Copper-amine speciation: an electrochemical investigation of the selection of volatile amines for steam generator water

Abstract

Addition of volatile amines for pH control to steam generator water of power plants to protect the steam water system for corrosion is called all volatile treatment (AVT) of steam generator water. Metal ion concentrations in steam generator water will generally be in the μg 1 −1 range. Pseudopolarography in combination with differential pulse anodic stripping voltammetry copper speciation studies (at 50 μg 1 −1 copper concentration) were carried out in aqueous media containing four important amines, viz. 3-methoxypropylamine (3MPA), 1-dimethylamino-2-propanol (DMPA), 2-dimethylaminoethanol (DMAE) and piperidine (Pip), all having a large potential for use as AVT reagents. The copper-amine complexes were identified and their log stability constants (log K) values were as follows: [Cu(I)(3MPA) 2]: 10.47; [Cu(II)(OH) 2(DMPA) 2]: 20.33; [Cu(II)(OH) 2(DMAE) 2]: 20.51; [Cu(I)(Pip)]: 8.29; [Cu(I)(Pip) 2]: 9.89; [Cu(I)(OH) 2(Pip) 2]: 16.67. Electroreduction mechanisms of these identified species at a hanging mercury drop electrode were studied. The ability of some of the amines to influence the stepwise reduction/oxidation of copper results in impeding its transport in dissolved form in the steam generator water. Hence it is recommended that only those amines that do not stabilize Cu(I) in solution be selected for use as AVT reagents for ensuring better performance of steam water circuits in power industries.