(533c) Binding Energetics of Dimethyl Ether and Sulfur Dioxide Using Both Ab Initio and Molecular Simulation Methods

Over the past few decades, molecular simulation has become an attractive method for predicting thermophysical properties and phase behavior of chemical compounds. In principle, the accuracy of molecular simulation is limited only by the intermolecular force field used to describe the interaction between molecules. However, previous studies of compounds such as carbon dioxide , dimethyl ether (DME) , hydrogen sulfide and acetone , have shown that there exist many sets of force field parameters that reproduce accurately the thermodynamic properties of the pure material. Although the prediction of mixture physical properties provides one route to reducing the number of candidate parameter sets, the development of new parameterization schemes is expected to lead to more efficient parameter optimization as well as greater insight to molecule-molecule interactions.

In this work, an effort is made to link potential energy surfaces (shape, magnitude and range) to predicted thermophysical properties for pure components and mixtures. A combination of ab inito and classical molecular mechanics force fields are used to map the potential energy surfaces surrounding DME and SO2 molecule and the shapes of the intersection of those two surfaces. This mixtures is of interest because it forms a minimum pressure azeotrope. Multiple orientations of DME and SO2 clusters were examined at the Hartee-Fock (HF), B3LYP and Moller-Plesset 2 (MP2) levels of theory, with basis sets ranging from 3-21g up to 6-311g+(d,p). Both the ab initio and molecular mechanics force field predictions of the binding energetics revealed that the unlike molecule interactions were stronger than the like-like interactions. Vapor-liquid equilibria for the pure components and mixtures is presented, as well as vapor pressures, heat capacities and surface tensions for each of the pure components.