Combining molecular dynamics and chemical process simulation: The SPEAD model

Discontinuous molecular dynamics simulation and thermodynamic perturbation theory have been used to study the thermodynamic and transport properties of a large number of organic compounds. The fundamental basis of the approach relies on a stepwise characterization of the disperse interactions and blister potentials for hydrogen bonding. It has been demonstrated that these types of attractive interactions can be quantitatively treated by thermodynamic perturbation theory (TPT). The vapor pressure is predicted to roughly 10% average error with reduced temperatures generally extending to 0.45 while applying transferable characterizations of the molecular interaction potentials. For branched, aromatic, and naphthenic compounds, it is necessary to distinguish between primary, secondary, and tertiary bonding of the attached group as well as the branched site. One key to this accuracy is the distinction between isomers at the molecular level by the rigorous molecular dynamics simulation of the repulsive part of the potential. The molecular dynamics simulations also permit predictions of transport properties. The transport results account for the repulsive structure, branching, bond angles, etc. through rigorous molecular simulation but there is no theory for transport properties comparable to TPT. Therefore, predictions for transport properties are semiempirical in the sense that attractive forces have been correlated with experimental data. The accuracy for diffusivity is within 30% for non-associative species. Disperse attractions appear to play a significant role in transport properties.