United States Patent (19) (11 Patent Number: 4,952,327 Amjad Et Al

United States Patent (19) (11 Patent Number: 4,952,327 Amjad et al. (45. Date of Patent: "Aug. 28, 1990

(54). SCALE CONTROL WITH TERPOLYMERS 4,532,048 7/1985 Amjad ...... 210/701 CONTAINING STYRENE SULFONCACD 4,536,292 8/1985 Matz ...... 210/701 4,552,665 1 1/1985 Ralston et al. . ... 2S2/180 (75) Inventors: Zahid Amjad, Avon Lake; William F. 4,560,481 12/1985 Hollander et al. . ... 252/180 Masler, Hinckley, both of Ohio 4,566,973 1/1986 Masler ...... 210/701 4,575,425 3/1986 Boffardi et al...... 210/697 73) Assignee: The B. F. Goodrich Company, Akron, 4,589,985 5/1986 Yorke ...... 210/699 Ohio 4,596,661 6/1986 Gill et al...... 210/728 4,618,448 10/1986 Cha et al...... 210/701

* Notice: The portion of the term of this patent 4,634,532 l/1987 Logan et al...... 210/697 subsequent to Dec. 5, 2006 has been 4,640,793 2/1987 Persinski et al...... 252/180 disclaimed. 4,711,725 12/1987 Amick et al...... 210/701 (21) Appl. No.: 235,270 4,784,774 11/1988 Amjad et al...... 210/701 (22 Filed: Aug. 23, 1988 FOREIGN PATENT DOCUMENTS WO83/02607 8/1983 PCT Int'l Appl...... 210/701 Related U.S. Application Data 2082600 3/1982 United Kingdom ...... 210/701 63) Continuation-in-part of Ser. No. 939,333, Dec. 8, 1986, Primary Examiner-Peter Hruskoci abandoned. Attorney, Agent, or Firm-Nestor W. Shust; George A. Kap 51) int.C...... CO2F5/12 52 U.S. Cl...... 210/701; 252/180 57 ABSTRACT 58) Field of Search ...... 210/698-701; Inhibition of scale is obtained by adding to an aqueous 252/180, 181 medium 0.5 to 500 ppm of a copolymer containing at (56) References Cited least one of each of the following three monomers: (a) monounsaturated carboxylic acids as well as salts U.S. PATENT DOCUMENTS and anhydrides thereof, the acids containing 3 to 5 3,682,224 8/1972 Bleyle...... 210/701 carbon atoms, such as acrylic acid, methacrylic acid, 3,709,815 1/1973 Boothe et al. . ... 210/701 maleic acid or its anhydride; 3,709,816 1/1973 Walker et al...... 210/701 (b) acrylamidoalkane sulfonic acids and salts thereof, 3,790,610 2/1974 Lum et al...... 20/701 such as 2-acrylamido-2-methylpropane sulfonic acid; 3,806,367 4/1974 Lange et al...... 210/701 3,898,037 8/1975 Lange et al...... 210/701 and 3,928,196 12/1975 Persinski et al...... 20/701 (c) styrene sulfonic acid and its salts. 4,425,326 1/1984 Guillon et al...... 424/61 4,500,693 2/1985 Takehara et al...... 210/701 10 Claims, No Drawings 4,952,327 1. 2 small amount, exhibit unexpectedly improved precipita SCALE CONTROL WITH TERPOLYMERS tion inhibition and dispersion performance for phos CONTAINING STYRENE SULFONCACD phates, iron, zinc, and inorganic particulates. The aque ous medium can contain or can be devoid of iron con REFERENCE TO RELATED APPLICATION 5 tamination. This is a continuation-in-part of application Ser. No. U.S. Pat. No. 4,707,271 discloses the use of copoly 939,333 filed Dec. 8, 1986, and entitled "Scale Control mers of acrylic acid and a substituted acrylamide as With Copolymers Containing Acrylamidoalkane Sul antiscalants in presence of soluble iron in solution. Up to fonic Acid'. about 30 weight parts, per 100 weight parts of all poly 10 merized monomers, of other monomers can be polymer BACKGROUND OF THE INVENTION ized with acrylic acid and substituted acrylamide. Most industrial waters contain alkaline earth and This invention generally relates to inhibition of scale transition metal cations such as calcium, barium, iron, formation and deposition in aqueous systems. This is zinc, manganese, and magnesium, and several anions accomplished by adding to an aqueous system at least a such as bicarbonate, carbonate, sulfate, phosphate, sili 15 threshold inhibition amount of a copolymer of at least cate, and fluoride. When combinations of these anions three different monomers, i.e., monounsaturated car and cations are present in concentrations which exceed boxylic acid, salts and anhydrides thereof of 3 to 5 car the solubility of their reaction products, precipitates bon atoms, an acrylamidoalkane sulfonic acid and salts form until these product solubility concentrations are thereof, and a styrene sulfonic acid. The resulting co no longer exceeded. For example, when the ionic prod 20 polymer is soluble in water and is effective in inhibiting uct of calcium and carbonate exceeds the solubility of precipitation of scale, particularly calcium scale such as calcium carbonate, a solid phase of calcium carbonate calcium phosphate, calcium sulfate, and calcium car will form. bonate. Inhibition of scale precipitation is accomplished Solubility product concentrations are exceeded for with the herein-defined copolymers which are effective reasons such as partial evaporation of the water phase, 25 against scale in the presence or the absence of soluble change in pH, pressure or temperature, and the intro metal ions such as iron, manganese, and zinc. Soluble duction of additional ions which form insoluble com iron ions referred to herein exist in either the II or the pounds with the ions already present in the solution. III oxidation state. As these reaction products precipitate on surfaces of Other related patent applications are concurrently the water-carrying system, they form scale or deposits. 