CA1062983A - Copolymers for the control of the formation and deposition of materials in aqueous mediums - Google Patents

Abstract

Abstract of the Disclosure The present invention relates to processes for controlling the formation and deposition of scale and sludge and in particular cal-cium phosphate which would otherwise occur in aqueous mediums con-taining the ions capable of forming sludge and the scale. The invention, more particularly, relates to the control, reduction and/or prevention of scale and sludge deposits in cooling water, scrubber and steam generating systems, evaporators, economisers, and the like by the introduction of a copolymer comprising sulfonated styrene and maleic anhydride moieties to the water used therein. The copolymers dis-covered to be effective for the purpose are those having a mole ratio of sulfonated styrene moieties to moieties derived from maleic anhydride of from about 2:1 to about 4:1.

Description

~6zg83 Background of the Invention ' ~

:, , Although the invention has general applicability to any given system where the formation and deposition of scale and in particular cal- ;
cium phosphate is a potential problern, the invention will be discussed in detail as it concerns boiler water systems.
As is well known and comprehensively described and dis-. . . -:
cu~sed in the Betz Handbook of Industrial Water Conditioning, 6th Edition, 1968, Betz Laboratories, Inc., Trevose, Pennsylvania, pages 151-171, the ormation of scale and sludge deposits on boiler heating surfaces is the moet serious water problem encountered in steam generation. Although current industrial steam producing systems make use of sophisticated external treatments of the boiler feed water, e. g., coagulation, {iltration, softening of water prior to its feed into the boiler system, those operations are oiily moderately effective. In all cases, external treatment does not in itself provide adequate treatment since muds, sludge, clay, silts, iron ~ ;
.oxides and hardness-imparting ions, 1. e., calcium, magnesium, and car-~onate ions, escape the treatment and eventually are introduced into the , - steam generating system.
The problems which result from their introduction into the .
;~ 20 steam generating system are apparent. Since the deposit forming materials ~- are present, they have a tendency to accumulate upon concentration of the `
water and to settle at points in the system where there is low flow and there-~` ~ore restrict water circulation. The baking of mud and/or sludge on tubes and sheets will result in overheating and failure, thereby requiring down time for repair or replacement of the structural parts. In addition, mud, - sludge, and silts may become incorporated in scale deposits adding to their volume and heat insulating effect.

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106Z9l33 Accordingly, internal treatments have been necessary to maintain the mud and silts in a suspended state. These internal treatments have been generally referred to in the industry as sludge conditioning agents.

In addition to the problems caused by mud, sludge or silts, the industry has also had to contend with boiler scale. Although external treatment is utilized specifically in an attempt to remove calcium and mag-nesium from the feed water, scale formation due to residual hardness, i. e., calcium and magnesium salts, is always experienced. Accordingly, internal treatment, i. e., treatment of the water fed to the system, i9 necessary to prevent, reduce and/or retard formation of the scale-imparting compounds and their deposition. The carbonates of magnesium and calcium are not the only problem compounds as regards scale, but also waters having high con-tenes of phosphate, sulfate and silicate ions elther occurring naturally or added for other purposeF are problematic since calcium and magnesium, and any iron or copper pre`sent, react with each, form the respective insoluble 8alt8 and deposit as boiler scale. The problem is compounded by the deposl-~ion of iron oxides and clay with the other scale salts. Iron oxides enter the Yy6tems by escaping the pretreatment procedures and/or are present due to corrosion of the metal parts in contact with the aqueous medium. As is ob-20 ' vious, the deposition of scale which by the present definition includes iron oxide on the structural parts of a steam generating system causes poorer eirculation and lower heat transfer capacity, resulting accordingly in an overall loss in efficiency. ~-Although the foregoing is directed to boiler water systems, or more specifically steam generating systems, the same problems occur in pulp and paper mill systems, cooling water systems, desalini~ation systems (cal- -eium sulfate formation and deposition), scrubber systems and the like. The '106;~9~3 problems encountered ;n these operations sometimes are more severe since complete external treatments are not commonly utilized. Any aqueous system having calcium and magnesium cations and the exemplified anions, in particular phosphate and silicate, wiIl experience the formation and deposition of the scaling salts.
Because of the foregoing, the water treatment industry is con-stantly evaluating new processes, new products, new techniques in an effort to permit the various process water systems to operate more effectively for longer periods and at lower costs.
Many and different type materials have been used for internal treatment of water systems, and in particular as sludge conditioning agents.
Of the vast number may be mentioned alginates, lignins, lignosulfonates, tannins, carboxymethyl cellulose materials, synthetic polymers such as polyacrylates and in particular polymethacrylates. U.S. Patents 2,723,956;
3,188,289; 3,519,538 are merëly representative of the type materials used and the functions thereof. U.S. Patents 2,723,956 and 3,519,538 disclose boiler treatments utilizing maleic anhydride and non-sulfonated styrene copolymers wherein the mole ratio of anhydride to styrene has an excess of anhydride and is at least 1:1 and preferably 2:1.

