AWT-Oct-13 Paper No. 201331

Association of Water Technologies 2013 Annual Convention & Exposition

Mohegan Sun, Uncasville, CT October 30 to November 2, 2013

The Impact of Thermal Stress on Deposit Control Polymer Performance

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

Lubrizol Advanced Materials, Inc. (Cleveland, OH 44141)

and

John F. Zibrida, ZIBEX, Inc. (Duluth, GA)

© 2013, The Lubrizol Corporation. All rights reserved.

Carbosperse™ K-700

Water Treatment Polymers

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Abstract

Deposit control polymers (DCPs) are critical components of successful water treatment programs. DCPs function as scale inhibitors, crystal modifiers, and dispersants thereby modifying precipitated solids so they are more readily kept in suspension and less likely to adhere to equipment surfaces. DCPs used as components of boiler water treatment programs should be able to sustain performance under system operating pressure and temperature environments. This study evaluates the impact of thermal stress on DCP architecture and performance. Keywords: deposit control polymers, thermal stability, molecular weight, polymer architecture, calcium carbonate inhibition

Introduction

Poor quality feedwater and inadequate treatment often lead to boiler tube failures and system breakdowns. Therefore, boiler feedwaters should be properly treated to ensure efficient operation, to minimize damage to boiler equipment, and to eliminate unforeseen production losses. The major challenges facing the water technologists seeking to provide high levels of steam purity from boilers include prevention of scale and deposit on heating surfaces; corrosion control in the boiler, steam lines, and condensate system; and minimizing carryover.1 Table 1 below presents an overview of boiler water system pressure categories, corresponding temperatures, feedwater types, and water treatment challenges.

Table 1 - Boiler Water Systems Overview

Type (psig) Temp. Feedwater Types* Water Treatment Challenges

Low Press. (<150)

<177ºC (351ºF)

SN and/or RO or

SN/RO and/or DM

Hardness- (leakage) and iron-(condensate & corrosion) based deposit control.

Corrosion control.

Shutdown & lay-up procedures.

Medium Press. (>150 and

<600)

>177ºC (351ºF)

& <251ºC (483ºF)

SN and/or RO

or SN/RO and/or DM

Hardness- (leakage) and iron-(condensate & corrosion) based deposit control.

Process contamination.

Corrosion control.

Shutdown & lay-up procedures.

High Press. (>600)

>251ºC (483ºF)

DM

Process contamination.

Corrosion control.

Shutdown & lay-up procedures. * Key to feedwater types above: SN = Softened, RO = Reverse Osmosis, DM = Demineralized Source: Reproduced from “The Impact of Thermal Stability on the Performance of Polymeric Dispersants for Boiler Water Systems,” AWT 2005 Annual Conference Paper.

Boiler water treatment (BWT) programs2 incorporate a variety of additives to achieve the following desired performance objectives of boiler systems:

Scale inhibitors [e.g., poly(acrylic acid), poly(maleic acid)] are used to prevent precipitation of scale forming salts on heat transfer surfaces, economizers, pumps, etc.

Polymeric dispersants/sludge conditioners are employed to condition and render sludge non-adherent to boiler surfaces so that it can be easily removed via blowdown.

Boiler corrosion control is achieved by eliminating dissolved oxygen, increasing alkalinity, and prevent under deposit control by incorporating specific additives in formulations.

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Boiler condensate control is generally achieved by adjusting feedwater pH and adding neutralizing and filming amines to steam and condensate lines.

A variety of water treatment programs have been developed to treat boiler systems3 including precipitation (carbonate cycle, phosphate cycle, and coordinated phosphate), chelant, and all polymer, which we previously discussed.4 The deposit control agents used as components of BWT programs have multi-functional roles including sludge conditioning, particulate dispersion, and hardness stabilization. Historically, a variety of DCPs has been used as components of BWT programs as described in Table 2 below.

