Stabilization of metal ions with terpolymers containing styrene sulfonic acid

Stabilization of metal ions in an aqueous medium is obtained by adding to said aqueous medium 0.5 to 500 ppm of a copolymer containing at least one of each of the following three monomers: PA0 (a) acrylic acid, methacrylic acid, and mixtures thereof; PA0 (b) acrylamidoalkane sulfonic acids and salts thereof, such as 2-acrylamido-2-methylpropane sulfonic acid; and PA0 (c) primary copolymerizable monomers selected from styrene sulfonates.

BACKGROUND OF THE INVENTION 
Citric acid, gluconic acid, ascorbic acid, tartaric acid, certain 
phosphonates, and other chelant materials have been used in the past to 
stabilize iron in solution and thus prevent its precipitation in forms 
such as ferric hydroxide and ferric oxide, wherein iron is in the second 
or third oxidation state. Citric acid and such prior art chelants 
effectively maintain iron in solution by forming complexes therewith which 
are soluble in water and thereby, remain dissolved in water. Although 
citric acid and cognate chelants are effective as solubilizing agents for 
iron in solution, they are not antiscalants and are ineffective against 
scale such as calcium carbonate, calcium phosphate, calcium sulfate, 
magnesium hydroxide, and the like. 
Furthermore, performance of the prior art chelants is strongly dependent on 
solution pH. For example, iron (III) stabilization at 2 ppm of citric acid 
was 79% at pH of 7 but only 2% at pH of 8. In other words, an increase in 
solution pH from 7 to 8 decreased citric acid performance approximately 
forty times. 
U.S. Pat. No. 4,552,665 discloses a process for stabilizing dissolved 
manganese ion and its reaction products in an aqueous solution by adding 
thereto 0.1 to 20 ppm of a copolymer of an unsaturated carboxylic acid or 
its salt and an unsaturated sulfonic acid or its salt. Acrylic acid is an 
example of the unsaturated carboxylic acid and 
2-acrylamido-2-methylpropane sulfonic acid (AMPS) is an example of the 
unsaturated sulfonic acid. The disclosed copolymers include 3-component 
copolymers or terpolymers. 
The Amick U.S. Pat. No. 4,711,725 discloses stabilization of an aqueous 
system by inhibiting precipitation of calcium phosphate with a copolymer 
antiscalant, said copolymer comprising 42 to 84% of (meth)acrylic acid and 
salts thereof, 11 to 40% acrylamido alkane, sulfonic acid, and 5 to 30% or 
one or more monomers selected from vinyl esters, vinyl acetate, and 
substituted acrylamide. The aqueous medium can contain or can be devoid of 
iron contamination. 
Other cases are being filed concurrently for Messrs. Amjad and Masler which 
relate to the use of same or similar polymers. One of the other cases is 
entitled "Scale Control with Copolymers Containing Acrylamidoalkane 
Sulfonic Acid," and the other case is entitled "Terpolymers for Dispersing 
Particulates In An Aqueous Medium". 
SUMMARY OF THE INVENTION 
This invention is directed to stabilization of metal ions in an aqueous 
medium by addition thereto of at least an effective amount of a copolymer 
which contains at least three different repeating groups for stabilization 
of soluble metal ions, particularly iron, zinc, and manganese, and 
especially iron in the (II) and (III) oxidation states. Such copolymers 
contain at least three different repeating units selected from polymerized 
monounsaturated carboxylic acids of 3 to 5 carbons and water-soluble salts 
and anhydrides thereof, acrylamidoalkane sulfonic acids and salts thereof, 
and primary comonomers selected from styrene sulfonic acids, their salts, 
and mixtures thereof. 
DETAILED DESCRIPTION OF THE INVENTION 
Copolymers are described herein which are effective in stabilizing 
transition metal ions, such as iron, zinc and manganese. Amount of such 
copolymer that is added to an aqueous medium is at least an effective 
amount which is in the range of 0.5 to 500 parts per million (ppm) of the 
aqueous medium, preferably 1 to 50 ppm. Although the aqueous medium can be 
acidic, in a preferred embodiment it is neutral or alkaline. 
Specific applications contemplated herein where the copolymers can be used 
include aqueous systems used in recirculating cooling towers, steam 
boilers, desalination, oil field applications in secondary oil recovery 
operations, flash distillation, as well as in aqueous systems such as 
sugar solutions. 
The copolymers can be in unneutralized or neutralized form. Such copolymers 
can be neutralized with a strong alkali, such as sodium hydroxide, in 
which instance, the hydrogen of the carboxyl group and sulfonic acid group 
in the copolymer will be replaced with sodium. With the use of an amine 
neutralizing agent, the hydrogen will be replaced with an ammonium group. 
Useful copolymers for purposes herein include copolymers that are 
unneutralized, partially neutralized, and completely neutralized. 
