Method for controlling scale deposition in aqueous systems using quaternary ammonium/maleic anhydride-type polymers

This invention is directed to a method for controlling the formation of scale deposits in aqueous systems by adding an effective amount, preferably at least 0.1 ppm, of a maleic anhydride/quaternary ammonium-type polymer to the aqueous system being treated.

BACKGROUND OF THE INVENTION 
U.S. Pat. No. 3,912,693 discloses a photopolymerization method for 
preparing diallyl quaternary ammonium/maleic acid copolymers. 
U.S. Pat. No. 4,640,793 discloses the use of admixtures containing 
carboxylic acid/sulfonic acid polymers and phosphonates as scale and 
corrosion inhibitors. 
EPO Pat. Appln. No. 84102890.5 discloses copolymers of maleic acid and an 
adduct of an oxyalkylene and allyl alcohol, and the use thereof for scale 
inhibition. 
Japanese No. 57-084794 discloses the use of copolymers of acrylic acid and 
allyl polyethylene glycol as scale inhibitors. 
U.S. Pat. No. 4,297,237 discloses the use of polymaleic anhydride and 
polyphosphates as corrosion inhibitors, and U.S. Pat. Nos. 3,810,834, 
3,963,363 and 4,089,796 disclose methods of treating the water of an 
aqueous system with hydrolyzed polymaleic anhydride to inhibit scale 
formation. 
U.S. Pat. Nos. 2,723,956, 3,289,734, 3,292,152, 3,578,589 and 3,715,307 
relate to the use of polymaleic anhydride and copolymers thereof as scale 
control agents. 
U.S. Pat No. 3,965,027 discloses the use of certain amine adducts of 
polymaleic anhydride as scale and corrosion inhibitors. 
European patent application 84301450.7 discloses carboxylic acid/sulfonic 
acid copolymers in combination with organic phosphonates as scale 
inhibitors. 
U.S. Pat. Nos. 4,176,059, 4,217,216, and 4,246,030 disclose the use of 
molybdate compositions for corrosion inhibition. 
However, none of the prior art references described above in any way 
suggest the use of the instant polymers as scale control agents. 
Many commercial waters contain alkaline earth metal cations, such as 
calcium, barium, magnesium, etc., and anions such as carbonate, sulfate, 
oxalate and/or phosphate. When the concentrations of these anions and 
cations are sufficiently high, their reaction products become insoluble 
and precipitates form until the solubility limits are no longer exceeded. 
These precipitates are alkaline earth metal scales. For example, when the 
concentrations of calcium ion and the any of the above mentioned anions 
are sufficient to exceed the solubility limitations of the calcium-anion 
reaction products, a solid phase of calcium scales will form as a 
precipitate. 
Solubility product concentrations are exceeded for various reasons, such as 
evaporation of the water phase, change in pH, pressure, or temperature, 
and the introduction of additional ions which can form insoluble compounds 
with the ions already present in the solution. As these reaction products 
precipitate on heat transfer surfaces in contact with aqueous streams, 
they form scale. The scale prevents effective heat transfer, interferes 
with fluid flow, facilitates corrosive processes, and harbors bacteria. 
Scale is an expensive problem in many industrial water systems, causing 
delays and shut downs for cleaning and removal. Alkaline earth metal 
scales commonly form on the metallic surfaces of apparatuses used for 
thermal treatment of aqueous solutions and suspensions. By alkaline earth 
metal scales, we mean scales including but not limited to calcium 
carbonate, calcium oxalate, magnesium carbonate, calcium phosphate, 
calcium sulfate, and barium sulfate. These scales frequently form in the 
tubes of heat exchangers and on other heat exchange surfaces. 
In the past, alkaline earth metal scale inhibition has been facilitated by 
the use of anionic polyelectrolytes such as polyacrylates, polymaleic 
anhydrides, copolymers of acrylates and sulfonates, and polymers of 
sulfonated styrenes. However, over the past few years, high pH and/or 
non-chromate corrosion treatment programs have become increasingly 
important. The use of corrosion inhibitors such as zinc salts and/or 
phosphates requires that an effective scale inhibitor be used to prevent 
the deposition of the reaction products formed when the added inhibitors 
combine with the ions present in the water. Also, an effective inhibitor 
can increase the solubility of the corrosion inhibitors, and thus improve 
corrosion protection. 
The deposition of iron oxide on surfaces is another severe problem in 
industrial cooling water systems. For example, the prevention of iron 
oxide precipitation is essential in nuclear power plants. 
