Using an Adaptive Parameter Method for Process Simulation of Nonideal Systems

A thermodynamic model of the φ/φ class of methods that can be easily used with commercial process simulators is proposed. The vapor-liquid equilibrium (VLE) is calculated by means of a Redlich-Kwong-type equation of state (EoS) that uses modified Huron-Vidal mixing rules with activity coefficients: the activity coefficients are derived from the NRTL model whose parameters are evaluated by fitting VLE data of binary mixtures. By means of the Aspen PLUS process simulator, a comparison is made between the performances of both the proposed method with user-created adaptive parameters that can be forced into the simulator database and the Predictive-Soave-Redlich-Kwong (PSRK) method that uses UNIFAC to compute the excess free energy. The ethanol-water separation by extractive distillation is analyzed to point out how an incorrect prediction of the azeotrope can lead to underestimation of the overall process energy requirement.