The copolymers are soluble in water up to about 20% solids concentration, 
and they must, of course, be soluble in water in amount used, to be 
effective metal ion stabilizers. The copolymers contemplated herein are 
polymers of at least three different monomers and include at least one 
monomer selected from each one of the groups (a), (b) and (c) The groups 
(a), (b) and (c) are defined as follows: 
(a) monounsaturated carboxylic acids of 3 to 5 carbon atoms, salts and 
anhydrides thereof; 
(b) acrylamidoalkane sulfonic acids and salts thereof containing up to 6, 
preferably 1 to 4, carbon atoms in the alkane moiety; and 
(c) primary copolymerizable monomers which aid in the stabilizing 
effectiveness of the copolymers selected from styrene sulfonic acids, 
their salts, and mixtures thereof. 
In addition to the above requisite monomers, a small amount of other or 
secondary copolymerizable monomers can also be used as long as they do not 
substantially deleteriously affect performance of the copolymers as metal 
ion stabilizers. Amount of such secondary copolymerizable monomers can 
generally vary up to about 20% by weight, preferably 2 to 10% by weight of 
the final copolymer. 
The copolymers suitable herein are random non-crosslinked polymers 
containing polymerized units of one or more of each of the monomers (a), 
(b), and (c), identified above, and can contain a small proportion of 
polymerized units of one or more of the secondary copolymerizable 
monomers. The copolymers have weight average molecular weight of 1,000 to 
100,000, preferably 2,000 to 50,000, and more preferably 2,000 to 20,000. 
The molecular weight given herein is measured by gel permeation 
chromatography. 
The copolymers contain 20 to 95% by weight of the Polymerized carboxylic 
acid or its salt or anhydride, preferably 30 to 75% and more preferably 30 
to 60%; 1 to 60% by weight of the polymerized acrylamidoalkane sulfonic 
acid or its salt, preferably 10 to 50% and more preferably 20 to 50%; 5 to 
30% of the primary copolymerizable monomer, and preferably about 10 to 
20%. The copolymers can also include one or more polymerizable, secondary 
comonomers in amount of up to about 20%, preferably up to about 10%, and 
more preferably about 2 to 10%, which exclude substituted acrylamides, 
vinyl esters, and acrylate esters. 
The carboxylic acid monomers contemplated herein include monounsaturated 
monocarboxylic and dicarboxylic acids, salts and anhydrides thereof. 
Preferred in this class are monounsaturated monocarboxylic acids of 3 to 4 
carbon atoms and water soluble salts thereof, particularly acrylic acid 
and methacrylic acid. Because of its availability, effectiveness and low 
price, acrylic acid is particularly preferred. Repeating units of an 
acrylic acid and salts thereof are represented as follows: 
##STR1## 
where R is hydrogen or methyl and X can be hydrogen, alkali metal, 
alkaline earth metal, or ammonium, particularly hydrogen, sodium, 
potassium, calcium, ammonium, and magnesium. 
The repeating units of acrylamidoalkane sulfonic acids and salts thereof 
are defined as follows: 
##STR2## 
where R is hydrogen or methyl; is hydrogen, alkali metal or an alkaline 
earth metal, particularly hydrogen, ammonium or an alkali metal; and 
R.sup.1 and R.sup.2 are individually selected from hydrogen and alkyl 
groups of 1 to 4 carbon atoms. In a preferred embodiment, R is hydrogen 
and R.sup.1 and R.sup.2 are each an alkyl group of 1 to 3 carbon atoms. In 
this group of sulfonic acids, 2-acrylamido-2-methylpropane sulfonic acid 
or AMPS.RTM. is a commercial, readily available monomer which is 
especially preferred for the stabilization effectiveness described herein. 
The primary copolymerizable monomers are selected from styrene sulfonic 
acids, their salts, and mixtures thereof. Repeating units of styrene 
sulfonic acids and salts thereof are defined as follows: 
##STR3## 
where R is hydrogen or a lower alkyl group of 1 to 6 carbon atoms 
preferably hydrogen, and X is hydrogen, alkali metal, alkaline earth 
metal, or ammonium, particularly hydrogen, ammonium or alkali metal. A 
particularly suitable sulfonic acid is styrene sulfonic acid where R is 
hydrogen and the --SO.sub.3 X group is at the 3 or 4 position on the 
phenyl ring or a mixture thereof. The salts of styrene sulfonic acids are 
water-soluble. The sodium salt of styrene sulfonic acid is available 
commercially. 
The monomers can be prepared, if desired, in a conventional manner but they 
are commercially available and therefore, can be purchased. 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. 
It is also a requirement that the copolymer be soluble in water. Typically, 
the copolymer is used in water in the range of 0.5 to 500 ppm. Thus, high 
solubility of water treatment compositions is not essential but desirable. 
