The sulphate content of a system increases when strong-acid cationic exchange resins leak into a system or when sulphonic acid groups on the resin organic chain detach. To solve this problem, a dynamic cycle method was used in dissolution experiments of several resins under H2O2 or residual chlorine conditions. Results show that after performing dynamic cycle experiments for 120 hours under oxidizing environments, the SO42− and total organic carbon (TOC) released by four kinds of resins increased with time, contrary to their release velocity. The quantity of released SO42− increased as the oxidizing ability of oxidants was enhanced. Results showed that the quantity and velocity of released SO42− under residual chlorine condition were larger than those under H2O2 condition. Data analysis of SO42− and TOC released from the four kinds of resins by the dynamic cycle experiment revealed that the strength of oxidation resistance of the four resins were as follows: 650C > 1500H > S200 > SP112H.

INTRODUCTION

Styrene strong-acid cationic exchange resin, with sulphonic acid group as its exchange group, is commonly used as a cationic exchange resin in mixed bed and as a main source of . Two conditions lead to the decomposition of cationic resins; one is by heating, which allows the sulphonic acid group on the benzene ring to detach, and the other is by oxidizing the α-carbon of the resin backbone to release sulphonic aromatic organic acids (Chun et al. 1998).

Crushed resin leakage occurs even when a resin trapper is set in the mixed-bed outlet. Resins can decompose at a high temperature and high pressure environment or dissolve in the presence of oxides once they enter the boiler water, producing large amounts of and organic acids (Leybros et al. 2010).

The ability of water and steam system to dissolve salt rapidly increases in a thermal power plant, especially in subcritical and supercritical states (Dooley & Svoboda 2010). On one hand, the in boiler water becomes concentrated and then deposits in water tube walls, which causes medium-concentration corrosion and corrosion under the scale; on the other hand, may also be carried into the steam phase and corrode the steam turbine (Vladana et al. 2011). Stainless steel and nickel-based alloys, such as types 316 and 316NG, which have high corrosion resistance, are commonly used as materials for secondary circuit system in nuclear power plants (Meng et al. 2011). Numerous studies have shown that can promote transgranular stress corrosion in 316 and 316NG under acidic conditions. Furthermore, is greatly hazardous for heating equipment materials whether in thermal or nuclear power plants (Dragana & Ljubinka 2011). Therefore, studies on the decomposition characteristics of cationic resins that produce are significant for a safe and economic operation of power plants.

Domestic and foreign studies on resin dissolution have focussed mainly on resin released in demineralized water, especially concerning production of organics. However, few studies on producing have been reported. A static immersion test, which was used in a previous study to examine resin dissolution, is time-consuming and has poor accuracy (Zhang & Liang 1999). In contrast, a dynamic cycle experiment, which is used to study dissolution characteristics of resins, can reflect the actual dissolution velocity of resin and the operation condition of resins in power plants (Søren & Kaj 2005). The current study was designed to use H2O2 generated in the primary loop of a nuclear power plant under nuclear irradiation conditions and residual chlorine produced by sterilization of raw water in a thermal power plant. The influence of these oxidants on strong-acid cationic resins that release and total organic carbon (TOC) in condensate-polishing systems was also determined.

MATERIALS AND METHODS

Types of resin tested

With the increase in unit parameters, a high demand for water used in power plant exists, and high-performance resins are used as ion exchangers in ion-exchange systems. The types of resin used in this study are listed in Table 1.

Table 1

Types of resin used in experiment

Resin classification Resin grades Manufacturers 
Average particle super gel type Amberjet 1500H Rohm & Hass 
Average particle super gel type Dowex Monosphere 650C Dow 
Average particle super gel type Lewatit MonoPlus S200KR Bayer 
Average particle macroporous type Lewatit MonoPlus SP112H Bayer 
Resin classification Resin grades Manufacturers 
Average particle super gel type Amberjet 1500H Rohm & Hass 
Average particle super gel type Dowex Monosphere 650C Dow 
Average particle super gel type Lewatit MonoPlus S200KR Bayer 
Average particle macroporous type Lewatit MonoPlus SP112H Bayer 

Experimental method

Resins were pretreated by washing them with demineralized water to remove mechanical impurities produced during resin production. Acid and alkali treatments of resins (GB/T 5476-1996) were conducted to convert the resins into unified form and activate them so that the dissolution characteristics of the resins become more evident in the experiments. A dynamic cycle dissolution test of resins (DL/T 1077-2007) was conducted after pretreatment, and the experimental setup is shown in Figure 1.

Figure 1

Schematic diagram of dynamic cycle dissolution experimental setup.

Figure 1

Schematic diagram of dynamic cycle dissolution experimental setup.

The dynamic cycle dissolution experiment was performed as follows:

  1. Demineralized water (1.5 L) was poured into a glass storage bottle.

  2. Strong-acid cationic resins (100 mL) pretreated with acid and alkali were transferred into a glass exchange column with 500 mL of demineralized water, ensuring that the level of demineralized water was 10–15 cm above the resin layer.

