2 to Fe+3, as Fe 3 compounds are typicaIly less soluble;
or promote the formation of insoluble Fe+3 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 ~rc~uct of this reaction is the hydroxyl (OH ) ion. Because of ~ydroxyl production, the PH at the surface of metals undergoi ~ oxygen-mediated corroiion is generally much higher than that of the surrounding medium. ~any 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 ele lca11y noncon~uctive.

Corrosion inhibitors func'.lion ~y 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 U.S. patent 3,88û,765 which teaches the use of polymers for prevencion of calcium carbonate precipitation.
The use of inorganic phosphates and phosphonates in conjunction with a threshold inhibitor in order to control corrosion by oxygenated waters is describeb by U.S. patent 4,303,568. This method is further elaborated by U.S. patent 4,443,340 which teaches that a composition comprised o~ only inorganic phosphates and a polymeric inhibitor perforns 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. U.S. patent 4,547,540 teaches a method of corrosion inhibition relying on operation under conditions of high pH anc alkalinity. This method does not rely on the use of inorganic , ;
phosphates, givlng a more desirable product from an environmental impact point of view.
The current invention describes phosphonate corrosion inhibiting compounds, containing a unique series of polymers, phosphonates and to which may optionally be added aromatic azoles. The use of these polymers results in signi-ficantly improved corrosion inhibitor performance. -~
The use of the copolymers of this invention ac scale inhibitors is discussed in U.S. Patent No 4,~66,973. In general, these compounds are copolymers containing t-butyl acrylamide unlts ln conjunctlon wlth other comonomers. We have found that these compounds are effectlve calcium phosphonate lnhibltors and that they functlon effectlvely as cornponents ln a phosphonate containing corroslon lnhlbitor compound.
According to one aspect of the present lnventlon there ls provlded a composltlon for lnhlbltlng corroslon ln lndustrlal coollng waters whlch contaln hardness and have a pH
of at least 8 whlch composltlon comprlses: I. e phosphonate blend of 2-phosphonobutane-1,2,4-trlcarboxyllc acld and 1 hydroxy-ethylldene-l, l-diphosphonlc acid, and II. a water-soluble non-crossllnked random terpolymer of 40 to 90 welght parts of an acryllc acld, 5 to 30 welght parts of methacrylic acld, and 5 to 50 welght parts of a t-butylacrylamlde, besed on a total of 100 welght parts of polymer, sald polymer havlng a weight average molecular weight in the range of about 1,000 to 50,000, and the polymerlzed unlts of an acryllc acld and a t-butyl acrylamlde are deflned by the followlng formula:

R Rl ~CH2 f~ ~CH2 ~~n / R
O = C - OX O = N -\ R3 where m i8 ln the range of about 10-700 and n ls ln the range of about 0~1 to 350, sub~ec$ to the molecular welght llmltatlons; R and Rl are lndivldually selected from hydrogen and methyl; X ls selected from hydrogen, sodlum, potasslum, calclum, ammonlum and magneslum moletles; and R~ and R3 are --indlvldually selected from hydrogen, and substituted and unsub~tltuted groups each contalnlng a total of 1 to 8 carbon ~ 32q474 atoms, whereln the substltuents on R2 3 and/or R are selected from alkyl, aryl, and keto groups, provlded that elther R2 and/or R3 ls t-butyl, wlth the welght ratlo of polymer , phosphonate blend belng wlthln the range of 0.2/1 to 2/1.
The welght ratlo of II to I ls preferably 0.75/1.

The Pho~Phonates Generally any water-soluble phosphonate may be used that ls capable of providlng corroslon lnhlbitlon ln alkallne systems; for example U.S. 4,303,568 list~ a number of representatlve phosphonates.

