Abstract

A phosphorus-free scale inhibitor (ionic liquid–carboxylic acid copolymer) was successfully synthesized by the reaction of 1-sulfobutyl-3-vinylimidazolium hydrogen sulfate (SVIS) and acrylic acid (AA). The structure of the product was characterized by Fourier transform infrared spectroscopy (FTIR), hydrogen nuclear magnetic resonance (1H NMR) and carbon-13 nuclear magnetic resonance (13C NMR). Then the scale inhibition efficiency of 1-sulfobutyl-3-vinylimidazolium hydrogen sulfate-acrylic acid (SVIS-AA) copolymer against CaCO3 and CaSO4 was determined. The results indicated that SVIS-AA copolymer showed better scale inhibition efficiency than poly (acrylic acid) (PAA). After that, the effects of temperature and Ca2+ concentration on the scale inhibition efficiency against CaCO3 were studied. Results showed that when the temperature reached 90 °C, the scale inhibition efficiency could still remain 91% at a concentration of 18 mg L−1. When the concentration of Ca2+ reached 1,200 mg L−1, the scale inhibition efficiency could remain 70% at a concentration of 20 mg L−1. At last, the effect of SVIS-AA copolymer on the morphologies of CaCO3 and CaSO4 scale was studied by scanning electron microscopy (SEM) and X-ray diffraction (XRD).

INTRODUCTION

Because of pollution, global warming and other reasons, the shortage of water resources is becoming more and more serious (Ren et al. 2018). In order to save water, circulating cooling water systems have been widely used in industry (Zhang et al. 2016).

However, a common problem we are facing in circulating cooling water systems is scale deposition. Scale deposition can bring many problems, for example, it can reduce the efficiency of heat transfer (Amjad & Koutsoukos 2014). The most effective method to inhibit the formation of scale is to use scale inhibitors, so scale inhibitors are widely used in circulating cooling water systems (Popov et al. 2017).

Currently, there are many types of scale inhibitors that are used to inhibit the formation of scale. Among them, phosphorus scale inhibitors, such as amino trimethylene phosphonic acid, are one of the most widely used scale inhibitors due to their good scale inhibition performance. Unfortunately, phosphorus scale inhibitors may cause eutrophication of water because they contain phosphorus (Zhao et al. 2016). Because of the major concern over global ecological and environmental problems, phosphorus scale inhibitors are gradually restricted in use (Wang et al. 2014). Therefore, it is necessary to prepare novel phosphorus-free scale inhibitors.

In recent years, phosphorus-free copolymer scale inhibitors have attracted great interest (Guo et al. 2014). Because they do not contain phosphorus, this can avoid eutrophication of water, so they are beneficial to protect the water environment and maintain the balance of the ecological environment. Besides, they usually show excellent scale inhibition performance because they contain double or multiple types of functional groups (Guo et al. 2012). Recently, a copolymer scale inhibitor was reported (Guo et al. 2014). It does not contain phosphorus and it shows excellent scale inhibition efficiency against CaCO3. An novel environmental friendly and hydrophilic terpolymer inhibitor has been reported (Yang et al. 2017). It does not contain phosphorus, and it also shows excellent scale inhibition efficiency against CaCO3. Therefore, we can draw the conclusion that phosphorus-free copolymer scale inhibitors show many advantages and are promising in the future.

Ionic liquids are low-temperature liquid salts with the advantages of both liquids and salts (Wang et al. 2018). As anions and cations of ionic liquids can be replaced flexibly, it is believed that scale inhibitors containing various functional groups can be prepared (Berthod et al. 2008). Therefore, it is necessary to study the application of ionic liquids in scale inhibitors.

In this study, we prepared a phosphorus-free copolymer scale inhibitor. It was synthesized from 1-sulfobutyl-3-vinylimidazolium hydrogen sulfate (SVIS) and acrylic acid. SVIS is an ionic liquid, and its molecule contains a sulfonic group. Then the scale inhibition efficiency against CaCO3 and CaSO4 of SVIS-AA copolymer and PAA were compared. The effects of temperature and Ca2+ concentration were also studied. At last, the effect of SVIS-AA copolymer on the structure of CaCO3 and CaSO4 scale was studied by scanning electron microscopy (SEM) and X-ray diffraction (XRD).

