AWT-10 (Oct-10)

Association of Water Technologies, Inc. Annual Convention & Exposition

The Grand Sierra Resort (Reno, NV) October 20 to 23, 2010

Effects of Thermal Stress on Silica-Silicate Deposit Control Agent Performance

Zahid Amjad, Ph.D. and Robert W. Zuhl, P.E.

Lubrizol Advanced Materials, Inc. 9911 Brecksville Road Cleveland, OH 44141

© 2010, The Lubrizol Corporation. All rights reserved.

Carbosperse™ K-700

Water Treatment Polymers

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Abstract

Controlling silica-silicate fouling in industrial water systems operating with high silica containing feed waters is very challenging and requires non-conventional deposit control agents. Several laboratory evaluations were conducted to better understand the performance of a new polymeric silica-silicate deposit control agent. The suitability of the new polymer for use in high temperature applications as silica polymerization inhibitor and particulate dispersant (e.g., silica, magnesium silicate, iron oxide, clay) is evaluated by efficacy testing after polymer exposure to thermal stress. Keywords: silica polymerization, inhibition, particulate matter, iron oxide, clay, silica, magnesium silicate, dispersion, fouling, thermal stability.

Introduction

Silica and silicate-based scaling that occurs in industrial water systems associated with the use of silica-laden feed waters poses significant technical and operational challenges. The systems affected by silica and silicate-based systems include cooling, reverse osmosis (RO) process, and geothermal. The commonly occurring scales are amorphous silica, calcium silicate, magnesium silicate, iron silicate, etc. These deposits generally accumulate on RO membrane and heat exchanger surfaces, pipes, pumps, and other equipment surfaces reducing heat transfer and RO membrane performance as well as causing increased operating costs, premature equipment replacement, etc. In evaporative cooling systems, water technologists must maintain silica at acceptable levels (usually <180 mg/L in absence of silica/-silicate control agents) to avoid the formation silica-based deposits. This requires (a) operating systems at low cycles of concentration which increases water consumption and/or (b) the incorporation of silica-silicate control agents in the water treatment programs. In geothermal applications, silica-scale formation typically occurs when brine is cooled in the course of brine handling and energy extraction. Factors contributing to of silica-based deposits include variable fluid compositions, fluctuating plant operating conditions, and the complex nature of silica polymerization reaction collectively contribute to silica-silicate fouling problem. The composition and the amount of silica scale as well as the rate at which it forms is dependent upon factors including mineral concentration of feed water, pH, temperature, flow velocity, metallurgy, and system pressure.1,2 Once formed, silica-silicate based deposits are particularly difficult to remove from industrial water systems. Both chemical and mechanical methods are used to remove silica-silicate based deposits. However, strong chemical cleaners (e.g., ammonium bifluoride, hydrofluoric acid) pose environmental challenges and require care to avoid damaging equipment whereas mechanical cleaning is labor intensive. Over the years, a variety of approaches have been proposed to combat silica-silicate fouling in industrial water systems. These methods fall into six (6) categories: 1) Operating systems at low silica-silicate supersaturation. 2) Reducing silica concentration by precipitation processes in feed water. 3) Using additive(s) to prevent silica polymerization. 4) Inhibiting metal-silicate precipitation.

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5) Incorporating additive(s) into water treatment programs to disperse silica-silicate deposits. 6) Effective control of other scales such as calcium carbonate to minimize the incorporation of