Table 2: Boiler Water Polymer Types

Polymer Types Examples

Natural Starches, alginates, lignins, tannins, and cellulose derivatives

Synthetic homopolymers Polyacrylates, polymethacrylates, and polymaleic acids

Synthetic copolymers of carboxylic acid monomers with a variety of other co-monomers (e.g., sulfonated monomers, substituted acrylamides)

Poly(acrylic acid: 2-acrylamido-2-methyl propane sulfonic acid) or poly(AA/SA), poly(sulfonated styrene: maleic anhydride) or poly(SS/MA), and poly(AA:SA: sulfonated styrene) or poly(AA/SA/SS)

Thermal degradation of polymers is a well-studied area. DPCs used in BWT programs should be able to sustain high temperature and pressure environments normally associated with boiler operations. Denman and Salutsky5 briefly examined the thermal stability of a sodium poly(methacrylate) under dry conditions and they found no change to 316ºC after one (1) hour but some charring at 371ºC. In 1982, Masler presented Lubrizol’s initial research efforts on the thermal stability of several homopolymers [i.e., polyacrylic acids (PAAs), polymethacrylic acids (PMAAs), polymaleic acid (PMAs)] commonly used in boiler applications.6 These homopolymers both before and after thermal stress were (a) characterized by various analytical techniques and (b) evaluated as calcium carbonate (CaCO3) inhibitors. Under the conditions employed [pH 10.5, 250ºC (594 psig), 18 hr], the PAA, PMAA, and PMA all underwent some structural changes. In terms of molecular weight (MW) loss, PMAA lost slightly less than PAA, which lost considerably less than PMA. As CaCO3 inhibitors, PAA and PMAA had minimal performance changes whereas PMA lost substantial performance. Gurkayanak et al.7 performed very short degradation tests on a 6,000 MW PAA at high temperature and different pH levels. Their study showed that the rate of decarboxylation depends upon various parameters, i.e., solution pH, ionic strength, and temperature. The thermal degradation of calcium and magnesium salts of PAA has been investigated by McNeil and Sadeghi8 whose study showed some similarities to the behavior of PMAA alkali metal

salts. Another study by Lepine and Gilbert9 on the thermal degradation of PAA between 180⁰C

and 260⁰C showed that PAA degradation follows a rather complex mechanism involving both

decarboxylation and the integrity of the polymer chain. During the last two decades we have presented work pertaining to DCP thermal stability evaluations at various technical organizations including AWT and NACE International. These studies3,4,10,11,12 showed that the performance of DCPs subjected to thermal stress is affected both by temperature level and exposure time. This paper is a continuation of Lubrizol’s efforts to understand the impact of thermal stress on DCP structure and the resulting changes in performance profiles. We specifically examined the effects of thermal stress on PAAs made by different processes, a PMAA, a PMA, acrylic acid/sulfonic acid copolymers, and acrylic

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acid/sulfonic acid/sulfonated styrene terpolymers. DCP compositions and MW were characterized and performance evaluated before and after thermal stress. The goal of the work and data presented herein is to provide industrial water technologists guidance for designing water treatment programs for high temperature applications (boilers, geothermal, oil production, and thermal distillation) where DCP thermal stability and/or performance retention is a critical criterion.

Experimental

Materials Reagent grade chemicals and grade A glassware were used. Stock solutions of calcium chloride, sodium carbonate, and sodium bicarbonate were prepared using distilled water, filtered through 0.22-micron filter paper and analyzed as described previously.3 The DCPs we evaluated are listed in Table 3. The stock DCP solutions were prepared in distilled water on an active solids basis.

Table 3: Polymers Evaluated

Product Composition MW* Acronym

K-752** Solvent polymerized poly(acrylic acid) or “SPPAA” 2k PAS1

K-7028** Water polymerized PAA or “WPPAA” 2.3k PAW1

K-732** SPPAA 6k PAS2

K-7058** WPPAA 7.3k PAW2

CPMA Poly(maleic acid) or “PMA” <1k PMA

K-766** Sodium polymethacrylate or “PMAA” 5k PMAA

K-775** Poly(acrylic acid: [2-acrylamido-2-methylpropane sulfonic acid]***) or poly(AA/SA) with 74/26 monomer weight ratio

<15k CP1

K-776** Poly(AA/SA) with 60/40 monomer weight ratio >10k CP2

K-781** Poly(AA:SA: sulfonated styrene) or poly(AA/SA/SS) <10k TP1

K-797** Poly(AA/SA/SS) <15k TP2

K-798** Poly(AA/SA/SS) <15k TP3 * MW = Molecular weight ** Carbosperse™ K-700 polymer supplied by The Lubrizol Corporation *** AMPS® monomer supplied by The Lubrizol Corporation