General-rbscription of the Invention - -The inventors discovered that if an effective amount of a particular type copolymer composed of essentially sulfonated styrene moieties ànd those derived from maleic anhydride was added or introduced -into the water of a process water system, the formation and deposition of scale, particularly calcium and magnesium phosphates, silicate and -iron oxide scale, on the metallic : , ., ': ~ : ';

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structures of the equipment could be controlled to a degree necessary to permit the continual and economical operation of the system.
The polymers which are the subject of the present invention are those containing essentially sulfonated styrene moieties, i. e., ~ ', . ' ' ' --~ C ----C ~

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and moieties derived from maleic anhydride, i. e., H H
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where the sulfonated styrene moieties exceed the moieties derived from the maleic anhydride.

Preferably the copolymers contain a mole ratio of styrene moieties to maleic anhydride derived moieties of from about 2:1 to about 4:1 and preferably 3:1, and possess a molecular weight of from 500 to 100,000. The copolymers have been found to be effective and provide best 20 results when used at levels of from about 0.5 to 100 parts per million of water and preferably from about 2, 5 to 25 parts per million parts of water contained in the steam generating equipment.
The polymers of the present invention can be produced in different ways, however, their manner of production does not affect in ; ,. .

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any way their effectiveness as scale, calcium and magnesium phosphate and silicate control agents.
One procedure for producing the polymers is to copolymerize styrene with maleic anhydride in the specified ratios. After the polymer is resolubilized by producing the various water- soluble salts (alkali metal), the polymer is then sulfonated in accordance with well-known techniques (note for example U. S. 2, 764, 576). The degree of sulfonation can vary but substantially complete sulfonation of the styrene moieties i9 preferred.
Conversion of the polymers into the water soluble metal salts such as the alkali metal salt forms is accomplished by normal methods. There-fore M may represent any one of or a mixture of NH4, H, Na, K, etc.
As is apparent, the other manner of producing the polymers ~`
is to first sulfonate the styrene monomer utilizing a technique such as des-cribed in the aforecited patent and then copolymerize the resulting sulfonatod styrene with the maleic anhydride. .
.' The methods and parameters of copolymerizing the two mono-mers is well known and illustrated by U. S. Z, 723, 956. Generally the co-polymerization may be affected at temperatures from about 80 to 120C
utilizing peroxide catalysts such as cumene hydroperoxide, benzyl peroxide, etc. in an inert medium.
.
The copolymers of the instant invention,which are quite different from the polymers of the cited patents, are very soluble in water which permits the obtention of greater protcction against the potential depositions as des-. . , -cribed earlier.
Commercial polymers suitable for the instant purpose are available from National Starch under the designation NSDP-2509-50 and 2727-18.