silica species in crystal matrix. The success of each method depends on the feed water chemistry, system design, and operating conditions. Although operating systems at low supersaturation levels is a common practice, this approach may not be feasible due to water consumption costs and/or water scarcity. The second approach to minimize silica-based fouling involves reducing system silica concentrations by pre-treating feed water. Commonly used chemicals for silica removal include polyvalent metal hydroxides, i.e., Al(OH)3, Fe(OH)3, and Mg(OH)2. It has been reported that these chemicals effectively remove both soluble and colloidal silica.3 In addition, the amount of hydroxide required for removing silica increases but not in direct proportion with increasing silica concentrations. Various processes involved in silica removal include chemical reaction and/or adsorption. The third approach or controlling silica fouling involves the use of additives that effectively inhibit silica polymerization in aqueous solutions. Neofotistou and Demadis4 in their study on the evaluation of polyaminoamide-based dendrimers as silica inhibitors for cooling water applications reported that polymer performance as silica polymerization inhibitor strongly depends on the branching present in the dendrimer. Amjad and Yorke5 reported that cationic-based copolymers are effective silica polymerization inhibitors. Similar conclusions were also reported by Harrar, et al.6 in their investigation on the use of cationic polymers and surfactants in inhibiting silica polymerization under geothermal conditions. Although these cationic-based homo- and co-polymers showed excellent silica polymerization inhibition, they exhibited poor silica-silicate dispersing activity. The use of boric acid and/or its water soluble salts to control silica-based deposits in cooling water systems operating at 250 to 300 mg/L silica has been reported. Silica inhibition presumably originates from the ability of borate to condense with silicate to form borate-silicate complexes which are more soluble than silica.7 The use of borate-based inhibitors to increase silica solubility is limited because of the high use levels for boron-based compounds as well as the associated costs and environmental impacts (effluent discharge limitations on boron). Another approach that has been used for minimizing silica-silicate fouling industrial water system involves the use of polymeric dispersants that impart negative charge via adsorption onto suspended particles. Because most silica-based deposits consist of amorphous silica and/or magnesium silicate, the ideal candidate must have two distinct properties. It must (a) disperse both silica and magnesium silicate and (b) disperse scalant particles (e.g., calcium carbonate, calcium sulfate) that can act as nuclei for silica-silicate deposits.8 The performance of a formulated product containing hydroxyl phosphono acetic acid and a copolymer of acrylic acid:hydroxyl sulfonate ether in high hardness waters containing high alkalinity and 225 mg/L silica, has been reported.9 The inspection of the heat exchanger showed essentially no deposits in the presence of formulated product compared to heavy scaling and silicate deposits in the control (no treatment). Momazaki, et al.10 reported the use of a poly(acrylamide)–based treatment program to control silica in recirculating cooling water

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systems. Gill and coworkers,11 in a study conducted using high silica water at above pH 9, documented that a blend of phosphonate and a copolymer of acrylic acid and 2-acrylamido-2-methyl propane sulfonic acid can effectively extend the operating limits for silica from 120 to 300 mg/L. The suitability of the silica-silicate deposit control agents for use in high temperature applications is also of importance to water technologists. The effect of heat treatment on polymer performance as a scale inhibitor and dispersant has been the subject of numerous investigations. However, there is relatively little practical information available to water treatment technologists pertaining to the thermal stability of low MW polymers used in high temperature applications. Polymers used in high temperature applications should be able to sustain performance where exposed to high temperature and pressure environments associated with boiler and thermal desalination processes. McGaugh and Kottle12 studied the thermal degradation of P-AA and later the thermal degradation of an acrylic acid-ethylene co-polymer. They used infrared and mass spectrographic analysis to examine the degradation processes that occurred in several temperature regions: 25 to 150ºC, 150 to 275ºC, 275 to 350ºC, and above 350ºC. Their results in air (minimal heating) suggest that dry P-AA decomposes by forming an anhydride, probably a six-member glutaric anhydride-type structure at temperature up to 150ºC. At 350ºC there is drastic un-measurable change and strong un-saturation absorption. Mass spectrographic analysis showed that carbon dioxide was the major volatile product at 350ºC. Masler13 investigated the thermal stability of several homopolymers [i.e., polyacrylic acids (PAAs), polymethacrylic acids (PMAAs), polymaleic acid (PMAs)] used for deposit control in boiler water treatment applications. It was demonstrated that under the experimental conditions employed (pH 10.5, 250°C, 18 hr) that PAA, PMAA, and PMA all underwent some degradation. In terms of molecular weight (MW) loss, PMAA lost slightly less MW than PAA which lost considerably less than PMA. Additionally, PAA and PMAA had minimal performance changes whereas PMA displayed a substantial loss in performance. Several years later, Zuhl and Amjad14 using a similar test method showed that polymer performance as dispersants of hydroxyapatite and iron oxide is affected both by temperature level and exposure time. More recently, Amjad and Zuhl15 reported that heat treatment has a significant effect on a polymer’s inhibitory properties. Heat treatment of co- and ter-polymers has been shown to cause (a) a decrease calcium phosphate inhibition and (b) a slight increase calcium carbonate inhibition. It is generally understood that exposing deposit control polymers to thermal stress causes varying degrees of performance loss depending up the temperature, exposure time, pH, concentrations, and the presence of oxidizing agents. Although, the mechanisms of silica-silicate inhibition, deposition, dispersion, etc., have been studied in great depth, no unified understanding of various processes involved in silica-silicate deposition has been fully developed. In previous papers, we reported the results of laboratory experiments designed to determine the efficacy of various commercially available polymeric additives touted as silica polymerization inhibitors and metal-silicate dispersants.16 It was shown that acrylic acid based homo- and co-polymers commonly used as deposit control agents are ineffective as silica polymerization inhibitors. The results of earlier studies also reveal that low level of metal ions (e.g., Al, Fe, cationic polymeric flocculant) exhibit marked adverse effects on silica inhibiting polymer performance.17

