CA1339521C - Composition and method for preventing corrosion in aqueous systems - Google Patents
Composition and method for preventing corrosion in aqueous systemsInfo
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- CA1339521C CA1339521C CA 530973 CA530973A CA1339521C CA 1339521 C CA1339521 C CA 1339521C CA 530973 CA530973 CA 530973 CA 530973 A CA530973 A CA 530973A CA 1339521 C CA1339521 C CA 1339521C
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Abstract
A composition and method for inhibiting corrosion in industrial cooling waters which contain hardness and a pH of at least 6.5, which composition comprises a water-soluble inorganic phosphate 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. A
water-soluble organic phosphonate capable of inhibiting corrosion in an alkaline environment may be used as an adjunct for the phosphate.
water-soluble organic phosphonate capable of inhibiting corrosion in an alkaline environment may be used as an adjunct for the phosphate.
Description
~ ~-- 133!~521 r~ INTRODUCTION
This invention is related to the preparation of ~orrosion inhibitin9 formulations containing inorganic ?hosphates or combinations of inorganic phosphates and phosphonates and a novel, random copolymer. In subsequent discussions and claims, concentrations of polymers, phosphonates, phosphates, azoles and combinations thereof are listed as actives.
aACK GROUND Of THE INVENTION
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 can occur through areas subject to deterio-ration, for example between a water system and a process stream.
Corrosion of iron in oxygenated waters is known to occur by the following coupled electrochemical processes:
1. Fe~- ~ Fe+2 + 2e (Anodic Reaction) 2. ~2 + 2e~ --~ 20H- (Cathodic Reaction) Inhi~ition of metal corrosion by oxygenated waters typically invo~ves the formation of protective oarriers on the metal surface. rnese barriers prevent oxygen from reaching the metal surface anc~ causing metal oxidation. In order to function as a corrosion inhibitor, a chemical additive must faciliate this process, so that an oxygen_impermeable barrier is formed and maintained. This can be done by interaction with either the cathodic or anodic half-cell reaction.
.
1~9521 Inhibitors can interact with the anodic reaction (1) by causing ~he resultant Fe 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, Fe 3compounds are typically 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 product of this reaction is the hydroxyl (OH-) -ion. Because of this production of hydroxyl, 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.
.
PRIûR ART
The use of inorganic phosphates and phosphonates in conjunction with a threshold inhibitor in order to control corrosion by oxysenated waters is descrioe~ in ~.S. 4,303,568.
This method is ~urther elaboratea in U.S. 4,443,340 which teaches that a compositicn comprised of only inorganic phosphates and a polymeric inhibitor gives superior performance in the presence of dissolved iron.
.. .. . .
:.
- '. .
, . .
-- The use of the polymers of this invention as scale inhibitors is discussed in U. S. 4,566,973. In general, these compounds are copolymers containing t-butyl acrylamide units in conjunction wlth other comonomers. It has been surprisingly ~,-~-found that these polymers can function effectively as components in a corrosion inhibitor formulation containing inorganic phosphates.
GENERAL DESCRIPTION OF THE INVENTION
According to the present invention, there is provided a concentrated composition for use in diluted form for inhibiting corrosion in industrial cooling waters which contain hardness and have a pH of at least 6.S which composition comprises:
I. a water-soluble inorganic phosphate capable of inhibiting corrosion in an aqueous alkaline environment as a first active ingredient, and II. a water-soluble non-crosslinked random polymer of 50 to 90 weight parts of an acrylic acid and 10 to 50 weight parts of a substituted acrylamide, on the basis of a total of 100 weight parts of polymerized monomers, 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 substituted acrylamide are defined by the following formula:
R R
( CH2 C ) m ( CH2 C 3 n O = C - OX O = C - R
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 Rl are individually selected from hydrogen and methyl;
- 13~9521 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 l to 8 carbon atoms, wherein the. substituents on R2 or R3 are selected from alkyl, aryl, and keto groups, provided that R2 or R3 is other than hydrogen, with the weight ratio of polymer:phosphate being within the range of 0.1:1 to 5:1 and, if required, III. a diluent or carrier with the proviso that the composition comprises, when taken together, at least 100 ppm of said active ingredients. In a preferred embodiment, R2 and R3 are individually selected from alkyl groups of 1 to 8 carbon atoms and substituted alkyl groups of 1 to 8 carbon atoms containing a keto substituent group. Specific examples of R and R include t-butyl, isopropyl, isobutyl, methyl, 2-(2,4,4-trimethylpentyl) and 2-(2-methyl-4-oxopentyl).
According to another aspect of the invention there is provided a method for inhibiting corrosion of steel in aqueous cooling systems having hardness and a pH of at least 6.5 by dosing said system with:
from 10-50 ppm of a composition comprising:
I. a water-soluble mixture of inorganic orthophosphate and condensed phosphate capable of inhibiting corrosion in an aqueous alkaline environment, and II. a water-soluble non-crosslinked randompolymer of 50 to 90 weight parts of an acrylic acid and lO to 50 weight parts of a substituted acrylamide, on the basis of a total of lO0 weight parts of polymerized monomers, said polymer having weight average molecular weight in the range of about 9,000 to 30,000 and the polymerized units of an acrylic acid and a substituted acrylamide are defined by the following formula:
B s . ~ . .
39~21 -- .
R R
CH2--lC ) m ( CH2 C--t--~n Hl 1 2 O = C - OX O = C - N C CH
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 Rl are individually selected from hydrogen and methyl;
X is selected from hydrogen, sodium, potassium, calcium, ammonium and magnesium moieties; with the weight ratio of polymer to phosphate being within the range of 0.1:1 to 5:1.
Suitable acrylic acids for purposes herein are generally defined as monounsaturated monocarboxylic acids containing 3 to 4 carbon atoms. Specific examples of such acids include acrylic and methacrylic acids, with acrylic acid being preferred. Substituted acrylamides referred to herein are generally defined to include the class of acrylamide substituted on the nitrogen atom with alkyl groups each containing 1 to 8 carbon atoms.
Other comonomers can be used with an acrylic acid and a substituted acrylamide provided that such additional comonomers do not deleteriously affect the desired properties.
Examples of such comonomers include acrylate and methacrylate esters, acrylamide and methacrylamide, acrylonitrile, vinyl esters, etc.
The acrylic acid units in the copolymer can be in the acid form or in a neutralized form where the hydrogen of the ' ~ ~ ' ' "' . . .
13~g5~1 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. '~ith 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 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 consisting preferably of amido, lower alkyl ester, and maleic acid salt groups, although other groups, as noted above, can ~e used.
Examples of preferred monomers that may be polymerized to form terpolymers are acrylamide, methyl or ethyl acrylate, and maleic anhydrides. Other polar monomers that may be used are, for example, vinyl acetate, acrylonitrile, the various vinvl 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, .. .. __ . ~ ;.
1339~21 methyl isobutyrate, cyclohexyl methacrylate, vinyl laurate, vinyl stearate, N-vinyl imides, N-vinyl lactams, oietnylene glycol dimethacrylate, diallylmaleate, allyl methacrylate, diallyl phthalate, diallyl adipate, etc.
The polymers formed may have weight average molecular weight in the range of about l,ûûO to about 5û,0ûû, and preferably about 2,ûOû to about 30,0ûû, as determined by aqueous gel permeation chromatography using polystyrene of known molecular weight as a reference material.
The acid numbers of the copolymers formed, as oetermined by a conventional titration with KOH, may range from 31û to about 740, corresponding to a weight fraction of from 40% to aDout 95%
by weight of monomer units having COûH groups. The preferred polymers have more than 50% by weight of free carboxyl groups and an acid number in the range from about 390 to about 700.
Preferred species are described in Table A below as Polymer Composition Nos. 1-12.
~- 1339521 .
, ~ Table A
Polymer Materials Polymer Composition No. M.W. Composition (mol%)**
1 (9300) AA/t-BAm (88:12) 2 (12000), "
This invention is related to the preparation of ~orrosion inhibitin9 formulations containing inorganic ?hosphates or combinations of inorganic phosphates and phosphonates and a novel, random copolymer. In subsequent discussions and claims, concentrations of polymers, phosphonates, phosphates, azoles and combinations thereof are listed as actives.
aACK GROUND Of THE INVENTION
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 can occur through areas subject to deterio-ration, for example between a water system and a process stream.
Corrosion of iron in oxygenated waters is known to occur by the following coupled electrochemical processes:
1. Fe~- ~ Fe+2 + 2e (Anodic Reaction) 2. ~2 + 2e~ --~ 20H- (Cathodic Reaction) Inhi~ition of metal corrosion by oxygenated waters typically invo~ves the formation of protective oarriers on the metal surface. rnese barriers prevent oxygen from reaching the metal surface anc~ causing metal oxidation. In order to function as a corrosion inhibitor, a chemical additive must faciliate this process, so that an oxygen_impermeable barrier is formed and maintained. This can be done by interaction with either the cathodic or anodic half-cell reaction.
.
1~9521 Inhibitors can interact with the anodic reaction (1) by causing ~he resultant Fe 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, Fe 3compounds are typically 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 product of this reaction is the hydroxyl (OH-) -ion. Because of this production of hydroxyl, 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.
.
PRIûR ART
The use of inorganic phosphates and phosphonates in conjunction with a threshold inhibitor in order to control corrosion by oxysenated waters is descrioe~ in ~.S. 4,303,568.
This method is ~urther elaboratea in U.S. 4,443,340 which teaches that a compositicn comprised of only inorganic phosphates and a polymeric inhibitor gives superior performance in the presence of dissolved iron.
.. .. . .
:.
- '. .
, . .
-- The use of the polymers of this invention as scale inhibitors is discussed in U. S. 4,566,973. In general, these compounds are copolymers containing t-butyl acrylamide units in conjunction wlth other comonomers. It has been surprisingly ~,-~-found that these polymers can function effectively as components in a corrosion inhibitor formulation containing inorganic phosphates.