~O~Z983 Specifi~ Embodiments - Steam Generation . . .
The copolymers of the invention were subjected to steam generat-ing conditions utilizing experimental boiler systems having an electrical heat source. The boilers are equipped with a system permitting circulation of water in a path via natural convection. Two probes are installed in the des-cribed path positloned vertically one above the other. These probes permit measurement of deposition, if any, at two different locations in the path -through which the water clrculated,~ These probes are referred to in the following Tables as the Upper and Lower probes.
~ - The tests conducted using the experimental boilers were operated under the conditions specified in the Tables which follow. The re-spective tests were designed to establish the effects, if any, of variations found in the different steam generating operations.
During operation of the boilers, pressurè and heat probe amperage were cont~nually monitored and the blowdown volumes and steam generation ~`
rate s were mea sured .
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After test completion, the heat transfer probes were re-moved and visual observations were recorded as to deposit color, quantity, and quality. Chemical analyses were employed to determine total deposit I -quantiy. In certain instances, the deposit was dissolved in hydrochloric ¦~
acid and hydrofluoric acid and the solution was analyzed for insolubles calcium, magnesium, phosphate and silica. Deposit weight waa calculated from the solution composition and these results have been reported in the Tables which follow.
In order to establish the ccope of the invention, polymers ha~ing a 1:1 mole ratio of sulfonated styrene to maleic anhydride were also tested It was felt that the comparative results provided the necessary evidence to establish the true parameters of the invention.

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~062983 It is evident from the data recorded in the foregoing Table that the copolymers containing less than 2 moles of sulfonated styrene moieties per mole of maleic anhydride moieties were less effective while those having 2 or more were quite effective.
Additional comparisons were conducted utiliæing various specific tests, the reqults of which are recorded in Table I.
In Table IA which follows are recorded specific data derived from a comparison of Copolymer A used at l0 ppm (Item 5 under Table I, Section B) ~rith a Control, i. e., no treatment. The test conditions and boiler balances were those as specified in Table I, Section B, Item 5. The scale was analyzed to establish the effect that treatment had on scala composition.
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TABLE IA

Scale Deposit (g/ft~) Deposit (g/ft2) % Scale Reduction ComponentControlCopolymer A on High Heat Transfer ~?pm Area t~a 3. 69 0. 06 98 P04 5.33 0.10 9B
MgO 1. 49 0. 08 9S
SiO2 0. 26 0. 06 77 Insolubles * 4. 08 0. 61 ~5 Total 14. 85 0. 91 94 * In~olubles are composed of magnesium silicate and iron oxide In Table IB which follows, the results of a deposit comparison are recorded utilizing a Control, the Commercial Polymethacrylate (Item 6, Table I, Section B) and Copolymer A (Item 3, Table 1, Section B). The con-ditions were those as specified in Table I in the réspective Section under boiler balances with the Control being conducted at comparable boiler balances.

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polymer of the invention but also the relative superiority of the 3:1 ratio polymer to the 2:1 polymer.

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1~6Z983 It is apparent from the testing and the data recorded in the foregoing Tables that the prescribed copolymers which are the subject of this invention performed quite impressively. This is particularly evident from the comparative results obtained with respect to the commercial product which has been and in some instances is currently being used for deposit control in steam generating systems.
A~ in Tables IA through IC, Table IIA contains data recorded relative to specific comparisons of the copolymer of the present invention ;
with the Control and PMA commercial grade. The conditions for the respective tests were those set forth in Table II, Section B, Items 1 and 4, with the Control being conducted at comparable conditions. Even at in-creased pressures, the instant polymers are significantly more effective than the PMA.

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iS;pe_ific Embodimcnts - General Aqueous Systems ,,, . ' , . ~ ' ' In order to establish that the present in~rention provided overall ~effectiveness, two different evaluations were conducted which assimilated water conditions found in cooling water systems where the concentration of calciumions and phosphate îons are such as to provide a calcium phosphate ~cale prone system.
Th~ evaluations were conducted utilizing solutions respectively cbntaining calcium ion and ortho-phosphate ion. After mixing the two solu-tions and the specified equilibration time, residual phosphate ion measure-ments were made after the mixture had been filtered. High residual phos-phate ion concentration indicated good inhibition.
The specifics of the test procedure are as follows:
Conditions of Test: Static; T = 70C; pH = 8~ 5; equilibration time - 17 hours;
Concentration of Ca++ as CaCO3 = 250 ppm; concentration of PO4 3 = 6. 0 ppm.
Treatment dosage = 10 ppm.