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It is generally accepted that lowest limit of amorphous silica saturation level in industrial water systems is ≈1.2x. Based on the previously published data, it can be assumed that a conservative maximum treated silica saturation level in cooling water systems is ≈2.2x. In the present study, for the purposes of evaluating silica polymerization inhibitors, we selected a more challenging water chemistry with a silica saturation level extended to 3.0x. The present study is primarily concerned with the thermal stability of commercially available silica-silicate deposit control agents. Polymers were exposed to high temperatures (i.e., 110 to 300ºC) and then evaluated for their efficacy as silica polymerization inhibitors and particulate (e.g., silica, magnesium silicate, iron oxide, and kaolin clay) dispersants. It is hoped that the data presented in this paper will enable the water technologists to select polymers that meet treatment program objectives for systems operating under stressed conditions (high pH, high temperature, high silica supersaturation, etc.).

Experimental

Reagent grade chemicals and distilled water were used throughout the study. Silica stock solutions were prepared from sodium metasilicate, standardized spectrophotometrically, and stored in polyethylene bottles. Calcium chloride and magnesium chloride solutions were prepared from calcium chloride dihydrate and magnesium chloride hexahydrate, and were standardized by titrating with standard ethylenediammine tetraacetic acid. Table 1 summarizes the descriptions, compositions, and acronyms of the polymeric commercially available additives evaluated in the present study including a new proprietary copolymer blend (CP7 or Carbosperse™ K-XP229 copolymer). The results herein are reported on a 100% active inhibitor basis. Polymer Heat Treatment Polymer solutions were prepared containing 10% polymer (as active solids) at pH 10.5 using sodium hydroxide to neutralize the polymer. Sodium sulfite was added as an oxygen scavenger. A known amount of polymer solution was retained for characterization and performance testing. The balance was charged to a stainless steel tube. The headspace was purged with nitrogen followed by tightening the fittings. The tube was then placed in the oven maintained at the required temperature [either 110ºC (35.5 psig), 150ºC (84 psig), 200ºC (241 psig), 250ºC (390 psig), or 300ºC (1,271 psig)]. After 20 hr, tubes were removed from the oven, cooled to room temperature, and the solutions transferred to vials for characterization and performance testing.

Silica Polymerization Inhibition Test Method Reagent grade chemicals and distilled water were used in accordance with Lubrizol’s “Silica Polymerization Inhibition Test Procedure,”18 schematically shown and discussed below.

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Silica Polymerization Inhibition Experimental Protocol

Distilled Water + Sodium Silicate

+ Inhibitor Solution

Adjust to pH 7.0

Calcium and

Magnesium Solution

Re-Adjust to pH 7.0

Sample and Filter through 0.22 micron

Analyze for SiO2

Silica polymerization experiments were performed in polyethylene containers placed in double-walled glass cells maintained at 40ºC. The supersaturated solutions were prepared by adding known volumes of stock solution of sodium silicate (expressed as SiO2) solution and water in polyethylene containers. After allowing the temperature to equilibrate, the silicate solutions were quickly adjusted to pH 7.0 using dilute hydrochloric acid [HCl]. The pH of the solutions was monitored using Brinkmann/Metrohm pH meter equipped with a combination electrode. The electrode was calibrated before each experiment with standard buffers. After pH adjustment, a known volume of calcium chloride and magnesium chloride stock solution was added to the silicate solutions. The supersaturated silicate solutions were re-adjusted to pH 7.0 with dilute HCl and/or NaOH and maintained constant throughout the silica polymerization experiments. Experiments involving inhibitors were performed by adding inhibitor solutions to the silicate solutions before adding the calcium chloride and magnesium chloride solution. The reaction containers were capped and kept at constant temperature and pH during the experiments. Silicate polymerization in these supersaturated solutions was monitored by analyzing the aliquots of the filtrate from 0.22-µm filter paper for soluble silica using the standard colorimetric method.18 The silicate polymerization inhibition values were calculated according to the following equation: [SiO2] sample --- [SiO2] blank

%SI = ------------------------------------------- x 100% [SiO2] initial --- [SiO2] blank

Where:

SI = Silica Inhibition (%) or %SI [SiO2] sample = Silica concentration in the presence of inhibitor at 22 hr

[SiO2] blank = Silica concentration in the absence of inhibitor at 22 hr [SiO2] initial = Silica concentration at the beginning of experiment Particulate Dispersion Test Methods Particulate dispersion experiments for silica, magnesium silicate, iron oxide, and kaolin clay were conducted in accordance with test procedures described previously.16 All the particulate matter used in the present study were commercial materials. Polymer performance as a particulate suspension dispersants was studied by monitoring transmittance (%T) readings at known time (“t”) intervals were taken using a colorimeter (Brinkmann PC/910) equipped with a 420 nm filter. The results as “% dispersed” (%D) were calculated from “%T” readings as a

