Photolysis of RDX and HMX in aqueous and organic solvents

Abstract

Direct photolysis of high explosives (HEs) is one of the most promising alternative methods for HE disposal. The procedure is fast and safe because it accomplishes almost a complete mineralization of Hes in a very short period of time. Conventionally, the first order kinetics has been adopted to the photolytic degradation of HEs at various initial concentration and it is reported that the reaction rate also depends on the initial concentration of HEs. In this study, the kinetics of photolysis of RDX and HMX has been extensively investigated through statistical analysis. Based on two nonlinear regression results, the best kinetic model was selected, and the selected kinetic model was tested using the lack of fit test to determine whether the model had a significant amount of lack-of-fit when it was applied to empirical data. Using the selected kinetic model, solvent parameters and the initial concentration of HEs were studied to see their effects on the photolysis rate. Solution pH, buffers, ionic strength and artificial ground water, which contains many cations, were selected as aqueous solution parameters and methanol and isopropanol were chosen as organic solvents. The characteristics of photolysis products were identified using the UV absorbance spectra data of RDX and HMX. Through statistical analyses, the first order kinetic model was chosen to be the best model for the photolysis of RDX and HMX at the initial concentration of 30ppm and 20ppm respectively. Though it follows the first order kinetics, it was detected that the degradation rate depends on the initial concentration of HEs. Na₂HPO₄, which was used as a buffering agent, increased the photolysis rate of RDX. The first order degradation constant of RDX became high in acidic solution. Ionic strength had negative effects on the photolysis rate. The photolysis rate of RDX was slowest in AGW among all aqueous solutions, and the degradation rate of both RDX and HMX increased in organic solvents. HMX was less susceptible to the photodegradation than RDX.