Journal of Physical Chemistry B, Vol.121, No.18, 4923-4944, 2017
Mesoscale Simulation and Machine Learning of Asphaltene Aggregation Phase Behavior and Molecular Assembly Landscapes
Asphalteries constitute the heaviest fraction of the aromatic group in crude oil. Aggregation and precipitation of asphaltenes during petroleum processing costs the petroleum industry billions of dollars each year due to downtime and production inefficiencies. Asphaltecie-aggregation proceeds Via a hierarchical self-assembly process that is well-described by the yen-Mullins model. Nevertheless, the microscopit details of the emergent cluster morphologies and their relative stability under different processing conditions remain poorly understood. We perform coarse-grained molecular dynamics simulations of a prototypical asphaltene molecule to establish a phase diagram mapping the self assembled mcirphnlpgies a function of temperature, pressure, and n-heptan:toluene-solvent ratio informing how to control asphaltene aggregation by regulating external processing Conditions. We then combine our simulations with graph matching and nonlinear manifold learning,to determine low-dimensional free energy surfaces governing asphaltene self-assembly. In doing so, we introduce a variant of,diffusion maps designed;to:handle data sets with large local density variations, and report the first application of many-body diffusion maps to molecular self assembly to recover a pseudo-1D free energy landscape: Increasing pressure only weakly affects the landscape, serving only to destabilize the largest aggregates. Increasing temperature and-toluene solvent fraction stabilizes small cluster sizes and loose bonding arrangements. Although the underlying molecular mechanisms differ, the strikingly similar effect of these variables On the free energy landscape suggests that toluene acts upon asphaltene self- assembly as an effective temperature.