Isothermal Oxidation of White Phosphorus Dispersed in Water in a Stirred-Tank Reactor

Abstract

A global, first-order kinetic model was found to fit the data for the isothermal wet oxidation of elemental white phosphorus (P) in a batch, stirred-tank reactor. The initial concentration of white phosphorus solids was held constant at 1 g/L and an air flow of 2.0 standard liters per minute was used to supply the oxygen for the reaction. A CD6-like turbine and an A2 impeller were evaluated at speeds from 1000-2250 rpm. For the CD6-like turbine, mass transfer effects were assumed to be eliminated above 2000 rpm. Thus, the CD6-like turbine with a speed of 2250 rpm was selected for the isothermal studies. Particle size and temperature were varied. For the isothermal conditions, the first order kinetic constant varied from 0.022 min at 46 °C to 0.078 min at 80 °C. The apparent activation energy was 6.78 kcal/mol. Oxygen reacted with the suspended P particles forming oxides of phosphorus, primarily phosphorus pentoxide (P0 or P O). Some of the PO reacted with the water to form PO as the primary product of white phosphorus oxidation. The amount of phosphorus pentoxide absorbed in the water increased with temperature. The rate of phosphate formation followed zero order kinetics and was independent of particle size. As the temperature increased, the ratio of PO/ PO increased. This observation and the apparently low activation energy suggest that diffusion effects may not have been eliminated completely.