All-Atom Force Field for the Prediction of Vapor−Liquid Equilibria and Interfacial Properties of HFA134a

Abstract

A new all-atom force field capable of accurately predicting the bulk and interfacial properties of 1,1,1,2-tetrafluoroethane (HFA134a) is reported. Parameterization of several force fields with different initial charge configurations from ab initio calculations was performed using the histogram reweighting method and Monte Carlo simulations in the grand canonical ensemble. The 12-6 Lennard-Jones well depth and diameter for the different HFA134a models were determined by fitting the simulation results to pure-component vapor-equilibrium data. Initial screening of the force fields was achieved by comparing the calculated and experimental bulk properties. The surface tension of pure HFA134a served as an additional screening property to help discriminate an optimum model. The proposed model reproduces the experimental saturated liquid and vapor densities, and the vapor pressure for HFA134a within average errors of 0.7%, 4.4%, and 3.1%, respectively. Critical density, temperature, vapor pressure, normal boiling point, and heat of vaporization at 298 K are also in good agreement with experimental data with errors of 0.2%, 0.1%, 6.2%, 0%, 2.2%, respectively. The calculated surface tension is found to be within the experimental range of 7.7-8.1 mN.m(-1). The dipole moment of the different models was found to significantly affect the prediction of the vapor pressure and surface tension. The ability of the HFA134a models in predicting the interfacial tension against water is also discussed. The results presented here are relevant in the development of technologies where the more environmentally friendly HFA134a is utilized as a substitute to the ozone depleting chlorofluorocarbon propellants.

Monte Carlo Simulation of Vapor–Liquid Equilibria for Perfluoropropane (R-218) and 2,3,3,3-Tetrafluoropropene (R-1234yf)

“…Fluorinated methanes and ethanes were previously investigated with MC methods [16][17][18][19]. The most recent work of Peguin et al [19] presented an all-atom forcefield model optimized for 1,1,1,2-tetrafluoroethane that was capable of accurately reproducing a wide range of thermopysical properties for this compound, including vapor-liquid equilibrium data.…”

“…The most recent work of Peguin et al [19] presented an all-atom forcefield model optimized for 1,1,1,2-tetrafluoroethane that was capable of accurately reproducing a wide range of thermopysical properties for this compound, including vapor-liquid equilibrium data. However, only limited MC studies were performed for fluorohydrocarbons beyond C 2 .…”

Transient evaluation of a city bus air conditioning system with R-445A as drop-in – From the molecules to the system

“…In Ref. [13], Raabe has employed the force field model for fluoropropenes together with common models from literature for CO 2 [14] and R134a [15], for Gibbs-Ensemble Monte Carlo (GEMC) simulation studies on the vapoureliquid phase equilibria of the ternary blend R-445A and its binary subsystems. For the binary subsystems CO 2 þ R-134a we found again good agreement between the predictions from molecular simulation, experimental data and calculations with REFPROP based on interaction parameters fitted to experiment.…”

SpaGrOW—A Derivative-Free Optimization Scheme for Intermolecular Force Field Parameters Based on Sparse Grid Methods

“…Furthermore, in most cases, they ware adjusted manually, which is always time-consuming. They are transferable to other substances, but a subsequent readjustment is indispensable [15]. Many users take standard force fields from the literature for their simulations, which may lead to satisfactory, but not to optimal, target properties.…”