GENERAL DESCRIPTION OF THE INVENTION
According to the present invention, there is provided a concentrated composition for use in diluted form for inhibiting corrosion in industrial cooling waters which contain hardness and have a pH of at least 6.S which composition comprises:
I. a water-soluble inorganic phosphate capable of inhibiting corrosion in an aqueous alkaline environment as a first active ingredient, and II. a water-soluble non-crosslinked random polymer of 50 to 90 weight parts of an acrylic acid and 10 to 50 weight parts of a substituted acrylamide, on the basis of a total of 100 weight parts of polymerized monomers, 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 substituted acrylamide are defined by the following formula:
R R
( CH2 C ) m ( CH2 C 3 n O = C - OX O = C - R
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 Rl are individually selected from hydrogen and methyl;
- 13~9521 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 l to 8 carbon atoms, wherein the. substituents on R2 or R3 are selected from alkyl, aryl, and keto groups, provided that R2 or R3 is other than hydrogen, with the weight ratio of polymer:phosphate being within the range of 0.1:1 to 5:1 and, if required, III. a diluent or carrier with the proviso that the composition comprises, when taken together, at least 100 ppm of said active ingredients. In a preferred embodiment, R2 and R3 are individually selected from alkyl groups of 1 to 8 carbon atoms and substituted alkyl groups of 1 to 8 carbon atoms containing a keto substituent group. Specific examples of R and R include t-butyl, isopropyl, isobutyl, methyl, 2-(2,4,4-trimethylpentyl) and 2-(2-methyl-4-oxopentyl).
According to another aspect of the invention there is provided a method for inhibiting corrosion of steel in aqueous cooling systems having hardness and a pH of at least 6.5 by dosing said system with:
from 10-50 ppm of a composition comprising:
I. a water-soluble mixture of inorganic orthophosphate and condensed phosphate capable of inhibiting corrosion in an aqueous alkaline environment, and II. a water-soluble non-crosslinked randompolymer of 50 to 90 weight parts of an acrylic acid and lO to 50 weight parts of a substituted acrylamide, on the basis of a total of lO0 weight parts of polymerized monomers, said polymer having weight average molecular weight in the range of about 9,000 to 30,000 and the polymerized units of an acrylic acid and a substituted acrylamide are defined by the following formula:
B s . ~ . .
39~21 -- .
R R
CH2--lC ) m ( CH2 C--t--~n Hl 1 2 O = C - OX O = C - N C CH
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 Rl are individually selected from hydrogen and methyl;
X is selected from hydrogen, sodium, potassium, calcium, ammonium and magnesium moieties; with the weight ratio of polymer to phosphate being within the range of 0.1:1 to 5:1.
Suitable acrylic acids for purposes herein are generally defined as monounsaturated monocarboxylic acids containing 3 to 4 carbon atoms. Specific examples of such acids include acrylic and methacrylic acids, with acrylic acid being preferred. Substituted acrylamides referred to herein are generally defined to include the class of acrylamide substituted on the nitrogen atom with alkyl groups each containing 1 to 8 carbon atoms.
Other comonomers can be used with an acrylic acid and a substituted acrylamide provided that such additional comonomers do not deleteriously affect the desired properties.
Examples of such comonomers include acrylate and methacrylate esters, acrylamide and methacrylamide, acrylonitrile, vinyl esters, etc.
The acrylic acid units in the copolymer can be in the acid form or in a neutralized form where the hydrogen of the ' ~ ~ ' ' "' . . .
13~g5~1 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. '~ith 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 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 consisting preferably of amido, lower alkyl ester, and maleic acid salt groups, although other groups, as noted above, can ~e used.
Examples of preferred monomers that may be polymerized to form terpolymers are acrylamide, methyl or ethyl acrylate, and maleic anhydrides. Other polar monomers that may be used are, for example, vinyl acetate, acrylonitrile, the various vinvl 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, .. .. __ . ~ ;.
1339~21 methyl isobutyrate, cyclohexyl methacrylate, vinyl laurate, vinyl stearate, N-vinyl imides, N-vinyl lactams, oietnylene glycol dimethacrylate, diallylmaleate, allyl methacrylate, diallyl phthalate, diallyl adipate, etc.
The polymers formed may have weight average molecular weight in the range of about l,ûûO to about 5û,0ûû, and preferably about 2,ûOû to about 30,0ûû, as determined by aqueous gel permeation chromatography using polystyrene of known molecular weight as a reference material.
The acid numbers of the copolymers formed, as oetermined by a conventional titration with KOH, may range from 31û to about 740, corresponding to a weight fraction of from 40% to aDout 95%
by weight of monomer units having COûH groups. The preferred polymers have more than 50% by weight of free carboxyl groups and an acid number in the range from about 390 to about 700.
Preferred species are described in Table A below as Polymer Composition Nos. 1-12.
~- 1339521 .
, ~ Table A
Polymer Materials Polymer Composition No. M.W. Composition (mol%)**
1 (9300) AA/t-BAm (88:12) 2 (12000), "
3 (17700) "
4 (25900) " ~~~ ~
_ (8900) AA/EA/t-BAm (86:3:6) _ 6 (9400) AA/Am/t-BuAm (84:11:6) -- -- _ _ _ _ _ _ _ _ _ _ _ _ 7 (8200) AA/MAA/t-BAm (58:19:13) 8 (13600)* "
9 (14300)* "
(15700)* ~
11 (15600) "
12 (23000) "
Weight ave. ige molecular weight, i.e. M.W. or Mw * Aqueous Mw estimatea from GPC value using THf eluent.
** AA: Acrylic Acid EA: Ethyl acrylate t-BAm: tert-butylacrylamide MAA: Methacrylic acid Am: Acrylamide ,~
,, ~
j ~ 5~ S~
Polymer Composition Nos. 1-4 are unneut.ali~ed copolymers of acrylic acid and t-butylacrylamide (t-~Am).
Polymer ComPosition No. 5, Polymer Composition No. 6, ana 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 appears to confer exceptional performance characteristics upon these polymers.
The coPolymers composed of acrylic acid and t-butyl acrylamide contain between 5û to 9û% by weight of acrylic acid and from lû-50% by weight of t-butyl acrylamide. Preferably the acrylic acid is present in a weight percent amount ranging between 7û-90 with the t-butylacrylamide being present at betweer lû-30. 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 10-2û.
The terpolymers are within the following weight percent composition ranges:
a) acrylic acid 40-90, more preferably 40-80, and most ~referably 60-80 b) metnacrylic acid 5-30, more preferably lG-30, and most preferably 10-20 c) t-ou.vl acrylamide 5-50, more preferably 10-30, and most p.eferably 10-20 g - 133~ The ?hos~honates Generally any water-soluble phosphonate may be used that i~ capable of providing corrosion inhiDition in alkaline systems. U. S. 4,303,568 wnich lists a number of representative phosphonates.
The organo-phosphonic acid compounds are those having a carbon to phosphorus bond, i.e., O
- C -P-OM
- OM
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:
o A. ~- 3~OM
OM
where R is lower alkyl having from aoout one to six caroon atoms, e.g., methyl, ethyl, butyl, Propyl~ isopropyl, Pentyl, isopentyl and hexyl; substituted lower alkyl of from one to six carbon atoms, e.g., hydloxyl-and amino-substituted alkyls; a mononuclear aromatic (aryl) Ladical, e.g., phenyl, nenzene, etc., or a substituted mcnsn~~lear aromatic compound, e.g., hydroxyl, amino, l~wer alkyl substituted aromatic, e.g., benzyl phosphonic acic;
and M is a water-soluble cation, e.g., sodium, potassium, ammonium, lit~ im, etc. or i~yarogen.
,,~.
h-- ~33g~21 Specific examples of compounds which are encompassea by th1s formula include:
methylphosphonic acid ethylphûsphonic acid CH CH Pû H
2-hydroxyetnyl~hosphonic acid CH2-CH2-~03H2 OH
2-amino-ethyl~hosphonic acid CH2-CH2-Po3 2 isopropylphosphonic acid ,CH3 benzene phosphonic acid benzylphosphonic acid O O
R. Mo-7~ 7 - 3M
-M OM
wherein Rl is an alkylene having from about one to about 12 carcbon atoms or a substituted al~ylene having from aoout 1 to about 12 caroon atoms, e.g., hydroxyl, amino etc. substituted alkylenes, and ~ lS as earlier defined above.
-~ 1339~21 Specific exemplary compounds and their respective _ formulas which are encompassed by the above formuia are as follows:
methylene diphosphonic acid H203P-CH2-Po3H2 ethylidene diphosphonic acid H2O3P-cH(cH3)po3 2 isopropylidene diphosphonic acid (CH3)2C(P03H2)2 l-hydroxy, ethylidene diphosphonic acid (HEDP) OH
H2O3P-c(cH3)-po3H2 hexamethylene diphosphonic acid H203P-CH2(cH2)4cH2-po3H2 trimethylene diphosphonic acid H2O3P-(cH2)3-po3 2 decamethylene diphosphonic acid ----H203P- (C H2 ) 10-PO3H2 l-hydroxy, propylidene diphosphonic acid H203p'' (OH)CH2(CH3)Po3H2 1,6-dihydrcxy, 1,6-dimethyl, hexamethylene diphosphonic acid 203P-('H3)(0H)(CH2)4c(cH3)(oH)po3H2 dihydroxy, ~.ethyl ethylene diphosphonic acid 203PC ~ JH ) (C2H5 )C (OH ) (C2H5 )PO3H2 -C. ~-R~ OM 1~ 3 9 ~ 2 ~
R~ 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-Pû3M2] H, OH, amino, substituted amino, an alkyl having from one to six caroon atoms, a substituted alkyl of from one to six carbon atoms (e.g., ûH, NH2 substituted) a mononuclear aromatic radical and a substituted mononuclear aromatic radical (e.g., OH, NH2 substituted); R4 is R3 or the group represented by the formula C ~z--~-0.
~n y where R5 and R6 are each hydrogen, lower alkyl of from about one to six carbon atoms, a substituted lower alkyl (e.g., OH, ~ ~
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 R5~ Q6' or the group R2-P~3M2 (R2 is as defined above); n is a number of from 1 through about 15; y is a number of from abou~ rough about 14; and 1~ is as earlier aeflnea.
