Global Phase Equilibrium Calculation and Critical Phase Behavior from a Group Contribution Equation of State in Binary Mixtures
Advancing the chemical engineering fundamentals
Thermodynamics (T2-1P)
Keywords: Critical points, ESD EOS, Binary mixture, Group Contribution
Predicting critical behavior of mixtures is an important topic in thermodynamic, which has been studied by a few equations of state such as van der Waals and SRK. This paper describes a procedure to predict critical phase behavior of binary mixtures, based on Elliott-Suresh-Donohue (ESD) EOS, which is a group contribution equation of state. The procedure is according to minimization of gibbs free energy at different temperatures, pressures and mole fractions for calculation of critical points. Each calculated point is analyzed for stability by means of tangent plane distance, and the occurrence of an unstable point is used to determine a critical endpoint. The critical endpoint, in turn, is used as the starting point for constructing the three-phase line.
Shape factor is calculated via two different methods: Correlated shape factor introduced by Elliott et al.(1990), and estimation using hydrocarbon group contributions by Elliott et al.(2002).
Phase calculation in critical region is strongly dependant on initial guess of mixture critical properties. Following Grieves and Thodos method (1962), we derived a correlation to be used to estimate the initial guess in the gibbs free energy minimization procedure.
A software package is prepared which allows user to observe phase behavior of binary mixtures near to and far from critical region.
Different types of critical phase diagrams have been constructed without adjusting any binary interaction coefficient. While the method is completely predictive, more accurate results have been obtained in comparison with the work of Scott-Van Konynenberg(1979) and Michelsen-Cismondi (2007).
Presented Monday 17, 13:30 to 15:00, in session Thermodynamics (T2-1P).
