Sodium Allyl Sulfonate Synthesis Essay

Synthesis of tri-allyl maleopimarate

Sodium maleopimarate and allyl chloride were used as raw materials to synthesize tri-allyl maleopimarate. Hexadecyl trimethyl ammonium bromide, was used as phase-transfer catalyst. In order to improve the yield of tri-allyl maleopimarate, different reaction conditions were studied, such as the microwave power, amount of phase transfer catalyst, amount of additives of allyl chloride, and reaction temperature. The effects of different parameters on the yield of the product are shown in Table 1.

Microwave power has a great influence on the yield and purity of tri-allyl maleopimarate. The optimal microwave power was 400 W, which corresponded to a yield of 59.1%. With regards to temperature, the reaction could not take place below 40 °C. For higher temperatures, the yield of tri-allyl maleopimarate increased with increasing reaction temperature. The yield of the product reached the maximum when the temperature up to 55 °C. A further increase in temperature caused a reduction in the yield due to the emergence of secondary reactions. The yield of tri-allyl maleopimarate at different reaction time was also investigated. The product yield increased to its maximum value of 59.1% at 4 h. Further increases in the reaction time caused a decrease in the yield. The molar ratio of raw materials was also tested. At lower ratios (≤1:1), product yield increased slightly. A maximum yield of 93.2% was observed at a ratio of 3:1. The yield of product decreased quite sharply at ratios >3:1. The yield of tri-allyl maleopimarate first increased then stabilized with increasing amounts of catalyst. The optimum catalyst amount was 5%, while the yield of the product was 93.2%. The optimum microwave power, reaction temperature, reaction time, n(allyl chloride)/n(sodium maleopimarate) and catalyst amount were 400 W, 55 °C, 4 h, 3:1 and 5%, respectively. The yield of tri-allyl maleopimarate was 93.2% under the optimum reaction conditions.

An interesting observation was made during the separation of tri-allyl maleopimarate from the reaction mixture. Following extraction with n-hexane, the monomer products were accompanied by a white precipitate byproduct. More detailed information concerning the byproduct, including its physiochemical and UV-curing properties, is provided in the the Supplementary Materials.

Physicochemical properties of the synthesized tri-allyl maleopimarate

FTIR analysis of tri-allyl maleopimarate

The infrared spectra of material and products are shown in Fig. 1. Figure 1(a) represents maleopimaric acid anhydride. The peaks at 1838 cm−1 and 1774 cm−1 were the stretching coupling vibration of the C=O bond in acid anhydride. The peak at 1700 cm−1 represents stretching vibration of the C=O bond in C18. Figure 1(b) is the FTIR spectrum of sodium maleopimarate. It can be seen that the peaks relative to the stretching coupling vibration of acid anhydride at 1838 cm−1 and 1774 cm−1, and to carboxyl absorption, at 1700 cm−1, disappeared. The peaks at 1557 cm−1 and 1393 cm−1 are attributable to the symmetric and anti-symmetric stretching vibration peaks of the —CO2− group. Figure 1(c) is the FTIR spectrum of tri-allyl maleopimarate. The absorption peak of carboxyl at 1700 cm−1 disappeared. Several new peaks appeared at 1724 cm−1, 1648 cm−1, and at 3080 cm−1, which are due to the adsorption of the ester, unsaturated C=C double bonds, and the =C—H group, respectively, indicating the successful introduction of the allyl group into the product. The byproduct was also analyzed and its FTIR spectrum is shown in Figure S1 of the Supplementary Materials.

Gas chromatographic analysis of tri-allyl maleopimarate

The raw materials and products were identified by GC analysis, which shown in Fig. 2. Figure 2(a) shows the GC results of the maleopimaric acid anhydride. The peaks for each component are: peaks 1, 2 and 3 are all due to malay pimaric acid trimethyl, and peak 4 is due to malay pimaric acid methyl ester. Figure 2(b) is the GC trace of tri-allyl maleopimarate and shows that after the esterification reaction the only detectable peak is the one associated with the product. According to the GC measurements, the content of tri-allyl maleopimarate is 96.1%, measured at a retention time of 37.9 min, and the content of the allyl maleopimarate byproduct is 3.9%, measured at a retention time of 26.7 min. The GC spectrum of the purified byproduct is shown in Figure S2 of the Supplementary Materials. It can be seen that the raw material peak has completely disappeared and the purity of the product is high.