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function of particulate matter dispersed compared to a control (experiment run without dispersant). Therefore, greater dispersion was indicated by higher %D values. The %D was calculated using the following equation: % Dispersed (%D) = (100 – [Te x (1/%Tc) x 100]) Where:

%Te = Percent transmittance of the experimental solution in the presence of dispersant at time “t”

%Tc = Percent transmittance of the experimental solution in the absence of dispersant at time “t” (control)

Results and Discussion

Silica Polymerization Inhibition

Polymer Concentration Effect As discussed in previous papers,16, 17, 19, 20 it is very important to understand the relationship between polymer dosage and silica polymerization inhibitor performance particularly at the high silica saturation level (3.0x) test conditions. Figure 1 shows silica concentration as a function of time at varying CP6 dosages (as active polymer) and indicates (a) that CP6 dosage strongly affects silica polymerization inhibitor performance and (b) that both 50 and 75 ppm CP6 dosages provide similar performance. The “silica conc.” (soluble silica) values for CP6 in Figure 1 converted to “% silica inhibition” values are summarized in the table below and indicate that the inhibitory effect of CP6 increases dramatically as dosage increases to 50 ppm and incrementally improves thereafter:

CP6 Dosage: 15 ppm 25 ppm 50 ppm >75 ppm

Silica Inhibition: 14% 52% 84% >90%

Performance Assessment: Poor Fair Excellent Excellent

Polymer Composition Effect

Our most recent AWT paper16 presents silica polymerization performance data for a wide variety of polymers (containing different functional groups) at both 25 and 350 ppm dosages. The previously published data clearly indicate that several representative well known homopolymers (P1 and P3) and copolymers (CP1, CP2, CP3, & CP5) used in water treatment programs as deposit control agents for mineral scales and suspended matter are poor (<10% inhibition) silica polymerization inhibitors whereas copolymer blends CP6 and CP7 provide significantly better (>90% inhibition) performance. These and other data led us to conclude that polymer composition is the most significant factor explaining the performance differences we observed; the compositions for C6 and CP7 contain <50% carboxylic monomer groups whereas the composition for all polymers (e.g., P1, P3, CP1, CP2, CP3, CP4, & CP5) tested are dominated (>50%) by carboxylic monomer groups. The thermal stability of the deposit control polymers is an important consideration in several types of industrial water systems including geothermal plants, boilers, and high temperature

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cooling water systems were silica and/or silicate deposit may occur. In an earlier paper,19 we reported the effects of thermal treatment (i.e., a variable temperature [150, 200, and 230ºC], pH 10.5, and 20 hr) on the silica polymerization inhibition performance of the polymers herein designated as P3, CP3, CP5, and CP6. The results of that study clearly show that the polyacrylate (P3) and copolymers CP3 and CP5 (promoted as silica-silicate deposit control agents) performed poorly (<5% inhibition) as silica polymerization inhibitors when exposed to 150 and 200ºC whereas CP6 retained >95% of is performance (vs. no thermal stress). In this study, to understand the impact of thermal treatment on the performance of CP7 as well as the other polymers discussed, we conducted a series of experiments involving exposing the polymer to thermal stress (variable temperature [200, 230, 250, and 300ºC], pH 10.5, and 20 hr) before evaluating the silica polymerization inhibitor performance. Figure 2 presents comparative silica polymerization inhibition data before and after thermal stress at 50 ppm polymer dosages. Figure 2 silica polymerization inhibition data for polymers in the absence of thermal stress show that the copolymer blends (i.e., CP6 & CP7) are effective but the other polymers evaluated are ineffective inhibitors under the high silica saturation level (3.0x) test conditions. More specifically the %SI values obtained for the homo- (i.e., P1 & P3) and copolymers (i.e., CP2, CP3, & CP5) are <20% compared to >80% obtained for the copolymer blends (CP6 & CP7). These data clearly show that the deposit control polymers containing greater than 50% carboxylic acid monomer groups (i.e., P1, P2, CP2, CP3, & CP5) exhibit poor performance as silica polymerization inhibitors. By contrast, the copolymer blends (CP6 and CP7) that contain less than 50% carboxylic acid monomer groups are significantly better silica polymerization inhibitors and a significant improvement over current silica inhibitor technology. Figure 2 silica inhibition data for polymers after thermal stress indicate the following: 1) The homopolymers (P1 & P3) and copolymers (CP2, CP3, & CP5) are ineffective (<10%)

silica polymerization inhibitors. 2) The two copolymer blends (CP6 & CP7) are very effective (≈80%) silica polymerization

inhibitors after thermal stress at 200ºC. 3) Thermal stress above 230ºC for CP6 causes a significant reduction performance. 4) Thermal stress above 250ºC for CP7 causes a reduction in performance. However, the

silica polymerization inhibition values for CP7 after thermal stress at 250 and 300ºC were greater than 70% and greater than 60%, respectively.