Polymer Thermal Stress Lubrizol’s protocol to simulate DCP thermal stress in BWT conditions was previously discussed.12 Ten percent polymer (as active solids) solution in deuterium oxide (to facilitate direct NMR analysis) was prepared by adding sodium hydroxide to pH 10.5 and sodium sulfite as an oxygen scavenger. A known amount of DCP solution was retained for characterization and performance testing. The balance of the DCP solution was charged to a stainless steel (SS) tube. The SS tube headspace was purged with nitrogen followed by tightening the fittings. The SS tube was then placed in an oven maintained at the required temperature [either 150ºC (84 psig), 200ºC (225 psig), or 250ºC (594 psig)]. After 20 hr, the SS tube was removed from the oven, cooled to room temperature, and the solution transferred to vials for DCP characterization and performance testing. Polymer Characterization DCP MWs were determined using Gel Permeation Chromatography (GPC). Nuclear magnetic resonance (NMR) spectra of DCPs before and after thermal treatment were obtained on a Bruker AV-500 NMR spectrometer at 500.13 MHz for proton detection.

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CaCO3 Inhibition Performance Testing Protocol DCP efficacy as a CaCO3 inhibitor was tested using a test procedure described previously13 and repeated herein. To a 125 mL glass bottle containing distilled water, known volumes of stock solutions of sodium bicarbonate, sodium carbonate, and polymer were added with stirring followed by the addition of a known volume of calcium chloride stock solution to create a 100 mL solution with a water chemistry as shown in Table 4 below and to which 0.25 to 5.0 mg/L active polymer was added. The bottles were capped and stored in a water bath maintained at 66°C for 24 hr. The progress of precipitation process was determined by titrating the filtered (0.22 µm, Millipore Corporation) aliquot of the test solution with standard EDTA solution for calcium ion concentration.

Table 4: Calcium Carbonate Inhibition Test Conditions

Parameter mg/L Parameter Value

Calcium (Ca2+) 560 as CaCO3 Calcite saturation (LSI) 56x (1.89)

Bicarbonate (HCO3)- 630 as CaCO3 pH ≈8.3

Carbonate (CO3)2- 30 as CaCO3 Temperature 66ºC

Active polymer 0 to 5.0 Time 24 hr

Polymer efficacy as a CaCO3 inhibitor was calculated using the Equation 1 below:

% Inhibition =

[ Ca2+] sample – [Ca2+] control

[Ca2+] initial – [Ca2+] control

x 100

(1)

Where the terms in Equation (1) above are as follows:

Inhibition (%) = %I

[Ca2+] sample = Ca2+ concentration in the presence of inhibitor at the end of the test

[Ca2+] control = Ca2+ concentration in the absence of inhibitor at the end of the test

[Ca2+] initial = Ca2+ concentration at the beginning of the test

Results and Discussion

Polymer Characterizations All DCPs (both synthetic and natural) undergo changes as a result of exposure to elevated temperature and pressure. The extent of DCP change depends upon several factors including thermal stress magnitude and duration as well as DCP composition. Our DCP sample observations before and after thermal stress include (1) DCP color intensity increased with greater thermal stress, (2) PAA & PMAA samples remained clear solutions, and (3) the PMA copolymer, and terpolymer samples became increasingly turbid and precipitate formation occurred.

Molecular Weight

MW is a key factor impacting DCP performance in industrial water systems. For example, low (<20k) MW polymers [e.g., poly(acrylic acid), acrylic acid: sulfonic), are effective scale control and dispersing agents whereas high (>100k) MW polymers are poor scale control agents but may be effective flocculants. We used an aqueous GPC method whose reproducibility is ±5% to measure DCP MW.

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Figures 1 to 5 present DCP GPC MW data as a function of thermal stress for PAW1, PMAA, and PMA, CP1, and TP1, respectively. These figures show DCP (a) MW distribution curves

before and after thermal stress at 250⁰C and (b) relative MW (weight average MW or Mw,

number average MW or Mn, and polydispersity [Mw/Mn]) as a function of thermal stress. Figures 1 and 2 depict DCP GPC MW as a function of thermal stress for PAW1 (WPPAA) and PMAA, respectively. Relatively small (<3%) MW losses are evident for both PAW1 and PMAA suggesting minimal cleaving of polymer chains.