MS analysis of tri-allyl maleopimarate

Typical fragmentation patterns of tri-allyl maleopimarate are shown in Figs 3 and 4. The fragment ion with molecular weight 538 represents the molecular ion [M]+. Loss of an allyl group from the tri-allyl maleopimarate substituent resulted in the formation of the [M–OCH2CHCH2]+ fragment. Loss of two allyl groups yielded the fragment ion 439, which retains the complete structure of allyl maleopimarate. The formation of the fragment ion with molecular weight 342 is the result of the reverse Diels–Alder reaction. The base peak is the fragment ion 197. Other fragmentation patterns of allyl maleopimarate are shown in Figures S3 and S4 of the Supplementary Materials.

1H NMR analysis of tri-allyl maleopimarate

The chemical structures of tri-allyl maleopimarate (Fig. 5) and its byproduct (allyl maleopimarate) (Figure S5) were studied by 1H NMR. The significant signals of 1H NMR observed when analyzing tri-allyl maleopimarate can be summarized as follows: δ 5.88 (C26—H), δ 5.87 (C29—H) and δ 5.87 (C32—H); double peaks of each 2H at δ 4.41 (C25—H), δ 4.56 (C28—H) and δ 4.58 (C31—H), δ 5.29~5.16 (C27—H, C30—H, C33—H). The results also proved the successful formation of the three vinyl double bonds in the product. The other 1H NMR signals can be summarized as follows (δH, ppm): δ 1.46 (m, 1H, C2—H), 1.26 (m, 1H, C2—H), 1.71 (t, 1H, C3—H), 1.58 (1H, C3—H), 2.83 (1H, C5—H), 1.43 (1H, C1—H), 1.25 (1H, C1—H), 1.54 (1H, C6—H), 1.25 (1H, C6—H), 1.49 (1H, C7—H), 1.25 (1H, C7—H), 1.42 (1H, C9—H), 5.38 (1H, C14—H), 2.79 (1H, C12—H), 1.54 (1H, C11—H), 1.25 (1H, C11—H), 5.34 (m,1H, C15—H), 1.06 and 1.03 (d, 3H, C16—H), 1.08 and 1.06 (d, 3H, C17—H), 0.62 (s, 3H, C19—H), 1.16 (s, 3H, C20—H), 2.92 (d, 1H, C21—H), 2.94 (s, 1H, C22—H), 4.41 (d, 2H, C25—H), 5.88 (m, 1H, C26—H), 4.56 (d, 2H, C28—H), 5.87 (m, 1H, C29—H), 4.58 (d, 2H, C31—H), 5.85 (m, 1H, C32—H), 5.29~5.16 (d, 6H, C27—H, C30—H, C33—H).

13C NMR analysis of tri-allyl maleopimarate

The 13C chemical shifts of tri-allyl maleopimarate were measured (Fig. 6 with chloroform; used as internal reference). In the 13C NMR spectrum, the signals of the C=O atoms, C-18, C-23 and C-24, appear at δ = 177.9, 171.2, and 171.9 ppm, respectively. The signals of the allyl double bonds appear at δ = 131.9 (C-26), 131.7 (C—29), 131.7 (C—32), 117.3 (C—27), 117.5 (C—30), 117.6 ppm (C—33). The 13C NMR chemical shifts and the 13C NMR signals relative to the byproduct (allyl maleopimarate) formed from tri-allyl maleopimarate are shown in Figure S6 and Table S1 of the Supplementary Materials.

The 13C NMR signals of tri-allyl maleopimarate are reported in Table 2.

Elemental analysis

The results of the elemental analysis, expressed in percentages, of tri-allyl maleopimarate are as follows: ω(C) = 72.7(73.6), ω(H) = 8.6(8.6), ω(O) = 18.3(17.8), where the values in parentheses represent the theoretical data. A good agreement between the analysis results and the theoretical data can be noticed.

Physical properties of tri-allyl maleopimarate

Table 3 shows the physiochemical properties of tri-allyl maleopimarate. The product was a viscous liquid with a viscosity of 8.5 × 103 mPa·s at 25 °C. Its density and acid value were 1.1097 × 103 kg/m3 and 2.5 mg/g, respectively.