Figure 3 takes a closer look at the silica polymerization inhibition performance of CP6 and CP7 after thermal stress as a function of polymer dosage in the range of 10 to 50 ppm. The post thermal stress results shown in Figure 3 indicate that (a) both CP6 and CP7 experience a modest (<15%) performance reduction (suggesting some degradation of the polymer functional groups) and (b) CP7 is a more effective silica polymerization inhibitor than CP6 at lower dosages both before and after thermal stress. Collectively, the results discussed above and data shown in Figures 2 clearly show that CP7 is a superior silica polymerization inhibitor over a wide range of dosages and after thermal stress. Thus, CP7 because of its superior thermal stability at high temperature may be a suitable candidate for high temperature silica control applications.

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Suspended Matter Dispersion Effective silica-silicate control agents must provide a combination of (a) silica polymerization inhibition and (b) dispersion of silica-silicate based colloidal and/or particulate matter. Accordingly, the following sections present screening test data for a several copolymers and copolymers blends as particulate matter (silica, magnesium silicate, iron oxide, and kaolin clay) dispersants.

Silica Dispersion

As previously discussed, the composition and quantity of a silica deposit and the rate at which it forms is dependent on pH, temperature, the ratio and concentration of calcium and magnesium, and the concentration of other polyvalent ions in the water. It has also been reported that polymerized colloidal silica in the presence of polyvalent metal ions forms flocculated silica. These precipitates can deposit on heat exchanger and RO membrane surfaces resulting in poor system performance. Figure 4 presents silica dispersion data in the presence of 1.0 ppm polymer dosages both before and after exposure to thermal stress. The polymers in the absence of thermal stress (at 23ºC) disperse silica to varying degrees and polymer performance strongly depends on the polymer architecture. The new silica-silicate deposit control agent (CP7) provides silica dispersion comparable to the best copolymers tested herein (i.e., CP2 and CP3).

Figure 4 also shows the influence of thermal stress on the silica dispersion performance of all polymers as evaluated under standard test conditions. All polymers incrementally lose dispersing activity depending upon the polymer architecture and the thermal stress. After exposure to 250ºC thermal stress, CP3, CP5, and CP7 provide comparable silica dispersion performance in the range of 40 to 45%.

Magnesium Silicate Dispersion

The precipitation and deposition of magnesium silicate on equipment surfaces poses serious operational problems in industrial applications (e.g., recirculating cooling water systems, geothermal plants, closed engine cooling systems) containing high silica and magnesium. It is well documented that several magnesium silicate salts can potentially precipitate out in aqueous systems depending on various factors including pH, temperature, magnesium, and silica concentration, etc. Several investigators have reported that acrylic-acid containing copolymers and non-polymeric additives such as borate compounds inhibit silica polymerization/precipitation. However, no proven technology exists for the control of magnesium silicate (except pH and concentration control). It is well known that the magnesium silicate system is very pH dependent. Below pH 7, magnesium silicate precipitation does not occur because silica is present essentially in an un-ionized form. As the solution pH is increased (especially, above pH 9), magnesium silicate is very likely to form. In addition, the magnesium silicate system is very complicated due to various species of different compositions that can precipitate depending on the water chemistry (Mg, SiO2, pH, temperature, etc.).

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Figure 5 presents magnesium silicate dispersion data collected under standard test conditions for various polymers (e.g., 2.5 ppm polymer dosages) both before and after exposure to thermal stress. The data in the absence of thermal stress (at 23ºC) indicate magnesium silicate dispersion performance varies with polymer architecture. Furthermore, the new silica-silicate deposit control agent (CP7) provides the best magnesium silicate dispersion among the copolymers tested which in order of performance (highest to lowest) were as follows:

CP7 > CP2 > CP1 > CP3 > CP6 > CP5. The impact of thermal stress on the performance of polymers as magnesium silicate dispersants was investigated. Figure 5 presents comparative performance data. Observations include: 1) All polymers lose efficacy to varying degrees as magnesium silicate dispersants as the

thermal stress increases from 110 to 250ºC. 2) CP5 provides the lowest performance before and after exposure to thermal stress. 3) CP3 and CP5 (copolymers promoted as silica-silicate deposit control agents) experience

the greatest performance loss when thermal stress increases from 200 to 250ºC. 4) CP7 provides the best thermal stress tolerance profile among the copolymers tested.