The Orqano-PhosPhonlc Acld Derlvatlves~:~

Organo-pho~phonlc acld compounds are those havlng a carbon to phosphoru~ bond, l.e., - C I - OM

OM ~
Such compounds generally are lncluded ln one of ~ ;
perhaps 3 categories whlch are respectlvely expressed by the followlng ~eneral formulas:

R - P - OM -;
OM

where R is lower alkyl havins from about one to six carbon atoms, e.g., methyl, ethyl, butyl, propyl, isopropyl, pentyl, isopentyl and hexyl; substituted lower alkyl of from one to six carbon atoms, e.g., hydroxyl and amino-substituted alkyls; a mononuclear aromatic (aryl) radical, e.g., phenyl, benzene, etc., as a substituted mononuclear aromatic compound, e.g., hydroxyl, amino, lower alkyl subsitituted aromatic, e.g., benzyl phosphonic acid;
and M is a water-soluble cation, e.g., sodium, potassium, ammonium, lithium, etc. or hydrogen.
Specific examples of compounds which are encompassed by this formula include:
methylphosphonic acid ethylphosphonic acid CH3CH2Po3H2 2-hydroxyethylphosphonic acid 2-amino-ethylphosphonic acid isopropylphosphonic acid CH3-CH-cH2-po3 2 benzene phosohonic acid benzylphosphonic acid C 5CH2~o3 Z

_ 7 -o o 1 32~474 B ~ MO---P--R ~ P--OM I .
OM OM
wherein Rl is an alkylene having from about one to about 1~
ci~rbon atoms or a substituted alkylene having ~rom about 1 to -abûut 12 carbon atoms, e.g., hydroxyl, amino etc. substituted alkylenes, and M is as earlier defined above.
Specific exemplary compounds and their respective formulas which are encompassed by the above formula are as follows:
methylene diphosphonic acid H203P-cH2-pû3H2 1' ethylidene diphosphonic acid l H203P-CH(CH3 )P03H2 ~ I
isopropylidene diphosphonic acid ¦ (CH3)2C(Po3~2)2 l-hydroxy-l,l-ethane diphosphonic acid (HEDP) ¦ OH
l H203P-c(cH3)-po3H2 . l ' ~
¦ hexamethylene diphosphonic acid ~;

H2U3p-6~2(~H2)4cH2-po3H2 ¦ trimethylene diphosphonic acid l H203P-~H~)3-po3H2 ~ ~
decamethylene diphosphonic acid H203P-(~-~2)~o P3H2 l-hydroxy, propylidene diphosphonic acid -~

~2o3pc(oH)cH2(cH3)pû3H2 .. .. . ... . ... . . . . . . .... . . . . . . . ... . . . . . .

1,6-dihydroxy, 1,6-dimethyl, hexamethylene diphosphonic acid , H203PC(CH3)(0H)(CH2)4C(CH3)(0H)P03H2 dihydroxy, diethyl ethylene diphosphonic acid , H2o3pc(OH)(c2H5)c(OH)(c2H5)po3H2 C . ~ R2--I--OM

where R2 is a lower alkylene having from about one to about four carbon atoms, or an amine or hydroxy substituted lower alkylene; R3 is [R2-PO3M2] H, OH, amino, substituted amino, an alkyl having from one to six carbon atomsl a substituted alkyl of from one to six carbon atoms ~e.g., OH, NH2 substituted) a mononuclear aromatic radical and a substituted mononuclear aromatic radical (e.g., OH t NH2 .
substitutedj; R4 is R3 or the group represented by the formula N~R ~--~ OM

where R5 and R6 are each hydrogen, lower al~yl of from about one to six carbon atoms, a substituted lower alkyl (e.g., OH, NH2 substituted), hydrogen, hydroxyl, amino group, suostituted amino group, a mononuclear aromatic radical, and a substituted mononuclear aromatic radical (e.g., OH and amine substitutea); R
is R5, R6, or the group R2-PO3M2 (R2 is as defined above); n is a number of from 1 through about 15; y is a num~er of from about 1 through about 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(CH2P03H2)2 n-butyl-amino-di(methyl phosphonic acid) C4H9N(CH2po3H2)2 decyl-amino-di(methyl phosphonic acid~

