Modeling of the N2O4-NO2 reacting system

Reaction systems containing the nitrogen oxides N2O4 and NO2 in equilibrium , pure or dissolved in organic solvents, are successfully modeled in two wa ys: (1) assuming that all species in the system are hard spheres with an at tractive mean field component (HSA); and (2) using a semiempirical equation of state (EOS) developed by Deiters. In both cases, estimates of the relat ive size of the species, obtained by Monte Carlo (MC) simulations, were mad e to reduce the number of adjustable parameters. As a result, for a pure sy stem, both the HSA model and the semiempirical EOS require only three adjus table parameters. MC simulations were also employed to estimate semiempiric al EOS anisotropy parameters for each species without a need of experimenta l data. In this way, the truly adjustable parameters were obtained by takin g only experimental data for the system at 296 K. The agreement between bot h model predictions and experimental results is good, with higher accuracy for the semiempirical EOS. The predicted effect of pressure on the equilibr ium constant of the gas mixture is underestimated by both models. For the c ase of the nitrogen oxides dissolved in a third species, the HSA model and the semiempirical EOS require two and three additional parameters respectiv ely, which are determined from experimental data of the neat solvent in the liquid-vapor coexistence region. Calculations were performed for CCl4 and cyclohexane as solvents. The predicted dissociation constants of N2O4 in th e liquid phase are underestimated by about 25% by the HSA model and overest imated by 5% by the semiempirical EOS.