Predictions of critical behavior using the Wong-Sandler mixing rule

Gonzalo Escobedo Alvarado, Marcelo Castier, Stanley I. Sandler

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7 Citations (Scopus)


Critical points were calculated using thermodynamic models obtained by the combination of cubic equations of state (here, the Peng-Robinson and Peng-Robinson-Stryjek-Vera equations of state) with excess free energy models (here, the NRTL and UNIQUAC models), using the Wong-Sandler mixing rule. Several types of critical phase diagrams could be predicted using these models. For binary mixtures of ethanol+light hydrocarbons, the transitions between different types of critical diagram were correctly predicted. We also show that critical behavior of type VI in the classification of van Konynenburg and Scott is predicted for the 2-butoxyethanol+water mixture when temperature-dependent parameters were used in the excess free energy models. This is an important result because cubic equations of state cannot predict type VI behavior when the classical one-fluid mixing rules are used. For the system carbon dioxide+water, satisfactory agreement was obtained at mole fractions of CO2 smaller than 0.25, though there is a poor representation of the vapor-liquid equilibrium at larger mole fractions.

Original languageEnglish
Pages (from-to)49-54
Number of pages6
JournalJournal of Supercritical Fluids
Issue number1-3
Publication statusPublished - 15 Jun 1998



  • Critical points
  • Equations of state
  • Excess free energy models
  • Mixing rules
  • Phase diagrams

ASJC Scopus subject areas

  • Chemical Engineering(all)
  • Condensed Matter Physics
  • Physical and Theoretical Chemistry

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