CloH21N(cH2Po3H2)2 trisodium-pentadecyl-amino-di-methyl phosphate ClSH31N(CH2P03HNa) (CH2P03Na2) n-butyl-amino-di(ethyl phosphonic acid) C4HgN(CH2cH2Pû3H2)2 tetrasodium-n-butyl-amino-di(methyl phosphate) C4H9N(CH2po3Na2)2 triammonium tetradecyl-amino-di(methyl phosphate) C14H2gN(CH2P03(NH4)2)CH2P03HNH4 phenyl-amino-di(methyl phosphonic acid) -:~
C6H5N(~H2Po3H2)2 4-hydroxy-phenyl-amino-di(methyl phosphonic acid) . Hoc6H4N(cH2po~H2)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) 203PCH2)2N(CH2)2N(CH2P03H2)2 trimethylene diamine tetra(methyl phosphonic acid) (H2o3pt~H2)2N( H2)3N(cH2po3H2)~
hepta me~hylene diamine tetra(methyl phosphonic acid) ¦ ~. (H2o3pcH2)2N(c~2)7N(cH2po3H2)2 decamethylene diamine tetra(methyl phosphonic acid) (H2o3pcH2)2N(cH2) 1oN(cH2po3H~)2 tetradecamethylene diamine tetra(methyl phosphonic acid) 2 3 CH2)2N(CH2)l4N(cH2po3H2)2 ethylene diamine tri(methyl phosphonic acid) ( 2o3P~H2)2N(CH2)2NHCH2P03H2 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(cH2po3 2) (CH2)2N(CH2Po3H2)2 ethanol amine di(methyl phosphonic acid) HO(CH2)2N(cH2po3H2)2 n-hexyl-amino(isopropylidene phosphonic acid)methylphosphonic acid 6 13N(C(cH3)2Po3H2)(cH2po3H2) trihydroxy methyl, methyl amine di(methyl phosphonic acid (HOCH2)3CN(cH2Po3H2)2 triethylene tetra amine hexa(methyl phosphonic acid) 2 3 2)2N(CH2)2N(CH2P03H2)(CH2)2N-(cH2po3H2) ~CH2)2N(cH2Po3H2)2 monoethanol, diethylene triamine tri(methyl phosphonic acid 2CH2N(CH2P03H2) (CH2)2NH(CH2)2N-(cH2po3H2)2 chloroethylene amine di(methyl phosphonic acid) ClCH2CH2N( (CH2P(H)2)2 The above compounds are lncluded for lllustratlon purposes and are not lntended to be a llstlng of compounds wlthln the conflnes of the lnventlon.
However, as deflned above, the present inventlon :~
relates to a blend of A. 2-phosphonobutane-1, 2; 4~trlcarboxyllc acld (PBTC~
and B. l-hydroxyethane-l, l-dlphosphonlc acld (HEDP~
While lndl~Jldual phosphonates may be used ln comblnatlon wlth polymer~s) it has now been found that better results are obtained by uslng a blend of phosphonates A and B.
They are preferably comblned ln a welght ratlo of A:~ of from .5/1-4/1 and are more preferably from .5/1-2/1 and most preferably about .67/1.
In additlon to phosphonates, addltlves such as tolyltrlazole may be utillzed. Tolyltrlazole ls effectlve ln the reductlon of copper substrate corrosion.

The Water-~oluble Noncrossed Llnked Random CoPolYmers These polymers are descrlbed in detall ln U.S.
4,566,973, whereln they are descrlbed by the patentee as follows:
The copolymers suitable hereln are random polymers contalnlng polymerlzed unlts of an acryllc acld and substltuted acrylamlde, represented by the followlng structural formula I:

Rl ~
-~CH - lt -~CH~ - C~ ~2 0 ~ C - OX O = C - N
\ R3 1 3 2 q 4 7 4 66530-434 whereln m and n are numbers ln the range of about 0.1 to 700, wlth m belng in the range of about 10 to 700 and n ls ln the range of about 0.1 to 350, sub~ect to molecular welght limitations; R and Rl are lndivldually selected from hydrogen and methyl; X ls hydrogen, alkall metal, alkaline earth metal, or ammonium, partlcularly hydrogen, sodlum, potasslum, calcium, ammonlum, and magneslum; and R and R3 are lndlvidually selected from hydrogen, alkyl and substltuted alkyl ~roups each contalnlng a total of 1 to 8 carbon atoms, provided that elther R and/or R ls t-butyl. Substltuents on the R and R groups include alkyl, aryl, and keto groups, however, ln a preferred embodlment, R2 and ~ are lndlvldually selected from alkyl groups of 1 to 8 carbon atoms and substltuted alkyl groups of 1 to 8 carbon atoms contalnlng a keto substltuent group.
Speclflc examples of R2 and R3 lnclude t-butyl, lsopropyl, lsobutyl, methyl, 2-~2,4,4-trlmethylpentyl) and 2-(2-methyl-4-o~opentyl).
Sultable acryllc aclds for purposes hereln are generally deflned as monounsaturated monocarboxyllc aclds contalning 3 to 4 carbon atoms. Speclflc examples of such aclds lnclude acryllc and methacryllc aclds, wlth acryllc acld belng preferred.
Other comonomers can be used wlth an acryllc acld and a t-butyl acrylamlde provlded that such addltlonal comonomers do not deleterlously affect the deslred properties. Examples of ~uch comonomer~ lnclude acrylate and methacrylate esters, acrylamlde and methacrylamlde, acrylonltrile, vlnyl esters, ~tc.
The acryllc acid unlts in the copolymer can be ln the acld for~ or ln a nPutrallzed form where the hydrogen of the ~ 13 1 329~7~ ~
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.
1~ 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 about 50% to about 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 o~ 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, vinyl ethers and the like. Illustrative of these monomers are the compounds: vinyl pyrrolidone, methyl vinyl ether, methacrylonitrile, allyl alcohol, methyl methacrylate, beta-diethylaminoethyl methacrylate, vinyl trimethylacetate, methyl lsobutyrate, cyclohexyl methacrylate, vlnyl laurate, vlnyl stearate, N-vinyl imldes, N-vlnyl lactams, diethylene glycol dimethacrylate, dlallylmaleate, allyl methacrylate, dlallyl phthalate, diallyl adlpate, etc.
The polymers formed may have weight average molecular welght in the range of about 1,000 to about 50,000, and prefer-ably about 2,000 to about 30,000, more preferably 9,000 to 30,000, as determlned by aqueous gel permeatlon chromatography uslng polys~yrene of known molecular weight as a reference material.
The acld numbers of the copolymers formed, as deter-mlned by a conventlonal tltratlon wlth KOH, may range from 310 to about 740, corresponding to a welght fractlon of from 40% to about 95% by welght of monomer units having COOH groups. The preferred polymers have more than 50% by welght of free car-bo~yl groups and an acld number ln the range from about 390 to about 700.
Preferred species are descrlbed ln Table A below as Polymer Composltion Nos. 1-12.

. ' ~ j~...

~ 32q474 ~ .

Table A
Polymer Materials Polymer Composition No. M.W. Composition (mol%)**
(9300) AA/ t-BAm (88: 12) 2 (12000) "

3 (17700) "

4 (25900) "

(8900) AA/EA/t-BAm (86: 8: 6) _ _ _ _ _ _ -- -- -- .
6 (9400) AA/Am/t-BAm (84: 11:6) .:
7 ( 8200) AA/MAA/ t-BAm (68 : 19 : 13) ::
8 (13300)~
9 (14300)* " , (15700)~
11 (15600) " :
12 (23000) 1l :
'~

Weight average molecular weight, i.e. M.W. or Mw.
* Aqueous Mw estimated from GPC value using the THF eluent.
** AA: Acrylic Acid t-BAm: tert-butyl acrylamide EA: ethyl acrylate Am: Acrylamide MAA: methacrylic ~cid ~ 3~q474 66530-4~4 Polymer Composltlon Nos. 1-4 are unneutrallzed copolymers of acryllc acld and t-butylacrylamlde (t-~Am).
Polymer Composltlon No. 5, Polymer Compositlon No. 6, and Polymer Composltlon Nos. 7-12 are terpolymers which respec-tlvely contaln the addltlonal mer unlts of ethyl acrylate (EA), acrylamlde (Am), and methacryllc acid (MAA).
A dlstlnctlve feature of all these polymers ls the t-butylacrylamlde unlt. That sterlcally-hindered, hydrophoblc alkylamlde group exhlblts excellent reslstance to hydrolysis and the unlt appears to confer exceptlonal performanse charac-terlstlcs upon polymers.
The copolymers composed of acrylic acld and t-butyl acrylamlde contalns between 50 to 90~ by welght of acryllc acld and from 10-50% by welght of t-butyl acrylamlde. Preferably the acryllc acid ls present in a weight percent amount ranging between 70-90 wlth the t-butyl acrylamlde belng present at between 10-30. Most preferably the acryllc acld ls present ln a weight percent amount ranglng between 80-90 with the t-butyl acrylamide being present at between 10-20.
The terpolymers are wlthin the followlng welght per- -cent composltion ranges:
a) acryllc acld 40-90 more preferably 40-80 and most preferably 60-80 b) methacryllc acld 5-30 more preferably 10-30 and most preferably 10-20 c) t-butyl acrylamlde 5-50 more preferably 10-30 and most preferably 10-20 Dosa~e The aqueous system ls dosed based on actlve lngredl-ents to provlde thereto on a welght basls from between 5-50ppm, preferably 8 to 30ppm, more preferably 8 to 40ppm and most pre-ferably 15-30ppm of Composltlons I and II prevlously descrlbed.