UV-curing performance of tri-allyl maleopimarate

The UV-curing reaction conditions were as follows: illumination distance 4.5 cm, illumination intensity 100%, photoinitiator 6512.

FTIR monitoring of tri-allyl maleopimarate conversion

The FTIR spectra of the product of tri-allyl maleopimarate polymerization under UV irradiation for different curing times are shown in Fig. 7. The C=C double bonds were gradually polymerized with the increase of curing time. The areas of the corresponding peaks at 1648 cm−1 and 3080 cm−1 decreased accordingly. It was also found that the area of the peak relative to the carbonyl group (1720 cm−1) remained the same after UV irradiation; however, it shifted towards a higher wavenumber because the disappearance of the C=C double bond cause the destruction of the its conjugate. As the curing reaction proceeds the C=C double bond becomes a C-C single bond, therefore, the characteristic absorption peak of =C-H at 3080 cm−1 gradually disappeared. Nonetheless, the absorption peak relative to the C=C double bond cannot disappear completely, regardless of the extent of the UV curing time, because the steric hindrance resulting from cross-linking polymerization prevents the reaction of all the double bonds. The FTIR spectra of the product polymerized from allyl maleopimarate (byproduct) before and after curing under UV irradiation are shown in Figure S7; the specific parameters were also reported in the Supplementary Materials.

Effects of curing conditions on the surface drying time from tri-allyl maleopimarate

Table 4 shows the surface drying time of tri-allyl maleopimarate with increasing dosages of photo initiators. The reaction conditions were as follows: illumination distance 4.5 cm, illumination intensity 100%, photo initiator 6512. The surface drying time of tri-allyl maleopimarate decreased rapidly with increasing photoinitiator dosage when the dosage was lower than 4%. That is because the number of primary free radicals, which can initiate chain growth and termination, increases with increasing photoinitiator dosage after irradiation with UV light. Further increases of the photoinitiator dosage, from 5% to 10%, did not affect the drying time. For photoinitiator dosages ≤5%, the surface drying time of allyl maleopimarate was obviously shorter than that of tri-allyl maleopimarate. This is because tri-allyl maleopimarate had undergone cross-linking polymerization and generated a space grid structure; by contrast, the byproduct of allyl maleopimarate has only one reactive vinyl group, which leads to a lower drying time (see Table S2 of the Supplementary Materials). Additionally, the conversion of the anhydride to carboxylic acid during photo polymerization is expected to introduce interchain hydrogen bonding interactions and further reduce the drying time.

From Table 4 it can be seen that the surface drying time increased linearly with the illumination distance, because as the distance increased the illumination intensity, and consequently the number of primary free radicals generated, increased.

Table 4 shows the influence of the illumination intensity on the surface drying time of tri-allyl maleopimarate. Surface drying time decreased rapidly with increasing illumination intensity because, when all other conditions were kept the same, the number of photons received per unit area increased with increasing illumination intensity and more primary free radicals were generated, thus decreasing the surface drying time.

Thermal stability evaluation

Figure 8 shows the weight loss of the UV-cured product of tri-allyl maleopimarate, recorded while heating the sample from 30 to 800 °C (10 °C /min) in N2 atmosphere. A bimodal weight-loss curve was observed with an initial loss at 312.0 °C. More detailed TG data of the UV-cured product is reported in Table 5.

Figure 9 shows the DSC curve of the cured product of tri-allyl maleopimarate. The following characteristic temperatures can be obserbed: an onset temperature of 76.46 °C, an end temperature of 89.17 °C, and a mid-point of specific heat change (Cp) of 0.195 J/(g·°C). The glass transition temperature of the UV-cured product from tri-allyl maleopimarate was higher than that of allyl maleopimarate (see Figure S9 of the Supplementary Materials). The results showed that the three-dimensional net structure of the polymer formed from tri-allyl maleopimarate had higher thermal stability than the two dimensional cross-linked structure of the polymer formed from allyl maleopimarate.

Mechanical properties of the UV-cured polymers of tri-allyl maleopimarate

Table 6 gives the mechanical properties of UV-cured product. The product was a smooth and transparent polymer film. TG data of the UV-cured product derived from the allyl maleopimarate based film is shown in Figure S8 and Table S3 of the Supplementary Materials.