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Figure 3 presents the PMA (polymaleic acid) GPC MW as a function of thermal stress and shows a pronounced change. Comparing Figures 1, 2, and 3 indicate that the relative MW loss for PMA is greater than for either PAW1 or PMAA.

Figures 4 and 5 show MW as a function of thermal stress for CP1 (AA/SA) and TP1 (AA/SA/SS), respectively. As indicated by the relative values, MW losses increases with

stress suggesting some scission of the polymer backbone at ≥200⁰C for both CP1 and TP1.

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Table 5 summarizes the MW losses for the DCPs listed in Table 3. Comparing the MW losses

before and after 250⁰C thermal stress for the homopolymers (PAS1, PAW1, PAS2, PAW2,

PAAP, PMAA, & PMA) leads to observations that PAA and PMAA MW losses were all <7%

whereas the PMA MW loss was ≈8%. By comparison, the MW losses due to thermal stress for

both the SA-based co- and ter-polymers were >10% at ≥200⁰C with the relative MW losses

varying depending upon the initial MW and DCP composition.

Table 5: Polymer MW Loss Caused by Thermal Stress Polymer MW loss @ 150⁰C MW loss @ 200⁰C MW loss @ 250⁰C

PAS1 1.0% 2.6% 4.3%

PAW1 0.8% 2.5% 0.6%

PAS2 0.0% 2.3% 1.2%

PAW2 0.6% 7.9% 6.8%

PMAA 1.0% 2.5% 4.0%

PMA 0.7% 1.5% 7.5%

CP1 3.3% 10.9% 12.9%

CP2 6.4% 21.2% 29.0%

TP1 3.1% 11.1% 11.5%

TP2 2.0% 13.4% 14.3%

TP3 7.7% 17.1% 18.5%

Decarboxylation

DCP scale inhibition and dispersant performance depends on DCP MW and amount and types of functional groups. DCPs containing carboxyl (-COOH) groups (e.g., PAA, PMA) exhibit excellent CaCO3, calcium sulfate, and calcium fluoride inhibition performance. DCPs

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containing bulkier, hydrophobic, and strong acidic groups provide better particulate (e.g., iron oxide) dispersion and calcium phosphate inhibition performance. DCP decarboxylation causes carboxyl content loss that decreases DCP functionality and presumably decreases associated efficacy as BWT program components. Decarboxylation has also been reported to proceed with the formation of unsaturation in the polymer backbone.14 We are currently determining the DCP carboxyl (–COOH) content loss as a function of temperature and data will be presented in a future paper.

NMR Characterization Reference proton NMR spectra were obtained for polymer samples not subjected to thermal

stress. Thermally stressed (at 150⁰C, 200⁰C, and 250⁰C) DCP samples prepared in deuterium oxide (D2O) were analyzed directly by using a proton NMR. All samples showed a partial, albeit increasing with temperature, replacement of the methyne proton [-CH(COOH)-]

backbone with its deuterated form [–CD(COOH)-] which indicates an alpha-deuteration reaction rather than DCP degradation. Figures 6 to 10 present the proton NMR spectra as a function of thermal stress for PAW1, PMAA, and PMA, CP1, and TP1, respectively. Analyses of these spectra are discussed in the following paragraphs. Figure 6 shows the PAW1 backbone methyne (CH) protons and methylene group (CH2)

protons appearing at 2.1 ppm (chemical shift) and at 1.2 to 1.9 ppm, respectively. In addition, DCP end/head groups appear unchanged at 2.8 to 3.4 ppm. The lack of new end groups indicates no MW change; an increase of type and size of end groups relative to the polymeric backbone would have been a sign of degradation. Some minor 3-hydroxypropionic acid (OH-CH2CH2-COOH) and substituted propionic acid (R-CH2CH2-COOH) small molecules that are present also deuterate in the alpha position.

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Figure 7 shows PMAA has very good stability up to 200⁰C. At 250⁰C, the methacrylic acid monomer formation suggests a small amount of polymer splitting albeit the original DCP end groups remain the same. The DCP methyl group (CH3) peaks appear at 0.8 to 1.3 ppm range while the backbone methylene group (CH2) protons appear at 1.6 to 2.2 ppm.

The commercial PMA sample MSDS indicates that this product contains about 50% PMA and low levels of monomeric maleic acid (this could also include isomeric fumaric acid) and small molecule impurities (butanedioic acid substituted with meta/paraxylene groups). These impurities probably originate during the PMA’s organic solvent manufacturing under radical initiation / polymerization conditions.