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Solutions: (1) prepare solution of 0.4482g. of Na2HPO4 per liter DI water - (2j prepare solutior OI 36. 76g. CaCl2 2Ei2O per liter DI water (3) to 1800 mi DI water, add 20 ml solution (2), followed by Z drop~ conc. HCl. Then add 40 ml solution (1) and bring volume to 2000 ml with DI water, Mcthod: Place 100 ml aliquot of solution (3) in clean 4 oz. glass bottle. Add 1 ml of .1% treatment solution and adjust pH to R. 5 using NaOH. Place bottle in water bath set to 70C and allow to equilibrate 17 hours.
Anatysis: Filtration - remove sample from water bath, filter through 0. 2 ,~L .
millipore filter. Allow filtrate to cool to room temperature and analyze for PO4 3 using Leitz Photometer.
Treatment waq added to phosphate solution before mixing~

1(1 629i33 , TABI.E III

Ratio sulfonated Dosage Residual phos-Treatment styrene-maleic ppm phate concentr3-anhvdride moieites _ tion (ppm PO~~ ) . ' ' . ' ' ' ~ ' .
Control _ o o Copolymer A 3:1 5 4.0 .
Copolymer A 3:1 10 5. ~

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The effectiveness of the polymer of the invention was apparent.
Without treatment all phosphate precipitated while almost 100% inhibition was ~0 obtained when 10 ppm of treatment was utilized.
A 6econd evaluation was conducted utilizing the aforedescribed procedure. In this evaluation comparisons were made again:t commercial gsade sulfonated polyst~renes and certain Inaleic aIYhydride polym:rs. In this test the percentage inhibition was determined from the measuren~ent of the residual phosphate ion. ~ -, .

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T.ABLE rv Sulfonated Maleic % Calcium Phosphate Treatment PolystyreneAnhydride Inhibition __. Moieties Moieties Copolymer A 75 25 100 Copolymer B 66.6 33.3 90.2 Copolymer C 50 50 75.4 SPS (MW 34, 000) 100 . _ . 62.3 SPS (MW 70, 000) 100 - - 47.6 ~ SPS (MW 400, 000) 100 _ 14. 6 SPS (MW 700, 000) 100 - . 4.1 .

Ethylene maleic - .100 < 5 anhydride polymer ~lalcic anhydride - 100 < 5 `~
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: ~ The data clearly established that the homopolymers of sul-fonated polystyrene, maleic anhydride and ethylene maleic anhydride poly-.mer~ do not control calcium phosphate as well as the polymers of the in- !1 . ,. ..
- stant inventlon. In addition, the data confirmed the importance of having at 20 - least a mole ratio of 2 or greater of sulfonated styrene to 1 of maleiF an- :`
hydride. . ' , ~ - .
The invention is applicable to any aqueous system where cal- .
dum phosphate formation and precipitation is a potential problem. For example, the inventive process would be effective in gas scrubbing systems .
where scrubbing mediums such as primary sewage effluents, which contain . .
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~L06Z9~33 high phosphate levels are used as the scrubbing or washing medium. These systems would have the prerequisite for the formation and deposition of calcium phosphate which is to be avoided. The additional areas of application will be apparent to those operating in the areas of process water systems.
Ef~icacy in Related Areas In order to determine the efficacy of the polymers of the invention in related areas, certain tests were conducted to (i) establish the dispersive effect of the polymers on sus-pended matter, more specifically clay and iron oxide, and (ii) establish the capability of the polymers to inhibit the formation and thereby the deposition of calcium carbonate ~
in an aqueous system where the effect was likely to occur. ~ -The protocols followed and the results of the tests were as follows:
A. Deflocculation and Dispersion of Suspended Matter A 0.1% iron oxide or clay suspension in deioni~ed water was prepared. The hardness of the slurry was adjusted to 200 ppm CaC03 and the resultant medium was mixed for a time required to obtain a uniform sus-pension. The pH was then adjusted to the testing level.
Aliquots of the suspension were drawn off, placed in glass `
bottles and the appropriate amount of treatment added. The samples were then shaken to insure good mixing of treatment and suspension. Using a turbidimeter or an instrument which measures light transmission, the effect of the treatment compared to a control (suspension to which no treat-ment was added) was measured. Treatments causing an increase in turbidity : : .
or a decrease in light transmitted are considered dispersants.