Iron Oxide Dispersion

Figure 6 shows the iron oxide dispersion by several copolymers and copolymer blends both before and after exposure to thermal stress as determined by a Lubrizol’s standard test method (conditions include synthetic water, pH 7.6, 200 ppm iron oxide, 1 ppm dispersant).21 We also evaluated the impact of increasing polymer dosage above 1 ppm. Based on the data presented in Figure 6 (see “23ºC @ 1 ppm” and “23ºC @ 2 ppm”) and data for other experiments not shown herein for brevity, we conclude: 1) Polymer performance profiles vary as a function of dosage. As a general rule, polymer

type and architecture are the most significant factors impacting performance with the greatest performance increases occurring when dosages are increased from 1 to 2 ppm and incremental if any performance improvements with dosage increases above 2 ppm.

2) All copolymers except CP5 and CP1 provide greater than 70% dispersion at 1 ppm dosages.

3) Increasing copolymer dosages from 1 to 2 ppm improves performance to varying degrees. a) All but CP5 provided excellent (>80%) iron oxide dispersion. b) CP7 and CP3 display comparable performance and improvement with dosage.

The impact of thermal stability on the polymer performance as iron oxide dispersants was evaluated by conducting several experiments under similar experimental conditions. Figure 6 also shows the comparative data for polymers after thermal exposure (@ 110, 150, and 200ºC). It can be seen that all copolymers lose efficacy to varying degrees depending on the polymer architecture and the thermal treatment. The data indicate that exposing the polymers to 110ºC causes insignificant (<10%) iron oxide dispersion performance loss suggesting minimal degradation of the functional groups and/or the loss in molecular weight. However, the situation was much different when the polymers were exposed to higher temperatures. Increasing the thermal stress to 200ºC causes all the polymers tested to lose some (from ≈5 to 60%) of their activity as iron oxide dispersants. It is evident CP7 outperformed and is a significant improvement to all the polymers investigated.

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Kaolin Clay Dispersion Kaolin clay dispersion by various polymers was investigated by carrying out several experiments under standard test conditions. Figure 7 presents clay dispersancy data in the presence of 10 ppm polymer dosages both before and after exposure to thermal stress. The data prior to thermal stress (23ºC) indicate good to excellent performance depending upon the polymer architecture and suggest the following: 1) The clay dispersion provided by CP1 and CP3 are comparable and better than that for CP5

and CP6 which are very similar. 2) CP2 and CP7 provide the best and comparable clay dispersion performance. Based on Figure 7 data, observations for polymers exposed to thermal stress up to 200ºC include: 1) All polymers lose dispersing activity dependent upon the polymer architecture and the

thermal stress. In general, dispersancy activity reductions after 200 ºC thermal stress vary from 5 to 40%.

2) CP7 as a clay dispersant after exposure to 200ºC thermal stress outperforms CP1, CP3, and CP6 and is comparable to the performance of both CP2 and CP5.

Summary

When evaluating silica-silicate deposit control agents, water technologists should take several performance properties into consideration including scale inhibition (e.g., silica polymerization inhibition), particulate dispersion (e.g., silica, magnesium silicate, iron oxide, and clay dispersion), and deposit control agent thermal stability. Exposing deposit control polymers to thermal stress causes varying degrees of performance loss depending upon several factors including the test conditions. The performance data presented herein have clearly shown that a new copolymer blend CP7 is a superior silica polymerization inhibitor, excellent particulate dispersant, and is resistance to performance loss caused by thermal stress.

Acknowledgements

The authors would like to thank Tina Dame for preparation of thermally treated polymer samples and The Lubrizol Corporation for supporting the research and allowing us to present the findings at the Association of Water Technologies’ Annual Convention.

References

1. P. P. Nicholas and Z. Amjad “Method for Inhibiting and Deposition of Silica and Silicate

Compounds” U. S. Patent No. 5,658,465 (1997). 2. K. D. Demadis, A. Stathoulopoulou, and A. Ketsetzi, “Inhibition and Control of Colloidal

Silica: Can Chemical Additives Untie the Gordian Knot of Scale Inhibition?” Paper No. 07058, CORROSION/2007, NACE International, Houston, TX (2007).

3. R. Sheikholeslami, I. S. Al-Muteaz, A. Tan, and S. D. Tan, “Some Aspects of Silica

Polymerization and Fouling and its Pretreatment by Sodium Aluminate Lime, and Soda Ash,” Desalination, 150, 85-92 (2002).

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4. E. Neofotisou and K. D. Demadis, “Use of Antiscalants for Mitigation of Silica Fouling and

Deposition: Fundamentals and Applications in Desalination Systems,” Desalination, 167, 257-272 (2004).

