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Jul 26, 2012 - high-performance, non-polluting green water treatment scale and corrosion inhibitors is a main way to improve the cooling water circulation ...
Advanced Materials Research Vols. 550-553 (2012) pp 643-647 © (2012) Trans Tech Publications, Switzerland doi:10.4028/www.scientific.net/AMR.550-553.643

Online: 2012-07-26

Effect of Synthesis Process Parameters of PESA on its Scale-inhibiting Performance Xia Li1, a, Huaizhi Wu2, b and Xiansen Li3, c 1, 2, 3

Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, Qingdao 266101, Shandong, China a

[email protected], [email protected], [email protected]

Keywords: PESA; Scale-inhibiting performance; Scale inhibitor

Abstract: Polyepoxy succinic acid (PESA) is a well-established green scale inhibitor. As compared with the testing results of the samples from some relevant domestic companies, it is found that the scale inhibition performance exhibits a significant deviation from batch to batch. Over the course of PESA synthesis, the focus was on the investigation of the effect of the main process parameters such as pH in the synthetic system, temperature and time upon the scale inhibition performance of the resultant product. The findings show that the pH in the synthetic system affects significantly the intermediate yield in the epoxidation step, and that there exists a correlation between the operational temperature and time in the polymerization process. When the 20 ppm sample prepared at the optimized polymerization temperature and time of 90 ℃ and 2 h, respectively, was dosed in a testing system, the scale inhibition performance at 10 h on stream is invariably no less than 95%. Introduction In chemical industry, the circulating utilization of cooling water can save a lot of water consumption. However, it can simultaneously produce large amounts of fouling in a circulating process, which is a significant restricting factor of wastewater recycling rate[1]. The development of high-performance, non-polluting green water treatment scale and corrosion inhibitors is a main way to improve the cooling water circulation rate and to minimize water pollution [2]. Polyepoxy succinic acid (referred to as PESA) was originally developed by U.S. Prector & Gamble, Betz, first as scale and corrosion inhibitors in the late 1980s and early 1990s [3,4,5]. As it has a clean manufacturing process and can be efficiently and stably degraded by microbe or fungal into environmentally-friendly product, it is considered as an “environmentally-benign” green water treatment agent [6]. Since the late 1990s some institutions have started studying PESA [7, 8]. As a result, it has promoted the application of PESA and the formulation of the industrial standards of the Ministry of Chemical Industry HG/T3823-2006 in China, which is limited due to the lack of scale inhibition performance indicators. In comparison with the scale inhibition performances of the domestic PESA samples, it is found that they basically meet the technical criteria of the Ministry of Chemical Industry. However, the scale inhibition performance of the product varies from 40% to 80%, which directly impacts the dosage and actual results. We study herein the effect of synthesis process parameters of PESA on its scale inhibition performance to improve both the performance and reliable quality of PESA.