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1Cl ~;2983 As apparent from the results of the studies, the polymers of the invention and even the SS/MA polymer having a 1:1 ratio were quite effective in dispersing the suspended matter after an 18 hour duration. The 1/2 hour duration results,although not overwhelming,were acceptable for all practical purposes since the 18 hour test is felt to be the more important re sult .
- '` :~ ' B. Calcium Carbonate Studies .
A synthetic environmental was produced containing known quantities of water soluble calciurxl chloride and sodium carbonate under Dpecific pH and temperature conditions. Treatments were added to various samples of the solution and the amount of calcium remaining in solution after à period of time was measured and compared to a Control.~ The test measured quite accurately the capacity of the polyIners to inhibit the forma-.
tion and ultlmate deposition of calcium carbonate.

The treatment utilized consisted of 10 ppm of A. a 3:1 SS/
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MA polymer; B. a 2:1 SS/MA polymer; and C. a l:l SSlMA polymer. The result~ expressed as % CaC03 Inhibition respectively were 29. 6~o; 29. 3~10;
and 36. 6%. The polymers were considered to be significant since they did establish efficacy. Although the degree of efficacy was perhaps lower than those polymers currently commercially available for calcium carbonate con-trol, this capacity of the polymers when considered together with the results achievable against calcium and magnesium phosphates, magnesium silicates, iron oxides, mud, and claSr make the use of these polymers clearly an im-portant advancement in the art.

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~L~6291~3 Sulonation Study The contribution of sulfonation sn the efficacy of the copolymers of the instant invention, i. e., sodium salt of sulfonated styrene-maleic an-hydride copolymers (SS/MA) was investigated to a certain degree and was only partially resolved. The data determined indicated that sulfonation con-tributes quite beneficially. The drawback to complete resolution of the question was due to the difficulty in obtaining a 100% solution of the 3:1 mole ratio fftyrene-maleic anhydride polymer so that a '~truly" representative sample could be evaluated.
The following is a synopsis of the work performed in this area:
Styrene-maleic anhydride polymers (SMA) are available in the 1:1, 2:1, and 3:1 styrene to maleic anhydride mole ratios and are reported to have a 1600 molecular weight. However, conversion to a useable eoluble ~orm (i. e., ammonium or sodium salts) becon~es more difficult as the styrene ~ ~ -content increases. En~phasis was directed toward the 3:1 mole ratio because .
this mole ratio was found to be the most effective copolymer of the present invention. Although the manu~acturer's literature recommended conversiop to the ammonium salt, attempts were made to convert the 3:1 SMA polymer to both the ammonium salt and the sodium salt. This manufacturer's pro-; ~ ~ cedure was not effective for the 3~1 SMA since some copolymer remained insoluble. Boiler test results indicated the material to be quite ineffective.
Therefore attention was directed toward neutralization as the sodium salt. The SMA (3:1 ratio) was at least partially converted to the sodium salt by a procedure outlined by the manufacturer except the proper amount of sodium hydroxide, rather than ammonium hydroxide, was employed based on the acid numbers provided and higher temperatures were used. The . .

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solution which resulted from the 3:1 solubilization still contained some in-soluble material and it is not known whether the resultant solution was repre-sentative of the dry material although it is estimated that 90 to 95% of the . ;:
copolymer went into solution.
However, the 3:1 copolymer (SMA) solutions (one the ammonium salt and the other the sodium salt) were evaluated and the results and the :
testing conditions are set forth in the following tahle. The comparative ~: :
teet results established quite conclusively that the sulfonated polymers of the .;
invention performed quite superiorly, ;

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Claims (36)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method of controlling the formation and deposition of deposits on the structural parts of a system containing an aqueous medium which comprises introducing into the aqueous medium an effective amount of a polymer or the water soluble salt of said polymer, which polymer is com-prised of sulfonated styrene moieties and moieties derived from maleic an-hydride, the ratio of said styrene moieties to said maleic anhydride deirived moieties being from about 2:1 to about 4:1.

