(63h) Liquid-Vapor Phase Behavior of Asphaltene-Like Molecules

Errington, J. R., University at Buffalo
Kumar, V., University at Buffalo
Rane, K. S., University at Buffalo, The State University of New York
Wierzchowski, S., Shell Global Solutions

Asphaltenes have a significant effect on the thermodynamic and transport properties of crude oil.  These molecules are known to clog pipes as well as clog the pores within rocks in the oil-field, thereby impeding oil extraction.  The identification and design of solutions to mitigate the impact of asphaltenes would benefit from a better understanding of their thermophysical properties, including their phase behavior.  In this presentation, we describe our recent efforts aimed at using molecular modeling to construct liquid-vapor phase diagrams for asphaltene-like molecules.  A collection of histogram-based Monte Carlo (MC) techniques are used to deduce saturation properties.  We first use direct grand canonical simulations to acquire coexistence properties at relatively high temperatures.  These calculations are followed by temperature expanded ensemble simulations, which provide a means to trace saturation curves to relatively low temperature.  Reservoir grand canonical MC, hybrid MC, and growth expanded ensemble strategies are employed to facilitate sampling the configuration space of these complex molecules.  We first provide results for the phase behavior of a collection of polycyclic aromatic molecules.  Such structures form the central unit of asphaltenes, and therefore represent a natural starting point for understanding the behavior of these molecules.  Next, we probe the extent to which nitrogen- and sulfur-containing chemistries influence the phase behavior of polycyclic aromatics.  Finally, we examine the phase behavior of realistic asphaltenes by decorating polycyclic aromatic molecules with tethered alkane chains.