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Experimental As reported in the literature [9, 10], the route of polyepoxy succinate synthesis is described as follows: maleic anhydride as starting material through hydrolysis, alkalization to generate disodium salt of the maleic acid, then epoxidation with hydrogen peroxide solutions and catalyst to produce the intermediate epoxy succinic acid sodium salt; the intermediate epoxy succinate polymerization with calcium hydroxide as an initiator into the targeted end product polyepoxy succinate. Raw Materials: maleic acid, tartaric acid, fumaric acid (Tianjin Guangfu Chemical Research Institute), and epoxy succinic acid (ACROS ORCANICS, USA) are all chromatographically pure; maleic anhydride, sodium hydroxide, hydrogen peroxide (30 wt.%), sodium tungstate, calcium hydroxide, calcium chloride, sodium bicarbonate, sodium tetraborate decahydrate, EDTA and hydrochloric acid are all of analytical grade. Instruments: magnetic stirrer, four flasks, thermometer, condenser, pH meter, water bath, ICS 3000 multifunctional ion chromatography (Dionex Company), and Milli-Q-Advantage A10 ultra-pure water preparation apparatus. Methods: the reaction process has two steps. The first step is using maleic anhydride to generate the intermediate epoxy succinic acid (ESA). The second step is related to the intermediate epoxy succinate polymerization to polyepoxy succinate. During the reaction period, part of the intermediate epoxy succinic acid may be converted into the byproduct of tartaric acid, thus affecting the yield of the intermediate epoxy succinic acid, thereby impacting further the polymerization time, the product selectivity and scale-inhibiting performance of the final product polyepoxy succinic acid. Therefore, the yield of epoxy succinic acid intermediate with a sufficiently high purity is a priority to improve both the product quality and scale inhibition performance. In order to identify the yield of the intermediate epoxy succinic acid, the ICS3000 ion chromatography system is used to quantify the sample composition through filtering, pre-column priming and separation with an IonPacAS11 column, gradient elution using automated eluent generator to generate KOH eluent, and analysis of chromatogram to calculate the percentage of each component. By comparing with tartaric acid, maleic acid, epoxy succinic acid and fumaric acid standard samples (chromatographic grade) to calculate the yield of epoxy succinic acid. The scale inhibition performance of as-synthesized polyepoxy succinate experimental products at different polymerization temperature and polymerization time was tested by the method in national standards of People's Republic of China named water treatment inhibitor in determining the performance of calcium carbonate deposition (GB/T16632-1996). Testing conditions: Ca2+ concentration is 240 mg/l; HCO3-concentration is 732 mg/l; water bath temperature is 80 °C; polymerization time is 10 h; and the dosage amount of scale inhibitor is 20 mg/l. Results and Discussion 3.1 The intermediate epoxy succinate Orthogonal experiment analysis is carried out herein to investigate the effect of the reaction process parameters such as pH, temperature and reaction time on the yield of ESA. The experimental results are showed in Table 1.

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Table 1 Orthogonal test results No.

Orthogonal testing factor Reaction time H2O2/maleic acid pH (h) ratio 1 6 1.0

ESA yield (%)

1

Temperature (˚C ) 60

2 3

60 60

1.5 2

7 8

1.1 1.2

95.8 78.7

4

65

1

7

1.2

96.9

5

65

1.5

8

1.0

81.3

6

65

2

6

1.1

91.2

7

70

1

8

1.1

80.2

8

70

1.5

6

1.2

86.5

9

70

2

7

1.0

96.5

R

6.3

2.8

49.0

5.1

88.6

It can be seen from Table 1 that the impacting extent of various experimental factors on the ESA yield follows the order: system pH > reaction temperature > H2O2 dosage amount > reaction time. The severest impact on the ESA yield is pH, and the optimal choice of process condition is C2A3D3B1. It is difficult to control the reaction process because the reaction proceeds violently together with pH and temperature fluctuations in the course of mixing the raw materials. The reason might be due to the fact that at the system pH < 7 the generated ESA is prone to hydrolysis into the byproduct of tartaric acid. On the other hand, at the system pH > 7 hydrogen peroxide is easily broken down, which causes maleic acid not to be fully reacted and thus lowers the production rate of epoxy succinic acid. The maximum yield of intermediate epoxy succinic acid was obtained in the C2A3D1B3 process with the pH ranging from 6.5 to 7. The ion chromatogram of the resultant epoxy succinate is shown in Fig. 1 and the relative content of each component is listed in Table 2. Excluding non-product impurities such as pure water, chloride ions and other factors, the purity of intermediate epoxy succinate acid is more than 99%.

Fig. 1. Ion chromatogram (IC) of the reactive intermediate ESA (1-4: impurities, e.g., Na+ and Cl-, etc.; 5: tartaric acid; 6: epoxy succinic acid (ESA))

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No. 1 2 3 4 5 6 Total:

Table 2 IC retention time of various products in an ESA synthetic system Retention time (min) Peak height (μS) Peak Area (μS*min) Relative area (%) 2.65 0.104 0.078 2.08 2.97 0.095 0.033 0.88 3.32 0.144 0.060 1.59 5.61 0.597 0.099 2.63 10.61 0.080 0.035 0.94 14.00 8.117 3.464 91.89 9.137 3.770 100.00

3.2 Polyepoxy succinic acid scale inhibition performance The scale inhibition performance of polyepoxy succinic acid product at the polymerization temperatures of 80 and 90 °C as a function of polymerization time is shown in Fig. 2.