30 This accumulation prevents effective heat transfer, in filed for Messrs. Amjad and Masler including one enti terferes with fluid flow, facilitates corrosive processes, tled "Terpolymers For Dispersing Particulates. In An and harbors bacteria. This scale is an expensive problem Aqueous Medium' and another entitled "Stabilization in many industrial water systems, such as recirculating of Metal Ions With Copolymers Containing cooling water systems in cooling towers, in that the 35 Acrylamidoalkane Sulfonic Acid". All of these cases scale causes delays and shutdowns for cleaning and disclose the use of same or similar polymers. removal of the scale. SUMMARY OF THE INVENTION Citric acid, gluconic acid, and other materials have been used in the past to stabilize iron in solution and This invention is directed to the inhibition of precipi thus prevent its precipitation in forms such as ferric tation of scale-forming salts in an aqueous medium by hydroxide and ferric oxide, wherein iron is in the third addition thereto of an effective threshold inhibition oxidation state. Citric acid and such materials effec amount of a copolymer which contains at least three tively maintain iron in solution by forming complexes different repeating groups. Such copolymers include therewith which are soluble in water and thereby, re polymerized monounsaturated carboxylic acid of 3 to 5 main dissolved in water. Although citric acid and cog 45 carbon atoms and salts thereof, polymerized nate materials are effective as stabilizing agents for iron acrylanidoalkane sulfonic acid, and a styrene sulfonic in solution, they are not antiscalants and are ineffective acid. against scale such as calcium carbonate, calcium phos DETAIEED DESCRIPTION OF THE phate, and calcium sulfate. INVENTION In U.S. Pat. No. 3,928,196, a method is disclosed for 50 inhibiting scale formation using two-component co Copolymers are described herein which are effective polymers. The copolymers, which contain 5-50 mole in reducing precipitation of scale-forming salts in aque percent acrylamidoalkane sulfonic acid and 95-50 mole ous media. Such salts include calcium phosphate, cal percent of acrylic acid or a similar acid, have molecular cium sulfate, barium sulfate, magnesium hydroxide, weight of 1,000 to 10,000. The 25/75 mole percent co 55 strontium sulfate, and calcium carbonate, and particu polymer of acrylamidomethylpropane sulfonic acid larly calcium salts such as calcium phosphate. Amount (AMPS) and acrylic acid (AA) is equivalent to 49/51 of such copolymer that is added to an aqueous medium weight ratio whereas the 75/25 mole percent copoly is at least an effective threshold inhibition amount mer of AMPS and AA, is equivalent to 89.5/10.5 which is in the range of 0.5 to 500 parts per million weight ratio. (ppm) of the aqueous medium, preferably 1 to 50 ppm. The Amick U.S. Pat. No. 4,711,725 discloses stabili Although the aqueous medium can be acidic, in a pre zation of an aqueous system by inhibiting precipitation ferred embodiment, it is neutral or alkaline. of scale with a copolymer antiscalant comprising 42 to Specific applications contemplated for the copoly 84% of (meth)acrylic acid and salts thereof, 11 to 40% mers disclosed herein include aqueous systems used in acrylamidoalkane sulfonic acid, and 5 to 30% of one or 65 recirculating cooling towers, steam boilers, desalina more monomers selected from vinyl esters, vinyl ace tion, oil field applications in the secondary oil recovery tate, and substituted acrylamide. The terpolymers of the operations, flash distillation, as well as in aqueous sys Amick patent, when added to an aqueous system in a tems such as sugar solutions. The copolymers are effec 4,952,327 3 4. tive in reducing precipitation of scale in the presence or of its availability, effectiveness and low price, acrylic the absence of soluble metal ions such as iron, manga acid is particularly