  3. The experimental device was installed, and the water bath was opened to maintain water temperature at 40 °C. The concentration and amount of the oxidizer mother liquor needed for the given volume of water in the storage bottle was calculated. The calculated amount of mother liquor was added into the storage bottle. The constant pump was opened, and its speed was set. The valve for exchange volume was adjusted to ensure that the liquid level was 10–15 cm above the resin layer.

  4. To keep the concentration of oxidizer constant throughout the experiment, the oxidizer concentration in the storage bottle was measured every 2 hours, and the volume of the oxidizer mother liquor that should be replenished was obtained by using Equation (1). 
    formula
    1
    where Vx is the volume of oxidizer mother liquor that should be replenished in the storage bottle (mL); V is the cycle solution volume in the storage bottle (mL); C is the preset concentration of oxidizer (mg/L); C1 is the oxidizer concentration in the storage bottle (mg/L); C0 is the concentration of oxidizer mother liquor (mg/L).
  5. Continuous cycling was done for 6 d, and 20 mL samples were placed into high-grade polypropylene bottles every 12 hours. The and TOC concentrations were determined by ion chromatography and TOC analyzer, respectively.

Analytical method

The H2O2 concentration was measured by potassium iodide spectrophotometry (Zhuang & Zuo 1991), whereas that of residual chlorine was measured using N,N-diethyl-1,4-phenylenediamine spectrophotometry (GB/T 14424-2008).

Calculation of results

The quantity of and TOC released from the resins were determined by ion chromatography and TOC analyzer, respectively, and the amount of and TOC released from the wet cationic resins were obtained by using Equations (2) and (3) 
formula
2
 
formula
3
where △GN is the increased amount of or TOC over the two-sampling interval time (μg /L of wet resin, μg TOC/L of wet resin); CN and CN−1 are the or TOC concentration of the nth and (n − 1)th sampling solution, respectively (μg/L); VN is the cycle solution volume of the nth sampling (mL); V is the wet resin volume (mL); GN is the corresponding total amount of or TOC released from resins of the nth time (μg /L of wet resins, μg TOC/L of wet resin).
The total average velocity of the and TOC released from resins can be calculated by Equation (4), 
formula
4
where νt is the corresponding total average velocity (μg/(L h)) of the or TOC released from resins, Gt is the total quantity of or TOC released from resins at t time (μg /L of wet cationic resins) and t is the corresponding time (h).

RESULTS AND DISCUSSION

Blank test results

The dissolution properties of the resins in the presence of oxide were investigated. Blank dissolution tests were necessary to eliminate the influence of demineralized water on the resins. High-purity water was used as circulating water in the blank test, and the relevant data obtained are shown in Figures 2 and 3. C1 is the amount of SO42− released from resins (μg /L wet resin) and V1 is the release velocity (μg/(L h)), whereas C2 and V2 are the quantity and velocity of TOC released from resins, respectively.

Figure 2

Variation trend of SO42− released from resins in blank test: (a) dynamic cycle quantity; (b) dynamic cycle velocity.

Figure 2

Variation trend of SO42− released from resins in blank test: (a) dynamic cycle quantity; (b) dynamic cycle velocity.

Figure 3

Variation trend of TOC released from resins in blank test: (a) dynamic cycle quantity; (b) dynamic cycle velocity.

Figure 3

Variation trend of TOC released from resins in blank test: (a) dynamic cycle quantity; (b) dynamic cycle velocity.

The quantity of and TOC released by the four kinds of resins gradually increased with time, contrary to the gradual decrease in release velocity. The maximum quantity and velocity of and TOC were obtained from 650C, whereas the minimum values were from SP112H, which soon became stable. This result indicates that macroporous type resins are more stable than gel-type resins, because the gel-type resin structure is more compact than that of the macroporous type, and it retains more organic sulphonate in the manufacturing process (Francis et al. 1989).

Dynamic cycle test in the presence of H2O2

The data on and TOC released from the four kinds of resins are shown in Figures 4 and 5.

Figure 4

Variation trend of SO42− released from resins under 0.1 mg/L H2O2: (a) dynamic cycle quantity; (b) dynamic cycle velocity.

Figure 4

Variation trend of SO42− released from resins under 0.1 mg/L H2O2: (a) dynamic cycle quantity; (b) dynamic cycle velocity.

Figure 5

Variation trend of TOC released from resins under 0.1 mg/L H2O2: (a) dynamic cycle quantity; (b) dynamic cycle velocity.

Figure 5

Variation trend of TOC released from resins under 0.1 mg/L H2O2: (a) dynamic cycle quantity; (b) dynamic cycle velocity.