The produce is preferably shipped in drums as a concentrated aqueous 
solution containing in the range of about 20% to about 50% by weight of 
solids per 100 parts of solution, which requires solubility to the extent 
of at least 20 weight parts per 100 parts of water. 
Polymerization of the monomers identified herein can be carried out in a 
mutual solvent for both, such as in a lower alkanol of about 1 to 6 carbon 
atoms, or in water, with an effective amount of a free radical initiator 
sufficient to produce the desired composition within an acceptable period 
of time. The monomeric acids can be used as such or can be in a partially 
or a completely neutralized from prior to polymerization. 
The reaction is conveniently carried out in water as the only reaction 
medium at a temperature in the range of about 30.degree. to about 
130.degree. usually at atmospheric pressure. 
The copolymer may also be formed in an acyclic ketone, such as acetone, in 
an alkanol, in water, or mixtures thereof. If, for example, the copolymer 
is formed in an organic solvent, or a mixture of an organic solvent and 
water, the copolymer is converted from the organic solvent solution to a 
water solution. Typically, the organic solvent is stripped from the 
solution with steam or distilled off with subsequent additions of water 
and repetition of distillation to remove the solvent, followed by the 
addition of water and a neutralizing agent such as caustic solution, 
ammonia, a hydrazine, or a low-boiling primary, secondary or tertiary 
aliphatic amine. 
The final aqueous solution of polymer salt is preferably in the range of 
about pH 2 to about pH 8, with a total solids content of about 5 to about 
50% by weight of polymer in water. 
The copolymers formed may have weight average molecular weight in the range 
of about 1,000 to about 100,000, preferably 2,000 to 50,000, and more 
preferably about 2,000 to 20,000, as determined by gel permeation 
chromatography. 
In a typical polymerization process, a glass lined or stainless steel 
jacketed reactor is charged with predetermined amounts of monomers along 
with solvent and the polymerization catalyst under a nitrogen blanket, and 
the reaction mixture allowed to exotherm under controlled temperature 
conditions maintained by a heat-transfer fluid in the jacket of the 
reactor. The pressure under which the reaction occurs is not critical, it 
being convenient to carry it out under atmospheric pressure. 
The copolymers described herein in connection with stabilizing metal ions 
in solution, can be used in combination with other conventional additives 
wherever appropriate. Examples of some of the conventional additions 
include anti-precipitating agents, oxygen scavengers, sequestering agents, 
corrosion inhibitors, antifoaming agents, and the like.

EXAMPLE 1 
This example demonstrates effectiveness of the AA/AMPS/SSS polymers as 
calcium phosphate scale inhibitors in presence or absence of iron. 
Pursuant to the procedure set forth herein, the copolymers formed in the 
manner described herein were used to treat water which contained calcium 
ions and phosphate ions in a stirred pH-STAT test while maintaining 
constant pH and using an automatic tritrator to gauge the effectiveness of 
the polymer for inhibiting the formation and deposition of calcium 
phosphate. The test was carried out as follows: a known volume of a 
phosphate salt solution, such as Na.sub.2 HPO.sub.4, or another soluble 
phosphate salt solution, was transferred to a known volume of distilled 
water in a double-walled glass cell to give a final concentration of about 
9 ppm of orthophosphate ions. To this solution was added slowly and with 
continuous stirring a known volume of testing polymer solution sufficient 
to give a dosage of 10 ppm. 
A pair of glass and reference electrodes, which were calibrated before and 
after each experiment with standard buffer solutions of pH 7.00 and 9.00, 
were then immersed in the solution which was maintained at 50.degree. C. 
by circulating water through the outside of a glass cell jacket. After 
about 45 minutes, a known volume of calcium chloride solution was slowly 
added to the continuously stirred solution containing phosphate and 
polymer, to give a final calcium ion concentration of 140 ppm. The pH of 
the solution was then immediately brought to pH 8.50 by automatic addition 
of 0.10M NaOH solution. The pH of the solution was then maintained at 
8.50.+-.0.01 throughout the experiment using the pH-stat technique. 
Solution samples were withdrawn after 22 hours, and analyzed, after 
filtration through 0.22 micrometer filter paper, for orthophosphate ions 
using the ascorbic acid method, as described in detail in "Standard 
Methods for the Examination of Water and Waste Water" 14th edition, 
prepared and published by American Health Association. The instrument used 
for the colorimetric measurements was a Beckman 5270 Spectrophotometer. 
Tests for calcium sulfate were carried out by the method of Ralston, see J. 
Pet. Tech., August 1969, 1029-1036. 