preferred. Repeating units of acrylic nese, zinc, and mixtures thereof and mixtures thereof acid, methacrylic acid, and salts thereof are represented with other metal ions. as follows: The copolymers can be in unneutralized or neutral- 5 ized form. Such copolymers can be neutralized with a strong alkali, such as sodium hydroxide, in which in R stance, the hydrogen of the carboxyl group in the co ech polymer is replaced with sodium. With the use of an OC-e OX amine neutralizing agent, the hydrogen will be replaced O with an ammonium group. Useful copolymers for pur where R is hydrogen or methyl and X can be hydrogen, poses herein include copolymers that are unneutralized, alkali metal, alkaline earth metal, or ammonium, partic partially neutralized, and completely neutralized. ularly hydrogen, sodium, potassium, calcium, ammo The copolymers are soluble in water up to at least nium, and magnesium. about 20% solids concentration, and they must, of 15 The repeating units of acrylamidoalkane sulfonic course, be soluble in water in amount used, to be effec acids and salts thereof are defined as follows: tive antiscalants. The copolymers contemplated herein are polymers of at least three different monomers and include at least one monomer selected from each one of the following groups (a), (b), and (c): 20 (a) monounsaturated carboxylic acids of 3 to 5 carbon ech-r atoms, salts and anhydrides thereof; O=C-NH-C-CH2-SOX (b) acrylamidoalkane sulfonic acids and salts thereof k: containing up to 6, preferably 1 to 4, carbon atoms in the alkane moiety; and 25 where R is hydrogen or methyl; X is hydrogen, ammo (c) a styrene sulfonic acid. nium, alkali metal or an alkaline earth metal, particu In addition to the above three requisite monomers, a larly hydrogen, ammonium or an alkali metal; and R small amount of other or secondary copolymerizable and R2 are individually selected from hydrogen and monomers can also be used as long as they do not sub alkyl groups of 1 to 4 carbon atoms. In a preferred stantially deleteriously affect performance of the co 30 embodiment, R is hydrogen and R1 and R2 are each an polymers as antiscalants. Amount of such secondary alkyl group of 1 to 3 carbon atoms. In this group of copolymerizable monomers can generally vary up to sulfonic acids, 2-acrylamido-2-methylpropane sulfonic about 20% by weight, preferably up to about 10%, and acid or AMPS (R) is a commercial, readily available more preferably 2 to 10% by weight of the final copoly monomer which is especially preferred for the antisca mer. Such secondary copolymerizable monomers ex 35 lant effectiveness described herein. clude substituted acrylamides, vinyl esters and acrylate Repeating units of styrene sulfonic acids and salts esters. thereof are defined as follows: 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), 40 identified above, and can contain a small proportion of --CH-C- polymerized units of one or more of the secondary copolymerizable monomers. The copolymers have weight average molecular weight of 1,000 to 100,000, SOX preferably 2,000 to 50,000, and more preferably 2,000 to 45 20,000. The molecular weight given herein is measured by gel permeation chromatography. where R is hydrogen or a lower alkyl group of 1 to 6 The antiscalant copolymers disclosed herein contain carbon atoms, preferably hydrogen, and X is alkali 20 to 95% by weight of the polymerized carboxylic acid metal or alkaline earth metal or ammonium, particularly or its salt or anhydride, preferably 40 to 90% and more 50 hydrogen, ammonium or alkali metal. A particularly preferably 50 to 70%; 1 to 60% by weight of the poly suitable sulfonic acid is styrene sulfonic acid where R is merized sulfonic acid or its salt, preferably 10 to 50%; 5 hydrogen and the -SO3X group is at the 3 or 4 position to 50% of a styrene sulfonic acid, preferably 5 to 40%; on the phenyl ring. The salts of styrene sulfonic acids with up to about 20%, preferably up to 10%, of one or are water-soluble. The sodium salt of styrene sulfonic more of the secondary copolymerizable monomers 55 acid is available commercially. which do not deleteriously affect performance of the The monomers can be prepared, if desired, in a con copolymers as antiscalants. The data herein shows per ventional manner but they are commercially available formance for terpolymers containing about 40 to 70% and therefore, can be purchased. Polymerization of the acrylic acid, about 10 to 50% acrylamido methylpro monomers results in an essentially non-crosslinked ran pane sulfonic acid, and about 5 to 35% styrene sulfonic dom copolymer, the