In the paper industry, the formation of scales such as barium sulfate and 
calcium oxalate on metal surfaces causes processing problems. These scales 
form rough, hard, tenacious deposits which can cause reduced stock flow, 
formation problems and machine down time due to the generation of fiber 
twists and the sloughing-off of biological debris. Sub-deposit corrosion 
can also be a major problem due to the activity of sulfate-reducing 
bacteria. 
Accordingly, the need exists for an inexpensive, efficient method and 
composition for preventing the formation of deposits on metallic surfaces 
in contact with water by inhibiting the formation of scales and/or by 
dispersing scale-forming compounds. 
The instant inventors have discovered a method for controlling scale 
deposition and/or dispersing scale-forming compounds in aqueous systems 
using maleic acid/quaternary ammonium-type polymers. While such polymers 
alone are effective inhibitors, other common scale and/or corrosion 
inhibitors may enhance their performance under certain conditions. 
The instant polymers are especially effective agents for controlling 
calcium scales, particularly calcium oxalate. 
DETAILED DESCRIPTION OF THE INVENTION 
The instant invention is directed to a method for controlling scale 
deposition in an aqueous system comprising adding to the system being 
treated an effective amount of a water-soluble polymer which comprises (a) 
an ethylenically unsaturated dibasic carboxylic acid or anhydride, 
preferably maleic acid or anhydride (MA), and (b) at least one quaternary 
dialkyldiallyl ammonium monomer, preferably dimethyldiallyl ammonium 
chloride (DMDAAC) or a homologue thereof, wherein the mole ratio of 
(a):(b) ranges from about 1:50 to about 5:1, preferably from about 1:10 to 
about 3:1, most preferably from about 1:2 to about 3:1. Water soluble 
salts of such polymers can also be used. 
Any ethylenically unsaturated dibasic carboxylic acid or anhydride can be 
used as monomer (a). For example, maleic acid or itaconic acid or their 
anhydrides can be used. Maleic acid and maleic anhydride are preferred. 
The maleic anhydride/quaternary ammonium-type polymers of the instant 
invention may be prepared by photopolymerization or by solution 
polymerization techniques, preferably by solution polymerization using a 
persulfate-type initiator. Since the maleic anhydride groups may be 
hydrolyzed very readily for example, by heating with water or by 
neutralizing with alkali, to form free carboxylic acid groups and/or 
carboxylate salts with possibly some residual anhydride groups, the term 
"maleic anhydride" as used in this specification includes the groups 
formed by the hydrolysis of maleic anhydride groups. For this reason, 
"maleic acid" and "maleic anhydride" are used interchangeably. 
The instant polymers are prepared by polymerizing at least one 
ethylenically unsaturated dibasic carboxylic acid or anhydride, preferably 
maleic acid or anhydride, in combination with at least one quaternary 
dialkyldiallyl ammonium monomer (monomer b). Any water-soluble 
dialkyldiallyl ammonium monomer can be used. The preferred monomers are 
those wherein the alkyl groups, which may be the same or different, are 
selected from the group consisting of C.sub.1 -C.sub.10 alkyls. The most 
preferred quaternary ammonium dialkyldiallyl ammonium monomers are 
dimethyldiallyl ammonium chloride (DMDAAC), diethyldiallyl ammonium 
chloride (DEDAAC), dimethyldiallyl ammonium bromide (DMDAAB) and 
diethyldiallyl ammonium bromide (DEDAAB). The corresponding iodine salts 
can also be used. 
Other quaternary ammonium salts of diallylamine derivatives, including but 
not limited to those disclosed in the '693 patent, can also be used as 
monomers in the instant process. A preferred monomer is diallyl 
methylamine. The quaternary ammonium salts of diallylamine derivatives 
disclosed in the '693 patent are hereby incorporated into this 
specification by reference. 
The mole ratio of the acid or anhydride to the quaternary dialkyldiallyl 
ammonium monomer in the monomer mix may range from about 1:50 to about 
5:1, preferably from about 1:10 to about 3:1 and most preferably from 
about 1:2 to about 3:1. The monomer mix is an aqueous solution or slurry 
comprising the monomers and water. 
An effective amount of an instant polymer should be added to the aqueous 
system being treated. As used herein, the term "effective amount" is that 
amount of polymer necessary to control scale deposition in the system 
being treated. Generally, the effective amount will range from about 0.1 
to about 200 ppm, on an active basis, based on the total weight of the 
aqueous system being treated, preferably from about 1 to about 200 ppm. 
