Liquid-vapor phase behavior of asphaltene-like molecules

Molecular simulation is used to predict liquid-vapor saturation properties of asphaltene-like molecules. We examine nine compounds that are adapted from a structure produced by Boek and co-workers [ Energy Fuels 2009, 23, 1209 ] via an optimization technique that generates quantitative molecular representations of asphaltenes. We first consider a sequence of four fused ring structures differentiated by their aromaticity. Next, a collection of structures with a single aromatic core decorated with side chains of variable length and position is examined. Finally, we consider a group of structures with heteroatoms. The general AMBER force field (GAFF) and the CHARMM general force field (CGenFF) are employed to describe molecular interactions. A general histogram-based approach introduced by Rane and co-workers [ J. Chem. Theory Comput. 2013, 9, 2552 ] is used to calculate saturated densities, vapor pressures, and enthalpies of vaporization over a wide range of temperatures. Simulation results are compared to estimates from select group contribution methods. Our results indicate that saturated liquid densities and critical temperatures of fused ring structures generally decrease with decreasing aromaticity. The length and distribution of side chains attached to an aromatic core have a significant impact on the saturated liquid densities and a minor impact on the boiling point temperature.