METHODS

Measurements

The structure of the product, SVIS, and AA were characterized by Fourier transform infrared spectroscopy (FTIR) (TENSOR 27, Bruker Co., Germany), 1H NMR (AVANCE400, Bruker Biospin AG Co., Switzerland) and 13C NMR (AVANCE400, Bruker Biospin AG Co., Switzerland). The morphologies of CaCO3 and CaSO4 were characterized by SEM (Quanta 450 FEG, FEI Co., Hong Kong) and XRD (Da Vinci, Bruker AXS Co., Germany).

Static scale inhibition method

The common methods to evaluate the scale inhibition efficiency of scale inhibitors include the static scale inhibition method and the bubbling method (Tang et al. 2008; Zhao et al. 2016). The static scale inhibition method presents the advantage of simple operation, so the static scale inhibition method was selected to evaluate the scale inhibition efficiency. The static scale inhibition method was performed to estimate the scale inhibition efficiency of SVIS-AA copolymer against CaCO3 and CaSO4 according to GB/T 16632-2008 (China) and SY/T 5673-93 (China), respectively. The static scale inhibition method for CaCO3: the test solution was formulated with NaHCO3, CaCl2 and deionized water, and the concentrations of Ca2+ and HCO3 were 240 mg L−1 and 732 mg L−1, respectively. A certain amount of SVIS-AA copolymer was added into the test solution. The pH of the solution was adjusted to 9 with borax buffer solution. The test solution was heated in a water bath at 80 °C for 10 h. The concentration of Ca2+ was titrated with ethylene diamine tetraacetic acid (EDTA) standard solution. When the color of the solution changed from purple to blue, the titration was finished. The static scale inhibition method for CaSO4: the test solution was formulated with CaCl2, Na2SO4 and deionized water, and the concentrations of Ca2+ and SO42– were 6,800 mg L−1 and 7,100 mg L−1, respectively. A certain amount of SVIS-AA copolymer was added into the test solution. The pH of the solution was adjusted to 7 with NaOH or HCl. The solution was heated in a water bath at 70 °C for 6 h. The concentration of Ca2+ was titrated with EDTA standard solution. The scale inhibition efficiencies against CaCO3 and CaSO4 were calculated by the following equations: 
formula
(1)
where A4 and A3 are Ca2+ concentration in the presence and absence of SVIS-AA copolymer after heating, respectively. A0 is the initial Ca2+ concentration before heating; η is the scale inhibition efficiency against CaCO3. 
formula
(2)
where B4 and B3 are Ca2+ concentration in the presence and absence of SVIS-AA copolymer after heating, respectively. B0 is the initial Ca2+ concentration before heating; η is the scale inhibition efficiency against CaSO4.

Synthesis of SVIS-AA copolymer

About 6.56 g (0.02 mol) SVIS and 1.38 g sodium hypophosphite (SHP) were initially dissolved in 50 ml deionized water in a four-necked flask, which was then heated to 60 °C under a nitrogen atmosphere. After that, the aqueous solution with about 7.2 g (0.1 mol) AA and 1.38 g ammonium persulfate (APS) was slowly added to the flask through a dropping funnel for 40 minutes. Then the reactant was heated to 85 °C and maintained for four hours before it was cooled down to room temperature. Afterwards, the pH of the system was adjusted to 7 with NaOH or HCl, followed by rotary evaporation in order to remove the solvent. Finally, the product could be obtained after the product was dried by a vacuum drying oven.

RESULTS AND DISCUSSION

FTIR analysis

The FTIR spectra of (a) AA, (b) SVIS and (c) the product are shown in Figure 1. The peaks the of functional groups are listed in Table 1. It is obvious that the stretching vibration peaks of –C = C– in AA and –C = C– in vinyl have disappeared.

Table 1

The peaks of the functional groups

The types of functional groups The peaks of functional groups (cm1)
 
AA SVIS SVIS-AA 
–OH 3,040 3,398 3,435 
–C=O 1,712  1,721 
–C=C– 1,635   
–C=C– in vinyl  1,654  
–C=C– in the imidazole ring  1,457 1,451 
–C=N–  1,552  
–S=O  1,174 1,188 
The types of functional groups The peaks of functional groups (cm1)
 
AA SVIS SVIS-AA 
–OH 3,040 3,398 3,435 
–C=O 1,712  1,721 
–C=C– 1,635   
–C=C– in vinyl  1,654  
–C=C– in the imidazole ring  1,457 1,451 
–C=N–  1,552  
–S=O  1,174 1,188 
Figure 1

FTIR spectra of (a) AA, (b) SVIS and (c) the product.

