Renaissance Palm Springs Hotel and Palm Springs Convention Center
Palm Springs, California September 19-22, 2012
Water Treater Deposit Control Polymer Evaluation Criteria and Considerations
Zahid Amjad, Ph.D. and Robert W. Zuhl, P.E.
Lubrizol Advanced Materials, Inc. 9911 Brecksville Road Cleveland, OH 44141
© 2012, The Lubrizol Corporation. All rights reserved.
Carbosperse™ K-700
1
Abstract
Industrial water systems that use water are often faced with a variety of challenges including
scaling, fouling, microbiological growth, and corrosion. To combat these operational problems,
water treaters have developed and apply effective treatment programs. Currently, a variety of
deposit control polymers are available and incorporated into formulation to control scaling and
suspended matter fouling of equipment surfaces. This paper presents new information on the
comparative performance of poly(acrylic acids) made in different polymerization solvents,
acrylate terpolymer, and polymer blend.
Introduction
combinations of synergistic components. Multi-functional deposit control polymers (DCPs)
that disperse particulates, inhibit scale formation, and stabilize metal ions are essential
components of nearly all water treatment formulations.1 Lubrizols AWT 2011 convention
paper2 and presentation evaluated and compared the performance characteristics of a low
molecular weight water-polymerized polyacrylate (PAA), a high performance acrylate
terpolymer (ATP), and a 50/50 (active solids basis) blend of the PAA & ATP. The work herein
compares the performance of two similar molecular weight (MW) polyacrylates (PAAs) made
by different manufacturing processes (water & solvent polymerization), the ATP, and 50/50
blends of each PAA and the ATP. The data provide insights as to the selection and blending
of DCPs as components of water treatment formulations.
Experimental
Materials
Reagent grade chemicals and grade A glassware were used. Stock solutions of calcium
chloride, magnesium chloride, disodium hydrogen phosphate, sodium carbonate, sodium
chloride, sodium sulfate, and sodium bicarbonate were prepared using distilled water, filtered
through 0.22-micron filter paper and analyzed as described previously.3 The polymers tested
are listed in Table 1. The stock solutions of these polymers were prepared in distilled water on
an active solids basis.
Table 1: Polymers Evaluated
K-798* Water polymerized <15k MW poly(acrylic acid: 2-acrylamido-2- methylpropane sulfonic acid: sulfonated styrene) or “AA/SA/SS”
ATP
Blend W 1:1 active solids blend of PAA-W & ATP TPB-W
Blend S 1:1 active solids blend of PAA-S & ATP TPB-S * Carbosperse™ K-700 polymer supplied by Lubrizol Advanced Materials, Inc.
2
Supersaturated solutions of calcium phosphate for precipitation experiments were prepared by
adding a known volume of phosphate stock solution to the thermostated-glass cell maintained
at constant temperature containing a known concentration of polymer in distilled water. After
temperature equilibration, a known volume of stock calcium chloride solution was added
making up the total volume to 600 mL. Spontaneous precipitation was induced by adjusting
the 600 mL calcium phosphate solution to pH 8.50 with 0.10M NaOH. During each
experiment, the test solution pH was maintained at 8.50 ± 0.01 with 0.10M NaOH solution
using the pH-stat unit (Model 600 series, Metrohm Brinkmann Instruments, NY) equipped with
a combination electrode. The pH electrode was calibrated before each experiment with
standard buffers. Unless specified otherwise, the calcium phosphate inhibition test conditions
were as shown in Table 2. Experiments involving Fe3+ were performed by adding a FeCl3
solution to the phosphate solution containing polymer before adding the stock calcium chloride
solution. The experimental set-up used to evaluate polymer as Ca/P inhibitor has been
presented in our earlier publication.4
Table 2: Calcium Phosphate Inhibition Test Conditions
Parameter mg/L Parameter Value
Phosphate (PO4) 3- 9 Temperature 50ºC
Iron (Fe3+) 0 to 3 Time 22 hr
Active polymer 0 to 20
The progress of precipitation process was determined by spectrophotometric analysis of
filtered (0.45 µm, Millipore Corporation) aliquot of the test solution for the phosphate ion. The
efficacy of polymer as a calcium phosphate inhibitor was calculated using Equation 1 below:
% Inhibition =
Inhibition (%) = %I
[PO4] sample = PO4 concentration in the presence of inhibitor at the end of the test
[PO4] control = PO4 concentration in the absence of inhibitor at the end of the test
[PO4] initial = PO4 concentration at the beginning of the test
Calcium Carbonate Inhibition
The efficacy of polymer as calcium carbonate inhibitor was tested using the test procedure
described 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 known volume of calcium chloride stock solution to create a 100 mL
3
solution whose water chemistry was as shown in the Table 3 below and to which 0.25 to
5.0 mg/L active polymer were added. The bottles were capped and stored in 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 3: 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 calcium carbonate inhibitor was calculated using the Equation 2 below:
% Inhibition =
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
Calcium Sulfate Inhibition
Polymer efficacy as calcium sulfate inhibitor was evaluated using the test procedure described
herein. To a 125 mL glass bottle containing distilled water, known volumes of stock solutions
of sodium sulfate and polymer were added with stirring followed by the addition of known
volume of calcium chloride stock solution to create a 100 mL solution whose composition was
as shown in Table 4 below. The solution pH was adjusted to 7.0 with dilute HCl or NaOH
solutions as appropriate. The bottles were capped and stored in 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. Polymer efficacy as a calcium sulfate inhibitor was calculated using
Equation 2 above.