The percent threshold inhibition (TI) attained for each experiment was 
obtained using the following formula, shown in this case for calcium 
phosphate: 
##EQU1## 
where 
(PO.sub.4) exp=concentration of phosphate ion in the filtrate in presence 
of the copolymer at time of 22 hours 
(PO.sub.4) final=concentration of phosphate ion in filtrate in absence of 
the copolymer at time 22 hours 
(PO.sub.4) initial=concentration of phosphate ion at time zero. 
Scale inhibition results referred to above are set forth in Table I, below: 
TABLE I 
______________________________________ 
Monomer Mol. % Ca/P.sup.(a) 
Composition Wt. Ratio Wt. Inhibition 
______________________________________ 
AA:AMPS:SSS 70:10:20 5,000 81 
" 70:10:20 15,000 77 
" 60:10:30 5,000 93 
" 60:10:30 10,000 95 
" 60:10:30 15,000 89 
" 60:30:10 5,000 92(72) 
" 60:30:10 15,000 99(79) 
" 60:30:10 29,000 94(67) 
" 60:30:10 33,000 86(71) 
" 60:32.5:7.5 
15,000 97 
" 50:30:20 5,000 92 
" 50:30:20 10,000 95 
" 50:30:20 15,000 96 
" 50:30:20 30,000 95 
" 40:30:30 5,000 66 
" 40:30:30 10,000 87 
" 40:30:30 15,000 95(85) 
" 40:50:10 15,000 83 
" 50:30:20 60,000 86 
" 50:40:10 50,000 95 
AA:AMPS:SSS:DADMAC 
60:25:10:5 
15,000 74 
______________________________________ 
.sup.(a) Conditions: 
calcium = 140 ppm; phosphate = 9 ppm; pH = 8.50; T = 50.degree. C.; time 
22 hr.; polymer = 10 ppm 
The following contractions appear in the above table: 
Ca/P=calcium phosphate 
AA=acrylic acid 
AMPS.RTM.=2-acrylamido-2-methylpropane sulfonic acid 
SSS=sodium styrene sulfonate 
DADMAC=diallyldimethylammonium chloride 
The numbers in parentheses indicate percent threshold inhibition of calcium 
phosphate in the presence of 1.0 ppm of soluble iron (III). 
It has been shown that copolymers disclosed herein are effective 
antiscalants in the presence or absence of soluble metal ions. Typical 
scales encompassed by the present invention include especially calcium 
scales such as calcium phosphate. 
EXAMPLE 2 
To determine effectiveness of the copolymers as metal ion stabilizers, a 
known amount of ferric chloride was added to 100 mls of synthetic water 
containing 0-5 ppm of the copolymers in a 125 ml glass bottle. The 
synthetic water used in the metal ion stabilization test was made by 
mixing standard solutions of calcium chloride, magnesium chloride, sodium 
bicarbonate, sodium sulfate and sodium chloride. Analysis of the water 
used in the tests, is given below: 
______________________________________ 
Ca = 300 ppm Cl = 2,170 ppm 
Mg = 300 ppm SO.sub.4 = 700 ppm 
Na = 1113 ppm HCO.sub.3 = 97 ppm 
Fe = 1 ppm 
______________________________________ 
The test was run for 2 hours, at room temperature and under static 
conditions. The solutions were filtered through a 0.22 micron filter and 
the filtrate was analyzed for soluble metal ion by atomic absorption 
spectroscopy. Percent metal ion stabilization was calculated as follows, 
here shown for iron: 
##EQU2## 
where: 
iron (exp)=concentration of iron in the presence of the copolymer at t=2 
hours 
iron (e)=concentration of iron in the absence of the copolymer at t=2 hours 
iron (initial)=concentration of iron at t=0 
The stabilization data is presented in Table II, below: 
TABLE II 
______________________________________ 
% Fe Stabilization 
Fe = 3 Fe = 1.0 
ppm ppm 
4 ppm 2.0 ppm 
Composition 
Monomer Wt. 
Mol. Wt. polymer 
polymer 
______________________________________ 
AA:AMPS:SSS 
70:10:20 5,000 -- 91 
" 60:10:30 5,000 -- 93 
" 60:10:30 15,000 -- 93 
" 40:30:30 5,000 88 100 
" 60:30:10 5,000 21 85 
" 60:30:10 14,000 55 97 
" 60:30:10 16,000 58 97 
" 60:32.5:7.5 
15,000 42 85 
" 50:30:20 5,000 50 93 
" 50:30:20 10,000 62 99 
" 50:30:20 15,000 51 95 
" 50:30:20 30,000 8 98 
" 50:30:20 60,000 -- 88 
" 40:30:30 5,000 85 99 
" 40:30:30 10,000 91 98 
" 40:30:30 15,000 83 99 
" 40:50:10 15,000 91 99 
______________________________________ 
The above terpolymers containing sodium styrene sulfonate are effective 
iron stabilizers in an aqueous medium defined above.