Figure 1

FTIR spectra of (a) AA, (b) SVIS and (c) the product.

1H NMR analysis

The structure of (a) AA, (b) SVIS and (c) the product were characterized by 1H NMR with D2O as the solvent. The results are shown in Figure 2. The chemical shifts of the hydrogen atoms are listed in Table 2. As can be seen from Figure 2 and Table 2, the peaks of CH2 = CH– have basically disappeared in the product.

Table 2

The chemical shifts of different types of hydrogen atoms

The types of hydrogen atoms The chemical shifts (ppm)
 
AA SVIS SVIS-AA 
D24.70 4.71 4.70 
CH2=CH– 5.77–5.82, 5.94–6.01, 6.20–6.25 5.29–5.31, 5.66–5.70, 6.99–7.05  
–CH=N–  8.95 8.91 
–CH=CH–  7.48, 7.66 7.36–7.62 
–CH2–  1.64–1.66, 1.91–1.95, 2.81–2.85, 4.15–4.19 1.56–1.94, 2.86, 4.18 
The types of hydrogen atoms The chemical shifts (ppm)
 
AA SVIS SVIS-AA 
D24.70 4.71 4.70 
CH2=CH– 5.77–5.82, 5.94–6.01, 6.20–6.25 5.29–5.31, 5.66–5.70, 6.99–7.05  
–CH=N–  8.95 8.91 
–CH=CH–  7.48, 7.66 7.36–7.62 
–CH2–  1.64–1.66, 1.91–1.95, 2.81–2.85, 4.15–4.19 1.56–1.94, 2.86, 4.18 
Figure 2

1H NMR of (a) AA, (b) SVIS and (c) the product.

Figure 2

1H NMR of (a) AA, (b) SVIS and (c) the product.

13C NMR analysis

The structure of (a) AA, (b) SVIS and (c) the product were characterized by 13C NMR with D2O as the solvent. The results are shown in Figure 3. The chemical shifts of the carbon atoms are listed in Table 3. The peaks of CH2 = CH– have basically disappeared according to Figure 3 and Table 3. By reading the results of FTIR, 1H NMR and 13C NMR, we mainly found that CH2 = CH– in SVIS and CH2 = CH– in AA have all disappeared. This proved that the free radical polymerization between SVIS and AA had occurred, so SVIS-AA copolymer had been successfully synthesized. The reaction equation is shown in Figure 4.

Table 3

The chemical shifts of different types of carbon atoms

The types of carbon atoms The chemical shifts (ppm)
 
AA SVIS SVIS-AA 
–COOH 170.11  174.80–178.42 
CH2=CH– 132.64, 127.58 128.20, 109.33  
–CH=N–  134.42 135.43, 134.27 
–CH=CH–  122.77, 119.58 119.70–123.41 
–CH2–  20.89, 27.91, 49.27, 49.99 20.83, 28.12, 41.39, 48.62–49.93 
The types of carbon atoms The chemical shifts (ppm)
 
AA SVIS SVIS-AA 
–COOH 170.11  174.80–178.42 
CH2=CH– 132.64, 127.58 128.20, 109.33  
–CH=N–  134.42 135.43, 134.27 
–CH=CH–  122.77, 119.58 119.70–123.41 
–CH2–  20.89, 27.91, 49.27, 49.99 20.83, 28.12, 41.39, 48.62–49.93 
Figure 3

13C NMR of (a) AA, (b) SVIS and (c) the product.

Figure 3

13C NMR of (a) AA, (b) SVIS and (c) the product.

Figure 4

The reaction equation of SVIS and AA.

Figure 4

The reaction equation of SVIS and AA.

Scale inhibition efficiency against CaCO3

The scale inhibition efficiency of SVIS-AA copolymer and PAA (molecular weight = 1,800) were tested according to GB/T 16632-2008 (China). The results are shown in Table 4. As the concentration of SVIS-AA copolymer and PAA increased, the scale inhibition efficiency increased at first. Then with the increase of the concentration of SVIS-AA copolymer and PAA, the scale inhibition efficiency gradually became unchanged, and this is due to the threshold effect. Compared with PAA, SVIS-AA copolymer showed the higher scale inhibition efficiency at the same concentration. The scale inhibition efficiency of SVIS-AA could reach 96% at the threshold concentration of 18 mg L−1, but the value was only 46% for PAA in the same conditions. The excellent scale inhibition performance of SVIS-AA copolymer may be assigned to the reason that carboxyl and sulfonic groups can both chelate Ca2+ to inhibit the formation of CaCO3. In addition to the excellent scale inhibition efficiency, it does not contain phosphorus, which could avoid eutrophication of water to a certain extent, so it is beneficial for protecting the water environment. Based on the above reasons, it can be used to inhibit the formation of CaCO3 scale in circulating cooling water systems.