Parameter mg/L Parameter Value
Sulfate (SO4) 2- 4,320 Temperature 66ºC
Active polymer 0 to 2.0 CaSO4 saturation 2.2x
Time 24 hr
Iron Oxide Dispersion
A known amount (0.12 g) of iron oxide was added to 800 mL beaker containing simulated
industrial water (600 mL) and known amount of polymer (dispersant) solution. The simulated
industrial water used in the dispersion tests was made by mixing standard solutions of calcium
chloride, magnesium chloride, sodium sulfate, sodium chloride, and sodium bicarbonate. The
simulated industrial water composition and iron oxide dispersion test conditions are shown in
Table 5 below.
Parameter mg/L Parameter Value
Magnesium (Mg2+) 30 pH 7.6 to 7.8
Sodium (Na+) 314 Room temperature ≈22ºC
Chloride (Cl-) 571 Time 0 to 3 hr
Sulfate (SO4) 2- 192 Active polymer 0 to 5 mg/L
Bicarbonate (HCO3) - 60
A typical test run consists of six simultaneous experiments using a gang-stirrer set to 110
revolutions per minute. At known time intervals, transmittance readings (%T) were taken with
Brinkmann® Probe Colorimeter equipped with 420 nm filter. The absorbance of several
filtered (0.22 µm) suspensions with low to high %T was measured at 420 nm; the absorbance
contribution due to dissolved species was insignificant (<3%). Polymer performance as
percent iron oxide dispersed (%D) was calculated based on %T readings taken as a function
of time and using Equation 3 below which includes an adjustment for readings obtained in the
absence of polymer.
%D = [100 - (1.11 x % transmittance)] (3)
The data presented herein had good reproducibility (±5% or better). Polymer performance
was determined by comparing the %D values of the slurries containing polymer to the control
(no polymer). Therefore, higher %D values indicate greater dispersion.
Calcium Ion Tolerance
One hundred (100) mL of 250 mg/L calcium ion solution in deionized water containing varying inhibitor amounts was placed in a 125-mL glass bottle. The pH of test solution was adjusted to
pH 9.50 with dilute NaOH or HCl. The bottles were capped and placed in reaction cell at 25C
and allowed to equilibrate. After stirring for 30 minutes, transmittance readings were taken using a fiber-optic probe. In order to avoid faulty signals, extreme care was taken to maintain system pH and to eliminate air bubbles in the solutions, especially in the vicinity of the turbidity probe.
5
Parameter Value Parameter Value
Chloride (Cl-) 444 mg/L Time 30 min
pH 9.50 Active polymer Variable
Temperature 25ºC
Polymer and Dosage Effects
A polymers ability to inhibit calcium phosphate formation is a very important function in
phosphate and phosphonate-based treatment programs. Figure 1 shows percent inhibition
(%I) as a function of polymer dosage up to 10 mg/L for the water and solvent polymerized
PAAs (i.e., PAA-W & PAA-S) and the acrylic acid:2-acrylamido-2-methylpropane sulfonic acid:
sulfonated styrene terpolymer (ATP). As indicated, performance increases as a function of
polymer dosage for all three polymers. PAA-S provides somewhat better performance than
PAA-W albeit both PAAs provide poor performance (<20%) at dosages below 8.5 mg/L
whereas ATP exhibits excellent performance (>90%) at dosages above 7.5 mg/L. ATP
performance is consistent with data reported in several other investigations5-7 indicating that
acrylic acid and maleic acid based co- and ter-polymers incorporating a variety of functional
groups (i.e., -SO3H, -COOR, s-CONH2, etc.) of different ionic charge (anionic, neutral) are
more effective calcium phosphate and calcium phosphonate scale inhibitors.