The Figure 8 PMA proton NMR spectra obtained before and after thermal stress in D2O at

150⁰C, 200⁰C, and 250°C agree with the composition above and show that the polymaleic backbone peaks decrease during thermal stress mostly due to an alpha-deuteration side reaction. The aromatic impurities are expected to undergo a similar reaction. A reduction in the PMA MW (i.e., <1,000 and 50% lower than PAS1 and PAW1 MW) via polymer chain scission is less obvious by NMR but is indicated by GPC analysis.

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Figure 8 also shows the PMA NMR spectra peak assignments. Compared to the PMAA NMR spectra, the PMA NMR spectra are much more complicated perhaps due to the presence of aliphatic and aromatic protons present in the impurities. The PMA NMR peaks in the 2.4 to 3.5 ppm range are assigned to the methyne proton [-CH(COOH)-]. The 2.3 ppm peak can be attributed to the methyl group (–CH3) present in the aromatic impurity. Similarly, peaks in the 7.0 to 7.5 ppm range can be assigned to protons present in aromatic impurity.

The Figure 9 CP1 (AA/SA copolymer) proton NMR spectra indicate stability up to 150⁰C. However, the 200°C and 250°C NMR spectra show a side chain hydrolysis of the “SA” co-monomer, resulting in a small molecule [2-amino-2-methyl-propanesulfonic acid, H2N-C(CH3)2CH2SO3H] and formation of additional poly(acrylic acid) in the backbone. At

250⁰C, this small molecule loses ammonia creating another small molecule [2-methyl-2-propenesulfonic acid, CH2=C(CH3)-CH2SO3H]. Despite these thermal stress changes, the original AA/SA copolymer end groups remain intact so that the actual copolymer length does not appear to change.

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The Figure 10 TP1 (AA/SA/SS terpolymer) proton NMR spectra show a pattern similar to CP1 in Figure 9. Above 150°C, the “SA” co-monomer side chain begins changing albeit the macromolecule size is unchanged. The “SS” component is unchanged with increasing temperature as is the case for the “AA” component including the previously described exchange of the methyne proton [-CH(COOH)-] into its deuterated form [–CD(COOH)-].

The SA-based DCPs (CP1 and TP1) compositional changes are presumably due to the hydrolysis of sulfonic acid (–SO3H) containing monomer, which is comparable to what Lubrizol and others have reported for DCPs incorporating other monomers or hydrolysable functional groups including acrylamide, tertiary butyl acrylamide, hydroxypropyl acrylate, ethyl acrylate, and other acrylate esters.

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Calcium Carbonate Inhibition CaCO3 is one of the most commonly encountered deposits in industrial water systems (e.g., boilers, cooling water, reverse osmosis). In these systems, CaCO3 may precipitate in several different forms including calcite, aragonite, vaterite, CaCO3 monohydrate, and CaCO3

hexahydrate. Among these CaCO3 polymorphs, calcite is the most thermodynamically stable form and adheres tenaciously on heat exchangers and RO membrane surfaces. CaCO3

precipitation and stabilization depends on system conditions (i.e., supersaturation level, pH, temperature, pressure, and both additive dosage and architecture).15,16

CaCO3 inhibition by the threshold mechanism is important for DCP efficacy as a component of BWT programs. In addition, DCP carboxyl content is well known to be important criteria for CaCO3 inhibitors. Thermal stress may cause changes in DCP carboxyl content that affect

performance in a static CaCO3 inhibition test at 66⁰C. If DCP carboxyl content changes occur,

it is reasonable to speculate that CaCO3 threshold inhibition performance will be impacted in boiler water systems. Therefore, Figures 11 and 12 present DCP CaCO3 inhibition as a function of thermal stress.

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Figure 11 presents CaCO3 inhibition data for homopolymers (PAAs, PMAA, and PMA) as a function of thermal stress and suggests:

Thermal stress (150⁰C, 200⁰C, or 250⁰C for 20 hr at pH 10.5) has limited adverse impact

on the CaCO3 inhibitory properties for the PAAs and PMAA.

Before thermal stress, PMA CaCO3 inhibition was slightly better than PAS1 and the best among the homopolymers but thermal stress significantly degraded PMA’s performance.