As used herein, the term "controlling scale deposition" is meant to include 
scale inhibition, threshold precipitation inhibition, stabilization, 
dispersion, solubilization, and/or particle size reduction of scales, 
especially alkaline earth metal, iron and zinc scales. Clearly, the 
instant additives are threshold precipitation inhibitors, but they also 
stabilize, disperse and solubilize scale forming compounds, such as iron 
oxide. 
Thus, the inventors have discovered that the instant polymers, alone or in 
combination with other scale and/or corrosion inhibitors, inhibit, 
minimize or prevent scaling, even under severe operating conditions, and 
intend that the instant specification describe this discovery, without 
attempting to describe the specific mechanism by which scale deposition is 
prevented or inhibited. 
The term "aqueous system", as used herein, is meant to include any type of 
system containing water, including, but not limited to, cooling water 
systems, boiler water systems, desalination systems, gas scrubber water 
systems, blast furnace water systems, reverse osmosis systems, evaporator 
systems, paper manufacturing systems, mining systems and the like. 
The use of a maleic anhydride/quaternary ammonium-type polymer is critical 
to the instant method. Such polymers inhibit and/or prevent scale 
deposition, even under severe saturation and/or temperature conditions, 
and are generally efficient up to a pH of approximately 9.0, preferably up 
to approximately 8.5, though exceptions may exist. 
Also, other monomers may be added to the monomer mix and polymerized with 
the acid/anhydride and quaternary ammonium monomers to produce polymers 
having additional moieties. Examples of such monomers include acrylic 
acid, acrylamide, sodium allyl sulfonate, allylamine, diallylamine and 
similar unsaturated vinyl/allyl compounds. 
Chain transfer agents may also be added to the monomer mix to produce lower 
molecular weight polymers. Examples of such chain transfer agents include 
2-propanol, formic acid and thioglycolic acid. 
The instant polymers may be added to the system being treated by any 
convenient means. A preferred method of addition is via makeup water 
streams. 
Additionally, other conventional water treatment agents, including but not 
limited to corrosion inhibitors such as zinc salts, orthophosphate sources 
and triazoles, can be used with the instant polymers.

EXAMPLES 
Polymer Preparation 
The polymers of the examples were produced by mixing maleic anhydride and 
dimethyldiallyl ammonium chloride in deionized water at the ratios 
indicated in Table I. The pH of the monomer mix was adjusted to 6 using 
sodium carbonate or sodium hydroxide, as indicated. Sodium persulfate was 
used as the initiator at a ratio of 6.3-6.5 mole % based on total 
monomers. The initiator solution was fed into the monomer mix over four 
hours at a temperature of 100.degree. C. The results are shown as Table I. 
TABLE I 
__________________________________________________________________________ 
Initial 
Neutral- 
MA/DMDAAC.sup.a Monomer 
izing Temp. Mole % 
Conversion (%) 
Molecular.sup.b 
Example 
Mole Ratio 
Wt. Ratio 
Conc. (%) 
Agent 
pH 
(.degree.C.) 
Type 
Initiator 
MA DMDAAC 
Overall 
Weight 
__________________________________________________________________________ 
1 1/1 42/58 40 Na.sub.2 CO.sub.3 
6.0 
100 NAPS 
6.4 100 
97 99 1,073 
2 2/1 59/41 40 Na.sub.2 CO.sub.3 
6.0 
100 NAPS 
6.4 77 85 80 1,492 
3 2.5/1 64/36 40 Na.sub.2 CO.sub.3 
6.0 
100 NAPS 
6.4 78 70 76 4,438 
4 3/1 68/32 40 Na.sub.2 CO.sub.3 
6.0 
100 NAPS 
6.4 83 74 81 -- 
5 2/1 59/41 40 Na.sub.2 CO.sub.3 
6.0 
100 NAPS 
9.4 96 94 95 -- 
6 2/1 59/41 40 NaOH 6.0 
100 NAPS 
5.4 91 88 90 -- 
7 1/1 42/58 40 -- 1.0 
105 NAPS.sup.c 
4.2 83 96 90 -- 
8 2/1 59/41 38 -- 1.0 
101 NAPS 
4.1 68 93 76 2,046 
9 2/1 59/41 41 Na.sub.2 CO.sub.3 
6.0 
100 V-50.sup.d 
3.6 59 60 60 -- 
__________________________________________________________________________ 
.sup.a MA: maleic acid, hydrolyzed from maleic anhydride 
DMDAAC: dimethyldiallyl ammonium chloride 
.sup.b Molecular weight: weight average molecular weight determined by ge 
permeation chromatography using polyDMDAAC as a standard 
.sup.c NAPS: sodium persulfate 
.sup.d V-50: 2,2azobis (2amidinopropane) hydrochloride 
Test Methods 
The test methods used to evaluate the ability of the instant polymers to 
prevent Ca/PO.sub.4, CaCO.sub.3, CaSO.sub.4, BaSO.sub.4, CaC.sub.2 
O.sub.4, Fe.sub.x O.sub.y, Zn(OH).sub.2 and Zn/PO.sub.4 scale formation 
and deposition in aqueous systems are described in the following sections. 
