Equations of State Based on Hybrid Data Sets - A Combined Approach for the Development of Fundamental Equations of State and of Accurate Molecular Models
Final Report Abstract
Based on new simulation data and experimental measurements from the literature seven fundamental equations of state in terms of the reduced Helmholtz energy were developed for the Lennard-Jones model fluid truncated and shifted at rc = 2.5σ, the Lennard-Jones model fluid, hexamethyldisiloxane, octamethylcyclotetrasiloxane, ethylene oxide, dichloroethane, and hydrogen chloride. With the help of hybrid data sets, the range of validity of the equations of state describing these fluids was extended to much higher temperatures, densities, and pressures. The accuracy of the equations of state cannot be assessed in these regions because no experimental measurements are available. However, for the verification of the underlying molecular models, test simulations were carried out to reproduce the most accurate density and speed of sound measurements as well as vapor-liquid equilibrium data. The results justify the application of molecular simulation data if no accurate experimental data are available. Furthermore, a new idea for the optimization of the molecular model parameters was developed. The results show two main restrictions regarding the molecular models. First, the optimization of the parameters by means of thermodynamic properties located at different fluid states (e.g., gas, liquid, vapor-liquid equilibrium, or supercritical) yields different values for the resulting model parameters. It was not possible to improve the description of the vapor-liquid equilibrium and homogeneous phases simultaneously. Therefore, the assumption of rigid models based on the Lennard-Jones potential seems to be an inadequate simplification if high accuracies need to be achieved. Second, similar to the common optimization methods from the literature, it was not possible to improve the representation of the vaporliquid equilibrium for carbon dioxide, although these data were primarily applied to the fit. These aspects have to be investigated more comprehensively with other model types including non-rigid force field approaches. The same findings were observed during the optimization of new molecular model parameters for hydrogen sulfide. This project successfully showed that the development of equations of state using hybrid data sets is not only possible but beneficial due to the lack of experimental data for most fluids. With the current software and expertise it is possible to develop fundamental equations of state purely from molecular simulation data or based on hybrid data sets as long as appropriate molecular models are available.
Publications
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“Communication: Fundamental equation of state correlation with hybrid data sets”, The Journal of Chemical Physics, 139:041102 (2013)
G. Rutkai, M. Thol, R. Lustig, J. Vrabec, R. Span
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“ms2: A molecular simulation tool for thermodynamic properties (new version release)”, Computer Physics Communications, 185:3302–3306 (2014)
C. W. Glass, S. Reiser, G. Rutkai, S. Deublein, A. Köster, G. Guevara-Carrion, A. Wafai, M. Horsch, M. Bernreuther, T. Windmann, H. Hasse, J. Vrabec
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“Empirical fundamental equation of state for phosgene based on molecular simulation data”, Journal of Chemical and Engineering Data, 60:2895–2905 (2015)
G. Rutkai, J. Vrabec
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“Equation of State for the Lennard-Jones Truncated and Shifted Model Fluid”, International Journal of Thermophysics, 36:25–43 (2015)
M. Thol, G. Rutkai, R. Span, J. Vrabec, R. Lustig
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“Fundamental equation of state for ethylene oxide based on a hybrid dataset”, Chemical Engineering Science, 121:87–99 (2015) and 134:887-890 (2015)
M. Thol, G. Rutkai, A. Köster, M. Kortmann, R. Span, J. Vrabec
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“Thermodynamic correlation of molecular simulation data” Molecular Physics, 113:910–931 (2015)
R. Lustig, G. Rutkai, J. Vrabec
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“Fundamental equation of state correlation for hexamethyldisiloxane based on experimental and molecular simulation data”, Fluid Phase Equilibria
M. Thol, F.H. Dubberke, G. Rutkai, T. Windmann, A. Köster, R. Span, J. Vrabec
