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Hydroxylamine decomposition in the presence of iron studied by calorimetry, online mid-IR and UV-vis spectroscopy

Recent explosions at two chemical plants, one in the United States and one in Japan, involving hydroxylamine manufacture underline the lack of mechanistic understanding about this industrially relevant compound. The basic chemical properties of hydroxylamine have been known for decades but its tendency to decompose in the presence of transition metals, in particular Fe(II)/Fe(III), still remains a mystery. Recent studies [1, 2] have not been successful in identifying without controversy the mechanism, products and intermediates of decomposition. In this context we are undertaking a research project to investigate the decomposition of hydroxylamine in aqueous solution in the presence of 3d transition metals. The final aim is to obtain a satisfactory description of the reaction mechanism. A concentration, pH and temperature dependence mechanistic study will be completed using a new pressure-proof small volume reactor [3] that combines calorimetry with online mid-infrared and UV-visible spectroscopy. Chemical models will be fitted to the measured data to determine the reaction mechanism and associated kinetic and thermodynamic parameters [4]. Since there is significant gas production during the decomposition process, the pressure increase inside the reactor will be used as a forth signal. Validation of the online measurements and determination of the chemical species present in the liquid and gas phases will be done by offline GC/MS analysis. Preliminary results for the decomposition of hydroxylamine in the presence of Fe(II)/Fe(III) will be presented including measurements from all the online instrumentation. [1] Cisneros, L. O.; Wu, X. et al. Process Safety and Environmental Protection 2003 81(B2), 121. [2] Wei, C. Y.; Saraf, S. R. et al. Thermochimica Acta 2004, 421(1-2), 1. [3] Visentin, F.; Gianoli, S. I. et al. Organic Process Research & Development 2004, 8(5), 725. [4] Puxty, G.; Maeder, M. et al. Journal of Chemometrics 2005, in print.