A simple, rapid and accurate method for the determination of monoethanolamine (MEA) in PHWR steam-water circuits has been developed. MEA is added in the feed water to provide protection against corrosion while hydrazine is added to scavenge dissolved oxygen. The quantitative determination of MEA in presence of hydrazine was accomplished using derivatization ion chromatography with conductometric detection in nonsuppressed mode. A Metrosep cation 1-2 analytical column and a Metrosep cartridge were used for cation separation. A mixture of 4 mM tartaric acid, 20% acetone and 0.05 mM HNO3 was used as eluent. Acetone in the mobile phase leads to the formation of different derivatives with MEA and hydrazine. The interferences due Na+ and NH4 + were eliminated by adopting a simple pretreatment procedure employing OnGuard-H cartridge. The limit of detection limit of MEA was 0.1
In Indian pressurized heavy water reactors (IPHWRs), the nuclear heat is transported by the heavy water (D2O) coolant in the primary heat transport system to the secondary light water (H2O) for steam production. In the steam-water circuit, two-phase erosion corrosion is a serious operational issue. To provide protection against the corrosion, volatile amines are added in the feed water of steam generators (SG) to raise the pH of the water. These amines volatilize along with the steam and are partly carried away to the turbine and condenser part, thereby providing protection against corrosion to the entire steam-water circuit. Along with amine, hydrazine is injected to scavenge dissolved oxygen, and thereby produce reducing conditions. The treatment is called as an all volatile treatment (AVT), and the amines are used as AVT reagents [
Quantification of MEA is an essential step in determining its appropriate amount to use for maximal protection. The accurate and reliable determination of MEA in the presence of hydrazine is a challenging analytical problem because of their similar chemical properties. The spectrophotometric method developed in our laboratory earlier could not be applied for the determination of MEA because of severe interference from hydrazine [
Ion chromatography (IC) finds wide applications in power plant industry for the determination of trace concentrations of ionic impurities in feed and process streams [
Ion chromatography was performed with Metrohm (Herisau, Switzerland) instrumentation consisting of a 709 IC Pump, 733 IC Separation Center and a 732 IC conductivity detector
Reagents used were of analytical grade and obtained from Sarabhai M. Chemicals, Baroda, India. Deionised water (18 MΩ) obtained from a Barnstead water purification system (Barnstead, Boston, Mass, USA) was employed throughout. OnGuard-H cartridge was obtained from Dionex (Sunnyvale, Calif, USA). Stock standard solutions (1 g L−1) were prepared for MEA and hydrazine. The working standard mixtures for calibration were prepared weekly from the stock standard.
Different eluents were tested for the separation of MEA and hydrazine because both coeluted from the analytical column (Table
Retention time (
Composition of mobile phase | MEA | Hydrazine |
---|---|---|
4 mM tartaric acid + 1 mM dipicolinic acid | 2.37 | 2.38 |
1 mM oxalic acid | 4.64 | 4.66 |
4 mM tartaric acid + 20% acetone + 0.05 mM HNO3 | 2.81 | No peak |
Steam generator water sample was passed through OnGuard-H cartridge to remove interfering cations (alkali and transition metal ions). The recommended guidelines for the use of OnGuard cartridges supplied by Dionex Corp. (Sunnyvale, Calif, USA) were followed. OnGuard-H cartridge was washed with 10 mL deionised water. About 5 mL of the sample solution was loaded on the cartridge and allowed to flow at the rate of 2 mL min−1. The first 3 mL of elute was rejected and the next 2 mL was collected. Before injection into the ion chromatograph, sample solutions were diluted (1 : 1) with mobile phase in order to maintain the same pH. This step also ensures that amines are in the protonated form.
Due to their similar chemical properties, both MEA and hydrazine coeluted from the analytical column (Table
Chromatogram of a synthetic mixture of MEA (2
The different selectivities of MEA and hydrazine for the stationary phase and hence their retention times on the column using this mobile phase could be explained by the rapid reactions of hydrazine and MEA with acetone. It is well known that simple mixing of amine and carbonyl compound at room temperature produces an imine, and in fact, the reaction is so vigorous in the case of hydrazine that not only the reaction mixture needs to be cooled in an ice bath, but also the rate of addition of hydrazine is controlled [
Thus, in the case of hydrazine, the acetone azine (
The aqueous elution media optimized in our study contained 100 fold dilute inorganic acid (0.05 mM HNO3) as compared to that used in the Metrohm application note C107 [
A linear calibration plot with a regression coefficient (
Typical water chemistry specifications in the secondary system of PHWR are given in Table
Typical water chemistry specifications in the secondary cycle of steam-generating systems: MEA, hydrazine and ionic impurities.
Parameter | Permissible range |
---|---|
MEA, | 3–7 |
Hydrazine, | 50–200 |
pH | 9-10 |
NH4 +, | <1 |
Na+, | <5 |
<1 | |
Total Hardness, | <2 |
Silica, | <20 |
Recovery of MEA in sample.
Added ( | Found ( | % Recovery |
---|---|---|
1 | 0.95 | 95 |
5 | 5.1 | 102 |
10 | 9.8 | 98 |
As samples were diluted 1 : 1 with mobile phase, a chromatogram of this blank solution was recorded in order to find out the contribution from impurities, if any, present in mobile phase. There was no peak observed for MEA or other cations in the blank solution. A typical chromatogram of steam generator (SG) water sample is shown in Figure
Chromatogram of steam generator water samples showing (a) MEA peak and an impurity peak (b) enhancement of the MEA peak on spiking the sample solution with MEA (5
The derivatization ion chromatographic method developed for MEA determination in the presence of hydrazine has been shown to be sensitive and specific. The required sensitivity and precision were achieved by the use of acetone in the mobile phase, a single-step pretreatment, low conductivity, and stable baseline. The technique was applied to the determination of MEA in steam generator water from the power plant. For solutions having high salt concentration, a single OnGuard-H may not be enough, and also the recovery of MEA needs to be carried out before the application of this method.
The authors are grateful to D. T. Mukherjee, Director, Chemistry Group, Bhabha Atomic Reasearch Centre, Mumbai, for his encouragement and support in carrying out this work. The authors wish to express their sincere thanks to Dr. A. V. R. Reddy, Head, Analytical Chemistry Division, Bhabha Atomic Research Centre, Mumbai, for his valuable suggestions.