Compounds or Cormulas therefore which can be considerea exemplary for tho above formulas are as follows:
nitrilo-trl(methylene phosphonic acid) N(CH2PO3H2)3 .~
~- 1339~21 imino-ai(methylene phosphonlc acid) NH(CH2po3H2)2 n-butyl-amino-di(methyl phosphonic acid) C4HgN(cH2Po3H2)2 decyl-amino-di(methyl phosphonic acid) CloH21N(cH2Po3H2)2 trisodium-pentadecyl-amino-di-methyl phosphate Cl5H31N(CH2PO3HNa) (CH2P03Na2) n-butyl-amino-di(ethyl phosphonic acid) C4HgN(cH2cH2Po3H2)2 tetrasodium-n-butyl-amino-di(methyl phosphate) C4H9N(CH2P~3Na2)2 triammonium tetradecyl-amino-di(methyl phosphate) Cl4H29N(cH2po3(NH4)2)cH2po3HNH4 phenyl-amino-di(methyl phosphonic acid) C 6 H 5 N(CH2P03H2)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) .
C 6 H 5(cH2)2N(cH2Po3Na2)2 ethylene diamine tetra(methyl pnosphonic acid) 2 3 C 2)2N(CH2)2N(CH2P03H2)2 trimethylene diamine tetra(methyl phosphonic acid) (H203PCH2)2N(cH2)3N(cH2Po3 2)2 hepta methylene diamine tetra(methyl phosphonic acid) (H2o3pcH2)2N(cH2)7N(cH2po3H2)2 1~9~21 decamethylene diamine tetra(methyl phosphonic acid) (H2o3pcH2)2N(cH2)loN(cH2 ~3 2)2 - tetradecamethylene diamine tetra(rnethyl phosphonic acia) ( 2o3PCH2)2N(CH2)l4N(CH2PO3H2)2 ethylene diamine tri(methyl phosphonic acid) (H2o3pcH2)2N(cH2)2NHcH2po3H2 ethylene diamine di(methyl phosphonic acid) 2 3 2)2 ( 2)2 C 2 03H2 n-hexyl amine di(methyl phosphonic acid) C6H13N(CH2Po3H2)2 diethylamine triamine penta(methyl phosphonic acid) 203PCH2)2N(cH2)2N(cH2po3H2) (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 Dh~sphonic acid) (HOCH2)3CN(CH2po3H2)2 triethylene tetra amine hexa(methyl phosphonic acid) (H2o3pcH2)2N(cH2)2N(cH2po3H2) (CH2)2N--(~H2~3~2)(CH2)2N(-H2po3 2)2 monoethancl, diethylene triamine tri(methyl phosphonic acia) ~-H~N(CH2P~ 3 H2)(CH2) 2 NH(CH 2) 2 N-(CH2~03~12)2 chloroethylene amine di(methyl phosphonic acia) C1CH2CH2N((CH2P~(~H)2)2 '~
S s~
The above compounds are included for illustration Pur~osesand 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-phosphonobutane-1, 2, 4-tricarboxylic acid(PBTC) and P. l-hydroxyethane-l, l-diphosphonic acid(HEDP).
The use of phosphonates is optional. when phosphonates are utilized, the inorganic phosphates (ortho anb/or condensed) and phosphonates are combined in a weight ratio of û.5:1:û.33 to 30:1:16.
In addition to phosphonates, additives such as aromaticazole~
may be utilized. For example, tolyltriazole is effective in the reduction of coPper substrate corrosion.
INORGANIC PHOSPHATES
Inorganic phosphates used in this invention are either the acid form of inorganic phosphate or any of their metal, ammonium or amine salts. The inorganic phosphates (ortho ana condenseo) of this invention are chosen from the group:
1. Orthophosphate 2. Pyrophosphate 3 Tripolyphosphate 4. Hexamet-phosphate 5. Higherimolecular weight polyphosphate oligomers Any of the ~bove inorganic phosphates may be usea alone or in combination. ~owever, orthophosphate is preferred. More preferably, a e~mbination of orthophosphate and one of the other inorganic phospnates ~ill be utilized.
.
Il ~ 339~2i COMPOSITION
- The corrosion inhibitor compositions of the invention are ,_ added to an aqueous system such that the total active ingredient~
are at the follo~ing concentrations:
1. General - 10 to 100 mg/liter (ppm) 2. Preferred - 10 to 50 mg/liter ~ppm) 3. Most preferred - 15 to 40 mg/liter (ppm) The inorganic phosphate portion of the composition consists of the previously defined group of inorganic phosphates or combinations thereof. The ~ost preferred inorganic phosphates are orthophosphate and pyrophosphate. These components comprise a certain percentage of the active ingredients of the composition of the invention:
1. General - 4% to 80%
2. Preferred - 20 to 75% ' 3. Most preferred - 40 to 70%
Based on the composition of ~ater being treated, it may be desirable to vary the ratio of orthophosphate to condensed phosphate. Desired ranges of this ratio (on active basis) are:
1. General - 0.5:l to 30:l 2. Preferred - 0.5:1 to lO:l 3. Most preferred - l:l to 4:1 It is also desirable to include an organic phosphonate in the composition, particularly at elevated pH and alkalinity levels. The previous enumeration of phosphonates gives many examples of suitable ingredients. Particularly preferred phosphonates are:
1. 1,1 hydroxyethylidene diphosphonic acid and its salts 2. 2-Phosphono butane l,2,4-tricarboxylic acid and its salts 39~2i Oesirea ratio ranyes of orthophosphate, condensed phosphate and phosphonate are: ;
~ 1. General - 0.5:1:0.33 to 30:1:16 2. Preferred - 0.5:1:1 to 10:1:10 3. Most preferred - 1:1:1 to 4:1:6 The aqueous systems to be dosed will generally have a pH
within the range of 6.5 to 9.2. Preferably the pH will be in the range of 7 to 8.5 Examole 1 - A diluted and base-neutralized solution of the polymer was prepared by adaing 45 grams of softened water to a glass or stainless steel container. ~ith stirring, 43 grams of acrylic, acid/t-butylacrylamide copolymer (poLymer composition #1, 49 wt%) and 9.2 grams of sodium hydroxide (50 wt%) were then added.
Cooling was aPplied to the container as needed to maintain temperature below 120~F. The pH of the mixture was adjusted to 5.1-6.0 and the solution diluted to 100 grams total weight using softened water. The resulting solution contains 21 wt% polymer actives. Other co- (ter)polymers containing t-butylacrylamice can be substituted for the acrylic acid/t-butylacrylamide copolymers. An increase or decrease in the polymer actives level was accomDl shed by corresponding changes in the amount of polymer and aquecus sodium hydroxide witn sufficient softened water addeC to ~ in-ain an equivalent total weight of solution.
Corrosion inhibitors can be included with Polymer solutions. For example, polyme. and aromatic azole combinations may be prepared with sufficient aqueous sodium hydroxide added to attain final pH 12.5 to 1~.
1 ~
Example 2 To a glass or stainless steel container was added 15 grams of softened water. With stirring, aqueous solutions of the following materials were added consecutively:
31.5 grams o~ acrylic acid/ethyl acrylate copolymer (AA/EA) 17 grams of acrylic acid/acrylamide copolymer (AA/Am) 19.2 grams of acrylic acid/t-~utylacrylamide copolymer (AA/t-BAm) The mixture was cooled in an ice-bath and then basified by slow addition of approximately 14 grams of aqueous potassium hydroxide (45 wt%) to the vigorously stirred solution. During --the addition of base, the solution's temperature was maintained belûw 120~F. The pH of the mixture was adjusted to 5.5-6.0 and the solution diluted to 100 grams total weight using softened¦ -water. The cooling bath was removed and the solution stirred until ambient temperature was attained. The final solution respectively contains 7.5, 4.7, and 9.4 wt% actives of AA/EA, AA/Am, and AA/t-aAm.
Changes in the formulation are easily accommodated by simp!e modification of the previously listed procedure. Decreasing the amount of polymer(s) and potassium hydroxide, followed by increasing the final amount of water added, will produce a formulation containing less polymer actives. Other co- (ter) polymers containing t-butylacrylaMi~e can be substituted for the acrylic acid/t-butylacrylamide copolymer.
. ~, ,, ... ,.~, .. _ , .. .. .
,,.
,: , 1339~21 Example 3 To a ~lass or stainless steel container is abded 12 grams of softened water. The sample was coole~ in an ice-bath and 39 grams of aqueous potassium hydroxide (45 wt%) was added. The solution temperature was maintained below 140 r . during consecutive addition of 10.7 grams of orthophosphonic acid (85 wt%) and 4 grams of l-hydroxyethane-l,l-oiphosphonic acid (6û wt%). The mixture was then maintained below 100~F. during additon of 26.7 grams tetrapûtassium pyrophosphate (60 wt%). As needed, the pH was adjusted to 12.5 to 13 using aqueous potassium hydroxide (45 wt%), and then 7 grams of sodium tolyltriazole (50 wt%) were added. ; -Additionally, 2-phosphonobutane-1, 2, 4-tricarboxylic acid (a/k/a PBTC or PBS-AM) is described in U.S. Patent No. 3,886,2û4 be entirely removed, with corresponding changes in aqueous potassium hydroxide and softened water levels.
Concurrent feeding of a single polymer (Example 1) ana the ortho/Dyrophosphate formulation (Example 3) is satisfactory in many applications. The relative amount of each formulation can be varied according to the oPerating conditions, environmental restrictions, and economics of the indiviaual systems. Under severe conditions, a mixture of polymers (Example 2) and the ortho/pyrophosphate formulation provide aaditional corrosion inhibition and 5i,persion of particulates.
- 2û -'~
Example 4 Another preferred composition employs analogous procedure for~ :
preparation as Examole 3, except for changes incomponent levels as indicated: ' 8.7 grams of softened water 48 grams of aqueous potassium hydroxide (45 wt%) 14.3 grams of orthophosphonic acid (85 wt%) 4.5 grams of l-hydroxyethane-l,l-diPhOsPhOniC acid (6û wt%) 18 grams of tetraPCtassium pyrophosphate (6û wt%) 7 grams of sodium tolyltriazole (5û wt%) The procedure for mixing of components and pH adjustment were the same as Example ~.
