Automatic Generation of Global Phase Diagram for Binary System from Equation of State
Advancing the chemical engineering fundamentals
Thermodynamics: General (T2-1e)
Keywords: Global Phase Diagrams, Homotopy Continuation, Equation of State
For any separation processes, especially for the processes operating at high pressure, knowledge of global phase behavior (P-T-x-y projections) is very crucial for analysis of process under different operation region (P-T space) and eventually to determine the most suitable operating condition. Moreover, successful prediction of global phase diagram from suitable equation of states can minimize the experimental efforts to generate the global phase diagram (GPD), and at the same time, provides a valuable tool to determine the most suitable thermodynamic model which reproduces the experimental behavior with best accuracy.
We propose a systematic strategy to calculate global phase diagram for binary system using equation of state model. As mentioned by Cismondi and Michelsen [1], the strategy to compute the global phase diagram proposed by them doesn’t take into account the possibility of appearance of solid phase. The authors also pointed out that the procedure can not detect type VI, or type VII phase behavior where closed liquid-liquid critical curve is present. Motivated by the need to improve reliability of global phase diagram calculations and importance of detection of solid phase for supercritical fluid technology, we developed a systematic strategy to calculate global phase diagram for binary system that can detect the presence of solid phase and can also check for existence of closed critical curves (type VI and type VII), if any. To perform the phase stability test [2] along a traced curve and to determine the existence of a closed critical curve, we use homotopy continuation based global method. The procedure enables automatic generation of GPD which incorporates calculations of all important landmarks such as critical endpoints (CEP), quadruple point (Q point, if any), critical line, liquid-liquid-vapor line (LLV, if any), solid-liquid-liquid line (SLL if any) and solid-liquid-vapor line (SLV). The proposed strategy is completely general that doesn’t require any knowledge about the type of phase diagram and can be applied to any equation of state model. To demonstrate the ability of our strategy, we generate different type of phase diagrams using equation of state model. Whole methodology is implemented in MATLAB programming environment.
References:
[1] Cismondi, Martin; Michelsen, Michael L. Global phase equilibrium calculations:
Critical lines, critical end points and liquid-liquid-vapour equilibrium in binary
mixtures. Journal of Supercritical Fluids (2007), 39(3), 287-295.
[2] Sun, Amy C.; Seider, Warren D. Homotopy-continuation method for stability analysis
in the global minimization of the Gibbs free energy. Fluid Phase Equilibria (1995),
103(2), 213-49.
Presented Tuesday 18, 16:40 to 17:00, in session Thermodynamics: General (T2-1e).