5. M. Yorke and Z. Amjad, “Carboxylic Functional Polyampholytes as Silica Polymerization

Inhibitors,” U.S. Patent No. 4,510,059 (1985). 6. J. E. Harrar, L. E. Lorensen, and F. E. Locke, “Method for Inhibiting Silica Precipitation

and Scaling in Geothermal Flow Systems,” U.S. Patent No. 4,328,106 (1982). 7. L. Dubin, “Silica Inhibition: Prevention of Silica Deposition by Boric Acid/Orthoborate Ion,”

U.S. Patent No. 4,584,104, 1986. 8. C. Smith, “Usage of Polymeric Dispersant for Control of Silica,” Industrial Water

Treatment, 20-24, July/Aug (1993). 9 L. A. Perez, J. M. Brown, and K. T. Nguyen, “Method for Controlling Silica and Water

Soluble Silicate Deposition,” U.S. Patent No. 5,256,302 (1993). 10. K. Momozaki, M. Kira, Y. Murano, M. Okamoto, and F. Kawamura, “Polyacrylamide

Based Treatment Program for Open Recirculating Cooling Water System with High Silica Content,” Paper No. 92-11, International Water Conference, Pittsburgh, PA (1992).

11. J. S. Gill, “Inhibition of Silica-Silicate Deposit in Industrial Water,” Colloids and Surfaces

A: A Physicochemical and Engineering Aspects,” 74 101-106 (1993). 12. M. C. McGaugh and S. Kottle, “The Thermal Degradation of Poly(acrylic acids),” Polym.

Lett 5, 817 (1967). 13. W. F. Masler, “Characterization and Thermal Stability of Polymers for Boiler Treatment,”

43rd Annual Meeting, International Water Conference, Pittsburgh, PA, October (1982). 14. R. W. Zuhl and Z. Amjad, “The Role of Polymers in Water Treatment Applications and

Criteria for Comparing Alternatives,” Association of Water Technologies 1993 Annual Convention, Las Vegas, NV, November (1993).

15. Z. Amjad and R. W. Zuhl, “The Impact of Thermal Stability on the Performance of

Polymeric Dispersants for Boiler Water Systems,” Association of Water Technologies, 2005 Annual Convention, Palm Springs, CA, September (2005).

16. Z. Amjad and R. W. Zuhl, “Silica Control in Industrial Water Systems with a New

Polymeric Dispersant,” AWT 2009 Annual Convention, Hollywood, FL, August (2009). 17. Amjad and R. W. Zuhl, “The Role of Water Chemistry on Preventing Silica Fouling in

Industrial Water Systems,” Paper No. 10048, CORROSION/2010, NACE International, Houston, TX (2010).

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18. “Silica Polymerization Inhibition Test Procedure,” Lubrizol technical bulletin Silica-PITP, Oct-2007.

19. Amjad and R. W. Zuhl, “An Evaluation of Silica Scale Control Additives for Industrial

Water System,” Paper No. 08368, CORROSION/2008, NACE International, Houston, TX (2008).

20. Z. Amjad and R. W. Zuhl, “Laboratory Evaluation of Process Variables Impacting the

Performance of Silica Control Agents in Industrial Water Treatment Programs,” AWT 2008 Annual Convention, Austin, TX, November (2008).

21. Z. Amjad, “Dispersion of Iron Oxide Particles in Industrial Waters,” Tenside Surfactants and Detergents, 36, 50-56 (1999).

Table 1: Polymeric and Non-Polymeric Additives Evaluated

Additive Composition Acronym

P-MA <2k MW poly(maleic acid) # P1

K-732* 6k MW poly(acrylic acid) # P3

K-775* <15k MW poly(acrylic acid: 2-acrylamido-2-methylpropane sulfonic acid) #

CP1

K-798* <15k MW poly(acrylic acid: 2-acrylamido-2-methylpropane sulfonic acid: sulfonated styrene) #

CP2

CCP-D** 5k MW poly(acrylic acid: 2-acrylamido-2-methylpropane sulfonic acid: non-ionic) #

CP3

CCP-A** Proprietary acrylic copolymer # CP5

K-XP212* Proprietary copolymer blend CP6

K-XP229* New proprietary copolymer blend CP7

Notes: MW = Weight average molecular weight. * Carbosperse™ K-700 polymer supplied by Lubrizol Advanced Materials, Inc. ** “CCP” = Competitive copolymer promoted as silica-silicate deposit control agent. # Polymer containing >50% carboxylic monomers.

