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.