Molecular simulation of the thermophysical properties of fluids: From understanding toward quantitative predictions

Abstract

Abstract The purpose of the present paper is to review what kind of thermophysical properties can be predicted, either qualitatively or quantitatively with molecular simulation. In a first part, the main types of molecular simulation methods are introduced. Molecular dynamics (MD) can be used to address equilibrium properties and dynamic behaviour as well. Monte Carlo simulation (MC) is particularly adapted to phase equilibria or physisorption. Both methods require to represent the potential energy, which is classically decomposed into intramolecular (bending, torsion, etc.) and intermolecular (dispersion, repulsion, electrostatic, polarization) contributions. In a second part, the prediction of fluid properties (PVT relationships, enthalpy, heat capacity, Joule–Thomson coefficient, etc.) is reviewed. Either MC or MD can be used to relate these properties and molecular structure, as shown by examples like high pressure hydrocarbon gases, CFCs, acid gases, and natural gases. Fluid phase equilibria are discussed in the third part. Examples are given in which MC is used to provide pure component properties when pure chemicals are not commercially available, such as heavy hydrocarbons of complex structure. MC is also capable of predicting phase behaviour for mixtures with little (or no) calibration on binary system data. This aspect is illustrated by the prediction of Henry constants of gases in polar liquids and by the prediction of phase diagrams of acid gases (H 2 S, CO 2 ) with water, methanol or hydrocarbons. The self-association of polar molecules and the critical scaling behaviour are also described. In the fourth part, transport properties (viscosity, diffusion coefficients, and thermal conductivity) are discussed. For many systems like hydrocarbons, carbon dioxide or hydrogen sulphide, very good predictions are obtained, and simulation is shown to predict detailed features such as the differences in viscosity between isomers. In Conclusion and perspectives , the current limitations and possible improvements of molecular simulation methods are mentioned.