Modeling the vapor-liquid equilibrium and association of nitrogen dioxide/dinitrogen tetroxide and its mixtures with carbon dioxide

A. Belkadi, F. Llovell, V. Gerbaud, L. F. Vega

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Abstract

We have used in this work the crossover soft-SAFT (soft-Statistical Associating Fluid Theory) equation of state to model nitrogen dioxide/dinitrogen tetroxide (NO2/N2O4), carbon dioxide (CO2) and their mixtures. The prediction of the vapor-liquid equilibrium of this mixture is of utmost importance to correctly assess the NO2 monomer amount that is the oxidizing agent of vegetal macromolecules in the CO2 + NO2/N2O4 reacting medium under supercritical conditions. The quadrupolar effect was explicitly considered when modeling carbon dioxide, enabling to obtain an excellent description of the vapor-liquid equilibria diagrams. NO2 was modeled as a self-associating molecule with a single association site to account for the strong associating character of the NO2 molecule. Again, the vapor-liquid equilibrium of NO2 was correctly modeled. The molecular parameters were tested by accurately predicting the very few available experimental data outside the phase equilibrium. Soft-SAFT was also able to predict the degree of dimerization of NO2 (mimicking the real NO2/N2O4 situation), in good agreement with experimental data. Finally, CO2 and NO2 pure compound parameters were used to predict the vapor-liquid coexistence of the CO2 + NO2/N2O4 mixture at different temperatures. Experimental pressure-CO2 mass fraction isotherms recently measured were well described using a unique binary parameter, independent of the temperature, proving that the soft-SAFT model is able to capture the non-ideal behavior of the mixture.

Original languageBritish English
Pages (from-to)154-163
Number of pages10
JournalFluid Phase Equilibria
Volume266
Issue number1-2
DOIs
StatePublished - 25 Apr 2008

Keywords

  • CO
  • Crossover
  • NO/NO
  • Reacting systems
  • Soft-SAFT

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