~ J
t ~

1 32~474 When the ccmpositions are first added it is beneficial if they are dosed on the high 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 pH
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 80 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.
Description of the PREFERRED Embodiment The following example is a representative formulation used in this program.
Example 1 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 l-hydroxyethane-l,l-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 solutlon. During the addition of base, the solutionls temperature was maintained 1 32q~74 ¦below 130F. The pH was adjusted to 13 with 4.7 grams of a 50 weight Percent of a sodium tolyltriazole solutiQn. Finally, sufficient softened water to produce 100 grams of product were ad~ed. 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.
EXPERIMENTAL PRûCEDURES
...., In laboratory tests, hardness cations and M alkalinity are expressed as CaCû3 or cycles of concentration. Fe'n 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.
Calcium Phosohonate Inhibition A standard heated "beaker" test was employed for evaluating perfor~ance of phosphonate inhibitors (Table B).
Calcium and inhibitor stock solutions from the calcium phosphate inhibition test were used. In addition, stock solutions (lOOû
ppm actives) of Bayer PBS-AM and Dequest 2ûlû were prepared.
Dequest-2ûlû, made by the Monsanto Company, St. Louis, Missouri is described as hydroxy ethylidene 1, l-diphosphonic acid (HEDP) (CF. U.S. Patent No. 3,95~,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+2C. The stock solutions were added to attain 36û ppm Ca+2, lû ppm inhibitor, 5.6 ppm Dequest and 8 ppm ~-P85-AM in the final 50û mL test volume. Next, the pH was adjusted to 9.2 usinQ aqueous sodium hydroxide.
- 19 - ~:
~rad ark ... . - . . - . - . . --: : . : , . , -.
1 32q474 . .
The pH of the test samples was manually adjusted at 15 minute intervals during tne first hour and at 1 hour intervals, subsequently. A four hour test duration 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, û.45 um). ~oth filtered and unfiltered aliquots were spectrophotometrically analyzed for total phosphate content. To study particle size effects, an additional sample ~as passed through a û.lû um Millipore filter (type VC). The % inhibition was determined by a following formula:
[filtered - blank]
inhibition = X 100 [unfiltered - blank]

* Trade Mark 1 32~474 Table B
Calcium Phosphonate Inhlbition 10 ppm polymer actives 5.6 Dpm Deauest 2010 & 8 cpm Bayer PBS-AM (as actives) 360 ppm Ca (as CaC03) 140F / pH 9.2 ~ 4 hrs.
% Inhibition Polymer ... filter size (um).............. ~ :
Oomp. No. (M-W- H20) 0-45 0.10 1 (9300) 8~ 26 _ (8900) 74 24 6 (9400~ 8 13 11 (15600) 98 5 _ Versa*TL-4 (19000) 95 26 :

* Trade Mark :~.

- 2 1 - :

132q474 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 û.45 um, 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 ¦um 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 um ¦ filter), but performance decreased rapidly when the filter pore ¦size was reduced to 0.10 um. In particular, Polymer Composition ¦NO. 11 exhibited the best overall performance in both bench-top ¦and PCT tests.
¦Performance in Products -_PCT Tests ¦pilot cooling tower test procedure The pilot cooling tower test is a dynamic test ~hich simulates many features present in an industrial recirculating cooling water system. The general test metnod is described in the article "Small-Scale Short-Term Methods of Evaluating Cooiing Water Treatments...Are They Worthwhile?", by D. T. Reed and R.
Nass, Minutes of the 36th Annual Meeting of the INTERNATIONAL
WArER CONFERENCE, Pittsburgh, Pennsylvania, November 4-6, 1975.
The general operating conditions are provided in Table C.