"
Example 5 Another preferred composition employs a c~mbination of polymeric comPonent and corrosion inhibitors into a single solution. The order of addition and amount of each component employed are listed below:
26 grams of softened water 33 grams of aqueous potassium hydroxide (45 wt%) 9.1 grams of polymer composition J~ll (46.5 wt%) 7.6 grams oforthophosphoric acid (85 w.%) 2.6 grams of l-hyaroxyethane-l,l-diDnosphonic acii (6û w~%) 17 grams of tetrapotassium pyrophosPhate (6û wt%) 4.5 grams cf sodium tolyltriazole (5û w~%) The procedure for mixing of the components and pH adjustment were the same as Example 3, except for inclusion of the polymeric materials.
, -, ....
~,, . ,~ .
EXAMP.ES 1339~21 Experimental Procedures In laboratory tests, hardness cations and M alkalinity are expressed as CaC03 or cycles of concentration. Ortho and pyrophosphate are listed as P04 and polymeric and phosphonate inhibitors (monomeric and polymeric) are as actives. In analyse of heat-exchanger deposits, all components are listed as wt% of the chemical element or acid-form of the compound.
To illustrate the invention, the following are given by way of example:
The first test method described below was used to determine the ability of the polymer compositions to inhibit calcium and magnesium phosphate.
Calcium and Magnesium Phosphate Inhibition Test Procedure Calcium and magnesium were added to provide initial concentrations of 25û and 125 ppm. An equal amount of phosphate was added to each test solution, and the inhibitor concentrations are listed in Table I. The temperature of the test solutions was maintained at 158~F (70~C). Using dilute aqueous NaûH, the -, pH was slowly increased to 8.5 and maintained during the four hour duration cf the test. Mineral solubility calculations indicate supersaturation values for calcium phosphate ~ lO,OOO
and magnesium phosphate ~ 600 were initially present and the system was under highly stressed conditions. At the conclusion of each test, each solution was filtered ~0.45 um) and the orthophosphate concentration was determined spectrophotometricaïly ~700 nm) after formation of a blue 1339~21 phosphomolybdate complex- The inhibition of calcium phos~hate is~
determined as indicated below:
E~uation 1.
[filtered - blank]
- % inhibition = - X lOû
[unfiltered - blank]
where, filtered sample = concentration of phosphate ion in filtrate in the presence of inhioitor after 4 hours.
initial sample = concentration of phosphate ion in test at solution time zero.
blank = concentration of phosphate ion in filtrate in absence of inhibitor after 4 hours.
'Using the above test method, a numoer of polymer compositions were tested. The results are show below in Taole I.
~'' ''.
1~39521 TABLE I
Calcium and Magnesium Phosphate Inhi~ition % Phosphate 5alt Polymer Inhibition Composition Composition* Molecular ppm polymer actives Number (Mole %) Weight 5 7.5 10 1 AA/t-BAm (88/12) 9,30û 6 71 82 3 AA/t-BAm (88/12)17,700 20 54 72 4 AA/t-BAm (88/12) 25,9ûû 25 68 90 AA/~A/t-BAm (86/8/6) 8,9ûû 7 37 75 6 AA/Am/t-BAm (84/11/6) 9,400 7 55 73 7 AA/MAA-t-~Am (68/19/13) 8,20û 18 78 81 8 AA/MAA/t-BAm (68/19/13)13,60û 15 -- 90 11 AA/MAA/t-BAm (68/19/13)15,600 60 77 84 12 AA/MAA/t-BAm (68/19/13)23,000 59 83 81 Commercial Reference Compounds -AA/HP4 (67/33-75/25) 7,400 13 -- 50 : MaA/S5 (75/25) 19,000 B 74 89 : AA/MA (83/17) 5,aO0 15 49 B7 AA/Am (23/77) 10,100 77 95 92 ~Abbreviations as follows:
AA - acrylic acid Am - acrylamide HPA - hydroxypropylacrylate ~A - methyl acrylate MaA - maleic acid anhydride i MAA - methacrylic acid '- SS - su.lfonated styrene t-BAm - t-butylacrylamide 1339~21 Calcium Phosphonate Inhibition Calcium and a mixture of HEDP and P~TC were added to the test solution to provide initial concentrations of 360 ppm and 8 ppm (total phosphorus as P04), respectively. The temperature was maintained at 140~F (60~C). Using dilute aqueous NaOH, the pH was slowly increased to 9.2 and maintained during the four hour duration of the test. At the conclusion of each test, the solution was filtered (0.45 and 0.10 um) and the total phosphorus concentration of each sample was determined by oxidation of the phosphonates to orthophosphate. Spectrophotometric analysis was accomplished by formation of a blue phosphomolybdate complex, as previously indicated. The percent inhibition of calcium organophosphorus compounds was determined by Equation l, where phosphate ion represents total phosphorus content (as P04).
The test results for polymeric inhibitors are set forth in Table II below.
- -- ~
~ :
':
TA~L_ II
Calcium Phosononate Inhibition ~ Inhi~ition Polymer Filter Size (um) Composition Number 0.45 0.10 , 74 24 6 ~ 13 , ~' '~.
Commercial Reference Compounds MaA/SS (75/25) 95 26 - AA/MA (83/17) 11 5 AA/HPA (67/33-75/25) 59 23 * For composition abbreviations, refer to Table I.
Hydrolytic Stability Gas chromatographic analysis was used to determine the resistance of t-butyl acrylamide-containing polymers against hydrolysis and degradation under high pH conaitions. The test - samples were prepared in polyethylene bottles by slow adaition of aqueous lû weight percent NaOH to a stirred solution containing 15 weight Percent actives of polymer. The rAsulting solution was r diluted to 7 height percent polymer actives with aistilled water and the final oH adjusted to 13.2+0.1. Each test solution was divided into two equal POrtionS with o,e samPle heateO to 123~r and the other s,m~le r-maining at 70OF~ ~ter 130 days, the samples wereanzlv7ea ~or polymer degradation proaucts and t-butylamine content. ,~o evicence of polymer degradation products or hydro~ysis ~as observed in any of the test samples.
The small variations in t-butylamine content indicated in Table III are ~ithin the statistical error of the analysis method¦.
_~ A
,_ _ _ ~__ ~ 339~21 These polymers are rePorted as having hydrolytic stabili'y up to pH 11 but we were surprised to find this hydrol~t~c stabilitY even at pH 13 and beyond. This unexpected result is important because azoles such as tolyltriazole require a pH ~ 12.5 for incorporation into a homogeneous formulation (e.g. Example 3) to provide corrosion inhibition.
Hydrolytic stability is a benefit, particularly with regard to the formulation of polymers in combination with corrosion inhibitors. Several other commercially successful polymers (e.g. acrylic acid/acrylate ester and acrylic acid/hydroxyalkyl esters) do not possess that beneficial quality.
Because of this hydrolytic stability, the polymers of this invention can be used in one drum formulations. Because prior art compounds lack hydrolytic stability, they cannot be packaged with other adjunct corrosion inhibitors, (e.g.
tolyltriazole) without suffering hydrolytic decomposition during storage. Therefore, these adjunct polymers are usually provided in a second formulation so that a two-drum feed system (i.e.
concurrent feed system) is required.
, ~339521 TACLE III
Resistance to Hydrolysis - Gas Chromato~raphic Results Polymer Composition Composition t-Butylamine Content (wt %) Number (Mole %) Raw Material* 70~F 120~F
1 AA/t-BAm (88/12) 0.039 û.034 0.035 11 AA/MAA/t-BAm (68/19/13) û.039 0.041 0.037 * Initial sample before addition of aqueous NaOH.
Pilot Cooling Tower Tests The pilot cooling tower(PCT)test is a dvnamic test which ~-simulates many features present in an industrial recirculating cooling water system. The general test method is described in ,the article "Small-Scale Short-Term Methods of Evaluating Coolins ' Water Treat~ents.. Are they Worthwhile?", by D. T. Reed and R. Nass, Minutes of the 36th Annual Meeting of the INTERNATIONAL
WATER CONFERENCE, Pittsburgh, Pennsylvania, November 4-6, 1975.
The general operating conditions are listed below in Table IV.
TABLE IV
Concentration Cycles* 3.7 - 4.0 ~asin Temperature 100~F
Holding Time Index 24 hr.
Flow ~a~e 2 gpm pH 7.0 - Test Ouration 14 days * At 4 cycles, the ion concentrations (as CaCû3) are: 360 ppm Ca , 2ûO ppm Mg , 440 ppm "M" Alkalinity, 360 ppm C1 , and 200 ppm sulfate.
_.
1339~21 PCT tests were conducted under extended conditions (e.g.
low and high hardness) and differences from general operating conditions are specified in Tables VI and VII and subsequent discussions of results.
A~t the beginning of a pilot cooling tower test, the mass of each heat-exchange tube is determined. After the test is completed, the tubes are dried in an oven and reweighed. Next, the tubes are cleaned with inhibited acid (dilute HCl and formaldehyde), dried, and the final weight determined. Those three weights are used to determine rates of deposition (mg/day) and corrosion (mils per year). As the performance of the treatment program and polymeric inhibitor increases, the deposit and corrosion rates decrease. The pilot cooling tower results are indicated in Tables V-VII below:
-TABLE V
Pilot Cooling Tower Tests (pH 7) Polymer Polymer Deposit - Corrosion -Composition Dosage Mild Steel Mild Steel Number (ppm actives) (mg/day) (mpy) None -- 89 4.1 3 ~.6 39 2.9 4 6.6 27 1.6 - 5 11.0 57 3.3 6 11.0 74 3.8 7 11.0 36 2.5 8 7.5 34 1.9 11 6.6 31 ~.2 12 7.5 34 1.9 AA/HPA 11.0 27 2.2 -.
1 1339~21 In the pilot cooling tower tests listed above, the benefitS of adding a polymer to control corrosion and de~osit on mild steel surfaces can be clearly observed by comparing results listed for polymer compositions #2-9 with the polymer Composition No. "None" above. Results comparable to those for polymer composition PA/HPA, particularly for inhibition of mild steel corrosion were obtained using significantly lower dosages of t-butylacrylamide-containing polymers (polymer compositions #4, 8, 11 and 12). For tests conducted at equivalen-t hardness levels, the corrosion rates for mild steel are considereo equivalent if differences are less than 0.5 mpy.