molecular weight of which can be acid, with up to 15% of a secondary polymerizable adjusted with a little trial and error. The copolymer is COOOet. preferably formed in a high yield ranging from about The carboxylic acid monomers contemplated herein 50% to about 99% by weight of the comonomers. include monounsaturated monocarboxylic and dicar It is also a requirement that the copolymer be soluble boxylic acids, salts and anhydrides thereof. Preferred in 65 in water. Typically, the copolymer is used in water in this class are monounsaturated monocarboxylic acids of the range of 0.5 to 500 ppm. Thus, high solubility of 3 to 4 carbon atoms and water soluble salts thereof, water treatment compositions is not essential but desir particularly acrylic acid and methacrylic acid. Because able. The product is preferably shipped in drums as a 4,952,327 5 6 concentrated aqueous solution containing in the range ppm of orthophosphate ions. To this solution was added of about 20% to about 50% by weight of solids per 100 slowly and with continuous stirring a known volume of parts of solution, which requires solubility to the extent testing polymer solution sufficient to give a dosage of 10 of at least 20 weight parts per 100 parts of water. ppm. Polymerization of the monomers identified herein A pair of glass and reference electrodes, which were can be carried out in a mutual solvent for both, such as calibrated before and after each experiment with stan in a lower alkanol of about 1 to 6 carbon atoms, or in dard buffer solutions of pH 7.00 and 9.00, were then water, with an effective amount of a free radical initia immersed in the solution which was maintained at 50 tor sufficient to produce the desired composition within C. by circulating water through the outside of a glass an acceptable period of time. The monomeric acids can O cell jacket. After about 45 minutes, a known volume of be used as such or can be in a partially or a completely calcium chloride solution was slowly added to the con neutralized form prior to polymerization. tinuously stirred solution containing phosphate and The reaction is conveniently carried out in water as polymer, to give a final calcium ion concentration of the only reaction medium at a temperature in the range 140 ppm. The pH of the solution was then immediately of about 30 to about 130 C. usually at atmospheric or 15 brought to pH 8.50 by automatic addition of 0.10 M slightly elevated pressure. The concentration of the NaOH solution. The pH of the solution was then main copolymer formed may range from about 5% to about tained at 8.50--0.01 throughout the experiment using 50% by weight, based on total solids, which solution the pH-stat technique. Solution samples were with can be shipped directly. drawn after 22 hours, and analyzed, after filtration The copolymer may also be formed in an acyclic 20 through 0.22 micrometer filter paper, for orthophos ketone, such as acetone, in an alkanol, in water, or mix phate ions using the ascorbic acid method, as described tures thereof. If, for example, the copolymer is formed in detail in "Standard Methods for the Examination of in an organic solvent, or a mixture of an organic solvent Water and Waste Water” 14th edition, prepared and and water, the copolymer is converted from the organic published by American Health Association. The instru solvent solution to a water solution. Typically, the or 25 ment used for the colorimetric measurements was a ganic solvent is stripped from the solution with steam or Beckman 5270 Spectrophotometer. distilled off with subsequent additions of water and Tests for calcium sulfate and calcium carbonate were repetition of distillation to remove the solvent, followed carried out by the method of Ralston, see J. Pet. Tech., by the addition of water and a neutralizing agent such as Aug. 1969, 1029-1036. caustic solution, ammonia, a hydrazine, or a low-boiling 30 The percent threshold inhibition (TI) attained for primary, secondary or tertiary aliphatic amine. each experiment was obtained using the following for The final aqueous solution of polymer salt is prefera mula, shown in this case for calcium phosphate: bly in the range of about pH 2 to about pH 8, with a total solids content of about 5 to about 50% by weight (PO4) exp - (PO4) final of polymer in water. 