Entwicklung von Force Field Modellen für alternative Kältemittel auf Basis fluorierter Propene, einschließlich HFO-1234yf
Zusammenfassung der Projektergebnisse
We have developed a transferable force field for molecular simulation studies of fluoropropenes that are composed of CF3-, -CF=, -CH=, CF2= and CH2= groups. The performance of the force field has been tested by GEMC simulation studies on the vapor-liquid phase equilibria properties of 2,3,3,3-tetrafluoro-1-propene (HFO-1234yf), 3,3,3-trifluoro-1-propene (HFO-1243zf) and hexafluoro-1-propene (HFO-1216). The simulated VLCC and vapor pressure curve of HFO-1234yf agree within their errors bars with recent experimental data. This also results in an excellent reproduction of the critical point and the normal boiling point. The simulated heats of vaporization fall within 1 kJ mol-1 of the estimates by Tanaka and Higashi. Although experimental data for the shear viscosity of HFO-1234yf were not used in the optimization of the force field, the simulation results agree very well with experiment within the range of their uncertainties. From the MD simulation studies, we also derived information on the self diffusion coefficient of HFO-1234yf that is not available from experiment yet. Limited and/or ambiguous experimental data hampers the validation of our force field for the compounds HFO-1243zf and HFO-1216. By using a slightly reduced σ value for the HC1 hydrogen in HFO-1243zf, the simulation results for the vapor pressure and the heat of vaporization of HFO-1243zf agree very well with experimental data that only recently became available. The refined force field also yields results for the critical point and normal boiling point of HFO-1243zf that compare well with experiment. However, the simulated liquid densities largely underestimate the recent experimental data by Singh, but note that these experimental data deviate by up to 20 % from other data from literature, and yield unusual high molar densities for HFO-1243zf compared to other fluoropropenene. Regarding HFO-1216 our simulations are pure predictions, as it was not included in the optimization of the LJ parameters. Our force field yields reasonable predictions of the vapor pressure curve at higher temperatures, of the liquid density and of the critical temperature. Deviations of simulated vapor pressures from experiment in the low temperature/high density region might be due to the fact that the LJ parameters were optimized for the compounds HFO- 1243zf and HFO-1234yf, which exhibit hydrogen bonding.
Projektbezogene Publikationen (Auswahl)
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Molecular modeling of the vapor-liquid equilibrium properties of the alternative refrigerant 2,3,3,3-tetrafluoro-1-propene HFO-1234yf. J. Phys. Chem. Letters 1 (2010) 93-96
G. Raabe, E. J. Maginn