In Table VI, a comparison is listed of the PCT test results obtained from using a commercially successful AA/HPA
copolymer and low dosages of AA/MAA/t-3Am terpolymer (polymer composition #8). The test conditions were the same as in Table V, except the polymer dosage and haroness levels were varied as indicated.
, TABLE VI 1339~21 Pilot Cooling Tower Tests (pH 7) Water Hardness and Polymer Dosage Ranges Polymer Polymer ppm Deposit - Corrosion -Composition Dosage Hardness* Mild Steel Mild Steel Number (ppm actives) Ca Mg(mg/day) (mpy) 8 3.0 2ûO 100 34 2.7 AA/HPA 7, 5 200 100 37 2.7 None -- 360 200 89 4.1 8 4.0 360 200 30 1.4 AA/HPA 7.5 360 200 40 2.3 8 4.0 600 300 22 2.2 AA/HPA 11.5 600 300 22 1.7 8 10.0 900 450 22 2.0 AA/HPA 17.5 900 450 38 2.0 8 9.5 1200 600 24 0.9 AA/HPA 22.5 1200 600 60 2.3 * Oesired levels of calcium and magnesium. Actual average - results were within +lû~ of ~es5red levels. Differences bet~een desired and actual levels of hardness ions are insignificant and do not affect test results.
13~9~21 In Table VI, the results demonstrate that equal or significantly better control of corrosion and deposit on mild steel surfaces can be obtained using a treatment containing low dosages of AA/MAA/t-BAm terpolymers, as compared to treatments containing approximately two to three times as much AA/HPA. At 360 ppm Ca+2 and 200 ppm Mg+2 hardness levels (as calcium carbonate), the benefits of using the AA/MAA/t-BAm terpolymer (polymer Composition No. 7) can be readily observed by the sharp reduction in mild steel corrosion and deposit rates, as compared to the "no Polymer" case.
~33~521 TAB~E VII
Pilot Cooling Tower Tests (p~ 8 and 8.5 at 120 F aasin) Effects water Hardness, Polymer, and "Phosphorus" Dosage Ranges Polymer Polymer Dosage ppm ppm Corrosion Deposit Composition (opm Hardness* Phosphorus Mild Steel Mild Steel Number actives) pH CA MG po4 P207 P~TC (mpy) (mg/day) no polymer** -- 7 360 200 9.7 9.1 -- 4.1 ' 8 7.5 8 360 200 8 4 6 1.7 32 8 7.5 8 360 200 8 4 4 1.7 28 8 7.5 8 360 200 8 4 2 1.9 30 8 7.5 8 360 200 8 2 2 1.9 26 8 4.0 8 360 200 8 0.0 0 2.5 36 8 7.5 8 360 200 6 3 3 1.8 23 8 7.5 8.5 360 200 4 1 2 1.7 23 _ 3 7.5 8 700 350 8 4 6 1.9 36 8 7.5 8 7ûO 350 6 3 3 1.7 31 8 7.5 8 700 350 6 û.0 3 1.9 30 8 7.5 8 700 350 4 2 4 2.3 31 8 7.5 8 700 350 4 2 2 2.4 31 8 7.5 8 7~0 350 4 1 ~ 2.6 31 * Desired levels of calcium ind magnesium. Actual average results were within +10%
of desired levels. Qifferences between desired and actual levels of hardness ions are inslgnificant and do not affect PCT test results.
** "no polymer" test was conducted under less severe conditions with 8asin Temperature equal to lOQ F and with pH 7 ~1 ~ 1339~21 ":~''li Results from the above Table indicate that using a combination of t-butylacrylamide containing polymer, phosphates ,_ and/or phosDhonates provides very good corrosion inhibition even under very stressful conditions of medium to high hardness levels, high basin temperature (120 F) and high pH (8 to 8.5).
All of the results are significantly better than the polymer Composition No. "no polymer" which had a basin temperature of 100~F.
"
- ~4 -~' , ~ , . .
' ~ >
_ (8900) AA/EA/t-BAm (86:3:6) _ 6 (9400) AA/Am/t-BuAm (84:11:6) -- -- _ _ _ _ _ _ _ _ _ _ _ _ 7 (8200) AA/MAA/t-BAm (58:19:13) 8 (13600)* "
9 (14300)* "
(15700)* ~
11 (15600) "
12 (23000) "
Weight ave. ige molecular weight, i.e. M.W. or Mw * Aqueous Mw estimatea from GPC value using THf eluent.
** AA: Acrylic Acid EA: Ethyl acrylate t-BAm: tert-butylacrylamide MAA: Methacrylic acid Am: Acrylamide ,~
,, ~
j ~ 5~ S~
Polymer Composition Nos. 1-4 are unneut.ali~ed copolymers of acrylic acid and t-butylacrylamide (t-~Am).
Polymer ComPosition No. 5, Polymer Composition No. 6, ana 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 appears to confer exceptional performance characteristics upon these polymers.
The coPolymers composed of acrylic acid and t-butyl acrylamide contain between 5û to 9û% by weight of acrylic acid and from lû-50% by weight of t-butyl acrylamide. Preferably the acrylic acid is present in a weight percent amount ranging between 7û-90 with the t-butylacrylamide being present at betweer lû-30. 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 10-2û.
The terpolymers are within the following weight percent composition ranges:
a) acrylic acid 40-90, more preferably 40-80, and most ~referably 60-80 b) metnacrylic acid 5-30, more preferably lG-30, and most preferably 10-20 c) t-ou.vl acrylamide 5-50, more preferably 10-30, and most p.eferably 10-20 g - 133~ The ?hos~honates Generally any water-soluble phosphonate may be used that i~ capable of providing corrosion inhiDition in alkaline systems. U. S. 4,303,568 wnich lists a number of representative phosphonates.
The organo-phosphonic acid compounds are those having a carbon to phosphorus bond, i.e., O
- C -P-OM
- OM
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:
o A. ~- 3~OM
OM
where R is lower alkyl having from aoout one to six caroon atoms, e.g., methyl, ethyl, butyl, Propyl~ isopropyl, Pentyl, isopentyl and hexyl; substituted lower alkyl of from one to six carbon atoms, e.g., hydloxyl-and amino-substituted alkyls; a mononuclear aromatic (aryl) Ladical, e.g., phenyl, nenzene, etc., or a substituted mcnsn~~lear aromatic compound, e.g., hydroxyl, amino, l~wer alkyl substituted aromatic, e.g., benzyl phosphonic acic;
and M is a water-soluble cation, e.g., sodium, potassium, ammonium, lit~ im, etc. or i~yarogen.
,,~.
h-- ~33g~21 Specific examples of compounds which are encompassea by th1s formula include:
methylphosphonic acid ethylphûsphonic acid CH CH Pû H
2-hydroxyetnyl~hosphonic acid CH2-CH2-~03H2 OH
2-amino-ethyl~hosphonic acid CH2-CH2-Po3 2 isopropylphosphonic acid ,CH3 benzene phosphonic acid benzylphosphonic acid O O
R. Mo-7~ 7 - 3M
-M OM
wherein Rl is an alkylene having from about one to about 12 carcbon atoms or a substituted al~ylene having from aoout 1 to about 12 caroon atoms, e.g., hydroxyl, amino etc. substituted alkylenes, and ~ lS as earlier defined above.
-~ 1339~21 Specific exemplary compounds and their respective _ formulas which are encompassed by the above formuia are as follows:
methylene diphosphonic acid H203P-CH2-Po3H2 ethylidene diphosphonic acid H2O3P-cH(cH3)po3 2 isopropylidene diphosphonic acid (CH3)2C(P03H2)2 l-hydroxy, ethylidene diphosphonic acid (HEDP) OH
H2O3P-c(cH3)-po3H2 hexamethylene diphosphonic acid H203P-CH2(cH2)4cH2-po3H2 trimethylene diphosphonic acid H2O3P-(cH2)3-po3 2 decamethylene diphosphonic acid ----H203P- (C H2 ) 10-PO3H2 l-hydroxy, propylidene diphosphonic acid H203p'' (OH)CH2(CH3)Po3H2 1,6-dihydrcxy, 1,6-dimethyl, hexamethylene diphosphonic acid 203P-('H3)(0H)(CH2)4c(cH3)(oH)po3H2 dihydroxy, ~.ethyl ethylene diphosphonic acid 203PC ~ JH ) (C2H5 )C (OH ) (C2H5 )PO3H2 -C. ~-R~ OM 1~ 3 9 ~ 2 ~
R~ 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-Pû3M2] H, OH, amino, substituted amino, an alkyl having from one to six caroon atoms, a substituted alkyl of from one to six carbon atoms (e.g., ûH, NH2 substituted) a mononuclear aromatic radical and a substituted mononuclear aromatic radical (e.g., OH, NH2 substituted); R4 is R3 or the group represented by the formula C ~z--~-0.
~n y where R5 and R6 are each hydrogen, lower alkyl of from about one to six carbon atoms, a substituted lower alkyl (e.g., OH, ~ ~
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 R5~ Q6' or the group R2-P~3M2 (R2 is as defined above); n is a number of from 1 through about 15; y is a number of from abou~ rough about 14; and 1~ is as earlier aeflnea.
Compounds or Cormulas therefore which can be considerea exemplary for tho above formulas are as follows:
nitrilo-trl(methylene phosphonic acid) N(CH2PO3H2)3 .~
~- 1339~21 imino-ai(methylene phosphonlc acid) NH(CH2po3H2)2 n-butyl-amino-di(methyl phosphonic acid) C4HgN(cH2Po3H2)2 decyl-amino-di(methyl phosphonic acid) CloH21N(cH2Po3H2)2 trisodium-pentadecyl-amino-di-methyl phosphate Cl5H31N(CH2PO3HNa) (CH2P03Na2) n-butyl-amino-di(ethyl phosphonic acid) C4HgN(cH2cH2Po3H2)2 tetrasodium-n-butyl-amino-di(methyl phosphate) C4H9N(CH2P~3Na2)2 triammonium tetradecyl-amino-di(methyl phosphate) Cl4H29N(cH2po3(NH4)2)cH2po3HNH4 phenyl-amino-di(methyl phosphonic acid) C 6 H 5 N(CH2P03H2)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) .
