Note: Descriptions are shown in the official language in which they were submitted.
~ ~-- 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.
- 2 -
.
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.
-- 3 --
.. .. . .
:.
- '. .
, . .
1339521
-- 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
CH3
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,
-- 6 --
.. .. __ . ~ ;.
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.
- 10 -
,,~.
h-- ~33g~21
Specific examples of compounds which are encompassea by
th1s formula include:
methylphosphonic acid
CH3P03H2
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
CH3-CH-CH2-P03H2
benzene phosphonic acid
C6H5-P03H2
benzylphosphonic acid
C6H5CH2 03H2
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
- 12 -
-
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.
R6 R7 OM
~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
- 14 -
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.
- 16 -
.
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
- 17 -
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~.
- 18 -
1 ~
1339521
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.
. ~, ,, ... ,.~, .. _ , .. .. .
- 19 -
,,.
,: ,
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 -
'~
1339521
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
- 22
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.
~'' ''.
- 23 -
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
- 24 -
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.
- -- ~
~ :
':
2 1
TA~L_ II
Calcium Phosononate Inhibition
~ Inhi~ition
Polymer Filter Size (um)
Composition Number 0.45 0.10
1 82 26
, 74 24
6 ~ 13
11 98 58
, ~' '~.
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
,_ _ _ ~__
- - 26 -
~ 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.
_.
- 28 -
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
- 29 -
-.
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.
- 30 -
, 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.
- 32 -
~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 -
~' ,
~ , . .
' ~ >