Fig. 2. Scale-inhibiting performance curve ( Reaction temperature is 90 ˚C; Reaction temperature is 80 ˚C) As shown in Fig. 2, when the polymerization temperature is 90 °C, with increasing polymerization time, the scale inhibition performance is improved. However, when the polymerization time is beyond 2.5 h, the scale inhibition performance turns worse. When the polymerization temperature is 80 °C, the scale inhibition performance is increasing with an increase in polymerization time, but with the slope gradually decreased. When the polymerization time is more than 3.5 h, the scale-inhibiting performance drops. It can be found that when the polymerization temperature is lower, achieving the same scale inhibition performance requires a longer polymerization time and the scale inhibition performance is slightly reduced. Hence, the optimal reaction conditions are listed as follows: reaction temperature of 90 ˚C and reaction time of 2.0 ~ 2.5 h. In order to optimize the synthetic parameters of polyepoxy succinate and achieve the reliable scalability (e.g., the mass production of 50 kg of polyepoxy succinate), with automatic control over the material feeding system, temperature, and strictly controllable pH indicator, it can meet the goal at a temperature of 65 °C, an epoxidation pH value of 6~7, an epoxidation reaction time of 1.5 h, a polymerization reaction pH value of 10~12, a polymerization temperature of 90 °C, and a reaction time of 2 h. It is found that the scale inhibition performance of each batch of polyepoxy succinate remains a high level, as shown in Table 3.

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Table 3 Pilot-scale scale inhibition performance of PESA PESA concentration (mg/l) Scale inhibition efficiency (%)

Pilot-scale-1

20

96.2

Pilot-scale-2 Pilot-scale-3 Pilot-scale-4

20 20 20

95.6 96.8 95.7

From Table 3, it can be seen that if we can effectively control the reaction pH value, temperature, reaction time and other important influential factors, PESA is able to achieve a superior scale inhibition performance even at a low dosage amount. Conclusions 1. The results based on orthogonal test and ion chromatographic analysis showed that the significance of experimental factors impacting the ESA yield from strong to weak can be ranked as follows: pH > reaction temperature > H2O2 dosage > reaction time. The effect of pH is most significant. For the dosing rate of hydrogen peroxide solutions will affect the pH value and reaction temperature, it should strictly control both the dosing rate of hydrogen peroxide and pH value of the reactive system. 2. In the reaction process, it exhibits a correlation between reaction temperature and time. With a high synthesis temperature, reaction time can be shortened accordingly. It is shown that the optimized polymerization temperature and reaction time are 90 ℃ and 2 h, respectively. 3. The pilot-scale scale inhibition performance of PESA is satisfactory and reliable. At a dosage amount of 20 mg/l, its steady-state scale inhibition efficiency can reach above 95%. Acknowledgements This work was financially supported by cooperative projects between academy and region (Y013011108) and Qingdao science and technology support projects in public area (Y134011108). References [1] Rong Wang, Bingyun Shen, Yao Wang: Boiler Technology. Vol. 03(2011), p. 14 (In Chinese) [2] Lihua Zhang, Chengsong Zheng, Yan Zhang, et al: Industrial Water Treatment. Vol. 30(2010), p. 5. (In Chinese) [3] J. Michael Brown, John F. McDowell, U.S. Patent 5062962. (1991) [4] Brown J., Michiael, Mcdowell, U.S. Patent 5147555. (1992) [5] Bush, Rodney D., Heinzman, Stephen W., et al. U.S. Patent 4654159. (1987) [6] Rongchun Xiong, Xueling Dong, Gang Wei: Environmental Engineering. Vol. 18(2000), p. 22 (In Chinese) [7] Rongchun Xiong, Gang Wei, Di Zhou, et al: Industrial Water Treatment. Vol. 19(1999), p. 11 (In Chinese) [8] Fengyun Wang, Zhifang Chang, Wei Dong, et al: Chinese Journal of Applied Chemistry. Vol. 18(2001), p. 746 (In Chinese) [9] Huaping Bai, Zhiren Zhao, Wu Lei, et al: Industrial Water Treatment. Vol. 22(2002), p. 24 (In Chinese) [10] Chunju Xu, Huilong Wang, Jian Xin: Petrochemical Technology. Vol. 35(2006), p. 84 (In Chinese)

Advances in Chemical Engineering II 10.4028/www.scientific.net/AMR.550-553

Effect of Synthesis Process Parameters of PESA on its Scale-Inhibiting Performance 10.4028/www.scientific.net/AMR.550-553.643