PAAs manufacturing process and MW impact CaCO3 inhibition performance. CaCO3 inhibition for SPPAAs was better than or equal to the WPPAAs of comparable MW as summarized in the table below, leading to the conclusion that lower MW PAAs provide better performance and SPPAAs provide better performance than WPPAAs.

Parameter Polymer Ranking (highest to lowest)

Molecular weight PAW2 > PAS2 > PAW1 ≈ PAS1

CaCO3 inhibition PAS1 > PAW1 > PAS2 ≈ PAW2

When comparing the CaCO3 inhibition performances for the homopolymers (i.e., PAA, PMA, and PMAA), it is important to recognize differences between the DCPs. PMA is made under different polymerization conditions, is structurally dissimilar (i.e., two carboxyl groups present on the adjacent carbon atoms compared to only carboxyl group present in the PAAs), and its MW is much lower than the other homopolymers. However, the data herein clearly indicate that PMA is not as thermally stable as either the PAAs or PMAA. PMA has previously been shown to lose carboxyl content during thermal stress and the MW loss reported herein is more than two times higher than for the PAAs and PMAA. These changes provide one explanation for the Figure 11 CaCO3 inhibition data wherein thermally stressed PMA retains less than 50% of its original (before thermal stress) inhibitory activity.

0

10

20

30

40

50

60

70

80

90

PAS1 PAW1 PAS2 PAW2 PMA PMAA

% C

aCO

3 In

hib

itio

n

Figure 11: CaCO3 Inhibition by Homopolymers vs. Thermal Stress

None (23⁰C) 150⁰C 200⁰C 250⁰C

"2k" MW PAAs "5k" MW PAAs

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Figure 12 presents CaCO3 inhibition data for copolymers (CP1 & CP2) and terpolymers (TP1, TP2, & TP3) as a function of exposure to thermal stress leading to the following observations and explanations:

CaCO3 inhibition for the AA/SA copolymers and AA/SA/SS terpolymers in the absence of thermal stress is less than for the homopolymers suggesting that both DCP carboxyl content and MW impact performance.

CaCO3 inhibition performance increases as a function of thermal stress for all the DCPs evaluated; this may be attributed to carboxyl content increases caused by possible hydrolysis of the “SA” group.

Both DCP carboxyl content and MW impact CaCO3 inhibition performance as summarized in the table below. The data suggest that the higher the carboxyl content and the lower the MW, the better the CaCO3 inhibition performance.

Parameter Copolymer Ranking Terpolymer Ranking

Carboxyl content CP1 > CP2 TP2 > TP1 ≈ TP3

Molecular weight CP2 > CP1 TP3 > TP2 > TP1

CaCO3 inhibition CP1 > CP2 TP2 > TP1 > TP3

Other Performance Testing Future investigations and technical papers will evaluate DCPs performance for other parameters before and after thermal stress.

0

10

20

30

40

50

60

70

80

90

CP1 CP2 TP1 TP2 TP3

% C

aCO

3 In

hib

itio

n

Figure 12: CaCO3 Inhibition by Copolymers vs. Thermal Stress

None (23⁰C) 150⁰C 200⁰C 250⁰C

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Conclusions

1. All polymers when subjected to the thermal stress conditions (up to 250⁰C for 20 hr at

pH 10.5) undergo some degradation or compositional changes.

2. Homopolymer molecular weight (MW) losses due to thermal stress at 250⁰C were all <8%

with PMA having the greatest MW loss.

3. The MW losses due to thermal stress for the SA-based copolymers were >11% at ≥200⁰C

and >12% at 250⁰C. CP2 (AA/SA copolymer containing 40% SA) had the highest MW loss

(>21% at ≥200⁰C).

4. Proton NMR characterizations of the thermally stressed polymers indicate the following;

a. The polyacrylates (e.g., PAW1) and PMAA showed only slight structural changes.

b. The polymaleate (PMA) showed significant structural changes which are not fully

understood.

c. The SA-based copolymers show limited structural changes below 150⁰C. However,

after thermal stress at ≥200⁰C, the SA co-monomer hydrolyzes to acrylic acid.

d. AA/SA/SS terpolymers are more thermally stable than the AA/SA copolymers.