The results are shown in Table II and Table III. 
Method 1 
Calcium Phosphate Scale Inhibition Test: 
Calcium phosphate scale inhibition was tested using stoppered flasks 
containing 9 ppm PO.sub.4.sup.-3 and 200 ppm Ca.sup.+2 and treated with 
two levels of inhibitor at a pH of 8.5 (buffered by bicarbonate/ 
carbonate). The flasks were incubated at 60.degree. C. for 24 hours. An 
aliquot of the solution was removed from the flask and tested for 
PO.sub.4.sup.-3 concentration. The percent inhibition was determined by 
the following equation: 
##EQU1## 
Method 2 
Calcium Carbonate Scale Inhibition Test: 
Calcium carbonate scale inhibition was tested at pH 8.0 using stoppered 
flasks containing 200 ppm Ca.sup.+2 and 600 ppm HCO.sub.3.sup.-. To a 
flask containing distilled water, HCO.sub.3.sup.-, inhibitor, and 
Ca.sup.+2 were added in that order. After mixing by swirling, the solution 
pH was measured and adjusted to pH 8.0, if necessary. The flask was 
stoppered and incubated at 60.degree. C. for 24 hours. An aliquot of the 
solution was removed from the flask, filtered and titrated for calcium 
content to determine percent inhibition. 
Method 3 
Calcium Sulfate Scale Inhibition Test: 
Calcium sulfate scale inhibition was tested at pH 7.0 using stoppered 
flasks containing 4800 ppm SO.sub.4.sup.2- and 2000 ppm Ca.sup.2+, added 
in that order. After mixing by swirling, the solution pH was measured and 
adjust to pH 7.0, if necessary. The flask was stoppered and incubated at 
60.degree. C. for 24 hours. An aliquot of the solution was removed from 
the flask, filtered, and titrated for calcium content to determine percent 
inhibition. 
Method 4 
Calcium Oxalate Scale Inhibition: 
Calcium oxalate scale inhibition was tested at pH 6 using stoppered flasks 
containing 20 ppm Ca.sup.+2, 110 ppm oxalate, 2000 ppm Na.sup.+ and 2000 
ppm SO.sub.4.sup.2-. 
To a flask containing distilled water, Na.sup.+, SO.sub.4.sup.2-, inhibitor 
and oxalate were added in that order. After swirling to mix, the solution 
pH was measured and adjusted to pH 6, if necessary. A calcium solution was 
then added to the flask. The flask was stoppered and incubated at 
65.degree. C. for 24 hours. An aliquot of the solution was removed from 
the flask, filtered, and titrated for calcium content to determine percent 
inhibition. 
Method 5 
Barium Sulfate Scale Inhibition Test: 
Barium sulfate scale inhibition was tested at pH 6 using stoppered flasks 
containing 69 ppm Ba.sup.2+, 48 ppm SO.sub.4.sup.2-, 23 ppm Na.sup.+, 36 
ppm Cl.sup.- and 1 ppm Al.sup.3+. To a flask containing distilled water, 
SO.sub.4.sup.2-, inhibitor, and Al.sup.3+ were added in that order. After 
swirling to mix, the solution pH was measured and adjusted to pH 6, if 
necessary. A barium solution was then added to the flask. The flask was 
stoppered and incubated at room temperature for 24 hours. An aliquot of 
the solution was removed from the flask, filtered, and titrated for barium 
content to determine percent inhibition. 
Method 6 
Zinc Hydroxide Scale Inhibition Test: 
Zinc hydroxide scale inhibition was tested at pH 8.5 using stoppered flasks 
containing 160 ppm Ca.sup.2+, 204 ppm SO.sub.4.sup.2-, and 5 ppm 
Zn.sup.2+. To a flask containing distilled water, inhibitor, 
SO.sub.4.sup.-2, Zn.sup.+2 and Ca.sup.+2 were added in that order. The pH 
of the solution was measured and adjusted to pH 8.5 with dilute NaOH, if 
necessary. The flask was stoppered and incubated at 60.degree. C. for 24 
hours. An aliquot of this solution was then removed, filtered, acidified 
with concentrated HCl, and analyzed for zinc content using atomic 
absorption spectroscopy. 
