A WINDOWS-BASED COMPUTER PROGRAM FOR GLOBAL PHASE EQUILIBRIA CALCULATIONS FOR BINARY SYSTEMS

M. CISMONDI; D. NUÑEZ; M.S. ZABALOY

Buenos Aires, Argentina

Congreso; XXII Congreso Interamericano de Ingeniería Química y V Congreso Argentino de Ingeniería Química; 2006

The simulation of separation processes requires the availability of thermodynamic models for representing the distribution of components between phases at equilibrium in multicomponent systems. Typically the model parameters are fitted to match binary experimental phase equilibria information, usually in relatively narrow ranges of conditions. Once the parameter values are set, it is important to study the model performance beyond the conditions of the experimental data used to arrive to such values. This is not a simple task, since it requires the computation of mixture critical lines, liquid-liquid-vapour (LLV) lines and critical end points. In other words, a thorough model performance evaluation requires the computation of so-called global phase equilibria diagrams and of isothermal and isobaric phase equilibria. To that end, a general algorithm for the calculation of global phase equilibrium diagrams for binary systems has been recently developed [1]. This algorithm, which integrates the calculation of critical lines, liquid-liquid-vapour (LLV) lines and critical end points, was implemented in the WINDOWS-based software program GPEC: Global Phase Equilibrium Calculations. This program makes possible, after choosing a binary system, an equation of state thermodynamic model (EOS) and values for its parameters, to predict the global phase behavior and to plot different projections of the temperaturepressure- composition-density space. These projections show the boundaries for regions of complete miscibility, and for different types of phase equilibria. Additionally, complete Pxy and Txy diagrams can also be generated using GPEC [2]. We illustrate the use of GPEC considering different types of EOSs. The program is useful for thoroughly understanding the different types of phase behaviour that can be calculated with an EOS and the transitions between them. It allows a straightforward study of the influence of a certain parameter on the predicted global phase equilibria behaviour for a given binary system. For models and parameters capable of a good representation of experimental data in proper ranges of conditions, the program becomes a useful tool in the search for promising operating conditions for specific applications. The programming language we used for developing the windows interface for GPEC is Visual Basic. GPEC is linked to the DIPPR database. This database provides constant and temperature-dependent physical properties for hundreds of pure compounds.