Table C
Pilot Cooling Tower Operating Conditicns Tube # ~t ~ (atu/ft2-hr) 8 MS/15,000 (top) 7 SS/15,000 6 ~S/12,400 Adm/5,000 4 MS/ 5,000 3 SS/12,400 2 Adm/12,400 1 SS/12,400 (bottom) Make-up water: Synthetic #3**
Desired Cycles: 4 Basin Volume/Temp.~** 50L/125F :
Holdinq Time Index 24 hr.
Flow Rate 2 gpm pH 9.2 Product - high level 200 ppm " - maintenance 100 ppm Test Duration 14 days *MS = Mild Steel Adm = Admiralty brass SS - 306 Stainless steel **Synthetic #3 contains total ion content of 90 ppm Ca~2, 50 ppm ~q~2, 90 pom Cl-, 50 DDm sulfate, 110 opm Na+, and 110-120 ppm "M" alkalinity (as CaC03).

***Return water is 10F higher Polymer Composition Nos. 1, 3, 5, 6, 7 and 11, as descri~ed 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 (120F./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:

l 3~9474 Table D
Heat Exchange Tube Results Polymer (ppm actives) Deposit (mg!day) Corrosion (mpy) MS Adm SS MS AdmSS

Blank - No polymer * 148 8 -- 8.80.6 --Polymer Composition No. 1(7.5) 72 10 42 2.8 0.45 0.0 Polymer Composition No. 3(7.5) 30 2 37 1.3 0.0 -0.1 Polymer Composition No. 5(7.5) 76 15 49 2.9 0.35 0.0 Polymer Composition No. 6(7.5) 101 26 72 3.1 0.20 0.1 Polymer Com,oosition No. 7(7.5) 57 10 94 1.3 0.05 0.0 Polymer Composition No. 11 (7.5) 21 3 15 1.3 0.25 0.1 Polymer Composition No. 11 (5) *~ 50 1 22 2.9 0.04 0.0 Versa TL-4 (7.5) 54 7 27 2.8 0.20.0 * Blank was run at return temperature of 11ûF. This reduction in severity of test conditions for the blank was necessitated by excessive scaling at higher temperatures.

** Averaqe of two tests.

-- ~5 --¦ It has been found advisable in some cases to add sma11 quantities Of tolyltriazole.
¦ Tolyltriazole is explained in Hackh's Chemical Dictionary, Fourth Edition, page 91 (CF. ~enzotriazole) 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 1-2ûppm by weight.
I . .

~ . ' ..
, ~

Claims (3)

1. A composition for inhibiting corrosion in industrial cooling waters which contain hardness and have a pH of at least 8 which composition comprises:
I. a phosphonate blend of 2-phosphonobutane-1,2,4 tricarboxylic acid and 1-hydroxyethylidene-1,1-diphosphonic acid, and II. a water-soluble non crosslinked random terpolymer of 40 to 90 weight parts of an acrylic acid, 5 to 30 weight parts of methacrylic acid, and 5 to 50 weight parts of a t-butylacrylamide, based on a total of 100 weight parts of polymer, said polymer having a weight average molecular weight in the range of about 1,000 to 50,000, and the polymerized units of an acrylic acid and a t-butyl acrylamides are defined by the following formula:

where m is in the range of about 10-700 and n is in the range of about 0.1 to 350, subject to the molecular weight limitations;
R and R1 are individually selected from hydrogen and methyl;
X is selected from hydrogen, sodium, potassium, calcium, ammonium and magnesium moieties; and R2 and R3 are individually selected from hydrogen, and substituted and unsubstituted groups each containing a total of 1 to 8 carbon atoms, wherein the substituents on R2 and/or R3 are selected from alkyl, aryl, and keto groups, provided that either R2 and/or R3 is t-butyl, with the weight ratio of polymer:phosphonate blend being within the range of 0.2/1 to 2/1.

2. The composition of claim 1 further including a corrosion inhibiting amount of tolytriazole.

3. The composition of claim 1, wherein the terpolymer has a weight average molecular weight of 9,000 to 30,000.