Table 4

Scale inhibition efficiency against CaCO3 of SVIS-AA and PAA

Scale inhibitors Scale inhibition efficiency against CaCO3 (%)
 
2 (dosage of scale inhibitors, mg L−110 12 14 16 18 20 22 24 
PAA 12.1 19.5 25.3 31.7 40.3 46.5 46.4 47.5 46.6 47.4 47.1 46.5 
SVIS-AA 13.2 18.1 29.4 42.4 68.5 80.6 91.2 94.3 96.5 96.8 96.3 97.1 
Scale inhibitors Scale inhibition efficiency against CaCO3 (%)
 
2 (dosage of scale inhibitors, mg L−110 12 14 16 18 20 22 24 
PAA 12.1 19.5 25.3 31.7 40.3 46.5 46.4 47.5 46.6 47.4 47.1 46.5 
SVIS-AA 13.2 18.1 29.4 42.4 68.5 80.6 91.2 94.3 96.5 96.8 96.3 97.1 

Scale inhibition efficiency against CaSO4

The scale inhibition efficiency against CaSO4 of SVIS-AA copolymer and PAA were tested according to SY/T 5673-93 (China). The results are exhibited in Table 5. As the concentration of SVIS-AA copolymer and PAA increased, the scale inhibition efficiency increased at first. Then with the increase of the concentration of SVIS-AA copolymer and PAA, scale inhibition efficiency gradually became unchanged. Similarly as above, SVIS-AA copolymer showed better scale inhibition efficiency than PAA. For example, the scale inhibition efficiency was 98% for SVIS-AA but 85% for PAA at the threshold concentration of 5 mg L−1. Aside from the excellent scale inhibition efficiency, it does not contain phosphorus, which could avoid eutrophication of water to a certain extent, so it is beneficial for protecting the water environment. Based on the above reasons, it can be used to inhibit the formation of CaSO4 scale in circulating cooling water systems.

Table 5

Scale inhibition efficiency against CaSO4 of SVIS-AA copolymer and PAA

Scale inhibitors Scale inhibition efficiency against CaSO4 (%)
 
1 (dosage of scale inhibitors, mg L−1
PAA 25.4 46.4 75.3 84.7 85.9 86.2 85.5 
SVIS-AA 43.2 73.6 88.3 94.2 98.6 98.3 97.8 
Scale inhibitors Scale inhibition efficiency against CaSO4 (%)
 
1 (dosage of scale inhibitors, mg L−1
PAA 25.4 46.4 75.3 84.7 85.9 86.2 85.5 
SVIS-AA 43.2 73.6 88.3 94.2 98.6 98.3 97.8 

Effect of temperature on scale inhibition efficiency against CaCO3

The effect of temperature on scale inhibition efficiency of SVIS-AA copolymer against CaCO3 was investigated, and the results are presented in Table 6. It was found that the scale inhibition efficiency decreased with the increase of temperature. It could be attributed that with the increase of temperature, the growth rate of CaCO3 was enhanced as the solubility of calcium carbonate reduced (Zhang et al. 2016), even though the scale inhibition efficiency could remain 91% at the threshold concentration of 18 mg L−1, which indicated the good resistance of SVIS-AA copolymer to high temperature. Therefore, it can be used in high-temperature water environments to inhibit the formation of CaCO3 scale.

Table 6

Effect of temperature on scale inhibition efficiency of SVIS-AA copolymer against CaCO3

Temperature (°C) Scale inhibition efficiency (%)
 
2 (dosage of scale inhibitors, mg L−110 12 14 16 18 20 22 24 
60 37.1 50.6 71.9 87.6 95.4 100 100 100 100 100 100 100 
70 26.4 30.5 53.2 71.6 83.5 89.9 93.6 100 100 100 99.9 100 
80 13.2 18.1 29.4 42.4 68.5 80.6 91.2 94.3 96.5 96.8 96.3 97.1 
90 6.5 10.2 20.4 35.8 52.5 75.5 83.2 86.8 91.7 91.4 90.8 91.9 
Temperature (°C) Scale inhibition efficiency (%)
 