Figure 2 show the effect of increasing polymer dosages from 10 to 20 mg/L. PAA-S
performance improves dramatically compared to an incremental increase for PAA-W. The
unexpected PAA-S performance is attributable to special architectural properties (e.g.,
distinctive end groups and branching not seen in PAA-W and other polymers) resulting from a
proprietary solvent polymerization manufacturing process.
0
20
40
60
80
100
0 1 2 3 4 5 6 7 8 9 10
% In
PAA-W
PAA-S
ATP
6
The calcium phosphate inhibition performance of the PAA-ATP blends (i.e., 1:1 active polymer
basis blends of PAA-W & ATP [TPB-W] and PAA-S & ATP [TPB-S]) as a function of dosage
compared to the component polymers is shown in Figure 3 and summarized below:
The performance of both PAA-TPB blends (i.e., TPB-W & TPB-S) increases with dosage.
The performance of both TPB-W and TPB-S is much better than expected based on the component polymer performances especially for TPB-W incorporating PAA-W which by itself provides poor performance across a broad dosage range.
The improved TPB performances observed in the present investigation are consistent with a
previous study evaluating polymer blends as stabilizers for amorphous calcium phosphate.8
0
20
40
60
80
100
0 2 4 6 8 10 12 14 16 18 20
% In
PAA-W
PAA-S
ATP
0
20
40
60
80
100
0 2 4 6 8 10 12 14 16 18 20
% In
PAA-W
PAA-S
ATP
TPB-W
TPB-S
7
Effect of Fe3+
The influence of trace levels of metal ions (i.e., Cu, Zn, Al, Fe, Mn, etc.) on the precipitation of
scale forming mineral have been investigated.7,9,10 These studies reveal that Fe3+ has an
antagonistic influence of the performance of both calcium phosphate/phosphonate inhibitors as
well as iron oxide dispersants. Figure 4 presents the effect of 1.0 mg/L Fe3+ on the PAAs,
ATP, and the polymer blends. As shown, adding 1.0 mg/L Fe3+ has a negligible impact on
ATP performance, ≥50% performance decreases for both PAAs, and reduces the performance
for the PAA-ATP blend by ≈25%. The adverse impact of soluble iron for both PAA-ATP blends
is less than expected if based on an additive effect for the component polymers.
Calcium Carbonate Inhibition
In both cooling water and reverse osmosis (RO) systems, calcium carbonate (CaCO3) is one of
the most commonly encountered scale deposits. 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 & architecture).11,12
Figure 5 presents CaCO3 inhibition data as a function of dosage for the polyacrylates, ATP, the
polymer blends leading to several observations discussed below.
1. PAA-S performs better than PAA-W with relatively small dosage of PAA-S (>0.7 mg/L) and PAA-W (>1.25 mg/L) providing >60% CaCO3 precipitation inhibition.
0
20
40
60
80
100
% I
n h
ib it
io n
Figure 4: Influence of Fe3+ on Ca/P Inhibition by Polymers (10 mg/L)
0 mg/L Fe³
1.0 mg/L Fe³
8
2. ATP CaCO3 precipitation inhibition performance is inferior to that for the PAAs. These
results indicate that ATP incorporating non-carboxyl co-monomers groups (e.g., SO3H as well as bulkier and hydrophobic styrene) reduces CaCO3 inhibition performance. The results also suggest that --COOH group present in the PAAs strongly interacts with the Ca present in CaCO3 crystallites formed during the precipitation process.
3. The performance for both PAA-ATP blends lags but closely parallels the PAA performance. Suggesting that adding ATP to CaCO3 supersaturated solutions does not deleteriously affect the performance of PAAs.
Calcium Sulfate Inhibition Although not as prevalent as calcium carbonate, calcium sulfate
precipitation can be a problem in some water systems including cooling systems (where
sulfuric acid is used for pH adjustment), RO systems, and geothermal systems. Gypsum
(CaSO4.2H2O) is the most commonly encountered calcium sulfate scale whereas calcium
sulfate hemihydrate (CaSO4 ½ H2O) and calcium sulfate anhydrite (CaSO4) are the most
frequently formed salts in high temperature processes.
Figure 6 presents gypsum inhibition data as a function of dosage for the PAAs, ATP, and the
polymer blends leading to the following observations:.
1. The polyacrylates (i.e., PAA-W and PAA-S) perform better than ATP which is attributable to the higher carboxyl content of the PAAs.
