Calculation of component activities for Se-based binary systems by NRTL equation

The activity of components is the fundamental thermodynamic property of vapor-liquid equilibrium in vacuum distillation of crude selenium. The activities of components for the Pb-Se, Bi-Se, Sb-Se, and Tl-Se binary systems were calculated and discussed using the Nonrandom two-liquid (NRTL) equation and Wilson equation. The interaction energy parameters of the NRTL equation for Se-based binary systems were employed to predict the activities of components at corresponding temperatures. The mixing enthalpies and Gibbs free energies of these systems were obtained based on the predicted activities and NRTL equation parameters. Compared to the experimental data from literature, the present calculations for the four binary systems using the NRTL equation are better than the Wilson equation. It shows that the NRTL equation is reasonable and accurate based on the concept of local composition and two-fluid theory, especially for binary systems containing liquid-liquid immiscibility. The method proposed in this work is reliable for predicting thermodynamic properties for Se-based binary systems.