2 (dosage of scale inhibitors, mg L−110 12 14 16 18 20 22 24 
60 37.1 50.6 71.9 87.6 95.4 100 100 100 100 100 100 100 
70 26.4 30.5 53.2 71.6 83.5 89.9 93.6 100 100 100 99.9 100 
80 13.2 18.1 29.4 42.4 68.5 80.6 91.2 94.3 96.5 96.8 96.3 97.1 
90 6.5 10.2 20.4 35.8 52.5 75.5 83.2 86.8 91.7 91.4 90.8 91.9 

Effect of Ca2+ concentration on scale inhibition efficiency against CaCO3

The effect of concentration of Ca2+ on scale inhibition efficiency of SVIS-AA against CaCO3 was studied, and the results are shown in Table 7. With the increase of Ca2+ concentration, the scale inhibition efficiency of SVIS-AA copolymer decreased. The reason should be that with the increase of Ca2+ concentration, the reaction probability among ions increased, so the growth of CaCO3 would accelerate (Zhang et al. 2016). Moreover, carboxyl groups were likely to react with Ca2+ and the formed polymer salt was insoluble in water, which could also cause the decrease of scale inhibition efficiency. At different Ca2+ concentrations, the threshold concentration of SVIS-AA copolymer is 18 mg L−1. Under the conditions of the threshold concentration of SVIS-AA copolymer, the scale inhibition efficiency decreased with the increase of Ca2+ concentration, but the scale inhibition efficiency could be 70% even when Ca2+ concentration was 1,200 mg L−1. This demonstrated that SVIS-AA copolymer has good resistance to high hardness. Therefore, it can be used in high hardness water environments to inhibit the formation of CaCO3 scale.

Table 7

Effect of Ca2+ concentration on scale inhibition efficiency of SVIS-AA against CaCO3

Ca2+ (mg L−1Scale inhibition efficiency (%)
 
2 (dosage of scale inhibitors, mg L−110 12 14 16 18 20 22 24 26 
300 9.2 17.1 26.4 37.4 60.5 77.6 87.2 90.3 94.5 94.8 93.3 94.7 94.3 
600 8.5 15.9 20.7 35.5 54.6 70.9 80.6 89.2 93.8 93 93.5 93.5 93.8 
900 7.6 12.1 13.7 21.3 37.8 48.2 67.8 78.9 83.7 83.5 94.6 82.9 83.6 
1,200 4.5 6.7 7.3 8.7 12.9 18.7 35.9 50.5 65.8 70.2 70.6 70.1 71.5 
Ca2+ (mg L−1Scale inhibition efficiency (%)
 
2 (dosage of scale inhibitors, mg L−110 12 14 16 18 20 22 24 26 
300 9.2 17.1 26.4 37.4 60.5 77.6 87.2 90.3 94.5 94.8 93.3 94.7 94.3 
600 8.5 15.9 20.7 35.5 54.6 70.9 80.6 89.2 93.8 93 93.5 93.5 93.8 
900 7.6 12.1 13.7 21.3 37.8 48.2 67.8 78.9 83.7 83.5 94.6 82.9 83.6 
1,200 4.5 6.7 7.3 8.7 12.9 18.7 35.9 50.5 65.8 70.2 70.6 70.1 71.5 

Morphology study of CaCO3 and CaSO4 after SVIS-AA treatment

SEM of CaCO3 and CaSO4

The morphologies of CaCO3 and CaSO4 were characterized by SEM before and after the treatment by SVIS-AA, and the results are shown in Figure 5. It can be seen that (a) the morphologies of CaCO3 without SVIS-AA copolymer (a) showed a cubic structure with layers, and the surfaces were compact and smooth (a). After SVIS-AA copolymer was added into the test solution, the morphologies of CaCO3 precipitate changed to a smooth sphere structure (b). Specifically, the crystal form of the former showed the characteristics of calcite, while the latter was more like vaterite (Ling et al. 2012).

Figure 5

SEM photographs of (a) CaCO3 without SVIS-AA copolymer, (b) after SVIS-AA treatment and (c) CaSO4 without SVIS-AA copolymer, (d) after SVIS-AA treatment.

Figure 5

SEM photographs of (a) CaCO3 without SVIS-AA copolymer, (b) after SVIS-AA treatment and (c) CaSO4 without SVIS-AA copolymer, (d) after SVIS-AA treatment.

