THERMAL-DECOMPOSITION OF NITRATED TRIBUTYL-PHOSPHATE

Extended contact between heated mixtures of trin-butyl phosphate (TBP) and aqueous solutions of nitric acid and/or heavy metal nitrate salts at elevated temperatures can lead to exothermic reactions of explosiv e violence. Most solvent extraction operations (e.g., Purer) are condu cted at ambient conditions without heating TBP and have been performed safely for decades, but several explosions involving TBP have occurre d in the United States, Canada, and the former Soviet Union. This inve stigation was undertaken to characterize the products of thermal decom position of both single- and two-phase mixtures of TBP, nitric acid, a nd water under a variety of conditions. The data indicate that the ext ent of reaction and the rate of gaseous product formation are affected by the presence of Zr4+, distillation compared with reflux conditions , temperature, water/HNO3 and HNO3/TBP ratios, and whether the decompo sition occurs under constant pressure or constant volume conditions. H igher reaction temperatures accelerate the rate of decomposition, but the extent of decomposition, as measured by the quantity of gaseous pr oducts, was greater at lower temperatures when the decomposition was p erformed under distillation conditions. Higher gas production occurs u nder reflux conditions, lower H2O/HNO3 ratios, and when a separate wat er-HNO3 phase is initially present. The major gaseous products include N-2, CO, CO2, NO, and N2O. Measurable amounts of NO2 were not present in the final product mixture, although an orange color suggesting the presence of NO2 was observed in the early stages of decomposition. Th e major liquid products were dibutyl phosphoric acid, butyl nitrate, a nd water. Small amounts of C-1-C-4 carboxylic acids were also present. Because of the small sample sizes that were employed and the isotherm al conditions of the decomposition, runaway reactions were not observe d. Some possible reaction path ways are considered.