0
20
40
60
80
100
% In
PAA-W PAA-S ATP TBP-W TPB-S
9
2. The performance of the PAAs is very similar; the polymerization solvent does not appear to make a significant difference under these laboratory test conditions.
3. The performance for both PAA-ATP blends appears to be an additive affect or performance that is midway between that of the two components.
Iron Oxide Dispersion
Iron and iron-based impurities present in feedwaters and/or caused by equipment corrosion
products can cause operational problems in industrial water systems (e.g., cooling waters, RO,
steam generation). Regardless of the source, soluble iron can precipitate under certain
conditions to form troublesome scales and deposits [e.g., Fe2O3, Fe3O4, Fe(OH)3, FePO4].
Therefore, deposit control polymers are frequently used to disperse and transport iron oxide
particles in industrial water systems.
Polymer Dosage Effect
The influence of PAA-S and ATP dosages (0.25 to 1.0 mg/L) on iron oxide dispersion as a
function of time (0 to 3 hr) are shown in Figures 7 and 8, respectively. It is evident that contact
time between polymer and iron oxide particles impacts a polymers iron oxide dispersion
performance. As shown in Figure 7, PAA-S performance increases with time and dosage with
the biggest increase occurring between 0.25 and 0.5 mg/L dosages.
0
20
40
60
80
100
% In
PAA-S PAA-W
ATP TPB-W
TPB-S
10
Figure 8 presents iron oxide dispersion data for ATP and indicates a „normal dosage-response
relationship; i.e., performance increases with polymer dosage. Increasing ATP dosage and/or
test duration increases iron oxide dispersion. However, increasing ATP dosage above
1.0 mg/L (i.e., from 1.0 to 2.0 mg/L) as shown in our previous study,2 has an insignificant iron
oxide dispersion improvement. This suggests that ATP adsorption on iron oxide particles is
essentially complete at ≈1.0 mg/L dosage and indicates that ATP is a highly effective iron
oxide dispersant.
% D
is p
e rs
e d
Time (hr)
Figure 7: Iron Oxide Dispersion as Functions of PAA-S Dosage & Time
0.25 mg/L 0.50 mg/L
0.75 mg/L 1.00 mg/L
% D
is p
e rs
e d
Time (hr)
Figure 8: Iron Oxide Dispersion as Functions of ATP Dosage & Time
0.25 mg/L 0.50 mg/L
0.75 mg/L 1.00 mg/L
composition polymers can contribute to performance differences as lower MW polymers
generally will adsorb faster than the high MW polymer due to steric hindrance. Figure 9
presents comparative iron oxide dispersion performance data for the two PAAs and ATP at
1 mg/L dosages vs. time and the results can be summarized as follows:
As expected based on the compositional, differences ATP outperforms the two PAAs.
The solvent polymerized PAA (PAA-S) provides approximately double the performance of
the water polymerized PAA (PAA-W) during the test period. Reasons for the unexpected
PAA-S performance were discussed earlier herein.
The iron oxide dispersion of the PAA-ATP blends (i.e., 1:1 active polymer basis blends of
PAA-W & ATP [TPB-W] and PAA-S & ATP [TPB-S]) as a function of dosage compared to the
component polymers is shown in Figure 10 and summarized below:
The performance of both PAA-ATP blends (TPB-W & TPB-S) increases with dosages.
The performance of TPB-W closely parallels the PAA-W component.
The performance for TPB-S appears to be hybrid of the two component polymers (PAA-S
and ATP) suggesting some synergy and is linked to the PAA-S component performance
discussed previously.
% D
is p
e rs
e d
Time (hr)
Figure 9: Iron Oxide Dispersion by Polymers (1 mg/L) vs. Time
PAA-W PAA-S ATP
Many deposit control agents (DCAs) including phosphonates (e.g., AMP, HEDP), PAAs, and
polymaleic acids when used at high concentrations or in high hardness applications can form
insoluble calcium-inhibitor salts that may lead to accelerated scale formation. Accordingly, the
compatibility of DCPs with calcium ions (or calcium ion tolerance) is of great concern to water
treatment technologists. A DCPs ability to resist the formation of calcium-polymer salts is an
indirect indication of potential performance in harsh conditions.
The calcium ion tolerance testing results for the two PAAs, ATP, and the polymer blends using
the procedure described earlier (a modified version of the method described in our AWT-2003
paper14) are shown in Figure 11 and summarized below:
The Ca ion tolerance of PAA-S is clearly superior to PAA-W. For comparative purposes, the Ca ion tolerance previously reported14 for PBTC (or 2-phosphonobutane 1,2,4- tricarboxylic acid a well-known high performance phosphonate) under these conditions was 100 mg/L inhibitor per 250 mg/L of calcium; performance between the Figure 11 values shown for PAA-W and PAA-S but closer to the former. The reasons for the distinctive PAA-S performance characteristics were discussed previously.