5. Polyacrylate (PAA) manufacturing process and MW impact CaCO3 inhibition performance.

The CaCO3 inhibition for solvent polymerized PAAs (SPPAAs) was better or equal to the

water polymerized PAAs (WPPAAs) of comparable MW as summarized in the table below.

This leads to the conclusion that lower MW PAAs provide better performance and SPPAAs

provide better performance than WPPAAs.

Parameter Polymer Ranking (highest to lowest)

Molecular weight PAW2 > PAS2 > PAW1 ≈ PAS1

CaCO3 inhibition PAS1 > PWA1 > PAS2 ≈ PAW2

6. PMA’s CaCO3 inhibition before thermal stress is approximately two times higher than after

250⁰C exposure suggesting that thermal stress causes structural changes.

7. Both the carboxyl content and MW for AA/SA copolymers and AA/SA/SS terpolymers

impact CaCO3 inhibition performance as summarized in the table below. The data suggest

that higher carboxyl content and lower MW DCPs provide better CaCO3 inhibition

performance.

Parameter Copolymer Ranking Terpolymer Ranking

Carboxyl content CP1 > CP2 TP2 > TP1 ≈ TP3

Molecular weight CP2 > CP1 TP3 > TP2 > TP1

CaCO3 inhibition CP1 > CP2 TP2 > TP1 > TP3

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8. When selecting DCPs for high temperature water treatment applications, it is important to

consider thermal stress implications on the DCP efficacy. Tools useful for evaluating thermal

stress impacts on DCPs include MW measurements, NMR analyses, carboxyl content

measurements, and performance testing.

Acknowledgements The authors thank Lubrizol’s Brecksville, OH measurement science department including George Benedikt, Dave Hanshumaker, Perry Matheny, Sue Mramor, Casey Pritts, and Elisa Seddon for conducting deposit control thermal stress testing and characterizing samples before and after thermal stress. We also appreciate Dave Smith and Hyungsoo Kim (polymer synthesis scientists) providing assistance with data interpretation. The authors also thank The Lubrizol Corporation for permission and support to conduct this study and present the results to Association of Water Technologies.

References

1. J. Fred Wilkes, “A Historical Perspective of Scale and Deposit Control (1943 to 1993),” Paper No. 458, CORROSION/93, NACE International, Houston, TX (1993). 2. J. S. Gill, “The Role of Calcium Phosphate in Internal Boiler Water Treatment,” Chapter

18 in Calcium Phosphates in Biological and Industrial Application, Z. Amjad (Ed.), Kluwer Academic Publishers, Boston, MA (1998).

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

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acid) and its Salts: Part 3. Magnesium and Calcium Salts,” Polymer Degradation and Stability 30, 267-282 (1990).

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Solution,” Polymer Degradation and Stability, 75, 337-345 (2002).

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10. R. W. Zuhl, “New Boiler Water Treatment Polymer Developments,” Presentation, Association of Water Technologies, Spring Convention, Las Vegas, NV, April (1990).

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Water Systems,” Paper No. 08368, NACE International, Houston, TX (2008). 12. Z. Amjad and R. W. Zuhl, “Effects of Thermal Stress on Silica-Silicate Deposit Control

Agent Performance,” Association of Water Technologies Annual Convention, Reno, NV (2010).

13. Z. Amjad and R. W. Zuhl, “Water Treater Deposit Control Polymer Evaluation Criteria and

Considerations,” Association of Water Technologies Annual Convention, Palm Springs, CA (2012).

14. K. Morimoto and Iida, “Thermal and Photodegradation of Acrylic Resins”, Progress in

Organic Coatings, 2 (1), 35-56 (September 1973). 15. P. G. Klepetsanis, A. Kladi, P. G. Koutsoukos, and Z. Amjad, “The Interaction of Water-

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Phosphonates and Calcium Carbonate in High Stressed Cooling Water Systems,”

Association of Water Technologies Annual Convention, Nashville, TN, November 3-6

(2004).

The Lubrizol Corporation • Cleveland, OH 44141-3247, U.S.A. Phone: 1-800-380-5397 or 440-347-7584 FAX: 216-447-6315 (USA Customer Service) 216-447-5270 (International Customer Service) 440-347-1968 (Marketing & Technical Service)

www.carbosperse.com, www.lubrizol.com Oct-2013

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.

The Lubrizol Corporation

9911 Brecksville Road, Cleveland, OH 44141