C 6 H 5(cH2)2N(cH2Po3Na2)2 ethylene diamine tetra(methyl pnosphonic acid) 2 3 C 2)2N(CH2)2N(CH2P03H2)2 trimethylene diamine tetra(methyl phosphonic acid) (H203PCH2)2N(cH2)3N(cH2Po3 2)2 hepta methylene diamine tetra(methyl phosphonic acid) (H2o3pcH2)2N(cH2)7N(cH2po3H2)2 1~9~21 decamethylene diamine tetra(methyl phosphonic acid) (H2o3pcH2)2N(cH2)loN(cH2 ~3 2)2 - tetradecamethylene diamine tetra(rnethyl phosphonic acia) ( 2o3PCH2)2N(CH2)l4N(CH2PO3H2)2 ethylene diamine tri(methyl phosphonic acid) (H2o3pcH2)2N(cH2)2NHcH2po3H2 ethylene diamine di(methyl phosphonic acid) 2 3 2)2 ( 2)2 C 2 03H2 n-hexyl amine di(methyl phosphonic acid) C6H13N(CH2Po3H2)2 diethylamine triamine penta(methyl phosphonic acid) 203PCH2)2N(cH2)2N(cH2po3H2) (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 Dh~sphonic acid) (HOCH2)3CN(CH2po3H2)2 triethylene tetra amine hexa(methyl phosphonic acid) (H2o3pcH2)2N(cH2)2N(cH2po3H2) (CH2)2N--(~H2~3~2)(CH2)2N(-H2po3 2)2 monoethancl, diethylene triamine tri(methyl phosphonic acia) ~-H~N(CH2P~ 3 H2)(CH2) 2 NH(CH 2) 2 N-(CH2~03~12)2 chloroethylene amine di(methyl phosphonic acia) C1CH2CH2N((CH2P~(~H)2)2 '~
S s~
The above compounds are included for illustration Pur~osesand 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-phosphonobutane-1, 2, 4-tricarboxylic acid(PBTC) and P. l-hydroxyethane-l, l-diphosphonic acid(HEDP).
The use of phosphonates is optional. when phosphonates are utilized, the inorganic phosphates (ortho anb/or condensed) and phosphonates are combined in a weight ratio of û.5:1:û.33 to 30:1:16.
In addition to phosphonates, additives such as aromaticazole~
may be utilized. For example, tolyltriazole is effective in the reduction of coPper substrate corrosion.
INORGANIC PHOSPHATES
Inorganic phosphates used in this invention are either the acid form of inorganic phosphate or any of their metal, ammonium or amine salts. The inorganic phosphates (ortho ana condenseo) of this invention are chosen from the group:
1. Orthophosphate 2. Pyrophosphate 3 Tripolyphosphate 4. Hexamet-phosphate 5. Higherimolecular weight polyphosphate oligomers Any of the ~bove inorganic phosphates may be usea alone or in combination. ~owever, orthophosphate is preferred. More preferably, a e~mbination of orthophosphate and one of the other inorganic phospnates ~ill be utilized.
.
Il ~ 339~2i COMPOSITION
- The corrosion inhibitor compositions of the invention are ,_ added to an aqueous system such that the total active ingredient~
are at the follo~ing concentrations:
1. General - 10 to 100 mg/liter (ppm) 2. Preferred - 10 to 50 mg/liter ~ppm) 3. Most preferred - 15 to 40 mg/liter (ppm) The inorganic phosphate portion of the composition consists of the previously defined group of inorganic phosphates or combinations thereof. The ~ost preferred inorganic phosphates are orthophosphate and pyrophosphate. These components comprise a certain percentage of the active ingredients of the composition of the invention:
1. General - 4% to 80%
2. Preferred - 20 to 75% ' 3. Most preferred - 40 to 70%
Based on the composition of ~ater being treated, it may be desirable to vary the ratio of orthophosphate to condensed phosphate. Desired ranges of this ratio (on active basis) are:
1. General - 0.5:l to 30:l 2. Preferred - 0.5:1 to lO:l 3. Most preferred - l:l to 4:1 It is also desirable to include an organic phosphonate in the composition, particularly at elevated pH and alkalinity levels. The previous enumeration of phosphonates gives many examples of suitable ingredients. Particularly preferred phosphonates are:
1. 1,1 hydroxyethylidene diphosphonic acid and its salts 2. 2-Phosphono butane l,2,4-tricarboxylic acid and its salts 39~2i Oesirea ratio ranyes of orthophosphate, condensed phosphate and phosphonate are: ;
~ 1. General - 0.5:1:0.33 to 30:1:16 2. Preferred - 0.5:1:1 to 10:1:10 3. Most preferred - 1:1:1 to 4:1:6 The aqueous systems to be dosed will generally have a pH
within the range of 6.5 to 9.2. Preferably the pH will be in the range of 7 to 8.5 Examole 1 - A diluted and base-neutralized solution of the polymer was prepared by adaing 45 grams of softened water to a glass or stainless steel container. ~ith stirring, 43 grams of acrylic, acid/t-butylacrylamide copolymer (poLymer composition #1, 49 wt%) and 9.2 grams of sodium hydroxide (50 wt%) were then added.
Cooling was aPplied to the container as needed to maintain temperature below 120~F. The pH of the mixture was adjusted to 5.1-6.0 and the solution diluted to 100 grams total weight using softened water. The resulting solution contains 21 wt% polymer actives. Other co- (ter)polymers containing t-butylacrylamice can be substituted for the acrylic acid/t-butylacrylamide copolymers. An increase or decrease in the polymer actives level was accomDl shed by corresponding changes in the amount of polymer and aquecus sodium hydroxide witn sufficient softened water addeC to ~ in-ain an equivalent total weight of solution.
Corrosion inhibitors can be included with Polymer solutions. For example, polyme. and aromatic azole combinations may be prepared with sufficient aqueous sodium hydroxide added to attain final pH 12.5 to 1~.
1 ~
Example 2 To a glass or stainless steel container was added 15 grams of softened water. With stirring, aqueous solutions of the following materials were added consecutively:
31.5 grams o~ acrylic acid/ethyl acrylate copolymer (AA/EA) 17 grams of acrylic acid/acrylamide copolymer (AA/Am) 19.2 grams of acrylic acid/t-~utylacrylamide copolymer (AA/t-BAm) The mixture was cooled in an ice-bath and then basified by slow addition of approximately 14 grams of aqueous potassium hydroxide (45 wt%) to the vigorously stirred solution. During --the addition of base, the solution's temperature was maintained belûw 120~F. The pH of the mixture was adjusted to 5.5-6.0 and the solution diluted to 100 grams total weight using softened¦ -water. The cooling bath was removed and the solution stirred until ambient temperature was attained. The final solution respectively contains 7.5, 4.7, and 9.4 wt% actives of AA/EA, AA/Am, and AA/t-aAm.
Changes in the formulation are easily accommodated by simp!e modification of the previously listed procedure. Decreasing the amount of polymer(s) and potassium hydroxide, followed by increasing the final amount of water added, will produce a formulation containing less polymer actives. Other co- (ter) polymers containing t-butylacrylaMi~e can be substituted for the acrylic acid/t-butylacrylamide copolymer.
. ~, ,, ... ,.~, .. _ , .. .. .
,,.
,: , 1339~21 Example 3 To a ~lass or stainless steel container is abded 12 grams of softened water. The sample was coole~ in an ice-bath and 39 grams of aqueous potassium hydroxide (45 wt%) was added. The solution temperature was maintained below 140 r . during consecutive addition of 10.7 grams of orthophosphonic acid (85 wt%) and 4 grams of l-hydroxyethane-l,l-oiphosphonic acid (6û wt%). The mixture was then maintained below 100~F. during additon of 26.7 grams tetrapûtassium pyrophosphate (60 wt%). As needed, the pH was adjusted to 12.5 to 13 using aqueous potassium hydroxide (45 wt%), and then 7 grams of sodium tolyltriazole (50 wt%) were added. ; -Additionally, 2-phosphonobutane-1, 2, 4-tricarboxylic acid (a/k/a PBTC or PBS-AM) is described in U.S. Patent No. 3,886,2û4 be entirely removed, with corresponding changes in aqueous potassium hydroxide and softened water levels.
Concurrent feeding of a single polymer (Example 1) ana the ortho/Dyrophosphate formulation (Example 3) is satisfactory in many applications. The relative amount of each formulation can be varied according to the oPerating conditions, environmental restrictions, and economics of the indiviaual systems. Under severe conditions, a mixture of polymers (Example 2) and the ortho/pyrophosphate formulation provide aaditional corrosion inhibition and 5i,persion of particulates.
- 2û -'~
Example 4 Another preferred composition employs analogous procedure for~ :
preparation as Examole 3, except for changes incomponent levels as indicated: ' 8.7 grams of softened water 48 grams of aqueous potassium hydroxide (45 wt%) 14.3 grams of orthophosphonic acid (85 wt%) 4.5 grams of l-hydroxyethane-l,l-diPhOsPhOniC acid (6û wt%) 18 grams of tetraPCtassium pyrophosphate (6û wt%) 7 grams of sodium tolyltriazole (5û wt%) The procedure for mixing of components and pH adjustment were the same as Example ~.
"
Example 5 Another preferred composition employs a c~mbination of polymeric comPonent and corrosion inhibitors into a single solution. The order of addition and amount of each component employed are listed below:
26 grams of softened water 33 grams of aqueous potassium hydroxide (45 wt%) 9.1 grams of polymer composition J~ll (46.5 wt%) 7.6 grams oforthophosphoric acid (85 w.%) 2.6 grams of l-hyaroxyethane-l,l-diDnosphonic acii (6û w~%) 17 grams of tetrapotassium pyrophosPhate (6û wt%) 4.5 grams cf sodium tolyltriazole (5û w~%) The procedure for mixing of the components and pH adjustment were the same as Example 3, except for inclusion of the polymeric materials.
