A Force Field for 3,3,3-Fluoro-1-propenes, Including HFO-1234yf

Abstract

The European Union (EU) legislation 2006/40/EC bans from January 2011 the cooperative marketing of new car types that use refrigerants in their heating, ventilation, and air conditioning (HVAC) systems with global warming potentials (GWP) higher than 150. Thus, the phase-out of the presently used tetrafluoroethane refrigerant R134a necessitates the adoption of alternative refrigerants. Fluoropropenes such as 2,3,3,3-tetrafluoro-1-propene (HFO-1234yf) are currently regarded as promising low GWP refrigerants, but the lack of experimental data on their thermophysical properties hampers independent studies on their performance in HVAC systems or in other technical applications. In principle, molecular modeling can be used to predict the relevant properties of refrigerants, but adequate intermolecular potential functions ("force fields") are lacking for fluoropropenes. Thus, we developed a transferable force field for fluoropropenes composed of CF(3)-, -CF=, -CH=, CF(2)=, and CH(2)= groups and applied the force field to study 3,3,3 trifluoro-1-propene (HFO-1243zf), 2,3,3,3-tetrafluoro-1-propene (HFO-1234yf), and hexafluoro-1-propene (HFO-1216). We performed Gibbs ensemble simulations on these three fluoropropenes to compute the vapor pressure, saturated densities, and heats of vaporization. In addition, molecular dynamics simulations were conducted to provide predictions for the density, thermal expansivity, isobaric heat capacity, and transport properties of liquid HFO-1234yf in the temperature range from 263.15 to 310 K and pressures up to 2 MPa. Agreement between simulation results and experimental data and/or correlations (when available) was good, thereby validating the predictive ability of the force field.