35 X 00 The copolymers formed may have weight average % TI- (PO) initial (PO) final molecular weight in the range of about 1,000 to about 100,000, preferably 2,000 to 50,000 and more preferably where about 2,000 to about 20,000, as determined by gel per (PO4) exp=concentration of phosphate ion in the fil meation chromatography. trate in presence of the copolymer at time of 22 hours In a typical polymerization process, a glass lined or (PO4) final=concentration of phosphate ion in filtrate stainless steel reactor is charged with predetermined in absence of the copolymer at time 22 hours amounts of monomers along with solvent and a free (PO4 l) initial= concentration of phosphate ion at time zero. radical polymerization catalyst under a nitrogen blan The invention disclosed herein is demonstrated by ket, and the reaction mixture allowed to exotherm 45 the following example which shows threshold inhibi under controlled temperature conditions maintained by tion tests thereof and other related polymers. a heat-transfer fluid in the jacket of the reactor. The EXAMPLE 1 pressure under which the reaction occurs is not critical, it being convenient to carry it out under atmospheric This example demonstrates threshold inhibition by pressure. 50 various polymers, including the copolymers of this The copolymers described herein in connection with invention, of calcium phosphate scale. The tests were threshold inhibition of salt-forming scales can be used in carried out in the manner described above for 22 or 24 combination with other conventional additives wher hours to determine percent threshold inhibition of cal ever appropriate. Examples of some of the conventional cium phosphate and calcium sulfate, respectively, using additions include anti-precipitating agents, oxygen 55 the various polymers indicated below with approximate scavengers, sequestering agents, corrosion inhibitors, weight average molecular weight. Results of the tests antifoaming agents, and the like. are given below in Table I. The copolymers formed in the manner described TABLE I herein, were used to treat water which contained cal Polymer Monomer Wt. Mol. 7% Ca/P(a) % CaSO4(b) cium ions and phosphate ions in a stirred pH-STAT test Composition Ratio Wt. Inhibition Inhibition while maintaining constant pH and using an automatic AA:AMPS: 70:10:20 5,000 81 99 tritrator to gauge the effectiveness of the polymer for SSS 70:10:20 15,000 77 - inhibiting the formation and deposition of calcium phos 60:10:30 5,000 93 97 phate. The test was carried out as follows: a known 60:10:30 10,000 95 98 65 60:10:30 15,000 89 99 volume of a phosphate salt solution, such as Na2HPO4, 60:30:10 5,000 92(72) 97 or another soluble phosphate salt solution, was trans 60:30:10 15,000 99(79) - ferred to a known volume of distilled water in a double 60:30:10 29,000 94(67) - walled glass cell to give a final concentration of about 9 60:30:0 33,000 86(71) --- 4,952,327 7 8 TABLE I-continued one would expect that such terpolymers would lose Polymer Monomer Wt. Mol. 7% Ca/P() 7% CaSO4(b) their effectiveness against scale in the presence of solu Composition Ratio Wt. Inhibition Inhibition ble metal ions. 60:32.5:1.5 15,000 97 98 We claim: 50:30:20 5,000 92 94. 1. A method of inhibiting precipitation of scale, in 50:30:20 10,000 95 cluding calcium phosphate, in an aqueous medium, in SO:30:20 15,000 96 97 S0:30:20 30,000 95 the presence or in the absence of iron, comprising add 40:30:30 5,000 66 96 ing to said aqueous medium an effective amount of a 40:30:30 10,000 87 95 water-soluble copolymer for the purpose of inhibiting 40:30:30 15,000 95(85) 92 10 0:50:10 15,000 83 7 precipitation of said scale, said copolymer consisting 50:30:20 60,000 86 -- essentially of (a) 40 to 70% by weight carboxylic mono SO:40:10 50,000 95 mer selected from acrylic acid, methacrylic acid, salts AAAMPS: 60:25:10:5 15,000 74 wo SSSDADMAC of such acids, and mixtures thereof, (b) 10 to 50% by conditions: calcium = 140 ppm; phosphate = 9 ppm; pH = 8.50; T = 50 C.; time 15 weight of a sulfonic monomer selected from 2 sc 22 hr.; polymer as 10 ppm acrylamido-2-methylpropane sulfonic acid, 2-metha conditions: calcium = 2000 ppm; sulfate = 4800 ppm; T = 66' C.; time = 24 hr.; crylamido-2-methylpropane sulfonic acid, salts of said polymer it 4 ppm acids, and mixtures thereof, (c) 5 to 30% of a styrene The following contractions appear in the above table: sulfonic acid, and (d) up to 20% by weight of one or Ca/P-calcium phosphate more secondary copolymerizable monomer which does AA= acrylic acid not deleteriously affect performance of said copolymer AMPS (R)=2-acrylamido-2-methylpropane sulfonic as antiscalant, said secondary copolymerizable mono acid mer excluding substituted acrylamides, vinyl esters, and SSS=sodium styrene sulfonate vinyl acetate; said copolymer having a weight average DMDMAC=diallyldimethylammonium