, -, ....
~,, . ,~ .
EXAMP.ES 1339~21 Experimental Procedures In laboratory tests, hardness cations and M alkalinity are expressed as CaC03 or cycles of concentration. Ortho and pyrophosphate are listed as P04 and polymeric and phosphonate inhibitors (monomeric and polymeric) are as actives. In analyse of heat-exchanger deposits, all components are listed as wt% of the chemical element or acid-form of the compound.
To illustrate the invention, the following are given by way of example:
The first test method described below was used to determine the ability of the polymer compositions to inhibit calcium and magnesium phosphate.
Calcium and Magnesium Phosphate Inhibition Test Procedure Calcium and magnesium were added to provide initial concentrations of 25û and 125 ppm. An equal amount of phosphate was added to each test solution, and the inhibitor concentrations are listed in Table I. The temperature of the test solutions was maintained at 158~F (70~C). Using dilute aqueous NaûH, the -, pH was slowly increased to 8.5 and maintained during the four hour duration cf the test. Mineral solubility calculations indicate supersaturation values for calcium phosphate ~ lO,OOO
and magnesium phosphate ~ 600 were initially present and the system was under highly stressed conditions. At the conclusion of each test, each solution was filtered ~0.45 um) and the orthophosphate concentration was determined spectrophotometricaïly ~700 nm) after formation of a blue 1339~21 phosphomolybdate complex- The inhibition of calcium phos~hate is~
determined as indicated below:
E~uation 1.
[filtered - blank]
- % inhibition = - X lOû
[unfiltered - blank]
where, filtered sample = concentration of phosphate ion in filtrate in the presence of inhioitor after 4 hours.
initial sample = concentration of phosphate ion in test at solution time zero.
blank = concentration of phosphate ion in filtrate in absence of inhibitor after 4 hours.
'Using the above test method, a numoer of polymer compositions were tested. The results are show below in Taole I.
~'' ''.
1~39521 TABLE I
Calcium and Magnesium Phosphate Inhi~ition % Phosphate 5alt Polymer Inhibition Composition Composition* Molecular ppm polymer actives Number (Mole %) Weight 5 7.5 10 1 AA/t-BAm (88/12) 9,30û 6 71 82 3 AA/t-BAm (88/12)17,700 20 54 72 4 AA/t-BAm (88/12) 25,9ûû 25 68 90 AA/~A/t-BAm (86/8/6) 8,9ûû 7 37 75 6 AA/Am/t-BAm (84/11/6) 9,400 7 55 73 7 AA/MAA-t-~Am (68/19/13) 8,20û 18 78 81 8 AA/MAA/t-BAm (68/19/13)13,60û 15 -- 90 11 AA/MAA/t-BAm (68/19/13)15,600 60 77 84 12 AA/MAA/t-BAm (68/19/13)23,000 59 83 81 Commercial Reference Compounds -AA/HP4 (67/33-75/25) 7,400 13 -- 50 : MaA/S5 (75/25) 19,000 B 74 89 : AA/MA (83/17) 5,aO0 15 49 B7 AA/Am (23/77) 10,100 77 95 92 ~Abbreviations as follows:
AA - acrylic acid Am - acrylamide HPA - hydroxypropylacrylate ~A - methyl acrylate MaA - maleic acid anhydride i MAA - methacrylic acid '- SS - su.lfonated styrene t-BAm - t-butylacrylamide 1339~21 Calcium Phosphonate Inhibition Calcium and a mixture of HEDP and P~TC were added to the test solution to provide initial concentrations of 360 ppm and 8 ppm (total phosphorus as P04), respectively. The temperature was maintained at 140~F (60~C). Using dilute aqueous NaOH, the pH was slowly increased to 9.2 and maintained during the four hour duration of the test. At the conclusion of each test, the solution was filtered (0.45 and 0.10 um) and the total phosphorus concentration of each sample was determined by oxidation of the phosphonates to orthophosphate. Spectrophotometric analysis was accomplished by formation of a blue phosphomolybdate complex, as previously indicated. The percent inhibition of calcium organophosphorus compounds was determined by Equation l, where phosphate ion represents total phosphorus content (as P04).
The test results for polymeric inhibitors are set forth in Table II below.
- -- ~
~ :
':
TA~L_ II
Calcium Phosononate Inhibition ~ Inhi~ition Polymer Filter Size (um) Composition Number 0.45 0.10 , 74 24 6 ~ 13 , ~' '~.
Commercial Reference Compounds MaA/SS (75/25) 95 26 - AA/MA (83/17) 11 5 AA/HPA (67/33-75/25) 59 23 * For composition abbreviations, refer to Table I.
Hydrolytic Stability Gas chromatographic analysis was used to determine the resistance of t-butyl acrylamide-containing polymers against hydrolysis and degradation under high pH conaitions. The test - samples were prepared in polyethylene bottles by slow adaition of aqueous lû weight percent NaOH to a stirred solution containing 15 weight Percent actives of polymer. The rAsulting solution was r diluted to 7 height percent polymer actives with aistilled water and the final oH adjusted to 13.2+0.1. Each test solution was divided into two equal POrtionS with o,e samPle heateO to 123~r and the other s,m~le r-maining at 70OF~ ~ter 130 days, the samples wereanzlv7ea ~or polymer degradation proaucts and t-butylamine content. ,~o evicence of polymer degradation products or hydro~ysis ~as observed in any of the test samples.
The small variations in t-butylamine content indicated in Table III are ~ithin the statistical error of the analysis method¦.
_~ A
,_ _ _ ~__ ~ 339~21 These polymers are rePorted as having hydrolytic stabili'y up to pH 11 but we were surprised to find this hydrol~t~c stabilitY even at pH 13 and beyond. This unexpected result is important because azoles such as tolyltriazole require a pH ~ 12.5 for incorporation into a homogeneous formulation (e.g. Example 3) to provide corrosion inhibition.
Hydrolytic stability is a benefit, particularly with regard to the formulation of polymers in combination with corrosion inhibitors. Several other commercially successful polymers (e.g. acrylic acid/acrylate ester and acrylic acid/hydroxyalkyl esters) do not possess that beneficial quality.
Because of this hydrolytic stability, the polymers of this invention can be used in one drum formulations. Because prior art compounds lack hydrolytic stability, they cannot be packaged with other adjunct corrosion inhibitors, (e.g.
tolyltriazole) without suffering hydrolytic decomposition during storage. Therefore, these adjunct polymers are usually provided in a second formulation so that a two-drum feed system (i.e.
concurrent feed system) is required.
, ~339521 TACLE III
Resistance to Hydrolysis - Gas Chromato~raphic Results Polymer Composition Composition t-Butylamine Content (wt %) Number (Mole %) Raw Material* 70~F 120~F
1 AA/t-BAm (88/12) 0.039 û.034 0.035 11 AA/MAA/t-BAm (68/19/13) û.039 0.041 0.037 * Initial sample before addition of aqueous NaOH.
Pilot Cooling Tower Tests The pilot cooling tower(PCT)test is a dvnamic test which ~-simulates many features present in an industrial recirculating cooling water system. The general test method is described in ,the article "Small-Scale Short-Term Methods of Evaluating Coolins ' Water Treat~ents.. Are they Worthwhile?", by D. T. Reed and R. Nass, Minutes of the 36th Annual Meeting of the INTERNATIONAL
WATER CONFERENCE, Pittsburgh, Pennsylvania, November 4-6, 1975.
The general operating conditions are listed below in Table IV.
TABLE IV
Concentration Cycles* 3.7 - 4.0 ~asin Temperature 100~F
Holding Time Index 24 hr.
Flow ~a~e 2 gpm pH 7.0 - Test Ouration 14 days * At 4 cycles, the ion concentrations (as CaCû3) are: 360 ppm Ca , 2ûO ppm Mg , 440 ppm "M" Alkalinity, 360 ppm C1 , and 200 ppm sulfate.
_.
1339~21 PCT tests were conducted under extended conditions (e.g.
low and high hardness) and differences from general operating conditions are specified in Tables VI and VII and subsequent discussions of results.
A~t the beginning of a pilot cooling tower test, the mass of each heat-exchange tube is determined. After the test is completed, the tubes are dried in an oven and reweighed. Next, the tubes are cleaned with inhibited acid (dilute HCl and formaldehyde), dried, and the final weight determined. Those three weights are used to determine rates of deposition (mg/day) and corrosion (mils per year). As the performance of the treatment program and polymeric inhibitor increases, the deposit and corrosion rates decrease. The pilot cooling tower results are indicated in Tables V-VII below:
-TABLE V
Pilot Cooling Tower Tests (pH 7) Polymer Polymer Deposit - Corrosion -Composition Dosage Mild Steel Mild Steel Number (ppm actives) (mg/day) (mpy) None -- 89 4.1 3 ~.6 39 2.9 4 6.6 27 1.6 - 5 11.0 57 3.3 6 11.0 74 3.8 7 11.0 36 2.5 8 7.5 34 1.9 11 6.6 31 ~.2 12 7.5 34 1.9 AA/HPA 11.0 27 2.2 -.
1 1339~21 In the pilot cooling tower tests listed above, the benefitS of adding a polymer to control corrosion and de~osit on mild steel surfaces can be clearly observed by comparing results listed for polymer compositions #2-9 with the polymer Composition No. "None" above. Results comparable to those for polymer composition PA/HPA, particularly for inhibition of mild steel corrosion were obtained using significantly lower dosages of t-butylacrylamide-containing polymers (polymer compositions #4, 8, 11 and 12). For tests conducted at equivalen-t hardness levels, the corrosion rates for mild steel are considereo equivalent if differences are less than 0.5 mpy.
In Table VI, a comparison is listed of the PCT test results obtained from using a commercially successful AA/HPA
copolymer and low dosages of AA/MAA/t-3Am terpolymer (polymer composition #8). The test conditions were the same as in Table V, except the polymer dosage and haroness levels were varied as indicated.