2. A method according to claim 1 wherein the amount of poly-mer introduced is from about 0.5 to about 100 parts of polymer per million parts of water in said system.

3. A method according to claim 2 wherein the polymer has a molecular weight of from about 500 to 100,000.

4. A method according to claim 1 wherein the polymer possesses a ratio of said styrene moieties to said anhydride derived moieties of 3:1.

5. A method according to claim 2 wherein the polymer possesses a ratio of said styrene moieties to said anhydride derived moieties of 3:1.

6. A method according to claim 4 wherein the polymer intro-duced is in an amount of from about 0.5 to about 100 parts per million parts of water.

7. A method according to claim 6 wherein the polymer has a molecular weight of form about 500 to 100,000.

8. A method according to claim 7 wherein the polymer intro-duced is from about 2.5 to 25 parts per million parts of water in said system.

9. A method according to claim 8 wherein the polymer is in the form of the sodium salt of said polymer.

10. A method according to claim 1 wherein the system is a steam generating system.

11. A method according to claim 2 wherein the system is a steam generating system.

12. A method according to claim 5 wherein the system is a steam generating system.

13. A method according to claim 1 wherein the system is a cooling water system.

14. A method according to claim 2 wherein the system is a cooling water system.

15. A method according to claim 5 wherein the system is a cooling water system.

16. A method according to claim 1 wherein the system is a gas scrubbing system.

17. A method of controlling the formation and deposition of at least one compound selected from the group consisting of calcium phosphate, magnesium phosphate, calcium carbonate, magnesium silicate, calcium sulfate, iron oxide and clay on the structural parts of a system containing an aqueous medium having the tendency for the formation and deposition of such which com-prises introducing into the aqueous medium an effective amount of a polymer or the water soluble salt of said polymer, which polymer is comprised of sulfonated styrene moieties and moieties derived from maleic anhydride, the ratio of said styrene moieties to said maleic anhydride derived moieties being from about 2:1 to about 4:1.

18. A method according to claim 17 wherein the amount of poly-mer introduced is from about 2.5 to about 100 parts of polymer per million parts of water in said system.

19. A method according to claim 18 wherein the polymer has a molecular weight of from about 500 to 100,000.

20. A method according to claim 17 wherein the polymer possesses a ratio of said styrene moieties to said anhydride derived moieties of 3:1.

21. A method according to claim 18 wherein the polymer possesses a ratio of said styrene moieties to said anhydride derived moieties of 3:1.

22. A method according to claim 20 wherein the polymer introduced is in an amount of from about 0. 5 to about 100 parts per million parts of water.

23. A method according to claim 22 wherein the polymer has a molecular weight of from about 500 to 100,000.

24. A method according to claim 23 wherein the polymer intro-duced is from about 2.5 to 25 parts per million parts of water in said system.

25. A method according to claim 24 wherein the polymer is in the form of the sodium salt of said polymer.

26. A method according to claim 17 wherein the system is a steam generating system.

27. A method according to claim 18 wherein the system is a steam generating system.

28. A method according to claim 21 wherein the system is a steam generating system.

29. A method according to claim 17 wherein the system is a cooling water system.

30. A method according to claim 18 wherein the system is a cooling water system.

31. A method according to claim 21 wherein the system is a cooling water system.

32. A method according to claim 17 wherein the system is a gas scrubbing system.

33. A method of dispersing a compound selected from the group of iron oxide, clay and mixtures thereof contained in an aqueous medium which com-prises introducing in said medium an effective amount of a polymer or the water soluble salt of said polymer, which polymer is comprised of sulfonated styrene moieties and moieties derived from maleic anhydride, the ratio of said styrene to said maleic anhydride derived moieties being from about 1:1 to about 4:1.

34. A method according to claim 33 wherein the aqueous medium is the cooling medium of a cooling water system.

35. A method according to claim 33 wherein the aqueous medium is the scrubbing medium for a gaseous system containing iron oxide.

36. A method according to claim 33 wherein the aqueous medium is contained in a steam generating system.