Models for predicting solubilities of 2,4,6-trinitrotoluene (TNT) and 1,3,5-trinitro-1,3,5-s-triazine (RDX) in supercritical CO2: isothermal–isobaric Monte Carlo simulations

Solubilities of explosives 2,4,6-trinitrotoluene (TNT) and 1,3,5-trinitro-1,3,5-s-triazine (RDX) in supercritical CO2 were calculated using isothermal–isobaric Monte Carlo (NPT–MC) simulations and the Widom test particle method. Multisite interaction potentials between functional groups on the explosives and CO2 molecular centers were chosen to describe the solute–solvent interactions, and calibrated using two experimental solubility values for both cases. The results were compared to experimental data and found to be in good agreement over the range of temperatures and pressures investigated. The results were also compared to those generated using simple pair additive interaction potentials between molecular centers. For low-density regimes, solubility predictions using either mono- or multisite interaction potentials are similar. For regions corresponding to high densities (low temperature or high pressure), the significant contributions to the solubilities predicted using the multisite interaction potentials are due to specific relative orientations of the solute–solvent molecules, indicating that molecular shape and anisotropy are important in this region. Conversely, the monosite interaction potentials are completely isotropic; thus, the results for the two models differ in this density regime.