ATP exhibits exceptional Ca ion tolerance as do the blends of ATP with the each PAA (i.e., TPB-W and TPB-S).
The Ca ion tolerance of PAA-W/ATP blend (TPB-W) is poorer than would be expected and this is attributable to the poor performance of PAA-W.
0
10
20
30
40
50
60
70
80
% D
Time (hr)
Figure 10: Iron Oxide Dispersion by Polymers (1 mg/L) vs. Time
PAA-W PAA-S ATP TPB-W TPB-S
13
Summary
Water treatment formulation development incorporates the use of synergistic components to
effectively control corrosion, scaling, and microbiological fouling in the industrial water system.
Using multiple deposit control polymers as components of treatment programs is a common
practice based on the expectation of synergism and optimizing cost vs. performance. A series
of laboratory screening tests were used to evaluate the performance of ≈2k MW water and
solvent polymerized PAAs (i.e., PAA-W and PAA-S, respectively), a high performance acrylate
terpolymer (ATP), and two PAA-ATP blends (i.e., 1:1 active polymer basis blends of PAA-W &
ATP [TPB-W] and PAA-S & ATP [TPB-S]) lead to the following performance ranking:
Screening Test Best Mid-Range Worst
Calcium phosphate (Ca/P) inhibition ATP > TPB-S > TPB-W > PAA-S >> PAA-W
Ca/P inhibition in presence of Fe3+ ATP > TPB-S > TPB-W > PAA-S > PAA-W
CaCO3 inhibition PAA-S > TPB-S ≈ TPB-W > PAA-W > ATP
CaSO4 inhibition PAA-S ≈ PAA-W > TPB-S ≈ TPB-W > ATP
Iron oxide dispersion ATP > TPB-S > PAA-S >> TPB-W > PAA-W
Ca-Ion Tolerance ATP ≈ TPB--S ≈ TPB-W ≈ PAA-S > PAA-W
The data presented herein indicate the following:
0
50
100
150
200
/L P
o ly
m e
r p
e r
2 5
0 m
g /L
C a
lc iu
m
Figure 11: Polymer Ca Ion Tolerance (pH 9.5, 25C, stirred, 30 min)
>200 mg/L >200 mg/L >200 mg/L >200 mg/L
14
1. ATP compared to the PAAs provides superior Ca/P inhibition and iron oxide dispersion
which is due to ATPs two sulfonic acid groups.
2. The PAAs (PAA-W & PAA-S) because of their greater carboxylate content provide better
calcium carbonate and calcium sulfate inhibition than ATP.
3. Blends of the PAAs and ATP provide performance characteristics that are a hybrid of the
components and some synergism most notably with solvent polymerized PAA (PAA-S).
4. PAA-S provides unexpected Ca/P inhibition, iron oxide dispersion, and calcium ion
tolerance properties that are attributable to the special architectural properties resulting
from Lubrizols solvent polymerization manufacturing process including distinctive end
groups and branching not reflected in water polymerized polymers such as PAA-W.
Other deposit control polymers and/or ratios of homopolymers and copolymers may lead to
alternative performance rankings. In addition, water technologists developing formulations and
treatment programs must take several other factors into consideration including:
Formulation component performance, synergy, and costs.
Working capital and operating cost implications associated with maintaining and using
multiple and/or a wide range of water treatment formulating components.
Formulated product stability.
Acknowledgements
The authors thank Scranton Associates Robert R. Cavano for his questions regarding the performance, economics, and wisdom of combining homopolymers and copolymers as components of water treatment formulations that were the key driver for this paper.
References
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Treaters,” Association of Water Technologies Annual Convention, Atlanta, GA,
September 14-17, 2011.
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Systems,” The Science and Technology of Industrial Water Systems,” Z. Amjad (ED),
CRC Press, Florida (2010).
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Boston, MA (1998).
5. Z. Amjad, “Performance of Polymers as Precipitation Inhibitors for Calcium
Phosphonates,” Tenside Surfactants Detergents, 34, 102-107 (1997).
15
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Lubrizol Advanced Materials, Inc. • Cleveland, OH 44141-3247, U.S.A. Phone: 1-800-380-5397 or 216-447-7584 FAX: 216-447-6315 (USA Customer Service) 216-447-5270 (International Customer Service) 216-447-5238 (Marketing & Technical Service)
www.carbosperse.com, www.lubrizol.com Sep-2012
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