Modeling of the N2O4–NO2 reacting system

Abstract

Reaction systems containing the nitrogen oxides N₂O₄ and NO₂ in equilibrium, pure or dissolved in organic solvents, are successfully modeled in two ways: (1) assuming that all species in the system are hard spheres with an attractive mean field component (HSA); and (2) using a semiempirical equation of state (EOS) developed by Deiters. In both cases, estimates of the relative size of the species, obtained by Monte Carlo (MC) simulations, were made to reduce the number of adjustable parameters. As a result, for a pure system, both the HSA model and the semiempirical EOS require only three adjustable parameters. MC simulations were also employed to estimate semiempirical EOS anisotropy parameters for each species without a need of experimental data. In this way, the truly adjustable parameters were obtained by taking only experimental data for the system at 296 K. The agreement between both model predictions and experimental results is good, with higher accuracy for the semiempirical EOS. The predicted effect of pressure on the equilibrium constant of the gas mixture is underestimated by both models. For the case of the nitrogen oxides dissolved in a third species, the HSA model and the semiempirical EOS require two and three additional parameters respectively, 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 the liquid phase are underestimated by about 25% by the HSA model and overestimated by 5% by the semiempirical EOS.