The UV-cured product showed excellent flexibility. An adhesion grade of 0 and an impact strength of over 50 cm were obtained. Due to the introduction of the rosin chain, the cured product passed the acid, alkali, salt, and water resistance tests. A difference between the two UV-cured products lay in their pencil hardness, which was measured to be 2H and 5H for the products of tri-allyl maleopimarate and allyl maleopimarate, respectively (See Table S4). The higher hardness value of the UV-cured product of allyl maleopimarate is attributable to the hardness of the acid anhydride thermally cured product.

UV curing mechanism of tri-allyl maleopimarate

A polymerization mechanism of tri-allyl maleopimarate was proposed and is shown in Fig. 10. The monomer took part in a free-radical polymerization reaction. Tri-allyl maleopimarate, bearing three allyl double bonds, was suitably predisposed for more complex polymerization involving cross-linking; on the other hand, the allyl maleopimarate could only form a polymer with a two dimensional cross-linked structure (see Figure S10).

This is a continuation of application Ser. No. 226,698, filed 8/1/88, now abandoned.

U.S. Pat. Nos. 3,706,717 and 3,879,288 disclose the use of vinyl sulfonate/monovinyl compound copolymers as scale inhibitors.

U.S. Pat. No. 4,001,134 discloses the use of maleic anhydride/allyl acetate copolymers as scale inhibitors in sea-water distillation plants.

U.S. Pat. No. 4,253,968 discloses the use of maleic acid/allyl monomer copolymers as cooling water scale inhibitors.

U.S. Pat. No. 4,342,652 discloses the use of maleic acid/allyl sulfonic acid copolymers as scale inhibitors in evaporative desalination units.

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.

U.S. Pat. No. 4,166,041 discloses the use of mixtures of polymers prepared from an ethylenically unsaturated dibasic acid and an ethylenically unsaturated sulfonic acid as magnesium hydroxide scale inhibitors in evaporative desalination units. Maleic anhydride/allyl sulfonic acid copolymers are used in these admixtures.

EPO Pat. Applin. No. 84102890.5 discloses copolymers of maleic acid and an adduct of an oxyalkylene and allyl alcohol, and the use thereof for scale inhibition.

U.S. Pat. No. 4,297,237 discloses the use of polymaleic anhydride and polyphosphonates 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 No. 84301450.7 discloses carboxylic acid/sulfonic acid copolymers in combination with organic phosphonates as scale inhibitors.

However, none of the prior art references described above in any way suggest the efficacy of the instant polymers as calcium scale control agents in systems operating under severe pH and/or calcite saturation levels.

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, insoluble reaction products (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 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 soluble compounds with the ions already present in the solution. As these reaction products precipitate on heat transfer surfaces in contact with aqueous systems, 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 scale including but not limited to calcium carbonate, calcium oxalate, magnesium oxalate, calcium phosphate, and calcium 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 and/or by the use of organo-phosphonates, such as hydroxyethylidene diphosphonic acid (HEDP) and aminotrimethylene phosphonic acid (AMP). However, these traditional scale inhibitors are ineffective or less effective in highly alkaline water. For example, HEDP is ineffective because it reacts with calcium at high pH's to form a calcium/phosphonate scale. Due to the difficulty in controlling alkaline earth metal scale under high pH and/or alkalinity conditions, operators generally add acid to lower the pH and consume alkalinity to prevent scaling. The handling of corrosive acid is dangerous and the maintenance of a desired pH may be difficult.

In recent years, increasing the cycles of concentration in industrial cooling towers has become important, especially in the regions where the water supply is limited. Higher cycles correspond to higher concentrations of scale forming elements. With the elimination of acid feed, the higher pH's generated bring a cooling system to high saturation levels more rapidly.

Accordingly, the need exists for an inexpensive, efficient method and polymer or polymer composition for preventing the formation of deposits on metallic surfaces in contact with water by inhibiting the formation of scale and/or by dispersing scale-forming compounds. This need is especially critical in systems which operate under severe pH and/or calcite saturation conditions.

The instant inventors have discovered a method for controlling scale deposition and/or dispersing scale-forming compounds in aqueous systems which operate under severe pH and/or calcite saturation conditions using maleic acid/allyl sulfonate polymers. While such polymers alone are effective inhibitors, other conventional scale and/or corrosion inhibitors may enhance their performance under certain conditions.