The quantity of TOC and released from resins was significantly greater than the blank values when the H2O2 concentration was 0.1 mg/L. The quantity released from 650C resin was most obvious, and the quantity of released reached 48,966.68 μg/L after a dynamic cycle of 120 hours. This result was caused not only by the dissolution of short-chain polymers and organic sulphonates inside the resin during cycling, but also by the reaction of H2O2 with α-carbon inside the resin matrix (Juang & Lee 2002), in which the sulpho-group detached, thereby increasing in the dissolution liquid.

In addition, H2O2 can aggravate the breakage and falling off of by-products during the resin manufacturing process, resulting in increased TOC released from resins. The quantity of released increased, but the release velocity declined. However, the downtrend of the release TOC velocity was not that obvious, showing that the desulphonation rate of cationic resin decreased over time, but the cleavage and shedding rate of organic chain changed diminutively. In terms of resistance strengths for H2O2, the four kinds of resins were ordered as follows: SP112H > S200 > 1500H > 650C.

Dynamic cycle test in the presence of residual chlorine

Chlorine ingot and sodium hypochlorite are used to sterilize raw water, and residual chlorine can be removed by an activated carbon filter. Although activated carbon exhibits good chlorine adsorption, portions of residual chlorine inevitably leak into the exchange system. Hence, a dynamic cycle test in the presence of residual chlorine was designed for this study.

The curves for the dynamic cycle quantity and velocity of released from four resins at 0.1 mg/L residual chlorine are shown in Figure 6. Compared with blank experiment data, residual chlorine had little effect on resins, even though some of the data were abnormal. Theoretically, oxidative chlorine has a strong role in the destruction of resins (Sang & Wang 2009). However, preliminary data showed that the quantity of released from resins under chlorine conditions was even lower than those in the blank experiment. To elucidate this phenomenon, the sample was first oxidized by H2O2 and subsequently boiled and volume-metered by high-purity water. The sample was then tested by ion chromatography.

Figure 6

Variation trend of SO42− released from resins under 0.1 mg/L residual chlorine: (a) dynamic cycle quantity; (b) dynamic cycle velocity.

Figure 6

Variation trend of SO42− released from resins under 0.1 mg/L residual chlorine: (a) dynamic cycle quantity; (b) dynamic cycle velocity.

The quantity of released from resins varied widely by H2O2 treatment, as shown in Figure 7. The in the dissolution liquid was masked by certain substances; that is, the chlorine used in the experiments disturbed the detection by ion chromatography.

Figure 7

Variation trend of released from resins under 0.1 mg/L residual chlorine by H2O2 treatment: (a) dynamic cycle quantity; (b) dynamic cycle velocity.

Figure 7

Variation trend of released from resins under 0.1 mg/L residual chlorine by H2O2 treatment: (a) dynamic cycle quantity; (b) dynamic cycle velocity.

The curves for the dynamic cycle quantity and velocity of TOC released from resins at 0.1 mg/L residual chlorine are shown in Figure 8. The quantity and velocity of TOC changed slightly compared with blank experimental results, and no obvious pattern was observed. Oxidizing chlorine was consumed quickly in the circulating liquid and dosed every 2 hours. Oxidizing chlorine had strong oxidation on resins, and low molecular organics were produced, which resulted in the TOC irregularity.

Figure 8

Variation trend of TOC released from resins under 0.1 mg/L residual chlorine by H2O2 treatment: (a) dynamic cycle quantity; (b) dynamic cycle velocity.

Figure 8

Variation trend of TOC released from resins under 0.1 mg/L residual chlorine by H2O2 treatment: (a) dynamic cycle quantity; (b) dynamic cycle velocity.

The quantity and velocity of released from resins in the presence of 0.1 mg/L residual chlorine were much larger than those with 0.1 mg/L H2O2; that is, the oxidizing ability of residual chlorine was greater than that of H2O2 at the same concentration. The figures show that the amount of and TOC increased with time, but the release velocity decreased. The oxidation resistance of the macro-reticular resin on residual chlorine was stronger than that of the gel type. In terms of anti-chlorine strength, the four kinds of resins were arranged as follows: SP112H > S200 > 1500H > 650C.

CONCLUSIONS

  1. In an oxidizing environment, the amount of and TOC from resins increases with time, contrary to the release velocity. The quantity and velocity of and TOC released from SP112H macroporous type resins are lower than those of the other three gel-type resins (S200, 650C and 1500H). The dynamic cycle quantity of released by the four kinds of resins are arranged as follows: 650C > 1500H > S200 > SP112H.

  2. The stronger the oxidizing ability of the oxidizing agent, the greater the amount of and TOC dissolved from the resins. The quantity and velocity of and TOC released from resins under residual chlorine condition are greater than those under H2O2 condition.

  3. The oxidation resistance of the four kinds of resins is arranged as follows: SP112H > S200 > 1500H > 650C.

ACKNOWLEDGEMENT

This research was financially supported by Large Advanced PWR Major Projects of China (2011ZX06004-017).

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