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To develop novel routes for the catalytic oxidation of cyclohexane, using carbon dioxide expanded media, it is aimed to explore and describe the thermodynamics of mixtures of oxygen, carbon dioxide, cyclohexane, cyclohexanol, and cyclohexanone. Experimental work is combined with molecular modeling and simulation. The key properties are vapor-liquid equilibria (VLE) and diffusivities.

In a first step, the thermodynamics of the bulk phase are studied. An equation of state based model for phase equilibria, thermal and caloric properties of the studied system is provided. The present work focuses on molecular modeling and simulation of the relevant pure substances and their mixtures. The molecular models are of the multi-center Lennard-Jones plus quadrupole, dipole or point charge type. Reliable molecular models for oxygen [1] and cyclohexane [2] are available from prior work, models for the other components are being developed here. The Grand Equilibrium method [3] is used for the calculation of the vapor-liquid equilibria. The expanded ensemble method [4] is applied for calculating the chemical potential in the liquid phase for large, strongly interacting molecules. New molecular models for carbon dioxide, cyclohexanol, and cyclohexanone [5] are presented. The mean unsigned errors in the full temperature range from triple point to critical point are for carbon dioxide 0.8 % in saturated liquid density, 0.9 % in vapor pressure, and 5 % in heat of vaporization. The analogous numbers for cyclohexanol are 0.4 % in saturated liquid density, and 4.1 % in vapor pressure. These models are also capable to predict transport properties properly. Therefore, the self- and transport diffusion coefficients are determined by equilibrium molecular dynamics simulation with the Green-Kubo method [6]. VLE for the investigated mixtures are determined and compared to experimental data where possible.

References

[1] Vrabec, J.; Stoll, J.; Hasse, H. J. Phys. Chem. B. 2001, 105, 12126-12133.

[2] Eckl, B.; Vrabec, J.; Hasse, H. J. Phys. Chem. B. 2008, submitted.

[3] Vrabec, J.; Hasse, H. Molec. Phys. 2002, 100, 3375-3383.

[4] Vrabec, J.; Kettler, M.; Hasse, H. Chem. Phys. Letters. 2002, 356, 431-436.

[5] Merker, T.; Vrabec, J.; Hasse, H. in preparation

[6] Fernandez, G. A.; Vrabec, J. ; Hasse, H. Int. J. Thermophysics. 2004, 25, 175-186.