chloride 25 molecular weight in the range of about 1,000 to 100,000. The numbers in parentheses indicate percent thresh 2. Method of claim 1 wherein amount of said copoly old inhibition of calcium phosphate in the presence of mer is 1 to 50 ppm and its molecular weight is in the 1.0 ppm of soluble iron (III). range of about 2,000 to 50,000. The sodium styrene sulfonate was commercial grade 3. Method of claim 2 wherein amount of said second material obtained from two different sources and is 30 ary monomer is up to 10% by weight and molecular believed to be primarily the p-isomer. weight of said copolymer is 2,000 to 20,000. It has been shown that the copolymers disclosed 4. Method of claim 3 wherein said aqueous medium is herein are effective antiscalants in the presence or ab alkaline and is selected from process water used in sence of soluble metal ions. Typical scales encompassed steam generating systems, recirculating cooling water by the present invention include calcium scales such as 35 systems, gas scrubbing systems, desalination water sys calcium phosphate, calcium sulfate, and calcium car tems, and crude petroleum recovery systems. bonate. The copolymers described herein can be used in 5. Method of claim 4 wherein in said copolymer, aqueous recirculating systems where the copolymers amount of said styrene sulfonic acid is about 5 to 30%. are effective in reducing deposition of scale in the pres 6. Method of claim 1 wherein said copolymer has ence or the absence of soluble metals, such as iron. As molecular weight of about 2,000 to 50,000 and is se an open recirculating cooling system is brought into lected from the following copolymers, given in weight operation, the concentration of scale-forming materials parts: (a) 40 to 70% acrylic acid, methacrylic acid, and increases due to evaporation of some of the water. As mixtures thereof; (b) 10 to 50% acrylamido methylpro the cycles of concentration increase, the scaling ten 45 pane sulfonic acid; (c) 5 to 30% styrene sulfonic acid; dency of the system also increases. When an intolerable and (d) up to 15% of one or more other polymerizable concentration of scale-forming ions is reached, addi IOIOS. tional copolymer may be added above the normal dos 7. Method of claim 6 wherein said styrene sulfonic age. However, in preferred operation mode, the system acids and salts thereof are defined as follows: is operated at a steady state. Make-up water is added to 50 compensate for evaporation and other losses. A contin R uous or intermittent blowdown is used to remove some of the water containing high levels of scalants, and copolymer is added along with the make-up water to maintain the desired copolymer concentration in the 55 system. In reverse osmosis systems, the system is oper SOX ated at a steady state. The dosage of polymer in the feed is chosen such that it will prevent deposition of scale in the concentrated brine solution. With appropriate where R is selected from hydrogen and alkyl groups of choice of polymer levels and operating conditions, a to 6 carbon atoms, and X is selected from hydrogen, reverse osmosis system may be operated for a very alkali metals, alkaline earth metals, ammonium groups, substantial length of time before shutdown must occur and mixtures thereof. to clean the membranes. In such reverse osmosis sys 8. Method of claim 7 wherein in the formula, R is tems, amount of soluble metals, such as soluble iron, is selected from hydrogen and alkyl groups of 1 to 2 car on the order of up to about 10 ppm, preferably 1-5 ppm. 65 bon atoms and X is sodium. It has been shown that the terpolymers disclosed 9. Method of claim 7 wherein in the formula, R is herein are effective scale inhibitors in the presence or hydrogen and the -SO3Xgroup is at the 3 or 4 position absence of soluble metal ions. This is surprising since on the phenyl ring. 4,952,327 9 10 10. Method of claim 1 wherein said copolymer is (h) 50/40/10 copolymer of AA/AMPS/SSS selected from the following copolymers, given in (i) 60/25/10/5 copolymer of AA/AMPS/SSS/- weight parts: DADMAC (a) 70/10/20 copolymer of AA/AMPS/SSS wherein the contractions are defined as follows: (b) 60/10/30 copolymer of AA/AMPS/SSS 5 AA= acrylic acid (c) 60/30/10 copolymer of AA/AMPS/SSS SSS=sodium styrene sulfonate (d) 60/32.5/7.5 copolymer of AA/AMPS/SSS AMPS=2-acrylamido-2-methylpropane sulfonic (e) 50/30/20 copolymer of AA/AMPS/SSS acid (f) 40/30/30 copolymer of AA/AMPS/SSS DADMAC= diallyldimethylammonium chloride. (g) 40/50/10 copolymer of AA/AMPS/SSS 10 k

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