Method 7 
Zinc Phosphate Scale Inhibition Test: 
Zinc phosphate scale inhibition was tested at pH 8.0 using stoppered flasks 
containing distilled water and 68 ppm Ca.sup.2+, 26 ppm Mg.sup.2+, 106 ppm 
SO.sub.4.sup.2-, 8 ppm SiO.sub.3.sup.2-, 5 ppm Zn.sup.2+, and 10 ppm 
PO.sub.4.sup.3-. SiO.sub.3.sup.2- was initially added to a flask 
containing distilled water. The solution pH was adjusted to pH 6 with 
concentrated HCl. Then Ca.sup.2+, Mg.sup.2+ (as MgSO.sub.4 .sup.. 7H.sub.2 
O), inhibitor, PO.sub.4.sup.3- and Zn.sup.+2 were added in that order with 
stirring. The pH of the solution was measured and adjusted to pH 8.0 with 
dilute NaOH if necessary. The flask was stoppered and incubated at 
50.degree. C. for 24 hours. An aliquot of this solution was then removed, 
filtered, acidified with concentrated HCl, and analyzed for zinc content 
using atomic absorption spectroscopy. 
Method 8 
Iron Oxide Dispersion Test 
Preparation of Amorphous Iron Oxide: 
Fresh amorphous iron oxide was prepared by the addition of NaOH to an 
FeCl.sub.3 solution at an OH:FE ratio of 4:1. This solution was stored for 
approximately 19 hours at 40.degree. C. The resulting iron oxide particle 
size was found to be approximately 10 nm. The amorphous iron oxide thus 
formed was diluted to give the desired level of iron oxide, usually 5 
mg/1. 
Dispersion Testing: 
Iron oxide dispersion was tested at pH 8.0-9.0 using stoppered flasks 
containing 5 mg/L Fe.sup.3+, 63 mg/L CO.sub.3.sup.2-, and 50 mg/L 
Ca.sup.2+. To a flask containing 46 ml of distilled water and dispersant, 
2 ml of CO.sub.3.sup.2- solution, 50 ml of 10 mg/l amorphous iron oxide 
stock solution, and 2 ml of Ca.sup.+2 solution were added. The flask was 
stoppered and incubated at 55.degree. C. for 24 hours. An aliquot of this 
solution was carefully removed, so as not to disturb the contents, and % 
transmission at 415 nm was measured using a spectrophotometer. Iron oxide 
dispersion was calculated as follows: 
##EQU2## 
TABLE II 
__________________________________________________________________________ 
Scale Inhibition Test Results for MA/DMDAAC Copolymers 
Cooling Water Applications 
Fe.sub.x O.sub.y 
pH 8.5 
MA/ pH 8.5; Ca/PO.sub.4 
pH 8; CaCO.sub.3 
pH 7; CaSO.sub.4 
Dispersion 
Zn(OH).sub.2 
pH 8; Zn/PO.sub.4 
Ex- DMDAAC 
8 10 1 2 4 2 4 6 5 7.5 
10 2 5 10 10 15 20 
ample 
mole ratio 
ppm ppm ppm 
ppm 
ppm 
ppm 
ppm 
ppm 
ppm 
ppm 
ppm 
ppm 
ppm 
ppm 
ppm 
ppm 
ppm 
__________________________________________________________________________ 
1 1/1 91 90 53 55 66 19 44 83 100 
98 99 69 92 94 81 77 78 
2 2/1 80 87 53 70 96 21 62 100 
15 103 
100 
88 90 96 86 89 91 
3 2.5/1 -- -- 70 79 98 22 98 100 
3 67 96 -- -- -- -- -- -- 
4 3/1 -- -- 74 83 87 19 42 69 0 1 4 76 74 74 20 22 33 
__________________________________________________________________________ 
TABLE III 
______________________________________ 
Scale Inhibition Test Results for MA/DMDAAC Copolymers 
Paper Industry Applications 
MA/DMDAAC ph 6 CaC.sub.2 O.sub.4 
pH 6 BaSO.sub.4 
mole ratio 1 ppm 2 ppm 15 ppm 
18 ppm 
______________________________________ 
1/1 14 26 31 31 
2/1 50 100 76 95 
2.5/1 96 98 94 94 
3/1 100 100 91 91 
______________________________________