Prediction of transport properties by molecular simulation: methanol and ethanol and their mixture.

Transport properties of liquid methanol and ethanol are predicted by molecular dynamics simulation. The molecular models for the alcohols are rigid, nonpolarizable, and of united-atom type. They were developed in preceding work using experimental vapor-liquid equilibrium data only. Self- and Maxwell-Stefan diffusion coefficients as well as the shear viscosity of methanol, ethanol, and their binary mixture are determined using equilibrium molecular dynamics and the Green-Kubo formalism. Nonequilibrium molecular dynamics is used for predicting the thermal conductivity of the two pure substances. The transport properties of the fluids are calculated over a wide temperature range at ambient pressure and compared with experimental and simulation data from the literature. Overall, a very good agreement with the experiment is found. For instance, the self-diffusion coefficient and the shear viscosity are predicted with average deviations of less than 8% for the pure alcohols and 12% for the mixture. The predicted thermal conductivity agrees on average within 5% with the experimental data. Additionally, some velocity and shear viscosity autocorrelation functions are presented and discussed. Radial distribution functions for ethanol are also presented. The predicted excess volume, excess enthalpy, and the vapor-liquid equilibrium of the binary mixture methanol + ethanol are assessed and agree well with experimental data.