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Figure 1: Silica Polymerization vs. Time

as a Function of CP6 Dosage (ppm)

0

100

200

300

400

500

600

0 5 10 15 20 25Time (hr)

Sil

ica

Co

nc

. (m

g/L

)

0 ppm 15 ppm 25 ppm 50 ppm 75 ppm

(550 mg/L silica, 200 mg/L Ca, 120 mg/L Mg, pH 7.0, 40ºC)

Figure 2: Silica Polymerization Inhibition by Polymers

as a Function of Thermal Stress

0

20

40

60

80

100

P1 P3 CP2 CP3 CP5 CP6 CP7

% S

ilic

a In

hih

itio

n

23ºC 200ºC

230ºC 250ºC

300ºC

(550 mg/L silica, 200 mg/L Ca, 120 mg/L Mg, pH 7.0, 40ºC, 50 ppm polymer)

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Figure 3: Silica Polymerization Inhibition as a Function

of Polymer Thermal Stress & Dosage

0

20

40

60

80

100

0 10 15 25 35 50

Polymer Dosage

% S

ilic

a In

hib

itio

n

CP6 @ 23ºC

CP6 @ 200ºC

CP7 @ 23ºC

CP7 @ 200ºC

(550 mg/L silica, 200 mg/L Ca, 120 mg/L Mg, pH 7.0, 40ºC)

Figure 4: SiO2 Dispersion by Polymers vs. Thermal Stress

(600 mg/L SiO2, 105 mg/L Ca, 31 mg/L Mg, 353 mg/L Na, 600 mg/L Ca,

202 mg/L SO4, 58 mg/L HC03, pH 7.6, 1 ppm polymer, 5 hr)

0

10

20

30

40

50

60

70

CP1 CP2 CP3 CP5 CP6 CP7

% S

iO2 D

isp

ers

ed

23ºC

110ºC

150ºC

200ºC

250ºC

15/16

Figure 5: MgSiO3 Dispersion by Polymers vs. Thermal Stress

(1,500 mg/L MgSiO3, 105 mg/L Ca, 31 mg/L Mg, 353 mg/L Na, 600 mg/L Cl,

202 mg/L SO4, 58 mg/L HCO3, pH 7.6, 2.5 ppm polymer, 2 hr)

0

10

20

30

40

50

60

CP1 CP2 CP3 CP5 CP6 CP7

% M

gS

iO3 D

isp

ers

ed

23ºC

110ºC

150ºC

200ºC

250ºC

Figure 6: Fe2O3 Dispersion by Polymers vs. Thermal Stress

(200 mg/L Fe203, 1 or 2 ppm polymer, 3 hr, pH 7.6, 100 mg/L Ca,

30 mg/L Mg, 671 mg/L SO4, 60 mg/L HCO3)

0

10

20

30

40

50

60

70

80

90

100

CP1 CP2 CP3 CP5 CP6 CP7

% F

e20

3 D

isp

ers

ed

23ºC @

1 ppm

23ºC @

2 ppm

110ºC @

1 ppm

150ºC @

1 ppm

200ºC @

1 ppm

16/16

Figure 7: Clay Dispersion by Polymers vs. Thermal Stress (100 mg/L clay, 105 mg/L Ca, 31 mg/L Mg, 353 mg/L Na, 600 mg/L Cl,

209 mg/L SO4, 116 mg/L HCO3, pH 7.6, 10 mg/L polymer, 3 hr)

0

10

20

30

40

50

60

70

80

90

CP1 CP2 CP3 CP5 CP6 CP7

% C

lay D

isp

ers

ed

23ºC

110ºC

150ºC

200ºC

Lubrizol Advanced Materials, Inc. • Cleveland, OH 44141-3247, U.S.A.

Phone: 1-800-380-5397 or 216-447-5000 FAX: 216-447-6315 (USA Customer Service) 216-447-5270 (International Customer Service) 216-447-5238 (Marketing & Technical Service)

http://www.carbosperse.com

Oct-2010(29-Jul-2011)

The information contained herein is believed to be reliable, but no representations, guarantees or warranties of any kind are made to its accuracy, suitability for particular applications, or the results to be obtained therefrom. The information is based on laboratory work with small-scale equipment and does not necessarily indicate end product performance. Because of the variations in methods, conditions and equipment used commercially in processing these materials, no warranties or guarantees are made as to the suitability of the products for the application disclosed. Full-scale testing and field application performances are the responsibility of the user. LUBRIZOL ADVANCED MATERIALS, INC. shall not be liable for and the customer assumes all risk and liability of any use or handling or any material beyond LUBRIZOL’s direct control. The SELLER MAKES NO WARRANTIES, EXPRESS OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANT ABILITY AND FITNESS FOR A PARTICULAR PURPOSE. Nothing contained herein is to be considered as permission, recommendation, nor as an inducement to practice any patented invention without permission of the patent owner.

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