The instant polymers are especially effective as agents for controlling calcium carbonate under high pH/high calcite saturation conditions.

The instant invention is directed to a method for controlling scale deposition in an aqueous system operating under severe pH and/or calcite saturation conditions 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) allyl sulfonic acid or a salt thereof, preferably sodium allyl sulfonate, wherein the mole ratio of (a):(b) ranges from about 1:3 to about 3:1, preferably from about 1:2 to about 2:1, most preferably from about 1:1.5 to about 1.5:1. Water soluble salts of such polymers can also be used.

The molecular weight of the instant polymer ranges from about 500 to about 50,000, preferably from about 500 to about 10,000.

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/allyl sulfonic acid 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 preferably prepared by polymerizing at least one ethylenically unsaturated dibasic carboxylic acid or anhydride, preferably maleic acid or anhydride, in combination with allyl sulfonic acid or a salt thereof, preferably sodium allyl sulfonate.

The mole ratio of the acid or anhydride to allyl sulfonic acid or salt thereof in the monomer mix may range from about 1:3 to about 3:1, preferably from about 1:2 to about 2:1 and most preferably from about 1:1.5 to about 1.5:1. 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.

The instant polymers are useful in controlling the formation of calcium carbonate scale in cooling water systems which have high calcite concentration, high pH and/or high alkalinity values. Such conditions are often times encountered as cycles of concentration increase.

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 under severe operating conditions, where conventional calcium carbonate inhibitors such as AMP, HEDP and polyacrylic acid are ineffective, 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, 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/allyl sulfonic acid polymer is critical to the instant method. These polymers inhibit and/or prevent scale deposition under severe saturation and/or temperature conditions, and are generally efficient in the alkaline pH ranges, preferably from about 7.5 to about 10.0, and most preferably from about 8.0 to about 9.5.

Also, other monomers may be added to the monomer mix and polymerized with the acid/anhydride and allyl sulfonic acid to produce polymers having additional moieties. Examples of such monomers include acrylic acid, acrylamide, dialkyldiallyl ammonium monomers, 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.

The inventors have found that compositions comprising the instant polymers, a phosphonate and/or an acrylic acid/acrylamidomethylpropyl sulfonic acid polymer (AA/AMPSA) to be especially effective in inhibiting and/or preventing scale deposition in systems operating under severe pH and/or calcite saturation conditions.

The following examples are illustrative of the instant invention. However, they are not intended to limit the scope of the invention in any way.

A mixture of maleic anhydride briquettes (98 g) and sodium allyl sulfonate solution (576 g, 25% active) was heated to reflux (105°-110° C.). A part of the condensate was stripped out to keep the initial monomer concentration at approximately 40%. A solution of sodium persulfate initiator (20 g Na2 S2 O8 /40 g H2 O) was fed over five hours. The result was a maleic anhydride/sodium allyl sulfonate polymer having a weight average molecular weight of about 2400.

A mixture of maleic anhydride briquettes (98 g) and sodium alkyl sulfonate solution (576 g, 25% active) was adjusted to pH 6 using sodium carbonate, and then heated to 100° C. A solution of sodium persulfate initiator (41%) was fed over four hours. The result was a maleic anhydride/sodium allyl sulfonate polymer having a weight average molecular weight of about 2400.

The following test demonstrates the efficacy of the instant compositions under severe operating conditions.

Calcium carbonate inhibition was determined by adding a given concentration of the designated inhibitor to a solution containing 250 mg/L Ca+2 (as CaCl2) and 600 mg/L of alkalinity as HCO3-1, at an initial pH of 9.0. The solution was stored in a stagnant flask for 24 hours at 55° C. Poor performing inhibitors allowed a precipitate of CaCO3 to form. To remove these "solids", the solution was filtered through a 2.5 micron filter. The inhibitor effectiveness under these conditions was obtained by determination of the soluble calcium content of the test solutions using the Schwarzenbach titration method (EDTA, chrome black T indicator). The soluble calcium ion concentration in the absence of inhibitor is equivalent to 0% scale inhibition. The percent inhibition for a given test is determined by:

Vo =the Schwarzenbach titration volume with no inhibitor present (control)

Vt =the Schwarzenbach titration volume when no precipitation occurs

Ve =the experimental Schwarzenbach titration volume when inhibitors are present in the test solution

Results are shown in Table I.