, TABLE VI 1339~21 Pilot Cooling Tower Tests (pH 7) Water Hardness and Polymer Dosage Ranges Polymer Polymer ppm Deposit - Corrosion -Composition Dosage Hardness* Mild Steel Mild Steel Number (ppm actives) Ca Mg(mg/day) (mpy) 8 3.0 2ûO 100 34 2.7 AA/HPA 7, 5 200 100 37 2.7 None -- 360 200 89 4.1 8 4.0 360 200 30 1.4 AA/HPA 7.5 360 200 40 2.3 8 4.0 600 300 22 2.2 AA/HPA 11.5 600 300 22 1.7 8 10.0 900 450 22 2.0 AA/HPA 17.5 900 450 38 2.0 8 9.5 1200 600 24 0.9 AA/HPA 22.5 1200 600 60 2.3 * Oesired levels of calcium and magnesium. Actual average - results were within +lû~ of ~es5red levels. Differences bet~een desired and actual levels of hardness ions are insignificant and do not affect test results.
13~9~21 In Table VI, the results demonstrate that equal or significantly better control of corrosion and deposit on mild steel surfaces can be obtained using a treatment containing low dosages of AA/MAA/t-BAm terpolymers, as compared to treatments containing approximately two to three times as much AA/HPA. At 360 ppm Ca+2 and 200 ppm Mg+2 hardness levels (as calcium carbonate), the benefits of using the AA/MAA/t-BAm terpolymer (polymer Composition No. 7) can be readily observed by the sharp reduction in mild steel corrosion and deposit rates, as compared to the "no Polymer" case.
~33~521 TAB~E VII
Pilot Cooling Tower Tests (p~ 8 and 8.5 at 120 F aasin) Effects water Hardness, Polymer, and "Phosphorus" Dosage Ranges Polymer Polymer Dosage ppm ppm Corrosion Deposit Composition (opm Hardness* Phosphorus Mild Steel Mild Steel Number actives) pH CA MG po4 P207 P~TC (mpy) (mg/day) no polymer** -- 7 360 200 9.7 9.1 -- 4.1 ' 8 7.5 8 360 200 8 4 6 1.7 32 8 7.5 8 360 200 8 4 4 1.7 28 8 7.5 8 360 200 8 4 2 1.9 30 8 7.5 8 360 200 8 2 2 1.9 26 8 4.0 8 360 200 8 0.0 0 2.5 36 8 7.5 8 360 200 6 3 3 1.8 23 8 7.5 8.5 360 200 4 1 2 1.7 23 _ 3 7.5 8 700 350 8 4 6 1.9 36 8 7.5 8 7ûO 350 6 3 3 1.7 31 8 7.5 8 700 350 6 û.0 3 1.9 30 8 7.5 8 700 350 4 2 4 2.3 31 8 7.5 8 700 350 4 2 2 2.4 31 8 7.5 8 7~0 350 4 1 ~ 2.6 31 * Desired levels of calcium ind magnesium. Actual average results were within +10%
of desired levels. Qifferences between desired and actual levels of hardness ions are inslgnificant and do not affect PCT test results.
** "no polymer" test was conducted under less severe conditions with 8asin Temperature equal to lOQ F and with pH 7 ~1 ~ 1339~21 ":~''li Results from the above Table indicate that using a combination of t-butylacrylamide containing polymer, phosphates ,_ and/or phosDhonates provides very good corrosion inhibition even under very stressful conditions of medium to high hardness levels, high basin temperature (120 F) and high pH (8 to 8.5).
All of the results are significantly better than the polymer Composition No. "no polymer" which had a basin temperature of 100~F.
"
- ~4 -~' , ~ , . .
' ~ >
Claims (23)
1. A concentrated composition for use in diluted form for inhibiting corrosion by industrial cooling waters which contain hardness and have a pH of at least 6.5 which composition comprises:
I. a water-soluble inorganic phosphate capable of inhibiting corrosion in an aqueous alkaline environment as a first active ingredient, and II. a water-soluble non-crosslinked random polymer of 50 to 90 weight parts of an acrylic acid and 10 to 50 weight parts of a substituted acrylamide, on the basis of a total of 100 weight parts of polymerized monomers, 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 substituted acrylamide 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 or R3 are selected from alkyl, aryl, and keto groups, provided that R2 or R3 is other than hydrogen as a second active ingredient, ,,, with the weight ratio of polymer:phosphate being within the range of 0.1:1 to 5:1 and,if required, III. a diluent or carrier with the proviso that the composition comprises, when taken together, at least 100 ppm of said active ingredients.
I. a water-soluble inorganic phosphate capable of inhibiting corrosion in an aqueous alkaline environment as a first active ingredient, and II. a water-soluble non-crosslinked random polymer of 50 to 90 weight parts of an acrylic acid and 10 to 50 weight parts of a substituted acrylamide, on the basis of a total of 100 weight parts of polymerized monomers, 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 substituted acrylamide 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 or R3 are selected from alkyl, aryl, and keto groups, provided that R2 or R3 is other than hydrogen as a second active ingredient, ,,, with the weight ratio of polymer:phosphate being within the range of 0.1:1 to 5:1 and,if required, III. a diluent or carrier with the proviso that the composition comprises, when taken together, at least 100 ppm of said active ingredients.
2. The composition of claim 1, further comprising a water-soluble organic phosphonate capable of inhibiting corrosion in an alkaline aqueous environment.
3. The composition of claim 1, wherein said random polymer further contains up to 30% by weight of a termonomer which contains either an anionic or non-anionic group.
4. The composition of claim 3, wherein said polymer is a terpolymer of acrylic acid, methacrylic acid and t-butyl acrylamide; and said phosphonate is selected from the group consisting of 1-hydroxyethane-1, 1-diphosphonic acid and 2-phosphonobutane-1, 2,4-tricarboxylic acid.
5. The composition of claim 4, further including a corrosion inhibiting amount of tolyltriazole.
6. The composition of claim 4, wherein the terpolymer has a weight average molecular weight of 9,000 to 30,000.
7. A composition according to claim 1, wherein said active ingredients comprise about 25% by weight of said composition.
8. A composition according to any one of claim 1 to claim 7, wherein said phosphate comprises orthophosphate and condensed phosphate, the ratio of orthophosphate to condensed phosphate being in the range (on an active basis) of 0.5:1 to 30:1.
9. A composition according to claim 8, wherein the ratio of orthophosphate to condensed phosphate is in the range of 0.5:1 to 10:1.
10. A composition according to claim 8, wherein the ratio of orthophosphate to condensed phosphate is in the range of 1:1 to 4:1.
11. A composition according to claim 8, additionally comprising an organic phosphonate and the ratio of ortho-phosphate, condensed phosphate and phosphonate is in the range 0.5:1:0.33 to 30:1:16.
12. A composition according to claim 9, additionally comprising an organic phosphonate and the ratio of ortho-phosphate, condensed phosphate and phosphonate is in the range 0.5:1:1 to 10:1:10.
13. A composition according to claim 10, additionally comprising an organic phosphonate and the ratio of ortho-phosphate, condensed phosphate and phosphonate is in the range 1:1:1 to 4:1:6.
14. A composition according to any one of claim 11 to claim 13, wherein the organic phosphonate is selected from the group consisting of 1,1-hydroxyethylidene diphosphonic acid and its salts and 2-phosphono-butane 1,2,4-tricarboxylic acid and its salts.
15. A commercial package comprising a composition according to any one of claims 1 to 7 and 9 to 13 together with instructions for use thereof to inhibit corrosion by industrial cooling water.
16. A commercial package according to claim 15 in the form of a one drum formulation.
17. A commercial package according to claim 15 in the form of a two drum formulation.
18. Use of a composition according to any one of claims 1 to 7 and 9 to 13 to inhibit corrosion in industrial cooling water.
19. Use according to claim 18, wherein said composition is diluted to between 10 and 100 ppm of industrial cooling water.
20. Use according to claim 18, wherein said composition is diluted to between 10 and 50 ppm of industrial cooling water.
21. Use according to claim 18, wherein said composition is diluted to between 15 and 40 ppm of industrial cooling water.
22. A method for inhibiting corrosion of steel in aqueous cooling systems having hardness and a pH of at least 6.5 by dosing said system with:
from 10-50 ppm of a composition comprising:
I. a water-soluble mixture of inorganic orthophosphate and condensed phosphate capable of inhibiting corrosion in an aqueous alkaline environment, and II. a water-soluble non-crosslinked random polymer of 50 to 90 weight parts of an acrylic acid and 10 to 50 weight parts of a substituted acrylamide, on the basis of a total of 100 weight parts of polymerized monomers, said polymer having weight average molecular weight in the range of about 9,000 to 30,000 and the polymerized units of an acrylic acid and a substituted acrylamide 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; with the weight ratio of polymer to phosphate being within the range of 0.1:1 to 5:1.
from 10-50 ppm of a composition comprising:
I. a water-soluble mixture of inorganic orthophosphate and condensed phosphate capable of inhibiting corrosion in an aqueous alkaline environment, and II. a water-soluble non-crosslinked random polymer of 50 to 90 weight parts of an acrylic acid and 10 to 50 weight parts of a substituted acrylamide, on the basis of a total of 100 weight parts of polymerized monomers, said polymer having weight average molecular weight in the range of about 9,000 to 30,000 and the polymerized units of an acrylic acid and a substituted acrylamide 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; with the weight ratio of polymer to phosphate being within the range of 0.1:1 to 5:1.
23. The method of claim 22, wherein said composition further includes a water-soluble organic phosphonate capable of inhibiting corrosion in an alkaline aqueous environment, the ratio of orthophosphate to condensed phosphate to phosphonate being in the range of 0.5:1:0.33 to 30:1:16.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US84405686A | 1986-03-26 | 1986-03-26 | |
| US844,056 | 1986-03-26 |
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| CA1339521C true CA1339521C (en) | 1997-11-04 |
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| CA 530973 Expired - Fee Related CA1339521C (en) | 1986-03-26 | 1987-03-03 | Composition and method for preventing corrosion in aqueous systems |
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| CA (1) | CA1339521C (en) |
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1987
- 1987-03-03 CA CA 530973 patent/CA1339521C/en not_active Expired - Fee Related
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