In Figure 5, it is clear that in the absence of SVIS-AA copolymer, the morphologies of CaSO4 were rod shape with sharp edges (c). However, after the treatment of SVIS-AA copolymer, the morphologies of CaSO4 were defective rod shape with a rough surface (d). In a word, the morphologies of both CaCO3 and CaSO4 changed a lot with the treatment of SVIS-AA copolymer.

XRD analysis of CaCO3 and CaSO4

The XRD spectra of CaCO3 are shown in Figure 6(a) and 6(b). A crystal may contain multiple types of crystal forms. A crystal form generally contains multiple characteristic diffraction peaks. Different characteristic diffraction peaks correspond to different diffraction angles (2θ). Calcium carbonate exists mainly in three crystal forms: calcite, aragonite and vaterite. In spectrum (a), CaCO3 mainly existed in the form of calcite owing to the diffraction peaks at 23.14°, 29.48°, 35.99°, 47.62°, and 48.60° according to relevant literature (Chen et al. 2015; Menzri et al. 2017; Wang et al. 2017). In spectrum (b), the diffraction peaks at 23.89°, 27.21°, 32.82°, 43.96° and 49.15° correspond to vaterite, and the diffraction peak at 29.49° corresponds to calcite. Compared with spectrum (a), the diffraction peaks of calcite have mostly disappeared, and CaCO3 mainly existed in the form of vaterite. Therefore, it shows the trend that the crystal form of CaCO3 changed from calcite into vaterite in the presence of SVIS-AA copolymer (dosage of SVIS-AA copolymer, 15 mg L1).

The XRD spectra of CaSO4 are presented in Figure 6(c) and 6(d). Calcium sulfate exists mainly in three crystal forms: CaSO4, CaSO4 · 2H2O and CaSO4 · 0.5H2O. In spectrum (c), the diffraction peaks at 11.73° and 23.48° correspond to CaSO4 · 2H2O. The diffraction peaks at 14.84°, 25.80°, 29.82° and 49.47° correspond to CaSO4 · 0.5H2O according to relevant literature (Ling et al. 2012; Zhao et al. 2016). In spectrum (d), the diffraction peaks at 14.84°, 25.84°, 29.82°, 32.01°, 42.38° and 49.42° correspond to CaSO4 · 0.5H2O. The diffraction peaks of CaSO4 · 2H2O disappeared and the intensity of the diffraction peaks of CaSO4 · 0.5H2O were significantly enhanced. It shows the trend that the crystal form of CaSO4 changed from the crystal phase mixture of CaSO4 · 2H2O and CaSO4 · 0.5H2O into CaSO4 · 0.5H2O.

Figure 6

XRD photographs of (a) CaCO3 without SVIS-AA copolymer, (b) after SVIS-AA treatment and (c) CaSO4 without SVIS-AA copolymer, (d) after SVIS-AA treatment.

Figure 6

XRD photographs of (a) CaCO3 without SVIS-AA copolymer, (b) after SVIS-AA treatment and (c) CaSO4 without SVIS-AA copolymer, (d) after SVIS-AA treatment.

Mechanism of calcium scale inhibition

SVIS-AA copolymer contains a large number of carboxyl and sulfonic groups, which are the structural basis of the copolymer to inhibit scale. Carboxyl and sulfonic groups could recognize and encapsulate Ca2+ in the solution of scale, and form water-soluble complexes (Ling et al. 2012; Wang et al. 2014). Furthermore, carboxyl and sulfonic groups could adsorb on the surface of CaCO3 and CaSO4 crystals, which would distort and damage the crystal structure. In addition, sulfonic groups can improve the water solubility of SVIS-AA copolymer and avoid the formation of polymer salt. Based on the above reasons, SVIS-AA copolymer possesses an excellent ability to control scale.

CONCLUSIONS

A phosphorus-free scale inhibitor was successfully synthesized. The structure of the product was characterized by FT-IR, 1H NMR and 13C NMR. It showed better scale inhibition efficiency against CaCO3 and CaSO4 than PAA in the same conditions. Meanwhile, SVIS-AA copolymer could maintain excellent scale inhibition efficiency in high temperature and high hardness environments. Finally, the SEM and XRD study of CaCO3 and CaSO4 indicated that SVIS-AA copolymer could change the morphologies of particles.

ACKNOWLEDGEMENTS

This study was funded by Colleges and Universities in Hebei Province Science and Technology Research Project (ZD2015118).

Conflict of interest

The authors declare that they have no conflict of interest.

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