TA8LE I______________________________________pH 9 CaCO.sub.3 Inhibition Dosage % InhibitionSample (ppm) after 24 hours______________________________________Example 1 (MA/SAS) 40 94Comparative Inhibitor A 40 83Comparative Inhibitor B 40 85______________________________________

Comparative Inhibitor A: polyacrylic acid MW 2,100 (PAA)

Comparative Inhibitor B: Belclene 200, polymaleic acid (PMA) commercially available from Ciba Geigy

1. Two-Component Mixtures

Calcium carbonate inhibition was measured using the procedure of Example 3. A MA/SAS copolymer (Example 1) was combined with various AA/AMPSA* copolymers. The results are shown in Table II.

TABLE II______________________________________pH 9 CaCO.sub.3 Inhibition: MA/SAS - AA/AMPSA Blends % Inhibi-Inhibitor Dosage Inhibitor Dosage tion after#1 (ppm) #2 (ppm) 24 hours______________________________________1:1 MA/SAS 40 60/40* AA/AMPSA 10 941:1 MA/SAS 40 75/25* AA/AMPSA 10 971:1 MA/SAS 40 90/10* AA/AMPSA 10 94______________________________________ *Mole ratios.

1. Three-Component Mixtures (24 hour test)

A 1:1 MA/SAS copolymer was tested in three-component mixtures with organic phosphonates and AA/AMPSA copolymers. As shown in Table III, these combinations gave excellent 24-hour inhibition performance. Comparison of the 1:1 MA/SAS copolymer with a PAA in the same three-component mixtures clearly shows the performance advantage provided by this copolymer over PAA under severe pH and/or calcite saturation conditions.

TABLE III______________________________________24-Hour, pH 9 CaCO.sub.3 Inhibition - Three-Component MixturesInhibitor Formulation Dosage (ppm) % Inhibition______________________________________(1:1 MA/SAS)/Dequest 2054*/ 30/10/10 100(75/25 AA/AMPSA)(1:1 MA/SAS)/Dequest 2054/ 30/10/10 100(60/40 AA/AMPSA)(1:1 MA/SAS) HEDP/ 30/10/10 94(60/40 AA/AMPSA)PAA/Dequest 2054/(60/40 30/10/10 92AA/AMPSA)PAA/Dequest 2054/(75/25 30/10/10 97AA/AMPSA)PAA/Dequest 2054/(60/40 10/20/20 95AA/AMPSA)(1:1 MA/SAS)/Dequest 2054/ 20/10/10 100(60/40 AA/AMPSA)(1:1 MA/SAS)/Dequest 2054/ 30/5/5 94(60/40 AA/AMPSA)p-AA/Dequest 2054/(60/40 30/5/5 80AA/AMPSA)______________________________________ *Dequest 2054:Hexamethylene diamine tetraphosphonic acid

2. Three Component Mixtures (5-day test)

Three component compositions of the MA/SAS polymer with organic phosphonates and AA/AMPSA copolymers were tested in a 5-day stagnant flask test. This test procedure is the same as the one described in Example 2 except that the flasks were incubated at 55° C. for 5 days. The results of this test are shown in Table IV.

TABLE IV______________________________________pH 9, CaCO.sub.3 Scale Inhibition - 5-Day Stagnant Flask TestInhibitor Formulation Dosage (ppm) % Inhibition______________________________________(1:1 MA/SAS)/Dequest 2054/ 36/12/12 98(75/25 AA/AMPSA)(1:1 MA/SAS)/Dequest 2054/ 30/10/10 99(75/25 AA/AMPSA)(1:1 MA/SAS)/Dequest 2054/ 24/8/8 98(75/25 AA/AMPSA)(1:1 MA/SAS)/Dequest 2054/ 18/6/6 85(75/25 AA/AMPSA)(1:1 MA/SAS)/Dequest 2054/ 30/10/10 98(60/40 AA/AMPSA)(1:1 MA/SAS/Bayhibit AM/ 30/10/10 95(75/25 AA/AMPSA)(1:1 MA/SAS)/HEDP/ 30/10/10 81(75/25 AA/AMPSA)______________________________________

Dequest 2054--Hexamethylenediamine tetraphosphonic acid

Bayhibit AM--2-phosphonobutane-1,2,4-tricarboxylic acid, ammonium salt

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