Statistical Optimization and Selective Separation of RDX and HMX Explosives by Using Binary Solvent Mixtures Containing Ethyl Acetate and Water

The present study introduces the application of a binary solvent of ethyl acetate and water for the selective separation of 1,3,5-trinitroperhydro-1,3,5-triazine (RDX) and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX). The effect of temperature and weight percent of ethyl acetate in water on the solubility of RDX and HMX over a temperature range of 273.15 K to 363.15 K and 70.0 wt.% to 100.0 wt.% ethyl acetate in water mixtures were modelled and optimized using a central composite design (CCD) and response surface methodology (RSM) in Minitab (ver. 16) software. Multiple regression analysis and analysis of variance (ANOVA) showed that the predicted results were in good agreement with the experimental data. The enthalpies of dissolution and mixing of the materials were determined experimentally from the solubility data. The experimental results showed that the solubility ratio of RDX to HMX can change 6.53- to 16.55-fold, indicating a much lower solubility of HMX in this binary solvent, for a relatively selective separation of RDX and HMX mixtures. Separation experiments under optimized conditions showed that 98.3% of the RDX impurity in HMX was recovered in the first precipitation with an HMX purity of > 99.5% as characterized by high performance liquid chromatography (HPLC).